Inflation with a massive vector field nonminimally coupled to gravity

NASA Astrophysics Data System (ADS)

Páramos, J.

2018-01-01

The possibility that inflation is driven by a massive vector field with SO(3) global symmetry nonminimally coupled to gravity is presented. Through an appropriate Ansatz for the vector field, the behaviour of the equations of motion is studied through the ensuing dynamical system, focusing on the characterisation of the ensuing fixed points.

Local Lunar Gravity Field Analysis over the South Pole-aitken Basin from SELENE Farside Tracking Data

NASA Technical Reports Server (NTRS)

Goossens, Sander Johannes; Ishihara, Yoshiaki; Matsumoto, Koji; Sasaki, Sho

2012-01-01

We present a method with which we determined the local lunar gravity field model over the South Pole-Aitken (SPA) basin on the farside of the Moon by estimating adjustments to a global lunar gravity field model using SELENE tracking data. Our adjustments are expressed in localized functions concentrated over the SPA region in a spherical cap with a radius of 45deg centered at (191.1 deg E, 53.2 deg S), and the resolution is equivalent to a 150th degree and order spherical harmonics expansion. The new solution over SPA was used in several applications of geophysical analysis. It shows an increased correlation with high-resolution lunar topography in the frequency band l = 40-70, and admittance values are slightly different and more leveled when compared to other, global gravity field models using the same data. The adjustments expressed in free-air anomalies and differences in Bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features. The Moho structure beneath the SPA basin is slightly modified in our solution, most notably at the southern rim of the Apollo basin and around the Zeeman crater

Gravity fields of the terrestrial planets - Long-wavelength anomalies and tectonics

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Lambeck, K.

1980-01-01

The paper discusses the gravity and topography data available for four terrestrial planets (earth, moon, Mars, and Venus), with particular emphasis on drawing inferences regarding the relationship of long-wavelength anomalies to tectonics. The discussion covers statistical analyses of global planetary gravity fields, relationship of gravity anomalies to elastic and viscoelastic models, relationship of gravity anomalies to convection models, finite strength, and isostasy (or the state of isostatic compensation). The cases of the earth and the moon are discussed in some detail. A summary of comparative planetology is presented.

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.

Constraining mass anomalies in the interior of spherical bodies using Trans-dimensional Bayesian Hierarchical inference.

NASA Astrophysics Data System (ADS)

Izquierdo, K.; Lekic, V.; Montesi, L.

2017-12-01

Gravity inversions are especially important for planetary applications since measurements of the variations in gravitational acceleration are often the only constraint available to map out lateral density variations in the interiors of planets and other Solar system objects. Currently, global gravity data is available for the terrestrial planets and the Moon. Although several methods for inverting these data have been developed and applied, the non-uniqueness of global density models that fit the data has not yet been fully characterized. We make use of Bayesian inference and a Reversible Jump Markov Chain Monte Carlo (RJMCMC) approach to develop a Trans-dimensional Hierarchical Bayesian (THB) inversion algorithm that yields a large sample of models that fit a gravity field. From this group of models, we can determine the most likely value of parameters of a global density model and a measure of the non-uniqueness of each parameter when the number of anomalies describing the gravity field is not fixed a priori. We explore the use of a parallel tempering algorithm and fast multipole method to reduce the number of iterations and computing time needed. We applied this method to a synthetic gravity field of the Moon and a long wavelength synthetic model of density anomalies in the Earth's lower mantle. We obtained a good match between the given gravity field and the gravity field produced by the most likely model in each inversion. The number of anomalies of the models showed parsimony of the algorithm, the value of the noise variance of the input data was retrieved, and the non-uniqueness of the models was quantified. Our results show that the ability to constrain the latitude and longitude of density anomalies, which is excellent at shallow locations (<200 km), decreases with increasing depth. With higher computational resources, this THB method for gravity inversion could give new information about the overall density distribution of celestial bodies even when there is no other geophysical data available.

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.

Global Lunar Gravity Field Determination Using Historical and Recent Tracking Data in Preparation for SELENE

NASA Astrophysics Data System (ADS)

Goossens, S.; Matsumoto, K.; Namiki, N.; Hanada, H.; Iwata, T.; Tsuruta, S.; Kawano, N.; Sasaki, S.

2006-12-01

In the near future, a number of satellite missions are planned to be launched to the Moon. These missions include initiatives by China, India, the USA, as well as the Japanese SELENE mission. These missions will gather a wealth of lunar data which will improve the knowledge of the Moon. One of the main topics to be addressed will be the lunar gravity field. Especially SELENE will contribute to improving the knowledge of the gravity field, by applying 4-way Doppler tracking between the main satellite and a relay satellite, and by applying a separate differential VLBI experiment. These will improve the determination of the global gravity field, especially over the far side and at the lower degrees (mostly for degrees lower than 30), as is shown by extensive simulations of the SELENE mission. This work focuses on the determination of the global lunar gravity field from all available tracking data to this date. In preparation for the SELENE mission, analysis using Lunar Prospector tracking data, as well as Clementine data and historical data from the Apollo and Lunar Orbiter projects is being conducted at NAOJ. Some SMART-1 tracking data are also included. The goal is to combine the good-quality data from the existing lunar missions up to this date with the tracking data from SELENE in order to derive a new lunar gravity field model. The focus therefore currently lies on processing the available data and extracting lunar gravity field information from them. It is shown that the historical tracking data contribute especially to the lower degrees of the global lunar gravity field model. Due to the large gap in tracking data coverage over the far side for the historical data, the higher degrees are almost fully determined by the a priori information in the form of a Kaula rule. The combination with SELENE data is thus expected to improve the estimate for the lower degrees even further, including coverage of the far side. Since historical tracking data are from orbits with different inclinations, this helps to break several correlations and assures better orbit predictions for those inclinations included, although the current models are still tuned heavily towards the polar orbit. Covariance analysis using the covariance of current solutions as well as the covariance from SELENE simulations also shows further improvement to be expected from the combination of the data sets. The expected improvement in the determination of the lower degrees also leads to an expectation of deriving stricter limits on the lunar k_2 Love number.

On the gravity and geoid effects of glacial isostatic adjustment in Fennoscandia - a short note

NASA Astrophysics Data System (ADS)

Sjöberg, L. E.

2015-12-01

Many geoscientists argue that there is a gravity low of 10-30 mGal in Fennoscandia as a remaining fingerprint of the last ice age and load, both vanished about 10 kyr ago. However, the extraction of the gravity signal related with Glacial Isostatic Adjustment (GIA) is complicated by the fact that the total gravity field is caused by many significant density distributions in the Earth. Here we recall a methodology originating with A. Bjerhammar 35 years ago, that emphasizes that the present land uplift phenomenon mainly occurs in the region thatwas covered by the ice cap, and it is highly correlated with the spectral window of degrees 10-22 of the global gravity field, whose lower limit fairly well corresponds to the wavelength that agrees with the size of the region. This implies that, although in principle the GIA is a global phenomenon, the geoid and gravity lows as well as the land upheaval in Fennoscandia are typically regional phenomena that cannot be seen in a global correlation study as it is blurred by many irrelevant gravity signals. It is suggested that a regional multi-regression analysis with a band-limited spectral gravity signal as the observable, a method tested already 2 decades ago, can absorb possible significant disturbing signals, e.g. from topographic and crustal depth variations, and thereby recover the GIA signal.

The estimation of the Earth's gravity field

NASA Astrophysics Data System (ADS)

Szabo, Bela

1986-06-01

The various methods for the description of the Earth's gravity field from direct and/or indirect observations are reviewed. Geopotential models produced by various organizations and in use during the past 15 years are discussed in detail. Recent and future programs for the improvement of global gravity fields are reviewed and the expected improvements from new observation and data processing techniques are estimated. The regional and local gravity field is also reviewed. The various data types and their spectral properties, the sensitivities of the different gravimetric quantities to datatypes are discussed. The techniques for the estimation of gravimetric quantities and the achievable accuracies are presented (e.g., integral formulae, collocation). The results of recent works in this area by prominent authors are reviewed. The prediction of gravity outside the earth from surface data is discussed in two forms: a) prediction of gravity disturbance at high altitudes and b) upward continuation of gravity anomalies. The achievable improvements of the high frequency field by airborne gradiometry are summarized utilizing recent investigations.

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.

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.

Application of precise altimetry to the study of precise leveling of the sea surface, the Earth's gravity field, and the rotation of the Earth

NASA Technical Reports Server (NTRS)

Segawa, J.; Ganeko, Y.; Sasaki, M.; Mori, T.; Ooe, M.; Nakagawa, I.; Ishii, H.; Hagiwara, Y.

1991-01-01

Our program includes five research items: (1) determination of a precision geoid and gravity anomaly field; (2) precise leveling and detection of tidal changes of the sea surface and study of the role of the tide in the global energy exchange; (3) oceanic effect on the Earth's rotation and polar motion; (4) geological and geophysical interpretation of the altimetry gravity field; and (5) evaluation of the effectiveness of local tracking of TOPEX/POSEIDON by use of a laser tracker.

High-resolution local gravity model of the south pole of the Moon from GRAIL extended mission data.

PubMed

Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Lemoine, Frank G; Rowlands, David D; Mazarico, Erwan; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-05-28

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6° by 1/6° (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40°. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models. We present a high-resolution gravity model of the south pole of the Moon Improved correlations with topography to higher degrees than global models Improved fits to the data and reduced striping that is present in global models.

High-resolution local gravity model of the south pole of the Moon from GRAIL extended mission data

PubMed Central

Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Lemoine, Frank G; Rowlands, David D; Mazarico, Erwan; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-01-01

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6° by 1/6° (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40°. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models. Key Points We present a high-resolution gravity model of the south pole of the Moon Improved correlations with topography to higher degrees than global models Improved fits to the data and reduced striping that is present in global models PMID:26074637

Validation of the EGSIEM combined monthly GRACE gravity fields

NASA Astrophysics Data System (ADS)

Li, Zhao; van Dam, Tonie; Chen, Qiang; Weigelt, Matthias; Güntner, Andreas; Jäggi, Adrian; Meyer, Ulrich; Jean, Yoomin; Altamimi, Zuheir; Rebischung, Paul

2016-04-01

Observations indicate that global warming is affecting the water cycle. Here in Europe predictions are for more frequent high precipitation events, wetter winters, and longer and dryer summers. The consequences of these changes include the decreasing availability of fresh water resources in some regions as well as flooding and erosion of coastal and low-lying areas in other regions. These weather related effects impose heavy costs on society and the economy. We cannot stop the immediate effects global warming on the water cycle. But there may be measures that we can take to mitigate the costs to society. The Horizon2020 supported project, European Gravity Service for Improved Emergency Management (EGSIEM), will add value to EO observations of variations in the Earth's gravity field. In particular, the EGSIEM project will interpret the observations of gravity field changes in terms of changes in continental water storage. The project team will develop tools to alert the public water storage conditions could indicate the onset of regional flooding or drought. As part of the EGSIEM project, a combined GRACE gravity product is generated, using various monthly GRACE solutions from associated processing centers (ACs). Since each AC follows a set of common processing standards but applies its own independent analysis method, the quality, robustness, and reliability of the monthly combined gravity fields should be significantly improved as compared to any individual solution. In this study, we present detailed and updated comparisons of the combined EGSIEM GRACE gravity product with GPS position time series, hydrological models, and existing GRACE gravity fields. The GPS residuals are latest REPRO2 station position residuals, obtained by rigorously stacking the IGS Repro 2 , daily solutions, estimating, and then restoring the annual and semi-annual signals.

An improved model for the Earth's gravity field

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Shum, C. K.; Yuan, D. N.; Ries, J. C.; Schutz, B. E.

1989-01-01

An improved model for the Earth's gravity field, TEG-1, was determined using data sets from fourteen satellites, spanning the inclination ranges from 15 to 115 deg, and global surface gravity anomaly data. The satellite measurements include laser ranging data, Doppler range-rate data, and satellite-to-ocean radar altimeter data measurements, which include the direct height measurement and the differenced measurements at ground track crossings (crossover measurements). Also determined was another gravity field model, TEG-1S, which included all the data sets in TEG-1 with the exception of direct altimeter data. The effort has included an intense scrutiny of the gravity field solution methodology. The estimated parameters included geopotential coefficients complete to degree and order 50 with selected higher order coefficients, ocean and solid Earth tide parameters, Doppler tracking station coordinates and the quasi-stationary sea surface topography. Extensive error analysis and calibration of the formal covariance matrix indicate that the gravity field model is a significant improvement over previous models and can be used for general applications in geodesy.

Isostasy, Stress and Gravitational Potential Energy in the Southern Atlantic - Insights from Satellite Gravity Observations

NASA Astrophysics Data System (ADS)

Goetze, H. J.; Klinge, L.; Scheck-Wenderoth, M.; Dressel, I.; Sippel, J.

2015-12-01

New satellite gravity fields e.g. EGM2008, GoCo3S and very recently EIGEN-6C4 (Förste et al., 2014) provide high-accuracy and globally uniform information of the Earth's gravity field and partly of its gradients. The main goal of this study is to investigate the impact of this new gravity field and its processed anomalies (Bouguer, Free-air and Vening-Meinesz residual fields) on lithospheric modelling of passive plate margins in the area of the Southern Atlantic. In an area fixed by the latitudes 20° N - 50° S and longitudes 70° W - 20° E we calculated station-complete Bouguer anomalies (bathymetry/topography corrected) both on- and offshore and compared them with the gravity effect of a velocity model which bases on S - waves tomography (Schaeffer and Lebedev, 2013). The corresponding maps provide more insight in the abnormal mass distribution of oceanic lithosphere and the ocean-continent transition zones on both sides of the Atlantic Ocean than Free-air anomalies which are masked by bathymetry. In a next step we calculated isostatic residual fields (Vening-Meinesz isostasy with regard to different lithospheric rigidities) to remove global components (long wavelengths) from the satellite gravity. The Isostatic residual field will be compared with the GPE (gravitational potential energy). GPE variations in the Southern Atlantic, relative to the reference state, were calculated as ΔGPE. Often the oceanic lithosphere is characterized by negative ΔGPE values indicating that the ocean basin is in compression. Differences from this observation will be compared with the state of stress in the area of the passive margins of South America and South Africa and the oceanic lithosphere in between. Schaeffer, A. J. and S. Lebedev, Global shear-speed structure of the upper mantle and transition zone. Geophys. J. Int., 194 (1), 417-449, 2013. doi:10.1093/gji/ggt095

The Study of Effects of Time Variations in the Earth's Gravity Field on Geodetic Satellites

NASA Technical Reports Server (NTRS)

Shum, C. K.

1998-01-01

The temporal variations in the Earth's gravity field are the consequences of complex interactions between atmosphere, ocean, solid Earth, hydrosphere and cryosphere. The signal ranges from several hours to 18.6 years to geological time scale. The direct and indirect consequences of these variations are manifested in such phenomena as changes in the global sea level and in the global climate pattern. These signals produce observable geodetic satellites. The primary objectives of the proposed effects on near-Earth orbiting investigation include (1) the improved determination of the time-varying gravity field parameters (scale from a few hour to 18.6 year and secular) using long-term satellite laser rs ranging (SLR) observations to multiple geodetic satellites, and (2) the enhanced understanding of these variations with their associated meteorological and geophysical consequences.

Comparison of regional hydrological excitation of polar motion derived from hydrological models and the GRACE gravity field data

NASA Astrophysics Data System (ADS)

Nastula, J.; Kolaczek, B.; Salstein, D. A.

2009-09-01

Global geophysical excitation functions of polar motion do not explain fully the observed polar motion as determined by geodetic techniques. The impact of continental hydrologic signals, from land water, snow, and ice, on polar motion excitation HAM (Hydrological Angular Momentum), is still inadequately estimated and not known so well as atmospheric and oceanic ones. Recently the GRACE (Gravity Recovery and Climate Experiment) satellite mission monitoring Earth's time variable gravity field has allowed us to determine global mass term of the polar motion excitation functions, which inherently includes the atmospheric, oceanic and hydrological portions. We use these terms to make comparisons with the mass term of the geodetic and geophysical excitation functions of polar motion on seasonal scales. Global GRACE excitation function of polar motion and hydrological excitation function of polar motion have been determined and were studied earlier

High-resolution Local Gravity Model of the South Pole of the Moon from GRAIL Extended Mission Data

NASA Technical Reports Server (NTRS)

Goossens, Sander Johannes; Sabaka, Terence J.; Nicholas, Joseph B.; Lemoine, Frank G.; Rowlands, David D.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2014-01-01

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6deg by 1/6deg (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40deg. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models.

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.

Estimation of the Earth's gravity field by combining normal equation matrices from GRACE and SLR

NASA Astrophysics Data System (ADS)

Haberkorn, Christoph; Bloßfeld, Mathis; Bouman, Johannes

2014-05-01

Since 2002, GRACE observes the Earth's gravity field with a spatial resolution up to 150 km. The main goal of this mission is the determination of temporal variations in the Earth's gravity field to detect mass displacements. The GRACE mission consists of two identical satellites, which observe the range along the line of sight of both satellites. GRACE observations can be linked with the Earth's gravitational potential, which is expressed in terms of spherical harmonics for global solutions. However, the estimation of low degree coefficients is difficult with GRACE. In contrast to gravity field missions, which observe the gravity field with high spectral resolution, SLR data allow to estimate the lower degree coefficients. Therefore, the coefficient C20 is often replaced by a value derived from Satellite Laser Ranging (SLR). Instead of replacing C20, it can be determined consistently by a combined estimation using GRACE and SLR data. We compute monthly normal equation (NEQ) matrices for GRACE and SLR. Coefficients from monthly GRACE gravity field models of different institutions (Center for Space Research (CSR), USA, Geoforschungszentrum Potsdam (GFZ), Germany and Jet Propulsion Laboratory (JPL), USA) and coefficients from monthly gravity field models of our SLR processing are then combined using the NEQ matrices from both techniques. We will evaluate several test scenarios with gravity field models from different institutions and with different set ups for the SLR NEQ matrices. The effect of the combination on the estimated gravity field will be analysed and presented.

Preprocessing of gravity gradients at the GOCE high-level processing facility

NASA Astrophysics Data System (ADS)

Bouman, Johannes; Rispens, Sietse; Gruber, Thomas; Koop, Radboud; Schrama, Ernst; Visser, Pieter; Tscherning, Carl Christian; Veicherts, Martin

2009-07-01

One of the products derived from the gravity field and steady-state ocean circulation explorer (GOCE) observations are the gravity gradients. These gravity gradients are provided in the gradiometer reference frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. To use these gravity gradients for application in Earth scienes and gravity field analysis, additional preprocessing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and nontidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/ f behaviour for low frequencies. In the outlier detection, the 1/ f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/ f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low-degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

Science and User Needs for Observing Global Mass Transport to Understand Global Change and to Benefit Society

NASA Astrophysics Data System (ADS)

Pail, Roland; Bingham, Rory; Braitenberg, Carla; Dobslaw, Henryk; Eicker, Annette; Güntner, Andreas; Horwath, Martin; Ivins, Eric; Longuevergne, Laurent; Panet, Isabelle; Wouters, Bert

2015-11-01

Satellite gravimetry is a unique measurement technique for observing mass transport processes in the Earth system on a global scale, providing essential indicators of both subtle and dramatic global change. Although past and current satellite gravity missions have achieved spectacular science results, due to their limited spatial and temporal resolution as well as limited length of the available time series numerous important questions are still unresolved. Therefore, it is important to move from current demonstration capabilities to sustained observation of the Earth's gravity field. In an international initiative performed under the umbrella of the International Union of Geodesy and Geophysics, consensus on the science and user needs for a future satellite gravity observing system has been derived by an international panel of scientists representing the main fields of application, i.e., continental hydrology, cryosphere, ocean, atmosphere and solid Earth. In this paper the main results and findings of this initiative are summarized. The required target performance in terms of equivalent water height has been identified as 5 cm for monthly fields and 0.5 cm/year for long-term trends at a spatial resolution of 150 km. The benefits to meet the main scientific and societal objectives are investigated, and the added value is demonstrated for selected case studies covering the main fields of application. The resulting consolidated view on the required performance of a future sustained satellite gravity observing system represents a solid basis for the definition of technological and mission requirements, and is a prerequisite for mission design studies of future mission concepts and constellations.

Gravity model development for precise orbit computations for satellite altimetry

NASA Technical Reports Server (NTRS)

Marsh, James G.; Lerch, Francis, J.; Smith, David E.; Klosko, Steven M.; Pavlis, Erricos

1986-01-01

Two preliminary gravity models developed as a first step in reaching the TOPEX/Poseidon modeling goals are discussed. They were obtained by NASA-Goddard from an analysis of exclusively satellite tracking observations. With the new Preliminary Gravity Solution-T2 model, an improved global estimate of the field is achieved with an improved description of the geoid.

Global Marine Gravity and Bathymetry at 1-Minute Resolution

NASA Astrophysics Data System (ADS)

Sandwell, D. T.; Smith, W. H.

2008-12-01

We have developed global gravity and bathymetry grids at 1-minute resolution. Three approaches are used to reduce the error in the satellite-derived marine gravity anomalies. First, we have retracked the raw waveforms from the ERS-1 and Geosat/GM missions resulting in improvements in range precision of 40% and 27%, respectively. Second, we have used the recently published EGM2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean. Third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids. Comparisons between shipboard gravity and the global gravity grid show errors ranging from 2.0 mGal in the Gulf of Mexico to 4.0 mGal in areas with rugged seafloor topography. The largest errors occur on the crests of narrow large seamounts. The bathymetry grid is based on prediction from satellite gravity and available ship soundings. Global soundings were assembled from a wide variety of sources including NGDC/GEODAS, NOAA Coastal Relief, CCOM, IFREMER, JAMSTEC, NSF Polar Programs, UKHO, LDEO, HIG, SIO and numerous miscellaneous contributions. The National Geospatial-intelligence Agency and other volunteering hydrographic offices within the International Hydrographic Organization provided global significant shallow water (< 300 m) soundings derived from their nautical charts. All soundings were converted to a common format and were hand-edited in relation to a smooth bathymetric model. Land elevations and shoreline location are based on a combination SRTM30, GTOPO30, and ICESAT data. A new feature of the bathymetry grid is a matching grid of source identification number that enables one to establish the origin of the depth estimate in each grid cell. Both the gravity and bathymetry grids are freely available.

Evaluation of using digital gravity field models for zoning map creation

NASA Astrophysics Data System (ADS)

Loginov, Dmitry

2018-05-01

At the present time the digital cartographic models of geophysical fields are taking a special significance into geo-physical mapping. One of the important directions to their application is the creation of zoning maps, which allow taking into account the morphology of geophysical field in the implementation automated choice of contour intervals. The purpose of this work is the comparative evaluation of various digital models in the creation of integrated gravity field zoning map. For comparison were chosen the digital model of gravity field of Russia, created by the analog map with scale of 1 : 2 500 000, and the open global model of gravity field of the Earth - WGM2012. As a result of experimental works the four integrated gravity field zoning maps were obtained with using raw and processed data on each gravity field model. The study demonstrates the possibility of open data use to create integrated zoning maps with the condition to eliminate noise component of model by processing in specialized software systems. In this case, for solving problem of contour intervals automated choice the open digital models aren't inferior to regional models of gravity field, created for individual countries. This fact allows asserting about universality and independence of integrated zoning maps creation regardless of detail of a digital cartographic model of geo-physical fields.

Topographic gravity modeling for global Bouguer maps to degree 2160: Validation of spectral and spatial domain forward modeling techniques at the 10 microGal level

NASA Astrophysics Data System (ADS)

Hirt, Christian; Reußner, Elisabeth; Rexer, Moritz; Kuhn, Michael

2016-09-01

Over the past years, spectral techniques have become a standard to model Earth's global gravity field to 10 km scales, with the EGM2008 geopotential model being a prominent example. For some geophysical applications of EGM2008, particularly Bouguer gravity computation with spectral techniques, a topographic potential model of adequate resolution is required. However, current topographic potential models have not yet been successfully validated to degree 2160, and notable discrepancies between spectral modeling and Newtonian (numerical) integration well beyond the 10 mGal level have been reported. Here we accurately compute and validate gravity implied by a degree 2160 model of Earth's topographic masses. Our experiments are based on two key strategies, both of which require advanced computational resources. First, we construct a spectrally complete model of the gravity field which is generated by the degree 2160 Earth topography model. This involves expansion of the topographic potential to the 15th integer power of the topography and modeling of short-scale gravity signals to ultrahigh degree of 21,600, translating into unprecedented fine scales of 1 km. Second, we apply Newtonian integration in the space domain with high spatial resolution to reduce discretization errors. Our numerical study demonstrates excellent agreement (8 μGgal RMS) between gravity from both forward modeling techniques and provides insight into the convergence process associated with spectral modeling of gravity signals at very short scales (few km). As key conclusion, our work successfully validates the spectral domain forward modeling technique for degree 2160 topography and increases the confidence in new high-resolution global Bouguer gravity maps.

Gravity Field Characterization around Small Bodies

NASA Astrophysics Data System (ADS)

Takahashi, Yu

A small body rendezvous mission requires accurate gravity field characterization for safe, accurate navigation purposes. However, the current techniques of gravity field modeling around small bodies are not achieved to the level of satisfaction. This thesis will address how the process of current gravity field characterization can be made more robust for future small body missions. First we perform the covariance analysis around small bodies via multiple slow flybys. Flyby characterization requires less laborious scheduling than its orbit counterpart, simultaneously reducing the risk of impact into the asteroid's surface. It will be shown that the level of initial characterization that can occur with this approach is no less than the orbit approach. Next, we apply the same technique of gravity field characterization to estimate the spin state of 4179 Touatis, which is a near-Earth asteroid in close to 4:1 resonance with the Earth. The data accumulated from 1992-2008 are processed in a least-squares filter to predict Toutatis' orientation during the 2012 apparition. The center-of-mass offset and the moments of inertia estimated thereof can be used to constrain the internal density distribution within the body. Then, the spin state estimation is developed to a generalized method to estimate the internal density distribution within a small body. The density distribution is estimated from the orbit determination solution of the gravitational coefficients. It will be shown that the surface gravity field reconstructed from the estimated density distribution yields higher accuracy than the conventional gravity field models. Finally, we will investigate two types of relatively unknown gravity fields, namely the interior gravity field and interior spherical Bessel gravity field, in order to investigate how accurately the surface gravity field can be mapped out for proximity operations purposes. It will be shown that these formulations compute the surface gravity field with unprecedented accuracy for a well-chosen set of parametric settings, both regionally and globally.

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.

Gravity fields. [Jovian, Martian, Cytherean, Mercurian and lunar mass distributions

NASA Technical Reports Server (NTRS)

Sjogren, W. L.; Anderson, J. D.; Phillips, R. J.; Trask, D. W.

1976-01-01

Detailed results on internal mass distribution have been obtained via earth-based Doppler radio tracking of deep space probes in the case of Mars, the earth's moon, Venus, Mercury, and Jupiter. Global gravity fields show close correlation with topography in the case of the moon and Mars, as data from orbiting spacecraft indicate. Some data are available on Jovian satellites. The gravity measuring instrumentation and data reduction techniques are described. Gravity profiles referable to lunar frontside mascons, craters, and mountain chains have been acquired from low-altitude (15-20 km) orbit surveys. Theoretically based cross sections through the moon and Jupiter are presented.

Gravity gradient preprocessing at the GOCE HPF

NASA Astrophysics Data System (ADS)

Bouman, J.; Rispens, S.; Gruber, T.; Schrama, E.; Visser, P.; Tscherning, C. C.; Veicherts, M.

2009-04-01

One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and non-tidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

A family of metric gravities

NASA Astrophysics Data System (ADS)

Shuler, Robert

2018-04-01

The goal of this paper is to take a completely fresh approach to metric gravity, in which the metric principle is strictly adhered to but its properties in local space-time are derived from conservation principles, not inferred from a global field equation. The global field strength variation then gains some flexibility, but only in the regime of very strong fields (2nd-order terms) whose measurement is now being contemplated. So doing provides a family of similar gravities, differing only in strong fields, which could be developed into meaningful verification targets for strong fields after the manner in which far-field variations were used in the 20th century. General Relativity (GR) is shown to be a member of the family and this is demonstrated by deriving the Schwarzschild metric exactly from a suitable field strength assumption. The method of doing so is interesting in itself because it involves only one differential equation rather than the usual four. Exact static symmetric field solutions are also given for one pedagogical alternative based on potential, and one theoretical alternative based on inertia, and the prospects of experimentally differentiating these are analyzed. Whether the method overturns the conventional wisdom that GR is the only metric theory of gravity and that alternatives must introduce additional interactions and fields is somewhat semantical, depending on whether one views the field strength assumption as a field and whether the assumption that produces GR is considered unique in some way. It is of course possible to have other fields, and the local space-time principle can be applied to field gravities which usually are weak-field approximations having only time dilation, giving them the spatial factor and promoting them to full metric theories. Though usually pedagogical, some of them are interesting from a quantum gravity perspective. Cases are noted where mass measurement errors, or distributions of dark matter, can cause one theory to mimic another implying that such estimates or distributions should be first obtained from weakfield measurements before being used to discriminate verification candidates. By this method theorists gain insight into the local constraints on space-time, and GR verification gains strong-field comparative objectives.

Time variations in the Earth's gravity field

NASA Astrophysics Data System (ADS)

Shum, C. K.; Eanes, R. J.

1992-01-01

At the present time, the causes and consequences of changes in the Earth's gravity field due to geophysical and meteorological phenomena are not well understood. The Earth's gravity field represents the complicated distribution of all of the matter that makes up our planet. Its variations are caused by the motions of the solid Earth interacting with the gravitational attraction of the Sun and the Moon (tides) and with the Earth's atmosphere, oceans, polar ice caps and groundwater due to changing weather patterns. These variations influence the rotation of the Earth, alter the orbits of Earth satellites, cause sea level fluctuations, and indirectly affect the global climate pattern.

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.

A surface spherical harmonic expansion of gravity anomalies on the ellipsoid

NASA Astrophysics Data System (ADS)

Claessens, S. J.; Hirt, C.

2015-10-01

A surface spherical harmonic expansion of gravity anomalies with respect to a geodetic reference ellipsoid can be used to model the global gravity field and reveal its spectral properties. In this paper, a direct and rigorous transformation between solid spherical harmonic coefficients of the Earth's disturbing potential and surface spherical harmonic coefficients of gravity anomalies in ellipsoidal approximation with respect to a reference ellipsoid is derived. This transformation cannot rigorously be achieved by the Hotine-Jekeli transformation between spherical and ellipsoidal harmonic coefficients. The method derived here is used to create a surface spherical harmonic model of gravity anomalies with respect to the GRS80 ellipsoid from the EGM2008 global gravity model. Internal validation of the model shows a global RMS precision of 1 nGal. This is significantly more precise than previous solutions based on spherical approximation or approximations to order or , which are shown to be insufficient for the generation of surface spherical harmonic coefficients with respect to a geodetic reference ellipsoid. Numerical results of two applications of the new method (the computation of ellipsoidal corrections to gravimetric geoid computation, and area means of gravity anomalies in ellipsoidal approximation) are provided.

Contribution of the GOCE gradiometer components to regional gravity solutions

NASA Astrophysics Data System (ADS)

Naeimi, Majid; Bouman, Johannes

2017-05-01

The contribution of the GOCE gravity gradients to regional gravity field solutions is investigated in this study. We employ radial basis functions to recover the gravity field on regional scales over Amazon and Himalayas as our test regions. In the first step, four individual solutions based on the more accurate gravity gradient components Txx, Tyy, Tzz and Txz are derived. The Tzz component gives better solution than the other single-component solutions despite the less accuracy of Tzz compared to Txx and Tyy. Furthermore, we determine five more solutions based on several selected combinations of the gravity gradient components including a combined solution using the four gradient components. The Tzz and Tyy components are shown to be the main contributors in all combined solutions whereas the Txz adds the least value to the regional gravity solutions. We also investigate the contribution of the regularization term. We show that the contribution of the regularization significantly decreases as more gravity gradients are included. For the solution using all gravity gradients, regularization term contributes to about 5 per cent of the total solution. Finally, we demonstrate that in our test areas, regional gravity modelling based on GOCE data provide more reliable gravity signal in medium wavelengths as compared to pre-GOCE global gravity field models such as the EGM2008.

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.

On the use of infrasound for constraining global climate models

NASA Astrophysics Data System (ADS)

Millet, Christophe; Ribstein, Bruno; Lott, Francois; Cugnet, David

2017-11-01

Numerical prediction of infrasound is a complex issue due to constantly changing atmospheric conditions and to the random nature of small-scale flows. Although part of the upward propagating wave is refracted at stratospheric levels, where gravity waves significantly affect the temperature and the wind, yet the process by which the gravity wave field changes the infrasound arrivals remains poorly understood. In the present work, we use a stochastic parameterization to represent the subgrid scale gravity wave field from the atmospheric specifications provided by the European Centre for Medium-Range Weather Forecasts. It is shown that regardless of whether the gravity wave field possesses relatively small or large features, the sensitivity of acoustic waveforms to atmospheric disturbances can be extremely different. Using infrasound signals recorded during campaigns of ammunition destruction explosions, a new set of tunable parameters is proposed which more accurately predicts the small-scale content of gravity wave fields in the middle atmosphere. Climate simulations are performed using the updated parameterization. Numerical results demonstrate that a network of ground-based infrasound stations is a promising technology for dynamically tuning the gravity wave parameterization.

Lunar Prospector Orbit Determination Uncertainties Using the High Resolution Lunar Gravity Models

NASA Technical Reports Server (NTRS)

Carranza, Eric; Konopliv, Alex; Ryne, Mark

1999-01-01

The Lunar Prospector (LP) mission began on January 6, 1998, when the LP spacecraft was launched from Cape Canaveral, Florida. The objectives of the mission were to determine whether water ice exists at the lunar poles, generate a global compositional map of the lunar surface, detect lunar outgassing, and improve knowledge of the lunar magnetic and gravity fields. Orbit determination of LP performed at the Jet Propulsion Laboratory (JPL) is conducted as part of the principal science investigation of the lunar gravity field. This paper will describe the JPL effort in support of the LP Gravity Investigation. This support includes high precision orbit determination, gravity model validation, and data editing. A description of the mission and its trajectory will be provided first, followed by a discussion of the orbit determination estimation procedure and models. Accuracies will be examined in terms of orbit-to-orbit solution differences, as a function of oblateness model truncation, and inclination in the plane-of-sky. Long term predictions for several gravity fields will be compared to the reconstructed orbits to demonstrate the accuracy of the orbit determination and oblateness fields developed by the Principal Gravity Investigator.

Altimeter measurements for the determination of the Earth's gravity field

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Schutz, B. E.; Shum, C. K.

1987-01-01

The ability of satellite-borne radar altimeter data to measure the global ocean surface with high precision and dense spatial coverage provides a unique tool for the mapping of the Earth's gravity field and its geoid. The altimeter crossover measurements, created by differencing direct altimeter measurements at the subsatellite points where the orbit ground tracks intersect, have the distinct advantage of eliminating geoid error and other nontemporal or long period oceanographic features. In the 1990's, the joint U.S./French TOPEX/POSEIDON mission and the European Space Agency's ERS-1 mission will carry radar altimeter instruments capable of global ocean mapping with high precision. This investigation aims at the development and application of dynamically consistent direct altimeter and altimeter crossover measurement models to the simultaneous mapping of the Earth's gravity field and its geoid, the ocean tides and the quasi-stationary component of the dynamic sea surface topography. Altimeter data collected by SEASAT, GEOS-3, and GEOSAT are used for the investigation.

Somigliana-Pizzetti gravity: the international gravity formula accurate to the sub-nanoGal level

NASA Astrophysics Data System (ADS)

Ardalan, A. A.; Grafarend, E. W.

2001-09-01

The Somigliana-Pizzetti gravity field (the International gravity formula), namely the gravity field of the level ellipsoid (the International Reference Ellipsoid), is derived to the sub-nanoGal accuracy level in order to fulfil the demands of modern gravimetry (absolute gravimeters, super conducting gravimeters, atomic gravimeters). Equations (53), (54) and (59) summarise Somigliana-Pizzetti gravity o({,u) as a function of Jacobi spheroidal latitude { and height u to the order ™(10m10 Gal), and o(B,H) as a function of Gauss (surface normal) ellipsoidal latitude B and height H to the order ™(10m10 Gal) as determined by GPS (`global problem solver'). Within the test area of the state of Baden-Württemberg, Somigliana-Pizzetti gravity disturbances of an average of 25.452 mGal were produced. Computer programs for an operational application of the new international gravity formula with (L,B,H) or (u,{,u) coordinate inputs to a sub-nanoGal level of accuracy are available on the Internet.

Mapping the earth's magnetic and gravity fields from space Current status and future prospects

NASA Technical Reports Server (NTRS)

Settle, M.; Taranik, J. V.

1983-01-01

The principal magnetic fields encountered by earth orbiting spacecraft include the main (core) field, external fields produced by electrical currents within the ionosphere and magnetosphere, and the crustal (anomaly) field generated by variations in the magnetization of the outermost portions of the earth. The first orbital field measurements which proved to be of use for global studies of crustal magnetization were obtained by a series of three satellites launched and operated from 1965 to 1971. Each of the satellites, known as a Polar Orbiting Geophysical Observatory (POGO), carried a rubidium vapor magnetometer. Attention is also given to Magsat launched in 1979, the scalar anomaly field derived from the Magsat measurements, satellite tracking studies in connection with gravity field surveys, radar altimetry, the belt of positive free air gravity anomalies situated along the edge of the Pacific Ocean basin, future technological capabilities, and information concerning data availability.

Satellite Laser Ranging in the 1990s: Report of the 1994 Belmont Workshop

NASA Technical Reports Server (NTRS)

Degnan, John J. (Editor)

1994-01-01

An international network of 43 stations in 30 countries routinely collects satellite ranging data which is used to study the solid Earth and its interactions with the oceans, atmosphere, and Moon. Data products include centimeter accuracy site positions on a global scale, tectonic plate motions, regional crustal deformation, long wavelength gravity field and geoid, polar motion, and variations in the Earth's spin rate. By calibrating and providing precise orbits for spaceborne microwave altimeters, satellite laser ranging also enables global measurement of sea and ice surface topography, mean sea level, global ocean circulation, and short wavelength gravity fields and marine geoids. It provides tests of general relativity and a means or subnanosecond time transfer. This workshop was convened to define future roles and directions in satellite laser ranging.

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.

High-resolution gravity field modeling using GRAIL mission data

NASA Astrophysics Data System (ADS)

Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Loomis, B.; Chinn, D. S.; Smith, D. E.; Zuber, M. T.

2015-12-01

The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were designed to map the structure of the Moon through high-precision global gravity mapping. The mission consisted of two spacecraft with Ka-band inter-satellite tracking complemented by tracking from Earth. The mission had two phases: a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km, and an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and 20 and 11 km after. High-resolution gravity field models using both these data sets have been estimated, with the current resolution being degree and order 1080 in spherical harmonics. Here, we focus on aspects of the analysis of the GRAIL data: we investigate eclipse modeling, the influence of empirical accelerations on the results, and we discuss the inversion of large-scale systems. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale, the south pole area, and the farside. We investigate the use of Ka-band Range Rate (KBRR) data versus numerical derivatives of KBRR data, and show that the latter have the capability to locally improve correlations with topography.

Refinement of Earth's gravity field with Topex GPS measurements

NASA Technical Reports Server (NTRS)

Wu, Sien-Chong; Wu, Jiun-Tsong

1989-01-01

The NASA Ocean Topography Experiment satellite TOPEX will carry a microwave altimeter accurate to a few centimeters for the measurement of ocean height. The capability can be fully exploited only if TOPEX altitude can be independently determined to 15 cm or better. This in turn requires an accurate gravity model. The gravity will be tuned with selected nine 10-day arcs of laser ranging, which will be the baseline tracking data type, collected in the first six months of TOPEX flight. TOPEX will also carry onboard an experimental Global Positioning System (GPS) flight receiver capable of simultaneously observing six GPS satellites above its horizon to demonstrate the capability of GPS carrier phase and P-code pseudorange for precise determination of the TOPEX orbit. It was found that subdecimeter orbit accuracy can be achieved with a mere two-hour arc of GPS tracking data, provided that simultaneous measurements are also made at six of more ground tracking sites. The precision GPS data from TOPEX are also valuable for refining the gravity model. An efficient technique is presented for gravity tuning using GPS measurements. Unlike conventional global gravity tuning, this technique solves for far fewer gravity parameters in each filter run. These gravity parameters yield local gravity anomalies which can later be combined with the solutions over other parts of the earth to generate a global gravity map. No supercomputing power will be needed for such combining. The approaches used in this study are described and preliminary results of a covariance analysis presented.

The Gravity Field, Orientation, and Ephemeris of Mercury from MESSENGER Observations After Three Years in Orbit

NASA Technical Reports Server (NTRS)

Mazarico, Erwan M.; Genova, Antonio; Goossens, Sander; Lemoine, Gregory; Neumann, Gregory A.; Zuber, Maria T.; Smith, David E.; Solomon, Sean C.

2014-01-01

We have analyzed three years of radio tracking data from the MESSENGER spacecraft in orbit around Mercury and determined the gravity field, planetary orientation, and ephemeris of the innermost planet. With improvements in spatial coverage, force modeling, and data weighting, we refined an earlier global gravity field both in quality and resolution, and we present here a spherical harmonic solution to degree and order 50. In this field, termed HgM005, uncertainties in low-degree coefficients are reduced by an order of magnitude relative to the earlier global field, and we obtained a preliminary value of the tidal Love number k(sub 2) of 0.451+/-0.014. We also estimated Mercury's pole position, and we obtained an obliquity value of 2.06 +/- 0.16 arcmin, in good agreement with analysis of Earth-based radar observations. From our updated rotation period (58.646146 +/- 0.000011 days) and Mercury ephemeris, we verified experimentally the planet's 3: 2 spin-orbit resonance to greater accuracy than previously possible. We present a detailed analysis of the HgM005 covariance matrix, and we describe some near-circular frozen orbits around Mercury that could be advantageous for future exploration.

Lunar Prospector: overview.

PubMed

Binder, A B

1998-09-04

Lunar Prospector is providing a global map of the composition of the moon and analyzing the moon's gravity and magnetic fields. It has been in a polar orbit around the moon since 16 January 1998. Neutron flux data show that there is abundant H, and hence probably abundant water ice, in the lunar polar regions. Gamma-ray and neutron data reveal the distribution of Fe, Ti, and other major and trace elements on the moon. The data delineate the global distributions of a key trace element-rich component of lunar materials called KREEP and of the major rock types. Magnetic mapping shows that the lunar magnetic fields are strong antipodal to Mare Imbrium and Mare Serenitatis and has discovered the smallest known magnetosphere, magnetosheath, and bow shock complex in the solar system. Gravity mapping has delineated seven new gravity anomalies and shown that the moon has a small Fe-rich core of about 300 km radius.

The IfE Global Gravity Field Model Recovered from GOCE Orbit and Gradiometer Data

NASA Astrophysics Data System (ADS)

Wu, Hu; Muiller, Jurgen; Brieden, Phillip

2015-03-01

An independent global gravity field model is computed from the GOCE orbit and gradiometer data using our own IfE software. We analysed the same data period that were considered for the first released GOCE models. The Acceleration Approach is applied to process the orbit data. The gravity gradients are processed in the framework of the remove-restore technique by which the low-frequency noise of the original gradients are removed. For the combined solution, the normal equations are summed by the Variance Component Estimation Approach. The result in terms of accumulated geoid height error calculated from the coefficient difference w.r.t. EGM2008 is about 11 cm at D/O 200, which corresponds to the accuracy level of the first released TIM and DIR solutions. This indicates that our IfE model has a comparable performance as the other official GOCE models.

Seasonal and Static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science

NASA Technical Reports Server (NTRS)

Genova, Antonio; Goossens, Sander; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2016-01-01

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k 2 Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k 2 of 0.1697 +/-0.0027 (3- sigma). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C 30 and, for the first time, C 50 . Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C 30 for approx.1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics ( l = 60–80) than previous solutions.

Seasonal and static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science

NASA Technical Reports Server (NTRS)

Genova, Antonio; Goossens, Sander; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2016-01-01

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k(sub 2) Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k(sub 2) solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k(sub 2) of 0.1697 +/- 0.0027 (3- sigma). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C(sub 30) and, for the first time, C 50. Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C(sub 30) for approximately 1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics ( l = 60-80) than previous solutions.

Detection of traveling ionospheric disturbances induced by atmospheric gravity waves using the global positioning system

NASA Technical Reports Server (NTRS)

Bassiri, Sassan; Hajj, George A.

1993-01-01

Natural and man-made events like earthquakes and nuclear explosions launch atmospheric gravity waves (AGW) into the atmosphere. Since the particle density decreases exponentially with height, the gravity waves increase exponentially in amplitude as they propagate toward the upper atmosphere and ionosphere. As atmospheric gravity waves approach the ionospheric heights, the neutral particles carried by gravity waves collide with electrons and ions, setting these particles in motion. This motion of charged particles manifests itself by wave-like fluctuations and disturbances that are known as traveling ionospheric disturbances (TID). The perturbation in the total electron content due to TID's is derived analytically from first principles. Using the tilted dipole magnetic field approximation and a Chapman layer distribution for the electron density, the variations of the total electron content versus the line-of-sight direction are numerically analyzed. The temporal variation associated with the total electron content measurements due to AGW's can be used as a means of detecting characteristics of the gravity waves. As an example, detection of tsunami generated earthquakes from their associated atmospheric gravity waves using the Global Positioning System is simulated.

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

Mars Gravity Field and Upper Atmosphere from MGS, Mars Odyssey, and MRO

NASA Astrophysics Data System (ADS)

Genova, A.; Goossens, S. J.; Lemoine, F. G.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2015-12-01

The NASA orbital missions Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) have been exploring and monitoring the planet Mars since 1997. MGS executed its mapping mission between 1999 and 2006 in a frozen sun-synchronous, near-circular, polar orbit with the periapsis altitude at ~370 km and the dayside equatorial crossing at 2 pm Local Solar Time (LST). The spacecraft was equipped with onboard instrumentation to acquire radio science data and to measure spacecraft ranges to the Martian surface (Mars Orbiter Laser Altimeter). These measurements resulted in static and time-varying gravity field and high-resolution global topography of the planet. ODY and MRO are still orbiting about Mars in two different sun-synchronous orbits, providing radio tracking data that indirectly measure both the static and time-varying gravity field and the atmospheric density. The orbit of ODY has its periapsis at ~390 km altitude and descending node at 4-5 pm LST. However, the spacecraft also collected measurements at lower altitudes (~220 km) in 2002 prior to the mapping phase. Since November 2006, MRO is in a low-altitude orbit with a periapsis altitude of 255 km and descending node at 3 pm LST. Radio data from MRO help improve the resolution of the static gravity field and measure the mass distribution of the polar caps, but the atmospheric drag at those altitudes may limit the benefits of these radio tracking observations. We present a combined solution of the Martian gravity field to degree and order 110 and atmospheric density profiles with radio tracking data from MGS, ODY and MRO. The gravity field solution is combined with the MOLA topography yielding an updated map of Mars crustal thickness. We also show our solution of the Love number k2 and time-variable gravity zonal harmonics (C20 and C30, in particular). The recovered atmospheric density profiles may be used in atmospheric models to constrain the long-term variability of the constituents in the upper atmosphere.

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

NASA Technical Reports Server (NTRS)

Griffin, D. W.; Yep, T. W.; Agrawal, A. K.

2005-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2- second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes change in gravity in the drop tower.

A comparison of the gravity field over Central Europe from superconducting gravimeters, GRACE and global hydrological models, using EOF analysis

NASA Astrophysics Data System (ADS)

Crossley, David; de Linage, Caroline; Hinderer, Jacques; Boy, Jean-Paul; Famiglietti, James

2012-05-01

We analyse data from seven superconducting gravimeter (SG) stations in Europe from 2002 to 2007 from the Global Geodynamics Project (GGP) and compare seasonal variations with data from GRACE and several global hydrological models - GLDAS, WGHM and ERA-Interim. Our technique is empirical orthogonal function (EOF) decomposition of the fields that allows for the inherent incompatibility of length scales between ground and satellite observations. GGP stations below the ground surface pose a problem because part of the attraction from soil moisture comes from above the gravimeter, and this gives rise to a complex (mixed) gravity response. The first principle component (PC) of the EOF decomposition is the main indicator for comparing the fields, although for some of the series it accounts for only about 50 per cent of the variance reduction. PCs for GRACE solutions RL04 from CSR and GFZ are filtered with a cosine taper (degrees 20-40) and a Gaussian window (350 km). Significant differences are evident between GRACE solutions from different groups and filters, though they all agree reasonably well with the global hydrological models for the predominantly seasonal signal. We estimate the first PC at 10-d sampling to be accurate to 1 μGal for GGP data, 1.5 μGal for GRACE data and 1 μGal between the three global hydrological models. Within these limits the CNES/GRGS solution and ground GGP data agree at the 79 per cent level, and better when the GGP solution is restricted to the three above-ground stations. The major limitation on the GGP side comes from the water mass distribution surrounding the underground instruments that leads to a complex gravity effect. To solve this we propose a method for correcting the SG residual gravity series for the effects of soil moisture above the station.

Global Mass Flux Solutions from GRACE: A Comparison of Parameter Estimation Strategies - Mass Concentrations Versus Stokes Coefficients

NASA Technical Reports Server (NTRS)

Rowlands, D. D.; Luthcke, S. B.; McCarthy J. J.; Klosko, S. M.; Chinn, D. S.; Lemoine, F. G.; Boy, J.-P.; Sabaka, T. J.

2010-01-01

The differences between mass concentration (mas con) parameters and standard Stokes coefficient parameters in the recovery of gravity infonnation from gravity recovery and climate experiment (GRACE) intersatellite K-band range rate data are investigated. First, mascons are decomposed into their Stokes coefficient representations to gauge the range of solutions available using each of the two types of parameters. Next, a direct comparison is made between two time series of unconstrained gravity solutions, one based on a set of global equal area mascon parameters (equivalent to 4deg x 4deg at the equator), and the other based on standard Stokes coefficients with each time series using the same fundamental processing of the GRACE tracking data. It is shown that in unconstrained solutions, the type of gravity parameter being estimated does not qualitatively affect the estimated gravity field. It is also shown that many of the differences in mass flux derivations from GRACE gravity solutions arise from the type of smoothing being used and that the type of smoothing that can be embedded in mas con solutions has distinct advantages over postsolution smoothing. Finally, a 1 year time series based on global 2deg equal area mascons estimated every 10 days is presented.

The Geopotential Research Mission - Mapping the near earth gravity and magnetic fields

NASA Technical Reports Server (NTRS)

Taylor, P. T.; Keating, T.; Smith, D. E.; Langel, R. A.; Schnetzler, C. C.; Kahn, W. D.

1983-01-01

The Geopotential Research Mission (GRM), NASA's low-level satellite system designed to measure the gravity and magnetic fields of the earth, and its objectives are described. The GRM will consist of two, Shuttle launched, satellite systems (300 km apart) that will operate simultaneously at a 160 km circular-polar orbit for six months. Current mission goals include mapping the global geoid to 10 cm, measuring gravity-field anomalies to 2 mgal with a spatial resolution of 100 km, detecting crustal magnetic anomalies of 100 km wavelength with 1 nT accuracy, measuring the vectors components to + or - 5 arc sec and 5 nT, and computing the main dipole or core field to 5 nT with a 2 nT/year secular variation detection. Resource analysis and exploration geology are additional applications considered.

Energy bounds in designer gravity

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

Amsel, Aaron J.; Marolf, Donald

We consider asymptotically anti-de Sitter gravity coupled to tachyonic scalar fields with mass at or slightly above the Breitenlohner-Freedman bound in d{>=}4 spacetime dimensions. The boundary conditions in these ''designer gravity'' theories are defined in terms of an arbitrary function W. We give a general argument that the Hamiltonian generators of asymptotic symmetries for such systems will be finite, and proceed to construct these generators using the covariant phase space method. The direct calculation confirms that the generators are finite and shows that they take the form of the pure gravity result plus additional contributions from the scalar fields. Bymore » comparing the generators to the spinor charge, we derive a lower bound on the gravitational energy when W has a global minimum and the Breitenlohner-Freedman bound is not saturated.« less

Asymptotic symmetries of colored gravity in three dimensions

NASA Astrophysics Data System (ADS)

Joung, Euihun; Kim, Jaewon; Kim, Jihun; Rey, Soo-Jong

2018-03-01

Three-dimensional colored gravity refers to nonabelian isospin extension of Einstein gravity. We investigate the asymptotic symmetry algebra of the SU( N)-colored gravity in (2+1)-dimensional anti-de Sitter spacetime. Formulated by the Chern-Simons theory with SU( N, N) × SU( N, N) gauge group, the theory contains graviton, SU( N) Chern-Simons gauge fields and massless spin-two multiplets in the SU( N) adjoint representation, thus extending diffeomorphism to colored, nonabelian counterpart. We identify the asymptotic symmetry as Poisson algebra of generators associated with the residual global symmetries of the nonabelian diffeomorphism set by appropriately chosen boundary conditions. The resulting asymptotic symmetry algebra is a nonlinear extension of \\widehat{su(N)} Kac-Moody algebra, supplemented by additional generators corresponding to the massless spin-two adjoint matter fields.

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.

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.

Time Changes of the European Gravity Field from GRACE: A Comparison with Ground Measurements from Superconducting Gravimeters and with Hydrology Model Predictions

NASA Technical Reports Server (NTRS)

Hinderer, J.; Lemoine, Frank G.; Crossley, D.; Boy, J.-P.

