GRACE gravity field recovery using refined acceleration approach

NASA Astrophysics Data System (ADS)

Li, Zhao; van Dam, Tonie; Weigelt, Matthias

2017-04-01

Since 2002, the GRACE mission has yielded monthly gravity field solutions with such a high level of quality that we have been able to observe so many changes to the Earth mass system. Based on GRACE L1B observations, a number of official monthly gravity field models have been developed and published using different methods, e.g. the CSR RL05, JPL RL05, and GFZ RL05 are being computed by a dynamic approach, the ITSG and Tongji GRACE are generated using what is known as the short-arc approach, the AIUB models are computed using celestial mechanics approach, and the DMT-1 model is calculated by means of an acceleration approach. Different from the DMT-1 model, which links the gravity field parameters directly to the bias-corrected range measurements at three adjacent epochs, in this work we present an alternative acceleration approach which connects range accelerations and velocity differences to the gradient of the gravitational potential. Due to the fact that GPS derived velocity difference is provided at a lower precision, we must reduce this approach to residual quantities using an a priori gravity field which allows us to subsequently neglect the residual velocity difference term. We find that this assumption would cause a problem in the low-degree gravity field coefficient, particularly for degree 2 and also from degree 16 to 26. To solve this problem, we present a new way of handling the residual velocity difference term, that is to treat this residual velocity difference term as unknown but estimable quantity, as it depends on the unknown residual gravity field parameters and initial conditions. In other word, we regard the kinematic orbit position vectors as pseudo observations, and the corrections of orbits are estimated together with both the geopotential coefficients and the accelerometer scale/bias by using a weighted least square adjustment. The new approach is therefore a refinement of the existing approach but offers a better approximation to reality. This result is especially important in view of the upcoming GRACE Follow-On mission, which will be equipped with a laser ranging instrument offering a higher precision. Our validation results show that this refined acceleration approach could produce monthly GRACE gravity solutions at the same level of precision as the other approaches.

Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

NASA Technical Reports Server (NTRS)

Noever, David A.; Koczor, Ronald J.; Roberson, Rick

1998-01-01

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

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.

GOCE gravity field simulation based on actual mission scenario

NASA Astrophysics Data System (ADS)

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

2009-04-01

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

GRAV-D Part II : Examining Airborne Gravity Processing Assumptions With an Aim Towards Producing a Better Gravimetric Geoid

NASA Astrophysics Data System (ADS)

Theresa, D. M.; Vicki, C.; Dan, R.; Dru, S.

2008-12-01

The primary objective of the GRAV-D (Gravity for the Redefinition of the American Vertical Datum) project is to redefine the American vertical datum by using an improved gravimetric geoid. This will be partially accomplished through an extensive airborne gravity measurement campaign, focusing first on the land/water interface (and later on interior areas) of the US and its holdings. This airborne campaign is designed specifically to capture intermediate wavelength gravity information by flying at high altitudes (35,000 ft, ~10 km) with a 10 km line spacing. The intermediate wavelengths captured by airborne gravity data are complementary to ground and satellite gravity data. Combining the GRAV-D airborne gravity data with the Gravity Recovery and Climate Experiment (GRACE) satellite gravity field will allow existing terrestrial data sets to be corrected for bias and trend problems. Ultimately, all three types of data can then be merged into a single accurate representation of the gravity field. Typically, the airborne gravity data reduction process is used to produce free-air anomalies for geological/geophysical applications that require more limited accuracy and precision than do geodetic applications. Thus we re-examine long-standing data reduction simplifications and assumptions with an aim toward improving both the accuracy and precision of airborne gravity data before their inclusion into a gravimetric geoid. The data reduction process is tested on a 400 km x 500 km airborne gravity survey in southern Alaska (in the vicinity of Anchorage) collected in the summer of 2008 as part of the GRAV-D project. Potential improvements in processing come from examining the impacts of various GPS processing schemes on free-air gravity results and re-considering all assumptions in standard airborne gravity processing methods, especially those that might introduce bias into absolute gravity levels.

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.

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.

Test-particle dynamics in general spherically symmetric black hole spacetimes

NASA Astrophysics Data System (ADS)

De Laurentis, Mariafelicia; Younsi, Ziri; Porth, Oliver; Mizuno, Yosuke; Rezzolla, Luciano

2018-05-01

To date, the most precise tests of general relativity have been achieved through pulsar timing, albeit in the weak-field regime. Since pulsars are some of the most precise and stable "clocks" in the Universe, present observational efforts are focused on detecting pulsars in the vicinity of supermassive black holes (most notably in the Galactic Centre), enabling pulsar timing to be used as an extremely precise probe of strong-field gravity. In this paper, a mathematical framework to describe test-particle dynamics in general black-hole spacetimes is presented and subsequently used to study a binary system comprising a pulsar orbiting a black hole. In particular, taking into account the parameterization of a general spherically symmetric black-hole metric, general analytic expressions for both the advance of the periastron and for the orbital period of a massive test particle are derived. Furthermore, these expressions are applied to four representative cases of solutions arising in both general relativity and in alternative theories of gravity. Finally, this framework is applied to the Galactic center S -stars and four distinct pulsar toy models. It is shown that by adopting a fully general-relativistic description of test-particle motion which is independent of any particular theory of gravity, observations of pulsars can help impose better constraints on alternative theories of gravity than is presently possible.

Recent results on modelling the spatial and temporal structure of the Earth's gravity field.

PubMed

Moore, P; Zhang, Q; Alothman, A

2006-04-15

The Earth's gravity field plays a central role in sea-level change. In the simplest application a precise gravity field will enable oceanographers to capitalize fully on the altimetric datasets collected over the past decade or more by providing a geoid from which absolute sea-level topography can be recovered. However, the concept of a static gravity field is now redundant as we can observe temporal variability in the geoid due to mass redistribution in or on the total Earth system. Temporal variability, associated with interactions between the land, oceans and atmosphere, can be investigated through mass redistributions with, for example, flow of water from the land being balanced by an increase in ocean mass. Furthermore, as ocean transport is an important contributor to the mass redistribution the time varying gravity field can also be used to validate Global Ocean Circulation models. This paper will review the recent history of static and temporal gravity field recovery, from the 1980s to the present day. In particular, mention will be made of the role of satellite laser ranging and other space tracking techniques, satellite altimetry and in situ gravity which formed the basis of gravity field determination until the last few years. With the launch of Challenging Microsatellite Payload and Gravity and Circulation Experiment (GRACE) our knowledge of the spatial distribution of the Earth's gravity field is taking a leap forward. Furthermore, GRACE is now providing insight into temporal variability through 'monthly' gravity field solutions. Prior to this data we relied on satellite tracking, Global Positioning System and geophysical models to give us insight into the temporal variability. We will consider results from these methodologies and compare them to preliminary results from the GRACE mission.

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.

Development of a Transportable Gravity Gradiometer Based on Atom Interferometry

NASA Astrophysics Data System (ADS)

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

2007-12-01

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

The determination of the orbit of the Japanese satellite Ajisai and the GEM-T1 and GEM-T2 gravity field models

NASA Technical Reports Server (NTRS)

Sanchez, Braulio V.

1990-01-01

The Japanese Experimental Geodetic Satellite Ajisai was launched on August 12, 1986. In response to the TOPEX-POSEIDON mission requirements, the GSFC Space Geodesy Branch and its associates are producing improved models of the Earth's gravitational field. With the launch of Ajisai, precise laser data is now available which can be used to test many current gravity models. The testing of the various gravity field models show improvements of more than 70 percent in the orbital fits when using GEM-T1 and GEM-T2 relative to results obtained with the earlier GEM-10B model. The GEM-T2 orbital fits are at the 13-cm level (RMS). The results of the tests with the various versions of the GEM-T1 model indicate that the addition of satellite altimetry and surface gravity anomalies as additional data types should improve future gravity field models.

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.

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

NASA Technical Reports Server (NTRS)

Valliant, H. D.

1989-01-01

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

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.

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.

Venus spherical harmonic gravity model to degree and order 60

NASA Technical Reports Server (NTRS)

Konopliv, Alex S.; Sjogren, William L.

1994-01-01

The Magellan and Pioneer Venus Orbiter radiometric tracking data sets have been combined to produce a 60th degree and order spherical harmonic gravity field. The Magellan data include the high-precision X-band gravity tracking from September 1992 to May 1993 and post-aerobraking data up to January 5, 1994. Gravity models are presented from the application of Kaula's power rule for Venus and an alternative a priori method using surface accelerations. Results are given as vertical gravity acceleration at the reference surface, geoid, vertical Bouguer, and vertical isostatic maps with errors for the vertical gravity and geoid maps included. Correlation of the gravity with topography for the different models is also discussed.

Inversion of marine gravity anomalies over southeastern China seas from multi-satellite altimeter vertical deflections

NASA Astrophysics Data System (ADS)

Zhang, Shengjun; Sandwell, David T.; Jin, Taoyong; Li, Dawei

2017-02-01

The accuracy and resolution of marine gravity field derived from satellite altimetry mainly depends on the range precision and dense spatial distribution. This paper aims at modeling a regional marine gravity field with improved accuracy and higher resolution (1‧ × 1‧) over Southeastern China Seas using additional data from CryoSat-2 as well as new data from AltiKa. Three approaches are used to enhance the precision level of satellite-derived gravity anomalies. Firstly we evaluate a suite of published retracking algorithms and find the two-step retracker is optimal for open ocean waveforms. Secondly, we evaluate the filtering and resampling procedure used to reduce the full 20 or 40 Hz data to a lower rate having lower noise. We adopt a uniform low-pass filter for all altimeter missions and resample at 5 Hz and then perform a second editing based on sea surface slope estimates from previous models. Thirdly, we selected WHU12 model to update the corrections provided in geophysical data record. We finally calculated the 1‧ × 1‧ marine gravity field model by using EGM2008 model as reference field during the remove/restore procedure. The root mean squares of the discrepancies between the new result and DTU10, DTU13, V23.1, EGM2008 are within the range of 1.8- 3.9 mGal, while the verification with respect to shipboard gravity data shows that the accuracy of the new result reached a comparable level with DTU13 and was slightly superior to V23.1, DTU10 and EGM2008 models. Moreover, the new result has a 2 mGal better accuracy over open seas than coastal areas with shallow water depth.

Development of Precise Lunar Orbit Propagator and Lunar Polar Orbiter's Lifetime Analysis

NASA Astrophysics Data System (ADS)

Song, Young-Joo; Park, Sang-Young; Kim, Hae-Dong; Sim, Eun-Sup

2010-06-01

To prepare for a Korean lunar orbiter mission, a precise lunar orbit propagator; Yonsei precise lunar orbit propagator (YSPLOP) is developed. In the propagator, accelerations due to the Moon's non-spherical gravity, the point masses of the Earth, Moon, Sun, Mars, Jupiter and also, solar radiation pressures can be included. The developed propagator's performance is validated and propagation errors between YSPOLP and STK/Astrogator are found to have about maximum 4-m, in along-track direction during 30 days (Earth's time) of propagation. Also, it is found that the lifetime of a lunar polar orbiter is strongly affected by the different degrees and orders of the lunar gravity model, by a third body's gravitational attractions (especially the Earth), and by the different orbital inclinations. The reliable lifetime of circular lunar polar orbiter at about 100 km altitude is estimated to have about 160 days (Earth's time). However, to estimate the reasonable lifetime of circular lunar polar orbiter at about 100 km altitude, it is strongly recommended to consider at least 50 × 50 degrees and orders of the lunar gravity field. The results provided in this paper are expected to make further progress in the design fields of Korea's lunar orbiter missions.

Radio-Frequency Illuminated Superconductive Disks: Reverse Josephson Effects and Implications for Precise Measuring of Proposed Gravity Effects

NASA Technical Reports Server (NTRS)

Noever, David A.; Koczor, Ronald J.

1998-01-01

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. It have been indicated three essential components to achieve anomalous gravity effects, namely large, two-layer high-temperature YBCO superconductors, magnetic levitation and AC input in the form of radio-frequency (RF) electromagnetic fields. We report experiments on RF-illuminated (1-15 MHz) superconducting disks with corresponding gravity readings indicating an apparent increase in observed gravity of approximately 3-5 x l0(exp -5)cm/sq s, above and to the side of the superconductor. In this preliminary study, RF- illumination is achieved using a series of large radius (15 cm) spiral antenna with RF power inputs equal to or greater than 90 W. The observed gravitational modification range is significantly lower than the 2.1% gravity modification. The error analyses of thermal and electromagnetic interference in a magnetically shielded gravimeter with vacuum enclosures, Faraday cages and shielded instrument leads, are outlined both experimentally and theoretically. The nearly exact correspondence between the peak gravity effects reported and the well-known peak in AC resistance in superconductors (2-7 MHz, owing to reverse Josephson quantum effects) suggests that electrical resistance will arise in this frequency range and subsequently any trapped magnetic fields in the superconductor may disperse partially into the measuring instrument's local environment. Implications for propulsion initiatives and RF-heating in superconductors will be discussed.

A SEA FLOOR GRAVITY SURVEY OF THE SLEIPNER FIELD TO MONITOR CO2 MIGATION

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

Mark Zumberge

2003-06-13

At the Sleipner gas field, excess CO{sub 2} is sequestered and injected underground into a porous saline aquifer 1000 m below the seafloor. A high precision micro-gravity survey was carried out on the seafloor to monitor the injected CO{sub 2}. A repeatability of 5 {micro}Gal in the station averages was observed. This is considerably better than pre-survey expectations. These data will serve as the baseline for time-lapse gravity monitoring of the Sleipner CO{sub 2} injection site. Simple modeling of the first year data give inconclusive results, thus a more detailed approach is needed. Work towards this is underway.

Orbit determination and gravity field recovery from Doppler tracking data to the Lunar Reconnaissance Orbiter

NASA Astrophysics Data System (ADS)

Maier, Andrea; Baur, Oliver

2016-03-01

We present results for Precise Orbit Determination (POD) of the Lunar Reconnaissance Orbiter (LRO) based on two-way Doppler range-rates over a time span of ~13 months (January 3, 2011 to February 9, 2012). Different orbital arc lengths and various sets of empirical parameters were tested to seek optimal parametrization. An overlap analysis covering three months of Doppler data shows that the most precise orbits are obtained using an arc length of 2.5 days and estimating arc-wise constant empirical accelerations in along track direction. The overlap analysis over the entire investigated time span of 13 months indicates an orbital precision of 13.79 m, 14.17 m, and 1.28 m in along track, cross track, and radial direction, respectively, with 21.32 m in total position. We compare our orbits to the official science orbits released by the US National Aeronautics and Space Administration (NASA). The differences amount to 9.50 m, 6.98 m, and 1.50 m in along track, cross track, and radial direction, respectively, as well as 12.71 m in total position. Based on the reconstructed LRO orbits, we estimated lunar gravity field coefficients up to spherical harmonic degree and order 60. The results are compared to gravity field solutions derived from data collected by other lunar missions.

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.

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.

Basic research and data analysis for the earth and ocean physics applications program and for the National Geodetic Satellite Program

NASA Technical Reports Server (NTRS)

1976-01-01

Data analysis and supporting research in connection with the following objectives are discussed: (1) provide a precise and accurate geometric description of the earth's surface, (2) provide a precise and accurate mathematical description of the earth's gravitational field, and (3) determine time variations of the geometry of the ocean surface, the solid earth, the gravity field and other geophysical parameters.

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.

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.

Constraining the interior density profile of a Jovian planet from precision gravity field data

NASA Astrophysics Data System (ADS)

Movshovitz, Naor; Fortney, Jonathan J.; Helled, Ravit; Hubbard, William B.; Thorngren, Daniel; Mankovich, Chris; Wahl, Sean; Militzer, Burkhard; Durante, Daniele

2017-10-01

The external gravity field of a planetary body is determined by the distribution of mass in its interior. Therefore, a measurement of the external field, properly interpreted, tells us about the interior density profile, ρ(r), which in turn can be used to constrain the composition in the interior and thereby learn about the formation mechanism of the planet. Planetary gravity fields are usually described by the coefficients in an expansion of the gravitational potential. Recently, high precision measurements of these coefficients for Jupiter and Saturn have been made by the radio science instruments on the Juno and Cassini spacecraft, respectively.The resulting coefficients come with an associated uncertainty. And while the task of matching a given density profile with a given set of gravity coefficients is relatively straightforward, the question of how best to account for the uncertainty is not. In essentially all prior work on matching models to gravity field data, inferences about planetary structure have rested on imperfect knowledge of the H/He equation of state and on the assumption of an adiabatic interior. Here we wish to vastly expand the phase space of such calculations. We present a framework for describing all the possible interior density structures of a Jovian planet, constrained only by a given set of gravity coefficients and their associated uncertainties. Our approach is statistical. We produce a random sample of ρ(a) curves drawn from the underlying (and unknown) probability distribution of all curves, where ρ is the density on an interior level surface with equatorial radius a. Since the resulting set of density curves is a random sample, that is, curves appear with frequency proportional to the likelihood of their being consistent with the measured gravity, we can compute probability distributions for any quantity that is a function of ρ, such as central pressure, oblateness, core mass and radius, etc. Our approach is also bayesian, in that it can utilize any prior assumptions about the planet's interior, as necessary, without being overly constrained by them.We demonstrate this approach with a sample of Jupiter interior models based on recent Juno data and discuss prospects for Saturn.

Action and entanglement in gravity and field theory.

PubMed

Neiman, Yasha

2013-12-27

In nongravitational quantum field theory, the entanglement entropy across a surface depends on the short-distance regularization. Quantum gravity should not require such regularization, and it has been conjectured that the entanglement entropy there is always given by the black hole entropy formula evaluated on the entangling surface. We show that these statements have precise classical counterparts at the level of the action. Specifically, we point out that the action can have a nonadditive imaginary part. In gravity, the latter is fixed by the black hole entropy formula, while in nongravitating theories it is arbitrary. From these classical facts, the entanglement entropy conjecture follows by heuristically applying the relation between actions and wave functions.

Constraining Saturn's interior density profile from precision gravity field measurement obtained during Grand Finale

NASA Astrophysics Data System (ADS)

Movshovitz, N.; Fortney, J. J.; Helled, R.; Hubbard, W. B.; Mankovich, C.; Thorngren, D.; Wahl, S. M.; Militzer, B.; Durante, D.

2017-12-01

The external gravity field of a planetary body is determined by the distribution of mass in its interior. Therefore, a measurement of the external field, properlyinterpreted, tells us about the interior density profile, ρ(r), which in turn can be used to constrain the composition in the interior and thereby learn about theformation mechanism of the planet. Recently, very high precision measurements of the gravity coefficients for Saturn have been made by the radio science instrument on the Cassini spacecraft during its Grand Finale orbits. The resulting coefficients come with an associated uncertainty. The task of matching a given density profile to a given set of gravity coefficients is relatively straightforward, but the question of how to best account for the uncertainty is not. In essentially all prior work on matching models to gravity field data inferences about planetary structure have rested on assumptions regarding the imperfectly known H/He equation of state and the assumption of an adiabatic interior. Here we wish to vastly expand the phase space of such calculations. We present a framework for describing all the possible interior density structures of a Jovian planet constrained by a given set of gravity coefficients and their associated uncertainties. Our approach is statistical. We produce a random sample of ρ(a) curves drawn from the underlying (and unknown) probability distribution of all curves, where ρ is the density on an interior level surface with equatorial radius a. Since the resulting set of density curves is a random sample, that is, curves appear with frequency proportional to the likelihood of their being consistent with the measured gravity, we can compute probability distributions for any quantity that is a function of ρ, such as central pressure, oblateness, core mass and radius, etc. Our approach is also Bayesian, in that it can utilize any prior assumptions about the planet's interior, as necessary, without being overly constrained by them. We apply this approach to produce a sample of Saturn interior models based on gravity data from Grand Finale orbits and discuss their implications.

Quantum Gravity in Everyday Life: General Relativity as an Effective Field Theory.

PubMed

Burgess, Cliff P

2004-01-01

This article is meant as a summary and introduction to the ideas of effective field theory as applied to gravitational systems, ideas which provide the theoretical foundations for the modern use of general relativity as a theory from which precise predictions are possible.

Motion and gravity effects in the precision of quantum clocks.

PubMed

Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

2015-05-19

We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.

Motion and gravity effects in the precision of quantum clocks

PubMed Central

Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

2015-01-01

We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions. PMID:25988238

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.

Initial conditions for cosmological N-body simulations of the scalar sector of theories of Newtonian, Relativistic and Modified Gravity

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

Valkenburg, Wessel; Hu, Bin, E-mail: valkenburg@lorentz.leidenuniv.nl, E-mail: hu@lorentz.leidenuniv.nl

2015-09-01

We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravitymore » outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.« less

Results from Radio Tracking the Rosetta Spacecraft: Gravity, Internal Structure and Nucleus Composition of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Hahn, M.; Andert, T.; Asmar, S.; Bird, M. K.; Häusler, B.; Peter, K.; Tellmann, S.; Weissman, P. R.; Barriot, J. P.; Sierks, H.

2017-12-01

When Rosetta arrived at its target comet 67P/Churyumov-Gerasimenko it first performed a series of distant flybys (100 - 30 km). During this mission phase the mass of the comets nucleus could be determined by analyzing the RSI radio tracking data. In combination with the volume from images of the OSIRIS camera this resulted in a precise bulk density determination. That already gave first insights into the comets interior structure. The nucleus appears to be a low-density, highly porous dusty body. From bound orbits with distances below 30 km the low degree and order gravity field coefficients could be derived. The gravity field coefficients strongly depend on the nucleus irregular shape and on the interior mass distribution. The shape is very well reconstructed from of the OSIRIS camera images. Various models of the interior nucleus structure and density distributions are used to compute simulated values of the gravity field coefficients. A comparison with the observed coefficients yields the feasibility of the theoretical interior structure. Thus, the gravity field helps constraining models of the internal structure, the composition and also of the origin and formation of the comets nucleus.

Basic research and data analysis for the National Geodetic Satellite Program and for the Earth and Ocean Physics Application Program

NASA Technical Reports Server (NTRS)

1974-01-01

Accomplishments in the continuing programs are reported. The data were obtained in support of the following broad objectives: (1) to provide a precise and accurate geometric description of the earth's surface; (2) to provide a precise and accurate mathematical description of the earth's gravitational field; and (3) to determine time variations of the geometry of the ocean surface, the solid earth, the gravity field, and other geophysical parameters.

The scheme of LLSST based on inter-satellite link for planet gravity field measurement in deep-space mission

NASA Astrophysics Data System (ADS)

Yang, Yikang; Li, Xue; Liu, Lei

2009-12-01

Gravity field measurement for the interested planets and their moos in solar system, such as Luna and Mars, is one important task in the next step of deep-space mission. In this paper, Similar to GRACE mission, LLSST and DOWR technology of common-orbit master-slave satellites around task planet is inherited in this scheme. Furthermore, by intersatellite 2-way UQPSK-DSSS link, time synchronization and data processing are implemented autonomously by masterslave satellites instead of GPS and ground facilities supporting system. Conclusion is derived that the ISL DOWR based on 2-way incoherent time synchronization has the same precise level to GRACE DOWR based on GPS time synchronization. Moreover, because of inter-satellite link, the proposed scheme is rather autonomous for gravity field measurement of the task planet in deep-space mission.

High Degree and Order Gravity Fields of the Moon Derived from GRAIL Data

NASA Technical Reports Server (NTRS)

Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Loomis, B. D.; Chinn, D. S.; Caprette, D. S.; McCarthy, J. J.;

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.

Impact of GNSS orbit modeling on LEO orbit and gravity field determination

NASA Astrophysics Data System (ADS)

Arnold, Daniel; Meyer, Ulrich; Sušnik, Andreja; Dach, Rolf; Jäggi, Adrian

2017-04-01

On January 4, 2015 the Center for Orbit Determination in Europe (CODE) changed the solar radiation pressure modeling for GNSS satellites to an updated version of the empirical CODE orbit model (ECOM). Furthermore, since September 2012 CODE operationally computes satellite clock corrections not only for the 3-day long-arc solutions, but also for the non-overlapping 1-day GNSS orbits. This provides different sets of GNSS products for Precise Point Positioning, as employed, e.g., in the GNSS-based precise orbit determination of low Earth orbiters (LEOs) and the subsequent Earth gravity field recovery from kinematic LEO orbits. While the impact of the mentioned changes in orbit modeling and solution strategy on the GNSS orbits and geophysical parameters was studied in detail, their implications on the LEO orbits were not yet analyzed. We discuss the impact of the update of the ECOM and the influence of 1-day and 3-day GNSS orbit solutions on zero-difference LEO orbit and gravity field determination, where the GNSS orbits and clock corrections, as well as the Earth rotation parameters are introduced as fixed external products. Several years of kinematic and reduced-dynamic orbits for the two GRACE LEOs are computed with GNSS products based on both the old and the updated ECOM, as well as with 1- and 3-day GNSS products. The GRACE orbits are compared by means of standard validation measures. Furthermore, monthly and long-term GPS-only and combined GPS/K-band gravity field solutions are derived from the different sets of kinematic LEO orbits. GPS-only fields are validated by comparison to combined GPS/K-band solutions, while the combined solutions are validated by analysis of the formal errors, as well as by comparing them to the combined GRACE solutions of the European Gravity Service for Improved Emergency Management (EGSIEM) project.

