GOCE gravity gradient data for lithospheric modeling - From well surveyed to frontier areas

NASA Astrophysics Data System (ADS)

Bouman, J.; Ebbing, J.; Gradmann, S.; Fuchs, M.; Fattah, R. Abdul; Meekes, S.; Schmidt, M.; Lieb, V.; Haagmans, R.

2012-04-01

We explore how GOCE gravity gradient data can improve modeling of the Earth's lithosphere and thereby contribute to a better understanding of the Earth's dynamic processes. The idea is to invert satellite gravity gradients and terrestrial gravity data in the well explored and understood North-East Atlantic Margin and to compare the results of this inversion, providing improved information about the lithosphere and upper mantle, with results obtained by means of models based upon other sources like seismics and magnetic field information. Transfer of the obtained knowledge to the less explored Rub' al Khali desert is foreseen. We present a case study for the North-East Atlantic margin, where we analyze the use of satellite gravity gradients by comparison with a well-constrained 3D density model that provides a detailed picture from the upper mantle to the top basement (base of sediments). The latter horizon is well resolved from gravity and especially magnetic data, whereas sedimentary layers are mainly constrained from seismic studies, but do in general not show a prominent effect in the gravity and magnetic field. We analyze how gravity gradients can increase confidence in the modeled structures by calculating a sensitivity matrix for the existing 3D model. This sensitivity matrix describes the relation between calculated gravity gradient data and geological structures with respect to their depth, extent and relative density contrast. As the sensitivity of the modeled bodies varies for different tensor components, we can use this matrix for a weighted inversion of gradient data to optimize the model. This sensitivity analysis will be used as input to study the Rub' al Khali desert in Saudi Arabia. In terms of modeling and data availability this is a frontier area. Here gravity gradient data will be used to better identify the extent of anomalous structures within the basin, with the goal to improve the modeling for hydrocarbon exploration purposes.

Control of deep lithospheric roots on crustal scale GOCE gravity and gradient fields evident in Gondwana reconstructions

NASA Astrophysics Data System (ADS)

Braitenberg, Carla; Mariani, Patrizia

2015-04-01

The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies based on age determination and mineral composition of rock samples propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events which induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Therefore gravity can be used as a globally available supportive tool for interpolation of isolated samples. Applying geodynamic plate reconstructions to the GOCE gravity field places today's observed field at the pre-breakup position. In order to test the possible deep control of the crustal features, the same reconstruction is applied to the seismic velocity models, and a joint gravity-velocity analysis is performed. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105 Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th International GOCE User Workshop, 25 - 28 November 2014. Braitenberg, C. (2015). Exploration of tectonic structures with GOCE in Africa and across-continents. Int. J.Appl. Earth Observ. Geoinf. 35, 88-95. http://dx.doi.org/10.1016/j.jag.2014.01.013 Braitenberg, C. (2015). A grip on geological units with GOCE, IAG Symp. 141, in press.

Europe's Preparation For GOCE Gravity Field Recovery

NASA Astrophysics Data System (ADS)

Suenkel, H.; Suenkel, H.

2001-12-01

The European Space Agency ESA is preparing for its first dedicated gravity field mission GOCE (Gravity Field and Steady-state Ocean Circulation Explorer) with a proposed launch in fall 2005. The mission's goal is the mapping of the Earth's static gravity field with very high resolution and utmost accuracy on a global scale. GOCE is a drag-free mission, flown in a circular and sun-synchronous orbit at an altitude between 240 and 250 km. Each of the two operational phases will last for 6 months. GOCE is based on a sensor fusion concept combining high-low satellite-to-satellite tracking (SST) and satellite gravity gradiometry (SGG). The transformation of the GOCE sensor data into a scientific product of utmost quality and reliability requires a well-coordinated effort of experts in satellite geodesy, applied mathematics and computer science. Several research groups in Europe do have this expertise and decided to form the "European GOCE Gravity Consortium (EGG-C)". The EGG-C activities are subdivided into tasks such as standard and product definition, data base and data dissemination, precise orbit determination, global gravity field model solutions and regional solutions, solution validation, communication and documentation, and the interfacing to level 3 product scientific users. The central issue of GOCE data processing is, of course, the determination of the global gravity field model using three independent mathematical-numerical techniques which had been designed and pre-developed in the course of several scientific preparatory studies of ESA: 1. The direct solution which is a least squares adjustment technique based on a pre-conditioned conjugated gradient method (PCGM). The method is capable of efficiently transforming the calibrated and validated SST and SGG observations directly or via lumped coefficients into harmonic coefficients of the gravitational potential. 2. The time-wise approach considers both SST and SGG data as a time series. For an idealized repeat mission such a time series can be very efficiently transformed into lumped coefficients using fast Fourier techniques. For a realistic mission scenario this transformation has to be extended by an iteration process. 3. The space-wise approach which, after having transformed the original observations onto a spatial geographical grid, transforms the pseudo-observations into harmonic coefficients using a fast collocation technique. A successful mission presupposed, GOCE will finally deliver the Earth's gravity field with a resolution of about 70 km half wavelength and a global geoid with an accuracy of about 1 cm.

Joint Analysis of GOCE Gravity Gradients Data with Seismological and Geodynamic Observations to Infer Mantle Properties

NASA Astrophysics Data System (ADS)

Metivier, L.; Greff-Lefftz, M.; Panet, I.; Pajot-Métivier, G.; Caron, L.

2014-12-01

Joint inversion of the observed geoid and seismic velocities has been commonly used to constrain the viscosity profile within the mantle as well as the lateral density variations. Recent satellite measurements of the second-order derivatives of the Earth's gravity potential give new possibilities to understand these mantle properties. We use lateral density variations in the Earth's mantle based on slab history or deduced from seismic tomography. The main uncertainties are the relationship between seismic velocity and density -the so-called density/velocity scaling factor- and the variation with depth of the density contrast between the cold slabs and the surrounding mantle, introduced here as a scaling factor with respect to a constant value. The geoid, gravity and gravity gradients at the altitude of the GOCE satellite (about 255 km) are derived using geoid kernels for given viscosity depth profiles. We assume a layered mantle model with viscosity and conversion factor constant in each layer, and we fix the viscosity of the lithosphere. We perform a Monte Carlo search for the viscosity and the density/velocity scaling factor profiles within the mantle which allow to fit the observed geoid, gravity and gradients of gravity. We test a 2-layer, a 3-layer and 4-layer mantle. For each model, we compute the posterior probability distribution of the unknown parameters, and we discuss the respective contributions of the geoid, gravity and gravity gradients in the inversion. Finally, for the best fit, we present the viscosity and scaling factor profiles obtained for the lateral density variations derived from seismic velocities and for slabs sinking into the mantle.

Regional gravity field modelling from GOCE observables

NASA Astrophysics Data System (ADS)

Pitoňák, Martin; Šprlák, Michal; Novák, Pavel; Tenzer, Robert

2017-01-01

In this article we discuss a regional recovery of gravity disturbances at the mean geocentric sphere approximating the Earth over the area of Central Europe from satellite gravitational gradients. For this purpose, we derive integral formulas which allow converting the gravity disturbances onto the disturbing gravitational gradients in the local north-oriented frame (LNOF). The derived formulas are free of singularities in case of r ≠ R . We then investigate three numerical approaches for solving their inverses. In the initial approach, the integral formulas are firstly modified for solving individually the near- and distant-zone contributions. While the effect of the near-zone gravitational gradients is solved as an inverse problem, the effect of the distant-zone gravitational gradients is computed by numerical integration from the global gravitational model (GGM) TIM-r4. In the second approach, we further elaborate the first scenario by reducing measured gravitational gradients for gravitational effects of topographic masses. In the third approach, we apply additional modification by reducing gravitational gradients for the reference GGM. In all approaches we determine the gravity disturbances from each of the four accurately measured gravitational gradients separately as well as from their combination. Our regional gravitational field solutions are based on the GOCE EGG_TRF_2 gravitational gradients collected within the period from November 1 2009 until January 11 2010. Obtained results are compared with EGM2008, DIR-r1, TIM-r1 and SPW-r1. The best fit, in terms of RMS (2.9 mGal), is achieved for EGM2008 while using the third approach which combine all four well-measured gravitational gradients. This is explained by the fact that a-priori information about the Earth's gravitational field up to the degree and order 180 was used.

GOCE and Future Gravity Missions for Geothermal Energy Exploitation

NASA Astrophysics Data System (ADS)

Pastorutti, Alberto; Braitenberg, Carla; Pivetta, Tommaso; Mariani, Patrizia

2016-08-01

Geothermal energy is a valuable renewable energy source the exploitation of which contributes to the worldwide reduction of consumption of fossil fuels oil and gas. The exploitation of geothermal energy is facilitated where the thermal gradient is higher than average leading to increased surface heat flow. Apart from the hydrologic circulation properties which depend on rock fractures and are important due to the heat transportation from the hotter layers to the surface, essential properties that increase the thermal gradient are crustal thinning and radiogenic heat producing rocks. Crustal thickness and rock composition form the link to the exploration with the satellite derived gravity field, because both induce subsurface mass changes that generate observable gravity anomalies. The recognition of gravity as a useful investigation tool for geothermal energy lead to a cooperation with ESA and the International Renewable Energy Agency (IRENA) that included the GOCE derived gravity field in the online geothermal energy investigation tool of the IRENA database. The relation between the gravity field products as the free air gravity anomaly, the Bouguer and isostatic anomalies and the heat flow values is though not straightforward and has not a unique relationship. It is complicated by the fact that it depends on the geodynamical context, on the geologic context and the age of the crustal rocks. Globally the geological context and geodynamical history of an area is known close to everywhere, so that a specific known relationship between gravity and geothermal potential can be applied. In this study we show the results of a systematic analysis of the problem, including some simulations of the key factors. The study relies on the data of GOCE and the resolution and accuracy of this satellite. We also give conclusions on the improved exploration power of a gravity mission with higher spatial resolution and reduced data error, as could be achieved in principle by flying an atom interferometer sensor on board a satellite.

Matching Lithosphere velocity changes to the GOCE gravity signal

NASA Astrophysics Data System (ADS)

Braitenberg, Carla

2016-07-01

Authors: Carla Braitenberg, Patrizia Mariani, Alberto Pastorutti Department of Mathematics and Geosciences, University of Trieste Via Weiss 1, 34100 Trieste Seismic tomography models result in 3D velocity models of lithosphere and sublithospheric mantle, which are due to mineralogic compositional changes and variations in the thermal gradient. The assignment of density is non-univocal and can lead to inverted density changes with respect to velocity changes, depending on composition and temperature. Velocity changes due to temperature result in a proportional density change, whereas changes due to compositional changes and age of the lithosphere can lead to density changes of inverted sign. The relation between velocity and density implies changes in the lithosphere rigidity. We analyze the GOCE gradient fields and the velocity models jointly, making simulations on thermal and compositional density changes, using the velocity models as constraint on lithosphere geometry. The correlations are enhanced by applying geodynamic plate reconstructions to the GOCE gravity field and the tomography models which places today's observed fields at the Gondwana pre-breakup position. We find that the lithosphere geometry is a controlling factor on the overlying geologic elements, defining the regions where rifting and collision alternate and repeat through time. The study is carried out globally, with focus on the conjugate margins of the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105---- Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th International GOCE User Workshop, 25 - 28 November 2014.---- Braitenberg, C. (2015). Exploration of tectonic structures with GOCE in Africa and across-continents. Int. J.Appl. Earth Observ. Geoinf. 35, 88-95. http://dx.doi.org/10.1016/j.jag.2014.01.013------ Braitenberg, C. (2015). A grip on geological units with GOCE, IAG Symp. 141

Slab Geometry and Segmentation on Seismogenic Subduction Zone; Insight from gravity gradients

NASA Astrophysics Data System (ADS)

Saraswati, A. T.; Mazzotti, S.; Cattin, R.; Cadio, C.

2017-12-01

Slab geometry is a key parameter to improve seismic hazard assessment in subduction zones. In many cases, information about structures beneath subduction are obtained from geophysical dedicated studies, including geodetic and seismic measurements. However, due to the lack of global information, both geometry and segmentation in seismogenic zone of many subductions remain badly-constrained. Here we propose an alternative approach based on satellite gravity observations. The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission enables to probe Earth deep mass structures from gravity gradients, which are more sensitive to spatial structure geometry and directional properties than classical gravitational data. Gravity gradients forward modeling of modeled slab is performed by using horizontal and vertical gravity gradient components to better determine slab geophysical model rather than vertical gradient only. Using polyhedron method, topography correction on gravity gradient signal is undertaken to enhance the anomaly signal of lithospheric structures. Afterward, we compare residual gravity gradients with the calculated signals associated with slab geometry. In this preliminary study, straightforward models are used to better understand the characteristic of gravity gradient signals due to deep mass sources. We pay a special attention to the delineation of slab borders and dip angle variations.

The GOCE end-to-end system simulator

NASA Astrophysics Data System (ADS)

Catastini, G.; Cesare, S.; de Sanctis, S.; Detoma, E.; Dumontel, M.; Floberghagen, R.; Parisch, M.; Sechi, G.; Anselmi, A.

2003-04-01

The idea of an end-to-end simulator was conceived in the early stages of the GOCE programme, as an essential tool for assessing the satellite system performance, that cannot be fully tested on the ground. The simulator in its present form is under development at Alenia Spazio for ESA since the beginning of Phase B and is being used for checking the consistency of the spacecraft and of the payload specifications with the overall system requirements, supporting trade-off, sensitivity and worst-case analyses, and preparing and testing the on-ground and in-flight calibration concepts. The software simulates the GOCE flight along an orbit resulting from the application of Earth's gravity field, non-conservative environmental disturbances (atmospheric drag, coupling with Earth's magnetic field, etc.) and control forces/torques. The drag free control forces as well as the attitude control torques are generated by the current design of the dedicated algorithms. Realistic sensor models (star tracker, GPS receiver and gravity gradiometer) feed the control algorithms and the commanded forces are applied through realistic thruster models. The output of this stage of the simulator is a time series of Level-0 data, namely the gradiometer raw measurements and spacecraft ancillary data. The next stage of the simulator transforms Level-0 data into Level-1b (gravity gradient tensor) data, by implementing the following steps: - transformation of raw measurements of each pair of accelerometers into common and differential accelerations - calibration of the common and differential accelerations - application of the post-facto algorithm to rectify the phase of the accelerations and to estimate the GOCE angular velocity and attitude - computation of the Level-1b gravity gradient tensor from calibrated accelerations and estimated angular velocity in different reference frames (orbital, inertial, earth-fixed); computation of the spectral density of the error of the tensor diagonal components (measured gravity gradient minus input gravity gradient) in order to verify the requirement on the error of gravity gradient of 4 mE/sqrt(Hz) within the gradiometer measurement bandwidth (5 to 100 mHz); computation of the spectral density of the tensor trace in order to verify the requirement of 4 sqrt(3) mE/sqrt(Hz) within the measurement bandwidth - processing of GPS observations for orbit reconstruction within the required 10m accuracy and for gradiometer measurement geolocation. The current version of the end-to-end simulator, essentially focusing on the gradiometer payload, is undergoing detailed testing based on a time span of 10 days of simulated flight. This testing phase, ending in January 2003, will verify the current implementation and conclude the assessment of numerical stability and precision. Following that, the exercise will be repeated on a longer-duration simulated flight and the lesson learnt so far will be exploited to further improve the simulator's fidelity. The paper will describe the simulator's current status and will illustrate its capabilities for supporting the assessment of the quality of the scientific products resulting from the current spacecraft and payload design.

Evaluation of GOCE-based global gravity field models over Japan after the full mission using free-air gravity anomalies and geoid undulations

NASA Astrophysics Data System (ADS)

Odera, Patroba Achola; Fukuda, Yoichi

2017-09-01

The performance of Gravity field and steady-state Ocean Circulation Explorer (GOCE) global gravity field models (GGMs), at the end of GOCE mission covering 42 months, is evaluated using geoid undulations and free-air gravity anomalies over Japan, including six sub-regions (Hokkaido, north Honshu, central Honshu, west Honshu, Shikoku and Kyushu). Seventeen GOCE-based GGMs are evaluated and compared with EGM2008. The evaluations are carried out at 150, 180, 210, 240 and 270 spherical harmonics degrees. Results show that EGM2008 performs better than GOCE and related GGMs in Japan and three sub-regions (Hokkaido, central Honshu and Kyushu). However, GOCE and related GGMs perform better than EGM2008 in north Honshu, west Honshu and Shikoku up to degree 240. This means that GOCE data can improve geoid model over half of Japan. The improvement is only evident between degrees 150 and 240 beyond which EGM2008 performs better than GOCE GGMs in all the six regions. In general, the latest GOCE GGMs (releases 4 and 5) perform better than the earlier GOCE GGMs (releases 1, 2 and 3), indicating the contribution of data collected by GOCE in the last months before the mission ended on 11 November 2013. The results indicate that a more accurate geoid model over Japan is achievable, based on a combination of GOCE, EGM2008 and terrestrial gravity data sets. [Figure not available: see fulltext. Caption: Standard deviations of the differences between observed and GGMs implied ( a) free-air gravity anomalies over Japan, ( b) geoid undulations over Japan. n represents the spherical harmonic degrees

Structure and State of Stress of the Chilean Subduction Zone from Terrestrial and Satellite-Derived Gravity and Gravity Gradient Data

NASA Astrophysics Data System (ADS)

Gutknecht, B. D.; Götze, H.-J.; Jahr, T.; Jentzsch, G.; Mahatsente, R.; Zeumann, St.

2014-11-01

It is well known that the quality of gravity modelling of the Earth's lithosphere is heavily dependent on the limited number of available terrestrial gravity data. More recently, however, interest has grown within the geoscientific community to utilise the homogeneously measured satellite gravity and gravity gradient data for lithospheric scale modelling. Here, we present an interdisciplinary approach to determine the state of stress and rate of deformation in the Central Andean subduction system. We employed gravity data from terrestrial, satellite-based and combined sources using multiple methods to constrain stress, strain and gravitational potential energy (GPE). Well-constrained 3D density models, which were partly optimised using the combined regional gravity model IMOSAGA01C (Hosse et al. in Surv Geophys, 2014, this issue), were used as bases for the computation of stress anomalies on the top of the subducting oceanic Nazca plate and GPE relative to the base of the lithosphere. The geometries and physical parameters of the 3D density models were used for the computation of stresses and uplift rates in the dynamic modelling. The stress distributions, as derived from the static and dynamic modelling, reveal distinct positive anomalies of up to 80 MPa along the coastal Jurassic batholith belt. The anomalies correlate well with major seismicity in the shallow parts of the subduction system. Moreover, the pattern of stress distributions in the Andean convergent zone varies both along the north-south and west-east directions, suggesting that the continental fore-arc is highly segmented. Estimates of GPE show that the high Central Andes might be in a state of horizontal deviatoric tension. Models of gravity gradients from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission were used to compute Bouguer-like gradient anomalies at 8 km above sea level. The analysis suggests that data from GOCE add significant value to the interpretation of lithospheric structures, given that the appropriate topographic correction is applied.

GOCE gravity field simulation based on actual mission scenario

NASA Astrophysics Data System (ADS)

Pail, R.; Goiginger, H.; Mayrhofer, R.; Höck, E.; Schuh, W.-D.; Brockmann, J. M.; Krasbutter, I.; Fecher, T.; Gruber, T.

2009-04-01

In the framework of the ESA-funded project "GOCE High-level Processing Facility", an operational hardware and software system for the scientific processing (Level 1B to Level 2) of GOCE data has been set up by the European GOCE Gravity Consortium EGG-C. One key component of this software system is the processing of a spherical harmonic Earth's gravity field model and the corresponding full variance-covariance matrix from the precise GOCE orbit and calibrated and corrected satellite gravity gradiometry (SGG) data. In the framework of the time-wise approach a combination of several processing strategies for the optimum exploitation of the information content of the GOCE data has been set up: The Quick-Look Gravity Field Analysis is applied to derive a fast diagnosis of the GOCE system performance and to monitor the quality of the input data. In the Core Solver processing a rigorous high-precision solution of the very large normal equation systems is derived by applying parallel processing techniques on a PC cluster. Before the availability of real GOCE data, by means of a realistic numerical case study, which is based on the actual GOCE orbit and mission scenario and simulation data stemming from the most recent ESA end-to-end simulation, the expected GOCE gravity field performance is evaluated. Results from this simulation as well as recently developed features of the software system are presented. Additionally some aspects on data combination with complementary data sources are addressed.

What have we gained from GOCE, and what is still to be expected?

NASA Astrophysics Data System (ADS)

Pail, R.; Fecher, T.; Mayer-Gürr, T.; Rieser, D.; Schuh, W. D.; Brockmann, J. M.; Jäggi, A.; Höck, E.

2012-04-01

So far three releases of GOCE-only gravity field models applying the time-wise method have been computed in the frame of the ESA project "GOCE High-Level Processing Facility". They have been complemented by satellite-only combination models generated by the GOCO ("Gravity Observation Combination") consortium. Due to the fact that the processing strategy has remained practically unchanged for all releases, the continuous improvement by including more and more GOCE data can be analyzed. One of the basic features of the time-wise gravity field models (GOCE_TIM) is the fact, that no gravity field prior information is used, neither as reference model nor for constraining the solution. Therefore, the gain of knowledge on the Earth's gravity field derived purely from the GOCE mission can be evaluated. The idea of the complementary GOCO models is to improve the long to medium wavelengths of the gravity field solutions, which are rather weakly defined by GOCE orbit information, by inclusion of additional data from satellite sources such as GRACE, CHAMP and SLR, taking benefit from the individual strengths and favourable features of the individual data types. In this contribution, we will review which impact GOCE has achieved so far on global and regional gravity field modelling. Besides the gravity field modelling itself, the contributions of GOCE to several application fields, such as the computation of geodetic mean dynamic topography (MDT), and also for geophysical modelling of the lithosphere, will be highlighted. Special emphasis shall be given to the discussion to what extent the full variance-covariance information, representing very realistic error estimates of the gravity field accuracy, can be utilized. Finally, also a GOCE performance prediction shall be given. After the end of the extended mission phase by December 2012, currently several mission scenarios are discussed, such as either extending the mission period further as long as possible at the same altitude, or lowering the satellite by 10-20 km for a shorter period. Based on numerical simulation studies the pros and cons of several scenarios regarding the achievable gravity field accuracy shall be evaluated and quantified.

Evaluation of GOCE-based Global Geoid Models in Finnish Territory

NASA Astrophysics Data System (ADS)

Saari, Timo; Bilker-Koivula, Mirjam

2015-04-01

The gravity satellite mission GOCE made its final observations in the fall of 2013. By then it had exceeded its expected lifespan of one year with more than three additional years. Thus, the mission collected more data from the Earth's gravitational field than expected, and more comprehensive global geoid models have been derived ever since. The GOCE High-level Processing Facility (HPF) by ESA has published GOCE global gravity field models annually. We compared all of the 12 HPF-models as well as 3 additional GOCE, 11 GRACE and 6 combined GOCE+GRACE models with GPS-levelling data and gravity observations in Finland. The most accurate models were compared against high resolution global geoid models EGM96 and EGM2008. The models were evaluated up to three different degrees and order: 150 (the common maximum for the GRACE models), 240 (the common maximum for the GOCE models) and maximum. When coefficients up to degree and order 150 are used, the results of the GOCE models are comparable with the results of the latest GRACE models. Generally, all of the latest GOCE and GOCE+GRACE models give standard deviations of the height anomaly differences of around 15 cm and of gravity anomaly differences of around 10 mgal over Finland. The best solutions were not always achieved with the highest maximum degree and order of the satellite gravity field models, since the highest coefficients (above 240) may be less accurately determined. Over Finland, the latest GOCE and GOCE+GRACE models give similar results as the high resolution models EGM96 and EGM2008 when coefficients up to degree and order 240 are used. This is mainly due to the high resolution terrestrial data available in the area of Finland, which was used in the high resolution models.

Orbital Gravity Gradiometry Beyond GOCE: Mission Concepts

NASA Technical Reports Server (NTRS)

Shirron, Peter J.; DiPirro, Michael J.; Canavan, Edgar R.; Paik, Ho Jung; Moody, M. Vol; Venkateswara, Krishna Y.; Han, Shin-Chan; Ditmar, Pavel; Klees, Roland; Jekeli, Christopher;

ESA BRAT (Broadview Radar Altimetry Toolbox) and GUT (GOCE User Toolbox) toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Ambrozio, A.; Restano, M.

2016-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including the upcoming Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's future release (4.0.0) is planned for September 2016. Based on the community feedback, the frontend has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.0 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's VCM (Variance-Covariance Matrix) tool for analysing GOCE's variance-covariance matrices. BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.

Evaluation of global satellite gravity models using terrestrial gravity observations over the Kingdom of Saudi Arabia A. Alothman and B. Elsaka

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Elsaka, Basem

The gravity field models from the GRACE and GOCE missions have increased the knowledge of the earth’s global gravity field. The latter GOCE mission has provided accuracies of about 1-2 cm and 1milli-Gal level in the global geoid and gravity anomaly, respectively. However, determining all wavelength ranges of the gravity field spectrum cannot be only achieved from satellite gravimetry but from the allowed terrestrial gravity data. In this contribution, we use a gravity network of 42 first-order absolute gravity stations, observed by LaCosta Romberg gravimeter during the period 1967-1969 by Ministry of Petroleum and Mineral Resources, to validate the GOCE gravity models in order to gain more detailed regional gravity information. The network stations are randomly distributed all over the country with a spacing of about 200 km apart. The results show that the geoid height and gravity anomaly determined from terrestrial gravity data agree with the GOCE based models and give additional information to the satellite gravity solutions.

Adaptive topographic mass correction for satellite gravity and gravity gradient data

NASA Astrophysics Data System (ADS)

Holzrichter, Nils; Szwillus, Wolfgang; Götze, Hans-Jürgen

2014-05-01

Subsurface modelling with gravity data includes a reliable topographic mass correction. Since decades, this mandatory step is a standard procedure. However, originally methods were developed for local terrestrial surveys. Therefore, these methods often include defaults like a limited correction area of 167 km around an observation point, resampling topography depending on the distance to the station or disregard the curvature of the earth. New satellite gravity data (e.g. GOCE) can be used for large scale lithospheric modelling with gravity data. The investigation areas can include thousands of kilometres. In addition, measurements are located in the flight height of the satellite (e.g. ~250 km for GOCE). The standard definition of the correction area and the specific grid spacing around an observation point was not developed for stations located in these heights and areas of these dimensions. This asks for a revaluation of the defaults used for topographic correction. We developed an algorithm which resamples the topography based on an adaptive approach. Instead of resampling topography depending on the distance to the station, the grids will be resampled depending on its influence at the station. Therefore, the only value the user has to define is the desired accuracy of the topographic correction. It is not necessary to define the grid spacing and a limited correction area. Furthermore, the algorithm calculates the topographic mass response with a spherical shaped polyhedral body. We show examples for local and global gravity datasets and compare the results of the topographic mass correction to existing approaches. We provide suggestions how satellite gravity and gradient data should be corrected.

Moho depth model for the Central Asian Orogenic Belt from satellite gravity gradients

NASA Astrophysics Data System (ADS)

Guy, Alexandra; Holzrichter, Nils; Ebbing, Jörg

2017-09-01

The main purpose of this study is to construct a new 3-D model of the Central Asian Orogenic Belt (CAOB) crust, which can be used as a starting point for future lithospheric studies. The CAOB is a Paleozoic accretionary orogen surrounded by the Siberian Craton to the north and the North China and Tarim Cratons to the south. This area is of great interest due to its enigmatic and still not completely understood geodynamic evolution. First, we estimate an initial crustal thickness by inversion of the vertical gravity component of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and DTU10 models. Second, 3-D forward modeling of the GOCE gravity gradients is performed, which determines the topography of the Moho, the geometry, and the density distribution of the deeper parts of the CAOB and its surroundings, taking into account the lateral and vertical density variations of the crust. The model is constrained by seismic refraction, reflection, and receiver function studies and geological studies. In addition, we discuss the isostatic implications of the differences between the seismic Moho and the resulting 3-D gravity Moho, complemented by the analysis of the lithostatic load distribution at the upper mantle level. Finally, the correlation between the contrasting tectonic domains and the thickness of the crust reveals the inheritance of Paleozoic and Mesozoic geodynamics, particularly the magmatic provinces and the orocline which preserve their crustal features.

Simulation-based evaluation of a cold atom interferometry gradiometer concept for gravity field recovery

NASA Astrophysics Data System (ADS)

Douch, Karim; Wu, Hu; Schubert, Christian; Müller, Jürgen; Pereira dos Santos, Franck

2018-03-01

The prospects of future satellite gravimetry missions to sustain a continuous and improved observation of the gravitational field have stimulated studies of new concepts of space inertial sensors with potentially improved precision and stability. This is in particular the case for cold-atom interferometry (CAI) gradiometry which is the object of this paper. The performance of a specific CAI gradiometer design is studied here in terms of quality of the recovered gravity field through a closed-loop numerical simulation of the measurement and processing workflow. First we show that mapping the time-variable field on a monthly basis would require a noise level below 5mE /√{Hz } . The mission scenarios are therefore focused on the static field, like GOCE. Second, the stringent requirement on the angular velocity of a one-arm gradiometer, which must not exceed 10-6 rad/s, leads to two possible modes of operation of the CAI gradiometer: the nadir and the quasi-inertial mode. In the nadir mode, which corresponds to the usual Earth-pointing satellite attitude, only the gradient Vyy , along the cross-track direction, is measured. In the quasi-inertial mode, the satellite attitude is approximately constant in the inertial reference frame and the 3 diagonal gradients Vxx,Vyy and Vzz are measured. Both modes are successively simulated for a 239 km altitude orbit and the error on the recovered gravity models eventually compared to GOCE solutions. We conclude that for the specific CAI gradiometer design assumed in this paper, only the quasi-inertial mode scenario would be able to significantly outperform GOCE results at the cost of technically challenging requirements on the orbit and attitude control.

Major Fault Patterns in Zanjan State of Iran Based of GECO Global Geoid Model

NASA Astrophysics Data System (ADS)

Beheshty, Sayyed Amir Hossein; Abrari Vajari, Mohammad; Raoufikelachayeh, SeyedehSusan

2016-04-01

A new Earth Gravitational Model (GECO) to degree 2190 has been developed incorporates EGM2008 and the latest GOCE based satellite solutions. Satellite gradiometry data are more sensitive information of the long- and medium- wavelengths of the gravity field than the conventional satellite tracking data. Hence, by utilizing this new technique, more accurate, reliable and higher degrees/orders of the spherical harmonic expansion of the gravity field can be achieved. Gravity gradients can also be useful in geophysical interpretation and prospecting. We have presented the concept of gravity gradients with some simple interpretations. A MATLAB based computer programs were developed and utilized for determining the gravity and gradient components of the gravity field using the GGMs, followed by a case study in Zanjan State of Iran. Our numerical studies show strong (more than 72%) correlations between gravity anomalies and the diagonal elements of the gradient tensor. Also, strong correlations were revealed between the components of the deflection of vertical and the off-diagonal elements as well as between the horizontal gradient and magnitude of the deflection of vertical. We clearly distinguished two big faults in North and South of Zanjan city based on the current information. Also, several minor faults were detected in the study area. Therefore, the same geophysical interpretation can be stated for gravity gradient components too. Our mathematical derivations support some of these correlations.

Isostatic GOCE Moho model for Iran

NASA Astrophysics Data System (ADS)

Eshagh, Mehdi; Ebadi, Sahar; Tenzer, Robert

2017-05-01

One of the major issues associated with a regional Moho recovery from the gravity or gravity-gradient data is the optimal choice of the mean compensation depth (i.e., the mean Moho depth) for a certain area of study, typically for orogens characterised by large Moho depth variations. In case of selecting a small value of the mean compensation depth, the pattern of deep Moho structure might not be reproduced realistically. Moreover, the definition of the mean compensation depth in existing isostatic models affects only low-degrees of the Moho spectrum. To overcome this problem, in this study we reformulate the Sjöberg and Jeffrey's methods of solving the Vening-Meinesz isostatic problem so that the mean compensation depth contributes to the whole Moho spectrum. Both solutions are then defined for the vertical gravity gradient, allowing estimating the Moho depth from the GOCE satellite gravity-gradiometry data. Moreover, gravimetric solutions provide realistic results only when a priori information on the crust and upper mantle structure is known (usually from seismic surveys) with a relatively good accuracy. To investigate this aspect, we formulate our gravimetric solutions for a variable Moho density contrast to account for variable density of the uppermost mantle below the Moho interface, while taking into consideration also density variations within the sediments and consolidated crust down to the Moho interface. The developed theoretical models are applied to estimate the Moho depth from GOCE data at the regional study area of the Iranian tectonic block, including also parts of surrounding tectonic features. Our results indicate that the regional Moho depth differences between Sjöberg and Jeffrey's solutions, reaching up to about 3 km, are caused by a smoothing effect of Sjöberg's method. The validation of our results further shows a relatively good agreement with regional seismic studies over most of the continental crust, but large discrepancies are detected under the Oman Sea and the Makran subduction zone. We explain these discrepancies by a low quality of seismic data offshore.

Sediment basin modeling through GOCE gradients controlled by thermo-isostatic constraints

NASA Astrophysics Data System (ADS)

Pivetta, Tommaso; Braitenberg, Carla

2015-04-01

Exploration of geodynamic and tectonic structures through gravity methods has experienced an increased interest in the recent years thank's to the possibilities offered by satellite gravimetry (e.g. GOCE). The main problem with potential field methods is the non-uniqueness of the underground density distributions that satisfy the observed gravity field. In terrestrial areas with scarce geological and geophysical information, valid constraints to the density model could be obtained from the application of geodynamic models. In this contribution we present the study of the gravity signals associated to the thermo-isostatic McKenzie-model (McKenzie, 1978) that predicts the development of sedimentary basins from the stretching of lithosphere. This model seems to be particularly intriguing for gravity studies as we could obtain estimates of densities and thicknesses of crust and mantle before and after a rifting event and gain important information about the time evolution of the sedimentary basin. The McKenzie-model distinguishes the rifting process into two distinct phases: a syn-rift phase that occurs instantly and is responsible of the basin formation, the thinning of lithosphere and the upwelling of hot asthenosphere. Then a second phase (post-rift), that is time dependent, and predicts further subsidence caused by the cooling of mantle and asthenosphere and subsequently increase in rock density. From the application of the McKenzie-model we have derived density underground distributions for two scenarios: the first scenario involves the lithosphere density distribution immediately after the stretching event; the second refers to the density model when thermal equilibrium between stretched and unstretched lithospheres is achieved. Calculations of gravity anomalies and gravity gradient anomalies are performed at 5km height and at the GOCE mean orbit quota (250km). We have found different gravity signals for syn-rift (gravimetric maximum) and post-rift (gravimetric minimum) scenarios and that satellite measurements are sufficiently precise to discriminate between them. The McKenzie-model is then applied to a real basin in Africa, the Benue Trough, which is an aborted rift that seems to be particularly adapt to be studied with satellite gravity techniques. McKenzie D., 1978, Some remarks on the development of sedimentary basins, Earth and Planetary Science Letters, 40, 25-32

Accuracy assessment of GOCE-based geopotential models and their use for modelling the gravimetric quasigeoid - A case study for Poland

NASA Astrophysics Data System (ADS)

Godah, Walyeldeen; Szelachowska, Malgorzata; Krynski, Jan

2014-06-01

The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) has significantly upgraded the knowledge on the Earth gravity field. In this contribution the accuracy of height anomalies determined from Global Geopotential Models (GGMs) based on approximately 27 months GOCE satellite gravity gradiometry (SGG) data have been assessed over Poland using three sets of precise GNSS/levelling data. The fits of height anomalies obtained from 4th release GOCE-based GGMs to GNSS/levelling data were discussed and compared with the respective ones of 3rd release GOCE-based GGMs and the EGM08. Furthermore, two highly accurate gravimetric quasigeoid models were developed over the area of Poland using high resolution Faye gravity anomalies. In the first, the GOCE-based GGM was used as a reference geopotential model, and in the second - the EGM08. They were evaluated with GNSS/levelling data and their accuracy performance was assessed. The use of GOCE-based GGMs for recovering the long-wavelength gravity signal in gravimetric quasigeoid modelling was discussed. Misja GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) przyczyniła się do znacznego poprawienia znajomości pola siły ciężkości Ziemi. W artykule przedstawiono wyniki oszacowania dokładności anomalii wysokości, wyznaczonych z globalnych modeli geopotencjału opracowanych na podstawie blisko 27 miesięcy pomiarów z satelitarnej misji gradiometrycznej GOCE. Do oszacowania wykorzystano trzy zbiory dokładnych danych satelitarno-niwelacyjnych z obszaru Polski. Omówiono wyniki wpasowania wartości anomalii wysokości otrzymanych z czwartej wersji globalnych modeli geopotencjału wyznaczonych na podstawie danych misji GOCE do danych satelitarno-niwelacyjnych oraz porównano je z wynikami odpowiedniego wpasowania trzeciej wersji globalnych modeli geopotencjału otrzymanych z GOCE oraz z modelu EGM08. Ponadto, wykorzystując wysokorozdzielczy zbiór grawimetrycznych anomalii Faye'a, wyznaczono dla obszaru Polski dwa grawimetryczne modele quasigeoidy o wysokiej dokładności. W pierwszym przypadku jako model referencyjny użyto model utworzony na podstawie danych z misji GOCE, w drugim - model EGM08. Wygenerowane modele quasigeoidy porównano z danymi satelitarno-niwelacyjnymi oraz oszacowano ich dokładność. Omówiono przydatność otrzymanych na podstawie danych z misji GOCE globalnych modeli geopotencjału do odtworzenia długofalowego sygnału grawimetrycznego przy modelowaniu grawimetrycznej quasigeoidy.

The BRAT and GUT Couple: Broadview Radar Altimetry and GOCE User Toolboxes

NASA Astrophysics Data System (ADS)

Benveniste, J.; Restano, M.; Ambrózio, A.

2017-12-01

The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from previous and current altimetry missions, including Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases. BRAT's next release (4.2.0) is planned for October 2017. Based on the community feedback, the front-end has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images. The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions. In the current 3.1 version, GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's Variance-Covariance Matrix tool (VCM). BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.

Effects of space weather on GOCE electrostatic gravity gradiometer measurements

NASA Astrophysics Data System (ADS)

Ince, E. Sinem; Pagiatakis, Spiros D.

2016-12-01

We examine the presence of residual nongravitational signatures in gravitational gradients measured by GOCE electrostatic gravity gradiometer. These signatures are observed over the magnetic poles during geomagnetically active days and can contaminate the trace of the gravitational gradient tensor by up to three to five times the expected noise level of the instrument (˜ 11 mE). We investigate these anomalies in the gradiometer measurements along many satellite tracks and examine possible causes using external datasets, such as interplanetary electric field measurements from the ACE (advanced composition explorer) and WIND spacecraft, and Poynting vector (flux) estimated from equivalent ionospheric currents derived from spherical elementary current systems over North America and Greenland. We show that the variations in the east-west and vertical electrical currents and Poynting vector components at the satellite position are highly correlated with the disturbances observed in the gradiometer measurements. The results presented in this paper reveal that the disturbances are due to intense ionospheric current variations that are enhanced by increased solar activity that causes a very dynamic drag environment. Moreover, successful modelling and removal of a high percentage of these disturbances are possible using external geomagnetic field observations.

Assessment of Gravity Field and Steady State Ocean Circulation Explorer (GOCE) geoid model using GPS levelling over Sabah and Sarawak

NASA Astrophysics Data System (ADS)

Othman, A. H.; Omar, K. M.; Din, A. H. M.; Som, Z. A. M.; Yahaya, N. A. Z.; Pa'suya, M. F.

2016-06-01

The GOCE satellite mission has significantly contributed to various applications such as solid earth physics, oceanography and geodesy. Some substantial applications of geodesy are to improve the gravity field knowledge and the precise geoid modelling towards realising global height unification. This paper aims to evaluate GOCE geoid model based on the recent GOCE Global Geopotential Model (GGM), as well as EGM2008, using GPS levelling data over East Malaysia, i.e. Sabah and Sarawak. The satellite GGMs selected in this study are the GOCE GGM models which include GOCE04S, TIM_R5 and SPW_R4, and the EGM2008 model. To assess these models, the geoid heights from these GGMs are compared to the local geometric geoid height. The GGM geoid heights was derived using EGMLAB1 software and the geometric geoid height was computed by available GPS levelling information obtained from the Department Survey and Mapping Malaysia. Generally, the GOCE models performed better than EGM2008 over East Malaysia and the best fit GOCE model for this region is the TIM_R5 model. The TIM_R5 GOCE model demonstrated the lowest R.M.S. of ± 16.5 cm over Sarawak, comparatively. For further improvement, this model should be combined with the local gravity data for optimum geoid modelling over East Malaysia.

Moho topography, ranges and folds of Tibet by analysis of global gravity models and GOCE data

PubMed Central

Shin, Young Hong; Shum, C.K.; Braitenberg, Carla; Lee, Sang Mook; Na, Sung -Ho; Choi, Kwang Sun; Hsu, Houtse; Park, Young-Sue; Lim, Mutaek

2015-01-01

The determination of the crustal structure is essential in geophysics, as it gives insight into the geohistory, tectonic environment, geohazard mitigation, etc. Here we present the latest advance on three-dimensional modeling representing the Tibetan Mohorovičić discontinuity (topography and ranges) and its deformation (fold), revealed by analyzing gravity data from GOCE mission. Our study shows noticeable advances in estimated Tibetan Moho model which is superior to the results using the earlier gravity models prior to GOCE. The higher quality gravity field of GOCE is reflected in the Moho solution: we find that the Moho is deeper than 65 km, which is twice the normal continental crust beneath most of the Qinghai-Tibetan plateau, while the deepest Moho, up to 82 km, is located in western Tibet. The amplitude of the Moho fold is estimated to be ranging from −9 km to 9 km with a standard deviation of ~2 km. The improved GOCE gravity derived Moho signals reveal a clear directionality of the Moho ranges and Moho fold structure, orthogonal to deformation rates observed by GPS. This geophysical feature, clearly more evident than the ones estimated using earlier gravity models, reveals that it is the result of the large compressional tectonic process. PMID:26114224

Density interface topography recovered by inversion of satellite gravity gradiometry observations

NASA Astrophysics Data System (ADS)

Ramillien, G. L.

2017-08-01

A radial integration of spherical mass elements (i.e. tesseroids) is presented for evaluating the six components of the second-order gravity gradient (i.e. second derivatives of the Newtonian mass integral for the gravitational potential) created by an uneven spherical topography consisting of juxtaposed vertical prisms. The method uses Legendre polynomial series and takes elastic compensation of the topography by the Earth's surface into account. The speed of computation of the polynomial series increases logically with the observing altitude from the source of anomaly. Such a forward modelling can be easily applied for reduction of observed gravity gradient anomalies by the effects of any spherical interface of density. An iterative least-squares inversion of measured gravity gradient coefficients is also proposed to estimate a regional set of juxtaposed topographic heights. Several tests of recovery have been made by considering simulated gradients created by idealistic conical and irregular Great Meteor seamount topographies, and for varying satellite altitudes and testing different levels of uncertainty. In the case of gravity gradients measured at a GOCE-type altitude of ˜ 300 km, the search converges down to a stable but smooth topography after 10-15 iterations, while the final root-mean-square error is ˜ 100 m that represents only 2 % of the seamount amplitude. This recovery error decreases with the altitude of the gravity gradient observations by revealing more topographic details in the region of survey.

Goce and Its Role in Combined Global High Resolution Gravity Field Determination

NASA Astrophysics Data System (ADS)

Fecher, T.; Pail, R.; Gruber, T.

2013-12-01

Combined high-resolution gravity field models serve as a mandatory basis to describe static and dynamic processes in system Earth. Ocean dynamics can be modeled referring to a high-accurate geoid as reference surface, solid earth processes are initiated by the gravity field. Also geodetic disciplines such as height system determination depend on high-precise gravity field information. To fulfill the various requirements concerning resolution and accuracy, any kind of gravity field information, that means satellite as well as terrestrial and altimetric gravity field observations have to be included in one combination process. A key role is here reserved for GOCE observations, which contribute with its optimal signal content in the long to medium wavelength part and enable a more accurate gravity field determination than ever before especially in areas, where no high-accurate terrestrial gravity field observations are available, such as South America, Asia or Africa. For our contribution we prepare a combined high-resolution gravity field model up to d/o 720 based on full normal equation including recent GOCE, GRACE and terrestrial / altimetric data. For all data sets, normal equations are set up separately, relative weighted to each other in the combination step and solved. This procedure is computationally challenging and can only be performed using super computers. We put special emphasis on the combination process, for which we modified especially our procedure to include GOCE data optimally in the combination. Furthermore we modified our terrestrial/altimetric data sets, what should result in an improved outcome. With our model, in which we included the newest GOCE TIM4 gradiometry results, we can show how GOCE contributes to a combined gravity field solution especially in areas of poor terrestrial data coverage. The model is validated by independent GPS leveling data in selected regions as well as computation of the mean dynamic topography over the oceans. Further, we analyze the statistical error estimates derived from full covariance propagation and compare them with the absolute validation with independent data sets.

Gravity Field Solution Derived from Recent Releases of GOCE-Based Geopotential Models and Terrestrial Gravity Observations over The Kingdom of Saudi Arabia

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Elsaka, Basem

2015-03-01

The free air gravity anomalies over Saudi Arabia (KSA) has been estimated from the final releases of GOCE-based global geopotential models (GGMs) compared with the terrestrial gravity anomalies of 3554 sites. Two GGMs; EGM08 and Eigen-6C3 have been applied. The free-air anomalies from GOCE-based, ΔgGGM, have been calculated over the 3554 stations in the medium and short spectrum of gravity wavelength of d/o 100, …, 250 (with 10 step). The short spectrum has been compensated once from d/o 101, …, 251 to 2190 and 1949 using EGM08 and Eigen-6C3 (i.e. ΔgGGM), respectively. The very short component was determined using residual terrain modelling approach. Our findings show firstly that the EGM08 is more reliable than Eigen-6C3. Second, the GOCE-based GGMs provide similar results within the spectral wavelength band from d/o 100 to d/o 180. Beyond d/o 180 till d/o 250, we found that GOCE-based TIM model releases provide substantial improvements within the spectral band from d/o 220 to d/o 250 with respect to the DIR releases. Third, the TIM_r5 model provides the least standard deviations (st. dev.) in terms of gravity anomalies.

GOCE: Mission Overview and Early Results (Invited)

NASA Astrophysics Data System (ADS)

Rummel, R. F.; Muzi, D.; Drinkwater, M. R.; Floberghagen, R.; Fehringer, M.

2009-12-01

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission is the first Earth Explorer Core mission of the Living Planet Programme of the European Space Agency (ESA). The primary objective of the GOCE mission is to provide global and regional models of the Earth gravity field and the geoid, its reference equi-potential surface, with unprecedented spatial resolution and accuracy. GOCE was launched successfully on 17 March 2009 from the Plesetsk Cosmodrome in northern Russia onboard a Rockot launch vehicle. System commissioning and payload calibration have been completed and the satellite is decaying to its initial measurement operating altitude of 255 km, which is expected to be reached in mid-September 2009. After one week of final payload calibration, GOCE will enter its first 6 month duration phase of uninterrupted science measurements at that altitude. This presentation will recall GOCE's main goals and its major development milestones. In addition, a description of the data products generated and some highlights of the satellite performance will be outlined. Artist's impression of GOCE Satellite in flight (courtesy AOES-Medialab).

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Benveniste, Jérôme; Knudsen, Per

2016-07-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products. GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations, and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy, Oceanography and Solid earth studies. Accordingly, the GUT version 3 has: - An attractive and easy to use Graphic User Interface (GUI) for the toolbox, - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients, anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies. - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

GOCE Precise Science Orbits for the Entire Mission and their Use for Gravity Field Recovery

NASA Astrophysics Data System (ADS)

Jäggi, Adrian; Bock, Heike; Meyer, Ulrich; Weigelt, Matthias

The Gravity field and steady-state Ocean Circulation Explorer (GOCE), ESA's first Earth Explorer Core Mission, was launched on March 17, 2009 into a sun-synchronous dusk-dawn orbit and re-entered into the Earth's atmosphere on November 11, 2013. It was equipped with a three-axis gravity gradiometer for high-resolution recovery of the Earth's gravity field, as well as with a 12-channel, dual-frequency Global Positioning System (GPS) receiver for precise orbit determination (POD), instrument time-tagging, and the determination of the long wavelength part of the Earth’s gravity field. A precise science orbit (PSO) product was provided during the entire mission by the GOCE High-level Processing Facility (HPF) from the GPS high-low Satellite-to-Satellite Tracking (hl-SST) data. We present the reduced-dynamic and kinematic PSO results for the entire mission period. Orbit comparisons and validations with independent Satellite Laser Ranging (SLR) measurements demonstrate the high quality of both orbit products being close to 2 cm 1-D RMS, but also reveal a correlation between solar activity, GPS data availability, and the quality of the orbits. We use the 1-sec kinematic positions of the GOCE PSO product for gravity field determination and present GPS-only solutions covering the entire mission period. The generated gravity field solutions reveal severe systematic errors centered along the geomagnetic equator, which may be traced back to the GPS carrier phase observations used for the kinematic orbit determination. The nature of the systematic errors is further investigated and reprocessed orbits free of systematic errors along the geomagnetic equator are derived. Eventually, the potential of recovering time variable signals from GOCE kinematic positions is assessed.

Selected Gravity Models in Terms of the fit to the GOCE Kinematic Orbit in the Dynamic Orbit Determination Process

NASA Astrophysics Data System (ADS)

Bobojć, Andrzej; Drożyner, Andrzej; Rzepecka, Zofia

2017-04-01

The work includes the comparison of performance of selected geopotential models in the dynamic orbit estimation of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. This was realized by fitting estimated orbital arcs to the official centimeter-accuracy GOCE kinematic orbit which is provided by the European Space Agency. The Cartesian coordinates of kinematic orbit were treated as observations in the orbit estimation. The initial satellite state vector components were corrected in an iterative process with respect to the J2000.0 inertial reference frame using the given geopotential model, the models describing the remaining gravitational perturbations and the solar radiation pressure. Taking the obtained solutions into account, the RMS values of orbital residuals were computed. These residuals result from the difference between the determined orbit and the reference one - the GOCE kinematic orbit. The performance of selected gravity models was also determined using various orbital arc lengths. Additionally, the RMS fit values were obtained for some gravity models truncated at given degree and order of spherical harmonic coefficients. The advantage of using the kinematic orbit is its independence from any a priori dynamical models. For the research such GOCE-independent gravity models as HUST-Grace2016s, ITU_GRACE16, ITSG-Grace2014s, ITSG-Grace2014k, GGM05S, Tongji-GRACE01, ULUX_CHAMP2013S, ITG-GRACE2010S, EIGEN-51C, EIGEN5S, EGM2008 and EGM96 were adopted.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Knudsen, Per; Benveniste, Jerome

2017-04-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products.
GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information
and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced
computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations,
and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT
Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development
of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for
oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming
on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy,
Oceanography and Solid earth studies.
Accordingly, the GUT version 3 has:
 - An attractive and easy to use Graphic User Interface (GUI) for the toolbox,
 - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients,
anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies.
 - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Knudsen, Per; Benveniste, Jerome; Team Gut

2016-04-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products.
GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information
and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced
computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations,
and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT
Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development
of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for
oceanography. The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming
on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy,
Oceanography and Solid earth studies.
Accordingly, the GUT version 3 has:
 - An attractive and easy to use Graphic User Interface (GUI) for the toolbox,
 - Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients,
anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies.
 - An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

Improvement of the GPS/A system for extensive observation along subduction zones around Japan

NASA Astrophysics Data System (ADS)

Fujimoto, H.; Kido, M.; Tadokoro, K.; Sato, M.; Ishikawa, T.; Asada, A.; Mochizuki, M.

2011-12-01

Combined high-resolution gravity field models serve as a mandatory basis to describe static and dynamic processes in system Earth. Ocean dynamics can be modeled referring to a high-accurate geoid as reference surface, solid earth processes are initiated by the gravity field. Also geodetic disciplines such as height system determination depend on high-precise gravity field information. To fulfill the various requirements concerning resolution and accuracy, any kind of gravity field information, that means satellite as well as terrestrial and altimetric gravity field observations have to be included in one combination process. A key role is here reserved for GOCE observations, which contribute with its optimal signal content in the long to medium wavelength part and enable a more accurate gravity field determination than ever before especially in areas, where no high-accurate terrestrial gravity field observations are available, such as South America, Asia or Africa. For our contribution we prepare a combined high-resolution gravity field model up to d/o 720 based on full normal equation including recent GOCE, GRACE and terrestrial / altimetric data. For all data sets, normal equations are set up separately, relative weighted to each other in the combination step and solved. This procedure is computationally challenging and can only be performed using super computers. We put special emphasis on the combination process, for which we modified especially our procedure to include GOCE data optimally in the combination. Furthermore we modified our terrestrial/altimetric data sets, what should result in an improved outcome. With our model, in which we included the newest GOCE TIM4 gradiometry results, we can show how GOCE contributes to a combined gravity field solution especially in areas of poor terrestrial data coverage. The model is validated by independent GPS leveling data in selected regions as well as computation of the mean dynamic topography over the oceans. Further, we analyze the statistical error estimates derived from full covariance propagation and compare them with the absolute validation with independent data sets.

Density and crosswind from GOCE - comparisons with other satellite data, ground-based observations and models

NASA Astrophysics Data System (ADS)

Doornbos, E.; Bruinsma, S.; Conde, M.; Forbes, J. M.

2013-12-01

Observations made by the European Space Agency (ESA) Gravity field and Ocean Circulation Explorer (GOCE) satellite have enabled the production of a spin-off product of high resolution and high accuracy data on thermosphere density, derived from aerodynamic analysis of acceleration measurements. In this regard, the mission follows in the footsteps of the earlier accelerometer-carrying gravity missions CHAMP and GRACE. The extremely high accuracy and redundancy of the six accelerometers carried by GOCE in its gravity gradiometer instrument has provided new insights on the performance and calibration of these instruments. Housekeeping data on the activation of the GOCE drag free control thruster, made available by ESA has made the production of the thermosphere data possible. The long duration low altitude of GOCE, enabled by its drag free control system, has ensured the presence of very large aerodynamic accelerations throughout its lifetime. This has been beneficial for the accurate derivation of data on the wind speed encountered by the satellite. We have compared the GOCE density observations with data from CHAMP and GRACE. The crosswind data has been compared with CHAMP observations, as well as ground-based observations, made using Scanning Doppler Imagers in Alaska. Models of the thermosphere can provide a bigger, global picture, required as a background in the interpretation of the local space- and ground-based measurements. The comparison of these different sources of information on thermosphere density and wind, each with their own strengths and weaknesses, can provide scientific insight, as well as inputs for further refinement of the processing algorithms and models that are part of the various techniques. Density and crosswind data derived from GOCE (dusk-dawn) and CHAMP (midnight-noon) satellite accelerometer data, superimposed over HWM07 modelled horizontal wind vectors.

Crust-mantle density distribution in the eastern Qinghai-Tibet Plateau revealed by satellite-derived gravity gradients

NASA Astrophysics Data System (ADS)

LI, Honglei; Fang, Jian; Braitenberg, Carla; Wang, Xinsheng

2015-04-01

As the highest, largest and most active plateau on Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure, especially in its eastern part. In response to the subduction of the lithospheric mantle of the Indian plate, large-scale crustal motion occurs in this area. Despite the many previous studies, geodynamic processes at depth remain unclear. Knowledge of crust and upper mantle density distribution allows a better definition of the deeper geological structure and thus provides critically needed information for understanding of the underlying geodynamic processes. With an unprecedented precision of 1-2 mGal and a spatial resolution better than 100 km, GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission products can be used to constrain the crust-mantle density distribution. Here we used GOCE gravitational gradients at an altitude of 10km after reducing the effects of terrain, sediment thickness variations, and Moho undulations to image the density structures of eastern Tibet up to 200 km depths. We inverted the residual satellite gravitational gradients using a least square approach. The initial density model for the inversion is based on seismic velocities from the tomography. The model is composed of rectangular blocks, having a uniform density, with widths of about 100 km and variable thickness and depths. The thickness of the rectangular cells changes from10 to 60km in accordance with the seismic model. Our results reveal some large-scale, structurally controlled density variations at depths. The lithospheric root defined by higher-density contrast features from southwest to northeast, with shallowing in the central part: base of lithosphere reaches a depth of180 km, less than 100km, and 200 km underneath the Lhasa, Songpan-Ganzi, and Ordos crustal blocks, respectively. However, these depth values only represent a first-order parameterization because they depend on model discretization inherited from the original seismic tomography model. For example, the thickness of the uniform density blocks centered at140 km depth is as large as 60 km. Low-density crustal anomalies beneath the southern Lhasa and Songpan-Ganzi blocks in our model support the idea of weak lower crust and possible crustal flow, as a result of the thermal anomalies caused by the upwelling of hot deep materials. The weak lower crust may cause the decoupling of the upper crust and the mantle. These results are consistent with many other geophysical studies, confirming the effectiveness of the GOCE gravitational gradient data. Using these data in combination with other geodynamic constraints (e.g., gravity and seismic structure and preliminary reference Earth model), an improved dynamic model can be derived.

GOCE SSTI GNSS Receiver Re-Entry Phase Analysis

NASA Astrophysics Data System (ADS)

Zin, A.; Zago, S.; Scaciga, L.; Marradi, L.; Floberghagen, R.; Fehringer, M.; Bigazzi, A.; Piccolo, A.; Luini, L.

2015-03-01

Gravity field and Ocean Circulation Explorer (GOCE) was an ESA Earth Explorer mission dedicated to the measure of the Earth Gravity field. The Spacecraft has been launched in 2009 and the re-entry in atmosphere happened at the end of 2013 [1]. The mean orbit altitude was set to 260 km to maximize the ultra-sensitive accelerometers on board. GOCE was equipped with two main payloads: the Electrostatic Gravity Gradiometer (EGG), a set of six 3-axis accelerometers able to measure the gravity field with unrivalled precision and then to produce the most accurate shape of the ‘geoid’ and two GPS receivers (nominal and redundant), used as a Satellite-to-Satellite Tracking Instrument (SSTI) to geolocate the gradiometer measurements and to measure the long wavelength components of the gravity field with an accuracy never reached before. Previous analyses have shown that the Precise Orbit Determination (POD) of the GOCE satellite, derived by processing the dual-frequency SSTI data (carrier phases and pseudoranges) are at the “state-of-art” of the GPS based POD: kinematic Orbits Average of daily 3D-RMS is 2,06 cm [2]. In most cases the overall accuracy is better than 2 cm 3D RMS. Moreover, the “almost continuous” [2] 1 Hz data availability from the SSTI receiver is unique and allows for a time series of kinematic positions with only 0.5% of missing epochs [2]. In October 2013 GOCE mission was concluded and in November the GOCE spacecraft re-entered in the atmosphere. During the re-entry phase the two SSTI receivers have been switched on simultaneously in order to maximize the data availability. In summer 2013, the SSTI firmware was tailored in order to sustain additional dynamic error (tracking loops robustness), expected during the re-entry phase. The SW was uploaded on SSTI-B (and purposely not on SSTI-A). Therefore this was an unique opportunity to compare a “standard” receiver behaviour (SSTI-A) with an improved one (SSTI-B) in the challenging reentry phase. This paper focuses on the analysis of the data from summer 2013 up to the re-entry phase in November 2013.

Cold Atom Interferometers Used In Space (CAIUS) for Measuring the Earth's Gravity Field

NASA Astrophysics Data System (ADS)

Carraz, O.; Luca, M.; Siemes, C.; Haagmans, R.; Silvestrin, P.

2016-12-01

In the past decades, it has been shown that atomic quantum sensors are a newly emerging technology that can be used for measuring the Earth's gravity field. There are two ways of making use of that technology: One is a gravity gradiometer concept and the other is in a low-low satellite-to-satellite ranging concept. Whereas classical accelerometers typically suffer from high noise at low frequencies, Cold Atom Interferometers are highly accurate over the entire frequency range. We recently proposed a concept using cold atom interferometers for measuring all diagonal elements of the gravity gradient tensor and the full spacecraft angular velocity in order to achieve better performance than the GOCE gradiometer over a larger part of the spectrum, with the ultimate goals of determining the fine structures in the gravity field better than today. This concept relies on a high common mode rejection, which relaxes the drag free control compare to GOCE mission, and benefits from a long interaction time with the free falling clouds of atoms due to the micro gravity environment in space as opposed to the 1-g environment on-ground. Other concept is also being studied in the frame of NGGM, which relies on the hybridization between quantum and classical techniques to improve the performance of accelerometers. This could be achieved as it is realized in frequency measurements where quartz oscillators are phase locked on atomic or optical clocks. This technique could correct the spectrally colored noise of the electrostatic accelerometers in the lower frequencies. In both cases, estimation of the Earth gravity field model from the instruments has to be evaluated taking into account different system parameters such as attitude control, altitude of the satellite, time duration of the mission, etc. Miniaturization, lower consumptions and upgrading Technical Readiness Level are the key engineering challenges that have to be faced for these space quantum technologie.

Assessment and Improvement of GOCE based Global Geopotential Models Using Wavelet Decomposition

NASA Astrophysics Data System (ADS)

Erol, Serdar; Erol, Bihter; Serkan Isik, Mustafa

2016-07-01

The contribution of recent Earth gravity field satellite missions, specifically GOCE mission, leads significant improvement in quality of gravity field models in both accuracy and resolution manners. However the performance and quality of each released model vary not only depending on the spatial location of the Earth but also the different bands of the spectral expansion. Therefore the assessment of the global model performances with validations using in situ-data in varying territories on the Earth is essential for clarifying their exact performances in local. Beside of this, their spectral evaluation and quality assessment of the signal in each part of the spherical harmonic expansion spectrum is essential to have a clear decision for the commission error content of the model and determining its optimal degree, revealed the best results, as well. The later analyses provide also a perspective and comparison on the global behavior of the models and opportunity to report the sequential improvement of the models depending on the mission developments and hence the contribution of the new data of missions. In this study a review on spectral assessment results of the recently released GOCE based global geopotential models DIR-R5, TIM-R5 with the enhancement using EGM2008, as reference model, in Turkey, versus the terrestrial data is provided. Beside of reporting the GOCE mission contribution to the models in Turkish territory, the possible improvement in the spectral quality of these models, via decomposition that are highly contaminated by noise, is purposed. In the analyses the motivation is on achieving an optimal amount of improvement that rely on conserving the useful component of the GOCE signal as much as possible, while fusing the filtered GOCE based models with EGM2008 in the appropriate spectral bands. The investigation also contain the assessment of the coherence and the correlation between the Earth gravity field parameters (free-air gravity anomalies and geoid undulations), derived from the validated geopotential models and terrestrial data (GPS/leveling, terrestrial gravity observations, DTM etc.), as well as the WGM2012 products. In the conclusion, with the numerical results, the performance of the assessed models are clarified in Turkish territory and the potential of the Wavelet decomposition in the improvement of the geopotential models is verified.

On High-Frequency Topography-Implied Gravity Signals for a Height System Unification Using GOCE-Based Global Geopotential Models

NASA Astrophysics Data System (ADS)

Grombein, Thomas; Seitz, Kurt; Heck, Bernhard

2017-03-01

National height reference systems have conventionally been linked to the local mean sea level, observed at individual tide gauges. Due to variations in the sea surface topography, the reference levels of these systems are inconsistent, causing height datum offsets of up to ±1-2 m. For the unification of height systems, a satellite-based method is presented that utilizes global geopotential models (GGMs) derived from ESA's satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE). In this context, height datum offsets are estimated within a least squares adjustment by comparing the GGM information with measured GNSS/leveling data. While the GNSS/leveling data comprises the full spectral information, GOCE GGMs are restricted to long wavelengths according to the maximum degree of their spherical harmonic representation. To provide accurate height datum offsets, it is indispensable to account for the remaining signal above this maximum degree, known as the omission error of the GGM. Therefore, a combination of the GOCE information with the high-resolution Earth Gravitational Model 2008 (EGM2008) is performed. The main contribution of this paper is to analyze the benefit, when high-frequency topography-implied gravity signals are additionally used to reduce the remaining omission error of EGM2008. In terms of a spectral extension, a new method is proposed that does not rely on an assumed spectral consistency of topographic heights and implied gravity as is the case for the residual terrain modeling (RTM) technique. In the first step of this new approach, gravity forward modeling based on tesseroid mass bodies is performed according to the Rock-Water-Ice (RWI) approach. In a second step, the resulting full spectral RWI-based topographic potential values are reduced by the effect of the topographic gravity field model RWI_TOPO_2015, thus, removing the long to medium wavelengths. By using the latest GOCE GGMs, the impact of topography-implied gravity signals on the estimation of height datum offsets is analyzed in detail for representative GNSS/leveling data sets in Germany, Austria, and Brazil. Besides considerable changes in the estimated offset of up to 3 cm, the conducted analyses show that significant improvements of 30-40% can be achieved in terms of a reduced standard deviation and range of the least squares adjusted residuals.

Using the GOCE star trackers for validating the calibration of its accelerometers

NASA Astrophysics Data System (ADS)

Visser, P. N. A. M.

2017-12-01

A method for validating the calibration parameters of the six accelerometers on board the Gravity field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations that was originally tested by an end-to-end simulation, has been updated and applied to real data from GOCE. It is shown that the method provides estimates of scale factors for all three axes of the six GOCE accelerometers that are consistent at a level significantly better than 0.01 compared to the a priori calibrated value of 1. In addition, relative accelerometer biases and drift terms were estimated consistent with values obtained by precise orbit determination, where the first GOCE accelerometer served as reference. The calibration results clearly reveal the different behavior of the sensitive and less-sensitive accelerometer axes.

Geological Implications From Complete Gondwana GOCE- Products Reconstructions and Link to Lithospheric Roots

NASA Astrophysics Data System (ADS)

Braitenberg, Carla; Mariani, Patrizia

2015-03-01

The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events that induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Applying geodynamic plate reconstructions to the GOCE gravity field places today’s observed field at the pre-breakup position. The same reconstruction can be applied to the seismic velocity models, to allow a joint gravity-velocity analysis. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents.

Airborne gravimetry for geoid, geopotential models and GOCE - Himalaya and Antarctica cases (Invited)

NASA Astrophysics Data System (ADS)

Forsberg, R.; Olesen, A. V.

2013-12-01

DTU-Space has since many years carried out large area airborne surveys over both polar, tropical and temperate regions, especially for geoid determination and global geopotential models. Recently we have started flying two gravimeters (LCR and Chekan-AM) side by side for increased reliability and redundancy. Typical gravity results are at the 2 mGal rms level, translating into 5-10 cm accuracy in geoid. However, in rough mountainous areas results can be more noisy, mainly due to long-period mountain waves and turbulence. In the paper we outline results of recent challenging campaigns in Nepal (2010) and Antarctica (Antarctic Peninsula and East Antarctica, 2010-13). The latest Antarctic campaign 2012/13, carried out in cooperation with the British Antarctic Survey, Norwegian Polar Institute, and the Argentine Antarctic Institute, involved air drops of fuel to a remote field camp in the Recovery Lakes region, one of the least explored region of deep interior Antarctica. The airborne data collected are validated by cross-over comparisons and comparisons to independent data (IceBridge), and serve at the same time as an independent validation of GOCE satellite gravity data, confirming the satellite data to contain information at half-wavelengths down to 80 km. With no bias between the airborne data and GOCE, airborne gravimetry is perfectly suited to cover the GOCE data gap south of 83 S. We recommend an international, coordinated airborne gravity effort should be carried out over the south polar gap as soon as possible, to ensure a uniform global accuracy of GOCE heritage future geopotential models.

Results from the ESA-funded project 'Height System Unification with GOCE'

NASA Astrophysics Data System (ADS)

Sideris, M. G.; Rangelova, E. V.; Gruber, T.; Rummel, R. F.; Woodworth, P. L.; Hughes, C. W.; Ihde, J.; Liebsch, G.; Schäfer, U.; Rülke, A.; Gerlach, C.; Haagmans, R.

2013-12-01

The paper summarizes the main results of a project, supported by the European Space Agency, whose main goal is to identify the impact of GOCE gravity field models on height system unification. In particular, the Technical University Munich, the University of Calgary and the National Oceanography Centre in Liverpool, together with the Bavarian Academy of Sciences, the Federal German Agency for Cartography and Geodesy, and the Geodetic Surveys of Canada, USA and Mexico, have investigated the role of GOCE-derived gravity and geoid models for regional and global height datum connection. GOCE provides three important components of height unification: highly accurate potential differences (geopotential numbers), a global geoid- or quasi-geoid-based reference surface for elevations that is independent of inaccuracies and inconsistencies of local and regional data, and a consistent way to refer to the same datum all the relevant gravimetric, topographic and oceanographic data. We introduce briefly the methodology that has been applied in order to unify height system in North America, North Atlantic Ocean and Europe, and present results obtained using the available GOCE-derived satellite-only geopotential models, and their combination with terrestrial data and ocean models. The effects of various factors, such as data noise, omission errors, indirect bias terms, ocean models and temporal variations, on height datum unification are also presented, highlighting their magnitude and importance in the estimation of offsets between vertical datums. Based on the experiences gained in this project, a general roadmap has been developed for height datum unification in regions with good, as well as poor, coverage in gravity and geodetic height and tide gauge control stations.

Mapping the gravity field in coastal areas: feasibility and interest of a new airborne planar gradiometer concept

NASA Astrophysics Data System (ADS)

Douch, Karim; Panet, Isabelle; Foulon, Bernard; Christophe, Bruno; Pajot-Métivier, Gwendoline; Diament, Michel

2014-05-01

Satellite missions such as CHAMP, GRACE and GOCE have led to an unprecedented improvement of global gravity field models during the past decade. However, for many applications these global models are not sufficiently accurate when dealing with wavelengths shorter than 100 km. This is all the more true in areas where gravity data are scarce and uneven as for instance in the poorly covered land-sea transition area. We suggest here, in line with spatial gravity gradiometry, airborne gravity gradiometry as a convenient way to amplify the sensitivity to short wavelengths and to cover homogeneously coastal region. Moreover, the directionality of the gravity gradients gives new information on the geometry of the gravity field and therefore of the causative bodies. In this respect, we analyze here the performances of a new airborne electrostatic acceleration gradiometer, GREMLIT, which permits along with ancillary measurements to determine the horizontal gradients of the horizontal components of the gravitational field in the instrumental frame. GREMLIT is composed of a compact assembly of 4 planar electrostatic accelerometers inheriting from technologies developed by ONERA for spatial accelerometers. After an overview of the functionals of the gravity field that are of interest for coastal oceanography, passive navigation and hydrocarbon exploration, we present the corresponding required precision and resolution. Then, we investigate the influence of the different parameters of the survey, such as altitude or cross-track distance, on the resolution and precision of the final measurements. To do so, we design numerical simulations of airborne survey performed with GREMLIT and compute the total error budget on the gravity gradients. Based on this error analysis, we infer by a method of error propagation the uncertainty on the different functionals of the gravity potential used for each application. This finally enables us to conclude on the requirements for a high resolution mapping of the gravity field in coastal areas.

Combining GOCE and in-situ gravity data for precise gravity field determination and geophysical applications around the Japanese Antarctic station, Syowa, in Antarctica

NASA Astrophysics Data System (ADS)

Fukuda, Y.; Nogi, Y.; Matsuzaki, K.

2012-12-01

Syowa is the Japanese Antarctic wintering station in Lützow-Holm Bay, East Antarctica. The area around the station is considered to be a key for investigating the formation of Gondwana, because reconstruction models suggest a junction of the continents locates in the area. It is also important from a glaciological point of view, because there locates the Shirase Glacier, one of the major glaciers in Antarctica, near the station. Therefore the Japanese Antarctic Research Expedition (JARE) has been conducting in-situ gravity measurements in the area for a long period. The data sets accumulated are land gravity data since 1967, surface ship data since 1985, and airborne gravity data in 2006. However these in-situ gravity data usually suffered from the effects of instrumental drifts and lack of reference points, their accuracies are decreasing toward the longer wavelength more than several tens km. In particular in Antarctica where very few gravity reference points are available, the long wavelength accuracy and/or consistency among the data sets are quite limited. GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite launched in March 2009 by ESA (European Space Agency) aims at improving static gravity fields, in particular at short wavelengths. In addition to its low-altitude orbit (250km), the sensitive gravity gradiometer installed is expected to reveal 1 mgal gravity anomalies at the spatial resolution of 100km (half wavelength). Actually recently released GOCE EGMs (Earth Gravity Models) have improved the accuracy of the static gravity filed tremendously. These EGMs are expected to serve as the long wavelength references for the in-situ gravity data. Thus, firstly, we aims at determining an improved gravity fields around Syowa by combining the JARE gravity data and the recent EGMs. And then, using the gravity anomalies, we determine the subsurface density structures. We also evaluated the impacts of the EGMs for estimating the density structures.

Intercontinental height datum connection with GOCE and GPS-levelling data

NASA Astrophysics Data System (ADS)

Gruber, T.; Gerlach, C.; Haagmans, R.

2012-12-01

In this study an attempt is made to establish height system datum connections based upon a gravity field and steady-state ocean circulation explorer (GOCE) gravity field model and a set of global positioning system (GPS) and levelling data. The procedure applied in principle is straightforward. First local geoid heights are obtained point wise from GPS and levelling data. Then the mean of these geoid heights is computed for regions nominally referring to the same height datum. Subsequently, these local mean geoid heights are compared with a mean global geoid from GOCE for the same region. This way one can identify an offset of the local to the global geoid per region. This procedure is applied to a number of regions distributed worldwide. Results show that the vertical datum offset estimates strongly depend on the nature of the omission error, i.e. the signal not represented in the GOCE model. For a smooth gravity field the commission error of GOCE, the quality of the GPS and levelling data and the averaging control the accuracy of the vertical datum offset estimates. In case the omission error does not cancel out in the mean value computation, because of a sub-optimal point distribution or a characteristic behaviour of the omitted part of the geoid signal, one needs to estimate a correction for the omission error from other sources. For areas with dense and high quality ground observations the EGM2008 global model is a good choice to estimate the omission error correction in theses cases. Relative intercontinental height datum offsets are estimated by applying this procedure between the United State of America (USA), Australia and Germany. These are compared to historical values provided in the literature and computed with the same procedure. The results obtained in this study agree on a level of 10 cm to the historical results. The changes mainly can be attributed to the new global geoid information from GOCE, rather than to the ellipsoidal heights or the levelled heights. These historical levelling data are still in use in many countries. This conclusion is supported by other results on the validation of the GOCE models.

Optimised Environmental Test Approaches in the GOCE Project

NASA Astrophysics Data System (ADS)

Ancona, V.; Giordano, P.; Casagrande, C.

2004-08-01

The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is dedicated to measuring the Earth's gravity field and modelling the geoid with extremely high accuracy and spatial resolution. It is the first Earth Explorer Core mission to be developed as part of ESA's Living Planet Programme and is scheduled for launch in 2006. The program is managed by a consortium of European companies: Alenia Spazio, the prime contractor, Astrium GmbH, the platform responsible, Alcatel Space Industries and Laben, suppliers of the main payloads, respectively the Electrostatic Gravity Gradiometer (EGG) and the Satellite to Satellite Tracking Instrument (SSTI), actually a precise GPS receiver. The GOCE Assembly Integration and Verification (AIV) approach is established and implemented in order to demonstrate to the customer that the satellite design meets the applicable requirements and to qualify and accept from lower level up to system level. The driving keywords of "low cost" and "short schedule" program, call for minimizing the development effort by utilizing off-the-shelf equipment combined with a model philosophy lowering the number of models to be used. The paper will deal on the peculiarities of the optimized environmental test approach in the GOCE project. In particular it introduces the logic of the AIV approach and describe the foreseen tests at system level within the SM environmental test campaign, outlining the Quasi Static test performed in the frame of the SM sine vibration tests, and the PFM environmental test campaign pinpointing the deletion of the Sine Vibration test on PFM model. Furthermore the paper highlights how the Model and Test Effectiveness Database (MATD) can be utilized for the prediction of the new space projects like GOCE Satellite.

Software Analysis of New Space Gravity Data for Geophysics and Climate Research

NASA Technical Reports Server (NTRS)

Deese, Rupert; Ivins, Erik R.; Fielding, Eric J.

2012-01-01

Both the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellites are returning rich data for the study of the solid earth, the oceans, and the climate. Current software analysis tools do not provide researchers with the ease and flexibility required to make full use of this data. We evaluate the capabilities and shortcomings of existing software tools including Mathematica, the GOCE User Toolbox, the ICGEM's (International Center for Global Earth Models) web server, and Tesseroids. Using existing tools as necessary, we design and implement software with the capability to produce gridded data and publication quality renderings from raw gravity data. The straight forward software interface marks an improvement over previously existing tools and makes new space gravity data more useful to researchers. Using the software we calculate Bouguer anomalies of the gravity tensor's vertical component in the Gulf of Mexico, Antarctica, and the 2010 Maule earthquake region. These maps identify promising areas of future research.

Optimal Geoid Modelling to determine the Mean Ocean Circulation - Project Overview and early Results

NASA Astrophysics Data System (ADS)

Fecher, Thomas; Knudsen, Per; Bettadpur, Srinivas; Gruber, Thomas; Maximenko, Nikolai; Pie, Nadege; Siegismund, Frank; Stammer, Detlef

2017-04-01

The ESA project GOCE-OGMOC (Optimal Geoid Modelling based on GOCE and GRACE third-party mission data and merging with altimetric sea surface data to optimally determine Ocean Circulation) examines the influence of the satellite missions GRACE and in particular GOCE in ocean modelling applications. The project goal is an improved processing of satellite and ground data for the preparation and combination of gravity and altimetry data on the way to an optimal MDT solution. Explicitly, the two main objectives are (i) to enhance the GRACE error modelling and optimally combine GOCE and GRACE [and optionally terrestrial/altimetric data] and (ii) to integrate the optimal Earth gravity field model with MSS and drifter information to derive a state-of-the art MDT including an error assessment. The main work packages referring to (i) are the characterization of geoid model errors, the identification of GRACE error sources, the revision of GRACE error models, the optimization of weighting schemes for the participating data sets and finally the estimation of an optimally combined gravity field model. In this context, also the leakage of terrestrial data into coastal regions shall be investigated, as leakage is not only a problem for the gravity field model itself, but is also mirrored in a derived MDT solution. Related to (ii) the tasks are the revision of MSS error covariances, the assessment of the mean circulation using drifter data sets and the computation of an optimal geodetic MDT as well as a so called state-of-the-art MDT, which combines the geodetic MDT with drifter mean circulation data. This paper presents an overview over the project results with focus on the geodetic results part.

First Release of Gravimetric Geoid Model over Saudi Arabia Based on Terrestrial Gravity and GOCE Satellite Data: KSAG01

NASA Astrophysics Data System (ADS)

Alothman, A. O.; Elsaka, B.