2004-01-01

We investigate the time-variable gravity changes in Europe retrieved from the initial GRACE monthly solutions spanning a 18 month duration from April 2002 to October 2003. Gravity anomaly maps are retrieved in Central Europe from the monthly satellite solutions we compare the fields according to various truncation levels (typically between degree 10 and 20) of the initial fields (expressed in spherical harmonics to degree 120). For these different degrees, an empirical orthogonal function (EOF) decomposition of the time-variable gravity field leads us to its main spatial and temporal characteristics. We show that the dominant signal is found to be annual with an amplitude and a phase both in agreement with predictions in Europe modeled using snow and soil-moisture variations from recent hydrology models. We compare these GRACE gravity field changes to surface gravity observations from 6 superconducting gravimeters of the GGP (Global Geodynamics Project) European sub-network, with a special attention to loading corrections. Initial results suggest that all 3 data sets (GRACE, hydrology and GGP) are responding to annual changes in near-surface water in Europe of a few microGal (at length scales of approx.1000 km) that show a high value in winter and a summer minimum. We also point out that the GRACE gravity field evolution seems to indicate that there is a trend in gravity between summer 2002 and summer 2003 which can be related to the 2003 heatwave in Europe and its hydrological consequences (drought). Despite the limited time span of our analysis and the uncertainties in retrieving a regional solution from the network of gravimeters, the calibration and validation aspects of the GRACE data processing based on the annual hydrology cycle in Europe are in progress.

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.

Intercomparison and Assessment of GRACE Temporal Gravity Solutions Performance

NASA Astrophysics Data System (ADS)

Choe, J.; Nerem, R. S.; Leuliette, E. W.

2006-12-01

The GRACE mission has been producing monthly estimates of changes in the Earth's gravity field since April 2002. Converting the raw GRACE range, accelerometer, and GPS measurements into estimates of the gravity field is a complex process, and therefore different analysis groups use various "recipes" resulting in different models of the time-varying gravity field. We have intercompared the solutions generated by a number of groups: Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), Goddard Space Flight Center (GSFC), Centre National d'Etudes Spatiales (CNES) and GeoForschungsZentrum (GFZ), to determine the characteristics of each group's solutions as applied to different scientific applications. For different scales of gaussian smoothing, we have examined the power spectrum of each model, the pattern of seasonal gravity variations, the residuals from a seasonal fit, and results from locations in the Sahara desert and Atlantic Ocean where the signals are known to be small. We have also characterized the level of "striping" in each center's solutions. In addition, we have compared each center's solutions for changes in Greenland and Antarctic ice mass, global ocean mass, and hydrologic changes over the continents. Using these tests and evaluations, we have been able to characterize the performance of each center's gravity solutions.

How to deal with the high condition number of the noise covariance matrix of gravity field functionals synthesised from a satellite-only global gravity field model?

NASA Astrophysics Data System (ADS)

Klees, R.; Slobbe, D. C.; Farahani, H. H.

2018-03-01

The posed question arises for instance in regional gravity field modelling using weighted least-squares techniques if the gravity field functionals are synthesised from the spherical harmonic coefficients of a satellite-only global gravity model (GGM), and are used as one of the noisy datasets. The associated noise covariance matrix, appeared to be extremely ill-conditioned with a singular value spectrum that decayed gradually to zero without any noticeable gap. We analysed three methods to deal with the ill-conditioned noise covariance matrix: Tihonov regularisation of the noise covariance matrix in combination with the standard formula for the weighted least-squares estimator, a formula of the weighted least-squares estimator, which does not involve the inverse noise covariance matrix, and an estimator based on Rao's unified theory of least-squares. Our analysis was based on a numerical experiment involving a set of height anomalies synthesised from the GGM GOCO05s, which is provided with a full noise covariance matrix. We showed that the three estimators perform similar, provided that the two regularisation parameters each method knows were chosen properly. As standard regularisation parameter choice rules do not apply here, we suggested a new parameter choice rule, and demonstrated its performance. Using this rule, we found that the differences between the three least-squares estimates were within noise. For the standard formulation of the weighted least-squares estimator with regularised noise covariance matrix, this required an exceptionally strong regularisation, much larger than one expected from the condition number of the noise covariance matrix. The preferred method is the inversion-free formulation of the weighted least-squares estimator, because of its simplicity with respect to the choice of the two regularisation parameters.

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.

Gravity field recovery in the framework of a Geodesy and Time Reference in Space (GETRIS)

NASA Astrophysics Data System (ADS)

Hauk, Markus; Schlicht, Anja; Pail, Roland; Murböck, Michael

2017-04-01

The study ;Geodesy and Time Reference in Space; (GETRIS), funded by European Space Agency (ESA), evaluates the potential and opportunities coming along with a global space-borne infrastructure for data transfer, clock synchronization and ranging. Gravity field recovery could be one of the first beneficiary applications of such an infrastructure. This paper analyzes and evaluates the two-way high-low satellite-to-satellite-tracking as a novel method and as a long-term perspective for the determination of the Earth's gravitational field, using it as a synergy of one-way high-low combined with low-low satellite-to-satellite-tracking, in order to generate adequate de-aliasing products. First planned as a constellation of geostationary satellites, it turned out, that an integration of European Union Global Navigation Satellite System (Galileo) satellites (equipped with inter-Galileo links) into a Geostationary Earth Orbit (GEO) constellation would extend the capability of such a mission constellation remarkably. We report about simulations of different Galileo and Low Earth Orbiter (LEO) satellite constellations, computed using time variable geophysical background models, to determine temporal changes in the Earth's gravitational field. Our work aims at an error analysis of this new satellite/instrument scenario by investigating the impact of different error sources. Compared to a low-low satellite-to-satellite-tracking mission, results show reduced temporal aliasing errors due to a more isotropic error behavior caused by an improved observation geometry, predominantly in near-radial direction within the inter-satellite-links, as well as the potential of an improved gravity recovery with higher spatial and temporal resolution. The major error contributors of temporal gravity retrieval are aliasing errors due to undersampling of high frequency signals (mainly atmosphere, ocean and ocean tides). In this context, we investigate adequate methods to reduce these errors. We vary the number of Galileo and LEO satellites and show reduced errors in the temporal gravity field solutions for this enhanced inter-satellite-links. Based on the GETRIS infrastructure, the multiplicity of satellites enables co-estimating short-period long-wavelength gravity field signals, indicating it as powerful method for non-tidal aliasing reduction.

Seamless geoids across coastal zones - a comparison of satellite-derived gravity to airborne gravity across the seven continents

NASA Astrophysics Data System (ADS)

Forsberg, R.; Olesen, A. V.; Barnes, D.; Ingalls, S. E.; Minter, C. F.; Presicci, M. R.

2017-12-01

An accurate coastal geoid model is important for determination of near-shore ocean dynamic topography and currents, as well as for land GPS surveys and global geopotential models. Since many coastal regions across the globe are regions of intense development and coastal protection projects, precise geoid models at cm-level accuracy are essential. The only way to secure cm-geoid accuracies across coastal regions is to acquire more marine gravity data; here airborne gravity is the obvious method of choice due to the uniform accuracy, and the ability to provide a seamless geoid accuracy across the coastline. Current practice for gravity and geoid models, such as EGM2008 and many national projects, is to complement land gravity data with satellite radar altimetry at sea, a procedure which can give large errors in regions close to the coast. To quantify the coastal errors in satellite gravity, we compare results of a large set of recent airborne gravity surveys, acquired across a range of coastal zones globally from polar to equatorial regions, and quantify the errors as a function of distance from the coast line for a number of different global altimetry gravity solutions. We find that accuracy in satellite altimetry solutions depend very much on the availability of gravity data along the coast-near land regions in the underlying reference fields (e.g., EGM2008), with satellite gravity accuracy in the near-shore zone ranging from anywhere between 5 to 20 mGal r.m.s., with occasional large outliers; we also show how these errors may typically propagate into coastal geoid errors of 5-10 cm r.m.s. or more. This highlight the need for airborne (land) gravity surveys to be extended at least 20-30 km offshore, especially for regions of insufficient marine gravity coverage; we give examples of a few such recent surveys and associated marine geoid impacts.

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.

GOCE, Satellite Gravimetry and Antarctic Mass Transports

NASA Astrophysics Data System (ADS)

Rummel, Reiner; Horwath, Martin; Yi, Weiyong; Albertella, Alberta; Bosch, Wolfgang; Haagmans, Roger

2011-09-01

In 2009 the European Space Agency satellite mission GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) was launched. Its objectives are the precise and detailed determination of the Earth's gravity field and geoid. Its core instrument, a three axis gravitational gradiometer, measures the gravity gradient components V xx , V yy , V zz and V xz (second-order derivatives of the gravity potential V) with high precision and V xy , V yz with low precision, all in the instrument reference frame. The long wavelength gravity field is recovered from the orbit, measured by GPS (Global Positioning System). Characteristic elements of the mission are precise star tracking, a Sun-synchronous and very low (260 km) orbit, angular control by magnetic torquing and an extremely stiff and thermally stable instrument environment. GOCE is complementary to GRACE (Gravity Recovery and Climate Experiment), another satellite gravity mission, launched in 2002. While GRACE is designed to measure temporal gravity variations, albeit with limited spatial resolution, GOCE is aiming at maximum spatial resolution, at the expense of accuracy at large spatial scales. Thus, GOCE will not provide temporal variations but is tailored to the recovery of the fine scales of the stationary field. GRACE is very successful in delivering time series of large-scale mass changes of the Antarctic ice sheet, among other things. Currently, emphasis of respective GRACE analyses is on regional refinement and on changes of temporal trends. One of the challenges is the separation of ice mass changes from glacial isostatic adjustment. Already from a few months of GOCE data, detailed gravity gradients can be recovered. They are presented here for the area of Antarctica. As one application, GOCE gravity gradients are an important addition to the sparse gravity data of Antarctica. They will help studies of the crustal and lithospheric field. A second area of application is ocean circulation. The geoid surface from the gravity field model GOCO01S allows us now to generate rather detailed maps of the mean dynamic ocean topography and of geostrophic flow velocities in the region of the Antarctic Circumpolar Current.

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.

Precise orbit determination based on raw GPS measurements

NASA Astrophysics Data System (ADS)

Zehentner, Norbert; Mayer-Gürr, Torsten

2016-03-01

Precise orbit determination is an essential part of the most scientific satellite missions. Highly accurate knowledge of the satellite position is used to geolocate measurements of the onboard sensors. For applications in the field of gravity field research, the position itself can be used as observation. In this context, kinematic orbits of low earth orbiters (LEO) are widely used, because they do not include a priori information about the gravity field. The limiting factor for the achievable accuracy of the gravity field through LEO positions is the orbit accuracy. We make use of raw global positioning system (GPS) observations to estimate the kinematic satellite positions. The method is based on the principles of precise point positioning. Systematic influences are reduced by modeling and correcting for all known error sources. Remaining effects such as the ionospheric influence on the signal propagation are either unknown or not known to a sufficient level of accuracy. These effects are modeled as unknown parameters in the estimation process. The redundancy in the adjustment is reduced; however, an improvement in orbit accuracy leads to a better gravity field estimation. This paper describes our orbit determination approach and its mathematical background. Some examples of real data applications highlight the feasibility of the orbit determination method based on raw GPS measurements. Its suitability for gravity field estimation is presented in a second step.

Combination of geodetic measurements by means of a multi-resolution representation

NASA Astrophysics Data System (ADS)

Goebel, G.; Schmidt, M. G.; Börger, K.; List, H.; Bosch, W.

2010-12-01

Recent and in particular current satellite gravity missions provide important contributions for global Earth gravity models, and these global models can be refined by airborne and terrestrial gravity observations. The most common representation of a gravity field model in terms of spherical harmonics has the disadvantages that it is difficult to represent small spatial details and cannot handle data gaps appropriately. An adequate modeling using a multi-resolution representation (MRP) is necessary in order to exploit the highest degree of information out of all these mentioned measurements. The MRP provides a simple hierarchical framework for identifying the properties of a signal. The procedure starts from the measurements, performs the decomposition into frequency-dependent detail signals by applying a pyramidal algorithm and allows for data compression and filtering, i.e. data manipulations. Since different geodetic measurement types (terrestrial, airborne, spaceborne) cover different parts of the frequency spectrum, it seems reasonable to calculate the detail signals of the lower levels mainly from satellite data, the detail signals of medium levels mainly from airborne and the detail signals of the higher levels mainly from terrestrial data. A concept is presented how these different measurement types can be combined within the MRP. In this presentation the basic principles on strategies and concepts for the generation of MRPs will be shown. Examples of regional gravity field determination are presented.

Ancient geodynamics and global-scale hydrology on Mars.

PubMed

Phillips, R J; Zuber, M T; Solomon, S C; Golombek, M P; Jakosky, B M; Banerdt, W B; Smith, D E; Williams, R M; Hynek, B M; Aharonson, O; Hauck , S A

2001-03-30

Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.

A space-time multiscale modelling of Earth's gravity field variations

NASA Astrophysics Data System (ADS)

Wang, Shuo; Panet, Isabelle; Ramillien, Guillaume; Guilloux, Frédéric

2017-04-01

The mass distribution within the Earth varies over a wide range of spatial and temporal scales, generating variations in the Earth's gravity field in space and time. These variations are monitored by satellites as the GRACE mission, with a 400 km spatial resolution and 10 days to 1 month temporal resolution. They are expressed in the form of gravity field models, often with a fixed spatial or temporal resolution. The analysis of these models allows us to study the mass transfers within the Earth system. Here, we have developed space-time multi-scale models of the gravity field, in order to optimize the estimation of gravity signals resulting from local processes at different spatial and temporal scales, and to adapt the time resolution of the model to its spatial resolution according to the satellites sampling. For that, we first build a 4D wavelet family combining spatial Poisson wavelets with temporal Haar wavelets. Then, we set-up a regularized inversion of inter-satellites gravity potential differences in a bayesian framework, to estimate the model parameters. To build the prior, we develop a spectral analysis, localized in time and space, of geophysical models of mass transport and associated gravity variations. Finally, we test our approach to the reconstruction of space-time variations of the gravity field due to hydrology. We first consider a global distribution of observations along the orbit, from a simplified synthetic hydrology signal comprising only annual variations at large spatial scales. Then, we consider a regional distribution of observations in Africa, and a larger number of spatial and temporal scales. We test the influence of an imperfect prior and discuss our results.

Geophysics-based method of locating a stationary earth object

DOEpatents

Daily, Michael R [Albuquerque, NM; Rohde, Steven B [Corrales, NM; Novak, James L [Albuquerque, NM

2008-05-20

A geophysics-based method for determining the position of a stationary earth object uses the periodic changes in the gravity vector of the earth caused by the sun- and moon-orbits. Because the local gravity field is highly irregular over a global scale, a model of local tidal accelerations can be compared to actual accelerometer measurements to determine the latitude and longitude of the stationary object.

New insights on intraplate volcanism in French Polynesia from wavelet analysis of GRACE, CHAMP, and sea surface data

NASA Astrophysics Data System (ADS)

Panet, I.; Chambodut, A.; Diament, M.; Holschneider, M.; Jamet, O.

2006-09-01

In this paper, we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry. We computed a refined gravity field in the south central Pacific based on the GRACE satellite GGM02S global gravity field and the KMS02 altimetric grid, and a magnetic anomaly field based on CHAMP data. The magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the Tuamotu region, which we interpret as evidence for crustal thickening. We interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution. We also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources. According to the gravity signature of the different chains as revealed by our analysis, various processes are at the origin of the volcanism in French Polynesia. As evidence, we show a large-scale anomaly over the Society Islands that we interpret as the gravity signature of a deeply anchored mantle plume. The gravity signature of the Cook-Austral chain indicates a complex origin which may involve deep processes. Finally, we discuss the particular location of the Marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field, or else related to the presence of the nearby Tuamotu plateau.

EIGEN-5C - the new GeoForschungsZentrum Potsdam / Groupe de Recherche de Geodesie Spatiale combined gravity field model

NASA Astrophysics Data System (ADS)

Foerste, C.; Flechtner, F.; Stubenvoll, R.; Rothacher, M.; Kusche, J.; Neumayer, H. K.; Biancale, R.; Lemoine, J.; Barthelmes, F.; Bruinsma, S.; Koenig, R.; Dahle, C.

2008-12-01

Global gravity field models play a fundamental role in geodesy and Earth sciences, ranging from practical purposes, like precise orbit determination, to applications in geosciences, like investigations of the density structure of the Earth's interior. In this presentation we report on the latest, recently released EIGEN-model, EIGEN-5C (EIGEN = European Improved Gravity model of the Earth by New techniques) and its associated satellite-only model EIGEN-5S. The global gravity field model EIGEN-5C is complete to degree and order 360 (corresponding to half-wavelength of 55 km) and was jointly elaborated by GFZ Potsdam and CNES/GRGS Toulouse. As its precursor EIGEN-GL04C (released in March 2006), this model is inferred from a combination of GRACE and LAGEOS satellite tracking data with surface gravity data, based on the accumulation of normal equations. However, this new model presents remarkable changes and improvements compared to its precursors. EIGEN-5C incorporates a further extended GRACE and LAGEOS data set, covering almost the entire GRACE period from mid 2002 to end of 2007, but also newly available gravity anomaly data sets for Europe and Australia. New processing features are the complete reprocessing of the GRACE and LAGEOS data using the recent RL04 standards and background models by GFZ (combined with the GRACE/LAGEOS 10-days time series derived at GRGS based on nearly identical standards and background models) and a further extension of the full normal equations (in contrast to block diagonal form) derived from terrestrial data to a maximum degree and order of 280 (which was restricted to 179 for EIGEN-GL04C). In particular, this presentation focuses on the inter-comparison of this latest EIGEN model with the recently presented EGM08 model, which was developed by the National Geospatial-Intelligence Agency (NGA) of the USA. The EIGEN-5C model and its associated satellite-only model EIGEN-5S are available for download at the ICGEM data base (International Center for Global Earth Models) at GFZ Potsdam via the following URL: http://icgem.gfz-potsdam.de/ICGEM/ potsdam.de/ICGEM/

Gravitational field of global monopole within the Eddington-inspired Born-Infeld theory of gravity

NASA Astrophysics Data System (ADS)

Lambaga, Reyhan D.; Ramadhan, Handhika S.

2018-06-01

Within the framework of the recent Eddington-inspired Born-Infeld (EiBI) theory we study gravitational field around an SO(3) global monopole. The solution also suffers from the deficit solid angle as in the Barriola-Vilenkin metric but shows a distinct feature that cannot be transformed away unless in the vanishing EiBI coupling constant, κ . When seen as a black hole eating up a global monopole, the corresponding Schwarzschild horizon is shrunk by κ . The deficit solid angle makes the space is globally not Euclidean, and to first order in κ (weak-field limit) the deflection angle of light is smaller than its Barriola-Vilenkin counterpart.

Preliminary Correlations of Gravity and Topography from Mars Global Surveyor

NASA Technical Reports Server (NTRS)

Zuber, M. T.; Tyler, G. L.; Smith, D. E.; Balmino, G. S.; Johnson, G. L.; Lemoine, F. G.; Neumann, G. A.; Phillips, R. J.; Sjogren, W. L.; Solomon, S. C.

1999-01-01

The Mars Global Surveyor (MGS) spacecraft is currently in a 400-km altitude polar mapping orbit and scheduled to begin global mapping of Mars in March of 1999. Doppler tracking data collected in this Gravity Calibration Orbit prior to the nominal mapping mission combined with observations from the MGS Science Phasing Orbit in Spring - Summer 1999 and the Viking and mariner 9 orbiters has led to preliminary high resolution gravity fields. Spherical harmonic expansions have been performed to degree and order 70 and are characterized by the first high spatial resolution coverage of high latitudes. Topographic mapping by the Mars Orbiter Laser Altimeter on MGS is providing measurements of the height of the martian surface with sub-meter vertical resolution and 5-30 m absolute accuracy. Data obtained during the circular mapping phase are expected to provide the first high resolution measurements of surface heights in the southern hemisphere. The combination of gravity and topography measurements provides information on the structure of the planetary interior, i.e. the rigidity and distribution of internal density. The observations can also be used to address the mechanisms of support of surface topography. Preliminary results of correlations of gravity and topography at long planetary wavelengths will be presented and the implications for internal structure will be addressed.

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.

Using the full tensor of GOCE gravity gradients for regional gravity field modelling

NASA Astrophysics Data System (ADS)

Lieb, Verena; Bouman, Johannes; Dettmering, Denise; Fuchs, Martin; Schmidt, Michael

2013-04-01

With its 3-axis gradiometer GOCE delivers 3-dimensional (3D) information of the Earth's gravity field. This essential advantage - e.g. compared with the 1D gravity field information from GRACE - can be used for research on the Earth's interior and for geophysical exploration. To benefit from this multidimensional measurement system, the combination of all 6 GOCE gradients and additionally the consistent combination with other gravity observations mean an innovative challenge for regional gravity field modelling. As the individual gravity gradients reflect the gravity field depending on different spatial directions, observation equations are formulated separately for each of these components. In our approach we use spherical localizing base functions to display the gravity field for specified regions. Therefore the series expansions based on Legendre polynomials have to be adopted to obtain mathematical expressions for the second derivatives of the gravitational potential which are observed by GOCE in the Cartesian Gradiometer Reference Frame (GRF). We (1) have to transform the equations from the spherical terrestrial into a Cartesian Local North-Oriented Reference Frame (LNOF), (2) to set up a 3x3 tensor of observation equations and (3) finally to rotate the tensor defined in the terrestrial LNOF into the GRF. Thus we ensure the use of the original non-rotated and unaffected GOCE measurements within the analysis procedure. As output from the synthesis procedure we then obtain the second derivatives of the gravitational potential for all combinations of the xyz Cartesian coordinates in the LNOF. Further the implementation of variance component estimation provides a flexible tool to diversify the influence of the input gradiometer observations. On the one hand the less accurate xy and yz measurements are nearly excluded by estimating large variance components. On the other hand the yy measurements, which show systematic errors increasing at high latitudes, could be manually down-weighted in the corresponding regions. We choose different test areas to compute regional gravity field models at mean GOCE altitudes for different spectral resolutions and varying relative weights for the observations. Further we compare the regional models with the static global GOCO03S model. Especially the flexible handling and combination of the 3D measurements promise a great benefit for geophysical applications from GOCE gravity gradients, as they contain information on radial as well as on lateral gravity changes.

Studying the Representation Accuracy of the Earth's Gravity Field in the Polar Regions Based on the Global Geopotential Models

NASA Astrophysics Data System (ADS)

Koneshov, V. N.; Nepoklonov, V. B.

2018-05-01

The development of studies on estimating the accuracy of the Earth's modern global gravity models in terms of the spherical harmonics of the geopotential in the problematic regions of the world is discussed. The comparative analysis of the results of reconstructing quasi-geoid heights and gravity anomalies from the different models is carried out for two polar regions selected within a radius of 1000 km from the North and South poles. The analysis covers nine recently developed models, including six high-resolution models and three lower order models, including the Russian GAOP2012 model. It is shown that the modern models determine the quasi-geoid heights and gravity anomalies in the polar regions with errors of 5 to 10 to a few dozen cm and from 3 to 5 to a few dozen mGal, respectively, depending on the resolution. The accuracy of the models in the Arctic is several times higher than in the Antarctic. This is associated with the peculiarities of gravity anomalies in every particular region and with the fact that the polar part of the Antarctic has been comparatively less explored by the gravity methods than the polar Arctic.

On the origin of Poincaré gauge gravity

NASA Astrophysics Data System (ADS)

Chkareuli, J. L.

2017-06-01

We argue that the origin of Poincaré gauge gravity (PGG) may be related to spontaneous violation of underlying spacetime symmetries involved and appearance of gauge fields as vector Goldstone bosons. In essence, we start with an arbitrary theory of some vector and fermion fields which possesses only global spacetime symmetries, such as Lorentz and translational invariance, in flat Minkowski space. The two vector field multiplets involved are assumed to belong, respectively, to the adjoint (Aμij) and vector (eμi) representations of the starting global Lorentz symmetry. We propose that these prototype vector fields are covariantly constrained, Aμij Aijμ = ±MA2 and eμi eiμ = ±Me2 , that causes a spontaneous violation of the accompanying global symmetries (MA,e are their presumed violation scales). It then follows that the only possible theory compatible with these length-preserving constraints is turned out to be the gauge invariant PGG, while the corresponding massless (pseudo)Goldstone modes are naturally collected in the emergent gauge fields of tetrads and spin-connections. In a minimal theory case being linear in a curvature we unavoidably come to the Einstein-Cartan theory. The extended theories with propagating spin-connection and tetrad modes are also considered and their possible unification with the Standard Model is briefly discussed.

The role of topography in geodetic gravity field modelling

NASA Technical Reports Server (NTRS)

Forsberg, R.; Sideris, M. G.

1989-01-01

Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the lowest harmonics. In practice, though, global effects need not be taken into account as such effects are included in the coefficients of the geopotential reference fields. On local scales, the short-wavelength gravity variations due to the topography may, in rugged terrain, be an order of magnitude larger than other effects. In such cases, explicit or implicit terrain reduction procedures are mandatory in order to obtain good prediction results. Such effects may be computed by space-domain integration or by fast Fourier transformation (FFT) methods. Numerical examples are given for areas of the Canadian Rockies. In principle, good knowledge of the topographic densities is required to produce the smoothest residual field. Densities may be determined from sample measurements or by gravimetric means, but both are somewhat troublesome methods in practice. The use of a standard density, e.g., 2.67 g/cu cm, may often yield satisfactory results and may be put within a consistent theoretical framework. The independence of density assumptions is the key point of the classical Molodensky approach to the geodetic boundary value problem. The Molodensky solutions take into account that land gravity field observations are done on a non-level surface. Molodensky's problem may be solved by integral expansions or more effective FFT methods, but the solution should not be intermixed with the use of terrain reductions. The methods are actually complimentary and may both be required in order to obtain the smoothest possible signal, least prone to aliasing and other effects coming from sparse data coverage, typical of rugged topography.

How is quantum information localized in gravity?

NASA Astrophysics Data System (ADS)

Donnelly, William; Giddings, Steven B.

2017-10-01

A notion of localization of information within quantum subsystems plays a key role in describing the physics of quantum systems, and in particular is a prerequisite for discussing important concepts such as entanglement and information transfer. While subsystems can be readily defined for finite quantum systems and in local quantum field theory, a corresponding definition for gravitational systems is significantly complicated by the apparent nonlocality arising due to gauge invariance, enforced by the constraints. A related question is whether "soft hair" encodes otherwise localized information, and the question of such localization also remains an important puzzle for proposals that gravity emerges from another structure such as a boundary field theory as in AdS/CFT. This paper describes different approaches to defining local subsystem structure, and shows that at least classically, perturbative gravity has localized subsystems based on a split structure, generalizing the split property of quantum field theory. This, and related arguments for QED, give simple explanations that in these theories there is localized information that is independent of fields outside a region, in particular so that there is no role for "soft hair" in encoding such information. Additional subtleties appear in quantum gravity. We argue that localized information exists in perturbative quantum gravity in the presence of global symmetries, but that nonperturbative dynamics is likely tied to a modification of such structure.

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.

Synoptic-scale variability of arctic gravity wave activity during summer and potential impacts on the high latitude middle atmosphere

NASA Astrophysics Data System (ADS)

Gerrard, Andrew John

Although the role of gravity waves in the global atmospheric circulation is generally understood, discussion of synoptic gravity wave activity, especially pertaining to high latitude summer environments, is lacking in the literature. Tropospherically generated gravity waves greatly contribute to the zonal drag necessary to induce meridional outflow and subsequent upwelling observed in the adiabatically cooled summer mesosphere, ultimately resulting in an environment conducive to mesospheric cloud formation. However, the very gravity wave activity responsible for this induced cooling is also believed to be a major source of variability on mesospheric clouds over shorter time scales, and this topic should be of considerable interest if such clouds are to be used as tracers of the global climate. It is therefore the purpose of this thesis to explore high latitude synoptic gravity wave activity and ultimately seek an understanding of the associated influence on overlaying summer mesospheric clouds. Another goal is to better understand and account for potential variability in high latitude middle and upper atmospheric measurements that can be directly associated with "weather conditions" at lower altitudes. These endeavors are addressed through Rayleigh/aerosol lidar data obtained from the ARCtic LIdar TEchnology (ARCLITE) facility located at Sondrestrom, Greenland (67°N, 310°E), global tropospheric and stratospheric analyses and forecasts, and the Gravity-wave Regional Or Global RAy Tracer (GROGRAT) model. In this study we are able to show that (a) the upper stratospheric gravity wave strength and the brightness of overlaying mesospheric clouds, as measured by representative field proxies, are negatively correlated over time scales of less than a day, (b) such upper stratospheric gravity wave variability is inversely related to mesospheric cloud variability on time scales of ˜1 to 4 hours, (c) gravity wave hindcasts faithfully reproduce experimental lidar observations taken over the month of August 1996, (d) the observed upper stratospheric gravity wave activity is shown to originate from regionalized, non-orographic sources in the troposphere, (e) such gravity wave activity can propagate through the middle atmosphere, potentially impacting overlaying mesospheric clouds, and (f) the forecasting of such upper stratospheric gravity wave activity, and therefore the corresponding mesospheric cloud activity, is feasible. In conclusion, the results herein provide additional evidence of gravity wave influence on mesospheric clouds, a step towards the forecasting of regional gravity wave activity, and ultimately a better understanding of synoptic gravity wave activity at high latitudes.

Satellite gravity gradient grids for geophysics

PubMed Central

Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

2016-01-01

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth’s mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets. PMID:26864314

KSC-2011-6804

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- NASA's Gravity Recovery and Interior Laboratory mission is readied for liftoff aboard a United Launch Alliance Delta II Heavy rocket from Space Launch Complex 17B on Cape Canaveral Air Force Station. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA

KSC-2011-6871

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – The United Launch Alliance Delta II Heavy rocket lifted off at 9:08 a.m. EDT Sept. 10 from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6869

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Surrounded by an early morning sky, the United Launch Alliance Delta II Heavy rocket sits on Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida as it waits to launch NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6807

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- Media representatives prepare to photograph the launch of NASA's Gravity Recovery and Interior Laboratory mission at Press Site 1 near Space Launch Complex 17B on Cape Canaveral Air Force Station. Liftoff aboard a United Launch Alliance Delta II Heavy rocket is scheduled for 8:37:06 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6812

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- The countdown to launch of the United Launch Alliance Delta II Heavy rocket for NASA's Gravity Recovery and Interior Laboratory mission nears T-0 at Space Launch Complex 17B on Cape Canaveral Air Force Station. Liftoff is scheduled for 8:37:06 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6802

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- Launch preparations are under way as dawn breaks at Space Launch Complex 17B on Cape Canaveral Air Force Station for NASA's Gravity Recovery and Interior Laboratory mission aboard a United Launch Alliance Delta II Heavy rocket. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA

KSC-2011-6867

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Surrounded by an early morning sky, the United Launch Alliance Delta II Heavy rocket sits on Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida as it waits to launch NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6868

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Bathed in light against an early morning sky, the United Launch Alliance Delta II Heavy rocket sits on Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida as it waits to launch NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6870

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – A U.S. Air Force helicopter flies overhead as the United Launch Alliance Delta II Heavy rocket sits on Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida waiting to launch NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6805

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- The countdown to launch of the United Launch Alliance Delta II Heavy rocket for NASA's Gravity Recovery and Interior Laboratory mission is winding down at Space Launch Complex 17B on Cape Canaveral Air Force Station. Liftoff is scheduled for 8:37:06 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

Development of a network RTK positioning and gravity-surveying application with gravity correction using a smartphone.

PubMed

Kim, Jinsoo; Lee, Youngcheol; Cha, Sungyeoul; Choi, Chuluong; Lee, Seongkyu

2013-07-12

This paper proposes a smartphone-based network real-time kinematic (RTK) positioning and gravity-surveying application (app) that allows semi-real-time measurements using the built-in Bluetooth features of the smartphone and a third-generation or long-term evolution wireless device. The app was implemented on a single smartphone by integrating a global navigation satellite system (GNSS) controller, a laptop, and a field-note writing tool. The observation devices (i.e., a GNSS receiver and relative gravimeter) functioned independently of this system. The app included a gravity module, which converted the measured relative gravity reading into an absolute gravity value according to tides; meter height; instrument drift correction; and network adjustments. The semi-real-time features of this app allowed data to be shared easily with other researchers. Moreover, the proposed smartphone-based gravity-survey app was easily adaptable to various locations and rough terrain due to its compact size.

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.

Global and Local Gravity Field Models of the Moon Using GRAIL Primary and Extended Mission Data

NASA Technical Reports Server (NTRS)

Goossens, Sander; Lemoine, Frank G.; Sabaka, Terence J.; Nicholas, Joseph B.; Mazarico, Erwan; Rowlands, David D.; Loomis, Bryant D.; Chinn, Douglas S.; Neumann, Gregory A.; Smith, David E.;

Venus - Global gravity and topography

NASA Technical Reports Server (NTRS)

Mcnamee, J. B.; Borderies, N. J.; Sjogren, W. L.

1993-01-01

A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisonsbetween this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.

The gravity field of Mars: results from Mars Global Surveyor.

PubMed

Smith, D E; Sjogren, W L; Tyler, G L; Balmino, G; Lemoine, F G; Konopliv, A S

1999-10-01

Observations of the gravity field of Mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes. The rough, elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near-isostatic compensation, whereas the smooth, low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south. The northern hemisphere shows evidence for buried impact basins, although none large enough to explain the hemispheric elevation difference. The gravitational potential signature of Tharsis is approximately axisymmetric and contains the Tharsis Montes but not the Olympus Mons or Alba Patera volcanoes. The gravity signature of Valles Marineris extends into Chryse and provides an estimate of material removed by early fluvial activity.

The 5'×5' global geoid model GGM2016

NASA Astrophysics Data System (ADS)

Shen, WenBin; Han, Jiancheng

2016-04-01

We provide an updated 5'×5' global geoid model GGM2016, which is determined based on the shallow layer method (Shen 2006). We choose an inner surface S below the EGM2008 geoid, and the layer bounded by the inner surface S and the Earth's geographical surface E is referred to as the shallow layer. The Earth's geographical surface E is determined by the digital topographic model DTM2006.0 combining with the DNSC2008 mean sea surface. We determine the 3D shallow layer model (SLM) using the refined crust density model CRUST1.0-5min, which is an improved 5'×5' density model of the CRUST1.0 with taking into account the corrections of the areas covered by ice sheets and the land-ocean crossing regions. Based on the SLM and the gravity field EGM2008 defined outside the Earth's geographical surface E, we determine the gravity field EGM2008S defined in the region outside the inner surface S, extending the gravity field's definition domain from the domain outside E to the domain outside S. Based on the geodetic equation W(P)=W0, where W0 is the geopotential constant on the geoid, we determine a 5'×5' global geoid model GGM2016, which provides both the 5'×5' grid values and spherical harmonic coefficient expressions. Comparisons show that the GGM2016 fits the globally available GPS/leveling points better than the EGM2008 geoid. This study is supported by National 973 Project China (grant Nos. 2013CB733301 and 2013CB733305), NSFC (grant Nos. 41174011, 41210006, 41429401, 41128003, 41021061).

Gravity field error analysis: Applications of GPS receivers and gradiometers on low orbiting platforms

NASA Technical Reports Server (NTRS)

Schrama, E.

1990-01-01

The concept of a Global Positioning System (GPS) receiver as a tracking facility and a gradiometer as a separate instrument on a low orbiting platform offers a unique tool to map the Earth's gravitational field with unprecedented accuracies. The former technique allows determination of the spacecraft's ephemeris at any epoch to within 3 to 10 cm, the latter permits the measurement of the tensor of second order derivatives of the gravity field to within 0.01 to 0.0001 Eotvos units depending on the type of gradiometer. First, a variety of error sources in gradiometry where emphasis is placed on the rotational problem pursuing as well a static as a dynamic approach is described. Next, an analytical technique is described and applied for an error analysis of gravity field parameters from gradiometer and GPS observation types. Results are discussed for various configurations proposed on Topex/Poseidon, Gravity Probe-B, and Aristoteles, indicating that GPS only solutions may be computed up to degree and order 35, 55, and 85 respectively, whereas a combined GPS/gradiometer experiment on Aristoteles may result in an acceptable solution up to degree and order 240.

Estimating the Earth's geometry, rotation and gravity field using a multi-satellite SLR solution

NASA Astrophysics Data System (ADS)

Stefka, V.; Blossfeld, M.; Mueller, H.; Gerstl, M.; Panafidina, N.

2012-12-01

Satellite Laser Ranging (SLR) is the unique technique to determine station coordinates, Earth Orientation Parameter (EOP) and Stokes coefficients of the Earth's gravity field in one common adjustment. These parameters form the so called "three pillars" (Plag & Pearlman, 2009) of the Global Geodetic Observing System (GGOS). In its function as official analysis center of the International Laser Ranging Service (ILRS), DGFI is developing and maintaining software to process SLR observations called "DGFI Orbit and Geodetic parameter estimation Software" (DOGS). The software is used to analyze SLR observations and to compute multi-satellite solutions. To take benefit of different orbit performances (e.g. inclination and altitude), a solution using ten different spherical satellites (ETALON1/2, LAGEOS1/2, STELLA, STARLETTE, AJISAI, LARETS, LARES, BLITS) covering the period of 12 years of observations is computed. The satellites are relatively weighted using a variance component estimation (VCE). The obtained weights are analyzed w.r.t. the potential of the satellite to monitor changes in the Earths geometry, rotation and gravity field. The estimated parameters (station coordinates and EOP) are validated w.r.t. official time series of the IERS. The Stokes coefficients are compared to recent gravity field solutions.

Estimating the Earth's gravity field using a multi-satellite SLR solution

NASA Astrophysics Data System (ADS)

Bloßfeld, Mathis; Stefka, Vojtech; Müller, Horst; Gerstl, Michael

2013-04-01

Satellite Laser Ranging (SLR) is the unique technique to determine station coordinates, Earth Orientation Parameter (EOP) and Stokes coefficients of the Earth's gravity field in one common adjustment. These parameters form the so called "three pillars" (Plag & Pearlman, 2009) of the Global Geodetic Observing System (GGOS). In its function as official analysis center of the International Laser Ranging Service (ILRS), DGFI is developing and maintaining software to process SLR observations called "DGFI Orbit and Geodetic parameter estimation Software" (DOGS). The software is used to analyze SLR observations and to compute multi-satellite solutions. To take benefit of different orbit performances (e.g. inclination and altitude), a solution using ten different spherical satellites (ETALON1/2, LAGEOS1/2, STELLA, STARLETTE, AJISAI, LARETS, LARES, BLITS) covering 12 years of observations is computed. The satellites are relatively weighted using a variance component estimation (VCE). The obtained weights are analyzed w.r.t. the potential of the satellite to monitor changes in the Earths geometry, rotation and gravity field. The estimated parameters (station coordinates and EOP) are validated w.r.t. official time series of the IERS. The obtained Stokes coefficients are compared to recent gravity field solutions and discussed in detail.

Consolidated science and user needs for a sustained satellite gravity observing system

NASA Astrophysics Data System (ADS)

Pail, R.

2015-12-01

In an internationally coordinated initiative among the main user communities of gravity field products the science requirements for a future gravity field mission constellation (beyond GRACE-FO) have been reviewed and defined. This activity was realized as a joint initiative of the IAG (International Association of Geodesy) Sub-Commissions 2.3 and 2.6, the GGOS (Global Geodetic Observing System) Working Group on Satellite Missions, and the IUGG (International Union of Geodesy and Geophysics). After about one year of preparation, in a user workshop that was held in September 2014 consensus among the user communities of hydrology, ocean, cryosphere, solid Earth and atmosphere on consolidated science requirements could be achieved.The consolidation of the user requirements became necessary, because several future gravity field studies have resulted in quite different performance numbers as a target for a future gravity mission (2025+). Based on limited number of mission scenarios which took also technical feasibility into account, a consolidated view on the science requirements among the international user communities was derived, research fields that could not be tackled by current gravity missions have been identified, and the added value (qualitatively and quantitatively) of these scenarios with respect to science return has been evaluated. The resulting document shall form the basis for further programmatic and technological developments. In this contribution, the main results of this initiative will be presented. An overview of the specific requirements of the individual user groups, the consensus on consolidated science and user needs as well as the new research fields that have been identified during this process will be discussed.

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.

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.

Structure and Dynamics of the Polar Regions of Mars from MGS Topography and Gravity

NASA Technical Reports Server (NTRS)

Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Lemoine, Frank G.

2000-01-01

The Mars Global Surveyor (MGS) spacecraft has been engaged in systematic mapping of Mars since insertion into Mars orbit in September, 1997. The objectives of the MGS mission are to globally map Mars as well as to quantify seasonal changes on the planet. MGS geophysical/geodetic observations of topography from the Mars Orbiter Laser Altimeter (MOLA) and gravity from the Radio Science investigation are providing significant new insights on both static and time-varying aspects of the polar regions of Mars. These observations have implications for polar processes on diurnal seasonal and climatic timescales. Thus far, MOLA has collected over 300 million precise measurements of Martian topography and cloud heights. The instrument has also provided measurements of the width of the backscattered optical pulse and of the 1064 nm reflectivity of the Martian surface and atmosphere. The along-track resolution of MOLA ground shots is approx. 300 m and the across-track spacing in the polar regions is a maximum of about four kilometers. The vertical accuracy of the topography is determined by the precision recovery of spacecraft orbits from the Radio Science investigation, which includes MOLA altimetry in the form of crossovers. This accuracy is currently approx. one meter. The gravity field is derived from X-band Doppler tracking with typical accuracy of 0.03 to 0.05 mm/s averaged over ten seconds. Current Mars gravity fields are to approximately degree and order 80 but are interpretable to the approximate degree and order 60 (spatial resolution < 180 km), which represents an estimate of the approximate coefficient limit of a field that can be produced without a power law constraint on the gravitational field inversion, which is commonly imposed for solution stability. Additional information is contained in the original extended abstract.

Towards consolidated science requirements for a next generation gravity field mission

NASA Astrophysics Data System (ADS)

Pail, R.; Braitenberg, C. F.; Eicker, A.; Floberghagen, R.; Forsberg, R.; Haagmans, R.; Horwath, M.; Kusche, J.; Labrecque, J. L.; Panet, I.; Rolstad Denby, C.; Schröter, J.; Wouters, B.

2013-12-01

As a joint initiative of the IAG (International Association of Geodesy) Sub-Commissions 2.3 and 2.6, the GGOS (Global Geodetic Observing System) Working Group on Satellite Missions, and the IUGG (International Union of Geodesy and Geophysics), we target on the consolidation of science requirements for a next generation gravity field mission (beyond GRACE-FO). Several future gravity field studies have resulted in quite different performance numbers as a target for a future gravity mission (2025+), and a consolidation within the different user groups is required, under the boundary condition of the technical feasibility of the mission concepts and before the background of double- and multi-pair formations. Therefore, this initiative shall concentrate on the consolidation of the science requirements, and should result in a document that can be used as a solid basis for further programmatic and technological developments. Based on limited number of realistic mission scenarios, a consolidated view on the science requirements within the international user communities shall be derived, research fields that could not be tackled by current gravity missions shall be identified, and the added value (qualitatively and quantitatively) of these scenarios with respect to science return shall be evaluated. The final science requirements shall be agreed upon during a workshop which is planned for the second half of 2014. In this contribution, the mission scenarios will be discussed and first results of the consolidation process will be presented.

Relevancy of mathematical support for geophysics determinations

NASA Astrophysics Data System (ADS)

Vîlceanu, Clara-Beatrice; Grecea, Carmen; Muşat, Cosmin

2017-07-01

The importance of gravity in geodesy is recognized even since the 16th century. Starting with the experiments and theories of Galileo Galilei, the gravity and its global variation has continued to play an important role for those preoccupied with measuring the Earth's surface. The benefits of Physical Geodesy (studying the Earth's gravitational field) are extended to other disciplines such as Seismology, Oceanography, Volcanology etc. The aim of the present paper consists in highlighting the connection between gravity and the geodesist's profession. This was possible only throughout an extended study of Physical Geodesy realized with the support given by the International Gravity Office, Military Topographic Direction, The National Centre of Cartography and different specialists from these domains. Gravity represents the main factor which influences the Earth's shape and dimensions and when it comes to geodetic measurements, the gravity and its influence upon the measurements realized by specialists in geodesy has to be considered.

The GISS global climate-middle atmosphere model. II - Model variability due to interactions between planetary waves, the mean circulation and gravity wave drag

NASA Technical Reports Server (NTRS)

Rind, D.; Suozzo, R.; Balachandran, N. K.

1988-01-01

The variability which arises in the GISS Global Climate-Middle Atmosphere Model on two time scales is reviewed: interannual standard deviations, derived from the five-year control run, and intraseasonal variability as exemplified by statospheric warnings. The model's extratropical variability for both mean fields and eddy statistics appears reasonable when compared with observations, while the tropical wind variability near the stratopause may be excessive possibly, due to inertial oscillations. Both wave 1 and wave 2 warmings develop, with connections to tropospheric forcing. Variability on both time scales results from a complex set of interactions among planetary waves, the mean circulation, and gravity wave drag. Specific examples of these interactions are presented, which imply that variability in gravity wave forcing and drag may be an important component of the variability of the middle atmosphere.

Expected precision of Europa Clipper gravity measurements

NASA Astrophysics Data System (ADS)

Verma, Ashok K.; Margot, Jean-Luc

2018-11-01

The primary gravity science objective of NASA's Clipper mission to Europa is to confirm the presence or absence of a global subsurface ocean beneath Europa's Icy crust. Gravity field measurements obtained with a radio science investigation can reveal much about Europa's interior structure. Here, we conduct extensive simulations of the radio science measurements with the anticipated spacecraft trajectory and attitude (17F12v2) and assets on the spacecraft and the ground, including antenna orientations and beam patterns, transmitter characteristics, and receiver noise figures. In addition to two-way Doppler measurements, we also include radar altimeter crossover range measurements. We concentrate on ± 2 h intervals centered on the closest approach of each of the 46 flybys. Our covariance analyses reveal the precision with which the tidal Love number k2, second-degree gravity coefficients Cbar20 and Cbar22 , and higher-order gravity coefficients can be determined. The results depend on the Deep Space Network (DSN) assets that are deployed to track the spacecraft. We find that some DSN allocations are sufficient to conclusively confirm the presence or absence of a global ocean. Given adequate crossover range performance, it is also possible to evaluate whether the ice shell is hydrostatic.

Global Modeling of Spur Formation in Spiral Galaxies

NASA Astrophysics Data System (ADS)

Shetty, Rahul; Ostriker, Eve C.

2006-08-01

We investigate the formation of substructure in spiral galaxies using global MHD simulations, including gas self-gravity. Local modeling by Kim & Ostriker previously showed that self-gravity and magnetic fields cause rapid growth of overdensities in spiral arms; differential compression of gas flowing through the arms then results in the formation of sheared structures in the interarms. These sheared structures resemble features described as spurs or feathers in optical and IR observations of many spiral galaxies. Global modeling extends previous local models by including the full effects of curvilinear coordinates, a realistic log-spiral perturbation, self-gravitational contribution from five radial wavelengths of the spiral shock, and variation of density and epicyclic frequency with radius. We show that with realistic Toomre Q-values self-gravity and galactic differential rotation produce filamentary gaseous structures with kiloparsec-scale separations, regardless of the strength-or even presence-of a stellar spiral potential. However, a sufficiently strong spiral potential is required to produce true spurs, consisting of interarm structures emerging from gas concentrations in the main spiral arms. In models where Q is initially constant, filaments due to interarm self-gravity grow mainly in the outer regions, whereas true arm spurs grow only in the inner regions. For models with Q~R, outer regions are intrinsically more stable, so background interarm filaments do not grow, but arm spurs can develop if the spiral potential is strong. Unlike independently growing background filaments, the orientation of arm spurs depends on galactic location. Inside corotation, spurs emanate outward, on the convex side of the arm; outside corotation, spurs grow inward, on the concave side of the arm. Based on orientation and the relation to arm clumps, it is possible to distinguish true spurs that originate as instabilities in the arms from independently growing background filaments. We measure spur spacings of ~3-5 times the Jeans length in the arm and arm clump masses of ~107 Msolar. Finally, we have also studied models without self-gravity, finding that magnetic fields suppress a purely hydrodynamic instability recently proposed by Wada & Koda as a means of growing interarm spurs and feathers. Our models also suggest that magnetic fields are important in preserving grand-design spiral structure when gas in the arms fragments via self-gravity into GMCs.

High-Resolution Gravity and Time-Varying Gravity Field Recovery using GRACE and CHAMP

NASA Technical Reports Server (NTRS)

Shum, C. K.

2002-01-01

This progress report summarizes the research work conducted under NASA's Solid Earth and Natural Hazards Program 1998 (SENH98) entitled High Resolution Gravity and Time Varying Gravity Field Recovery Using GRACE (Gravity Recovery and Climate Experiment) and CHAMP (Challenging Mini-satellite Package for Geophysical Research and Applications), which included a no-cost extension time period. The investigation has conducted pilot studies to use the simulated GRACE and CHAMP data and other in situ and space geodetic observable, satellite altimeter data, and ocean mass variation data to study the dynamic processes of the Earth which affect climate change. Results from this investigation include: (1) a new method to use the energy approach for expressing gravity mission data as in situ measurements with the possibility to enhance the spatial resolution of the gravity signal; (2) the method was tested using CHAMP and validated with the development of a mean gravity field model using CHAMP data, (3) elaborate simulation to quantify errors of tides and atmosphere and to recover hydrological and oceanic signals using GRACE, results show that there are significant aliasing effect and errors being amplified in the GRACE resonant geopotential and it is not trivial to remove these errors, and (4) quantification of oceanic and ice sheet mass changes in a geophysical constraint study to assess their contributions to global sea level change, while the results improved significant over the use of previous studies using only the SLR (Satellite Laser Ranging)-determined zonal gravity change data, the constraint could be further improved with additional information on mantle rheology, PGR (Post-Glacial Rebound) and ice loading history. A list of relevant presentations and publications is attached, along with a summary of the SENH investigation generated in 2000.

Gravitational and magnetic field variations synergize to cause subtle variations in the global transcriptional state of Arabidopsis in vitro callus cultures

PubMed Central

2012-01-01

Background Biological systems respond to changes in both the Earth's magnetic and gravitational fields, but as experiments in space are expensive and infrequent, Earth-based simulation techniques are required. A high gradient magnetic field can be used to levitate biological material, thereby simulating microgravity and can also create environments with a reduced or an enhanced level of gravity (g), although special attention should be paid to the possible effects of the magnetic field (B) itself. Results Using diamagnetic levitation, we exposed Arabidopsis thaliana in vitro callus cultures to five environments with different levels of effective gravity and magnetic field strengths. The environments included levitation, i.e. simulated μg* (close to 0 g* at B = 10.1 T), intermediate g* (0.1 g* at B = 14.7 T) and enhanced gravity levels (1.9 g* at B = 14.7 T and 2 g* at B = 10.1 T) plus an internal 1 g* control (B = 16.5 T). The asterisk denotes the presence of the background magnetic field, as opposed to the effective gravity environments in the absence of an applied magnetic field, created using a Random Position Machine (simulated μg) and a Large Diameter Centrifuge (2 g). Microarray analysis indicates that changes in the overall gene expression of cultured cells exposed to these unusual environments barely reach significance using an FDR algorithm. However, it was found that gravitational and magnetic fields produce synergistic variations in the steady state of the transcriptional profile of plants. Transcriptomic results confirm that high gradient magnetic fields (i.e. to create μg* and 2 g* conditions) have a significant effect, mainly on structural, abiotic stress genes and secondary metabolism genes, but these subtle gravitational effects are only observable using clustering methodologies. Conclusions A detailed microarray dataset analysis, based on clustering of similarly expressed genes (GEDI software), can detect underlying global-scale responses, which cannot be detected by means of individual gene expression techniques using raw or corrected p values (FDR). A subtle, but consistent, genome-scale response to hypogravity environments was found, which was opposite to the response in a hypergravity environment. PMID:22435851

Emergence of a classical Universe from quantum gravity and cosmology.

PubMed

Kiefer, Claus

2012-09-28

I describe how we can understand the classical appearance of our world from a universal quantum theory. The essential ingredient is the process of decoherence. I start with a general discussion in ordinary quantum theory and then turn to quantum gravity and quantum cosmology. There is a whole hierarchy of classicality from the global gravitational field to the fluctuations in the cosmic microwave background, which serve as the seeds for the structure in the Universe.

Computer Programs to Display and Modify Data in Geographic Coordinates and Methods to Transfer Positions to and from Maps, with Applications to Gravity Data Processing, Global Positioning Systems, and 30-Meter Digital Elevation Models

USGS Publications Warehouse

Plouff, Donald

1998-01-01

Computer programs were written in the Fortran language to process and display gravity data with locations expressed in geographic coordinates. The programs and associated processes have been tested for gravity data in an area of about 125,000 square kilometers in northwest Nevada, southeast Oregon, and northeast California. This report discusses the geographic aspects of data processing. Utilization of the programs begins with application of a template (printed in PostScript format) to transfer locations obtained with Global Positioning Systems to and from field maps and includes a 5-digit geographic-based map naming convention for field maps. Computer programs, with source codes that can be copied, are used to display data values (printed in PostScript format) and data coverage, insert data into files, extract data from files, shift locations, test for redundancy, and organize data by map quadrangles. It is suggested that 30-meter Digital Elevation Models needed for gravity terrain corrections and other applications should be accessed in a file search by using the USGS 7.5-minute map name as a file name, for example, file '40117_B8.DEM' contains elevation data for the map with a southeast corner at lat 40? 07' 30' N. and lon 117? 52' 30' W.

Internal gravity wave contributions to global sea surface variability

NASA Astrophysics Data System (ADS)

Savage, A.; Arbic, B. K.; Richman, J. G.; Shriver, J. F.; Buijsman, M. C.; Zamudio, L.; Wallcraft, A. J.; Sharma, H.