Global height datum unification: a new approach in gravity potential space

NASA Astrophysics Data System (ADS)

Ardalan, A. A.; Safari, A.

2005-12-01

The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W 0=62636855.8 m2/s2. According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.

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.

Earth's gravity field to the eighteenth degree and geocentric coordinates for 104 stations from satellite and terrestrial data

NASA Technical Reports Server (NTRS)

Gaposchkin, E. M.

1973-01-01

Geodetic parameters describing the earth's gravity field and the positions of satellite-tracking stations in a geocentric reference frame were computed. These parameters were estimated by means of a combination of five different types of data: routine and simultaneous satellite observations, observations of deep-space probes, measurements of terrestrial gravity, and surface-triangulation data. The combination gives better parameters than does any subset of data types. The dynamic solution used precision-reduced Baker-Nunn observations and laser range data of 25 satellites. Data from the 49-station National Oceanic and Atmospheric Administration BC-4 network, the 19-station Smithsonian Astrophysical Observatory Baker-Nunn network, and independent camera stations were employed in the geometrical solution. Data from the tracking of deep-space probes were converted to relative longitudes and distances to the earth's axis of rotation of the tracking stations. Surface-gravity data in the form of 550-km squares were derived from 19,328 1 deg X 1 deg mean gravity anomalies.

Discrete gravity on random tensor network and holographic Rényi entropy

NASA Astrophysics Data System (ADS)

Han, Muxin; Huang, Shilin

2017-11-01

In this paper we apply the discrete gravity and Regge calculus to tensor networks and Anti-de Sitter/conformal field theory (AdS/CFT) correspondence. We construct the boundary many-body quantum state |Ψ〉 using random tensor networks as the holographic mapping, applied to the Wheeler-deWitt wave function of bulk Euclidean discrete gravity in 3 dimensions. The entanglement Rényi entropy of |Ψ〉 is shown to holographically relate to the on-shell action of Einstein gravity on a branch cover bulk manifold. The resulting Rényi entropy S n of |Ψ〉 approximates with high precision the Rényi entropy of ground state in 2-dimensional conformal field theory (CFT). In particular it reproduces the correct n dependence. Our results develop the framework of realizing the AdS3/CFT2 correspondence on random tensor networks, and provide a new proposal to approximate the CFT ground state.

Gravity resonance spectroscopy constrains dark energy and dark matter scenarios.

PubMed

Jenke, T; Cronenberg, G; Burgdörfer, J; Chizhova, L A; Geltenbort, P; Ivanov, A N; Lauer, T; Lins, T; Rotter, S; Saul, H; Schmidt, U; Abele, H

2014-04-18

We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14  eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20  μm (95% C.L.).

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.

A Transportable Gravity Gradiometer Based on Atom Interferometry

NASA Technical Reports Server (NTRS)

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

2010-01-01

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

A historical review of gravimetric observations in Norway

NASA Astrophysics Data System (ADS)

Ragnvald Pettersen, Bjørn

2016-10-01

The first gravity determinations in Norway were made by Edward Sabine in 1823 with a pendulum instrument by Henry Kater. Seventy years later a Sterneck pendulum was acquired by the Norwegian Commission for the International Arc Measurements. It improved the precision and eventually reduced the bias of the absolute calibration from 85 to 15 mGal. The last pendulum observations in Norway were made in 1955 with an instrument from Cambridge University. At a precision of ±1 mGal, the purpose was to calibrate a section of the gravity line from Rome, Italy, to Hammerfest, Norway. Relative spring gravimeters were introduced in Norway in 1946 and were used to densify and expand the national gravity network. These data were used to produce regional geoids for Norway and adjacent ocean areas. Improved instrument precision allowed them to connect Norwegian and foreign fundamental stations as well. Extensive geophysical prospecting was made, as in other countries. The introduction of absolute gravimeters based on free-fall methods, especially after 2004, improved the calibration by 3 orders of magnitude and immediately revealed the secular changes of the gravity field in Norway. This was later confirmed by satellite gravimetry, which provides homogeneous data sets for global and regional gravity models. The first-ever determinations of gravity at sea were made by pendulum observations onboard the Norwegian polar vessel Fram during frozen-in conditions in the Arctic Ocean in 1893-1896. Simultaneously, an indirect method was developed at the University of Oslo for deducing gravity at sea with a hypsometer. The precision of both methods was greatly superseded by relative spring gravimeters 50 years later. They were employed extensively both at sea and on land. When GPS allowed precise positioning, relative gravimeters were mounted in airplanes to cover large areas of ocean faster than before. Gravimetry is currently being applied to study geodynamical phenomena relevant to climate change. The viscoelastic postglacial land uplift of Fennoscandia has been detected by terrestrial gravity time series as well as by satellite gravimetry. Corrections for local effects of snow load, hydrology, and ocean loading at coastal stations have been improved. The elastic adjustment of present-day melting of glaciers at Svalbard and in mainland Norway has been detected. Gravimetry is extensively employed at offshore oil facilities to monitor the subsidence of the ocean floor during oil and gas extraction.

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

Inter-satellite links: A versatile tool for geodesy and planetary and interplanetary navigation

NASA Astrophysics Data System (ADS)

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

2016-07-01

With the use of low-low satellite-to-satellite tracking gravity field recovery made a big step forward. Based on this technique the Gravity Recovery And Climate Experiment (GRACE) mission delivers monthly gravity field with high precision, allowing to measure effects in Earth water storage basins and variations in ice mass in Greenland and Antarctica from space. GRACE is using a Ka-band inter-satellite ranging technique, GRACE Follow-On will in addition test optical ranging. In fundamental physics high-precision optical inter-satellite tracking will be used to detect gravitational waves in space, as a first step LISA Pathfinder was launched recently. Inter-satellite links are not only used for ranging, also data transfer in space is based on such links. ESA's European Data Relay System will be established in up-coming years to collect data from the low orbiting Sentinel satellites and transfer the high data rate to ground. The same link may be used for ranging, data transfer and time transfer, a functionality that is discussed for next generation Galileo satellites. But to exploit this synergy a common concept for all three tasks has to be developed. In this paper we show that with inter-satellite ranging techniques with µm accuracy the limited accuracy of GNSS based orbit determination of low Earth orbiters (LEO), which is due to the limitations of one-way microwave tracking (unsynchronized clocks, phase center variations and offsets of the sending and receiving antennas) can be overcome. In the ESA study GETRIS the following question is answered: How can a highly accurate and precise GEO-based two-way ranging method support GNSS tracking? The reduction of systematic errors in LEO precise orbit determination (POD) by exploiting the synergy between ranging, data- and time-transfer is assessed in a concept consisting of precise two-way GEO-LEO tracking (as used for data transfer) and an ultra-stable oscillator on-board of the geostationary satellite (GEO) synchronized from ground. We now want to get a step further and design a versatile concept for the use of this synergy in a satellite constellation based on existing and future planned ESA infrastructure and highlight the benefits in different disciplines from geodesy to interplanetary ranging, with emphasis on gravity field recovery.

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

NASA Technical Reports Server (NTRS)

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

2016-01-01

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

Design of Superconducting Gravity Gradiometer Cryogenic System for Mars Mission

NASA Technical Reports Server (NTRS)

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

2016-01-01

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

27 CFR 30.25 - Use of precision specific gravity hydrometers.

Code of Federal Regulations, 2010 CFR

2010-04-01

... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest subdivision...

27 CFR 30.25 - Use of precision specific gravity hydrometers.

Code of Federal Regulations, 2012 CFR

2012-04-01

... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest subdivision...

27 CFR 30.25 - Use of precision specific gravity hydrometers.

Code of Federal Regulations, 2011 CFR

2011-04-01

... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest subdivision...

27 CFR 30.25 - Use of precision specific gravity hydrometers.

Code of Federal Regulations, 2013 CFR

2013-04-01

... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest subdivision...

27 CFR 30.25 - Use of precision specific gravity hydrometers.

Code of Federal Regulations, 2014 CFR

2014-04-01

... gravity hydrometers. 30.25 Section 30.25 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... precision specific gravity hydrometers. The provisions of § 30.23 respecting the care, handling, and use of... specific gravity hydrometers. Specific gravity hydrometers shall be read to the nearest subdivision...

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.

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.

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.

A new method for gravity field recovery based on frequency analysis of spherical harmonics

NASA Astrophysics Data System (ADS)

Cai, Lin; Zhou, Zebing

2017-04-01

All existing methods for gravity field recovery are mostly based on the space-wise and time-wise approach, whose core processes are constructing the observation equations and solving them by the least square method. It's should be pointed that the least square method means the approximation. On the other hand, we can directly and precisely obtain the coefficients of harmonics by computing the Fast Fourier Transform (FFT) when we do 1-D data (time series) analysis. So the question whether we directly and precisely obtain the coefficients of spherical harmonic by computing 2-D FFT of measurements of satellite gravity mission is of great significance, since this may guide us to a new understanding of the signal components of gravity field and make us determine it quickly by taking advantage of FFT. Like the 1-D data analysis, the 2-D FFT of measurements of satellite can be computed rapidly. If we can determine the relationship between spherical harmonics and 2-D Fourier frequencies and the transfer function from measurements to spherical coefficients, the question mentioned above can be solved. So the objective of this research project is to establish a new method based on frequency analysis of spherical harmonic, which directly compute the confidents of spherical harmonic of gravity field, which is differ from recovery by least squares. There is a one to one correspondence between frequency spectrum and the time series in 1-D FFT. The 2-D FFT has a similar relationship to 1-D FFT. Owing to the fact that any degree or order (higher than one) of spherical function has multi frequencies and these frequencies may be aliased. Fortunately, the elements and ratio of these frequencies of spherical function can be determined, and we can compute the coefficients of spherical function from 2-D FFT. This relationship can be written as equations and equivalent to a matrix, which is solid and can be derived in advance. Until now the relationship has be determined. Some preliminary results, which only compute lower degree spherical harmonics, indicates that the difference between the input (EGM2008) and output (coefficients from recovery) is smaller than 5E-17, while the minimal precision of computer software (Matlab) is 2.2204E-16.

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.

High Performance Clocks and Gravity Field Determination

NASA Astrophysics Data System (ADS)

Müller, J.; Dirkx, D.; Kopeikin, S. M.; Lion, G.; Panet, I.; Petit, G.; Visser, P. N. A. M.

2018-02-01

Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10^{-18}. This notable achievement along with the direct sensitivity of clocks to the strength of the gravitational field make them practically important for various geodetic applications that are addressed in the present paper. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of reference frames and time scales used in geodesy. We discuss the current definitions of basic geodetic concepts and come to the conclusion that the advances in clocks and other metrological technologies will soon require the re-definition of time scales or, at least, clarification to ensure their continuity and consistent use in practice. The relative frequency shift between two clocks is directly related to the difference in the values of the gravity potential at the points of clock's localization. According to general relativity the relative accuracy of clocks in 10^{-18} is equivalent to measuring the gravitational red shift effect between two clocks with the height difference amounting to 1 cm. This makes the clocks an indispensable tool in high-precision geodesy in addition to laser ranging and space geodetic techniques. We show how clock measurements can provide geopotential numbers for the realization of gravity-field-related height systems and can resolve discrepancies in classically-determined height systems as well as between national height systems. Another application of clocks is the direct use of observed potential differences for the improved recovery of regional gravity field solutions. Finally, clock measurements for space-borne gravimetry are analyzed along with closely-related deficiencies of this method like an extra-ordinary knowledge of the spacecraft velocity, etc. For all these applications besides the near-future prospects, we also discuss the challenges that are related to using those novel clock data in geodesy.

Hardware development for Gravity Probe-B

NASA Technical Reports Server (NTRS)

Bardas, D.; Cheung, W. S.; Gill, D.; Hacker, R.; Keiser, G. M.

1986-01-01

Gravity Probe-B (GP-B), also known as the Stanford Relativity Gyroscope Experiment, will test two fundamental predictions of Einstein's General Theory of Relativity by precise measurement of the precessions of nearly perfect gyroscopes in earth orbit. This endeavor embodies state-of-the-art technologies in many fields, including gyroscope fabrication and readout, cryogenics, superconductivity, magnetic shielding, precision optics and alignment methods, and satellite control systems. These technologies are necessary to enable measurement of the predicted precession rates to the milliarcsecond/year level, and to reduce to 'near zero' all non-General Relativistic torques on the gyroscopes. This paper provides a brief overview of the experiment followed by descriptions of several specific hardware items with highlights on progress to date and plans for future development and tests.

Grace-Fo satellites

NASA Image and Video Library

2017-11-09

The Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) mission is a partnership between NASA and the German Research Centre for Geosciences (GFZ). GRACE-FO is a successor to the original GRACE mission, which began orbiting Earth on March 17, 2002. GRACE-FO will carry on the extremely successful work of its predecessor while testing a new technology designed to dramatically improve the already remarkable precision of its measurement system. The GRACE missions measure variations in gravity over Earth's surface, producing a new map of the gravity field every 30 days. Thus, GRACE shows how the planet's gravity differs not only from one location to another, but also from one period of time to another. Airbus Defence and Space (Friedrichshafen/Germany) is the industrial prime contractor to build the satellites.

Shining light on modifications of gravity

NASA Astrophysics Data System (ADS)

Brax, Philippe; Burrage, Clare; Davis, Anne-Christine

2012-10-01

Many modifications of gravity introduce new scalar degrees of freedom, and in such theories matter fields typically couple to an effective metric that depends on both the true metric of spacetime and on the scalar field and its derivatives. Scalar field contributions to the effective metric can be classified as conformal and disformal. Disformal terms introduce gradient couplings between scalar fields and the energy momentum tensor of other matter fields, and cannot be constrained by fifth force experiments because the effects of these terms are trivial around static non-relativistic sources. The use of high-precision, low-energy photon experiments to search for conformally coupled scalar fields, called axion-like particles, is well known. In this article we show that these experiments are also constraining for disformal scalar field theories, and are particularly important because of the difficulty of constraining these couplings with other laboratory experiments.

Superconducting gravimeter

NASA Technical Reports Server (NTRS)

Goodkind, J. M.

1982-01-01

The superconducting gravimeter was developed and applied to field measurements. The stability of the instrument yielded the highest precision measurements of the Earth tides ever attained. It revealed unprecedented details about the effect of the atmosphere on gravity. Secular variations in gravity and the stability of the instruments were measured by comparing records from co-located instruments. These efforts have resulted in substantial reductions in the noise level at very low frequencies so that the peak differences between two instruments at the same location can be reduced to 0.1 micron gal.

Superconducting thin-film gyroscope readout for Gravity Probe-B

NASA Technical Reports Server (NTRS)

Lockhart, James M.; Cheung, W. Stephen; Gill, Dale K.

1987-01-01

The high-resolution gyroscope readout system for the Stanford Gravity Probe-B experiment, whose purpose is to measure two general relativistic precessions of gyroscopes in earth orbit, is described. In order to achieve the required resolution in angle (0.001 arcsec), the readout system combines high-precision mechanical fabrication and measurement techniques with superconducting thin-film technology, ultralow magnetic fields, and SQUID detectors. The system design, performance limits achievable with current technology, and the results of fabrication and laboratory testing to date are discussed.

Enhancement of subsurface geologic structure model based on gravity, magnetotelluric, and well log data in Kamojang geothermal field

NASA Astrophysics Data System (ADS)

Yustin Kamah, Muhammad; Armando, Adilla; Larasati Rahmani, Dinda; Paramitha, Shabrina

2017-12-01

Geophysical methods such as gravity and magnetotelluric methods commonly used in conventional and unconventional energy exploration, notably for exploring geothermal prospect. They used to identify the subsurface geology structures which is estimated as a path of fluid flow. This study was conducted in Kamojang Geothermal Field with the aim of highlighting the volcanic lineament in West Java, precisely in Guntur-Papandayan chain where there are three geothermal systems. Kendang Fault has predominant direction NE-SW, identified by magnetotelluric techniques and gravity data processing techniques. Gravity techniques such as spectral analysis, derivative solutions, and Euler deconvolution indicate the type and geometry of anomaly. Magnetotelluric techniques such as inverse modeling and polar diagram are required to know subsurface resistivity charactersitics and major orientation. Furthermore, the result from those methods will be compared to geology information and some section of well data, which is sufficiently suitable. This research is very useful to trace out another potential development area.

Potential fields & satellite missions: what they tell us about the Earth's core?

NASA Astrophysics Data System (ADS)

Mandea, M.; Panet, I.; Lesur, V.; de Viron, O.; Diament, M.; Le Mouël, J.

2012-12-01

Since the advent of satellite potential field missions, the search to find information they can carry about the Earth's core has been motivated both by an interest in understanding the structure of dynamics of the Earth's interior and by the possibility of applying new space data analysis. While it is agreed upon that the magnetic field measurements from space bring interesting information on the rapid variations of the core magnetic field and flows associated with, the question turns to whether the core process can have a signature in the space gravity data. Here, we tackle this question, in the light of the recent data from the GRACE mission, that reach an unprecedented precision. Our study is based on eight years of high-resolution, high-accuracy gravity and magnetic satellite data, provided by the GRACE and CHAMP satellite missions. From the GRACE CNES/GRGS geoid solutions, we have emphasized the long-term variability by using a specific post-processing technique. From the CHAMP magnetic data we have computed models for the core magnetic field and its temporal variations, and the flow at the top of the core. A correlation analysis between the gravity and magnetic gridded series indicates that the inter-annual changes in the core magnetic field - under a region from the Atlantic to Indian Oceans - coincide with similar changes in the gravity field. These results should be considered as a constituent when planning new Earth's observation space missions and future innovations relevant to both gravity (after GRACE Follow-On) and magnetic (after Swarm) missions.

Establishment of National Gravity Base Network of Iran

NASA Astrophysics Data System (ADS)

Hatam Chavari, Y.; Bayer, R.; Hinderer, J.; Ghazavi, K.; Sedighi, M.; Luck, B.; Djamour, Y.; Le Moign, N.; Saadat, R.; Cheraghi, H.

2009-04-01

A gravity base network is supposed to be a set of benchmarks uniformly distributed across the country and the absolute gravity values at the benchmarks are known to the best accessible accuracy. The gravity at the benchmark stations are either measured directly with absolute devices or transferred by gravity difference measurements by gravimeters from known stations. To decrease the accumulation of random measuring errors arising from these transfers, the number of base stations distributed across the country should be as small as possible. This is feasible if the stations are selected near to the national airports long distances apart but faster accessible and measurable by a gravimeter carried in an airplane between the stations. To realize the importance of such a network, various applications of a gravity base network are firstly reviewed. A gravity base network is the required reference frame for establishing 1st , 2nd and 3rd order gravity networks. Such a gravity network is used for the following purposes: a. Mapping of the structure of upper crust in geology maps. The required accuracy for the measured gravity values is about 0.2 to 0.4 mGal. b. Oil and mineral explorations. The required accuracy for the measured gravity values is about 5 µGal. c. Geotechnical studies in mining areas for exploring the underground cavities as well as archeological studies. The required accuracy is about 5 µGal and better. d. Subsurface water resource explorations and mapping crustal layers which absorb it. An accuracy of the same level of previous applications is required here too. e. Studying the tectonics of the Earth's crust. Repeated precise gravity measurements at the gravity network stations can assist us in identifying systematic height changes. The accuracy of the order of 5 µGal and more is required. f. Studying volcanoes and their evolution. Repeated precise gravity measurements at the gravity network stations can provide valuable information on the gradual upward movement of lava. g. Producing precise mean gravity anomaly for precise geoid determination. Replacing precise spirit leveling by the GPS leveling using precise geoid model is one of the forth coming application of the precise geoid. A gravity base network of 28 stations established over Iran. The stations were built mainly at bedrocks. All stations were measured by an FG5 absolute gravimeter, at least 12 hours at each station, to obtain an accuracy of a few micro gals. Several stations were repeated several times during recent years to estimate the gravity changes.

Parameterized post-Newtonian cosmology

NASA Astrophysics Data System (ADS)

Sanghai, Viraj A. A.; Clifton, Timothy

2017-03-01

Einstein’s theory of gravity has been extensively tested on solar system scales, and for isolated astrophysical systems, using the perturbative framework known as the parameterized post-Newtonian (PPN) formalism. This framework is designed for use in the weak-field and slow-motion limit of gravity, and can be used to constrain a large class of metric theories of gravity with data collected from the aforementioned systems. Given the potential of future surveys to probe cosmological scales to high precision, it is a topic of much contemporary interest to construct a similar framework to link Einstein’s theory of gravity and its alternatives to observations on cosmological scales. Our approach to this problem is to adapt and extend the existing PPN formalism for use in cosmology. We derive a set of equations that use the same parameters to consistently model both weak fields and cosmology. This allows us to parameterize a large class of modified theories of gravity and dark energy models on cosmological scales, using just four functions of time. These four functions can be directly linked to the background expansion of the universe, first-order cosmological perturbations, and the weak-field limit of the theory. They also reduce to the standard PPN parameters on solar system scales. We illustrate how dark energy models and scalar-tensor and vector-tensor theories of gravity fit into this framework, which we refer to as ‘parameterized post-Newtonian cosmology’ (PPNC).

Testing general relativity and alternative theories of gravity with space-based atomic clocks and atom interferometers

NASA Astrophysics Data System (ADS)

Bondarescu, Ruxandra; Schärer, Andreas; Jetzer, Philippe; Angélil, Raymond; Saha, Prasenjit; Lundgren, Andrew

2015-05-01

The successful miniaturisation of extremely accurate atomic clocks and atom interferometers invites prospects for satellite missions to perform precision experiments. We discuss the effects predicted by general relativity and alternative theories of gravity that can be detected by a clock, which orbits the Earth. Our experiment relies on the precise tracking of the spacecraft using its observed tick-rate. The spacecraft's reconstructed four-dimensional trajectory will reveal the nature of gravitational perturbations in Earth's gravitational field, potentially differentiating between different theories of gravity. This mission can measure multiple relativistic effects all during the course of a single experiment, and constrain the Parametrized Post-Newtonian Parameters around the Earth. A satellite carrying a clock of fractional timing inaccuracy of Δ f / f ˜ 10-16 in an elliptic orbit around the Earth would constrain the PPN parameters |β - 1|, |γ - 1| ≲ 10-6. We also briefly review potential constraints by atom interferometers on scalar tensor theories and in particular on Chameleon and dilaton models.

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.

Simulation of the Chang'E-5 mission contribution in lunar long wavelength gravity field improvement

NASA Astrophysics Data System (ADS)

Yan, Jianguo; Yang, Xuan; Ping, Jinsong; Ye, Mao; Liu, Shanhong; Jin, Weitong; Li, Fei; Barriot, Jean-Pierre

2018-06-01

The precision of lunar gravity field estimation has improved by means of three to five orders of magnitude since the successful GRAIL lunar mission. There are still discrepancies however, in the low degree coefficients and long wavelength components of the solutions developed by two space research centers (JPL and GSFC). These discrepancies hint at the possibilities for improving the accuracy in the long wavelength part of the lunar gravity field. In the near future, China will launch the Chang'E-5 lunar mission. In this sample-return mission, there will be a chance to do KBRR measurements between an ascending module and an orbiting module. These two modules will fly around lunar at an inclination of ˜49 degrees, with an orbital height of 100 km and an inter-satellite distance of 200 km. In our research, we simulated the contribution of the KBRR tracking mode for different GRAIL orbital geometries. This analysis indicated possible deficiencies in the low degree coefficient solutions for the polar satellite-to-satellite tracking mode at various orbital heights. We also investigated the potential contributions of the KBRR to the Chang'E-5 mission goal of lunar gravity field recovery, especially in the long wavelength component. Potential improvements were assessed using various power spectrums of the lunar gravity field models. In addition, we also investigated possible improvements in solving lunar tidal Love number K2. These results may assist the implementation of the Chang'E-5 mission.

Electrostatic analogy for symmetron gravity

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

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

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

GRACE-FO Spacecraft Artist Rendering

NASA Image and Video Library

2017-05-04

This artist's rendering shows the twin spacecraft of the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, a partnership between NASA and the German Research Centre for Geosciences (GFZ). GRACE-FO is a successor to the original GRACE mission, which began orbiting Earth on March 17, 2002. GRACE-FO will carry on the extremely successful work of its predecessor while testing a new technology designed to dramatically improve the already remarkable precision of its measurement system. The GRACE missions measure variations in gravity over Earth's surface, producing a new map of the gravity field every 30 days. Thus, GRACE shows how the planet's gravity differs not only from one location to another, but also from one period of time to another. https://photojournal.jpl.nasa.gov/catalog/PIA21607

Large scale mass redistribution and surface displacement from GRACE and SLR

NASA Astrophysics Data System (ADS)

Cheng, M.; Ries, J. C.; Tapley, B. D.