2015-12-01

A new gravimetric quasi-geoid, known as KSAG0, has been developed recently by Remove-Compute-Restore techniques (RCR), provided by the GRAVSOFT software, using gravimetric free air anomalies. The terrestrial gravity data used in this computations are: 1145 gravity field anomalies observed by ARAMCO (Saudi Arabian Oil Company) and 2470 Gravity measurements from BGI (Bureau Gravimétrique International). The computations were carried out implementing the least squares collocation method through the RCR techniques. The KSAG01 is based on merging in addition to the terrestrial gravity observations, GOCE satellite model (Eigen-6C4) and global gravity model (EGM2008) have been utilized in the computations. The long, medium and short wavelength spectrum of the height anomalies were compensated from Eigen-6C4 and EGM2008 geoid models truncated up to Degree and order (d/o) up to 2190. KSAG01 geoid covers 100 per cent of the kingdom, with geoid heights range from - 37.513 m in the southeast to 23.183 m in the northwest of the country. The accuracy of the geoid is governed by the accuracy, distribution, and spacing of the observations. The standard deviation of the predicted geoid heights is 0.115 m, with maximum errors of about 0.612 m. The RMS of geoid noise ranges from 0.019 m to 0.04 m. Comparison of the predicted gravimetric geoid with EGM, GOCE, and GPS/Levelling geoids, reveals a considerable improvements of the quasi-geoid heights over Saudi Arabia.

First Release of Gravimetric Geoid Model over Saudi Arabia Based on Terrestrial Gravity and GOCE Satellite Data: KSAG01

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Elsaka, Basem

2016-04-01

A new gravimetric quasi-geoid, known as KSAG0, has been developed recently by Remove-Compute-Restore techniques (RCR), provided by the GRAVSOFT software, using gravimetric free air anomalies. The terrestrial gravity data used in this computations are: 1145 gravity field anomalies observed by ARAMCO (Saudi Arabian Oil Company) and 2470 Gravity measurements from BGI (Bureau Gravimétrique International). The computations were carried out implementing the least squares collocation method through the RCR techniques. The KSAG01 is based on merging in addition to the terrestrial gravity observations, GOCE satellite model (Eigen-6C4) and global gravity model (EGM2008) have been utilized in the computations. The long, medium and short wavelength spectrum of the height anomalies were compensated from Eigen-6C4 and EGM2008 geoid models truncated up to Degree and order (d/o) up to 2190. KSAG01 geoid covers 100 per cent of the kingdom, with geoid heights range from - 37.513 m in the southeast to 23.183 m in the northwest of the country. The accuracy of the geoid is governed by the accuracy, distribution, and spacing of the observations. The standard deviation of the predicted geoid heights is 0.115 m, with maximum errors of about 0.612 m. The RMS of geoid noise ranges from 0.019 m to 0.04 m. Comparison of the predicted gravimetric geoid with EGM, GOCE, and GPS/Levelling geoids, reveals a considerable improvements of the quasi-geoid heights over Saudi Arabia.

The Space-Wise Global Gravity Model from GOCE Nominal Mission Data

NASA Astrophysics Data System (ADS)

Gatti, A.; Migliaccio, F.; Reguzzoni, M.; Sampietro, D.; Sanso, F.

2011-12-01

In the framework of the GOCE data analysis, the space-wise approach implements a multi-step collocation solution for the estimation of a global geopotential model in terms of spherical harmonic coefficients and their error covariance matrix. The main idea is to use the collocation technique to exploit the spatial correlation of the gravity field in the GOCE data reduction. In particular the method consists of an along-track Wiener filter, a collocation gridding at satellite altitude and a spherical harmonic analysis by integration. All these steps are iterated, also to account for the rotation between local orbital and gradiometer reference frame. Error covariances are computed by Montecarlo simulations. The first release of the space-wise approach was presented at the ESA Living Planet Symposium in July 2010. This model was based on only two months of GOCE data and partially contained a priori information coming from other existing gravity models, especially at low degrees and low orders. A second release was distributed after the 4th International GOCE User Workshop in May 2011. In this solution, based on eight months of GOCE data, all the dependencies from external gravity information were removed thus giving rise to a GOCE-only space-wise model. However this model showed an over-regularization at the highest degrees of the spherical harmonic expansion due to the combination technique of intermediate solutions (based on about two months of data). In this work a new space-wise solution is presented. It is based on all nominal mission data from November 2009 to mid April 2011, and its main novelty is that the intermediate solutions are now computed in such a way to avoid over-regularization in the final solution. Beyond the spherical harmonic coefficients of the global model and their error covariance matrix, the space-wise approach is able to deliver as by-products a set of spherical grids of potential and of its second derivatives at mean satellite altitude. These grids have an information content that is very similar to the original along-orbit data, but they are much easier to handle. In addition they are estimated by local least-squares collocation and therefore, although computed by a unique global covariance function, they could yield more information at local level than the spherical harmonic coefficients of the global model. For this reason these grids seem to be useful for local geophysical investigations. The estimated grids with their estimated errors are presented in this work together with proposals on possible future improvements. A test to compare the different information contents of the along-orbit data, the gridded data and the spherical harmonic coefficients is also shown.

Recovering the time-variable gravitational field using satellite gradiometry: requirements and gradiometer concept

NASA Astrophysics Data System (ADS)

Douch, Karim; Müller, Jürgen; Heinzel, Gerhard; Wu, Hu

2017-04-01

The successful GRACE mission and its far-reaching benefits have highlighted the interest to continue and extend the mapping of the Earth's time-variable gravitational field with follow-on missions and ideally a higher spatiotemporal resolution. Here, we would like to put forward satellite gravitational gradiometry as an alternative solution to satellite-to-satellite tracking for future missions. Besides the higher sensitivity to smaller scales compared to GRACE-like missions, a gradiometry mission would only require one satellite and would provide a direct estimation of a functional of the gravitational field. GOCE, the only gradiometry mission launched so far, was not sensitive enough to map the time-variable part of the gravity field. However, the unprecedented precision of the state-of-the-art optical metrology system on-board the LISA PATHFINDER satellite has opened the way to more performant space inertial sensors. We will therefore examine whether it is technically possible to go beyond GOCE performances and to quantify to what extent the time-variable gravitational field could be determined. First, we derive the requirements on the knowledge of the attitude and the position of the satellite and on the measured gradients in terms of sensitivity and calibration accuracy for a typical repeat low-orbit. We conclude in particular that a noise level smaller than 0.1 mE/√Hz- is required in the measurement bandwidth [5x10-4 ; 10-2]Hz so as to be sensitive to the time-variable gravity signal. We introduce then the design and characteristics of the new gradiometer concept and give an assessment of its noise budget. Contrary to the GOCE electrostatic gradiometer, the position of the test-mass in the accelerometer is measured here by laser interferometry rather than by a capacitive readout system, which improves the overall measurement chain. Finally, the first results of a performance analysis carried out thanks to an end-to-end simulator are discussed and compared to the previously defined requirements.

Using the Full Cycle of GOCE Data in the Quasi-Geoid Modelling of Finland

NASA Astrophysics Data System (ADS)

Saari, Timo; Bilker-Koivula, Mirjam; Poutanen, Markku

2016-08-01

In the Dragon 3 project 10519 "Case study on heterogeneous geoid/quasigeoid based on space borne and terrestrial data combination with special consideration of GOCE mission data impact" we combined the latest GOCE models with the terrestrial gravity data of Finland and surrounding areas to calculate a quasi-geoid model for Finland. Altogether 249 geoid models with different modifications were calculated using the GOCE DIR5 models up to spherical harmonic degree and order 240 and 300 and the EIGEN-6C4 up to degree and order 1000 and 2190.The calculated quasi-geoid models were compared against the ground truth in Finland with two independent GPS-levelling datasets. The best GOCE- only models gave standard deviations of 2.8 cm, 2.6 cm (DIR5 d/o 240) and 2.7 cm, 2.3 cm (DIR5 d/o 300) in Finnish territory for NLS-FIN and EUVN-DA datasets, respectively. For the high resolution model EIGEN-6C4 (which includes the full cycle of the GOCE data), the results were 2.4 cm, 1.8 cm (d/o 1000) and 2.5 cm, 1.7 (d/o 2190). The sub-2-centimetre (and near 2 cm with GOCE-only) accuracy is an improvement over the previous and current Finnish geoid models, thus leading to a conclusion of the great impact of the GOCE- mission on regional geoid modelling.

Satellite altimetry and GOCE contribution to the pre-definition of the Kingdom of Saudi Arabia (KSA) Vertical Network

NASA Astrophysics Data System (ADS)

Vergos, Georgios S.; Grebenitcharsky, Rossen S.; Natsiopoulos, Dimitrios A.; Al-Kherayef, Othman; Al-Muslmani, Bandar

2017-04-01

The availability of a unified and well-established national vertical system and frame is of outmost importance in support of everyday geodetic, surveying and engineering applications. Vertical reference system (VRS) modernization and unification has gained increased importance especially during the last years due to the advent of gravity-field dedicated missions and GOCE in particular, since it is the first time that an unprecedented in accuracy dataset of gravity field functionals has become available at a global scale. The Kingdom of Saudi Arabia VRS is outdated and exhibits significant tilts and biases, so that during the last couple of years an extensive effort has been put forth in order to: re-measure by traditional levelling the entire network, establish new benchmarks (BMs), perform high-quality absolute and relative gravity observations and construct new tide-gauge (TG) stations in both the Arab and Red Seas. The Current work focuses on the combined analysis of the existing, recently collected, terrestrial observations with satellite altimetry data and the latest GOCE-based Earth Geopotential Models (EGMs) in order to provide a pre-definition of the KSA VRS. To that respect, a 30-year satellite altimetry time-series is constructed for each TG station in order to derive both the Mean Sea Level (MSL) as well as the sea level trends. This information is analyzed, through Wavelet (WL) Multi-resolution Analysis (MRA), with the TG sea level records in order to determine annual, semi-annual and secular trends of the Red and Arab Sea variations. Finally, the so-derived trends and MSL are combined with local gravity observations at the TG BMs, levelling offsets between the TGs and the network BMs, levelling observations between the network BMs themselves and GOCE-based EGM-derived geoid heights and potential values. The validation of GOCE contribution and of the satellite altimetry derived MSL and trends is based on a simultaneous adjustment of the entire KSA vertical network, keeping fixed various TG stations and investigating the distortions introduced in the adjusted BM orthometric heights. Finally, a pre-definition of the KSA VRS is detailed as vertical offsets and potential differences δWo relative to the recently adopted conventional zero-level geopotential value by IAG. Conclusions regarding the contribution of satellite altimetry and GOCE are drown along with the necessary information for the definition of the KSA vertical datum and its connection to an International Height References System (IHRS).

Assessment of the suitability of GOCE-based geoid models for the unification of the North American vertical datums

NASA Astrophysics Data System (ADS)

Amjadiparvar, Babak; Sideris, Michael

2015-04-01

Precise gravimetric geoid heights are required when the unification of vertical datums is performed using the Geodetic Boundary Value Problem (GBVP) approach. Five generations of Global Geopotential Models (GGMs) derived from Gravity field and steady-state Ocean Circulation Explorer (GOCE) observations have been computed and released so far (available via IAG's International Centre for Global Earth Models, ICGEM, http://icgem.gfz-potsdam.de/ICGEM/). The performance of many of these models with respect to geoid determination has been studied in order to select the best performing model to be used in height datum unification in North America. More specifically, Release-3, 4 and 5 of the GOCE-based global geopotential models have been evaluated using GNSS-levelling data as independent control values. Comparisons against EGM2008 show that each successive release improves upon the previous one, with Release-5 models showing an improvement over EGM2008 in Canada and CONUS between spherical harmonic degrees 100 and 210. In Alaska and Mexico, a considerable improvement over EGM2008 was brought by the Release-5 models when used up to spherical harmonic degrees of 250 and 280, respectively. The positive impact of the Release-5 models was also felt when a gravimetric geoid was computed using the GOCE-based GGMs together with gravity and topography data in Canada. This geoid model, with appropriately modified Stokes kernel between spherical harmonic degrees 190 and 260, performed better than the official Canadian gravimetric geoid model CGG2013, thus illustrating the advantages of using the latest release GOCE-based models for vertical datum unification in North America.

Global Gravity Field Determination by Combination of terrestrial and Satellite Gravity Data

NASA Astrophysics Data System (ADS)

Fecher, T.; Pail, R.; Gruber, T.

2011-12-01

A multitude of impressive results document the success of the satellite gravity field mission GOCE with a wide field of applications in geodesy, geophysics and oceanography. The high performance of GOCE gravity field models can be further improved by combination with GRACE data, which is contributing the long wavelength signal content of the gravity field with very high accuracy. An example for such a consistent combination of satellite gravity data are the satellite-only models GOCO01S and GOCO02S. However, only the further combination with terrestrial and altimetric gravity data enables to expand gravity field models up to very high spherical harmonic degrees and thus to achieve a spatial resolution down to 20-30 km. First numerical studies for high-resolution global gravity field models combining GOCE, GRACE and terrestrial/altimetric data on basis of the DTU10 model have already been presented. Computations up to degree/order 600 based on full normal equations systems to preserve the full variance-covariance information, which results mainly from different weights of individual terrestrial/altimetric data sets, have been successfully performed. We could show that such large normal equations systems (degree/order 600 corresponds to a memory demand of almost 1TByte), representing an immense computational challenge as computation time and memory requirements put high demand on computational resources, can be handled. The DTU10 model includes gravity anomalies computed from the global model EGM08 in continental areas. Therefore, the main focus of this presentation lies on the computation of high-resolution combined gravity field models based on real terrestrial gravity anomaly data sets. This is a challenge due to the inconsistency of these data sets, including also systematic error components, but a further step to a real independent gravity field model. This contribution will present our recent developments and progress by using independent data sets at certain land areas, which are combined with DTU10 in the ocean areas, as well as satellite gravity data. Investigations have been made concerning the preparation and optimum weighting of the different data sources. The results, which should be a major step towards a GOCO-C model, will be validated using external gravity field data and by applying different validation methods.

Evaluation of the Geopotential value for the Local Vertical Datum of China using GRACE/GOCE GGMs and GPS/Leveling Data

NASA Astrophysics Data System (ADS)

He, Lin; Li, Jiancheng; Chu, Yonghai; Zhang, Tengxu

2017-04-01

National height reference systems have conventionally been linked to the coastal local mean sea level, observed at one tide gauge, such as the China national height datum 1985. Due to the effect of the local sea surface topography, the reference level surface of local datum is inconsistent with the global datum or other local datum. In order to unify or connect the local datum to the global height datum, it is necessary to obtain the zero-height geopotential value of local datum or the height offset with respect to the global datum. The GRACE and GOCE satellite mission are promising for purposes of unification of local vertical datums because they have brought a significant improvement in modeling of low-frequency or rather medium-frequency part of the Earth's static gravity field in the past ten years. The focus of this work is directed to the evaluation of most available Global Geopotential Models (GGMs) from GOCE and GRACE, both satellite only as well as combined ones. From the evaluation with the 649 GPS/Levelling benchmarks (BMs) in China, the GOCE/GRACE GGMs provide the accuracy at 42-52cm level, up to their max degree and order. The latest release 5 DIR, TIM GGMs improve the accuracies by 6-10cm compared to the release 1 models. The DIR_R1 is based on the fewer GOCE data performs equally well with the DIR_R4 and DIR_R5 model, this is attributed to the fact that during its development which used a priori information from EIGEN-51C. The zero-height geopotential value W0LVD for the China Local Vertical Datum (LVD) is 62636855.1606m2s-2 from the originally GOCE/GRACE GGMs. Taking into account the GPS/Levelling data contains the full spectral information, and the GOCE-only or GRACE-GOCE combined model are limited to the long wavelengths. To improve the accuracy of the GGMs, it is indispensable to account for the remaining signal above this maximum degree, known as the omission error of the GGM. The effect of GRACE/GOCE omission error is investigated by extending the models with the high-resolution gravity field model EGM2008. In China, the effect of the GRACE/GOCE GGMs omission error is at the decimeter level. The combined GGMs (up to 2160 degree and order) could provide an accuracy at 20cm level, which is better than that from EGM2008. Meanwhile, if an appropriate degree and order is chosen for the GOCE-only or GRACE-GOCE combined GGMs to connect with the EGM2008, the extended GGMs provide an accuracy at 16cm level. From the extended GGMs, the geopotential value W0LVD determined for the China local vertical datum is 62636853.4351 m2s-2 indicates a bias of about 2.5649 m2/s-2 compared to the conventional value of 62,636,856.0 m2s-2. This is support by National key research and development program No:2016YFB0501702. Keywords: Global Geopotential Models; GRACE; GOCE; GPS/Levelling; zero-height geopotential

Comparison of Selected Geopotential Models in Terms of the GOCE Orbit Determination Using Simulated GPS Observations

NASA Astrophysics Data System (ADS)

Bobojć, Andrzej

2016-12-01

This work contains a comparative study of the performance of six geopotential models in an orbit estimation process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For testing, such models as ULUX_CHAMP2013S, ITG-GRACE 2010S, EIGEN-51C, EIGEN5S, EGM2008, EGM96, were adopted. Different sets of pseudo-range simulations along reference GOCE satellite orbital arcs were obtained using real orbits of the Global Positioning System satellites. These sets were the basic observation data used in the adjustment. The centimeter-accuracy Precise Science Orbit (PSO) for the GOCE satellite provided by the European Space Agency (ESA) was adopted as the GOCE reference orbit. Comparing various variants of the orbital solutions, the relative accuracy of geopotential models in an orbital aspect is determined. Full geopotential models were used in the adjustment process. The solutions were also determined taking into account truncated geopotential models. In such case, an accuracy of the solutions was slightly enhanced. Different arc lengths were taken for the computation.

New evidence about the subduction of the Copiapó ridge beneath South America, and its connection with the Chilean-Pampean flat slab, tracked by satellite GOCE and EGM2008 models

NASA Astrophysics Data System (ADS)

Álvarez, Orlando; Gimenez, Mario; Folguera, Andres; Spagnotto, Silvana; Bustos, Emilce; Baez, Walter; Braitenberg, Carla

2015-11-01

Satellite-only gravity measurements and those integrated with terrestrial observations provide global gravity field models of unprecedented precision and spatial resolution, allowing the analysis of the lithospheric structure. We used the model EGM2008 (Earth Gravitational Model) to calculate the gravity anomaly and the vertical gravity gradient in the South Central Andes region, correcting these quantities by the topographic effect. Both quantities show a spatial relationship between the projected subduction of the Copiapó aseismic ridge (located at about 27°-30° S), its potential deformational effects in the overriding plate, and the Ojos del Salado-San Buenaventura volcanic lineament. This volcanic lineament constitutes a projection of the volcanic arc toward the retroarc zone, whose origin and development were not clearly understood. The analysis of the gravity anomalies, at the extrapolated zone of the Copiapó ridge beneath the continent, shows a change in the general NNE-trend of the Andean structures to an ENE-direction coincident with the area of the Ojos del Salado-San Buenaventura volcanic lineament. This anomalous pattern over the upper plate is interpreted to be linked with the subduction of the Copiapó ridge. We explore the relation between deformational effects and volcanism at the northern Chilean-Pampean flat slab and the collision of the Copiapó ridge, on the basis of the Moho geometry and elastic thicknesses calculated from the new satellite GOCE data. Neotectonic deformations interpreted in previous works associated with volcanic eruptions along the Ojos del Salado-San Buenaventura volcanic lineament is interpreted as caused by crustal doming, imprinted by the subduction of the Copiapó ridge, evidenced by crustal thickening at the sites of ridge inception along the trench. Finally, we propose that the Copiapó ridge could have controlled the northern edge of the Chilean-Pampean flat slab, due to higher buoyancy, similarly to the control that the Juan Fernandez ridge exerts in the geometry of the flat slab further south.

GOCO05c: A New Combined Gravity Field Model Based on Full Normal Equations and Regionally Varying Weighting

NASA Astrophysics Data System (ADS)

Fecher, T.; Pail, R.; Gruber, T.

2017-05-01

GOCO05c is a gravity field model computed as a combined solution of a satellite-only model and a global data set of gravity anomalies. It is resolved up to degree and order 720. It is the first model applying regionally varying weighting. Since this causes strong correlations among all gravity field parameters, the resulting full normal equation system with a size of 2 TB had to be solved rigorously by applying high-performance computing. GOCO05c is the first combined gravity field model independent of EGM2008 that contains GOCE data of the whole mission period. The performance of GOCO05c is externally validated by GNSS-levelling comparisons, orbit tests, and computation of the mean dynamic topography, achieving at least the quality of existing high-resolution models. Results show that the additional GOCE information is highly beneficial in insufficiently observed areas, and that due to the weighting scheme of individual data the spectral and spatial consistency of the model is significantly improved. Due to usage of fill-in data in specific regions, the model cannot be used for physical interpretations in these regions.

Geoid Determination Using GOCE-Based Models in Turkey

NASA Astrophysics Data System (ADS)

Serkan Işık, Mustafa; Erol, Bihter

2016-04-01

The maintenance of the vertical datum in tectonically active regions such as Turkey become more of an issue. The distortions in the vertical datum due to geodynamic phenomena necessitate the realization of geoid based vertical datum. The height modernization studies for transition to a "geoid based vertical datum definition" providing practical use of GNSS technologies to obtain orthometric heights in Turkey has accelerated rapidly in recent years and hence in the content of these efforts on-going projects contribute to improvement of quality and quantity of terrestrial gravity dataset as well as selection of the optimal computation algorithm to reach a precise geoid model in the territory. In this manner the assessment of the different methodologies with varying input parameters and referred models is obviously essential to in order to clarify the advantages of the algorithms in terms of providing an optimal combination of different data sets in regional geoid modeling. The performance of recently published GOCE-GRACE gravity field models show significant improvements in the medium frequency. This study investigates the contribution of the recently released Geopotential models with the contribution of GOCE and GRACE missions to the gravimetric geoid modeling specifically from Least squares modification of Stokes' (LSMS) formula point of view in Turkey territory. The algorithm developed by Royal Institute of Technology (KTH) that adopt the least squares modification of Stokes' kernel in order for providing an optimum combination of spherical harmonic expansion model and terrestrial gravity data and hence claims to optimize the drawbacks, may stem from the handicaps (such as low accuracy, sparse distribution etc.) of the terrestrial gravity data in the results. The additive corrective terms in order to account for downward continuation effect, atmospheric effect and ellipsoidal effect are proposed as the superiorities of this algorithm comparing to the conventional Remove-Restore method. The assessments of the geoid models are done at the homogeneously distributed thirty National Network points in Turkey. The positional accuracy of GNSS/Levelling points (belong the Turkey National Fundamental GNSS Network-TUTGA) are reported as ±1.0 cm in horizontal and ±1.5 cm in vertical components. The orthometric heights of these benchmarks are computed via adjustment of the Turkish National Vertical Control Network (TUDKA). All releases of direct (DIR), time-wise (TIM), space-wise (SPW) and Gravity Observation Combination (GOCO) models are evaluated using spectral enhancement method (SEM). DIR R5, TIM R5 and GOCO05S models, which show the best agreements with the GNSS/Levelling data, are included within the study and their performance are compared with EGM2008 model. In conclusion the GOCE gravity field models performs in the level very close to EGM2008 performance, when the same truncation degree of models are considered. The overall results reveal that the gravimetric geoid model which is computed using DIR R5 model provides the best performance having ±24.1 cm (without de-trending), though there is no significant improvement related with the contribution of GOCE gravity field models to the regional geoid determination based on LSMS approach in Turkey territory.

Beyond Currents: The Next Phase in GOCE Oceanographic Research

NASA Astrophysics Data System (ADS)

Bingham, Rory J.; Haines, Keith; Hughes, Chris W.

2015-03-01

GOCE has mapped the surface currents of the world’s oceans in unprecedented detail. What is now required is a concerted effort by the oceanographic community to go beyond currents and exploit these measurements for societal benefit. The aim of this review paper is to explore the ways in which this may be achieved, particularly in relation to ocean modelling. With the final gravity models now released, we begin by reviewing the progress GOCE has in made in measuring the ocean’s mean dynamic topography and associated ocean currents. In the light of this progress, we then examine the important oceanographic questions and technical challenges of societal relevance that can potentially be addressed with the help of the observations GOCE has delivered and outline the benefits their solution could deliver. Benefits may either be direct, through, for example, improved ocean modelling and operational forecasting, or indirect through improved understanding of particular oceanographic processes, such as heat transport by the Atlantic meridional overturning circulation or sea level change. Next we consider the technical challenges that must be overcome in bringing GOCE to bear on these problems. In particular we examine how best to use GOCE error information, this being an especially uncertain, underdeveloped and challenging area of investigation, due largely to the fact that such information has not been previously available to the user community. Finally, we consider measures of success; that is, metrics that can be used to quantify any GOCE-enabled progress that the community makes towards answering these questions. Such metrics are essential for demonstrating progress. Ultimately, with this review paper, we aim to paint a road map that will act as an impetus to the oceanography community to exploit the yet untapped potential of GOCE for scientific understanding and societal benefit.

Surface topography estimated by inversion of satellite gravity gradiometry observations

NASA Astrophysics Data System (ADS)

Ramillien, Guillaume

2015-04-01

An integration of mass elements is presented for evaluating the six components of the 2-order gravity tensor (i.e., second derivatives of the Newtonian mass integral for the gravitational potential) created by an uneven sphere topography consisting of juxtaposed vertical prisms. The method is based on Legendre polynomial series with the originality of taking elastic compensation of the topography by the Earth's surface into account. The speed of computation of the polynomial series increases logically with the observing altitude from the source of anomaly. Such a forward modelling can be easily used for reduction of observed gravity gradient anomalies by the effects of any spherical interface of density. Moreover, an iterative least-square inversion of the observed gravity tensor values Γαβ is proposed to estimate a regional set of topographic heights. Several tests of recovery have been made by considering simulated gradiometry anomaly data, and for varying satellite altitudes and a priori levels of accuracy. In the case of GOCE-type gradiometry anomalies measured at an altitude of ~300 km, the search converges down to a stable and smooth topography after 20-30 iterations while the final r.m.s. error is ~100 m. The possibility of cumulating satellite information from different orbit geometries is also examined for improving the prediction.

On the capability of Swarm for surface mass variation monitoring: Quantitative assessment based on orbit information from CHAMP, GRACE and GOCE

NASA Astrophysics Data System (ADS)

Baur, Oliver; Weigelt, Matthias; Zehentner, Norbert; Mayer-Gürr, Torsten; Jäggi, Adrian

2014-05-01

In the last decade, temporal variations of the gravity field from GRACE observations have become one of the most ubiquitous and valuable sources of information for geophysical and environmental studies. In the context of global climate change, mass balance of the Arctic and Antarctic ice sheets gained particular attention. Because GRACE has outlived its predicted lifetime by several years already, it is very likely that a gap between GRACE and its successor GRACE follow-on (supposed to be launched in 2017, at the earliest) occurs. The Swarm mission - launched on November 22, 2013 - is the most promising candidate to bridge this potential gap, i.e., to directly acquire large-scale mass variation information on the Earth's surface in case of a gap between the present GRACE and the upcoming GRACE follow-on projects. Although the magnetometry mission Swarm has not been designed for gravity field purposes, its three satellites have the characteristics for such an endeavor: (i) low, near-circular and near-polar orbits, (ii) precise positioning with high-quality GNSS receivers, (iii) on-board accelerometers to measure the influence of non-gravitational forces. Hence, from an orbit analysis point of view the Swarm satellites are comparable to the CHAMP, GRACE and GOCE spacecraft. Indeed and as data analysis from CHAMP has been shown, the detection of annual signals and trends from orbit analysis is possible for long-wavelength features of the gravity field, although the accuracy associated with the inter-satellite GRACE measurements cannot be reached. We assess the capability of the (non-dedicated) mission Swarm for mass variation detection in a real-case environment (opposed to simulation studies). For this purpose, we "approximate" the Swarm scenario by the GRACE+CHAMP and GRACE+GOCE constellations. In a first step, kinematic orbits of the individual satellites are derived from GNSS observations. From these orbits, we compute monthly combined GRACE+CHAMP and GRACE+GOCE time-variable gravity fields; sophisticated techniques based on Kalman filtering are applied to reduce noise in the time series. Finally, we infer mass variation in selected areas from to gravity signal. These results are compared to the findings obtained from mass variation detection exploiting CSR-RL05 gravity fields; due to their superior quality (which is due to the fact that they are derived from inter-satellite GRACE measurements), the CSR-RL05 solutions serve as benchmark. Our quantitative assessment shows the potential and limitations of what can be expected from Swarm with regard to surface mass variation monitoring.

Status of the planar electrostatic gradiometer GREMLIT for airborne geodesy

NASA Astrophysics Data System (ADS)

Boulanger, D.; Foulon, B.; Lebat, V.; Bresson, A.; Christophe, B.

2016-12-01

Taking advantage of technologies, developed by ONERA for the GRACE and GOCE space missions, the GREMLIT airborne gravity gradiometer is based of a planar electrostatic gradiometer configuration. The feasibility of the instrument and of its performance was proved by realistic simulations, based on actual data and recorded environmental aircraft perturbations, with performance of about one Eötvös along the two horizontal components of the gravity gradient. In order to assess the operation of the electrostatic gradiometer on its associated stabilized platform, a one axis prototype has also been built. The next step is the realization of the stabilization platform, controlled by the common mode outputs of the instrument itself, in order to reject the perturbations induced by the airborne environment in the horizontal directions. One of the interests of the GREMLIT instrument is the possibility of an easy hybrid configuration with a vertical one axis Cold Atoms Interferometer gravity gradiometer called GIBON and also under development at ONERA. In such hybrid instrument, The CAI instrument takes also advantage of the platform stabilized by the electrostatic one. The poster will emphasize the status of realization of the instrument and of its stabilized platform.

Satellite gravity gradient views help reveal the Antarctic lithosphere

NASA Astrophysics Data System (ADS)

Ferraccioli, F.; Ebbing, J.; Pappa, F.; Kern, M.; Forsberg, R.

2017-12-01

Here we present and analyse satellite gravity gradient signatures derived from GOCE and superimpose these on tectonic and bedrock topography elements, as well as seismically-derived estimates of crustal thickness for the Antarctic continent. The GIU satellite gravity component images the contrast between the thinner crust and lithosphere underlying the West Antarctic Rift System and the Weddell Sea Rift System and the thicker lithosphere of East Antarctica. The new images also suggest that more distributed wide-mode lithospheric and crustal extension affects both the Ross Sea Embayment and the less well known Ross Ice Shelf segment of the rift system. However, this pattern is less clear towards the Bellingshousen Embayment, indicating that the rift system narrows towards the southern edge of the Antarctic Peninsula. In East Antarctica, the satellite gravity data provides new views into the Archean to Mesoproterozoic Terre Adelie Craton, and clearly shows the contrast wrt to the crust and lithosphere underlying both the Wilkes Subglacial Basin to the east and the Sabrina Subglacial Basin to the west. This finding augments recent interpretations of aeromagnetic and airborne gravity data over the region, suggesting that the Mawson Continent is a composite lithospheric-scale entity, which was affected by several Paleoproterozoic and Mesoproterozoic orogenic events. Thick crust is imaged beneath the Transantarctic Mountains, the Terre Adelie Craton, the Gamburtsev Subglacial Mountains and also Eastern Dronning Maud Land, in particular beneath the recently proposed region of the Tonian Oceanic Arc Superterrane. The GIA and GIU components help delineate the edges of several of these lithospheric provinces. One of the most prominent lithospheric-scale features discovered in East Antarctica from satellite gravity gradient imaging is the Trans East Antarctic Shear Zone that separates the Gamburtsev Province from the Eastern Dronning Maud Land Province and appears to form the southern boundary of the Recovery Province. We propose, based on geological data in the Lutzow Holm Complex region and formerly adjacent segments of India, Madagascar and eastern Africa that it may represent a major Pan-African age suture and/or shear zone related to Gondwana assembly.

A 3D Finite Element Model with Improved Spatial Resolution to Investigate the Effect of Varying Viscosity on Antarctica

NASA Astrophysics Data System (ADS)

Blank, B.; van der Wal, W.; Pappa, F.; Ebbing, J.

2017-12-01

B. Blank1, H. Hu1, W. van der Wal1, F Pappa2, J. Ebbing21Delft University of Technology 2Christian-Albrechts-University of KielSince the beginning of the 2000's time-variable gravity data from GRACE has proved to be an effective method for mapping ice mass loss in Antarctica. However, Glacial Isostatic Adjustment (GIA) models are required to correct for GIA induced mass changes. While most GIA models have adopted an Earth model that only varies radially in parameters, it has long been clear that the Earth structure also varies with longitude and latitude. For this study a new global 3D GIA model has been developed within the finite element software package ABAQUS, which can be modified to operate on a spatial resolution down to 50 km locally. The model is being benchmarked against normal model models for surface loading. It will be used to investigate the effects of a 3D varying lithosphere and upper asthenosphere in Antarctica. Viscosity which will be computed from temperature estimates with laboratory based flow laws. A new 3D temperature map of the Antarctic lithosphere has been developed within ESA's GOCE+ project based on seismic data as well as on GOCE and GRACE inferred gravity gradients. Output from the GIA model with this new temperature estimates will be compared to that of 1D viscosity profiles and other recent 3D viscosity models based on seismic data. From these side to side comparisons we want to investigate the influence of the viscosity map on uplift rates and horizontal movement. Finally the results can be compared to GPS measurement to investigate the validity of all models.

Gravity field models from kinematic orbits of CHAMP, GRACE and GOCE satellites

NASA Astrophysics Data System (ADS)

Bezděk, Aleš; Sebera, Josef; Klokočník, Jaroslav; Kostelecký, Jan

2014-02-01

The aim of our work is to generate Earth's gravity field models from GPS positions of low Earth orbiters. Our inversion method is based on Newton's second law, which relates the observed acceleration of the satellite with forces acting on it. The observed acceleration is obtained as numerical second derivative of kinematic positions. Observation equations are formulated using the gradient of the spherical harmonic expansion of the geopotential. Other forces are either modelled (lunisolar perturbations, tides) or provided by onboard measurements (nongravitational perturbations). From this linear regression model the geopotential harmonic coefficients are obtained. To this basic scheme of the acceleration approach we added some original elements, which may be useful in other inversion techniques as well. We tried to develop simple, straightforward and still statistically correct model of observations. (i) The model is linear in the harmonic coefficients, no a priori gravity field model is needed, no regularization is applied. (ii) We use the generalized least squares to successfully mitigate the strong amplification of noise due to numerical second derivative. (iii) The number of other fitted parameters is very small, in fact we use only daily biases, thus we can monitor their behaviour. (iv) GPS positions have correlated errors. The sample autocorrelation function and especially the partial autocorrelation function indicate suitability of an autoregressive model to represent the correlation structure. The decorrelation of residuals improved the accuracy of harmonic coefficients by a factor of 2-3. (v) We found it better to compute separate solutions in the three local reference frame directions than to compute them together at the same time; having obtained separate solutions for along-track, cross-track and radial components, we combine them using the normal matrices. Relative contribution of the along-track component to the combined solution is 50 percent on average. (vi) The computations were performed on an ordinary PC up to maximum degree and order 120. We applied the presented method to orbits of CHAMP and GRACE spanning seven years (2003-2009) and to two months of GOCE (Nov/Dec 2009). The obtained long-term static gravity field models are of similar or better quality compared to other published solutions. We also tried to extract the time-variable gravity signal from CHAMP and GRACE orbits. The acquired average annual signal shows clearly the continental areas with important and known hydrological variations.

Analysis of Lithospheric Stresses Using Satellite Gravimetry: Hypotheses and Applications to North Atlantic

NASA Astrophysics Data System (ADS)

Minakov, A.; Medvedev, S.

2017-12-01

Analysis of lithospheric stresses is necessary to gain understanding of the forces that drive plate tectonics and intraplate deformations and the structure and strength of the lithosphere. A major source of lithospheric stresses is believed to be in variations of surface topography and lithospheric density. The traditional approach to stress estimation is based on direct calculations of the Gravitational Potential Energy (GPE), the depth integrated density moment of the lithosphere column. GPE is highly sensitive to density structure which, however, is often poorly constrained. Density structure of the lithosphere may be refined using methods of gravity modeling. However, the resulted density models suffer from non-uniqueness of the inverse problem. An alternative approach is to directly estimate lithospheric stresses (depth integrated) from satellite gravimetry data. Satellite gravity gradient measurements by the ESA GOCE mission ensures a wealth of data for mapping lithospheric stresses if a link between data and stresses or GPE can be established theoretically. The non-uniqueness of interpretation of sources of the gravity signal holds in this case as well. Therefore, the data analysis was tested for the North Atlantic region where reliable additional constraints are supplied by both controlled-source and earthquake seismology. The study involves comparison of three methods of stress modeling: (1) the traditional modeling approach using a thin sheet approximation; (2) the filtered geoid approach; and (3) the direct utilization of the gravity gradient tensor. Whereas the first two approaches (1)-(2) calculate GPE and utilize a computationally expensive finite element mechanical modeling to calculate stresses, the approach (3) uses a much simpler numerical treatment but requires simplifying assumptions that yet to be tested. The modeled orientation of principal stresses and stress magnitudes by each of the three methods are compared with the World Stress Map.

Suggestions for Improvement of User Access to GOCE L2 Data

NASA Astrophysics Data System (ADS)

Tscherning, C. C.

2011-07-01

ESA's has required that most GOCE L2 products are delivered in XML format. This creates difficulties for the users because a Parser written in Perl is needed to convert the files to files without XML tags. However several products, such as the coefficients of spherical harmonic coefficients are made available on standard form through the International Center for Global Gravity Field Models. The variance-covariance information for the gravity field models is only available without XML tags. It is suggested that all XML products are made available in the Virtual Data Archive as files without tags. This will besides making the data directly usable by a FORTRAN program also reduce the size (storage requirements) of the product to about 30 %. A further reduction of used storage should be made by tuning the number of digits for the individual quantities in the products, so that it corresponds to the actual number of significant digits.

Testing of Selected Geopotential Models in Terms of GOCE Satellite Orbit Determination Using Simulated GPS Observations

NASA Astrophysics Data System (ADS)

Bobojc, Andrzej; Drozyner, Andrzej

2016-04-01

This work contains a comparative study of performance of twenty geopotential models in an orbit estimation process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For testing, among others, such models as JYY_GOCE02S, ITG-GOCE02, ULUX_CHAMP2013S, GOGRA02S, ITG-GRACE2010S, EIGEN-51C, EGM2008, EGM96, JGM3, OSU91a, OSU86F were adopted. A special software package, called the Orbital Computation System (OCS), based on the classical method of least squares was used. In the frame of OCS, initial satellite state vector components are corrected in an iterative process, using the given geopotential model and the models describing the remaining gravitational perturbations. An important part of the OCS package is the 8th order Cowell numerical integration procedure, which enables a satellite orbit computation. Different sets of pseudorange simulations along reference GOCE satellite orbital arcs were obtained using real orbits of the Global Positioning System (GPS) satellites. These sets were the basic observation data used in the adjustment. The centimeter-accuracy Precise Science Orbit (PSO) for the GOCE satellite provided by the European Space Agency (ESA) was adopted as the GOCE reference orbit. Comparing various variants of the orbital solutions, the relative accuracy of geopotential models in an orbital aspect is determined. Full geopotential models were used in the adjustment process. However, the solutions were also determined taking into account truncated geopotential models. In such case, an accuracy of the orbit estimated was slightly enhanced. The obtained solutions refer to the orbital arcs with the lengths of 90-minute and 1-day.

Experiences with GOCE models in SONMICAT-BCN calibration site.

NASA Astrophysics Data System (ADS)

Martinez-Benjamin, J. J.; Termens, A.; Pros, F.

2016-12-01

SONMICAT - the integrated sea level observation system of Catalonia - aims at providing high-quality continous measurements of sea- and land levels at the Catalan coast from tide gauges and from modern geodetic techniques for studies on long-term sea level trends, but also the calibration of satellite altimeters, for instance. This synergy is indeed the only way to get a clear and unambigous picture of what is actually going on at the coast of Catalonia. Actually, there is a gap of sea level data in the coastal area of Catalonia, although several groups have started to do some work. SONMICAT will fill it and, as a goal, will be a regional implementation and densification of the GGOS . In the framework of SONMICAT project, the sea level infrastructure has been improved by providing the harbour of Barcelona with 3 tide gauges and a GPS station nearby. Furthermore, an airborne LiDAR campaign was carried out with two strips along two ICESat target tracks. The work focuses on the comparison between the GOCE gravity field solutions with existing local an regional gravity field models over the area of Barcelona harbour. The study will estimate how GOCE works on SONMICAT-BCN calibration site in order to prepare future geomatics issues .

The Use of GOCE/GRACE Information in the Latest NGS xGeoid15 Model for the USA

NASA Astrophysics Data System (ADS)

Holmes, S. A.; Li, X.; Youngman, M.

2015-12-01

The U.S. National Geodetic Survey [NGS], through its Gravity for the Redefinition of the American Vertical Datum [GRAV-D] program, is flying airborne gravity surveys over the USA and its territories. By 2022, NGS intends that all orthometric heights in the USA will be determined in the field using a reliable national gravimetric geoid model to transform from geodetic heights obtained from GPS. Towards this end, all available airborne data has been incorporated into a new NGS experimental geoid model - xGEOID15. The xGEOID15 model is the second in a series of annual experimental geoid models that incorporates NGS GRAV-D airborne data. This series provides a useful benchmark for assessing and improving current techniques, to ultimately compute a geoid model that can support a national physical height system by 2022. Here, we focus on the combination of the latest GOCE/GRACE models with the terrestrial gravimetry (land/airborne) that was applied for xGeoid15. Comparisons against existing combination gravitational solutions, such as EGM2008 and EIGEN6C4, as well as recent geoid models, such as xGeoid14 and CGG2013, are interesting for what they reveal about the respective use of the GOCE/GRACE satgrav information.

Satellite gravity field derivatives for identifying geological boundaries.

NASA Astrophysics Data System (ADS)

Alvarez, O.; Gimenez, M.; Braitenberg, C.; Folguera, A.

2012-04-01

The Pampean flat slab zone developed in the last 17 Ma between 27° and 33°S, and has denuded an intricate collage of crustal blocks amalgamated during the Pampean, Famatinian and San Rafael deformational stages, that is far of being completely understood. For potential field studies these amalgamations have the effect of defining important compositional and density heterogeneities. Geophysical data from different studies show a sharp boundary between the two adjacent and contrasting crusts of Pampia and the Cuyania terrane. Recent aeromagnetic surveys have inferred a mafic and ultramafic belt interpreted as a buried ophiolitic suite hosted in the corresponding suture. This boundary coincides locally with basement exposures of high to medium grade metamorphic rocks developed in close association with the Famatinian orogen of Early to Middle Ordovician age. Lower crustal rocks are exposed along this first order crustal discontinuity. The Río de la Plata basement crops out from southern Uruguay to eastern-center Argentina with an approximate surface of 20,000 km2. Oldest rocks have been dated in 2,200 and 1,700 Ma, indicating that they constituted a different block to Pampia. The boundary between Pampia and the Rio de la Plata craton is not exposed. However, a strong gravimetric anomaly identified in the central part of the foothills of the Sierras de Córdoba indicates a first order crustal discontinuity that has been related to their collision in Neoproterozoic times. This work focuses on the determination of mass heterogeneities over the Pampean flat slab zone using gravity anomaly and vertical gravity gradient, with the aim to determine discontinuities in the pattern of terrain amalgamation that conformed the basement. Satellite gravimetry is highly sensitive to these variations. Recent satellite missions, (CHAMP, GRACE, and GOCE) have introduced an extraordinary improvement in the global mapping of the gravity field. We control the quality of the terrestrial data entering the EGM2008 by a comparison analysis with the satellite only gravitational model of GOCE up to degree N=250. Using the global model EGM2008, the vertical gravity gradient and the gravity anomaly for South Central Andes are calculated. We correct the observations for the topographic effect using tesseroids by using a 1-arc minute global relief model of earth's surface. Results are compared to a schematic geological map of the South Central Andes region, which includes main geological features with regional dimensions presumably accompanied by crustal density variations. We clearly depict the geological structures and delineation of significant terrains such as Pampia, Cuyania, and Chilenia terranes. Of great interest is the contact between the Rio de la Plata craton and the Pampia Terrain, a boundary that has not been clearly defined till now. Our work aims to highlight the potential of this new tool of satellite gravimetry, with the addition of topographic correction, to achieve tectonic interpretation of medium to long wavelength of a determined study region. We demonstrate that the new gravity fields can be used for identifying geological boundaries related to density differences, in a regional dimension and thus are a new useful tool in geophysical exploration.

New geoid of Greenland - a case study of terrain and ice effects, GOCE and local sea level data

NASA Astrophysics Data System (ADS)

Forsberg, R.; Jensen, T.

2014-12-01

Making an accurate geoid model of Greenland has always been a challenge due to the ice sheet and glaciers, and the rough topography and deep fjords in the ice free parts. Terrestrial gravity coverage has for the same reasons been relatively sparse, with an older NRL high-level airborne survey of the interior being the only gravity field data over the interior, and terrain and ice thickness models being insufficient both in terms of resolution and accuracy. This data situation has in the later years changed substantially, first of all due to GOCE, but also due to new DTU-Space and NASA IceBridge airborne gravity, ice thickness data from IceBridge and European airborne measurements, and new terrain models from ASTER, SPOT-5 and digital photogrammetry. In the paper we use all available data to make a new geoid of Greenland and surrounding ocean regions, using remove-restore techniques for ice and topography, spherical FFT techniques and downward continuation by least squares collocation. The impact of GOCE and the new terrestrial data yielded a much improved geoid. Due to the lack of of levelling data connecting scattered towns, the new geoid is validated by local sea level and dynamic ocean topography data, and specially collected GPS-tide gauge profile data along fjords. The comparisons show significant improvements over EGM08 and older geoid models, and also highlight the problems of global sea level models, especially in sea ice covered regions, and the definition of a new consistent vertical datum of Greenland.

Weathering the Storm - GOCE Flight Operations in 2010

NASA Astrophysics Data System (ADS)

Steiger, C.; Da Costa, A.; Floberghagen, R.; Fehringer, M.; Emanuelli, P. P.

2011-07-01

ESA's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) was successfully launched on 17th March 2009. The mission is controlled by ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany. Following completion of commissioning, routine operations started in September 2009, keeping the S/C in drag-free mode at an altitude of 259.6 km. Operations are driven by the unique aspects of the mission, in particular the very low altitude and the high complexity of GOCE's drag- free control system. Following a general introduction, the main focus is put on the special events of 2010, when science operations were interrupted for several months due to problems with the main platform computer. These anomalies presented a major challenge, requiring to operate the spacecraft "in the blind" with no status information available, and extensive modifications of the on-board software to recover the mission.

An approach to Moho discontinuity recovery from on-orbit GOCE data with application over Indo-Pak region

NASA Astrophysics Data System (ADS)

Eshagh, Mehdi; Hussain, Matloob

2016-10-01

In this research, a modified form of Vening Meinesz-Moritz (VMM) theory of isostasy for the second-order radial derivative of gravitational potential, measured from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), is developed for local Moho depth recovery. An integral equation is organised for inverting the GOCE data to compute a Moho model in combination with topographic/bathymetric heights of SRTM30, sediment and consolidated crystalline basement and the laterally-varying density contrast model of CRUST1.0. A Moho model from EGM2008 to degree and order 180 is also computed based on the same principle for the purpose of comparison. In addition, we compare both of them with the 3 available seismic Moho models; two global and one regional over the Indo-Pak region. Numerical results show that our GOCE-based Moho model is closer to the all seismic models than that of EGM2008. The model is closest to the regional one with a standard deviation of 5.5 km and a root mean squares error of 7.8 km, which is 2.3 km smaller than the corresponding one based on EGM2008.

Global mean dynamic topography based on GOCE data and Wiener filters

NASA Astrophysics Data System (ADS)

Gilardoni, Maddalena; Reguzzoni, Mirko; Albertella, Alberta

2015-04-01

A mean dynamic ocean topography (MDT) has been computed by using a GOCE-only gravity model and a given mean sea surface (MSS) obtained from satellite altimetry. Since the used gravity model, i.e. the fifth release of the time-wise solution covering the full mission lifetime, is truncated at a maximum harmonic degree of 280, the obtained MDT has to be consistently filtered. This has been done globally by using the spherical harmonic representation and following a Wiener minimization principle. This global filtering approach is convenient from the computational point of view but requires to have MDT values all over the Earth surface and therefore to fill the continents with fictitious data. The main improvements with respect to the already presented results are in the MDT filling procedure (to guarantee that the global signal has the same covariance of the one over the oceans), in the error modelling of the input MSS and in the error estimation of the filtered MDT and of the corresponding geostrophic velocities. The impact of GOCE data in the ocean circulation global modelling has been assessed by comparing the pattern of the obtained geostrophic currents with those computed by using EGM2008. Comparisons with independent circulation data based on drifters and other MDT models have been also performed with the aim of evaluating the accuracy of the obtained results.

Upper Atmospheric Response to the April 2010 Storm as Observed by GOCE, CHAMP, and GRACE and Modeled by TIME-GCM

NASA Astrophysics Data System (ADS)

Hagan, Maura; Häusler, Kathrin; Lu, Gang; Forbes, Jeffrey; Zhang, Xiaoli; Doornbos, Eelco; Bruinsma, Sean

2014-05-01

We present the results of an investigation of the upper atmosphere during April 2010 when it was disturbed by a fast-moving coronal mass ejection. Our study is based on comparative analysis of observations made by the Gravity field and steady-state Ocean Circulation Explorer (GOCE), Challenging Minisatellite Payload (CHAMP), and Gravity Recovery And Climate Experiment (GRACE) satellites and a set of simulations with the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). We compare and contrast the satellite observations with TIME-GCM results from a realistic simulation based on prevailing meteorological and solar geomagnetic conditions. We diagnose the comparative importance of the upper atmospheric signatures attributable to meteorological forcing with those attributable to storm effects by diagnosing a series of complementary control TIME-GCM simulations. These results also quantify the extent to which lower and middle atmospheric sources of upper atmospheric variability precondition its response to the solar geomagnetic storm.

Use of Massive Parallel Computing Libraries in the Context of Global Gravity Field Determination from Satellite Data

NASA Astrophysics Data System (ADS)

Brockmann, J. M.; Schuh, W.-D.

2011-07-01

The estimation of the global Earth's gravity field parametrized as a finite spherical harmonic series is computationally demanding. The computational effort depends on the one hand on the maximal resolution of the spherical harmonic expansion (i.e. the number of parameters to be estimated) and on the other hand on the number of observations (which are several millions for e.g. observations from the GOCE satellite missions). To circumvent these restrictions, a massive parallel software based on high-performance computing (HPC) libraries as ScaLAPACK, PBLAS and BLACS was designed in the context of GOCE HPF WP6000 and the GOCO consortium. A prerequisite for the use of these libraries is that all matrices are block-cyclic distributed on a processor grid comprised by a large number of (distributed memory) computers. Using this set of standard HPC libraries has the benefit that once the matrices are distributed across the computer cluster, a huge set of efficient and highly scalable linear algebra operations can be used.

Gravity model for the North Atlantic ocean mantle: results, uncertainties and links to regional geodynamics

NASA Astrophysics Data System (ADS)

Barantsrva, O.; Artemieva, I. M.; Thybo, H.

2015-12-01

We present the results of gravity modeling for the North Atlantic region based on interpretation of GOCE gravity satellite data. First, to separate the gravity signal caused by density anomalies within the crust and the upper mantle, we subtract the lower harmonics in the gravity field, which are presumably caused by deep density structure of the Earth (the core and the lower mantle). Next, the gravity effect of the upper mantle is calculated by subtracting the gravity effect of the crustal model. Our "basic model" is constrained by a recent regional seismic model EUNAseis for the crustal structure (Artemieva and Thybo, 2013); for bathymetry and topography we use a global ETOPO1 model by NOAA. We test sensitivity of the results to different input parameters, such as bathymetry, crustal structure, and gravity field. For bathymetry, we additionally use GEBCO data; for crustal correction - a global model CRUST 1.0 (Laske, 2013); for gravity - EGM2008 (Pavlis, 2012). Sensitivity analysis shows that uncertainty in the crustal structure produces the largest deviation from "the basic model". Use of different bathymetry data has little effect on the final results, comparable to the interpolation error. The difference in mantle residual gravity models based on GOCE and EMG2008 gravity data is 5-10 mGal. The results based on two crustal models have a similar pattern, but differ significantly in amplitude (ca. 250 mGal) for the Greenland-Faroe Ridge. The results demonstrate the presence of a strong gravity and density heterogeneity in the upper mantle in the North Atlantic region. A number of mantle residual gravity anomalies are robust features, independent of the choice of model parameters. This include (i) a sharp contrast at the continent-ocean transition, (ii) positive mantle gravity anomalies associated with continental fragments (microcontinents) in the North Atlantic ocean; (iii) negative mantle gravity anomalies which mark regions with anomalous oceanic mantle and the Mid-Atlantic Ridge. To understand better a complex geodynamics mosaic in the region, we compare our results with regional geochemical data (Korenaga and Klemen, 2000), and find that residual mantle gravity anomalies are well correlated with anomalies in epsilon-Nd and iron-depletion.

Evaluation of gravitational curvatures of a tesseroid in spherical integral kernels

NASA Astrophysics Data System (ADS)

Deng, Xiao-Le; Shen, Wen-Bin

2018-04-01

Proper understanding of how the Earth's mass distributions and redistributions influence the Earth's gravity field-related functionals is crucial for numerous applications in geodesy, geophysics and related geosciences. Calculations of the gravitational curvatures (GC) have been proposed in geodesy in recent years. In view of future satellite missions, the sixth-order developments of the gradients are becoming requisite. In this paper, a set of 3D integral GC formulas of a tesseroid mass body have been provided by spherical integral kernels in the spatial domain. Based on the Taylor series expansion approach, the numerical expressions of the 3D GC formulas are provided up to sixth order. Moreover, numerical experiments demonstrate the correctness of the 3D Taylor series approach for the GC formulas with order as high as sixth order. Analogous to other gravitational effects (e.g., gravitational potential, gravity vector, gravity gradient tensor), numerically it is found that there exist the very-near-area problem and polar singularity problem in the GC east-east-radial, north-north-radial and radial-radial-radial components in spatial domain, and compared to the other gravitational effects, the relative approximation errors of the GC components are larger due to not only the influence of the geocentric distance but also the influence of the latitude. This study shows that the magnitude of each term for the nonzero GC functionals by a grid resolution 15^' } } × 15^' }} at GOCE satellite height can reach of about 10^{-16} m^{-1} s2 for zero order, 10^{-24 } or 10^{-23} m^{-1} s2 for second order, 10^{-29} m^{-1} s2 for fourth order and 10^{-35} or 10^{-34} m^{-1} s2 for sixth order, respectively.

Assessments on GOCE-based Gravity Field Model Comparisons with Terrestrial Data Using Wavelet Decomposition and Spectral Enhancement Approaches

NASA Astrophysics Data System (ADS)

Erol, Serdar; Serkan Isık, Mustafa; Erol, Bihter

2016-04-01

The recent Earth gravity field satellite missions data lead significant improvement in Global Geopotential Models in terms of both accuracy and resolution. However the improvement in accuracy is not the same everywhere in the Earth and therefore quantifying the level of improvement locally is necessary using the independent data. The validations of the level-3 products from the gravity field satellite missions, independently from the estimation procedures of these products, are possible using various arbitrary data sets, as such the terrestrial gravity observations, astrogeodetic vertical deflections, GPS/leveling data, the stationary sea surface topography. Quantifying the quality of the gravity field functionals via recent products has significant importance for determination of the regional geoid modeling, base on the satellite and terrestrial data fusion with an optimal algorithm, beside the statistical reporting the improvement rates depending on spatial location. In the validations, the errors and the systematic differences between the data and varying spectral content of the compared signals should be considered in order to have comparable results. In this manner this study compares the performance of Wavelet decomposition and spectral enhancement techniques in validation of the GOCE/GRACE based Earth gravity field models using GPS/leveling and terrestrial gravity data in Turkey. The terrestrial validation data are filtered using Wavelet decomposition technique and the numerical results from varying levels of decomposition are compared with the results which are derived using the spectral enhancement approach with contribution of an ultra-high resolution Earth gravity field model. The tests include the GO-DIR-R5, GO-TIM-R5, GOCO05S, EIGEN-6C4 and EGM2008 global models. The conclusion discuss the superiority and drawbacks of both concepts as well as reporting the performance of tested gravity field models with an estimate of their contribution to modeling the geoid in Turkish territory.

Local recovery of lithospheric stress tensor from GOCE gravitational tensor

NASA Astrophysics Data System (ADS)

Eshagh, Mehdi

2017-04-01

The sublithospheric stress due to mantle convection can be computed from gravity data and propagated through the lithosphere by solving the boundary-value problem of elasticity for the Earth's lithosphere. In this case, a full tensor of stress can be computed at any point inside this elastic layer. Here, we present mathematical foundations for recovering such a tensor from gravitational tensor measured at satellite altitudes. The mathematical relations will be much simpler in this way than the case of using gravity data as no derivative of spherical harmonics (SHs) or Legendre polynomials is involved in the expressions. Here, new relations between the SH coefficients of the stress and gravitational tensor elements are presented. Thereafter, integral equations are established from them to recover the elements of stress tensor from those of the gravitational tensor. The integrals have no closed-form kernels, but they are easy to invert and their spatial truncation errors are reducible. The integral equations are used to invert the real data of the gravity field and steady-state ocean circulation explorer mission (GOCE), in 2009 November, over the South American plate and its surroundings to recover the stress tensor at a depth of 35 km. The recovered stress fields are in good agreement with the tectonic and geological features of the area.

Modelling airborne gravity data by means of adapted Space-Wise approach

NASA Astrophysics Data System (ADS)

Sampietro, Daniele; Capponi, Martina; Hamdi Mansi, Ahmed; Gatti, Andrea

2017-04-01

Regional gravity field modelling by means of remove - restore procedure is nowadays widely applied to predict grids of gravity anomalies (Bouguer, free-air, isostatic, etc.) in gravimetric geoid determination as well as in exploration geophysics. Considering this last application, due to the required accuracy and resolution, airborne gravity observations are generally adopted. However due to the relatively high acquisition velocity, presence of atmospheric turbulence, aircraft vibration, instrumental drift, etc. airborne data are contaminated by a very high observation error. For this reason, a proper procedure to filter the raw observations both in the low and high frequency should be applied to recover valuable information. In this work, a procedure to predict a grid or a set of filtered along track gravity anomalies, by merging GGM and airborne dataset, is presented. The proposed algorithm, like the Space-Wise approach developed by Politecnico di Milano in the framework of GOCE data analysis, is based on a combination of along track Wiener filter and Least Squares Collocation adjustment and properly considers the different altitudes of the gravity observations. Among the main differences with respect to the satellite application of the Space-Wise approach there is the fact that, while in processing GOCE data the stochastic characteristics of the observation error can be considered a-priori well known, in airborne gravimetry, due to the complex environment in which the observations are acquired, these characteristics are unknown and should be retrieved from the dataset itself. Some innovative theoretical aspects focusing in particular on the theoretical covariance modelling are presented too. In the end, the goodness of the procedure is evaluated by means of a test on real data recovering the gravitational signal with a predicted accuracy of about 0.25 mGal.

That gravity thing

NASA Astrophysics Data System (ADS)

Jewess, Mike

2009-05-01

Your news article "New probe plots Earth's gravity field" (March p11) reports on the European Space Agency's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) - a satellite that will measure the Earth's gravitational field. It describes the way that g, the acceleration of free fall at the Earth's surface, varies with latitude; this variation is great enough to require adjustment of pendulum clocks between latitudes and also the recalibration of all balances that do not directly compare one mass with a reference mass. The article also notes that the spin of the (effectively fluid) Earth causes it to bulge at the equator, a realization that goes back to Newton's Principia.

Glacier mass balance in high-arctic areas with anomalous gravity

NASA Astrophysics Data System (ADS)

Sharov, A.; Rieser, D.; Nikolskiy, D.

2012-04-01

All known glaciological models describing the evolution of Arctic land- and sea-ice masses in changing climate treat the Earth's gravity as horizontally constant, but it isn't. In the High Arctic, the strength of the gravitational field varies considerably across even short distances under the influence of a density gradient, and the magnitude of free air gravity anomalies attains 100 mGal and more. On long-term base, instantaneous deviations of gravity can have a noticeable effect on the regime and mass budget of glaciological objects. At best, the gravity-induced component of ice mass variations can be determined on topographically smooth, open and steady surfaces, like those of arctic planes, regular ice caps and landfast sea ice. The present research is devoted to studying gravity-driven impacts on glacier mass balance in the outer periphery of four Eurasian shelf seas with a very cold, dry climate and rather episodic character of winter precipitation. As main study objects we had chosen a dozen Russia's northernmost insular ice caps, tens to hundreds of square kilometres in extent, situated in a close vicinity of strong gravity anomalies and surrounded with extensive fields of fast and/or drift ice for most of the year. The supposition about gravitational forcing on glacioclimatic settings in the study region is based on the results of quantitative comparison and joint interpretation of existing glacier change maps and available data on the Arctic gravity field and solid precipitation. The overall mapping of medium-term (from decadal to half-centennial) changes in glacier volumes and quantification of mass balance characteristics in the study region was performed by comparing reference elevation models of study glaciers derived from Russian topographic maps 1:200,000 (CI = 20 or 40 m) representing the glacier state as in the 1950s-1980s with modern elevation data obtained from satellite radar interferometry and lidar altimetry. Free-air gravity anomalies were graphically represented in the reference model geometry using Russian gravimetric maps 1:1000000 (1980s), ArcGP grid (2008) and GOCE gravity field data (Release 3, 2009-2011). 25-year long records of daily precipitation obtained from 38 coastal stations were involved in the causality analysis. Strong positive distance-weighted correlation was discovered between the magnitude of geopotential and gravity gradient on one hand and the precipitation amount, annual number of precipitation "events" and glacier elevation changes on the other, while it was noted that the correlation decreases in humid and mountainous areas. Relevant analytical and geophysical explanations were provided and tested using the basic concepts of hydrostatic stress, lapse rate and non-orographic gradient precipitation. It was concluded that the gravitational impact on the mass balance of arctic maritime ice caps is threefold. 1) Lateral variations of gravity influence directly the ambient lapse rate thereby modulating the atmospheric stability and leading to the increased intensity and frequency of heavy snowfalls over the areas with positive gravity anomalies. 2) Glacier ice deformation, flow, calving and meltwater runoff are gravity-driven phenomena, and the removal of glacier ice is closely interrelated with geopotential variations nearby. 3) Gravity anomalies affect processes of sea ice grow, drift and consolidation resulting in generally lower concentration and lesser thickness of the sea ice found in the aquatories with positive gravity. The advection of moist air to insular ice caps facilitates sea-effect snow events and makes glacier mass balance more positive. The effect is enhanced when the air mass advects toward the centre of positive anomaly. The idea about gradient (deviatoric) precipitation and related cryogravic processes does not contradict to the concept of gravity waves and has some analogy with the hypothesis on "ice lichens" devised by E.Gernet 80 years ago. Further analogies can be learned from another industry, e.g. technical chemistry. Several questions associated with the variability of evaporation, ice nucleation, aerosol deposition and snow redistribution in the heterogeneous field of gravity remain open.

Acceleration Noise Considerations for Drag-free Satellite Geodesy Missions

NASA Astrophysics Data System (ADS)

Hong, S. H.; Conklin, J. W.

2016-12-01

The GRACE mission, which launched in 2002, opened a new era of satellite geodesy by providing monthly mass variation solutions with spatial resolution of less than 200 km. GRACE proved the usefulness of a low-low satellite-to-satellite tracking formation. Analysis of the GRACE data showed that the K-Band ranging system, which is used to measure the range between the two satellites, is the limiting factor for the precision of the solution. Consequently, the GRACE-FO mission, schedule for launch in 2017, will continue the work of GRACE, but will also test a new, higher precision laser ranging interferometer compared with the K-Band ranging system. Beyond GRACE-FO, drag-free systems are being considered for satellite geodesy missions. GOCE tested a drag-free attitude control system with a gravity gradiometer and showed improvements in the acceleration noise compensation compared to the electrostatic accelerometers used in GRACE. However, a full drag-free control system with a gravitational reference sensor has not yet been applied to satellite geodesy missions. More recently, this type of drag-free system was used in LISA Pathfinder, launched in 2016, with an acceleration noise performance two orders of magnitude better than that of GOCE. We explore the effects of drag-free performance in satellite geodesy missions similar to GRACE-FO by applying three different residual acceleration noises from actual space missions: GRACE, GOCE and LISA Pathfinder. Our solutions are limited to degree 60 spherical harmonic coefficients with biweekly time resolution. Our analysis shows that a drag-free system with acceleration noise performance comparable to GOCE and LISA-Pathfinder would greatly improve the accuracy of gravity solutions. In addition to these results, we also present the covariance shaping process used in the estimation. In the future, we plan to use actual acceleration noise data measured using the UF torsion pendulum. This apparatus is a ground facility at University of Florida used to test the performance of precision inertial sensors. We also plan to evaluate the importance of acceleration noise when a second inclined pair of satellites is included in the analysis, following the work of Weise in 2012, which showed that two satellite pairs decreased aliasing errors.

High-frequency analysis of Earth gravity field models based on terrestrial gravity and GPS/levelling data: a case study in Greece

NASA Astrophysics Data System (ADS)

Papanikolaou, T. D.; Papadopoulos, N.

2015-06-01

The present study aims at the validation of global gravity field models through numerical investigation in gravity field functionals based on spherical harmonic synthesis of the geopotential models and the analysis of terrestrial data. We examine gravity models produced according to the latest approaches for gravity field recovery based on the principles of the Gravity field and steadystate Ocean Circulation Explorer (GOCE) and Gravity Recovery And Climate Experiment (GRACE) satellite missions. Furthermore, we evaluate the overall spectrum of the ultra-high degree combined gravity models EGM2008 and EIGEN-6C3stat. The terrestrial data consist of gravity and collocated GPS/levelling data in the overall Hellenic region. The software presented here implements the algorithm of spherical harmonic synthesis in a degree-wise cumulative sense. This approach may quantify the bandlimited performance of the individual models by monitoring the degree-wise computed functionals against the terrestrial data. The degree-wise analysis performed yields insight in the short-wavelengths of the Earth gravity field as these are expressed by the high degree harmonics.

Are higher degree even zonals really harmful for the LARES/LAGEOS frame-dragging experiment?

NASA Astrophysics Data System (ADS)

Renzetti, G.

2012-08-01

The low-altitude effects of LARES are examined to determined how they can impact the outcome of the hoped 1% frame-dragging measurement in the LARES-LAGEOS experiment. This analysis, based on a different approach than other studies recently appearing in the literature, shows that the spherical harmonics of the Earth gravity field with degree ℓ > 60 may represent a threat because their errors map significantly into LARES orbital disturbances compared to frame-dragging. The GIF48 model was used. It is questionable whether future Earth gravity models by GRACE and GOCE will be of sufficient accuracy.

2017 Updates: Earth Gravitational Model 2020

NASA Astrophysics Data System (ADS)

Barnes, D. E.; Holmes, S. A.; Ingalls, S.; Beale, J.; Presicci, M. R.; Minter, C.

2017-12-01

The National Geospatial-Intelligence Agency [NGA], in conjunction with its U.S. and international partners, has begun preliminary work on its next Earth Gravitational Model, to replace EGM2008. The new `Earth Gravitational Model 2020' [EGM2020] has an expected public release date of 2020, and will retain the same harmonic basis and resolution as EGM2008. As such, EGM2020 will be essentially an ellipsoidal harmonic model up to degree (n) and order (m) 2159, but will be released as a spherical harmonic model to degree 2190 and order 2159. EGM2020 will benefit from new data sources and procedures. Updated satellite gravity information from the GOCE and GRACE mission, will better support the lower harmonics, globally. Multiple new acquisitions (terrestrial, airborne and shipborne) of gravimetric data over specific geographical areas (Antarctica, Greenland …), will provide improved global coverage and resolution over the land, as well as for coastal and some ocean areas. Ongoing accumulation of satellite altimetry data as well as improvements in the treatment of this data, will better define the marine gravity field, most notably in polar and near-coastal regions. NGA and partners are evaluating different approaches for optimally combining the new GOCE/GRACE satellite gravity models with the terrestrial data. These include the latest methods employing a full covariance adjustment. NGA is also working to assess systematically the quality of its entire gravimetry database, towards correcting biases and other egregious errors. Public release number 15-564

Earth Gravitational Model 2020

NASA Astrophysics Data System (ADS)

Barnes, Daniel; Holmes, Simon; Factor, John; Ingalls, Sarah; Presicci, Manny; Beale, James

2017-04-01

The National Geospatial-Intelligence Agency [NGA], in conjunction with its U.S. and international partners, has begun preliminary work on its next Earth Gravitational Model, to replace EGM2008. The new 'Earth Gravitational Model 2020' [EGM2020] has an expected public release date of 2020, and will likely retain the same harmonic basis and resolution as EGM2008. As such, EGM2020 will be essentially an ellipsoidal harmonic model up to degree (n) and order (m) 2159, but will be released as a spherical harmonic model to degree 2190 and order 2159. EGM2020 will benefit from new data sources and procedures. Updated satellite gravity information from the GOCE and GRACE mission, will better support the lower harmonics, globally. Multiple new acquisitions (terrestrial, airborne and ship borne) of gravimetric data over specific geographical areas, will provide improved global coverage and resolution over the land, as well as for coastal and some ocean areas. Ongoing accumulation of satellite altimetry data as well as improvements in the treatment of this data, will better define the marine gravity field, most notably in polar and near-coastal regions. NGA and partners are evaluating different approaches for optimally combining the new GOCE/GRACE satellite gravity models with the terrestrial data. These include the latest methods employing a full covariance adjustment. NGA is also working to assess systematically the quality of its entire gravimetry database, towards correcting biases and other egregious errors where possible, and generating improved error models that will inform the final combination with the latest satellite gravity models. Outdated data gridding procedures have been replaced with improved approaches. For EGM2020, NGA intends to extract maximum value from the proprietary data that overlaps geographically with unrestricted data, whilst also making sure to respect and honor its proprietary agreements with its data-sharing partners. Approved for Public Release, 15-564

Earth Gravitational Model 2020

NASA Astrophysics Data System (ADS)

Barnes, D.; Factor, J. K.; Holmes, S. A.; Ingalls, S.; Presicci, M. R.; Beale, J.; Fecher, T.

2015-12-01

The National Geospatial-Intelligence Agency [NGA], in conjunction with its U.S. and international partners, has begun preliminary work on its next Earth Gravitational Model, to replace EGM2008. The new 'Earth Gravitational Model 2020' [EGM2020] has an expected public release date of 2020, and will likely retain the same harmonic basis and resolution as EGM2008. As such, EGM2020 will be essentially an ellipsoidal harmonic model up to degree (n) and order (m) 2159, but will be released as a spherical harmonic model to degree 2190 and order 2159. EGM2020 will benefit from new data sources and procedures. Updated satellite gravity information from the GOCE and GRACE mission, will better support the lower harmonics, globally. Multiple new acquisitions (terrestrial, airborne and shipborne) of gravimetric data over specific geographical areas, will provide improved global coverage and resolution over the land, as well as for coastal and some ocean areas. Ongoing accumulation of satellite altimetry data as well as improvements in the treatment of this data, will better define the marine gravity field, most notably in polar and near-coastal regions. NGA and partners are evaluating different approaches for optimally combining the new GOCE/GRACE satellite gravity models with the terrestrial data. These include the latest methods employing a full covariance adjustment. NGA is also working to assess systematically the quality of its entire gravimetry database, towards correcting biases and other egregious errors where possible, and generating improved error models that will inform the final combination with the latest satellite gravity models. Outdated data gridding procedures have been replaced with improved approaches. For EGM2020, NGA intends to extract maximum value from the proprietary data that overlaps geographically with unrestricted data, whilst also making sure to respect and honor its proprietary agreements with its data-sharing partners.

GOCE: The first seismometer in orbit around the Earth

NASA Astrophysics Data System (ADS)

Garcia, Raphael F.; Bruinsma, Sean; Lognonné, Philippe; Doornbos, Eelco; Cachoux, Florian

2013-03-01

The first in situ sounding of a post-seismic infrasound wavefront is presented, using data from the GOCE mission. The atmospheric infrasounds following the great Tohoku earthquake (on 11 March 2011) induce variations of air density and vertical acceleration of the GOCE platform. These signals are detected at two positions along the GOCE orbit corresponding to a crossing and a doubling of the infrasonic wavefront created by seismic surface waves. Perturbations up to 11% of air density and 1.35 × 10 - 7 m/s2 of vertical acceleration are observed and modeled with two different solid-atmosphere coupling codes. These perturbations are a due to acoustic waves creating vertical velocities up to 130 m/s. Amplitudes and arrival times of these perturbations are reproduced respectively within a factor 2, and within a 60 s time window. Waveforms present a good agreement with observed data. The vertical acceleration to air density perturbation ratio is higher for these acoustic waves than for gravity waves. Combining these two pieces of information offers a new way to distinguish between these two wave types. This new type of data is a benchmark for the models of solid-atmosphere coupling. Amplitude and frequency content constrain the infrasound attenuation related to atmosphere viscosity and thermal conductivity. Observed time shifts between data and synthetics are ascribed to lateral variations of the seismic and atmospheric sound velocities and to the influence of atmospheric winds. These effects should be included in future modeling. This validation of our modeling tools allows to specify more precisely future observation projects.

Simultaneous Observations of TADs in GOCE, CHAMP and GRACE Density Data Compared with CTIPe

NASA Astrophysics Data System (ADS)

Bruinsma, S. L.; Fedrizzi, M.

2012-12-01

The accelerometers on the CHAMP and GRACE satellites have made it possible to accumulate near-continuous records of thermosphere density between about 300 and 490 km since May 2001, and July 2002, respectively. Since November 2009, a third gravity field satellite mission, ESA's GOCE, is in a very low and near heliosynchronous dawn-dusk orbit at about 270 km. The spacecraft is actively maintained at that constant altitude using an ion propulsion engine that compensates the aerodynamic drag in the flight direction. The thrust level, combined with accelerometer and satellite attitude data, is used to compute atmospheric densities and cross-track winds. The response of the thermosphere to geomagnetic disturbances, i.e., space weather, has been extensively studied using the exceptional datasets of CHAMP and GRACE. Thanks to GOCE we now have a third excellent data set for these studies. In this presentation we will show the observed density and its variability for the geomagnetic storm of 5 April 2010, and compare it with predictions along the orbits obtained from a self-consistent physics-based coupled model of the thermosphere, ionosphere, plasmasphere and electrodynamics (CTIPe). For this storm, the CHAMP and GOCE orbit planes were perpendicular (12/24 Local Solar Time, and 6/18 LST, respectively) and the altitude difference was only approximately 30 km. The GRACE densities are at a much higher altitude of about 475 km. Wave-like features are revealed or enhanced after filtering of the densities and calculation of relative density variations. Traveling Atmospheric Disturbances are observed in the data, and the model's fidelity in reproducing the waves is evaluated.

Crustal density contrast detection by global gravity and topography models and in-situ gravity observations

NASA Astrophysics Data System (ADS)

Claessens, S. J.

2016-12-01

Mass density contrasts in the Earth's crust can be detected using an inversion of terrestrial or airborne gravity data. This contribution shows a technique to detect short-scale density contrasts using in-situ gravity observations in combination with a high-resolution global gravity model that includes variations in the gravity field due to topography. The technique is exemplified at various test sites using the Global Gravity Model Plus (GGMplus), which is a 7.2 arcsec resolution model of the Earth's gravitational field, covering all land masses and near-coastal areas within +/- 60° latitude. The model is a composite of GRACE and GOCE satellite observations, the EGM2008 global gravity model, and short-scale topographic gravity effects. Since variations in the Earth's gravity field due to topography are successfully modelled by GGMplus, any remaining differences with in-situ gravity observations are primarily due to mass density variations. It is shown that this technique effectively filters out large-scale density variations, and highlights short-scale near-surface density contrasts in the Earth's crust. Numerical results using recent high-density gravity surveys are presented, which indicate a strong correlation between density contrasts found and known lines of geological significance.

Space-Wise approach for airborne gravity data modelling

NASA Astrophysics Data System (ADS)

Sampietro, D.; Capponi, M.; Mansi, A. H.; Gatti, A.; Marchetti, P.; Sansò, F.

2017-05-01

Regional gravity field modelling by means of remove-compute-restore procedure is nowadays widely applied in different contexts: it is the most used technique for regional gravimetric geoid determination, and it is also used in exploration geophysics to predict grids of gravity anomalies (Bouguer, free-air, isostatic, etc.), which are useful to understand and map geological structures in a specific region. Considering this last application, due to the required accuracy and resolution, airborne gravity observations are usually adopted. However, due to the relatively high acquisition velocity, presence of atmospheric turbulence, aircraft vibration, instrumental drift, etc., airborne data are usually contaminated by a very high observation error. For this reason, a proper procedure to filter the raw observations in both the low and high frequencies should be applied to recover valuable information. In this work, a software to filter and grid raw airborne observations is presented: the proposed solution consists in a combination of an along-track Wiener filter and a classical Least Squares Collocation technique. Basically, the proposed procedure is an adaptation to airborne gravimetry of the Space-Wise approach, developed by Politecnico di Milano to process data coming from the ESA satellite mission GOCE. Among the main differences with respect to the satellite application of this approach, there is the fact that, while in processing GOCE data the stochastic characteristics of the observation error can be considered a-priori well known, in airborne gravimetry, due to the complex environment in which the observations are acquired, these characteristics are unknown and should be retrieved from the dataset itself. The presented solution is suited for airborne data analysis in order to be able to quickly filter and grid gravity observations in an easy way. Some innovative theoretical aspects focusing in particular on the theoretical covariance modelling are presented too. In the end, the goodness of the procedure is evaluated by means of a test on real data retrieving the gravitational signal with a predicted accuracy of about 0.4 mGal.

Microvibration and Centre-of-Gravity Shift Measurements on Thermally Stressed Thermal-Control Blankets

NASA Astrophysics Data System (ADS)

Magg, Manfred; Grillenbeck, Anton, , Dr.

2004-08-01

Several samples of thermal control blankets were subjected to transient thermal loads in a thermal vacuum chamber in order to study their ability to excite micro- vibrations on a carrier structure and to cause tiny centre- of-gravity shifts. The reason for this investigation was driven by the GOCE project in order to minimize micro- vibrations on-board of the spacecraft while on-orbit. The objectives of this investigation were to better understand the mechanism which may produce micro- vibrations induced by the thermal control blankets, and to identify thermal control blanket lay-ups with minimum micro-vibration activity.

Gravity and gravity gradient changes caused by a point dislocation

NASA Astrophysics Data System (ADS)

Huang, Jian-Liang; Li, Hui; Li, Rui-Hao

1995-02-01

In this paper we studied gravitational potential, gravity and its gradient changes, which are caused by a point dislocation, and gave the concise mathematical deduction with definite physical implication in dealing with the singular integral at a seismic source. We also analysed the features of the fields of gravity and gravity gradient, gravity-vertical-displacement gradient. The conclusions are: (1) Gravity and gravity gradient changes are very small with the change of vertical position; (2) Gravity change is much greater than the gravity gradient change which is not so distinct; (3) The gravity change due to redistribution of mass accounts for 10 50 percent of the total gravity change caused by dislocation. The signs (positive or negative) of total gravity change and vertical displacement are opposite each other at the same point for strike slip and dip slip; (4) Gravity-vertical-displacement-gradient is not constant; it manifests a variety of patterns for different dislocation models; (5) Gravity-vertical-displacement-gradient is approximately equal to apparent gravity-vertical-displacement-gradient.