2016-02-01

High-resolution (1/12th and 1/25th degree) 41-layer simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea-surface height (SSH). The HYCOM output has been separated into steric, non-steric, and total sea-surface height and the maps display variance in subtidal, tidal, and supertidal bands. Two of the global maps are of particular interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) wide-swath satellite altimeter mission; (1) a map of the nonstationary tidal signal (estimated after removing the stationary tidal signal via harmonic analysis), and (2) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum. Both of these maps display signals of order 1 cm2, the target accuracy for the SWOT mission. Therefore, both non-stationary internal tides and non-tidal internal gravity waves are likely to be important sources of "noise" that must be accurately removed before examination of lower-frequency phenomena can take place.

Effect of the Earth's inner structure on the gravity in definitions of height systems

NASA Astrophysics Data System (ADS)

Tenzer, Robert; Foroughi, Ismael; Pitoňák, Martin; Šprlák, Michal

2017-04-01

In context of the vertical datum unification, the geoid-to-quasi-geoid separation has been of significant interest in recent years, because most of existing local vertical datums are realized in the system of either normal or orthometric heights. Nevertheless, the normal-orthometric heights are still used in many other countries where the normal gravity values along leveling lines were adopted instead of the observed gravity. Whereas the conversion between the orthometric and normal heights is defined by means of the mean gravity disturbances (i.e. differences between the mean values of the actual and normal gravity) along the plumbline within the topography, differences between the normal and normal-orthometric heights can be described by means of the surface gravity disturbances. Since the normal gravity field does not reflect the topographic masses and actual mass density distribution inside the Earth, the definition of gravity represents a principal aspect for a realization of particular vertical datum. To address this issue in this study, we investigate effects of the Earth's inner density structure on the surface and mean gravity disturbances, and discuss their impact on the vertical datum realization. These two gravity field quantities are computed globally with a spectral resolution complete to a spherical harmonic degree 2160 using the global gravity, terrain, ice-thickness, inland bathymetry and crustal structure models. Our results reveal that both, the surface and mean gravity disturbances mostly comprise the gravitational signal of topography and masses distributed below the geoid surface. Moreover, in polar areas, a significant contribution comes from large glaciers. In contrast, the contributions of anomalous density distribution within the topography attributed to major lakes, sediments and bedrock density variations are much less pronounced. We also demonstrate that the mean gravity disturbances within the topography are significantly modified compared to the corresponding surface values mainly due to topographic elevation and terrain geometry as well as the presence of large glaciers in polar regions. Changes of the vertical gravity gradient within the topography attributed to the masses distributed below the geoid (dominated mainly by the isostatic signature and the long-wavelength gravitational signature of deep mantle density heterogeneities) are, on the other hand, relatively small. Despite differences between the normal and normal-orthometric heights could directly be assessed from the surface gravity disturbances only when taken along leveling lines with information about the spirit leveling height differences, our results indicate that differences between these two height systems can be significant.

Development of a Network RTK Positioning and Gravity-Surveying Application with Gravity Correction Using a Smartphone

PubMed Central

Kim, Jinsoo; Lee, Youngcheol; Cha, Sungyeoul; Choi, Chuluong; Lee, Seongkyu

2013-01-01

This paper proposes a smartphone-based network real-time kinematic (RTK) positioning and gravity-surveying application (app) that allows semi-real-time measurements using the built-in Bluetooth features of the smartphone and a third-generation or long-term evolution wireless device. The app was implemented on a single smartphone by integrating a global navigation satellite system (GNSS) controller, a laptop, and a field-note writing tool. The observation devices (i.e., a GNSS receiver and relative gravimeter) functioned independently of this system. The app included a gravity module, which converted the measured relative gravity reading into an absolute gravity value according to tides; meter height; instrument drift correction; and network adjustments. The semi-real-time features of this app allowed data to be shared easily with other researchers. Moreover, the proposed smartphone-based gravity-survey app was easily adaptable to various locations and rough terrain due to its compact size. PMID:23857258

The New Zealand gravimetric quasigeoid model 2017 that incorporates nationwide airborne gravimetry

NASA Astrophysics Data System (ADS)

McCubbine, J. C.; Amos, M. J.; Tontini, F. C.; Smith, E.; Winefied, R.; Stagpoole, V.; Featherstone, W. E.

2017-12-01

A one arc-minute resolution gravimetric quasigeoid model has been computed for New Zealand, covering the region 25°S -60°S and 160°E -170°W . It was calculated by Wong and Gore modified Stokes integration using the remove-compute-restore technique with the EIGEN-6C4 global gravity model as the reference field. The gridded gravity data used for the computation consisted of 40,677 land gravity observations, satellite altimetry-derived marine gravity anomalies, historical shipborne marine gravity observations and, importantly, approximately one million new airborne gravity observations. The airborne data were collected with the specific intention of reinforcing the shortcomings of the existing data in areas of rough topography inaccessible to land gravimetry and in coastal areas where shipborne gravimetry cannot be collected and altimeter-derived gravity anomalies are generally poor. The new quasigeoid has a nominal precision of ± 48 mm on comparison with GPS-levelling data, which is approximately 14 mm less than its predecessor NZGeoid09.

Global stability of self-gravitating discs in modified gravity

NASA Astrophysics Data System (ADS)

Ghafourian, Neda; Roshan, Mahmood

2017-07-01

Using N-body simulations, we study the global stability of a self-gravitating disc in the context of modified gravity (MOG). This theory is a relativistic scalar-tensor-vector theory of gravity and it is presented to address the dark matter problem. In the weak field limit, MOG possesses two free parameters α and μ0, which have already been determined using the rotation curve data of spiral galaxies. The evolution of a stellar self-gravitating disc and, more specifically, the bar instability in MOG are investigated and compared to a Newtonian case. Our models have exponential and Mestel-like surface densities as Σ ∝ exp (-r/h) and Σ ∝ 1/r. It is found that, surprisingly, the discs are more stable against the bar mode in MOG than in Newtonian gravity. In other words, the bar growth rate is effectively slower than the Newtonian discs. Also, we show that both free parameters (I.e. α and μ0) have stabilizing effects. In other words, an increase in these parameters will decrease the bar growth rate.

N=2 supersymmetry in two-dimensional dilaton gravity

NASA Astrophysics Data System (ADS)

Nelson, William M.; Park, Youngchul

1993-11-01

Actions for D=2, N=2 supergravity coupled to a scalar field are calculated, and it is shown that the most general power-counting renormalizable dilaton gravity action has an N=2 locally supersymmetric extension. The presence of chiral terms in the action leads one to hope that nonrenormalization theorems similar to those in global SUSY will apply; this would eliminate some of the renormalization ambiguities which plague ordinary bosonic (and N=1) dilaton gravity. To investigate this, the model is studied in the superconformal gauge, where it is found that one chiral term becomes nonchiral, so that only one term is safe from renormalization.

Topographic Change of the Dichotomy Boundary Suggested by Crustal Inversion

NASA Technical Reports Server (NTRS)

Neumann, G. A.

2004-01-01

Linear negative gravity anomalies in Acidalia Planitia along the eastern edge of Tempe Terra and along the northern edge of Arabia Terra have been noted in Mars Global Surveyor gravity fields. Once proposed to represent buried fluvial channels, it is now believed that these gravity troughs mainly arise from partial compensation of the hemispheric dichotomy topographic scarp. A recent inversion for crustal structure finds that mantle compensation of the scarp is offset from the present-day topographic expression of the dichotomy boundary. The offset suggests that erosion or other forms of mass wasting occurred after lithosphere thickened and no longer accomodated topographic change through viscous relaxation.

Normal gravity field in relativistic geodesy

NASA Astrophysics Data System (ADS)

Kopeikin, Sergei; Vlasov, Igor; Han, Wen-Biao

2018-02-01

Modern geodesy is subject to a dramatic change from the Newtonian paradigm to Einstein's theory of general relativity. This is motivated by the ongoing advance in development of quantum sensors for applications in geodesy including quantum gravimeters and gradientometers, atomic clocks and fiber optics for making ultra-precise measurements of the geoid and multipolar structure of the Earth's gravitational field. At the same time, very long baseline interferometry, satellite laser ranging, and global navigation satellite systems have achieved an unprecedented level of accuracy in measuring 3-d coordinates of the reference points of the International Terrestrial Reference Frame and the world height system. The main geodetic reference standard to which gravimetric measurements of the of Earth's gravitational field are referred is a normal gravity field represented in the Newtonian gravity by the field of a uniformly rotating, homogeneous Maclaurin ellipsoid of which mass and quadrupole momentum are equal to the total mass and (tide-free) quadrupole moment of Earth's gravitational field. The present paper extends the concept of the normal gravity field from the Newtonian theory to the realm of general relativity. We focus our attention on the calculation of the post-Newtonian approximation of the normal field that is sufficient for current and near-future practical applications. We show that in general relativity the level surface of homogeneous and uniformly rotating fluid is no longer described by the Maclaurin ellipsoid in the most general case but represents an axisymmetric spheroid of the fourth order with respect to the geodetic Cartesian coordinates. At the same time, admitting a post-Newtonian inhomogeneity of the mass density in the form of concentric elliptical shells allows one to preserve the level surface of the fluid as an exact ellipsoid of rotation. We parametrize the mass density distribution and the level surface with two parameters which are intrinsically connected to the existence of the residual gauge freedom, and derive the post-Newtonian normal gravity field of the rotating spheroid both inside and outside of the rotating fluid body. The normal gravity field is given, similarly to the Newtonian gravity, in a closed form by a finite number of the ellipsoidal harmonics. We employ transformation from the ellipsoidal to spherical coordinates to deduce a more conventional post-Newtonian multipolar expansion of scalar and vector gravitational potentials of the rotating spheroid. We compare these expansions with that of the normal gravity field generated by the Kerr metric and demonstrate that the Kerr metric has a fairly limited application in relativistic geodesy as it does not match the normal gravity field of the Maclaurin ellipsoid already in the Newtonian limit. We derive the post-Newtonian generalization of the Somigliana formula for the normal gravity field measured on the surface of the rotating spheroid and employed in practical work for measuring Earth's gravitational field anomalies. Finally, we discuss the possible choice of the gauge-dependent parameters of the normal gravity field model for practical applications and compare it with the existing EGM2008 model of a gravitational field.

KSC-2011-6765

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – – Maria Zuber, GRAIL principal investigator with the Massachusetts Institute of Technology, participates in the Gravity Recovery and Interior Laboratory (GRAIL) mission science briefing in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

Mars observer radio science (MORS) observations in polar regions

NASA Technical Reports Server (NTRS)

Simpson, Richard A.

1992-01-01

MORS observations will focus on two major areas of study: (1) the gravity field of Mars and its interpretation in terms of internal structure and history and (2) the structure of the atmosphere, with emphasis on both temperature-pressure profiles of the background atmosphere and small scale inhomogeneities resulting from turbulence. Scattering of cm wavelength radio signals from Mars' surface at highly oblique angles will also be studied during the primary mission; nongrazing scattering experiments may be possible during an extended mission. During the MORS primary mission, measurements of the spacecraft distance and velocity with respect to Earth based tracking stations will be used to develop models of the global gravity field. The improvement in knowledge of the gravity field will be especially evident in polar regions. The spatial and temporal coverage of atmospheric radio occultation measurements are determined by the geometry of the spacecraft orbit and the direction to the Earth. Profiles of atmospheric temperature and pressure will extend from the surface to altitudes of 50 to 70 km.

KSC-2011-6746

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – Tim Dunn, NASA launch director for the agency’s Launch Services Program, participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6771

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission is ready for launch. Preparations are under way to roll the mobile service tower away from the rocket. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6779

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, view of the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission is unobstructed as the mobile service tower rolls away. The "rollback" began at about 11:20 p.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6810

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- Media representatives check the lighting at Press Site 1 near Space Launch Complex 17B on Cape Canaveral Air Force Station during preparations to photograph the launch of NASA's Gravity Recovery and Interior Laboratory mission. Liftoff aboard a United Launch Alliance Delta II Heavy rocket is scheduled for 8:37:06 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6750

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – Joel Tumbiolo, launch weather officer, 45th Weather Squadron, Cape Canaveral Air Force Station, Fla., participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6748

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory, participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6786

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission undergoes final preparations for launch. The "rollback" of the mobile service tower began at about 11:20 p.m. EDT Sept. 7. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6764

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – Robert Fogel, NASA’s GRAIL program scientist, participates in the Gravity Recovery and Interior Laboratory (GRAIL) mission science briefing in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6751

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – John Henk, GRAIL program manager, Lockheed Martin Space Systems, Denver, Colo., participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6770

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, preparations are under way to roll the mobile service tower away from the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6878

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – An early morning sky illuminates the United Launch Alliance Delta II Heavy rocket that will launch NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. Liftoff is scheduled for 9:08:52 a.m. EDT Sept.10. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/ Kim Shiflett

KSC-2011-6749

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – Ed Weiler, NASA associate administrator, Science Mission Directorate, participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6875

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – With a clear blue sky for a background, the United Launch Alliance Delta II Heavy rocket is propelled skyward after lifting off at 9:08 a.m. EDT Sept. 10 from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The Delta II is carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6809

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- Television satellite trucks raise their antennas at Press Site 1 near Space Launch Complex 17B on Cape Canaveral Air Force Station during preparations to broadcast the launch of NASA's Gravity Recovery and Interior Laboratory mission. Liftoff aboard a United Launch Alliance Delta II Heavy rocket is scheduled for 8:37:06 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

Definition and Proposed Realization of the International Height Reference System (IHRS)

NASA Astrophysics Data System (ADS)

Ihde, Johannes; Sánchez, Laura; Barzaghi, Riccardo; Drewes, Hermann; Foerste, Christoph; Gruber, Thomas; Liebsch, Gunter; Marti, Urs; Pail, Roland; Sideris, Michael

2017-05-01

Studying, understanding and modelling global change require geodetic reference frames with an order of accuracy higher than the magnitude of the effects to be actually studied and with high consistency and reliability worldwide. The International Association of Geodesy, taking care of providing a precise geodetic infrastructure for monitoring the Earth system, promotes the implementation of an integrated global geodetic reference frame that provides a reliable frame for consistent analysis and modelling of global phenomena and processes affecting the Earth's gravity field, the Earth's surface geometry and the Earth's rotation. The definition, realization, maintenance and wide utilization of the International Terrestrial Reference System guarantee a globally unified geometric reference frame with an accuracy at the millimetre level. An equivalent high-precision global physical reference frame that supports the reliable description of changes in the Earth's gravity field (such as sea level variations, mass displacements, processes associated with geophysical fluids) is missing. This paper addresses the theoretical foundations supporting the implementation of such a physical reference surface in terms of an International Height Reference System and provides guidance for the coming activities required for the practical and sustainable realization of this system. Based on conceptual approaches of physical geodesy, the requirements for a unified global height reference system are derived. In accordance with the practice, its realization as the International Height Reference Frame is designed. Further steps for the implementation are also proposed.

Height unification using GOCE

NASA Astrophysics Data System (ADS)

Rummel, R.

2012-12-01

With the gravity field and steady-state ocean circulation explorer (GOCE) (preferably combined with the gravity field and climate experiment (GRACE)) a new generation of geoid models will become available for use in height determination. These models will be globally consistent, accurate (<3 cm) and with a spatial resolution up to degree and order 200, when expressed in terms of a spherical harmonic expansion. GOCE is a mission of the European Space Agency (ESA). It is the first satellite equipped with a gravitational gradiometer, in the case of GOCE it measures the gradient components Vxx , Vyy, Vzzand Vxz. The GOCE gravitational sensor system comprises also a geodetic global positioning system (GPS)-receiver, three star sensors and ion-thrusters for drag compensation in flight direction. GOCE was launched in March 2009 and will fly till the end of 2013. Several gravity models have been derived from its data, their maximum degree is typically between 240 and 250. In summer 2012 a first re-processing of all level-1b data took place. One of the science objectives of GOCE is the unification of height systems. The existing height offsets among the datum zones can be determined by least-squares adjustment. This requires several precise geodetic reference points available in each height datum zone, physical heights from spirit levelling (plus gravimetry), the GOCE geoid and, in addition, short wavelength geoid refinement from terrestrial gravity anomalies. GOCE allows for important simplifications of the functional and stochastic part of the adjustment model. The future trend will be the direct determination of physical heights (orthometric as well as normal) from precise global navigation satellite system (GNSS)-positioning in combination with a next generation combined satellite-terrestrial high-resolution geoid model.

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Bacmeister, Julio T.; Wu, Dong L.

1998-01-01

This is the first quarter's report on research to extract global gravity-wave data from satellite data and to model those observations synoptically. Preliminary analysis of global maps of extracted middle atmospheric temperature variance from the CRISTA instrument is presented, which appear to contain gravity-wave information. Corresponding simulations of global gravity-wave and mountain-wave activity during this mission period are described using global ray-tracing and mountain-wave models, and interesting similarities among simulated data and CRISTA data are noted. Climatological simulations of mesospheric gravity-wave activity using the HWM-03 wind-temperature climatology are also reported, for comparison with UARS MLS data. Preparatory work on modeling of gravity wave observations from space-based platforms and subsequent interpretation of the MLS gravity-wave product are also described. Preliminary interpretation and relation to the research objectives are provided, and further action for the next quarter's research is recommended.

Effect of the improved accelerometer calibration method on AIUB's GRACE monthly gravity field solution

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Arnold, Daniel; Bentel, Katrin; Jäggi, Adrian

2017-04-01

The monthly global gravity field solutions derived using the measurements from the GRACE (Gravity Recovery and Climate Experiment) satellites have been continuously improved by the processing centers. One of the improvements in the processing method is a more detailed calibration of the on-board accelerometers in the GRACE satellites. The accelerometer data calibration is usually restricted to the scale factors and biases. It has been assumed that the three different axes are perfectly orthogonal in the GRACE science reference frame. Recently, it was shown by Klinger and Mayer-Gürr (2016) that a fully-populated scale matrix considering the non-orthogonality of the axes and the misalignment of the GRACE science reference frame and the GRACE accelerometer frame improves the quality of the C20 coefficient in the GRACE monthly gravity field solutions. We investigate the effect of the more detailed calibration of the GRACE accelerometer data on the C20 coefficient in the case of the AIUB (Astronomical Institute of the University of Bern) processing method using the Celestial Mechanics Approach. We also investigate the effect of the new calibration parameters on the stochastic parameters in the Celestial Mechanics Approach.

Universal bounds on charged states in 2d CFT and 3d gravity

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

Benjamin, Nathan; Dyer, Ethan; Fitzpatrick, A. Liam

2016-08-04

We derive an explicit bound on the dimension of the lightest charged state in two dimensional conformal field theories with a global abelian symmetry. We find that the bound scales with c and provide examples that parametrically saturate this bound. We also prove that any such theory must contain a state with charge-to-mass ratio above a minimal lower bound. As a result, we comment on the implications for charged states in three dimensional theories of gravity.

Truncation of Spherical Harmonic Series and its Influence on Gravity Field Modelling

NASA Astrophysics Data System (ADS)

Fecher, T.; Gruber, T.; Rummel, R.

2009-04-01

Least-squares adjustment is a very common and effective tool for the calculation of global gravity field models in terms of spherical harmonic series. However, since the gravity field is a continuous field function its optimal representation by a finite series of spherical harmonics is connected with a set of fundamental problems. Particularly worth mentioning here are cut off errors and aliasing effects. These problems stem from the truncation of the spherical harmonic series and from the fact that the spherical harmonic coefficients cannot be determined independently of each other within the adjustment process in case of discrete observations. The latter is shown by the non-diagonal variance-covariance matrices of gravity field solutions. Sneeuw described in 1994 that the off-diagonal matrix elements - at least if data are equally weighted - are the result of a loss of orthogonality of Legendre polynomials on regular grids. The poster addresses questions arising from the truncation of spherical harmonic series in spherical harmonic analysis and synthesis. Such questions are: (1) How does the high frequency data content (outside the parameter space) affect the estimated spherical harmonic coefficients; (2) Where to truncate the spherical harmonic series in the adjustment process in order to avoid high frequency leakage?; (3) Given a set of spherical harmonic coefficients resulting from an adjustment, what is the effect of using only a truncated version of it?

Application of Satellite Gravimetry for Water Resource Vulnerability Assessment

NASA Technical Reports Server (NTRS)

Rodell, Matthew

2012-01-01

The force of Earth's gravity field varies in proportion to the amount of mass near the surface. Spatial and temporal variations in the gravity field can be measured via their effects on the orbits of satellites. The Gravity Recovery and Climate Experiment (GRACE) is the first satellite mission dedicated to monitoring temporal variations in the gravity field. The monthly gravity anomaly maps that have been delivered by GRACE since 2002 are being used to infer changes in terrestrial water storage (the sum of groundwater, soil moisture, surface waters, and snow and ice), which are the primary source of gravity variability on monthly to decadal timescales after atmospheric and oceanic circulation effects have been removed. Other remote sensing techniques are unable to detect water below the first few centimeters of the land surface. Conventional ground based techniques can be used to monitor terrestrial water storage, but groundwater, soil moisture, and snow observation networks are sparse in most of the world, and the countries that do collect such data rarely are willing to share them. Thus GRACE is unique in its ability to provide global data on variations in the availability of fresh water, which is both vital to life on land and vulnerable to climate variability and mismanagement. This chapter describes the unique and challenging aspects of GRACE terrestrial water storage data, examples of how the data have been used for research and applications related to fresh water vulnerability and change, and prospects for continued contributions of satellite gravimetry to water resources science and policy.

Global gravity survey by an orbiting gravity gradiometer

NASA Technical Reports Server (NTRS)

Paik, Ho Jung; Leung, Jurn-Sun; Morgan, Samuel H.; Parker, Joseph

1988-01-01

The scientific aims, design, and mission profile of the Superconducting Gravity Gradiometer Mission (SGGM), a NASA spacecraft mission proposed for the late 1990s, are discussed and illustrated with drawings and diagrams. SGGM would complement the two other planned gravimetry missions, GRM and Aristoteles, and would provide gravitational-field measurements with accuracy 2-3 mGal in 55 x 55-km blocks. The principal instruments are a (1) three-axis superconducting gravity gradiometer with intrinsic sensitivity 100 microeotvos/sq rt Hz, (2) a six-axis superconducting accelerometer with sensitivity 100 fg(E)/sq rt Hz linear and 10 prad/sec squared sq rt Hz angular, and (3) a six-axis shaker for active control of the platform. Consideration is given to the error budget and platform requirements, the orbit selection criteria, and the spacecraft design.

Great Red Spot's detection with the Juno gravity experiment

NASA Astrophysics Data System (ADS)

Parisi, M.; Folkner, W. M.

2017-12-01

The Juno spacecraft entered orbit about Jupiter in July 2016. During the perijoves (or closest approaches to Jupiter), Juno carries out observations of the magnetosphere, atmosphere and gravity field of the planet. The gravity field is estimated from precise measurements of the Doppler shift of the Juno radio signal and provides information on the Jovian interior structure.In July 2017 the 7th Juno perijove was over the Great Red Spot. The primary goal was determining differences in ammonia and water abundance in the GRS using the Microwave Radiometer instrument, while Doppler data was acquired acquired on a secondary basis. We present results of analysis of the PJ7 Doppler data to constrain the mass density variations of the GRS relative to the global average. We also present analysis to determine whether future Juno data will provide stronger constraints on the structure of the GRS.

Inversion of Gravity and Magnetic Field Data for Tyrrhena Patera

NASA Technical Reports Server (NTRS)

Milbury, C.; Schubert, G.; Raymond, C. A.; Smrekar, S. E.

2011-01-01

Tyrrhena Patera is located to the southeast/northeast of the Isidis/Hellas impact basin. It was geologically active into the Late Amazonian, although the main edifice was formed in the Noachian(approximately 3.7-4.0 Ga). Tyrrhena Patera and the surrounding area contain gravity and magnetic anomalies that appear to be correlated. The results presented here are for the anomalies 1a and 1b (closest to Tyrrhena Patera), however other anomalies in this region have been modeled and will be presented at the conference.The Mars Global Surveyor (MGS) free-air gravity signature of Tyrrhena Patera has been studied by Kiefer, who inferred the existence of an extinct magma chamber below it. The magnetic signature has been mapped by Lillis R. J. et al., who compared electron reflectometer data, analogous to the total magnetic field, for Syrtis Major and Tyrrhena Patera and argued for demagnetization of both volcanoes.

A model for methane production in sewers.

PubMed

Chaosakul, Thitirat; Koottatep, Thammarat; Polprasert, Chongrak

2014-09-19

Most sewers in developing countries are combined sewers which receive stormwater and effluent from septic tanks or cesspools of households and buildings. Although the wastewater strength in these sewers is usually lower than those in developed countries, due to improper construction and maintenance, the hydraulic retention time (HRT) could be relatively long and resulting considerable greenhouse gas (GHG) production. This study proposed an empirical model to predict the quantity of methane production in gravity-flow sewers based on relevant parameters such as surface area to volume ratio (A/V) of sewer, hydraulic retention time (HRT) and wastewater temperature. The model was developed from field survey data of gravity-flow sewers located in a peri-urban area, central Thailand and validated with field data of a sewer system of the Gold Coast area, Queensland, Australia. Application of this model to improve construction and maintenance of gravity-flow sewers to minimize GHG production and reduce global warming is presented.

Status of the geopotential. [earth gravity measurement

NASA Technical Reports Server (NTRS)

Lerch, F. J.

1983-01-01

Satellite laser ranging, satellite altimetry, and improved measurements of surface gravitational anomalies have broadened the data base on intermediate and short wavelength regions of the earth gravity field. The global data set served to develop new geopotential models with a resolution in spherical harmonics out to degree 180. The resolution was made possible using Seasat altimetry data containing 56,761 values of 1 x 1 deg gravity anomalies. Satellite-to-satellite tracking techniques involving the Geos-3 and Apollo spacecraft data for the sea surface temperature have yielded accurate intermediate wavelength gravity variations which correlate well with residual depth anomalies. Oceanic gravity anomalies have been computed directly from satellite altimetry or through statistical estimation using oceanic geoid heights. The data sets for gravimetric geoids have been compared with altimetric surfaces to identify areas which were of interest for geophysical investigation. Future data sets could become available from a proposed satellite-to-satellite Doppler tracking system (Gravsat) launched by NASA.

Research activities of the Geodynamics Branch

NASA Technical Reports Server (NTRS)

Kahn, W. D. (Editor); Cohen, S. C. (Editor)

1984-01-01

A broad spectrum of geoscience disciplines including space geodesy, geopotential field modeling, tectonophysics, and dynamic oceanography are discussed. The NASA programs, include the Geodynamics and Ocean Programs, the Crustal Dynamics Project, the proposed Ocean Topography Experiment (TOPEX), and the Geopotential Research Mission (GRM). The papers are grouped into chapters on Crustal Movements, Global Earth Dynamics, Gravity Field Model Development, Sea Surface Topography, and Advanced Studies.

GRACE Solutions for the Gravity Field over Central Europe Compared to the Surface Field as Recorded by the GGP Network.

NASA Astrophysics Data System (ADS)

Crossley, D. J.; de Linage, C.; Hinderer, J.; Boy, J.

2007-12-01

As the number of different solutions from the GRACE satellite gravity project evolves, we can make more meaningful comparisons between the satellite-derived field and the surface field as recorded by superconducting gravimeters. On the GRACE side, we use CSR Level 2 products RL01 and the recent RL04 solutions, GFZ RL04 solutions, and the CNES/GRGS 10-day solutions, all for the time periods these are available. On the GGP side, we take advantage of the 10 years of SG data since July 1997 from 6-8 ground stations in Europe, allowing for the change in the network configuration as stations begin and end recording. Only data since 2002 can be compared directly to GRACE. Our primary measure of variability is the first principal component of the EOF analysis of all the fields. Unsurprisingly, the seasonal components for all the comparisons are similar in phase, but different in amplitude, to the predictions from a global hydrology model (GLDAS), provided allowance is made for the location of the SG stations above or below the soil moisture horizon that controls the gravity signature. We use detailed modeling at the Strasbourg station, as well as published results for Moxa and Membach, to confirm the gravity effect of hydrology. Good agreement is found between the GGP and the CNES/GRGS 10-day solutions, indicating the higher temporal resolution of this satellite solution is valid for our limited geographical area. We also synthesize the gravity field over the sub-group of GGP stations in N.E. Asia to see how the GRACE variability compares to that for the European array and to assess future ground validation using new GGP stations in that part of the world.

A Test Run of the EGSIEM Near Real-Time Service Based on GRACE Mission Data

NASA Astrophysics Data System (ADS)

Kvas, A.; Gruber, C.; Gouweleeuw, B.; Guntner, A.; Mayer-Gürr, T.; Flechtner, F. M.

2017-12-01

To enable the use of GRACE and GRACE-FO data for rapid monitoring applications, the EGSIEM (European Gravity Service for Improved Emergency Management) project, funded by the Horizon 2020 Framework Program for Research and Innovation of the European Union, has implemented a demonstrator for a near real-time (NRT) gravity field service. The goal of this service is to provide daily gravity field solutions with a maximum latency of five days. For this purpose, two independent approaches were developed at the German Research Centre for Geosciences (GFZ) and Graz University of Technology (TUG). Based on these daily gravity field solutions, statistical flood and drought indicators are derived by the EGSIEM Hydrological Service, developed at GFZ. The NRT products are subsequently provided to the Center for Satellite based Crisis Information (ZKI) at the German Aerospace Center as well as the Global Flood Awareness System (GloFAS) at the Joint Research Center of the European Commission. In the first part of this contribution, the performance of the service based on a statistical analysis of historical flood events during the GRACE period is evaluated. Then, results from the six month long operational test run of the service which started on April 1st 2017 are presented and a comparison between historical and operational gravity products and flood indicators is made.

A climatology of gravity wave parameters based on satellite limb soundings

NASA Astrophysics Data System (ADS)

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

2017-04-01

Gravity waves are one of the main drivers of atmospheric dynamics. The resolution of most global circulation models (GCMs) and chemistry climate models (CCMs), however, is too coarse to properly resolve the small scales of gravity waves. Horizontal scales of gravity waves are in the range of tens to a few thousand kilometers. Gravity wave source processes involve even smaller scales. Therefore GCMs/CCMs usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified, and comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. In our study, we present a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). We provide various gravity wave parameters (for example, gravity variances, potential energies and absolute momentum fluxes). This comprehensive climatological data set can serve for comparison with other instruments (ground based, airborne, or other satellite instruments), as well as for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The purpose of providing various different parameters is to make our data set useful for a large number of potential users and to overcome limitations of other observation techniques, or of models, that may be able to provide only one of those parameters. We present a climatology of typical average global distributions and of zonal averages, as well as their natural range of variations. In addition, we discuss seasonal variations of the global distribution of gravity waves, as well as limitations of our method of deriving gravity wave parameters from satellite data.

Gravity Field Changes due to Long-Term Sea Level Changes

NASA Astrophysics Data System (ADS)

Makarynskyy, O.; Kuhn, M.; Featherstone, W. E.

2004-12-01

Long-term sea level changes caused by climatic changes (e.g. global warming) will alter the system Earth. This includes the redistribution of ocean water masses due to the migration of cold fresh water from formerly ice-covered regions to the open oceans mainly caused by the deglaciation of polar ice caps. Consequently also a change in global ocean circulation patterns will occur. Over a longer timescale, such mass redistributions will be followed by isostatic rebound/depression due to the changed surface un/loading, resulting in variable sea level change around the world. These, in turn, will affect the gravity field, location of the geocentre, and the Earth's rotation vector. This presentation focuses mainly on gravity field changes induced by long-term (hundredths to many thousand years) sea level changes using an Earth System Climate Model (ESCM) of intermediate complexity. In this study, the coupled University of Victoria (Victoria, Canada) Earth System Climate Model (Uvic ESCM) was used, which embraces the primary thermodynamic and hydrological components of the climate system including sea and land-ice information. The model was implemented to estimate changes in global precipitation, ocean mass redistribution, seawater temperature and salinity on timescales from hundreds to thousands years under different greenhouse warming scenarios. The sea level change output of the model has been converted into real mass changes by removing the steric effect, computed from seawater temperature and salinity information at different layers also provided by Uvic ESCM. Finally the obtained mass changes have been converted into changes of the gravitational potential and subsequently of the geoid height using a spherical harmonic representation of the different data. Preliminary numerical results are provided for sea level change as well as change in geoid height.

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.

Some results on a black hole with a global monopole in Poincaré gravity

NASA Astrophysics Data System (ADS)

Bezerra, Valdir B.; Ferreira, Cristine N.; Alvarenga, Elton P. J.

2018-06-01

The aim of this work is to study the thermodynamics and spin current of a system corresponding to a black hole containing a global monopole in the context of Poincaré gravity theory which is an extension of general relativity, in the sense that the intrinsic angular momentum of matter is also a source of gravitational interaction. Thus, in this work we find the solution corresponding to the spacetime under consideration by taking into account that the action which describes this system contains terms corresponding to the curvature and torsion. The metric obtained is a function of mass, solid angle deficit and the coupling constants of the quadratic terms of the curvature and torsion. In this model, the stability of the system is studied through the analysis of the Hawking temperature and the specific heat. In this context it was also studied the critical temperatures of the system considering positive or negative cosmological constant. In the vicinity of the black hole with a global monopole, where there is a logarithmic correction due to the relationship between the torsion and curvature fields, some analysis were done. We also study the AdS/dS limit where the black hole is analyzed from the topological point of view. Although the effect of spin current density at low energies is negligible, in the vicinity of strong gravitational fields it can generate an appreciable effect due to spin gravity coupling.

Global Biomass Variation and its Geodynamic Effects, 1982-1998

NASA Technical Reports Server (NTRS)

Rodell, M.; Chao, B. F.; Au, A. Y.; Kimball, J. S.; McDonald, K. C.

2005-01-01

Redistribution of mass near Earth's surface alters its rotation, gravity field, and geocenter location. Advanced techniques for measuring these geodetic variations now exist, but the ability to attribute the observed modes to individual Earth system processes has been hampered by a shortage of reliable global data on such processes, especially hydrospheric processes. To address one aspect of this deficiency, 17 yrs of monthly, global maps of vegetation biomass were produced by applying field-based relationships to satellite-derived vegetation type and leaf area index. The seasonal variability of biomass was estimated to be as large as 5 kg m(exp -2). Of this amount, approximately 4 kg m(exp -2) is due to vegetation water storage variations. The time series of maps was used to compute geodetic anomalies, which were then compared with existing geodetic observations as well as the estimated measurement sensitivity of the Gravity Recovery and Climate Experiment (GRACE). For gravity, the seasonal amplitude of biomass variations may be just within GRACE'S limits of detectability, but it is still an order of magnitude smaller than current observation uncertainty using the satellite-laser-ranging technique. The contribution of total biomass variations to seasonal polar motion amplitude is detectable in today's measurement, but it is obscured by contributions from various other sources, some of which are two orders of magnitude larger. The influence on the length of day is below current limits of detectability. Although the nonseasonal geodynamic signals show clear interannual variability, they are too small to be detected.

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.

One technique for refining the global Earth gravity models

NASA Astrophysics Data System (ADS)

Koneshov, V. N.; Nepoklonov, V. B.; Polovnev, O. V.

2017-01-01

The results of the theoretical and experimental research on the technique for refining the global Earth geopotential models such as EGM2008 in the continental regions are presented. The discussed technique is based on the high-resolution satellite data for the Earth's surface topography which enables the allowance for the fine structure of the Earth's gravitational field without the additional gravimetry data. The experimental studies are conducted by the example of the new GGMplus global gravity model of the Earth with a resolution about 0.5 km, which is obtained by expanding the EGM2008 model to degree 2190 with the corrections for the topograohy calculated from the SRTM data. The GGMplus and EGM2008 models are compared with the regional geoid models in 21 regions of North America, Australia, Africa, and Europe. The obtained estimates largely support the possibility of refining the global geopotential models such as EGM2008 by the procedure implemented in GGMplus, particularly in the regions with relatively high elevation difference.

Gravity and geoid model for South America

NASA Astrophysics Data System (ADS)

Blitzkow, Denizar; Oliveira Cancoro de Matos, Ana Cristina; do Nascimento Guimarães, Gabriel; Pacino, María Cristina; Andrés Lauría, Eduardo; Nunes, Marcelo; Castro Junior, Carlos Alberto Correia e.; Flores, Fredy; Orihuela Guevara, Nuris; Alvarez, Ruber; Napoleon Hernandez, José

2016-04-01

In the last 20 years, South America Gravity Studies (SAGS) project has undertaken an ongoing effort in establishing the fundamental gravity network (FGN); terrestrial, river and airborne relative gravity densifications; absolute gravity surveys and geoid (quasi-geoid) model computation for South America. The old FGN is being replaced progressively by new absolute measurements in different countries. In recent years, Argentina, Bolivia, Brazil, Ecuador, Paraguay and Venezuela organizations participated with relative gravity surveys. Taking advantage of the large amount of data available, GEOID2015 model was developed for 15°N and 57°S latitude and 30 ° W and 95°W longitude based on EIGEN-6C4 until degree and order 200 as a reference field. The ocean area was completed with mean free air gravity anomalies derived from DTU10 model. The short wavelength component was estimated using FFT. The global gravity field models EIGEN-6C4, DIR_R5 were used for comparison with the new model. The new geoid model has been evaluated against 1,319 GPS/BM, in which 592 are located in Brazil and the reminder in other countries. The preliminary RMS difference between GPS/BM and GEOID2015 throughout South America and in Brazil is 46 cm and 17 cm, respectively. New activities are carrying out with the support of the IGC (Geographic and Cartographic Institute) under the coordination of EPUSP/LTG and CENEGEO (Centro de Estudos de Geodesia). The new project aims to establish new gravity points with the A-10 absolute gravimeter in South America. Recent such surveys occurred in São Paulo state, Argentina and Venezuela.

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.

Blockage of hemichannels alters gene expression in osteocytes in a high magneto-gravitational environment

PubMed Central

Xu, Huiyun; Ning, Dandan; Zhao, Dezhi; Chen, Yunhe; Zhao, Dongdong; Gu, Sumin; Jiang, Jean X.; Shang, Peng

2017-01-01

Osteocytes, the most abundant cells in bone, are highly responsive to external environmental changes. We tested how Cx43 hemichannels which mediate the exchange of small molecules between cells and extracellular environment impact genome wide gene expression under conditions of abnormal gravity and magnetic field. To this end, we subjected osteocytic MLO-Y4 cells to a high magneto-gravitational environment and used microarray to examine global gene expression and a specific blocking antibody was used to assess the role of Cx43 hemichannels. While 3 hr exposure to abnormal gravity and magnetic field had relatively minor effects on global gene expression, blocking hemichannels significantly impacted the expression of a number of genes which are involved in cell viability, apoptosis, mineral absorption, protein absorption and digestion, and focal adhesion. Also, blocking of hemichannels enriched genes in multiple signaling pathways which are enaged by TGF-beta, Jak-STAT and VEGF. These results show the role of connexin hemichannels in bone cells in high magneto-gravitational environments. PMID:27814646

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.

Deconstructing the shallow internal structure of the Moon using GRAIL gravity and LOLA topography

NASA Astrophysics Data System (ADS)

Zuber, M. T.

2015-12-01

Globally-distributed, high-resolution gravity and topography observations of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission and Lunar Orbiter Laser Altimeter (LOLA) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft afford the unprecedented opportunity to explore the shallow internal structure of the Moon. Gravity and topography can be combined to produce Bouguer gravity that reveals the distribution of mass in the subsurface, with high degrees in the spherical harmonic expansion of the Bouguer anomalies sensitive to shallowest structure. For isolated regions of the lunar highlands and several basins we have deconstructed the gravity field and mapped the subsurface distribution of density anomalies. While specified spherical harmonic degree ranges can be used to estimate contributions at different depths, such analyses require considerable caution in interpretation. A comparison of filtered Bouguer gravity with forward models of disk masses with plausible densities illustrates the interdependencies of the gravitational power of density anomalies with depth and spatial scale. The results have implications regarding the limits of interpretation of lunar subsurface structure.

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.

Using the Multiplicative Schwarz Alternating Algorithm (MSAA) for Solving the Large Linear System of Equations Related to Global Gravity Field Recovery up to Degree and Order 120

NASA Astrophysics Data System (ADS)

Safari, A.; Sharifi, M. A.; Amjadiparvar, B.

2010-05-01

The GRACE mission has substantiated the low-low satellite-to-satellite tracking (LL-SST) concept. The LL-SST configuration can be combined with the previously realized high-low SST concept in the CHAMP mission to provide a much higher accuracy. The line of sight (LOS) acceleration difference between the GRACE satellite pair is the mostly used observable for mapping the global gravity field of the Earth in terms of spherical harmonic coefficients. In this paper, mathematical formulae for LOS acceleration difference observations have been derived and the corresponding linear system of equations has been set up for spherical harmonic up to degree and order 120. The total number of unknowns is 14641. Such a linear equation system can be solved with iterative solvers or direct solvers. However, the runtime of direct methods or that of iterative solvers without a suitable preconditioner increases tremendously. This is the reason why we need a more sophisticated method to solve the linear system of problems with a large number of unknowns. Multiplicative variant of the Schwarz alternating algorithm is a domain decomposition method, which allows it to split the normal matrix of the system into several smaller overlaped submatrices. In each iteration step the multiplicative variant of the Schwarz alternating algorithm solves linear systems with the matrices obtained from the splitting successively. It reduces both runtime and memory requirements drastically. In this paper we propose the Multiplicative Schwarz Alternating Algorithm (MSAA) for solving the large linear system of gravity field recovery. The proposed algorithm has been tested on the International Association of Geodesy (IAG)-simulated data of the GRACE mission. The achieved results indicate the validity and efficiency of the proposed algorithm in solving the linear system of equations from accuracy and runtime points of view. Keywords: Gravity field recovery, Multiplicative Schwarz Alternating Algorithm, Low-Low Satellite-to-Satellite Tracking

Global detailed geoid computation and model analysis

NASA Technical Reports Server (NTRS)

Marsh, J. G.; Vincent, S.

1974-01-01

Comparisons and analyses were carried out through the use of detailed gravimetric geoids which we have computed by combining models with a set of 26,000 1 deg x 1 deg mean free air gravity anomalies. The accuracy of the detailed gravimetric geoid computed using the most recent Goddard earth model (GEM-6) in conjunction with the set of 1 deg x 1 deg mean free air gravity anomalies is assessed at + or - 2 meters on the continents of North America, Europe, and Australia, 2 to 5 meters in the Northeast Pacific and North Atlantic areas, and 5 to 10 meters in other areas where surface gravity data are sparse. The R.M.S. differences between this detailed geoid and the detailed geoids computed using the other satellite gravity fields in conjuction with same set of surface data range from 3 to 7 meters.

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal, Ajay K.; Parthasarathy, Ramkumar

2004-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique suited for the microgravity environment. The flow structure was characterized by distributions of helium mole fraction obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. Experiments reveal that the global flow oscillations observed in Earth gravity are absent in microgravity. The report provides quantitative details of flow evolution as the experiment undergoes change in gravity in the drop tower.

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.

Mars Observer: Mission toward a basic understanding of Mars

NASA Technical Reports Server (NTRS)

Albee, Arden L.

1992-01-01

The Mars Observer Mission will provide a spacecraft platform about Mars from which the entire Martian surface and atmosphere will be observed and mapped by remote sensing instruments for at least 1 Martian year. The scientific objectives for the Mission emphasize qualitative and quantitative determination of the elemental and mineralogical composition of the surface; measurement of the global surface topography, gravity field, and magnetic field; and the development of a synoptic data base of climatological conditions. The Mission will provide basic global understanding of Mars as it exists today and will provide a framework for understanding its past.

Cap integration in spectral gravity forward modelling: near- and far-zone gravity effects via Molodensky's truncation coefficients

NASA Astrophysics Data System (ADS)

Bucha, Blažej; Hirt, Christian; Kuhn, Michael

2018-04-01

Spectral gravity forward modelling is a technique that converts a band-limited topography into its implied gravitational field. This conversion implicitly relies on global integration of topographic masses. In this paper, a modification of the spectral technique is presented that provides gravity effects induced only by the masses located inside or outside a spherical cap centred at the evaluation point. This is achieved by altitude-dependent Molodensky's truncation coefficients, for which we provide infinite series expansions and recurrence relations with a fixed number of terms. Both representations are generalized for an arbitrary integer power of the topography and arbitrary radial derivative. Because of the altitude-dependency of the truncation coefficients, a straightforward synthesis of the near- and far-zone gravity effects at dense grids on irregular surfaces (e.g. the Earth's topography) is computationally extremely demanding. However, we show that this task can be efficiently performed using an analytical continuation based on the gradient approach, provided that formulae for radial derivatives of the truncation coefficients are available. To demonstrate the new cap-modified spectral technique, we forward model the Earth's degree-360 topography, obtaining near- and far-zone effects on gravity disturbances expanded up to degree 3600. The computation is carried out on the Earth's surface and the results are validated against an independent spatial-domain Newtonian integration (1 μGal RMS agreement). The new technique is expected to assist in mitigating the spectral filter problem of residual terrain modelling and in the efficient construction of full-scale global gravity maps of highest spatial resolution.

KSC-2011-6853

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – Actress Nichelle Nichols (Lt. Uhura on Star Trek) signs autographs for a guest at the Kennedy Space Center Visitor Complex in Florida during activities for the agency’s Gravity Recovery and Interior Laboratory mission (GRAIL). Nichols was on hand to celebrate the 45th anniversary of the first airing of the Star Trek television series. The Kennedy Space Center Visitor Complex is hosting “Star Trek: The Exhibition” to show visitors where “science fiction meets science fact.” GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Frankie Martin

KSC-2011-6782

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission towers over the U.S. flag painted on the pad's structure. The mobile service tower has been rolled away from the vehicle for launch. The "rollback" began at about 11:20 p.m. EDT Sept. 7. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6846

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II heavy rocket that will launch NASA's Gravity Recovery and Interior Laboratory spacecraft is rolled back around to the mobile service tower after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6851

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II heavy rocket that will launch NASA's Gravity Recovery and Interior Laboratory spacecraft is rolled back around to the mobile service tower after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6799

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – Tweetup participants ask questions during prelaunch activities for NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission at the Kennedy Space Center Visitor Complex in Florida. Participants toured NASA’s Kennedy Space Center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Gianni Woods

KSC-2011-6884

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – At KARS Park 1 on Merritt Island in Florida, a group of Tweetup participants take pictures and watch excitedly as a United Launch Alliance Delta II Heavy rocket lifts off at 9:08 a.m. EDT Sept. 10 from Space Launch Complex 17B at Cape Canaveral Air Force Station carrying NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Frankie Martin

KSC-2011-6844

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – News media photograph the United Launch Alliance Delta II heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory spacecraft at Launch Complex 17B as the mobile service tower is rolled back around to the vehicle after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT. at Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6775

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. -- At Space Launch Complex 17B on Cape Canaveral Air Force Station, evening showers create the right conditions for the United Launch Alliance Delta II rocket that will launch NASA's Gravity Recovery and Interior Laboratory mission to be reflected on the surface of the pad. Preparations are under way to roll the mobile service tower away from the rocket. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6850

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II heavy rocket that will launch NASA's Gravity Recovery and Interior Laboratory spacecraft is rolled back around to the mobile service tower after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6845

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – At Space Launch Complex 17B on Cape Canaveral Air Force Station, the United Launch Alliance Delta II heavy rocket that will launch NASA's Gravity Recovery and Interior Laboratory spacecraft is rolled back around to the mobile service tower after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

KSC-2011-6882

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – At KARS Park 1 on Merritt Island in Florida, a group of Tweetup participants watch as a United Launch Alliance Delta II Heavy rocket lifts off at 9:08 a.m. EDT Sept. 10 from Space Launch Complex 17B at Cape Canaveral Air Force Station carrying NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Frankie Martin

KSC-2011-6847

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – A worker stands nearby as the United Launch Alliance Delta II heavy rocket at Space Launch Complex 17B, carrying NASA's Gravity Recovery and Interior Laboratory spacecraft, is rolled back around to the mobile service tower after the first launch attempt was scrubbed due to upper-level winds. GRAIL is scheduled for another launch attempt Sept.10 at 8:29:45 a.m. EDT at Cape Canaveral Air Force Station, Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Ken Thornsley

Study on relationship between evolution of regional gravity field and seismic hazard

NASA Astrophysics Data System (ADS)

Li, W.; Xu, C.; Shen, C.

2017-12-01

The lack of anomalous signal is a big issue for the study of geophysics using historical geodesy observations, which is a relatively new area of earth gravimetry application in seismology. Hence the use of the gravity anomaly (GA) derived from either a global geopotential model (GGM) or a regional gravity reanalysis (Ground Gravity Survey, GGS) becomes an important alternative solution. In this study, the GGS at 186 points for the period of 2010 2014 in the Sichuan-Yunnan region (SYR) stations are analyzed. To study the temporal and spatial distribution characteristics of regional gravity filed (RGF) and its evolution mechanism. Taking the geological and geophysical data as constraints. From the GGM expanded up to degree 360, GA were obtained after gravity reduction, especially removing the reference field. The dynamically evolutional characteristics of gravity field are closely relative to fault activity. The gravity changes with time about 5 years at LongMenShan fault (LMSF) have a slop of -12.83±2.9 μGal/a, indicating that LMSF has an uplift. To test the signal extraction algorithm in some geodynamic processes, GA from the SYR were inverted and it was also imposed as a priori information. Fortunately, some significant gravity variation have been detected at some stations in the thrust fault before and after four earthquakes, in which typical anomalies (earthquake precursor, EP) were positive GA variation near the epicenter and the occurrence of a high-gravity-gradient zone across the epicenter prior to the Lushan earthquake (Ms 7.0). The repeated observation results during about 5 years indicate that no significant gravity changes related to other geodynamical events were observed in most observation epochs. In addition, the mechanism of gravity changes at Lushan was also explored. We calculated the gravity change rates based on the model of Songpan-Ganze block (SGB) to Sichuan basin (SCB). And the changes is in good agreement with observed one, indicating that present gravity changes at Lushan were caused by SGB to SCB. The results and understanding are of great significance for further study of tectonic characteristics in this region, and the GGS-derived anomalies has the potential to be used as a reliable source of EP on a regional scale for seismic, or a favorable basis for seismic hazards.

GRACILE: a comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings

NASA Astrophysics Data System (ADS)

Ern, Manfred; Trinh, Quang Thai; Preusse, Peter; Gille, John C.; Mlynczak, Martin G.; Russell, James M., III; Riese, Martin

2018-04-01

Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground-based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.

Flexural isostasy: Constraints from gravity and topography power spectra

NASA Astrophysics Data System (ADS)

Watts, Tony; Moore, James

2017-04-01

We have used the spherical harmonic coefficients that describe the EGM2008 gravity and topography model (Pavlis et al. 2010) to quantify the role of flexural isostasy in contributing to Earth's gravity and topography. Power spectra show that the gravity effect of the topography and its flexural compensation contributes significantly to the observed free-air gravity anomaly field for degree 33-180, which corresponds approximately to wavelengths of 220-1200 km. The best fit is for an elastic thickness of the lithosphere, Te, of 34.0±4.0 km. Smaller values of Te, under-predict while high values of Te, over-predict the observed gravity spectra. The best fit value is a global average and so it is reasonable to speculate that regions exist where Te is both lower and higher. This is confirmed in studies of selected regions such as the Hawaiian-Emperor seamount chain and the Ganges-Himalaya foreland fold and thrust belt where we show that flexural isostatic anomalies are near zero in regions where Te approaches 34 km (e.g. Hawaiian ridge) and of large amplitude in regions of lower (e.g. Emperor) and higher Te (e.g. Ganges-Himalaya). Plate flexure may be significant at higher (180-441) and lower (12-33) degrees, but topography appears either uncompensated or fully compensated at these degrees, irrespective of the actual Te. Nevertheless, all isostatic models under-predict the observed gravity spectra at degree <12 and so we interpret the low order Earth's gravity field as caused by non-isostatic processes due to dynamic motions such as those associated with mantle convection.

Status and Assessments of CSR GRACE Level-2 Data Products

NASA Astrophysics Data System (ADS)

Bettadpur, Srinivas; Kang, Zhigui; Nagel, Peter; Pastor, Rick; Poole, Steve; Ries, John; Save, Himanshu

2015-04-01

The joint NASA/DLR GRACE mission has successfully operated for more than 13 years, and has provided a remarkable record of global mass flux due to a large variety of geophysical and climate processes at various spatio-temporal scales. The University of Texas Center for Space Research (CSR) hosts the mission PI, and is responsible for delivery of operational (presently denoted as Release-05 or RL05) gravity field data products. In addition, CSR generates and distributes a variety of other gravity field data products, including products generated from the use of satellite laser ranging data. This poster will provide an overview of all these data products, their relative quality, potential applications, and future plans for their development and delivery.

Bernese advances towards a global analysis of Lunar geodesy

NASA Astrophysics Data System (ADS)

Bertone, S.; Girardin, V.; Bourgoin, A.; Arnold, D.; Jaeggi, A.

2017-12-01

In this presentation we discuss our latest GRAIL-based lunar gravity fields generated with the Celestial Mechanics Approach using the planetary extension of the Bernese GNSS Software (BSW) developed at the Astronomical Institute of the University of Bern (AIUB).Based on one-way X band and two-way S-band Doppler data, we perform orbit determination by solving six initial orbital elements, dynamical parameters, and stochastic parameters in daily arcs using a least-squares adjustment. Significative improvements to our solutions come from the recent implementation of an accurate modeling of non-gravitational forces, including accelerations due to solar and planetary (albedo and IR) radiation pressure, based on the 28-plate macromodel to represent the GRAIL satellites. Also, as suggested in previous works, we deal with imperfections in the modeling of solar eclipses by both an accurate data screening at mid-latitudes and by taking into account solar panel voltage data in our processing. Empirical and pseudo-stochastic parameters are estimated on top of our dynamical modeling to absorb its deficiencies. We analyze the impact of different parametrizations using either pulses (i.e., instantaneous velocity changes) and piecewise constant accelerations (PCA) on our orbits.Based on these improved orbits, one- and two-way Doppler and KBRR data are then used together with an appropriate weighting for a combined orbit and gravity field determination process.We present our latest solutions of the lunar gravity field, based on the recent GRAIL GRGM900C gravity field (as validation of our modeling and parametrization) and on iterations from the SELENE SGM150J gravity field (to check the independence of our solution). We detail our procedure to gradually enlarge the parameter space while adding new data to our gravity field solution. In addition, we present our latest solution for the Moon tidal Love number k_2.Moreover, some important lunar geophysical parameters are best obtained by processing data from Lunar Laser Ranging (LLR) stations. We analyze the impact of a combined processing on the recovery of a set of parameters and we provide some preliminary results.Finally, we compare all of our results with the most recent solutions of the lunar gravity field and of other geodetic parameters released by other groups.