2012-12-01

Mass transport between the atmosphere, ocean and solid earth results in the temporal variations in the Earth gravity field and loading induced deformation of the Earth. Recent space-borne observations, such as GRACE mission, are providing extremely high precision temporal variations of gravity field. The results from 10-yr GRACE data has shown a significant annual variations of large scale vertical and horizontal displacements occurring over the Amazon, Himalayan region and South Asia, African, and Russian with a few mm amplitude. Improving understanding from monitoring and modeling of the large scale mass redistribution and the Earth's response are a critical for all studies in the geosciences, in particular for determination of Terrestrial Reference System (TRS), including geocenter motion. This paper will report results for the observed seasonal variations in the 3-dimentional surface displacements of SLR and GPS tracking stations and compare with the prediction from time series of GRACE monthly gravity solution.

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.

Improved artificial bee colony algorithm based gravity matching navigation method.

PubMed

Gao, Wei; Zhao, Bo; Zhou, Guang Tao; Wang, Qiu Ying; Yu, Chun Yang

2014-07-18

Gravity matching navigation algorithm is one of the key technologies for gravity aided inertial navigation systems. With the development of intelligent algorithms, the powerful search ability of the Artificial Bee Colony (ABC) algorithm makes it possible to be applied to the gravity matching navigation field. However, existing search mechanisms of basic ABC algorithms cannot meet the need for high accuracy in gravity aided navigation. Firstly, proper modifications are proposed to improve the performance of the basic ABC algorithm. Secondly, a new search mechanism is presented in this paper which is based on an improved ABC algorithm using external speed information. At last, modified Hausdorff distance is introduced to screen the possible matching results. Both simulations and ocean experiments verify the feasibility of the method, and results show that the matching rate of the method is high enough to obtain a precise matching position.

Improved Artificial Bee Colony Algorithm Based Gravity Matching Navigation Method

PubMed Central

Gao, Wei; Zhao, Bo; Zhou, Guang Tao; Wang, Qiu Ying; Yu, Chun Yang

2014-01-01

Gravity matching navigation algorithm is one of the key technologies for gravity aided inertial navigation systems. With the development of intelligent algorithms, the powerful search ability of the Artificial Bee Colony (ABC) algorithm makes it possible to be applied to the gravity matching navigation field. However, existing search mechanisms of basic ABC algorithms cannot meet the need for high accuracy in gravity aided navigation. Firstly, proper modifications are proposed to improve the performance of the basic ABC algorithm. Secondly, a new search mechanism is presented in this paper which is based on an improved ABC algorithm using external speed information. At last, modified Hausdorff distance is introduced to screen the possible matching results. Both simulations and ocean experiments verify the feasibility of the method, and results show that the matching rate of the method is high enough to obtain a precise matching position. PMID:25046019

Numerical binary black hole mergers in dynamical Chern-Simons gravity: Scalar field

NASA Astrophysics Data System (ADS)

Okounkova, Maria; Stein, Leo C.; Scheel, Mark A.; Hemberger, Daniel A.

2017-08-01

Testing general relativity in the nonlinear, dynamical, strong-field regime of gravity is one of the major goals of gravitational wave astrophysics. Performing precision tests of general relativity (GR) requires numerical inspiral, merger, and ringdown waveforms for binary black hole (BBH) systems in theories beyond GR. Currently, GR and scalar-tensor gravity are the only theories amenable to numerical simulations. In this article, we present a well-posed perturbation scheme for numerically integrating beyond-GR theories that have a continuous limit to GR. We demonstrate this scheme by simulating BBH mergers in dynamical Chern-Simons gravity (dCS), to linear order in the perturbation parameter. We present mode waveforms and energy fluxes of the dCS pseudoscalar field from our numerical simulations. We find good agreement with analytic predictions at early times, including the absence of pseudoscalar dipole radiation. We discover new phenomenology only accessible through numerics: a burst of dipole radiation during merger. We also quantify the self-consistency of the perturbation scheme. Finally, we estimate bounds that GR-consistent LIGO detections could place on the new dCS length scale, approximately ℓ≲O (10 ) km .

Accounting for time- and space-varying changes in the gravity field to improve the network adjustment of relative-gravity data

USGS Publications Warehouse

Kennedy, Jeffrey R.; Ferre, Ty P.A.

2015-01-01

The relative gravimeter is the primary terrestrial instrument for measuring spatially and temporally varying gravitational fields. The background noise of the instrument—that is, non-linear drift and random tares—typically requires some form of least-squares network adjustment to integrate data collected during a campaign that may take several days to weeks. Here, we present an approach to remove the change in the observed relative-gravity differences caused by hydrologic or other transient processes during a single campaign, so that the adjusted gravity values can be referenced to a single epoch. The conceptual approach is an example of coupled hydrogeophysical inversion, by which a hydrologic model is used to inform and constrain the geophysical forward model. The hydrologic model simulates the spatial variation of the rate of change of gravity as either a linear function of distance from an infiltration source, or using a 3-D numerical groundwater model. The linear function can be included in and solved for as part of the network adjustment. Alternatively, the groundwater model is used to predict the change of gravity at each station through time, from which the accumulated gravity change is calculated and removed from the data prior to the network adjustment. Data from a field experiment conducted at an artificial-recharge facility are used to verify our approach. Maximum gravity change due to hydrology (observed using a superconducting gravimeter) during the relative-gravity field campaigns was up to 2.6 μGal d−1, each campaign was between 4 and 6 d and one month elapsed between campaigns. The maximum absolute difference in the estimated gravity change between two campaigns, two months apart, using the standard network adjustment method and the new approach, was 5.5 μGal. The maximum gravity change between the same two campaigns was 148 μGal, and spatial variation in gravity change revealed zones of preferential infiltration and areas of relatively high groundwater storage. The accommodation for spatially varying gravity change would be most important for long-duration campaigns, campaigns with very rapid changes in gravity and (or) campaigns where especially precise observed relative-gravity differences are used in the network adjustment.

The prospects of pulsar timing with new-generation radio telescopes and the Square Kilometre Array

NASA Astrophysics Data System (ADS)

Stappers, B. W.; Keane, E. F.; Kramer, M.; Possenti, A.; Stairs, I. H.

2018-05-01

Pulsars are highly magnetized and rapidly rotating neutron stars. As they spin, the lighthouse-like beam of radio emission from their magnetic poles sweeps across the Earth with a regularity approaching that of the most precise clocks known. This precision combined with the extreme environments in which they are found, often in compact orbits with other neutron stars and white dwarfs, makes them excellent tools for studying gravity. Present and near-future pulsar surveys, especially those using the new generation of telescopes, will find more extreme binary systems and pulsars that are more precise `clocks'. These telescopes will also greatly improve the precision to which we can measure the arrival times of the pulses. The Square Kilometre Array will revolutionize pulsar searches and timing precision. The increased number of sources will reveal rare sources, including possibly a pulsar-black hole binary, which can provide the most stringent tests of strong-field gravity. The improved timing precision will reveal new phenomena and also allow us to make a detection of gravitational waves in the nanohertz frequency regime. It is here where we expect to see the signature of the binary black holes that are formed as galaxies merge throughout cosmological history. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

GOCE SSTI GNSS Receiver Re-Entry Phase Analysis

NASA Astrophysics Data System (ADS)

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

2015-03-01

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

CHAMP and GRACE Resonances and the Gravity Field of the Earth

NASA Astrophysics Data System (ADS)

Gooding, R. H.; Wagner, C. A.; Klokocnik, J.; Kostelecky, J.

With the far more precise orbits of CHAMP and GRACE today than was the standard 2-3 decades ago there was and is an unprecedented opportunity for determining precise and valuable values of certain lumped geopotential harmonic coefficients of selected orders independently of comprehensive gravity field models via the recently revived technique that capitalizes on the resonant variation of appropriate orbital elements the inclination in particular Here we first identify important resonances during the lifetime of CHAMP and GRACE in terms of the decaying semimajor axis these being 46 3 77 5 31 2 78 5 and 47 3 for CHAMP and 61 4 for GRACE Then we analyze state vectors for CHAMP and TLE for GRACE A from GFZ and determined the relevant lumped coefficients To increase its lifetime the CHAMP satellite orbit was raised twice in June and December 2002 so CHAMP passed through 31 2 resonance three times More accurate values for these coefficients are obtained than originally and the precision for the 62 4 overtone resonance implicit in 31 2 is striking comparable to that for 31 2 Most recently CHAMP passed throughout the 47 3 resonance yielding the opportunity to determine new lumped coefficients For GRACE we have no state vectors and have to work with the TLE only nevertheless we have lumped coefficients of 61st order from its strong 61 4 resonance In each case the resonant lumped values are compared with those derivable from various global gravity models We thereby confirm the continuing power of the resonance technique

Validity of the "Laplace Swindle" in Calculation of Giant-Planet Gravity Fields

NASA Astrophysics Data System (ADS)

Hubbard, William B.

2014-11-01

Jupiter and Saturn have large rotation-induced distortions, providing an opportunity to constrain interior structure via precise measurement of external gravity. Anticipated high-precision gravity measurements close to the surfaces of Jupiter (Juno spacecraft) and Saturn (Cassini spacecraft), possibly detecting zonal harmonics to J10 and beyond, will place unprecedented requirements on gravitational modeling via the theory of figures (TOF). It is not widely appreciated that the traditional TOF employs a formally nonconvergent expansion attributed to Laplace. This suspect expansion is intimately related to the standard zonal harmonic (J-coefficient) expansion of the external gravity potential. It can be shown (Hubbard, Schubert, Kong, and Zhang: Icarus, in press) that both Jupiter and Saturn are in the domain where Laplace's "swindle" works exactly, or at least as well as necessary. More highly-distorted objects such as rapidly spinning asteroids may not be in this domain, however. I present a numerical test for the validity and precision of TOF via polar "audit points". I extend the audit-point test to objects rotating differentially on cylinders, obtaining zonal harmonics to J20 and beyond. Models with only low-order differential rotation do not exhibit dramatic effects in the shape of the zonal harmonic spectrum. However, a model with Jupiter-like zonal winds exhibits a break in the zonal harmonic spectrum above about J10, and generally follows the more shallow Kaula power rule at higher orders. This confirms an earlier result obtained by a different method (Hubbard: Icarus 137, 357-359, 1999).

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.

Extent of Continental Crust Thickening Derived From Gravity Profile Leading From Aden Towards the Dhala Plateau in the Yemen Trap Series

NASA Astrophysics Data System (ADS)

Blecha, V.

2003-12-01

Gravity profile trends NNW from Aden and terminates at the Dhala plateau formed by Tertiary volcanics often referred to as the Yemen Trap Series. The length of profile is 120 km. Profile consists of 366 gravity stations with average distance of 300 m between stations. The mean square error of Bouguer anomalies is 0.06 mGal. This final error includes errors of gravity and altitude measurements and error in terrain corrections. Altitudes along profile are ranging from 0 m a.s.l. in the south to 1400 m a.s.l. at the northern side of profile. In the central part of the Gulf of Aden occurs juvenile oceanic crust. Stretched continental crust is assumed on the coast. Regional gravity field decreases from +38 mGal on the coast in Aden to -126 mGal at mountains of the Dhala plateau. According to gravity modeling the decrease of 164 mGal in gravity is caused by 8 km continental crust thickening over the distance of 120 km. Regional gravity field is accompanied by local anomalies with amplitudes of tens of mGal. Sources of local anomalies are from S to N: coastal sediments (negative), Tertiary intrusions and volcanics within the Dhala graben (positive), Mesozoic sediments (negative) and Tertiary volcanics of the Dhala plateau (positive). Gravity profile is most detailed and most precise regional gravity measurement carried out in the southern tip of Arabia and brings new information about geology of the area with scarce geophysical data.

Geophysical observations of Kilauea volcano, Hawaii, 1. temporal gravity variations related to the 29 November, 1975, M = 7.2 earthquake and associated summit collapse

USGS Publications Warehouse

Jachens, R.C.; Eaton, G.P.

1980-01-01

Repeated high-precision gravity measurements made near the summit of Kilauea volcano, Hawaii, have revealed systematic temporal variations in the gravity field associated with a major deflation of the volcano that followed the 29 November, 1975, earthquake and eruption. Changes in the gravity field with respect to a stable reference station on the south flank of neighboring Mauna Loa volcano were measured at 18 sites in the summit region of Kilauea and at 4 sites far removed from its summit. The original survey, conducted 10-23 November, 1975, was repeated during a two-week period after the earthquake. The results indicate that sometime between the first survey and the latter part of the second survey the gravity field at sites near the summit increased with respect to that at sites far removed from the summit. The pattern of gravity increase is essentially radially symmetrical, with a half-width slightly less than 3 km, about the point of maximum change 1.5 km southeast of Halemaumau pit crater. Gravity changes at sites near the summit correlate closely with elevation decreases that occurred sometime between leveling surveys conducted in late September 1975 and early January 1976. The systematic relation between gravity and elevation change (-1.71 ?? 0.05 (s.e.) ??gal/cm) shows that deflation was accompanied by a loss of mass from beneath the summit region. Mass balance calculations indicate that for all reasonable magma densities, the volume of magma withdrawn from beneath the summit region exceeded the volume of summit collapse. Analysis suggests that magma drained from at least two distinct areas south of Kilauea caldera that coincide roughly with two reservoir areas active during inflation before the 1967-1968 Kilauea eruption. ?? 1980.

Improvements in absolute seismometer sensitivity calibration using local earth gravity measurements

USGS Publications Warehouse

Anthony, Robert E.; Ringler, Adam; Wilson, David

2018-01-01

The ability to determine both absolute and relative seismic amplitudes is fundamentally limited by the accuracy and precision with which scientists are able to calibrate seismometer sensitivities and characterize their response. Currently, across the Global Seismic Network (GSN), errors in midband sensitivity exceed 3% at the 95% confidence interval and are the least‐constrained response parameter in seismic recording systems. We explore a new methodology utilizing precise absolute Earth gravity measurements to determine the midband sensitivity of seismic instruments. We first determine the absolute sensitivity of Kinemetrics EpiSensor accelerometers to 0.06% at the 99% confidence interval by inverting them in a known gravity field at the Albuquerque Seismological Laboratory (ASL). After the accelerometer is calibrated, we install it in its normal configuration next to broadband seismometers and subject the sensors to identical ground motions to perform relative calibrations of the broadband sensors. Using this technique, we are able to determine the absolute midband sensitivity of the vertical components of Nanometrics Trillium Compact seismometers to within 0.11% and Streckeisen STS‐2 seismometers to within 0.14% at the 99% confidence interval. The technique enables absolute calibrations from first principles that are traceable to National Institute of Standards and Technology (NIST) measurements while providing nearly an order of magnitude more precision than step‐table calibrations.

Gauge-invariant flow equation

NASA Astrophysics Data System (ADS)

Wetterich, C.

2018-06-01

We propose a closed gauge-invariant functional flow equation for Yang-Mills theories and quantum gravity that only involves one macroscopic gauge field or metric. It is based on a projection on physical and gauge fluctuations. Deriving this equation from a functional integral we employ the freedom in the precise choice of the macroscopic field and the effective average action in order to realize a closed and simple form of the flow equation.

Satellite Laser Ranging operations

NASA Technical Reports Server (NTRS)

Pearlman, Michael R.

1994-01-01

Satellite Laser Ranging (SLR) is currently providing precision orbit determination for measurements of: 1) Ocean surface topography from satellite borne radar altimetry, 2) Spatial and temporal variations of the gravity field, 3) Earth and ocean tides, 4) Plate tectonic and regional deformation, 5) Post-glacial uplift and subsidence, 6) Variations in the Earth's center-of-mass, and 7) Variations in Earth rotation. SLR also supports specialized programs in time transfer and classical geodetic positioning, and will soon provide precision ranging to support experiments in relativity.

Mapping experiment with space station

NASA Technical Reports Server (NTRS)

Wu, S. S. C.

1986-01-01

Mapping of the Earth from space stations can be approached in two areas. One is to collect gravity data for defining topographic datum using Earth's gravity field in terms of spherical harmonics. The other is to search and explore techniques of mapping topography using either optical or radar images with or without reference to ground central points. Without ground control points, an integrated camera system can be designed. With ground control points, the position of the space station (camera station) can be precisely determined at any instant. Therefore, terrestrial topography can be precisely mapped either by conventional photogrammetric methods or by current digital technology of image correlation. For the mapping experiment, it is proposed to establish four ground points either in North America or Africa (including the Sahara desert). If this experiment should be successfully accomplished, it may also be applied to the defense charting systems.

Using High-Precision Specific Gravity Measurements to Study Minerals in Undergraduate Geoscience Courses

ERIC Educational Resources Information Center

Brandriss, Mark E.

2010-01-01

This article describes ways to incorporate high-precision measurements of the specific gravities of minerals into undergraduate courses in mineralogy and physical geology. Most traditional undergraduate laboratory methods of measuring specific gravity are suitable only for unusually large samples, which severely limits their usefulness for student…

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.

Mapping the absolute magnetic field and evaluating the quadratic Zeeman-effect-induced systematic error in an atom interferometer gravimeter

NASA Astrophysics Data System (ADS)

Hu, Qing-Qing; Freier, Christian; Leykauf, Bastian; Schkolnik, Vladimir; Yang, Jun; Krutzik, Markus; Peters, Achim

2017-09-01

Precisely evaluating the systematic error induced by the quadratic Zeeman effect is important for developing atom interferometer gravimeters aiming at an accuracy in the μ Gal regime (1 μ Gal =10-8m /s2 ≈10-9g ). This paper reports on the experimental investigation of Raman spectroscopy-based magnetic field measurements and the evaluation of the systematic error in the gravimetric atom interferometer (GAIN) due to quadratic Zeeman effect. We discuss Raman duration and frequency step-size-dependent magnetic field measurement uncertainty, present vector light shift and tensor light shift induced magnetic field measurement offset, and map the absolute magnetic field inside the interferometer chamber of GAIN with an uncertainty of 0.72 nT and a spatial resolution of 12.8 mm. We evaluate the quadratic Zeeman-effect-induced gravity measurement error in GAIN as 2.04 μ Gal . The methods shown in this paper are important for precisely mapping the absolute magnetic field in vacuum and reducing the quadratic Zeeman-effect-induced systematic error in Raman transition-based precision measurements, such as atomic interferometer gravimeters.

The gravity field and orientation of Mercury after the MESSENGER mission

NASA Astrophysics Data System (ADS)

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

2015-12-01

After more than four years in orbit about Mercury, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the planet's surface north of Shakespeare crater (54.44° N, 210.12° E,) on 30 April 2015. One of the main goals of the mission was to determine the gravity field of Mercury in order to learn about Mercury's interior. Together with ground-based radar measurements of the obliquity and forced librations, MESSENGER-derived gravity models helped revise models of Mercury's interior. Nevertheless, the refinement of Mercury's orientation with the latest data from MESSENGER can further improve the interior modeling of the planet. The last eight months of the mission provided a special opportunity to conduct low-altitude measurements, with extensive radio tracking coverage below 200 km altitude north of ~30°N. MESSENGER's Mercury Laser Altimeter (MLA) mapped the topography of Mercury's northern hemisphere with a sub-meter vertical precision, an along-track sampling of ~500 m, and a longitudinal resolution (~0.1°) limited by the number of spacecraft orbits (~4,000). The combination of gravity and topography helps determine crustal thickness and interior properties. Altimetric ranges provide geodetic constraints to improve the spacecraft orbit determination, and thus the gravity field model. In particular, whereas the MESSENGER spacecraft was not tracked at each periapsis passage, MLA operated nearly continuously (outside of thermally challenging periods). From an analysis of the entire radiometric and altimetric datasets acquired by MESSENGER, a new gravity field to degree and order 100 has been obtained, resolving features down to ~75 km horizontal scale. The altimetric data help reduce the uncertainties in the determination of the pole position. A reanalysis of the Mercury flybys also constrains the spin rate over the longest available time span.

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

Kalaydzhyan, Tigran

Within the general theory of relativity, the curvature of spacetime is related to the energy and momentum of the present matter and radiation. One of the more specific predictions of general relativity is the deflection of light and particle trajectories in the gravitational field of massive objects. Bending angles for electromagnetic waves and light in particular were measured with a high precision. However, the effect of gravity on relativistic massive particles was never studied experimentally. Here we propose and analyze experiments devoted to that purpose. We demonstrate a high sensitivity of the laser Compton scattering at high energy accelerators tomore » the effects of gravity. The main observable – maximal energy of the scattered photons – would experience a significant shift in the ambient gravitational field even for otherwise negligible violation of the equivalence principle. In conclusion, we confirm predictions of general relativity for ultrarelativistic electrons of energy of tens of GeV at a current level of resolution and expect our work to be a starting point of further high-precision studies on current and future accelerators, such as PETRA, European XFEL and ILC.« less

Testing general relativity on accelerators

DOE PAGES

Kalaydzhyan, Tigran

2015-09-07

Within the general theory of relativity, the curvature of spacetime is related to the energy and momentum of the present matter and radiation. One of the more specific predictions of general relativity is the deflection of light and particle trajectories in the gravitational field of massive objects. Bending angles for electromagnetic waves and light in particular were measured with a high precision. However, the effect of gravity on relativistic massive particles was never studied experimentally. Here we propose and analyze experiments devoted to that purpose. We demonstrate a high sensitivity of the laser Compton scattering at high energy accelerators tomore » the effects of gravity. The main observable – maximal energy of the scattered photons – would experience a significant shift in the ambient gravitational field even for otherwise negligible violation of the equivalence principle. In conclusion, we confirm predictions of general relativity for ultrarelativistic electrons of energy of tens of GeV at a current level of resolution and expect our work to be a starting point of further high-precision studies on current and future accelerators, such as PETRA, European XFEL and ILC.« less

Bragg gravity-gradiometer using the 1S0–3P1 intercombination transition of 88Sr

NASA Astrophysics Data System (ADS)

del Aguila, R. P.; Mazzoni, T.; Hu, L.; Salvi, L.; Tino, G. M.; Poli, N.

2018-04-01

We present a gradiometer based on matter-wave interference of alkaline-earth-metal atoms, namely 88Sr. The coherent manipulation of the atomic external degrees of freedom is obtained by large-momentum-transfer Bragg diffraction, driven by laser fields detuned away from the narrow 1S0–3P1 intercombination transition. We use a well-controlled artificial gradient, realized by changing the relative frequencies of the Bragg pulses during the interferometer sequence, in order to characterize the sensitivity of the gradiometer. The sensitivity reaches 1.5 × 10‑5 s‑2 for an interferometer time of 20 ms, limited only by geometrical constraints. We observed extremely low sensitivity of the gradiometric phase to magnetic field gradients, approaching a value 104 times lower than the sensitivity of alkali-atom based gradiometers, limited by the interferometer sensitivity. An efficient double-launch technique employing accelerated red vertical lattices from a single magneto-optical trap cloud is also demonstrated. These results highlight strontium as an ideal candidate for precision measurements of gravity gradients, with potential application in future precision tests of fundamental physics.

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

Detecting chameleons through Casimir force measurements

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

Brax, Philippe; Bruck, Carsten van de; Davis, Anne-Christine

2007-12-15

The best laboratory constraints on strongly coupled chameleon fields come not from tests of gravity per se but from precision measurements of the Casimir force. The chameleonic force between two nearby bodies is more akin to a Casimir-like force than a gravitational one: The chameleon force behaves as an inverse power of the distance of separation between the surfaces of two bodies, just as the Casimir force does. Additionally, experimental tests of gravity often employ a thin metallic sheet to shield electrostatic forces; however, this sheet masks any detectable signal due to the presence of a strongly coupled chameleon field.more » As a result of this shielding, experiments that are designed to specifically test the behavior of gravity are often unable to place any constraint on chameleon fields with a strong coupling to matter. Casimir force measurements do not employ a physical electrostatic shield and as such are able to put tighter constraints on the properties of chameleons fields with a strong matter coupling than tests of gravity. Motivated by this, we perform a full investigation on the possibility of testing chameleon models with both present and future Casimir experiments. We find that present-day measurements are not able to detect the chameleon. However, future experiments have a strong possibility of detecting or rule out a whole class of chameleon models.« less

Landscape-scale water balance monitoring with an iGrav superconducting gravimeter in a field enclosure

NASA Astrophysics Data System (ADS)

Güntner, Andreas; Reich, Marvin; Mikolaj, Michal; Creutzfeldt, Benjamin; Schroeder, Stephan; Wziontek, Hartmut

2017-04-01

In spite of the fundamental role of the landscape water balance for the Earth's water and energy cycles, monitoring the water balance and its components beyond the point scale is notoriously difficult due to the multitude of flow and storage processes and their spatial heterogeneity. Here, we present the first deployment of an iGrav superconducting gravimeter (SG) in a minimized field enclosure on a grassland site for integrative monitoring of water storage changes. Results of the field SG were compared to data provided by a nearby SG located in the controlled environment of an observatory building. For wet-temperate climate conditions, the system proves to provide gravity time series that are similarly precise as those of the observatory SG. At the same time, the field SG is more sensitive to hydrological variations than the observatory SG. We demonstrate that the gravity variations observed by the field setup are almost independent of the depth below the terrain surface where water storage changes occur (contrary to SGs in buildings), and thus the field SG system directly observes the total water storage change, i.e., the water balance, in its surroundings in an integrative way. We provide a framework to single out the water balance components actual evapotranspiration and lateral subsurface discharge from the gravity time series on annual to daily time scales. With about 99% and 85% of the gravity signal originating within a radius of 4000 and 200 meter around the instrument, respectively, this setup paves the road towards gravimetry as a continuous hydrological field monitoring technique at the landscape scale.