Evaluation of gravitational gradients generated by Earth's crustal structures

NASA Astrophysics Data System (ADS)

Novák, Pavel; Tenzer, Robert; Eshagh, Mehdi; Bagherbandi, Mohammad

2013-02-01

Spectral formulas for the evaluation of gravitational gradients generated by upper Earth's mass components are presented in the manuscript. The spectral approach allows for numerical evaluation of global gravitational gradient fields that can be used to constrain gravitational gradients either synthesised from global gravitational models or directly measured by the spaceborne gradiometer on board of the GOCE satellite mission. Gravitational gradients generated by static atmospheric, topographic and continental ice masses are evaluated numerically based on available global models of Earth's topography, bathymetry and continental ice sheets. CRUST2.0 data are then applied for the numerical evaluation of gravitational gradients generated by mass density contrasts within soft and hard sediments, upper, middle and lower crust layers. Combined gravitational gradients are compared to disturbing gravitational gradients derived from a global gravitational model and an idealised Earth's model represented by the geocentric homogeneous biaxial ellipsoid GRS80. The methodology could be used for improved modelling of the Earth's inner structure.

Heterogeneity of the North Atlantic oceanic lithosphere based on integrated analysis of GOCE satellite gravity and geological data

NASA Astrophysics Data System (ADS)

Barantseva, Olga; Artemieva, Irina; Thybo, Hans; Herceg, Matija

2015-04-01

We present the results from modelling the gravity and density structure of the upper mantle for the off-shore area of the North Atlantic region. The crust and upper mantle of the region is expected to be anomalous: Part of the region affected by the Icelandic plume has an anomalously shallow bathymetry, whereas the northern part of the region is characterized by ultraslow spreading. In order to understand the links between deep geodynamical processes that control the spreading rate, on one hand, and their manifestations such as oceanic floor bathymetry and heat flow, on the other hand, we model the gravity and density structure of the upper mantle from satellite gravity data. The calculations are based on interpretation of GOCE gravity satellite data for the North Atlantics. To separate the gravity signal responsible for density anomalies within the crust and upper mantle, we subtract the lower harmonics caused by deep density structure of the Earth (the core and the lower mantle). The gravity effect of the upper mantle is calculated by subtracting the gravity effect of the crust for two crustal models. We use a recent regional seismic model for the crustal structure (Artemieva and Thybo, 2013) based om seismic data together with borehole data for sediments. For comparison, similar results are presented for the global CRUST 1.0 model as well (Laske, 2013). The conversion of seismic velocity data for the crustal structure to crustal density structure is crucial for the final results. We use a combination of Vp-to-density conversion based on published laboratory measurements for the crystalline basement (Ludwig, Nafe, Drake, 1970; Christensen and Mooney, 1995) and for oceanic sediments and oceanic crust based on laboratory measurements for serpentinites and gabbros from the Mid-Atlantic Ridge (Kelemen et al., 2004). Also, to overcome the high degree of uncertainty in Vp-to-density conversion, we account for regional tectonic variations in the Northern Atlantics as constrained by numerous published seismic profiles and potential-field models across the Norwegian off-shore crust (e.g. Breivik et al., 2005, 2007). The results demonstrate the presence of strong gravity and density heterogeneity of the upper mantle in the North Atlantic region. In particular, there is a sharp contrast at the continent-ocean transition, which also allows for recognising mantle gravity anomalies associated with continental fragments and with anomalous oceanic lithosphere.

Gravity Spectra from the Density Distribution of Earth's Uppermost 435 km

NASA Astrophysics Data System (ADS)

Sebera, Josef; Haagmans, Roger; Floberghagen, Rune; Ebbing, Jörg

2018-03-01

The Earth masses reside in a near-hydrostatic equilibrium, while the deviations are, for example, manifested in the geoid, which is nowadays well determined by satellite gravimetry. Recent progress in estimating the density distribution of the Earth allows us to examine individual Earth layers and to directly see how the sum approaches the observed anomalous gravitational field. This study evaluates contributions from the crust and the upper mantle taken from the LITHO1.0 model and quantifies the gravitational spectra of the density structure to the depth of 435 km. This is done without isostatic adjustments to see what can be revealed with models like LITHO1.0 alone. At the resolution of 290 km (spherical harmonic degree 70), the crustal contribution starts to dominate over the upper mantle and at about 150 km (degree 130) the upper mantle contribution is nearly negligible. At the spatial resolution <150 km, the spectra behavior is driven by the crust, the mantle lid and the asthenosphere. The LITHO1.0 model was furthermore referenced by adding deeper Earth layers from ak135, and the gravity signal of the merged model was then compared with the observed satellite-only model GOCO05s. The largest differences are found over the tectonothermal cold and old (such as cratonic), and over warm and young areas (such as oceanic ridges). The misfit encountered comes from the mantle lid where a velocity-density relation helped to reduce the RMS error by 40%. Global residuals are also provided in terms of the gravitational gradients as they provide better spatial localization than gravity, and there is strong observational support from ESA's satellite gradiometry mission GOCE down to the spatial resolution of 80-90 km.

Rigorous covariance propagation of geoid errors to geodetic MDT estimates

NASA Astrophysics Data System (ADS)

Pail, R.; Albertella, A.; Fecher, T.; Savcenko, R.

2012-04-01

The mean dynamic topography (MDT) is defined as the difference between the mean sea surface (MSS) derived from satellite altimetry, averaged over several years, and the static geoid. Assuming geostrophic conditions, from the MDT the ocean surface velocities as important component of global ocean circulation can be derived from it. Due to the availability of GOCE gravity field models, for the very first time MDT can now be derived solely from satellite observations (altimetry and gravity) down to spatial length-scales of 100 km and even below. Global gravity field models, parameterized in terms of spherical harmonic coefficients, are complemented by the full variance-covariance matrix (VCM). Therefore, for the geoid component a realistic statistical error estimate is available, while the error description of the altimetric component is still an open issue and is, if at all, attacked empirically. In this study we make the attempt to perform, based on the full gravity VCM, rigorous error propagation to derived geostrophic surface velocities, thus also considering all correlations. For the definition of the static geoid we use the third release of the time-wise GOCE model, as well as the satellite-only combination model GOCO03S. In detail, we will investigate the velocity errors resulting from the geoid component in dependence of the harmonic degree, and the impact of using/no using covariances on the MDT errors and its correlations. When deriving an MDT, it is spectrally filtered to a certain maximum degree, which is usually driven by the signal content of the geoid model, by applying isotropic or non-isotropic filters. Since this filtering is acting also on the geoid component, the consistent integration of this filter process into the covariance propagation shall be performed, and its impact shall be quantified. The study will be performed for MDT estimates in specific test areas of particular oceanographic interest.

Airborne geophysical surveys of unexplored regions of Antarctica - results of the ESA PolarGap campaign

NASA Astrophysics Data System (ADS)

Forsberg, R.; Olesen, A. V.; Ferraccioli, F.; Jordan, T. A.; Matsuoka, K.

2016-12-01

Major airborne geophysical surveys have recently mapped large unexplored regions in the interior of East Antarctica, in a Danish-UK-Norwegian cooperation. Long-range aerogeophysics data have been collected both over the Recovery Lakes region (2012/13), as well as around the Pole (2015/16). The primary purpose of these campaigns was to map gravity to fill-in data voids in global gravity field models and augment results from the European Space Agency GOCE gravity field satellite mission. Additionally magnetic, ice-penetrating radar and lidar data are used to explore and understand the subglacial topography and geological setting, providing an improved foundation for ice sheet modeling. The most recent ESA-sponsored Polar Gap project used a BAS Twin-Otter aircraft equipped with both spring gravimeter and IMU gravity sensors, magnetometers, ice penetrating radar over the essentially unmapped regions of the GOCE polar gap. Additional detailed flights over the subglacial Recovery Lakes region, followed up earlier 2013 flights over this region. The operations took place from two field camps (near Recovery Lakes and Thiel Mountains), as well as from the Amundsen-Scott South Pole station, thanks to a special arrangement with NSF. In addition to the airborne geophysics program, data with an ESA Ku-band radar were also acquired, in support of the CryoSat-2 mission, and scanning lidar collected across the polar gap, beyond the coverage of IceSat. In the talk we outline the Antarctic field operations, and show first results of the campaign, including performance of the gravity sensors, with comparison to limited existing data in the region (e.g., AGAP, IceBridge), as well as examples of lidar, magnetics and radar data. Significant new features detected from the geophysical data includes an extensive subglacial valley system between the Pole and the Filchner-Ronne ice shelf region, as well as extensive subglacial mountains, both consistent with observed ice stream patterns in the region. New data over the Recovery Lakes confirm the tectonic constraints on the lake system, and also hightlight the importantance of relatively dense flight tracks to constrain local subglacial hydrology.

A new degree-2190 (10 km resolution) gravity field model for Antarctica developed from GRACE, GOCE and Bedmap2 data

NASA Astrophysics Data System (ADS)

Hirt, Christian; Rexer, Moritz; Scheinert, Mirko; Pail, Roland; Claessens, Sten; Holmes, Simon

2016-02-01

The current high-degree global geopotential models EGM2008 and EIGEN-6C4 resolve gravity field structures to ˜ 10 km spatial scales over most parts of the of Earth's surface. However, a notable exception is continental Antarctica, where the gravity information in these and other recent models is based on satellite gravimetry observations only, and thus limited to about ˜ 80-120 km spatial scales. Here, we present a new degree-2190 global gravity model (GGM) that for the first time improves the spatial resolution of the gravity field over the whole of continental Antarctica to ˜ 10 km spatial scales. The new model called SatGravRET2014 is a combination of recent Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite gravimetry with gravitational signals derived from the 2013 Bedmap2 topography/ice thickness/bedrock model with gravity forward modelling in ellipsoidal approximation. Bedmap2 is a significantly improved description of the topographic mass distribution over the Antarctic region based on a multitude of topographic surveys, and a well-suited source for modelling short-scale gravity signals as we show in our study. We describe the development of SatGravRET2014 which entirely relies on spherical harmonic modelling techniques. Details are provided on the least-squares combination procedures and on the conversion of topography to implied gravitational potential. The main outcome of our work is the SatGravRET2014 spherical harmonic series expansion to degree 2190, and derived high-resolution grids of 3D-synthesized gravity and quasigeoid effects over the whole of Antarctica. For validation, six data sets from the IAG Subcommission 2.4f "Gravity and Geoid in Antarctica" (AntGG) database were used comprising a total of 1,092,981 airborne gravimetric observations. All subsets consistently show that the Bedmap2-based short-scale gravity modelling improves the agreement over satellite-only data considerably (improvement rates ranging between 9 and 75 % with standard deviations from residuals between SatGravRET2014 and AntGG gravity ranging between 8 and 25 mGal). For comparison purposes, a degree-2190 GGM was generated based on the year-2001 Bedmap1 (using the ETOPO1 topography) instead of 2013 Bedmap2 topography product. Comparison of both GGMs against AntGG consistently reveals a closer fit over all test areas when Bedmap2 is used. This experiment provides evidence for clear improvements in Bedmap2 topographic information over Bedmap1 at spatial scales of ˜ 80-10 km, obtained from independent gravity data used as validation tool. As a general conclusion, our modelling effort fills—in approximation—some gaps in short-scale gravity knowledge over Antarctica and demonstrates the value of the Bedmap2 topography data for short-scale gravity refinement in GGMs. SatGravRET2014 can be used, e.g. as a reference model for future gravity modelling efforts over Antarctica, e.g. as foundation for a combination with the AntGG data set to obtain further improved gravity information.

The lithosphere of the Antarctic continent: new insights from satellite gravity gradient data

NASA Astrophysics Data System (ADS)

Ferraccioli, Fausto; Ebbing, Jorg; Pappa, Folker; Kern, Michael; Forsberg, Rene

2017-04-01

The GOCE+Antarctica project, part of the Support to Science (STSE) program of the European Space Agency (ESA) is a new polar geosciences research initiative that aims to investigate the thermal and compositional structure of the Antarctic lithosphere by combing satellite gravity gradients (Bouman et al., 2016), airborne gravity data compilations (Scheinert et al., 2016), seismological (e.g. An et al., 2015) and petrological models in a forward and inverse manner. This approach promises to shed new light into the fundamental interplays between Antarctic lithospheric architecture, bedrock topography, ice sheet dynamics, and also its dynamic relations with Glacial Isostatic Adjustment (GIA). Here we focus on the satellite gravity gradient signatures and superimpose these on major known tectonic and bedrock topography elements, as well as independent seismically-derived estimates of crustal thickness for the Antarctic continent. An ad hoc India up reference system was used to facilitate the initial interpretation of the satellite gravity gradient data images. The GIU component clearly reveals the marked contrast between the thinner crust and lithosphere underlying the West Antarctic Rift System and also the Weddell Sea Rift System and the thicker lithosphere of East Antarctica. Notably, the new images suggests that more distributed wide-mode lithospheric and crustal extension affects the Ross Sea Embayment and continues under the Ross Ice Shelf, but this pattern is less clear towards the Bellingshousen Embayment. This suggests that the rift system narrows considerably as it reaches the southern edge of the Antarctic Peninsula, perhaps also in response to the relatively thicker crust and potentially relatively more rigid Precambrian lithosphere of the displaced Haag-Ellsworth block, which was originally located closer to East Antarctica, prior to distributed Jurassic lithospheric and crustal extension in the Weddell Sea Rift System. In East Antarctica, the satellite gravity data arguably provides one the clearest large-scale views to date of the potential extent of the Archean to Mesoproterozoic Terre Adelie Craton, and clearly shows the contrast wrt to the crust and lithosphere underlying both the Wilkes Subglacial Basin to the east and the Sabrina Subglacial Basin to the west. This finding corroborates and also augments recent independent interpretations of aeromagnetic and airborne gravity data over the region, suggesting that the Mawson Continent is a composite lithospheric-scale entity, which was affected by several Paleoproterozoic and Mesoproterozoic orogenic events (Aitken et al., 2016). Thick crust is clearly imaged beneath the Transantarctic Mountains, the Terre Adelie Craton, the Gamburtsev Subglacial Mountains and also Eastern Dronning Maud Land, in particular beneath the recently proposed region of the Tonian Oceanic Arc Superterrane (Jacobs et al., 2015). The GIA and GIU components help delineate the edges of several of these lithospheric provinces, both in West and East Antarctica. One of the largest and previously unknown lithospheric-scale features discovered in East Antarctica from the satellite gravity gradient images is a linear feature that appears to cut across East Antarctica, potentially extending from the area of the Lutzow Holm Complex on the Indian side of East Antarctica right across the continent to South Pole. We name this feature the Trans East Antarctic Shear Zone and propose that it represents a major lithospheric scale shear zone and possibly a major suture zone that separates the Gamburtsev Province from the Eastern Dronning Maud Land Province and also appears to form the southern boundary of the composite Recovery Province. We infer based on geological data in the Lutzow Holm Complex region and formerly adjacent segments of India and Madagascar and eastern Africa that it may represent a major hitherto unrecongnised Pan-African age suture zone related to the assembly of the Gondwana supercontinent. New aerogeophysical surveys in interior East Antarctica, between the Recovery region, the Gamburtsev Province and the southern edge of the Eastern Dronning Maud Province are however required to investigate the detailed crustal architecture, evolution and also kinematics of this newly proposed shear/suture zone and to help understand its relationships with the previously proposed Gamburtsev and Shackleton Range suture zones.

Possibilities of the regional gravity field recovery from first-, second- and third-order radial derivatives of the disturbing gravitational potential measured on moving platforms

NASA Astrophysics Data System (ADS)

Pitonak, Martin; Sprlak, Michal; Novak, Pavel; Tenzer, Robert

2016-04-01

Recently realized gravity-dedicated satellite missions allow for measuring values of scalar, vectorial (Gravity Recovery And Climate Experiment - GRACE) and second-order tensorial (Gravity field and steady-state Ocean Circulation Explorer - GOCE) parameters of the Earth's gravitational potential. Theoretical aspects related to using moving sensors for measuring elements of the third-order gravitational tensor are currently under investigation, e.g., the gravity field-dedicated satellite mission OPTIMA (OPTical Interferometry for global Mass change detection from space) should measure third-order derivatives of the Earth's gravitational potential. This contribution investigates regional recovery of the disturbing gravitational potential on the Earth's surface from satellite and aerial observations of the first-, second- and third-order radial derivatives of the disturbing gravitational potential. Synthetic measurements along a satellite orbit at the altitude of 250 km and along an aircraft track at the altitude of 10 km are synthetized from the global gravitational model EGM2008 and polluted by the Gaussian noise. The process of downward continuation is stabilized by the Tikhonov regularization. Estimated values of the disturbing gravitational potential are compared with the same quantity synthesized directly from EGM2008.

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

Marine Geoid Undulation Assessment Over South China Sea Using Global Geopotential Models and Airborne Gravity Data

NASA Astrophysics Data System (ADS)

Yazid, N. M.; Din, A. H. M.; Omar, K. M.; Som, Z. A. M.; Omar, A. H.; Yahaya, N. A. Z.; Tugi, A.

2016-09-01

Global geopotential models (GGMs) are vital in computing global geoid undulations heights. Based on the ellipsoidal height by Global Navigation Satellite System (GNSS) observations, the accurate orthometric height can be calculated by adding precise and accurate geoid undulations model information. However, GGMs also provide data from the satellite gravity missions such as GRACE, GOCE and CHAMP. Thus, this will assist to enhance the global geoid undulations data. A statistical assessment has been made between geoid undulations derived from 4 GGMs and the airborne gravity data provided by Department of Survey and Mapping Malaysia (DSMM). The goal of this study is the selection of the best possible GGM that best matches statistically with the geoid undulations of airborne gravity data under the Marine Geodetic Infrastructures in Malaysian Waters (MAGIC) Project over marine areas in Sabah. The correlation coefficients and the RMS value for the geoid undulations of GGM and airborne gravity data were computed. The correlation coefficients between EGM 2008 and airborne gravity data is 1 while RMS value is 0.1499.In this study, the RMS value of EGM 2008 is the lowest among the others. Regarding to the statistical analysis, it clearly represents that EGM 2008 is the best fit for marine geoid undulations throughout South China Sea.

Assessing New GRAV-D Airborne Gravimetry Collected over the United States

NASA Astrophysics Data System (ADS)

Holmes, S. A.; Li, X.; Roman, D. R.

2013-12-01

The U.S. National Geodetic Survey [NGS], through their Gravity for the Redefinition of the American Vertical Datum [GRAV-D] program, is updating its terrestrial gravimetry holdings by flying new airborne gravity surveys over a large fraction of the USA and its territories. By 2020, NGS intends that all orthometric heights in the USA will be determined in the field by using a reliable national gravimetric geoid model to transform from geodetic heights obtained from GPS. Towards this end, the newly-collected airborne-gravimety is repeatedly evaluated by using it to support experimental gravitational models and gravimetric geoids, and then comparing these against independent data sets, such as ';satgrav' models (GRACE/GOCE), GPS/Leveling, astronomical vertical defections, and others. Here we show some results from these tests for GRAV-D airborne gravimetry collected over 2012/2013.

Regional Recovery of the Disturbing Gravitational Potential from Satellite Observations of First-, Second- and Third-order Radial Derivatives of the Disturbing Gravitational Potential

NASA Astrophysics Data System (ADS)

Novak, P.; Pitonak, M.; Sprlak, M.

2015-12-01

Recently realized gravity-dedicated satellite missions allow for measuring values of scalar, vectorial (Gravity Recovery And Climate Experiment - GRACE) and second-order tensorial (Gravity field and steady-state Ocean Circulation Explorer - GOCE) parameters of the Earth's gravitational potential. Theoretical aspects related to using moving sensors for measuring elements of a third-order gravitational tensor are currently under investigation, e.g. the gravity-dedicated satellite mission OPTIMA (OPTical Interferometry for global Mass change detection from space) should measure third-order derivatives of the Earth's gravitational potential. This contribution investigates regional recovery of the disturbing gravitational potential on the Earth's surface from satellite observations of first-, second- and third-order radial derivatives of the disturbing gravitational potential. Synthetic measurements along a satellite orbit at the altitude of 250 km are synthetized from the global gravitational model EGM2008 and polluted by the Gaussian noise. The process of downward continuation is stabilized by the Tikhonov regularization. Estimated values of the disturbing gravitational potential are compared with the same quantity synthesized directly from EGM2008. Finally, this contribution also discusses merging a regional solution into a global field as a patchwork.

Nonlinear diffusion filtering of the GOCE-based satellite-only MDT

NASA Astrophysics Data System (ADS)

Čunderlík, Róbert; Mikula, Karol

2015-04-01

A combination of the GRACE/GOCE-based geoid models and mean sea surface models provided by satellite altimetry allows modelling of the satellite-only mean dynamic topography (MDT). Such MDT models are significantly affected by a stripping noise due to omission errors of the spherical harmonics approach. Appropriate filtering of this kind of noise is crucial in obtaining reliable results. In our study we use the nonlinear diffusion filtering based on a numerical solution to the nonlinear diffusion equation on closed surfaces (e.g. on a sphere, ellipsoid or the discretized Earth's surface), namely the regularized surface Perona-Malik model. A key idea is that the diffusivity coefficient depends on an edge detector. It allows effectively reduce the noise while preserve important gradients in filtered data. Numerical experiments present nonlinear filtering of the satellite-only MDT obtained as a combination of the DTU13 mean sea surface model and GO_CONS_GCF_2_DIR_R5 geopotential model. They emphasize an adaptive smoothing effect as a principal advantage of the nonlinear diffusion filtering. Consequently, the derived velocities of the ocean geostrophic surface currents contain stronger signal.

First look at GOCE-derived thermosphere density and wind measurements

NASA Astrophysics Data System (ADS)

Doornbos, E.; Bruinsma, S. L.; Koppenwallner, G.; Fritsche, B.; Visser, P. N.; van den IJssel, J.; Kern, M.

2011-12-01

Accelerometers carried by low-Earth orbiters such as GOCE have the ability to provide highly detailed data on thermospheric density and winds. Like its predecessor missions, CHAMP and GRACE, GOCE has not been specifically designed for studies of the thermosphere. Nevertheless, their application in this domain has resulted in density and wind data sets containing information at unprecedented levels of coverage and precision, resulting in many scientific papers. The orbit of GOCE is unique. It is nearly sun-synchronous, and due to its drag free control system, its altitude can be kept fixed for several years, at about 270 km. This leads to sampling characteristics that are ideal for studying the effect of variations in solar and magnetospheric energy input on the thermosphere density and wind. Besides the presentation of the first GOCE-derived density and wind measurements, this poster will describe the GOCE data processing approach, which differs from that of the earlier missions in the special consideration required for both the handling of the thruster accelerations and the aerodynamic modelling.

Global ionospheric and thermospheric response to the 5 April 2010 geomagnetic storm: An integrated data-model investigation

NASA Astrophysics Data System (ADS)

Lu, G.; Hagan, M. E.; Häusler, K.; Doornbos, E.; Bruinsma, S.; Anderson, B. J.; Korth, H.

2014-12-01

We present a case study of the 5 April 2010 geomagnetic storm using observations and numerical simulations. The event was driven by a fast-moving coronal mass ejection and despite being a moderate storm with a minimum Dst near -50 nT, the event exhibited elevated thermospheric density and surges of traveling atmospheric disturbances (TADs) more typically seen during major storms. The Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIMEGCM) was used to assess how these features were generated and developed during the storm. The model simulations gave rise to TADs that were highly nonuniform with strong latitude and longitude/local time dependence. The TAD phase speeds ranged from 640 m/s to 780 m/s at 400 km and were ~5% lower at 300 km and approximately 10-15% lower at 200 km. In the lower thermosphere around 100 km, the TAD signatures were nearly unrecognizable due to much stronger influence of upward propagating atmospheric tides. The thermosphere simulation results were compared to observations available from the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE), CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites. Comparison with GOCE data shows that the TIMEGCM reproduced the cross-track winds over the polar region very well. The model-data comparison also revealed some differences, specifically, the simulations underestimated neutral mass density in the upper thermosphere above ~300 km and overestimated the storm recovery tome by 6 h. These discrepancies indicate that some heating or circulation dynamics and potentially cooling processes are not fully represented in the simulations, and also that updates to some parameterization schemes in the TIMEGCM are warranted.

Crustal thickness of Antarctica estimated using data from gravimetric satellites

NASA Astrophysics Data System (ADS)

Llubes, Muriel; Seoane, Lucia; Bruinsma, Sean; Rémy, Frédérique

2018-04-01

Computing a better crustal thickness model is still a necessary improvement in Antarctica. In this remote continent where almost all the bedrock is covered by the ice sheet, seismic investigations do not reach a sufficient spatial resolution for geological and geophysical purposes. Here, we present a global map of Antarctic crustal thickness computed from space gravity observations. The DIR5 gravity field model, built from GOCE and GRACE gravimetric data, is inverted with the Parker-Oldenburg iterative algorithm. The BEDMAP products are used to estimate the gravity effect of the ice and the rocky surface. Our result is compared to crustal thickness calculated from seismological studies and the CRUST1.0 and AN1 models. Although the CRUST1.0 model shows a very good agreement with ours, its spatial resolution is larger than the one we obtain with gravimetric data. Finally, we compute a model in which the crust-mantle density contrast is adjusted to fit the Moho depth from the CRUST1.0 model. In East Antarctica, the resulting density contrast clearly shows higher values than in West Antarctica.

3D joint inversion of gravity-gradient and borehole gravity data

NASA Astrophysics Data System (ADS)

Geng, Meixia; Yang, Qingjie; Huang, Danian

2017-12-01

Borehole gravity is increasingly used in mineral exploration due to the advent of slim-hole gravimeters. Given the full-tensor gradiometry data available nowadays, joint inversion of surface and borehole data is a logical next step. Here, we base our inversions on cokriging, which is a geostatistical method of estimation where the error variance is minimised by applying cross-correlation between several variables. In this study, the density estimates are derived using gravity-gradient data, borehole gravity and known densities along the borehole as a secondary variable and the density as the primary variable. Cokriging is non-iterative and therefore is computationally efficient. In addition, cokriging inversion provides estimates of the error variance for each model, which allows direct assessment of the inverse model. Examples are shown involving data from a single borehole, from multiple boreholes, and combinations of borehole gravity and gravity-gradient data. The results clearly show that the depth resolution of gravity-gradient inversion can be improved significantly by including borehole data in addition to gravity-gradient data. However, the resolution of borehole data falls off rapidly as the distance between the borehole and the feature of interest increases. In the case where the borehole is far away from the target of interest, the inverted result can be improved by incorporating gravity-gradient data, especially all five independent components for inversion.

Future geodesy missions: Tethered systems and formation flying

NASA Astrophysics Data System (ADS)

Fontdecaba, Jordi; Sanjurjo, Manuel; Pelaez, Jesus; Metris, Gilles; Exertier, Pierre

Recent gravity field determination missions have shown the possibility of improving our Earth knowledge from space. GRACE has helped to the determination of temporal variations of low and mean degrees of the field while GOCE will improve the precision in the determination of higher degrees. But there is still some needs for geophysics which are not satisfied by these missions. Two areas where improvements must be done are (i) perenniality of the observations, and (ii) determination of temporal variations of higher degrees of the gravity field. These improvements can be achieved thanks to new measurement technologies with higher precision, but also using new observables. Historically, space determination of the gravity field has been done observing the perturbations of the orbit of the satellites. More recently, GRACE has introduced the use of satellite-tosatellite ranging. Goce will use onboard gradiometry. The authors have explored the possibilities of two new technologies for the determination of the gravity field: (i) tethered systems, and (ii) formation flying for all kind of configurations (not just leader-follower). To analyze the possibilities of these technologies, we obtain the covariance matrix of the coefficients of the gravity field for the different observables. This can be done providing some very reasonable hypothesis are accepted. This matrix contains a lot of information concerning the behavior of the observable. In order to obtain the matrix, we use the so-called lumped coefficients approach. We have used this method for three observables (i) tethered systems, (ii) formation flying and (iii) gradiometry (for comparison purposes). Tethers appear as a very long base gradiometers, with very interesting properties, but also very challenging from a technological point of view. One of the major advantages of the tethered systems is their multitask design. Indeed, the same cable can be used for propulsion purposes in some phases of the mission, and for geodesy purposes in other phases. Several studies have been presented using formation flying, but none of them is exhaustive in terms of number of satellites, configuration, and plan of the motion. We study formation flying using differential orbital elements in order to be as general as possible. The advantage of this representation is the possibility to study all sort of initial conditions and reference orbits with a posterior analysis of covariance matrices. Our results show the intrinsic possibilities of these new two systems and their comparison with existing ones. We also define some baseline scenarios for future missions.

Integrated approach to estimate the ocean's time variable dynamic topography including its covariance matrix

NASA Astrophysics Data System (ADS)

Müller, Silvia; Brockmann, Jan Martin; Schuh, Wolf-Dieter

2015-04-01

The ocean's dynamic topography as the difference between the sea surface and the geoid reflects many characteristics of the general ocean circulation. Consequently, it provides valuable information for evaluating or tuning ocean circulation models. The sea surface is directly observed by satellite radar altimetry while the geoid cannot be observed directly. The satellite-based gravity field determination requires different measurement principles (satellite-to-satellite tracking (e.g. GRACE), satellite-gravity-gradiometry (GOCE)). In addition, hydrographic measurements (salinity, temperature and pressure; near-surface velocities) provide information on the dynamic topography. The observation types have different representations and spatial as well as temporal resolutions. Therefore, the determination of the dynamic topography is not straightforward. Furthermore, the integration of the dynamic topography into ocean circulation models requires not only the dynamic topography itself but also its inverse covariance matrix on the ocean model grid. We developed a rigorous combination method in which the dynamic topography is parameterized in space as well as in time. The altimetric sea surface heights are expressed as a sum of geoid heights represented in terms of spherical harmonics and the dynamic topography parameterized by a finite element method which can be directly related to the particular ocean model grid. Besides the difficult task of combining altimetry data with a gravity field model, a major aspect is the consistent combination of satellite data and in-situ observations. The particular characteristics and the signal content of the different observations must be adequately considered requiring the introduction of auxiliary parameters. Within our model the individual observation groups are combined in terms of normal equations considering their full covariance information; i.e. a rigorous variance/covariance propagation from the original measurements to the final product is accomplished. In conclusion, the developed integrated approach allows for estimating the dynamic topography and its inverse covariance matrix on arbitrary grids in space and time. The inverse covariance matrix contains the appropriate weights for model-data misfits in least-squares ocean model inversions. The focus of this study is on the North Atlantic Ocean. We will present the conceptual design and dynamic topography estimates based on time variable data from seven satellite altimeter missions (Jason-1, Jason-2, Topex/Poseidon, Envisat, ERS-2, GFO, Cryosat2) in combination with the latest GOCE gravity field model and in-situ data from the Argo floats and near-surface drifting buoys.

GRAIL Spots Gravity Anomaly

NASA Image and Video Library

2012-12-05

A 300-mile-long linear gravity anomaly on the far side of the moon has been revealed by gravity gradients measured by NASA GRAIL mission. GRAIL data are shown on the left, with red and blue corresponding to stronger gravity gradients.

Extent of partial melting beneath the Cascade Range, Oregon: Constraints from gravity anomalies and ideal-body theory

NASA Astrophysics Data System (ADS)

Blakely, Richard J.

1994-02-01

The spatial correlation between a horizontal gradient in heat flow and a horizontal gradient in residual gravity in the Western Cascades of central Oregon has been interpreted by others as evidence of the western edge of a pervasive zone of high temperatures and partial melting at midcrustal depths (5-15 km). Both gradients are steep and relatively linear over north-south distances in excess of 150 km. The Western Cascades gravity gradient is the western margin of a broad gravity depression over most of the Oregon Cascade Range, implying that the midcrustal zone of anomalous temperatures lies throughout this region. Ideal-body theory applied to the gravity gradient, however, shows that the source of the Western Cascades gravity gradient cannot be deeper than about 2.5 km and is considerably shallower in some locations. These calculations are unique determinations, assuming that density contrasts associated with partial melting and elevated temperatures in the crust do not exceed 500 kg/cu m. Consequently, the gravity gradient and the heat flow gradient in the Western Cascades cannot be caused directly by the same source if the heat flow gradient originates at midcrustal depths. This conclusion in itself does not disprove the existence of a widespread midcrustal zone of anomalously high temperatures and partial melting in this area, but it does eliminate a major argument in support of its existence. The gravity gradient is most likely caused by lithologic varitions in the shallow crust, perhaps reflecting a relict boundary between the Cascade extensional trough to the west and Tertiary oceanic crust to the west. The boundary must have formed prior to Oligocene time, the age of the oldest rocks that now conceal it.

A Transportable Gravity Gradiometer Based on Atom Interferometry

NASA Technical Reports Server (NTRS)

Yu, Nan; Thompson, Robert J.; Kellogg, James R.; Aveline, David C.; Maleki, Lute; Kohel, James M.

2010-01-01

A transportable atom interferometer-based gravity gradiometer has been developed at JPL to carry out measurements of Earth's gravity field at ever finer spatial resolutions, and to facilitate high-resolution monitoring of temporal variations in the gravity field from ground- and flight-based platforms. Existing satellite-based gravity missions such as CHAMP and GRACE measure the gravity field via precise monitoring of the motion of the satellites; i.e. the satellites themselves function as test masses. JPL's quantum gravity gradiometer employs a quantum phase measurement technique, similar to that employed in atomic clocks, made possible by recent advances in laser cooling and manipulation of atoms. This measurement technique is based on atomwave interferometry, and individual laser-cooled atoms are used as drag-free test masses. The quantum gravity gradiometer employs two identical atom interferometers as precision accelerometers to measure the difference in gravitational acceleration between two points (Figure 1). By using the same lasers for the manipulation of atoms in both interferometers, the accelerometers have a common reference frame and non-inertial accelerations are effectively rejected as common mode noise in the differential measurement of the gravity gradient. As a result, the dual atom interferometer-based gravity gradiometer allows gravity measurements on a moving platform, while achieving the same long-term stability of the best atomic clocks. In the laboratory-based prototype (Figure 2), the cesium atoms used in each atom interferometer are initially collected and cooled in two separate magneto-optic traps (MOTs). Each MOT, consisting of three orthogonal pairs of counter-propagating laser beams centered on a quadrupole magnetic field, collects up to 10(exp 9) atoms. These atoms are then launched vertically as in an atom fountain by switching off the magnetic field and introducing a slight frequency shift between pairs of lasers to create a moving rest frame for the trapped atoms. While still in this moving-frame molasses, the laser frequencies are further detuned from the atomic resonance (while maintaining this relative frequency shift) to cool the atom cloud's temperature to 2 K or below, corresponding to an rms velocity of less than 2 cm/s. After launch, the cold atoms undergo further state and velocity selection to prepare for atom interferometry. The atom interferometers are then realized using laser-induced stimulated Raman transitions to perform the necessary manipulations of each atom, and the resulting interferometer phase is measured using laser-induced fluorescence for state-normalized detection. More than 20 laser beams with independent controls of frequency, phase, and intensity are required for this measurement sequence. This instrument can facilitate the study of Earth's gravitational field from surface and air vehicles, as well as from space by allowing gravity mapping from a low-cost, single spacecraft mission. In addition, the operation of atom interferometer-based instruments in space offers greater sensitivity than is possible in terrestrial instruments due to the much longer interrogation times available in the microgravity environment. A space-based quantum gravity gradiometer has the potential to achieve sensitivities similar to the GRACE mission at long spatial wavelengths, and will also have resolution similar to GOCE for measurement at shorter length scales.

Ground Based Investigation of Electrostatic Accelerometer in HUST

NASA Astrophysics Data System (ADS)

Bai, Y.; Zhou, Z.

2013-12-01

High-precision electrostatic accelerometers with six degrees of freedom (DOF) acceleration measurement were successfully used in CHAMP, GRACE and GOCE missions which to measure the Earth's gravity field. In our group, space inertial sensor based on the capacitance transducer and electrostatic control technique has been investigated for test of equivalence principle (TEPO), searching non-Newtonian force in micrometer range, and satellite Earth's field recovery. The significant techniques of capacitive position sensor with the noise level at 2×10-7pF/Hz1/2 and the μV/Hz1/2 level electrostatic actuator are carried out and all the six servo loop controls by using a discrete PID algorithm are realized in a FPGA device. For testing on ground, in order to compensate one g earth's gravity, the fiber torsion pendulum facility is adopt to measure the parameters of the electrostatic controlled inertial sensor such as the resolution, and the electrostatic stiffness, the cross couple between different DOFs. A short distance and a simple double capsule equipment the valid duration about 0.5 second is set up in our lab for the free fall tests of the engineering model which can directly verify the function of six DOF control. Meanwhile, high voltage suspension method is also realized and preliminary results show that the horizontal axis of acceleration noise is about 10-8m/s2/Hz1/2 level which limited mainly by the seismic noise. Reference: [1] Fen Gao, Ze-Bing Zhou, Jun Luo, Feasibility for Testing the Equivalence Principle with Optical Readout in Space, Chin. Phys. Lett. 28(8) (2011) 080401. [2] Z. Zhu, Z. B. Zhou, L. Cai, Y. Z. Bai, J. Luo, Electrostatic gravity gradiometer design for the advanced GOCE mission, Adv. Sp. Res. 51 (2013) 2269-2276. [3] Z B Zhou, L Liu, H B Tu, Y Z Bai, J Luo, Seismic noise limit for ground-based performance measurements of an inertial sensor using a torsion balance, Class. Quantum Grav. 27 (2010) 175012. [4] H B Tu, Y Z Bai, Z B Zhou, L Liu, L Cai, and J Luo, Performance measurements of an inertial sensor with a two-stage controlled torsion pendulum, Class Quantum. Grav. 27 (2010) 205016.

Kelvin wave coupling from TIMED and GOCE: Inter/intra-annual variability and solar activity effects

NASA Astrophysics Data System (ADS)

Gasperini, Federico; Forbes, Jeffrey M.; Doornbos, Eelco N.; Bruinsma, Sean L.

2018-06-01

The primary mechanism through which energy and momentum are transferred from the lower atmosphere to the thermosphere is through the generation and propagation of atmospheric waves. It is becoming increasingly evident that a few waves from the tropical wave spectrum preferentially propagate into the thermosphere and contribute to modify satellite drag. Two of the more prominent and well-established tropical waves are Kelvin waves: the eastward-propagating 3-day ultra-fast Kelvin wave (UFKW) and the eastward-propagating diurnal tide with zonal wave number 3 (DE3). In this work, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures at 110 km and Gravity field and steady-state Ocean Circulation Explorer (GOCE) neutral densities and cross-track winds near 260 km are used to demonstrate vertical coupling in this height regime due to the UFKW and DE3. Significant inter- and intra-annual variability is found in DE3 and the UFKW, with evidence of latitudinal broadening and filtering of the latitude structures with height due to the effect of dissipation and mean winds. Additionally, anti-correlation between the vertical penetration of these waves to the middle thermosphere and solar activity level is established and explained through the effect of molecular dissipation.

Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

NASA Astrophysics Data System (ADS)

Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

1995-09-01

Differing interpretations of the Bouguer gravity anomaly over the Chicxulub crater, Yucatan Peninsula, Mexico, have yielded diameter estimates of 170 to 320 km. Knowing the crater's size is necessary to quantify the lethal perturbations to the Cretaceous environment associated with its formation. The crater's size (and internal structure) is revealed by the horizontal gradient of the Bouguer gravity anomaly over the structure, and by mapping the karst features of the Yucatan region. To improve our resolution of the crater's gravity signature we collected additional gravity measurements primarily along radial profiles, but also to fill in previously unsurveyed areas. Horizontal gradient analysis of Bouguer gravity data objectively highlights the lateral density contrasts of the impact lithologies and suppresses regional anomalies which may obscure the gravity signature of the Chicxulub crater lithologies. This gradient technique yields a striking circular structure with at least 6 concentric gradient features between 25 and 85 km radius. These features are most distinct in the southwest probably because of denser sampling of the gravity field. Our detailed profiles detected an additional feature and steeper gradients (up to 5 mGal/km) than the original survey. We interpret the outer four gradient maxima to represent concentric faults in the crater's zone of slumping as is also revealed by seismic reflection data. The inner two probably represent the margin of the central uplift and the peak ring and or collapsed transient cavity. Radial gradients in the SW quadrant over the inferred ~40 km-diameter central uplift (4) may represent structural "puckering" as revealed at eroded terrestrial craters. Gradient features related to regional gravity highs and lows are visible outside the crater, but no concentric gradient features are apparent at distances > 90 km radius. The marginal gradient features may be modelled by slump faults as observed in large complex craters on the other terrestrial planets. A modeled fault of 1.5 km displacement (slightly slumped block exterior and impact breccia interior) reproduces the steepest gradient feature. This model is incompatible with models that place these gradient features inside the collapsed transient cavity. Locations of the karst features of the northern Yucatan region were digitized from 1:50,000 topographic maps, which show most but not all the water-filled sinkholes (locally known as cenotes). A prominent ring of cenotes is visible over the crater that is spatially correlated to the outer steep gravity gradient feature. The mapped cenotes constitute an unbiased sampling of the region's karst surface features of >50 m diameter. The gradient maximum and the cenote ring both meander with amplitudes of up to 2 km. The wiggles in the gradient feature and the cenote distribution probably correspond to the "scalloping" observed at the headwall of terraces in large complex craters. A second partial cenote ring exterior to the southwest side of the main ring corresponds to a less-prominent gravity gradient feature. No concentric structure is observable in the distribution of karst features at radii >90 km. The cenote ring is bounded by the outer peripheral steep gradient feature and must be related to it; the slump faults must have been reactivated sufficiently to create fracturing in the overlying and much younger sediment. Long term subsidence, as found at other terrestrial craters is a possible mechanism for the reactivation. Such long term subsidence may be caused by differential compaction or thermal relaxation. Elevations acquired during gravity surveys show that the cenote ring also corresponds to a topographic low along some of its length that probably reflects preferential erosion.

Gravity Gradients Frame Oceanus Procellarum

NASA Image and Video Library

2014-10-01

Topography of Earth moon generated from data NASA LRO, with the gravity anomalies bordering the Procellarum region superimposed in blue. The border structures are shown using gravity gradients calculated with data from NASA GRAIL mission.

Canceling the Gravity Gradient Phase Shift in Atom Interferometry.

PubMed

D'Amico, G; Rosi, G; Zhan, S; Cacciapuoti, L; Fattori, M; Tino, G M

2017-12-22

Gravity gradients represent a major obstacle in high-precision measurements by atom interferometry. Controlling their effects to the required stability and accuracy imposes very stringent requirements on the relative positioning of freely falling atomic clouds, as in the case of precise tests of Einstein's equivalence principle. We demonstrate a new method to exactly compensate the effects introduced by gravity gradients in a Raman-pulse atom interferometer. By shifting the frequency of the Raman lasers during the central π pulse, it is possible to cancel the initial position- and velocity-dependent phase shift produced by gravity gradients. We apply this technique to simultaneous interferometers positioned along the vertical direction and demonstrate a new method for measuring local gravity gradients that does not require precise knowledge of the relative position between the atomic clouds. Based on this method, we also propose an improved scheme to determine the Newtonian gravitational constant G towards the 10 ppm relative uncertainty.

Canceling the Gravity Gradient Phase Shift in Atom Interferometry

NASA Astrophysics Data System (ADS)

D'Amico, G.; Rosi, G.; Zhan, S.; Cacciapuoti, L.; Fattori, M.; Tino, G. M.

2017-12-01

Gravity gradients represent a major obstacle in high-precision measurements by atom interferometry. Controlling their effects to the required stability and accuracy imposes very stringent requirements on the relative positioning of freely falling atomic clouds, as in the case of precise tests of Einstein's equivalence principle. We demonstrate a new method to exactly compensate the effects introduced by gravity gradients in a Raman-pulse atom interferometer. By shifting the frequency of the Raman lasers during the central π pulse, it is possible to cancel the initial position- and velocity-dependent phase shift produced by gravity gradients. We apply this technique to simultaneous interferometers positioned along the vertical direction and demonstrate a new method for measuring local gravity gradients that does not require precise knowledge of the relative position between the atomic clouds. Based on this method, we also propose an improved scheme to determine the Newtonian gravitational constant G towards the 10 ppm relative uncertainty.

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

NASA Technical Reports Server (NTRS)

Li, X.; Lemoine, F. G.; Paik, H. J.; Zagarola, M.; Shirron, P. J.; Griggs, C. E.; Moody, M. V.; Han, S.-C.

2016-01-01

Measurement of a planet's gravity field provides fundamental information about the planet's mass properties. The static gravity field reveals information about the internal structure of the planet, including crustal density variations that provide information on the planet's geological history and evolution. The time variations of gravity result from the movement of mass inside the planet, on the surface, and in the atmosphere. NASA is interested in a Superconducting Gravity Gradiometer (SGG) with which to measure the gravity field of a planet from orbit. An SGG instrument is under development with the NASA PICASSO program, which will be able to resolve the Mars static gravity field to degree 200 in spherical harmonics, and the time-varying field on a monthly basis to degree 20 from a 255 x 320 km orbit. The SGG has a precision two orders of magnitude better than the electrostatic gravity gradiometer that was used on the ESA's GOCE mission. The SGG operates at the superconducting temperature lower than 6 K. This study developed a cryogenic thermal system to maintain the SGG at the design temperature in Mars orbit. The system includes fixed radiation shields, a low thermal conductivity support structure and a two-stage cryocooler. The fixed radiation shields use double aluminized polyimide to emit heat from the warm spacecraft into the deep space. The support structure uses carbon fiber reinforced plastic, which has low thermal conductivity at cryogenic temperature and very high stress. The low vibration cryocooler has two stages, of which the high temperature stage operates at 65 K and the low temperature stage works at 6 K, and the heat rejection radiator works at 300 K. The study also designed a second option with a 4-K adiabatic demagnetization refrigerator (ADR) and two-stage 10-K turbo-Brayton cooler.

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

NASA Technical Reports Server (NTRS)

Li, X.; Lemoine, F. G.; Shirron, P. J.; Paik, H. J.; Griggs, C. E.; Moody, M. V.; Han, S. C.; Zagarola, M.

2016-01-01

Measurement of a planets gravity field provides fundamental information about the planets mass properties. The static gravity field reveals information about the internal structure of the planet, including crustal density variations that provide information on the planets geological history and evolution. The time variations of gravity result from the movement of mass inside the planet, on the surface, and in the atmosphere. NASA is interested in a Superconducting Gravity Gradiometer (SGG) with which to measure the gravity field of a planet from orbit. An SGG instrument is under development with the NASA PICASSO program, which will be able to resolve the Mars static gravity field to degree 200 in spherical harmonics, and the time-varying field on a monthly basis to degree 20 from a 255 x 320 km orbit. The SGG has a precision two orders of magnitude better than the electrostatic gravity gradiometer that was used on the ESAs GOCE mission. The SGG operates at the superconducting temperature lower than 6 K. This study developed a cryogenic thermal system to maintain the SGG at the design temperature in Mars orbit. The system includes fixed radiation shields, a low thermal conductivity support structure and a two-stage cryocooler. The fixed radiation shields use double aluminized polyimide to emit heat from the warm spacecraft into the deep space. The support structure uses carbon fiber reinforced plastic, which has low thermal conductivity at cryogenic temperature and very high stress. The low vibration cryocooler has two stages, of which the high temperature stage operates at 65 K and the low temperature stage works at 6 K, and the heat rejection radiator works at 300 K. The study also designed a second option with a 4-K adiabatic demagnetization refrigerator (ADR) and two-stage 10-K turbo-Brayton cooler.

Hierarchical matrices implemented into the boundary integral approaches for gravity field modelling

NASA Astrophysics Data System (ADS)

Čunderlík, Róbert; Vipiana, Francesca

2017-04-01

Boundary integral approaches applied for gravity field modelling have been recently developed to solve the geodetic boundary value problems numerically, or to process satellite observations, e.g. from the GOCE satellite mission. In order to obtain numerical solutions of "cm-level" accuracy, such approaches require very refined level of the disretization or resolution. This leads to enormous memory requirements that need to be reduced. An implementation of the Hierarchical Matrices (H-matrices) can significantly reduce a numerical complexity of these approaches. A main idea of the H-matrices is based on an approximation of the entire system matrix that is split into a family of submatrices. Large submatrices are stored in factorized representation, while small submatrices are stored in standard representation. This allows reducing memory requirements significantly while improving the efficiency. The poster presents our preliminary results of implementations of the H-matrices into the existing boundary integral approaches based on the boundary element method or the method of fundamental solution.

Comparisons Between TIME-GCM/MERRA Simulations and LEO Satellite Observations

NASA Astrophysics Data System (ADS)

Hagan, M. E.; Haeusler, K.; Forbes, J. M.; Zhang, X.; Doornbos, E.; Bruinsma, S.; Lu, G.

2014-12-01

We report on yearlong National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) simulations where we utilize the recently developed lower boundary condition based on 3-hourly MERRA (Modern-Era Retrospective Analysis for Research and Application) reanalysis data to account for tropospheric waves and tides propagating upward into the model domain. The solar and geomagnetic forcing is based on prevailing geophysical conditions. The simulations show a strong day-to-day variability in the upper thermospheric neutral temperature tidal fields, which is smoothed out quickly when averaging is applied over several days, e.g. up to 50% DE3 amplitude reduction for a 10-day average. This is an important result with respect to tidal diagnostics from satellite observations where averaging over multiple days is inevitable. In order to assess TIME-GCM performance we compare the simulations with measurements from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites.

High stability laser for next generation gravity missions

NASA Astrophysics Data System (ADS)

Nicklaus, K.; Herding, M.; Wang, X.; Beller, N.; Fitzau, O.; Giesberts, M.; Herper, M.; Barwood, G. P.; Williams, R. A.; Gill, P.; Koegel, H.; Webster, S. A.; Gohlke, M.

2017-11-01

With GRACE (launched 2002) and GOCE (launched 2009) two very successful missions to measure earth's gravity field have been in orbit, both leading to a large number of publications. For a potential Next Generation Gravity Mission (NGGM) from ESA a satellite-to-satellite tracking (SST) scheme, similar to GRACE is under discussion, with a laser ranging interferometer instead of a Ka-Band link to enable much lower measurement noise. Of key importance for such a laser interferometer is a single frequency laser source with a linewidth <10 kHz and extremely low frequency noise down to 40 Hz / √Hz in the measurement frequency band of 0.1 mHz to 1 Hz, which is about one order of magnitude more demanding than LISA. On GRACE FO a laser ranging interferometer (LRI) will fly as a demonstrator. The LRI is a joint development between USA (JPL,NASA) and Germany(GFZ,DLR). In this collaboration the JPL contributions are the instrument electronics, the reference cavity and the single frequency laser, while STI as the German industry prime is responsible for the optical bench and the retroreflector. In preparation of NGGM an all European instrument development is the goal.

Tidal Signals In GOCE Measurements And Time-GCM

NASA Astrophysics Data System (ADS)

Hausler, K.; Hagan, M. E.; Lu, G.; Doornbos, E.; Bruinsma, S.; Forbes, J. M.

2013-12-01

In this paper we investigate tidal signatures in GOCE measurements during 15-24 November 2009 and complementary simulations with the Thermosphere-Ionosphere- Mesosphere-Electrodynamics General Circulation Model (TIME-GCM). The TIME-GCM simulations are driven by inputs that represent the prevailing solar and geomagnetic conditions along with tidal and planetary waves applied at the lower boundary (ca. 30km). For this pilot study, the resultant TIME-GCM densities are analyzed in two ways: 1) we use results along the GOCE orbital track, to calculate ascending/descending orbit longitude- latitude density difference and sum maps for direct comparison with the GOCE diagnostics, and 2) we conduct a complete analysis of TIME-GCM results to unambiguously characterize the simulated atmospheric tides and to attribute the observed longitude variations to specific tidal components. TIME-GCM captures some but not all of the observed longitudinal variability. The good data- model agreement for wave-2, wave-3, and wave-4 suggests that thermospheric impacts can be attributed to the DE1, DE2, DE3, S0, SE1, and SE2 tides. Discrepancies between TIME-GCM and GOCE results are most prominent in the wave-1 variations, and suggest that further refinement of the lower boundary forcing is necessary before we extend our analysis and interpretation to densities associated with the remainder of the GOCE mission.

Project SKYLITE: A Design Exploration.

DTIC Science & Technology

1987-09-01

5. Gravity Gradient Boom The SKYLITE satellite uses gravity gradient stabilization. This technique requires a gravity gradient boom for attitude ... attitude of the satellite. To satisfy SKYLITE mission requirements, the satellite contains an array of IR sensors for evaluation of radiation from the ...3.1 Extended GAS Canister. The Orion satellite has been designed with 7 thrusters. Six thrusters are .1 lbr rated, and used for spin up and attitude

Seafloor Topography Estimation from Gravity Gradient Using Simulated Annealing

NASA Astrophysics Data System (ADS)

Yang, J.; Jekeli, C.; Liu, L.

2017-12-01

Inferring seafloor topography from gravimetry is an indirect yet proven and efficient means to map the ocean floor. Standard techniques rely on an approximate, linear relationship (Parker's formula) between topography and gravity. It has been reported that in the very rugged areas the discrepancies between prediction and ship soundings are very large, partly because the linear term of Parker's infinite series is dominant only in areas where the local topography is small compared with the regional topography. The validity of the linear approximation is therefore in need of analysis. In this study the nonlinear effects caused by terrain are quantified by both numerical tests and an algorithmic approach called coherency. It is shown that the nonlinear effects are more significant at higher frequencies, which suggests that estimation algorithms with nonlinear approximation in the modeled relationship between gravity gradient and topography should be developed in preparation for future high-resolution gravity gradient missions. The simulated annealing (SA) method is such an optimization technique that can process nonlinear inverse problems, and is used to estimate the seafloor topography parameters in a forward model by minimizing the difference between the observed and forward-computed vertical gravity gradients. Careful treatments like choosing suitable truncation distance, padding the vicinity of the study area with a known topography model, and using the relative cost function, are considered to improve the estimation accuracy. This study uses the gravity gradient, which is more sensitive to topography at short wavelengths than gravity anomaly. The gravity gradient data are derived from satellite altimetry, but the SA has no restrictions on data distribution, as required in Parker's infinite series model, thus enabling the use of airborne gravity gradient data, whose survey trajectories are irregular. The SA method is tested in an area of Guyots (E 156°-158° in longitude, N 20°-22° in latitude). Comparison between the estimation and ship sounding shows that half of the discrepancy is within 110 m, which improves the result from standard techniques by 32%.

Three-Axis Superconducting Gravity Gradiometer

NASA Technical Reports Server (NTRS)

Paik, Ho Jung

1987-01-01

Gravity gradients measured even on accelerating platforms. Three-axis superconducting gravity gradiometer based on flux quantization and Meissner effect in superconductors and employs superconducting quantum interference device as amplifier. Incorporates several magnetically levitated proof masses. Gradiometer design integrates accelerometers for operation in differential mode. Principal use in commercial instruments for measurement of Earth-gravity gradients in geo-physical surveying and exploration for oil.

Microgravimetry and the Measurement and Application of Gravity Gradients,

DTIC Science & Technology

1980-06-01

Neumann, R., 1972, High precision gravimetry--recent develop- ments: Report to Paris Commission of E.A.E.G., Compagnie Generale de Geophysique , Massy...experimentation on vertical gradient: Compagnie Generale de Geophysique , Massy, France. 12. Fajklewicz, Z. J., 1976, Gravity vertical gradient

Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts

NASA Astrophysics Data System (ADS)

Ren, Zhengyong; Zhong, Yiyuan; Chen, Chaojian; Tang, Jingtian; Kalscheuer, Thomas; Maurer, Hansruedi; Li, Yang

2018-03-01

During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets.

INSIGHT (interaction of low-orbiting satellites with the surrounding ionosphere and thermosphere)

NASA Astrophysics Data System (ADS)

Schlicht, Anja; Reussner, Elisabeth; Lühr, Hermann; Stolle, Claudia; Xiong, Chao; Schmidt, Michael; Blossfeld, Mathis; Erdogan, Eren; Pancetta, Francesca; Flury, Jakob

2016-04-01

In the framework of the DFG special program "Dynamic Earth" the project INSIGHT, started in September 2015, is studying the interactions between the ionosphere and thermosphere as well as the role of the satellites and their instruments in observing the space environment. Accelerometers on low-Earth orbiters (LEOs) are flown to separate non-gravitational forces acting on the satellite from influences of gravitational effects. Amongst others these instruments provide valuable information for improving our understanding of thermospheric properties like densities and winds. An unexpected result, for example, is the clear evidence of geomagnetic field control on the neutral upper atmosphere. The charged particles of the ionosphere act as mediators between the magnetic field and the thermosphere. In the framework of INSIGHT the climatology of the thermosphere will be established and the coupling between the ionosphere and thermosphere is studied. There are indications that the accelerometers are influenced by systematic errors not identified up to now. For GRACE it is one of the discussed reasons, why this mission so far did not reach the baseline accuracy. Beutler et al. 2010 discussed the limited use of the GRACE accelerometer measurements in comparison to stochastic pulses in gravity field recovery. Analysis of the accelerometer measurements show many structures in the high frequency region which can be traced back to switching processes of electric circuits in the spacecraft, like heater and magnetic torquer switching, or so called twangs, which can be associated with discharging of non-conducting surfaces of the satellite. As all observed signals have the same time dependency a common origin is very likely, namely the coupling of time variable electric currents into the accelerometer signal. In GOCE gravity field gradients non-gravitational signatures around the magnetic poles are found indicating that even at lower frequencies problems occur. INSIGHT will identify systematic errors in the accelerometer measurements and establish an algorithm to separate these errors from real accelerations with the analysis of satellite rotations on GOCE. A transfer to other accelerometer missions will be studied. Accelerometer missions are characterized by satellites of a complex geometry and surface structure making it necessary to take their shape and surface interactions into account. On the other hand accelerometers have to be calibrated in space as biases and bias drifts are inherent. These two facts make it difficult to scale thermospheric densities. To overcome this problem a high precision orbit determination of satellites of simpler structure is more suitable. In the framework of INSIGHT a multi-satellite solution of satellite laser ranging (SLR) measurements is aimed for absolute density determination of the thermosphere. Besides, due to the coupling processes between the ionosphere and thermosphere it shall be studied how ionospheric target quantities such as the electron density can be used to improve thermospheric density modeling. This presentation provides the overall structure of the project INSIGHT as well as first results.

Atom interferometric gravity gradiometer: Disturbance compensation and mobile gradiometry

NASA Astrophysics Data System (ADS)

Mahadeswaraswamy, Chetan

First ever mobile gravity gradient measurement based on Atom Interferometric sensors has been demonstrated. Mobile gravity gradiometers play a significant role in high accuracy inertial navigation systems in order to distinguish inertial acceleration and acceleration due to gravity. The gravity gradiometer consists of two atom interferometric accelerometers. In each of the accelerometer an ensemble of laser cooled Cesium atoms is dropped and using counter propagating Raman pulses (pi/2-pi-pi/2) the ensemble is split into two states for carrying out atom interferometry. The interferometer phase is proportional to the specific force experienced by the atoms which is a combination of inertial acceleration and acceleration due to gravity. The difference in phase between the two atom interferometric sensors is proportional to gravity gradient if the platform does not undergo any rotational motion. However, any rotational motion of the platform induces spurious gravity gradient measurements. This apparent gravity gradient due to platform rotation is considerably different for an atom interferometric sensor compared to a conventional force rebalance type sensor. The atoms are in free fall and are not influenced by the motion of the case except at the instants of Raman pulses. A model for determining apparent gravity gradient due to rotation of platform was developed and experimentally verified for different frequencies. This transfer function measurement also lead to the development of a new technique for aligning the Raman laser beams with the atom clusters to within 20 mu rad. This gravity gradiometer is situated in a truck for the purpose of undertaking mobile surveys. A disturbance compensation system was designed and built in order to compensate for the rotational disturbances experienced on the floor of a truck. An electric drive system was also designed specifically to be able to move the truck in a uniform motion at very low speeds of about 1cm/s. A 250 x10-9 s-2 gravity gradient signature due to an underground void at Hansen Experimental Physics Building at Stanford was successfully measured using this mobile gradiometer.

Regional recovery of the disturbing gravitational potential by inverting satellite gravitational gradients

NASA Astrophysics Data System (ADS)

Pitoňák, Martin; Šprlák, Michal; Hamáčková, Eliška; Novák, Pavel

2016-04-01

Regional recovery of the disturbing gravitational potential in the area of Central Europe from satellite gravitational gradients data is discussed in this contribution. The disturbing gravitational potential is obtained by inverting surface integral formulas which transform the disturbing gravitational potential onto disturbing gravitational gradients in the spherical local north-oriented frame. Two numerical approaches that solve the inverse problem are considered. In the first approach, the integral formulas are rigorously decomposed into two parts, that is, the effects of the gradient data within near and distant zones. While the effect of the near zone data is sought as an inverse problem, the effect of the distant zone data is synthesized from the global gravitational model GGM05S using spectral weights given by truncation error coefficients up to the degree 150. In the second approach, a reference gravitational field up to the degree 180 is applied to reduce and smooth measured gravitational gradients. In both cases we recovered the disturbing gravitational potential from each of the four well-measured gravitational gradients of the GOCE satellite separately as well as from their combination. Obtained results are compared with the EGM2008, DIR-r2, TIM-r2 and SPW-r2 global gravitational models. The best fit was achieved for EGM2008 and the second approach combining all four well-measured gravitational gradients with rms of 1.231 m2 s-2.

Estimating Gravity Biases with Wavelets in Support of a 1-cm Accurate Geoid Model

NASA Astrophysics Data System (ADS)

Ahlgren, K.; Li, X.

2017-12-01

Systematic errors that reside in surface gravity datasets are one of the major hurdles in constructing a high-accuracy geoid model at high resolutions. The National Oceanic and Atmospheric Administration's (NOAA) National Geodetic Survey (NGS) has an extensive historical surface gravity dataset consisting of approximately 10 million gravity points that are known to have systematic biases at the mGal level (Saleh et al. 2013). As most relevant metadata is absent, estimating and removing these errors to be consistent with a global geopotential model and airborne data in the corresponding wavelength is quite a difficult endeavor. However, this is crucial to support a 1-cm accurate geoid model for the United States. With recently available independent gravity information from GRACE/GOCE and airborne gravity from the NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project, several different methods of bias estimation are investigated which utilize radial basis functions and wavelet decomposition. We estimate a surface gravity value by incorporating a satellite gravity model, airborne gravity data, and forward-modeled topography at wavelet levels according to each dataset's spatial wavelength. Considering the estimated gravity values over an entire gravity survey, an estimate of the bias and/or correction for the entire survey can be found and applied. In order to assess the accuracy of each bias estimation method, two techniques are used. First, each bias estimation method is used to predict the bias for two high-quality (unbiased and high accuracy) geoid slope validation surveys (GSVS) (Smith et al. 2013 & Wang et al. 2017). Since these surveys are unbiased, the various bias estimation methods should reflect that and provide an absolute accuracy metric for each of the bias estimation methods. Secondly, the corrected gravity datasets from each of the bias estimation methods are used to build a geoid model. The accuracy of each geoid model provides an additional metric to assess the performance of each bias estimation method. The geoid model accuracies are assessed using the two GSVS lines and GPS-leveling data across the United States.

Spectral analysis of the Earth's topographic potential via 2D-DFT: a new data-based degree variance model to degree 90,000

NASA Astrophysics Data System (ADS)

Rexer, Moritz; Hirt, Christian

2015-09-01

Classical degree variance models (such as Kaula's rule or the Tscherning-Rapp model) often rely on low-resolution gravity data and so are subject to extrapolation when used to describe the decay of the gravity field at short spatial scales. This paper presents a new degree variance model based on the recently published GGMplus near-global land areas 220 m resolution gravity maps (Geophys Res Lett 40(16):4279-4283, 2013). We investigate and use a 2D-DFT (discrete Fourier transform) approach to transform GGMplus gravity grids into degree variances. The method is described in detail and its approximation errors are studied using closed-loop experiments. Focus is placed on tiling, azimuth averaging, and windowing effects in the 2D-DFT method and on analytical fitting of degree variances. Approximation errors of the 2D-DFT procedure on the (spherical harmonic) degree variance are found to be at the 10-20 % level. The importance of the reference surface (sphere, ellipsoid or topography) of the gravity data for correct interpretation of degree variance spectra is highlighted. The effect of the underlying mass arrangement (spherical or ellipsoidal approximation) on the degree variances is found to be crucial at short spatial scales. A rule-of-thumb for transformation of spectra between spherical and ellipsoidal approximation is derived. Application of the 2D-DFT on GGMplus gravity maps yields a new degree variance model to degree 90,000. The model is supported by GRACE, GOCE, EGM2008 and forward-modelled gravity at 3 billion land points over all land areas within the SRTM data coverage and provides gravity signal variances at the surface of the topography. The model yields omission errors of 9 mGal for gravity (1.5 cm for geoid effects) at scales of 10 km, 4 mGal (1 mm) at 2-km scales, and 2 mGal (0.2 mm) at 1-km scales.

EUPOS and SLR Contribution to GOCE Mission

NASA Astrophysics Data System (ADS)

Balodis, J.; Caunite, M.; Janpaule, I.; Kenyeres, A.; Rubans, A.; Silabriedis, G.; Rosenthal, G.; Zarinsjh, A.; Zvirgzds, J.; Abel, M.

2010-12-01

After the interest of geodesists from several East European countries on successful use of SAPOS in Germany the European Position Determination System EUPOS® project has been established at 2002 under the leadership of Gerd Rosenthal, Berlin State Department of Urban Development. Currently the ground based GNSS augmentation system EUPOS® sub-networks has been developed successfully in 17 countries and the wish to join has been expressed by several other countries. EUPOS® is widely used in many practical applications. Two proposals - "EUPOS® Contribution to GOCE Mission" (Id 4307), "GOCE Observations using SLR for LEO satellites" (Id 4333), were submitted to ESA when ESA in autumn 2006 invited research people to submit proposals for GOCE mission applications. The report is presented in this article on the work which has been done in EUPOS® community and at the University of Latvia. During last 3 years the EUPOS® sub- networks has been completed (Poland, Lithuania, Slovakia, Bulgaria, they tied to the National levelling networks, detailed system behaviour has been depicted on the bases of EUPOS®-Riga network. The development of the SLR for LEO satellites is presented. Initially it was developed for GOCE spacecraft positioning. However, SLR till now was able to observe satellites at night.

3D inversion of full gravity gradient tensor data in spherical coordinate system using local north-oriented frame

NASA Astrophysics Data System (ADS)

Zhang, Yi; Wu, Yulong; Yan, Jianguo; Wang, Haoran; Rodriguez, J. Alexis P.; Qiu, Yue

2018-04-01

In this paper, we propose an inverse method for full gravity gradient tensor data in the spherical coordinate system. As opposed to the traditional gravity inversion in the Cartesian coordinate system, our proposed method takes the curvature of the Earth, the Moon, or other planets into account, using tesseroid bodies to produce gravity gradient effects in forward modeling. We used both synthetic and observed datasets to test the stability and validity of the proposed method. Our results using synthetic gravity data show that our new method predicts the depth of the density anomalous body efficiently and accurately. Using observed gravity data for the Mare Smythii area on the moon, the density distribution of the crust in this area reveals its geological structure. These results validate the proposed method and potential application for large area data inversion of planetary geological structures.[Figure not available: see fulltext.

Nepal and Papua Airborne Gravity Surveys

NASA Astrophysics Data System (ADS)

Olesen, A. V.; Forsberg, R.; Kasenda, F.; Einarsson, I.; Manandhar, N.

2011-12-01

Airborne gravimetry offers a fast and economic way to cover vast areas and it allows access to otherwise difficult accessible areas like mountains, jungles and the near coastal zone. It has the potential to deliver high resolution and bias free data that may bridge the spectral gap between global satellite gravity models and the high resolution gravity information embedded in digital terrain models. DTU Space has for more than a decade done airborne gravity surveys in many parts of the world. Most surveys were done with a LaCoste & Romberg S-meter updated for airborne use. This instrument has proven to deliver near bias free data when properly processed. A Chekan AM gravimeter was recently added to the airborne gravity mapping system and will potentially enhance the spatial resolution and the robustness of the system. This paper will focus on results from two recent surveys over Nepal, flown in December 2010, and over Papua (eastern Indonesia), flown in May and June 2011. Both surveys were flown with the new double gravimeter setup and initial assessment of system performance indicates improved spatial resolution compared to the single gravimeter system. Comparison to EGM08 and to the most recent GOCE models highlights the impact of the new airborne gravity data in both cases. A newly computed geoid model for Nepal based on the airborne data allows for a more precise definition of the height of Mt. Everest in a global height system. This geoid model suggests that the height of Mt. Everest should be increased by approximately 1 meter. The paper will also briefly discuss system setup and will highlight a few essential processing steps that ensure that bias problems are minimized and spatial resolution enhanced.

Unification of Intercontinental Height Systems based on the Fixed Geodetic Boundary Value Problem - A Case Study in Spherical Approximation

NASA Astrophysics Data System (ADS)

Grombein, T.; Seitz, K.; Heck, B.

2013-12-01

In general, national height reference systems are related to individual vertical datums defined by specific tide gauges. The discrepancy of these vertical datums causes height system biases that range in an order of 1-2 m at a global scale. Continental height systems can be connected by spirit leveling and gravity measurements along the leveling lines as performed for the definition of the European Vertical Reference Frame. In order to unify intercontinental height systems, an indirect connection is needed. For this purpose, global geopotential models derived from recent satellite missions like GOCE provide an important contribution. However, to achieve a highly-precise solution, a combination with local terrestrial gravity data is indispensable. Such combinations result in the solution of a Geodetic Boundary Value Problem (GBVP). In contrast to previous studies, mostly related to the traditional (scalar) free GBVP, the present paper discusses the use of the fixed GBVP for height system unification, where gravity disturbances instead of gravity anomalies are applied as boundary values. The basic idea of our approach is a conversion of measured gravity anomalies to gravity disturbances, where unknown datum parameters occur that can be associated with height system biases. In this way, the fixed GBVP can be extended by datum parameters for each datum zone. By evaluating the GBVP at GNSS/leveling benchmarks, the unknown datum parameters can be estimated in a least squares adjustment. Beside the developed theory, we present numerical results of a case study based on the spherical fixed GBVP and boundary values simulated by the use of the global geopotential model EGM2008. In a further step, the impact of approximations like linearization as well as topographic and ellipsoidal effects is taken into account by suitable reduction and correction terms.

Gravity and Aeromagnetic Gradients within the Yukon-Tanana Upland, Black Mountain Tectonic Zone, Big Delta Quadrangle, east-central Alaska

USGS Publications Warehouse

Saltus, R.W.; Day, W.C.

2006-01-01

The Yukon-Tanana Upland is a complex composite assemblage of variably metamorphosed crystalline rocks with strong North American affinities. At the broadest scale, the Upland has a relatively neutral magnetic character. More detailed examination, however, reveals a fundamental northeast-southwest-trending magnetic gradient, representing a 20-nT step (as measured at a flight height of 300 m) with higher values to the northwest, that extends from the Denali fault to the Tintina fault and bisects the Upland. This newly recognized geophysical gradient is parallel to, but about 100 km east of, the Shaw Creek fault. The Shaw Creek fault is mapped as a major left-lateral, strike-slip fault, but does not coincide with a geophysical boundary. A gravity gradient coincides loosely with the southwestern half of the magnetic gradient. This gravity gradient is the eastern boundary of a 30-mGal residual gravity high that occupies much of the western and central portions of the Big Delta quadrangle. The adjacent lower gravity values to the east correlate, at least in part, with mapped post-metamorphic granitic rocks. Ground-based gravity and physical property measurements were made in the southeastern- most section of the Big Delta quadrangle in 2004 to investigate these geophysical features. Preliminary geophysical models suggest that the magnetic boundary is deeper and more fundamental than the gravity boundary. The two geophysical boundaries coincide in and around the Tibbs Creek region, an area of interest to mineral exploration. A newly mapped tectonic zone (the Black Mountain tectonic zone of O'Neill and others, 2005) correlates with the coincident geophysical boundaries.

Insights into the Lurking Structures and Related Intraplate Earthquakes in the Region of Bay of Bengal Using Gravity and Full Gravity Gradient Tensor

NASA Astrophysics Data System (ADS)

Dubey, C. P.; Tiwari, V. M.; Rao, P. R.

2017-12-01

Comprehension of subsurface structures buried under thick sediments in the region of Bay of Bengal is vital as structural features are the key parameters that influence or are caused by the subsurface deformation and tectonic events like earthquakes. Here, we address this issue using the integrated analysis and interpretation of gravity and full gravity gradient tensor with few seismic profiles available in the poorly known region. A 2D model of the deep earth crust-mantle is constructed and interpreted with gravity gradients and seismic profiles, which made it possible to obtain a visual image of a deep seated fault below the basement associated with thick sediments strata. Gravity modelling along a NE-SW profile crossing the hypocentre of the earthquake of 21 May 2014 ( M w 6.0) in the northern Bay of Bengal suggests that the location of intraplate normal dip fault earthquake in the upper mantle is at the boundary of density anomalies, which is probably connected to the crustal fault. We also report an enhanced structural trend of two major ridges, the 85°E and the 90°E ridges hidden under the sedimentary cover from the computed full gravity gradients tensor components.

Joint Interpretation of Bathymetric and Gravity Anomaly Maps Using Cross and Dot-Products.

NASA Astrophysics Data System (ADS)

Jilinski, Pavel; Fontes, Sergio Luiz

2010-05-01

0.1 Summary We present the results of joint map interpretation technique based on cross and dot-products applied to bathymetric and gravity anomaly gradients maps. According to the theory (Gallardo, Meju, 2004) joint interpretation of different gradient characteristics help to localize and empathize patterns unseen on one image interpretation and gives information about the correlation of different spatial data. Values of angles between gradients and their cross and dot-product were used. This technique helps to map unseen relations between bathymetric and gravity anomaly maps if they are analyzed separately. According to the method applied for the southern segment of Eastern-Brazilian coast bathymetrical and gravity anomaly gradients indicates a strong source-effect relation between them. The details of the method and the obtained results are discussed. 0.2 Introduction We applied this method to investigate the correlation between bathymetric and gravity anomalies at the southern segment of the Eastern-Brazilian coast. Gridded satellite global marine gravity data and bathymetrical data were used. The studied area is located at the Eastern- Brazilian coast between the 20° W and 30° W meridians and 15° S and 25° S parallels. The volcanic events responsible for the uncommon width of the continental shelf at the Abrolhos bank also were responsible for the formation of the Abrolhos islands and seamounts including the major Vitoria-Trindade chain. According to the literature this volcanic structures are expected to have a corresponding gravity anomaly (McKenzie, 1976, Zembruscki, S.G. 1979). The main objective of this study is to develop and test joint image interpretation method to compare spatial data and analyze its relations. 0.3 Theory and Method 0.3.1 Data sources The bathymetrical satellite data were derived bathymetry 2-minute grid of the ETOPO2v2 obtained from NOAA's National Geophysical Data Center (http://www.ngdc.noaa.gov). The satellite marine gravity 1-minute gridded data were obtained from the Satellite Geodesy at the Scripps Institution of Oceanography, Smith & Sandwell (1997; http://topex.ucsd.edu. Gravity anomaly data were re-gridded using the ETOPO2v2 grid. All calculations and maps were made using MatLab 2007 software. 0.3.2 Cross-Product Cross-product is the result of multiplication of bathymetric and gravity anomaly gradient magnitudes by the sine of the angle between them. According to the definition of gradient cross-product minimal values are expected to be found in points where the angle between gradients is close to zero or where one or both of the gradient magnitudes have values close to zero. It creates an ambiguity and a problem for data interpretation since there is no exact correspondence between bathymetric structures and gravity anomalies. 0.3.3 Dot-Product Dot-product is the result of multiplication of bathymetric and gravity anomaly magnitudes by the cosine on the angle between them. According to the definition of dot-product, values close to zero can be generated by near perpendicular orientation of the gradients or small magnitudes of one or both gradients. So, the results are mutually increased in areas with larger magnitudes or smaller angles between gradients. Due to this mutual amplification dot-products are less affected by the ambiguity of cross-product explained above. The same statistical separation of cross-product was used to support the conclusions. 0.3.4 Statistics and Significance Criteria Statistical analysis was made in order to sort the data into two groups to reduce ambiguity effect: first group - data with magnitudes that could be considered anomalous (where the main minimizing source is the angle between the gradients and the second group - data with magnitudes variations that could be considered as (non significant or background (where cross-product value is determined by the small magnitude). It was chosen to use the mean value and standard deviation (std) to sort the data in such two groups. These values were determined for bathymetric and gravity anomaly gradient magnitudes creating two data sets - one where one or both gradient magnitudes are one standard deviation larger than the mean value with a total of 7831 (anomalous) and a second one where both magnitudes differ smaller than one standard deviation from the mean value with 85584 (background ). Statistical analysis of distribution patterns for both groups was made. 0.4 Examples of Method Application 0.4.1 Map of Angles Between Gradients Figure 1 shows the map of angle values. The angle values were divided into 4 equal intervals. The statistical distribution of angles between gradient in the given intervals is the following (percents of the total): 0 to 60° - 51.39% of the values; 60° to 90° -12.08%; 90° to 120° -14.92%; 120° to 180° -21.18%. It can be seen that 51% of the gradients have a small angle between them, 72% of gradients can be considered as parallel (72%) with angles smaller than 60° or bigger than 120° between them. After statistical separation in the anomalous group almost 91% of the gradients have an angle smaller than 60° while in the background group just 48.6%. From these results we can make a conclusion that the majority of the bathymetric and gravity anomaly gradients are related. Regions with higher gradient magnitudes are characterized by cosine values close to 1 (indicating a small angle between them). The size of the areas characterized by small angles between gradients exceed the size of bathymetric and gravity anomaly isolines characterizing the area of influence of the structures and their effects. Regions with no significant anomalies show uncorrelated value spots. 0.4.2 Map of Cross-Product The resulting map shows small spots of higher cross-product magnitudes following magnitude isolines. About 90% of the values are close to minimum. As was mentioned before, we can presume that areas where bathymetry and gravity anomaly gradient cross-products have smallest magnitudes there is a good correspondence between them indicating a good correspondence between shapes. According to these results for the studied area the shapes and positions of bathymetric structures and gravity anomalies are well correlated suggesting strong correlation between source and its effect. 0.4.3 Map of Dot-Product The resulting map resembles bathymetric and gravity anomaly isolines. All the sea mounts, banks, continental slope and other notable geomorphologic structures and gravity anomalies are well delimitated in the dot-product map eliminating uncorrelated areas where gradient orientations can be considered as near perpendicular. The dot-product map of the studied area suggests a strong source-effect between bathymetry and gravity anomaly. 0.5 Conclusions The joint image interpretation technique uses three different criteria that are sensitive to different gradient properties. Angles between gradients are a good indicator of areas where data are related and it is not sensitive to the magnitudes of the gradients. Angles maps can be used to find areas with direct and inverse relation between mapped properties and contour areas of influence of anomalies unseen on gradient magnitude maps alone. Statistical measures of distribution of angles can be an indicator of relation between data sets as show using significance criteria. Cross-product map has a spotted character of contours. To reduce the effects of the ambiguity the separation into two groups proved to be useful. It helps to separate the cross-product values that are minimized due to gradient magnitudes from those that minimize due to sine values which is a measure of correlation between them. Dot-product values contour areas where gradients are correlated. According to joint image interpretation technique applied bathymetric structures especially the volcanic seamounts and banks in the southern part of East-Brazilian Coast are closely related to the observed gravity anomalies and can be interpreted as sources and effect. This technique also helps to evaluate the shape and dispersion of the gravitational effect from a bathymetrical source. 0.6 References Dehlinger P., Marine Gravity, Elsevier, 1978. Gallardo, L. A., and M. A. Meju., Joint 2D cross-gradient imaging of magnetotelluric and seismic travel-time data for structural and lithological classification, Geophys. J. Int., 169, 1261-1272. (2007) Gallardo, L.A., M. A. Meju (2004), Joint two-dimensional dc resistivity and seismic traveltime inversion with cross-gradients constraints, J. Geophys. Res., 109, B03311, doi:10.1029/2003JB002716 Jacoby, W., and Smilde P. L., Gravity Interpretation, Springer, 2009. McKenzie D. & Bowin C. 1976. The relationship between bathymetry and gravity in Atlantic Ocean. Journal of Geophysical Research, 81: 1903-1915. Roy. K. K., Potential Theory in Applied Geophysics, Springer, 2008. Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997. Sandwell, D. T., and W. H. F. Smith, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge Segmentation versus spreading rate, J. Geophys. Res., 114, B01411, doi:10.1029/2008JB006008, 2009. Zembruscki, S.G. 1979. Geomorfologia da Margem Continental Sul Brasileira e das Bacias Oceânicas Adjacentes. In: Geomorfologia da margem continental brasileira e das áreas oceânicas adjacentes. Série Projeto REMAC, N° 7.