Gravity and crustal movements: The canadian experience

NASA Astrophysics Data System (ADS)

Tanner, J. G.; Lambert, A.

1987-07-01

Repeated high precision gravity measurement have already played an important role in the detection of crustal deformation in Canada and elsewhere, but even more useful results can be expected through more widespread use of gravity in combination with other techniques. The crucial element in the process is the development of a good physical model on which the experiment can be based. Otherwise, considerable time and effort can be spent on determining the most appropriate field strategy. New technical developments on the horizon appear to offer enhanced opportunities for gravity studies of crustal processes. The coming availability of the Global Positioning System and transportable absolute gravimeters will open up the possibility of regional studies (i.e., areas of the order of 100 km or perhaps greater) of crustal movements at reasonable cost. Within Africa the development of an African Gravity Standardization Net will be a major first step in any program to provide a better understanding of the neo-tectonic framework of this vast continent.

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.

Poincaré gauge gravity: An emergent scenario

NASA Astrophysics Data System (ADS)

Chkareuli, J. L.

2017-04-01

The Poincaré gauge gravity (PGG) with the underlying vector fields of tetrads and spin-connections is perhaps the best theory candidate for gravitation to be unified with the other three elementary forces of nature. There is a clear analogy between the local frame in PGG and the local internal symmetry space in the Standard Model. As a result, the spin-connection fields, gauging the local frame Lorentz symmetry group S O (1 ,3 )LF , appear in PGG much as photons and gluons appear in SM. We propose that such an analogy may follow from their common emergent nature allowing us to derive PGG in the same way as conventional gauge theories. In essence, we start with an arbitrary theory of some vector and fermion fields which possesses only global spacetime symmetries, such as Lorentz and translational invariance, in flat Minkowski space. The two vector field multiplets involved are proposed to belong, respectively, to the adjoint (Aμi j) and vector (eμi) representations of the starting global Lorentz symmetry. We show that if these prototype vector fields are covariantly constrained, Aμi jAij μ=±MA2 and eμieiμ=±Me2 , thus causing a spontaneous violation of the accompanying global symmetries (MA ,e are their proposed violation scales), then the only possible theory compatible with these length-preserving constraints is turned out to be the gauge invariant PGG, while the corresponding massless (pseudo)Goldstone modes are naturally collected in the emergent gauge fields of tetrads and spin-connections. In a minimal theory case being linear in a curvature we unavoidably come to the Einstein-Cartan theory. The extended theories with propagating spin-connection and tetrad modes are also considered and their possible unification with the Standard Model is briefly discussed.

Global correlation of topographic heights and gravity anomalies

NASA Technical Reports Server (NTRS)

Roufosse, M. C.

1977-01-01

The short wavelength features were obtained by subtracting a calculated 24th-degree-and-order field from observed data written in 1 deg x 1 deg squares. The correlation between the two residual fields was examined by a program of linear regression. When run on a worldwide scale over oceans and continents separately, the program did not exhibit any correlation; this can be explained by the fact that the worldwide autocorrelation function for residual gravity anomalies falls off much faster as a function of distance than does that for residual topographic heights. The situation was different when the program was used in restricted areas, of the order of 5 deg x 5 deg square. For 30% of the world,fair-to-good correlations were observed, mostly over continents. The slopes of the regression lines are proportional to apparent densities, which offer a large spectrum of values that are being interpreted in terms of features in the upper mantle consistent with available heat-flow, gravity, and seismic data.

Picture of the global field of quasi-monochromatic gravity waves observed by stratospheric balloons and MST radars

NASA Technical Reports Server (NTRS)

Yamanaka, M. D.

1989-01-01

In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.

Geophysics From Terrestrial Time-Variable Gravity Measurements

NASA Astrophysics Data System (ADS)

Van Camp, Michel; de Viron, Olivier; Watlet, Arnaud; Meurers, Bruno; Francis, Olivier; Caudron, Corentin

2017-12-01

In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field. Time-variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the changing Earth. Ground-based gravimetry can determine the change in gravity related to the Earth rotation fluctuation, to celestial body and Earth attractions, to the mass in the direct vicinity of the instruments, and to vertical displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed by ground gravimeters used to monitor time-variable gravity. This is done in relation to the instrumental characteristics, noise sources, and good practices. We also discuss the next challenges to be met by ground gravimetry, the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation.

Investigations on gravity data processing in airborne and shipborne gravimetry

NASA Astrophysics Data System (ADS)

Lu, Biao; Barthelmes, Franz; Petrovic, Svetozar; Förste, Christoph; Ince, Sinem; Flechtner, Frank

2017-04-01

Nowadays, airborne and shipborne gravimetry are very important methods to improve our knowledge about the Earth gravity field. The gravimeter Chekan-AM onboard the German High Altitude and Long Range (HALO) aircraft anables gravimetry at hardly accessible places like the polar regions of the Earth. One preparatory campaign on HALO has been carried out over Italy in 2012 to test the performance of the gravimeter Chekan-AM onboard such a jet aircraft. Specifically, the processing strategy of data achieved with this gravimeter has been studied. To investigate how future airborne gravity campaigns could be designed over regions like Antarctica, a dedicated flight track during the GEOHALO experiment had been run two times at different heights and velocities of the aircraft. These two flight paths are investigated and the results show that the equipment worked well also at higher altitude and speed. Comparisons with the global gravity field model EIGEN-6C4 and an analysis of the gravity differences at the crossover points show that the accuracy of this campaign is approximately 1 mGal. For geodetic purpose, a local geoid is computed by combining point mass modelling and the remove-compute-restore technique which is also taking into account the topography effect. Shipborne gravimetry can provide us high accurate and high resolution information of the Earth gravity field. Four campaigns of shipborne gravimetry by using the Chekan-AM on different research vessels have been conducted within the framework of the ongoing project "Finalising Surveys for the Baltic Motorways of the Sea" (FAMOS) since 2015. It turned out that problems due to influences of stormy sea and an abnormal drift behavior of the instrument at some parts of these campaigns need some additional investigations. The current processing of these gravity campaigns results in RMS of gravity differences at crossover points of about 0.5 mGal. Further investigations will continue to improve these results. Lastly, a high quality regional geoid will be built in the future based on the gravity data collected in this project and already existing gravity data.

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.

Accuracy of mapping the Earth's gravity field fine structure with a spaceborne gravity gradiometer mission

NASA Technical Reports Server (NTRS)

Kahn, W. D.

1984-01-01

The spaceborne gravity gradiometer is a potential sensor for mapping the fine structure of the Earth's gravity field. Error analyses were performed to investigate the accuracy of the determination of the Earth's gravity field from a gravity field satellite mission. The orbital height of the spacecraft is the dominating parameter as far as gravity field resolution and accuracies are concerned.

Development and analysis of a twelfth degree and order gravity model for Mars

NASA Technical Reports Server (NTRS)

Christensen, E. J.; Balmino, G.

1979-01-01

Satellite geodesy techniques previously applied to artificial earth satellites have been extended to obtain a high-resolution gravity field for Mars. Two-way Doppler data collected by 10 Deep Space Network (DSN) stations during Mariner 9 and Viking 1 and 2 missions have been processed to obtain a twelfth degree and order spherical harmonic model for the martian gravitational potential. The quality of this model was evaluated by examining the rms residuals within the fit and the ability of the model to predict the spacecraft state beyond the fit. Both indicators show that more data and higher degree and order harmonics will be required to further refine our knowledge of the martian gravity field. The model presented shows much promise, since it resolves local gravity features which correlate highly with the martian topography. An isostatic analysis based on this model, as well as an error analysis, shows rather complete compensation on a global (long wavelength) scale. Though further model refinements are necessary to be certain, local (short wavelength) features such as the shield volcanos in Tharsis appear to be uncompensated. These are interpreted to place some bounds on the internal structure of Mars.

General Relativity and Gravitation

NASA Astrophysics Data System (ADS)

Ashtekar, Abhay; Berger, Beverly; Isenberg, James; MacCallum, Malcolm

2015-07-01

Part I. Einstein's Triumph: 1. 100 years of general relativity George F. R. Ellis; 2. Was Einstein right? Clifford M. Will; 3. Cosmology David Wands, Misao Sasaki, Eiichiro Komatsu, Roy Maartens and Malcolm A. H. MacCallum; 4. Relativistic astrophysics Peter Schneider, Ramesh Narayan, Jeffrey E. McClintock, Peter Mészáros and Martin J. Rees; Part II. New Window on the Universe: 5. Receiving gravitational waves Beverly K. Berger, Karsten Danzmann, Gabriela Gonzalez, Andrea Lommen, Guido Mueller, Albrecht Rüdiger and William Joseph Weber; 6. Sources of gravitational waves. Theory and observations Alessandra Buonanno and B. S. Sathyaprakash; Part III. Gravity is Geometry, After All: 7. Probing strong field gravity through numerical simulations Frans Pretorius, Matthew W. Choptuik and Luis Lehner; 8. The initial value problem of general relativity and its implications Gregory J. Galloway, Pengzi Miao and Richard Schoen; 9. Global behavior of solutions to Einstein's equations Stefanos Aretakis, James Isenberg, Vincent Moncrief and Igor Rodnianski; Part IV. Beyond Einstein: 10. Quantum fields in curved space-times Stefan Hollands and Robert M. Wald; 11. From general relativity to quantum gravity Abhay Ashtekar, Martin Reuter and Carlo Rovelli; 12. Quantum gravity via unification Henriette Elvang and Gary T. Horowitz.

Monthly gravity field solutions based on GRACE observations generated with the Celestial Mechanics Approach

NASA Astrophysics Data System (ADS)

Meyer, Ulrich; Jäggi, Adrian; Beutler, Gerhard

2012-09-01

The main objective of the Gravity Recovery And Climate Experiment (GRACE) satellite mission consists of determining the temporal variations of the Earth's gravity field. These variations are captured by time series of gravity field models of limited resolution at, e.g., monthly intervals. We present a new time series of monthly models, which was computed with the so-called Celestial Mechanics Approach (CMA), developed at the Astronomical Institute of the University of Bern (AIUB). The secular and seasonal variations in the monthly models are tested for statistical significance. Calibrated errors are derived from inter-annual variations. The time-variable signal can be extracted at least up to degree 60, but the gravity field coefficients of orders above 45 are heavily contaminated by noise. This is why a series of monthly models is computed up to a maximum degree of 60, but only a maximum order of 45. Spectral analysis of the residual time-variable signal shows a distinctive peak at a period of 160 days, which shows up in particular in the C20 spherical harmonic coefficient. Basic filter- and scaling-techniques are introduced to evaluate the monthly models. For this purpose, the variability over the oceans is investigated, which serves as a measure for the noisiness of the models. The models in selected regions show the expected seasonal and secular variations, which are in good agreement with the monthly models of the Helmholtz Centre Potsdam, German Research Centre for Geosciences (GFZ). The results also reveal a few small outliers, illustrating the necessity for improved data screening. Our monthly models are available at the web page of the International Centre for Global Earth Models (ICGEM).

Scalar Measurements and Analysis of Helium Jets in Earth Gravity and Microgravity using Rainbow Schlieren Deflectometry

NASA Technical Reports Server (NTRS)

Yep, Tze Wing

2001-01-01

Recent experiments have shown that low-density gas jets injected into a high-density gas undergo an instability mode leading to highly periodic oscillations in the flow field. The transition from laminar to turbulent flow in these jets is abrupt, without a gradual change in scales. Although this type of instability at high Richardson numbers has been attributed to buoyancy, direct physical evidence was not acquired through experiments. In this study, several experiments were conducted in Earth gravity and microgravity to acquire qualitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The operating parameters of this study included the tube inside diameter, the jet Reynolds number, and the jet Richardson number. Tubes with inside diameters of 19.05 mm and 31.75 mm were used in the experiments conducted in the drop tower. The jet flow was analyzed using quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and the resulting helium mole fraction obtained from color schlieren images taken at 60 Hz. Three sets of experimental data with respect to three schlieren fields of view were acquired for each tube. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low-density jet was buoyancy-induced. This study provides quantitative details of temporal flow evolution as the experiments undergo change in gravity in the drop tower.

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.

Inversion of gravity and bathymetry in oceanic regions for long-wavelength variations in upper mantle temperature and composition

NASA Technical Reports Server (NTRS)

Solomon, Sean C.; Jordan, Thomas H.

1993-01-01

Long-wavelength variations in geoid height, bathymetry, and SS-S travel times are all relatable to lateral variations in the characteristic temperature and bulk composition of the upper mantle. The temperature and composition are in turn relatable to mantle convection and the degree of melt extraction from the upper mantle residuum. Thus the combined inversion of the geoid or gravity field, residual bathymetry, and seismic velocity information offers the promise of resolving fundamental aspects of the pattern of mantle dynamics. The use of differential body wave travel times as a measure of seismic velocity information, in particular, permits resolution of lateral variations at scales not resolvable by conventional global or regional-scale seismic tomography with long-period surface waves. These intermediate scale lengths, well resolved in global gravity field models, are crucial for understanding the details of any chemical or physical layering in the mantle and of the characteristics of so-called 'small-scale' convection beneath oceanic lithosphere. In 1991 a three-year project to the NASA Geophysics Program was proposed to carry out a systematic inversion of long-wavelength geoid anomalies, residual bathymetric anomalies, and differential SS-S travel time delays for the lateral variation in characteristic temperature and bulk composition of the oceanic upper mantle. The project was funded as a three-year award, beginning on 1 Jan. 1992.

New Mars free-air and Bouguer gravity: Correlation with topography, geology and large impact basins

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 (MGM635), derived at the Goddard Space Flight Center, with global topography, geology, and the distribution of large impact basins was compared. The free-air gravity anomalies were derived from re-analysis of Viking Orbiter and Mariner 9 tracking data and have a spatial resolution of 250-300 km. Bouguer anomalies were calculated using a 50x50 expansion of the current Mars topography and the GSFC degree 50 geoid as the equipotential reference surface. Rotational flattening was removed using a moment of inertia of 0.365 and the corrections from Table B2 of Sleep and Phillips. Crustal density and mean density were assumed to be 2.9 and 3.93 gm/cm(sup 3). The spherical harmonic topography used has zero mean elevation, and differs from the USGS maps by about 2 km. Comparisons with global geology use a simplified map with about 1/3 the number of units on the current maps. For correlation with impact basins, the recent compilation by Schultz and Frey was used.

Report of the panel on lithospheric structure and evolution, section 3

NASA Technical Reports Server (NTRS)

Chase, Clement G.; Lang, Harold; Mcnutt, Marcia K.; Paylor, Earnest D.; Sandwell, David T.; Stern, Robert J.

1991-01-01

The panel concluded that NASA can contribute to developing a refined understanding of the compositional, structural, and thermal differences between continental and oceanic lithosphere through a vigorous program in solid Earth science with the following objectives: determine the most fundamental geophysical property of the planet; determine the global gravity field to an accuracy of a few milliGals at wavelengths of 100 km or less; determine the global lithospheric magnetic field to a few nanoTeslas at a wavelength of 100 km; determine how the lithosphere has evolved to its present state via acquiring geologic remote sensing data over all the continents.

Observations of high manganese layers by the Curiosity rover at the Kimberley, Gale crater, Mars

NASA Astrophysics Data System (ADS)

Lanza, N.; Wiens, R. C.; Fischer, W. W.; Grotzinger, J. P.; Cousin, A.; Rice, M. S.; Clark, B. C.; Arvidson, R. E.; Hurowitz, J.; Gellert, R.; McLennan, S. M.; Maurice, S.; Mangold, N.; Le Mouelic, S.; Anderson, R. B.; Nachon, M.; Ollila, A.; Schmidt, M. E.; Berger, J. A.; Blank, J. G.; Clegg, S. M.; Forni, O.; Hardgrove, C. J.; Hardy, K.; Johnson, J. R.; Melikechi, N.; Newsom, H. E.; Sautter, V.; Martín-Torres, J.; Zorzano, M. P.

2014-12-01

The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were designed to map the structure of the Moon through high-precision global gravity mapping. The mission consisted of two spacecraft with Ka-band inter-satellite tracking complemented by tracking from Earth. The mission had two phases: a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km, and an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and 20 and 11 km after. High-resolution gravity field models using both these data sets have been estimated, with the current resolution being degree and order 1080 in spherical harmonics. Here, we focus on aspects of the analysis of the GRAIL data: we investigate eclipse modeling, the influence of empirical accelerations on the results, and we discuss the inversion of large-scale systems. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale, the south pole area, and the farside. We investigate the use of Ka-band Range Rate (KBRR) data versus numerical derivatives of KBRR data, and show that the latter have the capability to locally improve correlations with topography.

Forward modeling magnetic fields of induced and remanent magnetization in the lithosphere using tesseroids

NASA Astrophysics Data System (ADS)

Baykiev, Eldar; Ebbing, Jörg; Brönner, Marco; Fabian, Karl

2016-11-01

A newly developed software package to calculate the magnetic field in a spherical coordinate system near the Earth's surface and on satellite height is shown to produce reliable modeling results for global and regional applications. The discretization cells of the model are uniformly magnetized spherical prisms, so called tesseroids. The presented algorithm extends an existing code for gravity calculations by applying Poisson's relation to identify the magnetic potential with the sum over pseudogravity fields of tesseroids. By testing different lithosphere discretization grids it is possible to determine the optimal size of tesseroids for field calculations on satellite altitude within realistic measurement error bounds. Also the influence of the Earth's ellipticity upon the modeling result is estimated and global examples are studied. The new software calculates induced and remanent magnetic fields for models at global and regional scale. For regional models far-field effects are evaluated and discussed. This provides bounds for the minimal size of a regional model that is necessary to predict meaningful satellite total field anomalies over the corresponding area.

Time-Variable Gravity from Satellite Laser-Ranging: The Low-Degree Components and Their Connections with Geophysical/Climatic Changes

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.; Cox, Christopher M.

2004-01-01

Satellite laser-ranging (SLR) has been observing the tiny variations in Earth s global gravity for over 2 decades. The oblateness of the Earth's gravity field, J2, has been observed to undergo a secular decrease of J2 due mainly to the post-glacial rebound of the mantle. Sometime around 1998 this trend reversed quite suddenly. This reversal persisted until 2001, at which point the atmosphere-corrected time series appears to have reversed yet again towards normal. This anomaly signifies a large interannual change in global mass distribution. A number of possible causes have been considered, with oceanic mass redistribution as the leading candidate although other effects, such as glacial melting and core effects may be contributing. In fact, a strong correlation has been found between the J2 variability and the Pacific decadal oscillation. It is relatively more difficult to solve for corresponding signals in the shorter wavelength harmonics from the existing SLR-derived time variable gravity results, although it appears that geophysical fluid mass transport is being observed. For example, the recovered J3 time series shows remarkable agreement with NCEP-derived estimates of atmospheric gravity variations. Likewise, some of the non-zonal harmonic components have significant interannual signal that appears to be related to mass transport related to climatic effects such as El Nino Southern Oscillation. We will present recent updates on the J2 evolution, as well as a monthly time sequence of low-degree component map of the time-variable gravity complete through degree 4, and examine possible geophysical/climatic causes.

Determination of crustal motions using satellite laser ranging

NASA Technical Reports Server (NTRS)

1991-01-01

Satellite laser ranging has matured over the last decade into one of the essential space geodesy techniques. It has demonstrated centimeter site positioning and millimeter per year velocity determinations in a frame tied dynamically to the mass center of the solid Earth hydrosphere atmosphere system. Such a coordinate system is a requirement for studying long term eustatic sea level rise and other global change phenomena. Earth orientation parameters determined with the coordinate system have been produced in near real time operationally since 1983, at a relatively modest cost. The SLR ranging to Lageos has also provided a rich spectrum of results based upon the analysis of Lageos orbital dynamics. These include significant improvements in the knowledge of the mean and variable components of the Earth's gravity field and the Earth's gravitational parameter. The ability to measure the time variations of the Earth's gravity field has opened as exciting area of study in relating global processes, including meteorologically derived mass transport through changes in the satellite dynamics. New confirmation of general relativity was obtained using the Lageos SLR data.

KSC-2011-6821

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are Joe Lackovich, NASA advisory manager, NASA's Launch Services Program (LSP); Amanda Mitskevich, manager, LSP; and Oscar Toledo, NASA Headquarters senior advisor, LSP. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation.

PubMed

Tsuda, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10-100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50-90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10-50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet.

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation

PubMed Central

TSUDA, Toshitaka

2014-01-01

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet. PMID:24492645

Hydrological signal in polar motion excitation from a combination of geophysical and gravimetric series

NASA Astrophysics Data System (ADS)

Nastula, Jolanta; Winska, Malgorzata; Salstein, David A.

2015-08-01

One can estimate the hydrological signal in polar motion excitation as a residual, namely the difference between observed geodetic excitation functions (Geodetic Angular Momentum, GAM) and the sum of Atmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM).The aim of this study is to find the optimal model and results for hydrological excitation functions in terms of their agreement with the computed difference between GAM and atmospheric and oceanic signals.The atmospheric and oceanic model-based data that we use in this study are the geophysical excitation functions of AAM, OAM available from the Special Bureaus for the Atmosphere and Oceans of the Geophysical Global Fluids Center (GGFC) of the International Earth Rotation and Reference Systems Service (IERS). For the atmosphere and ocean, these functions are based on the mass and motion fields of the fluids.Global models of land hydrology are used to estimate hydrological excitation functions of polar motion (Hydrological Angular Momentum - HAM). These HAM series are the mass of water substance determined from the various types of land-based hydrological reservoirs. In addition the HAM are estimated from spherical harmonic coefficients of the Earth’s gravity field. We use several sets of degree-2, order-1 harmonics of the Earth’s gravity field, derived from the Gravity Recovery and Climate Experiment (GRACE), Satellite Laser Ranging (SLR), and Global Navigation Satellite Systems (GNSS) data.Finally, these several different HAM series are used to determine the best model of hydrological excitation of polar motion. The model is found by looking for the combination of these series that fits the geodetic residuals using the least-square method.In addition, we will access model results from the Coupled Model Intercomparison Project, fifth experiment (CMIP-5) to examine atmospheric excitations from the twentieth century and estimates for the twenty-first century to see the possible signals and trends of these excitation series to help understand the potential range in the derived of hydrological excitation results.

KSC-2011-6854

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – CAPE CANAVERAL, Fla. – Actress Nichelle Nichols (Lt. Uhura on Star Trek) signs autographs for a guest at the Kennedy Space Center Visitor Complex in Florida during activities for the agency’s Gravity Recovery and Interior Laboratory mission (GRAIL). Nichols was on hand to celebrate the 45th anniversary of the first airing of the Star Trek television series. The Kennedy Space Center Visitor Complex is hosting “Star Trek: The Exhibition” to show visitors where “science fiction meets science fact.” GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Frankie Martin

KSC-2011-6794

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – Maria Zuber, GRAIL principal investigator at the Massachusetts Institute of Technology in Cambridge, speaks to a group of Tweetup participants at the Kennedy Space Center Visitor Complex in Florida during prelaunch activities for NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured NASA’s Kennedy Space Center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Gianni Woods

KSC-2011-6769

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – – A Gravity Recovery and Interior Laboratory (GRAIL) mission science briefing is held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. From left are DC Agle, NASA Public Affairs; Robert Fogel, NASA’s GRAIL program scientist; Maria Zuber, GRAIL principal investigator with the Massachusetts Institute of Technology; Sami Asmar, GRAIL deputy project scientist, NASA’s Jet Propulsion Laboratory; and Leesa Hubbard, teacher in residence, Sally Ride Science, San Diego. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6767

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – – A Gravity Recovery and Interior Laboratory (GRAIL) mission science briefing is held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. From left are Robert Fogel, NASA’s GRAIL program scientist; Maria Zuber, GRAIL principal investigator with the Massachusetts Institute of Technology; Sami Asmar, GRAIL deputy project scientist, NASA’s Jet Propulsion Laboratory; and Leesa Hubbard, teacher in residence, Sally Ride Science, San Diego. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6925

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Over a group of trees and bushes, the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission launches off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/George Roberts

KSC-2011-6891

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – At ignition, flames from the engines begin liftoff of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Sandra Joseph and Don Kight

KSC-2011-6899

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Plumes of smoke surround of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station In Florida. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Sandra Joseph and Don Kight

KSC-2011-6889

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Overlooking the Central Florida coast, engine ignition begins liftoff of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Sandra Joseph and Don Kight

KSC-2011-6789

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – NASA Administrator Charlie Bolden shares a humorous moment with a group of Tweetup participants at the Kennedy Space Center Visitor Complex in Florida during prelaunch activities for the agency’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured NASA’s Kennedy Space Center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Gianni Woods

KSC-2011-6893

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Flames and smoke from the engines surround the United Launch Alliance Delta II rocket at liftoff carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Sandra Joseph and Don Kight

KSC-2011-6864

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Fire and smoke light up the sky as a United Launch Alliance Delta II Heavy rocket propels NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission into space. Liftoff from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida was at 9:08:52 a.m. EDT Sept.10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Darrell McCall

KSC-2011-6813

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – A Tweetup participant searches for the right photo angle along the NASA Causeway launch viewing area at NASA’s Kennedy Space Center in Florida during prelaunch activities for the agency’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured the center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

The Electric Wind of Venus: A Global and Persistent Polar Wind -Like Ambipolar Electric Field Sufficient for the Direct Escape of Heavy Ionospheric Ions

NASA Technical Reports Server (NTRS)

Collinson, Glyn A.; Frahm, Rudy A.; Glocer, Alex; Coates, Andrew J.; Grebowsky, Joseph M.; Barabash, Stas; Domagal-Goldman, Shawn D.; Federov, Andrei; Futaana, Yoshifumi; Gilbert, Lin K.;

Multilayer densities using a wavelet-based gravity method and their tectonic implications beneath the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, Chuang; Luo, Zhicai; Sun, Rong; Zhou, Hao; Wu, Yihao

2018-06-01

Determining density structure of the Tibetan Plateau is helpful in better understanding of tectonic structure and development. Seismic method, as traditional approach obtaining a large number of achievements of density structure in the Tibetan Plateau except in the centre and west, is primarily inhibited by the poor seismic station coverage. As the implementation of satellite gravity missions, gravity method is more competitive because of global homogeneous gravity coverage. In this paper, a novel wavelet-based gravity method with high computation efficiency and excellent local identification capability is developed to determine multilayer densities beneath the Tibetan Plateau. The inverted six-layer densities from 0 to 150 km depth can reveal rich tectonic structure and development of study area: (1) The densities present a clockwise pattern, nearly east-west high-low alternating pattern in the west and nearly south-north high-low alternating pattern in the east, which is almost perpendicular to surface movement direction relative to the stable Eurasia from the Global Positioning System velocity field; (2) Apparent fold structure approximately from 10 to 110 km depth can be inferred from the multilayer densities, the deformational direction of which is nearly south-north in the west and east-west in the east; (3) Possible channel flows approximately from 30 to 110 km depth can also be observed clearly during the multilayer densities. Moreover, the inverted multilayer densities are in agreement with previous studies, which verify the correctness and effectiveness of our method.

Multilayer Densities Using a Wavelet-based Gravity Method and Their Tectonic Implications beneath the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, Chuang; Luo, Zhicai; Sun, Rong; Zhou, Hao; Wu, Yihao

2018-03-01

Determining density structure of the Tibetan Plateau is helpful in better understanding tectonic structure and development. Seismic method, as traditional approach obtaining a large number of achievements of density structure in the Tibetan Plateau except in the center and west, is primarily inhibited by the poor seismic station coverage. As the implementation of satellite gravity missions, gravity method is more competitive because of global homogeneous gravity coverage. In this paper, a novel wavelet-based gravity method with high computation efficiency and excellent local identification capability is developed to determine multilayer densities beneath the Tibetan Plateau. The inverted 6-layer densities from 0 km to 150 km depth can reveal rich tectonic structure and development of study area: (1) The densities present a clockwise pattern, nearly east-west high-low alternating pattern in the west and nearly south-north high-low alternating pattern in the east, which is almost perpendicular to surface movement direction relative to the stable Eurasia from the Global Positioning System velocity field; (2) Apparent fold structure approximately from 10 km to 110 km depth can be inferred from the multilayer densities, the deformational direction of which is nearly south-north in the west and east-west in the east; (3) Possible channel flows approximately from 30 km to 110 km depth can be also observed clearly during the multilayer densities. Moreover, the inverted multilayer densities are in agreement with previous studies, which verify the correctness and effectiveness of our method.

Gravity and Nonconservative Force Model Tuning for the GEOSAT Follow-On Spacecraft

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Zelensky, Nikita P.; Rowlands, David D.; Luthcke, Scott B.; Chinn, Douglas S.; Marr, Gregory C.; Smith, David E. (Technical Monitor)

2000-01-01

The US Navy's GEOSAT Follow-On spacecraft was launched on February 10, 1998 and the primary objective of the mission was to map the oceans using a radar altimeter. Three radar altimeter calibration campaigns have been conducted in 1999 and 2000. The spacecraft is tracked by satellite laser ranging (SLR) and Doppler beacons and a limited amount of data have been obtained from the Global Positioning Receiver (GPS) on board the satellite. Even with EGM96, the predicted radial orbit error due to gravity field mismodelling (to 70x70) remains high at 2.61 cm (compared to 0.88 cm for TOPEX). We report on the preliminary gravity model tuning for GFO using SLR, and altimeter crossover data. Preliminary solutions using SLR and GFO/GFO crossover data from CalVal campaigns I and II in June-August 1999, and January-February 2000 have reduced the predicted radial orbit error to 1.9 cm and further reduction will be possible when additional data are added to the solutions. The gravity model tuning has improved principally the low order m-daily terms and has reduced significantly the geographically correlated error present in this satellite orbit. In addition to gravity field mismodelling, the largest contributor to the orbit error is the non-conservative force mismodelling. We report on further nonconservative force model tuning results using available data from over one cycle in beta prime.

Glacial isostatic adjustment on the Northern Hemisphere - new results from GRACE

NASA Astrophysics Data System (ADS)

Mueller, J.; Steffen, H.; Gitlein, O.; Denker, H.; Timmen, L.

2007-12-01

The Earth's gravity field mapped by the Gravity Recovery and Climate Experiment (GRACE) satellite mission shows variations due to the integral effect of mass variations in the atmosphere, hydrosphere and geosphere. The Earth's gravity field is provided in form of monthly solutions by several institutions, e.~g. GFZ Potsdam, CSR and JPL. During the GRACE standard processing of these analysis centers, oceanic and atmospheric contributions as well as tidal effects are reduced. The solutions of the analysis centers differ slightly, which is due the application of different reduction models and center-specific processing schemes. We present our investigation of mass variations in the areas of glacial isostatic adjustment (GIA) in North America and Northern Europe from GRACE data. One key issue is the separation of GIA parts and the reduction of the observed quantities by applying dedicated filters (e.~g. isotropic, non-isotropic, and destriping filters) and global models of hydrological variations (e.~g. WGHM, LaDWorld, GLDAS). In a further step, we analyze the results of both regions regarding their reliability, and finally present a comparison to results of a geodynamical modeling and absolute gravity measurements. Our results clearly show that the quality of the GRACE-derived gravity- change signal benefits from improved reduction models and chosen analysis techniques. Nevertheless, the comparison to results of geodynamic models still reveals differences, and thus further studies are in progress.

AIUB-RL02: an improved time-series of monthly gravity fields from GRACE data

NASA Astrophysics Data System (ADS)

Meyer, U.; Jäggi, A.; Jean, Y.; Beutler, G.

2016-05-01

The new release AIUB-RL02 of monthly gravity models from GRACE GPS and K-Band range-rate data is based on reprocessed satellite orbits referring to the reference frame IGb08. The release is consistent with the IERS2010 conventions. Improvements with respect to its predecessor AIUB-RL01 include the use of reprocessed (RL02) GRACE observations, new atmosphere and ocean dealiasing products (RL05), an upgraded ocean tide model (EOT11A), and the interpolation of shallow ocean tides (admittances). The stochastic parametrization of AIUB-RL02 was adapted to include daily accelerometer scale factors, which drastically reduces spurious signal at the 161 d period in C20 and at other low degree and order gravity field coefficients. Moreover, the correlation between the noise in the monthly gravity models and solar activity is considerably reduced in the new release. The signal and the noise content of the new AIUB-RL02 monthly gravity fields are studied and calibrated errors are derived from their non-secular and non-seasonal variability. The short-period time-variable signal over the oceans, mostly representing noise, is reduced by 50 per cent with respect to AIUB-RL01. Compared to the official GFZ-RL05a and CSR-RL05 monthly models, the AIUB-RL02 stands out by its low noise at high degrees, a fact emerging from the estimation of seasonal variations for selected river basins and of mass trends in polar regions. Two versions of the monthly AIUB-RL02 gravity models, with spherical harmonics resolution of degree and order 60 and 90, respectively, are available for the time period from March 2003 to March 2014 at the International Center for Global Earth Models or from ftp://ftp.unibe.ch/aiub/GRAVITY/GRACE (last accessed 22 March 2016).

Simulation study on combination of GRACE monthly gravity field solutions

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2016-04-01

The GRACE monthly gravity fields from different processing centers are combined in the frame of the project EGSIEM. This combination is done on solution level first to define weights which will be used for a combination on normal equation level. The applied weights are based on the deviation of the individual gravity fields from the arithmetic mean of all involved gravity fields. This kind of weighting scheme relies on the assumption that the true gravity field is close to the arithmetic mean of the involved individual gravity fields. However, the arithmetic mean can be affected by systematic errors in individual gravity fields, which consequently results in inappropriate weights. For the future operational scientific combination service of GRACE monthly gravity fields, it is necessary to examine the validity of the weighting scheme also in possible extreme cases. To investigate this, we make a simulation study on the combination of gravity fields. Firstly, we show how a deviated gravity field can affect the combined solution in terms of signal and noise in the spatial domain. We also show the impact of systematic errors in individual gravity fields on the resulting combined solution. Then, we investigate whether the weighting scheme still works in the presence of outliers. The result of this simulation study will be useful to understand and validate the weighting scheme applied to the combination of the monthly gravity fields.

Terrestrial Water Mass Load Changes from Gravity Recovery and Climate Experiment (GRACE)

NASA Technical Reports Server (NTRS)

Seo, K.-W.; Wilson, C. R.; Famiglietti, J. S.; Chen, J. L.; Rodell M.

2006-01-01

Recent studies show that data from the Gravity Recovery and Climate Experiment (GRACE) is promising for basin- to global-scale water cycle research. This study provides varied assessments of errors associated with GRACE water storage estimates. Thirteen monthly GRACE gravity solutions from August 2002 to December 2004 are examined, along with synthesized GRACE gravity fields for the same period that incorporate simulated errors. The synthetic GRACE fields are calculated using numerical climate models and GRACE internal error estimates. We consider the influence of measurement noise, spatial leakage error, and atmospheric and ocean dealiasing (AOD) model error as the major contributors to the error budget. Leakage error arises from the limited range of GRACE spherical harmonics not corrupted by noise. AOD model error is due to imperfect correction for atmosphere and ocean mass redistribution applied during GRACE processing. Four methods of forming water storage estimates from GRACE spherical harmonics (four different basin filters) are applied to both GRACE and synthetic data. Two basin filters use Gaussian smoothing, and the other two are dynamic basin filters which use knowledge of geographical locations where water storage variations are expected. Global maps of measurement noise, leakage error, and AOD model errors are estimated for each basin filter. Dynamic basin filters yield the smallest errors and highest signal-to-noise ratio. Within 12 selected basins, GRACE and synthetic data show similar amplitudes of water storage change. Using 53 river basins, covering most of Earth's land surface excluding Antarctica and Greenland, we document how error changes with basin size, latitude, and shape. Leakage error is most affected by basin size and latitude, and AOD model error is most dependent on basin latitude.

Measurement and Interpretation of Temporal Variations of the Earths Gravity Field Using GPS and SLR Data

NASA Technical Reports Server (NTRS)

Nerem, R. Steven; Leuliette, Eric; Russell, Gary

2003-01-01

This investigation has had four main thrusts: 1) The analysis of seasonal variations of the Earth's gravitational field using Lageos 1 and 2 SLR data and comparisons to geophysical models. We have estimated the annual variation of the gravity field via a spherical harmonic expansion complete to degree and order 4. We have also constructed a similar model using models of the annual variation in the gravity field due to atmospheric, hydrologic, and ocean mass redistribution. These three models, when combined together, are in excellent agreement with the variations observed by satellite laser ranging. An article on these results was published in the journal Geophysical Research Letters. 2) The second thrust of our investigation has been to analyze the output of a Global Climate Model (GCM) to determine if the GRACE gravity mission can be expected to detect climate change signals. Working with Gary Russell at the Goddard Institute for Space Studies (GISS), we have determined that there are several large secular signals that GRACE might be able to detect, including secular changes in snow cover, sea ice, polar ice, ocean mass, and other variables. It is possible that some of these signals could be detected with 5 years of GRACE measurements - its hard to judge this because the interannual variability in the GCM, which could mask the climate signals, is unreliable. Certainly a follow-on GRACE mission could detect these signals when compared to the data from the initial GRACE mission.). An article on these results will be published in the journal Journal of Geophysical Research. 3) In the last year of the investigation, we developed a new technique for analyzing temporal gravity variations using "geophysical fingerprints", which was successfully demonstrated on 20 years of satellite laser ranging data [Nerem et al., 20031. 4]. We also participated in a workshop on future satellite gravity measurements, which resulted in paper on measuring ocean mass variations using GRACE [Nerem et al., 20031 and on using laser interferometry for future gravity missions [Bender et al., 20031].

Coseismic Gravity and Displacement Signatures Induced by the 2013 Okhotsk Mw8.3 Earthquake.

PubMed

Zhang, Guoqing; Shen, Wenbin; Xu, Changyi; Zhu, Yiqing

2016-09-01

In this study, Gravity Recovery and Climate Experiment (GRACE) RL05 data from January 2003 to October 2014 were used to extract the coseismic gravity changes induced by the 24 May 2013 Okhotsk Mw8.3 deep-focus earthquake using the difference and least square fitting methods. The gravity changes obtained from GRACE data agreed well with those from dislocation theory in both magnitude and spatial pattern. Positive and negative gravity changes appeared on both sides of the epicenter. The positive signature appeared on the western side, and the peak value was approximately 0.4 microgal (1 microgal = 10(-8) m/s²), whereas on the eastern side, the gravity signature was negative, and the peak value was approximately -1.1 microgal. It demonstrates that deep-focus earthquakes Mw ≤ 8.5 are detectable by GRACE observations. Moreover, the coseismic displacements of 20 Global Positioning System (GPS) stations on the Earth's surface were simulated using an elastic dislocation theory in a spherical earth model, and the results are consistent with the GPS results, especially the near-field results. We also estimated the gravity contributions from the coseismic vertical displacements and density changes, analyzed the proportion of these two gravity change factors (based on an elastic dislocation theory in a spherical earth model) in this deep-focus earthquake. The gravity effect from vertical displacement is four times larger than that caused by density redistribution.

Two decades of ice melt reconstruction in Greenland and Antarctica from time-variable gravity

NASA Astrophysics Data System (ADS)

Talpe, M.; Nerem, R. S.; Lemoine, F. G.

2014-12-01

In this study, we present a record of ice-sheet melt derived from space-borne gravity that spans over two decades—beyond the time-frame of the GRACE mission. GRACE fields are merged with conventional tracking data (SLR/DORIS) spanning 1992 to the present. They are provided as weekly global fields of degree and order five without C50 and S50 but with C61 and S61. Their multi-decade timespan complements the monthly fields of GRACE of degree and order 60 that start in 2003 and will end when the GRACE mission terminates. The two datasets are combined via an empirical orthogonal function analysis, whereby the conventional tracking data temporal modes are obtained by fitting the SLR/DORIS coefficients to the GRACE spatial modes via linear least squares. Combining those temporal modes with GRACE spatial modes yields the reconstructed global gravity fields. The error budget of the reconstructions is composed of three components: the SLR/DORIS covariances, the errors estimated from the assumption that GRACE spatial modes can be mapped over the SLR/DORIS timeframe, and the covariances from the least squares fit applied to obtain the SLR/DORIS temporal modes. The reconstructed surface mass changes in Greenland and Antarctica, predominantly captured in the first mode, show a rate of mass loss that is increasing since 1992. The trend of mass changes in Greenland over various epochs match with an overarching study assembling altimetry, gravimetry, and interferometry estimates of ice-sheet balance over a 1992-2011 time-frame [Shepherd et al., 2012]. Antarctica shows a trend that is different because of updated GIA models [A et al., 2013] compared to the other studies. We will also show regional mass changes over various other basins, as well as the influence of each SLR/DORIS coefficient on the reconstructions. The consistency of these results underscores the possibility of using low-resolution SLR/DORIS time-variable gravity solutions as a way to continuously monitor the behavior of the polar ice-sheets in the absence of GRACE. Shepherd, A., et al. (2012), Science 338, 1183. A, G., J. Wahr, and S. Zhong (2013), GJI 192, 557.

Geodynamics Branch research report, 1982

NASA Technical Reports Server (NTRS)

Kahn, W. D. (Editor); Cohen, S. C. (Editor)

1983-01-01

The research program of the Geodynamics Branch is summarized. The research activities cover a broad spectrum of geoscience disciplines including space geodesy, geopotential field modeling, tectonophysics, and dynamic oceanography. The NASA programs which are supported by the work described include the Geodynamics and Ocean Programs, the Crustal Dynamics Project, the proposed Ocean Topography Experiment (TOPEX) and Geopotential Research Mission. The individual papers are grouped into chapters on Crustal Movements, Global Earth Dynamics, Gravity Field Model Development, Sea Surface Topography, and Advanced Studies.

A tale of two superpotentials: Stability and instability in designer gravity

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

Amsel, Aaron J.; Marolf, Donald; Hertog, Thomas

We investigate the stability of asymptotically anti-de Sitter gravity coupled to tachyonic scalar fields with mass at or slightly above the Breitenlohner-Freedman bound. The boundary conditions in these 'designer gravity' theories are defined in terms of an arbitrary function W. Previous work had suggested that the energy in designer gravity is bounded below if (i) W has a global minimum and (ii) the scalar potential admits a superpotential P. More recently, however, certain solutions were found (numerically) to violate the proposed energy bound. We resolve the discrepancy by observing that a given scalar potential can admit two possible branches ofmore » the corresponding superpotential, P{sub {+-}}. When there is a P{sub -} branch, we rigorously prove a lower bound on the energy; the P{sub +} branch alone is not sufficient. Our numerical investigations (i) confirm this picture, (ii) confirm other critical aspects of the (complicated) proofs, and (iii) suggest that the existence of P{sub -} may in fact be necessary (as well as sufficient) for the energy of a designer gravity theory to be bounded below.« less

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.

GRGM900C: A degree 900 lunar gravity model from GRAIL primary and extended mission data

PubMed Central

Lemoine, Frank G; Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Mazarico, Erwan; Rowlands, David D; Loomis, Bryant D; Chinn, Douglas S; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-01-01

We have derived a gravity field solution in spherical harmonics to degree and order 900, GRGM900C, from the tracking data of the Gravity Recovery and Interior Laboratory (GRAIL) Primary (1 March to 29 May 2012) and Extended Missions (30 August to 14 December 2012). A power law constraint of 3.6 ×10−4/ℓ2 was applied only for degree ℓ greater than 600. The model produces global correlations of gravity, and gravity predicted from lunar topography of ≥ 0.98 through degree 638. The model's degree strength varies from a minimum of 575–675 over the central nearside and farside to 900 over the polar regions. The model fits the Extended Mission Ka-Band Range Rate data through 17 November 2012 at 0.13 μm/s RMS, whereas the last month of Ka-Band Range-Rate data obtained from altitudes of 2–10 km fit at 0.98 μm/s RMS, indicating that there is still signal inherent in the tracking data beyond degree 900. PMID:26074638

GRGM900C: A degree 900 lunar gravity model from GRAIL primary and extended mission data.

PubMed

Lemoine, Frank G; Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Mazarico, Erwan; Rowlands, David D; Loomis, Bryant D; Chinn, Douglas S; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-05-28

We have derived a gravity field solution in spherical harmonics to degree and order 900, GRGM900C, from the tracking data of the Gravity Recovery and Interior Laboratory (GRAIL) Primary (1 March to 29 May 2012) and Extended Missions (30 August to 14 December 2012). A power law constraint of 3.6 ×10 -4 / ℓ 2 was applied only for degree ℓ greater than 600. The model produces global correlations of gravity, and gravity predicted from lunar topography of ≥ 0.98 through degree 638. The model's degree strength varies from a minimum of 575-675 over the central nearside and farside to 900 over the polar regions. The model fits the Extended Mission Ka-Band Range Rate data through 17 November 2012 at 0.13 μm/s RMS, whereas the last month of Ka-Band Range-Rate data obtained from altitudes of 2-10 km fit at 0.98 μm/s RMS, indicating that there is still signal inherent in the tracking data beyond degree 900.

GRGM900C: A Degree 900 Lunar Gravity Model from GRAIL Primary and Extended Mission Data

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Goossens, Sander; Sabaka, Terence J.; Nicholas, Joseph B.; Mazarico, Erwan; Rowlands, David D.; Bryant, D. Loomis; Chinn, Douglas S.; Neumann, Gregory A.; Smith, David E.;

New Views of Earth's Gravity Field from GRACE

NASA Technical Reports Server (NTRS)

2003-01-01

[figure removed for brevity, see original site] [figure removed for brevity, see original site] Map 1Map 2

Gravity and the Earth's Shape Gravity is the force that is responsible for the weight of an object and is determined by how the material that makes up the Earth is distributed throughout the Earth. Because gravity changes over the surface of the Earth, the weight of an object changes along with it. One can define standard gravity as the value of gravity for an perfectly smooth 'idealized' Earth, and the gravity 'anomaly' is a measure of how actual gravity deviates from this standard. Gravity reflects the Earth's surface topography to a high degree and is associated with features that most people are familiar with such as large mountains and deep ocean trenches.

Progress in Measuring the Earth's Gravity Field Through GRACE Prior to GRACE, the Earth's gravity field was determined using measurements of varying quality from different satellites and of incomplete coverage. Consequently the accuracy and resolution of the gravity field were limited. As is shown in Figure 1, the long wavelength components of the gravity field determined from satellite tracking were limited to a resolution of approximately 700 km. At shorter wavelengths, the errors were too large to be useful. Only broad geophysical features of the Earth's structure could be detected (see map 1).

In contrast, GRACE, by itself, has provided accurate gravity information with a resolution of 200 km. Now, much more detail is clearly evident in the Earth's geophysical features (see map 2). High resolution features detected by GRACE that are representative of geophysical phenomena include the Tonga/Kermadec region (a zone where one tectonic plate slides under another), the Himalayan/Tibetan Plateau region (an area of uplift due to colliding plates), and the mid-Atlantic ridge (an active spreading center in the middle of the Atlantic ocean where new crust is being created). Future GRACE gravity models are expected to increase the resolution further. The second figure confirms that the Grace data is global, homogeneous and highly accurate. These are all properties that have been sought for gravity model development.

[figure removed for brevity, see original site] Ocean Circulation Measurements from Grace The arrows in the three data sets in Figure 3 depict ocean currents off the East Coast of the United States, 1,000 meters (approximately 3,280 feet) beneath the surface. The top panel is obtained from the GRACE geoid, satellite altimetry and ship measurements of temperature and salt. The bottom panel is computed in the same manner as the top one, except that the best geoid prior to GRACE is used instead of the GRACE geoid. The middle panel shows direct measurement of those currents by floats deployed from ships. Notice that the current arrows in the Gulf Stream extension, East and slightly South of Washington DC, point eastward, toward Europe, in the two upper panels, but in the opposite direction in the lower panel. Colors indicate the strength of the ocean current, with red being strongest and blue-green weakest. Areas in white have no available data.

The Gulf Stream region of the North Atlantic is among the best studied in the world's oceans, with a significant quantity of high-quality data available on it as a result of shipborne instrument measurements. In less well studied regions, the new information provided by GRACE, together with satellite altimetry, will increase our knowledge of ocean circulation.

High-latitude filtering in a global grid-point model using model normal modes. [Fourier filters for synoptic weather forecasting

NASA Technical Reports Server (NTRS)

Takacs, L. L.; Kalnay, E.; Navon, I. M.

1985-01-01

A normal modes expansion technique is applied to perform high latitude filtering in the GLAS fourth order global shallow water model with orography. The maximum permissible time step in the solution code is controlled by the frequency of the fastest propagating mode, which can be a gravity wave. Numerical methods are defined for filtering the data to identify the number of gravity modes to be included in the computations in order to obtain the appropriate zonal wavenumbers. The performances of the model with and without the filter, and with a time tendency and a prognostic field filter are tested with simulations of the Northern Hemisphere winter. The normal modes expansion technique is shown to leave the Rossby modes intact and permit 3-5 day predictions, a range not possible with the other high-latitude filters.

The use of absolute gravity data for the validation of Global Geopotential Models and for improving quasigeoid heights determined from satellite-only Global Geopotential Models

NASA Astrophysics Data System (ADS)

Godah, Walyeldeen; Krynski, Jan; Szelachowska, Malgorzata

2018-05-01

The objective of this paper is to demonstrate the usefulness of absolute gravity data for the validation of Global Geopotential Models (GGMs). It is also aimed at improving quasigeoid heights determined from satellite-only GGMs using absolute gravity data. The area of Poland, as a unique one, covered with a homogeneously distributed set of absolute gravity data, has been selected as a study area. The gravity anomalies obtained from GGMs were validated using the corresponding ones determined from absolute gravity data. The spectral enhancement method was implemented to overcome the spectral inconsistency in data being validated. The quasigeoid heights obtained from the satellite-only GGM as well as from the satellite-only GGM in combination with absolute gravity data were evaluated with high accuracy GNSS/levelling data. Estimated accuracy of gravity anomalies obtained from GGMs investigated is of 1.7 mGal. Considering omitted gravity signal, e.g. from degree and order 101 to 2190, satellite-only GGMs can be validated at the accuracy level of 1 mGal using absolute gravity data. An improvement up to 59% in the accuracy of quasigeoid heights obtained from the satellite-only GGM can be observed when combining the satellite-only GGM with absolute gravity data.

The BepiColombo MORE gravimetry and rotation experiments with the ORBIT14 software

NASA Astrophysics Data System (ADS)

Cicalò, S.; Schettino, G.; Di Ruzza, S.; Alessi, E. M.; Tommei, G.; Milani, A.

2016-04-01

The BepiColombo mission to Mercury is an ESA/JAXA cornerstone mission, consisting of two spacecraft in orbit around Mercury addressing several scientific issues. One spacecraft is the Mercury Planetary Orbiter, with full instrumentation to perform radio science experiments. Very precise radio tracking from Earth, on-board accelerometer and optical measurements will provide large data sets. From these it will be possible to study the global gravity field of Mercury and its tidal variations, its rotation state and the orbit of its centre of mass. With the gravity field and rotation state, it is possible to constrain the internal structure of the planet. With the orbit of Mercury, it is possible to constrain relativistic theories of gravitation. In order to assess that all the scientific goals are achievable with the required level of accuracy, full cycle numerical simulations of the radio science experiment have been performed. Simulated tracking, accelerometer and optical camera data have been generated, and a long list of variables including the spacecraft initial conditions, the accelerometer calibrations and the gravity field coefficients have been determined by a least-squares fit. The simulation results are encouraging: the experiments are feasible at the required level of accuracy provided that some critical terms in the accelerometer error are moderated. We will show that BepiColombo will be able to provide at least an order of magnitude improvement in the knowledge of Love number k2, libration amplitudes and obliquity, along with a gravity field determination up to degree 25 with a signal-to-noise ratio of 10.

The Hawking temperature in the context of dark energy

NASA Astrophysics Data System (ADS)

Gangopadhyay, Debashis; Manna, Goutam

2012-11-01

An emergent-gravity metric incorporating k-essence scalar fields ϕ having a Born-Infeld-type Lagrangian is mapped into a metric whose structure is similar to that of a blackhole of large mass M that has swallowed a global monopole. However, here the field is not that of a monopole but rather that of a k-essence scalar field. If ϕemergent are the solutions of the emergent-gravity equations of motion under cosmological boundary conditions at ∞, then for r\\rightarrow \\infty the rescaled field \\frac {\\phi _{emergent}}{2GM-1} has exact correspondence with ϕ with ϕ(r,t) = ϕ1(r) + ϕ2(t). The Hawking temperature of this metric is T_{ emergent}= \\frac {\\hbar c^{3}}{8\\pi GM k_{B}}(1-K)^{2}\\equiv \\frac {\\hbar }{8\\pi GM k_{B}}(1-K)^{2} , taking the speed of light c = 1. Here K=\\dot \\phi _{2}^{2} is the kinetic energy of the k-essence field ϕ and K is always less than unity, kB is the Boltzmann constant. This is phenomenologically interesting in the context of Belgiorno et al.'s gravitational analogue experiment.

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.