Development of the lunar gravity field model GrazLGM300b in the framework of project GRAZIL

NASA Astrophysics Data System (ADS)

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

2015-04-01

The objective of project GRAZIL is to compile a high-accurate gravity field model of the Moon based on measurements provided by the Gravity Recovery And Interior Laboratory (GRAIL) mission. In order to reach this goal we perform dynamic precise orbit determination from radio science observations (Doppler range-rates) in combination with the analysis of inter-satellite ranging observations. We present an updated version of the lunar gravity field models GrazLGM200a (Klinger et al. 2014; doi: 10.1016/j.pss.2013.12.001) and GrazLGM300a (prepared for the 2014 AGU Fall Meeting) derived from inter-satellite Ka-band ranging (KBR) observations collected by GRAIL during the primary mission phase (March 1 to May 29, 2012). We exploit the KBR data by an integral equation approach using short orbital arcs. The basic idea behind this technique is to reformulate Newton's equation of motion as a boundary value problem. In this contribution particular attention is paid to processing details associated with the error structure of the observations and the incorporation of non-gravitational accelerations (with emphasis on solar radiation pressure, lunar albedo and self-shadowing). We validate our results against recent GRAIL models computed at NASA-GSFC and NASA-JPL.

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.

The prospects of pulsar timing with new-generation radio telescopes and the Square Kilometre Array.

PubMed

Stappers, B W; Keane, E F; Kramer, M; Possenti, A; Stairs, I H

2018-05-28

Pulsars are highly magnetized and rapidly rotating neutron stars. As they spin, the lighthouse-like beam of radio emission from their magnetic poles sweeps across the Earth with a regularity approaching that of the most precise clocks known. This precision combined with the extreme environments in which they are found, often in compact orbits with other neutron stars and white dwarfs, makes them excellent tools for studying gravity. Present and near-future pulsar surveys, especially those using the new generation of telescopes, will find more extreme binary systems and pulsars that are more precise 'clocks'. These telescopes will also greatly improve the precision to which we can measure the arrival times of the pulses. The Square Kilometre Array will revolutionize pulsar searches and timing precision. The increased number of sources will reveal rare sources, including possibly a pulsar-black hole binary, which can provide the most stringent tests of strong-field gravity. The improved timing precision will reveal new phenomena and also allow us to make a detection of gravitational waves in the nanohertz frequency regime. It is here where we expect to see the signature of the binary black holes that are formed as galaxies merge throughout cosmological history.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'. © 2018 The Author(s).

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.

Prospects for Probing Strong Gravity with a Pulsar-Black Hole System

NASA Technical Reports Server (NTRS)

Wex, N.; Liu, K.; Eatough, R. P.; Kramer, M.; Cordes, J. M.; Lazio, T. J. W.

2012-01-01

The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems.

An atlas of Rapp's 180-th order geopotential.

NASA Astrophysics Data System (ADS)

Melvin, P. J.

1986-08-01

Deprit's 1979 approach to the summation of the spherical harmonic expansion of the geopotential has been modified to spherical components and normalized Legendre polynomials. An algorithm has been developed which produces ten fields at the users option: the undulations of the geoid, three anomalous components of the gravity vector, or six components of the Hessian of the geopotential (gravity gradient). The algorithm is stable to high orders in single precision and does not treat the polar regions as a special case. Eleven contour maps of components of the anomalous geopotential on the surface of the ellipsoid are presented to validate the algorithm.

The gravitomagnetic interaction and its relationship to other relativistic gravitational effects

NASA Technical Reports Server (NTRS)

Nordtvedt, Kenneth

1991-01-01

To better understand the relationship between the expected precession rates of an orbiting gyroscope (GP-B) and other observable consequences in the solar system of relativistic, post-Newtonian gravity, a phenomenological model was developed of post-Newtonian gravity which presupposes the very minimum possible concerning the nature and foundations of the gravitational interaction. Solar system observations, chiefly interplanetary ranging, fix all the parameters in the phenomenological model to various levels of precision. This permits prediction of gyroscope precession rates to better than 10 pct. accuracy. A number of new precession terms are calculated which would exist if gravity were not a metric field phenomenon, but this would clash with other empirical observations of post-Newtonian effects in gravity. It is shown that gravitomagnetism, the post-Newtonian gravitational corrections to the interactions between moving matter, plays a ubiquitous role in determining a wide variety of gravitational effects, including the precession of orbiting gyroscopes.

f (T ) gravity after GW170817 and GRB170817A

NASA Astrophysics Data System (ADS)

Cai, Yi-Fu; Li, Chunlong; Saridakis, Emmanuel N.; Xue, Ling-Qin

2018-05-01

The combined observation of GW170817 and its electromagnetic counterpart GRB170817A reveals that gravitational waves propagate at the speed of light in high precision. We apply the standard analysis of cosmological perturbations, as well as the effective field theory approach, to investigate the experimental consequences for the theory of f (T ) gravity. Our analysis verifies for the first time that the speed of gravitational waves within f (T ) gravity is equal to the light speed, and hence, the constraints from GW170817 and GRB170817A are trivially satisfied. Nevertheless, by examining the dispersion relation and the frequency of cosmological gravitational waves, we observe a deviation from the results of general relativity, quantified by a new parameter. Although its value is relatively small in viable f (T ) models, its possible future measurement in advancing gravitational-wave astronomy would be the smoking gun of testing this type of modified gravity.

Assessing the likely value of gravity and drawdown measurements to constrain estimates of hydraulic conductivity and specific yield during unconfined aquifer testing

USGS Publications Warehouse

Blainey, Joan B.; Ferré, Ty P.A.; Cordova, Jeffrey T.

2007-01-01

Pumping of an unconfined aquifer can cause local desaturation detectable with high‐resolution gravimetry. A previous study showed that signal‐to‐noise ratios could be predicted for gravity measurements based on a hydrologic model. We show that although changes should be detectable with gravimeters, estimations of hydraulic conductivity and specific yield based on gravity data alone are likely to be unacceptably inaccurate and imprecise. In contrast, a transect of low‐quality drawdown data alone resulted in accurate estimates of hydraulic conductivity and inaccurate and imprecise estimates of specific yield. Combined use of drawdown and gravity data, or use of high‐quality drawdown data alone, resulted in unbiased and precise estimates of both parameters. This study is an example of the value of a staged assessment regarding the likely significance of a new measurement method or monitoring scenario before collecting field data.

Efficient Modeling of Gravity Fields Caused by Sources with Arbitrary Geometry and Arbitrary Density Distribution

NASA Astrophysics Data System (ADS)

Wu, Leyuan

2018-01-01

We present a brief review of gravity forward algorithms in Cartesian coordinate system, including both space-domain and Fourier-domain approaches, after which we introduce a truly general and efficient algorithm, namely the convolution-type Gauss fast Fourier transform (Conv-Gauss-FFT) algorithm, for 2D and 3D modeling of gravity potential and its derivatives due to sources with arbitrary geometry and arbitrary density distribution which are defined either by discrete or by continuous functions. The Conv-Gauss-FFT algorithm is based on the combined use of a hybrid rectangle-Gaussian grid and the fast Fourier transform (FFT) algorithm. Since the gravity forward problem in Cartesian coordinate system can be expressed as continuous convolution-type integrals, we first approximate the continuous convolution by a weighted sum of a series of shifted discrete convolutions, and then each shifted discrete convolution, which is essentially a Toeplitz system, is calculated efficiently and accurately by combining circulant embedding with the FFT algorithm. Synthetic and real model tests show that the Conv-Gauss-FFT algorithm can obtain high-precision forward results very efficiently for almost any practical model, and it works especially well for complex 3D models when gravity fields on large 3D regular grids are needed.

Gravity changes, soil moisture and data assimilation

NASA Astrophysics Data System (ADS)

Walker, J.; Grayson, R.; Rodell, M.; Ellet, K.

2003-04-01

Remote sensing holds promise for near-surface soil moisture and snow mapping, but current techniques do not directly resolve the deeper soil moisture or groundwater. The benefits that would arise from improved monitoring of variations in terrestrial water storage are numerous. The year 2002 saw the launch of NASA's Gravity Recovery And Climate Experiment (GRACE) satellites, which are mapping the Earth's gravity field at such a high level of precision that we expect to be able to infer changes in terrestrial water storage (soil moisture, groundwater, snow, ice, lake, river and vegetation). The project described here has three distinct yet inter-linked components that all leverage off the same ground-based monitoring and land surface modelling framework. These components are: (i) field validation of a relationship between soil moisture and changes in the Earth's gravity field, from ground- and satellite-based measurements of changes in gravity; (ii) development of a modelling framework for the assimilation of gravity data to constrain land surface model predictions of soil moisture content (such a framework enables the downscaling and disaggregation of low spatial (500 km) and temporal (monthly) resolution measurements of gravity change to finer spatial and temporal resolutions); and (iii) further refining the downscaling and disaggregation of space-borne gravity measurements by making use of other remotely sensed information, such as the higher spatial (25 km) and temporal (daily) resolution remotely sensed near-surface soil moisture measurements from the Advanced Microwave Scanning Radiometer (AMSR) instruments on Aqua and ADEOS II. The important field work required by this project will be in the Murrumbidgee Catchment, Australia, where an extensive soil moisture monitoring program by the University of Melbourne is already in place. We will further enhance the current monitoring network by the addition of groundwater wells and additional soil moisture sites. Ground-based gravity measurements will also be made on a monthly basis at each monitoring site. There will be two levels of modelling and monitoring; regional across the entire Murrumbidgee Catchment (100,000 km2), and local across a small sub-catchment (150 km2).

Future geodesy missions: Tethered systems and formation flying

NASA Astrophysics Data System (ADS)

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

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

Binary Systems as Test-Beds of Gravity Theories

NASA Astrophysics Data System (ADS)

Damour, Thibault

The discovery of binary pulsars in 1974 [1] opened up a new testing ground for relativistic gravity. Before this discovery, the only available testing ground for relativistic gravity was the solar system. As Einstein's theory of General Relativity (GR) is one of the basic pillars of modern science, it deserves to be tested, with the highest possible accuracy, in all its aspects. In the solar sys tem, the gravitational field is slowly varying and represents only a very small deformation of a flat spacetime. As a consequence, solar system tests can only probe the quasi-stationary (non-radiative) weak-field limit of relativis tic gravity. By contrast binary systems containing compact objects (neutron stars or black holes) involve spacetime domains (inside and near the compact objects) where the gravitational field is strong. Indeed, the surface relativistic gravitational field h 00 ≈ 2 GM/c 2 R of a neutron star is of order 0.4, which is close to the one of a black hole (2GM/c 2 R = 1) and much larger than the surface gravitational fields of solar system bodies: (2GM/c 2 R)Sun ˜ 10-6, (2GM/c 2 R)Earth ˜ 10-9. In addition, the high stability of “pulsar clocks” has made it possible to monitor the dynamics of its orbital motion down to a precision allowing one to measure the small (˜ (v/c)5) orbital effects linked to the propagation of the gravitational field at the velocity of light between the pulsar and its companion.

Landscape-scale water balance monitoring with an iGrav superconducting gravimeter in a field enclosure

NASA Astrophysics Data System (ADS)

Güntner, Andreas; Reich, Marvin; Mikolaj, Michal; Creutzfeldt, Benjamin; Schroeder, Stephan; Wziontek, Hartmut

2017-06-01

In spite of the fundamental role of the landscape water balance for the Earth's water and energy cycles, monitoring the water balance and its components beyond the point scale is notoriously difficult due to the multitude of flow and storage processes and their spatial heterogeneity. Here, we present the first field deployment of an iGrav superconducting gravimeter (SG) in a minimized enclosure for long-term integrative monitoring of water storage changes. Results of the field SG on a grassland site under wet-temperate climate conditions were compared to data provided by a nearby SG located in the controlled environment of an observatory building. The field system proves to provide gravity time series that are similarly precise as those of the observatory SG. At the same time, the field SG is more sensitive to hydrological variations than the observatory SG. We demonstrate that the gravity variations observed by the field setup are almost independent of the depth below the terrain surface where water storage changes occur (contrary to SGs in buildings), and thus the field SG system directly observes the total water storage change, i.e., the water balance, in its surroundings in an integrative way. We provide a framework to single out the water balance components actual evapotranspiration and lateral subsurface discharge from the gravity time series on annual to daily timescales. With about 99 and 85 % of the gravity signal due to local water storage changes originating within a radius of 4000 and 200 m around the instrument, respectively, this setup paves the road towards gravimetry as a continuous hydrological field-monitoring technique at the landscape scale.

Mariner 9 celestial mechanics experiment - A status report.

NASA Technical Reports Server (NTRS)

Lorell, J.; Shapiro, I. I.

1973-01-01

There are two basic efforts in the Mariner 9 celestial mechanics experiment: the determination of the gravity field of Mars and the performance of a very precise test of the theory of general relativity. In addition, there are a number of astrodynamic constants that are being determined. All the analyses are based on the Mariner 9 radio tracking data.

Satellite-tracking and Earth dynamics research programs

NASA Technical Reports Server (NTRS)

1983-01-01

Tracking of LAGEOS for polar motion and Earth rotation studies and for other geophysical investigations, including crustal dynamics, Earth and ocean tides, and the general development of precision orbit determination continues. The BE-C and Starlette satellites were tracked for refined determinations of station coordinates and the Earth's gravity field and for studies of solid Earth dynamics.

GEOS observation systems intercomparison investigation results

NASA Technical Reports Server (NTRS)

Berbert, J. H.

1974-01-01

The results of an investigation designed to determine the relative accuracy and precision of the different types of geodetic observation systems used by NASA is presented. A collocation technique was used to minimize the effects of uncertainties in the relative station locations and in the earth's gravity field model by installing accurate reference tracking systems close to the systems to be compared, and by precisely determining their relative survey. The Goddard laser and camera systems were shipped to selected sites, where they tracked the GEOS satellite simultaneously with other systems for an intercomparison observation.

Superconducting gravity gradiometer and a test of inverse square law

NASA Technical Reports Server (NTRS)

Moody, M. V.; Paik, Ho Jung

1989-01-01

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

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.

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.

Processing of Bulk YBa2Cu3O(7-x) High Temperature Superconductor Materials for Gravity Modification Experiments and Performance Under AC Levitation

NASA Technical Reports Server (NTRS)

Koczor, Ronald; Noever, David; Hiser, Robert

1999-01-01

We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of bulk-processed high temperature superconductor disks. Others have indicated that large annular disks (on the order of 25cm diameter) and AC levitation fields play an essential role in their observed experiments. We report experiments in processing such large bulk superconductors. Successful results depend on material mechanical characteristics, and pressure and heat treat protocols. Annular disks having rough dimensions of 30cm O.D., 7cm I.D. and 1 cm thickness have been routinely fabricated and tested under AC levitation fields ranging from 45 to 300OHz. Implications for space transportation initiatives and power storage flywheel technology will be discussed.

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

Titan gravity investigation with the Oceanus mission

NASA Astrophysics Data System (ADS)

Tortora, Paolo; Zannoni, Marco; Nimmo, Francis; Mazarico, Erwan; Iess, Luciano; Sotin, Christophe; Hayes, Alexander; Malaska, Michael

2017-04-01

Oceanus is a proposed mission for NASA's New Frontiers 4 Announcement of Opportunity to study Saturn's largest moon Titan. One of the main goals of Oceanus is to examine crustal properties and determine the potential interaction of organics with the subsurface ocean, with implications for potential habitability of Titan. To this end, Oceanus could potentially characterize the thickness of the external icy shell and determine the extent of convection in the shell. The product (average ice rigidity) x (ice shell thickness) can be retrieved from the Love numbers k2 and h2, which describe Titan's gravity and shape response to Saturn's tidal field during its orbital motion around the planet, using a combined analysis of gravity and topography but also measuring Titan's physical librations from gravity data and the on-board camera surface landmarks. The gravity science experiment is crucial to accomplish the mission goals, because precise orbit determination of the spacecraft provides a direct measure of Titan's static gravitational field, the real and imaginary parts of the Love number k2, and its rotational state (obliquity and amplitude of physical librations in longitude). Moreover, a precise spacecraft orbit reconstruction throughout the entire mission is necessary to process radar altimetry data and accurately measure Titan's h2 through crossover analysis. We present the expected accuracy in the estimation of the scientific parameters of interest, obtained through numerical simulations of the orbit determination of the Oceanus spacecraft during its 2-year mission around Titan. The main observable quantities used in the analysis are two-way Doppler data obtained from the frequency shift of a highly stable microwave carrier between the spacecraft and the stations of NASA's Deep Space Network. White Gaussian noise was added to the simulated data, with a realistic standard deviation obtained from an accurate noise budget derived from the experience with Cassini Ka-band Doppler data. A covariance analysis was carried out using a multi-arc approach, comparing different observational and modeling strategies, in particular for the non-gravitational perturbations. Our results show that Oceanus will allow estimating the real and imaginary parts of Titan's k2 to an accuracy of 0.0001, the gravity field to at least degree 12 with SNR of 10, and also provide spacecraft orbit reconstruction with a radial uncertainty better than 0.5 meter during the mission.

Mass Intrusion at Mount St. Helens (WA) From Temporal Gravity Variations

NASA Astrophysics Data System (ADS)

Battaglia, M.; Lisowski, M.; Dzurisin, D.; Poland, M. P.; Schilling, S. P.; Diefenbach, A. K.; Wynn, J.

2015-12-01

Repeated high-precision gravity measurements made at Mount St. Helens (WA) have revealed systematic temporal variations in the gravity field several years after the end of the 2004-2008 dome-building eruption. Changes in gravity with respect to a stable reference station 36 km NW of the volcano were measured at 10 sites on the volcanic edifice and at 4 sites far afield (10 to 36 km) from the summit in August 2010, August 2012 and August 2014. After simulating and removing the gravity signal associated with changes in mass of the crater glacier, the local hydrothermal aquifer, and vertical deformation, the residual gravity field observed at sites near the volcano's summit significantly increased with respect to the stable reference site during 2010-2012 (maximum change 48 ± 15 mgal). No significant change was measured during 2012-2014. The pattern of gravity increase is radially symmetrical, with a half-width of about 2.5 km and a point of maximum change centered at the 2004-2008 lava dome. Forward modeling of residual gravity data using the same source geometry, depth, and location as that inferred from geodetic data (a spheroidal source centered 7.5 km beneath the 2004-2008 dome) indicates a mass increase rate of the order of 1011 kg/year. For a reasonable magma density (~2250 kg/m3), the volume rate of magma intrusion beneath the summit region inferred from gravity (~ 0.1 km3/yr) greatly exceeds the volume inferred from inversion of geodetic data (0.001 km3/yr between 2008-2011), suggesting that either magma compressibility or other processes are important aspects of magma storage at Mount St. Helens, or that the data argue for a different source.

Testing Quantum Gravity Induced Nonlocality via Optomechanical Quantum Oscillators.

PubMed

Belenchia, Alessio; Benincasa, Dionigi M T; Liberati, Stefano; Marin, Francesco; Marino, Francesco; Ortolan, Antonello

2016-04-22

Several quantum gravity scenarios lead to physics below the Planck scale characterized by nonlocal, Lorentz invariant equations of motion. We show that such nonlocal effective field theories lead to a modified Schrödinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of optomechanical quantum oscillators is characterized by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the nonlocality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.

Research on the impact factors of GRACE precise orbit determination by dynamic method

NASA Astrophysics Data System (ADS)

Guo, Nan-nan; Zhou, Xu-hua; Li, Kai; Wu, Bin

2018-07-01

With the successful use of GPS-only-based POD (precise orbit determination), more and more satellites carry onboard GPS receivers to support their orbit accuracy requirements. It provides continuous GPS observations in high precision, and becomes an indispensable way to obtain the orbit of LEO satellites. Precise orbit determination of LEO satellites plays an important role for the application of LEO satellites. Numerous factors should be considered in the POD processing. In this paper, several factors that impact precise orbit determination are analyzed, namely the satellite altitude, the time-variable earth's gravity field, the GPS satellite clock error and accelerometer observation. The GRACE satellites provide ideal platform to study the performance of factors for precise orbit determination using zero-difference GPS data. These factors are quantitatively analyzed on affecting the accuracy of dynamic orbit using GRACE observations from 2005 to 2011 by SHORDE software. The study indicates that: (1) with the altitude of the GRACE satellite is lowered from 480 km to 460 km in seven years, the 3D (three-dimension) position accuracy of GRACE satellite orbit is about 3˜4 cm based on long spans data; (2) the accelerometer data improves the 3D position accuracy of GRACE in about 1 cm; (3) the accuracy of zero-difference dynamic orbit is about 6 cm with the GPS satellite clock error products in 5 min sampling interval and can be raised to 4 cm, if the GPS satellite clock error products with 30 s sampling interval can be adopted. (4) the time-variable part of earth gravity field model improves the 3D position accuracy of GRACE in about 0.5˜1.5 cm. Based on this study, we quantitatively analyze the factors that affect precise orbit determination of LEO satellites. This study plays an important role to improve the accuracy of LEO satellites orbit determination.

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.

Ramsey's method of separated oscillating fields and its application to gravitationally induced quantum phase shifts

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

Abele, H.; Jenke, T.; Leeb, H.

2010-03-15

We propose to apply Ramsey's method of separated oscillating fields to the spectroscopy of the quantum states in the gravity potential above a horizontal mirror. This method allows a precise measurement of quantum mechanical phaseshifts of a Schroedinger wave packet bouncing off a hard surface in the gravitational field of the Earth. Measurements with ultracold neutrons will offer a sensitivity to Newton's law or hypothetical short-ranged interactions, which is about 21 orders of magnitude below the energy scale of electromagnetism.

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation.

PubMed

Tie, Junbo; Cao, Juliang; Chang, Lubing; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-03-16

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method.

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation

PubMed Central

Cao, Juliang; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-01-01

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method. PMID:29547552

Canceling the Gravity Gradient Phase Shift in Atom Interferometry.

PubMed

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

2017-12-22

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

Canceling the Gravity Gradient Phase Shift in Atom Interferometry

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

EFTofPNG: a package for high precision computation with the effective field theory of post-Newtonian gravity

NASA Astrophysics Data System (ADS)

Levi, Michele; Steinhoff, Jan

2017-12-01

We present a novel public package ‘EFTofPNG’ for high precision computation in the effective field theory of post-Newtonian (PN) gravity, including spins. We created this package in view of the timely need to publicly share automated computation tools, which integrate the various types of physics manifested in the expected increasing influx of gravitational wave (GW) data. Hence, we created a free and open source package, which is self-contained, modular, all-inclusive, and accessible to the classical gravity community. The ‘EFTofPNG’ Mathematica package also uses the power of the ‘xTensor’ package, suited for complicated tensor computation, where our coding also strategically approaches the generic generation of Feynman contractions, which is universal to all perturbation theories in physics, by efficiently treating n-point functions as tensors of rank n. The package currently contains four independent units, which serve as subsidiaries to the main one. Its final unit serves as a pipeline chain for the obtainment of the final GW templates, and provides the full computation of derivatives and physical observables of interest. The upcoming ‘EFTofPNG’ package version 1.0 should cover the point mass sector, and all the spin sectors, up to the fourth PN order, and the two-loop level. We expect and strongly encourage public development of the package to improve its efficiency, and to extend it to further PN sectors, and observables useful for the waveform modelling.