Eigenvector of gravity gradient tensor for estimating fault dips considering fault type

NASA Astrophysics Data System (ADS)

Kusumoto, Shigekazu

2017-12-01

The dips of boundaries in faults and caldera walls play an important role in understanding their formation mechanisms. The fault dip is a particularly important parameter in numerical simulations for hazard map creation as the fault dip affects estimations of the area of disaster occurrence. In this study, I introduce a technique for estimating the fault dip using the eigenvector of the observed or calculated gravity gradient tensor on a profile and investigating its properties through numerical simulations. From numerical simulations, it was found that the maximum eigenvector of the tensor points to the high-density causative body, and the dip of the maximum eigenvector closely follows the dip of the normal fault. It was also found that the minimum eigenvector of the tensor points to the low-density causative body and that the dip of the minimum eigenvector closely follows the dip of the reverse fault. It was shown that the eigenvector of the gravity gradient tensor for estimating fault dips is determined by fault type. As an application of this technique, I estimated the dip of the Kurehayama Fault located in Toyama, Japan, and obtained a result that corresponded to conventional fault dip estimations by geology and geomorphology. Because the gravity gradient tensor is required for this analysis, I present a technique that estimates the gravity gradient tensor from the gravity anomaly on a profile.

A gradient of endogenous calcium forms in mucilage of graviresponding roots of Zea mays

NASA Technical Reports Server (NTRS)

Moore, R.; Fondren, W. M.

1988-01-01

Agar blocks that contacted the upper sides of tips of horizontally-oriented roots of Zea mays contain significantly less calcium (Ca) than blocks that contacted the lower sides of such roots. This gravity-induced gradient of Ca forms prior to the onset of gravicurvature, and does not form across tips of vertically-oriented roots or roots of agravitropic mutants. These results indicate that (1) Ca can be collected from mucilage of graviresponding roots, (2) gravity induces a downward movement of endogenous Ca in mucilage overlying the root tip, (3) this gravity-induced gradient of Ca does not form across tips of agravitropic roots, and (4) formation of a Ca gradient is not a consequence of gravicurvature. These results are consistent with gravity-induced movement of Ca being a trigger for subsequent redistribution of growth effectors (e.g. auxin) that induce differential growth and gravicurvature.

The influence of installation angle of GGIs on full-tensor gravity gradient measurement

NASA Astrophysics Data System (ADS)

Wei, Hongwei; Wu, Meiping

2018-03-01

Gravity gradient plays an important role in many disciplines as a fundamental signal to reflect the information of the earth. Full-tensor gravity gradient measurement (FGGM) is an effective way to obtain the gravity gradient signal. In this paper, the installation mode of GGIs in FGGM is studied. It is expected that the accuracy of FGGM will be improved by optimizing the installation mode of GGIs. In addition, we analysed the relationship between GGIs’ installation angle and FGGM by establishing the measurement model of FGGM. Then the following conclusions was proved that there was no relationship between GGIs’ installation angle and the measurement result. This conclusion showed that there was no optimal angle for the GGIs’ installation in FGGM, and the installation angle only need to satisfy the relationship shown in the conclusion section of this paper. Finally, this conclusion was demonstrated by computer simulations.

High rate GPS positioning , JASON altimetry and marine gravimetry : monitoring the Antarctic Circumpolar Current (ACC) through the DRAKE campaigns.

NASA Astrophysics Data System (ADS)

Melachroinos, S. A.; Biancale, R.; Menard, Y.; Sarrailh, M.

2008-12-01

The Drake campaign which took place from Jan 14, 2006 - 08 Feb, 2006 has been a very successful mission in collecting a wide range of GPS and marine gravity data all along JASON altimetry ground track n° 104. The same campaign will be repeated in 2009 along 028 and 104 JASON-2 ground track. The Drake Passage (DP) chokepoint is not only well suited geographically, as the Antarctic Circumpolar Current (ACC) is constricted to its narrowest extent of 700 km, but observations and models suggest that dynamical balances are particular effective in this area. Furthermore the space geodesy observations and their products provided from several altimetry missions (currently operating ENVISAT, JASON 1 and 2, GFO, ERS and other plannified for the future such as Altika, SWOT) require the cross comparison with independent geodetic techniques at the DP. The current experiment comprises a kinematic GPS and marine gravimetry Cal/Val geodetic approach and it aims to : validate with respect to altimetry data and surface models such a kinematic high frequency GPS technique for measuring sea state and sea surface height (SSH), compare the GPS SSH profiles with altimetry mean dynamic topography (MDT) and mean sea surface (MSS) models, give recommendations for future "offshore" Cal/Val activities on the ground tracks of altimeter satellites such as JASON-2, GFO, Altika using the GNSS technology etc. The GPS observations are collected from GPS antennas installed on a wave-rider buoy , aboard the R/V "Polarstern" and from continuous geodetic reference stations in the proximity. We also analyse problems related to the ship's attitude variations in roll, pitch and yaw and a way to correct them. We also give emphasis on the impact of the ship's acceleration profiles on the so called "squat effect" and ways to deal with it. The project will in particular benefit the GOCE mission by proposing to integrate GOCE in the ocean circulation study and validate GOCE products with our independent geodetic data set. The high rate GPS SSH solutions are derived using two different GPS kinematic software, GINS (CNES) and TRACK (MIT).

Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

PubMed Central

Blaser, Nicole; Guskov, Sergei I.; Meskenaite, Virginia; Kanevskyi, Valerii A.; Lipp, Hans-Peter

2013-01-01

The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates. PMID:24194860

Altered orientation and flight paths of pigeons reared on gravity anomalies: a GPS tracking study.

PubMed

Blaser, Nicole; Guskov, Sergei I; Meskenaite, Virginia; Kanevskyi, Valerii A; Lipp, Hans-Peter

2013-01-01

The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The "gravity vector" theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates.

Changes in gravitational parameters inferred from time variable GRACE data-A case study for October 2005 Kashmir earthquake

NASA Astrophysics Data System (ADS)

Hussain, Matloob; Eshagh, Mehdi; Ahmad, Zulfiqar; Sadiq, M.; Fatolazadeh, Farzam

2016-09-01

The earth's gravity changes are attributed to the redistribution of masses within and/or on the surface of the earth, which are due to the frictional sliding, tensile cracking and/or cataclastic flow of rocks along the faults and detectable by earthquake events. Inversely, the gravity changes are useful to describe the earthquake seismicity over the active orogenic belts. The time variable gravimetric data are hardly available to the public domain. However, Gravity Recovery and Climatic Experiment (GRACE) is the only satellite mission dedicated to model the variation of the gravity field and an available source to the science community. Here, we have tried to envisage gravity changes in terms of gravity anomaly (Δg), geoid (N) and the gravity gradients over the Indo-Pak plate with emphasis upon Kashmir earthquake of October 2005. For this purpose, we engaged the spherical harmonic coefficients of monthly gravity solutions from the GRACE satellite mission, which have good coverage over the entire globe with unprecedented accuracy. We have analysed numerically the solutions after removing the hydrological signals, during August to November 2005, in terms of corresponding monthly differentials of gravity anomaly, geoid and the gradients. The regional structures like Main Mantle Thrust (MMT), Main Karakoram Thrust (MKT), Herat and Chaman faults are in closed association with topography and with gravity parameters from the GRACE gravimetry and EGM2008 model. The monthly differentials of these quantities indicate the stress accumulation in the northeast direction in the study area. Our numerical results show that the horizontal gravity gradients seem to be in good agreement with tectonic boundaries and differentials of the gravitational elements are subtle to the redistribution of rock masses and topography caused by 2005 Kashmir earthquake. Moreover, the gradients are rather more helpful for extracting the coseismic gravity signatures caused by seismicity over the area. Higher positive values of gravity components having higher terrain elevations are more vulnerable to the seismicity and lower risk of diastrophism otherwise.

Least squares collocation applied to local gravimetric solutions from satellite gravity gradiometry data

NASA Technical Reports Server (NTRS)

Robbins, J. W.

1985-01-01

An autonomous spaceborne gravity gradiometer mission is being considered as a post Geopotential Research Mission project. The introduction of satellite diometry data to geodesy is expected to improve solid earth gravity models. The possibility of utilizing gradiometer data for the determination of pertinent gravimetric quantities on a local basis is explored. The analytical technique of least squares collocation is investigated for its usefulness in local solutions of this type. It is assumed, in the error analysis, that the vertical gravity gradient component of the gradient tensor is used as the raw data signal from which the corresponding reference gradients are removed to create the centered observations required in the collocation solution. The reference gradients are computed from a high degree and order geopotential model. The solution can be made in terms of mean or point gravity anomalies, height anomalies, or other useful gravimetric quantities depending on the choice of covariance types. Selected for this study were 30 x 30 foot mean gravity and height anomalies. Existing software and new software are utilized to implement the collocation technique. It was determined that satellite gradiometry data at an altitude of 200 km can be used successfully for the determination of 30 x 30 foot mean gravity anomalies to an accuracy of 9.2 mgal from this algorithm. It is shown that the resulting accuracy estimates are sensitive to gravity model coefficient uncertainties, data reduction assumptions and satellite mission parameters.

Preparation, testing and analysis of zinc diffusion samples, NASA Skylab experiment M-558

NASA Technical Reports Server (NTRS)

Braski, D. N.; Kobisk, E. H.; Odonnell, F. R.

1974-01-01

Transport mechanisms of zinc atoms in molten zinc were investigated by radiotracer techniques in unit and in near-zero gravity environments. Each melt in the Skylab flight experiments was maintained in a thermal gradient of 420 C to 790 C. Similar tests were performed in a unit gravity environment for comparison. After melting in the gradient furnace followed by a thermal soak period (the latter was used for flight samples only), the samples were cooled and analyzed for Zn-65 distribution. All samples melted in a unit gravity environment were found to have uniform Zn-65 distribution - no concentration gradient was observed even when the sample was brought rapidly to melting and then quenched. Space-melted samples, however, showed textbook distributions, obviously the result of diffusion. It was evident that convection phenomena were the dominant factors influencing zinc transport in unit gravity experiments, while diffusion was the dominant factor in near-zero gravity experiments.

Implications for seismic hazard from new gravity data in Napa and vicinity, California

NASA Astrophysics Data System (ADS)

Morgan, K.; Langenheim, V. E.; Ritzinger, B. T.

2015-12-01

New gravity data refine the basin structure beneath the city of Napa, California and suggest continuity of the West Napa fault to the SE, near the city of Vallejo. Previous regional gravity data defined a basin 2-3 km deep beneath Napa where the 2014 M6.0 South Napa and the 2000 M4.9 Yountville earthquakes caused considerable damage. Higher ground motions were also recorded within the area of the gravity low. About 100 new gravity measurements sharpen gravity gradients along the eastern margin of the gravity low, where there was a concentration of red-tagged buildings from the 2014 earthquake. The new data also confirm the presence of an intrabasinal, arch, defined by slightly higher gravity values (~ 1 mGal) in the center of the basin and marked by the edge of a significant magnetic high (~150 nT). This arch coincides with the highest concentration of red-tagged buildings from the 2014 earthquake. Comparison of the potential-field anomalies with rock types encountered in water wells suggests that the arch is underlain by sediments which thin to the south where they are underlain by thick Sonoma Volcanics.. We speculate that the concentration of damage may be caused by shallowing of the basement or by a thicker sequence of basin sediments in the arch or both. Red-tagged buildings from the Yountville earthquake are near the western edge of the basin defined by significant potential-field gradients of the West Napa fault. A sharp basin boundary or guided waves along the fault may have contributed to concentration of damage in this area. Although the potential-field gradients decrease south of Napa, our new gravity data define a gradient aligned to the SE beneath the town of Vallejo. The gradient resides within Mesozoic basement rocks because it traverses outcrops of Great Valley Sequence. Although these data cannot prove Quaternary slip on this structure, its trend and location may indicate continuation of the West Napa fault to the SE.

Superconducting gravity gradiometer and a test of inverse square law

NASA Technical Reports Server (NTRS)

Moody, M. V.; Paik, Ho Jung

1989-01-01

The equivalence principle prohibits the distinction of gravity from acceleration by a local measurement. However, by making a differential measurement of acceleration over a baseline, platform accelerations can be cancelled and gravity gradients detected. In an in-line superconducting gravity gradiometer, this differencing is accomplished with two spring-mass accelerometers in which the proof masses are confined to motion in a single degree of freedom and are coupled together by superconducting circuits. Platform motions appear as common mode accelerations and are cancelled by adjusting the ratio of two persistent currents in the sensing circuit. The sensing circuit is connected to a commercial SQUID amplifier to sense changes in the persistent currents generated by differential accelerations, i.e., gravity gradients. A three-axis gravity gradiometer is formed by mounting six accelerometers on the faces of a precision cube, with the accelerometers on opposite faces of the cube forming one of three in-line gradiometers. A dedicated satellite mission for mapping the earth's gravity field is an important one. Additional scientific goals are a test of the inverse square law to a part in 10(exp 10) at 100 km, and a test of the Lense-Thirring effect by detecting the relativistic gravity magnetic terms in the gravity gradient tensor for the earth.

Analytic Expressions for the Gravity Gradient Tensor of 3D Prisms with Depth-Dependent Density

NASA Astrophysics Data System (ADS)

Jiang, Li; Liu, Jie; Zhang, Jianzhong; Feng, Zhibing

2017-12-01

Variable-density sources have been paid more attention in gravity modeling. We conduct the computation of gravity gradient tensor of given mass sources with variable density in this paper. 3D rectangular prisms, as simple building blocks, can be used to approximate well 3D irregular-shaped sources. A polynomial function of depth can represent flexibly the complicated density variations in each prism. Hence, we derive the analytic expressions in closed form for computing all components of the gravity gradient tensor due to a 3D right rectangular prism with an arbitrary-order polynomial density function of depth. The singularity of the expressions is analyzed. The singular points distribute at the corners of the prism or on some of the lines through the edges of the prism in the lower semi-space containing the prism. The expressions are validated, and their numerical stability is also evaluated through numerical tests. The numerical examples with variable-density prism and basin models show that the expressions within their range of numerical stability are superior in computational accuracy and efficiency to the common solution that sums up the effects of a collection of uniform subprisms, and provide an effective method for computing gravity gradient tensor of 3D irregular-shaped sources with complicated density variation. In addition, the tensor computed with variable density is different in magnitude from that with constant density. It demonstrates the importance of the gravity gradient tensor modeling with variable density.

Fast gravity, gravity partials, normalized gravity, gravity gradient torque and magnetic field: Derivation, code and data

NASA Technical Reports Server (NTRS)

Gottlieb, Robert G.

1993-01-01

Derivation of first and second partials of the gravitational potential is given in both normalized and unnormalized form. Two different recursion formulas are considered. Derivation of a general gravity gradient torque algorithm which uses the second partial of the gravitational potential is given. Derivation of the geomagnetic field vector is given in a form that closely mimics the gravitational algorithm. Ada code for all algorithms that precomputes all possible data is given. Test cases comparing the new algorithms with previous data are given, as well as speed comparisons showing the relative efficiencies of the new algorithms.

Computational analysis of microbubble flows in bifurcating airways: role of gravity, inertia, and surface tension.

PubMed

Chen, Xiaodong; Zielinski, Rachel; Ghadiali, Samir N

2014-10-01

Although mechanical ventilation is a life-saving therapy for patients with severe lung disorders, the microbubble flows generated during ventilation generate hydrodynamic stresses, including pressure and shear stress gradients, which damage the pulmonary epithelium. In this study, we used computational fluid dynamics to investigate how gravity, inertia, and surface tension influence both microbubble flow patterns in bifurcating airways and the magnitude/distribution of hydrodynamic stresses on the airway wall. Direct interface tracking and finite element techniques were used to simulate bubble propagation in a two-dimensional (2D) liquid-filled bifurcating airway. Computational solutions of the full incompressible Navier-Stokes equation were used to investigate how inertia, gravity, and surface tension forces as characterized by the Reynolds (Re), Bond (Bo), and Capillary (Ca) numbers influence pressure and shear stress gradients at the airway wall. Gravity had a significant impact on flow patterns and hydrodynamic stress magnitudes where Bo > 1 led to dramatic changes in bubble shape and increased pressure and shear stress gradients in the upper daughter airway. Interestingly, increased pressure gradients near the bifurcation point (i.e., carina) were only elevated during asymmetric bubble splitting. Although changes in pressure gradient magnitudes were generally more sensitive to Ca, under large Re conditions, both Re and Ca significantly altered the pressure gradient magnitude. We conclude that inertia, gravity, and surface tension can all have a significant impact on microbubble flow patterns and hydrodynamic stresses in bifurcating airways.

Airborne geoid mapping of land and sea areas of East Malaysia

NASA Astrophysics Data System (ADS)

Jamil, H.; Kadir, M.; Forsberg, R.; Olesen, A.; Isa, M. N.; Rasidi, S.; Mohamed, A.; Chihat, Z.; Nielsen, E.; Majid, F.; Talib, K.; Aman, S.

2017-02-01

This paper describes the development of a new geoid-based vertical datum from airborne gravity data, by the Department of Survey and Mapping Malaysia, on land and in the South China Sea out of the coast of East Malaysia region, covering an area of about 610,000 square kilometres. More than 107,000 km flight line of airborne gravity data over land and marine areas of East Malaysia has been combined to provide a seamless land-to-sea gravity field coverage; with an estimated accuracy of better than 2.0 mGal. The iMAR-IMU processed gravity anomaly data has been used during a 2014-2016 airborne survey to extend a composite gravity solution across a number of minor gaps on selected lines, using a draping technique. The geoid computations were all done with the GRAVSOFT suite of programs from DTU-Space. EGM2008 augmented with GOCE spherical harmonic model has been used to spherical harmonic degree N = 720. The gravimetric geoid first was tied at one tide-gauge (in Kota Kinabalu, KK2019) to produce a fitted geoid, my_geoid2017_fit_kk. The fitted geoid was offset from the gravimetric geoid by +0.852 m, based on the comparison at the tide-gauge benchmark KK2019. Consequently, orthometric height at the six other tide gauge stations was computed from HGPS Lev = hGPS - Nmy_geoid2017_.t_kk. Comparison of the conventional (HLev) and GPS-levelling heights (HGPS Lev) at the six tide gauge locations indicate RMS height difference of 2.6 cm. The final gravimetric geoidwas fitted to the seven tide gauge stations and is known as my_geoid2017_fit_east. The accuracy of the gravimetric geoid is estimated to be better than 5 cm across most of East Malaysia land and marine areas

Evidence for an east-west regional gravity trend in northern Tunisia: Insight into the structural evolution of northern Tunisian Atlas

NASA Astrophysics Data System (ADS)

Jallouli, Chokri; Mogren, Saad; Mickus, Kevin; Turki, Mohamed Moncef

2013-11-01

The Atlas orogeny in northern Algeria and Tunisia led to the destruction of Tethys oceanic lithosphere and cumulated in a collision of microplates rifted off the European margin with the North African continental margin. The location of the boundary between African plate and Kabylian microplate is expressed in northern Algeria by a crustal wedge with double vergence of thrust sheets, whereas in northern Tunisia the geologic environment is more complex and the location of the plate boundary is ambiguous. In this study, we analyzed gravity data to constrain the crustal structure along the northern margin of Tunisia. The analysis includes a separation of regional and residual gravity anomalies and the application of gradient operators to locate density contrast boundaries. The horizontal gradient magnitude and directional gradient highlight a prominent regional E-W gravity gradient in the northern Tunisian Atlas interpreted as a deep fault (active since at least the Early Mesozoic) having a variable kinematic activity depending on the tectonic regime in the region. The main E-W gravity gradient separates two blocks having different gravitational and seismic responses. The southern block has numerous gravity lineaments trending in different directions implying several density variations within the crust, whereas the northern block shows a long-wavelength negative gravity anomaly with a few lineaments. Taking into account the geologic context of the Western Mediterranean region, we consider the E-W prominent feature as the boundary between African plate and Kabylian microplate in northern Tunisia that rifted off Europe. This hypothesis fits most previous geological and geophysical studies and has an important impact on the petroleum and mineral resource prospection as these two blocks were separated by an ocean and they did not belong to the same margin.

Application Number 3: Using Tethers for Attitude Control

NASA Technical Reports Server (NTRS)

Muller, R. M.

1985-01-01

Past application of the gravity gradient concept to satellite attitude control produced attitude stabilities of from 1 to 10 degrees. The satellite members were rigigly interconnected and any motion in one part of the satellite would cause motion in all members. This experience has restricted gravity gradient stabilization to applications that need attitude stability no better than 1 degree. A gravity gradient technique that combines the flexible tether with an active control that will allow control stability much better than 1 degree is proposed. This could give gravity gradient stabilization much broader application. In fact, for a large structure like a space station, it may become the preferred method. Two possible ways of demonstrating the techniques using the Tethered Satellite System (TSS) tether to control the attitude of the shuttle are proposed. Then a possible space station tether configuration is shown that could be used to control the initial station. It is then shown how the technique can be extended to the control of space stations of virtually any size.

Polyhedral shape model for terrain correction of gravity and gravity gradient data based on an adaptive mesh

NASA Astrophysics Data System (ADS)

Guo, Zhikui; Chen, Chao; Tao, Chunhui

2016-04-01

Since 2007, there are four China Da yang cruises (CDCs), which have been carried out to investigate polymetallic sulfides in the southwest Indian ridge (SWIR) and have acquired both gravity data and bathymetry data on the corresponding survey lines(Tao et al., 2014). Sandwell et al. (2014) published a new global marine gravity model including the free air gravity data and its first order vertical gradient (Vzz). Gravity data and its gradient can be used to extract unknown density structure information(e.g. crust thickness) under surface of the earth, but they contain all the mass effect under the observation point. Therefore, how to get accurate gravity and its gradient effect of the existing density structure (e.g. terrain) has been a key issue. Using the bathymetry data or ETOPO1 (http://www.ngdc.noaa.gov/mgg/global/global.html) model at a full resolution to calculate the terrain effect could spend too much computation time. We expect to develop an effective method that takes less time but can still yield the desired accuracy. In this study, a constant-density polyhedral model is used to calculate the gravity field and its vertical gradient, which is based on the work of Tsoulis (2012). According to gravity field attenuation with distance and variance of bathymetry, we present an adaptive mesh refinement and coarsening strategies to merge both global topography data and multi-beam bathymetry data. The local coarsening or size of mesh depends on user-defined accuracy and terrain variation (Davis et al., 2011). To depict terrain better, triangular surface element and rectangular surface element are used in fine and coarse mesh respectively. This strategy can also be applied to spherical coordinate in large region and global scale. Finally, we applied this method to calculate Bouguer gravity anomaly (BGA), mantle Bouguer anomaly(MBA) and their vertical gradient in SWIR. Further, we compared the result with previous results in the literature. Both synthetic model tests and field applications indicate that the adaptive terrain correction method can be adopted as a rapid and accurate tool of marine gravity data processing. References Davis, K. &Kass, M.A. & Li, Y., 2011. Rapid gravity and gravity gradiometry terrain corrections via an adaptive quadtree mesh discretization, EXPLOR GEOPHYS, 42, 88-97. Sandwell, D.T., Müller, R.D., Smith, W.H., Garcia, E. & Francis, R., 2014. New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure, SCIENCE, 346, 65-67. Tao, C., Li, H., Jin, X., Zhou, J., Wu, T., He, Y., Deng, X., Gu, C., Zhang, G. & Liu, W., 2014. Seafloor hydrothermal activity and polymetallic sulfide exploration on the southwest Indian ridge, CHINESE SCI BULL, 59, 2266-2276. Tsoulis, D., 2012. Analytical computation of the full gravity tensor of a homogeneous arbitrarily shaped polyhedral source using line integrals, GEOPHYSICS, 77, F1-F11.

Relation of the lunar volcano complexes lying on the identical linear gravity anomaly

NASA Astrophysics Data System (ADS)

Yamamoto, K.; Haruyama, J.; Ohtake, M.; Iwata, T.; Ishihara, Y.

2015-12-01

There are several large-scale volcanic complexes, e.g., Marius Hills, Aristarchus Plateau, Rumker Hills, and Flamsteed area in western Oceanus Procellarum of the lunar nearside. For better understanding of the lunar thermal history, it is important to study these areas intensively. The magmatisms and volcanic eruption mechanisms of these volcanic complexes have been discussed from geophysical and geochemical perspectives using data sets acquired by lunar explorers. In these data sets, precise gravity field data obtained by Gravity Recovery and Interior Laboratory (GRAIL) gives information on mass anomalies below the lunar surface, and useful to estimate location and mass of the embedded magmas. Using GRAIL data, Andrews-Hanna et al. (2014) prepared gravity gradient map of the Moon. They discussed the origin of the quasi-rectangular pattern of narrow linear gravity gradient anomalies located along the border of Oceanus Procellarum and suggested that the underlying dikes played important roles in magma plumbing system. In the gravity gradient map, we found that there are also several small linear gravity gradient anomaly patterns in the inside of the large quasi-rectangular pattern, and that one of the linear anomalies runs through multiple gravity anomalies in the vicinity of Aristarchus, Marius and Flamstead volcano complexes. Our concern is whether the volcanisms of these complexes are caused by common factors or not. To clarify this, we firstly estimated the mass and depth of the embedded magmas as well as the directions of the linear gravity anomalies. The results were interpreted by comparing with the chronological and KREEP distribution maps on the lunar surface. We suggested providing mechanisms of the magma to these regions and finally discussed whether the volcanisms of these multiple volcano complex regions are related with each other or not.

Three-dimensional Gravity Inversion with a New Gradient Scheme on Unstructured Grids

NASA Astrophysics Data System (ADS)

Sun, S.; Yin, C.; Gao, X.; Liu, Y.; Zhang, B.

2017-12-01

Stabilized gradient-based methods have been proved to be efficient for inverse problems. Based on these methods, setting gradient close to zero can effectively minimize the objective function. Thus the gradient of objective function determines the inversion results. By analyzing the cause of poor resolution on depth in gradient-based gravity inversion methods, we find that imposing depth weighting functional in conventional gradient can improve the depth resolution to some extent. However, the improvement is affected by the regularization parameter and the effect of the regularization term becomes smaller with increasing depth (shown as Figure 1 (a)). In this paper, we propose a new gradient scheme for gravity inversion by introducing a weighted model vector. The new gradient can improve the depth resolution more efficiently, which is independent of the regularization parameter, and the effect of regularization term will not be weakened when depth increases. Besides, fuzzy c-means clustering method and smooth operator are both used as regularization terms to yield an internal consecutive inverse model with sharp boundaries (Sun and Li, 2015). We have tested our new gradient scheme with unstructured grids on synthetic data to illustrate the effectiveness of the algorithm. Gravity forward modeling with unstructured grids is based on the algorithm proposed by Okbe (1979). We use a linear conjugate gradient inversion scheme to solve the inversion problem. The numerical experiments show a great improvement in depth resolution compared with regular gradient scheme, and the inverse model is compact at all depths (shown as Figure 1 (b)). AcknowledgeThis research is supported by Key Program of National Natural Science Foundation of China (41530320), China Natural Science Foundation for Young Scientists (41404093), and Key National Research Project of China (2016YFC0303100, 2017YFC0601900). ReferencesSun J, Li Y. 2015. Multidomain petrophysically constrained inversion and geology differentiation using guided fuzzy c-means clustering. Geophysics, 80(4): ID1-ID18. Okabe M. 1979. Analytical expressions for gravity anomalies due to homogeneous polyhedral bodies and translations into magnetic anomalies. Geophysics, 44(4), 730-741.

Effect of Baffle on Gravity-Gradient-Excited Slosh Waves and Spacecraft Moment and Angular-Momentum Fluctuations in Microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Lee, C. C.

1995-01-01

The dynamical behavior of fluids affected by the asymmetric gravity gradient acceleration has been investigated. In particular, the effects of surface tension on partially filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank with and without baffles are studied. Results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient acceleration indicate that the gravity gradient acceleration is equivalent to the combined effect of a twisting force and a torsional moment acting on the spacecraft. The results are clearly seen from one-up one-down and one-down one-up oscillations in the cross-section profiles of two bubbles in the vertical (r, z)-plane of the rotating dewar, and from the eccentric contour of the bubble rotating around the axis of the dewar in a horizontal (r, theta)-plane. As the viscous force, between liquid and solid interface, greatly contributes to the damping of slosh wave excitation, a rotating dewar with baffles provides more areas of liquid-solid interface than that of a rotating dewar without baffles. Results show that the damping effect provided by the baffles reduces the amplitude of slosh wave excitation and lowers the degree of asymmetry in liquid-vapor distribution. Fluctuations of angular momentum and fluid moment caused by the slosh wave excited by gravity gradient acceleration with and without baffle boards are also investigated. It is also shown that the damping effect provided by the baffles greatly reduces the amplitudes of angular momentum and fluid moment fluctuations.

Simulation of sloshing dynamics induced forces and torques actuated on dewar container driven by gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1993-01-01

Some experimental spacecraft use superconducting sensors for gyro read-out and so must be maintained at a very low temperature. The boil-off from the cryogenic liquid used to cool the sensors can also be used, as the Gravity Probe B (GP-B) spacecraft does, as propellant to maintain attitude control and drag-free operation of the spacecraft. The cryogenic liquid for such spacecraft is, however, susceptible to both slosh-like motion and non-axisymmetric configurations under the influence of various kinds of gravity jitter and gravity gradient accelerations. Hence, it is important to quantify the magnitude of the liquid-induced perturbations on the spacecraft. We use the example of the GP-B to investigate such perturbations by numerical simulations. For this spacecraft disturbances can be imposed on the liquid by atmospheric drag, spacecraft attitude control maneuvers, and the earth's gravity gradient. More generally, onboard machinery vibrations and crew motion can also create disturbances. Recent studies suggest that high frequency disturbances are relatively unimportant in causing liquid motions in comparison to low frequency ones. The results presented here confirm this conclusion. After an initial calibration period, the GP-B spacecraft rotates in orbit at 0.1 rpm about the tank symmetry axis. For this rotation rate, the equilibrium liquid free surface shape is a 'doughnut' configuration for all residual gravity levels of 10(exp -6) g(sub 0) or less, as shown by experiments and by numerical simulations; furthermore, the superfluid behavior of the 1.8 K liquid helium used in GP-B eliminates temperature gradients and therefore such effects as Marangoni convection do not have to be considered. Classical fluid dynamics theory is used as the basis of the numerical simulations here, since Mason's experiments show that the theory is applicable for cryogenic liquid helium in large containers. To study liquid responses to various disturbances, we investigate and simulate three levels of gravity jitter (10(exp -6), 10(exp -7), and 10(exp -8) g(sub 0)) each at three predominant frequencies (0.1, 1.0, and 10 Hz), combined with a gravity gradient appropriate for the GP-B orbit. Dynamical evolution of sloshing dynamics excited fluid forces and torque fluctuations exerted on the dewar container driven by the combined gravity gradient and jitter accelerations are also investigated and simulated.

Singular boundary method for global gravity field modelling

NASA Astrophysics Data System (ADS)

Cunderlik, Robert

2014-05-01

The singular boundary method (SBM) and method of fundamental solutions (MFS) are meshless boundary collocation techniques that use the fundamental solution of a governing partial differential equation (e.g. the Laplace equation) as their basis functions. They have been developed to avoid singular numerical integration as well as mesh generation in the traditional boundary element method (BEM). SBM have been proposed to overcome a main drawback of MFS - its controversial fictitious boundary outside the domain. The key idea of SBM is to introduce a concept of the origin intensity factors that isolate singularities of the fundamental solution and its derivatives using some appropriate regularization techniques. Consequently, the source points can be placed directly on the real boundary and coincide with the collocation nodes. In this study we deal with SBM applied for high-resolution global gravity field modelling. The first numerical experiment presents a numerical solution to the fixed gravimetric boundary value problem. The achieved results are compared with the numerical solutions obtained by MFS or the direct BEM indicating efficiency of all methods. In the second numerical experiments, SBM is used to derive the geopotential and its first derivatives from the Tzz components of the gravity disturbing tensor observed by the GOCE satellite mission. A determination of the origin intensity factors allows to evaluate the disturbing potential and gravity disturbances directly on the Earth's surface where the source points are located. To achieve high-resolution numerical solutions, the large-scale parallel computations are performed on the cluster with 1TB of the distributed memory and an iterative elimination of far zones' contributions is applied.

Seasonal Dependence of Geomagnetic Active-Time Northern High-Latitude Upper Thermospheric Winds

NASA Astrophysics Data System (ADS)

Dhadly, Manbharat S.; Emmert, John T.; Drob, Douglas P.; Conde, Mark G.; Doornbos, Eelco; Shepherd, Gordon G.; Makela, Jonathan J.; Wu, Qian; Nieciejewski, Richard J.; Ridley, Aaron J.

2018-01-01

This study is focused on improving the poorly understood seasonal dependence of northern high-latitude F region thermospheric winds under active geomagnetic conditions. The gaps in our understanding of the dynamic high-latitude thermosphere are largely due to the sparseness of thermospheric wind measurements. With current observational facilities, it is infeasible to construct a synoptic picture of thermospheric winds, but enough data with wide spatial and temporal coverage have accumulated to construct a meaningful statistical analysis. We use long-term data from eight ground-based and two space-based instruments to derive climatological wind patterns as a function of magnetic local time, magnetic latitude, and season. These diverse data sets possess different geometries and different spatial and solar activity coverage. The major challenge is to combine these disparate data sets into a coherent picture while overcoming the sampling limitations and biases among them. In our previous study (focused on quiet time winds), we found bias in the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) cross-track winds. Here we empirically quantify the GOCE bias and use it as a correction profile for removing apparent bias before empirical wind formulation. The assimilated wind patterns exhibit all major characteristics of high-latitude neutral circulation. The latitudinal extent of duskside circulation expands almost 10∘ from winter to summer. The dawnside circulation subsides from winter to summer. Disturbance winds derived from geomagnetic active and quiet winds show strong seasonal and latitudinal variability. Comparisons between wind patterns derived here and Disturbance Wind Model (DWM07) (which have no seasonal dependence) suggest that DWM07 is skewed toward summertime conditions.

Water mass changes inferred by gravity field variations with GRACE

NASA Astrophysics Data System (ADS)

Fagiolini, Elisa; Gruber, Christian; Apel, Heiko; Viet Dung, Nguyen; Güntner, Andreas

2013-04-01

Since 2002 the Gravity Recovery And Climate Experiment (GRACE) mission has been measuring temporal variations of Earth's gravity field depicting with extreme accuracy how mass is distributed and varies around the globe. Advanced signal separation techniques enable to isolate different sources of mass such as atmospheric and oceanic circulation or land hydrology. Nowadays thanks to GRACE, floods, droughts, and water resources monitoring are possible on a global scale. At GFZ Potsdam scientists have been involved since 2000 in the initiation and launch of the GRACE precursor CHAMP satellite mission, since 2002 in the GRACE Science Data System and since 2009 in the frame of ESÁs GOCE High Processing Facility as well as projected GRACE FOLLOW-ON for the continuation of time variable gravity field determination. Recently GFZ has reprocessed the complete GRACE time-series of monthly gravity field spherical harmonic solutions with improved standards and background models. This new release (RL05) already shows significantly less noise and spurious artifacts. In order to monitor water mass re-distribution and fast moving water, we still need to reach a higher resolution in both time and space. Moreover, in view of disaster management applications we need to act with a shorter latency (current latency standard is 2 months). For this purpose, we developed a regional method based on radial base functions that is capable to compute models in regional and global representation. This new method localizes the gravity observation to the closest regions and omits spatial correlations with farther regions. Additionally, we succeeded to increase the temporal resolution to sub-monthly time scales. Innovative concepts such as Kalman filtering and regularization, along with sophisticated regional modeling have shifted temporal and spatial resolution towards new frontiers. We expect global hydrological models as WHGM to profit from such accurate outcomes. First results comparing the mass changes over the Mekong Delta observed with GRACE with spatial explicit hydraulic simulations of the large scale annual inundation volume during the flood season are presented and discussed.

Measuring attitude with a gradiometer

NASA Technical Reports Server (NTRS)

Sonnabend, David; Born, George H.

1994-01-01

Static attitude estimation and dynamic attitude estimation are used to describe a gradiometer composed of a number of accelerometers that are used to measure a combination of the local gravity gradient and instrument rotation effects. After a series of measures to isolate the gradient, a global mesh of measurements can be obtained that determine the planetary external gravity potential. Orbital and spacecraft models are developed to determine if, when the gravity potential is known, the same measurements, unsupported by any other information can be used to infer the spacecraft attitude.

Analysis of magnetic gradients to study gravitropism.

PubMed

Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

2013-01-01

Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

Geodynamics and temporal variations in the gravity field

NASA Technical Reports Server (NTRS)

Mcadoo, D. C.; Wagner, C. A.

1989-01-01

Just as the Earth's surface deforms tectonically, so too does the gravity field evolve with time. Now that precise geodesy is yielding observations of these deformations it is important that concomitant, temporal changes in the gravity field be monitored. Although these temporal changes are minute they are observable: changes in the J2 component of the gravity field were inferred from satellite (LAGEOS) tracking data; changes in other components of the gravity field would likely be detected by Geopotential Research Mission (GRM), a proposed but unapproved NASA gravity field mission. Satellite gradiometers were also proposed for high-precision gravity field mapping. Using simple models of geodynamic processes such as viscous postglacial rebound of the solid Earth, great subduction zone earthquakes and seasonal glacial mass fluctuations, we predict temporal changes in gravity gradients at spacecraft altitudes. It was found that these proposed gravity gradient satellite missions should have sensitivities equal to or better than 10(exp -4) E in order to reliably detect these changes. It was also found that satellite altimetry yields little promise of useful detection of time variations in gravity.

Gravity anomaly map of Mars and Moon and analysis of Venus gravity field: New analysis procedures

NASA Technical Reports Server (NTRS)

1984-01-01

The technique of harmonic splines allows direct estimation of a complete planetary gravity field (geoid, gravity, and gravity gradients) everywhere over the planet's surface. Harmonic spline results of Venus are presented as a series of maps at spacecraft and constant altitudes. Global (except for polar regions) and local relations of gravity to topography are described.

Gravity Anomaly Intersects Moon Basin

NASA Image and Video Library

2012-12-05

A linear gravity anomaly intersecting the Crisium basin on the nearside of the moon has been revealed by NASA GRAIL mission. The GRAIL gravity gradient data are shown at left, with the location of the anomaly indicated.

Theory of an experiment in an orbiting space laboratory to determine the gravitational constant.

NASA Technical Reports Server (NTRS)

Vinti, J. P.

1972-01-01

An experiment is discussed for determining the gravitational constant with the aid of an isolated system consisting of an artificial satellite moving around an artificial planet. The experiment is to be conducted in a spherical laboratory traveling in an orbit around the earth. Difficulties due to the gravity-gradient term are considered, and the three-tunnel method proposed by Wilk (1969) is examined. The rotation of the sphere is discussed together with aspects of the reference systems used, the equations of motion of the spacecraft and of the test objects, the field from the earth's gravity gradient at the test object, higher harmonic terms in the gravity gradient force, gravitational effects of the spacecraft itself, and a computer simulation.

The effect of spaceflight on the gravity-sensing auxin gradient of roots: GFP reporter gene microscopy on orbit

PubMed Central

Ferl, Robert J; Paul, Anna-Lisa

2016-01-01

Our primary aim was to determine whether gravity has a direct role in establishing the auxin-mediated gravity-sensing system in primary roots. Major plant architectures have long been thought to be guided by gravity, including the directional growth of the primary root via auxin gradients that are then disturbed when roots deviate from the vertical as a gravity sensor. However, experiments on the International Space Station (ISS) now allow physical clarity with regard to any assumptions regarding the role of gravity in establishing fundamental root auxin distributions. We examined the spaceflight green fluorescent protein (GFP)-reporter gene expression in roots of transgenic lines of Arabidopsis thaliana: pDR5r::GFP, pTAA1::TAA1–GFP, pSCR::SCR–GFP to monitor auxin and pARR5::GFP to monitor cytokinin. Plants on the ISS were imaged live with the Light Microscopy Module (LMM), and compared with control plants imaged on the ground. Preserved spaceflight and ground control plants were examined post flight with confocal microscopy. Plants on orbit, growing in the absence of any physical reference to the terrestrial gravity vector, displayed typically “vertical” distribution of auxin in the primary root. This confirms that the establishment of the auxin-gradient system, the primary guide for gravity signaling in the root, is gravity independent. The cytokinin distribution in the root tip differs between spaceflight and the ground controls, suggesting spaceflight-induced features of root growth may be cytokinin related. The distribution of auxin in the gravity-sensing portion of the root is not dependent on gravity. Spaceflight appears benign to auxin and its role in the development of the primary root tip, whereas spaceflight may influence cytokinin-associated processes. PMID:28725721

Crustal architecture of the Pensacola-Pole Basin region in East Antarctica

NASA Astrophysics Data System (ADS)

Ferraccioli, F.; Jordan, T. A.; Forsberg, R.; Olesen, A. V.; Matsuoka, K.; Casal, T. G. D.

2017-12-01

During the 2015-2016 Antarctic campaign we flew a major aerogeophysical survey over the South Pole frontier, collecting ca 30,000 line km of new radio echo sounding, laser altimetry, airborne gravity and aeromagnetic data. The main aim of the PolarGAP project, supported by ESA was to fill in the data void in GOCE satellite gravity south of 83.3°S. Here we present the ice thickness, bedrock topography, and gravity and magnetic anomaly images derived from the survey and interpret these to investigate the crustal architecture and tectonic evolution of the South Pole region. Linear free-air gravity lows within the Pensacola-Pole Basin are interpreted as a system of glacially overdeepened grabens flanked by uplifted horst blocks, including the Pensacola Mountains, Patuxent Range and the Argentine Range. We link the grabens to the Jurassic Transantarctic rift system, which is also associated with voluminous tholeiitic magmatism of the Ferrar Large Igneous province. To investigate the potential influence of basement provinces and their tectonic boundaries on the Pensacola-Pole basin region, we combined PolarGAP aeromagnetic data with existing aeromagnetic datasets and satellite magnetic (MF7) patterns. Our magnetic compilation reveals that part of the eastern flank of the basin is controlled by a major inherited crustal boundary. The boundary is interpreted here as the southern edge of a hitherto unrecognised composite Precambrian microplate, extending from the Shackleton Range to the Pensacola-Pole basin itself. This inferred microplate forms a key missing link between the southern sector of the subduction-related Ross Orogen and the Pan-African age collisional suture and transpressional shear zones identified in the Shackleton Range.

Swarm- Validation of Star Tracker and Accelerometer Data

NASA Astrophysics Data System (ADS)

Schack, Peter; Schlicht, Anja; Pail, Roland; Gruber, Thomas

2016-08-01

The ESA Swarm mission is designed to advance studies in the field of magnetosphere, thermosphere and gravity field. To be fortunate on this task precise knowledge of the orientation of the Swarm satellites is required together with knowledge about external forces acting on the satellites. The key sensors providing this information are the star trackers and the accelerometers. Based on star tracker studies conducted by the Denmark Technical University (DTU), we found interesting patterns in the interboresight angles on all three satellites, which are partly induced by temperature alterations. Additionally, structures of horizontal stripes seem to be caused by the unique distribution of observed stars on the charge-coupled device of the star trackers. Our accelerometer analyses focus on spikes and pulses in the observations. Those short term events on Swarm might originate from electrical processes introduced by sunlight illuminating the nadir foil. Comparisons to GOCE and GRACE are included.

Mean Dynamic Topography of the Arctic Ocean

NASA Technical Reports Server (NTRS)

Farrell, Sinead Louise; Mcadoo, David C.; Laxon, Seymour W.; Zwally, H. Jay; Yi, Donghui; Ridout, Andy; Giles, Katherine

2012-01-01

ICESat and Envisat altimetry data provide measurements of the instantaneous sea surface height (SSH) across the Arctic Ocean, using lead and open water elevation within the sea ice pack. First, these data were used to derive two independent mean sea surface (MSS) models by stacking and averaging along-track SSH profiles gathered between 2003 and 2009. The ICESat and Envisat MSS data were combined to construct the high-resolution ICEn MSS. Second, we estimate the 5.5-year mean dynamic topography (MDT) of the Arctic Ocean by differencing the ICEn MSS with the new GOCO02S geoid model, derived from GRACE and GOCE gravity. Using these satellite-only data we map the major features of Arctic Ocean dynamical height that are consistent with in situ observations, including the topographical highs and lows of the Beaufort and Greenland Gyres, respectively. Smaller-scale MDT structures remain largely unresolved due to uncertainties in the geoid at short wavelengths.

Precise Orbit Determination of the GOCE Re-Entry Phase

NASA Astrophysics Data System (ADS)

Gini, Francesco; Otten, Michiel; Springer, Tim; Enderle, Werner; Lemmens, Stijn; Flohrer, Tim

2015-03-01

During the last days of the GOCE mission, after the GOCE spacecraft ran out of fuel, it slowly decayed before finally re-entering the atmosphere on the 11th November 2013. As an integrated part of the AOCS, GOCE carried a GPS receiver that was in operations during the re-entry phase. This feature provided a unique opportunity for Precise Orbit Determination (POD) analysis. As part of the activities carried out by the Navigation Support Office (HSO-GN) at ESOC, precise ephemerides of the GOCE satellite have been reconstructed for the entire re-entry phase based on the available GPS observations of the onboard LAGRANGE receiver. All the data available from the moment the thruster was switched off on the 21st of October 2013 to the last available telemetry downlink on the 10th November 2013 have been processed, for a total of 21 daily arcs. For this period a dedicated processing sequence has been defined and implemented within the ESA/ESOC NAvigation Package for Earth Observation Satellites (NAPEOS) software. The computed results show a post-fit RMS of the GPS undifferenced carrier phase residuals (ionospheric-free linear combination) between 6 and 14 mm for the first 16 days which then progressively increases up to about 80 mm for the last available days. An orbit comparison with the Precise Science Orbits (PSO) generated at the Astronomical Institute of the University of Bern (AIUB, Bern, Switzerland) shows an average difference around 9 cm for the first 8 daily arcs and progressively increasing up to 17 cm for the following days. During this reentry phase (21st of October - 10th November 2013) a substantial drop in the GOCE altitude is observed, starting from about 230 km to 130 km where the last GPS measurements were taken. During this orbital decay an increment of a factor of 100 in the aerodynamic acceleration profile is observed. In order to limit the mis-modelling of the non-gravitational forces (radiation pressure and aerodynamic effects) the newly developed software ARPA (Aerodynamics and Radiation Pressure Analysis) has been adopted to compute the forces acting on GOCE. An overview of the software techniques and the results of its implementation is presented in this paper. The use of the ARPA modelling leads to an average reduction of the carrier phase post-fit RMS of about 2 mm and decrement of the difference with the PSO orbits of more than 1 cm.

Interpretation of Local Gravity Anomalies in Northern New York

NASA Astrophysics Data System (ADS)

Revetta, F. A.

2004-05-01

About 10,000 new gravity measurements at a station spacing of 1 to 2 Km were made in the Adirondack Mountains, Lake Champlain Valley, St. Lawrence River Valley and Tug Hill Plateau. These closely spaced gravity measurements were compiled to construct computer contoured gravity maps of the survey areas. The gravity measurements reveal local anomalies related to seismicity, faults, mineral resources and gas fields that are not seen in the regional gravity mapping. In northern New York gravity and seismicity maps indicate epicenters are concentrated in areas of the most pronounced gravity anomalies along steep gravity gradients. Zones of weakness along the contacts of these lithologies of different density could possibly account for the earthquakes in this high stress area. Also, a computer contoured gravity map of the 5.3 magnitude Au Sable Forks earthquake of April 20, 2002 indicates the epicenter lies along a north-south trending gravity gradient produced by a high angle fault structure separating a gravity low in the west from high gravity in the east. In the St. Lawrence Valley, the Carthage-Colton Mylonite Zone, a major northeast trending structural boundary between the Adirondack Highlands and Northwest Lowlands, is represented as a steep gravity gradient extending into the eastern shore of Lake Ontario. At Russell, New York near the CCMZ, a small circular shaped gravity high coincides with a cluster of earthquakes. The coincidence of the epicenters over the high may indicate stress amplification at the boundary of a gabbro pluton. The Morristown fault located in the Morristown Quadrangle in St. Lawrence County produces both gravity and magnetic anomalies due to Precambrian Basement faulting. This faulting indicates control of the Morristown fault in the overlying Paleozoics by the Precambrian faults. Gravity and magnetic anomalies also occur over proposed extensions of the Gloucester and Winchester Springs faults into northern New York. Gravity and magnetic surveys were conducted at the closed Benson Mines magnetite mine and the Zinc Mines at Balmat, New York. The gravity and magnetic anomalies at Benson Mines indicate that significant amounts of magnetite remain in the subsurface and the steep gradients indicate a shallow depth. A gravity high of 35 gravity units in the Sylvia Lake Zinc District at Balmat, New York occurs over the upper marble and a 100 gu anomaly occurs just northeast of the zinc district. Abandoned natural gas fields exist along the southern and southwestern boundary of the Tug Hill Plateau. Gravity surveys were conducted in the vicinity of three of these gas fields in the Tug Hill Plateau (Camden, Sandy Creek and Pulaski). The Tug Hill Plateau is thought to be an uplifted-fault-bounded block which, if correct, might account for the existence of those gas fields. The trends of the gravity contours on the gravity maps lends credence to the fault interpretation. Also gravity and magnetic traverses were conducted across faults in the Trenton-Black River. These traverses show gravity anomalies across the faults which indicate control by faulting in the Precambrian.

System noise analysis of the dumbbell tethered satellite for gravity-gradient measurements

NASA Technical Reports Server (NTRS)

Colombo, G.

1979-01-01

An analysis of the dumbbell gravity gradiometer concept for measuring short wavelength variations in the earth's gravity gradient is presented. Variations in the gradient are recorded by measuring tension variations in a vertically stabilized satellite consisting of heavy masses connected by a long wire or rod. Tension noise arises from the excitation of various mechanical oscillations of the system. The principal noise sources that were identified are fluctuations in atmospheric drag heating and drag force resulting from density variations and winds. Approximate analytical expressions are presented for the tension noise as a function of the system design parameters for various possible configurations. Computer simulations using numerical integration were performed to study the tension noise for several sample cases. Three designs consistent with Shuttle launch capabilities are discussed.

Proposed gravity-gradient dynamics experiments in lunar orbit using the RAE-B spacecraft

NASA Technical Reports Server (NTRS)

Blanchard, D. L.; Walden, H.

1973-01-01

A series of seven gravity-gradient dynamics experiments is proposed utilizing the Radio Astronomy Explorer (RAE-B) spacecraft in lunar orbit. It is believed that none of the experiments will impair the spacecraft structure or adversely affect the continuation of the scientific mission of the satellite. The first experiment is designed to investigate the spacecraft dynamical behavior in the absence of libration damper action and inertia. It requires stable gravity-gradient capture of the spacecraft in lunar orbit with small amplitude attitude librations as a prerequisite. Four subsequent experiments involve partial retraction, ultimately followed by full redeployment, of one or two of the 230-meter booms forming the lunar-directed Vee-antenna. These boom length change operations will induce moderate amplitude angular librations of the spacecraft.

Evaluation of Gravitational Field Models Based on the Laser Range Observation of Low Earth Orbit Satellites

NASA Astrophysics Data System (ADS)

Wang, H. B.; Zhao, C. Y.; Zhang, W.; Zhan, J. W.; Yu, S. X.

2015-09-01

The Earth gravitational filed model is a kind of important dynamic model in satellite orbit computation. In recent years, several space gravity missions have obtained great success, prompting a lot of gravitational filed models to be published. In this paper, 2 classical models (JGM3, EGM96) and 4 latest models, including EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008 are evaluated by being employed in the precision orbit determination (POD) and prediction, based on the laser range observation of four low earth orbit (LEO) satellites, including CHAMP, GFZ-1, GRACE-A, and SWARM-A. The residual error of observation in POD is adopted to describe the accuracy of six gravitational field models. We show the main results as follows: (1) for LEO POD, the accuracies of 4 latest models (EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008) are at the same level, and better than those of 2 classical models (JGM3, EGM96); (2) If taking JGM3 as reference, EGM96 model's accuracy is better in most situations, and the accuracies of the 4 latest models are improved by 12%-47% in POD and 63% in prediction, respectively. We also confirm that the model's accuracy in POD is enhanced with the increasing degree and order if they are smaller than 70, and when they exceed 70 the accuracy keeps stable, and is unrelated with the increasing degree, meaning that the model's degree and order truncated to 70 are sufficient to meet the requirement of LEO orbit computation with centimeter level precision.

Gravity and the geoid in the Nepal Himalaya

NASA Technical Reports Server (NTRS)

Bilham, Roger

1992-01-01

Materials within the Himalaya are rising due to convergence between India and Asia. If the rate of erosion is comparable to the rate of uplift the mean surface elevation will remain constant. Any slight imbalance in these two processes will lead to growth or attrition of the Himalaya. The process of uplift of materials within the Himalaya coupled with surface erosion is similar to the advance of a glacier into a region of melting. If the melting rate exceeds the rate of downhill motion of the glacier then the terminus of the glacier will receed up-valley despite the downhill motion of the bulk of the glacier. Thus although buried rocks, minerals and surface control points in the Himalaya are undoubtably rising, the growth or collapse of the Himalaya depends on the erosion rate which is invisible to geodetic measurements. Erosion rates are currently estimated from suspended sediment loads in rivers in the Himalaya. These typically underestimate the real erosion rate since bed-load is not measured during times of heavy flood, and it is difficult to integrate widely varying suspended load measurements over many years. An alternative way to measure erosion rate is to measure the rate of change of gravity in a region of uplift. If a control point moves vertically it should be accompanied by a reduction in gravity as the point moves away from the Earth's center of mass. There is a difference in the change of gravity between uplift with and without erosion corresponding to the difference between the free-air gradient and the gradient in the acceleration due to gravity caused by a corresponding thickness of rock. Essentially gravity should change precisely in accord with a change in elevation of the point in a free-air gradient if erosion equals uplift rate. We were funded by NASA to undertake a measurement of absolute gravity simultaneously with measurements of GPS height within the Himalaya. Since both absolute gravity and time are known in an absolute sense to 1 part in 10(exp 10) it is possible to estimate gravity with a precision of 0.1 mu gal. Known systematic errors reduce the measurement to an absolute uncertainty of 6 mu gal. The free air gradient at the point of measurement is typically about 3 mu gals/cm. At Simikot where our experiment was conducted we determined a vertical gravity gradient of 4.4 mu gals/cm.

Using absolute gravimeter data to determine vertical gravity gradients

USGS Publications Warehouse

Robertson, D.S.

2001-01-01

The position versus time data from a free-fall absolute gravimeter can be used to estimate the vertical gravity gradient in addition to the gravity value itself. Hipkin has reported success in estimating the vertical gradient value using a data set of unusually good quality. This paper explores techniques that may be applicable to a broader class of data that may be contaminated with "system response" errors of larger magnitude than were evident in the data used by Hipkin. This system response function is usually modelled as a sum of exponentially decaying sinusoidal components. The technique employed here involves combining the x0, v0 and g parameters from all the drops made during a site occupation into a single least-squares solution, and including the value of the vertical gradient and the coefficients of system response function in the same solution. The resulting non-linear equations must be solved iteratively and convergence presents some difficulties. Sparse matrix techniques are used to make the least-squares problem computationally tractable.

Mechanism of dynamic reorientation of cortical microtubules due to mechanical stress.

PubMed

Muratov, Alexander; Baulin, Vladimir A

2015-12-01

Directional growth caused by gravitropism and corresponding bending of plant cells has been explored since 19th century, however, many aspects of mechanisms underlying the perception of gravity at the molecular level are still not well known. Perception of gravity in root and shoot gravitropisms is usually attributed to gravisensitive cells, called statocytes, which exploit sedimentation of macroscopic and heavy organelles, amyloplasts, to sense the direction of gravity. Gravity stimulus is then transduced into distal elongation zone, which is several mm far from statocytes, where it causes stretching. It is suggested that gravity stimulus is conveyed by gradients in auxin flux. We propose a theoretical model that may explain how concentration gradients and/or stretching may indirectly affect the global orientation of cortical microtubules, attached to the cell membrane and induce their dynamic reorientation perpendicular to the gradients. In turn, oriented microtubule arrays direct the growth and orientation of cellulose microfibrils, forming part of the cell external skeleton and determine the shape of the cell. Reorientation of microtubules is also observed in reaction to light in phototropism and mechanical bending, thus suggesting universality of the proposed mechanism. Copyright © 2015 Elsevier B.V. All rights reserved.

Horizontal gravity gradient - An aid to the definition of crustal structure in North America

NASA Technical Reports Server (NTRS)

Sharpton, V. L.; Grieve, R. A. F.; Thomas, M. D.; Halpenny, J. F.

1987-01-01

A map of the magnitude of the horizontal Bouguer gravity gradient over the North American continent is used to delineate lateral discontinuities in upper crustal density and/or thickness associated with such processes as suturing and rifting. The usefulness of gradient trends in mapping major structural boundaries, which are sometimes poorly exposed or completely buried, is demonstrated by examples such as the buried southward extension of the Grenville Front and buried boundaries of the Superior Province. Gradient trends also draw attention to poorly known structures, which may have major tectonic significance, and to a continent-wide structural fabric, which may provide a record of the tectonic growth of the North American continent.

Consequences of flight height and line spacing on airborne (helicopter) gravity gradient resolution in the Great Sand Dunes National Park and Preserve, Colorado

USGS Publications Warehouse

Kass, M. Andy

2013-01-01

Line spacing and flight height are critical parameters in airborne gravity gradient surveys; the optimal trade-off between survey costs and desired resolution, however, is different for every situation. This article investigates the additional benefit of reducing the flight height and line spacing though a study of a survey conducted over the Great Sand Dunes National Park and Preserve, which is the highest-resolution public-domain airborne gravity gradient data set available, with overlapping high- and lower-resolution surveys. By using Fourier analysis and matched filtering, it is shown that while the lower-resolution survey delineates the target body, reducing the flight height from 80 m to 40 m and the line spacing from 100 m to 50 m improves the recoverable resolution even at basement depths.

Preliminary isostatic residual gravity map of the Tremonton 30' x 60' quadrangle, Box Elder and Cache Counties, Utah, and Franklin and Oneida Counties, Idaho

USGS Publications Warehouse

Langenheim, Victoria; Oaks, R.Q.; Willis, H.; Hiscock, A.I.; Chuchel, Bruce A.; Rosario, Jose J.; Hardwick, C.L.

2014-01-01

A new isostatic residual gravity map of the Tremonton 30' x 60' quadrangle of Utah is based on compilation of preexisting data and new data collected by the Utah and U.S. Geological Surveys. Pronounced gravity lows occur over North Bay, northwest of Brigham City, and Malad and Blue Creek Valleys, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Promontory, Clarkston, and Wellsville Mountains. The highest gravity values are located in southern Curlew Valley and may be produced in part by deeper crustal density variations or crustal thinning. Steep, linear gravity gradients coincide with Quaternary faults bounding the Wellsville and Clarkston Mountains. Steep gradients also coincide with the margins of the Promontory Mountains, Little Mountain, West Hills, and the eastern margin of the North Promontory Mountains and may define concealed basin-bounding faults.

Physics of Artificial Gravity

NASA Technical Reports Server (NTRS)

Bukley, Angie; Paloski, William; Clement, Gilles

2006-01-01

This chapter discusses potential technologies for achieving artificial gravity in a space vehicle. We begin with a series of definitions and a general description of the rotational dynamics behind the forces ultimately exerted on the human body during centrifugation, such as gravity level, gravity gradient, and Coriolis force. Human factors considerations and comfort limits associated with a rotating environment are then discussed. Finally, engineering options for designing space vehicles with artificial gravity are presented.

Dynamics of a gravity-gradient stabilized flexible spacecraft

NASA Technical Reports Server (NTRS)

Meirovitch, L.; Juang, J. N.

1974-01-01

The dynamics of gravity-gradient stabilized flexible satellite in the neighborhood of a deformed equilibrium configuration are discussed. First the equilibrium configuration was determined by solving a set of nonlinear differential equations. Then stability of motion about the deformed equilibrium was tested by means of the Liapunov direct method. The natural frequencies of oscillation of the complete structure were calculated. The analysis is applicable to the RAE/B satellite.

Bubble behavior in molten glass in a temperature gradient. [in reduced gravity rocket experiment

NASA Technical Reports Server (NTRS)

Meyyappan, M.; Subramanian, R. S.; Wilcox, W. R.; Smith, H.

1982-01-01

Gas bubble motion in a temperature gradient was observed in a sodium borate melt in a reduced gravity rocket experiment under the NASA SPAR program. Large bubbles tended to move faster than smaller ones, as predicted by theory. When the bubbles contacted a heated platinum strip, motion virtually ceased because the melt only imperfectly wets platinum. In some cases bubble diameter increased noticeably with time.

Atmospheric gravity wave detection following the 2011 Tohoku earthquakes combining COSMIC occultation and GPS observations

NASA Astrophysics Data System (ADS)

Yan, X.; Tao, Y.; Xia, C.; Qi, Y.; Zuo, X.

2017-12-01

Several studies have reported the earthquake-induced atmospheric gravity waves detected by some new technologies such as airglow (Makela et al., 2011), GOCE (Garcia et al., 2013), GRACE (Yang et al., 2014), F3/C radio occultation sounding (Coïsson et al., 2015). In this work, we collected all occultation events on 11 March, and selected four events to analyze at last. The original and filtered podTEC is represented as function of the altitude of the impact parameter and UT of the four events. Then, the travel time diagrams of filtered podTEC derived from the events were analyzed. The occultation signal from one event (marked as No.73) is consistent with the previous results reported by Coïsson. 2015, which is corresponds to the ionospheric signal induced from tsunami gravity wave. What is noticeable, in this work, is that three occultation events of No.403, 77 and 118 revealed a disturbance of atmospheric gravity wave with velocity 300m/s, preceding the tsunami. It would probably be correspond to the gravity waves caused by seismic rupture but not tsunami. In addition, it can be seen that the perturbation height of occultation observation TEC is concentrated at 200-400km, corresponding ionosphere F region. The signals detected above are compared with GPS measurements of TEC from GEONET and IGS. From GPS data, traveling ionospheric disturbances were observed spreading out from the epicenter as a quasi-circular propagation pattern with the time. Exactly, we observed an acoustic wave coupled with Rayleigh wave starting from the epicenter with a speed of 3.0km/s and a superimposed acoustic-gravity wave moving with a speed of 800m/s. The acoustic-gravity wave generated at the epicenter and gradually attenuated 800km away, then it is replaced by a gravity wave coupled with the tsunami that moves with a speed of between 100 and 300m/s. It is necessary to confirm the propagation process of the waves if we attempt to evaluate the use of ionospheric seismology as a potential support for future earthquake and tsunami warning systems. Acknowledgement: This work is supported by NSFC (41604135), China Postdoctoral Science Foundation funded project (1231703), State Key Laboratory of Earthquake Dynamics (LED2015B04), Key Laboratory of Earth and Planetary Physics, Hubei Subsurface Multi-scale Imaging Key Laboratory.

Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method

NASA Astrophysics Data System (ADS)

Sun, Yong; Meng, Zhaohai; Li, Fengting

2018-03-01

Following the development of gravity gradiometer instrument technology, the full tensor gravity (FTG) data can be acquired on airborne and marine platforms. Large-scale geophysical data can be obtained using these methods, making such data sets a number of the "big data" category. Therefore, a fast and effective inversion method is developed to solve the large-scale FTG data inversion problem. Many algorithms are available to accelerate the FTG data inversion, such as conjugate gradient method. However, the conventional conjugate gradient method takes a long time to complete data processing. Thus, a fast and effective iterative algorithm is necessary to improve the utilization of FTG data. Generally, inversion processing is formulated by incorporating regularizing constraints, followed by the introduction of a non-monotone gradient-descent method to accelerate the convergence rate of FTG data inversion. Compared with the conventional gradient method, the steepest descent gradient algorithm, and the conjugate gradient algorithm, there are clear advantages of the non-monotone iterative gradient-descent algorithm. Simulated and field FTG data were applied to show the application value of this new fast inversion method.

Co-Seismic Gravity Gradient Changes of the 2006-2007 Great Earthquakes in the Central Kuril Islands from GRACE Observations

NASA Astrophysics Data System (ADS)

Rahimi, A.; Shahrisvand, M.

2017-09-01

GRACE satellites (the Gravity Recovery And climate Experiment) are very useful sensors to extract gravity anomalies after earthquakes. In this study, we reveal co-seismic signals of the two combined earthquakes, the 2006 Mw8.3 thrust and 2007 Mw8.1 normal fault earthquakes of the central Kuril Islands from GRACE observations. We compute monthly full gravitational gradient tensor in the local north-east-down frame for Kuril Islands earthquakes without spatial averaging and de-striping filters. Some of gravitational gradient components (e.g. ΔVxx, ΔVxz) enhance high frequency components of the earth gravity field and reveal more details in spatial and temporal domain. Therefore, co-seismic activity can be better illustrated. For the first time, we show that the positive-negative-positive co-seismic ΔVxx due to the Kuril Islands earthquakes ranges from - 0.13 to + 0.11 milli Eötvös, and ΔVxz shows a positive-negative-positive pattern ranges from - 0.16 to + 0.13 milli Eötvös, agree well with seismic model predictions.

Using gravity as a proxy for stress accumulation in complex fault systems

NASA Astrophysics Data System (ADS)

Hayes, Tyler Joseph

The gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks. A general method for calculating the total, dilatational, and free-air gravity for fault systems with arbitrary geometry, slip motion, and number of fault segments is presented. The technique uses a Green's function approach for a fault buried within an elastic half-space with an underlying driver plate forcing the system. A stress-evolution time-dependent earthquake fault model was used to create simulated slip histories over the San Andreas Fault network in California. Using a sum of the gravity signals from each fault segment in the model, via coseismic gravity Green's functions, a time-dependent gravity model was created. The steady-state gravity from the long term plate motion generates a signal over five years with magnitudes of +/- ˜2 muGal; the current limit of portable instrument observations. Moderate to large events generate signal magnitudes in the range of ˜10 muGal to ˜80 muGal, well within the range of ground based observations. The complex fault network geometry of California significantly affects the spatial extent of the gravity signal from the three events studied. Statistical analysis of 55 000 years of simulated slip histories were used to investigate the use of the dilatational gravity signal as a proxy for precursory stress and strain changes. Results indicate that the precursory dilatational gravity signal is dependent upon the fault orientation with respect the tectonic loading plate velocity. This effect is interpreted as a consequence of preferential amplification of the shear stress or reduction of the normal stress, depending on the steady-state regime investigated. Finally, solutions for the corresponding gravity gradients of the coseismic dilatational gravity signals are developed for a vertical strike-slip fault. Gravity gradient solutions exhibit similar spatial distributions as those calculated for Coulomb stress changes, reflecting their physical relationship to the stress changes. The magnitude of the signals, on the order of 1 x 10-4 E, are beyond the resolution of typical exploration instruments at the present time. Keywords. numerical solutions; seismic cycle; gravity; gravity gradients; time variable gravity; earthquake interaction; forecasting; and prediction

Perimeter Security and Intruder Detection Using Gravity Gradiometry: A Feasibility Study

DTIC Science & Technology

2011-03-24

design, build, and operate, and it is usually not feasible to integrate new technology into an already existing system. So far, however, the...gravitational gradients is not a new concept and has been applied across a variety of industries. The first device for gravity gradient measurement was the...which generates a new simulated GGI reading. The program loops for a set number of iterations, and then ends by calculating algorithm performance

Stellar occultation spikes as probes of atmospheric structure and composition. [for Jupiter

NASA Technical Reports Server (NTRS)

Elliot, J. L.; Veverka, J.

1976-01-01

The characteristics of spikes observed in occultation light curves of Beta Scorpii by Jupiter are discussed in terms of the gravity-gradient model. The occultation of Beta Sco by Jupiter on May 13, 1971, is reviewed, and the gravity-gradient model is defined as an isothermal atmosphere of constant composition in which the refractivity is a function only of the radial coordinate from the center of refraction, which is assumed to lie parallel to the local gravity gradient. The derivation of the occultation light curve in terms of the atmosphere, the angular diameter of the occulted star, and the occultation geometry is outlined. It is shown that analysis of the light-curve spikes can yield the He/H2 concentration ratio in a well-mixed atmosphere, information on fine-scale atmospheric structure, high-resolution images of the occulted star, and information on ray crossing. Observational limits are placed on the magnitude of horizontal refractivity gradients, and it is concluded that the spikes are the result of local atmospheric density variations: atmospheric layers, density waves, or turbulence.

A simple Bouguer gravity anomaly map of southwestern Saudi Arabia and an initial interpretation

USGS Publications Warehouse

Gettings, M.E.

1983-01-01

Approximately 2,200 gravity stations on a 10-km2 grid were used to construct a simple Bouguer gravity anomaly map at 1:2,000,000 scale along a 150-km-wide by 850-km-long strip of the Arabian Peninsula from Sanam, southwest of Ar Riyad, through the Farasan Islands and including offshore islands, the coastal plain, and the Hijaz-Asir escarpment from Jiddah to the Yemen border. On the Precambrian Arabian Shield, local positive gravity anomalies are associated with greenstone belts, gneiss domes, and the Najd fault zones. Local negative gravity anomalies correlate with granitic plutonic rocks. A steep gravity gradient of as much as 4 mgal-km-1 marks the continental margin on the coastal plain near the southwestern end of the strip. Bouguer gravity anomaly values range from -10 to +40 mgal southwest of this gradient and from -170 to -100 mgal in a 300-km-wide gravity minimum northeast of the gradient. Farther northeast, the minimum is terminated by a regional gradient of about 0.1 mgal-km-1 that increases toward the Arabian Gulf. The regional gravity anomaly pattern has been modeled by using seismic refraction and Raleigh wave studies, heat-flow measurements, and isostatic considerations as constraints. The model is consistent with the hypothesis of upwelling of hot mantle material beneath the Red Sea and lateral mantle flow beneath the Arabian plate. The model yields best-fitting average crustal densities of 2.80 g-cm-3 (0-20 km depth) and 3.00 g-cm-3 (20-40 km depth) southwest of the Nabitah suture zone and 2.74 g-cm-3 (0-20 km depth) and 2.94 g-cm-3 (20-40 km depth) northeast of the suture zone. The gravity model requires that the crust be about 20 km thick at the continental margin and that the lower crust between the margin and Bishah (lat 20? N., long 42.5? E.) be somewhat denser than the lower crust to the northeast. Detailed correlations between 1:250,000- and 1:500,000-scale geologic maps and the gravity anomaly map suggest that the greenstone belts associated with gravity highs contain a large proportion of gabbroic and dioritic intrusive rocks and that the bulk density of the upper crust associated with some of the batholithic complexes has been lowered by the large-scale intrusion of granitic material at depth, as well as by that exposed at the surface. A comparison of known base and precious metals occurrences with the Bouguer gravity anomaly field shows, in some cases, a correlation between such occurrences and the features of the gravity anomaly map. Several areas were identified between known mineral occurrences along gravity-defined structures that may contain mineral deposits if the lithologic environment is favorable.

Downward continuation of the free-air gravity anomalies to the ellipsoid using the gradient solution and terrain correction: An attempt of global numerical computations

NASA Technical Reports Server (NTRS)

Wang, Y. M.

1989-01-01

The formulas for the determination of the coefficients of the spherical harmonic expansion of the disturbing potential of the earth are defined for data given on a sphere. In order to determine the spherical harmonic coefficients, the gravity anomalies have to be analytically downward continued from the earth's surface to a sphere-at least to the ellipsoid. The goal is to continue the gravity anomalies from the earth's surface downward to the ellipsoid using recent elevation models. The basic method for the downward continuation is the gradient solution (the g sub 1 term). The terrain correction was also computed because of the role it can play as a correction term when calculating harmonic coefficients from surface gravity data. The fast Fourier transformation was applied to the computations.

The dynamics and optimal control of spinning spacecraft and movable telescoping appendages, part B: Effect of gravity-gradient torques on the dynamics of a spinning spacecraft with telescoping appendages

NASA Technical Reports Server (NTRS)

Bainum, P. M.; Rajan, M.

1977-01-01

The effects of gravity gradient torques during boom deployment maneuvers of a spinning spacecraft are examined. Configurations where the booms extended only along the hub principal axes and where one or two booms are offset from the principal axes were considered. For the special case of symmetric deployment (principal axes booms) the stability boundaries are determined, and a stability chart is used to study the system behavior. Possible cases of instability during this type of maneuver are identified. In the second configuration an expression for gravity torque about the hub center of mass was developed. The nonlinear equations of motion are solved numerically, and the substantial influence of the gravity torque during asymmetric deployment maneuvers is indicated.

Principal facts for gravity stations in the vicinity of San Bernardino, Southern California

USGS Publications Warehouse

Anderson, Megan L.; Roberts, Carter W.; Jachens, Robert C.

2000-01-01

New gravity measurements in the vicinity of San Bernardino, California were collected to help define the characteristics of the Rialto-Colton fault. The data were processed using standard reduction formulas and parameters. Rock properties such as lithology, magnetic susceptibility and density also were measured at several locations. Rock property measurements will be helpful for future modeling and density inversion calculations from the gravity data. On both the Bouguer and isostatic gravity maps, a prominent, 13-km long (8 mi), approximately 1-km (0.62 mi) wide gradient with an amplitude of 7 mGal, down to the northeast, is interpreted as the gravity expression of the Rialto-Colton fault. The gravity gradient strikes in a northwest direction and runs from the San Jacinto fault zone at its south end to San Sevine Canyon at the foot of the San Gabriel mountains at its north end. The Rialto-Colton fault has experienced both right-lateral strike-slip and normal fault motion that has offset basement rocks; therefore it is interpreted as a major, through-going fault.

Improvement of Latvian Geoid Model Using GNSS/Levelling, GOCE Data and Vertical Deflection Measurements

NASA Astrophysics Data System (ADS)

Janpaule, Inese; Haritonova, Diana; Balodis, Janis; Zarins, Ansis; Silabriedis, Gunars; Kaminskis, Janis

2015-03-01

Development of a digital zenith telescope prototype, improved zenith camera construction and analysis of experimental vertical deflection measurements for the improvement of the Latvian geoid model has been performed at the Institute of Geodesy and Geoinformatics (GGI), University of Latvia. GOCE satellite data was used to compute geoid model for the Riga region, and European gravimetric geoid model EGG97 and 102 data points of GNSS/levelling were used as input data in the calculations of Latvian geoid model.

Geophysical investigation using gravity data in Kinigi geothermal field, northwest Rwanda

NASA Astrophysics Data System (ADS)

Uwiduhaye, Jean d.'Amour; Mizunaga, Hideki; Saibi, Hakim

2018-03-01

A land gravity survey was carried out in the Kinigi geothermal field, Northwest Rwanda using 184 gravity stations during August and September, 2015. The aim of the gravity survey was to understand the subsurface structure and its relation to the observed surface manifestations in the study area. The complete Bouguer Gravity anomaly was produced with a reduction density of 2.4 g/cm3. Bouguer anomalies ranging from -52 to -35 mGals were observed in the study area with relatively high anomalies in the east and northwest zones while low anomalies are observed in the southwest side of the studied area. A decrease of 17 mGals is observed in the southwestern part of the study area and caused by the low-density of the Tertiary rocks. Horizontal gradient, tilt angle and analytical signal methods were applied to the observed gravity data and showed that Mubona, Mpenge and Cyabararika surface springs are structurally controlled while Rubindi spring is not. The integrated results of gravity gradient interpretation methods delineated a dominant geological structure trending in the NW-SE, which is in agreement with the regional geological trend. The results of this gravity study will help aid future geothermal exploration and development in the Kinigi geothermal field.

Calibration of a rotating accelerometer gravity gradiometer using centrifugal gradients

NASA Astrophysics Data System (ADS)

Yu, Mingbiao; Cai, Tijing

2018-05-01

The purpose of this study is to calibrate scale factors and equivalent zero biases of a rotating accelerometer gravity gradiometer (RAGG). We calibrate scale factors by determining the relationship between the centrifugal gradient excitation and RAGG response. Compared with calibration by changing the gravitational gradient excitation, this method does not need test masses and is easier to implement. The equivalent zero biases are superpositions of self-gradients and the intrinsic zero biases of the RAGG. A self-gradient is the gravitational gradient produced by surrounding masses, and it correlates well with the RAGG attitude angle. We propose a self-gradient model that includes self-gradients and the intrinsic zero biases of the RAGG. The self-gradient model is a function of the RAGG attitude, and it includes parameters related to surrounding masses. The calibration of equivalent zero biases determines the parameters of the self-gradient model. We provide detailed procedures and mathematical formulations for calibrating scale factors and parameters in the self-gradient model. A RAGG physical simulation system substitutes for the actual RAGG in the calibration and validation experiments. Four point masses simulate four types of surrounding masses producing self-gradients. Validation experiments show that the self-gradients predicted by the self-gradient model are consistent with those from the outputs of the RAGG physical simulation system, suggesting that the presented calibration method is valid.