Source Parameter Inversion for Recent Great Earthquakes from a Decade-long Observation of Global Gravity Fields

NASA Technical Reports Server (NTRS)

Han, Shin-Chan; Riva, Ricccardo; Sauber, Jeanne; Okal, Emile

2013-01-01

We quantify gravity changes after great earthquakes present within the 10 year long time series of monthly Gravity Recovery and Climate Experiment (GRACE) gravity fields. Using spherical harmonic normal-mode formulation, the respective source parameters of moment tensor and double-couple were estimated. For the 2004 Sumatra-Andaman earthquake, the gravity data indicate a composite moment of 1.2x10(exp 23)Nm with a dip of 10deg, in agreement with the estimate obtained at ultralong seismic periods. For the 2010 Maule earthquake, the GRACE solutions range from 2.0 to 2.7x10(exp 22)Nm for dips of 12deg-24deg and centroid depths within the lower crust. For the 2011 Tohoku-Oki earthquake, the estimated scalar moments range from 4.1 to 6.1x10(exp 22)Nm, with dips of 9deg-19deg and centroid depths within the lower crust. For the 2012 Indian Ocean strike-slip earthquakes, the gravity data delineate a composite moment of 1.9x10(exp 22)Nm regardless of the centroid depth, comparing favorably with the total moment of the main ruptures and aftershocks. The smallest event we successfully analyzed with GRACE was the 2007 Bengkulu earthquake with M(sub 0) approx. 5.0x10(exp 21)Nm. We found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events. Deeper sources (i.e., in the upper mantle) could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume, thus reducing the negative gravity component. Focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum.

A SmallSat constellation mission architecture for a GRACE-type mission design

NASA Astrophysics Data System (ADS)

Deccia, C. M. A.; Nerem, R. S.; Yunck, T.

2017-12-01

The Gravity Recovery and Climate Experiment (GRACE) launched in 2002 and has been providing invaluable information of Earth's time-varying gravity field and GRACE-FO will continue this time series. For this work, we focus on architectures of future post-GRACE-FO like missions. Single pairs of satellites like GRACE and GRACE-FO are inherently limited in their spatio-temporal coverage. Full global coverage for a single pair can take up to 30 days for spatial resolutions of a few hundred kilometers, thus a single satellite pair is unable to observe sub-monthly signals in the Earth's time varying gravity field (e.g. hydrologic signals, etc.). Small satellite systems are becoming increasingly affordable and will soon allow a constellation of GRACE-type satellites to be deployed, with the capability to range between multiple satellites. Here, using simulation studies, we investigate the performance of such a constellation for different numbers of satellites (N) and different orbital configurations, in order to understand the improved performance that might be gained from such future mission architectures.

The formation and analysis of a 5 deg equal area block terrestrial gravity field

NASA Technical Reports Server (NTRS)

Rapp, R. H.

1972-01-01

A set of 23,355 1 degree x 1 degree mean free air anomalies were used to predict a set of 5 degree equal area anomalies and their standard errors. Using the 1 degree data incorporating geophysically predicted values of ACIC, 1283 5 degree blocks were computed. Excluding the geophysically predicted anomalies 1249 blocks were computed. The 1 degree data were also used to compute covariance functions and the equatorial gravity and flattening implied by this data. The predicted anomalies were supplemented by model anomalies to form a complete 1654 global anomaly field. These data were used in a weighted least squares to determine potential coefficients to degree 15, and in a summation type formulation to determine potential coefficients to degree 25. These potential coefficients sets are compared to recent satellite determinations.

KSC-2011-6820

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are David Lehman, spacecraft mission director and GRAIL project manager, NASA's Jet Propulsion Laboratory (JPL); Tom Hoffman, deputy spacecraft mission director, JPL; and John Henk, GRAIL program manager, Lockheed Martin Space Systems. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

Comparison result of inversion of gravity data of a fault by particle swarm optimization and Levenberg-Marquardt methods.

PubMed

Toushmalani, Reza

2013-01-01

The purpose of this study was to compare the performance of two methods for gravity inversion of a fault. First method [Particle swarm optimization (PSO)] is a heuristic global optimization method and also an optimization algorithm, which is based on swarm intelligence. It comes from the research on the bird and fish flock movement behavior. Second method [The Levenberg-Marquardt algorithm (LM)] is an approximation to the Newton method used also for training ANNs. In this paper first we discussed the gravity field of a fault, then describes the algorithms of PSO and LM And presents application of Levenberg-Marquardt algorithm, and a particle swarm algorithm in solving inverse problem of a fault. Most importantly the parameters for the algorithms are given for the individual tests. Inverse solution reveals that fault model parameters are agree quite well with the known results. A more agreement has been found between the predicted model anomaly and the observed gravity anomaly in PSO method rather than LM method.

Fast calculation of low altitude disturbing gravity for ballistics

NASA Astrophysics Data System (ADS)

Wang, Jianqiang; Wang, Fanghao; Tian, Shasha

2018-03-01

Fast calculation of disturbing gravity is a key technology in ballistics while spherical cap harmonic(SCH) theory can be used to solve this problem. By using adjusted spherical cap harmonic(ASCH) methods, the spherical cap coordinates are projected into a global coordinates, then the non-integer associated Legendre functions(ALF) of SCH are replaced by integer ALF of spherical harmonics(SH). This new method is called virtual spherical harmonics(VSH) and some numerical experiment were done to test the effect of VSH. The results of earth's gravity model were set as the theoretical observation, and the model of regional gravity field was constructed by the new method. Simulation results show that the approximated errors are less than 5mGal in the low altitude range of the central region. In addition, numerical experiments were conducted to compare the calculation speed of SH model, SCH model and VSH model, and the results show that the calculation speed of the VSH model is raised one order magnitude in a small scope.

Users Guide to the JPL Doppler Gravity Database

NASA Technical Reports Server (NTRS)

Muller, P. M.; Sjogren, W. L.

1986-01-01

Local gravity accelerations and gravimetry have been determined directly from spacecraft Doppler tracking data near the Moon and various planets by the Jet Propulsion Laboratory. Researchers in many fields have an interest in planet-wide global gravimetric mapping and its applications. Many of them use their own computers in support of their studies and would benefit from being able to directly manipulate these gravity data for inclusion in their own modeling computations. Pubication of some 150 Apollo 15 subsatellite low-altitude, high-resolution, single-orbit data sets is covered. The doppler residuals with a determination of the derivative function providing line-of-sight-gravity are both listed and plotted (on microfilm), and can be ordered in computer readable forms (tape and floppy disk). The form and format of this database as well as the methods of data reduction are explained and referenced. A skeleton computer program is provided which can be modified to support re-reductions and re-formatted presentations suitable to a wide variety of research needs undertaken on mainframe or PC class microcomputers.

Time-Variable Gravity from Space: Quarter Century of Observations, Mysteries, and Prospects

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.

2003-01-01

Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth s dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease - until around 1998, when it switched quite suddenly to an increase trend which has continued to date. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this 52 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution @e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

Introduction to the AdS/CFT Correspondence

NASA Astrophysics Data System (ADS)

Nąstase, Horaǧiu

2015-09-01

Preface; Introduction; Part I. Background: 1. Elements of quantum field theory and gauge theory; 2. Basics of general relativity. Anti-de Sitter space; 3. Basics of supersymmetry; 4. Basics of supergravity; 5. Kaluza-Klein dimensional reduction; 6. Black holes and p-branes; 7. String theory actions and spectra; 8. Elements of conformal field theory; 9. D-branes; Part II. Basics of AdS/CFT for N = 4 SYM vs AdS5 × S5: 10. The AdS/CFT correspondence: motivation, definition and spectra; 11. Witten prescription and 3-point correlator calculations; 12. Holography in Lorentzian signature: Poincaré and global; 13. Solitonic objects in AdS/CFT; 14. Quarks and the Wilson loop; 15. Finite temperature and N = 4 SYM plasmas; 16. Scattering processes and gravitational shockwave limit; 17. The pp-wave correspondence; 18. Spin chains; Part III. AdS/CFT Developments and Gauge-Gravity Dualities: 19. Other conformal cases; 20. The 3 dimensional ABJM model vs. AdS4 × CP3; 21. Gravity duals; 22. Holographic renormalization; 23. RG flow between fixed points; 24. Phenomenological gauge-gravity duality I: AdS/QCD; 25. Phenomenological gauge-gravity duality II: AdS/CMT; 26. Gluon scattering: the Alday-Maldacena prescription; 27. Holographic entanglement entropy: the Ryu-Takayanagi prescription.

Quantum statistical relation for black holes in nonlinear electrodynamics coupled to Einstein-Gauss-Bonnet AdS gravity

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

Miskovic, Olivera; Olea, Rodrigo

2011-03-15

We consider curvature-squared corrections to Einstein-Hilbert gravity action in the form of a Gauss-Bonnet term in D>4 dimensions. In this theory, we study the thermodynamics of charged static black holes with anti-de Sitter (AdS) asymptotics, and whose electric field is described by nonlinear electrodynamics. These objects have received considerable attention in recent literature on gravity/gauge dualities. It is well-known that, within the framework of anti-de Sitter/conformal field theory (AdS/CFT) correspondence, there exists a nonvanishing Casimir contribution to the internal energy of the system, manifested as the vacuum energy for global AdS spacetime in odd dimensions. Because of this reason, wemore » derive a quantum statistical relation directly from the Euclidean action and not from the integration of the first law of thermodynamics. To this end, we employ a background-independent regularization scheme which consists, in addition to the bulk action, of counterterms that depend on both extrinsic and intrinsic curvatures of the boundary (Kounterterm series). This procedure results in a consistent inclusion of the vacuum energy and chemical potential in the thermodynamic description for Einstein-Gauss-Bonnet AdS gravity regardless of the explicit form of the nonlinear electrodynamics Lagrangian.« less

Determining the 3D Subsurface Density Structure of Taurus Littrow Valley Using Apollo 17 Gravity Data

NASA Technical Reports Server (NTRS)

Urbancic, N.; Ghent, R.; Stanley, S,; Johnson, C. L.; Carroll, K. A.; Hatch, D.; Williamson, M. C.; Garry, W. B.; Talwani, M.

2016-01-01

Surface gravity surveys can detect subsurface density variations that can reveal subsurface geologic features. In 1972, the Apollo 17 (A17) mission conducted the Traverse Gravimeter Experiment (TGE) using a gravimeter that measured the local gravity field near Taurus Littrow Valley (TLV), located on the south-eastern rim of the Serenitatis basin. TLV is hypothesized to be a basaltfilled radial graben resulting from the impact that formed Mare Serenitatis. It is bounded by both the North and South Massifs (NM and SM) as well as other smaller mountains to the East that are thought to be mainly composed of brecciated highland material. The TGE is the first and only successful gravity survey on the surface of the Moon. Other more recent satellite surveys, such as NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission (2011- 2012), have produced the best global gravity field to date (approx. 13km resolution). However, these satellite surveys are not sensitive enough to detect fine-scale (<1km) lunar subsurface structures. This underscores the value of the data collected at the surface by A17. In the original analysis of the data a 2D forward-modelling approach was used to derive a thickness of the subsurface basalt layer of 1.0 km by assuming a simple flat-faced rectangular geometry and using densities derived from Apollo lunar samples. We are investigating whether modern 3D modelling techniques in combination with high-resolution topographical and image datasets can reveal additional fine-scale subsurface structure in TLV.

A Direct Georeferencing Method for Terrestrial Laser Scanning Using GNSS Data and the Vertical Deflection from Global Earth Gravity Models

PubMed Central

Borkowski, Andrzej; Owczarek-Wesołowska, Magdalena; Gromczak, Anna

2017-01-01

Terrestrial laser scanning is an efficient technique in providing highly accurate point clouds for various geoscience applications. The point clouds have to be transformed to a well-defined reference frame, such as the global Geodetic Reference System 1980. The transformation to the geocentric coordinate frame is based on estimating seven Helmert parameters using several GNSS (Global Navigation Satellite System) referencing points. This paper proposes a method for direct point cloud georeferencing that provides coordinates in the geocentric frame. The proposed method employs the vertical deflection from an external global Earth gravity model and thus demands a minimum number of GNSS measurements. The proposed method can be helpful when the number of georeferencing GNSS points is limited, for instance in city corridors. It needs only two georeferencing points. The validation of the method in a field test reveals that the differences between the classical georefencing and the proposed method amount at maximum to 7 mm with the standard deviation of 8 mm for all of three coordinate components. The proposed method may serve as an alternative for the laser scanning data georeferencing, especially when the number of GNSS points is insufficient for classical methods. PMID:28672795

A Direct Georeferencing Method for Terrestrial Laser Scanning Using GNSS Data and the Vertical Deflection from Global Earth Gravity Models.

PubMed

Osada, Edward; Sośnica, Krzysztof; Borkowski, Andrzej; Owczarek-Wesołowska, Magdalena; Gromczak, Anna

2017-06-24

Terrestrial laser scanning is an efficient technique in providing highly accurate point clouds for various geoscience applications. The point clouds have to be transformed to a well-defined reference frame, such as the global Geodetic Reference System 1980. The transformation to the geocentric coordinate frame is based on estimating seven Helmert parameters using several GNSS (Global Navigation Satellite System) referencing points. This paper proposes a method for direct point cloud georeferencing that provides coordinates in the geocentric frame. The proposed method employs the vertical deflection from an external global Earth gravity model and thus demands a minimum number of GNSS measurements. The proposed method can be helpful when the number of georeferencing GNSS points is limited, for instance in city corridors. It needs only two georeferencing points. The validation of the method in a field test reveals that the differences between the classical georefencing and the proposed method amount at maximum to 7 mm with the standard deviation of 8 mm for all of three coordinate components. The proposed method may serve as an alternative for the laser scanning data georeferencing, especially when the number of GNSS points is insufficient for classical methods.

Modeling Airborne Gravity Data with Local Functions for Regional Geoid Enhancement ---- A Case Study in Puerto Rico Area

NASA Astrophysics Data System (ADS)

Li, Xiaopeng

2016-04-01

Airborne gravimetry has been used as the primary method to quickly and economically obtain updated gravity field information over a region, targeted specifically. Thus, unlike the satellite missions that provide global or near global data coverage, the observables from airborne campaigns are apparently space limited. Moreover, they are also band limited in the frequency domain, considering that various filter banks and/or de-noising techniques have to be applied to overcome the low signal to noise ratio problem that are presented in the airborne systems due to mechanical and mathematical limitations in computing the accelerations, both the kinematic one and the dynamic one. As a result, in this study, a band-limited local function system based on the point mass model is used to process these airborne gravity data that have both a limited frequency domain and a limited space domain in the target area: Puerto Rico Island and its nearby ocean areas. The resulting geoid model show obvious middle to short wavelength geoid changes due to airborne gravity data contribution. In the land area, these changes improved the geoid precision from 3.27cm to 2.09cm at the local GNSS/Leveling bench marks. More importantly, the error trend in the geoid models is largely reduced if not completely removed. Various oceanographic models will be used to validate the geoid changes in the nearby open sea areas.

The DYNAMO Orbiter Project: High Resolution Mapping of Gravity/Magnetic Fields and In Situ Investigation of Mars Atmospheric Escape

NASA Technical Reports Server (NTRS)

Smrekar, S.; Chassefiere, E.; Forget, F.; Reme, H.; Mazelle, C.; Blelly, P. -L.; Acuna, M.; Connerney, J.; Purucker, M.; Lin, R.

2000-01-01

Dynamo is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for Dynamo of 120-130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere, and water, from the planet. There is much room for debate on the importance of current atmosphere escape processes in the evolution of the Martian atmosphere, as early "exotic" processes including hydrodynamic escape and impact erosion are traditionally invoked to explain the apparent sparse inventory of present-day volatiles. Yet, the combination of low surface gravity and the absence of a substantial internally generated magnetic field have undeniable effects on what we observe today. In addition to the current losses in the forms of Jeans and photochemical escape of neutrals, there are solar wind interaction-related erosion mechanisms because the upper atmosphere is directly exposed to the solar wind. The solar wind related loss rates, while now comparable to those of a modest comet, nonetheless occur continuously, with the intriguing possibility of important cumulative and/or enhanced effects over the several billion years of the solar system's life. If the detailed history of the Martian internal field could be traced back, and the current escape processes could be understood well enough to model the expected stronger losses under early Sun conditions, one could go a long way toward constraining this part of the mysterious history of Mars' atmosphere.

The report of the Gravity Field Workshop

NASA Astrophysics Data System (ADS)

Smith, D. E.

1982-04-01

A Gravity Field Workshop was convened to review the actions which could be taken prior to a GRAVSAT mission to improve the Earth's gravity field model. This review focused on the potential improvements in the Earth's gravity field which could be obtained using the current satellite and surface gravity data base. In particular, actions to improve the quality of the gravity field determination through refined measurement corrections, selected data augmentation and a more accurate reprocessing of the data were considered. In addition, recommendations were formulated which define actions which NASA should take to develop the necessary theoretical and computation techniques for gravity model determination and to use these approaches to improve the accuracy of the Earth's gravity model.

Moho Modeling Using FFT Technique

NASA Astrophysics Data System (ADS)

Chen, Wenjin; Tenzer, Robert

2017-04-01

To improve the numerical efficiency, the Fast Fourier Transform (FFT) technique was facilitated in Parker-Oldenburg's method for a regional gravimetric Moho recovery, which assumes the Earth's planar approximation. In this study, we extend this definition for global applications while assuming a spherical approximation of the Earth. In particular, we utilize the FFT technique for a global Moho recovery, which is practically realized in two numerical steps. The gravimetric forward modeling is first applied, based on methods for a spherical harmonic analysis and synthesis of the global gravity and lithospheric structure models, to compute the refined gravity field, which comprises mainly the gravitational signature of the Moho geometry. The gravimetric inverse problem is then solved iteratively in order to determine the Moho depth. The application of FFT technique to both numerical steps reduces the computation time to a fraction of that required without applying this fast algorithm. The developed numerical producers are used to estimate the Moho depth globally, and the gravimetric result is validated using the global (CRUST1.0) and regional (ESC) seismic Moho models. The comparison reveals a relatively good agreement between the gravimetric and seismic models, with the RMS of differences (of 4-5 km) at the level of expected uncertainties of used input datasets, while without the presence of significant systematic bias.

The Role of GRAIL Orbit Determination in Preprocessing of Gravity Science Measurements

NASA Technical Reports Server (NTRS)

Kruizinga, Gerhard; Asmar, Sami; Fahnestock, Eugene; Harvey, Nate; Kahan, Daniel; Konopliv, Alex; Oudrhiri, Kamal; Paik, Meegyeong; Park, Ryan; Strekalov, Dmitry;

Co-Seismic Mass Displacement and its Effect on Earth's Rotation and Gravity

NASA Technical Reports Server (NTRS)

Chao, B. F.; Gross, R. S.

2004-01-01

Mantle processes often involve large-scale mass transport, ranging from mantle convection, tectonic motions, glacial isostatic adjustment, to tides, atmospheric and oceanic loadings, volcanism and seismicity. On very short time scale of less than an hour, co-seismic event, apart from the "shaking" that is the earthquake, leaves behind permanent (step-function-like) displacements in the crust and mantle. This redistribution of mass changes the Earth's inertia tensor (and hence Earth's rotation in both length-of-day and polar motion), and the gravity field. The question is whether these effects are large enough to be of any significance. In this paper we report updated calculation results based on Chao & Gross. The calculation uses the normal mode summation scheme, applied to over twenty thousand major earthquakes that occurred during 1976-2002, according to source mechanism solutions given by the Harvard Centroid Moment Tensor catalog. Compared to the truly large ones earlier in the century, the earthquakes we study are individually all too small to have left any discernible signature in geodetic records of Earth rotation or global gravity field. However, their collective effects continue to exhibit an extremely strong statistical tendencies, conspiring to decrease J2 and J22 while shortening LOD, resulting in a rounder and more compact Earth. Strong tendency is also seen in the earthquakes trying to "nudge" the Earth rotation pole towards approx. 140 deg.E, roughly opposite to the observed polar drift direction. Currently, the Gravity Recovery And Climate Experiment (GRACE) is measuring the time-variable gravity to high degree and order with unprecedented accuracy. Our results show that great earthquakes such as the 1960 Chilean or 1964 Alaskan events cause gravitational field changes that are large enough to be detected by GRACE.

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.

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Bacmeister, Julio T.; Wu, Dong L.

1998-01-01

Progress in research into the global morphology of gravity wave activity using UARS data is described for the period March-June, 1998. Highlights this quarter include further progress in the analysis and interpretation of CRISTA temperature variances; model-generated climatologies of mesospheric gravity wave activity using the HWM-93 wind and temperature model; and modeling of gravity wave detection from space-based platforms. Preliminary interpretations and recommended avenues for further analysis are also described.

Global detailed gravimetric geoid. [based on gravity model derived from satellite tracking and surface gravity data

NASA Technical Reports Server (NTRS)

Vincent, S.; Marsh, J. G.

1973-01-01

A global detailed gravimetric geoid has been computed by combining the Goddard Space Flight Center GEM-4 gravity model derived from satellite and surface gravity data and surface 1 deg-by-1 deg mean free air gravity anomaly data. The accuracy of the geoid is + or - 2 meters on continents, 5 to 7 meters in areas where surface gravity data are sparse, and 10 to 15 meters in areas where no surface gravity data are available. Comparisons have been made with the astrogeodetic data provided by Rice (United States), Bomford (Europe), and Mather (Australia). Comparisons have also been carried out with geoid heights derived from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.

Power laws for gravity and topography of Solar System bodies

NASA Astrophysics Data System (ADS)

Ermakov, A.; Park, R. S.; Bills, B. G.

2017-12-01

When a spacecraft visits a planetary body, it is useful to be able to predict its gravitational and topographic properties. This knowledge is important for determining the level of perturbations in spacecraft's motion as well as for planning the observation campaign. It has been known for the Earth that the power spectrum of gravity follows a power law, also known as the Kaula rule (Kaula, 1963; Rapp, 1989). A similar rule was derived for topography (Vening-Meinesz, 1951). The goal of this paper is to generalize the power law that can characterize the gravity and topography power spectra for bodies across a wide range of size. We have analyzed shape power spectra of the bodies that have either global shape and gravity field measured. These bodies span across five orders of magnitude in their radii and surface gravities and include terrestrial planets, icy moons and minor bodies. We have found that despite having different internal structure, composition and mechanical properties, the topography power spectrum of these bodies' shapes can be modeled with a similar power law rescaled by the surface gravity. Having empirically found a power law for topography, we can map it to a gravity power law. Special care should be taken for low-degree harmonic coefficients due to potential isostatic compensation. For minor bodies, uniform density can be assumed. The gravity coefficients are a linear function of the shape coefficients for close-to-spherical bodoes. In this case, the power law for gravity will be steeper than the power law of topography due to the factor (2n+1) in the gravity expansion (e.g. Eq. 10 in Wieczorek & Phillips, 1998). Higher powers of topography must be retained for irregularly shaped bodies, which breaks the linearity. Therefore, we propose the following procedure to derive an a priori constraint for gravity. First, a surface gravity needs to be determined assuming typical density for the relevant class of bodies. Second, the scaling coefficient of the power law can be found by rescaling the values known for other bodies. Third, an ensemble of synthetic shapes that follow the defined power law can be generated and gravity-from-shape can be found. The averaged power spectrum can be used as an a priori constraint for the gravity field and variance of power can be computed for individual degrees.

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.

Phases of global AdS black holes

NASA Astrophysics Data System (ADS)

Basu, Pallab; Krishnan, Chethan; Subramanian, P. N. Bala

2016-06-01

We study the phases of gravity coupled to a charged scalar and gauge field in an asymptotically Anti-de Sitter spacetime ( AdS 4) in the grand canonical ensemble. For the conformally coupled scalar, an intricate phase diagram is charted out between the four relevant solutions: global AdS, boson star, Reissner-Nordstrom black hole and the hairy black hole. The nature of the phase diagram undergoes qualitative changes as the charge of the scalar is changed, which we discuss. We also discuss the new features that arise in the extremal limit.

Coseismic Gravity and Displacement Signatures Induced by the 2013 Okhotsk Mw8.3 Earthquake

PubMed Central

Zhang, Guoqing; Shen, Wenbin; Xu, Changyi; Zhu, Yiqing

2016-01-01

In this study, Gravity Recovery and Climate Experiment (GRACE) RL05 data from January 2003 to October 2014 were used to extract the coseismic gravity changes induced by the 24 May 2013 Okhotsk Mw8.3 deep-focus earthquake using the difference and least square fitting methods. The gravity changes obtained from GRACE data agreed well with those from dislocation theory in both magnitude and spatial pattern. Positive and negative gravity changes appeared on both sides of the epicenter. The positive signature appeared on the western side, and the peak value was approximately 0.4 microgal (1 microgal = 10−8 m/s2), whereas on the eastern side, the gravity signature was negative, and the peak value was approximately −1.1 microgal. It demonstrates that deep-focus earthquakes Mw ≤ 8.5 are detectable by GRACE observations. Moreover, the coseismic displacements of 20 Global Positioning System (GPS) stations on the Earth’s surface were simulated using an elastic dislocation theory in a spherical earth model, and the results are consistent with the GPS results, especially the near-field results. We also estimated the gravity contributions from the coseismic vertical displacements and density changes, analyzed the proportion of these two gravity change factors (based on an elastic dislocation theory in a spherical earth model) in this deep-focus earthquake. The gravity effect from vertical displacement is four times larger than that caused by density redistribution. PMID:27598158

Time-Variable Gravity from Space: Quarter Century of Observations, Mysteries, and Prospects

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.

2003-01-01

Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth's dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease -- until around 1998, when it switched quite suddenly to an increase trend which has continued to date. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this J2 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution (i.e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. In addition, although less precise than GRACE, the GPS/Meteorology constellation mission COSMIC, with 6 mini-satellites to be launched in late 2005, is expected to provide continued and complementary time-variable gravity observations. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

Annual, Seasonal, and Secular Changes in Time-Variable Gravity from GRACE

NASA Astrophysics Data System (ADS)

Lemoine, F. G.; Luthcke, S. B.; Klosko, S. M.; Rowlands, D. D.; Chinn, D. S.; McCarthy, J. J.; Ray, R. D.; Boy, J.

2007-12-01

The NASA/DLR GRACE mission, launched in 2002, has now operated for more than five years, producing monthly and ten-day snapshots of the variations of the gravity field of the Earth. The available solutions, either from spherical harmonics or from mascons, allow us new insights into the variations of surface gravity on the Earth at annual, inter-annual, and secular time scales. Our baseline time series, based on GGM02C, NCEP Atmospheric Gravity with IB, and GOT00 tides now is extended to July 2007, spanning four+ years, and we analyze both mascon and spherical harmonic solutions from this time series with respect to global hydrology variations. Our 4degx4deg mascon solutions are extended to cover all continental regions of the globe. Comparisons with hydrology (land-surface) models can offer insights into how these models might be improved. We compare our baseline time series, with new time series that include an updated Goddard Ocean Tide (GOT) model, ECMWF- 3hr atmosphere de-aliasing data, and the MOG-2D ocean dealiasing product. Finally, we intercompare the spherical harmonic solutions at low degree from GRACE from the various product centers (e.g., GFZ, CSR, GRGS), and look for secular signals in both the GSFC mascon and spherical harmonic solutions, taking care to compare the results for secular gravity field change with independent solutions developed over 25 years of independent tracking to geodetic satellites by Satellite Laser Ranging (SLR) and DORIS.

Unique geologic insights from "non-unique" gravity and magnetic interpretation

USGS Publications Warehouse

Saltus, R.W.; Blakely, R.J.

2011-01-01

Interpretation of gravity and magnetic anomalies is mathematically non-unique because multiple theoretical solutions are always possible. The rigorous mathematical label of "nonuniqueness" can lead to the erroneous impression that no single interpretation is better in a geologic sense than any other. The purpose of this article is to present a practical perspective on the theoretical non-uniqueness of potential-field interpretation in geology. There are multiple ways to approach and constrain potential-field studies to produce significant, robust, and definitive results. The "non-uniqueness" of potential-field studies is closely related to the more general topic of scientific uncertainty in the Earth sciences and beyond. Nearly all results in the Earth sciences are subject to significant uncertainty because problems are generally addressed with incomplete and imprecise data. The increasing need to combine results from multiple disciplines into integrated solutions in order to address complex global issues requires special attention to the appreciation and communication of uncertainty in geologic interpretation.

The interior structure of Enceladus from Cassini gravity measurements

NASA Astrophysics Data System (ADS)

Iess, Luciano

2015-04-01

The Cassini spacecraft flew by the small Saturnian moon Enceladus in three close flybys (April 28, 2010, November 30, 2010 and May 2, 2012, to carry out measurements of the satellite's gravity field [1]. One of the main motivations was the search for a hemispherical asymmetry in the gravity field, the gravitational counterpart of the striking North-South asymmetry shown by optical imaging and other Cassini instruments in the geological features of the moon. The estimation of Enceladus' gravity field by Cassini was especially complex because of the small surface gravity (0.11 m/s2), the short duration of the gravitational interaction (only a few minutes) and the small, nearly impulsive, neutral particles drag occurring when the spacecraft crossed the south polar plume during the first and the third flyby. Including the non-gravitational acceleration due to the plume in the dynamical model was crucial to obtain a reliable solution for the gravity field. In order to maximize the sensitivity to the hemispherical asymmetry, controlled by the spherical harmonic coefficient J3, the closest approaches occurred at the low altitudes (respectively 100, 48 and 70 km), and at high latitudes in both hemispheres (89°S, 62°N, and 72°S). Enceladus' gravity field is dominated by large quadrupole terms not far from those expected for a body in a relaxed shape. Although the deviations from the hydrostaticity are weak (J2/C22=3.55±0.05), the straightforward application of the Radau-Darwin approximation yields a value of the moment of inertia factor (MOIF=C/MR2) that is incompatible (0.34) with the differentiated interior structure suggested by cryovolcanism and the large heat flow. The other remarkable feature of the gravity field is the small but still statistically significant value of J3 (106 x J3 = -115.3±22.9). A differentiated interior structure (corresponding to a smaller MOIF) may be reconciled with the gravity measurement by assuming that the rocky core has retained some memory of a faster rotation rate (about 10% above current). J3, whose value is uncontaminated by tides and rotation, provides a way to separate the non-hydrostatic contribution to J2 and C22, from which we infer a MOIF of about 0.336, now compatible with a differentiated structure. Similar conclusions are obtained from the analysis of the admittance. The interpretation of J3 and the associated, negative gravity anomaly (about 2.5 mGal) is non-unique. In a proposed explanation, the anomaly originates in the core and is not directly related to the presence of liquid masses beneath the surface. Our interpretation seeks the source of the anomaly in the observed 1 km depression in the southern polar region. This mass deficiency generates indeed a negative anomaly, but its magnitude is far smaller (about 20%) than expected from an uncompensated topography. An obvious source of compensation is a reservoir of liquid water at depth, in contact with the rocky core. This interpretation is consistent with the observed cryovolcanism and the presence of silicate grains in the plumes. The estimated gravity field is more consistent with a reservoir that extends in latitude about halfway to the equator, but our data cannot rule out a thin, global ocean.

KSC-2011-6815

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – Astrophysicist Dr. Neil deGrasse Tyson with the American Museum of Natural History’s Hayden Planetarium in New York, speaks to a group of Tweetup participants at NASA Kennedy Space Center’s NASA Causeway launch viewing site in Florida during prelaunch activities for the agency’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured the center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6814

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. – Astrophysicist Dr. Neil deGrasse Tyson with the American Museum of Natural History’s Hayden Planetarium in New York, speaks to a group of Tweetup participants at NASA Kennedy Space Center’s NASA Causeway launch viewing site in Florida during prelaunch activities for the agency’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured the center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter.GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6800

NASA Image and Video Library

2011-09-07

CAPE CANAVERAL, Fla. – Astrophysicist Dr. Neil deGrasse Tyson with the American Museum of Natural History’s Hayden Planetarium in New York, speaks to a group of Tweetup participants at the Kennedy Space Center Visitor Complex in Florida during prelaunch activities for the agency’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Participants toured NASA’s Kennedy Space Center and got a close-up view of Space Launch Complex 17B at Cape Canaveral Air Force Station. The tweeters will share their experiences with followers through the social networking site Twitter. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon’s gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon’s crust and mantle and will help answer fundamental questions about the moon’s internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon’s gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Gianni Woods

KSC-2011-6928

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Over a group of trees and bushes, the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission launches off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. At left is the pad’s mobile service tower. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kenny Allen

KSC-2011-6924

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – A group of trees and bushes provides a frame for the launch of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/George Roberts

KSC-2011-6927

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Over a group of trees and bushes, the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission launches off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. At left is the pad’s mobile service tower. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kenny Allen

KSC-2011-6901

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Engine ignition begins liftoff of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. At right is the pad’s mobile service tower. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Tom Farrar and Tony Gray

KSC-2011-6897

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – At ignition, flames and smoke from the engines begin liftoff of the United Launch Alliance Delta II Heavy rocket carrying NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission off Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft launched at 9:08:52 a.m. EDT Sept. 10. GRAIL-A will separate from the second stage of the rocket at about one hour, 21 minutes after liftoff, followed by GRAIL-B at 90 minutes after launch. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Sandra Joseph and Don Kight

Crustal Structure of Mars from Mars Global Surveyor Topography and Gravity

NASA Technical Reports Server (NTRS)

Zuber, M. T.; Solomon, S. C.; Phillips, R. J.; Smith, D. E.; Tyler, G. L.; Aharonson, O.; Balmino, G.; Banerdt, W. B.; Head, J. W.; Johnson, C. L.

2000-01-01

In this analysis we invert global models of Mars' topography from Mars Orbiter Laser Altimeter (MOLA) and gravity from Doppler tracking obtained during the mapping mission of Mars Global Surveyor (MGS). We analyze the distribution of Martian crust and discuss implications for Mars' thermal history.

Combination of monthly gravity field solutions from different processing centers

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2015-04-01

Currently, the official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. Combinations are well-established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI), where regular comparisons and combinations of space-geodetic products have tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. In the frame of the recently started Horizon 2020 project European Gravity Service for Improved Emergency Management (EGSIEM), a scientific combination service shall therefore be established to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community. In a first step the large variety of available monthly GRACE gravity field solutions shall be mutually compared spatially and spectrally. We assess the noise of the raw as well as filtered solutions and compare the secular and seasonal periodic variations fitted to the monthly solutions. In a second step we will explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the potential benefits for the GRACE and GRACE-FO user community.

Towards combined global monthly gravity field solutions

NASA Astrophysics Data System (ADS)

Jaeggi, Adrian; Meyer, Ulrich; Beutler, Gerhard; Weigelt, Matthias; van Dam, Tonie; Mayer-Gürr, Torsten; Flury, Jakob; Flechtner, Frank; Dahle, Christoph; Lemoine, Jean-Michel; Bruinsma, Sean

2014-05-01

Currently, official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. This procedure seriously limits the accessibility of these valuable data. Combinations are well established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). Regularly comparing and combining space-geodetic products has tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. Therefore, we propose in a first step to mutually compare the large variety of available monthly GRACE gravity field solutions, e.g., by assessing the signal content over selected regions, by estimating the noise over the oceans, and by performing significance tests. We make the attempt to assign different solution characteristics to different processing strategies in order to identify subsets of solutions, which are based on similar processing strategies. Using these subsets we will in a second step explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the potential benefits for the GRACE and GRACE-FO user community, but also address minimum processing requirements to be met by each analysis centre to enable a meaningful combination (either performed on the solution level or, preferably, on the normal equation level).

Impact of recent Global Digital Bathymetry and Topography Models on geoid modelling: Results from two case studies in Balearic and Aegean Seas

NASA Astrophysics Data System (ADS)

Delikaraoglou, D.; Mintourakis, I.; Kallianou, F.

2009-04-01

With the realization of the Shuttle Radar Topographic Mission (SRTM) and the free distribution of its global elevation dataset with 3 arcsec (90 m) resolution and less than 16 m vertical accuracy, together with the availability of the higher resolution (30 m) and accuracy (10 m) Digital Terrain Models (DTM) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), these two valuable sources of uniform DEM data represent a revolution in the world of terrain modelling. DEMs are an important source of data for the generation of high resolution geoids since they provide the high-frequency content of the gravity field spectrum and are suitable for the computation of terrain effects to gravity and indirect effects to the geoid, thus allowing the combination of global geopotential models, local gravity anomalies and information about the earth's topography (represented by a given DEM). However, although such models are available for land, there are no readily accessible Digital Bathymetry Models (DBMs) of equivalent quality for the coastal and oceanic regions. Most of the global DBM's (e.g. ETOPO1, SRTM30, and GEBCO global bathymetric grid) are compilations of heterogeneous data with medium resolution and accuracy. This prevents to exploit the potential of the recent high resolution (1 arcmin) marine free-air gravity anomalies datasets derived from satellite altimetry (such as the DNSC08, and the Sandwell & Smith v18.1 (S&Sv18.1) global solutions) in conjunction with such global DBM's. Fortunately, for some regions, recently have become available DBM's of much better accuracy and resolution, such as the DBM of 1 km resolution for many regions of the Mediterranean Sea which is distributed by IFREMER, the French Research Institute for Exploitation of the Sea. The scope of this study is to use this latest regional DBM in combination with the newly available DNSC08 and SSV18.1 global marine free-air gravity anomalies datasets for marine and near shore geoid modelling of archipelagic (island) areas. We have concentrated in two test regions: (a) the Catalano-Balearic Sea (South of Spain in the NW Meditteranean), where adequate marine and land gravity data allow a detailed evaluation of our processing methodologies and their results and, (b) the Aegean Sea where the presence of many islands in varying distances from the mainland Greece and located on the continental shelf and/or divided by steep sea floor topography present some unique challenges for any high resolution geoid modelling efforts. For both test regions, we generated a combined DEM (C-DEM) using the IFREMER and SRTM 30 arcsec bathymetric data for the sea areas and SRTM 3 arcsec data for the surrounding land areas. In this contribution, we discuss various computational aspects relating to the so-called "Direct Topographical Effect" (DTE) and the "Indirect Topographical Effect" (ITE), the two most significant topographical effects that have to be evaluated when a precise geoid is being compiled. In addition, we outline the evaluation and the impact of the results obtained, especially with regard to the differences in the geoid models when different elevation data are used, and point out the main limitations and possibilities for further improvements in the use of the aforementioned satellite and terrestrial data for regional and local geoid mapping in coastal and island regions. Keywords: IFREMER, SRTM, terrain effects, free-air gravity anomalies, geoid modelling,Digital Bathymetry Models.

The JPL Mars gravity field, Mars50c, based upon Viking and Mariner 9 Doppler tracking data

NASA Technical Reports Server (NTRS)

Konopliv, Alexander S.; Sjogren, William L.

1995-01-01

This report summarizes the current JPL efforts of generating a Mars gravity field from Viking 1 and 2 and Mariner 9 Doppler tracking data. The Mars 50c solution is a complete gravity field to degree and order 50 with solutions as well for the gravitational mass of Mars, Phobos, and Deimos. The constants and models used to obtain the solution are given and the method for determining the gravity field is presented. The gravity field is compared to the best current gravity GMM1 of Goddard Space Flight Center.

The GPlates Portal: Cloud-Based Interactive 3D Visualization of Global Geophysical and Geological Data in a Web Browser.

PubMed

Müller, R Dietmar; Qin, Xiaodong; Sandwell, David T; Dutkiewicz, Adriana; Williams, Simon E; Flament, Nicolas; Maus, Stefan; Seton, Maria

2016-01-01

The pace of scientific discovery is being transformed by the availability of 'big data' and open access, open source software tools. These innovations open up new avenues for how scientists communicate and share data and ideas with each other and with the general public. Here, we describe our efforts to bring to life our studies of the Earth system, both at present day and through deep geological time. The GPlates Portal (portal.gplates.org) is a gateway to a series of virtual globes based on the Cesium Javascript library. The portal allows fast interactive visualization of global geophysical and geological data sets, draped over digital terrain models. The globes use WebGL for hardware-accelerated graphics and are cross-platform and cross-browser compatible with complete camera control. The globes include a visualization of a high-resolution global digital elevation model and the vertical gradient of the global gravity field, highlighting small-scale seafloor fabric such as abyssal hills, fracture zones and seamounts in unprecedented detail. The portal also features globes portraying seafloor geology and a global data set of marine magnetic anomaly identifications. The portal is specifically designed to visualize models of the Earth through geological time. These space-time globes include tectonic reconstructions of the Earth's gravity and magnetic fields, and several models of long-wavelength surface dynamic topography through time, including the interactive plotting of vertical motion histories at selected locations. The globes put the on-the-fly visualization of massive data sets at the fingertips of end-users to stimulate teaching and learning and novel avenues of inquiry.

The GPlates Portal: Cloud-Based Interactive 3D Visualization of Global Geophysical and Geological Data in a Web Browser

PubMed Central

Müller, R. Dietmar; Qin, Xiaodong; Sandwell, David T.; Dutkiewicz, Adriana; Williams, Simon E.; Flament, Nicolas; Maus, Stefan; Seton, Maria

2016-01-01

The pace of scientific discovery is being transformed by the availability of ‘big data’ and open access, open source software tools. These innovations open up new avenues for how scientists communicate and share data and ideas with each other and with the general public. Here, we describe our efforts to bring to life our studies of the Earth system, both at present day and through deep geological time. The GPlates Portal (portal.gplates.org) is a gateway to a series of virtual globes based on the Cesium Javascript library. The portal allows fast interactive visualization of global geophysical and geological data sets, draped over digital terrain models. The globes use WebGL for hardware-accelerated graphics and are cross-platform and cross-browser compatible with complete camera control. The globes include a visualization of a high-resolution global digital elevation model and the vertical gradient of the global gravity field, highlighting small-scale seafloor fabric such as abyssal hills, fracture zones and seamounts in unprecedented detail. The portal also features globes portraying seafloor geology and a global data set of marine magnetic anomaly identifications. The portal is specifically designed to visualize models of the Earth through geological time. These space-time globes include tectonic reconstructions of the Earth’s gravity and magnetic fields, and several models of long-wavelength surface dynamic topography through time, including the interactive plotting of vertical motion histories at selected locations. The globes put the on-the-fly visualization of massive data sets at the fingertips of end-users to stimulate teaching and learning and novel avenues of inquiry. PMID:26960151

From Mars to Greenland: Charting gravity with space and airborne instruments - Fields, tides, methods, results

NASA Technical Reports Server (NTRS)

Colombo, Oscar L. (Editor)

1992-01-01

This symposium on space and airborne techniques for measuring gravity fields, and related theory, contains papers on gravity modeling of Mars and Venus at NASA/GSFC, an integrated laser Doppler method for measuring planetary gravity fields, observed temporal variations in the earth's gravity field from 16-year Starlette orbit analysis, high-resolution gravity models combining terrestrial and satellite data, the effect of water vapor corrections for satellite altimeter measurements of the geoid, and laboratory demonstrations of superconducting gravity and inertial sensors for space and airborne gravity measurements. Other papers are on airborne gravity measurements over the Kelvin Seamount; the accuracy of GPS-derived acceleration from moving platform tests; airborne gravimetry, altimetry, and GPS navigation errors; controlling common mode stabilization errors in airborne gravity gradiometry, GPS/INS gravity measurements in space and on a balloon, and Walsh-Fourier series expansion of the earth's gravitational potential.

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.

Numerical Simulations of Buoyancy Effects in low Density Gas Jets

NASA Technical Reports Server (NTRS)

Satti, R. P.; Pasumarthi, K. S.; Agrawal, A. K.

2004-01-01

This paper deals with the computational analysis of buoyancy effects in the near field of an isothermal helium jet injected into quiescent ambient air environment. The transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum were solved using a staggered grid finite volume method. Laminar, axisymmetric, unsteady flow conditions were considered for the analysis. An orthogonal system with non-uniform grids was used to capture the instability phenomena. Computations were performed for Earth gravity and during transition from Earth to different gravitational levels. The flow physics was described by simultaneous visualizations of velocity and concentration fields at Earth and microgravity conditions. Computed results were validated by comparing with experimental data substantiating that buoyancy induced global flow oscillations present in Earth gravity are absent in microgravity. The dependence of oscillation frequency and amplitude on gravitational forcing was presented to further quantify the buoyancy effects.

KSC-2011-6819

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are Dana Grieco, launch operations manager, Analex, NASA's Launch Services Program (LSP); Bruce Reid, GRAIL mission manager, LSP; Al Sierra, manager of the Flight Project Office, LSP; Omar Baez, GRAIL assistant launch director, LSP; and Tim Dunn, GRAIL launch director, LSP. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6818

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, United Launch Alliance (ULA) personnel in the Delta Operations Building prepare for the launch of NASA's Gravity Recovery and Interior Laboratory mission aboard a ULA Delta II Heavy rocket. Physical control of the rocket is maintained from the building, located about a mile from Space Launch Complex 17B. The room functions as a "soft blockhouse" and is the room from which the computer-generated command to launch the rocket is issued two seconds before liftoff. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6817

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, United Launch Alliance (ULA) personnel in the Delta Operations Building prepare for the launch of NASA's Gravity Recovery and Interior Laboratory mission aboard a ULA Delta II Heavy rocket. Physical control of the rocket is maintained from the building, located about a mile from Space Launch Complex 17B. The room functions as a "soft blockhouse" and is the room from which the computer-generated command to launch the rocket is issued two seconds before liftoff. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6816

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, United Launch Alliance (ULA) personnel in the Delta Operations Building prepare for the launch of NASA's Gravity Recovery and Interior Laboratory mission aboard a ULA Delta II Heavy rocket. Physical control of the rocket is maintained from the building, located about a mile from Space Launch Complex 17B. The room functions as a "soft blockhouse" and is the room from which the computer-generated command to launch the rocket is issued two seconds before liftoff. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

Canonical transformation path to gauge theories of gravity

NASA Astrophysics Data System (ADS)

Struckmeier, J.; Muench, J.; Vasak, D.; Kirsch, J.; Hanauske, M.; Stoecker, H.

2017-06-01

In this paper, the generic part of the gauge theory of gravity is derived, based merely on the action principle and on the general principle of relativity. We apply the canonical transformation framework to formulate geometrodynamics as a gauge theory. The starting point of our paper is constituted by the general De Donder-Weyl Hamiltonian of a system of scalar and vector fields, which is supposed to be form-invariant under (global) Lorentz transformations. Following the reasoning of gauge theories, the corresponding locally form-invariant system is worked out by means of canonical transformations. The canonical transformation approach ensures by construction that the form of the action functional is maintained. We thus encounter amended Hamiltonian systems which are form-invariant under arbitrary spacetime transformations. This amended system complies with the general principle of relativity and describes both, the dynamics of the given physical system's fields and their coupling to those quantities which describe the dynamics of the spacetime geometry. In this way, it is unambiguously determined how spin-0 and spin-1 fields couple to the dynamics of spacetime. A term that describes the dynamics of the "free" gauge fields must finally be added to the amended Hamiltonian, as common to all gauge theories, to allow for a dynamic spacetime geometry. The choice of this "dynamics" Hamiltonian is outside of the scope of gauge theory as presented in this paper. It accounts for the remaining indefiniteness of any gauge theory of gravity and must be chosen "by hand" on the basis of physical reasoning. The final Hamiltonian of the gauge theory of gravity is shown to be at least quadratic in the conjugate momenta of the gauge fields—this is beyond the Einstein-Hilbert theory of general relativity.

An improved GRACE monthly gravity field solution by modeling the non-conservative acceleration and attitude observation errors

NASA Astrophysics Data System (ADS)

Chen, Qiujie; Shen, Yunzhong; Chen, Wu; Zhang, Xingfu; Hsu, Houze

2016-06-01

The main contribution of this study is to improve the GRACE gravity field solution by taking errors of non-conservative acceleration and attitude observations into account. Unlike previous studies, the errors of the attitude and non-conservative acceleration data, and gravity field parameters, as well as accelerometer biases are estimated by means of weighted least squares adjustment. Then we compute a new time series of monthly gravity field models complete to degree and order 60 covering the period Jan. 2003 to Dec. 2012 from the twin GRACE satellites' data. The derived GRACE solution (called Tongji-GRACE02) is compared in terms of geoid degree variances and temporal mass changes with the other GRACE solutions, namely CSR RL05, GFZ RL05a, and JPL RL05. The results show that (1) the global mass signals of Tongji-GRACE02 are generally consistent with those of CSR RL05, GFZ RL05a, and JPL RL05; (2) compared to CSR RL05, the noise of Tongji-GRACE02 is reduced by about 21 % over ocean when only using 300 km Gaussian smoothing, and 60 % or more over deserts (Australia, Kalahari, Karakum and Thar) without using Gaussian smoothing and decorrelation filtering; and (3) for all examples, the noise reductions are more significant than signal reductions, no matter whether smoothing and filtering are applied or not. The comparison with GLDAS data supports that the signals of Tongji-GRACE02 over St. Lawrence River basin are close to those from CSR RL05, GFZ RL05a and JPL RL05, while the GLDAS result shows the best agreement with the Tongji-GRACE02 result.

Ellipsoidal Harmonic Vertical Deflections. Global and Regional Modeling of The Horizontal Derivative of The Terrestrial Garvity Field

NASA Astrophysics Data System (ADS)

Grafarend, E. W.; Ardalan, A.; Finn, G.

In terms of elliptic coordinates of Jacobi type (longitude, latitude, semi-minor axis) the horizontal derivative is computed as a linear operator acting on an ellipsoidal har- monic disturbing/incremental gravitational potential. Such disturbing potential is de- fined with respect to the Somigliana-Pizzetti Reference Potential, the potential field of a level ellipsoid, and the International Reference Ellipsoid/WGS84 or World Geode- tic Datum 2000/WGD2000. Case studies of those vertical deflections on a global as well as regional scale are presented which take advantage of SEGEN (Special Ellipsoidal Gravity Earth Normal: ellipsoidal harmonics expansion 130321 coeffi- cients: http://www.uni-stuttgart.de/gi/research/paper/coefficients/coefficients.zip) and of CENT (precise centrifugal potential)

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 Of The Continental Roots: Compositional And Thermal Effects

NASA Astrophysics Data System (ADS)

Kaban, M. K.; Schwintzer, P.; Artemieva, I.; Mooney, W. D.

We use gravity, thermal, and seismic data to examine how the density and composi- tion of lithospheric roots vary beneath the cratons. Our interpretation is based on the gravity anomalies calculated by subtracting the gravitational effects of bathymetry, to- pography, and the crust from the observed gravity field, and the residual topography that characterizes the isostatic state of the lithosphere. We distinguish the effects of temperature and compositional variations in producing lithospheric density anomalies using two independent temperature constrains: based on interpretation of the surface heat flow data and estimated from global seismic tomography data. We find that in situ lithospheric density differs significantly between individual cratons, with the most dense values found beneath Eurasia and the least dense values beneath South Africa. This demonstrates that there is not a simple compensation of thermal and composition effects. We present a new gravity anomaly map that was corrected for crustal density structure and lithospheric temperatures. This map reveals differences in lithospheric composition, that are the result of the petrologic processes that have formed and mod- ified the lithosphere. All significant negative gravity anomalies are found in cratonic regions. In contrast, positive gravity anomalies are found in two distinct regions: near ocean-continent and continent-continent subduction zones, and within some continen- tal interiors. The origin of the latter positive anomalies is uncertain.

Quantifying Variations in Airborne Gravity Data Quality Due to Aircraft Selection with the Gravity for the Re-Definition of the American Vertical Datum Project

NASA Astrophysics Data System (ADS)

Youngman, M.; Weil, C.; Salisbury, T.; Villarreal, C.

2015-12-01

The U.S. National Geodetic Survey is collecting airborne gravity with the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project to produce a geoid supporting heights accurate to 2 centimeters, where possible, with a modernized U.S. vertical datum in 2022. Targeting 15.6 million square kilometers, the GRAV-D project is unprecedented in its scope of consistently collected airborne gravity data across the entire U.S. and its holdings. Currently over 42% of data collection has been completed by 42 surveys (field campaigns) covering 34 completed blocks (data collection areas). The large amount of data available offers a unique opportunity to evaluate the causes of data quality variation from survey to survey. Two metrics were chosen to use as a basis for comparing the quality of each survey/block: 1. total crossover error (i.e. difference in gravity recorded at all locations of crossing flight lines) and 2. the statistical difference of the airborne gravity from the EGM2008 global model. We have determined that the aircraft used for surveying contributes significantly to the variation in data quality. This paper will further expand upon that recent work, using statistical analysis to determine the contribution of aircraft selection to data quality taking into account other variables such as differences in survey setup or weather conditions during surveying.

Gravity effects obtained from global hydrology models in comparison with high precision gravimetric time series

NASA Astrophysics Data System (ADS)

Wziontek, Hartmut; Wilmes, Herbert; Güntner, Andreas; Creutzfeldt, Benjamin

2010-05-01

Water mass changes are a major source of variations in residual gravimetric time series obtained from the combination of observations with superconducting and absolute gravimeters. Changes in the local water storage are the main influence, but global variations contribute to the signal significantly. For three European gravity stations, Bad Homburg, Wettzell and Medicina, different global hydrology models are compared. The influence of topographic effects is discussed and due to the long-term stability of the combined gravity time series, inter-annual signals in model data and gravimetric observations are compared. Two sources of influence are discriminated, i.e., the effect of a local zone with an extent of a few kilometers around the gravimetric station and the global contribution beyond 50km. Considering their coarse resolution and uncertainties, local effects calculated from global hydrological models are compared with the in-situ gravity observations and, for the station Wettzell, with local hydrological monitoring data.

Low degree Earth's gravity coefficients determined from different space geodetic observations and climate models

NASA Astrophysics Data System (ADS)

Wińska, Małgorzata; Nastula, Jolanta

2017-04-01

Large scale mass redistribution and its transport within the Earth system causes changes in the Earth's rotation in space, gravity field and Earth's ellipsoid shape. These changes are observed in the ΔC21, ΔS21, and ΔC20 spherical harmonics gravity coefficients, which are proportional to the mass load-induced Earth rotational excitations. In this study, linear trend, decadal, inter-annual, and seasonal variations of low degree spherical harmonics coefficients of Earth's gravity field, determined from different space geodetic techniques, Gravity Recovery and Climate Experiment (GRACE), satellite laser ranging (SLR), Global Navigation Satellite System (GNSS), Earth rotation, and climate models, are examined. In this way, the contribution of each measurement technique to interpreting the low degree surface mass density of the Earth is shown. Especially, we evaluate an usefulness of several climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) to determine the low degree Earth's gravity coefficients using GRACE satellite observations. To do that, Terrestrial Water Storage (TWS) changes from several CMIP5 climate models are determined and then these simulated data are compared with the GRACE observations. Spherical harmonics ΔC21, ΔS21, and ΔC20 changes are calculated as the sum of atmosphere and ocean mass effect (GAC values) taken from GRACE and a land surface hydrological estimate from the selected CMIP5 climate models. Low degree Stokes coefficients of the surface mass density determined from GRACE, SLR, GNSS, Earth rotation measurements and climate models are compared to each other in order to assess their consistency. The comparison is done by using different types of statistical and signal processing methods.