Precise Orbit Determination for GEOSAT Follow-On Using Satellite Laser Ranging Data and Intermission Altimeter Crossovers

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Rowlands, David D.; Luthcke, Scott B.; Zelensky, Nikita P.; Chinn, Douglas S.; Pavlis, Despina E.; Marr, Gregory

2001-01-01

The US Navy's GEOSAT Follow-On Spacecraft was launched on February 10, 1998 with the primary objective of the mission to map the oceans using a radar altimeter. Following an extensive set of calibration campaigns in 1999 and 2000, the US Navy formally accepted delivery of the satellite on November 29, 2000. Satellite laser ranging (SLR) and Doppler (Tranet-style) beacons track the spacecraft. Although limited amounts of GPS data were obtained, the primary mode of tracking remains satellite laser ranging. The GFO altimeter measurements are highly precise, with orbit error the largest component in the error budget. We have tuned the non-conservative force model for GFO and the gravity model using SLR, Doppler and altimeter crossover data sampled over one year. Gravity covariance projections to 70x70 show the radial orbit error on GEOSAT was reduced from 2.6 cm in EGM96 to 1.3 cm with the addition of SLR, GFO/GFO and TOPEX/GFO crossover data. Evaluation of the gravity fields using SLR and crossover data support the covariance projections and also show a dramatic reduction in geographically-correlated error for the tuned fields. In this paper, we report on progress in orbit determination for GFO using GFO/GFO and TOPEX/GFO altimeter crossovers. We will discuss improvements in satellite force modeling and orbit determination strategy, which allows reduction in GFO radial orbit error from 10-15 cm to better than 5 cm.

Adventures in Topological Field Theory

NASA Astrophysics Data System (ADS)

Horne, James H.

1990-01-01

This thesis consists of 5 parts. In part I, the topological Yang-Mills theory and the topological sigma model are presented in a superspace formulation. This greatly simplifies the field content of the theories, and makes the Q-invariance more obvious. The Feynman rules for the topological Yang -Mills theory are derived. We calculate the one-loop beta-functions of the topological sigma model in superspace. The lattice version of these theories is presented. The self-duality constraints of both models lead to spectrum doubling. In part II, we show that conformally invariant gravity in three dimensions is equivalent to the Yang-Mills gauge theory of the conformal group in three dimensions, with a Chern-Simons action. This means that conformal gravity is finite and exactly soluble. In part III, we derive the skein relations for the fundamental representations of SO(N), Sp(2n), Su(m| n), and OSp(m| 2n). These relations can be used recursively to calculate the expectation values of Wilson lines in three-dimensional Chern-Simons gauge theory with these gauge groups. A combination of braiding and tying of Wilson lines completely describes the skein relations. In part IV, we show that the k = 1 two dimensional gravity amplitudes at genus 3 agree precisely with the results from intersection theory on moduli space. Predictions for the genus 4 intersection numbers follow from the two dimensional gravity theory. In part V, we discuss the partition function in two dimensional gravity. For the one matrix model at genus 2, we use the partition function to derive a recursion relation. We show that the k = 1 amplitudes completely determine the partition function at arbitrary genus. We present a conjecture for the partition function for the arbitrary topological field theory coupled to topological gravity.

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

Dynamics and structure of the Alpine Fold Belt

NASA Technical Reports Server (NTRS)

Kahle, H. G.

1985-01-01

The structure and present-day dynamics of the Alps interms of geodesy and gravimetry are discusssed. A strong correlation of precise leveling and isostatic gravity along the central Alpine chain, especially in Canton Graubunden, East Switzerland are shown. It is assumed that the uplift is partly controlled by isostatic rebound effects. Field observations indicate that these phenomena are still active in the Alps. The study of the uplift processes by applying a number of geodetic and gravimetric measuring techniques, such as the determination of nonperiodic secular variations of gravity, of the deflections of the vertical and tilt changes monitored by hydrostatic leveling is proposed.

Surface Gravity Data Contribution to the Puerto Rico and U.S. Virgin Islands Geoid Model

NASA Astrophysics Data System (ADS)

Li, X.; Gerhards, C.; Holmes, S. A.; Saleh, J.; Shaw, B.

2015-12-01

The Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project provides updated local gravity field information for the XGEOID15 models. In particular, its airborne gravity data in the area of Puerto Rico and U.S. Virgin Islands (PRVI) made substantial improvements (~60%) on the precision of the geoid models at the local GNSS/Leveling bench marks in the target area. Fortunately, PRVI is free of the huge systematic error in the North American Vertical Datum of 1988 (NAVD88). Thus, the airborne contribution was evaluated more realistically. In addition, the airborne data picked up more detailed gravity field information in the medium wavelength band (spherical harmonic degree 200 to 600) that are largely beyond the resolution of the current satellite missions, especially along the nearby ocean trench areas. Under this circumstance (significant airborne contributions in the medium band), local surface gravity data need to be examined more carefully than before during merging with the satellite and airborne information for local geoid improvement, especially considering the well-known systematic problems in the NGS historical gravity holdings (Saleh et al 2013 JoG). Initial tests showed that it is very important to maintain high consistency between the surface data sets and the airborne enhanced reference model. In addition, a new aggregation method (Gerhards 2014, Inverse Problems) will also be tested to optimally combine the local surface data with the reference model. The data cleaning and combining procedures in the target area will be summarized here as reference for future applications.

Investigations on vertical crustal movements in the Venezuelan Andes by gravimetric methods

NASA Technical Reports Server (NTRS)

Drewes, H.

1978-01-01

A precise gravimetric network has been installed in the Venezuelan Andes to study eventual gravity changes due to vertical tectonic movements. The design and the measurements of the network are described and the accuracy is estimated. In the center of the region a local gravity network has been reobserved three times. The detected variations are discussed. In order to obtain a genuine statement as far as possible about the significance of observed gravity changes, requirements for the procedure of monitoring precise gravity networks are pointed out.

Near Earth Asteroid Rendezvous (NEAR) Revised Eros Orbit Phase Trajectory Design

NASA Technical Reports Server (NTRS)

Helfrich, J; Miller, J. K.; Antreasian, P. G.; Carranza, E.; Williams, B. G.; Dunham, D. W.; Farquhar, R. W.; McAdams, J. V.

1999-01-01

Trajectory design of the orbit phase of the NEAR mission involves a new process that departs significantly from those procedures used in previous missions. In most cases, a precise spacecraft ephemeris is designed well in advance of arrival at the target body. For NEAR, the uncertainty in the dynamic environment around Eros does not allow the luxury of a precise spacecraft trajectory to be defined in advance. The principal cause of this uncertainty is the limited knowledge oi' the gravity field a,-id rotational state of Eros. As a result, the concept for the NEAR trajectory design is to define a number of rules for satisfying spacecraft, mission, and science constraints, and then apply these rules to various assumptions for the model of Eros. Nominal, high, and low Eros mass models are used for testing the trajectory design strategy and to bracket the ranges of parameter variations that are expected upon arrival at the asteroid. The final design is completed after arrival at Eros and determination of the actual gravity field and rotational state. As a result of the unplanned termination of the deep space rendezvous maneuver on December 20, 1998, the NEAR spacecraft passed within 3830 km of Eros on December 23, 1998. This flyby provided a brief glimpse of Eros, and allowed for a more accurate model of the rotational parameters and gravity field uncertainty. Furthermore, after the termination of the deep space rendezvous burn, contact with the spacecraft was lost and the NEAR spacecraft lost attitude control. During the subsequent gyrations of the spacecraft, hydrazine thruster firings were used to regain attitude control. This unplanned thruster activity used Much of the fuel margin allocated for the orbit phase. Consequently, minimizing fuel consumption is now even more important.

High-precision gravimetric survey in support of lunar laser ranging at Haleakala, Maui, 1976 - 1978

NASA Technical Reports Server (NTRS)

Schenck, B. E.; Laurila, S. H.

1978-01-01

The planning, observations and adjustment of high-precision gravity survey networks established on the islands of Maui and Oahu as part of the geodetic-geophysical program in support of lunar laser ranging at Haleakala, Maui, Hawaii are described. The gravity survey networks include 43 independently measured gravity differences along the gravity calibration line from Kahului Airport to the summit of Mt. Haleakala, together with some key points close to tidal gauges on Maui, and 40 gravity differences within metropolitan Honolulu. The results of the 1976-1978 survey are compared with surveys made in 1961 and in 1964-1965. All final gravity values are given in the system of the international gravity standardization net 1971 (IGSN 71); values are obtained by subtracting 14.57 mgal from the Potsdam value at the gravity base station at the Hickam Air Force Base, Honolulu.

Gravity field, shape, and moment of inertia of Titan.

PubMed

Iess, Luciano; Rappaport, Nicole J; Jacobson, Robert A; Racioppa, Paolo; Stevenson, David J; Tortora, Paolo; Armstrong, John W; Asmar, Sami W

2010-03-12

Precise radio tracking of the spacecraft Cassini has provided a determination of Titan's mass and gravity harmonics to degree 3. The quadrupole field is consistent with a hydrostatically relaxed body shaped by tidal and rotational effects. The inferred moment of inertia factor is about 0.34, implying incomplete differentiation, either in the sense of imperfect separation of rock from ice or a core in which a large amount of water remains chemically bound in silicates. The equilibrium figure is a triaxial ellipsoid whose semi-axes a, b, and c differ by 410 meters (a-c) and 103 meters (b-c). The nonhydrostatic geoid height variations (up to 19 meters) are small compared to the observed topographic anomalies of hundreds of meters, suggesting a high degree of compensation appropriate to a body that has warm ice at depth.

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

Anisotropy in Gravity and Holography

NASA Astrophysics Data System (ADS)

Melby-Thompson, Charles Milton

In this thesis, we examine the dynamical structure of Hořava-Lifshitz gravity, and investigate its relationship with holography for anisotropic systems. Hořava-Lifshitz gravity refers to a broad class of gravitational models that incorporate anisotropy at a fundamental level. The idea behind Hořava-Lifshitz gravity is to utilize ideas from the theory of dynamical critical phenomena into gravity to produce a theory of dynamical spacetime that is power-counting renormalizable, and is thus a candidate renormalizable quantum field theory of gravity. One of the most distinctive features of Hořava-Lifshitz gravity is that its group of symmetries consists not of the diffeomorphisms of spacetime, but instead of the group of diffeomorphisms that preserve a given foliation by spatial slices. As a result of having a smaller group of symmetries, HL gravity naturally has one more propagating degree of freedom than general relativity. The extra mode presents two possible difficulties with the theory, one relating to consistency, and the second to its viability as a phenomenological model. (1) It may destabilize the theory. (2) Phenomenologically, there are severe constraints on the existence of an extra propagating graviton polarization, as well as strong experimental constraints on the value of a parameter appearing in the dispersion relation of the extra mode. In the first part of this dissertation we show that the extra mode can be eliminated by introducing a new local symmetry which steps in and takes the place of general covariance in the anisotropic context. While the identification of the appropriate symmetry is quite subtle in the full non-linear theory, once the dust settles, the resulting theory has a spectrum which matches that of general relativity in the infrared. This goes a good way toward answering the question of how close Hořava-Lifshitz gravity can come to reproducing general relativity in the infrared regime. In the second part of the thesis we pursue the relationship between Hořava-Lifshitz gravity and holographic duals for anisotropic systems. A holographic correspondence is one that posits an equivalence between a theory of gravity on a given spacetime background and a field theory living on the "boundary" of that spacetime, which resides at infinite spatial separation from the interior. It is a non-trivial problem how to define this boundary, but in the case of relativistic boundary field theories, there is a well-known definition due to Penrose of the boundary which produces the geometric structure required to make sense of the correspondence. However, the proposed dual geometries to anisotropic quantum field theories have a Penrose boundary that is incompatible with the assumed correspondence. We generalize Penrose's approach, using concepts from Hořava-Lifshitz gravity, to spacetimes with anisotropic boundary conditions, thereby arriving at the concept of anisotropic conformal infinity that is compatible with the holographic correspondence in these spacetimes. We then apply this work to understanding the structure of holography for anisotropic systems in more detail. In particular, we examine the structure of divergences of a certain theory of gravity on Lifshitz space. We find, using our construction of anisotropic conformal infinity, that the appropriate geometric structure of the boundary is that of a foliated spacetime with an anisotropic metric complex. We then perform holographic renormalization in these spacetimes, yielding a computation of the divergent part of the effective action, and find that it exhibits precisely the structure of a Hořava-Lifshitz action. Moreover, we find that, for dynamical exponent z = 2, the logarithmic divergence gives rise to a conformal anomaly in 2+1 dimensions, whose general form is precisely that of conformal Hořava-Lifshitz gravity with detailed balance.

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

Kramer, Michael; Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester M13 9PL

The last years have seen continuing activities in the exploration of our understanding of gravity, motivated by results from precision cosmology and new precision astrophysical experiments. At the centre of attention lies the question as to whether general relativity is the correct theory of gravity. In answering this question, we work not only towards correctly interpreting the phenomenon of 'dark energy' but also towards the goal of achieving a quantum theory of gravity. In these efforts, the observations of pulsars, especially those in binary systems, play an important role. Pulsars do not only provide the only evidence for the existencemore » of gravitational waves so far, but they also provide precision tests of general relativity and alternative theories of gravity. This talk summarizes the current state-of-art in these experiments and looks into the future.« less

Integrative monitoring of water storage variations at the landscape-scale with an iGrav superconducting gravimeter in a field enclosure

NASA Astrophysics Data System (ADS)

Guntner, A.; Reich, M.; Mikolaj, M.; Creutzfeldt, B.; Schroeder, S.; Wziontek, H.

2017-12-01

In spite of the fundamental role of the landscape water balance for the Earth's water and energy cycles, monitoring the water balance and related storage dynamics beyond the point scale is notoriously difficult due to the multitude of flow and storage processes and their spatial heterogeneity. We present the first outdoor deployment of an iGrav superconducting gravimeter (SG) in a minimized field enclosure on a wet-temperate grassland site for integrative monitoring of water storage changes. It is shown that the system performs similarly precise as SGs that have hitherto been deployed in observatory buildings, but with higher sensitivity to hydrological variations in the surroundings of the instrument. Gravity variations observed by the field setup are almost independent of the depth below the terrain surface where water storage changes occur, and thus the field SG system directly observes the total water storage change in an integrative way. We provide a framework to single out the water balance components actual evapotranspiration and lateral subsurface discharge from the gravity time series on annual to daily time scales. With about 99% and 85% of the gravity signal originating within a radius of 4000 and 200 meter around the instrument, respectively, the setup paves the road towards gravimetry as a continuous hydrological field monitoring technique for water storage dynamics at the landscape scale.

The German joint research project "concepts for future gravity satellite missions"

NASA Astrophysics Data System (ADS)

Reubelt, Tilo; Sneeuw, Nico; Fichter, Walter; Müller, Jürgen

2010-05-01

Within the German joint research project "concepts for future gravity satellite missions", funded by the Geotechnologies programme of the German Federal Ministry of Education and Research, options and concepts for future satellite missions for precise (time-variable) gravity field recovery are investigated. The project team is composed of members from science and industry, bringing together experts in geodesy, satellite systems, metrology, sensor technology and control systems. The majority of team members already contributed to former gravity missions. The composition of the team guarantees that not only geodetic aspects and objectives are investigated, but also technological and financial constraints are considered. Conversely, satellite, sensor and system concepts are developed and improved in a direct exchange with geodetic and scientific claims. The project aims to develop concepts for both near and mid-term future satellite missions, taking into account e.g. advanced satellite formations and constellations, improved orbit design, innovative metrology and sensor systems and advances in satellite systems.

The measurement of surface gravity

NASA Technical Reports Server (NTRS)

Harrison, J. C.; Lacoste, L. J. B.

1978-01-01

LaCoste and Romberg G and D gravity meters are normally employed when attempting high precision measurement of gravity differences on land. The capabilities and limitations of these instruments are discussed.

An Online Gravity Modeling Method Applied for High Precision Free-INS

PubMed Central

Wang, Jing; Yang, Gongliu; Li, Jing; Zhou, Xiao

2016-01-01

For real-time solution of inertial navigation system (INS), the high-degree spherical harmonic gravity model (SHM) is not applicable because of its time and space complexity, in which traditional normal gravity model (NGM) has been the dominant technique for gravity compensation. In this paper, a two-dimensional second-order polynomial model is derived from SHM according to the approximate linear characteristic of regional disturbing potential. Firstly, deflections of vertical (DOVs) on dense grids are calculated with SHM in an external computer. And then, the polynomial coefficients are obtained using these DOVs. To achieve global navigation, the coefficients and applicable region of polynomial model are both updated synchronously in above computer. Compared with high-degree SHM, the polynomial model takes less storage and computational time at the expense of minor precision. Meanwhile, the model is more accurate than NGM. Finally, numerical test and INS experiment show that the proposed method outperforms traditional gravity models applied for high precision free-INS. PMID:27669261

An Online Gravity Modeling Method Applied for High Precision Free-INS.

PubMed

Wang, Jing; Yang, Gongliu; Li, Jing; Zhou, Xiao

2016-09-23

For real-time solution of inertial navigation system (INS), the high-degree spherical harmonic gravity model (SHM) is not applicable because of its time and space complexity, in which traditional normal gravity model (NGM) has been the dominant technique for gravity compensation. In this paper, a two-dimensional second-order polynomial model is derived from SHM according to the approximate linear characteristic of regional disturbing potential. Firstly, deflections of vertical (DOVs) on dense grids are calculated with SHM in an external computer. And then, the polynomial coefficients are obtained using these DOVs. To achieve global navigation, the coefficients and applicable region of polynomial model are both updated synchronously in above computer. Compared with high-degree SHM, the polynomial model takes less storage and computational time at the expense of minor precision. Meanwhile, the model is more accurate than NGM. Finally, numerical test and INS experiment show that the proposed method outperforms traditional gravity models applied for high precision free-INS.

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.

Was Newton right? A search for non-Newtonian behavior of weak-field gravity

NASA Astrophysics Data System (ADS)

Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven

2014-06-01

Empirical tests of Einstein's metric theory of gravitation, even in the non-relativistic, weak-field limit, could play an important role in judging theory-driven extensions of the current Standard Model of fundamental interactions. Guided by Galileo's work and his own experiments, Newton formulated a theory of gravity in which the force of attraction between two bodies is independent of composition and proportional to the inertia of each, thereby transparently satisfying Galileo's empirically informed conjecture regarding the Universality of Free Fall. Similarly, Einstein honored the manifest success of Newton's theory by assuring that the linearized equations of GTR matched the Newtonian formalism under "classical" conditions. Each of these steps, however, was explicitly an approximation raised to the status of principle. Perhaps, at some level, Newtonian gravity does not accurately describe the physical interaction between uncharged, unmagnetized, macroscopic bits of ordinary matter. What if Newton were wrong? Detecting any significant deviation from Newtonian behavior, no matter how small, could provide new insights and possibly reveal new physics. In the context of physics as an empirical science, for us this yet unanswered question constitutes sufficient motivation to attempt precision measurements of the kind described here. In this paper we report the current status of a project to search for violation of the Newtonian inverse square law of gravity.

Orbit Determination of the SELENE Satellites Using Multi-Satellite Data Types and Evaluation of SELENE Gravity Field Models

NASA Technical Reports Server (NTRS)

Goossens, S.; Matsumoto, K.; Noda, H.; Araki, H.; Rowlands, D. D.; Lemoine, F. G.

2011-01-01

The SELENE mission, consisting of three separate satellites that use different terrestrial-based tracking systems, presents a unique opportunity to evaluate the contribution of these tracking systems to orbit determination precision. The tracking data consist of four-way Doppler between the main orbiter and one of the two sub-satellites while the former is over the far side, and of same-beam differential VLBI tracking between the two sub-satellites. Laser altimeter data are also used for orbit determination. The contribution to orbit precision of these different data types is investigated through orbit overlap analysis. It is shown that using four-way and VLBI data improves orbit consistency for all satellites involved by reducing peak values in orbit overlap differences that exist when only standard two-way Doppler and range data are used. Including laser altimeter data improves the orbit precision of the SELENE main satellite further, resulting in very smooth total orbit errors at an average level of 18m. The multi-satellite data have also resulted in improved lunar gravity field models, which are assessed through orbit overlap analysis using Lunar Prospector tracking data. Improvements over a pre-SELENE model are shown to be mostly in the along-track and cross-track directions. Orbit overlap differences are at a level between 13 and 21 m with the SELENE models, depending on whether l-day data overlaps or I-day predictions are used.

The simulation of lunar gravity field recovery from D-VLBI of Chang’E-1 and SELENE lunar orbiters

NASA Astrophysics Data System (ADS)

Yan, Jianguo; Ping, Jingsong; Matsumoto, K.; Li, Fei

2008-07-01

The lunar gravity field is a foundation to study the lunar interior structure, and to recover the evolution history of the Moon. It is still an open and key topic for lunar science. For above mentioned reasons, it becomes one of the important scientific objectives of recent lunar missions, such as KAGUYA (SELENE) the Japanese lunar mission and Chang’E-1, the Chinese lunar mission. The Chang’E-1 and the SELENE were successfully launched in 2007. It is estimated that these two missions can fly around the Moon longer than 6 months simultaneously. In these two missions, the Chinese new VLBI (Very Long Baseline Interferometry) network will be applied for precise orbit determination (POD) by using a differential VLBI (D-VLBI) method during the mission period. The same-beam D-VLBI technique will contribute to recover the lunar gravity field together with other conventional observables, i.e. R&RR (Range and Range Rate) and multi-way Doppler. Taking VLBI tracking conditions into consideration and using the GEODYNII/SOVLE software of GSFC/NASA/USA [Rowlands, D.D., Marshall, J.A., Mccarthy, J., et al. GEODYN II System Description, vols. 1 5. Contractor Report, Hughes STX Corp. Greenbelt, MD, 1997; Ullman, R.E. SOLVE program: mathematical formulation and guide to user input, Hughes/STX Contractor Report, Contract NAS5-31760. NASA Goddard Space Flight Center, Greenbelt, Maryland, 1994], we simulated the lunar gravity field recovering ability with and without D-VLBI between the Chang’E-1 and SELENE main satellite. The cases of overlapped flying and tracking period of 30 days, 60 days and 90 days have been analyzed, respectively. The results show that D-VLBI tracking between two lunar satellites can improve the gravity field recovery remarkably. The results and methods introduced in this paper will benefit the actual missions.

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.

Empirical Foundations of the Relativistic Gravity

NASA Astrophysics Data System (ADS)

Ni, Wei-Tou

In 1859, Le Verrier discovered the mercury perihelion advance anomaly. This anomaly turned out to be the first relativistic-gravity effect observed. During the 141 years to 2000, the precisions of laboratory and space experiments, and astrophysical and cosmological observations on relativistic gravity have been improved by 3 orders of magnitude. In 1999, we envisaged a 3-6 order improvement in the next 30 years in all directions of tests of relativistic gravity. In 2000, the interferometric gravitational wave detectors began their runs to accumulate data. In 2003, the measurement of relativistic Shapiro time-delay of the Cassini spacecraft determined the relativistic-gravity parameter γ to be 1.000021 ± 0.000023 of general relativity — a 1.5-order improvement. In October 2004, Ciufolini and Pavlis reported a measurement of the Lense-Thirring effect on the LAGEOS and LAGEOS2 satellites to be 0.99 ± 0.10 of the value predicted by general relativity. In April 2004, Gravity Probe B (Stanford relativity gyroscope experiment to measure the Lense-Thirring effect to 1%) was launched and has been accumulating science data for more than 170 days now. μSCOPE (MICROSCOPE: MICRO-Satellite à trainée Compensée pour l'Observation du Principle d'Équivalence) is on its way for a 2008 launch to test Galileo equivalence principle to 10-15. LISA Pathfinder (SMART2), the technological demonstrator for the LISA (Laser Interferometer Space Antenna) mission is well on its way for a 2009 launch. STEP (Satellite Test of Equivalence Principle), and ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) are in good planning stage. Various astrophysical tests and cosmological tests of relativistic gravity will reach precision and ultra-precision stages. Clock tests and atomic interferometry tests of relativistic gravity will reach an ever-increasing precision. These will give revived interest and development both in experimental and theoretical aspects of gravity, and may lead to answers to some profound questions of gravity and the cosmos.

Correcting the spectroscopic surface gravity using transits and asteroseismology. No significant effect on temperatures or metallicities with ARES and MOOG in local thermodynamic equilibrium

NASA Astrophysics Data System (ADS)

Mortier, A.; Sousa, S. G.; Adibekyan, V. Zh.; Brandão, I. M.; Santos, N. C.