Daily variation of diurnal thermal tides from CHAMP and GOCE accelerometer measurements

NASA Astrophysics Data System (ADS)

Gasperini, Federico; Doornbos, Eelco; Forbes, Jeffrey M.; Bruinsma, Sean; Haeusler, Kathrin; Hagan, Maura

Daily migrating and non-migrating diurnal tides in exospheric temperature derived from simultaneous accelerometer measurements on CHAMP (near 300 km) and GOCE (near 260 km) are studied for the intervals November-December 2009 and March-April 2010. Neutral densities are converted to exospheric temperatures using the NRLMSISe00 empirical model and by iterating on a convenient parameter (e.g. F10.7 solar flux). This methodology is validated using NCAR TIME-GCM simulations for this period as a mock data set, and results are compared to an approach where differences between ascending and descending orbital measurements are used to estimate diurnal tides for CHAMP and GOCE separately. The tidal components analyzed are the westward-propagating components with zonal wave numbers s=1 and s=2 (DW1 and DW2) and the eastward-propagating components with s=-2 and s=-3 (DE2 and DE3). Spectral analyses are used to reveal potential planetary wave modulations of the daily tidal amplitudes.

From Germany to Antarctica: Airborne geodesy and geophysics and the utilization of the research aircraft HALO (Invited)

NASA Astrophysics Data System (ADS)

Scheinert, M.; Barthelmes, F.; Foerste, C.; Heyde, I.

2013-12-01

The geoid as an equipotential surface of the gravity potential plays a crucial role for the realiziation of the Global Geodetic Observation System (GGOS) of IAG (International Association of Geodesy). It is the major reference surface for physical height systems. The gravity potential is needed to precisely predict the orbits of artificial satellites of the earth. A precise static solution enters analyses of temporal changes of the gravity field due to mass transport processes between the different subsystems of the earth. However, also in neighbouring disciplines the geoid is applied. In oceanography, for example, the geoid serves as a reference surface for the determination of the mean sea-surface topography (MSST). In glaciology, it enters analyses of the thickness of ice bodies floating in polar waters, based on freeboard heights and the equilibrium supposition. To come up with high resolution global gravity field models, satellite observations - preferably of the dedicated satellite gravity missions - have to be combined with surface gravity data. Although the majority of the continental surface is captured by ground-based or near-surface gravity measurements - and gravity over the oceans is determined by satellite altimetry - still large gaps in surface gravity data exist. In this respect it is the Antarctic continent which suffers large data gaps, not only in surface gravity but also due to the polar gap of GOCE satellite gravimetry. Chairing the IAG Subcommission 2.4f 'Gravity and Geoid in Antarctica' (AntGG) the author will discuss the current status of gravity surveys in Antarctica. Especially airborne gravimetry has been and is being widely applied as the only reasonable method to survey large areas in this vast and hostile environment. As a novel application the German research aircraft HALO was utilized for a geodetic-geophysical flight mission. Measurements were realized to acquire data of the gravity and magnetic fields, of GNSS remote sensing and of laser altimetry over Italy and adjacent (Tyrrhenian, Adriatic and Ionian) seas. This so-called GEOHALO flight mission was carried out in the time period from June 2 to 12, 2012. The flights comprised seven parallel profiles directing from north-west to south-east, in a height of about 3,500 m, with a length of about 1,000 km each and a line spacing of about 40 km. These long profiles were complemented by four crossing profiles and a profile at an altitude of approx. 10 km along the same track as the center long profile. Special focus will be given to the results of airborne gravimetry and laser altimetry to further investigate the gravity field and the sea-surface topography in the Mediterranean. Furthermore, the status of HALO and future plans to utilize HALO for an Antarctic flight mission will be discussed. Applications of airborne gravimetry to investigate geodetic problems in Antarctica shall be shortly discussed, together with an outlook of AntGG.

Complex physiological and molecular processes underlying root gravitropism

NASA Technical Reports Server (NTRS)

Chen, Rujin; Guan, Changhui; Boonsirichai, Kanokporn; Masson, Patrick H.

2002-01-01

Gravitropism allows plant organs to guide their growth in relation to the gravity vector. For most roots, this response to gravity allows downward growth into soil where water and nutrients are available for plant growth and development. The primary site for gravity sensing in roots includes the root cap and appears to involve the sedimentation of amyloplasts within the columella cells. This process triggers a signal transduction pathway that promotes both an acidification of the wall around the columella cells, an alkalinization of the columella cytoplasm, and the development of a lateral polarity across the root cap that allows for the establishment of a lateral auxin gradient. This gradient is then transmitted to the elongation zones where it triggers a differential cellular elongation on opposite flanks of the central elongation zone, responsible for part of the gravitropic curvature. Recent findings also suggest the involvement of a secondary site/mechanism of gravity sensing for gravitropism in roots, and the possibility that the early phases of graviresponse, which involve differential elongation on opposite flanks of the distal elongation zone, might be independent of this auxin gradient. This review discusses our current understanding of the molecular and physiological mechanisms underlying these various phases of the gravitropic response in roots.

Worldwide complete spherical Bouguer and isostatic anomaly maps

NASA Astrophysics Data System (ADS)

Bonvalot, S.; Balmino, G.; Briais, A.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

2011-12-01

We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free air and Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, submitted). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis et al., 2008), which represents the best up-to-date global gravity model (including surface gravity measurements from land, marine and airborne surveys as well as gravity and altimetry satellite measurements). The surface gravity anomaly (free air) is computed at the Earth's surface in the context of Molodensky theory and includes corrections from the mass of the atmosphere. The way gravity anomalies are computed on a worldwide basis slightly differs from the classical usage, but meets modern concerns which tend to take the real Earth into account. The resulting anomaly maps and grids will be distributed for scientific and education purposes by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. Upgraded versions might be done as soon as new global gravity model is available (including satellite GOCE and new surface measurements: ground, airborne). Visit / contact BGI (http://bgi.omp.obs-mip.fr) and CCMW (http://ccgm.free.fr) for more information.

Response of Materials Subjected to Magnetic Fields

DTIC Science & Technology

2011-08-31

is a superconducting Helmholtz coil capable of operating at up to 6 Tesla. Access to the high magnetic field at the center of the magnet is by...conducting sphere moves through the magnetic field gradient (0 to 4 Tesla over ~20cm) at low velocity (under the influence of gravity for 1 meter). Area...sphere moves through the magnetic field gradient (0 to 4 Tesla over ~20cm) at high velocity (under the influence of gravity for 1 meter). Figure 8

Precise Orbit Determination Of Low Earth Satellites At AIUB Using GPS And SLR Data

NASA Astrophysics Data System (ADS)

Jaggi, A.; Bock, H.; Thaller, D.; Sosnica, K.; Meyer, U.; Baumann, C.; Dach, R.

2013-12-01

An ever increasing number of low Earth orbiting (LEO) satellites is, or will be, equipped with retro-reflectors for Satellite Laser Ranging (SLR) and on-board receivers to collect observations from Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS) and the Russian GLONASS and the European Galileo systems in the future. At the Astronomical Institute of the University of Bern (AIUB) LEO precise orbit determination (POD) using either GPS or SLR data is performed for a wide range of applications for satellites at different altitudes. For this purpose the classical numerical integration techniques, as also used for dynamic orbit determination of satellites at high altitudes, are extended by pseudo-stochastic orbit modeling techniques to efficiently cope with potential force model deficiencies for satellites at low altitudes. Accuracies of better than 2 cm may be achieved by pseudo-stochastic orbit modeling for satellites at very low altitudes such as for the GPS-based POD of the Gravity field and steady-state Ocean Circulation Explorer (GOCE).

Investigation of Electrostatic Accelerometer in HUST for Space Science Missions

NASA Astrophysics Data System (ADS)

Bai, Yanzheng; Hu, Ming; Li, Gui; Liu, Li; Qu, Shaobo; Wu, Shuchao; Zhou, Zebing

2014-05-01

High-precision electrostatic accelerometers are significant payload in CHAMP, GRACE and GOCE gravity missions to measure the non-gravitational forces. In our group, space electrostatic accelerometer and inertial sensor based on the capacitive sensors and electrostatic control technique has been investigated for space science research in China such as testing of equivalence principle (TEPO), searching non-Newtonian force in micrometer range, satellite Earth's field recovery and so on. In our group, a capacitive position sensor with a resolution of 10-7pF/Hz1/2 and the μV/Hz1/2 level electrostatic actuator are developed. The fiber torsion pendulum facility is adopt to measure the parameters of the electrostatic controlled inertial sensor such as the resolution, and the electrostatic stiffness, the cross couple between different DOFs. Meanwhile, high voltage suspension and free fall methods are applied to verify the function of electrostatic accelerometer. Last, the engineering model of electrostatic accelerometer has been developed and tested successfully in space and preliminary results are present.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brumbaugh, William D.; Cook, Kenneth L.

During the summers of 1975 and 1976, a gravity survey was conducted in the Cove Fort - Sulphurdale KGRA and north Mineral Mountains area, Millard and Beaver counties, Utah. The survey consisted of 671 gravity stations covering an area of about 1300 km{sup 2}, and included two orthogonal gravity profiles traversing the area. The gravity data are presented as a terrain-corrected Bouguer gravity anomaly map with a contour interval of 1 mgal and as an isometric three-dimensional gravity anomaly surface. Selected anomaly separation techniques were applied to the hand-digitized gravity data (at 1-km intervals on the Universal Transverse Mercator grid)more » in both the frequency and space domains, including Fourier decomposition, second vertical derivative, strike-filter, and polynomial fitting analysis, respectively. Residual gravity gradients of 0.5 to 8.0 mgal/km across north-trending gravity contours observed through the Cove Fort area, the Sulphurdale area, and the areas east of the East Mineral Mountains, along the west flanks of the Tushar Mountains, and on both the east and west flanks of the north Mineral Mountains, were attributed to north-trending Basin and Range high-angle faults. Gravity highs exist over the community of Black Rock area, the north Mineral Mountains, the Paleozoic outcrops in the east Cove Creek-Dog Valley-White Sage Flats areas, the sedimentary thrust zone of the southern Payant Range, and the East Mineral Mountains. The gravity lows over north Milford Valley, southern Black Rock Desert, Cunningham Wash, and northern Beaver Valley are separated from the above gravity highs by steep gravity gradients attributed to a combination of crustal warping and faulting. A gravity low with a closure of 2 mgal corresponds with Sulphur Cove, a circular topographic features containing sulphur deposits.« less

Ring faults and ring dikes around the Orientale basin on the Moon.

PubMed

Andrews-Hanna, Jeffrey C; Head, James W; Johnson, Brandon; Keane, James T; Kiefer, Walter S; McGovern, Patrick J; Neumann, Gregory A; Wieczorek, Mark A; Zuber, Maria T

2018-08-01

The Orientale basin is the youngest and best-preserved multiring impact basin on the Moon, having experienced only modest modification by subsequent impacts and volcanism. Orientale is often treated as the type example of a multiring basin, with three prominent rings outside of the inner depression: the Inner Rook Montes, the Outer Rook Montes, and the Cordillera. Here we use gravity data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission to reveal the subsurface structure of Orientale and its ring system. Gradients of the gravity data reveal a continuous ring dike intruded into the Outer Rook along the plane of the fault associated with the ring scarp. The volume of this ring dike is ~18 times greater than the volume of all extrusive mare deposits associated with the basin. The gravity gradient signature of the Cordillera ring indicates an offset along the fault across a shallow density interface, interpreted to be the base of the low-density ejecta blanket. Both gravity gradients and crustal thickness models indicate that the edge of the central cavity is shifted inward relative to the equivalent Inner Rook ring at the surface. Models of the deep basin structure show inflections along the crust-mantle interface at both the Outer Rook and Cordillera rings, indicating that the basin ring faults extend from the surface to at least the base of the crust. Fault dips range from 13-22° for the Cordillera fault in the northeastern quadrant, to 90° for the Outer Rook in the northwestern quadrant. The fault dips for both outer rings are lowest in the northeast, possibly due to the effects of either the direction of projectile motion or regional gradients in pre-impact crustal thickness. Similar ring dikes and ring faults are observed around the majority of lunar basins.

Root gravitropism

NASA Technical Reports Server (NTRS)

Masson, P. H.

1995-01-01

When a plant root is reoriented within the gravity field, it responds by initiating a curvature which eventually results in vertical growth. Gravity sensing occurs primarily in the root tip. It may involve amyloplast sedimentation in the columella cells of the root cap, or the detection of forces exerted by the mass of the protoplast on opposite sides of its cell wall. Gravisensing activates a signal transduction cascade which results in the asymmetric redistribution of auxin and apoplastic Ca2+ across the root tip, with accumulation at the bottom side. The resulting lateral asymmetry in Ca2+ and auxin concentration is probably transmitted to the elongation zone where differential cellular elongation occurs until the tip resumes vertical growth. The Cholodny-Went theory proposes that gravity-induced auxin redistribution across a gravistimulated plant organ is responsible for the gravitropic response. However, recent data indicate that the gravity-induced reorientation is more complex, involving both auxin gradient-dependent and auxin gradient-independent events.

e.motion - European Initiatives for a Future Gravity Field Mission

NASA Astrophysics Data System (ADS)

Gruber, T.

2017-12-01

Since 2010 a large team of European scientists, with the support of technological and industrial partners, is preparing proposals for new gravity field missions as follow-up to GRACE, GOCE and GRACE-FO. The main goal of the proposed mission concepts is the long term observation of the time variable gravity field with significantly increased spatial and temporal resolution as it can be performed nowadays with GRACE or in the near future with GRACE Follow-On. These observations are crucial for long term monitoring of mass variations in the system Earth in order to improve our knowledge about the global and regional water cycle as well as about processes of the solid Earth. Starting from the existing concepts of single pair mission like GRACE and GRACE-FO, sensitivity, spatial and temporal resolution shall be increased, such that also smaller scale time variable signals can be resolved, which cannot be detected with the current techniques. For such a mission concept new and significantly improved observation techniques are needed. This concerns in particular the measurement of inter-satellite distances, the observation of non-gravitational accelerations, the configuration of the satellite orbit and most important the implementation of constellation of satellite pairs. All in all three proposals have been prepared by the e.motion team specifying in detail the mission design and the performance in terms of science applications. Starting with a single-pair pendulum mission, which was proposed for ESA's Earth Explorer 8 call (EE8), more recently a double-pair Bender-type mission was proposed for the ESA's EE9 call. In between several studies on European (DLR and ESA) and inter-agency level (ESA-NASA) have been performed. The presentation provides a summary about all these initiatives, derives some conclusions which can be drawn from the mission proposals and study results and gives an outlook about future initiatives for gravity field missions in Europe.

GRAV-D for Puerto Rico and the U.S. Virgin Islands

NASA Astrophysics Data System (ADS)

Roman, D. R.; Li, X.; Smith, D. A.; Geoid; GRAV-D Teams

2013-05-01

NOAA's National Geodetic Survey began the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) program in an effort to modernize and unify vertical datums in all states and territories. As a part of this program, NGS collected aerogravity profiles over the islands of Puerto Rico and the U.S. Virgin Islands in January 2009. A Citation II aircraft was equipped with an airborne gravimeter, GPS receiver, and a GPS/Inertial unit. Absolute gravity and GPS ties were made to multiple ground sites to ensure consistency in the results. The main survey covered a region of approximately 400 km by 500 km with flight altitudes of 10,668 m (35,000ft) and with 10 km track spacing. Cross-track profiles at 40 km spacing were also collected to establish an accuracy of 1.34 mGals RMSE. In addition to the high altitude flights, two more flights were made primarily over terrestrial areas at 1,524 m (5,000 ft) to obtain higher resolution information in these regions. There were no cross-ties established for these lower altitude flights. Additionally, terrestrial surveys were also conducted to better tie ground sites and to serve as control for later analysis for available but older terrestrial and marine gravity data in the region already held by NGS. The aerogravity data were analyzed and at least internally compared to obtain the optimal results before being published on the web. In this study, the aerogravity data were compared to available global gravity models derived from satellite missions (GRACE & GOCE) to evaluate their long wavelength character (e.g., potential biases and trends). The vetted satellite-aerogravity data were then combined and used to evaluate surface data (terrestrial and marine) in the region to remove any potential systematic effects. Finally, all these data were combined into a gravimetric geoid height model and evaluated with an eye to eventual use as a GNSS-accessed vertical datum.

Gravity domains and assembly of the North American continent by collisional tectonics

NASA Technical Reports Server (NTRS)

Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

1988-01-01

A gravity trend map of North America, based on a horizontal Bouguer gravity gradient map produced from gravity data for Canada and the conterminous United States, is presented and used to define a continental mosaic of gravity trend domains akin to structural domains. Contrasting trend characteristics at gravity domain boundaries support the concept of outward growth of the continent primarily by accretionary tectonics. Gravity patterns, however, indicate a different style of tectonics dominated in the development of now-buried Proterozoic orogenic belts in the south-central United States, supporting a view that these belts formed along the leading edge of a southward-migrating Proterozoic continental margin.

Results of Gravity Fieldwork Conducted in March 2008 in the Moapa Valley Region of Clark County, Nevada

USGS Publications Warehouse

Scheirer, Daniel S.; Andreasen, Arne Dossing

2008-01-01

In March 2008, we collected gravity data along 12 traverses across newly-mapped faults in the Moapa Valley region of Clark County, Nevada. In areas crossed by these faults, the traverses provide better definition of the gravity field and, thus, the density structure, than prior gravity observations. Access problems prohibited complete gravity coverage along all of the planned gravity traverses, and we added and adjusted the locations of traverses to maximize our data collection. Most of the traverses exhibit isostatic gravity anomalies that have gradients characteristic of exposed or buried faults, including several of the newly-mapped faults.

Hybrid gravity survey to search for submarine ore deposit

NASA Astrophysics Data System (ADS)

Araya, A.; Kanazawa, T.; Fujimoto, H.; Shinohara, M.; Yamada, T.; Mochizuki, K.; Iizasa, K.; Ishihara, T.; Omika, S.

2011-12-01

Along with seismic surveys, gravity survey is a useful method to profile the underground density structure. We propose a hybrid gravity survey using gravimeters and gravity gradiometers to detect submarine ore deposits as density anomalies by towing the instruments using an AUV (Autonomous Underwater Vehicle) or an ROV (Remotely Operated Vehicle). Gravimeters measure the regional density structure below the seafloor, whereas gravity gradiometers are sensitive to localized mass distribution. A gravity gradiometer comprises two accelerometers arranged with a vertical separation, and a gravity gradient can be obtained from the acceleration difference. Compared to gravimeters, gravity gradiometers are insensitive to common disturbances such as parallel acceleration, thermal drift, and apparent gravity effect (Eötvös effect). We made two accelerometers using astatic pendulums, and obtained common acceleration reduction more than two orders of magnitude. With these pendulums of 500-mm separation, resolution of 7E (=7x10^{-9}(1/s^2)), enough to detect a typical ore deposit buried 50m below the seafloor, was evaluated. During measurements using a submersible mobile object, instrument orientation is required to be controlled to keep verticality and to reduce centrifugal force associated with rotation of the instrument. Using a gyro and a tiltmeter, angular rotation was shown to be controlled within 0.001deg/s which corresponds to 0.3E in effective gravity gradient due to the centrifugal force. In this paper, target of this research, details of the instruments and their performance, and development for the submarine gravity survey using an AUV will be presented.

Theoretical and numerical investigations towards a new geoid model for the Mediterranean Sea - The GEOMED2 project

NASA Astrophysics Data System (ADS)

Barzaghi, Riccardo; Vergos, Georgios S.; Albertella, Alberta; Carrion, Daniela; Cazzaniga, Noemi; Tziavos, Ilias N.; Grigoriadis, Vassilios N.; Natsiopoulos, Dimitrios A.; Bruinsma, Sean; Bonvalot, Sylvain; Lequentrec-Lalancette, Marie-Françoise; Bonnefond, Pascal; Knudsen, Per; Andersen, Ole; Simav, Mehmet; Yildiz, Hasan; Basic, Tomislav; Gil, Antonio J.

2016-04-01

The unique features of the Mediterranean Sea, with its large gravity variations, complex circulation, and geodynamic peculiarities have always constituted this semi-enclosed sea area as a unique geodetic, geodynamics and ocean laboratory. The main scope of the GEOMED 2 project is the collection of all available gravity, topography/bathymetry and satellite altimetry data in order to improve the representation of the marine geoid and estimate the Mean Dynamic sea surface Topography (MDT) and the circulation with higher accuracy and resolution. Within GEOMED2, the data employed are land and marine gravity data, GOCE/GRACE based Global Geopotential Models and a combination after proper validation of MISTRAL, HOMONIM and SRTM/bathymetry terrain models. In this work we present the results achieved for an inner test region spanning the Adriatic Sea area, bounded between 36o < φ < 48o and 10o < λ < 22o. Within this test region, the available terrain/bathymetry models have been evaluated in terms of their contribution to geoid modeling, the processing methodologies have been tested in terms of the provided geoid accuracy and finally some preliminary results on the MDT determination have been compiled. The aforementioned will server as the guide for the Mediterranean-wide marine geoid estimation. The processing methodology was based on the well-known remove-compute-restore method following both stochastic and spectral methods. Classic least-squares collocation (LSC) with errors has been employed, along with fast Fourier transform (FFT)-based techniques, the Least-Squares Modification of Stokes' Formula (KTH) method and windowed LSC. All methods have been evaluated against in-situ collocated GPS/Levelling geoid heights, using EGM2008 as a reference, in order to conclude on the one(s) to be used for the basin-wide geoid evaluation.

Progress towards a space-borne quantum gravity gradiometer

NASA Technical Reports Server (NTRS)

Yu, Nan; Kohel, James M.; Ramerez-Serrano, Jaime; Kellogg, James R.; Lim, Lawrence; Maleki, Lute

2004-01-01

Quantum interferometer gravity gradiometer for 3D mapping is a project for developing the technology of atom interferometer-based gravity sensor in space. The atom interferometer utilizes atomic particles as free fall test masses to measure inertial forces with unprecedented sensitivity and precision. It also allows measurements of the gravity gradient tensor components for 3D mapping of subsurface mass distribution. The overall approach is based on recent advances of laser cooling and manipulation of atoms in atomic and optical physics. Atom interferometers have been demonstrated in research laboratories for gravity and gravity gradient measurements. In this approach, atoms are first laser cooled to micro-kelvin temperatures. Then they are allowed to freefall in vacuum as true drag-free test masses. During the free fall, a sequence of laser pulses is used to split and recombine the atom waves to realize the interferometric measurements. We have demonstrated atom interferometer operation in the Phase I period, and we are implementing the second generation for a complete gradiometer demonstration unit in the laboratory. Along with this development, we are developing technologies at component levels that will be more suited for realization of a space instrument. We will present an update of these developments and discuss the future directions of the quantum gravity gradiometer project.

Preliminary Gravity and Magnetic Data of the Lake Pillsbury Region, Northern Coast Ranges, California

USGS Publications Warehouse

Langenheim, V.E.; Jachens, Robert C.; Morin, Robert L.; McCabe, Craig A.

2007-01-01

The Lake Pillsbury region is transected by the Bartlett Springs Fault zone, one of the main strike-slip faults of the San Andreas system north of San Francisco Bay, California. Gravity and magnetic data were collected to help characterize the geometry and offset of the fault zone as well as determine the geometry of the Gravelly Valley pull-apart basin and Potter Valley, an alluvial intermontane basin southwest of Lake Pillsbury. The Bartlett Springs fault zone lies at the base of a significant gravity gradient. Superposed on the gradient is a small gravity low centered over Lake Pillsbury and Gravelly Valley. Another small gravity low coincides with Potter Valley. Inversion of gravity data for basin thickness indicates a maximum thickness of 400 and 440 m for the Gravelly and Potter Valley depressions, respectively. Ground magnetic data indicate that the regional aeromagnetic data likely suffer from positional errors, but that large, long-wavelength anomalies, sourced from serpentinite, may be offset 8 km along the Bartlett Springs Fault zone. Additional gravity data collected either on the lake surface or bottom and in Potter Valley would better determine the shape of the basins. A modern, high-resolution aeromagnetic survey would greatly augment the ability to map and model the fault geometry quantitatively.

Isostatic Gravity Map with Geology of the Santa Ana 30' x 60' Quadrangle, Southern California

USGS Publications Warehouse

Langenheim, V.E.; Lee, Tien-Chang; Biehler, Shawn; Jachens, R.C.; Morton, D.M.

2006-01-01

This report presents an updated isostatic gravity map, with an accompanying discussion of the geologic significance of gravity anomalies in the Santa Ana 30 by 60 minute quadrangle, southern California. Comparison and analysis of the gravity field with mapped geology indicates the configuration of structures bounding the Los Angeles Basin, geometry of basins developed within the Elsinore and San Jacinto Fault zones, and a probable Pliocene drainage network carved into the bedrock of the Perris block. Total cumulative horizontal displacement on the Elsinore Fault derived from analysis of the length of strike-slip basins within the fault zone is about 5-12 km and is consistent with previously published estimates derived from other sources of information. This report also presents a map of density variations within pre-Cenozoic metamorphic and igneous basement rocks. Analysis of basement gravity patterns across the Elsinore Fault zone suggests 6-10 km of right-lateral displacement. A high-amplitude basement gravity high is present over the San Joaquin Hills and is most likely caused by Peninsular Ranges gabbro and/or Tertiary mafic intrusion. A major basement gravity gradient coincides with the San Jacinto Fault zone and marked magnetic, seismic-velocity, and isotopic gradients that reflect a discontinuity within the Peninsular Ranges batholith in the northeast corner of the quadrangle.

Time Variable Gravity modeling for Precise Orbits Across the TOPEX/Poseidon, Jason-l and Jason-2 Missions

NASA Technical Reports Server (NTRS)

Zelensky, Nikita P.; Lemoine, Frank G.; Chinn, Douglas; Beckley, Brain D.; Melachroinos, Stavros; Rowlands, David D.; Luthcke, Scott B.

2011-01-01

Modeling of the Time Variable Gravity (TVG) is believed to constitute one of the the largest remaining source of orbit error for altimeter satellite POD. The GSFC operational TVG model consists of forward modeling the atmospheric gravity using ECMWF 6-hour pressure data, a GRACE derived 20x20 annual field to account for changes in the hydrology and ocean water mass, and linear rates for C20, C30, C40, based on 17 years of SLR data analysis (IERS 2003) using the EIGEN-GL04S1 (a GRACE+Lageos-based geopotential solution). Although the GSFC Operational model can be applied from 1987, there may be long-term variations not captured by these linear models, and more importantly the linear models may not be consistent with more recent surface mass trends due to global climate change, We have evaluated the impact of TVG in two different wavs: (1) by using the more recent EIGEN-6S gravity model developed by the GFZ/GRGS tearm, which consists of annual, semi-annual and secular changes in the coefficients to 50x50 determined over 8(?) years of GRACE+Lageos+GOCE data (2003-200?): (2) Application of 4x4 solutions developed from a multi satellite SLR+DORIS solution based on GGM03S that span the period from 1993 to 2011. We have evaluated the recently released EIGEN6s static and time-varying gravity field for Jason-2 (J2). Jason-I (J1), and TOPEX/Posiedon (TP) Precise Orbit Determination (POD) spanning 1993-2011. Although EIGEN6s shows significant improvement for J2POD spanning 2008 - 2011, it also shows significant degradation for TP POD from 1992. The GSFC 4x4 time SLR+DORIS-based series spans 1993 to mid 2011, and shows promise for POD. We evaluate the performance of the different TVG models based on analysis of tracking data residuals use of independent data such as altimeter crossovers, and through analysis of differences with internally-generated and externally generated orbits.

Anomalous Structure of Oceanic Lithosphere in the North Atlantic and Arctic Oceans: A Preliminary Analysis Based on Bathymetry, Gravity and Crustal Structure

NASA Astrophysics Data System (ADS)

Barantsrva, O.

2014-12-01

We present a preliminary analysis of the crustal and upper mantle structure for off-shore regions in the North Atlantic and Arctic oceans. These regions have anomalous oceanic lithosphere: the upper mantle of the North Atlantic ocean is affected by the Iceland plume, while the Arctic ocean has some of the slowest spreading rates. Our specific goal is to constrain the density structure of the upper mantle in order to understand the links between the deep lithosphere dynamics, ocean spreading, ocean floor bathymetry, heat flow and structure of the oceanic lithosphere in the regions where classical models of evolution of the oceanic lithosphere may not be valid. The major focus is on the oceanic lithosphere, but the Arctic shelves with a sufficient data coverage are also included into the analysis. Out major interest is the density structure of the upper mantle, and the analysis is based on the interpretation of GOCE satellite gravity data. To separate gravity anomalies caused by subcrustal anomalous masses, the gravitational effect of water, crust and the deep mantle is removed from the observed gravity field. For bathymetry we use the global NOAA database ETOPO1. The crustal correction to gravity is based on two crustal models: (1) global model CRUST1.0 (Laske, 2013) and, for a comparison, (2) a regional seismic model EUNAseis (Artemieva and Thybo, 2013). The crustal density structure required for the crustal correction is constrained from Vp data. Previous studies have shown that a large range of density values corresponds to any Vp value. To overcome this problem and to reduce uncertainty associated with the velocity-density conversion, we account for regional tectonic variations in the Northern Atlantics as constrained by numerous published seismic profiles and potential-field models across the Norwegian off-shore crust (e.g. Breivik et al., 2005, 2007), and apply different Vp-density conversions for different parts of the region. We present preliminary results, which we use to examine factors that control variations in bathymetry, sedimentary and crustal thicknesses in these anomalous oceanic domains.

New insights into root gravitropic signalling

PubMed Central

Sato, Ethel Mendocilla; Hijazi, Hussein; Bennett, Malcolm J.; Vissenberg, Kris; Swarup, Ranjan

2015-01-01

An important feature of plants is the ability to adapt their growth towards or away from external stimuli such as light, water, temperature, and gravity. These responsive plant growth movements are called tropisms and they contribute to the plant’s survival and reproduction. Roots modulate their growth towards gravity to exploit the soil for water and nutrient uptake, and to provide anchorage. The physiological process of root gravitropism comprises gravity perception, signal transmission, growth response, and the re-establishment of normal growth. Gravity perception is best explained by the starch–statolith hypothesis that states that dense starch-filled amyloplasts or statoliths within columella cells sediment in the direction of gravity, resulting in the generation of a signal that causes asymmetric growth. Though little is known about the gravity receptor(s), the role of auxin linking gravity sensing to the response is well established. Auxin influx and efflux carriers facilitate creation of a differential auxin gradient between the upper and lower side of gravistimulated roots. This asymmetric auxin gradient causes differential growth responses in the graviresponding tissue of the elongation zone, leading to root curvature. Cell biological and mathematical modelling approaches suggest that the root gravitropic response begins within minutes of a gravity stimulus, triggering genomic and non-genomic responses. This review discusses recent advances in our understanding of root gravitropism in Arabidopsis thaliana and identifies current challenges and future perspectives. PMID:25547917

Forward calculation of gravity and its gradient using polyhedral representation of density interfaces: an application of spherical or ellipsoidal topographic gravity effect

NASA Astrophysics Data System (ADS)

Zhang, Yi; Chen, Chao

2018-02-01

A density interface modeling method using polyhedral representation is proposed to construct 3-D models of spherical or ellipsoidal interfaces such as the terrain surface of the Earth and applied to forward calculating gravity effect of topography and bathymetry for regional or global applications. The method utilizes triangular facets to fit undulation of the target interface. The model maintains almost equal accuracy and resolution at different locations of the globe. Meanwhile, the exterior gravitational field of the model, including its gravity and gravity gradients, is obtained simultaneously using analytic solutions. Additionally, considering the effect of distant relief, an adaptive computation process is introduced to reduce the computational burden. Then features and errors of the method are analyzed. Subsequently, the method is applied to an area for the ellipsoidal Bouguer shell correction as an example and the result is compared to existing methods, which shows our method provides high accuracy and great computational efficiency. Suggestions for further developments and conclusions are drawn at last.

Development of an Artificial Gravity Sleeper (AGS)

NASA Technical Reports Server (NTRS)

Cardus, David; Mctaggart, Wesley G.; Diamandis, Peter; Campbell, Scott

1990-01-01

The design and construction of a 2-meter radius 'human compatible' centrifuge termed the Artificial Gravity Sleeper (AGS) is considered. The centrifuge will accommodate up to four subjects at a time, operate at a broad range of speeds, and have safety features. Experiments that will be conducted on the AGS will help to investigate the quality of sleep during 100 percent gradient centrifugation. A microgravity simulation also will be studied using bed rest to assess the ability of 100 percent gradient centrifugation to function as a countermeasure to cardiovascular deconditioning.

Autonomous momentum management for space station

NASA Technical Reports Server (NTRS)

Hahn, E.

1984-01-01

Momentum management for the CDG planar space platform is discussed. It is assumed that the external torques on the space station are gravity gradient and aerodynamic, both have bias and cyclic terms. The integrals of the cyclic torques are the cyclic momenti which will be stored in the momentum storage actuator. Techniques to counteract the bias torques and center the cyclic momentum and gravity gradient desaturation by adjusting vehicle attitude, aerodynamic desaturation using solar panels and radiators and the deployment of flat plates at the end of long booms generating aerodynamic torques are investigated.

Fugacity and concentration gradients in a gravity field

NASA Technical Reports Server (NTRS)

May, C. E.

1986-01-01

Equations are reviewed which show that at equilibrium fugacity and concentration gradients can exist in gravitational fields. At equilibrium, the logarithm of the ratio of the fugacities of a species at two different locations in a gravitational field is proportional to the difference in the heights of the two locations and the molecular weight of the species. An analogous relation holds for the concentration ratios in a multicomponent system. The ratio is calculated for a variety of examples. The kinetics for the general process are derived, and the time required to approach equilibrium is calculated for several systems. The following special topics are discussed: ionic solutions, polymers, multiphase systems, hydrostatic pressure, osmotic pressure, and solubility gradients in a gravity field.

Correlation of Aerogravity and BHT Data to Develop a Geothermal Gradient Map of the Northern Western Desert of Egypt using an Artificial Neural Network

NASA Astrophysics Data System (ADS)

Mohamed, Haby S.; Abdel Zaher, Mohamed; Senosy, Mahmoud M.; Saibi, Hakim; El Nouby, Mohamed; Fairhead, J. Derek

2015-06-01

The northern part of the Western Desert of Egypt represents the second most promising area of hydrocarbon potential after the Gulf of Suez province. An artificial neural network (ANN) approach was used to develop a new predictive model for calculation of the geothermal gradients in this region based on gravity and corrected bottom-hole temperature (BHT) data. The best training data set was obtained with an ANN architecture composed of seven neurons in the hidden layer, which made it possible to predict the geothermal gradient with satisfactory efficiency. The BHT records of 116 deep oil wells (2,000-4,500 m) were used to evaluate the geothermal resources in the northern Western Desert. Corrections were applied to the BHT data to obtain the true formation equilibrium temperatures, which can provide useful constraints on the subsurface thermal regime. On the basis of these corrected data, the thermal gradient was computed for the linear sections of the temperature-versus-depth data at each well. The calculated geothermal gradient using temperature log data was generally 30 °C/km, with a few local high geothermal gradients in the northwestern parts of the study area explained by potential local geothermal fields. The Bouguer gravity values from the study area ranged from -60 mGal in the southern parts to 120 mGal in the northern areas, and exhibited NE-SW and E-W trends associated with geological structures. Although the northern Western Desert of Egypt has low regional temperature gradients (30 °C/km), several potential local geothermal fields were found (>40 °C/km). The heat flow at each well was also computed by combining sets of temperature gradients and thermal conductivity data. Aerogravity data were used to delineate the subsurface structures and tectonic framework of the region. The result of this study is a new geothermal gradient map of the northern Western Desert developed from gravity and BHT log data.

Improving a maximum horizontal gradient algorithm to determine geological body boundaries and fault systems based on gravity data

NASA Astrophysics Data System (ADS)

Van Kha, Tran; Van Vuong, Hoang; Thanh, Do Duc; Hung, Duong Quoc; Anh, Le Duc

2018-05-01

The maximum horizontal gradient method was first proposed by Blakely and Simpson (1986) for determining the boundaries between geological bodies with different densities. The method involves the comparison of a center point with its eight nearest neighbors in four directions within each 3 × 3 calculation grid. The horizontal location and magnitude of the maximum values are found by interpolating a second-order polynomial through the trio of points provided that the magnitude of the middle point is greater than its two nearest neighbors in one direction. In theoretical models of multiple sources, however, the above condition does not allow the maximum horizontal locations to be fully located, and it could be difficult to correlate the edges of complicated sources. In this paper, the authors propose an additional condition to identify more maximum horizontal locations within the calculation grid. This additional condition will improve the method algorithm for interpreting the boundaries of magnetic and/or gravity sources. The improved algorithm was tested on gravity models and applied to gravity data for the Phu Khanh basin on the continental shelf of the East Vietnam Sea. The results show that the additional locations of the maximum horizontal gradient could be helpful for connecting the edges of complicated source bodies.

Biological patterns: Novel indicators for pharmacological assays

NASA Technical Reports Server (NTRS)

Johnson, Jacqueline U.

1991-01-01

Variable gravity testing using the KC-135 demonstrated clearly that biological pattern formation was definitely shown to result from gravity alone, and not from oxygen gradients in solution. Motile pattern formation of spermatozoa are driven by alternate mechanisms, and apparently not affected by short-term changes in gravity. The chemical effects found appear to be secondary to the primary effect of gravity. Cryopreservation may be the remedy to the problem of 'spare' or 'standing order' biological samples for testing of space lab investigations, but further studies are necessary.

Tests of general relativity in earth orbit using a superconducting gravity gradiometer

NASA Technical Reports Server (NTRS)

Paik, H. J.

1989-01-01

Interesting new tests of general relativity could be performed in earth orbit using a sensitive superconducting gravity gradiometer under development. Two such experiments are discussed here: a null test of the tracelessness of the Riemann tensor and detection of the Lense-Thirring term in the earth's gravity field. The gravity gradient signals in various spacecraft orientations are derived, and dominant error sources in each experimental setting are discussed. The instrument, spacecraft, and orbit requirements imposed by the experiments are derived.

Measurement of the gravity-field curvature by atom interferometry.

PubMed

Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M

2015-01-09

We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.

Terrestrial gravity instrumentation in the 20th Century: A brief review

NASA Technical Reports Server (NTRS)

Valliant, H. D.

1989-01-01

At the turn of the century, only pendulum apparatuses and torsion balances were available for general exploration work. Both of these early techniques were cumbersome and time-consuming. It was no wonder that the development of the gravity meter was welcomed with a universal sigh of relief. By 1935 potential field measurements with gravity meters supplanted gradient measurements with torsion balances. Potential field measurements are generally characterized by three types: absolute - measurements are made in fundamental units, traceable to national standards of length and time at each observation site; relative with absolute scale - differences in gravity are measured in fundamental units traceable to national standards of length and time; and relative - differences in gravity are measured with arbitrary scale. Improvements in the design of gravity meters since their introduction has led to a significant reduction in size and greatly increased precision. As the precision increased, applications expanded to include the measurement of crustal motion, the search for non-Newtonian forces, archeology, and civil engineering. Apart from enhancements to the astatic gravity meter, few developments in hardware were achieved. One of these was the vibrating string gravity meter which was developed in the 1950s and was employed briefly for marine and borehole applications. Another is the cryogenic gravity meter which utilizes the stability of superconducting current to achieve a relative instrument with extremely low drift suitable for tidal and secular gravity measurements. An advance in performing measurements from a moving platform was achieved with the development of the straight-line gravity meter. The latter part of the century also saw the rebirth of gradient measurements which offers advantages for observations from a moving platform. Definitive testing of the Bell gradiometer was recently reported.

Search for Earthquake-Induced Prompt Gravity Signals in Gravimetric Data: Data Analysis and a New Observation Model

NASA Astrophysics Data System (ADS)

Kimura, M.; Kame, N.; Watada, S.; Ohtani, M.; Araya, A.; Imanishi, Y.; Ando, M.; Kunugi, T.

2017-12-01

Seismic waves radiated from an earthquake rupture induces density perturbations of the medium, which in turn generates prompt gravity changes at all distances before the arrival of seismic waves. Detection of the gravity signal before the seismic one is a challenge in seismology. In this study, we searched for the prompt gravity changes from the 2011 Tohoku-Oki earthquake in data recorded by gravimeters, seismometers, and tiltmeters. Predicted changes from the currently used simplified model were not identified using band-pass filtering and multi-station stacking even though sufficient signal-to-noise ratios were achieved. Our data analysis raised discrepancy between the data and the theoretical model. To interpret the absence of signals in the data, we investigated the effect of self-gravity deformation on the measurement of gravitational acceleration, which has been ignored in the existing theory. We analytically calculated the displacement of the observation station induced by the prompt gravity changes in an infinite homogeneous medium, and showed that before the arrival of P waves each point in the medium moves at an acceleration identical to the applied gravity change, i.e., free-falls. As a result of the opposite inertial force, gravity sensors attached to the medium lose their sensitivity to the prompt gravity changes. This new observation model incorporated with the self-gravity effect explains the absence of such prompt signals in the acceleration data. We have shown the negative observability in acceleration, but there remains a possibility of detection of its spatial gradients or spatial strain. For a future detection experiment, we derived an analytical expression of the theoretical gravity gradients from a general seismic source described as a moment tensor.

Fast inversion of gravity data using the symmetric successive over-relaxation (SSOR) preconditioned conjugate gradient algorithm

NASA Astrophysics Data System (ADS)

Meng, Zhaohai; Li, Fengting; Xu, Xuechun; Huang, Danian; Zhang, Dailei

2017-02-01

The subsurface three-dimensional (3D) model of density distribution is obtained by solving an under-determined linear equation that is established by gravity data. Here, we describe a new fast gravity inversion method to recover a 3D density model from gravity data. The subsurface will be divided into a large number of rectangular blocks, each with an unknown constant density. The gravity inversion method introduces a stabiliser model norm with a depth weighting function to produce smooth models. The depth weighting function is combined with the model norm to counteract the skin effect of the gravity potential field. As the numbers of density model parameters is NZ (the number of layers in the vertical subsurface domain) times greater than the observed gravity data parameters, the inverse density parameter is larger than the observed gravity data parameters. Solving the full set of gravity inversion equations is very time-consuming, and applying a new algorithm to estimate gravity inversion can significantly reduce the number of iterations and the computational time. In this paper, a new symmetric successive over-relaxation (SSOR) iterative conjugate gradient (CG) method is shown to be an appropriate algorithm to solve this Tikhonov cost function (gravity inversion equation). The new, faster method is applied on Gaussian noise-contaminated synthetic data to demonstrate its suitability for 3D gravity inversion. To demonstrate the performance of the new algorithm on actual gravity data, we provide a case study that includes ground-based measurement of residual Bouguer gravity anomalies over the Humble salt dome near Houston, Gulf Coast Basin, off the shore of Louisiana. A 3D distribution of salt rock concentration is used to evaluate the inversion results recovered by the new SSOR iterative method. In the test model, the density values in the constructed model coincide with the known location and depth of the salt dome.

Direct measurement of sub-surface mass change using the variable-baseline gravity gradient method

USGS Publications Warehouse

Kennedy, Jeffrey; Ferré, Ty P.A.; Güntner, Andreas; Abe, Maiko; Creutzfeldt, Benjamin

2014-01-01

Time-lapse gravity data provide a direct, non-destructive method to monitor mass changes at scales from cm to km. But, the effectively infinite spatial sensitivity of gravity measurements can make it difficult to isolate the signal of interest. The variable-baseline gravity gradient method, based on the difference of measurements between two gravimeters, is an alternative to the conventional approach of individually modeling all sources of mass and elevation change. This approach can improve the signal-to-noise ratio for many applications by removing the contributions of Earth tides, loading, and other signals that have the same effect on both gravimeters. At the same time, this approach can focus the support volume within a relatively small user-defined region of the subsurface. The method is demonstrated using paired superconducting gravimeters to make for the first time a large-scale, non-invasive measurement of infiltration wetting front velocity and change in water content above the wetting front.

Gravity-regulated differential auxin transport from columella to lateral root cap cells

NASA Technical Reports Server (NTRS)

Ottenschlager, Iris; Wolff, Patricia; Wolverton, Chris; Bhalerao, Rishikesh P.; Sandberg, Goran; Ishikawa, Hideo; Evans, Mike; Palme, Klaus

2003-01-01

Gravity-induced root curvature has long been considered to be regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients, and the transport mechanisms involved, remain to be identified. Here, we describe a GFP-based auxin biosensor to monitor auxin during Arabidopsis root gravitropism at cellular resolution. We identify elevated auxin levels at the root apex in columella cells, the site of gravity perception, and an asymmetric auxin flux from these cells to the lateral root cap (LRC) and toward the elongation zone after gravistimulation. We differentiate between an efflux-dependent lateral auxin transport from columella to LRC cells, and an efflux- and influx-dependent basipetal transport from the LRC to the elongation zone. We further demonstrate that endogenous gravitropic auxin gradients develop even in the presence of an exogenous source of auxin. Live-cell auxin imaging provides unprecedented insights into gravity-regulated auxin flux at cellular resolution, and strongly suggests that this flux is a prerequisite for root gravitropism.

Effective Inertial Frame in an Atom Interferometric Test of the Equivalence Principle

NASA Astrophysics Data System (ADS)

Overstreet, Chris; Asenbaum, Peter; Kovachy, Tim; Notermans, Remy; Hogan, Jason M.; Kasevich, Mark A.

2018-05-01

In an ideal test of the equivalence principle, the test masses fall in a common inertial frame. A real experiment is affected by gravity gradients, which introduce systematic errors by coupling to initial kinematic differences between the test masses. Here we demonstrate a method that reduces the sensitivity of a dual-species atom interferometer to initial kinematics by using a frequency shift of the mirror pulse to create an effective inertial frame for both atomic species. Using this method, we suppress the gravity-gradient-induced dependence of the differential phase on initial kinematic differences by 2 orders of magnitude and precisely measure these differences. We realize a relative precision of Δ g /g ≈6 ×10-11 per shot, which improves on the best previous result for a dual-species atom interferometer by more than 3 orders of magnitude. By reducing gravity gradient systematic errors to one part in 1 013 , these results pave the way for an atomic test of the equivalence principle at an accuracy comparable with state-of-the-art classical tests.

Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

NASA Astrophysics Data System (ADS)

Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

2006-12-01

Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys to the new network, the regional compilation of Bouguer gravity data and a new updated Bouguer gravity anomaly map for northeastern Mexico.

Analytical characterization of selective benthic flux components in estuarine and coastal waters

USGS Publications Warehouse

King, Jeffrey N.

2011-01-01

Benthic flux is the rate of flow across the bed of a water body, per unit area of bed. It is forced by component mechanisms, which interact. For example, pressure gradients across the bed, forced by tide, surface gravity waves, density gradients, bed–current interaction, turbulence, and terrestrial hydraulic gradients, drive an advective benthic flux of water and constituents between estuarine and coastal waters, and surficial aquifers. Other mechanisms also force benthic flux, such as chemical gradients, bioturbation, and dispersion. A suite of component mechanisms force a total benthic flux at any given location, where each member of the suite contributes a component benthic flux. Currently, the types and characteristics of component interactions are not fully understood. For example, components may interact linearly or nonlinearly, and the interaction may be constructive or destructive. Benthic flux is a surface water–groundwater interaction process. Its discharge component to a marine water body is referred to, in some literature, as submarine groundwater discharge. Benthic flux is important in characterizing water and constituent budgets of estuarine and coastal systems. Analytical models to characterize selective benthic flux components are reviewed. Specifically, these mechanisms are for the component associated with the groundwater tidal prism, and forced by surface gravity wave setup, surface gravity waves on a plane bed, and the terrestrial hydraulic gradient. Analytical models are applied to the Indian River Lagoon, Florida; Great South Bay, New York; and the South Atlantic Bight in South Carolina and portions of North Carolina.

Actin-based gravity-sensing mechanisms in unicellular plant model systems

NASA Astrophysics Data System (ADS)

Braun, Markus; Limbach, Christoph

2005-08-01

Considerable progress has been made in the understanding of the molecular and cellular mechanisms underlying gravity sensing and gravity-oriented polarized growth in single-celled rhizoids and protonemata of the characean algae. It is well known that the actin cytoskeleton plays a key role in these processes. Numerous actin-binding proteins control apical actin polymerization and the dynamic remodeling of the actin arrangement. An actomyosin-based system mediates the delivery and incorporation of secretory vesicles at the growing tip and coordinates the tip-high gradient of cytoplasmic free calcium which is required for local exocytosis. Additionally, the actomyosin system precisely controls the position of statoliths and, upon a change in orientation relative to the gravity vector, directs sedimenting statoliths to the confined graviperception sites of the plasma membrane where gravitropic signalling is initiated. The upward growth response of protonemata is preceded by an actin-dependent relocalization of the Ca2+-gradient to the upper flank. The downward growth response of rhizoids, however, is caused by differential growth of the opposite flankes due to a local reduction of cytoplasmic free calcium limited to the plasma membrane area where statoliths are sedimented. Thus, constant actin polymerization in the growing tip and the spatiotemporal control of actin remodeling are essential for gravity sensing and gravity-oriented polarized growth of characean rhizoids and protonemata.

Expression of terrain and surface geology in high-resolution helicopter-borne gravity gradient (AGG) data: examples from Great Sand Dunes National Park, Rio Grande Rift, Colorado

USGS Publications Warehouse

Drenth, Benjamin J.

2013-01-01

Airborne gravity gradient (AGG) data are rapidly becoming standard components of geophysical mapping programs, due to their advantages in cost, access, and resolution advantages over measurements of the gravity field on the ground. Unlike conventional techniques that measure the gravity field, AGG methods measure derivatives of the gravity field. This means that effects of terrain and near-surface geology are amplified in AGG data, and that proper terrain corrections are critically important for AGG data processing. However, terrain corrections require reasonable estimates of density for the rocks and sediments that make up the terrain. A recommended philosophical approach is to use the terrain and surface geology, with their strong expression in AGG data, to the interpreter’s advantage. An example of such an approach is presented here for an area with very difficult ground access and little ground gravity data. Nettleton-style profiling is used with AGG data to estimate the densities of the sand dunefield and adjacent Precambrian rocks from the area of Great Sand Dunes National Park in southern Colorado. Processing of the AGG data using the density estimate for the dunefield allows buried structures, including a hypothesized buried basement bench, to be mapped beneath the sand dunes.

A simple algorithm for sequentially incorporating gravity observations in seismic traveltime tomography

USGS Publications Warehouse

Parsons, T.; Blakely, R.J.; Brocher, T.M.

2001-01-01

The geologic structure of the Earth's upper crust can be revealed by modeling variation in seismic arrival times and in potential field measurements. We demonstrate a simple method for sequentially satisfying seismic traveltime and observed gravity residuals in an iterative 3-D inversion. The algorithm is portable to any seismic analysis method that uses a gridded representation of velocity structure. Our technique calculates the gravity anomaly resulting from a velocity model by converting to density with Gardner's rule. The residual between calculated and observed gravity is minimized by weighted adjustments to the model velocity-depth gradient where the gradient is steepest and where seismic coverage is least. The adjustments are scaled by the sign and magnitude of the gravity residuals, and a smoothing step is performed to minimize vertical streaking. The adjusted model is then used as a starting model in the next seismic traveltime iteration. The process is repeated until one velocity model can simultaneously satisfy both the gravity anomaly and seismic traveltime observations within acceptable misfits. We test our algorithm with data gathered in the Puget Lowland of Washington state, USA (Seismic Hazards Investigation in Puget Sound [SHIPS] experiment). We perform resolution tests with synthetic traveltime and gravity observations calculated with a checkerboard velocity model using the SHIPS experiment geometry, and show that the addition of gravity significantly enhances resolution. We calculate a new velocity model for the region using SHIPS traveltimes and observed gravity, and show examples where correlation between surface geology and modeled subsurface velocity structure is enhanced.

Low-gravity fluid flows

NASA Technical Reports Server (NTRS)

Ostrach, S.

1982-01-01

The behavior of fluids in micro-gravity conditions is examined, with particular regard to applications in the growth of single crystals. The effects of gravity on fluid behavior are reviewed, and the advent of Shuttle flights are noted to offer extended time for experimentation and processing in a null-gravity environment, with accelerations resulting solely from maneuvering rockets. Buoyancy driven flows are considered for the cases stable-, unstable-, and mixed-mode convection. Further discussion is presented on g-jitter, surface-tension gradient, thermoacoustic, and phase-change convection. All the flows are present in both gravity and null gravity conditions, although the effects of buoyancy and g-jitter convection usually overshadow the other effects while in a gravity field. Further work is recommended on critical-state and sedimentation processes in microgravity conditions.

Autonomous momentum management for space station, exhibit A

NASA Technical Reports Server (NTRS)

Hahn, E.

1984-01-01

The report discusses momentum management for the CDG Planar Space Platform. The external torques on the Space Station are assumed to be gravity gradient and aerodynamic with both having bias and cyclic terms. The integrals of the cyclic torques are the cyclic momenti which will be stored in the momentum storage actuator. Various techniques to counteract the bias torques and center the cyclic momentum were investigated including gravity gradient desaturation by adjusting vehicle attitude, aerodynamic desaturation using solar panels and radiators and the deployment of flat plates at the end of long booms generating aerodynamic torques.

Gravity dependent processes and intracellular motion

NASA Technical Reports Server (NTRS)

Todd, Paul

1991-01-01

Most organelles large enough to sediment or to undergo isothermal settling within eukaryotic cells are held in position by one or more components of the cytoskeleton. The interior of eukaryotic cells is considered to be very crowded, and the evaluation of natural-convective processes is very difficult. In a most simple view, the cell may be considered as consisting of four immiscible phases among which solutes are exchanged causing steep concentration gradients and thermodynamic conditions far from equilibrium. Extracellular gravity-related forces may include natural convection due to solute gradients external to single cells or the work performed by swimming, ciliated, or elongating cells.

World Gravity Map: a set of global complete spherical Bouguer and isostatic anomaly maps and grids

NASA Astrophysics Data System (ADS)

Bonvalot, S.; Balmino, G.; Briais, A.; Kuhn, M.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

2012-04-01

We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. The Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, 2011). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy-Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis et al., 2008) and the DTU10 (Andersen, 2010) who represents the best up-to-date global gravity models (including surface gravity measurements from land, marine and airborne surveys as well as gravity and altimetry satellite measurements). The surface free-air anomaly is computed at the Earth's surface in the context of Molodensky theory and includes corrections from the mass of the atmosphere. The way gravity anomalies are computed on a worldwide basis slightly differs from the classical usage, but meets modern concerns which tend to take into account of the real Earth. The resulting anomaly maps and grids will be distributed for scientific and education purposes by the Commission for the Geological Map of the World (CGMW) (http://ccgm.free.fr) and by the Bureau Gravimetrique International (BGI) (http://bgi.omp.obs-mip.fr). Upgraded versions might be done as soon as new global gravity model will be available (including satellite GOCE data for instance). Institutions who are interested to contribute with new datasets of surface gravity measurements (i.e. ground, marine or airborne gravity data) are also invited to contact BGI bgi@cnes.fr.

The dynamical simulation of transient three-dimensional cryogenic liquid sloshing oscillations under low-gravity and microgravity

NASA Astrophysics Data System (ADS)

Chi, Yong Mann

A numerical simulation model has been developed for the dynamical behavior of spacecraft propellant, both during the draining and the closing of the tank outlet at the onset of suction dip affected by the asymmetric combined gravity gradient and gravity jitter accelerations. In particular the effect of the surface tension of the fluids in the partially filled dewar (applicable to the Gravity Probe-B spacecraft dewar tank and fuel tanks for a liquid rocket) with rotation has been simulated and investigated. Two different cases of accelerations, one with gravity jitter dominated and the other equally weighted between gravity gradient and gravity jitter accelerations, are studied. In the development of this numerical simulation model, the NASA-VOF3D has been used as a supplement to the numerical program of this dissertation. The NASA-VOF3D code has been used for performing the three-dimensional incompressible flows with free surface. This is also used for controlling liquid sloshing inside the tank when the spacecraft is orbiting. To keep track of the location of the liquid, the fractional volume of fluid (VOF) technique was used. The VOF is based on the indicator function of the region occupied by the liquid with an Eulerian approach to solve the free surface phenomena between liquid and gas phases. For the calculation of surface tension force, the VOF model is also used. The newly developed simulation model is used to investigate the characteristics of liquid hydrogen draining in terms of the residual amount of trapped liquid at the onset of the suction dip and residual liquid volume at the time the dip of the liquid-vapor interface formed. This investigation simulates the characteristics of liquid oscillations due to liquid container outlet shut-off at the onset of suction dip. These phenomena checked how these mechanisms affected the excitation of slosh waves during the course of liquid draining and after shut-off tank outlet. In the present study, the dynamical evolution of sloshing dynamics excited by fluid stress forces, fluid stress moments, and the arm of fluid moment exerted on the dewar container, is considered. This excitation was driven by the combined gravity gradient and gravity jitter acceleration inside the tank during the draining process and closing the tank outlet. The time evolution of the liquid-vapor interface profiles and the bubble mass center fluctuation, as well as liquid mass center and fluctuations of angular momentum caused by slosh wave excitations with 0.1 rpm in a reduced gravity, are also investigated and simulated. Force, angular momentum, and torque vector time histories and Power Spectral Density (PSD) are also plotted and discussed. The results of this investigation may be applied to determine the magnitude and nature of control forces and torques needed to minimize influence of slosh on the dynamics of liquid fueled vehicles in near earth orbit. Results show that induced fluid forces (or angular momentum) exerted on the container wall along x and y-axes, which are non-existent at the beginning, are introduced by the slosh waves excited by asymmetric gravity gradient and the gravity jitter acceleration.

A numerical investigation into the ability of the Poisson PDE to extract the mass-density from land-based gravity data: A case study of salt diapirs in the north coast of the Persian Gulf

NASA Astrophysics Data System (ADS)

AllahTavakoli, Yahya; Safari, Abdolreza

2017-08-01

This paper is counted as a numerical investigation into the capability of Poisson's Partial Differential Equation (PDE) at Earth's surface to extract the near-surface mass-density from land-based gravity data. For this purpose, first it focuses on approximating the gradient tensor of Earth's gravitational potential by means of land-based gravity data. Then, based on the concepts of both the gradient tensor and Poisson's PDE at the Earth's surface, certain formulae are proposed for the mass-density determination. Furthermore, this paper shows how the generalized Tikhonov regularization strategy can be used for enhancing the efficiency of the proposed approach. Finally, in a real case study, the formulae are applied to 6350 gravity stations located within a part of the north coast of the Persian Gulf. The case study numerically indicates that the proposed formulae, provided by Poisson's PDE, has the ability to convert land-based gravity data into the terrain mass-density which has been used for depicting areas of salt diapirs in the region of the case study.

Laser Vacuum Furnace for Zone Refining

NASA Technical Reports Server (NTRS)

Griner, D. B.; Zurburg, F. W.; Penn, W. M.

1986-01-01

Laser beam scanned to produce moving melt zone. Experimental laser vacuum furnace scans crystalline wafer with high-power CO2-laser beam to generate precise melt zone with precise control of temperature gradients around zone. Intended for zone refining of silicon or other semiconductors in low gravity, apparatus used in normal gravity.

GOCE User Toolbox and Tutorial

NASA Astrophysics Data System (ADS)

Knudsen, P.; Benveniste, J.

2011-07-01

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products. GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations, and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT Install Guide. A set of a-priori data and models are made available as well. GUT has been developed in a collaboration within the GUT Core Group. The GUT Core Group: S. Dinardo, D. Serpe, B.M. Lucas, R. Floberghagen, A. Horvath (ESA), O. Andersen, M. Herceg (DTU), M.-H. Rio, S. Mulet, G. Larnicol (CLS), J. Johannessen, L.Bertino (NERSC), H. Snaith, P. Challenor (NOC), K. Haines, D. Bretherton (NCEO), C. Hughes (POL), R.J. Bingham (NU), G. Balmino, S. Niemeijer, I. Price, L. Cornejo (S&T), M. Diament, I Panet (IPGP), C.C. Tscherning (KU), D. Stammer, F. Siegismund (UH), T. Gruber (TUM),

Airborne surveys in the Arctic and Antarctic for geophysics, sea-ice thickness, and CryoSat validation

NASA Astrophysics Data System (ADS)

Forsberg, R.; Olesen, A. V.; Hvidegaard, S.; Skourup, H.

2010-12-01

Airborne laser and radar measurements over the Greenland ice sheet, Svalbard, and adjacent parts of the Arctic Ocean have been carried out by DTU-Space in a number of recent Danish/Greenlandic and European project campaigns, with the purpose to monitor ice sheet and sea-ice changes, support of Greenland societal needs (oil exploration and hydropower), and support of CryoSat pre-launch calibration and validation campaigns. The Arctic campaigns have been done using a Twin-Otter aircraft, carrying laser scanners and various radars. Since 2009 a new program of long-range gravity and magnetic surveys have been initiated using a Basler DC3 aircraft for large-scale surveys in the Arctic Ocean and Antarctica, with the 2010 cooperative Danish-Argentinean-Chilean-US ICEGRAV survey of the Antarctic Peninsula additionally including a UTIG 60 MHz ice-penetrating radar. In the paper we outline the recent and upcoming airborne survey activities, outline the usefulness of the airborne data for satellite validation (CryoSat and GOCE), and give examples of measurements and comparisons to satellite and in-situ data.

Direction of unsaturated flow in a homogeneous and isotropic hillslope

USGS Publications Warehouse

Lu, Ning; Kaya, Basak Sener; Godt, Jonathan W.

2011-01-01

The distribution of soil moisture in a homogeneous and isotropic hillslope is a transient, variably saturated physical process controlled by rainfall characteristics, hillslope geometry, and the hydrological properties of the hillslope materials. The major driving mechanisms for moisture movement are gravity and gradients in matric potential. The latter is solely controlled by gradients of moisture content. In a homogeneous and isotropic saturated hillslope, absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface, flow is always in the lateral downslope direction, under either transient or steady state conditions. However, under variably saturated conditions, both gravity and moisture content gradients drive fluid motion, leading to complex flow patterns. In general, the flow field near the ground surface is variably saturated and transient, and the direction of flow could be laterally downslope, laterally upslope, or vertically downward. Previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes. This work, however, shows that under time-varying rainfall conditions, vertical, downslope, and upslope lateral flow can concurrently occur at different depths and locations within the hillslope. More importantly, we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and/or laterally upslope flow occurs.

Direction of unsaturated flow in a homogeneous and isotropic hillslope

USGS Publications Warehouse

Lu, N.; Kaya, B.S.; Godt, J.W.

2011-01-01

The distribution of soil moisture in a homogeneous and isotropic hillslope is a transient, variably saturated physical process controlled by rainfall characteristics, hillslope geometry, and the hydrological properties of the hillslope materials. The major driving mechanisms for moisture movement are gravity and gradients in matric potential. The latter is solely controlled by gradients of moisture content. In a homogeneous and isotropic saturated hillslope, absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface, flow is always in the lateral downslope direction, under either transient or steady state conditions. However, under variably saturated conditions, both gravity and moisture content gradients drive fluid motion, leading to complex flow patterns. In general, the flow field near the ground surface is variably saturated and transient, and the direction of flow could be laterally downslope, laterally upslope, or vertically downward. Previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes. This work, however, shows that under time-varying rainfall conditions, vertical, downslope, and upslope lateral flow can concurrently occur at different depths and locations within the hillslope. More importantly, we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and/or laterally upslope flow occurs. Copyright 2011 by the American Geophysical Union.

On the Resolvability of Steam Assisted Gravity Drainage Reservoirs Using Time-Lapse Gravity Gradiometry

NASA Astrophysics Data System (ADS)

Elliott, E. Judith; Braun, Alexander

2017-11-01

Unconventional heavy oil resource plays are important contributors to oil and gas production, as well as controversial for posing environmental hazards. Monitoring those reservoirs before, during, and after operations would assist both the optimization of economic benefits and the mitigation of potential environmental hazards. This study investigates how gravity gradiometry using superconducting gravimeters could resolve depletion areas in steam assisted gravity drainage (SAGD) reservoirs. This is achieved through modelling of a SAGD reservoir at 1.25 and 5 years of operation. Specifically, the density change structure identified from geological, petrological, and seismic observations is forward modelled for gravity and gradients. Three main parameters have an impact on the resolvability of bitumen depletion volumes and are varied through a suitable parameter space: well pair separation, depth to the well pairs, and survey grid sampling. The results include a resolvability matrix, which identifies reservoirs that could benefit from time-lapse gravity gradiometry monitoring. After 1.25 years of operation, during the rising phase, the resolvable maximum reservoir depth ranges between the surface and 230 m, considering a well pair separation between 80 and 200 m. After 5 years of production, during the spreading phase, the resolvability of depletion volumes around single well pairs is greatly compromised as the depletion volume is closer to the surface, which translates to a larger portion of the gravity signal. The modelled resolvability matrices were derived from visual inspection and spectral analysis of the gravity gradient signatures and can be used to assess the applicability of time-lapse gradiometry to monitor reservoir density changes.

Baroclinic instability with variable gravity: A perturbation analysis

NASA Technical Reports Server (NTRS)

Giere, A. C.; Fowliss, W. W.; Arias, S.

1980-01-01

Solutions for a quasigeostrophic baroclinic stability problem in which gravity is a function of height were obtained. Curvature and horizontal shear of the basic state flow were omitted and the vertical and horizontal temperature gradients of the basic state were taken as constant. The effect of a variable dielectric body force, analogous to gravity, on baroclinic instability for the design of a spherical, baroclinic model for Spacelab was determined. Such modeling could not be performed in a laboratory on the Earth's surface because the body force could not be made strong enough to dominate terrestrial gravity. A consequence of the body force variation and the preceding assumptions was that the potential vorticity gradient of the basic state vanished. The problem was solved using a perturbation method. The solution gives results which are qualitatively similar to Eady's results for constant gravity; a short wavelength cutoff and a wavelength of maximum growth rate were observed. The averaged values of the basic state indicate that both the wavelength range of the instability and the growth rate at maximum instability are increased. Results indicate that the presence of the variable body force will not significantly alter the dynamics of the Spacelab experiment. The solutions are also relevant to other geophysical fluid flows where gravity is constant but the static stability or Brunt-Vaisala frequency is a function of height.

Measuring attitude with a gradiometer

NASA Technical Reports Server (NTRS)

Sonnabend, David; Gardner, Thomas G.

1994-01-01

This paper explores using a gravity gradiometer to measure the attitude of a satellite, given that the gravity field is accurately known. Since gradiometers actually measure a combination of the gradient and attitude rate and acceleration terms, the answer is far from obvious. The paper demonstrates that it can be done and at microradian accuracy. The technique employed is dynamic estimation, based on the momentum biased Euler equations. The satellite is assumed nominally planet pointed, and subject to control, gravity gradient, and partly radom drag torques. The attitude estimator is unusual. While the standard method of feeding back measurement residuals is used, the feedback gain matrix isn't derived from Kalman theory. instead, it's chosen to minimize a measure of the terminal covariance of the error in the estimate. This depends on the gain matrix and the power spectra of all the process and measurement noises. An integration is required over multiple solutions of Lyapunov equations.

Analysis of gravity data beneath Endut geothermal prospect using horizontal gradient and Euler deconvolution

NASA Astrophysics Data System (ADS)

Supriyanto, Noor, T.; Suhanto, E.

2017-07-01

The Endut geothermal prospect is located in Banten Province, Indonesia. The geological setting of the area is dominated by quaternary volcanic, tertiary sediments and tertiary rock intrusion. This area has been in the preliminary study phase of geology, geochemistry, and geophysics. As one of the geophysical study, the gravity data measurement has been carried out and analyzed in order to understand geological condition especially subsurface fault structure that control the geothermal system in Endut area. After precondition applied to gravity data, the complete Bouguer anomaly have been analyzed using advanced derivatives method such as Horizontal Gradient (HG) and Euler Deconvolution (ED) to clarify the existance of fault structures. These techniques detected boundaries of body anomalies and faults structure that were compared with the lithologies in the geology map. The analysis result will be useful in making a further realistic conceptual model of the Endut geothermal area.

DenInv3D: a geophysical software for three-dimensional density inversion of gravity field data

NASA Astrophysics Data System (ADS)

Tian, Yu; Ke, Xiaoping; Wang, Yong

2018-04-01

This paper presents a three-dimensional density inversion software called DenInv3D that operates on gravity and gravity gradient data. The software performs inversion modelling, kernel function calculation, and inversion calculations using the improved preconditioned conjugate gradient (PCG) algorithm. In the PCG algorithm, due to the uncertainty of empirical parameters, such as the Lagrange multiplier, we use the inflection point of the L-curve as the regularisation parameter. The software can construct unequally spaced grids and perform inversions using such grids, which enables changing the resolution of the inversion results at different depths. Through inversion of airborne gradiometry data on the Australian Kauring test site, we discovered that anomalous blocks of different sizes are present within the study area in addition to the central anomalies. The software of DenInv3D can be downloaded from http://159.226.162.30.

Diffusive-convective physical vapor transport of PbTe from a Te-rich solid source

NASA Technical Reports Server (NTRS)

Zoutendyk, J.; Akutagawa, W.

1982-01-01

Crystal growth of PbTe by physical vapor transport (sublimation) in a closed ampoule is governed by the vapor species in thermal equilibrium with the solid compound. Deviations from stoichiometry in the source material cause diffusion limitation of the transport rate, which can be modified by natural (gravity-driven) convection. Mass-transport experiments have been performed using Te-rich material wherein sublimation rates have been measured in order to study the effects of natural convection in diffusion-limited vapor transport. Linear velocities for both crystal growth and evaporation (back sublimation) have been measured for transport in the direction of gravity, horizontally, and opposite to gravity. The experimental results are discussed in terms of both the one-dimensional diffusive-advective model and current, more sophisticated theory which includes natural convection. There is some evidence that convection effects from radial temperature gradients and solutal density gradients have been observed.

Gravity and thermal deformation of large primary mirror in space telescope

NASA Astrophysics Data System (ADS)

Wang, Xin; Jiang, Shouwang; Wan, Jinlong; Shu, Rong

2016-10-01

The technology of integrating mechanical FEA analysis with optical estimation is essential to simulate the gravity deformation of large main mirror and the thermal deformation such as static or temperature gradient of optical structure. We present the simulation results of FEA analysis, data processing, and image performance. Three kinds of support structure for large primary mirror which have the center holding structure, the edge glue fixation and back support, are designed and compared to get the optimal gravity deformation. Variable mirror materials Zerodur/SiC are chosen and analyzed to obtain the small thermal gradient distortion. The simulation accuracy is dependent on FEA mesh quality, the load definition of structure, the fitting error from discrete data to smooth surface. A main mirror with 1m diameter is designed as an example. The appropriate structure material to match mirror, the central supporting structure, and the key aspects of FEA simulation are optimized for space application.

Dynamic regimes of buoyancy-affected two-phase flow in unconsolidated porous media.

PubMed

Stöhr, M; Khalili, A

2006-03-01

The invasion and subsequent flow of a nonwetting fluid (NWF) in a three-dimensional, unconsolidated porous medium saturated with a wetting fluid of higher density and viscosity have been studied experimentally using a light-transmission technique. Distinct dynamic regimes have been found for different relative magnitudes of viscous, capillary, and gravity forces. It is shown that the ratio of viscous and hydrostatic pressure gradients can be used as a relevant dimensionless number K for the characterization of the different flow regimes. For low values of K, the invasion is characterized by the migration and fragmentation of isolated clusters of the NWF resulting from the prevalence of gravity and capillary forces. At high values of K, the dominance of viscous and gravity forces leads to an anisotropic fingerlike invasion. When the invasion stops after the breakthrough of the NWF at the open upper boundary, the invasion structure retracts under the influence of gravity and transforms into stable vertical channels. It is shown that the stability of these channels is the result of a balance between hydrostatic and viscous pressure gradients.

High resolution Slovak Bouguer gravity anomaly map and its enhanced derivative transformations: new possibilities for interpretation of anomalous gravity fields

NASA Astrophysics Data System (ADS)

Pašteka, Roman; Zahorec, Pavol; Kušnirák, David; Bošanský, Marián; Papčo, Juraj; Szalaiová, Viktória; Krajňák, Martin; Ivan, Marušiak; Mikuška, Ján; Bielik, Miroslav

2017-06-01

The paper deals with the revision and enrichment of the present gravimetric database of the Slovak Republic. The output of this process is a new version of the complete Bouguer anomaly (CBA) field on our territory. Thanks to the taking into account of more accurate terrain corrections, this field has significantly higher quality and higher resolution capabilities. The excellent features of this map will allow us to re-evaluate and improve the qualitative interpretation of the gravity field when researching the structural and tectonic geology of the Western Carpathian lithosphere. In the contribution we also analyse the field of the new CBA based on the properties of various transformed fields - in particular the horizontal gradient, which by its local maximums defines important density boundaries in the lateral direction. All original and new transformed maps make a significant contribution to improving the geological interpretation of the CBA field. Except for the horizontal gradient field, we are also interested in a new special transformation of TDXAS, which excellently separates various detected anomalies of gravity field and improves their lateral delimitation.

A study of numerical methods of solution of the equations of motion of a controlled satellite under the influence of gravity gradient torque

NASA Technical Reports Server (NTRS)

Thompson, J. F.; Mcwhorter, J. C.; Siddiqi, S. A.; Shanks, S. P.

1973-01-01

Numerical methods of integration of the equations of motion of a controlled satellite under the influence of gravity-gradient torque are considered. The results of computer experimentation using a number of Runge-Kutta, multi-step, and extrapolation methods for the numerical integration of this differential system are presented, and particularly efficient methods are noted. A large bibliography of numerical methods for initial value problems for ordinary differential equations is presented, and a compilation of Runge-Kutta and multistep formulas is given. Less common numerical integration techniques from the literature are noted for further consideration.

Nanogravity gradiometer based on a sharp optical nonlinearity in a levitated particle optomechanical system

NASA Astrophysics Data System (ADS)

Liu, Jian; Zhu, Ka-Di

2017-02-01

In the present paper, we provide a scheme to probe the gradient of gravity at the nanoscale in a levitated nanomechanical resonator coupled to a cavity via two-field optical control. The enhanced sharp peak on the probe spectrum will suffer a distinct shift with the nonuniform force being taken into consideration. The nonlinear optics with very narrow bandwidth (10-8 Hz ) resulting from the extremely high-quality factor will lead to a superresolution of 10-20 N /m for the measurement of gravity gradient. The improved sensitivity may offer new opportunities for detecting Yukawa moduli forces and Kaluza-Klein gravitons in extra dimensions.

Extended mimetic gravity: Hamiltonian analysis and gradient instabilities

NASA Astrophysics Data System (ADS)

Takahashi, Kazufumi; Kobayashi, Tsutomu

2017-11-01

We propose a novel class of degenerate higher-order scalar-tensor theories as an extension of mimetic gravity. By performing a noninvertible conformal transformation on "seed" scalar-tensor theories which may be nondegenerate, we can generate a large class of theories with at most three physical degrees of freedom. We identify a general seed theory for which this is possible. Cosmological perturbations in these extended mimetic theories are also studied. It is shown that either of tensor or scalar perturbations is plagued with gradient instabilities, except for a special case where the scalar perturbations are presumably strongly coupled, or otherwise there appear ghost instabilities.

Gravitational force and torque on a solar power satellite considering the structural flexibility

NASA Astrophysics Data System (ADS)

Zhao, Yi; Zhang, Jingrui; Zhang, Yao; Zhang, Jun; Hu, Quan

2017-11-01

The solar power satellites (SPS) are designed to collect the constant solar energy and beam it to Earth. They are traditionally large in scale and flexible in structure. In order to obtain an accurate model of such system, the analytical expressions of the gravitational force, gravity gradient torque and modal force are investigated. They are expanded to the fourth order in a Taylor series with the elastic displacements considered. It is assumed that the deformation of the structure is relatively small compared with its characteristic length, so that the assumed mode method is applicable. The high-order moments of inertia and flexibility coefficients are presented. The comprehensive dynamics of a large flexible SPS and its orbital, attitude and vibration evolutions with different order gravitational forces, gravity gradient torques and modal forces in geosynchronous Earth orbit are performed. Numerical simulations show that an accurate representation of the SPS‧ dynamic characteristics requires the retention of the higher moments of inertia and flexibility. Perturbations of orbit, attitude and vibration can be retained to the 1-2nd order gravitational forces, the 1-2nd order gravity gradient torques and the 1-2nd order modal forces for a large flexible SPS in geosynchronous Earth orbit.

Estimation of Gravitation Parameters of Saturnian Moons Using Cassini Attitude Control Flight Data

NASA Technical Reports Server (NTRS)

Krening, Samantha C.

2013-01-01

A major science objective of the Cassini mission is to study Saturnian satellites. The gravitational properties of each Saturnian moon is of interest not only to scientists but also to attitude control engineers. When the Cassini spacecraft flies close to a moon, a gravity gradient torque is exerted on the spacecraft due to the mass of the moon. The gravity gradient torque will alter the spin rates of the reaction wheels (RWA). The change of each reaction wheel's spin rate might lead to overspeed issues or operating the wheel bearings in an undesirable boundary lubrication condition. Hence, it is imperative to understand how the gravity gradient torque caused by a moon will affect the reaction wheels in order to protect the health of the hardware. The attitude control telemetry from low-altitude flybys of Saturn's moons can be used to estimate the gravitational parameter of the moon or the distance between the centers of mass of Cassini and the moon. Flight data from several low altitude flybys of three Saturnian moons, Dione, Rhea, and Enceladus, were used to estimate the gravitational parameters of these moons. Results are compared with values given in the literature.

Gravity increase at the south pole

USGS Publications Warehouse

Behrendt, John C.

1967-01-01

Abstract. Measurements made between December 1957 and January 1966 of the gravity difference between the McMurdo Sound pendulum station, which is on bedrock, and the South Pole station, which is on the Antarctic ice sheet, show a gravity increase at the South Pole of 0.11 milligals per year. The most likely hypothesis for the increase is that it was caused by ice flowing downslope across a gravity gradient and by the sinking of the South Pole station as a result of accumulation of ice. An alternate hypothesis that the gravity increase was caused by a decrease in ice thickness, of about 40 centimeters per year, is theoretically possible but is not supported by direct evidence.

Gravity and magnetic anomalies used to delineate geologic features associated with earthquakes and aftershocks in the central Virginia seismic zone

NASA Astrophysics Data System (ADS)

Shah, A. K.; Horton, J.; McNamara, D. E.; Spears, D.; Burton, W. C.