Equatorial Magnetohydrodynamic Shallow Water Waves in the Solar Tachocline

NASA Astrophysics Data System (ADS)

Zaqarashvili, Teimuraz

2018-03-01

The influence of a toroidal magnetic field on the dynamics of shallow water waves in the solar tachocline is studied. A sub-adiabatic temperature gradient in the upper overshoot layer of the tachocline causes significant reduction of surface gravity speed, which leads to trapping of the waves near the equator and to an increase of the Rossby wave period up to the timescale of solar cycles. Dispersion relations of all equatorial magnetohydrodynamic (MHD) shallow water waves are obtained in the upper tachocline conditions and solved analytically and numerically. It is found that the toroidal magnetic field splits equatorial Rossby and Rossby-gravity waves into fast and slow modes. For a reasonable value of reduced gravity, global equatorial fast magneto-Rossby waves (with the spatial scale of equatorial extent) have a periodicity of 11 years, matching the timescale of activity cycles. The solutions are confined around the equator between latitudes ±20°–40°, coinciding with sunspot activity belts. Equatorial slow magneto-Rossby waves have a periodicity of 90–100 yr, resembling the observed long-term modulation of cycle strength, i.e., the Gleissberg cycle. Equatorial magneto-Kelvin and slow magneto-Rossby-gravity waves have the periodicity of 1–2 years and may correspond to observed annual and quasi-biennial oscillations. Equatorial fast magneto-Rossby-gravity and magneto-inertia-gravity waves have periods of hundreds of days and might be responsible for observed Rieger-type periodicity. Consequently, the equatorial MHD shallow water waves in the upper overshoot tachocline may capture all timescales of observed variations in solar activity, but detailed analytical and numerical studies are necessary to make a firm conclusion toward the connection of the waves to the solar dynamo.

Harmonic analysis of the DTU10 global gravity anomalies

NASA Astrophysics Data System (ADS)

Abrykosov, O.; Förste, Ch.; Gruber, Ch.; Shako, R.; Barthelmes, F.

2012-04-01

We have computed the Earth's gravity models to degree/order 5400 and 10800 (in terms of the ellipsoidal and spherical harmonics) from a rigorous integration of the 2'x2' and 1'x1' global grids of gravity anomalies provided by the Danish Technical University (DTU). The gravity signal recovered from the DTU10 data shows 1) a strong dependency on the truncation of the EGM2008 gravity model which were used to fill-in land areas in the DTU10 grids and 2) an irregular behaviour at frequencies behind the resolution of the EGM2008. We discuss the gravity signal and its accuracy estimation computed from the complete DTU10 grids as well as separately from the data over land and ocean areas.

High-resolution combined global gravity field modelling: Solving large kite systems using distributed computational algorithms

NASA Astrophysics Data System (ADS)

Zingerle, Philipp; Fecher, Thomas; Pail, Roland; Gruber, Thomas

2016-04-01

One of the major obstacles in modern global gravity field modelling is the seamless combination of lower degree inhomogeneous gravity field observations (e.g. data from satellite missions) with (very) high degree homogeneous information (e.g. gridded and reduced gravity anomalies, beyond d/o 1000). Actual approaches mostly combine such data only on the basis of the coefficients, meaning that previously for both observation classes (resp. models) a spherical harmonic analysis is done independently, solving dense normal equations (NEQ) for the inhomogeneous model and block-diagonal NEQs for the homogeneous. Obviously those methods are unable to identify or eliminate effects as spectral leakage due to band limitations of the models and non-orthogonality of the spherical harmonic base functions. To antagonize such problems a combination of both models on NEQ-basis is desirable. Theoretically this can be achieved using NEQ-stacking. Because of the higher maximum degree of the homogeneous model a reordering of the coefficient is needed which leads inevitably to the destruction of the block diagonal structure of the appropriate NEQ-matrix and therefore also to the destruction of simple sparsity. Hence, a special coefficient ordering is needed to create some new favorable sparsity pattern leading to a later efficient computational solving method. Such pattern can be found in the so called kite-structure (Bosch, 1993), achieving when applying the kite-ordering to the stacked NEQ-matrix. In a first step it is shown what is needed to attain the kite-(NEQ)system, how to solve it efficiently and also how to calculate the appropriate variance information from it. Further, because of the massive computational workload when operating on large kite-systems (theoretically possible up to about max. d/o 100.000), the main emphasis is put on to the presentation of special distributed algorithms which may solve those systems parallel on an indeterminate number of processes and are therefore suitable for the application on supercomputers (such as SuperMUC). Finally, (if time or space) some in-detail problems are shown that occur when dealing with high degree spherical harmonic base functions (mostly due to instabilities of Legendre polynomials), introducing also an appropriate solution for each.

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.

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

Cooperstock, F.I., E-mail: cooperst@uvic.ca; Dupre, M.J., E-mail: mdupre@tulane.edu

We introduce a naturally-defined totally invariant spacetime energy expression for general relativity incorporating the contribution from gravity. The extension links seamlessly to the action integral for the gravitational field. The demand that the general expression for arbitrary systems reduces to the Tolman integral in the case of stationary bounded distributions, leads to the matter-localized Ricci integral for energy–momentum in support of the energy localization hypothesis. The role of the observer is addressed and as an extension of the special relativistic case, the field of observers comoving with the matter is seen to compute the intrinsic global energy of a system.more » The new localized energy supports the Bonnor claim that the Szekeres collapsing dust solutions are energy-conserving. It is suggested that in the extreme of strong gravity, the Heisenberg Uncertainty Principle be generalized in terms of spacetime energy–momentum. -- Highlights: •We present a totally invariant spacetime energy expression for general relativity incorporating the contribution from gravity. •Demand for the general expression to reduce to the Tolman integral for stationary systems supports the Ricci integral as energy–momentum. •Localized energy via the Ricci integral is consistent with the energy localization hypothesis. •New localized energy supports the Bonnor claim that the Szekeres collapsing dust solutions are energy-conserving. •Suggest the Heisenberg Uncertainty Principle be generalized in terms of spacetime energy–momentum in strong gravity extreme.« less

Global Bathymetric Prediction For Ocean Modeling and Marine Geophysics

NASA Technical Reports Server (NTRS)

Sandwell, David T.; Smith, Walter H. F.; Sichoix, Lydie; Frey, Herbert V. (Technical Monitor)

2001-01-01

We proposed to construct a complete bathymetric map of the oceans at a 3-10 km resolution by combining all of the available depth soundings collected over the past 30 years with high resolution marine gravity information provided by the Geosat, ERS-1/2, and Topex/Poseidon altimeters. Detailed bathymetry is essential for understanding physical oceanography and marine geophysics. Currents and tides are controlled by the overall shapes of the ocean basins as well as the smaller sharp ocean ridges and seamounts. Because erosion rates are low in the deep oceans, detailed bathymetry reveals the mantle convection patterns, the plate boundaries, the cooling/subsidence of the oceanic lithosphere, the oceanic plateaus, and the distribution of off-ridge volcanoes. We proposed to: (1) Accumulate all available depth soundings collected over the past 30 years; (2) Use the short wavelength (< 160 km) satellite gravity information to interpolate between sparse ship soundings; (3) Improve the resolution of the marine gravity field using enhanced estimates along repeat altimeter profiles together with the dense altimeter measurements; (4) Refine/improve bathymetric predictions using the improved resolution gravity field and also by investigating computer-intensive methods for bathymetric prediction such as inverse theory; and (5) Produce a 'Globe of the Earth' similar to the globe of Venus prepared by the NASA Magellan investigation. This will also include the best available digital land data.

Time-Variable Gravity from Space: Quarter Century of Observations, Mysteries, and Prospects

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.; Boy, John-Paul

2003-01-01

Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of satellite-laser ranging in the last quarter century, the Earth's dynamic oblateness J2 (the lowest-degree harmonic component of the gravity field) has been observed to undergo a slight decrease -- until around 1998, when it switched quite suddenly to an increase trend which has continued to 2001 before sharply turning back to the value which it is "supposed to be"!. The secular decrease in J2 has long been attributed primarily to the post-glacial rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this J2 change. New techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much higher precision and spatial resolution (i.e., much higher harmonic degrees). The most important example is the GRACE mission launched in March 2002, following the success of the CHAMP mission. Such observations are becoming a new and powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.

First independent lunar gravity field solution in the framework of project GRAZIL

NASA Astrophysics Data System (ADS)

Wirnsberger, Harald; Krauss, Sandro; Klinger, Beate; Mayer-Gürr, Torsten

2017-04-01

The twin satellite mission Gravity Recovery and Interior Laboratory (GRAIL) aims to recovering the lunar gravity field by means of intersatellite Ka-band ranging (KBR) observations. In order to exploit the potential of KBR data, absolute position information of the two probes is required. Hitherto, the Graz lunar gravity field models (GrazLGM) relies on the official orbit products provided by NASA. In this contribution, we present for the first time a completely independent Graz lunar gravity field model to spherical harmonic degree and order 420. The reduced dynamic orbits of the two probes are determined using variational equations following a batch least squares differential adjustment process. These orbits are based on S-band radiometric tracking data collected by the Deep Space Network and are used for the independent GRAIL gravity field recovery. To reveal a highly accurate lunar gravity field, an integral equation approach using short orbital arcs is adopted to process the KBR data. A comparison to state-of-the-art lunar gravity models computed at NASA-GSFC, NASA-JPL and AIUB demonstrate the progress of Graz lunar gravity field models derived within the project GRAZIL.

First-order discrete Faddeev gravity at strongly varying fields

NASA Astrophysics Data System (ADS)

Khatsymovsky, V. M.

2017-11-01

We consider the Faddeev formulation of general relativity (GR), which can be characterized by a kind of d-dimensional tetrad (typically d = 10) and a non-Riemannian connection. This theory is invariant w.r.t. the global, but not local, rotations in the d-dimensional space. There can be configurations with a smooth or flat metric, but with the tetrad that changes abruptly at small distances, a kind of “antiferromagnetic” structure. Previously, we discussed a first-order representation for the Faddeev gravity, which uses the orthogonal connection in the d-dimensional space as an independent variable. Using the discrete form of this formulation, we considered the spectrum of (elementary) area. This spectrum turns out to be physically reasonable just on a classical background with large connection like rotations by π, that is, with such an “antiferromagnetic” structure. In the discrete first-order Faddeev gravity, we consider such a structure with periodic cells and large connection and strongly changing tetrad field inside the cell. We show that this system in the continuum limit reduces to a generalization of the Faddeev system. The action is a sum of related actions of the Faddeev type and is still reduced to the GR action.

Evidence of Tropospheric 90 Day Oscillations in the Thermosphere

NASA Astrophysics Data System (ADS)

Gasperini, F.; Hagan, M. E.; Zhao, Y.

2017-10-01

In the last decade evidence demonstrated that terrestrial weather greatly impacts the dynamics and mean state of the thermosphere via small-scale gravity waves and global-scale solar tidal propagation and dissipation effects. While observations have shown significant intraseasonal variability in the upper mesospheric mean winds, relatively little is known about this variability at satellite altitudes (˜250-400 km). Using cross-track wind measurements from the Challenging Minisatellite Payload and Gravity field and steady-state Ocean Circulation Explorer satellites, winds from a Modern-Era Retrospective Analysis for Research and Applications/Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model simulation, and outgoing longwave radiation data, we demonstrate the existence of a prominent and global-scale 90 day oscillation in the thermospheric zonal mean winds and in the diurnal eastward propagating tide with zonal wave number 3 (DE3) during 2009-2010 and present evidence of its connection to variability in tropospheric convective activity. This study suggests that strong coupling between the troposphere and the thermosphere occurs on intraseasonal timescales.

The gravity field and crustal structure of the northwestern Arabian Platform in Jordan

NASA Astrophysics Data System (ADS)

Batayneh, A. T.; Al-Zoubi, A. S.

2001-01-01

The Bouguer gravity field over the northwestern Arabian Platform in Jordan is dominated by large variations, ranging from -132 to +4 mGal. A study of the Bouguer anomaly map shows that the gravity field maintains a general north-northeasterly trend in the Wadi Araba-Dead Sea-Jordan Riff, Northern Highlands and Northeast Jordanian Limestone Area, while the remainder of the area shows north-northwesterly-trending gravity anomalies. Results of 2-D gravity modeling of the Bouguer gravity field indicate that the crustal thickness in Jordan is ˜ 38 km, which is similar to crustal thicknesses obtained from refraction data in northern Jordan and Saudi Arabia, and from gravity data in Syria.

Active Response Gravity Offload and Method

NASA Technical Reports Server (NTRS)

Dungan, Larry K. (Inventor); Lieberman, Asher P. (Inventor); Shy, Cecil (Inventor); Bankieris, Derek R. (Inventor); Valle, Paul S. (Inventor); Redden, Lee (Inventor)

2015-01-01

A variable gravity field simulator can be utilized to provide three dimensional simulations for simulated gravity fields selectively ranging from Moon, Mars, and micro-gravity environments and/or other selectable gravity fields. The gravity field simulator utilizes a horizontally moveable carriage with a cable extending from a hoist. The cable can be attached to a load which experiences the effects of the simulated gravity environment. The load can be a human being or robot that makes movements that induce swinging of the cable whereby a horizontal control system reduces swinging energy. A vertical control system uses a non-linear feedback filter to remove noise from a load sensor that is in the same frequency range as signals from the load sensor.

A daily wetness index from satellite gravity for near-real time global monitoring of hydrological extremes

NASA Astrophysics Data System (ADS)

Gouweleeuw, Ben; Kvas, Andreas; Gruber, Christian; Mayer-Gürr, Torsten; Flechtner, Frank; Hasan, Mehedi; Güntner, Andreas

2017-04-01

Since April 2002, the Gravity Recovery and Climate Experiment (GRACE) satellite mission has been churning out water storage anomaly data, which has been shown to be a unique descriptor of large-scale hydrological extreme events. Nonetheless, efforts to assess the comprehensive information from GRACE on total water storage variations for near-real time flood or drought monitoring have been limited so far, primarily due to its coarse temporal (weekly to monthly) and spatial (> 150.000 km2) resolution and the latency of standard products of about 2 months,. Pending the status of the aging GRACE satellite mission, the Horizon 2020 funded EGSIEM (European Gravity Service for Improved Emergency Management) project is scheduled to launch a 6 month duration near-real time test run of GRACE gravity field data from April 2017 onward, which will provide daily gridded data with a latency of 5 days. This fast availability allows the monitoring of total water storage variations related to hydrological extreme events, as they occur, as opposed to a 'confirmation after occurrence', which is the current situation. This contribution proposes a global GRACE-derived gridded wetness indicator, expressed as a gravity anomaly in dimensionless units of standard deviation. Results of a retrospective evaluation (April 2002-December 2015) of the proposed index against databases of hydrological extremes will be presented. It is shown that signals for large extreme floods related to heavy/monsoonal rainfall are picked up really well in the Southern Hemisphere and lower Northern Hemisphere (Africa, S-America, Australia, S-Asia), while extreme floods in the Northern Hemisphere (Russia) related to snow melt are often not. The latter is possibly related to a lack of mass movement over longer distances, e.g. when melt water is not drained due to river ice blocking.

Three-dimensional Crustal Structure beneath the Tibetan Plateau Revealed by Multi-scale Gravity Analysis

NASA Astrophysics Data System (ADS)

Xu, C.; Luo, Z.; Sun, R.; Li, Q.

2017-12-01

The Tibetan Plateau, the largest and highest plateau on Earth, was uplifted, shorten and thicken by the collision and continuous convergence of the Indian and Eurasian plates since 50 million years ago, the Eocene epoch. Fine three-dimensional crustal structure of the Tibetan Plateau is helpful in understanding the tectonic development. At present, the ordinary method used for revealing crustal structure is seismic method, which is inhibited by poor seismic station coverage, especially in the central and western plateau primarily due to the rugged terrain. Fortunately, with the implementation of satellite gravity missions, gravity field models have demonstrated unprecedented global-scale accuracy and spatial resolution, which can subsequently be employed to study the crustal structure of the entire Tibetan Plateau. This study inverts three-dimensional crustal density and Moho topography of the Tibetan Plateau from gravity data using multi-scale gravity analysis. The inverted results are in agreement with those provided by the previous works. Besides, they can reveal rich tectonic development of the Tibetan Plateau: (1) The low-density channel flow can be observed from the inverted crustal density; (2) The Moho depth in the west is deeper than that in the east, and the deepest Moho, which is approximately 77 km, is located beneath the western Qiangtang Block; (3) The Moho fold, the directions of which are in agreement with the results of surface movement velocities estimated from Global Positioning System, exists clearly on the Moho topography.This study is supported by the National Natural Science Foundation of China (Grant No. 41504015), the China Postdoctoral Science Foundation (Grant No. 2015M572146), and the Surveying and Mapping Basic Research Programme of the National Administration of Surveying, Mapping and Geoinformation (Grant No. 15-01-08).

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.

Towards a first realization of the International Height Reference System (IHRS)

NASA Astrophysics Data System (ADS)

Sanchez, Laura; Ihde, Johannes; Pail, Roland; Gruber, Thomas; Barzaghi, Riccardo; Marti, Urs; Agren, Jonas; Sideris, Michael; Novak, Pavel

2017-04-01

The IAG Resolution No. 1 released during the IUGG 2015 General Assembly outlines five conventions for the definition of the International Height Reference System (IHRS). The definition is given in terms of potential parameters: the vertical coordinates are geopotential numbers referring to an equipotential surface of the Earth's gravity field realized by the conventional value W0 = 62 636 853.4 m2s-2. The spatial reference of the position P for the potential W(P) = W(X) is given by coordinates X of the International Terrestrial Reference Frame (ITRF). This Resolution also states that parameters, observations, and data shall be related to the mean tidal system/mean crust. At present, the main challenge is the realization of the IHRS; i.e., the establishment of the International Height Reference Frame (IHRF). It is expected that the IHRF follows the same structure as the ITRF: a global network with regional and national densifications, whose geopotential numbers referring to the global IHRS are known. According to the GGOS objectives, the target accuracy of these global geopotential numbers is 1 x 10-2 m2s-2. In practice, the precise realization of the IHRS is limited by different aspects; for instance, no unified standards or methods for the determination of the potential values W(P); application of different conventions for the gravity field modelling and the estimation of the position vectors X; inhomogeneous distribution of the geodetic infrastructure; restricted accessibility to terrestrial gravity data to increase the GGM resolution; insufficient modelling of geodynamic phenomena, etc. This may restrict the expected accuracy of 1 x 10-2 m2s-2 to some orders lower (from 10 x 10-2 m2s-2 to 100 x 10-2 m2s-2). This contribution discusses the required steps to outline a sustainable realization of the IHRS.

Global Distribution of Seamounts as Inferred from Ship Depth Soundings and Satellite Altimetry

NASA Astrophysics Data System (ADS)

Wessel, P.; Kim, S.; Sandwell, D. T.

2006-12-01

Traditionally, seamounts are active or extinct undersea volcanoes rising more than 1 km above the abyssal plain, but scientists now regularly apply the seamount label to features of just a few tens of meters in height. As constructional features they represent a small but significant fraction of the total volcanic extrusive budget for oceanic seafloor and their distribution provides key information on the variations in intraplate volcanic activity through space and time. Furthermore, they sustain significant ecological communities, determine habitats for fish, and act as obstacles to ocean currents, thus enhancing tidal energy dissipation and ocean mixing. Consequently, it is of some importance to locate and characterize seamounts. Two approaches are used to map the global distribution of seamounts. Depth soundings from single- and multi-beam echo sounders can provide the most detailed maps with up to 100--200 m horizontal resolution. However, soundings from the 5600 publicly available cruises sample only a small fraction of the ocean floor. Direct radar measurements of the ocean surface by satellite-borne altimeters have been used to infer the marine gravity field. By examining such gravity data one can characterize seamounts taller than ~2 km and such studies have produced seamount catalogues holding almost 15,000 seamounts. Recent retracking of the original radar altimeter waveforms to improve the accuracy of the gravity field has resulted in a two-fold increase in resolution. By extrapolating the inferred power-law that relates seamount size to frequency we estimate that 45,000 smaller seamounts taller than 1.5 km still remain uncharted. Future altimetry missions could improve on resolution and decrease noise levels even further, allowing for an even larger number of small (1--1.5 km) seamounts to be separated from the background abyssal hill fabric. Mapping the complete global distribution of seamounts will help constrain competing models of seamount formation as well as facilitate the understanding of marine habitats and deep ocean circulation.

Global accuracy estimates of point and mean undulation differences obtained from gravity disturbances, gravity anomalies and potential coefficients

NASA Technical Reports Server (NTRS)

Jekeli, C.

1979-01-01

Through the method of truncation functions, the oceanic geoid undulation is divided into two constituents: an inner zone contribution expressed as an integral of surface gravity disturbances over a spherical cap; and an outer zone contribution derived from a finite set of potential harmonic coefficients. Global, average error estimates are formulated for undulation differences, thereby providing accuracies for a relative geoid. The error analysis focuses on the outer zone contribution for which the potential coefficient errors are modeled. The method of computing undulations based on gravity disturbance data for the inner zone is compared to the similar, conventional method which presupposes gravity anomaly data within this zone.

Variability in Terrestrial Water Storage and its effect on polar motion

NASA Astrophysics Data System (ADS)

Śliwińska, Justyna; Nastula, Jolanta

2017-04-01

Explaining the hydrological part of observed polar motion excitation has been a major challenge over a dozen years. The terrestrial water storage (TWS) excitation of polar motion - hydrological angular momentum (HAM), has been investigated widely using global hydrological models mainly at seasonal timescales. Unfortunately, the results from the models do not fully explain the role of hydrological signal in polar motion excitation. The determination of TWS from the Earth's gravity field observations represents an indirect approach for estimating land hydrology. Throughout the past decade, the Gravity Recovery and Climate Experiment (GRACE) has given an unprecedented view on global variations in Terrestrial Water Storage. Our investigations are focused on the influence of Terrestrial Water Storage (TWS) variations obtained from Gravity Recovery and Climate Experiment (GRACE) mission on polar motion excitation functions at decadal and inter-annual timescales. The global and regional trend, seasonal cycle as well as some extremes in TWS variations are considered here. Here TWS are obtained from the monthly mass grids land GRACE Tellus data: GRACE CSR RL05, GRACE GFZ RL05 and GRACE JPL RL05. As a comparative dataset, we also use TWS estimates determined from the World Climate Research Programme's Coupled Model Intercomparison Project Phase 5 (CMIP5). GRACE data and state-of-the-art CMIP5 climate models allow us to show the variability of hydrological part of polar motion under climate changes. Our studies include two steps: first, the determination and comparisons of regional patterns of TWS obtained from GRACE data and climate models, and second, comparison of the regional and global hydrological excitation functions of polar motion with a hydrological signal in the geodetic excitation functions of polar motion.

Hydrology in Central Europe - a Comparison Between Data from the GRACE Satellite Mission and Ground Superconducting Gravimeters

NASA Astrophysics Data System (ADS)

Crossley, D.; de Linage, C.; Boy, J.-P.; Hinderer, J.

2009-04-01

The surface gravity field is subject to many influences of mass redistribution within the Earth system, operating at the microgal (10-8 m s-2) level and at timescales from minutes to years. We include deformation within the Earth (tides, polar motion), motions within the atmosphere (local, regional, and global loading; also mass attractions), the oceans (non-tidal currents), and near-surface hydrology derived from rainfall (local, regional, and global contributions). In central Europe a network of 7 superconducting gravimeters (the only instrument with the required resolution for this type of work) has been operating for many years, recording variations at the sub-microgal level. Hydrology is the largest component in the un-modelled residual signal, most of which comes from an area within a few hundred m of the instrument. We use data from 2002-2007 to construct a regionalized ground gravity data set that is analyzed by Principal Component (EOF) analysis to extract the predominantly seasonal signal common to all stations. This we compare with the GRACE-derived field using solutions from GFZ Potsdam, CSR Texas, and GRGS Toulouse. There is very good agreement on the phase of the two different types of data, but the amplitude of the ground signal is complicated by the local hydrology around several of the stations, which is both above and below the instrument. We show our most recent analysis and compare the results with the GLDAS global hydrology model from NASA.

A contrastive study on the influences of radial and three-dimensional satellite gravity gradiometry on the accuracy of the Earth's gravitational field recovery

NASA Astrophysics Data System (ADS)

Zheng, Wei; Hsu, Hou-Tse; Zhong, Min; Yun, Mei-Juan

2012-10-01

The accuracy of the Earth's gravitational field measured from the gravity field and steady-state ocean circulation explorer (GOCE), up to 250 degrees, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij from the satellite gravity gradiometry (SGG) are contrastively demonstrated based on the analytical error model and numerical simulation, respectively. Firstly, the new analytical error model of the cumulative geoid height, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are established, respectively. In 250 degrees, the GOCE cumulative geoid height error measured by the radial gravity gradient Vzz is about 2½ times higher than that measured by the three-dimensional gravity gradient Vij. Secondly, the Earth's gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij by numerical simulation, respectively. The study results show that when the measurement error of the gravity gradient is 3 × 10-12/s2, the cumulative geoid height errors using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are 12.319 cm and 9.295 cm at 250 degrees, respectively. The accuracy of the cumulative geoid height using the three-dimensional gravity gradient Vij is improved by 30%-40% on average compared with that using the radial gravity gradient Vzz in 250 degrees. Finally, by mutual verification of the analytical error model and numerical simulation, the orders of magnitude from the accuracies of the Earth's gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients, respectively. Therefore, it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10-13/s2-10-15/s2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.

Electromagnetic fields of slowly rotating magnetized compact stars in conformal gravity

NASA Astrophysics Data System (ADS)

Turimov, Bobur; Ahmedov, Bobomurat; Abdujabbarov, Ahmadjon; Bambi, Cosimo

2018-06-01

In this paper we investigate the exterior vacuum electromagnetic fields of slow-rotating magnetized compact stars in conformal gravity. Assuming the dipolar magnetic field configuration, we obtain an analytical solution of the Maxwell equations for the magnetic and the electric fields outside a slowly rotating magnetized star in conformal gravity. Furthermore, we study the dipolar electromagnetic radiation and energy losses from a rotating magnetized star in conformal gravity. In order to get constraints on the L parameter of conformal gravity, the theoretical results for the magnetic field of a magnetized star in conformal gravity are combined with the precise observational data of radio pulsar period slowdown, and it is found that the maximum value of the parameter of conformal gravity is less than L ≲9.5 ×105 cm (L /M ≲5 ).

Renormalization of Einstein gravity through a derivative-dependent field redefinition

NASA Astrophysics Data System (ADS)

Slovick, Brian

2018-01-01

This work explores an alternative solution to the problem of renormalizability in Einstein gravity. In the proposed approach, Einstein gravity is transformed into the renormalizable theory of four-derivative gravity by applying a local field redefinition containing an infinite number of higher derivatives. It is also shown that the current-current amplitude is invariant with the field redefinition, and thus the unitarity of Einstein gravity is preserved.

Some aspects of reconstruction using a scalar field in f( T) gravity

NASA Astrophysics Data System (ADS)

Chakrabarti, Soumya; Said, Jackson Levi; Farrugia, Gabriel

2017-12-01

General relativity characterizes gravity as a geometric property exhibited on spacetime by massive objects, while teleparallel gravity achieves the same results at the level of equations, by taking a torsional perspective of gravity. Similar to the f( R) theory teleparallel gravity can also be generalized to f( T), with the resulting field equations being inherently distinct from f( R) gravity in that they are second order, while in the former case they turn out to be fourth order. In the present case, a minimally coupled scalar field is investigated in the f( T) gravity context for several forms of the scalar field potential. A number of new f( T) solutions are found for these potentials. Their respective state parameters are also being examined.

10. The surface and interior of venus

USGS Publications Warehouse

Masursky, H.; Kaula, W.M.; McGill, G.E.; Pettengill, G.H.; Phillips, R.J.; Russell, C.T.; Schubert, G.; Shapiro, I.I.

1977-01-01

Present ideas about the surface and interior of Venus are based on data obtained from (1) Earth-based radio and radar: temperature, rotation, shape, and topography; (2) fly-by and orbiting spacecraft: gravity and magnetic fields; and (3) landers: winds, local structure, gamma radiation. Surface features, including large basins, crater-like depressions, and a linear valley, have been recognized from recent ground-based radar images. Pictures of the surface acquired by the USSR's Venera 9 and 10 show abundant boulders and apparent wind erosion. On the Pioneer Venus 1978 Orbiter mission, the radar mapper experiment will determine surface heights, dielectric constant values and small-scale slope values along the sub-orbital track between 50??S and 75??N. This experiment will also estimate the global shape and provide coarse radar images (40-80 km identification resolution) of part of the surface. Gravity data will be obtained by radio tracking. Maps combining radar altimetry with spacecraft and ground-based images will be made. A fluxgate magnetometer will measure the magnetic fields around Venus. The radar and gravity data will provide clues to the level of crustal differentiation and tectonic activity. The magnetometer will determine the field variations accurately. Data from the combined experiments may constrain the dynamo mechanism; if so, a deeper understanding of both Venus and Earth will be gained. ?? 1977 D. Reidel Publishing Company.

KSC-2011-6752

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – A Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference is held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. From left are George Diller, NASA Public Affairs; Ed Weiler, NASA associate administrator, Science Mission Directorate; Tim Dunn, NASA launch director for the agency’s Launch Services Program; Vernon Thorp, program manager, NASA Missions, United Launch Alliance; David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory; John Henk, GRAIL program manager, Lockheed Martin Space Systems, Denver, Colo.; and Joel Tumbiolo, launch weather officer, 45th Weather Squadron, Cape Canaveral Air Force Station, Fla. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6753

NASA Image and Video Library

2011-09-06

CAPE CANAVERAL, Fla. – News media participate in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. On the dais, panelist from left are Ed Weiler, NASA associate administrator, Science Mission Directorate; Tim Dunn, NASA launch director for the agency’s Launch Services Program; Vernon Thorp, program manager, NASA Missions, United Launch Alliance; David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory; John Henk, GRAIL program manager, Lockheed Martin Space Systems, Denver, Colo.; and Joel Tumbiolo, launch weather officer, 45th Weather Squadron, Cape Canaveral Air Force Station, Fla. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

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.

Scalar resonant frequencies and Hawking effect of an f ( R ) global monopole

NASA Astrophysics Data System (ADS)

Vieira, H. S.; Morais Graça, J. P.; Bezerra, V. B.

2017-09-01

Massive scalar fields are considered in the gravitational field produced by a Schwarzschild black hole with a global monopole in f(R) gravity. The exact solution of the radial part of the Klein-Gordon equation in this background is obtained and is given in terms of the general Heun functions. We apply the properties of the general Heun functions to study the Hawking radiation and the resonant frequencies of scalar particles. H.S.V. is funded by the Brazilian research agencies CNPq (research Project No. 140612/2014-9) and CAPES (PDSE Process No. 88881.133092/2016-01). J.P.M.G. is funded by the CNPq through the research Project No. 150565/2016-0. V.B.B. is partially supported by the CNPq through the research Project No. 304553/2010-7

Earth survey applications division: Research leading to the effective use of space technology in applications relating to the Earth's surface and interior

NASA Technical Reports Server (NTRS)

Carpenter, L. (Editor)

1980-01-01

Accomplishments and future plans are described for the following areas: (1) geology - geobotanical indicators and geopotential data; (2) modeling magnetic fields; (3) modeling the structure, composition, and evolution of the Earth's crust; (4) global and regional motions of the Earth's crust and earthquake occurrence; (5) modeling geopotential from satellite tracking data; (6) modeling the Earth's gravity field; (7) global Earth dynamics; (8) sea surface topography, ocean dynamics; and geophysical interpretation; (9) land cover and land use; (10) physical and remote sensing attributes important in detecting, measuring, and monitoring agricultural crops; (11) prelaunch studies using LANDSAT D; (12) the multispectral linear array; (13) the aircraft linear array pushbroom radiometer; and (14) the spaceborne laser ranging system.

Hyperunified field theory and gravitational gauge-geometry duality

NASA Astrophysics Data System (ADS)

Wu, Yue-Liang

2018-01-01

A hyperunified field theory is built in detail based on the postulates of gauge invariance and coordinate independence along with the conformal scaling symmetry. All elementary particles are merged into a single hyper-spinor field and all basic forces are unified into a fundamental interaction governed by the hyper-spin gauge symmetry SP(1, D_h-1). The dimension D_h of hyper-spacetime is conjectured to have a physical origin in correlation with the hyper-spin charge of elementary particles. The hyper-gravifield fiber bundle structure of biframe hyper-spacetime appears naturally with the globally flat Minkowski hyper-spacetime as a base spacetime and the locally flat hyper-gravifield spacetime as a fiber that is viewed as a dynamically emerged hyper-spacetime characterized by a non-commutative geometry. The gravitational origin of gauge symmetry is revealed with the hyper-gravifield that plays an essential role as a Goldstone-like field. The gauge-gravity and gravity-geometry correspondences bring about the gravitational gauge-geometry duality. The basic properties of hyperunified field theory and the issue on the fundamental scale are analyzed within the framework of quantum field theory, which allows us to describe the laws of nature in deriving the gauge gravitational equation with the conserved current and the geometric gravitational equations of Einstein-like type and beyond.

On resonant coupling of acoustic waves and gravity waves

NASA Astrophysics Data System (ADS)

Millet, Christophe

2017-11-01

Acoustic propagation in the atmosphere is often modeled using modes that are confined within waveguides causing the sound to propagate through multiple paths to the receiver. On the other hand, direct observations in the lower stratosphere show that the gravity wave field is intermittent, and is often dominated by rather well defined large-amplitude wave packets. In the present work, we use normal modes to describe both the gravity wave field and the acoustic field. The gravity wave spectrum is obtained by launching few monochromatic waves whose properties are chosen stochastically to mimic the intermittency. Owing to the disparity of the gravity and acoustic length scales, the interactions between the gravity wave field and each of the acoustic modes can be described using a multiple-scale analysis. The appropriate amplitude evolution equation for the acoustic field involves certain random terms that can be directly related to the gravity wave sources. We will show that the cumulative effect of gravity wave breakings makes the sensitivity of ground-based acoustic signals large, in that small changes in the gravity wave parameterization can create or destroy specific acoustic features.

Basement structures over Rio Grande Rise from gravity inversion

NASA Astrophysics Data System (ADS)

Constantino, Renata; Hackspacker, Peter Christian; Anderson de Souza, Iata; Sousa Lima Costa, Iago

2017-04-01

In this study, we show that from satellite-derived gravity field, bathymetry and sediment thicknesses, it is possible to give a 3-D model of the basement over oceanic areas, and for this purpose, we have chosen the Rio Grande Rise, in South Atlantic Ocean, to build a gravity-equivalent basement topography. The advantages of the method applied in this study are manifold: does not depend directly on reflection seismic data; can be applied quickly and with fewer costs for acquiring and interpreting the data; and as the main result, presents the physical surface below the sedimentary layer, which may be different from the acoustic basement. We evaluated the gravity effect of the sediments using the global sediment thickness model of NOAA, fitting a sediment compaction model to observed density values from Deep Sea Drilling Program (DSDP) reports. The Global Relief Model ETOPO1 and constraining data from seismic interpretation on crustal thickness are integrated in the gravity inversion procedure. The modeled Moho depth values vary between 6 to 27 km over the area, being thicker under the Rio Grande Rise and also in the direction of São Paulo Plateau. The inversion for the gravity-equivalent basement topography is applied for a gravity residual data, which is free from the gravity effect of sediments and from the gravity effect of the estimated Moho interface. A description of the basement depth over Rio Grande Rise area is unprecedented in the literature, however, our results could be compared to in situ data, provided by DSDP, and a small difference of only 9 m between our basement depth and leg 516 F was found. Our model shows a rift crossing the entire Rio Grande Rise deeper than previously presented in literature, with depths up to 5 km in the East Rio Grande Rise (ERGR) and deeper in the West Rio Grande Rise (WRGR), reaching 6.4 km. We find several short-wavelengths structures not present in the bathymetry data. Seamounts, guyots and fracture zones are much more clearly defined in the basement than in the bathymetric model. An interesting NS structure that goes from 34S and extends through de São Paulo Ridge is interpreted in the basement model, and we propose that this feature can be related to the South Atlantic opening, revealing an extinct spreading center.

The ITSG-Grace2014 Gravity Field Model

NASA Astrophysics Data System (ADS)

Kvas, Andreas; Mayer-Gürr, Torsten; Zehenter, Norbert; Klinger, Beate

2015-04-01

The ITSG-Grace2014 GRACE-only gravity field model consists of a high resolution unconstrained static model (up to degree 200) with trend and annual signal, monthly unconstrained solutions with different spatial resolutions as well as daily snapshots derived by using a Kalman smoother. Apart from the estimated spherical harmonic coefficients, full variance-covariance matrices for the monthly solutions and the static gravity field component are provided. Compared to the previous release, multiple improvements in the processing chain are implemented: updated background models, better ionospheric modeling for GPS observations, an improved satellite attitude by combination of star camera and angular accelerations, estimation of K-band antenna center variations within the gravity field recovery process as well as error covariance function determination. Furthermore, daily gravity field variations have been modeled in the adjustment process to reduce errors caused by temporal leakage. This combined estimation of daily gravity variations field variations together with the static gravity field component represents a computational challenge due to the significantly increased parameter count. The modeling of daily variations up to a spherical harmonic degree of 40 for the whole GRACE observation period results in a system of linear equations with over 6 million unknown gravity field parameters. A least squares adjustment of this size is not solvable in a sensible time frame, therefore measures to reduce the problem size have to be taken. The ITSG-Grace2014 release is presented and selected parts of the processing chain and their effect on the estimated gravity field solutions are discussed.

Stress analysis of Tellus Regio, Venus, based on gravity and topography - Comparison with Venera 15/16 radar images

NASA Technical Reports Server (NTRS)

Williams, David R.; Gaddis, Lisa

1991-01-01

The tectonics of the Tellus Region highland on Venus is examined using the altimetry and gravity data collected by Pioneer Venus, which were incorporated into a thin elastic shell model to calculate both the global (long-wavelength) and the regional (short-wavelength) stresses for various assumed values of crust, lithosphere, and mantle thickness and modes of compensation. The resultant stress fields were compared to the surface morphology observed in the Venera 15/16 radar images and interpreted in terms of stress history of Tellus Regio. The best fitting parameters were found to be consistent with minor amounts of lithospheric flexure being necessary to produce the observed surface features of this region.

Spectroscopy of late type giant stars

NASA Astrophysics Data System (ADS)

Spaenhauer, A.; Thevenin, F.

1984-06-01

An attempt to calibrate broadband RGU colors of late type giant stars in terms of the physical parameters of the objects is reported. The parameters comprise the effective temperature, surface gravity and global metal abundance with respect to the sun. A selection of 21 giant star candidates in the Basel fields Plaut 1, Centaurus III and near HD 95540 were examined to obtain a two color plot. Attention is focused on the G-R color range 1.5-2.15 mag, i.e., spectral types K0-K5. A relationship between R and the metallicity is quantified and shown to have a correlation coefficient of 0.93. No correlation is found between metallicity and gravity or R and the effective temperature.

Earth and ocean physics. [results of ERTS-1 imagery for determining earth gravity and tectonic conditions

NASA Technical Reports Server (NTRS)

1975-01-01

A procedure for obtaining a parameterization of the marine geoid for suitable orthogonality properties in altimetry data is discussed. The application of the technique to the Puerto Rico trench is explained and a map of the data is developed. The Goddard Earth Model (GEM-6) is described to show the method for determining the earth gravity field using data obtained from satellite tracking stations. The derivation of a global ocean tide model from satellite data is explained. The influence of solid earth and ocean tides on the inclination of GEOS-1 is plotted. The delineation of the geographical fracture pattern and boundary system of the tectonic plates using ERTS satellite is shown.

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.

Lithospheric Structure from Mars Global Surveyor Topography and Gravity and Implications for the Early Thermal Evolution of Mars

NASA Technical Reports Server (NTRS)

Solomon, Sean C.; Zuber, Maria T.; Phillips, Roger J.; Smith, David E.; Tyler, G. Leonard; Aharonson, Oded; Balmino, Georges; Banerdt, W. B.; Head, James W.; Johnson, Catherine L.

2000-01-01

Regional variations in the thickness of the elastic lithosphere on Mars derived from a combined analysis of topography and gravity anomalies determined by Mars Global Surveyor provide new insight into the planet's thermal history.

Regional models of the gravity field from terrestrial gravity data of heterogeneous quality and density

NASA Astrophysics Data System (ADS)

Talvik, Silja; Oja, Tõnis; Ellmann, Artu; Jürgenson, Harli

2014-05-01

Gravity field models in a regional scale are needed for a number of applications, for example national geoid computation, processing of precise levelling data and geological modelling. Thus the methods applied for modelling the gravity field from surveyed gravimetric information need to be considered carefully. The influence of using different gridding methods, the inclusion of unit or realistic weights and indirect gridding of free air anomalies (FAA) are investigated in the study. Known gridding methods such as kriging (KRIG), least squares collocation (LSCO), continuous curvature (CCUR) and optimal Delaunay triangulation (ODET) are used for production of gridded gravity field surfaces. As the quality of data collected varies considerably depending on the methods and instruments available or used in surveying it is important to somehow weigh the input data. This puts additional demands on data maintenance as accuracy information needs to be available for each data point participating in the modelling which is complicated by older gravity datasets where the uncertainties of not only gravity values but also supplementary information such as survey point position are not always known very accurately. A number of gravity field applications (e.g. geoid computation) demand foran FAA model, the acquisition of which is also investigated. Instead of direct gridding it could be more appropriate to proceed with indirect FAA modelling using a Bouguer anomaly grid to reduce the effect of topography on the resulting FAA model (e.g. near terraced landforms). The inclusion of different gridding methods, weights and indirect FAA modelling helps to improve gravity field modelling methods. It becomes possible to estimate the impact of varying methodical approaches on the gravity field modelling as statistical output is compared. Such knowledge helps assess the accuracy of gravity field models and their effect on the aforementioned applications.

Gravity Field of Venus and Comparison with Earth

NASA Technical Reports Server (NTRS)

Bowin, C.

1985-01-01

The acceleration (gravity) anomaly estimates by spacecraft tracking, determined from Doppler residuals, are components of the gravity field directed along the spacecraft Earth line of sight (LOS). These data constitute a set of vector components of a planet's gravity field, the specific component depending upon where the Earth happened to be at the time of each measurement, and they are at varying altitudes above the planet surface. From this data set the gravity field vector components were derived using the method of harmonic splines which imposes a smoothness criterion to select a gravity model compatible with the LOS data. Given the piecewise model it is now possible to upward and downward continue the field quantities desired with a few parameters unlike some other methods which must return to the full dataset for each desired calculation.

SLR in the framework of the EGSIEM project

NASA Astrophysics Data System (ADS)

Maier, Andrea; Sušnik, Andreja; Meyer, Ulrich; Arnold, Daniel; Dach, Rolf; Jäggi, Adrian; Sośnica, Krzysztof; Thaller, Daniela

2016-04-01

This contribution describes the three roles Satellite Laser Ranging (SLR) is playing within the European Gravity Service for the Improved Emergency Management (EGSIEM). The purpose of this Horizon 2020 project is to combine monthly gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) mission that are derived by different institutions. The combined gravity field product will provide complementary information to traditional products for flood and drought monitoring and forecasting. First, SLR is used to validate Global Navigational Satellite System (GNSS) orbits, which are computed at the Astronomical Institute of the University of Bern. To ensure a consistent set of GNSS products (orbits, Earth rotation parameters, and clocks) a reprocessing campaign was initiated. The reprocessed products are based on the new Empirical CODE Orbit Model, which is used for all orbit products generated at the Center for Orbit Determination in Europe (CODE) from January 4, 2015 onwards. Since the kinematic orbits of GRACE will be based on these orbits, we present an in-depth validation of the GNSS orbits using SLR. Second, SLR to geodetic satellites is crucial for the estimation of the dynamical Earth's flattening term (C20) since this coefficient is degraded by aliasing when derived from GRACE data. We will compare the temporal variation of C20 with external solutions and demonstrate the benefit of involving a larger number of geodetic satellites. The third aspect is based on the fact that the gravity field product delivered by EGSIEM will include GRACE and SLR data. It is thus desirable to establish a reference frame based on both GNSS data and SLR observations. For this purpose it is planned to analyze SLR measurements to GNSS satellites equipped with a retroreflector array and to estimate common parameters such as station coordinates and geocenter coordinates from a combined set of SLR and GNSS data. We will present a workflow how to derive a common reference frame.

On holographic Rényi entropy in some modified theories of gravity

NASA Astrophysics Data System (ADS)

Dey, Anshuman; Roy, Pratim; Sarkar, Tapobrata

2018-04-01

We perform a detailed analysis of holographic entanglement Rényi entropy in some modified theories of gravity with four dimensional conformal field theory duals. First, we construct perturbative black hole solutions in a recently proposed model of Einsteinian cubic gravity in five dimensions, and compute the Rényi entropy as well as the scaling dimension of the twist operators in the dual field theory. Consistency of these results are verified from the AdS/CFT correspondence, via a corresponding computation of the Weyl anomaly on the gravity side. Similar analyses are then carried out for three other examples of modified gravity in five dimensions that include a chemical potential, namely Born-Infeld gravity, charged quasi-topological gravity and a class of Weyl corrected gravity theories with a gauge field, with the last example being treated perturbatively. Some interesting bounds in the dual conformal field theory parameters in quasi-topological gravity are pointed out. We also provide arguments on the validity of our perturbative analysis, whenever applicable.

Physics of Gravitational Interaction: Geometry of Space or Quantum Field in Space

NASA Astrophysics Data System (ADS)

Baryshev, Yurij

2006-03-01

Thirring-Feynman's tensor field approach to gravitation opens new understanding on the physics of gravitational interaction and stimulates novel experiments on the nature of gravity. According to Field Gravity, the universal gravity force is caused by exchange of gravitons - the quanta of gravity field. Energy of this field is well-defined and excludes the singularity. All classical relativistic effects are the same as in General Relativity. The intrinsic scalar (spin 0) part of gravity field corresponds to ``antigravity'' and only together with the pure tensor (spin 2) part gives the usual Newtonian force. Laboratory and astrophysical experiments which may test the predictions of FG, will be performed in near future. In particular, observations at gravity observatories with bar and interferometric detectors, like Explorer, Nautilus, LIGO and VIRGO, will check the predicted scalar gravitational waves from supernova explosions. New types of cosmological models in Minkowski space are possible too.

Calculation of the temporal gravity variation from spatially variable water storage change in soils and aquifers

NASA Astrophysics Data System (ADS)

Leirião, Sílvia; He, Xin; Christiansen, Lars; Andersen, Ole B.; Bauer-Gottwein, Peter

2009-02-01

SummaryTotal water storage change in the subsurface is a key component of the global, regional and local water balances. It is partly responsible for temporal variations of the earth's gravity field in the micro-Gal (1 μGal = 10 -8 m s -2) range. Measurements of temporal gravity variations can thus be used to determine the water storage change in the hydrological system. A numerical method for the calculation of temporal gravity changes from the output of hydrological models is developed. Gravity changes due to incremental prismatic mass storage in the hydrological model cells are determined to give an accurate 3D gravity effect. The method is implemented in MATLAB and can be used jointly with any hydrological simulation tool. The method is composed of three components: the prism formula, the MacMillan formula and the point-mass approximation. With increasing normalized distance between the storage prism and the measurement location the algorithm switches first from the prism equation to the MacMillan formula and finally to the simple point-mass approximation. The method was used to calculate the gravity signal produced by an aquifer pump test. Results are in excellent agreement with the direct numerical integration of the Theis well solution and the semi-analytical results presented in [Damiata, B.N., and Lee, T.-C., 2006. Simulated gravitational response to hydraulic testing of unconfined aquifers. Journal of Hydrology 318, 348-359]. However, the presented method can be used to forward calculate hydrology-induced temporal variations in gravity from any hydrological model, provided earth curvature effects can be neglected. The method allows for the routine assimilation of ground-based gravity data into hydrological models.

Using Radial Basis Functions in Airborne Gravimetry for Local Geoid Improvement

NASA Astrophysics Data System (ADS)

Li, Xiaopeng

2017-04-01

Radial basis functions (RBF, Schmidt et al 2007, Klees and Wittwer 2007, Klees et al 2008) have been extensively used in satellite geodetic applications (Eicker 2008, Wittwer 2009, Naeimi 2013, among others). However, to date, to the author's knowledge, their roles in processing and modeling airborne gravity data have not been fully advocated or extensively investigated in detail, though compared with satellite missions, the airborne data is more suitable for this kind of localized basis functions especially considering the following facts: (1) Unlike the satellite missions that can provide global or near global data coverage, airborne gravity data is usually geographically limited. (2) It is also band limited in the frequency domain, considering that various filter banks and/or de-noising techniques (Li 2007) have to be applied to overcome the low signal-to-noise ratio problem that is present in airborne gravimetric systems. This is mainly due to the mechanical and mathematical limitations in computing the accelerations (both the kinematic and dynamic accelerations, Jekeli 2000). (3) It is much easier to formulate the RBF observation equations from an airborne gravimetric system (either a scalar one (Forsberg and Olesen 2010) or a vector one (Kwon and Jekeli 2001)) than from any satellite mission, especially compared with Gravity Recovery and Climate Experiment satellites (GRACE, Tapley et al. 2004) where many accurate background environmental models have to be used in order to separate out the gravity related functionals. As a result, in this study, a set of band-limited RBF is developed to model and downward continue the airborne gravity data for local geoid improvement. First, the algorithm is tested with synthesized data from global coefficient models such as EIGEN6c4 (Försteet al. 2014), during which the RBF not only successfully recovers a harmonic field but also presents filtering properties due to its particular design in the frequency domain. Then, the software is tested for the GSVS14 (Geoid Slope Validation Survey 2014) area as well as for the area around Puerto Rico and the U.S. Virgin Islands by using the real airborne gravity data from the Gravity for the Redefinition of the American Vertical Datum (GRAV-D, Smith 2007) project. The newly acquired cm-level accurate GPS/Leveling bench marks prove the RBF airborne enhanced geoid models are not inferior to other models computed by conventional approaches. By fully utilizing the three dimensional correlation information among the flight tracks, the RBF can also be used as a data editing tool for airborne data adjustment and cleaning.

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.

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.

Frequency content of sea surface height variability from internal gravity waves to mesoscale eddies

NASA Astrophysics Data System (ADS)

Savage, Anna C.; Arbic, Brian K.; Richman, James G.; Shriver, Jay F.; Alford, Matthew H.; Buijsman, Maarten C.; Thomas Farrar, J.; Sharma, Hari; Voet, Gunnar; Wallcraft, Alan J.; Zamudio, Luis

2017-03-01

High horizontal-resolution (1/12.5° and 1/25°) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical coverage and that also cover a wide range of frequencies—a set of 351 tide gauges that measure full SSH and a set of 14 in situ vertical profilers from which steric SSH can be calculated. Three of the global maps are of interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) two-dimensional swath altimeter mission: (1) maps of the total and (2) nonstationary internal tidal signal (the latter calculated after removing the stationary internal tidal signal via harmonic analysis), with an average variance of 1.05 and 0.43 cm2, respectively, for the semidiurnal band, and (3) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum, with an average variance of 0.15 cm2. Stationary internal tides (which are predictable), nonstationary internal tides (which will be harder to predict), and nontidal internal gravity waves (which will be very difficult to predict) may all be important sources of high-frequency "noise" that could mask lower frequency phenomena in SSH measurements made by the SWOT mission.

Computing the Deflection of the Vertical for Improving Aerial Surveys: A Comparison between EGM2008 and ITALGEO05 Estimates.

PubMed

Barzaghi, Riccardo; Carrion, Daniela; Pepe, Massimiliano; Prezioso, Giuseppina

2016-07-26

Recent studies on the influence of the anomalous gravity field in GNSS/INS applications have shown that neglecting the impact of the deflection of vertical in aerial surveys induces horizontal and vertical errors in the measurement of an object that is part of the observed scene; these errors can vary from a few tens of centimetres to over one meter. The works reported in the literature refer to vertical deflection values based on global geopotential model estimates. In this paper we compared this approach with the one based on local gravity data and collocation methods. In particular, denoted by ξ and η, the two mutually-perpendicular components of the deflection of the vertical vector (in the north and east directions, respectively), their values were computed by collocation in the framework of the Remove-Compute-Restore technique, applied to the gravity database used for estimating the ITALGEO05 geoid. Following this approach, these values have been computed at different altitudes that are relevant in aerial surveys. The (ξ, η) values were then also estimated using the high degree EGM2008 global geopotential model and compared with those obtained in the previous computation. The analysis of the differences between the two estimates has shown that the (ξ, η) global geopotential model estimate can be reliably used in aerial navigation applications that require the use of sensors connected to a GNSS/INS system only above a given height (e.g., 3000 m in this paper) that must be defined by simulations.