2014-12-01

Context. Precise stellar parameters (effective temperature, surface gravity, metallicity, stellar mass, and radius) are crucial for several reasons, amongst which are the precise characterization of orbiting exoplanets and the correct determination of galactic chemical evolution. The atmospheric parameters are extremely important because all the other stellar parameters depend on them. Using our standard equivalent-width method on high-resolution spectroscopy, good precision can be obtained for the derived effective temperature and metallicity. The surface gravity, however, is usually not well constrained with spectroscopy. Aims: We use two different samples of FGK dwarfs to study the effect of the stellar surface gravity on the precise spectroscopic determination of the other atmospheric parameters. Furthermore, we present a straightforward formula for correcting the spectroscopic surface gravities derived by our method and with our linelists. Methods: Our spectroscopic analysis is based on Kurucz models in local thermodynamic equilibrium, performed with the MOOG code to derive the atmospheric parameters. The surface gravity was either left free or fixed to a predetermined value. The latter is either obtained through a photometric transit light curve or derived using asteroseismology. Results: We find first that, despite some minor trends, the effective temperatures and metallicities for FGK dwarfs derived with the described method and linelists are, in most cases, only affected within the errorbars by using different values for the surface gravity, even for very large differences in surface gravity, so they can be trusted. The temperatures derived with a fixed surface gravity continue to be compatible within 1 sigma with the accurate results of the infrared flux method (IRFM), as is the case for the unconstrained temperatures. Secondly, we find that the spectroscopic surface gravity can easily be corrected to a more accurate value using a linear function with the effective temperature. Tables 1 and 2 are available in electronic form at http://www.aanda.org

Laser Vacuum Furnace for Zone Refining

NASA Technical Reports Server (NTRS)

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

1986-01-01

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

Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits

NASA Astrophysics Data System (ADS)

Lück, Christina; Kusche, Jürgen; Rietbroek, Roelof; Löcher, Anno

2018-03-01

Measuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided monthly snapshots of the Earth's time-variable gravity field, from which one can derive ocean mass variability. However, GRACE has reached the end of its lifetime with data degradation and several gaps occurred during the last years, and there will be a prolonged gap until the launch of the follow-on mission GRACE-FO. Therefore, efforts focus on generating a long and consistent ocean mass time series by analyzing kinematic orbits from other low-flying satellites, i.e. extending the GRACE time series. Here we utilize data from the European Space Agency's (ESA) Swarm Earth Explorer satellites to derive and investigate ocean mass variations. For this aim, we use the integral equation approach with short arcs (Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields with different parameterizations from kinematic orbits. We investigate the potential to bridge the gap between the GRACE and the GRACE-FO mission and to substitute missing monthly solutions with Swarm results of significantly lower resolution. Our monthly Swarm solutions have a root mean square error (RMSE) of 4.0 mm with respect to GRACE, whereas directly estimating constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE of only 1.7 mm. Concerning monthly gaps, our CTAS Swarm solution appears better than interpolating existing GRACE data in 13.5 % of all cases, when artificially removing one solution. In the case of an 18-month artificial gap, 80.0 % of all CTAS Swarm solutions were found closer to the observed GRACE data compared to interpolated GRACE data. Furthermore, we show that precise modeling of non-gravitational forces acting on the Swarm satellites is the key for reaching these accuracies. Our results have implications for sea level budget studies, but they may also guide further research in gravity field analysis schemes, including satellites not dedicated to gravity field studies.

Precise Determination of the Zero-Gravity Surface Figure of a Mirror without Gravity-Sag Modeling

NASA Technical Reports Server (NTRS)

Bloemhof, Eric E.; Lam, Jonathan C.; Feria, V. Alfonso; Chang, Zensheu

2007-01-01

The zero-gravity surface figure of optics used in spaceborne astronomical instruments must be known to high accuracy, but earthbound metrology is typically corrupted by gravity sag. Generally, inference of the zero-gravity surface figure from a measurement made under normal gravity requires finite-element analysis (FEA), and for accurate results the mount forces must be well characterized. We describe how to infer the zero-gravity surface figure very precisely using the alternative classical technique of averaging pairs of measurements made with the direction of gravity reversed. We show that mount forces as well as gravity must be reversed between the two measurements and discuss how the St. Venant principle determines when a reversed mount force may be considered to be applied at the same place in the two orientations. Our approach requires no finite-element modeling and no detailed knowledge of mount forces other than the fact that they reverse and are applied at the same point in each orientation. If mount schemes are suitably chosen, zero-gravity optical surfaces may be inferred much more simply and more accurately than with FEA.

Gravity model improvement using the DORIS tracking system on the SPOT 2 satellite

NASA Technical Reports Server (NTRS)

Nerem, R. S.; Lerch, F. J.; Williamson, R. G.; Klosko, S. M.; Robbins, J. W.; Patel, G. B.

1994-01-01

A high-precision radiometric satellite tracking system, Doppler Orbitography and Radio-positioning Integrated by Satellite system (DORIS), has recently been developed by the French space agency, Centre National d'Etudes Spatiales (CNES). DORIS was designed to provide tracking support for missions such as the joint United States/French TOPEX/Poseidon. As part of the flight testing process, a DORIS package was flown on the French SPOT 2 satellite. A substantial quantity of geodetic quality tracking data was obtained on SPOT 2 from an extensive international DORIS tracking network. These data were analyzed to assess their accuracy and to evaluate the gravitational modeling enhancements provided by these data in combination with the Goddard Earth Model-T3 (GEM-T3) gravitational model. These observations have noise levels of 0.4 to 0.5 mm/s, with few residual systematic effects. Although the SPOT 2 satellite experiences high atmospheric drag forces, the precision and global coverage of the DORIS tracking data have enabled more extensive orbit parameterization to mitigate these effects. As a result, the SPOT 2 orbital errors have been reduced to an estimated radial accuracy in the 10-20 cm RMS range. The addition of these data, which encompass many regions heretofore lacking in precision satellite tracking, has significantly improved GEM-T3 and allowed greatly improved orbit accuracies for Sun-synchronous satellites like SPOT 2 (such as ERS 1 and EOS). Comparison of the ensuing gravity model with other contemporary fields (GRIM-4C2, TEG2B, and OSU91A) provides a means to assess the current state of knowledge of the Earth's gravity field. Thus, the DORIS experiment on SPOT 2 has provided a strong basis for evaluating this new orbit tracking technology and has demonstrated the important contribution of the DORIS network to the success of the TOPEX/Poseidon mission.

Gravity discharge vessel revisited: An explicit Lambert W function solution

NASA Astrophysics Data System (ADS)

Digilov, Rafael M.

2017-07-01

Based on the generalized Poiseuille equation modified by a kinetic energy correction, an explicit solution for the time evolution of a liquid column draining under gravity through an exit capillary tube is derived in terms of the Lambert W function. In contrast to the conventional exponential behavior, as implied by the Poiseuille law, a new analytical solution gives a full account for the volumetric flow rate of a fluid through a capillary of any length and improves the precision of viscosity determination. The theoretical consideration may be of interest to students as an example of how implicit equations in the field of physics can be solved analytically using the Lambert function.

Impact of nonlinear effective interactions on group field theory quantum gravity condensates

NASA Astrophysics Data System (ADS)

Pithis, Andreas G. A.; Sakellariadou, Mairi; Tomov, Petar

2016-09-01

We present the numerical analysis of effectively interacting group field theory models in the context of the group field theory quantum gravity condensate analog of the Gross-Pitaevskii equation for real Bose-Einstein condensates including combinatorially local interaction terms. Thus, we go beyond the usually considered construction for free models. More precisely, considering such interactions in a weak regime, we find solutions for which the expectation value of the number operator N is finite, as in the free case. When tuning the interaction to the strongly nonlinear regime, however, we obtain solutions for which N grows and eventually blows up, which is reminiscent of what one observes for real Bose-Einstein condensates, where a strong interaction regime can only be realized at high density. This behavior suggests the breakdown of the Bogoliubov ansatz for quantum gravity condensates and the need for non-Fock representations to describe the system when the condensate constituents are strongly correlated. Furthermore, we study the expectation values of certain geometric operators imported from loop quantum gravity in the free and interacting cases. In particular, computing solutions around the nontrivial minima of the interaction potentials, one finds, already in the weakly interacting case, a nonvanishing condensate population for which the spectra are dominated by the lowest nontrivial configuration of the quantum geometry. This result indicates that the condensate may indeed consist of many smallest building blocks giving rise to an effectively continuous geometry, thus suggesting the interpretation of the condensate phase to correspond to a geometric phase.

TESTING GRAVITY WITH QUASI-PERIODIC OSCILLATIONS FROM ACCRETING BLACK HOLES: THE CASE OF THE EINSTEIN–DILATON–GAUSS–BONNET THEORY

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

Maselli, Andrea; Gualtieri, Leonardo; Ferrari, Valeria

Quasi-periodic oscillations (QPOs) observed in the X-ray flux emitted by accreting black holes are associated with phenomena occurring near the horizon. Future very large area X-ray instruments will be able to measure QPO frequencies with very high precision, thus probing this strong-field region. Using the relativistic precession model, we show the way in which QPO frequencies could be used to test general relativity (GR) against those alternative theories of gravity which predict deviations from the classical theory in the strong-field and high-curvature regimes. We consider one of the best-motivated high-curvature corrections to GR, namely, the Einstein–Dilaton–Gauss–Bonnet theory, and show thatmore » a detection of QPOs with the expected sensitivity of the proposed ESA M-class mission LOFT would set the most stringent constraints on the parameter space of this theory.« less

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

A Combined Gravity Compensation Method for INS Using the Simplified Gravity Model and Gravity Database.

PubMed

Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang

2018-05-14

In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS's solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method.

A Combined Gravity Compensation Method for INS Using the Simplified Gravity Model and Gravity Database

PubMed Central

Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang

2018-01-01

In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS’s solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method. PMID:29757983

Techniques for increasing the efficiency of Earth gravity calculations for precision orbit determination

NASA Technical Reports Server (NTRS)

Smith, R. L.; Lyubomirsky, A. S.

1981-01-01

Two techniques were analyzed. The first is a representation using Chebyshev expansions in three-dimensional cells. The second technique employs a temporary file for storing the components of the nonspherical gravity force. Computer storage requirements and relative CPU time requirements are presented. The Chebyshev gravity representation can provide a significant reduction in CPU time in precision orbit calculations, but at the cost of a large amount of direct-access storage space, which is required for a global model.

Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?

PubMed

Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim

2009-10-09

We show the importance of properly including the perturbations of the dark energy component in the dynamical dark energy models based on a scalar field and modified gravity theories in order to meet with present and future observational precisions. Based on a simple scaling scalar field dark energy model, we show that observationally distinguishable substantial differences appear by ignoring the dark energy perturbation. By ignoring it the perturbed system of equations becomes inconsistent and deviations in (gauge-invariant) power spectra depend on the gauge choice.

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

High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability?

NASA Astrophysics Data System (ADS)

Eppelbaum, Lev

2015-04-01

Microgravity investigations are comparatively rarely used for searching of hidden ancient targets (e.g., Eppelbaum, 2013). It is caused mainly by small geometric size of the desired archaeological objects and various types of noise complicating the observed useful signal. At the same time, development of modern generation of field gravimetric equipment allows to register microGal (10-8 m/s2) anomalies that offer a new challenge in this direction. Correspondingly, an accuracy of gravity variometers (gradientometers) is also sharply increased. How we can improve the interpretation effectiveness and reliability? Undoubtedly, it must be a multi-stage process. I believe that we must begin since nonconventional methodologies for reducing topographic effect and terrain correction computation. Topographic effect reducing The possibilities of reducing topographic effects by grouping the points of additional gravimetric observations around the central point located on the survey network were demonstrated in (Khesin et al., 1996). A group of 4 to 8 additional points is located above and below along the relief approximately symmetrically and equidistant from the central point. The topographic effect is reduced to the obtained difference between the gravity field in the center of the group and its mean value for the whole group. Application of this methodology in the gold-pyrite deposit Gyzyl-Bulakh (Lesser Caucasus, western Azerbaijan) indicated its effectiveness. Computation of terrain correction Some geophysicists compare the new ideas in the field of terrain correction (TC) in gravimetry with the 'perpetuum mobile' invention. However, when we speak about very detailed gravity observations, the problem of most optimal computation of surrounding relief influence is of a great importance. Let us will consider two approaches applied earlier in ore geophysics. First approach A first method was applied in the Gyzyl-Bulakh gold-pyrite deposit situated in the Mekhmana ore region of the Lesser Caucasus (western Azerbaijan) under conditions of rugged relief and complex geology. This deposit is well investigated by mining and drilling operations and therefore was used as a reference field polygon for testing this approach. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly and the gravity field determined from a 3D model of a uniform medium with a real topography. 3-D terrain relief model with an interval of its description of 80 km (the investigated 6 profiles of 800 m length are in the center of this interval) was employed to compute (by the use of GSFC software (Khesin et al., 1996)) the gravitational effect of the medium (σ = 2670 kg/m3). With applying such a scheme the Bouguer anomalies were obtained with accuracy in two times higher than that of TC received by the conventional methods. As a result, on the basis of the improved Bouguer gravity with the precise TC data, the geological structure of the deposit was defined (Khesin et al., 1996). Second approach Second approach was employed at the complex Katekh pyrite-polymetallic deposit, which is located at the southern slope of the Greater Caucasus (northern Azerbaijan). The main peculiarities of this area are very rugged topography of SW-NE trend, complex geology and severe tectonics. Despite the availability of conventional ΔgB (TC far zones were computed up to 200 km), for the enhanced calculation of surrounding terrain topography a digital terrain relief model was created (Eppelbaum and Khesin, 2004). The SW-NE regional topography trend in the area of the Katekh deposit occurrence was computed as a rectangular digital terrain relief model (DTRM) of 20 km long and 600 m wide (our interpretation profile with a length of 800 m was located in the geometrical center of the DTRM). As a whole, about 1000 characteristic points were used to describe the DTRM (most frequently points were focused in the center of the DTRM and more rarely - on the margins). Thus, in the interactive 3D ΔgB modeling (by the use of GSFC software) was computed effect not only from geological bodies occurring in this area, but also from surrounding DTRM. In the issue of this scheme application, two new ore bodies were discovered. Quantitative analysis of gravity anomalies The trivial formulas of quantitative analysis (based on simple relationships between the gravity field intensity and geometrical parameters of the anomalous body) are widely presented in the geophysical literature (e.g., Telford et al., 1993; Parasnis, 1997). However, absence of reliable information about the normal gravity field in the studied areas strongly limits practical application of these methods. Gravity field intensity F is expressed as F = - gradW, (1) where W is the gravity potential. For anomalous magnetic field Ua we can write (when magnetic susceptibility ≤ 0.1 SI unit) (Khesin et al., 1996): Ua = - gradV, (2) where V represents the magnetic potential. Let's consider analytical expressions of some typical models employed in magnetic and gravity fields (Table 1). Table 1. Comparison of some analytical expressions for magnetic and gravity fields Field Analytical expression MagneticThin bed (TB) z Zv = 2I2b-2--2 x + z (3) Point source (rod) mz Zv = ----3/2 (x2 + z2) (4) Gravity Horizontal Circular Cylinder (HCC) -z-- Δg = 2Gσ x2 + z2 (5) Sphere --z--- Δg = GM (x2 + z2)3/2 (6)

Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey

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

Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.

2017-03-20

We combine 131 new medium-resolution ( R ∼ 2000) J -band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K i lines at 1.1692, 1.1778, and 1.2529 μ m, and the 1.2 μ m FeH{sub J} absorption index. Our resultsmore » are consistent with previous surface gravity measurements, showing a distinct double peak—at ∼L5 and T5—in K i EW as a function of spectral type. We analyze the K i EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.« less

Simulation Study of a Follow-on Gravity Mission to GRACE

NASA Technical Reports Server (NTRS)

Loomis, Bryant D.; Nerem, R. S.; Luthcke, Scott B.

2012-01-01

The gravity recovery and climate experiment (GRACE) has been providing monthly estimates of the Earth's time-variable gravity field since its launch in March 2002. The GRACE gravity estimates are used to study temporal mass variations on global and regional scales, which are largely caused by a redistribution of water mass in the Earth system. The accuracy of the GRACE gravity fields are primarily limited by the satellite-to-satellite range-rate measurement noise, accelerometer errors, attitude errors, orbit errors, and temporal aliasing caused by unmodeled high-frequency variations in the gravity signal. Recent work by Ball Aerospace and Technologies Corp., Boulder, CO has resulted in the successful development of an interferometric laser ranging system to specifically address the limitations of the K-band microwave ranging system that provides the satellite-to-satellite measurements for the GRACE mission. Full numerical simulations are performed for several possible configurations of a GRACE Follow-On (GFO) mission to determine if a future satellite gravity recovery mission equipped with a laser ranging system will provide better estimates of time-variable gravity, thus benefiting many areas of Earth systems research. The laser ranging system improves the range-rate measurement precision to approximately 0.6 nm/s as compared to approx. 0.2 micro-seconds for the GRACE K-band microwave ranging instrument. Four different mission scenarios are simulated to investigate the effect of the better instrument at two different altitudes. The first pair of simulated missions is flown at GRACE altitude (approx. 480 km) assuming on-board accelerometers with the same noise characteristics as those currently used for GRACE. The second pair of missions is flown at an altitude of approx. 250 km which requires a drag-free system to prevent satellite re-entry. In addition to allowing a lower satellite altitude, the drag-free system also reduces the errors associated with the accelerometer. All simulated mission scenarios assume a two satellite co-orbiting pair similar to GRACE in a near-polar, near-circular orbit. A method for local time variable gravity recovery through mass concentration blocks (mascons) is used to form simulated gravity estimates for Greenland and the Amazon region for three GFO configurations and GRACE. Simulation results show that the increased precision of the laser does not improve gravity estimation when flown with on-board accelerometers at the same altitude and spacecraft separation as GRACE, even when time-varying background models are not included. This study also shows that only modest improvement is realized for the best-case scenario (laser, low-altitude, drag-free) as compared to GRACE due to temporal aliasing errors. These errors are caused by high-frequency variations in the hydrology signal and imperfections in the atmospheric, oceanographic, and tidal models which are used to remove unwanted signal. This work concludes that applying the updated technologies alone will not immediately advance the accuracy of the gravity estimates. If the scientific objectives of a GFO mission require more accurate gravity estimates, then future work should focus on improvements in the geophysical models, and ways in which the mission design or data processing could reduce the effects of temporal aliasing.

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

NASA Technical Reports Server (NTRS)

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

2011-01-01

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

Bathymetry of Patagonia glacier fjords and glacier ice thickness from high-resolution airborne gravity combined with other data

NASA Astrophysics Data System (ADS)

An, L.; Rignot, E.; Rivera, A.; Bunetta, M.

2012-12-01

The North and South Patagonia Ice fields are the largest ice masses outside Antarctica in the Southern Hemisphere. During the period 1995-2000, these glaciers lost ice at a rate equivalent to a sea level rise of 0.105 ± 0.001 mm/yr. In more recent years, the glaciers have been thinning more quickly than can be explained by warmer air temperatures and decreased precipitation. A possible cause is an increase in flow speed due to enhanced ablation of the submerged glacier fronts. To understand the dynamics of these glaciers and how they change with time, it is critical to have a detailed view of their ice thickness, the depth of the glacier bed below sea or lake level, how far inland these glaciers remain below sea or lake level, and whether bumps or hollows in the bed may slow down or accelerate their retreat. A grid of free-air gravity data over the Patagonia Glaciers was collected in May 2012 and October 2012, funded by the Gordon and Betty Moore Foundation (GBMF) to measure ice thickness and sea floor bathymetry. This survey combines the Sander Geophysics Limited (SGL) AIRGrav system, SGL laser altimetry and Chilean CECS/UCI ANDREA-2 radar. To obtain high-resolution and high-precision gravity data, the helicopter operates at 50 knots (25.7 m/s) with a grid spacing of 400m and collects gravity data at sub mGal level (1 Gal =1 Galileo = 1 cm/s2) near glacier fronts. We use data from the May 2012 survey to derive preliminarily high-resolution, high-precision thickness estimates and bathymetry maps of Jorge Montt Glacier and San Rafael Glacier. Boat bathymetry data is used to optimize the inversion of gravity over water and radar-derived thickness over glacier ice. The bathymetry maps will provide a breakthrough in our knowledge of the ice fields and enable a new era of glacier modeling and understanding that is not possible at present because ice thickness is not known.

Towards precision constraints on gravity with the Effective Field Theory of Large-Scale Structure

NASA Astrophysics Data System (ADS)

Bose, Benjamin; Koyama, Kazuya; Lewandowski, Matthew; Vernizzi, Filippo; Winther, Hans A.

2018-04-01

We compare analytical computations with numerical simulations for dark-matter clustering, in general relativity and in the normal branch of DGP gravity (nDGP). Our analytical frameword is the Effective Field Theory of Large-Scale Structure (EFTofLSS), which we use to compute the one-loop dark-matter power spectrum, including the resummation of infrared bulk displacement effects. We compare this to a set of 20 COLA simulations at redshifts z = 0, z = 0.5, and z = 1, and fit the free parameter of the EFTofLSS, called the speed of sound, in both ΛCDM and nDGP at each redshift. At one-loop at z = 0, the reach of the EFTofLSS is kreach ≈ 0.14 Mpc‑1 for both ΛCDM and nDGP. Along the way, we compare two different infrared resummation schemes and two different treatments of the time dependence of the perturbative expansion, concluding that they agree to approximately 1% over the scales of interest. Finally, we use the ratio of the COLA power spectra to make a precision measurement of the difference between the speeds of sound in ΛCDM and nDGP, and verify that this is proportional to the modification of the linear coupling constant of the Poisson equation.

THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS

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

Liu, Michael C.; Dupuy, Trent J.; Allers, Katelyn N., E-mail: mliu@ifa.hawaii.edu

We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectralmore » type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s{sup −1}) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β  Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.« less

Progress in the Determination of the Earth's Gravity Field

NASA Technical Reports Server (NTRS)

Rapp, Richard H. (Editor)

1989-01-01

Topics addressed include: global gravity model development; methods for approximation of the gravity field; gravity field measuring techniques; global gravity field applications and requirements in geophysics and oceanography; and future gravity missions.

High-Precision Simulation of the Gravity Field of Rapidly-Rotating Barotropes in Hydrostatic Equilibrium

NASA Astrophysics Data System (ADS)

Hubbard, W. B.

2013-12-01

The so-called theory of figures (TOF) uses potential theory to solve for the structure of highly distorted rotating liquid planets in hydrostatic equilibrium. TOF is noteworthy both for its antiquity (Maclaurin 1742) and its mathematical complexity. Planned high-precision gravity measurements near the surfaces of Jupiter and Saturn (possibly detecting signals ~ microgal) will place unprecedented requirements on TOF, not because one expects hydrostatic equilibrium to that level, but because nonhydrostatic components in the surface gravity, at expected levels ~ 1 milligal, must be referenced to precise hydrostatic-equilibrium models. The Maclaurin spheroid is both a useful test of numerical TOF codes (Hubbard 2012, ApJ Lett 756:L15), and an approach to an efficient TOF code for arbitrary barotropes of variable density (Hubbard 2013, ApJ 768:43). For the latter, one trades off vertical resolution by replacing a continuous barotropic pressure-density relation with a stairstep relation, corresponding to N concentric Maclaurin spheroids (CMS), each of constant density. The benefit of this trade-off is that two-dimensional integrals over the mass distributions at each interface are reduced to one-dimensional integrals, quickly and accurately evaluated by Gaussian quadrature. The shapes of the spheroids comprise N level surfaces within the planet and at its surface, are gravitationally coupled to each other, and are found by self-consistent iteration, relaxing to a final configuration to within the computer's precision limits. The angular and radial variation of external gravity (using the usual geophysical expansion in multipole moments) can be found to the limit of typical floating point precision (~ 1.e-14), much better than the expected noise/signal for either the Juno or Cassini gravity experiments. The stairstep barotrope can be adjusted to fit a prescribed continuous or discontinuous interior barotrope, and can be made to approximate it to any required precision by increasing N. One can insert a higher density of CMSs toward the surface of an interior model in order to more accurately model high-order gravitational moments. The magnitude of high-order moments predicted by TOF declines geometrically with order number, and falls below the magnitude of expected non-hydrostatic terms produced by interior dynamics at ~ order 10 and above. Juno's sensitivity is enough to detect tidal gravity signals from Galilean satellites. The CMS method can be generalized to predict tidal zonal and tesseral terms consistent with an interior model fitted to measured zonal harmonics. For this purpose, two-dimensional Gaussian quadrature is necessary at each CMS interface. However, once the model is relaxed to equilibrium, one need not refit the model to the average zonal harmonics because of the smallness of the tidal terms. I will describe how the CMS method has been validated through comparisons with standard TOF models for which fully or partially analytic solutions exist, as well as through consistency checks. At this stage in software development in preparation for Jupiter orbit, we are focused on increasing the speed of the code in order to more efficiently search the parameter space of acceptable Jupiter interior models, as well as to interface it with advanced hydrogen-helium equations of state.

Gravity Compensation Using EGM2008 for High-Precision Long-Term Inertial Navigation Systems

PubMed Central

Wu, Ruonan; Wu, Qiuping; Han, Fengtian; Liu, Tianyi; Hu, Peida; Li, Haixia

2016-01-01

The gravity disturbance vector is one of the major error sources in high-precision and long-term inertial navigation applications. Specific to the inertial navigation systems (INSs) with high-order horizontal damping networks, analyses of the error propagation show that the gravity-induced errors exist almost exclusively in the horizontal channels and are mostly caused by deflections of the vertical (DOV). Low-frequency components of the DOV propagate into the latitude and longitude errors at a ratio of 1:1 and time-varying fluctuations in the DOV excite Schuler oscillation. This paper presents two gravity compensation methods using the Earth Gravitational Model 2008 (EGM2008), namely, interpolation from the off-line database and computing gravity vectors directly using the spherical harmonic model. Particular attention is given to the error contribution of the gravity update interval and computing time delay. It is recommended for the marine navigation that a gravity vector should be calculated within 1 s and updated every 100 s at most. To meet this demand, the time duration of calculating the current gravity vector using EGM2008 has been reduced to less than 1 s by optimizing the calculation procedure. A few off-line experiments were conducted using the data of a shipborne INS collected during an actual sea test. With the aid of EGM2008, most of the low-frequency components of the position errors caused by the gravity disturbance vector have been removed and the Schuler oscillation has been attenuated effectively. In the rugged terrain, the horizontal position error could be reduced at best 48.85% of its regional maximum. The experimental results match with the theoretical analysis and indicate that EGM2008 is suitable for gravity compensation of the high-precision and long-term INSs. PMID:27999351

Gravity Compensation Using EGM2008 for High-Precision Long-Term Inertial Navigation Systems.