2013-12-01

Estimating seismic hazard in intraplate environments can be challenging partly because events are relatively rare and associated data thus limited. Additionally, in areas such as the central Virginia seismic zone, numerous pre-existing faults may or may not be candidates for modern tectonic activity, and other faults may not have been mapped. It is thus important to determine whether or not specific geologic features are associated with seismic events. Geophysical and geologic data collected in response to the Mw5.8 August 23, 2011 central Virginia earthquake provide excellent tools for this purpose. Portable seismographs deployed within days of the main shock showed a series of aftershocks mostly occurring at depths of 3-8 km along a southeast-dipping tabular zone ~10 km long, interpreted as the causative fault or fault zone. These instruments also recorded shallow (< 4 km) aftershocks clustered in several areas at distances of ~2-15 km from the main fault zone. We use new airborne geophysical surveys (gravity, magnetics, radiometrics, and LiDAR) to delineate the distribution of various surface and subsurface geologic features of interest in areas where the earthquake and aftershocks took place. The main (causative fault) aftershock cluster coincides with a linear, NE-trending gravity gradient (~ 2 mgal/km) that extends over 20 km in either direction from the Mw5.8 epicenter. Gravity modeling incorporating seismic estimates of Moho variations suggests the presence of a shallow low-density body overlying the main aftershock cluster, placing it within the upper 2-4 km of the main-fault hanging wall. The gravity, magnetic, and radiometric data also show a bend in generally NE-SW orientation of anomalies close to the Mw5.8 epicenter. Most shallow aftershock clusters occur near weaker short-wavelength gravity gradients of one to several km length. In several cases these gradients correspond to geologic contacts mapped at the surface. Along the gravity gradients, the aftershocks appear to cluster near areas with cross-cutting geologic features such as Jurassic diabase dikes. These associations suggest that local variations in rock density and/or rheology may have contributed to modifications of local stress regimes in a manner encouraging localized seismicity associated with the Mw5.8 event and its aftershocks. Such associations are comparable to results of previous studies recognizing correspondences between seismicity and features such as intrusive bodies and failed rifts in the New Madrid seismic zone and elsewhere. To explore whether similar correspondences may have occurred in the past, we use regional gravity and magnetic data to consider possible relations between historical earthquakes and comparable geologic features elsewhere in the central Virginia seismic zone.

Weakening gravity on redshift-survey scales with kinetic matter mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

D'Amico, Guido; Huang, Zhiqi; Mancarella, Michele

We explore general scalar-tensor models in the presence of a kinetic mixing between matter and the scalar field, which we call Kinetic Matter Mixing. In the frame where gravity is de-mixed from the scalar this is due to disformal couplings of matter species to the gravitational sector, with disformal coefficients that depend on the gradient of the scalar field. In the frame where matter is minimally coupled, it originates from the so-called beyond Horndeski quadratic Lagrangian. We extend the Effective Theory of Interacting Dark Energy by allowing disformal coupling coefficients to depend on the gradient of the scalar field asmore » well. In this very general approach, we derive the conditions to avoid ghost and gradient instabilities and we define Kinetic Matter Mixing independently of the frame metric used to described the action. We study its phenomenological consequences for a ΛCDM background evolution, first analytically on small scales. Then, we compute the matter power spectrum and the angular spectra of the CMB anisotropies and the CMB lensing potential, on all scales. We employ the public version of COOP, a numerical Einstein-Boltzmann solver that implements very general scalar-tensor modifications of gravity. Rather uniquely, Kinetic Matter Mixing weakens gravity on short scales, predicting a lower σ{sub 8} with respect to the ΛCDM case. We propose this as a possible solution to the tension between the CMB best-fit model and low-redshift observables.« less

First Impressions of a Scintrex CG-6 Portable Gravimeter in an Extensive Field Campaign

NASA Astrophysics Data System (ADS)

van Westrum, D.; Kanney, J.

2017-12-01

First Impressions of a Scintrex CG-6 Portable Gravimeter in an Extensive Field Campaign AGU Fall Meeting 2017 Derek van Westrum and Jeff Kanney NOAA's National Geodetic Survey conducted its third and final Geoid Slope Validation Survey (GSVS) this past summer in the rugged mountains of southern Colorado. In addition to leveling, long period GPS, and defelction of vertical observations, absolute gravity and vertical gravity gradients were measured at 235 bench marks (approximately 1.5 km spacing) along US-160 between Durango and Walsenburg, Colorado. In previous surveys (Texas-2011 and Iowa-2014), an A10 absolute gravimeter was used to measure graivty at approximately 10-15% of the bench marks. The remaining marks were determined by using LaCoste & Romberg relative gravimeters. The same relative instruments were also used to measure two-tier (linear) vertical gravity gradients at the A10 sites. In the current work - becuase of the rapidly changing terrain in the Rocky Mountains - it was decided to employ the A10 at all 235 bench marks, and acquire three-tier (quadratic) gradients at every bench mark using the new Scintrex CG-6 Autograv relative gravimeter. Using these results, we will provide a real worldsummary of the CG-6's behavior by examining noise levels, repeatability, and acquisition rates. In addition, the coincident A10 absolute data set allows us to evaluate the CG-6's accuracy, and allows us to simulate and discuss various relative gravity survey designs.

Electrostatic analogy for symmetron gravity

NASA Astrophysics Data System (ADS)

Ogden, Lillie; Brown, Katherine; Mathur, Harsh; Rovelli, Kevin

2017-12-01

The symmetron model is a scalar-tensor theory of gravity with a screening mechanism that suppresses the effect of the symmetron field at high densities characteristic of the Solar System and laboratory scales but allows it to act with gravitational strength at low density on the cosmological scale. We elucidate the screening mechanism by showing that in the quasistatic Newtonian limit there are precise analogies between symmetron gravity and electrostatics for both strong and weak screening. For strong screening we find that large dense bodies behave in a manner analogous to perfect conductors in electrostatics. Based on this analogy we find that the symmetron field exhibits a lightning rod effect wherein the field gradients are enhanced near the ends of pointed or elongated objects. An ellipsoid placed in a uniform symmetron gradient is shown to experience a torque. By symmetry there is no gravitational torque in this case. Hence this effect unmasks the symmetron and might serve as the basis for future laboratory experiments. The symmetron force between a point mass and a large dense body includes a component corresponding to the interaction of the point mass with its image in the larger body. None of these effects have counterparts in the Newtonian limit of Einstein gravity. We discuss the similarities between symmetron gravity and the chameleon model as well as the differences between the two.

On the stability conditions for theories of modified gravity in the presence of matter fields

NASA Astrophysics Data System (ADS)

De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios

2017-03-01

We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all the scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.

Inversion of gravity gradient tensor data: does it provide better resolution?

NASA Astrophysics Data System (ADS)

Paoletti, V.; Fedi, M.; Italiano, F.; Florio, G.; Ialongo, S.

2016-04-01

The gravity gradient tensor (GGT) has been increasingly used in practical applications, but the advantages and the disadvantages of the analysis of GGT components versus the analysis of the vertical component of the gravity field are still debated. We analyse the performance of joint inversion of GGT components versus separate inversion of the gravity field alone, or of one tensor component. We perform our analysis by inspection of the Picard Plot, a Singular Value Decomposition tool, and analyse both synthetic data and gradiometer measurements carried out at the Vredefort structure, South Africa. We show that the main factors controlling the reliability of the inversion are algebraic ambiguity (the difference between the number of unknowns and the number of available data points) and signal-to-noise ratio. Provided that algebraic ambiguity is kept low and the noise level is small enough so that a sufficient number of SVD components can be included in the regularized solution, we find that: (i) the choice of tensor components involved in the inversion is not crucial to the overall reliability of the reconstructions; (ii) GGT inversion can yield the same resolution as inversion with a denser distribution of gravity data points, but with the advantage of using fewer measurement stations.

2D data-space cross-gradient joint inversion of MT, gravity and magnetic data

NASA Astrophysics Data System (ADS)

Pak, Yong-Chol; Li, Tonglin; Kim, Gang-Sop

2017-08-01

We have developed a data-space multiple cross-gradient joint inversion algorithm, and validated it through synthetic tests and applied it to magnetotelluric (MT), gravity and magnetic datasets acquired along a 95 km profile in Benxi-Ji'an area of northeastern China. To begin, we discuss a generalized cross-gradient joint inversion for multiple datasets and model parameters sets, and formulate it in data space. The Lagrange multiplier required for the structural coupling in the data-space method is determined using an iterative solver to avoid calculation of the inverse matrix in solving the large system of equations. Next, using model-space and data-space methods, we inverted the synthetic data and field data. Based on our result, the joint inversion in data-space not only delineates geological bodies more clearly than the separate inversion, but also yields nearly equal results with the one in model-space while consuming much less memory.

A spaceborne superconducting gravity gradiometer for mapping the earth's gravity field

NASA Technical Reports Server (NTRS)

Paik, H. J.

1981-01-01

The principles of a satellite gravity gradiometer system which measures all five independent components of the gravity gradient tensor with a sensitivity of 0.001 E/Hz to the 1/2 power or better, are analyzed, and the status of development of the system is reviewed. The superconducting gravity gradiometer uses sensitive superconducting accelerometers, each of which are composed of a weakly suspended superconducting proof mass, a superconducting magnetic transducer, and a low-noise superconducting magnetometer. The magnetic field produced by the transducer coils is modulated by the motion of the proof mass and detected by the magnetometer. A combination of two or four of such accelerometers with proper relative orientation of sensitive axes results in an in-line or a cross component gravity gradiometer.

Dimensional stability of flakeboards as affected by board specific gravity and flake alignment

Treesearch

Robert L. Geimer

1982-01-01

The objective was to determine the relationship between the variables specific gravity (SG) and flake alignment and the dimensional stability properties of flakeboard. Boards manufactured without a density gradient were exposed to various levels of relative humidity and a vacuum-pressure soak (VPS) treatment. Changes in moisture content (MC), thickness swelling, and...

GEOPHYSICAL INVESTIGATIONS OF THE STRUCTURE OF THE EARTH’S CRUST IN THE ATLANTIC OCEAN REGION,

DTIC Science & Technology

50--100 mgal and then increase to +50--70mgal. The Bouguer isoanomaly lines are denser in the transition zone and a considerable gravity gradient...data has also become more abundent. Investigations to determine relation between Bouguer gravity anomalies and the thickness of the earth’s crust

Advanced Magnetic Materials Methods and Numerical Models for Fluidization in Microgravity and Hypogravity

NASA Technical Reports Server (NTRS)

Atwater, James; Wheeler, Richard, Jr.; Akse, James; Jovanovic, Goran; Reed, Brian

2013-01-01

To support long-duration manned missions in space such as a permanent lunar base, Mars transit, or Mars Surface Mission, improved methods for the treatment of solid wastes, particularly methods that recover valuable resources, are needed. The ability to operate under microgravity and hypogravity conditions is essential to meet this objective. The utilization of magnetic forces to manipulate granular magnetic media has provided the means to treat solid wastes under variable gravity conditions by filtration using a consolidated magnetic media bed followed by thermal processing of the solid wastes in a fluidized bed reactor. Non-uniform magnetic fields will produce a magnetic field gradient in a bed of magnetically susceptible media toward the distributor plate of a fluidized bed reactor. A correctly oriented magnetic field gradient will generate a downward direct force on magnetic media that can substitute for gravitational force in microgravity, or which may augment low levels of gravity, such as on the Moon or Mars. This approach is termed Gradient Magnetically Assisted Fluidization (G-MAFB), in which the magnitude of the force on the fluidized media depends upon the intensity of the magnetic field (H), the intensity of the field gradient (dH/dz), and the magnetic susceptibility of the media. Fluidized beds based on the G-MAFB process can operate in any gravitational environment by tuning the magnetic field appropriately. Magnetic materials and methods have been developed that enable G-MAFB operation under variable gravity conditions.

Spectral characteristics of the Hellenic vertical network - Validation over Central and Northern Greece using GOCE/GRACE global geopotential models

NASA Astrophysics Data System (ADS)

Andritsanos, Vassilios D.; Vergos, George S.; Grigoriadis, Vassilios N.; Pagounis, Vassilios; Tziavos, Ilias N.

2014-05-01

The Elevation project, funded by the action "Archimedes III - Funding of research groups in T.E.I.", co-financed by the E.U. (European Social Fund) and national funds under the Operational Program "Education and Lifelong Learning 2007-2013" aims mainly to the validation of the Hellenic vertical datum. This validation is carried out over two areas under study, one in Central and another in Northern Greece. During the first stage of the validation process, satellite-only as well as combined satellite-terrestrial models of the Earth's geopotential are used. GOCE and GRACE satellite information is compared against recently measured GPS/Levelling observations at specific benchmarks of the vertical network in Attiki (Central Greece) and Thessaloniki (Northern Greece). A spectral enhancement approach is followed where, given the GOCE/GRACE GGM truncation degree, EGM2008 is used to fill-in the medium and high-frequency content along with RTM effects for the high and ultra high part. The second stage is based on the localization of possible blunders of the vertical network using the spectral information derived previously. The undoubted accuracy of the contemporary global models at the low frequency band leads to some initial conclusions about the consistency of the Hellenic vertical datum.

GOCE Re-Entry Predictions for the Italian Civil Protection Authorities

NASA Astrophysics Data System (ADS)

Pardini, Carmen; Anselmo, Luciano

2015-03-01

The uncommon nature of the GOCE reentry campaign, sharing an uncontrolled orbital decay with a finely controlled attitude along the atmospheric drag direction, made the reentry predictions for this satellite an interesting case study, especially because nobody was able to say a priori if and when the attitude control would have failed, leading to an unrestrained tumbling and a sudden variation of the orbital decay rate. As in previous cases, ISTI/CNR was in charge of reentry predictions for the Italian civil protection authorities, monitoring also the satellite decay in the frame of an international reentry campaign promoted by the Inter-Agency Space Debris Coordination Committee (IADC). Due to the peculiar nature of the GOCE reentry, the definition of reliable uncertainty windows was not easy, especially considering the critical use of this information for civil protection evaluations. However, after an initial period of test and analysis, reasonable and conservative criteria were elaborated and applied, with good and consistent results through the end of the reentry campaign. In the last three days of flight, reentries were simulated over Italy to obtain quite accurate ground tracks, debris swaths and air space crossing time windows associated with the critical passes over the national territory still included in the global uncertainty windows.

Satellite observations of atmosphere-ionosphere vertical coupling by gravity waves

NASA Astrophysics Data System (ADS)

Trinh, Thai; Ern, Manfred; Preusse, Peter; Riese, Martin

2017-04-01

The Earth's thermosphere/ionosphere (T/I) is strongly influenced by various processes from above as well as from below. One of the most important processes from below is vertical coupling by atmospheric waves. Among these waves, gravity waves (GWs) excited in the lower atmosphere, mainly in the troposphere and tropopause region, are likely essential for the mean state of the T/I system. The penetration of GWs into the T/I system is however not well understood in modeling as well as observations. In this work, we analyze the correlation between different GW parameters at lower altitudes (below 90 km) and GW induced perturbations in the T/I. At lower altitudes, GW parameters are derived from temperature observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). In the T/I, GW induced perturbations of neutral density measured by Gravity field and Ocean Circulation Explorer (GOCE) and CHAllenging Minisatellite Payload (CHAMP) are analyzed. Interestingly, we find positive correlations between the spatial distributions at low altitudes (i.e. below 90km) and the spatial distributions of GW-induced density fluctuations in the T/I (at 200km and above), which suggests that many waves seen in the T/I have their origins in the troposphere or lower stratosphere. It is also indicated that mountain waves generated near the Andes and Antarctic Peninsula propagate up to the T/I. Strong positive correlations between GW perturbations in the T/I and GW parameters at 30 km are mainly found at mid latitudes, which may be an indicator of propagation of convectively generated GWs. Increase of correlation starting from 70 km in many cases shows that filtering of the GW distribution by the background atmosphere is very important. Processes that are likely involved are GW dissipation, generation of secondary GWs, as well as horizontal propagation of GWs. Limitations of our method and of the observations are also discussed.

Integrated exploration for low-temperature geothermal resources in the Honey Lake basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schimschal, U.

An integrated exploration study is presented to locate low-temperature geothermal reservoirs in the Honey Lake area of northern California. Regional studies to locate the geothermal resources included gravity, infrared, water-temperature, and water-quality analyses. Five anomalies were mapped from resistivity surveys. Additional study of three anomalies by temperature-gradient and seismic methods was undertaken to define structure and potential of the geothermal resource. The gravity data show a graben structure in the area. Seismic reflection data, indicate faults associated with surface-resistivity and temperature-gradient data. The data support the interpretation that the shallow reservoirs are replenished along the fault zones by deeply circulatingmore » heated meteoric waters.« less

The snake geothermal drilling project. Innovative approaches to geothermal exploration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shervais, John W.; Evans, James P.; Liberty, Lee M.

2014-02-21

The goal of our project was to test innovative technologies using existing and new data, and to ground-truth these technologies using slim-hole core technology. The slim-hole core allowed us to understand subsurface stratigraphy and alteration in detail, and to correlate lithologies observed in core with surface based geophysical studies. Compiled data included geologic maps, volcanic vent distribution, structural maps, existing well logs and temperature gradient logs, groundwater temperatures, and geophysical surveys (resistivity, magnetics, gravity). New data included high-resolution gravity and magnetic surveys, high-resolution seismic surveys, three slimhole test wells, borehole wireline logs, lithology logs, water chemistry, alteration mineralogy, fracture distribution,more » and new thermal gradient measurements.« less

Integrated exploration for low-temperature geothermal resources in the Honey Lake Basin, California

USGS Publications Warehouse

Schimschal, U.

1991-01-01

An integrated exploration study is presented to locate low-temperature geothermal reservoirs in the Honey Lake area of northern California. Regional studies to locate the geothermal resources included gravity, infra-red, water-temperature, and water-quality analyses. Five anomalies were mapped from resistivity surveys. Additional study of three anomalies by temperature-gradient and seismic methods was undertaken to define structure and potential of the geothermal resource. The gravity data show a graben structure in the area. Seismic reflection data indicate faults associated with surface-resistivity and temperature-gradient data. The data support the interpretation that the shallow reservoirs are replenished along the fault zones by deeply circulating heated meteoric waters. -Author

Instability of a gravity gradient satellite due to thermal distortion

NASA Technical Reports Server (NTRS)

Goldman, R. L.

1975-01-01

A nonlinear analytical model and a corresponding computer program were developed to study the influence of solar heating on the anomalous low frequency, orbital instability of the Naval Research Laboratory's gravity gradient satellite 164. The model's formulation was based on a quasi-static approach in which deflections of the satellite's booms were determined in terms of thermally induced bending without consideration of boom vibration. Calculations, which were made for variations in absorptivity, sun angle, thermal lag, and hinge stiffness, demonstrated that, within the confines of a relatively narrow stability criteria, the quasi-static model of NRL 164 not only becomes unstable, but, in a number of cases, responses were computed that closely resembled flight data.

Experimental observation of the thermocapillary driven motion of bubbles in a molten glass under low gravity conditions

NASA Technical Reports Server (NTRS)

Smith, H. D.; Mattox, D. M.; Wilcox, W. R.; Subramanian, R. S.; Meyyappan, M.

1982-01-01

An experiment was carried out on board a Space Processing Applications Rocket with the aim of demonstrating bubble migration in molten glass due to a temperature gradient under low gravity conditions. During the flight, a sample of a sodium borate melt with a specific bubble array, contained in a platinum/fused silica cell, was subjected to a well defined temperature gradient for more than 4 minutes. Photographs taken at one second intervals during the experiment clearly show that the bubbles move toward the hot spot on the platinum heater strip. This result is consistent with the predictions of the theory of thermocapillary driven bubble motion.

Superconducting tensor gravity gradiometer

NASA Technical Reports Server (NTRS)

Paik, H. J.

1981-01-01

The employment of superconductivity and other material properties at cryogenic temperatures to fabricate sensitive, low-drift, gravity gradiometer is described. The device yields a reduction of noise of four orders of magnitude over room temperature gradiometers, and direct summation and subtraction of signals from accelerometers in varying orientations are possible with superconducting circuitry. Additional circuits permit determination of the linear and angular acceleration vectors independent of the measurement of the gravity gradient tensor. A dewar flask capable of maintaining helium in a liquid state for a year's duration is under development by NASA, and a superconducting tensor gravity gradiometer for the NASA Geodynamics Program is intended for a LEO polar trajectory to measure the harmonic expansion coefficients of the earth's gravity field up to order 300.

Demarcation of continental-oceanic transition zone using angular differences between gradients of geophysical fields

NASA Astrophysics Data System (ADS)

Jilinski, Pavel; Meju, Max A.; Fontes, Sergio L.

2013-10-01

The commonest technique for determination of the continental-oceanic crustal boundary or transition (COB) zone is based on locating and visually correlating bathymetric and potential field anomalies and constructing crustal models constrained by seismic data. In this paper, we present a simple method for spatial correlation of bathymetric and potential field geophysical anomalies. Angular differences between gradient directions are used to determine different types of correlation between gravity and bathymetric or magnetic data. It is found that the relationship between bathymetry and gravity anomalies can be correctly identified using this method. It is demonstrated, by comparison with previously published models for the southwest African margin, that this method enables the demarcation of the zone of transition from oceanic to continental crust assuming that this it is associated with geophysical anomalies, which can be correlated using gradient directions rather than magnitudes. We also applied this method, supported by 2-D gravity modelling, to the more complex Liberia and Cote d'Ivoire-Ghana sectors of the West African transform margin and obtained results that are in remarkable agreement with past predictions of the COB in that region. We suggest the use of this method for a first-pass interpretation as a prelude to rigorous modelling of the COB in frontier areas.

Microgravity Segregation in Binary Mixtures of Inelastic Spheres Driven by Velocity Fluctuation Gradients

NASA Technical Reports Server (NTRS)

Jenkins, James T.; Louge, Michel Y.

1996-01-01

We are interested in collisional granular flows of dry materials in reduced gravity. Because the particles interact through collisions, the energy of the particle velocity fluctuations plays an important role in the physics. Here we focus on the separation of grains by properties - size, for example - that is driven by spatial gradients in the fluctuation energy of the grains. The segregation of grains by size is commonly observed in geophysical flows and industrial processes. Segregation of flowing grains can also take place based on other properties, e.g. shape, mass, friction, and coefficient of restitution. Many mechanisms may be responsible for segregation; most of these are strongly influenced by gravity. Here, we outline a mechanism that is independent of gravity. This mechanism may be important but is often obscured in terrestrial grain flows. It is driven by gradients in fluctuation energy. In microgravity, the separation of grains by property will proceed slowly enough to permit flight observations to provide an unambiguous measurement of the transport coefficients associated with the segregation. In this context, we are planning a microgravity shear cell experiment that contains a mixture of two types of spherical grains. The grains will be driven to interact with two different types of boundaries on either sides of the cell. The resulting separation will be observed visually.

Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism

PubMed Central

Band, Leah R.; Wells, Darren M.; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M.; French, Andrew P.; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H.; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M.; Estelle, Mark; Owen, Markus R.; Vissenberg, Kris; Hodgman, T. Charlie; Pridmore, Tony P.; King, John R.; Vernoux, Teva; Bennett, Malcolm J.

2012-01-01

Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a “tipping point” mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution. PMID:22393022

Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism.

PubMed

Band, Leah R; Wells, Darren M; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M; French, Andrew P; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M; Estelle, Mark; Owen, Markus R; Vissenberg, Kris; Hodgman, T Charlie; Pridmore, Tony P; King, John R; Vernoux, Teva; Bennett, Malcolm J

2012-03-20

Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.

Turbulent Mixing in Gravity Currents with Transverse Shear

NASA Astrophysics Data System (ADS)

White, Brian; Helfrich, Karl; Scotti, Alberto

2010-11-01

A parallel flow with horizontal shear and horizontal density gradient undergoes an intensification of the shear by gravitational tilting and stretching, rapidly breaking down into turbulence. Such flows have the potential for substantial mixing in estuaries and the coastal ocean. We present high-resolution numerical results for the mixing efficiency of these flows, which can be viewed as gravity currents with transverse shear, and contrast them with the well-studied case of stably stratified, homogeneous turbulence (uniform vertical density and velocity gradients). For a sheared gravity current, the buoyancy flux, turbulent Reynolds stress, and dissipation are well out of equilibrium. The total kinetic energy first increases as potential energy is transferred to the gravity current, but rapidly decays once turbulence sets in. Despite the non-equilibrium character, mixing efficiencies are slightly higher but qualitatively similar to homogeneous stratified turbulence. Efficiency decreases in the highly energetic regime where the dissipation rate is large compared with viscosity and stratification, ɛ/(νN^2)>100, further declining as turbulence decays and kinetic energy dissipation dominates the buoyancy flux. In general, the mixing rate, parameterized by a turbulent eddy diffusivity, increases with the strength of the transverse shear.

Geophysical expression of a buried niobium and rare earth element deposit: the Elk Creek carbonatite, Nebraska, USA

USGS Publications Warehouse

Drenth, Benjamin J.

2014-01-01

The lower Paleozoic Elk Creek carbonatite is a 6–8-km-diameter intrusive complex buried under 200 m of sedimentary rocks in southeastern Nebraska. It hosts the largest known niobium deposit in the U.S. and a rare earth element (REE) deposit. The carbonatite is composed of several lithologies, the relations of which are poorly understood. Niobium mineralization is most enriched within a magnetite beforsite (MB) unit, and REE oxides are most concentrated in a barite beforsite unit. The carbonatite intrudes Proterozoic country rocks. Efforts to explore the carbonatite have used geophysical data and drilling. A high-resolution airborne gravity gradient and magnetic survey was flown over the carbonatite in 2012. The carbonatite is associated with a roughly annular vertical gravity gradient high and a subdued central low and a central magnetic high surrounded by magnetic field values lower than those over the country rocks. Geophysical, borehole, and physical property data are combined for an interpretation of these signatures. The carbonatite is denser than the country rocks, explaining the gravity gradient high. Most carbonatite lithologies have weaker magnetic susceptibilities than those of the country rocks, explaining why the carbonatite does not produce a magnetic high at its margin. The primary source of the central magnetic high is interpreted to be mafic rocks that are strongly magnetized and are present in large volumes. MB is very dense (mean density 3200  kg/m3) and strongly magnetized (median 0.073 magnetic susceptibility), producing a gravity gradient high and contributing to the aeromagnetic high. Barite beforsite has physical properties similar to most of the carbonatite volume, making it a poor geophysical target. Geophysical anomalies indicate the presence of dense and strongly magnetized rocks at depths below existing boreholes, either a large volume of MB or another unknown lithology.

Earth's gravity gradient and eddy currents effects on the rotational dynamics of space debris objects: Envisat case study

NASA Astrophysics Data System (ADS)

Gómez, Natalia Ortiz; Walker, Scott J. I.

2015-08-01

The space debris population has grown rapidly over the last few decades with the consequent growth of impact risk between current objects in orbit. Active Debris Removal (ADR) has been recommended to be put into practice by several National Agencies in order to remove objects that pose the biggest risk for the space community. The most immediate target that is being considered for ADR by the European Space Agency is the Earth-observing satellite Envisat. In order to safely remove such a massive object from its orbit, a capturing process followed by a controlled reentry is necessary. However, current ADR methods that require physical contact with the target have limitations on the maximum angular momentum that can be absorbed and a de-tumbling phase prior to the capturing process may be required. Therefore, it is of utmost importance for the ADR mission design to be able to predict accurately how the target will be rotating at the time of capture. This article analyses two perturbations that affect an object in Low Earth Orbit (LEO), the Earth's gravity gradient and the eddy currents induced by the Earth's magnetic field. The gravity gradient is analysed using the equation of conservation of total energy and a graphical method is presented to understand the expected behaviour of any object under the effect of this perturbation. The eddy currents are also analysed by studying the total energy of the system. The induced torque and the characteristic time of decay are presented as a function of the object's magnetic tensor. In addition, simulations were carried out for the Envisat spacecraft including the gravity gradient perturbation as well as the eddy currents effect using the International Geomagnetic Reference Field IGRF-11 to model the Earth's magnetic field. These simulations show that the combined effect of these two perturbations is a plausible explanation for the rotational speed decay observed between April 2013 and September 2013.

Impact of Orbit Position Errors on Future Satellite Gravity Models

NASA Astrophysics Data System (ADS)

Encarnacao, J.; Ditmar, P.; Klees, R.

2015-12-01

We present the results of a study of the impact of orbit positioning noise (OPN) caused by incomplete knowledge of the Earth's gravity field on gravity models estimated from satellite gravity data. The OPN is simulated as the difference between two sets of orbits integrated on the basis of different static gravity field models. The OPN is propagated into ll-SST data, here computed as averaged inter-satellite accelerations projected onto the Line of Sight (LoS) vector between the two satellites. We consider the cartwheel formation (CF), pendulum formation (PF), and trailing formation (TF) as they produce a different dominant orientation of the LoS vector. Given the polar orbits of the formations, the LoS vector is mainly aligned with the North-South direction in the TF, with the East-West direction in the PF (i.e. no along-track offset), and contains a radial component in the CF. An analytical analysis predicts that the CF suffers from a very high sensitivity to the OPN. This is a fundamental characteristic of this formation, which results from the amplification of this noise by diagonal components of the gravity gradient tensor (defined in the local frame) during the propagation into satellite gravity data. In contrast, the OPN in the data from PF and TF is only scaled by off-diagonal gravity gradient components, which are much smaller than the diagonal tensor components. A numerical analysis shows that the effect of the OPN is similar in the data collected by the TF and the PF. The amplification of the OPN errors for the CF leads to errors in the gravity model that are three orders of magnitude larger than those in case of the PF. This means that any implementation of the CF will most likely produce data with relatively low quality since this error dominates the error budget, especially at low frequencies. This is particularly critical for future gravimetric missions that will be equipped with highly accurate ranging sensors.

On the stability conditions for theories of modified gravity in the presence of matter fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios, E-mail: antonio.defelice@yukawa.kyoto-u.ac.jp, E-mail: fruscian@iap.fr, E-mail: papadomanolakis@lorentz.leidenuniv.nl

We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all themore » scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.« less

Rhizoids and protonemata of characean algae: model cells for research on polarized growth and plant gravity sensing.

PubMed

Braun, M; Limbach, C

2006-12-01

Gravitropically tip-growing rhizoids and protonemata of characean algae are well-established unicellular plant model systems for research on gravitropism. In recent years, considerable progress has been made in the understanding of the cellular and molecular mechanisms underlying gravity sensing and gravity-oriented growth. While in higher-plant statocytes the role of cytoskeletal elements, especially the actin cytoskeleton, in the mechanisms of gravity sensing is still enigmatic, there is clear evidence that in the characean cells actin is intimately involved in polarized growth, gravity sensing, and the gravitropic response mechanisms. The multiple functions of actin are orchestrated by a variety of actin-binding proteins which control actin polymerisation, regulate the dynamic remodelling of the actin filament architecture, and mediate the transport of vesicles and organelles. Actin and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Experiments performed in microgravity provided evidence that actomyosin is a key player for gravity sensing: it coordinates the position of statoliths and, upon a change in the cell's orientation, directs sedimenting statoliths to specific areas of the plasma membrane, where contact with membrane-bound gravisensor molecules elicits short gravitropic pathways. In rhizoids, gravitropic signalling leads to a local reduction of cytoplasmic free calcium and results in differential growth of the opposite subapical cell flanks. The negative gravitropic response of protonemata involves actin-dependent relocation of the calcium gradient and displacement of the centre of maximal growth towards the upper flank. On the basis of the results obtained from the gravitropic model cells, a similar fine-tuning function of the actomyosin system is discussed for the early steps of gravity sensing in higher-plant statocytes.

Tectonic evolution of the Tualatin basin, northwest Oregon, as revealed by inversion of gravity data

USGS Publications Warehouse

McPhee, Darcy K.; Langenheim, Victoria E.; Wells, Ray; Blakely, Richard J.

2014-01-01

The Tualatin basin, west of Portland (Oregon, USA), coincides with a 110 mGal gravity low along the Puget-Willamette lowland. New gravity measurements (n = 3000) reveal a three-dimensional (3-D) subsurface geometry suggesting early development as a fault-bounded pull-apart basin. A strong northwest-trending gravity gradient coincides with the Gales Creek fault, which forms the southwestern boundary of the Tualatin basin. Faults along the northeastern margin in the Portland Hills and the northeast-trending Sherwood fault along the southeastern basin margin are also associated with gravity gradients, but of smaller magnitude. The gravity low reflects the large density contrast between basin fill and the mafic crust of the Siletz terrane composing basement. Inversions of gravity data indicate that the Tualatin basin is ∼6 km deep, therefore 6 times deeper than the 1 km maximum depth of the Miocene Columba River Basalt Group (CRBG) in the basin, implying that the basin contains several kilometers of low-density pre-CRBG sediments and so formed primarily before the 15 Ma emplacement of the CRBG. The shape of the basin and the location of parallel, linear basin-bounding faults along the southwest and northeast margins suggest that the Tualatin basin originated as a pull-apart rhombochasm. Pre-CRBG extension in the Tualatin basin is consistent with an episode of late Eocene extension documented elsewhere in the Coast Ranges. The present fold and thrust geometry of the Tualatin basin, the result of Neogene compression, is superimposed on the ancestral pull-apart basin. The present 3-D basin geometry may imply stronger ground shaking along basin edges, particularly along the concealed northeast edge of the Tualatin basin beneath the greater Portland area.

Role of actin in auxin transport and transduction of gravity

NASA Astrophysics Data System (ADS)

Hu, S.; Basu, S.; Brady, S.; Muday, G.

Transport of the plant hormone auxin is polar and the direction of the hormone movement appears to be controlled by asymmetric distribution of auxin transport protein complexes. Changes in the direction of auxin transport are believed to drive asymmetric growth in response to changes in the gravity vector. To test the possibility that asymmetric distribution of the auxin transport protein complex is mediated by attachment to the actin cytoskeleton, a variety of experimental approaches have been used. The most direct demonstration of the role of the actin cytoskeleton in localization of the protein complex is the ability of one protein in this complex to bind to affinity columns containing actin filaments. Additionally, treatments of plant tissues with drugs that fragment the actin c toskeleton reducey polar transport. In order to explore this actin interaction and the affect of gravity on auxin transport and developmental polarity, embryos of the brown alga, Fucus have been examined. Fucus zygotes are initially symmetrical, but develop asymmetry in response to environmental gradients, with light gradients being the best- characterized signal. Gravity will polarize these embryos and gravity-induced polarity is randomized by clinorotation. Auxin transport also appears necessary for environmental controls of polarity, since auxin efflux inhibitors perturb both photo- and gravity-polarization at a very discrete temporal window within six hours after fertilization. The actin cytoskeleton has previously been shown to reorganize after fertilization of Fucus embryos leading to formation of an actin patch at the site of polar outgrowth. These actin patches still form in Fucus embryos treated with auxin efflux inhibitors, yet the position of these patches is randomized. Together, these results suggest that there are connections between the actin cytoskeleton, auxin transport, and gravity oriented growth and development. (Supported by NASA Grant: NAG2-1203)

Geothermal Exploration of the Winston Graben, Central New Mexico, USA

NASA Astrophysics Data System (ADS)

Sophy, M. J.; Kelley, S. A.

2011-12-01

We are assessing the geothermal potential of the Winston Graben of central New Mexico using borehole temperature logs and geophysical data. The Winston Graben is a late Cenozoic rift basin, part of the larger Rio Grande rift, which is 5 to 10 km wide and 56 km long with northern and southern termini occurring at accommodation zones that coincide with late Cenozoic volcanic lineaments. The graben is interpreted to be symmetric based on geologic mapping, with 2 km of stratigraphic offset on both the western and eastern margins. The graben is bordered by the Black Range to the west and is separated from the Rio Grande valley by the Sierra Cuchillo, a horst block made of Paleozoic rocks intruded by a laccolith. Geothermal and geophysical data, including water table measurements, well temperature logs, thermal conductivity samples, bottom hole temperatures, water chemistry, and gravity data have been extracted from the New Mexico Geothermal Database, part of the National Geothermal Database, and the Geonet Gravity and Magnetic Dataset Repository. Combined with existing geologic maps of the Winston Graben and surroundings, these data help to identify spatial relationships between geologic structures and groundwater parameters and distribution. Geothermal gradients from industry temperature-depth well profiles range from 20°C/km to 60°C/km with a spatial distribution of higher gradients located on the eastern side of the Sierra Cuchillo horst, which is where a mapped warm spring is located. Lower thermal gradients were observed to the west in the groundwater recharge area of the basin. Analysis of Bouguer gravity data indicate a gravity low coinciding with the center of the Winston Graben, which is attributed to be the deepest part of the basin, symetrically surrounded by gravity highs. Gravity highs coincide with the middle Cenozoic Morenci and Chise volcanic lineaments along the northern and southern ends of the graben. The mapped warm spring occurs at the intersection of basin bounding faults and the Chise lineament. Water table gradient information from phreatic aquifers less than 75 meters deep suggests both along axis and cross axis flow direction within the basin. Because the temperature anomalies trend east-west and water table gradients trend north-south, a two component hydrogeologic system may exist. The east-west trend may be the result of deep groundwater, heated along its flowpath beneath the basin and the Sierra Cuchillo, being forced to the surface at structural zones. Major rift bounding faults along the Sierra Cuchillo horst block serve as fluid pathways for the existing warm springs, and a low temperature geothermal resource may have formed as deep warm, and shallow cool waters interact. Planned work on this project includes collecting hydrogen and oxygen isotopic data of precipitation and groundwater which may show distinct water chemistries of a two component system, continued temperature logging of deeper wells in order to understand temperature distributions at depth, and an increased number of gravity measurements of the southern end of the Winston Graben to improve mapping of the southern accommodation zone relative to the hydrogeologic system.

Design of a Low Gravity Simulator for Performing Non-Equilibrium Investigations near the Lambda Transition of ^4He

NASA Technical Reports Server (NTRS)

Israelsson, U. E.; Duncan, R. V.

1993-01-01

A design is presented of a low gravity simulator where a magnetic field gradient is employed to oppose the hydrostatic pressure effects of gravity. It appears feasible to reduce the effective gravity environment of the helium in the cell by about two orders of magnitude. The corresponding shift in transition temperature with vertical height would be reduced to 12.7 nK/cm. Methods for instrumenting the simulator to perform high resolution investigations of non-equilibrium phenomena near the lambda point are presented. The advantages of using a low gravity simulator in searching for the predicted change in character of the superfluid transition from continuous to first order in the presence of a heat current are also discussed.

Interpretation of recent gravity profiles over the ophiolite belt, Northern Oman Mountains, United Arab Emirates

NASA Astrophysics Data System (ADS)

Khattab, M. M.

1993-04-01

The compiled Bouguer gravity anomaly map over parts of the ophiolite rocks of the Northern Oman Mountains suggests the existence of three partially serpentinized nappes: two along the Gulf of Oman coast with axes near Dadnah, near Fujira and the third 17 km SSE of Masafi. Modeling of the subsurface geology, beneath two gravity profiles (Diba-Kalba and Masafi-Fujira), is based on the occurrence (field evidence) of multiphase low-angle thrusting of the members of the Tethyan lithosphere in northern and Oman Mountains. An assumed crustal model at the Arabian continental margin, beneath the Masafi-Fujira profile, is made to explain an intense gravity gradient. Gravity interpretation is not inconsistent with a gliding mechanism for obduction of the ophiolite on this part of the Arabian continental margin.

Atmospheric gravity waves with small vertical-to-horizotal wavelength ratios

NASA Astrophysics Data System (ADS)

Song, I. S.; Jee, G.; Kim, Y. H.; Chun, H. Y.

2017-12-01

Gravity wave modes with small vertical-to-horizontal wavelength ratios of an order of 10-3 are investigated through the systematic scale analysis of governing equations for gravity wave perturbations embedded in the quasi-geostrophic large-scale flow. These waves can be categorized as acoustic gravity wave modes because their total energy is given by the sum of kinetic, potential, and elastic parts. It is found that these waves can be forced by density fluctuations multiplied by the horizontal gradients of the large-scale pressure (geopotential) fields. These theoretical findings are evaluated using the results of a high-resolution global model (Specified Chemistry WACCM with horizontal resolution of 25 km and vertical resolution of 600 m) by computing the density-related gravity-wave forcing terms from the modeling results.

LAZY Genes Mediate the Effects of Gravity on Auxin Gradients and Plant Architecture1[OPEN

PubMed Central

2017-01-01

A rice (Oryza sativa) mutant led to the discovery of a plant-specific LAZY1 protein that controls the orientation of shoots. Arabidopsis (Arabidopsis thaliana) possesses six LAZY genes having spatially distinct expression patterns. Branch angle phenotypes previously associated with single LAZY genes were here studied in roots and shoots of single and higher-order atlazy mutants. The results identify the major contributors to root and shoot branch angles and gravitropic behavior of seedling hypocotyls and primary roots. AtLAZY1 is the principal determinant of inflorescence branch angle. The weeping inflorescence phenotype of atlazy1,2,4 mutants may be due at least in part to a reversal in the gravitropism mechanism. AtLAZY2 and AtLAZY4 determined lateral root branch angle. Lateral roots of the atlazy2,4 double mutant emerged slightly upward, approximately 10° greater than perpendicular to the primary root axis, and they were agravitropic. Etiolated hypocotyls of the quadruple atlazy1,2,3,4 mutant were essentially agravitropic, but their phototropic response was robust. In light-grown seedlings, the root of the atlazy2,3,4 mutant was also agravitropic but when adapted to dim red light it displayed a reversed gravitropic response. A reversed auxin gradient across the root visualized by a fluorescent signaling reporter explained the reversed, upward bending response. We propose that AtLAZY proteins control plant architecture by coupling gravity sensing to the formation of auxin gradients that override a LAZY-independent mechanism that creates an opposing gravity-induced auxin gradient. PMID:28821594

Supplementary active stabilization of nonrigid gravity gradient satellites

NASA Technical Reports Server (NTRS)

Keat, J. E.

1972-01-01

The use of active control for stability augmentation of passive gravity gradient satellites is investigated. The reaction jet method of control is the main interest. Satellite nonrigidity is emphasized. The reduction in the Hamiltonian H is used as a control criteria. The velocities, relative to local vertical, of the jets along their force axes are shown to be of fundamental significance. A basic control scheme which satisfies the H reduction criteria is developed. Each jet is fired when its velocity becomes appropriately large. The jet is de-energized when velocity reaches zero. Firing constraints to preclude orbit alteration may be needed. Control is continued until H has been minimized. This control policy is investigated using impulse and rectangular pulse models of the jet outputs.

Preliminary Isostatic Gravity Map of Joshua Tree National Park and Vicinity, Southern California

USGS Publications Warehouse

Langenheim, V.E.; Biehler, Shawn; McPhee, D.K.; McCabe, C.A.; Watt, J.T.; Anderson, M.L.; Chuchel, B.A.; Stoffer, P.

2007-01-01

This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in Joshua Tree National Park, southern California. This map will serve as a basis for modeling the shape of basins beneath the Park and in adjacent valleys and also for determining the location and geometry of faults within the area. Local spatial variations in the Earth's gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure, reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic or structural boundaries. High-density basement rocks exposed within the Eastern Transverse Ranges include crystalline rocks that range in age from Proterozoic to Mesozoic and these rocks are generally present in the mountainous areas of the quadrangle. Alluvial sediments, usually located in the valleys, and Tertiary sedimentary rocks are characterized by low densities. However, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of basement rocks. Tertiary volcanic rocks are characterized by a wide range of densities, but, on average, are less dense than the pre-Cenozoic basement rocks. Basalt within the Park is as dense as crystalline basement, but is generally thin (less than 100 m thick; e.g., Powell, 2003). Isostatic residual gravity values within the map area range from about 44 mGal over Coachella Valley to about 8 mGal between the Mecca Hills and the Orocopia Mountains. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the San Andreas Fault bounding the east side of Coachella Valley and east-west-striking, left-lateral faults, such as the Pinto Mountain, Blue Cut, and Chiriaco Faults (Fig. 1). Gravity gradients also define concealed basin-bounding faults, such as those beneath the Chuckwalla Valley (e.g. Rotstein and others, 1976). These gradients result from juxtaposing dense basement rocks against thick Cenozoic sedimentary rocks.

Maui Gravity and Soil Gas Surveys

DOE Data Explorer

John Akerley

2010-04-01

Contains a ground-based gravity survey of South Maui and a series of soil CO2 flux and temperature surveys encompassing Maui and the Big Island. The gravity survey was collected from approximately 284 km2 and consisted of 400 gravity stations with 400 m spacing. Locations were derived with full DGPS. Station and line location, Complete Bouger Anomaly, first vertical derivative and horizontal gradient maps were calculated and produced. The soil CO2 flux and temperature surveys were conducted on the islands of Hawaii and Maui in April and July 2010. Average soil temperatures were measured over 10 cm depth using a hand-held thermocouple. Soil CO2 fluxes were measured using a portable accumulation chamber instrument.

Quantum spreading of a self-gravitating wave-packet in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-01-01

In this paper we will study for the first time how the wave-packet of a self-gravitating meso-scopic system spreads in theories beyond Einstein's general relativity. In particular, we will consider a ghost-free infinite derivative gravity, which resolves the 1 / r singularity in the potential - such that the gradient of the potential vanishes within the scale of non-locality. We will show that a quantum wave-packet spreads faster for a ghost-free and singularity-free gravity as compared to the Newtonian case, therefore providing us a unique scenario for testing classical and quantum properties of short-distance gravity in a laboratory in the near future.

Development of a Transportable Gravity Gradiometer Based on Atom Interferometry

NASA Astrophysics Data System (ADS)

Yu, N.; Kohel, J. M.; Aveline, D. C.; Kellogg, J. R.; Thompson, R. J.; Maleki, L.

2007-12-01

JPL is developing a transportable gravity gradiometer based on light-pulse atom interferometers for NASA's Earth Science Technology Office's Instrument Incubator Program. The inertial sensors in this instrument employ a quantum interference measurement technique, analogous to the precise phase measurements in atomic clocks, which offers increased sensitivity and improved long-term stability over traditional mechanical devices. We report on the implementation of this technique in JPL's gravity gradiometer, and on the current performance of the mobile instrument. We also discuss the prospects for satellite-based gravity field mapping, including high-resolution monitoring of time-varying fields from a single satellite platform and multi-component measurements of the gravitational gradient tensor, using atom interferometer-based instruments.

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

NASA Astrophysics Data System (ADS)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

Investigation of the relative effects of vascular branching structure and gravity on pulmonary arterial blood flow heterogeneity via an image-based computational model.

PubMed

Burrowes, Kelly S; Hunter, Peter J; Tawhai, Merryn H

2005-11-01

A computational model of blood flow through the human pulmonary arterial tree has been developed to investigate the relative influence of branching structure and gravity on blood flow distribution in the human lung. Geometric models of the largest arterial vessels and lobar boundaries were first derived using multidetector row x-ray computed tomography (MDCT) scans. Further accompanying arterial vessels were generated from the MDCT vessel endpoints into the lobar volumes using a volume-filling branching algorithm. Equations governing the conservation of mass and momentum were solved within the geometric model to calculate pressure, velocity, and vessel radius. Blood flow results in the anatomically based model, with and without gravity, and in a symmetric geometric model were compared to investigate their relative contributions to blood flow heterogeneity. Results showed a persistent blood flow gradient and flow heterogeneity in the absence of gravitational forces in the anatomically based model. Comparison with flow results in the symmetric model revealed that the asymmetric vascular branching structure was largely responsible for producing this heterogeneity. Analysis of average results in varying slice thicknesses illustrated a clear flow gradient because of gravity in "lower resolution" data (thicker slices), but on examination of higher resolution data, a trend was less obvious. Results suggest that although gravity does influence flow distribution, the influence of the tree branching structure is also a dominant factor. These results are consistent with high-resolution experimental studies that have demonstrated gravity to be only a minor determinant of blood flow distribution.

A Technique for Rapidly Deploying a Concentration Gradient with Applications to Microgravity

NASA Technical Reports Server (NTRS)

Leslie, Fred; Ramachandran, Narayanan

2000-01-01

The latter half of the last century has seen rapid advancements in semiconductor crystal growth powered by the demand for high performance electronics in myriad applications. The reduced gravity environment of space has also been used for crystal growth tests, especially in instances where terrestrial growth has largely been unsuccessful. While reduced gravity crystal growth affords some control of the gravity parameter, many crystals grown in space, to date, have structural flaws believed to result from convective motions during the growth phase. The character of these instabilities is not well understood but is associated with thermal and solutal density variations near the solidification interface in the presence of residual gravity and g-jitter. In order to study these instabilities in a separate, controlled space experiment, a concentration gradient would first have to be artificially established in a timely manner as an initial condition. This is generally difficult to accomplish in a microgravity environment because the momentum of the fluid injected into a test cell tends to swirl around and mix in the absence of a restoring force. The use of magnetic fields to control the motion and position of liquids has received growing interest in recent times. The possibility of using the force exerted by a non-uniform magnetic field on a ferrofluid to not only achieve fluid manipulation but also to actively control fluid motion makes it an attractive candidate for space applications. This paper describes a technique for quickly establishing a linear or exponential fluid concentration gradient using a magnetic field in place of gravity to stabilize the deployment. Also discussed is a photometric technique for measuring the concentration profile using light attenuation. Results of the ground-based experiments indicate that the concentration distribution is within 3% of the predicted value. Although any range of concentations can be realized, photometric constraints are discussed which impose some limitations on measurements.

Gravity-height correlations for unrest at calderas

NASA Astrophysics Data System (ADS)

Berrino, G.; Rymer, H.; Brown, G. C.; Corrado, G.

1992-11-01

Calderas represent the sites of the world's most serious volcanic hazards. Although eruptions are not frequent at such structures on the scale of human lifetimes, there are nevertheless often physical changes at calderas that are measurable over periods of years or decades. Such calderas are said to be in a state of unrest, and it is by studying the nature of this unrest that we may begin to understand the dynamics of eruption precursors. Here we review combined gravity and elevation data from several restless calderas, and present new data on their characteristic signatures during periods of inflation and deflation. We find that unless the Bouguer gravity anomaly at a caldera is extremely small, the free-air gradient used to correct gravity data for observed elevation changes must be the measured or calculated gradient, and not the theoretical gradient, use of which may introduce significant errors. In general, there are two models that fit most of the available data. The first involves a Mogi-type point source, and the second is a Bouguer-type infinite horizontal plane source. The density of the deforming material (usually a magma chamber) is calculated from the gravity and ground deformation data, and the best fitting model is, to a first approximation, the one producing the most realistic density. No realistic density is obtained where there are real density changes, or where the data do not fit the point source or slab model. We find that a point source model fits most of the available data, and that most data are for periods of caldera inflation. The limited examples of deflation from large silicic calderas indicate that the amount of mass loss, or magma drainage, is usually much less than the mass gain during the preceding magma intrusion. In contrast, deflationary events at basaltic calderas formed in extensional tectonic environments are associated with more significant mass loss as magma is injected into the associated fissure swarms.

Preliminary isostatic residual gravity map of the Newfoundland Mountains 30' by 60' quadrangle and east part of the Wells 30' by 60' quadrangle, Box Elder County, Utah

USGS Publications Warehouse

Langenheim, Victoria; Athens, N.D.; Churchel, B.A.; Willis, H.; Knepprath, N.E.; Rosario, Jose J.; Roza, J.; Kraushaar, S.M.; Hardwick, C.L.

2013-01-01

A new isostatic residual gravity map of the Newfoundland Mountains and east of the Wells 30×60 quadrangles of Utah is based on compilation of preexisting data and new data collected by the Utah and U.S. Geological Surveys. Pronounced gravity lows occur over Grouse Creek Valley and locally beneath the Great Salt Lake Desert, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Newfoundland, Silver Island, and Little Pigeon Mountains. Gravity values measured on pre-Tertiary basement to the north in the Bovine and Hogup Mountains are as much as 10mGal lower. Steep, linear gravity gradients may define basin-bounding faults concealed along the margins of the Newfoundland, Silver Island, and Little Pigeon Mountains, Lemay Island and the Pilot Range.

Preferred negative geotactic orientation in mobile cells: Tetrahymena results.

PubMed Central

Noever, D A; Cronise, R; Matsos, H C

1994-01-01

For the protozoan species Tetrahymena a series of airplane experiments are reported, which varied gravity as an active laboratory parameter and tested for corresponding changes in geotaxic orientation of single cells. The airplane achieved alternating periods of low (0.01 g) and high (1.8 g; g = 980 cm/s) gravity by flying repeated Keplerian parabolas. The experimental design was undertaken to clearly distinguish gravity from competing aerodynamic and chemical gradients. In this way, each culture served as its own control, with gravity level alone determining the orientational changes. On average, 6.3% of the Tetrahymena oriented vertically in low gravity, while 27% oriented vertically in high-gravity phases. Simplified physical models are explored for describing these cell trajectories as a function of gravity, aerodynamic drag, and lift. The notable effect of gravity on turning behavior is emphasized as the biophysical cause of the observed negative geotaxis in Tetrahymena. A fundamental investigation of the biological gravity receptor (if it exists) and improved modeling for vertical migration in important types of ocean plankton motivate the present research. Images FIGURE 1 PMID:7858146

Preferred Negative Geotactic Orientation in Mobile Cells: Tetrahymena Results

NASA Technical Reports Server (NTRS)

Noever, David A.; Cronise, Raymond; Matsos, Helen C.

1994-01-01

For the protozoan species Tetrahymena a series of airplane experiments are reported, which varied gravity as an active laboratory parameter and tested for corresponding changes in geotaxic orientation of single cells. The airplane achieved altemating periods of low (0.01 g) and high (1.8 g, g = 980 cm/s) gravity by flying repeated Keplerian parabolas. The experimental design was undertaken to clearly distinguish gravity from competing aerodynamic and chemical gradients. In this way, each culture served as its own control, with gravity level alone determining the orientational changes. On average, 6.3% of the Tetrahymena oriented vertically in low gravity, while 27% oriented vertically in high-gravity phases. Simplified physical models are explored for describing these cell trajectores as a function of gravity, aerodynamic drag, and lift. The notable effect of gravity on turning behavior is emphasized as the biophysical cause of the observed negative geotaxis in Tetrahymena. A fundamental investigation of the biological gravity receptor (it it exists) and improved modeling for vertical migration in important types of ocean plankton motivate the present research.

Joint Inversion of Gravity and Gravity Tensor Data Using the Structural Index as Weighting Function Rate Decay

NASA Astrophysics Data System (ADS)

Ialongo, S.; Cella, F.; Fedi, M.; Florio, G.

2011-12-01

Most geophysical inversion problems are characterized by a number of data considerably higher than the number of the unknown parameters. This corresponds to solve highly underdetermined systems. To get a unique solution, a priori information must be therefore introduced. We here analyze the inversion of the gravity gradient tensor (GGT). Previous approaches to invert jointly or independently more gradient components are by Li (2001) proposing an algorithm using a depth weighting function and Zhdanov et alii (2004), providing a well focused inversion of gradient data. Both the methods give a much-improved solution compared with the minimum length solution, which is invariably shallow and not representative of the true source distribution. For very undetermined problems, this feature is due to the role of the depth weighting matrices used by both the methods. Recently, Cella and Fedi (2011) showed however that for magnetic and gravity data the depth weighting function has to be defined carefully, under a preliminary application of Euler Deconvolution or Depth from Extreme Point methods, yielding the appropriate structural index and then using it as the rate decay of the weighting function. We therefore propose to extend this last approach to invert jointly or independently the GGT tensor using the structural index as weighting function rate decay. In case of a joint inversion, gravity data can be added as well. This multicomponent case is also relevant because the simultaneous use of several components and gravity increase the number of data and reduce the algebraic ambiguity compared to the inversion of a single component. The reduction of such ambiguity was shown in Fedi et al, (2005) decisive to get an improved depth resolution in inverse problems, independently from any form of depth weighting function. The method is demonstrated to synthetic cases and applied to real cases, such as the Vredefort impact area (South Africa), characterized by a complex density distribution, well defining a central uplift area, ring structures and low density sediments. REFERENCES Cella F., and Fedi M., 2011, Inversion of potential field data using the structural index as weighting function rate decay, Geophysical Prospecting, doi: 10.1111/j.1365-2478.2011.00974.x Fedi M., Hansen P. C., and Paoletti V., 2005 Analysis of depth resolution in potential-field inversion. Geophysics, 70, NO. 6 Li, Y., 2001, 3-D inversion of gravity gradiometry data: 71st Annual Meeting, SEG, Expanded Abstracts, 1470-1473. Zhdanov, M. S., Ellis, R. G., and Mukherjee, S., 2004, Regularized focusing inversion of 3-D gravity tensor data: Geophysics, 69, 925-937.

Effects of artificial gravity on the cardiovascular system: Computational approach

NASA Astrophysics Data System (ADS)

Diaz Artiles, Ana; Heldt, Thomas; Young, Laurence R.

2016-09-01

Artificial gravity has been suggested as a multisystem countermeasure against the negative effects of weightlessness. However, many questions regarding the appropriate configuration are still unanswered, including optimal g-level, angular velocity, gravity gradient, and exercise protocol. Mathematical models can provide unique insight into these questions, particularly when experimental data is very expensive or difficult to obtain. In this research effort, a cardiovascular lumped-parameter model is developed to simulate the short-term transient hemodynamic response to artificial gravity exposure combined with ergometer exercise, using a bicycle mounted on a short-radius centrifuge. The model is thoroughly described and preliminary simulations are conducted to show the model capabilities and potential applications. The model consists of 21 compartments (including systemic circulation, pulmonary circulation, and a cardiac model), and it also includes the rapid cardiovascular control systems (arterial baroreflex and cardiopulmonary reflex). In addition, the pressure gradient resulting from short-radius centrifugation is captured in the model using hydrostatic pressure sources located at each compartment. The model also includes the cardiovascular effects resulting from exercise such as the muscle pump effect. An initial set of artificial gravity simulations were implemented using the Massachusetts Institute of Technology (MIT) Compact-Radius Centrifuge (CRC) configuration. Three centripetal acceleration (artificial gravity) levels were chosen: 1 g, 1.2 g, and 1.4 g, referenced to the subject's feet. Each simulation lasted 15.5 minutes and included a baseline period, the spin-up process, the ergometer exercise period (5 minutes of ergometer exercise at 30 W with a simulated pedal cadence of 60 RPM), and the spin-down process. Results showed that the cardiovascular model is able to predict the cardiovascular dynamics during gravity changes, as well as the expected steady-state cardiovascular behavior during sustained artificial gravity and exercise. Further validation of the model was performed using experimental data from the combined exercise and artificial gravity experiments conducted on the MIT CRC, and these results will be presented separately in future publications. This unique computational framework can be used to simulate a variety of centrifuge configuration and exercise intensities to improve understanding and inform decisions about future implementation of artificial gravity in space.

Solitary plasma rings and magnetic field generation involving gravity and differential rotation

NASA Astrophysics Data System (ADS)

Coppi, B.

2012-12-01

A new theoretical framework for describing how magnetic fields are generated and amplified is provided by finding magneto-gravitational modes that involve gravity, density gradients, and differential rotation in an essential way. Other factors, such as the presence of a high temperature particle population or of a temperature gradient, can contribute to their excitation. These modes identified by a linearized analysis are shown to be important for the evolution of plasma disks surrounding black holes toward different configurations. Since the nonlinear development of these modes can lead to radially localized regions with a relatively small differential rotation, new stationary structures have been identified, in the (fully) nonlinear limit, which are localized radially over regions with negligible gradients of the rotation frequency. These structures, characterized by solitary plasma rings, do not involve a pre-existing "seed" magnetic field, unlike other configurations found previously. The relevant magnetic energy density is comparable to the gravitationally confined plasma pressure. The "source" of these configurations is the combination of the gravitational force and of the plasma density gradient orthogonal to it that is an important factor in the theory of magneto-gravitational modes, another important factor being an anisotropy of the plasma pressure.

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

NASA Astrophysics Data System (ADS)

Featherstone, W. E.; McCubbine, J. C.; Brown, N. J.; Claessens, S. J.; Filmer, M. S.; Kirby, J. F.

2018-02-01

We describe the computation of the first Australian quasigeoid model to include error estimates as a function of location that have been propagated from uncertainties in the EGM2008 global model, land and altimeter-derived gravity anomalies and terrain corrections. The model has been extended to include Australia's offshore territories and maritime boundaries using newer datasets comprising an additional {˜ }280,000 land gravity observations, a newer altimeter-derived marine gravity anomaly grid, and terrain corrections at 1^' ' }× 1^' ' } resolution. The error propagation uses a remove-restore approach, where the EGM2008 quasigeoid and gravity anomaly error grids are augmented by errors propagated through a modified Stokes integral from the errors in the altimeter gravity anomalies, land gravity observations and terrain corrections. The gravimetric quasigeoid errors (one sigma) are 50-60 mm across most of the Australian landmass, increasing to {˜ }100 mm in regions of steep horizontal gravity gradients or the mountains, and are commensurate with external estimates.

Satellite borne gravity gradiometer study

NASA Technical Reports Server (NTRS)

Metzger, E.; Jircitano, A.; Affleck, C.

1976-01-01

Gravity gradiometry is recognized to be a very difficult instrumentation problem because extremely small differential acceleration levels have to be measured, 0.1 EU corresponds to an acceleration of 10 to the minus 11th power g at two points 1 meter apart. A feasibility model of a gravity gradiometer is being developed for airborne applications using four modified versions of the proven Model VII accelerometers mounted on a slowly rotating fixture. Gravity gradients are being measured to 1.07 EU in a vertical rotation axis orientation. Equally significant are the outstanding operational characteristics such as fast reaction time, low temperature coefficients and high degree of bias stability over long periods of time. The rotating accelerometer gravity gradiometer approach and its present status is discussed and it is the foundation for the orbital gravity gradiometer analyzed. The performance levels achieved in a 1 g environment of the earth and under relatively high seismic disturbances, lend the orbital gravity gradiometer a high confidence level of success.

Aeromagnetic and Gravity Maps of the Central Marysvale Volcanic Field, Southwestern Utah

USGS Publications Warehouse

Campbell, David L.; Steven, Thomas A.; Cunningham, Charles G.; Rowley, Peter D.

1999-01-01

Gravity and aeromagnetic features in the Marysvale volcanic field result from the composite effects of many factors, including rock composition, style of magmatic emplacement, type and intensity of rock alteration, and effects of structural evolution. Densities and magnetic properties measured on a suite of rock samples from the Marysvale volcanic field differ in systematic ways. Generally, the measured densities, magnetic susceptibilities, and natural remanent magnetizations all increase with mafic index, but decrease with degree of alteration, and for tuffs, with degree of welding. Koenigsberger Q indices show no such systematic trends. The study area is divided into three geophysical domains. The northern domain is dominated by aeromagnetic lows that probably reflect reversed-polarity volcanic flows. There are no intermediate-sized magnetic highs in the northern domain that might reflect plutons. The northern domain has a decreasing-to-the-south gravity gradient that reflects the Pavant Range homocline. The central domain has gravity lows that reflect altered rocks in calderas and low-density plutons of the Marysvale volcanic field. Its aeromagnetic signatures consist of rounded highs that reflect plutons and birdseye patterns that reflect volcanic flows. In many places the birdseyes are attenuated, indicating that the flows there have been hydrothermally altered. We interpret the central domain to reflect an east-trending locus of plutons in the Marysvale volcanic field. The southern domain has intermediate gravity fields, indicating somewhat denser rocks there than in the central domain, and high-amplitude aeromagnetic birdseyes that reflect unaltered volcanic units. The southern domain contains no magnetic signatures that we interpret to reflect plutons. Basin-and-range tectonism has overprinted additional gravity features on the three domains. A deep gravity low follows the Sevier and Marysvale Valleys, reflecting grabens there. The gravity gradient in the north reflects the southern flank of a structural dome that led to the Pavant Range homocline and whose southern edge lies along the Clear Creek downwarp.

Toward an improved determination of Earth's lithospheric magnetic field from satellite observations

NASA Astrophysics Data System (ADS)

Kotsiaros, S.

2016-12-01

An analytical and numerical analysis of the spectral properties of the gradient tensor, initially performed by Rummel and van Gelderen (1992) for the gravity potential, shows that when the tensor elements are grouped into sets of semi-tangential and pure-tangential parts, they produce almost identical signal content as the normal element. Moreover, simple eigenvalue relations can be derived between these sets and the spherical harmonic expansion of the potential. This theoretical development generally applies to any potential field. First, the analysis of Rummel and van Gelderen (1992) is adapted to the magnetic field case and then the elements of the magnetic gradient tensor are estimated by 2 years of Swarm data and grouped into Γ(1) = {[∇B]rθ,[∇B]rφ} resp. Γ(2) = {[∇B]θθ-[∇B]φφ, 2[∇B]θφ}. It is shown that the estimated combinations Γ(1) and Γ(2) produce similar signal content as the theoretical radial gradient [∇B]rr. These results demonstrate the ability of multi-satellite missions such as Swarm, which cannot directly measure the radial gradient, to retrieve similar signal content by means of the horizontal gradients. Finally, lithospheric field models are derived using the gradient combinations Γ(1) and Γ(2) and compared with models derived from traditional vector and gradient data. The model resulting from Γ(1) leads to a very similar, and in particular cases improved, model compared to models retrieved by using approximately three times more data, i.e. a full set of vector, North-South and East-West gradients. ReferencesRummel, R., and M. van Gelderen (1992), Spectral analysis of the full gravity tensor, Geophysical Journal International, 111 (1), 159-169.

Improving the quality of marine geophysical track line data: Along-track analysis

NASA Astrophysics Data System (ADS)

Chandler, Michael T.; Wessel, Paul

2008-02-01

We have examined 4918 track line geophysics cruises archived at the U.S. National Geophysical Data Center (NGDC) using comprehensive error checking methods. Each cruise was checked for observation outliers, excessive gradients, metadata consistency, and general agreement with satellite altimetry-derived gravity and predicted bathymetry grids. Thresholds for error checking were determined empirically through inspection of histograms for all geophysical values, gradients, and differences with gridded data sampled along ship tracks. Robust regression was used to detect systematic scale and offset errors found by comparing ship bathymetry and free-air anomalies to the corresponding values from global grids. We found many recurring error types in the NGDC archive, including poor navigation, inappropriately scaled or offset data, excessive gradients, and extended offsets in depth and gravity when compared to global grids. While ˜5-10% of bathymetry and free-air gravity records fail our conservative tests, residual magnetic errors may exceed twice this proportion. These errors hinder the effective use of the data and may lead to mistakes in interpretation. To enable the removal of gross errors without over-writing original cruise data, we developed an errata system that concisely reports all errors encountered in a cruise. With such errata files, scientists may share cruise corrections, thereby preventing redundant processing. We have implemented these quality control methods in the modified MGD77 supplement to the Generic Mapping Tools software suite.

Gravitropic mechanisms derived from space experiments and magnetic gradients.

NASA Astrophysics Data System (ADS)

Hasenstein, Karl H.; Park, Myoung Ryoul

2016-07-01

Gravitropism is the result of a complex sequence of events that begins with the movement of dense particles, typically starch-filled amyloplasts in response to reorientation. Although these organelles change positions, it is not clear whether the critical signal is derived from sedimentation or dynamic interactions of amyloplasts with relevant membranes. Substituting gravity by high-gradient magnetic fields (HGMF) provides a localized stimulus for diamagnetic starch that is specific for amyloplasts and comparable to gravity without affecting other organelles. Experiments with Brassica rapa showed induction of root curvature by HGMF when roots moved sufficiently close to the magnetic gradient-inducing foci. The focused and short-range effectiveness of HGMFs provided a gravity-like stimulus and affected related gene expression. Root curvature was sensitive to the mutual alignment between roots and HGMF direction. Unrelated to any HGMF effects, the size of amyloplasts in space-grown roots increased by 30% compared to ground controls and suggests enhanced sensitivity in a gravity-reduced environment. Accompanying gene transcription studies showed greater differences between HGMF-exposed and space controls than between space and ground controls. This observation may lead to the identification of gravitropism-relevant genes. However, space grown roots showed stronger transcription of common reference genes such as actin and ubiquitin in magnetic fields than in non-magnetic conditions. In contrast, α-amylase, glucokinase and PIN encoding genes were transcribed stronger under non-magnetic conditions than under HGMF. The large number of comparisons between space, ground, and HGMF prompted the assessment of transcription differences between root segments, root-shoot junction, and seeds. Because presumed transcription of reference genes varied more than genes of interest, changes in gene expression cannot be based on reference genes. The data provide an example of complex and different responses to microgravity conditions, induced curvature, ground controls, clinorotation, and magnetic field exposure.

Spaceborne gravity gradiometry characterizing the data type

NASA Technical Reports Server (NTRS)

Sonnabend, D.

1987-01-01

Satellite gravity gradiometers, particularly the two stage drag free carrier vehicle are discussed. An inner stage, carrying the tracking antenna(s), measures the relative position of the internal free proof mass, and feeds this to a set of magnetic forcers, acting against the outer or main vehicle. As the external forces on the inner stage are low, and as the position relative to the proof mass is tightly controlled, carrier phase disturbances are greatly reduced. The arrangement lowers instantaneous accelerations. It is stressed that gravity gradiometers do not measure gradients, they measure components of an intrinsic tensor.

New 2D dilaton gravity for nonsingular black holes

NASA Astrophysics Data System (ADS)

Kunstatter, Gabor; Maeda, Hideki; Taves, Tim

2016-05-01

We construct a two-dimensional action that is an extension of spherically symmetric Einstein-Lanczos-Lovelock (ELL) gravity. The action contains arbitrary functions of the areal radius and the norm squared of its gradient, but the field equations are second order and obey Birkhoff’s theorem. In complete analogy with spherically symmetric ELL gravity, the field equations admit the generalized Misner-Sharp mass as the first integral that determines the form of the vacuum solution. The arbitrary functions in the action allow for vacuum solutions that describe a larger class of interesting nonsingular black hole spacetimes than previously available.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohner, Bíborka; Endrődi, Balázs; Tóth, Ágota, E-mail: atoth@chem.u-szeged.hu

The precipitation reaction of calcium oxalate is studied experimentally in the presence of spatial gradients by controlled flow of calcium into oxalate solution. The density difference between the reactants leads to strong convection in the form of a gravity current that drives the spatiotemporal pattern formation. The phase diagram of the system is constructed, the evolving precipitate patterns are analyzed and quantitatively characterized by their diameters and the average height of the gravity flow. The compact structures of calcium oxalate monohydrate produced at low flow rates are replaced by the thermodynamically unstable calcium oxalate dihydrate favored in the presence ofmore » a strong gravity current.« less

Geographic variation in wood specific gravity: effects of latitude, temperature, and precipitation

Treesearch

Michael C. Wiemann; G. Bruce Williamson

2002-01-01

Wood basic specific gravity (SG) was compared at sites located along a gradient from 52°N latitude to the equator. Mean SG increased by 0.0049 per °C mean annual temperature (MAT), and decreased by 0.00017 per cm of mean annual precipitation (MAP). Considered alone, MAT was a better predictor of mean SG across the temperate zone (3-22°C MAT,...

Lineaments in the Shamakhy-Gobustan and Absheron hydrocarbon containing areas using gravity data

NASA Astrophysics Data System (ADS)

Elmas, Ali; Karsli, Hakan; Kadirov, Fakhraddin A.

2017-12-01

In this study, we purposed to investigate the edge of geostructures and position of existing faults of the Shamakhy-Gobustan and Absheron hydrocarbon containing regions in Azerbaijan. For this purpose, the horizontal gradient, analytic signal, tilt angle, and hyperbolic of tilt angle methods were applied to the first vertical derivative of gravity data instead of Bouguer gravity data. We obtained the maps that show the previous lineaments which were designated by considering the maximum contours of horizontal gradient, analytic signal maps, and zero values of tilt angle, hyperbolic of tilt angle maps. The geometry of basement interface was also modeled utilizing the Parker-Oldenburg algorithm to understand the sediment thickness and coherency or incoherency between the gravity values and basement topography. The lineaments were held a candle to most current tectonic structure map of the study area. It was seen that the techniques used in this study are very effective to determine the old and new lineaments in the Shamakhy-Gobustan and Absheron regions. The epicenter distribution of earthquakes within the study area supports the new lineaments which are extracted by our interpretation. We concluded that better comprehension of Azerbaijan geostructures and its effect on the large scale works will be provided by means of this study.

Lineaments in the Shamakhy-Gobustan and Absheron hydrocarbon containing areas using gravity data

NASA Astrophysics Data System (ADS)

Elmas, Ali; Karsli, Hakan; Kadirov, Fakhraddin A.

2018-02-01

In this study, we purposed to investigate the edge of geostructures and position of existing faults of the Shamakhy-Gobustan and Absheron hydrocarbon containing regions in Azerbaijan. For this purpose, the horizontal gradient, analytic signal, tilt angle, and hyperbolic of tilt angle methods were applied to the first vertical derivative of gravity data instead of Bouguer gravity data. We obtained the maps that show the previous lineaments which were designated by considering the maximum contours of horizontal gradient, analytic signal maps, and zero values of tilt angle, hyperbolic of tilt angle maps. The geometry of basement interface was also modeled utilizing the Parker-Oldenburg algorithm to understand the sediment thickness and coherency or incoherency between the gravity values and basement topography. The lineaments were held a candle to most current tectonic structure map of the study area. It was seen that the techniques used in this study are very effective to determine the old and new lineaments in the Shamakhy-Gobustan and Absheron regions. The epicenter distribution of earthquakes within the study area supports the new lineaments which are extracted by our interpretation. We concluded that better comprehension of Azerbaijan geostructures and its effect on the large scale works will be provided by means of this study.

Numerical Analysis of Temperature Gradients and Interface Shape During Directional Solidification of Al and Al-Cu Alloy Under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Bune, Andris V.; Sen, Subhayu; Mukherjee, Sundeep; Catalina, Adrian; Stefanescu, Doru M.

1999-01-01

Numerical modeling was undertaken to analyze the influence of radial thermal gradient on solid/liquid (s/1) interface shape and convection patterns during solidification of pure Al and Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a s/l interface. These predictions would then be used to define the minimum gravity level (g) required to investigate the fundamental physics of interaction between a particle and a s/I interface. To satisfy this objective, steady state calculations were performed for different gravity levels and orientations with the gravity vector. ne furnace configuration used in this analysis is the proposed International Space Station Furnace, Quench Module Insert (QMI) 1. Results from a thermal model of the furnace core were used as initial boundary conditions for solidification modeling. General model of binary alloy solidification was based on the finite element code FIDAP. It was found that for the worst case orientation of 90 degrees with the gravity vector and a g level of 10(exp -4)g(sub o) (g(sub o) = 9.8 m/s(exp 2)) the dominant forces acting on the particle would be the fundamental drag and interfacial forces.

Selection of suitable reference genes from bone cells in large gradient high magnetic field based on GeNorm algorithm.

PubMed

Di, Shengmeng; Tian, Zongcheng; Qian, Airong; Gao, Xiang; Yu, Dan; Brandi, Maria Luisa; Shang, Peng

2011-12-01

Studies of animals and humans subjected to spaceflight demonstrate that weightlessness negatively affects the mass and mechanical properties of bone tissue. Bone cells could sense and respond to the gravity unloading, and genes sensitive to gravity change were considered to play a critical role in the mechanotransduction of bone cells. To evaluate the fold-change of gene expression, appropriate reference genes should be identified because there is no housekeeping gene having stable expression in all experimental conditions. Consequently, expression stability of ten candidate housekeeping genes were examined in osteoblast-like MC3T3-E1, osteocyte-like MLO-Y4, and preosteoclast-like FLG29.1 cells under different apparent gravities (μg, 1 g, and 2 g) in the high-intensity gradient magnetic field produced by a superconducting magnet. The results showed that the relative expression of these ten candidate housekeeping genes was different in different bone cells; Moreover, the most suitable reference genes of the same cells in altered gravity conditions were also different from that in strong magnetic field. It demonstrated the importance of selecting suitable reference genes in experimental set-ups. Furthermore, it provides an alternative choice to the traditionally accepted housekeeping genes used so far about studies of gravitational biology and magneto biology.

Density response of the mesospheric sodium layer to gravity wave perturbations

NASA Technical Reports Server (NTRS)

Shelton, J. D.; Gardner, C. S.; Sechrist, C. F., Jr.

1980-01-01

Lidar observations of the mesospheric sodium layer often reveal wavelike features moving through the layer. It is often assumed that these features are a layer density response to gravity waves. Chiu and Ching (1978) described the approximate form of the linear response of atmospheric layers to gravity waves. In this paper, their results are used to predict the response of the sodium layer to gravity waves. These simulations are compared with experimental observations and a good correlation is found between the two. Because of the thickness of the sodium layer and the density gradients found in it, a linear model of the layer response is not always adequate to describe gravity wave-sodium layer interactions. Inclusion of nonlinearities in the layer response is briefly discussed. Experimental data is seen to contain features consistent with the predicted nonlinearities.

Preliminary isostatic gravity map of the Grouse Creek and east part of the Jackpot 30 by 60 quadrangles, Box Elder County, Utah, and Cassia County, Idaho

USGS Publications Warehouse

Langenheim, Victoria; Willis, H.; Athens, N.D.; Chuchel, Bruce A.; Roza, J.; Hiscock, H.I.; Hardwick, C.L.; Kraushaar, S.M.; Knepprath, N.E.; Rosario, Jose J.

2013-01-01

A new isostatic residual gravity map of the northwest corner of Utah is based on compilation of preexisting data and new data collected by the Utah and United States Geological Surveys. Pronounced gravity lows occur over Junction, Grouse Creek, and upper Raft River Valleys, indicating significant thickness of low-density Tertiary sedimentary rocks and deposits. Gravity highs coincide with exposures of dense pre-Cenozoic rocks in the Raft River Mountains. Higher values in the eastern part of the map may be produced in part by deeper crustal density variations or crustal thinning. Steep linear gravity gradients coincide with mapped Neogene normal faults near Goose Creek and may define basin-bounding faults concealed beneath Junction and Upper Raft River Valleys.

Electrostatic Accelerometer for the Gravity Recovery and Climate Experiment Follow-On Mission (GRACE FO)

NASA Astrophysics Data System (ADS)

Perrot, Eddy; Christophe, Bruno; Foulon, Bernard; Boulanger, Damien; Liorzou, Françoise; Lebat, Vincent

2013-04-01

The GRACE FO mission, led by the JPL (Jet Propulsion Laboratory), is an Earth-orbiting gravity mission, continuation of the GRACE mission, that will produce an accurate model of the Earth's gravity field variation providing global climatic data during five year at least. The mission involves two satellites in a loosely controlled tandem formation, with a micro-wave link measuring the inter-satellites distance variation. Non-uniformities in the distribution of the Earth's mass cause the distance between the two satellites to vary. This variation is measured to recover gravity, after substracting the non-gravitational contributors, as the residual drag. ONERA (the French Aerospace Lab) is developing and manufacturing electrostatic accelerometers measuring this residual drag applied on the satellites. The accelerometer is composed of two main parts: the Sensor Unit (including the Sensor Unit Mechanics and the Front-End Electronic Unit) and the Interface Control Unit. In the Accelerometer Core, located in the Sensor Unit Mechanics, the proof mass is levitated and maintained in a center of an electrode cage by electrostatic forces. Thus, any drag acceleration applied on the satellite involves a variation on the servo-controlled electrostatic suspension of the mass. The voltage on the electrodes providing this electrostatic force is the measurement output of the accelerometer. The impact of the accelerometer defaults (geometry, electronic and parasitic forces) leads to bias, misalignment and scale factor error, non-linearity and noise. Some of these accelerometer defaults are characterized by tests with micro-gravity pendulum bench and with drops in ZARM catapult. Besides, a thermal stability is needed for the accelerometer core and front-end electronics to avoid bias and scale factor variation. To reach this stability, the sensor unit is enclosed in a thermal box designed by Astrium, spacecraft manufacturer. The accelerometers are designed to endure mechanical excitation especially due to launching vibrations. As the measure must be accurate, no displacements or sliding must appear during excitations. The electrode cage is made of glass material (ULE), which is very critical, in particular due to the free motion of the proof-mass during the launch. Specific analysis on this part is realized to ensure mechanical behavior. The design of electrostatic accelerometer of the GRACE Follow-On mission benefits of the GRACE heritage, GOCE launched in 2009 and MICROSCOPE which will be launched in 2016, including some improvement to win in performance, in particular the thermal sensitivity of the measurements.