Computing the Deflection of the Vertical for Improving Aerial Surveys: A Comparison between EGM2008 and ITALGEO05 Estimates

PubMed Central

Barzaghi, Riccardo; Carrion, Daniela; Pepe, Massimiliano; Prezioso, Giuseppina

2016-01-01

Recent studies on the influence of the anomalous gravity field in GNSS/INS applications have shown that neglecting the impact of the deflection of vertical in aerial surveys induces horizontal and vertical errors in the measurement of an object that is part of the observed scene; these errors can vary from a few tens of centimetres to over one meter. The works reported in the literature refer to vertical deflection values based on global geopotential model estimates. In this paper we compared this approach with the one based on local gravity data and collocation methods. In particular, denoted by ξ and η, the two mutually-perpendicular components of the deflection of the vertical vector (in the north and east directions, respectively), their values were computed by collocation in the framework of the Remove-Compute-Restore technique, applied to the gravity database used for estimating the ITALGEO05 geoid. Following this approach, these values have been computed at different altitudes that are relevant in aerial surveys. The (ξ, η) values were then also estimated using the high degree EGM2008 global geopotential model and compared with those obtained in the previous computation. The analysis of the differences between the two estimates has shown that the (ξ, η) global geopotential model estimate can be reliably used in aerial navigation applications that require the use of sensors connected to a GNSS/INS system only above a given height (e.g., 3000 m in this paper) that must be defined by simulations. PMID:27472333

Mars Gravity Field Model Development from Mars Global Surveyor Tracking Data

NASA Technical Reports Server (NTRS)

Lemoine, F. G.; Zuber, M. T.

1999-01-01

Since Feb. 99 the MGS spacecraft has been in a near circular orbit at about 400 km altitude. The MGS has been regularly tracked by the Deep Space Network (DSN) at X-band and for a 3 week period in February was tracked almost continuously for an intensive gravity modeling activity that would form the basis of the orbital computations for the rest of the mission. The data collected during this calibration period and the earlier SPO and Hiatus periods have now been used to develop a new gravity field model for Mars that is showing considerable new detail in both the northern and southern hemispheres. Until February no data at 400 km altitude or lower had been acquired on any previous mission south of about 35S and all the previous data were of significantly lower quality. Low altitude data (-170 km) were obtained over the higher latitudes of the northern hemisphere during the SPO periods but because of the high eccentricity of the orbit nothing of similar quality was obtainable for the southern hemisphere. The new models are of spherical harmonic degree and order 70 or higher and are suggesting large anomalies are often associated with the large impact features. Gravity data have also been obtained over both the northern and southern polar ice caps. The MGS orbit quality resulting from the use of these newer models is better than any previous Mars missions and is approaching the ten's of meter level that had been hoped would be eventually realizable.

Towards causal patch physics in dS/CFT

NASA Astrophysics Data System (ADS)

Neiman, Yasha

2018-01-01

This contribution is a status report on a research program aimed at obtaining quantum-gravitational physics inside a cosmological horizon through dS/CFT, i.e. through a holographic description at past/future infinity of de Sitter space. The program aims to bring together two main elements. The first is the observation by Anninos, Hartman and Strominger that Vasiliev's higher-spin gravity provides a working model for dS/CFT in 3+1 dimensions. The second is the proposal by Parikh, Savonije and Verlinde that dS/CFT may prove more tractable if one works in so-called "elliptic" de Sitter space - a folded-in-half version of global de Sitter where antipodal points have been identified. We review some relevant progress concerning quantum field theory on elliptic de Sitter space, higher-spin gravity and its holographic duality with a free vector model. We present our reasons for optimism that the approach outlined here will lead to a full holographic description of quantum (higher-spin) gravity in the causal patch of a de Sitter observer.

Gravity quantized: Loop quantum gravity with a scalar field

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

Domagala, Marcin; Kaminski, Wojciech; Giesel, Kristina

2010-11-15

...''but we do not have quantum gravity.'' This phrase is often used when analysis of a physical problem enters the regime in which quantum gravity effects should be taken into account. In fact, there are several models of the gravitational field coupled to (scalar) fields for which the quantization procedure can be completed using loop quantum gravity techniques. The model we present in this paper consists of the gravitational field coupled to a scalar field. The result has similar structure to the loop quantum cosmology models, except that it involves all the local degrees of freedom of the gravitational fieldmore » because no symmetry reduction has been performed at the classical level.« less

Equivalent water height extracted from GRACE gravity field model with robust independent component analysis

NASA Astrophysics Data System (ADS)

Guo, Jinyun; Mu, Dapeng; Liu, Xin; Yan, Haoming; Dai, Honglei

2014-08-01

The Level-2 monthly GRACE gravity field models issued by Center for Space Research (CSR), GeoForschungs Zentrum (GFZ), and Jet Propulsion Laboratory (JPL) are treated as observations used to extract the equivalent water height (EWH) with the robust independent component analysis (RICA). The smoothing radii of 300, 400, and 500 km are tested, respectively, in the Gaussian smoothing kernel function to reduce the observation Gaussianity. Three independent components are obtained by RICA in the spatial domain; the first component matches the geophysical signal, and the other two match the north-south strip and the other noises. The first mode is used to estimate EWHs of CSR, JPL, and GFZ, and compared with the classical empirical decorrelation method (EDM). The EWH STDs for 12 months in 2010 extracted by RICA and EDM show the obvious fluctuation. The results indicate that the sharp EWH changes in some areas have an important global effect, like in Amazon, Mekong, and Zambezi basins.

KSC-2011-6822

NASA Image and Video Library

2011-09-08

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are Dana Grieco, launch operations manager, Analex, NASA's Launch Services Program (LSP); Bruce Reid, GRAIL mission manager, LSP; Al Sierra, manager of the Flight Project Office, LSP; Omar Baez, GRAIL assistant launch director, LSP; and Tim Dunn, GRAIL launch director, LSP; David Lehman, spacecraft mission director and GRAIL project manager, NASA's Jet Propulsion Laboratory (JPL); and John Henk, GRAIL program manager, Lockheed Martin Space Systems. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

KSC-2011-6887

NASA Image and Video Library

2011-09-10

CAPE CANAVERAL, Fla. – Managers of NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission participate in a post-launch news conference in the Press Site television auditorium at NASA's Kennedy Space Center in Florida. From left are Jim Adams, deputy director, Planetary Science Division, NASA's Science Mission Directorate; Maria Zuber, GRAIL principal investigator, Massachusetts Institute of Technology; and David Lehman, GRAIL project manager, Jet Propulsion Laboratory. Liftoff of the twin GRAIL spacecraft aboard a United Launch Alliance Delta II Heavy rocket was at 9:08:52 EDT Sept. 10 from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft are embarking on a three-month journey to reach the moon. GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

The quest for the perfect gravity anomaly: Part 2 - Mass effects and anomaly inversion

USGS Publications Warehouse

Keller, Gordon R.; Hildenbrand, T.G.; Hinze, W. J.; Li, X.; Ravat, D.; Webring, M.

2006-01-01

Gravity anomalies have become an important tool for geologic studies since the widespread use of high-precision gravimeters after the Second World War. More recently the development of instrumentation for airborne gravity observations, procedures for acquiring data from satellite platforms, the readily available Global Positioning System for precise vertical and horizontal control, improved global data bases, and enhancement of computational hardware and software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases that are made available to the geoscience community by broadening their observational holdings and increasing the accuracy and precision of the included data. Currently the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States of America are being revised using new formats and standards. The objective of this paper is to describe the use of the revised standards for gravity data processing and modeling and there impact on geological interpretations. ?? 2005 Society of Exploration Geophysicists.

Gravity Field Recovery from the Cartwheel Formation by the Semi-analytical Approach

NASA Astrophysics Data System (ADS)

Li, Huishu; Reubelt, Tilo; Antoni, Markus; Sneeuw, Nico; Zhong, Min; Zhou, Zebing

2016-04-01

Past and current gravimetric satellite missions have contributed drastically to our knowledge of the Earth's gravity field. Nevertheless, several geoscience disciplines push for even higher requirements on accuracy, homogeneity and time- and space-resolution of the Earth's gravity field. Apart from better instruments or new observables, alternative satellite formations could improve the signal and error structure. With respect to other methods, one significant advantage of the semi-analytical approach is its effective pre-mission error assessment for gravity field missions. The semi-analytical approach builds a linear analytical relationship between the Fourier spectrum of the observables and the spherical harmonic spectrum of the gravity field. The spectral link between observables and gravity field parameters is given by the transfer coefficients, which constitutes the observation model. In connection with a stochastic model, it can be used for pre-mission error assessment of gravity field mission. The cartwheel formation is formed by two satellites on elliptic orbits in the same plane. The time dependent ranging will be considered in the transfer coefficients via convolution including the series expansion of the eccentricity functions. The transfer coefficients are applied to assess the error patterns, which are caused by different orientation of the cartwheel for range-rate and range acceleration. This work will present the isotropy and magnitude of the formal errors of the gravity field coefficients, for different orientations of the cartwheel.

Global properties of physically interesting Lorentzian spacetimes

NASA Astrophysics Data System (ADS)

Nawarajan, Deloshan; Visser, Matt

Under normal circumstances most members of the general relativity community focus almost exclusively on the local properties of spacetime, such as the locally Euclidean structure of the manifold and the Lorentzian signature of the metric tensor. When combined with the classical Einstein field equations this gives an extremely successful empirical model of classical gravity and classical matter — at least as long as one does not ask too many awkward questions about global issues, (such as global topology and global causal structure). We feel however that this is a tactical error — even without invoking full-fledged “quantum gravity” we know that the standard model of particle physics is also an extremely good representation of some parts of empirical reality; and we had better be able to carry over all the good features of the standard model of particle physics — at least into the realm of semi-classical quantum gravity. Doing so gives us some interesting global features that spacetime should possess: On physical grounds spacetime should be space-orientable, time-orientable, and spacetime-orientable, and it should possess a globally defined tetrad (vierbein, or in general a globally defined vielbein/n-bein). So on physical grounds spacetime should be parallelizable. This strongly suggests that the metric is not the fundamental physical quantity; a very good case can be made for the tetrad being more fundamental than the metric. Furthermore, a globally-defined “almost complex structure” is almost unavoidable. Ideas along these lines have previously been mooted, but much is buried in the pre-arXiv literature and is either forgotten or inaccessible. We shall revisit these ideas taking a perspective very much based on empirical physical observation.

The Dawn Gravity Investigation at Vesta and Ceres

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Asmar, S.W.; Bills, B. G.; Mastrodemos, N.; Park, R. S.; Raymond, C. A.; Smith, D. E.; Zuber, M. T.

2011-01-01

The objective of the Dawn gravity investigation is to use high precision X-band Doppler tracking and landmark tracking from optical images to measure the gravity fields of Vesta and Ceres to a half-wavelength surface resolution better than 90-km and 300-km, respectively. Depending on the Doppler tracking assumptions, the gravity field will be determined to somewhere between harmonic degrees 15 and 25 for Vesta and about degree 10 for Ceres. The gravity fields together with shape models determined from Dawn's framing camera constrain models of the interior from the core to the crust. The gravity field is determined jointly with the spin pole location. The second degree harmonics together with assumptions on obliquity or hydrostatic equilibrium may determine the moments of inertia.

Emergence of gravity, fermion, gauge and Chern-Simons fields during formation of N-dimensional manifolds from joining point-like ones

NASA Astrophysics Data System (ADS)

Sepehri, Alireza; Shoorvazi, Somayyeh

In this paper, we will consider the birth and evolution of fields during formation of N-dimensional manifolds from joining point-like ones. We will show that at the beginning, only there are point-like manifolds which some strings are attached to them. By joining these manifolds, 1-dimensional manifolds are appeared and gravity, fermion, and gauge fields are emerged. By coupling these manifolds, higher dimensional manifolds are produced and higher orders of fermion, gauge fields and gravity are emerged. By decaying N-dimensional manifold, two child manifolds and a Chern-Simons one are born and anomaly is emerged. The Chern-Simons manifold connects two child manifolds and leads to the energy transmission from the bulk to manifolds and their expansion. We show that F-gravity can be emerged during the formation of N-dimensional manifold from point-like manifolds. This type of F-gravity includes both type of fermionic and bosonic gravity. G-fields and also C-fields which are produced by fermionic strings produce extra energy and change the gravity.

EGSIEM: Combination of GRACE monthly gravity models on normal equation level

NASA Astrophysics Data System (ADS)

Meyer, Ulrich; Jean, Yoomin; Jäggi, Adrian; Mayer-Gürr, Torsten; Neumayer, Hans; Lemoine, Jean-Michel

2016-04-01

One of the three geodetic services to be realized in the frame of the EGSIEM project is a scientific combination service. Each associated processing center (AC) will follow a set of common processing standards but will apply its own, independent analysis method. Therefore the quality, robustness and reliability of the combined monthly gravity fields is expected to improve significantly compared to the individual solutions. The Monthly GRACE gravity fields of all ACs are combined on normal equation level. The individual normal equations are weighted depending on pairwise comparisons of the individual gravity field solutions. To derive these weights and for quality control of the individual contributions first a combination of the monthly gravity fields on solution level is performed. The concept of weighting and of the combination on normal equation level is introduced and the formats used for normal equation exchange and gravity field solutions is described. First results of the combination on normal equation level are presented and compared to the corresponding combinations on solution level. EGSIEM has an open data policy and all processing centers of GRACE gravity fields are invited to participate in the combination.

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.

On the interpretation of satellite-derived gravity and magnetic data for studies of crustal geology and metallogenesis

NASA Technical Reports Server (NTRS)

Hastings, D. A.

1985-01-01

Satellite-derived global gravity and magnetic maps have been shown to be useful in large-scale studies of the Earth's crust, despite the relative infancy of such studies. Numerous authors have made spatial associations of gravity or magnetic anomalies with geological provinces. Gravimetric interpretations are often made in terms of isostasy, regional variations of density, or of geodesy in general. Interpretations of satellite magnetic anomalies often base assumptions of overall crustal magnetism on concepts of the vertical and horizontal distribution of magnetic susceptibility, then make models of these assumed distributions. The opportunity of improving our satellite gravity and magnetic data through the proposed Geopotential Research Mission should considerably improve the scientific community's ability to analyze and interpret global magnetic and gravity data.

Space Shuttle to deploy Magellan planetary science mission

NASA Technical Reports Server (NTRS)

1989-01-01

The objectives of Space Shuttle Mission STS-30 are described along with major flight activities, prelaunch and launch operations, trajectory sequence of events, and landing and post-landing operations. The primary objective of STS-30 is to successfully deploy the Magellan spacecraft into low earth orbit. Following deployment, Magellan will be propelled to its Venus trajectory by an Inertial Upper Stage booster. The objectives of the Magellan mission are to obtain radar images of more than 70 percent of Venus' surface, a near-global topographic map, and near-global gravity field data. Secondary STS-30 payloads include the Fluids Experiment Apparatus (FEA) and the Mesoscale Lightning Experiment (MLE).

Physical Processes for Driving Ionospheric Outflows in Global Simulations

NASA Technical Reports Server (NTRS)

Moore, Thomas Earle; Strangeway, Robert J.

2009-01-01

We review and assess the importance of processes thought to drive ionospheric outflows, linking them as appropriate to the solar wind and interplanetary magnetic field, and to the spatial and temporal distribution of their magnetospheric internal responses. These begin with the diffuse effects of photoionization and thermal equilibrium of the ionospheric topside, enhancing Jeans' escape, with ambipolar diffusion and acceleration. Auroral outflows begin with dayside reconnexion and resultant field-aligned currents and driven convection. These produce plasmaspheric plumes, collisional heating and wave-particle interactions, centrifugal acceleration, and auroral acceleration by parallel electric fields, including enhanced ambipolar fields from electron heating by precipitating particles. Observations and simulations show that solar wind energy dissipation into the atmosphere is concentrated by the geomagnetic field into auroral regions with an amplification factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Internal plasmas thus enable electromagnetic driving via coupling to the plasma, neutral gas and by extension, the entire body " We assess the Importance of each of these processes in terms of local escape flux production as well as global outflow, and suggest methods for their implementation within multispecies global simulation codes. We complete 'he survey with an assessment of outstanding obstacles to this objective.

Terrestrial Gravity Fluctuations

NASA Astrophysics Data System (ADS)

Harms, Jan

2015-12-01

Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10-23 Hz-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article.

Terrestrial Gravity Fluctuations.

PubMed

Harms, Jan

2015-01-01

Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10 -23 Hz -1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article.

The Global Geophysical Fluids Center of IERS (and its Special Bureau for Mantle)

NASA Astrophysics Data System (ADS)

Chao, B. F.

2002-12-01

The Global Geophysical Fluids Center (GGFC) was established by the International Earth Rotation Service (IERS) on IERS's 10th anniversary day January 1, 1998, in an effort to expand IERS's services to the scientific community. Under the GGFC, eight Special Bureaus (SB) have been selected, each to be responsible for research and data service activities pertaining to mass transports and related geophysical processes in specific components of the Earth system, or "global geophysical fluids," including the atmosphere, oceans, solid Earth, core, and geophysical processes of gravity, loading, tides and hydrological cycles. GGFC and the SBs have the responsibility of supporting, facilitating, and providing services to the worldwide research community, in areas related to the variations in Earth rotation, gravity field and geocenter that are caused by mass transport in the global geophysical fluids. These minute variations have been observed by various space geodetic techniques, as effective remote sensing tools, with ever increasing precision/accuracy and temporal/spatial resolution. The GGFC and SBs have organized dedicated workshops and special sessions at international conferences, published articles, and held regular business meetings. The SBs maintain individual website for data services and information exchanges. See URL bowie.gsfc.nasa.gov/ggfc/. In particular, the SB for Mantle focuses on large-scale mass redistributions that occur in the mantle in association with various dynamic processes, including seismic activities, the post-glacial rebound, and mantle convections.

Bubble Detachment in Variable Gravity Under the Influence of a Non-Uniform Electric Field

NASA Technical Reports Server (NTRS)

Chang, Shinan; Herman, Cila; Iacona, Estelle

2002-01-01

The objective of the study reported in this paper is to investigate the effects of variable, reduced gravity on the formation and detachment behavior of individual air bubbles under the influence of a non-uniform electric field. For this purpose, variable gravity experiments were carried out in parabolic nights. The non-uniform electric field was generated by a spherical electrode and a plate electrode. The effect of the magnitude of the non-uniform electric field and gravity level on bubble formation, development and detachment at an orifice was investigated. An image processing code was developed that allows the measurement of bubble volume, dimensions and contact angle at detachment. The results of this research can be used to explore the possibility of enhancing boiling heat transfer in the variable and low gravity environments by substituting the buoyancy force with a force induced by the electric field. The results of experiments and measurements indicate that the level of gravity significantly affects bubble shape, size and frequency. The electric field magnitude also influences bubble detachment, however, its impact is not as profound as that of variable gravity for the range of electric field magnitudes investigated in the present study.

Titan's interior constrained from its obliquity and tidal Love number

NASA Astrophysics Data System (ADS)

Baland, Rose-Marie; Coyette, Alexis; Yseboodt, Marie; Beuthe, Mikael; Van Hoolst, Tim

2016-04-01

In the last few years, the Cassini-Huygens mission to the Saturn system has measured the shape, the obliquity, the static gravity field, and the tidally induced gravity field of Titan. The large values of the obliquity and of the k2 Love number both point to the existence of a global internal ocean below the icy crust. In order to constrain interior models of Titan, we combine the above-mentioned data as follows: (1) we build four-layer density profiles consistent with Titan's bulk properties; (2) we determine the corresponding internal flattening compatible with the observed gravity and topography; (3) we compute the obliquity and tidal Love number for each interior model; (4) we compare these predictions with the observations. Previously, we found that Titan is more differentiated than expected (assuming hydrostatic equilibrium), and that its ocean is dense and less than 100 km thick. Here, we revisit these conclusions using a more complete Cassini state model, including: (1) gravitational and pressure torques due to internal tidal deformations; (2) atmosphere/lakes-surface exchange of angular momentum; (3) inertial torque due to Poincaré flow. We also adopt faster methods to evaluate Love numbers (i.e. the membrane approach) in order to explore a larger parameter space.

Future missions for observing Earth's changing gravity field: a closed-loop simulation tool

NASA Astrophysics Data System (ADS)

Visser, P. N.

2008-12-01

The GRACE mission has successfully demonstrated the observation from space of the changing Earth's gravity field at length and time scales of typically 1000 km and 10-30 days, respectively. Many scientific communities strongly advertise the need for continuity of observing Earth's gravity field from space. Moreover, a strong interest is being expressed to have gravity missions that allow a more detailed sampling of the Earth's gravity field both in time and in space. Designing a gravity field mission for the future is a complicated process that involves making many trade-offs, such as trade-offs between spatial, temporal resolution and financial budget. Moreover, it involves the optimization of many parameters, such as orbital parameters (height, inclination), distinction between which gravity sources to observe or correct for (for example are gravity changes due to ocean currents a nuisance or a signal to be retrieved?), observation techniques (low-low satellite-to-satellite tracking, satellite gravity gradiometry, accelerometers), and satellite control systems (drag-free?). A comprehensive tool has been developed and implemented that allows the closed-loop simulation of gravity field retrievals for different satellite mission scenarios. This paper provides a description of this tool. Moreover, its capabilities are demonstrated by a few case studies. Acknowledgments. The research that is being done with the closed-loop simulation tool is partially funded by the European Space Agency (ESA). An important component of the tool is the GEODYN software, kindly provided by NASA Goddard Space Flight Center in Greenbelt, Maryland.

High-Resolution Gravity Field Modeling for Mercury to Estimate Crust and Lithospheric Properties

NASA Astrophysics Data System (ADS)

Goossens, S.; Mazarico, E.; Genova, A.; James, P. B.

2018-05-01

We estimate a gravity field model for Mercury using line-of-sight data to improve the gravity field model at short wavelengths. This can be used to infer crustal density and infer the support mechanism of the lithosphere.

Gravity Fields and Interiors of the Saturnian Satellites

NASA Technical Reports Server (NTRS)

Rappaport, N. J.; Armstrong, J. W.; Asmar, Sami W.; Iess, L.; Tortora, P.; Somenzi, L.; Zingoni, F.

2006-01-01

This viewgraph presentation reviews the Gravity Science Objectives and accomplishments of the Cassini Radio Science Team: (1) Mass and density of icy satellites (2) Quadrupole field of Titan and Rhea (3) Dynamic Love number of Titan (4) Moment of inertia of Titan (in collaboration with the Radar Team) (5) Gravity field of Saturn. The proposed measurements for the extended tour are: (1) Quadrupole field of Enceladus (2) More accurate measurement of Titan k2 (3) Local gravity/topography correlations for Iapetus (4) Verification/disproof of "Pioneer anomaly".

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.

Using the IMS infrasound network for the identification of mountain-associated waves and gravity waves hotspots

NASA Astrophysics Data System (ADS)

Hupe, Patrick; Ceranna, Lars; Pilger, Christoph; Le Pichon, Alexis

2017-04-01

The infrasound network of the International Monitoring System (IMS) has been established for monitoring the atmosphere to detect violations of the Comprehensive nuclear-Test-Ban Treaty (CTBT). The IMS comprises 49 certified infrasound stations which are globally distributed. Each station provides data for up to 16 years. Due to the uniform distribution of the stations, the IMS infrasound network can be used to derive global information on atmospheric dynamics' features. This study focuses on mountain-associated waves (MAWs), i.e. acoustic waves in the frequency range between approximately 0.01 Hz and 0.05 Hz. MAWs can be detected in infrasound data by applying the Progressive Multi-Channel Correlation (PMCC) algorithm. As a result of triangulation, global hotspots of MAWs can be identified. Previous studies on gravity waves indicate that global hotspots of gravity waves are similar to those found for MAWs by using the PMCC algorithm. The objective of our study is an enhanced understanding of the excitation sources and of possible interactions between MAWs and gravity waves. Therefore, spatial and temporal correlation analyses will be performed. As a preceding step, we will present (seasonal) hotspots of MAWs as well as hotspots of gravity waves derived by the IMS infrasound network.

Direct Measurement of Daily Evapotranspiration From a Deciduous Forest Using a Superconducting Gravimeter

NASA Astrophysics Data System (ADS)

Van Camp, M. J.; de Viron, O.; Pajot-Métivier, G.; Cazenave, F.; Watlet, A.; Dassargues, A.; Vanclooster, M.

2015-12-01

The conversion of liquid water into water vapor strongly controls the energy transfer between the Earth and the atmosphere, and plays one of the most important roles in the hydrological cycle. This process, called evapotranspiration (ET), deeply constraints the amount of green water in the total global water balance. However, assessing the ET from terrestrial ecosystems remains a key challenge in hydrology. We show that the liquid water mass losses can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution varies through the system, changing its gravity field. Using continuous superconducting gravity measurements, we were able to identify a daily changes in gravity at the level of, or smaller than 10-10 g per day. This corresponds to 2.0 mm of water over an area of 50 ha.The strength of this method is its ability to ensure a direct, traceable and continuous monitoring of actual ET for years at the mesoscale (~50 ha) with a precision of a few tenths of mm of water. This paves the way for the development of the method in different land-use, land-cover and geological contexts, using superconducting and coming quantum gravimeters.

Gravity field, geoid and ocean surface by space techniques

NASA Technical Reports Server (NTRS)

Anderle, R. J.

1978-01-01

Knowledge of the earth's gravity field continued to increase during the last four years. Altimetry data from the GEOS-3 satellite has provided the geoid over most of the ocean to an accuracy of about one meter. Increasing amounts of laser data has permitted the solution for 566 terms in the gravity field with which orbits of the GEOS-3 satellite have been computed to an accuracy of about one to two meters. The combination of satellite tracking data, altimetry and gravimetry has yielded a solution for 1360 terms in the earth's gravity field. A number of problems remain to be solved to increase the accuracy of the gravity field determination. New satellite systems would provide gravity data in unsurveyed areas and correction for topographic features of the ocean and improved computational procedures together with a more extensive laser network will considerably improve the accuracy of the results.

Reprocessing the GRACE-derived gravity field time series based on data-driven method for ocean tide alias error mitigation

NASA Astrophysics Data System (ADS)

Liu, Wei; Sneeuw, Nico; Jiang, Weiping

2017-04-01

GRACE mission has contributed greatly to the temporal gravity field monitoring in the past few years. However, ocean tides cause notable alias errors for single-pair spaceborne gravimetry missions like GRACE in two ways. First, undersampling from satellite orbit induces the aliasing of high-frequency tidal signals into the gravity signal. Second, ocean tide models used for de-aliasing in the gravity field retrieval carry errors, which will directly alias into the recovered gravity field. GRACE satellites are in non-repeat orbit, disabling the alias error spectral estimation based on the repeat period. Moreover, the gravity field recovery is conducted in non-strictly monthly interval and has occasional gaps, which result in an unevenly sampled time series. In view of the two aspects above, we investigate the data-driven method to mitigate the ocean tide alias error in a post-processing mode.

The QBO in Two GISS Global Climate Models: 1. Generation of the QBO

NASA Technical Reports Server (NTRS)

Rind, David; Jonas, Jeffrey A.; Balachandra, Nambath; Schmidt, Gavin A.; Lean, Judith

2014-01-01

The adjustment of parameterized gravity waves associated with model convection and finer vertical resolution has made possible the generation of the quasi-biennial oscillation (QBO) in two Goddard Institute for Space Studies (GISS) models, GISS Middle Atmosphere Global Climate Model III and a climate/middle atmosphere version of Model E2. Both extend from the surface to 0.002 hPa, with 2deg × 2.5deg resolution and 102 layers. Many realistic features of the QBO are simulated, including magnitude and variability of its period and amplitude. The period itself is affected by the magnitude of parameterized convective gravity wave momentum fluxes and interactive ozone (which also affects the QBO amplitude and variability), among other forcings. Although varying sea surface temperatures affect the parameterized momentum fluxes, neither aspect is responsible for the modeled variation in QBO period. Both the parameterized and resolved waves act to produce the respective easterly and westerly wind descent, although their effect is offset in altitude at each level. The modeled and observed QBO influences on tracers in the stratosphere, such as ozone, methane, and water vapor are also discussed. Due to the link between the gravity wave parameterization and the models' convection, and the dependence on the ozone field, the models may also be used to investigate how the QBO may vary with climate change.

Long-term Global Morphology of Gravity Wave Activity Using UARS Data

NASA Technical Reports Server (NTRS)

Eckermann, Stephen D.; Jackman, C. (Technical Monitor)

2000-01-01

An extensive body of research this quarter is documented. Further methodical analysis of temperature residuals in Cryogenic Limb Array Etalon Spectrometer (CLAES) Version 8 level 3AT data show signatures during December 1992 at middle and high northern latitudes that, when compared to Naval Research Laboratory/Mountain Wave Forecast Model (NRL)/(MWFM) mountain wave hindcasts, reveal evidence of long mountain waves in these data over Eurasia, Greenland, Scandinavia and North America. The explicit detection of gravity waves in limb-scanned Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) temperatures is modeled at length, to derive visibility functions. These insights are used to convert CRISTA gravity wave temperature residuals into data that more closely resemble gravity wave fluctuations detected in data from other satellite instruments, such as Microwave Limb Sounder (MLS), Limb Infrared Monitor of the Stratosphere (LIMS) and Global Positioning System/Meteorology (GPS)/(MET). Finally, newly issued mesospheric temperatures from inversion of CRISTA 15gin emissions are analyzed using a new method that uses separate Kalman fits to the ascending and descending node data. This allows us to study global gravity wave amplitudes at two local times, 12 hours apart. In the equatorial mesosphere, where a large diurnal tidal temperature signal exists, we see modulations of gravity wave activity that are consistent with gravity wave-tidal interactions produced by tidal temperature variability.

Decomposing Worldwide Complete Spherical Bouguer Gravity Anomaly Using 2-D Empirical Method

NASA Astrophysics Data System (ADS)

Firdaus, Ruhul; Mey Ekawati, Gestin

2017-04-01

Currently available worldwide gravity anomaly data provides a high-resolution (2’×2’) of Complete Spherical Bouguer Anomaly (CSBA) based on the available information of the Earth gravity field from surface and satellite measurements. The data has not only been provided and processed thoroughly but it also has been claimed to be appropriate for various geophysical applications. Therefore, the analysis of gravity anomaly is becoming increasingly significant for the earth sciences as a whole and assisting both shallow and deep geological problems. Earth gravity anomaly has to be analyzed carefully as it has very complex data due to anomaly mixing of the density masses spread over the Earth horizontally and vertically. The bigger the spatial coverage of data (e.g. global scale data), the more severe the data from anomaly mixing due to various wavelength. BEMD is an empirical method supposedly suitable with highly oscillation-mixing data. It can effectively isolate each local anomaly in details and is analogized as successively reverse moving average with local windowing. BEMD is designed to reduce multi-component, non-linear gravity field data to a series of single local anomaly contributions. Anomaly from a single body was assumed as a mono-component signal. The main advantage of BEMD processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. As the result, we have identified regional anomalies due to the drift of continental and oceanic masses considered as crust-regional anomaly (CRA). We remove the CRA from the CBA to provide surface-residual anomaly (SRA) where shallow geologic bodies reveal. Meanwhile, the CRA itself can be used as reference to reduce this high magnitude anomaly from any measurement data to exhibit only shallow body anomaly. Further analysis can be carried out to build a general understanding of the details and parameters of the shallower or deeper causative body distributions.

Estimating Jupiter’s Gravity Field Using Juno Measurements, Trajectory Estimation Analysis, and a Flow Model Optimization

NASA Astrophysics Data System (ADS)

Galanti, Eli; Durante, Daniele; Finocchiaro, Stefano; Iess, Luciano; Kaspi, Yohai

2017-07-01

The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulated Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.

Estimating Jupiter’s Gravity Field Using Juno Measurements, Trajectory Estimation Analysis, and a Flow Model Optimization

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

Galanti, Eli; Kaspi, Yohai; Durante, Daniele

The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulatedmore » Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.« less

Analysis of harmonic spline gravity models for Venus and Mars

NASA Technical Reports Server (NTRS)

Bowin, Carl

1986-01-01

Methodology utilizing harmonic splines for determining the true gravity field from Line-Of-Sight (LOS) acceleration data from planetary spacecraft missions was tested. As is well known, the LOS data incorporate errors in the zero reference level that appear to be inherent in the processing procedure used to obtain the LOS vectors. The proposed method offers a solution to this problem. The harmonic spline program was converted from the VAX 11/780 to the Ridge 32C computer. The problem with the matrix inversion routine that improved inversion of the data matrices used in the Optimum Estimate program for global Earth studies was solved. The problem of obtaining a successful matrix inversion for a single rev supplemented by data for the two adjacent revs still remains.

Time-Variable Gravity: The Low-Degree Components and their Connections with Geophysical/Climatic Changes

NASA Technical Reports Server (NTRS)

Cox, Christopher M.; Chao, Benjamin F.; Au, Andrew Y.

2004-01-01

The oblateness of the Earth's gravity field, J2, has long been observed to undergo a slight decrease due to post-glacial rebound of the mantle. Sometime around 1998 this trend reversed quite suddenly. This reversal persisted until 2001, at which point the atmosphere-corrected time series appears to have reversed yet again. Presently, the time series appears to be returning to the value that would nominally have been reached had the anomaly not occurred. This anomaly signifies a large interannual change in global mass distribution whose J2 effect overshadows that of the post-glacial rebound over such timescales. A number of possible causes have been considered, with oceanic mass redistribution as the leading candidate although other effects, such as glacial melting and core effects may be contributing.

Insights into the Earth System mass variability from CSR-RL05 GRACE gravity fields

NASA Astrophysics Data System (ADS)

Bettadpur, S.

2012-04-01

The next-generation Release-05 GRACE gravity field data products are the result of extensive effort applied to the improvements to the GRACE Level-1 (tracking) data products, and to improvements in the background gravity models and processing methodology. As a result, the squared-error upper-bound in RL05 fields is half or less than the squared-error upper-bound in RL04 fields. The CSR-RL05 field release consists of unconstrained gravity fields as well as a regularized gravity field time-series that can be used for several applications without any post-processing error reduction. This paper will describe the background and the nature of these improvements in the data products, and provide an error characterization. We will describe the insights these new series offer in measuring the mass flux due to diverse Hydrologic, Oceanographic and Cryospheric processes.

Bounds on Lithospheric Thickness on Venus from Magellan Gravity and Topography Data

NASA Technical Reports Server (NTRS)

Johnson, Catherine L.; Sandwell, David

1997-01-01

The primary objective of the work executed under NAGW-4784 is to provide constraints on the thermal and tectonic evolution of Venus. Establishing thermal and tectonic evolution models requires not only geological, but geophysical constraints, in particular the nature of temporal and spatial variations in crustal and lithospheric thickness. The major topics of study completed under NAGW-4784 (described more fully below) are: (1) detailed analyses of the resolution of Magellan Line-Of-Site (LOS) Doppler data to establish the minimum resolvable wavelength in the gravity data; (2) calculations of the global strain field in the venusian lithosphere and comparisons with global strain patterns from geological mapping; (3) study of the geological history of coronae at E. Eistla Regio; (4) estimation of crustal and lithospheric thickness by modeling of topography at asymmetric and symmetric rift-like chasmata; (5) preliminary investigations of spatial versus temporal variations in lithospheric thickness. Both the PI and Co-I have presented papers based on these topics at national and international meetings (American Geophysical Union Meetings, Lunar and Planetary Science Conferences, Chapman Conference on the Geodynamics of Venus).

Impact of tracking loop settings of the Swarm GPS receiver on gravity field recovery

NASA Astrophysics Data System (ADS)

Dahle, C.; Arnold, D.; Jäggi, A.

2017-06-01

The Swarm mission consists of three identical satellites equipped with GPS receivers and orbiting in near-polar low Earth orbits. Thus, they can be used to determine the Earth's gravity field by means of high-low satellite-to-satellite tracking (hl-SST). However, first results by several groups have revealed systematic errors both in precise science orbits and resulting gravity field solutions which are caused by ionospheric disturbances affecting the quality of Swarm GPS observations. Looking at gravity field solutions, the errors lead to systematic artefacts located in two bands north and south of the geomagnetic equator. In order to reduce these artefacts, erroneous GPS observations can be identified and rejected before orbit and gravity field processing, but this may also lead to slight degradations of orbit and low degree gravity field coefficient quality. Since the problems were believed to be receiver-specific, the GPS tracking loop bandwidths onboard Swarm have been widened several times starting in May 2015. The influence of these tracking loop updates on Swarm orbits and, particularly, gravity field solutions is investigated in this work. The main findings are that the first updates increasing the bandwidth from 0.25 Hz to 0.5 Hz help to significantly improve the quality of Swarm gravity fields and that the improvements are even larger than those achieved by GPS data rejection. It is also shown that these improvements are indeed due to an improved quality of GPS observations around the geomagnetic equator, and not due to missing observations in these regions. As the ionospheric activity is rather low in the most recent months, the effect of the tracking loop updates in summer 2016 cannot be properly assessed yet. Nevertheless, the quality of Swarm gravity field solutions has already improved after the first updates which is especially beneficial in view of filling the upcoming gap between the GRACE and GRACE Follow-on missions with hl-SST gravity products.

Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

NASA Technical Reports Server (NTRS)

Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

2000-01-01

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

ARISTOTELES: A European approach for an Earth gravity field recovery mission

NASA Technical Reports Server (NTRS)

Benz, R.; Faulks, H.; Langemann, M.

1989-01-01

Under contract of the European Space Agency a system study for a spaceborne gravity field recovery mission was performed, covering as a secondary mission objective geodetic point positioning in the cm range as well. It was demonstrated that under the given programmatic constraints including dual launch and a very tight development schedule, a six months gravity field mission in a 200 km near polar, dawn-dusk orbit is adequate to determine gravity anomalies to better than 5 mgal with a spatial resolution of 100 x 100 km half wavelength. This will enable scientists to determine improved spherical harmonic coefficients of the Earth gravity field equation to the order and degree of 180 or better.

Near real-time GRACE gravity field solutions for hydrological monitoring applications

NASA Astrophysics Data System (ADS)

Kvas, Andreas; Gouweleeuw, Ben; Mayer-Gürr, Torsten; Güntner, Andreas

2016-04-01

Within the EGSIEM (European Gravity Service for Improved Emergency Management) project, a demonstrator for a near real-time (NRT) gravity field service which provides daily GRACE gravity field solutions will be established. Compared to the official GRACE gravity products, these NRT solutions will increase the temporal resolution from one month to one day and reduce the latency from currently two months to five days. This fast availability allows the monitoring of total water storage variations and of hydrological extreme events as they occur, in contrast to a 'confirmation after occurrence' as is the situation today. The service will be jointly run by GFZ (German Research Centre for Geosciences) and Graz University of Technology, with each analysis center providing an independent solution. A Kalman filter framework, in which GRACE data is combined with prior information, serves as basis for the gravity field recovery in order to increase the redundancy of the gravity field estimates. The on-line nature of the NRT service necessitates a tailored smoothing algorithm as opposed to post-processing applications, where forward-backward smoothing can be applied. This contribution gives an overview on the near real-time processing chain and highlights differences between the computed NRT solutions and the standard GRACE products. We discuss the special characteristics of the Kalman filtered gravity field models as well as derived products and give an estimate of the expected error levels. Additionally, we show the added value of the NRT solutions through comparison of the first results of the pre-operational phase with in-situ data and monthly GRACE gravity field models.

Dynamics of the Antarctic Circumpolar Current as seen by GRACE (Invited)

NASA Astrophysics Data System (ADS)

Thomas, M.; Dobslaw, H.; Bergmann, I.

2010-12-01

The Antarctic Circumpolar Current, being the strongest and longest ocean current on Earth, connects the three great ocean basins and contributes substantially to the global re-distribution of water masses, with a significant impact on global climate. Observational coverage from in-situ measurements is sparse due to the harsh environmental conditions, and satellite altimetry does not capture the full extent of the current due to seasonal sea-ice coverage. Ocean bottom pressure variations as sensed with the satellite gravity mission GRACE provide a promising way to broaden our observational basis. Besides monthly mean gravity fields that provide ocean bottom pressure variations averaged over 30 days, several alternative GRACE products with higher temporal resolution have been developed during the most recent years. These include 10-day solutions from GRGS Toulouse, weekly solutions from the GFZ Potsdam as well as constrained daily solutions from the University of Bonn which have been obtained by means of a Kalman filtering approach. In this presentation, ocean bottom pressure derived from these alternative GRACE releases will be contrasted against both in-situ observations and output from a numerical ocean model, highlighting the additional information contained in these GRACE solutions with respect to the standard monthly fields. By means of statistical analyses of ocean bottom pressure variations and barotropic transports it will be demonstrated how these new GRACE releases are contributing to our understanding of this highly dynamic great ocean conveyor.

An Exact Solution of Einstein-Maxwell Gravity Coupled to a Scalar Field

NASA Technical Reports Server (NTRS)

Turyshev, S. G.

1995-01-01

The general solution to low-energy string theory representing static spherically symmetric solution of the Einstein-Maxwell gravity with a massless scalar field has been found. Some of the partial cases appear to coincide with known solutions to black holes, naked singularities, and gravity and electromagnetic fields.

Combination of GRACE monthly gravity field solutions from different processing strategies

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2018-02-01

We combine the publicly available GRACE monthly gravity field time series to produce gravity fields with reduced systematic errors. We first compare the monthly gravity fields in the spatial domain in terms of signal and noise. Then, we combine the individual gravity fields with comparable signal content, but diverse noise characteristics. We test five different weighting schemes: equal weights, non-iterative coefficient-wise, order-wise, or field-wise weights, and iterative field-wise weights applying variance component estimation (VCE). The combined solutions are evaluated in terms of signal and noise in the spectral and spatial domains. Compared to the individual contributions, they in general show lower noise. In case the noise characteristics of the individual solutions differ significantly, the weighted means are less noisy, compared to the arithmetic mean: The non-seasonal variability over the oceans is reduced by up to 7.7% and the root mean square (RMS) of the residuals of mass change estimates within Antarctic drainage basins is reduced by 18.1% on average. The field-wise weighting schemes in general show better performance, compared to the order- or coefficient-wise weighting schemes. The combination of the full set of considered time series results in lower noise levels, compared to the combination of a subset consisting of the official GRACE Science Data System gravity fields only: The RMS of coefficient-wise anomalies is smaller by up to 22.4% and the non-seasonal variability over the oceans by 25.4%. This study was performed in the frame of the European Gravity Service for Improved Emergency Management (EGSIEM; http://www.egsiem.eu) project. The gravity fields provided by the EGSIEM scientific combination service (ftp://ftp.aiub.unibe.ch/EGSIEM/) are combined, based on the weights derived by VCE as described in this article.

Neutron stars in a perturbative f(R) gravity model with strong magnetic fields

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

Cheoun, Myung-Ki; Deliduman, Cemsinan; Güngör, Can

2013-10-01

In Kaluza-Klein electromagnetism it is natural to associate modified gravity with strong electromagnetic fields. Hence, in this paper we investigate the combined effects of a strong magnetic field and perturbative f(R) gravity on the structure of neutron stars. The effect of an interior strong magnetic field of about 10{sup 17−18} G on the equation of state is derived in the context of a quantum hadrodynamics (QHD) equation of state (EoS) including effects of the magnetic pressure and energy along with occupied Landau levels. Adopting a random orientation of interior field domains, we solve the modified spherically symmetric hydrostatic equilibrium equationsmore » derived for a gravity model with f(R) = R+αR{sup 2}. Effects of both the finite magnetic field and the modified gravity are detailed for various values of the magnetic field and the perturbation parameter α along with a discussion of their physical implications. We show that there exists a parameter space of the modified gravity and the magnetic field strength, in which even a soft equation of state can accommodate a large ( > 2 M{sub s}un) maximum neutron star mass.« less

Secondary Gravity Waves in the Winter Mesosphere: Results From a High-Resolution Global Circulation Model

NASA Astrophysics Data System (ADS)

Becker, Erich; Vadas, Sharon L.

2018-03-01

This study analyzes a new high-resolution general circulation model with regard to secondary gravity waves in the mesosphere during austral winter. The model resolves gravity waves down to horizontal and vertical wavelengths of 165 and 1.5 km, respectively. The resolved mean wave drag agrees well with that from a conventional model with parameterized gravity waves up to the midmesosphere in winter and up to the upper mesosphere in summer. About half of the zonal-mean vertical flux of westward momentum in the southern winter stratosphere is due to orographic gravity waves. The high intermittency of the primary orographic gravity waves gives rise to secondary waves that result in a substantial eastward drag in the winter mesopause region. This induces an additional eastward maximum of the mean zonal wind at z ˜ 100 km. Radar and lidar measurements at polar latitudes and results from other high-resolution global models are consistent with this finding. Hence, secondary gravity waves may play a significant role in the general circulation of the winter mesopause region.

Reconstruction from scalar-tensor theory and the inhomogeneous equation of state in f( T) gravity

NASA Astrophysics Data System (ADS)

Said, Jackson Levi

2017-12-01

General relativity (GR) characterizes gravity as a geometric properly exhibited as curvature on spacetime. Teleparallelism describes gravity through torsional properties, and can reproduce GR at the level of equations. Similar to f( R) gravity, on taking a generalization, f( T) gravity can produce various modifications its gravitational mechanism. The resulting field equations are inherently distinct to f( R) gravity in that they are second order. In the present work, f( T) gravity is examined in the cosmological context with a number of solutions reconstructed by means of an auxiliary scalar field. To do this, various forms of the Hubble parameter are considered with an f( T) Lagrangian emerging for each instance. In addition, the inhomogeneous equation of state (EoS) is investigated with a particular Hubble parameter model used to show how this can be used to reconstruct the f( T) Lagrangian. Observationally, the auxiliary scalar field and the exotic terms in the FRW field equations give the same results, meaning that the variation in the Hubble parameter may be interpreted as the need to reformulate gravity in some way, as in f( T) gravity.

Existence of global weak solution for a reduced gravity two and a half layer model

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

Guo, Zhenhua, E-mail: zhenhua.guo.math@gmail.com; Li, Zilai, E-mail: lizilai0917@163.com; Yao, Lei, E-mail: yaolei1056@hotmail.com

2013-12-15

We investigate the existence of global weak solution to a reduced gravity two and a half layer model in one-dimensional bounded spatial domain or periodic domain. Also, we show that any possible vacuum state has to vanish within finite time, then the weak solution becomes a unique strong one.

Optic nerve dysfunction during gravity inversion. Visual field abnormalities.

PubMed

Sanborn, G E; Friberg, T R; Allen, R

1987-06-01

Inversion in a head-down position (gravity inversion) results in an intraocular pressure of 35 to 40 mm Hg in normal subjects. We used computerized static perimetry to measure the visual fields of normal subjects during gravity inversion. There were no visual field changes in the central 6 degrees of the visual field compared with the baseline (preinversion) values. However, when the central 30 degrees of the visual field was tested, reversible visual field defects were found in 11 of 19 eyes. We believe that the substantial elevation of intraocular pressure during gravity inversion may pose potential risks to the eyes, and we recommend that inversion for extended periods of time be avoided.

Magnetic Field Is the Dominant Factor to Induce the Response of Streptomyces avermitilis in Altered Gravity Simulated by Diamagnetic Levitation

PubMed Central

Shang, Peng; Zhou, Xianlong; Ashforth, Elizabeth; Zhuo, Ying; Chen, Difei; Ren, Biao; Liu, Zhiheng; Zhang, Lixin

2011-01-01

Background Diamagnetic levitation is a technique that uses a strong, spatially varying magnetic field to simulate an altered gravity environment, as in space. In this study, using Streptomyces avermitilis as the test organism, we investigate whether changes in magnetic field and altered gravity induce changes in morphology and secondary metabolism. We find that a strong magnetic field (12T) inhibit the morphological development of S. avermitilis in solid culture, and increase the production of secondary metabolites. Methodology/Principal Findings S. avermitilis on solid medium was levitated at 0 g*, 1 g* and 2 g* in an altered gravity environment simulated by diamagnetic levitation and under a strong magnetic field, denoted by the asterix. The morphology was obtained by electromicroscopy. The production of the secondary metabolite, avermectin, was determined by OD245 nm. The results showed that diamagnetic levitation could induce a physiological response in S. avermitilis. The difference between 1 g* and the control group grown without the strong magnetic field (1 g), showed that the magnetic field was a more dominant factor influencing changes in morphology and secondary metabolite production, than altered gravity. Conclusion/Significance We have discovered that magnetic field, rather than altered gravity, is the dominant factor in altered gravity simulated by diamagnetic levitation, therefore care should to be taken in the interpretation of results when using diamagnetic levitation as a technique to simulate altered gravity. Hence, these results are significant, and timely to researchers considering the use of diamagnetic levitation to explore effects of weightlessness on living organisms and on physical phenomena. PMID:22039402

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.

VERITAS (Venus Emissivity, Radio Science, InSAR, Topo-graphy And Spectroscopy): A Proposed Discovery Mission

NASA Astrophysics Data System (ADS)

Smrekar, Suzanne; Dyar, Melinda; Hensley, Scott; Helbert, Joern; VERITAS Science Team

2016-10-01

VERITAS addresses one of the most fundamental questions in planetary evolution: How Earth-like is Venus? These twin planets diverged down different evolutionary paths, yet Venus may hold lessons for past and future Earth, as well as for Earth-sized exoplanets. VERITAS will search for the mineralogical fingerprints of past water, follow up on the discoveries of recent volcanism and the possible young surface age, and reveal the conditions that have prevented plate tectonics from developing. Collectively these questions address how Venus ended up a sulfurous inferno while Earth became habitable.VERITAS carries the Venus Interferometric Synthetic Aperture Radar (VISAR) and the Venus Emissivity Mapper (VEM), plus a gravity science investigation.The VISAR X-band radar produces: 1) a global digital elevation model (DEM) with 250 m postings, 5 m height accuracy, 2) Synthetic aperture radar (SAR) global imaging with 30 m pixels, 3) SAR imaging at 15 m for targeted areas, and 4) surface deformation from repeat pass interferometry (RPI) at 2 mm height precision for targeted, potentially active areas. VEM [see Helbert abstract] will measure surface emissivity, look for active volcanic flows and outgassing of water over ~78% of the surface using 6 NIR surface bands within 5 atmospheric windows and 8 bands for calibration of clouds, stray light, and water vapor.VERITAS uses Ka-band uplink and downlink to create a global gravity field with 3 mgal accuracy and 145 km resolution (130 spherical harmonic degree and order or d&o) and providing a significantly higher resolution field with much more uniform resolution than that available from Magellan.VERITAS will create a rich data set of high resolution topography, imaging, spectroscopy, and gravity. These co-registered data sets will be on par with those acquired for Mercury, Mars and the Moon that have revolutionized our understanding of these bodies. VERITAS would be a valuable asset for future lander or probe missions, collecting the data needed to select landing or entry sites. VERITAS also provides a baseline for future missions to detect surface change, and contributes to our ability to predict the nature of Earth-sized exoplanets.

Forward modeling of the Earth's lithospheric field using spherical prisms

NASA Astrophysics Data System (ADS)

Baykiev, Eldar; Ebbing, Jörg; Brönner, Marco; Fabian, Karl

2014-05-01

The ESA satellite mission Swarm consists of three satellites that measure the magnetic field of the Earth at average flight heights of about 450 km and 530 km above surface. Realistic forward modeling of the expected data is an indispensible first step for both, evaluation and inversion of the real data set. This forward modeling requires a precise definition of the spherical geometry of the magnetic sources. At satellite height only long wavelengths of the magnetic anomalies are reliably measured. Because these are very sensitive to the modeling error in case of a local flat Earth approximation, conventional magnetic modeling tools cannot be reliably used. For an improved modeling approach, we start from the existing gravity modeling code "tesseroids" (http://leouieda.github.io/tesseroids/), which calculates gravity gradient tensor components for any collection of spherical prisms (tesseroids). By Poisson's relation the magnetic field is mathematically equivalent to the gradient of a gravity field. It is therefore directly possible to apply "tesseroids" for magnetic field modeling. To this end, the Earth crust is covered by spherical prisms, each with its own prescribed magnetic susceptibility and remanent magnetization. Induced magnetizations are then derived from the products of the local geomagnetic fields for the chosen main field model (such as the International Geomagnetic Reference Field), and the corresponding tesseroid susceptibilities. Remanent magnetization vectors are directly set. This method inherits the functionality of the original "tesseroids" code and performs parallel computation of the magnetic field vector components on any given grid. Initial global calculations for a simplified geometry and piecewise constant magnetization for each tesseroid show that the method is self-consistent and reproduces theoretically expected results. Synthetic induced crustal magnetic fields and total field anomalies of the CRUST1.0 model converted to magnetic tesseroids reproduce the results of previous forward modelling methods (e.g. using point dipoles as magnetic sources), while reducing error terms. Moreover the spherical-prism method can easily be linked to other geophysical forward or inverse modelling tools. Sensitivity analysis over Fennoscandia will be used to estimate if and how induced and remanent magnetization can be distinguished in data from the Swarm satellite mission.

An evaluation of gravity waves and gravity wave sources in the Southern Hemisphere in a 7 km global climate simulation.

PubMed

Holt, L A; Alexander, M J; Coy, L; Liu, C; Molod, A; Putman, W; Pawson, S

2017-07-01

In this study, gravity waves (GWs) in the high-resolution GEOS-5 Nature Run are first evaluated with respect to satellite and other model results. Southern Hemisphere winter sources of non-orographic GWs in the model are then investigated by linking measures of tropospheric non-orographic gravity wave generation tied to precipitation and frontogenesis with absolute gravity wave momentum flux in the lower stratosphere. Finally, non-orographic GW momentum flux is compared to orographic gravity wave momentum flux and compared to previous estimates. The results show that the global patterns in GW amplitude, horizontal wavelength, and propagation direction are realistic compared to observations. However, as in other global models, the amplitudes are weaker and horizontal wavelengths longer than observed. The global patterns in absolute GW momentum flux also agree well with previous model and observational estimates. The evaluation of model non-orographic GW sources in the Southern Hemisphere winter shows that strong intermittent precipitation (greater than 10 mm h -1 ) is associated with GW momentum flux over the South Pacific, whereas frontogenesis and less intermittent, lower precipitation rates (less than 10 mm h -1 ) are associated with GW momentum flux near 60°S. In the model, orographic GWs contribute almost exclusively to a peak in zonal mean momentum flux between 70 and 75°S, while non-orographic waves dominate at 60°S, and non-orographic GWs contribute a third to a peak in zonal mean momentum flux between 25 and 30°S.