PubMed

Wu, Ruonan; Wu, Qiuping; Han, Fengtian; Liu, Tianyi; Hu, Peida; Li, Haixia

2016-12-18

The gravity disturbance vector is one of the major error sources in high-precision and long-term inertial navigation applications. Specific to the inertial navigation systems (INSs) with high-order horizontal damping networks, analyses of the error propagation show that the gravity-induced errors exist almost exclusively in the horizontal channels and are mostly caused by deflections of the vertical (DOV). Low-frequency components of the DOV propagate into the latitude and longitude errors at a ratio of 1:1 and time-varying fluctuations in the DOV excite Schuler oscillation. This paper presents two gravity compensation methods using the Earth Gravitational Model 2008 (EGM2008), namely, interpolation from the off-line database and computing gravity vectors directly using the spherical harmonic model. Particular attention is given to the error contribution of the gravity update interval and computing time delay. It is recommended for the marine navigation that a gravity vector should be calculated within 1 s and updated every 100 s at most. To meet this demand, the time duration of calculating the current gravity vector using EGM2008 has been reduced to less than 1 s by optimizing the calculation procedure. A few off-line experiments were conducted using the data of a shipborne INS collected during an actual sea test. With the aid of EGM2008, most of the low-frequency components of the position errors caused by the gravity disturbance vector have been removed and the Schuler oscillation has been attenuated effectively. In the rugged terrain, the horizontal position error could be reduced at best 48.85% of its regional maximum. The experimental results match with the theoretical analysis and indicate that EGM2008 is suitable for gravity compensation of the high-precision and long-term INSs.

Precise positioning with sparse radio tracking: How LRO-LOLA and GRAIL enable future lunar exploration

NASA Astrophysics Data System (ADS)

Mazarico, E.; Goossens, S. J.; Barker, M. K.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

2017-12-01

Two recent NASA missions to the Moon, the Lunar Reconnaissance Orbiter (LRO) and the Gravity Recovery and Interior Laboratory (GRAIL), have obtained highly accurate information about the lunar shape and gravity field. These global geodetic datasets resolve long-standing issues with mission planning; the tidal lock of the Moon long prevented collection of accurate gravity measurements over the farside, and deteriorated precise positioning of topographic data. We describe key datasets and results from the LRO and GRAIL mission that are directly relevant to future lunar missions. SmallSat and CubeSat missions especially would benefit from these recent improvements, as they are typically more resource-constrained. Even with limited radio tracking data, accurate knowledge of topography and gravity enables precise orbit determination (OD) (e.g., limiting the scope of geolocation and co-registration tasks) and long-term predictions of altitude (e.g., dramatically reducing uncertainties in impact time). With one S-band tracking pass per day, LRO OD now routinely achieves total position knowledge better than 10 meters and radial position knowledge around 0.5 meter. Other tracking data, such as Laser Ranging from Earth-based SLR stations, can further support OD. We also show how altimetry can be used to substantially improve orbit reconstruction with the accurate topographic maps now available from Lunar Orbiter Laser Altimeter (LOLA) data. We present new results with SELENE extended mission and LRO orbits processed with direct altimetry measurements. With even a simple laser altimeter onboard, high-quality OD can be achieved for future missions because of the datasets acquired by LRO and GRAIL, without the need for regular radio contact. Onboard processing of altimetric ranges would bring high-quality real-time position knowledge to support autonomous operation. We also describe why optical ranging transponders are ideal payloads for future lunar missions, as they can address both communication and navigation needs with little resources.

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.

JPL-20180522-GRACFOf-0001-NASAs GRACE FO Satellite Launches Aboard a SpaceX Falcon 9 Rocket

NASA Image and Video Library

2018-05-22

3-2-1 liftoff of Falcon 9 with GRACE-FO! NASA's Gravity Recovery and Climate Experiment Follow-on, or GRACE-FO, launched from Vandenberg Air Force Base on California's Central Coast on May 22, 2018. The twin orbiters shared a ride to space with five Iridium NEXT communications satellites. GRACE-FO will continue a study begun by the original GRACE mission, which proved that water movement can be tracked with high precision by its effect on Earth's gravitational field. GRACE-FO will continue the record of regional variations in gravity, telling us about changes in glaciers, ground water, sea levels and the health of our planet as a whole. For more, visit https://gracefo.jpl.nasa.gov .

Atom Interferometer Technologies in Space for Gravity Mapping and Gravity Science

NASA Astrophysics Data System (ADS)

Williams, Jason; Chiow, Sheng-Wey; Kellogg, James; Kohel, James; Yu, Nan

2015-05-01

Atom interferometers utilize the wave-nature of atomic gases for precision measurements of inertial forces, with potential applications ranging from gravity mapping for planetary science to unprecedented tests of fundamental physics with quantum gases. The high stability and sensitivity intrinsic to these devices already place them among the best terrestrial sensors available for measurements of gravitational accelerations, rotations, and gravity gradients, with the promise of several orders of magnitude improvement in their detection sensitivity in microgravity. Consequently, multiple precision atom-interferometer-based projects are under development at the Jet Propulsion Laboratory, including a dual-atomic-species interferometer that is to be integrated into the Cold Atom Laboratory onboard the International Space Station and a highly stable gravity gradiometer in a transportable design relevant for earth science measurements. We will present JPL's activities in the use of precision atom interferometry for gravity mapping and gravitational wave detection in space. Our recent progresses bringing the transportable JPL atom interferometer instrument to be competitive with the state of the art and simulations of the expected capabilities of a proposed flight project will also be discussed. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

A Lifetime of Geodesy and Geophysics: In Rememberence of Bill Kaula

NASA Technical Reports Server (NTRS)

Smith, David E.

2000-01-01

In the early 1960's the secrets that knowledge of the Earth's gravity field would eventually reveal about the processes that govern our planet were yet to be appreciated. It was the beginning of a new science known as space geodesy, which arose at a time when most efforts were devoted to understanding how to extract precise measurements of Earth structure and motions from an orbiting spacecraft. Bill Kaula was central to that beginning and showed the way for many who were to follow, both in time and in the development of approaches most likely to yield results. Bill laid out the theory, analyzed the data, and argued strenuously for a spacecraft mission devoted to measuring gravity to make it all come true in the way he knew it really could. That mission, GRACE, was a long time coming and Bill would not see its final staging, but his influence in making it happen was everywhere. With time, the concepts for measuring the static gravity field of the Earth and terrestrial planets became well advanced, although not universally agreed upon, and certainly not by Bill, who was always eager to argue and challenge traditional methods and thinking. The extension of space geodetic techniques to the planets and the development of new techniques to measure time variations in gravity have recently brought geodesy even closer to the geophysical processes that Bill sought to understand. This presentation will contain a little geodesy, a little history, and a little reminiscing about the leader in our field.

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.

Basic research and data analysis for the earth and ocean physics applications program and for the National Geodetic Satellite program

NASA Technical Reports Server (NTRS)

1975-01-01

Data acquisition using single image and seven image data processing is used to provide a precise and accurate geometric description of the earth's surface. Transformation parameters and network distortions are determined, Sea slope along the continental boundaries of the U.S. and earth rotation are examined, along with close grid geodynamic satellite system. Data are derived for a mathematical description of the earth's gravitational field; time variations are determined for geometry of the ocean surface, the solid earth, gravity field, and other geophysical parameters.

Expected orbit determination performance for the TOPEX/Poseidon mission

NASA Technical Reports Server (NTRS)

Nerem, R. S.; Putney, Barbara H.; Marshall, J. A.; Lerch, Francis J.; Pavlis, Erricos C.; Klosko, Steven M.; Luthcke, Scott B.; Patel, Girish B.; Williamson, Ronald G.; Zelensky, Nikita P.

1993-01-01

Each of the components required for the computation of precise orbits for the TOPEX/Poseidon (T/P) spacecraft - gravity field modeling, nonconservative force modeling, and satellite tracking technologies - is examined. The research conducted in the Space Geodesy Branch at Goddard Space Flight Center in preparation for meeting the 13-cm radial orbit accuracy requirement for the T/P mission is outlined. New developments in modeling the earth's gravitational field and modeling the complex nonconservative forces acting on T/P are highlighted. The T/P error budget is reviewed, and a prelaunch assessment of the predicted orbit determination accuracies is summarized.

Secular gravity variation at Svalbard (Norway) from ground observations and GRACE satellite data

NASA Astrophysics Data System (ADS)

Mémin, A.; Rogister, Y.; Hinderer, J.; Omang, O. C.; Luck, B.

2011-03-01

The Svalbard archipelago, Norway, is affected by both the present-day ice melting (PDIM) and Glacial Isostatic Adjustment (GIA) subsequent to the Last Pleistocene deglaciation. The induced deformation of the Earth is observed by using different techniques. At the Geodetic Observatory in Ny-Ålesund, precise positioning measurements have been collected since 1991, a superconducting gravimeter (SG) has been installed in 1999, and six campaigns of absolute gravity (AG) measurements were performed between 1998 and 2007. Moreover, the Gravity Recovery and Climate Experiment (GRACE) satellite mission provides the time variation of the Earth gravity field since 2002. The goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the GIA and Earth's response to the PDIM. We estimate the secular gravity variation by superimposing the SG series with the six AG measurements. We collect published estimates of the vertical velocity based on GPS and VLBI data. We analyse the GRACE solutions provided by three groups (CSR, GFZ, GRGS). The crux of the problem lies in the separation of the contributions from the GIA and PDIM to the Earth's deformation. To account for the GIA, we compute the response of viscoelastic Earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ICE-3G or ICE-5G. To account for the effect of PDIM, we compute the deformation of an elastic Earth model for six models of ice-melting extension and rates. Errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the GRACE solutions and GIA and PDIM models. The ground observations agree with models that involve a current ice loss of 25 km3 water equivalent yr-1 over Svalbard, whereas the space observations give a value in the interval [5, 18] km3 water equivalent yr-1. A better modelling of the PDIM, which would include the precise topography of the glaciers and altitude-dependency of ice melting, is necessary to decrease the discrepancy between the two estimates.

Geopotential models in the Australian region

NASA Technical Reports Server (NTRS)

Kearsley, A. H. W.; Holloway, R. D.

1989-01-01

The ability of three high-order geopotential models (OSU81, GPM2 and OSU86E) to recover the gravity anomaly field (delta g) in the Australian region was tested. The region was divided into 2 x 2 deg blocks, and the mean and rms of the residual gravity (delta g measured - delta g modeled) was found to estimate the fit of the model to the point gravity data. The results showed that OSU81 and GPM2 performed similarly, recovering the delta g with a mean value of less than plus or minus 5 mGal in 63 and 70 percent of the blocks, respectively. However, both these models achieved a fit of worse that was plus or minus 13 mGal in 6 to 7 percent of cases. These were in areas either on or near the coast, or in the Central Australian region, inferring that for a precise geoid slope determination in these regions, a detailed analysis of delta g in region is needed. On the other hand, OSU86E produced a very good result, having a mean fit of less than plus or minus 5 mGal in 80 percent of the blocks, and worse than plus or minus 13 mGal in only 1 percent of cases. The rms values for this model were also improved over the other two models, indicating that for applications requiring highest precision, the preferred model is OSU86E.

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

Differential results integrated with continuous and discrete gravity measurements between nearby stations

NASA Astrophysics Data System (ADS)

Xu, Weimin; Chen, Shi; Lu, Hongyan

2016-04-01

Integrated gravity is an efficient way in studying spatial and temporal characteristics of the dynamics and tectonics. Differential measurements based on the continuous and discrete gravity observations shows highly competitive in terms of both efficiency and precision with single result. The differential continuous gravity variation between the nearby stations, which is based on the observation of Scintrex g-Phone relative gravimeters in every single station. It is combined with the repeated mobile relative measurements or absolute results to study the regional integrated gravity changes. Firstly we preprocess the continuous records by Tsoft software, and calculate the theoretical earth tides and ocean tides by "MT80TW" program through high precision tidal parameters from "WPARICET". The atmospheric loading effects and complex drift are strictly considered in the procedure. Through above steps we get the continuous gravity in every station and we can calculate the continuous gravity variation between nearby stations, which is called the differential continuous gravity changes. Then the differential results between related stations is calculated based on the repeated gravity measurements, which are carried out once or twice every year surrounding the gravity stations. Hence we get the discrete gravity results between the nearby stations. Finally, the continuous and discrete gravity results are combined in the same related stations, including the absolute gravity results if necessary, to get the regional integrated gravity changes. This differential gravity results is more accurate and effective in dynamical monitoring, regional hydrologic effects studying, tectonic activity and other geodynamical researches. The time-frequency characteristics of continuous gravity results are discussed to insure the accuracy and efficiency in the procedure.

GGOS working group on ground networks and communications

NASA Technical Reports Server (NTRS)

Pearlman, M.; Altamimi, Z.; Beck, N.; Forsberg, R.; Gurtner, W.; Kenyon, S.; Behrend, D.; Lemoine, F. G.; Ma, C.; Noll, C. E.;

On the recovery of gravity anomalies from high precision altimeter data

NASA Technical Reports Server (NTRS)

Lelgemann, D.

1976-01-01

A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

27 CFR 30.24 - Specific gravity hydrometers.

Code of Federal Regulations, 2010 CFR

2010-04-01

... hydrometers. 30.24 Section 30.24 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE... hydrometers. (a) The specific gravity hydrometers furnished by proprietors to appropriate TTB officers shall... instruments. Such specific gravity hydrometers shall be of a precision grade, standardization temperature 60...

27 CFR 30.21 - Requirements.

Code of Federal Regulations, 2012 CFR

2012-04-01

... thermometers furnished by the Government. However, where this part requires the use of a specific gravity hydrometer, TTB officers shall use precision grade specific gravity hydrometers conforming to the provisions... determination of specific gravity and for gauging. From time to time appropriate TTB officers shall verify the...

27 CFR 30.21 - Requirements.

Code of Federal Regulations, 2014 CFR

2014-04-01

... thermometers furnished by the Government. However, where this part requires the use of a specific gravity hydrometer, TTB officers shall use precision grade specific gravity hydrometers conforming to the provisions... determination of specific gravity and for gauging. From time to time appropriate TTB officers shall verify the...

27 CFR 30.21 - Requirements.

Code of Federal Regulations, 2011 CFR

2011-04-01

... thermometers furnished by the Government. However, where this part requires the use of a specific gravity hydrometer, TTB officers shall use precision grade specific gravity hydrometers conforming to the provisions... determination of specific gravity and for gauging. From time to time appropriate TTB officers shall verify the...

27 CFR 30.21 - Requirements.

Code of Federal Regulations, 2013 CFR

2013-04-01

... thermometers furnished by the Government. However, where this part requires the use of a specific gravity hydrometer, TTB officers shall use precision grade specific gravity hydrometers conforming to the provisions... determination of specific gravity and for gauging. From time to time appropriate TTB officers shall verify the...

Detection of magnetic fields in chemically peculiar stars observed with the K2 space mission

NASA Astrophysics Data System (ADS)

Buysschaert, B.; Neiner, C.; Martin, A. J.; Aerts, C.; Bowman, D. M.; Oksala, M. E.; Van Reeth, T.

2018-05-01

We report the results of an observational study aimed at searching for magnetic pulsating hot stars suitable for magneto-asteroseismology. A sample of sixteen chemically peculiar stars was selected and analysed using both high-resolution spectropolarimetry with ESPaDOnS and K2 high-precision space photometry. For all stars, we derive the effective temperature, surface gravity, rotational and non-rotational line broadening from our spectropolarimetric data. High-quality K2 light curves were obtained for thirteen of the sixteen stars and revealed rotational modulation, providing accurate rotation periods. Two stars show evidence for roAp pulsations, and one star shows signatures of internal gravity waves or unresolved g-mode pulsations. We confirm the presence of a large-scale magnetic field for eleven of the studied stars, of which nine are first detections. Further, we report one marginal detection and four non-detections. Two of the stars with a non-detected magnetic field show rotational modulation due to surface abundance inhomogeneities in the K2 light curve, and we confirm that the other two are chemically peculiar. Thus, these five stars likely host a weak (undetected) large-scale magnetic field.

Chameleon dark energy models with characteristic signatures

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

Gannouji, Radouane; Department of Physics, Faculty of Science, Tokyo University of Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601; Moraes, Bruno

2010-12-15

In chameleon dark energy models, local gravity constraints tend to rule out parameters in which observable cosmological signatures can be found. We study viable chameleon potentials consistent with a number of recent observational and experimental bounds. A novel chameleon field potential, motivated by f(R) gravity, is constructed where observable cosmological signatures are present both at the background evolution and in the growth rate of the perturbations. We study the evolution of matter density perturbations on low redshifts for this potential and show that the growth index today {gamma}{sub 0} can have significant dispersion on scales relevant for large scale structures.more » The values of {gamma}{sub 0} can be even smaller than 0.2 with large variations of {gamma} on very low redshifts for the model parameters constrained by local gravity tests. This gives a possibility to clearly distinguish these chameleon models from the {Lambda}-cold-dark-matter ({Lambda}CDM) model in future high-precision observations.« less

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.

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

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.

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.

APOKASC 2.0: Asteroseismology and Spectroscopy for Cool Stars

NASA Astrophysics Data System (ADS)

Pinsonneault, Marc H.; Elsworth, Yvonne P.; APOKASC

2017-01-01

The APOGEE survey has obtained and analyzed high resolution H band spectra of more than 10,000 cool dwarfs and giants in the original Kepler fields. The APOKASC effort combines this data with asteroseismology and star spot studies, resulting in more than 7,000 stellar mass estimates for dwarfs and giants with high quality abundances, temperatures, and surface gravities. We highlight the main results from this effort so far, which include a tight correlation between surface abundances in giants and stellar mass, precise absolute gravity calibrations, and the discovery of unexpected stellar populations, such as young alpha-enhanced stars. We discuss grid modeling estimates for stellar masses and compare the absolute asteroseismic mass scale to calibrators in star clusters and the halo Directions for future efforts are discussed.

New Data Bases and Standards for Gravity Anomalies

NASA Astrophysics Data System (ADS)

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

2008-12-01

Ever since the use of high-precision gravimeters emerged in the 1950's, gravity surveys have been an important tool for geologic studies. Recent developments that make geologically useful measurements from airborne and satellite platforms, the ready availability of the Global Positioning System that provides precise vertical and horizontal control, improved global data bases, and the increased availability of processing and modeling software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases publicly available to the geoscience community by expanding their holdings and increasing the accuracy and precision of the data in them. Specifically the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States are being revised using new formats and standards to improve their coverage, standardization, and accuracy. An important part of this effort is revision of procedures and standards for calculating gravity anomalies taking into account the enhanced computational power available, modern satellite-based positioning technology, improved terrain databases, and increased interest in more accurately defining the different components of gravity anomalies. The most striking revision is the use of one single internationally accepted reference ellipsoid for the horizontal and vertical datums of gravity stations as well as for the computation of the calculated value of theoretical gravity. The new standards hardly impact the interpretation of local anomalies, but do improve regional anomalies in that long wavelength artifacts are removed. Most importantly, such new standards can be consistently applied to gravity database compilations of nations, continents, and even the entire world. Although many types of gravity anomalies have been described, they fall into three main classes. The primary class incorporates planetary effects, which are analytically prescribed, to derive the predicted or modeled gravity, and thus, anomalies of this class are termed planetary. The most primitive version of a gravity anomaly is simply the difference between the value of gravity predicted by the effect of the reference ellipsoid and the observed gravity anomaly. When the height of the gravity station increases, the ellipsoidal gravity anomaly decreases because of the increased distance of measurement from the anomaly- producing masses. The two primary anomalies in geophysics, which are appropriately classified as planetary anomalies, are the Free-air and Bouguer gravity anomalies. They employ models that account for planetary effects on gravity including the topography of the earth. A second class of anomaly, geological anomalies, includes the modeled gravity effect of known or assumed masses leading to the predicted gravity by using geological data such as densities and crustal thickness. The third class of anomaly, filtered anomalies, removes arbitrary gravity effects of largely unknown sources that are empirically or analytically determined from the nature of the gravity anomalies by filtering.

46 CFR 28.535 - Inclining test.

Code of Federal Regulations, 2010 CFR

2010-10-01

... section, each vessel for which the lightweight displacement and centers of gravity must be determined in... of the vessel which was inclined and the location of the longitudinal center of gravity differs less... characteristics can be made and the precise location of the position of the vessel's vertical center of gravity is...

46 CFR 28.535 - Inclining test.

Code of Federal Regulations, 2013 CFR

2013-10-01

... section, each vessel for which the lightweight displacement and centers of gravity must be determined in... of the vessel which was inclined and the location of the longitudinal center of gravity differs less... characteristics can be made and the precise location of the position of the vessel's vertical center of gravity is...

46 CFR 28.535 - Inclining test.

Code of Federal Regulations, 2014 CFR

2014-10-01

... section, each vessel for which the lightweight displacement and centers of gravity must be determined in... of the vessel which was inclined and the location of the longitudinal center of gravity differs less... characteristics can be made and the precise location of the position of the vessel's vertical center of gravity is...

A method for estimating radioactive cesium concentrations in cattle blood using urine samples.

PubMed

Sato, Itaru; Yamagishi, Ryoma; Sasaki, Jun; Satoh, Hiroshi; Miura, Kiyoshi; Kikuchi, Kaoru; Otani, Kumiko; Okada, Keiji

2017-12-01

In the region contaminated by the Fukushima nuclear accident, radioactive contamination of live cattle should be checked before slaughter. In this study, we establish a precise method for estimating radioactive cesium concentrations in cattle blood using urine samples. Blood and urine samples were collected from a total of 71 cattle on two farms in the 'difficult-to-return zone'. Urine 137 Cs, specific gravity, electrical conductivity, pH, sodium, potassium, calcium, and creatinine were measured and various estimation methods for blood 137 Cs were tested. The average error rate of the estimation was 54.2% without correction. Correcting for urine creatinine, specific gravity, electrical conductivity, or potassium improved the precision of the estimation. Correcting for specific gravity using the following formula gave the most precise estimate (average error rate = 16.9%): [blood 137 Cs] = [urinary 137 Cs]/([specific gravity] - 1)/329. Urine samples are faster to measure than blood samples because urine can be obtained in larger quantities and has a higher 137 Cs concentration than blood. These advantages of urine and the estimation precision demonstrated in our study, indicate that estimation of blood 137 Cs using urine samples is a practical means of monitoring radioactive contamination in live cattle. © 2017 Japanese Society of Animal Science.

Around the world with professor Vening Meinesz onboard the submarine K-XVIII

NASA Astrophysics Data System (ADS)

Root, Bart; Hanssen, Ramon; Vermeersen, Bert; Munnik, Michiel; Vlijm, Rozemarijn

2015-04-01

In November 1934, Den Helder, The Netherlands, the start of a remarkable voyage commenced. The Hr. Ms. K-XVIII, a Dutch submarine, was about to set sail to Soerabaya, Indonesia. Onboard was a Dutch professor, Felix Andries Vening Meinesz. He was able to measure the Earth's gravity field with similar precision as on land for the first time in history using his innovative pendulum apparatus. His ground breaking data and systematic way of working changed the way of performing scientific expeditions. With the Library of the TUDelft and "Stichting Academisch Erfgoed" (Academic Heritage Foundation), we revisit this particular expedition and use it as a stepping stone to web-based geodetic and geophysical education for students and the public. The K-XVIII sailed over spreading ridges, transform faults, hotspot volcanos, subduction zones and many more interesting geological structures, which are discussed in this application. The importance of geodetic research is heavily present along the complete voyage in the form of global geoid determination. Moreover, the precision of the observations onboard the K-XVIII are compared with current satellite gravimetry and prove to be remarkable accurate. The goal of the project is to make the several datasets of Vening Meinesz, his measurements, articles, media, old foto's and other objects of the K-XVIII voyage, accessible for the public. The user can follow the famous voyage from Den Helder to Soerabaya in an interactive web application, stopping at interesting geophysical or historical places in space and time. The user can learn about plate tectonics and its historical findings, study the equipment that Vening Meinesz used to observe the gravity field with extreme precision, and learn about the important collaboration between science and the Navy. Dive into the adventure of the geo-scientific research of professor Vening Meinesz.