The Role of the Upper Atmosphere for Dawn-Dusk and Interhemispheric Differences in the Coupled Magnetosphere-Ionosphere-Thermosphere System

NASA Astrophysics Data System (ADS)

Foerster, M.; Doornbos, E.; Haaland, S.

2016-12-01

Solar wind and IMF interaction with the geomagnetic field sets up a large-scale plasma circulation in the Earth's magnetosphere and the magnetically tightly connected ionosphere. The ionospheric ExB ion drift at polar latitudes accelerates the neutral gas as a nondivergent momentum source primarily in force balance with pressure gradients, while the neutral upper thermosphere circulation is essentially modified by apparent forces due to Earth's rotation (Coriolis and centrifugal forces) as well as advection and viscous forces. The apparent forces affect the dawn and dusk side asymmetrically, favouring a large dusk-side neutral wind vortex, while the non-dipolar portions of the Earth's magnetic field constitute significant hemispheric differences in magnetic flux and field configurations that lead to essential interhemispheric differences of the ion-neutral interaction. We present statistical studies of both the high-latitude ionospheric convection and the upper thermospheric circulation patterns based on measurements of the electron drift instrument (EDI) on board the Cluster satellites and by the accelerometer on board the CHAMP, GOCE, and Swarm spacecraft, respectively.

Analysis of the depletion of a stored aerosol in low gravity

NASA Technical Reports Server (NTRS)

Squires, P.

1977-01-01

The depletion of an aerosol stored in a container has been studied in l-g and in low gravity. Models were developed for sedimentation, coagulation and diffusional losses to the walls. The overall depletion caused by these three mechanisms is predicted to be of order 5 to 8 percent per hour in terrestrial conditions, which agrees with laboratory experience. Applying the models to a low gravity situation indicates that there only coagulation will be significant. (Gravity influences diffusional losses because of convection currents caused by random temperature gradients). For the types of aerosol studied, the rate of depletion of particles should be somewhat less than 0.001 N percent per hour, where N is the concentration per cu cm.

The mean Evershed flow

NASA Astrophysics Data System (ADS)

Hu, W.-R.

1984-09-01

The paper gives a theoretical analysis of the overall characteristics of the Evershed flow (one of the main features of sunspots), with particular attention given to its outward flow from the umbra in the photosphere, reaching a maximum somewhere in the penumbra, and decreasing rapidly further out, and its inward flow of a comparable magnitude in chromosphere. Because the inertial force of the flow is small, the relevant dynamic process can be divided into a base state and a perturbation. The base-state solution yields the equilibrium relations between the pressure gradient, the Lorentz force, and gravity, and the flow law. The perturbation describes the force driving the Evershed flow. Since the pressure gradient in the base state is already in equilibrium with the Lorentz force and the gravity, the driving force of the mean Evershed flow is small.

Calculated in situ rock density from gravity observations, UA-1 (Cannikin) emplacement hole, Amchitka Island, Alaska

USGS Publications Warehouse

Healey, D.L.

1971-01-01

Gravity observations were made on the ground surface and at a depth of 5,854 feet in drill hole UA-1. Two attempts to measure the free-air gradient utilizing the headframe over the drill hole were unsuccessful owing to mechanical vibrations in the structure. Because of the uncertainty in the measured free-air gradients these values were discarded and the average value (0.09406 mgal/ft) was used in the calculations. The calculated in situ bulk density is 2.36 g/cc. The weighted average bulk density determined from 47 core samples taken in the adjacent UAE-1 drill hole is also 2.36 g/cc. An analysis of selected portions of density logs provides an in situ bulk density of 2.37 g/cc.

Interpretation of gravity anomalies in the northwest Adirondack lowlands, northern New York

DOE Office of Scientific and Technical Information (OSTI.GOV)

Revetta, F.A.; O'Brian, B.

1993-03-01

Twelve hundred gravity measurements were made in the Adirondack Highlands and northwest Adirondack Lowlands, New York between 44[degree]15 minutes and 44[degree]30 minutes N. Latitude and 75[degree]00 minutes W. Longitude. A Bouguer gravity map constructed from the gravity measurements includes the Carthage-Colton Mylonite Zone, a major structural boundary between the highlands and lowlands. The gravity map indicates the gravity contours trend parallel to the CCMZ along most of its length however in some areas the contours cross the boundary. No clear-cut relationships exists between the CCMZ and gravity contours. The Bouguer gravity map shows several prominent gravity anomalies which correlate withmore » the geology seismicity and mineral deposits in the area. Gravity lows of 20 to 30 g.u. are centered over the Gouverneur, Hyde and Payne Lake Alaskite gneiss bodies. A gravity high of 20 g.u. occurs over the Pleasant Lake gabbro pluton. Gravity highs of 35 and 100 g.u. occur over the Sylvia Lake Zinc District and marble just north of the district. A gravity high at Russell, N.Y. coincides with a cluster of nine earthquake epicenters. Finally a steep gravity gradient separates high density rocks from lower density rocks along the Black Lake fault. Two-dimensional computer modeling of the geologic features is underway and quantitative models of the structures will be presented.« less

GOCE-based height system unification between Greece and Turkey. First considerations over marine and land areas

NASA Astrophysics Data System (ADS)

Vergos, Georgios S.; Erol, Bihter; Natsiopoulos, Dimitrios A.; Grigoriadis, Vassilios N.; Serkan Işık, Mustafa; Tziavos, Ilias N.

2016-04-01

The unification of local vertical Datums (LVDs) at a country-wide scale has gained significant attention lately, due to the availability of GOCE-based Global Geopotential Models (GGMs). The latter, offer unprecedented geoid height accuracies at the 1-1.5 cm level for spherical harmonic expansions to d/o 225-230. Within a single country, several LVDs may be used, especially in the event of islandic nations, therefore the unification of all of them to a single nation-wide LVD is of utmost importance. The same holds for neighboring countries, where the unification of their vertical datums is necessary as a tool of engineering, cross-border collaboration and environmental and risk management projects. The aforementioned set the main scope of the work carried out in the frame of the present study, which referred to the use of GOCE and GOCE/GRACE GGMs in order to unify the LVDs of Greece and Turkey. It is well-known that the two countries share common borders and are a path for large-scale engineering projects in the energy sector. Therefore, the availability of a common reference for orthometric heights in both countries and/or the determination of the relative offset of their individual zero-level geopotential value poses an emerging issue. The determination of the geopotential value Wo(LVD) for the Greek and Turkish LVDs was first carried out separately for each region performing as well different estimates for the marine area of the Aegean Sea and the terrestrial border-region along eastern Thrace. From that, possible biases of the Hellenic and Turkish LVDs themselves have been drawn and analyzed to determine spatial correlations. Then, the relative offset between the two LVDs was determined employing GPS/Levelling data for both areas and the latest GO-DIR-R5, GO-TIM-R5 and GOCO05s models as well as EGM2008. The estimation of the mean offset was used to provide as well a direct link between the Greek and Turkish LVDs with the IAG conventional value recently proposed as a Wo for a global WHS.

Progress towards a Drag-free SmallSat

NASA Astrophysics Data System (ADS)

Saraf, Shailendhar

The net force acting on a drag-free satellite is purely gravitational as all other forces, mainly atmospheric drag and solar radiation pressure, are canceled out. In order to achieve this, a free floating reference (test mass) inside the satellite is shielded against all forces but gravity and a system of thrusters is commanded by a control algorithm such that the relative displacement between the reference and the satellite stays constant. The main input to that control algorithm is the output of a sensor which measures the relative displacement between the satellite and the test mass. Internal disturbance forces such as electrostatic or magnetic forces cannot be canceled out his way and have to be minimized by a careful design of the satellite. A drag-free technology package is under development at Stanford since 2004. It includes an optical displacement sensor to measure the relative position of the test mass inside the satellite, a caging mechanism to lock the test mass during launch, a UV LED based charge management system to minimize the effect of electrostatic forces, a thermal enclosure, and the drag-free control algorithms. Possible applications of drag-free satellites in fundamental physics (Gravity Probe B, LISA), geodesy (GOCE), and navigation (TRIAD I). In this presentation we will highlight the progress of the technology development towards a drag-free mission. The planned mission on a SaudiSat bus will demonstrate drag-free technology on a small spacecraft at a fraction of the cost of previous drag-free missions. The target acceleration noise is 10-12 m/sec2. With multiple such satellites a GRACE-like mission with improved sensitivity and potentially improved spatial and temporal resolution can be achieved.

Three-dimensional cross-gradient joint inversion of gravity and normalized magnetic source strength data in the presence of remanent magnetization

NASA Astrophysics Data System (ADS)

Zhou, Junjie; Meng, Xiaohong; Guo, Lianghui; Zhang, Sheng

2015-08-01

Three-dimensional cross-gradient joint inversion of gravity and magnetic data has the potential to acquire improved density and magnetization distribution information. This method usually adopts the commonly held assumption that remanent magnetization can be ignored and all anomalies present are the result of induced magnetization. Accordingly, this method might fail to produce accurate results where significant remanent magnetization is present. In such a case, the simplification brings about unwanted and unknown deviations in the inverted magnetization model. Furthermore, because of the information transfer mechanism of the joint inversion framework, the inverted density results may also be influenced by the effect of remanent magnetization. The normalized magnetic source strength (NSS) is a transformed quantity that is insensitive to the magnetization direction. Thus, it has been applied in the standard magnetic inversion scheme to mitigate the remanence effects, especially in the case of varying remanence directions. In this paper, NSS data were employed along with gravity data for three-dimensional cross-gradient joint inversion, which can significantly reduce the remanence effects and enhance the reliability of both density and magnetization models. Meanwhile, depth-weightings and bound constraints were also incorporated in this joint algorithm to improve the inversion quality. Synthetic and field examples show that the proposed combination of cross-gradient constraints and the NSS transform produce better results in terms of the data resolution, compatibility, and reliability than that of separate inversions and that of joint inversions with the total magnetization intensity (TMI) data. Thus, this method was found to be very useful and is recommended for applications in the presence of strong remanent magnetization.

Subsurface geologic features of the 2011 central Virginia earthquakes revealed by airborne geophysics

USGS Publications Warehouse

Shah, Anjana K.; Horton, J. Wright; Burton, William C.; Spears, David B; Gilmer, Amy K

2014-01-01

Characterizing geologic features associated with major earthquakes provides insights into mechanisms contributing to fault slip and assists evaluation of seismic hazard. We use high-resolution airborne geophysical data combined with ground sample measurements to image subsurface geologic features associated with the 2011 moment magnitude (Mw) 5.8 central Virginia (USA) intraplate earthquake and its aftershocks. Geologic mapping and magnetic data analyses suggest that the earthquake occurred near a complex juncture of geologic contacts. These contacts also intersect a >60-km-long linear gravity gradient. Distal aftershocks occurred in tight, ~1-km-wide clusters near other obliquely oriented contacts that intersect gravity gradients, in contrast to more linearly distributed seismicity observed at other seismic zones. These data and corresponding models suggest that local density contrasts (manifested as gravity gradients) modified the nearby stress regime in a manner favoring failure. However, along those gradients seismic activity is localized near structural complexities, suggesting a significant contribution from variations in associated rock characteristics such as rheological weakness and/or rock permeability, which may be enhanced in those areas. Regional magnetic data show a broader bend in geologic structures within the Central Virginia seismic zone, suggesting that seismic activity may also be enhanced in other nearby areas with locally increased rheological weaknesses and/or rock permeability. In contrast, away from the Mw5.8 epicenter, geophysical lineaments are nearly continuous for tens of kilometers, especially toward the northeast. Continuity of associated geologic structures probably contributed to efficient propagation of seismic energy in that direction, consistent with moderate to high levels of damage from Louisa County to Washington, D.C., and neighboring communities.

A Subnano-g Electrostatic Force-Rebalanced Flexure Accelerometer for Gravity Gradient Instruments.

PubMed

Yan, Shitao; Xie, Yafei; Zhang, Mengqi; Deng, Zhongguang; Tu, Liangcheng

2017-11-18

A subnano-g electrostatic force-rebalanced flexure accelerometer is designed for the rotating accelerometer gravity gradient instrument. This accelerometer has a large proof mass, which is supported inversely by two pairs of parallel leaf springs and is centered between two fixed capacitor plates. This novel design enables the proof mass to move exactly along the sensitive direction and exhibits a high rejection ratio at its cross-axis directions. Benefiting from large proof mass, high vacuum packaging, and air-tight sealing, the thermal Brownian noise of the accelerometer is lowered down to less than 0.2 ng / Hz with a quality factor of 15 and a natural resonant frequency of about 7.4 Hz . The accelerometer's designed measurement range is about ±1 mg. Based on the correlation analysis between a commercial triaxial seismometer and our accelerometer, the demonstrated self-noise of our accelerometers is reduced to lower than 0.3 ng / Hz over the frequency ranging from 0.2 to 2 Hz, which meets the requirement of the rotating accelerometer gravity gradiometer.

A Subnano-g Electrostatic Force-Rebalanced Flexure Accelerometer for Gravity Gradient Instruments

PubMed Central

Yan, Shitao; Xie, Yafei; Zhang, Mengqi; Deng, Zhongguang

2017-01-01

A subnano-g electrostatic force-rebalanced flexure accelerometer is designed for the rotating accelerometer gravity gradient instrument. This accelerometer has a large proof mass, which is supported inversely by two pairs of parallel leaf springs and is centered between two fixed capacitor plates. This novel design enables the proof mass to move exactly along the sensitive direction and exhibits a high rejection ratio at its cross-axis directions. Benefiting from large proof mass, high vacuum packaging, and air-tight sealing, the thermal Brownian noise of the accelerometer is lowered down to less than 0.2 ng/Hz with a quality factor of 15 and a natural resonant frequency of about 7.4 Hz. The accelerometer’s designed measurement range is about ±1 mg. Based on the correlation analysis between a commercial triaxial seismometer and our accelerometer, the demonstrated self-noise of our accelerometers is reduced to lower than 0.3 ng/Hz over the frequency ranging from 0.2 to 2 Hz, which meets the requirement of the rotating accelerometer gravity gradiometer. PMID:29156587

Validation of gravity data from the geopotential field model for subsurface investigation of the Cameroon Volcanic Line (Western Africa)

NASA Astrophysics Data System (ADS)

Marcel, Jean; Abate Essi, Jean Marcel; Nouck, Philippe Njandjock; Sanda, Oumarou; Manguelle-Dicoum, Eliézer

2018-03-01

Belonging to the Cameroon Volcanic Line (CVL), the western part of Cameroon is an active volcanic zone with volcanic eruptions and deadly gas emissions. The volcanic flows generally cover areas and bury structural features like faults. Terrestrial gravity surveys can hardly cover entirely this mountainous area due to difficult accessibility. The present work aims to evaluate gravity data derived from the geopotential field model, EGM2008 to investigate the subsurface of the CVL. The methodology involves upward continuation, horizontal gradient, maxima of horizontal gradient-upward continuation combination and Euler deconvolution techniques. The lineaments map inferred from this geopotential field model confirms several known lineaments and reveals new ones covered by lava flows. The known lineaments are interpreted as faults or geological contacts such as the Foumban fault and the Pan-African Belt-Congo craton contact. The lineaments highlighted coupled with the numerous maar lakes identified in this volcanic sector attest of the vulnerability of the CVL where special attention should be given for geohazard prevention.

Gravity of Living Systems: May the Force Be With You

NASA Technical Reports Server (NTRS)

Hargens, Alan R.; Holton, Emily M. (Technical Monitor)

1998-01-01

Gravity, the force which shapes the architecture of organisms from single cells to dinosaurs, has been the most constant environmental factor during the evolution of species on Earth. With long-duration space flight, an understanding of how gravity affects living systems gains greater urgency in order to maintain the health and performance of crews who will explore the solar system. For example, the cardiovascular and musculoskeletal systems are normally exposed to gravitational gradients of blood pressure and weight on Earth. Such gradients increase blood pressure and tissue weight in dependent tissues of the body. Thus, from a physiologic standpoint, these systems are greatly affected by altered gravity. Exposure to actual and simulated microgravity causes blood and tissue fluid to shift from the legs to the head. Studies of humans in space have documented facial edema, space adaptation syndrome, decreased plasma volume, muscle atrophy, and loss of bone strength. Return of astronauts to Earth is accompanied by orthostatic intolerance, decreased neuromuscular coordination, and reduced exercise capacity. These factors decrease performance during descent from orbit and increase risk during emergency egress from the space craft. Models of simulated microgravity include 60 head-down tilt, immersion, and prolonged horizontal bedrest. Head-down tilt and dry immersion are the most accepted models and studies using these models of up to one year have been performed in Russia. Sensitive animal models which offer clear insights into the role of gravity on structure and function include the developing giraffe and snakes from various habitats. Finally, possible countermeasures to speed readaptation of astronauts to gravity after prolonged space flight include exercise, lower body negative pressure, and centrifugation.

Integration of Full Tensor Gravity and Z-Axis Tipper Electromagnetic Passive Low Frequency EM Instruments for Simultaneous Data Acquisition - Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wieberg, Scott

Ground gravity is a common and useful tool for geothermal exploration. Gravity surveys map density changes in the subsurface that may be caused by tectonic deformation such as faulting, fracturing, plutonism, volcanism, hydrothermal alteration, etc. Full Tensor Gravity Gradient (FTG) data has been used for over a decade in both petroleum and mining exploration to map changes in density associated with geologic structure. Measuring the gravity gradient, rather than the gravity field, provides significantly higher resolution data. Modeling studies have shown FTG data to be a viable tool for geothermal exploration, but no FTG data had been acquired for geothermalmore » applications to date. Electromagnetic methods have been used for geothermal exploration for some time. The Z-Axis Tipper Electromagnetic (ZTEM) was a newer technology that had found success in mapping deep conductivity changes for mining applications. ZTEM had also been used in limited tests for geothermal exploration. This newer technology provided the ability to cost effectively map large areas whilst detailing the electrical properties of the geological structures at depths. The ZTEM is passive and it uses naturally occurring audio frequency magnetic (AFMAG) signals as the electromagnetic triggering source. These geophysical methods were to be tested over a known geothermal site to determine whether or not the data provided the information required for accurately interpreting the subsurface geologic structure associated with a geothermal deposit. After successful acquisition and analysis of the known source area, an additional survey of a “greenfield” area was to be completed. The final step was to develop a combined interpretation model and determine if the combination produced a higher confident geophysical model compared to models developed using each of the technologies individually.« less

Microgravity Particle Dynamics

NASA Technical Reports Server (NTRS)

Clark, Ivan O.; Johnson, Edward J.

1996-01-01

This research seeks to identify the experiment design parameters for future flight experiments to better resolve the effects of thermal and velocity gradients on gas-solid flows. By exploiting the reduced body forces and minimized thermal convection current of reduced gravity experiments, features of gas-solid flow normally masked by gravitationally induced effects can be studied using flow regimes unattainable under unigravity. This paper assesses the physical scales of velocity, length, time, thermal gradient magnitude, and velocity gradient magnitude likely to be involved in laminar gas-solid multiphase flight experiments for 1-100 micro-m particles.

Suppression of morphogenesis in embryonic mouse limbs exposed in vitro to excess gravity.

PubMed

Duke, J C

1983-06-01

This paper is a report of the first investigation of the effect of excess gravity on in vitro mammalian limb chondrogenesis. Limb buds from mice of various gestational stages were exposed to excess gravity (2.6G) using a culture centrifuge. Both forelimbs and hind limbs were cultured and the development of various limb elements was scored after four to six days. The 2.6G force significantly depressed the development of limb elements when applied during the teratogen-sensitive period of chondrogenesis. There was a proximodistal gradient of sensitivity to excess gravity in the limb with proximal structures being less susceptible than distal ones. In some cases, proximal limb elements present prior to explantation disappeared upon exposure to excess gravity. Hypergravity's teratogenic effect is assumed to operate via changes in tension and/or pressure on the cells, accompanied by alterations in cell morphometry and membrane properties.

Maglev Facility for Simulating Variable Gravity

NASA Technical Reports Server (NTRS)

Liu, Yuanming; Strayer, Donald M.; Israelsson, Ulf E.

2010-01-01

An improved magnetic levitation apparatus ("Maglev Facility") has been built for use in experiments in which there are requirements to impose variable gravity (including zero gravity) in order to assess the effects of gravity or the absence thereof on physical and physiological processes. The apparatus is expected to be especially useful for experiments on the effects of gravity on convection, boiling, and heat transfer in fluids and for experiments on mice to gain understanding of bone loss induced in human astronauts by prolonged exposure to reduced gravity in space flight. The maglev principle employed by the apparatus is well established. Diamagnetic cryogenic fluids such as liquid helium have been magnetically levitated for studying their phase transitions and critical behaviors. Biological entities consist mostly of diamagnetic molecules (e.g., water molecules) and thus can be levitated by use of sufficiently strong magnetic fields having sufficiently strong vertical gradients. The heart of the present maglev apparatus is a vertically oriented superconducting solenoid electromagnet (see figure) that generates a static magnetic field of about 16 T with a vertical gradient sufficient for levitation of water in normal Earth gravity. The electromagnet is enclosed in a Dewar flask having a volume of 100 L that contains liquid helium to maintain superconductivity. The Dewar flask features a 66-mm-diameter warm bore, lying within the bore of the magnet, wherein experiments can be performed at room temperature. The warm bore is accessible from its top and bottom ends. The superconducting electromagnet is run in the persistent mode, in which the supercurrent and the magnetic field can be maintained for weeks with little decay, making this apparatus extremely cost and energy efficient to operate. In addition to water, this apparatus can levitate several common fluids: liquid hydrogen, liquid oxygen, methane, ammonia, sodium, and lithium, all of which are useful, variously, as rocket fuels or as working fluids for heat transfer devices. A drop of water 45 mm in diameter and a small laboratory mouse have been levitated in this apparatus.

Low-gravity Orbiting Research Laboratory Environment Potential Impact on Space Biology Research

NASA Technical Reports Server (NTRS)

Jules, Kenol

2006-01-01

One of the major objectives of any orbital space research platform is to provide a quiescent low gravity, preferably a zero gravity environment, to perform fundamental as well as applied research. However, small disturbances exist onboard any low earth orbital research platform. The impact of these disturbances must be taken into account by space research scientists during their research planning, design and data analysis in order to avoid confounding factors in their science results. The reduced gravity environment of an orbiting research platform in low earth orbit is a complex phenomenon. Many factors, among others, such as experiment operations, equipment operation, life support systems and crew activity (if it is a crewed platform), aerodynamic drag, gravity gradient, rotational effects as well as the vehicle structural resonance frequencies (structural modes) contribute to form the overall reduced gravity environment in which space research is performed. The contribution of these small disturbances or accelerations is precisely why the environment is NOT a zero gravity environment, but a reduced acceleration environment. This paper does not discuss other factors such as radiation, electromagnetic interference, thermal and pressure gradient changes, acoustic and CO2 build-up to name a few that affect the space research environment as well, but it focuses solely on the magnitude of the acceleration level found on orbiting research laboratory used by research scientists to conduct space research. For ease of analysis this paper divides the frequency spectrum relevant to most of the space research disciplines into three regimes: a) quasi-steady, b) vibratory and c) transient. The International Space Station is used as an example to illustrate the point. The paper discusses the impact of these three regimes on space biology research and results from space flown experiments are used to illustrate the potential negative impact of these disturbances (accelerations) on space biology research.

The lung in space.

PubMed

Prisk, G Kim

2005-09-01

The lung is exquisitely sensitive to gravity, which induces gradients in ventilation, blood flow, and gas exchange. Studies of lungs in microgravity provide a means of elucidating the effects of gravity. They suggest a mechanism by which gravity serves to match ventilation to perfusion, making for a more efficient lung than anticipated. Despite predictions, lungs do not become edematous, and there is no disruption to, gas exchange in microgravity. Sleep disturbances in microgravity are not a result of respiratory-related events; obstructive sleep apnea is caused principally by the gravitational effects on the upper airways. In microgravity, lungs may be at greater risk to the effects of inhaled aerosols.

Dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth

NASA Technical Reports Server (NTRS)

Revenaugh, Justin; Parsons, Barry

1987-01-01

Adopting the formalism of Parsons and Daly (1983), analytical integral equations (Green's function integrals) are derived which relate gravity anomalies and dynamic boundary topography with temperature as a function of wavenumber for a fluid layer whose viscosity varies exponentially with depth. In the earth, such a viscosity profile may be found in the asthenosphere, where the large thermal gradient leads to exponential decrease of viscosity with depth, the effects of a pressure increase being small in comparison. It is shown that, when viscosity varies rapidly, topography kernels for both the surface and bottom boundaries (and hence the gravity kernel) are strongly affected at all wavelengths.

The lung in space

NASA Technical Reports Server (NTRS)

Prisk, G. Kim

2005-01-01

The lung is exquisitely sensitive to gravity, which induces gradients in ventilation, blood flow, and gas exchange. Studies of lungs in microgravity provide a means of elucidating the effects of gravity. They suggest a mechanism by which gravity serves to match ventilation to perfusion, making for a more efficient lung than anticipated. Despite predictions, lungs do not become edematous, and there is no disruption to, gas exchange in microgravity. Sleep disturbances in microgravity are not a result of respiratory-related events; obstructive sleep apnea is caused principally by the gravitational effects on the upper airways. In microgravity, lungs may be at greater risk to the effects of inhaled aerosols.

Flow-driven pattern formation in the calcium-oxalate system.

PubMed

Bohner, Bíborka; Endrődi, Balázs; Horváth, Dezső; Tóth, Ágota

2016-04-28

The precipitation reaction of calcium oxalate is studied experimentally in the presence of spatial gradients by controlled flow of calcium into oxalate solution. The density difference between the reactants leads to strong convection in the form of a gravity current that drives the spatiotemporal pattern formation. The phase diagram of the system is constructed, the evolving precipitate patterns are analyzed and quantitatively characterized by their diameters and the average height of the gravity flow. The compact structures of calcium oxalate monohydrate produced at low flow rates are replaced by the thermodynamically unstable calcium oxalate dihydrate favored in the presence of a strong gravity current.

Bragg gravity-gradiometer using the 1S0–3P1 intercombination transition of 88Sr

NASA Astrophysics Data System (ADS)

del Aguila, R. P.; Mazzoni, T.; Hu, L.; Salvi, L.; Tino, G. M.; Poli, N.

2018-04-01

We present a gradiometer based on matter-wave interference of alkaline-earth-metal atoms, namely 88Sr. The coherent manipulation of the atomic external degrees of freedom is obtained by large-momentum-transfer Bragg diffraction, driven by laser fields detuned away from the narrow 1S0–3P1 intercombination transition. We use a well-controlled artificial gradient, realized by changing the relative frequencies of the Bragg pulses during the interferometer sequence, in order to characterize the sensitivity of the gradiometer. The sensitivity reaches 1.5 × 10‑5 s‑2 for an interferometer time of 20 ms, limited only by geometrical constraints. We observed extremely low sensitivity of the gradiometric phase to magnetic field gradients, approaching a value 104 times lower than the sensitivity of alkali-atom based gradiometers, limited by the interferometer sensitivity. An efficient double-launch technique employing accelerated red vertical lattices from a single magneto-optical trap cloud is also demonstrated. These results highlight strontium as an ideal candidate for precision measurements of gravity gradients, with potential application in future precision tests of fundamental physics.

Magnetic method for stimulating transport in fluids

DOEpatents

Martin, James E.; Solis, Kyle J.

2016-10-18

A method for producing mass and heat transport in fluids, wherein the method does not rely on conventional convection, that is, it does not require gravity, a thermal gradient, or a magnetic field gradient. This method gives rise to a unique class of vigorous, field-controllable flow patterns termed advection lattices. The advection lattices can be used to transport heat and/or mass in any desired direction using only magnetic fields.

Major results of gravity and magnetic studies at Yucca Mountain, Nevada

USGS Publications Warehouse

Oliver, H.W.; Ponce, D.A.; Sikora, R.F.; ,

1991-01-01

About 4,000 gravity stations have been obtained at Yucca Mountain and vicinity since the beginning of radioactive-waste studies there in 1978. These data have been integrated with data from about 29,000 stations previously obtained in the surrounding region to produce a series of Bouguer and isostatic-residual-gravity maps of the Nevada Test Site and southeastern Nevada. Yucca Mountain is characterized by a WNW-dipping gravity gradient whereby residual values of -10 mGal along the east edge of Yucca Mountain decrease to about -38 mGal over Crater Flat. Using these gravity data, two-dimensional modeling predicted the depth to pre-Cenozoic rocks near the proposed repository to be about 1,220??150 m, an estimate that was subsequently confirmed by drilling to be 1,244 m. Three-dimensional modeling of the gravity low over Crater Flat indicates the thickness of Cenozoic volcanic rocks and alluvial cover to be about 3,000 m. Gravity interpretations also identified the Silent Canyon caldera before geologic mapping of Pahute Mesa and provided an estimate of the thickness of the volcanic section there of nearly 5 km.

The interaction of bubbles with solidification interfaces. [during coasting phase of sounding rocket flight

NASA Technical Reports Server (NTRS)

Papazian, J. M.; Wilcox, W. R.

1977-01-01

The behavior of bubbles at a dendritic solidification interface was studied during the coasting phase of a sounding rocket flight. Sequential photographs of the gradient freeze experiment showed nucleation, growth and coalescence of bubbles at the moving interface during both the low-gravity and one-gravity tests. In the one-gravity test the bubbles were observed to detach from the interface and float to the top of the melt. However, in the low-gravity tests no bubble detachment from the interface or steady state bubble motion occurred and large voids were grown into the crystal. These observations are discussed in terms of the current theory of thermal migration of bubbles and in terms of their implications on the space processing of metals.

Gravitational dynamics of biosystems - Some speculations

NASA Technical Reports Server (NTRS)

Kessler, J. O.; Bier, M.

1976-01-01

The response of organisms to gravity is generally discussed in terms of hypotheses involving sedimentation and other static effects. This paper considers several complex, inhomogeneous fluid-containing systems that are intended to model some possible dynamic effects of gravity on biosystems. It is shown that the presence of gravity may result in modified long range transport, concentration oscillations, and broken symmetries. The magnitude of density-gradient-driven convective transport times, and their ratios to diffusive transport times, are calculated for cell dimensions of six different plant varieties. The results indicate that further investigation of gravitational convection effects may be realistic in some cases and is definitely not in others. The results of this paper should aid in the planning of 'zero-gravity' experiments concerning plant geotropism and bio-materials processing.

The origin of lunar mascon basins.

PubMed

Melosh, H J; Freed, Andrew M; Johnson, Brandon C; Blair, David M; Andrews-Hanna, Jeffrey C; Neumann, Gregory A; Phillips, Roger J; Smith, David E; Solomon, Sean C; Wieczorek, Mark A; Zuber, Maria T

2013-06-28

High-resolution gravity data from the Gravity Recovery and Interior Laboratory spacecraft have clarified the origin of lunar mass concentrations (mascons). Free-air gravity anomalies over lunar impact basins display bull's-eye patterns consisting of a central positive (mascon) anomaly, a surrounding negative collar, and a positive outer annulus. We show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool. We used a hydrocode to simulate the impact and a self-consistent finite-element model to simulate the subsequent viscoelastic relaxation and cooling. The primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy, the lunar thermal gradient at the time of impact, the crustal thickness, and the extent of volcanic fill.

Spacecraft stability and control

NASA Technical Reports Server (NTRS)

Barret, Chris

1992-01-01

The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Today, satellite stability and control has become a higher priority. For a satellite design that is to have a life expectancy of 14 years, appropriate spacecraft flight control systems will be reviewed, stability requirements investigated, and an appropriate flight control system recommended in order to see the design process. Disturbance torques, including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques, will be assessed to quantify the disturbance environment so that the required compensating torques can be determined. The control torques, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, inertia augmentation techniques, three-axis control, and reaction control systems (RCSs), will be considered. Conditions for stability will also be considered.

Gravity survey of the Nevada Test Site and vicinity, Nye, Lincoln, and Clark Counties, Nevada--interim report

USGS Publications Warehouse

Healy, D.L.; Miller, C.H.

1962-01-01

The gravity survey of the Nevada Test Site and contiguous areas of southern Nevada and southeastern California (fig. 1) has been made by the U.S. Geological Survey on behalf of the U.S. Atomic Energy Commission.The objective of this study is to delineate and interpret gravity anomalies and regional trends so that the configuration and depth of the buried erosional surface of the Paleozoic rocks may be determined. This buried surface is of utmost importance in understanding the geologic history of the Nevada Test Site region, the thickness and distribution of the overlying volcanic rocks and alluvium, and the movement of ground water. The Paleozoic rocks cause positive gravity anomalies where they outcrop or occur near the surface and negative anomalies where they are buried in valleys or capped by low-density Tertiary volcanic rocks. Gravity trends which extend over the entire area provide a basis for computing the regional gravity gradient. The regional gravity gradient must be removed from the data for geologic interpretation of the paleotopographic surface in any limited area. Knowledge of the thickness of low-density material overlying the paleotopographic surface is useful in several ways. Proposed underground test sites, such as drill holes and tunnels, may be evaluated in terms of rock unit thickness and alluvial cover requirements. Recent work by the Water Resources Division of the U.S. Geological Survey has demonstrated ground-water movement through the Paleozoic rocks in the vicinity of the Nevada Test Site. Therefore, knowledge of the position of buried Paleozoic rocks is important in evaluating (a) the rate and direction of flow of the ground water, (b) ground-water supplies for domestic and industrial uses, and (c) the possibility of radioactive contamination of ground water. Finally, regional gravity trends and paleotopography are useful in working out the structural history of the area in connection with geologic studies now in progress. The purpose of this interim report is to present the major part of the gravity data obtained as of December 31, 1961. The data are presented as a complete Bouguer gravity anomaly map. Although the gravity contours are somewhat generalized because the map has a scale of 1:250,000 and a contour interval of 5 milligals, the largest anomalies are adequately delineated. Preliminary results of this gravity survey have been reported by Wilmarth and others, 1960, and by Diment and others, 1959 and 1960.

Fluid mechanics and solidification investigations in low-gravity environments

NASA Technical Reports Server (NTRS)

Fichtl, G. H.; Lundquist, C. A.; Naumann, R. J.

1980-01-01

Fluid mechanics of gases and liquids and solidification processes were investigated under microgravity conditions during Skylab and Apollo-Soyuz missions. Electromagnetic, acoustic, and aerodynamic levitation devices, drop tubes, aircraft parabolic flight trajectories, and vertical sounding rockets were developed for low-g simulation. The Spacelab 3 mission will be carried out in a gravity gradient flight attitude; analyses of sources of vehicle dynamic accelerations with associated g-levels and angular rates will produce results for future specific experiments.

The measurement of solute diffusion coefficients in dilute liquid alloys: the influence of unit gravity and g-jitter on buoyancy convection.

PubMed

Smith, R W; Yang, B J; Huang, W D

2004-11-01

Liquid diffusion experiments conducted on the MIR space station using the Canadian Space Agency QUELD II processing facility and the microgravity isolation mount (MIM) showed that g-jitter significantly increased the measured solute diffusion coefficients. In some experiments, milli-g forced vibration was superimposed on the sample when isolated from the ambient g-jitter; this resulted in markedly increased solute transport. To further explore the effects arising in these long capillary diffusion couples from the absence of unit-gravity and the presence of the forced g-jitter, the effects of a 1 milli-g forcing vibration on the mass transport in a 1.5 mm diameter long capillary diffusion couple have been simulated. In addition, to increase understanding of the role of unit gravity in determining the extent to which gravity can influence measured diffusion coefficient values, comparative experiments involving gold, silver, and antimony diffusing in liquid lead have been carried out using a similar QUELD II facility to that employed in the QUELD II/MIM/MIR campaign but under terrestrial conditions. It was found that buoyancy-driven convection may still persist in the liquid even when conditions are arranged for a continuously decreasing density gradient up the axis of a vertical long capillary diffusion couple due to the presence of small radial temperature gradients.

Structural Control and Groundwater Flow in the Nubian Aquifer

NASA Astrophysics Data System (ADS)

Fathy, K.; Sultan, M.; Ahmed, M.; Save, H.; Emil, M. K.; Elkaliouby, B.

2017-12-01

An integrated research approach (remote sensing, field, geophysics) was conducted to investigate the structural control on groundwater flow in large aquifers using the less studied Nubian Sandstone Aquifer System (NSAS) of NE Africa as a test site. The aquifer extends over 2.2 x 106 km2 in Egypt, Libya, Chad, and Sudan and consists of thick (> 3 kms), water-bearing, Paleozoic and Mesozoic sandstone with intercalations of Tertiary shale and clay. It is subdivided into three sub-basins (Northern Sudan Platform [NSP], Dakhla [DAS], and Kufra) that are separated by basement uplifts (e.g., E-W trending Uweinat-Aswan uplift that separates DAS from the NSP). Aquifer recharge occurs in the south (NSP and southern Kufra) where the aquifer is unconfined and precipitation is high (Average Annual Precipitation [AAP]: 117 mm/yr.) and discharge is concentrated in the north (DAS and northern Kufra). Our approach is a three-fold exercise. Firstly, we compared GOCE-based Global Geopotential Models (GGMs) to terrestrial gravity anomalies for 21262 sites to select the optimum model for deriving Bouguer gravity anomalies. Secondly, structures and uplifts were mapped using hill shade images and their extension in the subsurface were mapped using the Eigen_6C4 model-derived Bouguer anomalies and their Tilt Derivative products (TDR). Thirdly, hydrological analysis was conducted using GRACE CSR 1° x 1° mascon solutions to investigate the mass variations in relation to the mapped structures. Our findings include: (1) The Eigen-6C4 is the optimum model having the lowest deviation (9.122 mGal) from the terrestrial gravity anomalies; (2) the surface expressions of structures matched fairly well with their postulated extensions in the subsurface; (3) identified fault systems include: Red Sea rift-related N-S to NW-SE trending grabens formed by reactivating basement structures during Red Sea opening and Syrian arc-related NE-SW trending dextral shear systems; (4) TWS patterns are uniform throughout the length (hundreds of kilometers) of the identified shear systems but are dissimilar from those extracted in areas proximal to, but outside of, the shear zones; and (5) basement uplifts impede or redirect the groundwater flow.

The International Service for the Geoid and its products

NASA Astrophysics Data System (ADS)

Reguzzoni, Mirko; Sona, Giovanna; Barzaghi, Riccardo; Sansò, Fernando; Albertella, Alberta; Carrion, Daniela; Iapige De Gaetani, Carlo; Rossi, Lorenzo

2017-04-01

The International Service for the Geoid (ISG) was established in 1992 and it is currently an official service of the International Association of Geodesy (IAG). Its activities are coordinated by the International Gravity Field Service (IGFS) and they are also related to those of the IAG Commission 2 on Gravity Field. ISG is hosted by Politecnico di Milano in Italy. The main task of ISG is to collect, analyze and redistribute local, regional and even continental geoid models, which are therefore the main products of the service. In this work the geoid repository is described, specifying the information provided for the models, the unified ASCII format used for their storing and the possible policy rules for their redistribution. Moreover, the current state-of-art of the repository is presented, in particular analyzing the geographical distribution of the available models and their years of computation. Note that not only the latest released geoid models are collected in the ISG repository, but also less recent ones, with the aim of keeping memory of the progress done in this research field during the years. Software for estimating and handling geoid models is provided too. Apart from distributing geoid models and software, the service has also educational and research purposes. From this perspective, additional products are the international schools on geoid computation that have been organized by ISG since 1994, basically every 2-3 years. A historical overview of the schools, with emphasis on the school program and its evolution in time, is here presented. As for the research activities, apart from participating to international projects and working groups, the main ISG product was the publication of the IGeS Bulletin in the past and the Newton's Bulletin nowadays, in cooperation with the International Gravimetric Bureau (BGI). The Newton's Bulletin has a technical and applied nature and it has been recently selected by the geodetic community for publications on the assessment of EGM2008 and GOCE global gravity models. Finally a short presentation of the service website as the main platform for the product distribution and advertising is here provided.

Satellite observations of middle atmosphere-thermosphere vertical coupling by gravity waves

NASA Astrophysics Data System (ADS)

Trinh, Quang Thai; Ern, Manfred; Doornbos, Eelco; Preusse, Peter; Riese, Martin

2018-03-01

Atmospheric gravity waves (GWs) are essential for the dynamics of the middle atmosphere. Recent studies have shown that these waves are also important for the thermosphere/ionosphere (T/I) system. Via vertical coupling, GWs can significantly influence the mean state of the T/I system. However, the penetration of GWs into the T/I system is not fully understood in modeling as well as observations. In the current study, we analyze the correlation between GW momentum fluxes observed in the middle atmosphere (30-90 km) and GW-induced perturbations in the T/I. In the middle atmosphere, GW momentum fluxes are derived from temperature observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. In the T/I, GW-induced perturbations are derived from neutral density measured by instruments on the Gravity field and Ocean Circulation Explorer (GOCE) and CHAllenging Minisatellite Payload (CHAMP) satellites. We find generally positive correlations between horizontal distributions at low altitudes (i.e., below 90 km) and horizontal distributions of GW-induced density fluctuations in the T/I (at 200 km and above). Two coupling mechanisms are likely responsible for these positive correlations: (1) fast GWs generated in the troposphere and lower stratosphere can propagate directly to the T/I and (2) primary GWs with their origins in the lower atmosphere dissipate while propagating upwards and generate secondary GWs, which then penetrate up to the T/I and maintain the spatial patterns of GW distributions in the lower atmosphere. The mountain-wave related hotspot over the Andes and Antarctic Peninsula is found clearly in observations of all instruments used in our analysis. Latitude-longitude variations in the summer midlatitudes are also found in observations of all instruments. These variations and strong positive correlations in the summer midlatitudes suggest that GWs with origins related to convection also propagate up to the T/I. Different processes which likely influence the vertical coupling are GW dissipation, possible generation of secondary GWs, and horizontal propagation of GWs. Limitations of the observations as well as of our research approach are discussed.

Thermotropism by primary roots of maize

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fortin, M.-C.; Poff, K.L.

1990-05-01

Sensing in the roots of higher plants has long been recognized to be restricted mainly to gravitropism and thigmotropism. However, root responses to temperature gradients have not been extensively studied. We have designed experiments under controlled conditions to test if and how root direction of maize can be altered by thermal gradients perpendicular to the gravity vector. Primary roots of maize grown on agar plates exhibit positive thermotropism (curvature toward the warmer temperature) when exposed to gradients of 0.5 to 4.2{degree}C cm{sup {minus}1}. The extent of thermotropism depends on the temperature gradient and the temperature at which the root ismore » placed within the gradient. The curvature cannot be accounted for by differential growth as a direct effect of temperature on each side of the root.« less

On the West Coast of the Ocean of Storms Artist Concept

NASA Image and Video Library

2014-10-01

A view of Earth moon looking south across Oceanus Procellarum, representing how the western border structures may have looked while active. This image combines gravity gradient from NASA GRAIL and LRO.

Temperature sensing by primary roots of maize

NASA Technical Reports Server (NTRS)

Poff, K. L.

1990-01-01

Zea mays L. seedlings, grown on agar plates at 26 degrees C, reoriented the original vertical direction of their primary root when exposed to a thermal gradient applied perpendicular to the gravity vector. The magnitude and direction of curvature can not be explained simply by either a temperature or a humidity effect on root elongation. It is concluded that primary roots of maize sense temperature gradients in addition to sensing the gravitational force.

Magnetophoretic induction of curvature in coleoptiles and hypocotyls

NASA Technical Reports Server (NTRS)

Kuznetsov, O. A.; Hasenstein, K. H.

1997-01-01

Coleoptiles of barley (Hordeum vulgare) were positioned in a high gradient magnetic field (HGMF, dynamic factor gradient of H(2)/2 of 10(9)-10(10) Oe2 cm-1), generated by a ferromagnetic wedge in a uniform magnetic field and rotated on a 1 rpm clinostat. After 4 h 90% of coleoptiles had curved toward the HGMF. The cells affected by HGMF showed clear intracellular displacement of amyloplasts. Coleoptiles in a magnetic field next to a non-ferromagnetic wedge showed no preferential curvature. The small size of the area of nonuniformity of the HGMF allowed mapping of the sensitivity of the coleoptiles by varying the initial position of the wedge relative to the coleoptile apex. When the ferromagnetic wedge was placed 1 mm below the coleoptile tip only 58% of the coleoptiles curved toward the wedge indicating that the cells most sensitive to intracellular displacement of amyloplasts and thus gravity sensing are confined to the top 1 mm portion of barley coleoptiles. Similar experiments with tomato hypocotyls (Lycopersicum esculentum) also resulted in curvature toward the HGMF. The data strongly support the amyloplast-based gravity-sensing system in higher plants and the usefulness of HGMF to substitute gravity in shoots.

The lithospheric Structure of the Sahara Metacraton From Joint Analysis of Satellite Gravity Gradients and Seismological Data

NASA Astrophysics Data System (ADS)

Sobh, M.; Ebbing, J.; Goetze, H. J.; Abdelsalam, M. G.

2016-12-01

For the Saharan Metacraton in northern Africa only a few geophysical results exists, which can be used to characterize its deep structure. We combine recent seismological models with satellite gravity gradients to build a 3D lithospheric density model of the metacraton and its surrounding regions. Due to the sparse distribution of seismic data, we estimate the Moho boundary by non-linear gravity inversion in spherical coordinates. The model is constrained by some wide angle refraction seismic profiles and receiver function Moho depths. Despite the high topography of the Darfur and Tibisti Cenozoic volcanic provinces, we estimate thin crust which indicates an upper mantle contribution to the isostatic balance. In combination with seismic tomography models, we found that the lithospheric thickness in the western part of the Metacraton is thicker than in the eastern part. This indicates that the western resembles the remnants of the pre-Neoproterozoic Sahara craton (e.g. the Marzuk craton which escaped the metacratonization process). In order to explain the partial loss of the expected cratonic root beneath the Metacraton, we present different petrological-geophysical scenario testing for different upper mantle compositions.

The free versus fixed geodetic boundary value problem for different combinations of geodetic observables

NASA Astrophysics Data System (ADS)

Grafarend, E. W.; Heck, B.; Knickmeyer, E. H.

1985-03-01

Various formulations of the geodetic fixed and free boundary value problem are presented, depending upon the type of boundary data. For the free problem, boundary data of type astronomical latitude, astronomical longitude and a pair of the triplet potential, zero and first-order vertical gradient of gravity are presupposed. For the fixed problem, either the potential or gravity or the vertical gradient of gravity is assumed to be given on the boundary. The potential and its derivatives on the boundary surface are linearized with respect to a reference potential and a reference surface by Taylor expansion. The Eulerian and Lagrangean concepts of a perturbation theory of the nonlinear geodetic boundary value problem are reviewed. Finally the boundary value problems are solved by Hilbert space techniques leading to new generalized Stokes and Hotine functions. Reduced Stokes and Hotine functions are recommended for numerical reasons. For the case of a boundary surface representing the topography a base representation of the solution is achieved by solving an infinite dimensional system of equations. This system of equations is obtained by means of the product-sum-formula for scalar surface spherical harmonics with Wigner 3j-coefficients.

The orbital mechanics of flight mechanics

NASA Technical Reports Server (NTRS)

Dunning, R. S.

1973-01-01

A reference handbook on modern dynamic orbit theory is presented. Starting from the most basic inverse-square law, the law of gravity for a sphere is developed, and the motion of point masses under the influence of a sphere is considered. The reentry theory and the orbital theory are discussed along with the relative motion between two bodies in orbit about the same planet. Relative-motion equations, rectangular coordinates, and the mechanics of simple rigid bodies under the influence of a gravity gradient field are also discussed.

Moving base Gravity Gradiometer Survey System (GGSS) program

NASA Astrophysics Data System (ADS)

Pfohl, Louis; Rusnak, Walter; Jircitano, Albert; Grierson, Andrew

1988-04-01

The GGSS program began in early 1983 with the objective of delivering a landmobile and airborne system capable of fast, accurate, and economical gravity gradient surveys of large areas anywhere in the world. The objective included the development and use of post-mission data reduction software to process the survey data into solutions for the gravity disturbance vector components (north, east and vertical). This document describes the GGSS equipment hardware and software, integration and lab test procedures and results, and airborne and land survey procedures and results. Included are discussions on test strategies, post-mission data reduction algorithms, and the data reduction processing experience. Perspectives and conclusions are drawn from the results.

Using Magnetic Forces to Probe the Gravi-response of Swimming Paramecium

NASA Astrophysics Data System (ADS)

Guevorkian, Karine; Valles, James M., Jr.

2004-03-01

Paramecium Caudatum, a single celled ciliate, alters its swimming behavior when subjected to different gravity environments (e.g. centrifugation and micro-gravity). To dissect the mechanisms behind this gravi-response and that of other biological systems, we are developing the use of magnetic body forces as a means of creating a rapidly tunable, simulated variable gravity environment. Since biological materials are weakly diamagnetic, we must subject them to intense inhomogeneous magnetic fields with characteristic field-field gradient products on the order of 16 T^2/cm. We will describe experiments on Paramecium Caudatum in which we adjust their net buoyancy with magnetic forces and measure the resulting changes in their swimming behavior.

Preparative liquid column electrophoresis of T and B lymphocytes at gravity = 1

NASA Technical Reports Server (NTRS)

Van Oss, C. J.; Bigazzi, P. E.; Gillman, C. F.; Allen, R. E.

1974-01-01

Vertical liquid columns containing low-molecular-weight dextran density gradients can be used for preparative lymphocyte electrophoresis on earth, in simulation of zero gravity conditions. Another method that has been tested at 1 g, is the electrophoresis of lymphocytes in an upward direction in vertical columns. By both methods up to 100 million lymphocytes can be separated at one time in a 30-cm glass column of 8-mm inside diameter, at 12 V/cm, in two hours. Due to convection and sedimentation problems, the separation at 1 g is less than ideal, but it is expected that at zero gravity electrophoresis will probe to be a uniquely powerful cell separation tool.

Deer Lodge Valley investigations, western Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wideman, C.J.; Sonderegger, J.; Crase, E.

1982-07-01

A review of the geothermal investigations conducted in the Deer Lodge Valley of Western Montana is briefly presented. Maps of the generalized geology and Bouguer gravity and graphs of selected geothermal gradients and resistivity sounding profiles are presented. (MJF)

Digital data from the Great Sand Dunes airborne gravity gradient survey, south-central Colorado

USGS Publications Warehouse

Drenth, B.J.; Abraham, J.D.; Grauch, V.J.S.; Labson, V.F.; Hodges, G.

2013-01-01

This report contains digital data and supporting explanatory files describing data types, data formats, and survey procedures for a high-resolution airborne gravity gradient (AGG) survey at Great Sand Dunes National Park, Alamosa and Saguache Counties, south-central Colorado. In the San Luis Valley, the Great Sand Dunes survey covers a large part of Great Sand Dunes National Park and Preserve. The data described were collected from a high-resolution AGG survey flown in February 2012, by Fugro Airborne Surveys Corp., on contract to the U.S. Geological Survey. Scientific objectives of the AGG survey are to investigate the subsurface structural framework that may influence groundwater hydrology and seismic hazards, and to investigate AGG methods and resolution using different flight specifications. Funding was provided by an airborne geophysics training program of the U.S. Department of Defense's Task Force for Business & Stability Operations.

Sloshing of Cryogenic Helium Driven by Lateral Impulse/Gravity Gradient-Dominated/or g-Jitter-Dominated Accelerations and Orbital Dynamics

NASA Technical Reports Server (NTRS)

Hung, R. J.; Long, Y. T.; Zu, G. J.

1996-01-01

The coupling of slosh dynamics within a partially filled rotating dewar of superfluid helium 11 with spacecraft orbital dynamics is investigated in response to the environmental disturbances of (a) lateral impulses, (b) gravity gradients and (c) g-jitter forces. The purpose of this study is to investigate how the coupling of helium 11 fluid slosh dynamics driven by three cases of environmental force with spacecraft dynamics can affect the bubble deformations and their associated fluid and spacecraft mass centre fluctuations. The numerical computation of slosh dynamics is based on a rotational frame, while the spacecraft dynamics is associated with a non-rotational frame. Results show that the major contribution of orbital dynamics is driven by coupling with slosh dynamics. Neglecting the effect of slosh dynamics acting on the spacecraft may lead to the wrong results for the development of orbital and attitude control techniques.

Theory of Metastable State Relaxation in a Gravitational Field for Non-Critical Binary Systems with Non-Conserved Order Parameter

NASA Technical Reports Server (NTRS)

Izmailov, Alexander F.; Myerson, Allan S.

1993-01-01

A new mathematical ansatz is developed for solution of the time-dependent Ginzburg-Landau nonlinear partial differential equation describing metastable state relaxation in binary (solute+solvent) non-critical solutions with non-conserved scalar order parameter in presence of a gravitational field. It has been demonstrated analytically that in such systems metastability initiates heterogeneous solute redistribution which results in the formation of a non-equilibrium singly-periodic spatial solute structure in the new solute-rich phase. The critical radius of nucleation and the induction time in these systems are gravity-dependent. It has also been proved that metastable state relaxation in vertical columns of supersaturated non-critical binary solutions leads to formation of the solute concentration gradient. Analytical expression for this concentration gradient is found and analysed. It is concluded that gravity can initiate phase separation (nucleation or spinodal decomposition).

Gradient Heating Facility in the Materials Science Double Rack (MSDR) on Spacelab-1 Module

NASA Technical Reports Server (NTRS)

1983-01-01

The Space Shuttle was designed to carry large payloads into Earth orbit. One of the most important payloads is Spacelab. The Spacelab serves as a small but well-equipped laboratory in space to perform experiments in zero-gravity and make astronomical observations above the Earth's obscuring atmosphere. In this photograph, Payload Specialist, Ulf Merbold, is working at Gradient Heating Facility on the Materials Science Double Rack (MSDR) inside the science module in the Orbiter Columbia's payload bay during STS-9, Spacelab-1 mission. Spacelab-1, the joint ESA (European Space Agency)/NASA mission, was the first operational flight for the Spacelab, and demonstrated new instruments and methods for conducting experiments that are difficult or impossible in ground-based laboratories. This facility performed, in extremely low gravity, a wide variety of materials processing experiments in crystal growth, fluid physics, and metallurgy. The Marshall Space Flight Center had overall management responsibilities.

A gravity gradient stabilized solar power satellite design

NASA Technical Reports Server (NTRS)

Bowden, M. L.

1981-01-01

The concept of a solar power satellite (SPS) is reviewed, and a design proposed for such a satellite taking advantage of solar radiation pressure and gravity gradient forces to eliminate much of the structure from the baseline configuration. The SPS design consists of a solar cell array lying in the orbital plane and a free floating mirror above to reflect sunlight down onto it. The structural modes of the solar cell array are analyzed and found to be well within control limitations. Preliminary calculations concerning the free floating mirror and its position-keeping propellant requirements are also performed. A numerical example is presented, which shows that, even in terms of mass only, this configuration is a competitive design when compared to the conventional Department of Energy reference design. Other advantages, such as easier assembly in orbit, lower position-keeping propellant requirements, possibilities for decreasing necessary solar cell area, and longer solar cell life, may make this design superior.

Test and On-Orbit Experiences of FalconSAT-3

NASA Astrophysics Data System (ADS)

Saylor, W. W.; France, M. E. B.

2008-08-01

The fundamental objectives of the capstone design project in the Department of Astronautics at the United States Air Force Academy (USAFA) are for cadets to learn important engineering lessons by executing a real space mission on a Department of Defense-funded satellite project. FalconSAT-3 is a 50 kg, gravity gradient-stabilized designed and built by cadets and launched March 2007 on the first ESPA (Enhanced extended launch vehicle Satellite Payload Adapter) mission. FalconSAT-3 was one of six satellites integrated onto the launch vehicle and the nature of the mission made it that the satellite was subject to the full formality of testing requirements. Two successive gravity gradient booms failed either design requirements or environmental testing; design requirements grew dramatically during the design phase; ambiguous thermal vacuum test results led to uncertainty at launch; and after launch it was not possible to contact the satellite for several weeks.

Building complex simulations rapidly using MATRIX(x): The Space Station redesign

NASA Technical Reports Server (NTRS)

Carrington, C. K.

1994-01-01

MSFC's quick response to the Space Station redesign effort last year required the development of a computer simulation to model the attitude and station-keeping dynamics of a complex body with rotating solar arrays in orbit around the Earth. The simulation was written using a rapid-prototyping graphical simulation and design tool called MATRIX(x) and provided the capability to quickly remodel complex configuration changes by icon manipulation using a mouse. The simulation determines time-dependent inertia properties, and models forces and torques from gravity-gradient, solar radiation, and aerodynamic disturbances. Surface models are easily built from a selection of beams, plates, tetrahedrons, and cylinders. An optimization scheme was written to determine the torque equilibrium attitudes that balance gravity-gradient and aerodynamic torques over an orbit, and propellant-usage estimates were determined. The simulation has been adapted to model the attitude dynamics for small spacecraft.

A novel Gravity-FREAK feature extraction and Gravity-KLT tracking registration algorithm based on iPhone MEMS mobile sensor in mobile environment

PubMed Central

Lin, Fan; Xiao, Bin

2017-01-01

Based on the traditional Fast Retina Keypoint (FREAK) feature description algorithm, this paper proposed a Gravity-FREAK feature description algorithm based on Micro-electromechanical Systems (MEMS) sensor to overcome the limited computing performance and memory resources of mobile devices and further improve the reality interaction experience of clients through digital information added to the real world by augmented reality technology. The algorithm takes the gravity projection vector corresponding to the feature point as its feature orientation, which saved the time of calculating the neighborhood gray gradient of each feature point, reduced the cost of calculation and improved the accuracy of feature extraction. In the case of registration method of matching and tracking natural features, the adaptive and generic corner detection based on the Gravity-FREAK matching purification algorithm was used to eliminate abnormal matches, and Gravity Kaneda-Lucas Tracking (KLT) algorithm based on MEMS sensor can be used for the tracking registration of the targets and robustness improvement of tracking registration algorithm under mobile environment. PMID:29088228

Diffusion phenomenon at the interface of Cu-brass under a strong gravitational field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogata, Yudai; Tokuda, Makoto; Januszko, Kamila

2015-03-28

To investigate diffusion phenomenon at the interface between Cu and brass under a strong gravitational field generated by ultracentrifuge apparatus, we performed gravity experiments on samples prepared by electroplating with interfaces normal and parallel to the direction of gravity. For the parallel-mode sample, for which sedimentation cannot occur thorough the interface, the concentration change was significant within the lower gravity region; many pores were observed in this region. Many vacancies arising from crystal strain due to the strong gravitational field moved into the lower gravity region, and enhanced the atoms mobilities. For the two normal-mode samples, which have interface normalmore » to the direction of gravity, the composition gradient of the brass-on-Cu sample was steeper than that for Cu-on-brass. This showed that the atoms of denser Cu diffuse in the direction of gravity, whereas Zn atoms diffuse in the opposite direction by sedimentation. The interdiffusion coefficients became higher in the Cu-on-brass sample, and became lower in the brass-on-Cu sample. This rise may be related to the behavior of the vacancies.« less

A novel Gravity-FREAK feature extraction and Gravity-KLT tracking registration algorithm based on iPhone MEMS mobile sensor in mobile environment.

PubMed

Hong, Zhiling; Lin, Fan; Xiao, Bin

2017-01-01

Based on the traditional Fast Retina Keypoint (FREAK) feature description algorithm, this paper proposed a Gravity-FREAK feature description algorithm based on Micro-electromechanical Systems (MEMS) sensor to overcome the limited computing performance and memory resources of mobile devices and further improve the reality interaction experience of clients through digital information added to the real world by augmented reality technology. The algorithm takes the gravity projection vector corresponding to the feature point as its feature orientation, which saved the time of calculating the neighborhood gray gradient of each feature point, reduced the cost of calculation and improved the accuracy of feature extraction. In the case of registration method of matching and tracking natural features, the adaptive and generic corner detection based on the Gravity-FREAK matching purification algorithm was used to eliminate abnormal matches, and Gravity Kaneda-Lucas Tracking (KLT) algorithm based on MEMS sensor can be used for the tracking registration of the targets and robustness improvement of tracking registration algorithm under mobile environment.

^4He experiments near T_λ with a heat current and reduced gravity in a low-gravity simulator

NASA Astrophysics Data System (ADS)

Liu, Yuanming; Larson, Melora; Israelsson, Ulf

1998-03-01

Conventional ground-based helium experiments experience limitations due to a variation of the superfluid transition temperature (T_λ) caused by the gravity-induced hydrostatic pressure in a ^4He sample cell. A low-gravity simulator consisting a high field superconducting magnet has been built in our laboratory and the preliminary measurements demonstrated a reduction of gravity in the sample cell. (Melora Larson, Feng-Chuan Liu, and Ulf Israelsson, Czech. J. of Phys. 46, 179 (1996).) We report our latest improvements on the simulator and measurements with a new sample cell which had copper end plates, Vepsel sidewalls, and sidewall probes. The measurements showed that gravity can be canceled with a field-field gradient product of 20.7 T^2/cm (or B=15.5 Tesla), in excellent agreement with the theoretical prediction. The measurements also revealed that the boundary resistance between the thermometers and liquid helium increased from 1.6 cm^2 K/W at zero field to 2.0 cm^2 K/W at B=13.8 Tesla. The preliminary dynamic measurements near T_λ with a heat current and reduced gravity will also be presented. This research was supported by NASA.

An analytical model of SAGD process considering the effect of threshold pressure gradient

NASA Astrophysics Data System (ADS)

Morozov, P.; Abdullin, A.; Khairullin, M.

2018-05-01

An analytical model is proposed for the development of super-viscous oil deposits by the method of steam-assisted gravity drainage, taking into account the nonlinear filtration law with the limiting gradient. The influence of non-Newtonian properties of oil on the productivity of a horizontal well and the cumulative steam-oil ratio are studied. Verification of the proposed model based on the results of physical modeling of the SAGD process was carried out.

Local gravity field modeling using spherical radial basis functions and a genetic algorithm

NASA Astrophysics Data System (ADS)

Mahbuby, Hany; Safari, Abdolreza; Foroughi, Ismael

2017-05-01

Spherical Radial Basis Functions (SRBFs) can express the local gravity field model of the Earth if they are parameterized optimally on or below the Bjerhammar sphere. This parameterization is generally defined as the shape of the base functions, their number, center locations, bandwidths, and scale coefficients. The number/location and bandwidths of the base functions are the most important parameters for accurately representing the gravity field; once they are determined, the scale coefficients can then be computed accordingly. In this study, the point-mass kernel, as the simplest shape of SRBFs, is chosen to evaluate the synthesized free-air gravity anomalies over the rough area in Auvergne and GNSS/Leveling points (synthetic height anomalies) are used to validate the results. A two-step automatic approach is proposed to determine the optimum distribution of the base functions. First, the location of the base functions and their bandwidths are found using the genetic algorithm; second, the conjugate gradient least squares method is employed to estimate the scale coefficients. The proposed methodology shows promising results. On the one hand, when using the genetic algorithm, the base functions do not need to be set to a regular grid and they can move according to the roughness of topography. In this way, the models meet the desired accuracy with a low number of base functions. On the other hand, the conjugate gradient method removes the bias between derived quasigeoid heights from the model and from the GNSS/leveling points; this means there is no need for a corrector surface. The numerical test on the area of interest revealed an RMS of 0.48 mGal for the differences between predicted and observed gravity anomalies, and a corresponding 9 cm for the differences in GNSS/leveling points.

Egg buoyancy variability in local populations of Atlantic cod (Gadus morhua).

PubMed

Jung, Kyung-Mi; Folkvord, Arild; Kjesbu, Olav Sigurd; Agnalt, Ann Lisbeth; Thorsen, Anders; Sundby, Svein

2012-01-01

Previous studies have found strong evidences for Atlantic cod ( Gadus morhua ) egg retention in fjords, which are caused by the combination of vertical salinity structure, estuarine circulation, and egg specific gravity, supporting small-scaled geographical differentiations of local populations. Here, we assess the variability in egg specific gravity for selected local populations of this species, that is, two fjord-spawning populations and one coastal-spawning population from Northern Norway (66-71°N/10-25°E). Eggs were naturally spawned by raised broodstocks (March to April 2009), and egg specific gravity was measured by a density-gradient column. The phenotype of egg specific gravity was similar among the three local populations. However, the associated variability was greater at the individual level than at the population level. The noted gradual decrease in specific gravity from gastrulation to hatching with an increase just before hatching could be a generic pattern in pelagic marine fish eggs. This study provides needed input to adequately understand and model fish egg dispersal.

Gravitropism interferes with hydrotropism via counteracting auxin dynamics in cucumber roots: clinorotation and spaceflight experiments.

PubMed

Morohashi, Keita; Okamoto, Miki; Yamazaki, Chiaki; Fujii, Nobuharu; Miyazawa, Yutaka; Kamada, Motoshi; Kasahara, Haruo; Osada, Ikuko; Shimazu, Toru; Fusejima, Yasuo; Higashibata, Akira; Yamazaki, Takashi; Ishioka, Noriaki; Kobayashi, Akie; Takahashi, Hideyuki

2017-09-01

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood. Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism. Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth's surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein CsPIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots. Our results suggest that roots become hydrotropically sensitive in μG, and CsPIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Gravity-stimulated changes in auxin and invertase gene expression in maize pulvinal cells

NASA Technical Reports Server (NTRS)

Long, Joanne C.; Zhao, Wei; Rashotte, Aaron M.; Muday, Gloria K.; Huber, Steven C.; Brown, C. S. (Principal Investigator)

2002-01-01

Maize (Zea mays) stem gravitropism involves differential elongation of cells within a highly specialized region, the stem internodal pulvinus. In the present study, we investigated factors that control gravitropic responses in this system. In the graviresponding pulvinus, hexose sugars (D-Glc and D-Fru) accumulated asymmetrically across the pulvinus. This correlated well with an asymmetric increase in acid invertase activity across the pulvinus. Northern analyses revealed asymmetric induction of one maize acid invertase gene, Ivr2, consistent with transcriptional regulation by gravistimulation. Several lines of evidence indicated that auxin redistribution, as a result of polar auxin transport, is necessary for gravity-stimulated Ivr2 transcript accumulation and differential cell elongation across the maize pulvinus. First, the auxin transport inhibitor, N-1-naphthylphthalamic acid, inhibited gravistimulated curvature and Ivr2 transcript accumulation. Second, a transient gradient of free indole-3-acetic acid (IAA) across the pulvinus was apparent shortly after initiation of gravistimulation. This temporarily free IAA gradient appears to be important for differential cell elongation and Ivr2 transcript accumulation. This is based on the observation that N-1-naphthylphthalamic acid will not inhibit gravitropic responses when applied to pulvinus tissue after the free IAA gradient peak has occurred. Third, IAA alone can stimulate Ivr2 transcript accumulation in non-gravistimulated pulvini. The gravity- and IAA-stimulated increase in Ivr2 transcripts was sensitive to the protein synthesis inhibitor, cycloheximide. Based on these results, a two-phase model describing possible relationships between gravitropic curvature, IAA redistribution, and Ivr2 expression is presented.

Interpretation of Source Parameters from Total Gradient of Gravity and Magnetic Anomalies Caused by Thin Dyke using Nonlinear Global Optimization Technique

NASA Astrophysics Data System (ADS)

Biswas, A.

2016-12-01

A proficient way to deal with appraisal model parameters from total gradient of gravity and magnetic data in light of Very Fast Simulated Annealing (VFSA) has been exhibited. This is the first run through of applying VFSA in deciphering total gradient of potential field information with another detailing estimation brought on because of detached causative sources installed in the subsurface. The model parameters translated here are the amplitude coefficient (k), accurate origin of causative source (x0) depth (z0) and the shape factor (q). The outcome of VFSA improvement demonstrates that it can exceptionally decide all the model parameters when shape variable is fixed. The model parameters assessed by the present strategy, for the most part the shape and depth of the covered structures was observed to be in astounding concurrence with the genuine parameters. The technique has likewise the capability of dodging very uproarious information focuses and enhances the understanding results. Investigation of Histogram and cross-plot examination likewise proposes the translation inside the assessed ambiguity. Inversion of noise-free and noisy synthetic data information for single structures and field information shows the viability of the methodology. The procedure has been carefully and adequately connected to genuine field cases (Leona Anomaly, Senegal for gravity and Pima copper deposit, USA for magnetic) with the nearness of mineral bodies. The present technique can be to a great degree material for mineral investigation or ore bodies of dyke-like structure rooted in the shallow and more deep subsurface. The calculation time for the entire procedure is short.

Wave Dynamics and Transport in the Stratosphere

NASA Technical Reports Server (NTRS)

Holton, James R.; Alexander, M. Joan

1999-01-01

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model.

Application of indexes of underground structure using land gravity data to the Eastern Boundary Fault zone of the Shonai Plain, northeastern Japan.

NASA Astrophysics Data System (ADS)

Tanaka, T.; Hiramatsu, Y.; Matsumoto, N.; Honda, R.; Wada, S.; Sawada, A.; Okada, S.

2016-12-01

Gravity gradients, which are directly measured and are also derived by differentiating land gravity anomaly data, are sensitive to the density structure of shallow subsurfaces and therefore can be used to formulate ratings for Indexes of Underground Structure (IUS) [e.g., Kusumoto,2015,2016]. Recently, dense land gravity data measurements for almost entire Japan have been available [Honda et al., 2012]. In this study, we use gravity gradient tensors from the data to apply IUS to the Eastern Boundary Fault zone of the Shonai Plain (EBFSP), which spans 40 km in length and caused the historical Mjma 7.0 earthquake in 1894. The IUS we adopt here comprises the dip angle of the structural boundary (Beta) [Beiki, 2013], the dimensionality index (I) [Pedersen and Rasmussen, 1990], the structural boundary (Horizontal First Derivation(HFD) and TDX [Cooper and Cowan, 2006]), and density anomaly cylinder bodies in the depth direction (TD) [Copper, 2011]. The IUS show that the northern part of the EBFSP is characterized by high-Beta, low-I (dyke-like), intense-(HFD and TDX), and many short TD. Contrary to this, the southern part exhibits low-Beta, high-I, mild-(HFD and TDX), and few long TD. Previous geological/geomorphological surveys of the EBFSP [Ikeda et al., 2002] distinguish between the northern part comprising parallel/echelon short faults and the southern part comprising a single long fault. These findings are consistent with the gravimetrical IUS. However, the IUS more emphasizes the Aosawa Fault zone, which is geologically old and runs nearly parallel to the EBFSP at about 5-10 km distance on the eastern side of the EBFSP. Because gravity anomalies are a time-integrated representation of crustal activity, it is difficult to identify the relative timing of faulting events in an analysis range. However, the IUS can objectively contribute to producing comprehensive characterizations of target faults. This study is supported by JSPS KAKENHI Grant Number 26400450.

Normal Isocurvature Surfaces and Special Isocurvature Circles (SIC)

NASA Astrophysics Data System (ADS)

Manoussakis, Gerassimos; Delikaraoglou, Demitris

2010-05-01

An isocurvature surface of a gravity field is a surface on which the value of the plumblines' curvature is constant. Here we are going to study the isocurvature surfaces of the Earth's normal gravity field. The normal gravity field is a symmetric gravity field therefore the isocurvature surfaces are surfaces of revolution. But even in this case the necessary relations for their study are not simple at all. Therefore to study an isocurvature surface we make special assumptions to form a vector equation which will hold only for a small coordinate patch of the isocurvature surface. Yet from the definition of the isocurvature surface and the properties of the normal gravity field is possible to express very interesting global geometrical properties of these surfaces without mixing surface differential calculus. The gradient of the plumblines' curvature function is vertical to an isocurvature surface. If P is a point of an isocurvature surface and "Φ" is the angle of the gradient of the plumblines' curvature with the equatorial plane then this direction points to the direction along which the curvature of the plumbline decreases / increases the most, and therefore is related to the strength of the normal gravity field. We will show that this direction is constant along a line of curvature of the isocurvature surface and this line is an isocurvature circle. In addition we will show that at each isocurvature surface there is at least one isocurvature circle along which the direction of the maximum variation of the plumblines' curvature function is parallel to the equatorial plane of the ellipsoid of revolution. This circle is defined as a Special Isocurvature Circle (SIC). Finally we shall prove that all these SIC lye on a special surface of revolution, the so - called SIC surface. That is to say, a SIC is not an isolated curve in the three dimensional space.

Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Witte, Larry C.; Bousman, W. Scott; Fore, Larry B.

1996-01-01

The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same flow conditions. Nusselt numbers can be correlated in a fashion similar to Chu and Jones.

Large Gradient High Magnetic Fields Affect Osteoblast Ultrastructure and Function by Disrupting Collagen I or Fibronectin/αβ1 Integrin

PubMed Central

Qian, Ai-Rong; Gao, Xiang; Zhang, Wei; Li, Jing-Bao; Wang, Yang; Di, Sheng-Meng; Hu, Li-Fang; Shang, Peng

2013-01-01

The superconducting magnet generates a field and field gradient product that can levitate diamagnetic materials. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. The effects of LG-HMF on the ultrastructure and function of osteoblast-like cells (MG-63 and MC3T3-E1) and the underlying mechanism were investigated by transmission electromicroscopy (TEM), MTT, and cell western (ICW) assays. Under LG-HMF significant morphologic changes in osteoblast-like cells occurred, including expansion of endoplasmic reticulum and mitochondria, an increased number of lysosomes, distorted microvilli, and aggregates of actin filaments. Compared to controls, cell viability and alkaline phosphatase (ALP) secretion were significantly increased, and collagen I (col I), fibronectin (FN), vinculin, integrin α3, αv, and β1 expression were changed under LG-HMF conditions. In conclusion, LG-HMF affects osteoblast ultrastructure, cell viability, and ALP secretion, and the changes caused by LG-HMF may be related to disrupting col I or FN/αβ1 integrin. PMID:23382804

Large gradient high magnetic fields affect osteoblast ultrastructure and function by disrupting collagen I or fibronectin/αβ1 integrin.

PubMed

Qian, Ai-Rong; Gao, Xiang; Zhang, Wei; Li, Jing-Bao; Wang, Yang; Di, Sheng-Meng; Hu, Li-Fang; Shang, Peng

2013-01-01

The superconducting magnet generates a field and field gradient product that can levitate diamagnetic materials. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. The effects of LG-HMF on the ultrastructure and function of osteoblast-like cells (MG-63 and MC3T3-E1) and the underlying mechanism were investigated by transmission electromicroscopy (TEM), MTT, and cell western (ICW) assays. Under LG-HMF significant morphologic changes in osteoblast-like cells occurred, including expansion of endoplasmic reticulum and mitochondria, an increased number of lysosomes, distorted microvilli, and aggregates of actin filaments. Compared to controls, cell viability and alkaline phosphatase (ALP) secretion were significantly increased, and collagen I (col I), fibronectin (FN), vinculin, integrin α3, αv, and β1 expression were changed under LG-HMF conditions. In conclusion, LG-HMF affects osteoblast ultrastructure, cell viability, and ALP secretion, and the changes caused by LG-HMF may be related to disrupting col I or FN/αβ1 integrin.

Isostatic gravity map of the Point Sur 30 x 60 quadrangle and adjacent areas, California

USGS Publications Warehouse

Watt, J.T.; Morin, R.L.; Langenheim, V.E.

2011-01-01

This isostatic residual gravity map is part of a regional effort to investigate the tectonics and water resources of the central Coast Range. This map serves as a basis for modeling the shape of basins and for determining the location and geometry of faults in the area. Local spatial variations in the Earth's gravity field (after removing variations caused by instrument drift, earth-tides, latitude, elevation, terrain, and deep crustal structure), as expressed by the isostatic anomaly, reflect the distribution of densities in the mid- to upper crust, which in turn can be related to rock type. Steep gradients in the isostatic gravity field often indicate lithologic or structural boundaries. Gravity highs reflect the Mesozoic granitic and Franciscan Complex basement rocks that comprise both the northwest-trending Santa Lucia and Gabilan Ranges, whereas gravity lows in Salinas Valley and the offshore basins reflect the thick accumulations of low-density alluvial and marine sediment. Gravity lows also occur where there are thick deposits of low-density Monterey Formation in the hills southeast of Arroyo Seco (>2 km, Marion, 1986). Within the map area, isostatic residual gravity values range from approximately -60 mGal offshore in the northern part of the Sur basin to approximately 22 mGal in the Santa Lucia Range.

3D interactive forward and inversion gravity modelling at different scales: From subduction zone modelling to cavity detection.

NASA Astrophysics Data System (ADS)

Götze, Hans-Jürgen; Schmidt, Sabine

2014-05-01

Modern geophysical interpretation requires an interdisciplinary approach, particularly when considering the available amount of 'state of the art' information. A combination of different geophysical surveys employing seismic, gravity and EM, together with geological and petrological studies, can provide new insights into the structures and tectonic evolution of the lithosphere, natural deposits and underground cavities. Interdisciplinary interpretation is essential for any numerical modelling of these structures and the processes acting on them Interactive gravity and magnetic modeling can play an important role in the depth imaging workflow of complex projects. The integration of the workflow and the tools is important to meet the needs of today's more interactive and interpretative depth imaging workflows. For the integration of gravity and magnetic models the software IGMAS+ can play an important role in this workflow. For simplicity the focus is on gravity modeling, but all methods can be applied to the modeling of magnetic data as well. Currently there are three common ways to define a 3D gravity model. Grid based models: Grids define the different geological units. The densities of the geological units are constant. Additional grids can be introduced to subdivide the geological units, making it possible to represent density depth relations. Polyhedral models: The interfaces between different geological units are defined by polyhedral, typically triangles. Voxel models: Each voxel in a regular cube has a density assigned. Spherical Earth modeling: Geophysical investigations may cover huge areas of several thousand square kilometers. The depression of the earth's surface due to the curvature of the Earth is 3 km at a distance of 200 km and 20 km at a distance of 500 km. Interactive inversion: Inversion is typically done in batch where constraints are defined beforehand and then after a few minutes or hours a model fitting the data and constraints is generated. As examples I show results from the Central Andes and the North Sea. Both gravity and geoid of the two areas were investigated with regard to their isostatic state, the crustal density structure and rigidity of the Lithosphere. Modern satellite measurements of the recent ESA campaigns are compared to ground observations in the region. Estimates of stress and GPE (gravitational potential energy) at the western South American margin have been derived from an existing 3D density model. Here, sensitivity studies of gravity and gravity gradients indicate that short wavelength lithospheric structures are more pronounced in the gravity gradient tensor than in the gravity field. A medium size example of the North Sea underground demonstrates how interdisciplinary data sets can support aero gravity investigations. At the micro scale an example from the detection of a crypt (Alversdorf, Northern Germany) is shown.

Scientific uses and technical implementation of a variable gravity centrifuge on Space Station Freedom

NASA Technical Reports Server (NTRS)

Johnson, C. C.; Hargens, A. R.