Middle Atmosphere Dynamics with Gravity Wave Interactions in the Numerical Spectral Model: Tides and Planetary Waves

NASA Technical Reports Server (NTRS)

Mayr, Hans G.; Mengel, J. G.; Chan, K. L.; Huang, F. T.

2010-01-01

As Lindzen (1981) had shown, small-scale gravity waves (GW) produce the observed reversals of the zonal-mean circulation and temperature variations in the upper mesosphere. The waves also play a major role in modulating and amplifying the diurnal tides (DT) (e.g., Waltersheid, 1981; Fritts and Vincent, 1987; Fritts, 1995a). We summarize here the modeling studies with the mechanistic numerical spectral model (NSM) with Doppler spread parameterization for GW (Hines, 1997a, b), which describes in the middle atmosphere: (a) migrating and non-migrating DT, (b) planetary waves (PW), and (c) global-scale inertio gravity waves. Numerical experiments are discussed that illuminate the influence of GW filtering and nonlinear interactions between DT, PW, and zonal mean variations. Keywords: Theoretical modeling, Middle atmosphere dynamics, Gravity wave interactions, Migrating and non-migrating tides, Planetary waves, Global-scale inertio gravity waves.

Torus Approach in Gravity Field Determination from Simulated GOCE Gravity Gradients

NASA Astrophysics Data System (ADS)

Liu, Huanling; Wen, Hanjiang; Xu, Xinyu; Zhu, Guangbin

2016-08-01

In Torus approach, observations are projected to the nominal orbits with constant radius and inclination, lumped coefficients provides a linear relationship between observations and spherical harmonic coefficients. Based on the relationship, two-dimensional FFT and block-diagonal least-squares adjustment are used to recover Earth's gravity field model. The Earth's gravity field model complete to degree and order 200 is recovered using simulated satellite gravity gradients on a torus grid, and the degree median error is smaller than 10-18, which shows the effectiveness of Torus approach. EGM2008 is employed as a reference model and the gravity field model is resolved using the simulated observations without noise given on GOCE orbits of 61 days. The error from reduction and interpolation can be mitigated by iterations. Due to polar gap, the precision of low-order coefficients is lower. Without considering these coefficients the maximum geoid degree error and cumulative error are 0.022mm and 0.099mm, respectively. The Earth's gravity field model is also recovered from simulated observations with white noise 5mE/Hz1/2, which is compared to that from direct method. In conclusion, it is demonstrated that Torus approach is a valid method for processing massive amount of GOCE gravity gradients.

Adiabatic pumping solutions in global AdS

NASA Astrophysics Data System (ADS)

Carracedo, Pablo; Mas, Javier; Musso, Daniele; Serantes, Alexandre

2017-05-01

We construct a family of very simple stationary solutions to gravity coupled to a massless scalar field in global AdS. They involve a constantly rising source for the scalar field at the boundary and thereby we name them pumping solutions. We construct them numerically in D = 4. They are regular and, generically, have negative mass. We perform a study of linear and nonlinear stability and find both stable and unstable branches. In the latter case, solutions belonging to different sub-branches can either decay to black holes or to limiting cycles. This observation motivates the search for non-stationary exactly timeperiodic solutions which we actually construct. We clarify the role of pumping solutions in the context of quasistatic adiabatic quenches. In D = 3 the pumping solutions can be related to other previously known solutions, like magnetic or translationally-breaking backgrounds. From this we derive an analytic expression.

Numerical modeling of the thin shallow solar dynamo

NASA Astrophysics Data System (ADS)

O'Bryan, J. B.; Jarboe, T. R.

2017-10-01

Nonlinear, numerical computation with the NIMROD code is used to explore and validate the thin shallow solar dynamo model [T.R. Jarboe et al. 2017], which explains the observed global temporal evolution (e.g. magnetic field reversal) and local surface structures (e.g. sunspots) of the sun. The key feature of this model is the presence and magnetic self-organization of global magnetic structures (GMS) lying just below the surface of the sun, which resemble 1D radial Taylor states of size comparable to the supergranule convection cells. First, we seek to validate the thin shallow solar dynamo model by reproducing the 11 year timescale for reversal of the solar magnetic field. Then, we seek to model formation of GMS from convection zone turbulence. Our computations simulate a slab covering a radial depth 3Mm and include differential rotation and gravity. Density, temperature, and resistivity profiles are taken from the Christensen-Dalsgaard model.

Electric Field Effects in Self-Propagating High-Temperature Synthesis under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Frederick, D. M.; Shaw, B. D.; Munir, Z. A.

2003-01-01

Self-propagating high-temperature synthesis (SHS) has been used to form many materials. SHS generally involves mixing reactants together (e.g., metal powders) and igniting the mixture such that a combustion (deflagration) wave passes though the mixture. The imposition of an electric field (AC or DC) across SHS reactants has been shown to have a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product . The use of an electric field with SHS has been termed "field-assisted SHS". Combustion wave velocities and temperatures are directly affected by the field, which is typically perpendicular to the average wave velocity. The degree of activation by the field (e.g., combustion rate) is related to the current density distribution within the sample, and is therefore related to the temperature-dependent spatial distribution of the effective electrical conductivity of reactants and products. Furthermore, the field can influence other important SHS-related phenomena including capillary flow, mass-transport in porous media, and Marangoni flows. These phenomena are influenced by gravity in conventional SHS processes (i.e., without electric fields). As a result the influence of the field on SHS under reduced gravity is expected to be different than under normal gravity. It is also known that heat loss rates from samples, which can depend significantly on gravity, can influence final products in SHS. This research program is focused on studying field-assisted SHS under reduced gravity conditions. The broad objective of this research program is to understand the role of an electric field in SHS reactions under conditions where gravity-related effects are suppressed. The research will allow increased understanding of fundamental aspects of field-assisted SHS processes as well as synthesis of materials that cannot be formed in normal gravity.

Integration of potential-field and digital geologic data for two North American geoscience transects

USGS Publications Warehouse

Phillips, J.D.

1990-01-01

Two North American contributions to the Global Geoscience Transects Program, the Quebec-Maine-Gulf of Maine transect and the Great Lakes portion of the United States-Canadian Border transect, are among the first to produce digital geology in a form that can be combined with gridded gravity and aeromagnetic data. Maps of shaded relief and color-composite bandpass-filtered potential-field data combined with overlays of digitized geologic contacts and faults reveal significant new geologic information, including the relative thickness of plutons, the structure of poorly exposed or concealed magnetic units, and possible evidence for mineralized ground. -from Author

Validation of the Gravity Model in Predicting the Global Spread of Influenza

PubMed Central

Li, Xinhai; Tian, Huidong; Lai, Dejian; Zhang, Zhibin

2011-01-01

The gravity model is often used in predicting the spread of influenza. We use the data of influenza A (H1N1) to check the model’s performance and validation, in order to determine the scope of its application. In this article, we proposed to model the pattern of global spread of the virus via a few important socio-economic indicators. We applied the epidemic gravity model for modelling the virus spread globally through the estimation of parameters of a generalized linear model. We compiled the daily confirmed cases of influenza A (H1N1) in each country as reported to the WHO and each state in the USA, and established the model to describe the relationship between the confirmed cases and socio-economic factors such as population size, per capita gross domestic production (GDP), and the distance between the countries/states and the country where the first confirmed case was reported (i.e., Mexico). The covariates we selected for the model were all statistically significantly associated with the global spread of influenza A (H1N1). However, within the USA, the distance and GDP were not significantly associated with the number of confirmed cases. The combination of the gravity model and generalized linear model provided a quick assessment of pandemic spread globally. The gravity model is valid if the spread period is long enough for estimating the model parameters. Meanwhile, the distance between donor and recipient communities has a good gradient. Besides, the spread should be at the early stage if a single source is taking into account. PMID:21909295

Validation of the gravity model in predicting the global spread of influenza.

PubMed

Li, Xinhai; Tian, Huidong; Lai, Dejian; Zhang, Zhibin

2011-08-01

The gravity model is often used in predicting the spread of influenza. We use the data of influenza A (H1N1) to check the model's performance and validation, in order to determine the scope of its application. In this article, we proposed to model the pattern of global spread of the virus via a few important socio-economic indicators. We applied the epidemic gravity model for modelling the virus spread globally through the estimation of parameters of a generalized linear model. We compiled the daily confirmed cases of influenza A (H1N1) in each country as reported to the WHO and each state in the USA, and established the model to describe the relationship between the confirmed cases and socio-economic factors such as population size, per capita gross domestic production (GDP), and the distance between the countries/states and the country where the first confirmed case was reported (i.e., Mexico). The covariates we selected for the model were all statistically significantly associated with the global spread of influenza A (H1N1). However, within the USA, the distance and GDP were not significantly associated with the number of confirmed cases. The combination of the gravity model and generalized linear model provided a quick assessment of pandemic spread globally. The gravity model is valid if the spread period is long enough for estimating the model parameters. Meanwhile, the distance between donor and recipient communities has a good gradient. Besides, the spread should be at the early stage if a single source is taking into account.

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.

Estimating geocenter motion and barystatic sea-level variability from GRACE observations with explicit consideration of self-attraction and loading effects

NASA Astrophysics Data System (ADS)

Bergmann-Wolf, I.; Dobslaw, H.

2015-12-01

Estimating global barystatic sea-level variations from monthly mean gravity fields delivered by the Gravity Recovery and Climate Experiment (GRACE) satellite mission requires additional information about geocenter motion. These variations are not available directly due to the mission implementation in the CM-frame and are represented by the degree-1 terms of the spherical harmonics expansion. Global degree-1 estimates can be determined with the method of Swenson et al. (2008) from ocean mass variability, the geometry of the global land-sea distribution, and GRACE data of higher degrees and orders. Consequently, a recursive relation between the derivation of ocean mass variations from GRACE data and the introduction of geocenter motion into GRACE data exists.In this contribution, we will present a recent improvement to the processing strategy described in Bergmann-Wolf et al. (2014) by introducing a non-homogeneous distribution of global ocean mass variations in the geocenter motion determination strategy, which is due to the effects of loading and self-attraction induced by mass redistributions at the surface. A comparison of different GRACE-based oceanographic products (barystatic signal for both the global oceans and individual basins; barotropic transport variations of major ocean currents) with degree-1 terms estimated with a homogeneous and non-homogeneous ocean mass representation will be discussed, and differences in noise levels in most recent GRACE solutions from GFZ (RL05a), CSR, and JPL (both RL05) and their consequences for the application of this method will be discussed.

The Gravity Field of Mars From MGS, Mars Odyssey, and MRO Radio Science

NASA Technical Reports Server (NTRS)

Genova, Antonio; Goossens, Sander; Lemoine, Frank G.; Mazarico, Erwan; Smith, David E.; Zuber, Maria T.

2015-01-01

The Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) missions have enabled NASA to conduct reconnaissance and exploration of Mars from orbit for sixteen consecutive years. These radio systems on these spacecraft enabled radio science in orbit around Mars to improve the knowledge of the static structure of the Martian gravitational field. The continuity of the radio tracking data, which cover more than a solar cycle, also provides useful information to characterize the temporal variability of the gravity field, relevant to the planet's internal dynamics and the structure and dynamics of the atmosphere [1]. MGS operated for more than 7 years, between 1999 and 2006, in a frozen sun-synchronous, near-circular, polar orbit with the periapsis at approximately 370 km altitude. ODY and MRO have been orbiting Mars in two separate sun-synchronous orbits at different local times and altitudes. ODY began its mapping phase in 2002 with the periapis at approximately 390 km altitude and 4-5pm Local Solar Time (LST), whereas the MRO science mission started in November 2006 with the periapis at approximately 255 km altitude and 3pm LST. The 16 years of radio tracking data provide useful information on the atmospheric density in the Martian upper atmosphere. We used ODY and MRO radio data to recover the long-term periodicity of the major atmospheric constituents -- CO2, O, and He -- at the orbit altitudes of these two spacecraft [2]. The improved atmospheric model provides a better prediction of the annual and semi-annual variability of the dominant species. Therefore, the inclusion of the recovered model leads to improved orbit determination and an improved gravity field model of Mars with MGS, ODY, and MRO radio tracking data.

Tilted string cosmologies

NASA Astrophysics Data System (ADS)

Clancy, Dominic; Feinstein, Alexander; Lidsey, James E.; Tavakol, Reza

1999-04-01

Global symmetries of the string effective action are employed to generate tilted, homogeneous Bianchi type VIh string cosmologies from a previously known stiff perfect fluid solution to Einstein gravity. The dilaton field is not constant on the surfaces of homogeneity. The future asymptotic state of the models is interpreted as a plane wave and is itself an exact solution to the string equations of motion to all orders in the inverse string tension. An inhomogeneous generalization of the Bianchi type III model is also found.

Beyond the biosphere. [aerospace environments and human life support

NASA Technical Reports Server (NTRS)

Nicogossian, A. E.; Parker, J. F.

1985-01-01

The near-earth-space, planetary and interplanetary environments are described with emphasis on their biomedical significance. The characteristics of the microgravity field, low gravity and radiation conditions in earth orbit are described, noting the necessity of avoiding materials which can outgas toxic substances during long-term mission. Details of the atmospheres, global meteorology, and terrains of Venus, Mars, Jupiter, the Jovian satellites, and Saturn are reviewed. Finally, a brief discussion is provided of the life-support systems which will be required on interstellar voyages.

Density of the continental roots: Compositional and thermal contributions

USGS Publications Warehouse

Kaban, M.K.; Schwintzer, P.; Artemieva, I.M.; Mooney, W.D.

2003-01-01

The origin and evolution of cratonic roots has been debated for many years. Precambrian cratons are underlain by cold lithospheric roots that are chemically depleted. Thermal and petrologic data indicate that Archean roots are colder and more chemically depleted than Proterozoic roots. This observation has led to the hypothesis that the degree of depletion in a lithospheric root depends mostly on its age. Here we test this hypothesis using gravity, thermal, petrologic, and seismic data to quantify differences in the density of cratonic roots globally. In the first step in our analysis we use a global crustal model to remove the crustal contribution to the observed gravity. The result is the mantle gravity anomaly field, which varies over cratonic areas from -100 to +100 mGal. Positive mantle gravity anomalies are observed for cratons in the northern hemisphere: the Baltic shield, East European Platform, and the Siberian Platform. Negative anomalies are observed over cratons in the southern hemisphere: Western Australia, South America, the Indian shield, and Southern Africa. This indicates that there are significant differences in the density of cratonic roots, even for those of similar age. Root density depends on temperature and chemical depletion. In order to separate these effects we apply a lithospheric temperature correction using thermal estimates from a combination of geothermal modeling and global seismic tomography models. Gravity anomalies induced by temperature variations in the uppermost mantle range from -200 to +300 mGal, with the strongest negative anomalies associated with mid-ocean ridges and the strongest positive anomalies associated with cratons. After correcting for thermal effects, we obtain a map of density variations due to lithospheric compositional variations. These maps indicate that the average density decrease due to the chemical depletion within cratonic roots varies from 1.1% to 1.5%, assuming the chemical boundary layer has the same thickness as the thermal boundary layer. The maximal values of the density drop are in the range 1.7-2.5%, and correspond to the Archean portion of each craton. Temperatures within cratonic roots vary strongly, and our analysis indicates that density variations in the roots due to temperature are larger than the variations due to chemical differences. ?? 2003 Elsevier Science B.V. All rights reserved.

A new approach for estimating the Jupiter and Saturn gravity fields using Juno and Cassini measurements, trajectory estimation analysis, and a dynamical wind model optimization

NASA Astrophysics Data System (ADS)

Galanti, Eli; Durante, Daniele; Iess, Luciano; Kaspi, Yohai

2017-04-01

The ongoing Juno spacecraft measurements are improving our knowledge of Jupiter's gravity field. Similarly, the Cassini Grand Finale will improve the gravity estimate of Saturn. The analysis of the Juno and Cassini Doppler data will provide a very accurate reconstruction of spacial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity fields of Jupiter and Saturn, additional information needs to be incorporated into the analysis, especially with regards to the planets' wind structures. In this work we propose a new iterative approach for the estimation of Jupiter and Saturn gravity fields, using simulated measurements, a trajectory estimation model, and an adjoint based inverse thermal wind model. Beginning with an artificial gravitational field, the trajectory estimation model is used to obtain the gravitational moments. The solution from the trajectory model is then used as an initial guess for the thermal wind model, and together with an optimization method, the likely penetration depth of the winds is computed, and its uncertainty is evaluated. As a final step, the gravity harmonics solution from the thermal wind model is given back to the trajectory model, along with an estimate of their uncertainties, to be used as a priori for a new calculation of the gravity field. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that by using this method some of the gravitational moments are fitted better to the `observed' ones, mainly due to the added information from the dynamical model which includes the wind structure and its depth. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity moments estimated from the Juno and Cassini radio science experiments.

Quantization of systems with temporally varying discretization. II. Local evolution moves

NASA Astrophysics Data System (ADS)

Höhn, Philipp A.

2014-10-01

Several quantum gravity approaches and field theory on an evolving lattice involve a discretization changing dynamics generated by evolution moves. Local evolution moves in variational discrete systems (1) are a generalization of the Pachner evolution moves of simplicial gravity models, (2) update only a small subset of the dynamical data, (3) change the number of kinematical and physical degrees of freedom, and (4) generate a dynamical (or canonical) coarse graining or refining of the underlying discretization. To systematically explore such local moves and their implications in the quantum theory, this article suitably expands the quantum formalism for global evolution moves, constructed in Paper I [P. A. Höhn, "Quantization of systems with temporally varying discretization. I. Evolving Hilbert spaces," J. Math. Phys. 55, 083508 (2014); e-print arXiv:1401.6062 [gr-qc

Comparison of the hydrological excitation functions HAM of polar motion for the period 1980.0-2007.0

NASA Astrophysics Data System (ADS)

Nastula, J.; Pasnicka, M.; Kolaczek, B.

2011-10-01

In this study we compared contributions of polar motion excitation determined from hydrological models and harmonic coefficients of the Earth gravity field obtained from Gravity Recovery and Climate Experiment (GRACE). Hydrological excitation function (hydrological angular momentum - HAM) has been estimated from models of global hydrology, based on the observed distribution of surface water, snow, ice and soil moisture. All of them were compared with observed Geodetic Angular Momentum (GAM), excitations of polar motion. The spectra of these excitation functions of polar motion and residual geodetic excitation function G-A-O obtained from GAM by elimination of atmospheric and oceanic excitation functions were computed too. Phasor diagrams of the seasonal components of the polar motion excitation functions of all HAM excitation functions as well as of two GRACE solutions: CSR, CNES were determined and discussed.

Gravity measurements in southeastern Alaska reveal negative gravity rate of change caused by glacial isostatic adjustment

NASA Astrophysics Data System (ADS)

Sun, W.; Miura, S.; Sato, T.; Sugano, T.; Freymueller, J.; Kaufman, M.; Larsen, C. F.; Cross, R.; Inazu, D.

2010-12-01

For the past 300 years, southeastern Alaska has undergone rapid ice-melting and land uplift attributable to global warming. Corresponding crustal deformation (3 cm/yr) caused by the Little Ice Age retreat is detectable with modern geodetic techniques such as GPS and tidal gauge measurements. Geodetic deformation provides useful information for assessing ice-melting rates, global warming effects, and subcrustal viscosity. Nevertheless, integrated geodetic observations, including gravity measurements, are important. To detect crustal deformation caused by glacial isostatic adjustment and to elucidate the viscosity structure in southeastern Alaska, Japanese and U.S. researchers began a joint 3-year project in 2006 using GPS, Earth tide, and absolute gravity measurements. A new absolute gravity network was established, comprising five sites around Glacier Bay, near Juneau, Alaska. This paper reports the network's gravity measurements during 2006-2008. The bad ocean model in this area hindered ocean loading correction: Large tidal residuals remain in the observations. Accurate tidal correction necessitated on-site tidal observation. Results show high observation precision for all five stations: <1 μGal. The gravity rate of change was found to be -3.5 to -5.6 μGal/yr in the gravity network. Furthermore, gravity results obtained during the 3 years indicate a similar gravity change rate. These gravity data are anticipated for application in geophysical studies of southeastern Alaska. Using gravity and vertical displacement data, we constructed a quantity to remove viscoelastic effects. The observations are thus useful to constrain present-day ice thickness changes. A gravity bias of about -13.2 ± 0.1 mGal exists between the Potsdam and current FG5 gravity data.

Joint Optimization of Vertical Component Gravity and Seismic P-wave First Arrivals by Simulated Annealing

NASA Astrophysics Data System (ADS)

Louie, J. N.; Basler-Reeder, K.; Kent, G. M.; Pullammanappallil, S. K.

2015-12-01

Simultaneous joint seismic-gravity optimization improves P-wave velocity models in areas with sharp lateral velocity contrasts. Optimization is achieved using simulated annealing, a metaheuristic global optimization algorithm that does not require an accurate initial model. Balancing the seismic-gravity objective function is accomplished by a novel approach based on analysis of Pareto charts. Gravity modeling uses a newly developed convolution algorithm, while seismic modeling utilizes the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests show that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Detailed first arrival picking followed by trial velocity modeling remediates inconsistent data. We use a set of highly refined first arrival picks to compare results of a convergent joint seismic-gravity optimization to the Plotrefa™ and SeisOpt® Pro™ velocity modeling packages. Plotrefa™ uses a nonlinear least squares approach that is initial model dependent and produces shallow velocity artifacts. SeisOpt® Pro™ utilizes the simulated annealing algorithm and is limited to depths above the deepest raypath. Joint optimization increases the depth of constrained velocities, improving reflector coherency at depth. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts caused by limitations in refraction ray coverage. Seismic and gravity data from the San Emidio Geothermal field of the northwest Basin and Range province demonstrate that joint optimization changes interpretation outcomes. The prior shallow-valley interpretation gives way to a deep valley model, while shallow antiformal reflectors that could have been interpreted as antiformal folds are flattened. Furthermore, joint optimization provides a clearer image of the rangefront fault. This technique can readily be applied to existing datasets and could replace the existing strategy of forward modeling to match gravity data.

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.

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.

Bubble Formation and Detachment in Reduced Gravity Under the Influence of Electric Fields

NASA Technical Reports Server (NTRS)

Herman, Cila; Iacona, Estelle; Chang, Shinan

2002-01-01

The objective of the study is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Both uniform and nonuniform electric field configurations were considered. Bubble formation and detachment were recorded and visualized in reduced gravity (corresponding to gravity levels on Mars, on the Moon as well as microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angle at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. Measured data and model predictions show good agreement and indicate that the level of gravity and the electric field magnitude significantly affect bubble shape, volume and dimensions.

A critical analysis of the numerical and analytical methods used in the construction of the lunar gravity potential model.

NASA Astrophysics Data System (ADS)

Tuckness, D. G.; Jost, B.

1995-08-01

Current knowledge of the lunar gravity field is presented. The various methods used in determining these gravity fields are investigated and analyzed. It will be shown that weaknesses exist in the current models of the lunar gravity field. The dominant part of this weakness is caused by the lack of lunar tracking data information (farside, polar areas), which makes modeling the total lunar potential difficult. Comparisons of the various lunar models reveal an agreement in the low-order coefficients of the Legendre polynomials expansions. However, substantial differences in the models can exist in the higher-order harmonics. The main purpose of this study is to assess today's lunar gravity field models for use in tomorrow's lunar mission designs and operations.

The celestial mechanics approach: application to data of the GRACE mission

NASA Astrophysics Data System (ADS)

Beutler, Gerhard; Jäggi, Adrian; Mervart, Leoš; Meyer, Ulrich

2010-11-01

The celestial mechanics approach (CMA) has its roots in the Bernese GPS software and was extensively used for determining the orbits of high-orbiting satellites. The CMA was extended to determine the orbits of Low Earth Orbiting satellites (LEOs) equipped with GPS receivers and of constellations of LEOs equipped in addition with inter-satellite links. In recent years the CMA was further developed and used for gravity field determination. The CMA was developed by the Astronomical Institute of the University of Bern (AIUB). The CMA is presented from the theoretical perspective in (Beutler et al. 2010). The key elements of the CMA are illustrated here using data from 50 days of GPS, K-Band, and accelerometer observations gathered by the Gravity Recovery And Climate Experiment (GRACE) mission in 2007. We study in particular the impact of (1) analyzing different observables [Global Positioning System (GPS) observations only, inter-satellite measurements only], (2) analyzing a combination of observations of different types on the level of the normal equation systems (NEQs), (3) using accelerometer data, (4) different orbit parametrizations (short-arc, reduced-dynamic) by imposing different constraints on the stochastic orbit parameters, and (5) using either the inter-satellite ranges or their time derivatives. The so-called GRACE baseline, i.e., the achievable accuracy of the GRACE gravity field for a particular solution strategy, is established for the CMA.

Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

NASA Astrophysics Data System (ADS)

Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

2016-06-01

An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of M-H sampler. Although it is not a common inversion technique in geophysics, it can be stated that DE algorithm is worth to get more interest for parameter estimations from potential field data in geophysics considering its good accuracy, less computational cost (in the present problem) and the fact that a well-constructed initial guess is not required to reach the global minimum.

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.

A comparison of satellite systems for gravity field measurements

NASA Technical Reports Server (NTRS)

Argentiero, P. D.; Lowrey, B. E.

1977-01-01

A detailed and accurate earth gravity field model is important to the understanding of the structure and composition of the earth's crust and upper mantle. Various satellite-based techniques for providing more accurate models of the gravity field are analyzed and compared. A high-low configuration satellite-to-satellite tracking mission is recommended for the determination of both the long wavelength and short wavelength portions of the field. Satellite altimetry and satellite gradiometry missions are recommended for determination of the short wavelength portion of the field.

Specific Yields Estimated from Gravity Change during Pumping Test

NASA Astrophysics Data System (ADS)

Chen, K. H.; Hwang, C.; Chang, L. C.

2017-12-01

Specific yield (Sy) is the most important parameter to describe available groundwater capacity in an unconfined aquifer. When estimating Sy by a field pumping test, aquifer heterogeneity and well performers will cause a large uncertainty. In this study, we use a gravity-based method to estimate Sy. At the time of pumping test, amounts of mass (groundwater) are forced to be taken out. If drawdown corn is big and close enough to high precision gravimeter, the gravity change can be detected. The gravity-based method use gravity observations that are independent from traditional flow computation. Only the drawdown corn should be modeled with observed head and hydrogeology data. The gravity method can be used in most groundwater field tests, such as locally pumping/injection tests initiated by active man-made or annual variations due to natural sources. We apply our gravity method at few sites in Taiwan situated over different unconfined aquifer. Here pumping tests for Sy determinations were also carried out. We will discuss why the gravity method produces different results from traditional pumping test, field designs and limitations of the gravity method.

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).

Height system unification based on the Fixed Geodetic Boundary Value Problem with limited availability of gravity data

NASA Astrophysics Data System (ADS)

Porz, Lucas; Grombein, Thomas; Seitz, Kurt; Heck, Bernhard; Wenzel, Friedemann

2017-04-01

Regional height reference systems are generally related to individual vertical datums defined by specific tide gauges. The discrepancies of these vertical datums with respect to a unified global datum cause height system biases that range in an order of 1-2 m at a global scale. One approach for unification of height systems relates to the solution of a Geodetic Boundary Value Problem (GBVP). In particular, the fixed GBVP, using gravity disturbances as boundary values, is solved at GNSS/leveling benchmarks, whereupon height datum offsets can be estimated by least squares adjustment. In spherical approximation, the solution of the fixed GBVP is obtained by Hotine's spherical integral formula. However, this method relies on the global availability of gravity data. In practice, gravity data of the necessary resolution and accuracy is not accessible globally. Thus, the integration is restricted to an area within the vicinity of the computation points. The resulting truncation error can reach several meters in height, making height system unification without further consideration of this effect unfeasible. This study analyzes methods for reducing the truncation error by combining terrestrial gravity data with satellite-based global geopotential models and by modifying the integral kernel in order to accelerate the convergence of the resulting potential. For this purpose, EGM2008-derived gravity functionals are used as pseudo-observations to be integrated numerically. Geopotential models of different spectral degrees are implemented using a remove-restore-scheme. Three types of modification are applied to the Hotine-kernel and the convergence of the resulting potential is analyzed. In a further step, the impact of these operations on the estimation of height datum offsets is investigated within a closed loop simulation. A minimum integration radius in combination with a specific modification of the Hotine-kernel is suggested in order to achieve sub-cm accuracy for the estimation of height datum offsets.

Lithospheric Stress Tensor from Gravity and Lithospheric Structure Models

NASA Astrophysics Data System (ADS)

Eshagh, Mehdi; Tenzer, Robert

2017-07-01

In this study we investigate the lithospheric stresses computed from the gravity and lithospheric structure models. The functional relation between the lithospheric stress tensor and the gravity field parameters is formulated based on solving the boundary-value problem of elasticity in order to determine the propagation of stresses inside the lithosphere, while assuming the horizontal shear stress components (computed at the base of the lithosphere) as lower boundary values for solving this problem. We further suppress the signature of global mantle flow in the stress spectrum by subtracting the long-wavelength harmonics (below the degree of 13). This numerical scheme is applied to compute the normal and shear stress tensor components globally at the Moho interface. The results reveal that most of the lithospheric stresses are accumulated along active convergent tectonic margins of oceanic subductions and along continent-to-continent tectonic plate collisions. These results indicate that, aside from a frictional drag caused by mantle convection, the largest stresses within the lithosphere are induced by subduction slab pull forces on the side of subducted lithosphere, which are coupled by slightly less pronounced stresses (on the side of overriding lithospheric plate) possibly attributed to trench suction. Our results also show the presence of (intra-plate) lithospheric loading stresses along Hawaii islands. The signature of ridge push (along divergent tectonic margins) and basal shear traction resistive forces is not clearly manifested at the investigated stress spectrum (between the degrees from 13 to 180).

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

Notes on "Quantum Gravity" and Noncommutative Geometry

NASA Astrophysics Data System (ADS)

Gracia-Bondía, J. M.

I hesitated for a long time before giving shape to these notes, originally intended for preliminary reading by the attendees to the Summer School "New paths towards quantum gravity" (Holbaek Bay, Denmark, May 2008). At the end, I decide against just selling my mathematical wares, and for a survey, necessarily very selective, but taking a global phenomenological approach to its subject matter. After all, noncommutative geometry does not purport yet to solve the riddle of quantum gravity; it is more of an insurance policy against the probable failure of the other approaches. The plan is as follows: the introduction invites students to the fruitful doubts and conundrums besetting the application of even classical gravity. Next, the first experiments detecting quantum gravitational states inoculate us a healthy dose of scepticism on some of the current ideologies. In Sect. 1.3 we look at the action for general relativity as a consequence of gauge theory for quantum tensor fields. Section 1.4 briefly deals with the unimodular variants. Section 1.5 arrives at noncommutative geometry. I am convinced that, if this is to play a role in quantum gravity, commutative and noncommutative manifolds must be treated on the same footing, which justifies the place granted to the reconstruction theorem. Together with Sect. 1.3, this part constitutes the main body of the notes. Only very summarily at the end of this section do we point to some approaches to gravity within the noncommutative realm. The last section delivers a last dose of scepticism. My efforts will have been rewarded if someone from the young generation learns to mistrust current mindsets.

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.

Implications of postseismic gravity change following the great 2004 Sumatra-Andaman earthquake from the regional harmonic analysis of GRACE intersatellite tracking data

USGS Publications Warehouse

Han, S.-C.; Sauber, J.; Luthcke, S.B.; Ji, C.; Pollitz., F. F.

2008-01-01

We report Gravity Recovery and Climate Experiment (GRACE) satellite observations of coseismic displacements and postseismic transients from the great Sumatra-Andaman Islands (thrust event; Mw ???9.2) earthquake in December 2004. Instead of using global spherical harmonic solutions of monthly gravity fields, we estimated the gravity changes directly using intersatellite range-rate data with regionally concentrated spherical Slepian basis functions every 15-day interval. We found significant step-like (coseismic) and exponential-like (postseismic) behavior in the time series of estimated coefficients (from May 2003 to April 2007) for the spherical Slepian function's. After deriving coseismic slip estimates from seismic and geodetic data that spanned different time intervals, we estimated and evaluated postseismic relaxation mechanisms with alternate asthenosphere viscosity models. The large spatial coverage and uniform accuracy of our GRACE solution enabled us to clearly delineate a postseismic transient signal in the first 2 years of postearthquake GRACE data. Our preferred interpretation of the long-wavelength components of the postseismic avity change is biviscous viscoelastic flow. We estimated a transient viscosity of 5 ??17 Pa s and a steady state viscosity of 5 ?? 1018 - 1019 Pa s. Additional years of the GRACE observations should provide improved steady state viscosity estimates. In contrast to our interpretation of coseismic gravity change, the prominent postearthquake positive gravity change around the Nicobar Islands is accounted for by seafloor uplift with less postseismic perturbation in intrinsic density in the region surrounding the earthquake. Copyright 2008 by the American Geophysical Union.

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.

Observations of geographically correlated orbit errors for TOPEX/Poseidon using the global positioning system

NASA Technical Reports Server (NTRS)

Christensen, E. J.; Haines, B. J.; Mccoll, K. C.; Nerem, R. S.

1994-01-01

We have compared Global Positioning System (GPS)-based dynamic and reduced-dynamic TOPEX/Poseidon orbits over three 10-day repeat cycles of the ground-track. The results suggest that the prelaunch joint gravity model (JGM-1) introduces geographically correlated errors (GCEs) which have a strong meridional dependence. The global distribution and magnitude of these GCEs are consistent with a prelaunch covariance analysis, with estimated and predicted global rms error statistics of 2.3 and 2.4 cm rms, respectively. Repeating the analysis with the post-launch joint gravity model (JGM-2) suggests that a portion of the meridional dependence observed in JGM-1 still remains, with global rms error of 1.2 cm.

Altimeter measurements for the determination of the Earth's gravity field

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Schutz, B. E.; Shum, C. K.

1986-01-01

Progress in the following areas is described: refining altimeter and altimeter crossover measurement models for precise orbit determination and for the solution of the earth's gravity field; performing experiments using altimeter data for the improvement of precise satellite ephemerides; and analyzing an optimal relative data weighting algorithm to combine various data types in the solution of the gravity field.

A Tour Through Shape Dynamic Black Holes

NASA Astrophysics Data System (ADS)

Herczeg, Gabriel

Shape dynamics is a classical theory of gravity which agrees with general relativity in many important cases, but possesses different gauge symmetries and constraints. Rather than spacetime diffeomorphism invariance, shape dynamics takes spatial diffeomorphism invariance and spatial Weyl invariance as the fundamental gauge symmetries associated with the gravitational field. Despite these differences, shape dynamics and general relativity generically predict the same dynamics--there exist gauge-fixings of each theory that ensure agreement with the other. However, these gauge-fixing conditions are not necessarily globally well-defined and it is therefore possible to find solutions of the shape dynamics equations of motion that agree with general relativity on some open neighborhoods, but which have different global structures. In particular, the black hole solutions of the two theories disagree globally. Understanding these novel "shape dynamic black holes" is the primary goal of this thesis.

Inflation, symmetry, and B-modes

DOE PAGES

Hertzberg, Mark P.

2015-04-20

Here, we examine the role of using symmetry and effective field theory in inflationary model building. We describe the standard formulation of starting with an approximate shift symmetry for a scalar field, and then introducing corrections systematically in order to maintain control over the inflationary potential. We find that this leads to models in good agreement with recent data. On the other hand, there are attempts in the literature to deviate from this paradigm by envoking other symmetries and corrections. In particular: in a suite of recent papers, several authors have made the claim that standard Einstein gravity with amore » cosmological constant and a massless scalar carries conformal symmetry. They claim this conformal symmetry is hidden when the action is written in the Einstein frame, and so has not been fully appreciated in the literature. They further claim that such a theory carries another hidden symmetry; a global SO(1,1) symmetry. By deforming around the global SO(1,1) symmetry, they are able to produce a range of inflationary models with asymptotically flat potentials, whose flatness is claimed to be protected by these symmetries. These models tend to give rise to B-modes with small amplitude. Here we explain that standard Einstein gravity does not in fact possess conformal symmetry. Instead these authors are merely introducing a redundancy into the description, not an actual conformal symmetry. Furthermore, we explain that the only real (global) symmetry in these models is not at all hidden, but is completely manifest when expressed in the Einstein frame; it is in fact the shift symmetry of a scalar field. When analyzed systematically as an effective field theory, deformations do not generally produce asymptotically flat potentials and small B-modes as suggested in these recent papers. Instead, deforming around the shift symmetry systematically, tends to produce models of inflation with B-modes of appreciable amplitude. Such simple models typically also produce the observed red spectral index, Gaussian fluctuations, etc. In short: simple models of inflation, organized by expanding around a shift symmetry, are in excellent agreement with recent data.« less

Measuring wood specific gravity, correctly

Treesearch

G. Bruce Williamson; Michael C. Wiemann

2010-01-01

The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a forester’s variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these...

A harmonic analysis of lunar gravity

NASA Technical Reports Server (NTRS)

Bills, B. G.; Ferrari, A. J.

1980-01-01

An improved model of lunar global gravity has been obtained by fitting a sixteenth-degree harmonic series to a combination of Doppler tracking data from Apollo missions 8, 12, 15, and 16, and Lunar Orbiters 1, 2, 3, 4, and 5, and laser ranging data to the lunar surface. To compensate for the irregular selenographic distribution of these data, the solution algorithm has also incorporated a semi-empirical a priori covariance function. Maps of the free-air gravity disturbance and its formal error are presented, as are free-air anomaly and Bouguer anomaly maps. The lunar gravitational variance spectrum has the form V(G; n) = O(n to the -4th power), as do the corresponding terrestrial and martian spectra. The variance spectra of the Bouguer corrections (topography converted to equivalent gravity) for these bodies have the same basic form as the observed gravity; and, in fact, the spectral ratios are nearly constant throughout the observed spectral range for each body. Despite this spectral compatibility, the correlation between gravity and topography is generally quite poor on a global scale.

Fake conformal symmetry in unimodular gravity

NASA Astrophysics Data System (ADS)

Oda, Ichiro

2016-08-01

We study Weyl symmetry (local conformal symmetry) in unimodular gravity. It is shown that the Noether currents for both Weyl symmetry and global scale symmetry vanish exactly as in conformally invariant scalar-tensor gravity. We clearly explain why in the class of conformally invariant gravitational theories, the Noether currents vanish by starting with conformally invariant scalar-tensor gravity. Moreover, we comment on both classical and quantum-mechanical equivalences in Einstein's general relativity, conformally invariant scalar-tensor gravity, and the Weyl-transverse gravity. Finally, we discuss the Weyl current in the conformally invariant scalar action and see that it is also vanishing.

Daily GRACE gravity field solutions track major flood events in the Ganges-Brahmaputra Delta

NASA Astrophysics Data System (ADS)

Gouweleeuw, Ben T.; Kvas, Andreas; Gruber, Christian; Gain, Animesh K.; Mayer-Gürr, Thorsten; Flechtner, Frank; Güntner, Andreas

2018-05-01

Two daily gravity field solutions based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are evaluated against daily river runoff data for major flood events in the Ganges-Brahmaputra Delta (GBD) in 2004 and 2007. The trends over periods of a few days of the daily GRACE data reflect temporal variations in daily river runoff during major flood events. This is especially true for the larger flood in 2007, which featured two distinct periods of critical flood level exceedance in the Brahmaputra River. This first hydrological evaluation of daily GRACE gravity field solutions based on a Kalman filter approach confirms their potential for gravity-based large-scale flood monitoring. This particularly applies to short-lived, high-volume floods, as they occur in the GBD with a 4-5-year return period. The release of daily GRACE gravity field solutions in near-real time may enable flood monitoring for large events.

AN ADJOINT-BASED METHOD FOR THE INVERSION OF THE JUNO AND CASSINI GRAVITY MEASUREMENTS INTO WIND FIELDS

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

Galanti, Eli; Kaspi, Yohai, E-mail: eli.galanti@weizmann.ac.il

2016-04-01

During 2016–17, the Juno and Cassini spacecraft will both perform close eccentric orbits of Jupiter and Saturn, respectively, obtaining high-precision gravity measurements for these planets. These data will be used to estimate the depth of the observed surface flows on these planets. All models to date, relating the winds to the gravity field, have been in the forward direction, thus only allowing the calculation of the gravity field from given wind models. However, there is a need to do the inverse problem since the new observations will be of the gravity field. Here, an inverse dynamical model is developed tomore » relate the expected measurable gravity field, to perturbations of the density and wind fields, and therefore to the observed cloud-level winds. In order to invert the gravity field into the 3D circulation, an adjoint model is constructed for the dynamical model, thus allowing backward integration. This tool is used for the examination of various scenarios, simulating cases in which the depth of the wind depends on latitude. We show that it is possible to use the gravity measurements to derive the depth of the winds, both on Jupiter and Saturn, also taking into account measurement errors. Calculating the solution uncertainties, we show that the wind depth can be determined more precisely in the low-to-mid-latitudes. In addition, the gravitational moments are found to be particularly sensitive to flows at the equatorial intermediate depths. Therefore, we expect that if deep winds exist on these planets they will have a measurable signature by Juno and Cassini.« less

Cartan gravity, matter fields, and the gauge principle

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

Westman, Hans F., E-mail: hwestman74@gmail.com; Zlosnik, Tom G., E-mail: t.zlosnik@imperial.ac.uk

Gravity is commonly thought of as one of the four force fields in nature. However, in standard formulations its mathematical structure is rather different from the Yang–Mills fields of particle physics that govern the electromagnetic, weak, and strong interactions. This paper explores this dissonance with particular focus on how gravity couples to matter from the perspective of the Cartan-geometric formulation of gravity. There the gravitational field is represented by a pair of variables: (1) a ‘contact vector’ V{sup A} which is geometrically visualized as the contact point between the spacetime manifold and a model spacetime being ‘rolled’ on top ofmore » it, and (2) a gauge connection A{sub μ}{sup AB}, here taken to be valued in the Lie algebra of SO(2,3) or SO(1,4), which mathematically determines how much the model spacetime is rotated when rolled. By insisting on two principles, the gauge principle and polynomial simplicity, we shall show how one can reformulate matter field actions in a way that is harmonious with Cartan’s geometric construction. This yields a formulation of all matter fields in terms of first order partial differential equations. We show in detail how the standard second order formulation can be recovered. In particular, the Hodge dual, which characterizes the structure of bosonic field equations, pops up automatically. Furthermore, the energy–momentum and spin-density three-forms are naturally combined into a single object here denoted the spin-energy–momentum three-form. Finally, we highlight a peculiarity in the mathematical structure of our first-order formulation of Yang–Mills fields. This suggests a way to unify a U(1) gauge field with gravity into a SO(1,5)-valued gauge field using a natural generalization of Cartan geometry in which the larger symmetry group is spontaneously broken down to SO(1,3)×U(1). The coupling of this unified theory to matter fields and possible extensions to non-Abelian gauge fields are left as open questions. -- Highlights: •Develops Cartan gravity to include matter fields. •Coupling to gravity is done using the standard gauge prescription. •Matter actions are manifestly polynomial in all field variables. •Standard equations recovered on-shell for scalar, spinor and Yang–Mills fields. •Unification of a U(1) field with gravity based on the orthogonal group SO(1,5)« less

Solution to the spectral filter problem of residual terrain modelling (RTM)

NASA Astrophysics Data System (ADS)

Rexer, Moritz; Hirt, Christian; Bucha, Blažej; Holmes, Simon

2018-06-01

In physical geodesy, the residual terrain modelling (RTM) technique is frequently used for high-frequency gravity forward modelling. In the RTM technique, a detailed elevation model is high-pass-filtered in the topography domain, which is not equivalent to filtering in the gravity domain. This in-equivalence, denoted as spectral filter problem of the RTM technique, gives rise to two imperfections (errors). The first imperfection is unwanted low-frequency (LF) gravity signals, and the second imperfection is missing high-frequency (HF) signals in the forward-modelled RTM gravity signal. This paper presents new solutions to the RTM spectral filter problem. Our solutions are based on explicit modelling of the two imperfections via corrections. The HF correction is computed using spectral domain gravity forward modelling that delivers the HF gravity signal generated by the long-wavelength RTM reference topography. The LF correction is obtained from pre-computed global RTM gravity grids that are low-pass-filtered using surface or solid spherical harmonics. A numerical case study reveals maximum absolute signal strengths of ˜ 44 mGal (0.5 mGal RMS) for the HF correction and ˜ 33 mGal (0.6 mGal RMS) for the LF correction w.r.t. a degree-2160 reference topography within the data coverage of the SRTM topography model (56°S ≤ φ ≤ 60°N). Application of the LF and HF corrections to pre-computed global gravity models (here the GGMplus gravity maps) demonstrates the efficiency of the new corrections over topographically rugged terrain. Over Switzerland, consideration of the HF and LF corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 4.41 to 3.27 mGal, which translates into ˜ 26% improvement. Over a second test area (Canada), our corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 5.65 to 5.30 mGal (˜ 6% improvement). Particularly over Switzerland, geophysical signals (associated, e.g. with valley fillings) were found to stand out more clearly in the RTM-reduced gravity measurements when the HF and LF correction are taken into account. In summary, the new RTM filter corrections can be easily computed and applied to improve the spectral filter characteristics of the popular RTM approach. Benefits are expected, e.g. in the context of the development of future ultra-high-resolution global gravity models, smoothing of observed gravity data in mountainous terrain and geophysical interpretations of RTM-reduced gravity measurements.

Investigating Jupiter's Deep Flow Structure using the Juno Magnetic and Gravity Measurements

NASA Astrophysics Data System (ADS)

Duer, K.; Galanti, E.; Cao, H.; Kaspi, Y.

2017-12-01

Jupiter's flow below its cloud-level is still largely unknown. The gravity measurements from Juno provide now an initial insight into the depth of the flow via the relation between the gravity field and the flow field. Furthermore, additional constraints could be put on the flow if the expected Juno magnetic measurements are also used. Specifically, the gravity and magnetic measurements can be combined to allow a more robust estimate of the deep flow structure. However, a complexity comes from the fact that both the radial profile of the flow, and it's connection to the induced magnetic field, might vary with latitude. In this study we propose a method for using the expected Juno's high-precision measurements of both the magnetic and gravity fields, together with latitude dependent models that relate the measurements to the structure of the internal flow. We simulate possible measurements by setting-up specific deep wind profiles and forward calculate the resulting anomalies in both the magnetic and gravity fields. We allow these profiles to include also latitude dependency. The relation of the flow field to the gravity field is based on thermal wind balance, and it's relation to the magnetic field is via a mean-field electrodynamics balance. The latter includes an alpha-effect, describing the mean magnetic effect of turbulent rotating convection, which might also vary with latitude. Using an adjoint based optimization process, we examine the ability of the combined magnetic-gravity model to decipher the flow structure under the different potential Juno measurements. We investigate the effect of different latitude dependencies on the derived solutions and their associated uncertainties. The novelty of this study is the combination of two independent Juno measurements for the calculation of a latitudinal dependent interior flow profile. This method might lead to a better constraint of Jupiter's flow structure.

African Plate Seismicity and Gravity Field Anomalies

NASA Astrophysics Data System (ADS)

Ryzhii, B. P.; Nachapkin, N. I.; Milanovsky, Svet

The analysis of connection plate of earthquakes of the African continent with Bouguer gravity anomalies is carried out. As input dataSs were used the catalog of earthquakes and numeral map of Bouguer gravity field. The catalog contains geographical coor- dinates of epicenters and magnitudes of 8027 earthquakes recorded on continent and adjacent oceanic areas for the period from 1904 to 1988 years. The values of a gravity field preset in knots of a grid with a step 1 grade. For the analysis of plate seismicity from the catalog the parameters of 6408 earthquakes were chosen, which one have taken place in the field of restricted shore line. The earthquakes fixed in a band of a concatenation of continent with the Arabian plate were excluded from the analysis. On the basis of a numeral gravity map for everyone epicenter the value of Bouguer anomaly was calculated. The allocation of epicenters of earthquakes with magnitude M is obtained depending on value of a gravity Bouguer field. The outcomes of a sta- tistical analysis testify that practically all earthquakes are associated with the areas with negative values of Bouguer gravity field. Thus in areas with values of a field -160 mgal to -100 mgal there was 80 % of all earthquakes. It is necessary to note, that the mean value of the field for the African continent is -70 mgal. Obtained result gives us the possibility to make a conclusion about connection of plate earthquakes of Africa predominantly with structural complexes of earth crust with lower density. These out- comes are in the consent with a hypothesis of one of the authors (Ryzhii B.P.) about connection of plate earthquakes hypocenters on the territory of Russia with negative values of a gravity field and heightened silica content in the Earth crust. This work was supported with RFFI grant N 00-05-65067

Recovery of the Three-Gorges Reservoir Impoundment Signal from ICESat altimetry and GRACE

NASA Astrophysics Data System (ADS)

Carabajal, C. C.; Boy, J.; Luthcke, S. B.; Harding, D. J.; Rowlands, D. D.; Lemoine, F. G.

2006-12-01

The Three Gorges Dam along the Yangtze River in China is one of the largest dams in the world. The water impoundment of the Three-Gorges Reservoir started in June 2003, and the volume of water will continuously increase up to about 40 km3 in 2009, over a length of about 600 km. Although water-level changes along the Yangtze River and the Three Gorges Reservoir are measured by in situ water gauges, access to these data can be quite difficult. Estimates of inland water height and extent can also be recovered from altimetry measurements performed from satellite platforms, such as those acquired by the Geoscience laser Altimetry System (GLAS) on board the Ice, Cloud and Land Elevation Satellite (ICESat). ICESat has produced a comprehensive, highly precise, set of along-track elevation measurements, every three months since its launch in 2003, which intersect the Yangtze River along its East-West extent. In addition, the water impoundment of major artificial reservoirs induces variations of global geodetic quantities, such as the gravity field and Earth rotation (Chao, 1995, Boy & Chao, 2002). Water level changes within the reservoir are compared to GRACE (Gravity Recovery And Climate Experiment) recovered water mass changes. In addition, we compare the GRACE observations of mass change in the Yangtze region to hydrological changes computed from different global soil-moisture and snow models, such as GLDAS (Global Land Data Assimilation System).

On the feasibility of using satellite gravity observations for detecting large-scale solid mass transfer events

NASA Astrophysics Data System (ADS)

Peidou, Athina C.; Fotopoulos, Georgia; Pagiatakis, Spiros

2017-10-01

The main focus of this paper is to assess the feasibility of utilizing dedicated satellite gravity missions in order to detect large-scale solid mass transfer events (e.g. landslides). Specifically, a sensitivity analysis of Gravity Recovery and Climate Experiment (GRACE) gravity field solutions in conjunction with simulated case studies is employed to predict gravity changes due to past subaerial and submarine mass transfer events, namely the Agulhas slump in southeastern Africa and the Heart Mountain Landslide in northwestern Wyoming. The detectability of these events is evaluated by taking into account the expected noise level in the GRACE gravity field solutions and simulating their impact on the gravity field through forward modelling of the mass transfer. The spectral content of the estimated gravity changes induced by a simulated large-scale landslide event is estimated for the known spatial resolution of the GRACE observations using wavelet multiresolution analysis. The results indicate that both the Agulhas slump and the Heart Mountain Landslide could have been detected by GRACE, resulting in {\\vert }0.4{\\vert } and {\\vert }0.18{\\vert } mGal change on GRACE solutions, respectively. The suggested methodology is further extended to the case studies of the submarine landslide in Tohoku, Japan, and the Grand Banks landslide in Newfoundland, Canada. The detectability of these events using GRACE solutions is assessed through their impact on the gravity field.

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.

The Effects of Core-Mantle Interactions on Earth Rotation, Surface Deformation, and Gravity Changes

NASA Astrophysics Data System (ADS)

Watkins, A.; Gross, R. S.; Fu, Y.

2017-12-01

The length-of-day (LOD) contains a 6-year signal, the cause of which is currently unknown. The signal remains after removing tidal and surface fluid effects, thus the cause is generally believed to be angular momentum exchange between the mantle and core. Previous work has established a theoretical relationship between pressure variations at the core-mantle boundary (CMB) and resulting deformation of the overlying mantle and crust. This study examines globally distributed GPS deformation data in search of this effect, and inverts the discovered global inter-annual component for the CMB pressure variations. The geostrophic assumption is then used to obtain fluid flow solutions at the edge of the core from the CMB pressure variations. Taylor's constraint is applied to obtain the flow deeper within the core, and the equivalent angular momentum and LOD changes are computed and compared to the known 6-year LOD signal. The amplitude of the modeled and measured LOD changes agree, but the degree of period and phase agreement is dependent upon the method of isolating the desired component in the GPS position data. Implications are discussed, and predictions are calculated for surface gravity field changes that would arise from the CMB pressure variations.

Generation, estimation, utilization, availability and compatibility aspects of geodetic and meteorological data

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

Luetzow, H.B.v.

1983-08-01

Following an introduction, the paper discusses in section 2 the collection or generation of final geodetic data from conventional surveys, satellite observations, satellite altimetry, the Global Positioning System, and moving base gravity gradiometers. Section 3 covers data utilization and accuracy aspects including gravity programmed inertial positioning and subterraneous mass detection. Section 4 addresses the usefulness and limitation of the collocation method of physical geodesy. Section 5 is concerned with the computation of classical climatological data. In section 6, meteorological data assimilation is considered. Section 7 deals with correlated aspects of initial data generation with emphasis on initial wind field determination,more » parameterized and classical hydrostatic prediction models, non-hydrostatic prediction, computational networks, and computer capacity. The paper concludes that geodetic and meteorological data are expected to become increasingly more diversified and voluminous both regionally and globally, that its general availability will be more or less restricted for some time to come, that its quality and quantity are subject to change, and that meteorological data generation, accuracy and density have to be considered in conjunction with advanced as well as cost-effective numerical weather prediction models and associated computational efforts.« less