1990-01-01

The potential need and science requirements for a centrifuge to be designed and flown on Space Station Freedom are discussed, with a focus on a design concept for a centrifuge developed at NASA Ames. Applications identified for the centrifuge include fundamental studies in which gravity is a variable under experimental control, the need to provide a 1-g control, attempts to discover the threshold value of gravitation force for psychological response, and an effort to determine the effects of intermittent hypergravity. Science requirements specify the largest possible diameter at approximately 2.5 m, gravity levels ranging from 0.01 to 2 g, a nominal ramp-up rate of 0.01 g/sec, and life support for plants and animals. Ground-based studies using rats and squirrel monkeys on small-diameter centrifuges have demonstrated that animals can adapt to centrifugation at gravity gradients higher than those normally used in ground-based hypergravity studies.

Tethered orbital refueling study

NASA Technical Reports Server (NTRS)

Fester, Dale A.; Rudolph, L. Kevin; Kiefel, Erlinda R.; Abbott, Peter W.; Grossrode, Pat

1986-01-01

One of the major applications of the space station will be to act as a refueling depot for cryogenic-fueled space-based orbital transfer vehicles (OTV), Earth-storable fueled orbit maneuvering vehicles, and refurbishable satellite spacecraft using hydrazine. One alternative for fuel storage at the space station is a tethered orbital refueling facility (TORF), separated from the space station by a sufficient distance to induce a gravity gradient force that settles the stored fuels. The technical feasibility was examined with the primary focus on the refueling of LO2/LH2 orbital transfer vehicles. Also examined was the tethered facility on the space station. It was compared to a zero-gravity facility. A tethered refueling facility should be considered as a viable alternative to a zero-gravity facility if the zero-gravity fluid transfer technology, such as the propellant management device and no vent fill, proves to be difficult to develop with the required performance.

Integration of satellite gravity data with ground-based geophysical data for a better understanding of the structural control of groundwater flow in the Nubian Sandstone Aquifer System

NASA Astrophysics Data System (ADS)

Fathy, K.; Sultan, M.; Bettadpur, S. V.; Save, H.; Ahmed, M.; Zahran, K. H.; Emil, M. K.; Helaly, A.; Abotalib, A. Z.; Ismaiel, A.

2016-12-01

The Nubian Sandstone Aquifer System (NSAS) extends beyond Egypt's political boundaries to cover eastern Libya, northern and central Sudan and northeast Chad. The optimum utilization of this resource requires a better understanding of the connectivity of the NSAS sub-basins and the structural control on groundwater flow throughout the system. We provide an integrated (geophysics, remote sensing and field) approach to address these issues. Firstly, we evaluated GOCE-based global Geopotential models (GGMs) compared to the terrestrial gravity anomalies for 21262 sites to select the optimum model for deriving Bouguer gravity datasets. The Eigen-6C4 was found to have the lowest deviation from the terrestrial gravity anomalies. Secondly, structures and uplifts were mapped on the surface and in the sub-surface. Extensive N-S to NW-SE trending grabens were delineated in areas proximal to the Nile Valley using Palsar-derived DEMs, and hill shade maps; these depressions are here interpreted as basement structures that were reactivated during the opening of the Red Sea and the Gulf of Suez. The sinistral E-W trending faults and shear zones of the Syrian Arc were mapped in northern Egypt from Sinai and across the Eastern and Western Deserts. These structures were mapped on the surface using hill shade images and their extension in the subsurface was successfully detected from Eigen-6C4 model-derived Bouguer and TDR maps. The E-W trending basement uplift (Uweinat-Aswan uplift) was mapped in southern Egypt and the N-S trending Uweinat-Howar uplift was delineated in western Sudan and eastern Chad using TDR maps. Thirdly, hydrological analysis was conducted using GRACE spherical harmonic solutions (RL05), and CSR 0.5° X 0.5°, and JPL Mascon solutions. These showed: (1) pronounced TWS depletion over the Dakhla basin (average of three solutions: -3.03 mm/yr); (2) the south to north groundwater flow from Sudan to Egypt is impeded by the E-W trending Uweinat-Aswan basement uplift, yet the southwest to northeast flow from Chad into Sudan is not obstructed by the Uweinat-Howar uplift, (3) the E-W trending faults and shear zones impede groundwater flow to the north and act as conduits for deep-seated groundwater discharge on the surface in natural depressions (e.g., Qattara) and in the overlying layers.

Phobos Mobility Simulation

NASA Technical Reports Server (NTRS)

Bielski, Paul

2015-01-01

Phobos, the larger of Mars' moons, provides a potential staging location for human exploration of the Martian surface. Its low gravity (about 1/200th of Earth) and lack of atmosphere makes it an attractive destination before a more complex human landing on Mars is attempted. While easier to approach and depart than Mars itself, Phobos provides unique challenges to visiting crews. It is irregularly shaped, so its local gravitational field does not always point straight down with respect to the visible horizon. It is very close to Mars and tidally locked, so the Martian gravity gradient and applied acceleration greatly affect the perceived surface gravity direction and magnitude. This simulation allows the assessment of unique mobility approaches on the surface of Phobos, including hopping in particular.

ESA airborne campaigns in support of Earth Explorers

NASA Astrophysics Data System (ADS)

Casal, Tania; Davidson, Malcolm; Schuettemeyer, Dirk; Perrera, Andrea; Bianchi, Remo

2013-04-01

In the framework of its Earth Observation Programmes the European Space Agency (ESA) carries out ground based and airborne campaigns to support geophysical algorithm development, calibration/validation, simulation of future spaceborne earth observation missions, and applications development related to land, oceans and atmosphere. ESA has been conducting airborne and ground measurements campaigns since 1981 by deploying a broad range of active and passive instrumentation in both the optical and microwave regions of the electromagnetic spectrum such as lidars, limb/nadir sounding interferometers/spectrometers, high-resolution spectral imagers, advanced synthetic aperture radars, altimeters and radiometers. These campaigns take place inside and outside Europe in collaboration with national research organisations in the ESA member states as well as with international organisations harmonising European campaign activities. ESA campaigns address all phases of a spaceborne missions, from the very beginning of the design phase during which exploratory or proof-of-concept campaigns are carried out to the post-launch exploitation phase for calibration and validation. We present four recent campaigns illustrating the objectives and implementation of such campaigns. Wavemill Proof Of Concept, an exploratory campaign to demonstrate feasibility of a future Earth Explorer (EE) mission, took place in October 2011 in the Liverpool Bay area in the UK. The main objectives, successfully achieved, were to test Astrium UKs new airborne X-band SAR instrument capability to obtain high resolution ocean current and topology retrievals. Results showed that new airborne instrument is able to retrieve ocean currents to an accuracy of ± 10 cms-1. The IceSAR2012 campaign was set up to support of ESA's EE Candidate 7,BIOMASS. Its main objective was to document P-band radiometric signatures over ice-sheets, by upgrading ESA's airborne POLARIS P-band radar ice sounder with SAR capability. Campaign comprised three airborne campaigns in Greenland from April to June 2012 separated by roughly one month and preliminary results showed the instrument capability to detect ice motion. CryoVEx 2012 was a large collaborative effort to help ensure the accuracy of ESA's ice mission CryoSat. The aim of this large-scale Arctic campaign was to record sea-ice thickness and conditions of the ice exactly below the CryoSat-2 path. A range of sensors installed on different aircraft included simple cameras to get a visual record of the sea ice, laser scanners to clearly map the height of the ice, an ice-thickness sensor (EM-Bird), ESA's radar altimeter (ASIRAS) and NASA's snow and Ku-band radars, which mimic CryoSat's measurements but at a higher resolution. Preliminary results reveal the ability to detect centimetre differences between sea-ice and thin ice/water which in turn allow for the estimation of actual sea ice thickness. In support of two currently operating EE Missions: SMOS (Soil Moisture and Ocean Salinity) and GOCE (Gravity field and steady-state Ocean Circulation Explorer), DOMECair airborne campaign will take place in Antarctica, in the Dome C region during the middle of January 2013. The two main objectives are to quantify and document the spatial variability in the DOME C area, important to establish long-term cross-calibrated multi-mission L-band measurement time-series (SMOS) and fill in the gap in the high-quality gravity anomaly maps in Antarctica since airborne gravity measurements are sparse (GOCE). Key airborne instruments in the campaign are EMIRAD-2 L-band radiometer, designed and operated by DTU and a gravimeter from AWI. ESA campaigns have been fundamental and an essential part in the preparation of new Earth Observation missions, as well as in the independent validation of their measurements and quantification of error sources. For the different activities a rich variety of datasets has been recorded, are archived and users can access campaign data through the EOPI web portal [http://eopi.esa.int].

Equations of motion of a space station with emphasis on the effects of the gravity gradient

NASA Technical Reports Server (NTRS)

Tuell, L. P.

1987-01-01

The derivation of the equations of motion is based upon the principle of virtual work. As developed, these equations apply only to a space vehicle whose physical model consists of a rigid central carrier supporting several flexible appendages (not interconnected), smaller rigid bodies, and point masses. Clearly evident in the equations is the respect paid to the influence of the Earth's gravity field, considerably more than has been the custom in simulating vehicle motion. The effect of unpredictable crew motion is ignored.

Observations of earth eigen vibrations possibly excited by low frequency gravity waves

NASA Technical Reports Server (NTRS)

Tuman, V. S.

1971-01-01

A cryogenic gravity meter made of two parts, a magnetic suspension unit and a detection module, was used to monitor earth eigen vibrations. The magnetic field and field gradient are generated by energizing a set of superconducting coils made of niobium-zirconium alloy wire. The detection module is a double Josephson junction magnetometer. The output is printed on a chart recorder and later digitized using a computer; a Fourier transformation is performed on the accumulated data. The measurements of eigen vibrations are summarized in tabular and graphical representations.

An Investigation Into the Feasibility of Using a Modern Gravity Gradient Instrument for Passive Aircraft Navigation and Terrain Avoidance

DTIC Science & Technology

2009-03-01

the research objectives for this study are presented. It should be noted that sensor cost was not considered for this study. Additionally, further...development costs ) for gravity compensation require- ments of its trident submarine inertial navigation systems and by the Air Force Geo- physics...52]: T (r, φ, λ) = GM ae Nmax∑ n=2 n∑ m=0 (a r )n+1 (Cnm cosmλ+ Snm sinmλ)P nm(cos φ) (31) 44 where r, φ, λ are the geocentric distance, lattitude and

Two phase flow and heat transfer in porous beds under variable body forces, part 2

NASA Technical Reports Server (NTRS)

Evers, J. L.; Henry, H. R.

1969-01-01

Analytical and experimental investigations of a pilot model of a channel for the study of two-phase flow under low or zero gravity are presented. The formulation of dimensionless parameters to indicate the relative magnitude of the effects of capillarity, gravity, pressure gradient, viscosity, and inertia is described. The investigation is based on the principal equations of fluid mechanics and thermodynamics. Techniques were investigated by using a laser velocimeter for measuring point velocities of the fluid within the porous material without disturbing the flow.

Optimum gradient of mountain paths.

PubMed

Minetti, A E

1995-11-01

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions.

A new formula of the Gravitational Curvature for the prism

NASA Astrophysics Data System (ADS)

Grazia D'Urso, Maria

2017-04-01

Gravitational Curvatures (GC) are the components of the third-order gravitational tensor and physically represent the rate of change of the gravity gradient. While scalar, vector and second-order tensor quantities of the Earth's gravitational field have extensively been studied and their properties have been well understood [1], the first successful terrestrial measurements of the third-order vertical gravitational gradients have been recently performed in [2] by atom interferometry sensors in laboratory environment. Possible benefits of the airborne third-order gravitational gradients for exploration geophysics are discussed in [3] while Brieden et al. (2010) [4] have proposed a new satellite mission called OPTical Interferometry for global Mass change detection from space (OPTIMA) sensing the third-order gravitational gradients in space. Moreover, exploitation of GC for modelling the Earth's gravitational field has been object of recent studies [5-7]. We extend the approach presented by the author in previous papers [8-10] by evaluating the algebraic expression of the third-order gravitational tensor for a prism. Comparisons with previous results [11-12] are also included. [1] Freeden W, Schreiner M (2009) Spherical functions of mathematical geosciences. A scalar, vectorial, and tensorial setup. In: Advances in geophysical and environmental mechanics and mathematics. Springer, Berlin [2] Rosi G, Cacciapuoti L, Sorrentino F, Menchetti M, Prevedelli M, Tino GM (2015) Measurements of the gravity-field curvature by atom interferometry. Phys Rev Lett 114:013001 [3] Di Francesco D, Meyer T, Christensen A, FitzGerald D (2009) Gravity gradiometry - today and tomorrow. In: 11th SAGA Biennial technical meeting and exhibition, 13-18 September 2009, Switzerland, pp 80-83 [4] Brieden P, Müller J, Flury J, Heinzel G (2010) The mission OPTIMA - novelties and benefit. In: Geotechnologien science report No. 17, Potsdam, pp 134-139 [5] Šprlák M, Novák P (2015) Integral formulas for computing a third-order gravitational tensor from volumetric mass density, disturbing gravitational potential, gravity anomaly and gravity disturbance. J Geod 89:141-157 [6] Šprlák M, Novák P (2016) Spherical gravitational curvature boundary-value problem. J Geod 90:727-739 [7] Hamáčková E, Šprlák M , Pitoňák M, Novák P (2016) Non-singular expressions for the spherical harmonic synthesis of gravitational curvatures in a local north-oriented reference frame. Comp & Geosc 88: 152-162 [8] D'Urso MG (2012) New expressions of the gravitational potential and its derivates for the prism. In Hotine-Marussi International Symposium on Mathematical Geodesy, 7rd. Sneeuw N, Novak P, Crespi M, Sansò F. Springer-Verlag, Berlin Heidelberg pp. 251-256 [9] D'Urso MG (2013) On the evaluation of the gravity effects of polyhedral bodies and a consistent treatment of related singularities. J Geod 87:239-252 [10] D'Urso MG (2014)Analytical computation of gravity effects for polyhedral bodies. J Geod 88:13-29 [11] Nagy D, Papp G, Benedek J (2000) The gravitational potential and its derivatives for the prism. J Geod 74:552-560 [12] Holstein H, Fitzgerald DJ, H. Stefanov H (2013) Gravimagnetic similarity for homogeneous rectangular prisms. 75th EAGE Conference & Exhibition, London

Characteristics of satellite accelerometer measurements of thermospheric neutral winds at high latitudes

NASA Astrophysics Data System (ADS)

Doornbos, E.; Ridley, A. J.; Cnossen, I.; Aruliah, A. L.; Foerster, M.

2015-12-01

Thermospheric neutral winds play an important part in the coupled thermosphere-ionosphere system at high latitudes. Neutral wind speeds have been derived from the CHAMP and GOCE satellites, which carried precise accelerometers in low Earth orbits. Due to the need to simultaneously determine thermosphere neutral density from the accelerometer in-track measurements, only information on the wind component in the cross-track direction, perpendicular to the flight direction can be derived. However, contrary to ground-based Fabry-Perot interferometer and scanning Doppler imager observations of the thermosphere wind, these satellite-based measurements provide equally distributed coverage over both hemispheres. The sampling of seasonal and local time variations depend on the precession rate of the satellite's orbital plane, with CHAMP covering about 28 cycles of 24-hour local solar time coverage, during its 10 year mission (2000-2010), while the near sun-synchronous orbit of GOCE resulted in a much more limited local time coverage ranging from 6:20 to 8:00 (am and pm), during a science mission duration of 4 years (2009-2013). For this study, the wind data from both CHAMP and GOCE have been analysed in terms of seasonal variations and geographic and geomagnetic local solar time and latitude coordinates, in order to make statistical comparisons for both the Northern and Southern polar areas. The wind data from both satellites were studied independently and in combination, in order to investigate how the strengths and weaknesses of the instruments and orbit parameters of these missions affect investigations of interhemispheric differences. Finally, the data have been compared with results from coupled ionosphere-thermosphere models and from ground-based FPI and SDI measurements.

Cellular Mechanisms of Gravitropic Response in Higher Plants

NASA Astrophysics Data System (ADS)

Medvedev, Sergei; Smolikova, Galina; Pozhvanov, Gregory; Suslov, Dmitry

The evolutionary success of land plants in adaptation to the vectorial environmental factors was based mainly on the development of polarity systems. In result, normal plant ontogenesis is based on the positional information. Polarity is a tool by which the developing plant organs and tissues are mapped and the specific three-dimensional structure of the organism is created. It is due to their polar organization plants are able to orient themselves relative to the gravity vector and different vectorial cues, and to respond adequately to various stimuli. Gravitation is one of the most important polarized environmental factor that guides the development of plant organisms in space. Every plant can "estimate" its position relative to the gravity vector and correct it, if necessary, by means of polarized growth. The direction and the magnitude of gravitational stimulus are constant during the whole plant ontogenesis. The key plant response to the action of gravity is gravitropism, i.e. the directed growth of organs with respect to the gravity vector. This response is a very convenient model to study the mechanisms of plant orientation in space. The present report is focused on the main cellular mechanisms responsible for graviropic bending in higher plants. These mechanisms and structures include electric polarization of plant cells, Ca ({2+) }gradients, cytoskeleton, G-proteins, phosphoinositides and the machinery responsible for asymmetric auxin distribution. Those mechanisms tightly interact demonstrating some hierarchy and multiple feedbacks. The Ca (2+) gradients provide the primary physiological basis of polarity in plant cells. Calcium ions influence on the bioelectric potentials, the organization of actin cytoskeleton, the activity of Ca (2+) -binding proteins and Ca (2+) -dependent protein kinases. Protein kinases modulate transcription factors activity thereby regulating the gene expression and switching the developmental programs. Actin cytoskeleton affects the molecular machinery of polar auxin transport. It results in the changes of auxin gradients in plant organs and tissues, which modulate all cellular mechanisms of polarity via multiple feedback loops. The understanding of the mechanisms of plant organism orientation relative to the gravity vector will allow us to develop efficient technologies for plant growing in microgravity conditions at orbital space stations and during long piloted space flights. This work was supported by the grant of Russian Foundation for Basic Research (N 14-04-01-624) and by the grant of St.-Petersburg State University (N 1.38.233.2014).

Performance Evaluation and Requirements Assessment for Gravity Gradient Referenced Navigation

PubMed Central

Lee, Jisun; Kwon, Jay Hyoun; Yu, Myeongjong

2015-01-01

In this study, simulation tests for gravity gradient referenced navigation (GGRN) are conducted to verify the effects of various factors such as database (DB) and sensor errors, flight altitude, DB resolution, initial errors, and measurement update rates on the navigation performance. Based on the simulation results, requirements for GGRN are established for position determination with certain target accuracies. It is found that DB and sensor errors and flight altitude have strong effects on the navigation performance. In particular, a DB and sensor with accuracies of 0.1 E and 0.01 E, respectively, are required to determine the position more accurately than or at a level similar to the navigation performance of terrain referenced navigation (TRN). In most cases, the horizontal position error of GGRN is less than 100 m. However, the navigation performance of GGRN is similar to or worse than that of a pure inertial navigation system when the DB and sensor errors are 3 E or 5 E each and the flight altitude is 3000 m. Considering that the accuracy of currently available gradiometers is about 3 E or 5 E, GGRN does not show much advantage over TRN at present. However, GGRN is expected to exhibit much better performance in the near future when accurate DBs and gravity gradiometer are available. PMID:26184212

Investigating the probability of detection of typical cavity shapes through modelling and comparison of geophysical techniques

NASA Astrophysics Data System (ADS)

James, P.

2011-12-01

With a growing need for housing in the U.K., the government has proposed increased development of brownfield sites. However, old mine workings and natural cavities represent a potential hazard before, during and after construction on such sites, and add further complication to subsurface parameters. Cavities are hence a limitation to certain redevelopment and their detection is an ever important consideration. The current standard technique for cavity detection is a borehole grid, which is intrusive, non-continuous, slow and expensive. A new robust investigation standard in the detection of cavities is sought and geophysical techniques offer an attractive alternative. Geophysical techniques have previously been utilised successfully in the detection of cavities in various geologies, but still has an uncertain reputation in the engineering industry. Engineers are unsure of the techniques and are inclined to rely on well known techniques than utilise new technologies. Bad experiences with geophysics are commonly due to the indiscriminate choice of particular techniques. It is imperative that a geophysical survey is designed with the specific site and target in mind at all times, and the ability and judgement to rule out some, or all, techniques. To this author's knowledge no comparative software exists to aid technique choice. Also, previous modelling software limit the shapes of bodies and hence typical cavity shapes are not represented. Here, we introduce 3D modelling software (Matlab) which computes and compares the response to various cavity targets from a range of techniques (gravity, gravity gradient, magnetic, magnetic gradient and GPR). Typical near surface cavity shapes are modelled including shafts, bellpits, various lining and capping materials, and migrating voids. The probability of cavity detection is assessed in typical subsurface and noise conditions across a range of survey parameters. Techniques can be compared and the limits of detection distance assessed. The density of survey points required to achieve a required probability of detection can be calculated. The software aids discriminate choice of technique, improves survey design, and increases the likelihood of survey success; all factors sought in the engineering industry. As a simple example, the response from magnetometry, gravimetry, and gravity gradient techniques above an example 3m deep, 1m cube air cavity in limestone across a 15m grid was calculated. The maximum responses above the cavity are small (amplitudes of 0.018nT, 0.0013mGal, 8.3eotvos respectively), but at typical site noise levels the detection reliability is over 50% for the gradient gravity method on a single survey line. Increasing the number of survey points across the site increases the reliability of detection of the anomaly by the addition of probabilities. We can calculate the probability of detection at different profile spacings to assess the best possible survey design. At 1m spacing the overall probability of by the gradient gravity method is over 90%, and over 60% for magnetometry (at 3m spacing the probability drops to 32%). The use of modelling in near surface surveys is a useful tool to assess the feasibility of a range of techniques to detect subtle signals. Future work will integrate this work with borehole measured parameters.

Implications of Preliminary Gravity and Magnetic Surveys to the Understanding of the Bartlett Springs Fault Zone, Northern California Coast Ranges

NASA Astrophysics Data System (ADS)

Langenheim, V. E.; Jachens, R. C.; Morin, R. L.; McCabe, C. M.; Page, W. D.

2007-12-01

We use new gravity and magnetic data in the Lake Pillsbury region to help understand the geometry and character of the Bartlett Springs fault zone, one of the three main strands of the San Andreas system north of the San Francisco Bay area. We collected 153 new gravity stations in the Lake Pillsbury region that complement the sparse regional dataset and are used to estimate the thickness of Quaternary deposits in the inferred Gravelly Valley (Lake Pillsbury) pull-apart basin. We also collected 38 line-km of ground magnetic data on roads and 65 line-km by boat on the lake to supplement regional aeromagnetic surveys and to map concealed fault strands beneath the lake. The new gravity data show a significant northwest-striking gravity gradient at the base of which lies the Bartlett Springs fault zone. Superposed on this major east-facing gravity gradient is a 5 mGal low centered on Lake Pillsbury and Gravelly Valley. Inversion of the gravity field for basin thickness assuming a density contrast of 400 kg/m3 indicates the deepest part of the basin is about 400 m and located in the northern part of the valley, although the inversion lacks gravity stations within the lake. The basin is about 3 km wide and 5 km long and basin edges coincide with strands of the Bartlett Springs fault zone. Our gravity data suggest that Potter Valley, which lies between the Maacama and Bartlett Springs faults, is also as much as 400 m deep in the southern part of the valley, although additional data west of the valley would better isolate the gravity low. Geomorphologic characteristics of the valley suggest that this structure has been quiescent during the late Quaternary. Ground magnetic data are very noisy but the data in conjunction with 9.6 km-spaced NURE aeromagnetic lines suggest that regional analog aeromagnetic data flown in 1962 may suffer from location errors. The regional and NURE data show a northwest-striking magnetic high that extends across Lake Pillsbury. The northeast edge of this anomaly, caused by ultramafic rocks, coincides with the Bartlett Springs fault zone for nearly 15 km. Lake magnetic data indicate as many as three right-stepping strands of the Bartlett Springs fault zone within the gravity- defined pull-apart basin. Two pairs of magnetic anomalies appear to be dextrally offset along the fault, arguing for about 8-9 km of cumulative offset on the fault since the passage of the triple junction at about 3.5 Ma. This estimate is similar to proposed offsets of the Eel River (8.6-10.9 km) at Lake Pillsbury. The minimum long-term slip rate is thus 2.3-3.1 mm/yr, considerably slower than geodetic rates of 5-8 mm/yr. Seismicity forms a 5-km-wide diffuse zone along the Bartlett Springs fault zone in the Lake Pillsbury area, with fewer earthquakes about 5 km northwest of the lake and its associated magnetic anomaly. The McCreary Glade seismicity lineament, located between Potter Valley and Lake Pillsbury, has been attributed to a dike intrusion at depth or reactivation of an older structure. These earthquakes coincide with the northeast edge of a 100-km-long belt of aeromagnetic anomalies and thus appear to have reactivated an older basement feature. The coincidence of the Bartlett Springs fault zone and significant gravity gradients also argues that the much younger fault zone has reactivated older basement features. Our analysis shows that a modern, high-resolution aeromagnetic survey is needed to confirm these preliminary interpretations.

Slip in Great Megathrust Earthquakes and its Relation to Crustal Structure as Revealed by Satellite Free-air Gravity

NASA Astrophysics Data System (ADS)

Wells, R. E.; Blakely, R. J.; Scholl, D.

2007-12-01

In 2003, Song and Simons and Wells et al. showed that approximately 70% of the moment released during past large, shallow subduction zone thrust earthquakes occurred beneath trench-parallel, free-air gravity lows outlining the deep-sea slope terrace and its basins. The authors suggested that the basin-centered, fore-arc gravity lows might be good predictors of high seismic slip in future earthquakes. Since 2001, ten megathrust earthquakes have occurred with magnitudes greater than Mw 7.7, including the giant, Mw 9.17 Sumatra earthquake of 2004. These earthquakes provide a robust test of the idea that seismic slip is focused beneath basin-centered gravity lows, and also the related ideas that the landward maximum gravity gradient marks the effective down-dip limit of large coseismic slip, and that intrabasin, transverse gravity highs are areas of lower slip. A compilation of seismic and geodetic slip inversions for the post-2001 earthquakes and new analyses of slip for the great Antofagasta, Jalisco, and Peru events in 1995 and 1996 indicate that more than 80% of the high-slip areas occur beneath deep-sea terrace gravity lows (DSTL), and that half of the earthquake asperities lie beneath fore-arc basins or local gravity lows. The maximum gravity gradient along the landward margin of the deep-sea terrace may mark the point where thicker overlying crust and higher temperatures on the megathrust limit the down dip extent of stick-slip behavior. Onland analogues are the mountain front of the Himalaya, which approximately marks the down-dip limit of large coseismic slip along the Main Frontal Thrust, and the front of the Taiwan Central Ranges, which coincides with the limit of slip during the 1999 Chi-Chi earthquake (Mw 7.6). In the up dip direction, coseismic slip may be partitioned onto splay faults in the wedge, as occurred in the 1964 Alaska earthquake. The observed pattern of greater slip at depth beneath fore arc basins is consistent with partitioning of slip up dip, especially if outer wedge materials deform more slowly, as suggested for parts of the 2004 Sumatra rupture. Along strike variations in fore-arc gravity also correlate with changing seismic behavior. At Cape Erimo on Hokkaido, three Mw 8+ earthquakes (1952, 1968, 2003) have occurred on either side of the gravity high that overlies the Cape, with little coseismic slip beneath the high. To the northeast, the deep-sea terrace gradually narrows, as does the rupture width of the great earthquakes, until off the central Kurile Islands, the terrace disappears and the arc gravity high occupies the fore-arc. The gravity high had been an historic seismic gap that was filled by the 2006 Kurile Island earthquake (Mw 8.3). Although the earthquake nucleated under the high, the slip occurred beneath the adjacent gravity low to the northeast. This might suggest the gravity highs are not likely sources of large seismic moment, at least in M8 earthquakes. In contrast, the main asperity associated with the 2005 Sumatra (Mw 8.7) earthquake was beneath the large gravity high of Nias Island. An alternative view is that the gravity highs are stronger asperities that only rupture in giant earthquakes. Globally, the coincidence of basin- centered coseismic slip with geologic evidence of sustained subsidence of the fore-arc suggests that subduction erosion is occurring in the seismogenic zone. Recent work off Chile, Colombia, Peru, and elsewhere shows that subduction erosion is an important process in many subduction zones.

Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

NASA Astrophysics Data System (ADS)

Wu, Guiju; Shen, Chongyang; Tan, Hongbo; Yang, Guangliang

2016-08-01

This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly ( G h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault ( F1) or the southeast boundary of Alxa block is in accord with the western change belt of G h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault ( F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.

Tectonic significance of magnetic and gravity data across northern California (lat. 39[degree]N. to lat. 41[degree]N. )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griscom, A.; Roberts, C.W.; Halvorson, P.F.

1993-04-01

Aeromagnetic and isostatic residual gravity maps of an east-west transect across northern California show important tectonic features. A linear magnetic anomaly and west-sloping gradient extends over 300 km along the Franciscan-Great Valley contact (FGC) and across the Klamath Mountains province (KM) north to lat. 40[degree]45'N. The anomaly source lies at depths of 5--10 km beneath the KM and the FGC, and implies that the Franciscan complex of the Coast Ranges is thrust (and wedged) at least 80 km eastward beneath the KM to approximately long. 122[degree]40 minutes W. Calculations on a circular gravity low of [minus]50 mGal centered at themore » circular Bald Rock pluton (diameter about 15 km) in the Sierran foothills indicate a pluton thickness of about 15 km. The nearby Cascade and Merrimac plutons are located on the gradients of this gravity anomaly, have a relatively minor effect on it, and thus are interpreted to be thick (up to 5 km) laccolithic sills that emanate from the Bald Rock pluton, thinning away from it to a feather edge. Model studies indicate that the northeast contact of the Feather River periodotite body (FRPB) north of lat. 39[degree]40 minutes N. generally dips steeply northeast or vertical. The same contact south of this latitude dips east at angles of about 45[degree] to depths of at least 10 km. Magnetic patterns extending from the northern Sierra across the Cascades to the Klamath Mountains suggest that the FRPB may correlate with the Trinity ophiolite.« less

Study of fluid behaviour under gravity compensated by a magnetic field

NASA Astrophysics Data System (ADS)

Chatain, D.; Beysens, D.; Madet, K.; Nikolayev, V.; Mailfert, A.

2006-09-01

Fluids, and especially cryogenic fluids like hydrogen and oxygen, are widely used in space technology for propulsion and cooling. The knowledge of fluid behaviour during the acceleration variation and under reduced gravity is necessary for an efficient management of fluids in space. Such a management also rises fundamental questions about thermo-hydrodynamics and phase change once buoyancy forces are cancelled. For security reasons, it is nearly impossible to use the classical microgravity means to experiment with such cryofluids. However, it is possible to counterbalance gravity by using the paramagnetic (O2) or diamagnetic (H2) properties of fluids. By applying a magnetic field gradient on these materials, a volume force is created that is able to impose to the fluid a varying effective gravity, including microgravity. We have set up a magnetic levitation facility for H2 in which numerous experiments have been performed. A new facility for O2 is under construction. It will enable fast change in the effective gravity by quenching down the magnetic field. The facilities and some particularly representative experimental results are presented.

Double Diffusive Convection in Materials Processing

NASA Technical Reports Server (NTRS)

Ramachandra, Narayanan; Leslie, Fred W.

1999-01-01

A great number of crystals grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity (g-jitter). As a specific example, past HgCdTe crystal growth space experiments by Lehoczky and co-workers indicate radial compositional asymmetry in the grown crystals. In the case of HgCdTe the rejected component into the melt upon solidification is HgTe which is denser than the melt. The space grown crystals indicate the presence of three dimensional flow with the heavier HgTe-rich material clearly aligned with the residual gravity (0.55-1.55 micro g) vector. This flow stems from double-diffusive convection, namely, thermal and solutal buoyancy driven flow in the melt. The study of double-diffusive convection is multi-faceted and rather vast. In our investigation, we seek to focus on one specific aspect of this discipline that is of direct relevance to materials processing especially crystal growth, namely, the side ways heating regime. This problem has been widely studied, both experimentally and numerically, in the context of solar ponds wherein the system is characterized by a linear salt (solutal) gradient with an imposed lateral temperature gradient. The induced flow instabilities arise from the wide disparity between the fluid thermal diffusivity and the solute diffusivity. The extension of the analysis to practical crystal growth applications has however not been rigorously made and understood. One subtle but important difference in crystal growth systems is the fact that die system solute gradient is non-linear (typically exponential). Besides, the crystal growth problem has the added complexities of solidification, both lateral and longitudinal thermal gradients and segregation phenomena in systems where binary and ternary compounds are being grown. This paper treats the side ways heating problem alone in a model fluid system. Results from detailed numerical calculations, mainly two dimensional are provided. The interactions between a non-linear solute gradient and an imposed transverse thermal gradient are investigated. The buoyancy effects are treated in the traditional Boussinesq approximation and also in a more complete density formulation to address recent concerns of the first approach especially in simulations of the system response in a reduced gravity environment. Detailed flow, temperature and solute field plots along with heat and mass transfer results are presented in the paper. Implications to practical crystal growth systems as discerned from the modeling results are also explored and reported.

Pulmonary function in microgravity: Spacelab 4 and beyond

NASA Technical Reports Server (NTRS)

Guy, H. J.; Prisk, G. K.; West, J. B.

1988-01-01

This paper refers principally to the composition gradient of gases within the lung in various conditions of gravity, as revealed by exhaled breath. A rapid gas analyzer-based system has been developed for tests in Spacelab 4. The test sequence and expected results are presented.

A simple orbit-attitude coupled modelling method for large solar power satellites

NASA Astrophysics Data System (ADS)

Li, Qingjun; Wang, Bo; Deng, Zichen; Ouyang, Huajiang; Wei, Yi

2018-04-01

A simple modelling method is proposed to study the orbit-attitude coupled dynamics of large solar power satellites based on natural coordinate formulation. The generalized coordinates are composed of Cartesian coordinates of two points and Cartesian components of two unitary vectors instead of Euler angles and angular velocities, which is the reason for its simplicity. Firstly, in order to develop natural coordinate formulation to take gravitational force and gravity gradient torque of a rigid body into account, Taylor series expansion is adopted to approximate the gravitational potential energy. The equations of motion are constructed through constrained Hamilton's equations. Then, an energy- and constraint-conserving algorithm is presented to solve the differential-algebraic equations. Finally, the proposed method is applied to simulate the orbit-attitude coupled dynamics and control of a large solar power satellite considering gravity gradient torque and solar radiation pressure. This method is also applicable to dynamic modelling of other rigid multibody aerospace systems.

Performance analysis of a GPS Interferometric attitude determination system for a gravity gradient stabilized spacecraft. M.S. Thesis

NASA Technical Reports Server (NTRS)

Stoll, John C.

1995-01-01

The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested.

Hydrotropism Interacts with Gravitropism by Degrading Amyloplasts in Seedling Roots of Arabidopsis and Radish1

PubMed Central

Takahashi, Nobuyuki; Yamazaki, Yutaka; Kobayashi, Akie; Higashitani, Atsushi; Takahashi, Hideyuki

2003-01-01

In response to a moisture gradient, roots exhibit hydrotropism to control the orientation of their growth. To exhibit hydrotropism, however, they must overcome the gravitropism that is dominant on Earth. We found that moisture gradient or water stress caused immediate degradation of the starch anchors, amyloplasts, in root columella cells of Arabidopsis and radish (Raphanus sativus). Namely, development of hydrotropic response was accompanied by a simultaneous reduction in starch content in columella cells. Rapid degradation of amyloplasts in columella cells also occurred in the water-stressed roots with sorbitol or mannitol. Both hydrotropically stimulated and water-stressed roots showed a reduced responsiveness to gravity. Roots of a starchless mutant, pgm1-1, showed an enhanced hydrotropism compared with that of the wild type. These results suggest that the reduced responsiveness to gravity is, at least in part, attributable to the degradation of amyloplasts in columella cells. Thus, the reduction in gravitropism allows the roots to exhibit hydrotropism. PMID:12805610

Magnetic Field Generation Processes Involving Gravity and Differential Rotation. Solitary Plasma Rings Formation around Black Holes

NASA Astrophysics Data System (ADS)

Coppi, Bruno

2012-10-01

A clear theoretical framework to describe how magnetic fields are generated and amplified is provided by the magneto-gravitational modes that involve both differential rotation and gravity and for which other factors such as temperature gradients can contribute to their excitation. These modes are shown to be important for the evolution of plasma disks surrounding black holes.footnotetextB. Coppi, Phys. Plasmas 18, 032901 (2011) Non-linear and axi-symmetric plasmas and associated field configurations are found under stationary conditions that do not involve the presence of a pre-existing ``seed'' magnetic field unlike other configurations found previously.footnotetextIbid. The relevant magnetic energy density is of the order of the gravitationally confined plasma pressure. The solitary plasma rings that characterize these configurations are localized radially over regions with vanishing differential rotation and can be envisioned as the saturated state of magneto-gravitational modes. The ``source'' of these configurations is the combination of the gravitational force and of the plasma density gradient orthogonal to it.

Integrated Orbit, Attitude, and Structural Control System Design for Space Solar Power Satellites

NASA Technical Reports Server (NTRS)

Woods-Vedeler, Jessica (Technical Monitor); Moore, Chris (Technical Monitor); Wie, Bong; Roithmayr, Carlos

2001-01-01

The major objective of this study is to develop an integrated orbit, attitude, and structural control system architecture for very large Space Solar Power Satellites (SSPS) in geosynchronous orbit. This study focuses on the 1.2-GW Abacus SSPS concept characterized by a 3.2 x 3.2 km solar-array platform, a 500-m diameter microwave beam transmitting antenna, and a 500 700 m earth-tracking reflector. For this baseline Abacus SSPS configuration, we derive and analyze a complete set of mathematical models, including external disturbances such as solar radiation pressure, microwave radiation, gravity-gradient torque, and other orbit perturbation effects. The proposed control system architecture utilizes a minimum of 500 1-N electric thrusters to counter, simultaneously, the cyclic pitch gravity-gradient torque, the secular roll torque caused by an o.set of the center-of-mass and center-of-pressure, the cyclic roll/yaw microwave radiation torque, and the solar radiation pressure force whose average value is about 60 N.

Integrated Orbit, Attitude, and Structural Control Systems Design for Space Solar Power Satellites

NASA Technical Reports Server (NTRS)

Wie, Bong; Roithmayr, Carlos M.

2001-01-01

The major objective of this study is to develop an integrated orbit, attitude, and structural control systems architecture for very large Space Solar Power Satellites (SSPS) in geosynchronous orbit. This study focuses on the 1.2-GW Abacus SSPS concept characterized by a 3.2 x 3.2 km solar-array platform, a 500-m diameter microwave beam transmitting antenna, and a 500 x 700 m earth-tracking reflector. For this baseline Abacus SSPS configuration, we derive and analyze a complete set of mathematical models, including external disturbances such as solar radiation pressure, microwave radiation, gravity-gradient torque, and other orbit perturbation effects. The proposed control systems architecture utilizes a minimum of 500 1-N electric thrusters to counter, simultaneously, the cyclic pitch gravity-gradient torque, the secular roll torque caused by an offset of the center-of-mass and center-of-pressure, the cyclic roll/yaw microwave radiation torque, and the solar radiation pressure force whose average value is about 60 N.

Spacecraft flight control system design selection process for a geostationary communication satellite

NASA Technical Reports Server (NTRS)

Barret, C.

1992-01-01

The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Now, as we launch the Mars observer and the Cassini spacecraft, stability and control have become higher priorities. The flight control system design selection process is reviewed using as an example a geostationary communication satellite which is to have a life expectancy of 10 to 14 years. Disturbance torques including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques are assessed to quantify the disturbance environment so that the required compensating torque can be determined. Then control torque options, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, nutation dampers, inertia augmentation techniques, three-axis control, reactions control system (RCS), and RCS sizing, are considered. A flight control system design is then selected and preliminary stability criteria are met by the control gains selection.

Application of GPS attitude determination to gravity gradient stabilized spacecraft

NASA Technical Reports Server (NTRS)

Lightsey, E. G.; Cohen, Clark E.; Parkinson, Bradford W.

1993-01-01

Recent advances in the Global Positioning System (GPS) technology have initiated a new era in aerospace navigation and control. GPS receivers have become increasingly compact and affordable, and new developments have made attitude determination using subcentimeter positioning among two or more antennas feasible for real-time applications. GPS-based attitude control systems will become highly portable packages which provide time, navigation, and attitude information of sufficient accuracy for many aerospace needs. A typical spacecraft application of GPS attitude determination is a gravity gradient stabilized satellite in low Earth orbit that employs a GPS receiver and four body mounted patch antennas. The coupled, linearized equations of motion enable complete position and attitude information to be extracted from only two antennas. A discussion of the various error sources for spaceborne GPS attitude measurement systems is included. Attitude determination of better than 0.3 degrees is possible for 1 meter antenna separation. Suggestions are provided to improve the accuracy of the attitude solution.

Gravity anomaly and crustal structure characteristics in North-South Seismic Belt of China

NASA Astrophysics Data System (ADS)

Shen, Chongyang; Xuan, Songtbai; Yang, Guangliang; Wu, Guiju

2017-04-01

The North-South Seismic Belt (NSSB) is the binary system boundary what is formed by the western Indian plate subduction pushing and the eastern west Pacific asthenosphere rising, and it is one of the three major seismic belts (Tianshan, Taiwan and NSSB) and mainly located between E102°and E107°. And it is mainly composed of topographic gradient zones, faults, cenozoic basins and strong earthquake zones, which form two distinct parts of tectonic and physical features in the west and east. The research results of geophysical and deep tectonic setting in the NSSB show that it is not only a gravity anomaly gradient zone, it is but also a belt of crustal thickness increasing sharply westward of abrupt change. Seismic tomography results show that the anomaly zone is deeper than hundreds of kilometers in the NSSB, and the composition and structure of the crust are more complex. We deployed multiple Gravity and GNSS synchronous detection profiles in the NSSB, and these profiles crossed the mainly faults structure and got thousands of points data. In the research, source analysis, density structure inversion, residual gravity related imaging and normalized full gradient methods were used, and analyzed gravity field, density and their structure features in different positions, finally obtained the crustal density structure section characteristics and depth structure differences. The research results showed that the gravity Bouguer anomaly is similar to the existing large scale result. The Bouguer anomaly is rising significantly from west to east, its trend variation coincides well with the trend change of Moho depth, which is agreeing with the material flows to the peripheral situation of the Tibetan plateau. The obvious difference changes of the residual anomaly is relative to the boundary of structure or main tectonics, it's also connected with the stop degree of the eurasian plate when the material migrates around. The density structure of the gravity profiles mainly reflects basic frame work of the regional crust structure. The earth's crust basically present three layer structure, nearly horizontally distributes, undulation of Moho is obvious, which is consistent with the results of seismic sounding and seismic array detection; in the local area, there are lower density layer zonal distribution in the earth's crust what accelerates the lateral movement in up and middle crust; when the substance of the Tibetan plateau spreads around, the integrity in up and middle crust is well, and it is basically a coupling movement together; in the lower crust, the thickness of the Tibetan plateau is outward gradually thinning, there is decoupling phenomenon in crust-mantle; The results of the gravity and the crustal density structure show that the research area can be divided into several part such as Qinghai-Tibet Plateau, Sichuan-Yunnan block, Ordos block and Alxa block, the transitional zones of the Qinghai-Tibet Plateau and Sichuan basin, and Alxa and Ordos are complex, and Moho slope is bigger, where is the part of strong tectonic activity and strong earthquakes occur easily. The research is of great significance for study the crustal deep structure, geodynamic evolution process and environment of earthquake gestation of the NSSB region.

Hybrid Atom Electrostatic System for Satellite Geodesy

NASA Astrophysics Data System (ADS)

Zahzam, Nassim; Bidel, Yannick; Bresson, Alexandre; Huynh, Phuong-Anh; Liorzou, Françoise; Lebat, Vincent; Foulon, Bernard; Christophe, Bruno

2017-04-01

The subject of this poster comes within the framework of new concepts identification and development for future satellite gravity missions, in continuation of previously launched space missions CHAMP, GRACE, GOCE and ongoing and prospective studies like NGGM, GRACE 2 or E-GRASP. We were here more focused on the inertial sensors that complete the payload of such satellites. The clearly identified instruments for space accelerometry are based on the electrostatic technology developed for many years by ONERA and that offer a high level of performance and a high degree of maturity for space applications. On the other hand, a new generation of sensors based on cold atom interferometry (AI) is emerging and seems very promising in this context. These atomic instruments have already demonstrated on ground impressive results, especially with the development of state-of-the-art gravimeters, and should reach their full potential only in space, where the microgravity environment allows long interaction times. Each of these two types of instruments presents their own advantages which are, for the electrostatic sensors (ES), their demonstrated short term sensitivity and their high TRL, and for AI, amongst others, the absolute nature of the measurement and therefore no need for calibration processes. These two technologies seem in some aspects very complementary and a hybrid sensor bringing together all their assets could be the opportunity to take a big step in this context of gravity space missions. We present here the first experimental association on ground of an electrostatic accelerometer and an atomic accelerometer and underline the interest of calibrating the ES instrument with the AI. Some technical methods using the ES proof-mass as the Raman Mirror seem very promising to remove rotation effects of the satellite on the AI signal. We propose a roadmap to explore further in details and more rigorously this attractive hybridization scheme in order to assess its potential for a future geodesy space mission with theoretical and experimental work.

Dynamic Heights in the Great Lakes at Different Epochs

NASA Astrophysics Data System (ADS)

Roman, D. R.

2016-12-01

Vertical control in the Great Lakes region is currently defined by the International Great Lakes Datum of 1985 (IGLD 85) in the form of dynamic heights. Starting in 2025, dynamic heights will be defined through GNSS-derived geometric coordinates and a geopotential model. This paper explores the behavior of an existing geopotential model at different epochs when the Great Lakes were at significantly different (meter-level) geopotential surfaces. Water surfaces were examined in 2015 and 2010 at six sites on Lakes Superior and Lake Erie (three on each Lake). These sites have collocated a Continuously Operating Reference Station (CORS) and a Water Level Sensor (WLS). The offset between the antenna phase center for the CORS and the WLS datum are known at each site. The WLS then measures the distance from its datum to the Lake surface via an open well. Thus it is possible to determine the height above an ellipsoid datum at these sites as long as both the CORS and WLS are operational. The geometric coordinates are then used to estimate the geopotential value from the xGEOID16B model. This accomplished in two steps. To provide an improved reference model, EGM2008 was spectrally enhanced using observations from the GOCE satellite gravity mission and aerogravity from the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project. This enhanced model, xGEOID16B_Ref, is still only a five arcminute resolution model (d/o 2160), but resolves dynamic heights at about 2 cm on Lake Superior for December 2015. The reference model was primarily developed to determine a one arcminute geoid height grid, xGEOID16B, available on the NGS website. This geoid height model was used to iteratively develop improved geopotential value for each of the site locations, which then improved comparisons to the cm-level. Comparisons were then made at the 2010 epoch for these same locations to determine if the performance of the geopotential model was consistent.

Improved preconditioned conjugate gradient algorithm and application in 3D inversion of gravity-gradiometry data

NASA Astrophysics Data System (ADS)

Wang, Tai-Han; Huang, Da-Nian; Ma, Guo-Qing; Meng, Zhao-Hai; Li, Ye

2017-06-01

With the continuous development of full tensor gradiometer (FTG) measurement techniques, three-dimensional (3D) inversion of FTG data is becoming increasingly used in oil and gas exploration. In the fast processing and interpretation of large-scale high-precision data, the use of the graphics processing unit process unit (GPU) and preconditioning methods are very important in the data inversion. In this paper, an improved preconditioned conjugate gradient algorithm is proposed by combining the symmetric successive over-relaxation (SSOR) technique and the incomplete Choleksy decomposition conjugate gradient algorithm (ICCG). Since preparing the preconditioner requires extra time, a parallel implement based on GPU is proposed. The improved method is then applied in the inversion of noisecontaminated synthetic data to prove its adaptability in the inversion of 3D FTG data. Results show that the parallel SSOR-ICCG algorithm based on NVIDIA Tesla C2050 GPU achieves a speedup of approximately 25 times that of a serial program using a 2.0 GHz Central Processing Unit (CPU). Real airborne gravity-gradiometry data from Vinton salt dome (southwest Louisiana, USA) are also considered. Good results are obtained, which verifies the efficiency and feasibility of the proposed parallel method in fast inversion of 3D FTG data.

Earthquake precursors: spatial-temporal gravity changes before the great earthquakes in the Sichuan-Yunnan area

NASA Astrophysics Data System (ADS)

Zhu, Yi-Qing; Liang, Wei-Feng; Zhang, Song

2018-01-01

Using multiple-scale mobile gravity data in the Sichuan-Yunnan area, we systematically analyzed the relationships between spatial-temporal gravity changes and the 2014 Ludian, Yunnan Province Ms6.5 earthquake and the 2014 Kangding Ms6.3, 2013 Lushan Ms7.0, and 2008 Wenchuan Ms8.0 earthquakes in Sichuan Province. Our main results are as follows. (1) Before the occurrence of large earthquakes, gravity anomalies occur in a large area around the epicenters. The directions of gravity change gradient belts usually agree roughly with the directions of the main fault zones of the study area. Such gravity changes might reflect the increase of crustal stress, as well as the significant active tectonic movements and surface deformations along fault zones, during the period of gestation of great earthquakes. (2) Continuous significant changes of the multiple-scale gravity fields, as well as greater gravity changes with larger time scales, can be regarded as medium-range precursors of large earthquakes. The subsequent large earthquakes always occur in the area where the gravity changes greatly. (3) The spatial-temporal gravity changes are very useful in determining the epicenter of coming large earthquakes. The large gravity networks are useful to determine the general areas of coming large earthquakes. However, the local gravity networks with high spatial-temporal resolution are suitable for determining the location of epicenters. Therefore, denser gravity observation networks are necessary for better forecasts of the epicenters of large earthquakes. (4) Using gravity changes from mobile observation data, we made medium-range forecasts of the Kangding, Ludian, Lushan, and Wenchuan earthquakes, with especially successful forecasts of the location of their epicenters. Based on the above discussions, we emphasize that medium-/long-term potential for large earthquakes might exist nowadays in some areas with significant gravity anomalies in the study region. Thus, the monitoring should be strengthened.

Rayleigh-Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries

NASA Technical Reports Server (NTRS)

Titarchuk, Lev

2002-01-01

Accretion onto compact objects in X-ray binaries (black hole, neutron star (NS), white dwarf) is characterized by non-uniform flow density profiles. Such an effect of heterogeneity in presence of gravitational forces and pressure gradients exhibits Rayleigh-Taylor gravity waves (RTGW). They should be seen as quasiperiodic wave oscillations (QPO) of the accretion flow in the transition (boundary) layer between the Keplerian disk and the central object. In this paper the author shows that the main QPO frequency, which is very close to the Keplerian frequency, is split into separate frequencies (hybrid and low branch) under the influence of the gravitational forces in the rotational frame of reference. The RTGWs must be present and the related QPOs should be detected in any system where the gravity, buoyancy and Coriolis force effects cannot be excluded (even in the Earth and solar environments). The observed low and high QPO frequencies are an intrinsic signature of the RTGW. The author elaborates the conditions for the density profile when the RTGW oscillations are stable. A comparison of the inferred QPO frequencies with QPO observations is presented. The author finds that hectohertz frequencies detected from NS binaries can be identified as the RTGW low branch frequencies. The author also predicts that an observer can see the double NS spin frequency during the NS long (super) burst events when the pressure gradients and buoyant forces are suppressed. The Coriolis force is the only force which acts in the rotational frame of reference and its presence causes perfect coherent pulsations with a frequency twice of the NS spin. The QPO observations of neutron binaries have established that the high QPO frequencies do not go beyond of the certain upper limit. The author explains this observational effect as a result of the density profile inversions. Also the author demonstrates that a particular problem of the gravity waves in the rotational frame of reference in the approximation of very small pressure gradients is reduced to the problem of the classical oscillator in the rotational frame of reference which was previously introduced and applied for the interpretation of kHZ QPO observation by Osherovich & Titarchuk.

Use of surface drifters to increase resolution and accuracy of oceanic geostrophic circulation mapped from satellite only (altimetry and gravimetry)

NASA Astrophysics Data System (ADS)

Mulet, Sandrine; Rio, Marie-Hélène; Etienne, Hélène

2017-04-01

Strong improvements have been made in our knowledge of the surface ocean geostrophic circulation thanks to satellite observations. For instance, the use of the latest GOCE (Gravity field and steady-state Ocean Circulation Explorer) geoid model with altimetry data gives good estimate of the mean oceanic circulation at spatial scales down to 125 km. However, surface drifters are essential to resolve smaller scales, it is thus mandatory to carefully process drifter data and then to combine these different data sources. In this framework, the global 1/4° CNES-CLS13 Mean Dynamic Topography (MDT) and associated mean geostrophic currents have been computed (Rio et al, 2014). First a satellite only MDT was computed from altimetric and gravimetric data. Then, an important work was to pre-process drifter data to extract only the geostrophic component in order to be consistent with physical content of satellite only MDT. This step include estimate and remove of Ekman current and wind slippage. Finally drifters and satellite only MDT were combined. Similar approaches are used regionally to go further toward higher resolution, for instance in the Agulhas current or along the Brazilian coast. Also, a case study in the Gulf of Mexico intends to use drifters in the same way to improve weekly geostrophic current estimate.

New Mexico Geothermal Play Fairway Analysis from LANL

DOE Data Explorer

Rick Kelley

2015-10-27

This submission contains geospatial (GIS) data on water table gradient and depth, subcrop gravity and magnetic, propsectivity, heat flow, physiographic, boron and BHT for the Southwest New Mexico Geothermal Play Fairway Analysis by LANL Earth & Environmental Sciences. GIS data is in ArcGIS map package format.

The development of the GSFC DORIS contribution to ITRF2014

NASA Astrophysics Data System (ADS)

Lemoine, F. G.; Chinn, D. S.; Zelensky, N. P.; Beall, J. W.; Le Bail, K.

2016-12-01

The NASA GSFC DORIS analysis center has processed data from January 1993 to December 2014 and provided 1141 weekly solutions in the form of normal equations for incorporation into the DORIS solution for ITRF2014. The solution time series, designated as gscwd26, were based on tracking data to eleven DORIS satellites divided generally into seven-day arcs. With respect to the ITRF2008 submission (Le Bail et al., 2010), the measurement model was updated to model the beacon frequency variations at certain DORIS sites, to apply the DORIS antenna phase law for the Starec and Alcatel antennae, and to apply the antenna offset corrections in the NASA GSFC orbit determination software rather than using the data-supplied corrections. We show that computing the antenna offset corrections in the orbit determination software is superior to using the offset corrections that are supplied with the DORIS data, and that this improves the RMS of fit for SPOT-2, Envisat, SPOT-4, and SPOT-5. The updates for the force model included: (1) the development of improved nonconservative force modeling for SPOT-2, SPOT-3, SPOT-5, Envisat, and HY-2A, and (2) the application of an updated static gravity model based on GRACE and GOCE data, and weekly models of the variations in the low degree gravity field deduced independently from tracking by Satellite Laser Ranging (SLR) and DORIS. The post-ITRF2008 DORIS coordinate WRMS after the launch of Envisat and SPOT-5 is improved from 11.20 to 12.45 mm with ITRF2008 (Le Bail et al., 2010), to between 8.50 and 9.99 mm with the gscwd26 SINEX solution. The application of the DORIS antenna phase laws shifts the DORIS scale wrt DPOD2008 by +6.0 mm from 1993/01/03 to 2002/06/06, and by +11.4 mm from 2002/06/13 to 2011/10/30. The application of more detailed models of time-variable gravity reduces the slopes in the Helmert transformation parameters Tx, and Ty (w.r.t. DPOD2008) after 2005. The annual amplitude in these parameters is reduced from 3.2 mm (for Tx), 4.1 mm (for Ty), to 1.7 mm (for Tx) and 2.8 mm (for Ty).

Artificial gravity studies and design considerations for Space Station centrifuges

NASA Technical Reports Server (NTRS)

Halstead, T. W.; Brown, A. H.; Fuller, C. A.; Oyama, J.

1984-01-01

The requirements to and capabilities of a Space Station biological facility centrifuge are discussed on the basis of an assessment of the objectives and subjects of future microgravity biological experiments. It is argued that the facility should be capable of both acute and extended chronic exposure of test subjects and biological materials to altered-g loading. In addition, the experimental approaches and equipment for microgravity studies on a Space Station are outlined. Finally, the engineering requirements of such a centrifuge are examined, with consideration of radial gravity gradients, size, and physical access to animals.

Transport of heat and mass in near-critical fluids

NASA Astrophysics Data System (ADS)

Garrabos, Yves; Leneindre, B.; Guenoun, P.; Perrot, F.; Beysens, Daniel

1992-08-01

In order to investigate some aspects of heat and mass transport in fluids in the absence of gravity, thermal cycles were performed near the liquid-phase critical point of CO2 and SF6 in the TEXUS 25 rocket and during the International Microgravity Laboratory (IML-1) Spacelab mission. In the absence of gravity driven convection, the heat transport is expected to be diffusive and very slow. Experimentally, although the local density and temperature gradients indeed relax by a diffusive process, clear evidence is found of fast and uniform thermal equilibration. This new mechanism is a 'piston effect'.

Glass fining experiments in zero gravity

NASA Technical Reports Server (NTRS)

Smith, H. D.

1977-01-01

Ground based experiments were conducted to demonstrate that thermal migration actually operated in glass melts. Thermal migration consistent with the theory was found in one experiment on a borax melt, i.e., there was an approximately linear relation between the bubble diameter and bubble velocity for a given temperature and temperature gradient. It also appeared that nearby bubbles were attracted to one another, which could greatly aid fining. Interpretation of these results was not possible because of complications arising from gravity, i.e., floating of the bubbles, circulation currents due to buoyancy-driven natural connection, and flow of the melt out from the cell.

An atlas of Rapp's 180-th order geopotential.

NASA Astrophysics Data System (ADS)

Melvin, P. J.

1986-08-01

Deprit's 1979 approach to the summation of the spherical harmonic expansion of the geopotential has been modified to spherical components and normalized Legendre polynomials. An algorithm has been developed which produces ten fields at the users option: the undulations of the geoid, three anomalous components of the gravity vector, or six components of the Hessian of the geopotential (gravity gradient). The algorithm is stable to high orders in single precision and does not treat the polar regions as a special case. Eleven contour maps of components of the anomalous geopotential on the surface of the ellipsoid are presented to validate the algorithm.

Influence of zero-G on single-cell systems and zero-G fermenter design concepts

NASA Technical Reports Server (NTRS)

Mayeux, J. V.

1977-01-01

An analysis was made to identify potential gravity-sensitive mechanisms that may be present in the single-cell growth system. Natural convection (density gradients, induced sedimentation, and buoyancy) is important in microbial systems. The absence of natural convection in the space-flight environment could provide an opportunity for new approaches for developments in industrial fermentation and agriculture. Some of the potential influences of gravity (i.e., convection, sedimentation, etc.) on the cell were discussed to provide insight into what experimental areas may be pursued in future space-flight research programs.

Crustal architecture and tectonic evolution in the South Pole frontier, East Antarctica, in light of recent aerogeophysical observations

NASA Astrophysics Data System (ADS)

Ferraccioli, Fausto; Jordan, Tom; Forsberg, Rene; Olesen, Arne; Eagles, Graeme; Matsuoka, Kenichi; Casal, Tania

2017-04-01

Our knowledge of interior East Antarctica has increased significantly in recent years, aided by major aerogeophysical exploration efforts conducted by the geosciences community since the International Polar Year. Aerogeophysical and satellite imaging is helping unveil cryptic crustal provinces and this is enabling new studies of the major tectonic process that shaped East Antarctica through the supercontinent cycle (e.g. Ferraccioli et al., 2011, Nature; Aitken et al., 2014, GRL). However, the South Pole itself has remained one of the largest "poles of ignorance", as very little data have been acquired here since pioneering aerogeophysical surveys performed in the 1970's and a single more detailed US survey flown in the late 1990's from the Transantarctic Mountains to South Pole (Studinger et al., 2006, EPSL). During the 2015-2016 Antarctic campaign we flew a major aerogeophysical survey over the South Pole frontier, collecting ca 30,000 line km of new radio echo sounding, laser altimetry, airborne gravity and aeromagnetic data. The main aim of the PolarGAP project, supported by the European Space Agency was to fill in the data void in GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite gravity south of 83.3°S. Here we present the new ice thickness, bedrock topography, and gravity and magnetic anomaly images derived from the survey and interpret them to investigate the crustal architecture and tectonic evolution of the South Pole region. The Free-air gravity and radar data reveal the form and extent of the Pensacola-Pole Subglacial Basin that stretches from the Weddell Sea to South Pole. Linear free-air gravity lows within the basin are interpreted here as a system of glacially overdeepened grabens flanked by uplifted horst blocks, including the Pensacola Mountains, Patuxent Range and the Argentine Range. The grabens are inferred to be linked to the Jurassic Transantarctic rift system, which at regional to continental-scale, is associated with voluminous tholeiitic magmatism of the Ferrar Large Igneous province. Whether these grabens were reactivated in post-Jurassic times in response to intraplate stresses following Gondwana breakup, such as proposed in some sectors of the Transantarctic Mountains (e.g. Ferraccioli and Bozzo, 2003 Geol. Soc. London) or the Shackleton Range (e.g. Paxman et al., 2017 JGR in review) remains to be more fully evaluated. To investigate the potential influence of basement provinces and their tectonic boundaries on the Pensacola-Pole basin, we combined the new PolarGAP aeromagnetic data with recent aeromagnetic data acquired over the Recovery Glacier region and also examined satellite magnetic (MF7) patterns. Our new compilation reveals that part of the eastern flank of the basin is controlled by a major inherited crustal boundary, interpreted here as the southern edge of a hitherto unrecognised composite Precambrian microplate, extending from the Shackleton Range to the Pensacola-Pole basin. We further hypothesise that this inferred microplate is a key "missing link" between the southern end of the subduction-related Ross Orogen and the inferred Pan-African age collisional suture and transpressional shear zones of the Shackleton Range region.

Free-air and Bouguer gravity anomalies and the Martian crustal dichotomy

NASA Technical Reports Server (NTRS)

Frey, Herbert; Bills, Bruce G.; Kiefer, Walter S.; Nerem, R. Steven; Roark, James H.; Zuber, Maria T.

1993-01-01

Free-air and Bouguer gravity anomalies from a 50x50 field, derived from re-analysis of Viking Orbiter and Mariner 9 tracking data and using a 50x50 expansion of the current Mars topography and the GSFC degree 50 geoid as the equipotential reference surface, with the Martian crustal dichotomy are compared. The spherical harmonic topography used has zero mean elevation, and differs from the USGS maps by about 2 km. In this field the dichotomy boundary in eastern Mars lies mostly at -1 to -2 km elevation. Bouguer gravity anomalies are shown on a map of Noachian, Hesperian, and Amazonian age terrains, simplified from current geologic maps. The map is centered at 300 deg W to show the continuity of the dichotomy boundary. Contour interval is 100 mgals. Gravity and topography were compared along approximately 40 profiles oriented parallel to the dichotomy boundary topographic gradient, to determine how the geophysical character of the boundary changes along its length and what this implies for its origin and development.

Human Research Program Human Health Countermeasures Element: Evidence Report - Artificial Gravity

NASA Technical Reports Server (NTRS)

Clement, Gilles

2015-01-01

The most serious risks of long-duration flight involve radiation, behavioral stresses, and physiological deconditioning. Artificial gravity (AG), by substituting for the missing gravitational cues and loading in space, has the potential to mitigate the last of these risks by preventing the adaptive responses from occurring. The rotation of a Mars-bound spacecraft or an embarked human centrifuge offers significant promise as an effective, efficient multi-system countermeasure against the physiological deconditioning associated with prolonged weightlessness. Virtually all of the identified risks associated with bone loss, muscle weakening, cardiovascular deconditioning, and sensorimotor disturbances might be alleviated by the appropriate application of AG. However, experience with AG in space has been limited and a human-rated centrifuge is currently not available on board the ISS. A complete R&D program aimed at determining the requirements for gravity level, gravity gradient, rotation rate, frequency, and duration of AG exposure is warranted before making a decision for implementing AG in a human spacecraft.

Genetic analysis of gravity signal transduction in roots

NASA Astrophysics Data System (ADS)

Masson, Patrick; Strohm, Allison; Baldwin, Katherine

To grow downward into the soil, roots use gravity as a guide. Specialized cells, named stato-cytes, enable this directional growth response by perceiving gravity. Located in the columella region of the cap, these cells sense a reorientation of the root within the gravity field through the sedimentation of, and/or tension/pressure exerted by, dense amyloplasts. This process trig-gers a gravity signal transduction pathway that leads to a fast alkalinization of the cytoplasm and a change in the distribution of the plasma membrane-associated auxin-efflux carrier PIN3. The latter protein is uniformly distributed within the plasma membrane on all sides of the cell in vertically oriented roots. However, it quickly accumulates at the bottom side upon gravis-timulation. This process correlates with a preferential transport of auxin to the bottom side of the root cap, resulting in a lateral gradient across the tip. This gradient is then transported to the elongation zone where it promotes differential cellular elongation, resulting in downward curvature. We isolated mutations that affect gravity signal transduction at a step that pre-cedes cytoplasmic alkalinization and/or PIN3 relocalization and lateral auxin transport across the cap. arg1 and arl2 mutations identify a common genetic pathway that is needed for all three gravity-induced processes in the cap statocytes, indicating these genes function early in the pathway. On the other hand, adk1 affects gravity-induced PIN3 relocalization and lateral auxin transport, but it does not interfere with cytoplasmic alkalinization. ARG1 and ARL2 encode J-domain proteins that are associated with membranes of the vesicular trafficking path-way whereas ADK1 encodes adenosine kinase, an enzyme that converts adenosine derived from nucleic acid metabolism and the AdoMet cycle into AMP, thereby alleviating feedback inhibi-tion of this important methyl-donor cycle. Because mutations in ARG1 (and ARL2) do not completely eliminate gravitropism, we sought genetic enhancers of arg1 as a way to identify new gravity signal transducers. Two of these modifiers, named mar1 and mar2, were found to affect genes that encode two subunits of the plastidic outer-membrane protein import complex, TOC75 and TOC132, respectively. mar2 did not affect the ultrastructure of amyloplasts in the statocytes nor did it alter their ability to sediment in response to gravistimulation, suggesting a role for the outer membrane of the amyloplasts in gravity signal transduction (reviewed in Stanga et al., 2009, Plant Signal Behavior 4(10): 1-9). The contribution of TOC132 in gravity signal transduction is being investigated by analyzing the regions of this protein that are needed for the pathway, and investigating the contribution of a putative TOC132-interacting protein in gravity signal transduction. We have also isolated additional putative enhancers of arg1-2 in the hope of identifying new plastid-associated gravity signal transducers, and have initiated a screen for genetic enhancers of mar2 to seek new transducers in the ARG1 branch of the pathway.

Preliminary isostatic gravity map of the Sonoma volcanic field and vicinity, Sonoma and Napa Counties, California

USGS Publications Warehouse

Langenheim, V.E.; Roberts, C.W.; McCabe, C.A.; McPhee, D.K.; Tilden, J.E.; Jachens, R.C.

2006-01-01

This isostatic residual gravity map is part of a three-dimensional mapping effort focused on the subsurface distribution of rocks of the Sonoma volcanic field in Napa and Sonoma counties, northern California. This map will serve as a basis for modeling the shapes of basins beneath the Santa Rosa Plain and Napa and Sonoma Valleys, and for determining the location and geometry of faults within the area. Local spatial variations in the Earth's gravity field (after accounting for variations caused by elevation, terrain, and deep crustal structure explained below) reflect the distribution of densities in the mid to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic boundaries. High-density basement rocks exposed within the northern San Francisco Bay area include those of the Mesozoic Franciscan Complex and Great Valley Sequence present in the mountainous areas of the quadrangle. Alluvial sediment and Tertiary sedimentary rocks are characterized by low densities. However, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of basement rocks. Tertiary volcanic rocks are characterized by a wide range in densities, but, on average, are less dense than the Mesozoic basement rocks. Isostatic residual gravity values within the map area range from about -41 mGal over San Pablo Bay to about 11 mGal near Greeg Mountain 10 km east of St. Helena. Steep linear gravity gradients are coincident with the traces of several Quaternary strike-slip faults, most notably along the West Napa fault bounding the west side of Napa Valley, the projection of the Hayward fault in San Pablo Bay, the Maacama Fault, and the Rodgers Creek fault in the vicinity of Santa Rosa. These gradients result from juxtaposing dense basement rocks against thick Tertiary volcanic and sedimentary rocks.

Hydrodynamic Controls on Muddy Sedimentary Fabric Development on Low-Gradient Shelves: Atchafalaya Chenier Plain Subaqueous Delta

NASA Astrophysics Data System (ADS)

Denommee, K.; Bentley, S. J.; Harazim, D.; Macquaker, J.

2016-02-01

Short sediment cores and geophysical data collected on the Southwest Louisiana Chenier Plain inner shelf have been studied in order to examine the sedimentary products of current-wave-enhanced sediment gravity flows (CWESGFs), a type of sediment gravity flow where the driving energy required to transport sediment across low-gradient settings is augmented by the near-bed orbital velocity of surface gravity wave and near-bed currents. Sedimentary fabrics observed on the SWLA shelf document the following flow evolution: (1) the erosion of the underlying substrate in response to wave-generated shear stresses in the bottom boundary layer, followed by (2) the deposition of ripple a crossbeded unit during wave-mediated oscillatory motions in low-viscosity suspension; (3) the deposition of subtle intercalated laminae during laminar flow at higher suspended sediment concentrations; followed by the deposition of (4) normally graded sediments during the waning phases of the flow. Significantly, the sedimentary fabrics deposited by CWESGFs on SWLA shelf show diagnostic variations from CWESGF-generated sedimentary fabrics observed on the Eel and Amazon shelves. Differences between the observed sedimentary fabrics are hypothesized to result from variations in the relative contribution of near-bed currents, wave orbital velocities, and bed slope (gravity) to the driving energy of the CWESGF, and as such can be catalogued as diagnostic recognition criteria using a prismatic ternary diagram where current-, wave-, and gravity-dominated end members form the vertices of a triangle, and wave period forms the prism axis. In this framework forcing mechanisms can be represented quantitatively, based on wave period and the relative contribution of each of the CWESGF velocity terms. This framework can be used to explore relationships between hydrodynamics and CWESGF fabrics, providing geologists with a tool with which to better recognize the depositional products of CWESGFs in the rock record; allowing for more accurate paleoenvironmental interpretations of extensive muddy successions.

Ductile crustal flow in Europe's lithosphere

NASA Astrophysics Data System (ADS)

Tesauro, Magdala; Burov, Evgene B.; Kaban, Mikhail K.; Cloetingh, Sierd A. P. L.

2011-12-01

Potential gravity theory (PGT) predicts the presence of significant gravity-induced horizontal stresses in the lithosphere associated with lateral variations in plate thickness and composition. New high resolution crustal thickness and density data provided by the EuCRUST-07 model are used to compute the associated lateral pressure gradients (LPG), which can drive horizontal ductile flow in the crust. Incorporation of these data in channel flow models allows us to use potential gravity theory to assess horizontal mass transfer and stress transmission within the European crust. We explore implications of the channel flow concept for a possible range of crustal strength, using end-member 'hard' and 'soft' crustal rheologies to estimate strain rates at the bottom of the ductile crustal layers. The models show that the effects of channel flow superimposed on the direct effects of plate tectonic forces might result in additional significant horizontal and vertical movements associated with zones of compression or extension. To investigate relationships between crustal and mantle lithospheric movements, we compare these results with the observed directions of mantle lithospheric anisotropy and GPS velocity vectors. We identify areas whose evolution could have been significantly affected by gravity-driven ductile crustal flow. Large values of the LPG are predicted perpendicular to the axes of European mountain belts, such as the Alps, Pyrenees-Cantabrian Mountains, Dinarides-Hellenic arc and Carpathians. In general, the crustal flow is directed away from orogens towards adjacent weaker areas. Gravitational forces directed from areas of high gravitational potential energy to subsiding basin areas can strongly reduce lithospheric extension in the latter, leading to a gradual late stage inversion of the entire system. Predicted pressure and strain rate gradients suggest that gravity driven flow may play an essential role in European intraplate tectonics. In particular, in a number of regions the predicted strain rates are comparable to tectonically induced strain rates. These results are also important for quantifying the thickness of the low viscosity zones in the lowermost part of the crustal layers.

Genetical approach to gravitropism

NASA Astrophysics Data System (ADS)

Boonsirichai, K.; Chen, R.; Guan, C.; Rosen, E.; Young, L.; Masson, P.

Gravitropism guides the growth of plant organs at a defined angle from the gravity vector. Accordingly, most roots grow downward, undergoing positive gravitropism. Gravity perception by roots appears to involve the sedimentation of amyloplasts within the columella cells of the cap. Amyloplast sedimentation triggers a signal transduction pathway that promotes the development of an auxin gradient across the root tip. This gradient is then transmitted to the elongation zones where it promotes a differential cellular elongation, partly responsible for the development of a root-tip curvature. To better understand the mechanisms involved in gravity signal transduction, we have identified and characterized several Arabidopsis thaliana mutants that show specific defects in root gravitropism. Several of these genes were characterized. ARG1 functions in gravity signal transduction, and encodes a dnaJ-like protein whose structure suggests an interaction with the cytoskeleton. Two other genes encode similar proteins (ARL1 and ARL2) in Arabidopsis. One of them (ARL2) also appears to function in gravity signal transduction. Because loss-of-function mutations in ARG1 result in partial alterations of gravitropism, we were able to identify and characterize two genetic enhancers of arg1-2: mar1-1 and mar2-1. These enhancers increased the gravitropism defect of arg1-2 roots and hypocotyls, and changed its orientation. Hence, MAR1 and MAR2 also appear to function in gravity signal transduction. AGR1, on the other hand, encodes a transmembrane component of the auxin efflux carrier complex involved in polar auxin transport through the elongation zones of Arabidopsis root tips. It belongs to a large gene family, several members of which are expressed in the root cap. Upon gravistimulation, the AGR3 protein appears to quickly relocate within the columella cells, accumulating in membranes at the new physical bottom. Hence, the gravity signal transduction pathway that includes the ARG1, ARL2, MAR1 and MAR2 gene products, appears to control the cellular distribution of auxin efflux carriers in the columella cells of the root cap, thereby controlling the polarity of lateral auxin transport in response to gravistimulation. Work is in progress to identify new proteins that interact genetically or physically with ARG1, ARL2 or AGR1, and characterize their involvement in gravitropism.

Electro-gravity via geometric chrononfield

NASA Astrophysics Data System (ADS)

Suchard, Eytan H.

2017-05-01

In De Sitter / Anti De Sitter space-time and in other geometries, reference sub-manifolds from which proper time is measured along integral curves, are described as events. We introduce here a foliation with the help of a scalar field. The scalar field need not be unique but from the gradient of the scalar field, an intrinsic Reeb vector of the foliations perpendicular to the gradient vector is calculated. The Reeb vector describes the acceleration of a physical particle that moves along the integral curves that are formed by the gradient of the scalar field. The Reeb vector appears as a component of an anti-symmetric matrix which is a part of a rank-2, 2-Form. The 2-form is extended into a non-degenerate 4-form and into rank-4 matrix of a 2-form, which when multiplied by a velocity of a particle, becomes the acceleration of the particle. The matrix has one U(1) degree of freedom and an additional SU(2) degrees of freedom in two vectors that span the plane perpendicular to the gradient of the scalar field and to the Reeb vector. In total, there are U(1) x SU(2) degrees of freedom. SU(3) degrees of freedom arise from three dimensional foliations but require an additional symmetry to exist in order to have a valid covariant meaning. Matter in the Einstein Grossmann equation is replaced by the action of the acceleration field, i.e. by a geometric action which is not anticipated by the metric alone. This idea leads to a new formalism that replaces the conventional stress-energy-momentum-tensor. The formalism will be mainly developed for classical physics but will also be discussed for quantized physics based on events instead of particles. The result is that a positive charge manifests small attracting gravity and a stronger but small repelling acceleration field that repels even uncharged particles that have a rest mass. Negative charge manifests a repelling anti-gravity but also a stronger acceleration field that attracts even uncharged particles that have rest mass. Preliminary version: http://sciencedomain.org/abstract/9858

Electrostatic Accelerometer for the Gravity Recovery and Climate Experiment Follow-On Mission (GRACE FO)

NASA Astrophysics Data System (ADS)

Lebat, V.; Foulon, B.; Christophe, B.

2013-12-01

The GRACE FO mission, led by the JPL (Jet Propulsion Laboratory), is an Earth-orbiting gravity mission, continuation of the GRACE mission, that will produce an accurate model of the Earth's gravity field variation providing global climatic data during five year at least. The mission involves two satellites in a loosely controlled tandem formation, with a micro-wave link measuring the inter-satellites distance variation. Non-uniformities in the distribution of the Earth's mass cause the distance between the two satellites to vary. This variation is measured to recover gravity, after subtracting the non-gravitational contributors, as the residual drag. ONERA (the French Aerospace Lab) is developing, manufacturing and testing electrostatic accelerometers measuring this residual drag applied on the satellites. The accelerometer is composed of two main parts: the Sensor Unit (including the Sensor Unit Mechanics and the Front-End Electronic Unit) and the Interface Control Unit. In the Accelerometer Core, located in the Sensor Unit Mechanics, the proof mass is levitated and maintained in a center of an electrode cage by electrostatic forces. Thus, any drag acceleration applied on the satellite involves a variation on the servo-controlled electrostatic suspension of the mass. The voltage on the electrodes providing this electrostatic force is the measurement output of the accelerometer. The impact of the accelerometer defaults (geometry, electronic and parasitic forces) leads to bias, misalignment and scale factor error, non-linearity and noise. Some of these accelerometer defaults are characterized by tests with micro-gravity pendulum bench and with drops in ZARM catapult. Besides, a thermal stability is needed for the accelerometer core and front-end electronics to avoid bias and scale factor variation, and reached by a thermal box designed by Astrium, spacecraft manufacturer. The accelerometers are designed to endure the launch vibrations and the thermal environment at ground and in orbit. As the measure must be accurate, no sliding of the core must appear in regard of the accelerometer external reference. To ensure the thermal core stability, the electrode cage of the core is made of glass material (ULE), which is very critical, in particular due to the free motion of the proof-mass during the launch. To assess the design of the accelerometer in particular the critical parts of the core, specific analysis is realized to ensure mechanical behavior. The design of electrostatic accelerometer of the GRACE Follow-On mission benefits of the GRACE heritage, GOCE launched in 2009 and MICROSCOPE which will be launched in 2016, including some improvement to improve the performance, in particular the thermal sensitivity of the measurements. The Preliminary Design Review of electronics was achieved successfully on July 2013, and the PDR of the whole instrument is forecasted on November 2013. The integration of the Engineering Model will begin on October 2013 and its status will be presented.