Weber's gravitational force as static weak field approximation

NASA Astrophysics Data System (ADS)

Tiandho, Yuant

2016-02-01

Weber's gravitational force (WGF) is one of gravitational model that can accommodate a non-static system because it depends not only on the distance but also on the velocity and the acceleration. Unlike Newton's law of gravitation, WGF can predict the anomalous of Mercury and gravitational bending of light near massive object very well. Then, some researchers use WGF as an alternative model of gravitation and propose a new mechanics theory namely the relational mechanics theory. However, currently we have known that the theory of general relativity which proposed by Einstein can explain gravity with very accurate. Through the static weak field approximation for the non-relativistic object, we also have known that the theory of general relativity will reduce to Newton's law of gravity. In this work, we expand the static weak field approximation that compatible with relativistic object and we obtain a force equation which correspond to WGF. Therefore, WGF is more precise than Newton's gravitational law. The static-weak gravitational field that we used is a solution of the Einstein's equation in the vacuum that satisfy the linear field approximation. The expression of WGF with ξ = 1 and satisfy the requirement of energy conservation are obtained after resolving the geodesic equation. By this result, we can conclude that WGF can be derived from the general relativity.

Methods for multiple-telescope beam imaging and guiding in the near-infrared

NASA Astrophysics Data System (ADS)

Anugu, N.; Amorim, A.; Gordo, P.; Eisenhauer, F.; Pfuhl, O.; Haug, M.; Wieprecht, E.; Wiezorrek, E.; Lima, J.; Perrin, G.; Brandner, W.; Straubmeier, C.; Le Bouquin, J.-B.; Garcia, P. J. V.

2018-05-01

Atmospheric turbulence and precise measurement of the astrometric baseline vector between any two telescopes are two major challenges in implementing phase-referenced interferometric astrometry and imaging. They limit the performance of a fibre-fed interferometer by degrading the instrument sensitivity and the precision of astrometric measurements and by introducing image reconstruction errors due to inaccurate phases. A multiple-beam acquisition and guiding camera was built to meet these challenges for a recently commissioned four-beam combiner instrument, GRAVITY, at the European Southern Observatory Very Large Telescope Interferometer. For each telescope beam, it measures (a) field tip-tilts by imaging stars in the sky, (b) telescope pupil shifts by imaging pupil reference laser beacons installed on each telescope using a 2 × 2 lenslet and (c) higher-order aberrations using a 9 × 9 Shack-Hartmann. The telescope pupils are imaged to provide visual monitoring while observing. These measurements enable active field and pupil guiding by actuating a train of tip-tilt mirrors placed in the pupil and field planes, respectively. The Shack-Hartmann measured quasi-static aberrations are used to focus the auxiliary telescopes and allow the possibility of correcting the non-common path errors between the adaptive optics systems of the unit telescopes and GRAVITY. The guiding stabilizes the light injection into single-mode fibres, increasing sensitivity and reducing the astrometric and image reconstruction errors. The beam guiding enables us to achieve an astrometric error of less than 50 μas. Here, we report on the data reduction methods and laboratory tests of the multiple-beam acquisition and guiding camera and its performance on-sky.

Astrophysics, cosmology, and fundamental physics with compact binary coalescence and the Einstein Telescope

NASA Astrophysics Data System (ADS)

Van Den Broeck, C.

2014-03-01

The second-generation interferometric gravitational wave detectors, currently under construction are expected to make their first detections within this decade. This will firmly establish gravitational wave physics as an empirical science, and will open up a new era in astrophysics, cosmology, and fundamental physics. Already with the first detections, we will be able to, among other things, establish the nature of short-hard gamma ray bursts, definitively confirm the existence of black holes, measure the Hubble constant in a completely independent way, and for the first time gain access to the genuinely strong-field dynamics of gravity. Hence, it is time to consider the longer-term future of this new field. The Einstein Telescope (ET) is a concrete conceptual proposal for a third-generation gravitational wave observatory, which will be ~ 10 times more sensitive in strain than the second-generation detectors. This will give access to sources at cosmological distances, with a correspondingly higher detection rate. We have given an overview of the science case for ET, with a focus on what can be learned from signals emitted by coalescing compact binaries. Third-generation observatories will allow us to map the coalescence rate out to redshifts z ~ 3, determine the mass functions of neutron stars and black holes, and perform precision measurements of the neutron star equation of state. ET will enable us to study the large-scale structure and evolution of the Universe without recourse to a cosmic distance ladder. Finally, we have discussed how it will allow for high-precision measurements of strong-field, dynamical gravity.

Venus Gravity: 180th Degree and Order Model

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Banerdt, W. B.; Sjogren, W. L.

1998-01-01

The Megallan Doppler radiometric tracking data provides unprecedented precision for spacecraft based gravity measurements with the maximum resolution approaching spherical harmonic degree and order 180 in selected equatorial regions.

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.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.; Logsdon, Sarah E.; Rice, Emily L.; Kirkpatrick, J. Davy; Burgasser, Adam J.; McGovern, Mark R.; Prato, Lisa

2017-03-01

We combine 131 new medium-resolution (R ˜ 2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6-L7 objects in our sample by measuring the equivalent widths (EW) of the K I lines at 1.1692, 1.1778, and 1.2529 μm, and the 1.2 μm FeH J absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ˜L5 and T5—in K I EW as a function of spectral type. We analyze the K I EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6-L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

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.

Advances and Best Practices in Airborne Gravimetry from the U.S. GRAV-D Project

NASA Astrophysics Data System (ADS)

Diehl, Theresa; Childers, Vicki; Preaux, Sandra; Holmes, Simon; Weil, Carly

2013-04-01

The Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project, an official policy of the U.S. National Geodetic Survey as of 2007, is working to survey the entire U.S. and its holdings with high-altitude airborne gravimetry. The goal of the project is to provide a consistent, high-quality gravity dataset that will become the cornerstone of a new gravimetric geoid and national vertical datum in 2022. Over the last five years, the GRAV-D project has surveyed more than 25% of the country, accomplishing almost 500 flights on six different aircraft platforms and producing more than 3.7 Million square km of data thus far. This wealth of experience has led to advances in the collection, processing, and evaluation of high-altitude (20,000 - 35,000 ft) airborne gravity data. This presentation will highlight the most important practical and theoretical advances of the GRAV-D project, giving an introduction to each. Examples of innovation include: 1. Use of navigation grade inertial measurement unit data and precise lever arm measurements for positioning; 2. New quality control tests and software for near real-time analysis of data in the field; 3. Increased accuracy of gravity post-processing by reexamining assumptions and simplifications that were inconsistent with a goal of 1 mGal precision; and 4. Better final data evaluation through crossovers, additional statistics, and inclusion of airborne data into harmonic models that use EGM08 as a base model. The increases in data quality that resulted from implementation of the above advances (and others) will be shown with a case study of the GRAV-D 2008 southern Alaska survey near Anchorage, over Cook Inlet. The case study's statistics and comparisons to global models illustrate the impact that these advances have had on the final airborne gravity data quality. Finally, the presentation will summarize the best practices identified by the project from its last five years of experience.

Development of a sensitive superconducting gravity gradiometer for geological and navigational applications

NASA Technical Reports Server (NTRS)

Paik, H. J.; Richard, J. P.

1986-01-01

A sensitive and stable gravity gradiometer would provide high resolution gravity measurements from space. The instrument could also provide precision tests of fundamental laws of physics and be applied to inertial guidance systems of the future. This report describes research on the superconducting gravity gradiometer program at the University of Maryland from July 1980 to July 1985. The report describes the theoretical and experimental work on a prototype superconducting gravity gradiometer. The design of an advanced three-axis superconducting gravity gradiometer is also discussed.

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/

Mercury's Interior from MESSENGER Radio Science Data

NASA Astrophysics Data System (ADS)

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

2017-12-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft provided precise radio tracking data in orbit about Mercury for more than 4 years, from March 2011 to April 2015. These geodetic measurements enable us to investigate the interior structure of the planet from the inner core to the crust. The first three years of radio data allowed us to determine the gravity field of Mercury with a resolution of 150 km in the northern hemisphere (degree and order 50 in spherical harmonics) since the periapsis was located at higher latitudes (>65˚N) and 200-500 km altitudes. The comparison of this gravity solution with Mercury's topography, which was retrieved by using over 25 million individual measurements of the Mercury Laser Altimeter (MLA), resulted in a preliminary map of the crustal thickness of the planet. However, those results were limited by the resolution of the gravity field since the topography was defined in spherical harmonics up to degree and order 125. The last year of the MESSENGER extended mission was dedicated to a low-altitude campaign, where the spacecraft periapsis was maintained at altitudes between 25 and 100 km. The radio data collected during this mission phase allowed us to significantly improve the resolution of the gravity field locally in the northern hemisphere up to degree and order 100 in spherical harmonics. We present the gravity anomalies and crustal thickness maps that lead to a better understanding on the formation and evolution of specific regions. We present our estimated orientation model, which slightly differs from the solutions that were obtained by using Earth-based radar measurements and the co-registration of MESSENGER imaging and altimetry data. These previous estimates provide a direct measurement of the surface response, whereas the orientation model from gravity is more sensitive to the inner and outer core. A discrepancy between core and surface obliquities may provide fundamental information on the status of the outer core and the presence of a solid inner core. We also present the latest solution of the tidal Love number k2 that enables us to constrain the basal temperature and rigidity of the outer molten core.

Innovative Technique for Noise Reduction in Spacecraft Doppler Tracking for Planetary Interior Studies

NASA Astrophysics Data System (ADS)

Notaro, V.; Armstrong, J. W.; Asmar, S.; Di Ruscio, A.; Iess, L.; Mariani, M., Jr.

2017-12-01

Precise measurements of spacecraft range rate, enabled by two-way microwave links, are used in radio science experiments for planetary geodesy including the determination of planetary gravitational fields for the purpose of modeling the interior structure. The final accuracies in the estimated gravity harmonic coefficients depend almost linearly on the Doppler noise in the link. We ran simulations to evaluate the accuracy improvement attainable in the estimation of the gravity harmonic coefficients of Venus (with a representative orbiter) and Mercury (with the BepiColombo spacecraft), using our proposed innovative noise-cancellation technique. We showed how the use of an additional, smaller and stiffer, receiving-only antenna could reduce the leading noise sources in a Ka-band two-way link such as tropospheric and antenna mechanical noises. This is achieved through a suitable linear combination (LC) of Doppler observables collected at the two antennas at different times. In our simulations, we considered a two-way link either from NASA's DSS 25 antenna in California or from ESA's DSA-3 antenna in Malargüe (Argentina). Moreover, we selected the 12-m Atacama Pathfinder EXperiment (APEX) in Chile as the three-way antenna and developed its tropospheric noise model using available atmospheric data and mechanical stability specifications. For an 8-hour Venus orbiter tracking pass in Chajnantor's winter/night conditions, the accuracy of the simulated LC Doppler observable at 10-s integration time is 6 mm/s, to be compared to 23 mm/s for the two-way link. For BepiColombo, we obtained 16.5 mm/s and 35 mm/s, respectively for the LC and two-way links. The benefits are even larger at longer time scales. Numerical simulations indicate that such noise reduction would provide significant improvements in the determination of Venus's and Mercury's gravity field coefficients. If implemented, this noise-reducing technique will be valuable for planetary geodesy missions, where the accuracy in the estimation of high-order gravity harmonic coefficients is limited by tropospheric and antenna mechanical noises that are difficult to reduce at short integration times. Benefits are however expected in all precision radio science experiments with deep space probes.

Determination of Enceladus' gravity field from Cassini radio science data

NASA Astrophysics Data System (ADS)

Parisi, Marzia; Iess, Luciano; Ducci, Marco

2014-05-01

In May 2012 the Cassini spacecraft completed its last gravity flyby of Saturn's moon Enceladus (identified as E19 in the sequence), following E9 in April 2010 and E12 in November 2010. The multiarc analysis of the gravity data collected during these low-altitude encounters has produced a stable solution for the gravity field of Enceladus, leading to compelling inferences and implications on the interior structure, but also raising new questions on the evolution of this small but yet fascinating icy body. The gravitational signature of the satellite was detected by means of precise Doppler tracking of the Cassini spacecraft around closest approach (±3h) of the three flybys. Cassini tracking system exploits both X/X and X/Ka links, with accuracies that range between 0.02 - 0.09 mm/s at 60 s integration time. Range-rate measurements were processed into a multi-arc least square filter so as to attain a solution for the quadrupole field of Enceladus and its degree-3 zonal harmonic J3, the most important indication of hemispherical asymmetries. In addition to these crucial parameters, corrections to the estimated orbits of Cassini and Enceladus were applied. The inclusion in the dynamical model of the neutral particle drag exerted by Enceladus south polar plumes (1) is essential for a satisfactory orbital fit. The results of the analysis show that Enceladus is indeed characterized by a predominant quadrupole term, with its J2/C22 ratio being that of a body not in hydrostatic equilibrium. The estimate of tesseral degree-2 coefficients (C21, S21 and C22), being statistically close to 0 (at a 3-σ level), imply that the adopted rotational model for the satellite is consistent with the observed gravity field. Furthermore, the estimated value for J3 turned out to be statistically significant (although only about 1/50 of J2) and pointing at a significant hemispherical asymmetry that is consistent with the presence of a regional sea at depth. References (1) C.C. Porco et al., Science 311, 1393 (2006).

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.

Holographic heat current as Noether current

NASA Astrophysics Data System (ADS)

Liu, Hai-Shan; Lü, H.; Pope, C. N.

2017-09-01

We employ the Noether procedure to derive a general formula for the radially conserved heat current in AdS planar black holes with certain transverse and traceless perturbations, for a general class of gravity theories. For Einstein gravity, the general higher-order Lovelock gravities and also a class of Horndeski gravities, we derive the boundary stress tensor and show that the resulting boundary heat current matches precisely the bulk Noether current.

Laser-ranging long-baseline differential atom interferometers for space

NASA Astrophysics Data System (ADS)

Chiow, Sheng-wey; Williams, Jason; Yu, Nan

2015-12-01

High-sensitivity differential atom interferometers (AIs) are promising for precision measurements in science frontiers in space, including gravity-field mapping for Earth science studies and gravitational wave detection. Difficulties associated with implementing long-baseline differential AIs have previously included the need for a high optical power, large differential Doppler shifts, and narrow dynamic range. We propose a configuration of twin AIs connected by a laser-ranging interferometer (LRI-AI) to provide precise information of the displacements between the two AI reference mirrors and also to phase-lock the two independent interferometer lasers over long distances, thereby drastically improving the practical feasibility of long-baseline differential AI measurements. We show that a properly implemented LRI-AI can achieve equivalent functionality to the conventional differential AI measurement configuration.

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

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

VizieR Online Data Catalog: Surface gravity determination in late-type stars (Morel+, 2012)

NASA Astrophysics Data System (ADS)

Morel, T.; Miglio, A.

2012-06-01

The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsating stars with gravities derived using classical methods (ionization balance, pressure-sensitive spectral features or location with respect to evolutionary tracks) supports the validity of this technique and reveals an overall remarkable agreement with mean differences not exceeding 0.05dex (although with a dispersion of up to ~0.2dex). It is argued that interpolation in theoretical isochrones may be the most precise way of estimating the gravity by traditional means in nearby dwarfs. Attention is drawn to the usefulness of seismic targets as benchmarks in the context of large-scale surveys. (1 data file).

Comparison of Einstein-Boltzmann solvers for testing general relativity

NASA Astrophysics Data System (ADS)

Bellini, E.; Barreira, A.; Frusciante, N.; Hu, B.; Peirone, S.; Raveri, M.; Zumalacárregui, M.; Avilez-Lopez, A.; Ballardini, M.; Battye, R. A.; Bolliet, B.; Calabrese, E.; Dirian, Y.; Ferreira, P. G.; Finelli, F.; Huang, Z.; Ivanov, M. M.; Lesgourgues, J.; Li, B.; Lima, N. A.; Pace, F.; Paoletti, D.; Sawicki, I.; Silvestri, A.; Skordis, C.; Umiltà, C.; Vernizzi, F.

2018-01-01

We compare Einstein-Boltzmann solvers that include modifications to general relativity and find that, for a wide range of models and parameters, they agree to a high level of precision. We look at three general purpose codes that primarily model general scalar-tensor theories, three codes that model Jordan-Brans-Dicke (JBD) gravity, a code that models f (R ) gravity, a code that models covariant Galileons, a code that models Hořava-Lifschitz gravity, and two codes that model nonlocal models of gravity. Comparing predictions of the angular power spectrum of the cosmic microwave background and the power spectrum of dark matter for a suite of different models, we find agreement at the subpercent level. This means that this suite of Einstein-Boltzmann solvers is now sufficiently accurate for precision constraints on cosmological and gravitational parameters.

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;

Hydrologic Interpretations of Long-Term Gravity Records at Tucson, Arizona

NASA Astrophysics Data System (ADS)

Pool, D. R.; Kennedy, J.; MacQueen, P.; Niebauer, T. M.

2016-12-01

The USGS Arizona Water Science Center monitors groundwater storage using gravity methods at sites across the western United States. A site at the USGS office in Tucson serves as a test station that has been monitored since 1997 using several types of gravity meters. Prior to 2007, the site was observed twice each year by the National Geodetic Survey using an FG5 absolute gravity meter for the purpose of establishing control for local relative gravity surveys of aquifer storage change. Beginning in 2003 the site has also served as a reference to verify the accuracy of an A10 absolute gravity meter that is used for field surveys. The site is in an alluvial basin where gravity can vary with aquifer storage change caused by variable groundwater withdrawals, elevation change caused by aquifer compaction or expansion, and occasional recharge. In addition, continuous gravity records were collected for periods of several months using a super-conducting meter during 2010-2011 and using a spring-based gPhone meter during 2015-2016. The purpose of the continuous records was to provide more precise information about monthly and shorter period variations that could be related to variations in nearby groundwater withdrawals. The record of absolute gravity observations displays variations of as much as 35 microGal that correspond with local hydrologic variations documented from precipitation, streamflow, elevation, depths to water, and well pumping records. Depth to water in nearby wells display variations related to occasional local heavy precipitation events, runoff, recharge, and groundwater withdrawals. Increases in gravity that occur over periods of several months or longer correspond with occasional heavy precipitation and recharge. Periods of gravity decline occur during extended periods between recharge events and periods of increased local groundwater withdrawals. Analysis of the continuous records from both instruments indicate that groundwater drains slowly from storage in response to pumping variations, requiring several days or longer for the aquifer to drain, which is consistent with other hydrologic records.

Utilizing the Upcoming Gravity Measurements from Cassini's Proximal Orbits for Studying the Atmospheric Dynamics of Saturn - How Deep Do the Winds Penetrate?

NASA Astrophysics Data System (ADS)

Kaspi, Y.; Galanti, E.

2014-12-01

At the end of the Cassini mission, the spacecraft will descend into close-by proximal orbits around Saturn. During those proximal orbits, Cassini will obtain high precision gravity measurements of the planet. In this talk, we will discuss how this data can be used to estimate the depth of the observed flows on the planet. This can be done in several ways: 1. measurements of the high order even harmonics which beyond J10 are dominated by the dynamics; 2. measurements of odd gravity harmonics which have no contribution from a static planet, and therefore are a pure signature of dynamics; 3. upper limits on the depth can be obtained by comparing low order even harmonics from dynamical models to the difference between the measured low order even harmonics and the largest possible values of a static planet; 4. direct latitudinally varying measurements of the gravity field exerted on the spacecraft. We will discuss how these methods may be applied and show that given the expected sensitivity of Cassini the odd harmonics J3 and J5 will have the best sensitivity to deep dynamics, allowing detection of winds reaching only O(100km) deep, if those exist on Saturn. We use a hierarchy of dynamical models ranging from full 3D dynamical circulation models to simplified dynamical models where the sensitivity of the gravity field to the dynamics can be explored. In order to invert the gravity field to be measured by Cassini into the depth dependent circulation, an adjoint inverse model is constructed for the dynamical models, thus allowing backward integration of the dynamical model. This tool can be used for examination of various scenarios, including cases in which the depth of the wind depends on latitudinal position. In summary, we expect that the very end of Cassini's tour holds an opportunity for gravity measurements that may finally allow answering one of the long-lasting puzzles in planetary science regarding the depth of the zonal jets on the gas giants. In fact, as Juno will be performing similar measurements we hope to be able to build a picture of the dynamics for both Jupiter and Saturn. Answering this puzzle, will likely help explain the origin of the multiple jet streams and strong equatorial superrotation on the gas giants.

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

NASA Astrophysics Data System (ADS)

Papanikolaou, T. D.; Papadopoulos, N.

2015-06-01

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

Field-driven mesoscale phase transition in polarized colloids in microgravity

NASA Astrophysics Data System (ADS)

Khusid, Boris; Elele, Ezinwa

2014-11-01

An unexpected phase transition in a polarized suspension was reported by Kumar, Khusid, Acrivos, PRL 95, 258301, 2005 and Agarwal, Yethiraj, PRL 102, 198301, 2009. Following the field application, particles aggregated head-to-tail into chains that bridged the interelectrode gap and then formed a cellular pattern, in which large-scale particle-free voids were enclosed by particle-rich thin walls. Surprisingly, the size of particle-free domains scales linearly with the gap thickness but is insensitive to the particle size and the field strength and frequency. Cellular structures were not observed in simulations of equilibrium in a polarized suspension (Richardi, Weis, J. Chem. Phys. 135, 124502, 2011; Almudallal, Saika-Voivod, PRE 84, 011402, 2011). Nonequilibrium simulations (Park, Saintillan, PRE 83, 041409, 2011) showed cellular-like structures but at a particle concentration much higher than in experiments. A requirement for precise matching of densities between particles and a fluid to avoid gravity effects limits terrestrial experiments to negatively polarized particles. We will present data on positively polarized non-buoyancy-matched particles and the development of experiments in the International Space Station needed to evaluate gravity contribution. Supported by NASA's Physical Science Research Program, NNX13AQ53G.

The Laser Astrometric Test of Relativity (LATOR) Mission

NASA Technical Reports Server (NTRS)

Turyshev, Slava G.; Shao, Michael; Nordtvedt, Kenneth, Jr.

2003-01-01

This paper discusses new fundamental physics experiment that will test relativistic gravity at the accuracy better than the effects of the second order in the gravitational field strength, proportional to G(sup 2). The Laser Astrometric Test Of Relativity (LATOR) mission uses laser interferometry between two micro-spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (100 m) multi-channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. In Euclidean geometry, determination of a triangle s three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR will not only improve the value of the parameterized post-Newtonian (PPN) gamma to unprecedented levels of accuracy of 1 part in 10(exp 8), it will also reach ability to measure effects of the next post-Newtonian order (c(sup -4)) of light deflection resulting from gravity s intrinsic non-linearity. The solar quadrupole moment parameter, J(sub 2), will be measured with high precision, as well as a variety of other relativistic effects including Lense-Thirring precession. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.

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.

A special case of the Poisson PDE formulated for Earth's surface and its capability to approximate the terrain mass density employing land-based gravity data, a case study in the south of Iran

NASA Astrophysics Data System (ADS)

AllahTavakoli, Yahya; Safari, Abdolreza; Vaníček, Petr

2016-12-01

This paper resurrects a version of Poisson's Partial Differential Equation (PDE) associated with the gravitational field at the Earth's surface and illustrates how the PDE possesses a capability to extract the mass density of Earth's topography from land-based gravity data. Herein, first we propound a theorem which mathematically introduces this version of Poisson's PDE adapted for the Earth's surface and then we use this PDE to develop a method of approximating the terrain mass density. Also, we carry out a real case study showing how the proposed approach is able to be applied to a set of land-based gravity data. In the case study, the method is summarized by an algorithm and applied to a set of gravity stations located along a part of the north coast of the Persian Gulf in the south of Iran. The results were numerically validated via rock-samplings as well as a geological map. Also, the method was compared with two conventional methods of mass density reduction. The numerical experiments indicate that the Poisson PDE at the Earth's surface has the capability to extract the mass density from land-based gravity data and is able to provide an alternative and somewhat more precise method of estimating the terrain mass density.

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.

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.

A Test of General Relativity with MESSENGER Mission Data

NASA Astrophysics Data System (ADS)

Genova, A.; Mazarico, E.; Goossens, S. J.; Lemoine, F. G.; Neumann, G. A.; Nicholas, J. B.; Rowlands, D. D.; Smith, D. E.; Zuber, M. T.; Solomon, S. C.

2016-12-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft initiated collection of scientific data from the innermost planet during its first flyby of Mercury in January 2008. After two additional Mercury flybys, MESSENGER was inserted into orbit around Mercury on 18 March 2011 and operated for more than four Earth years through 30 April 2015. Data acquired during the flyby and orbital phases have provided crucial information on the formation and evolution of Mercury. The Mercury Laser Altimeter (MLA) and the radio science system, for example, obtained geodetic observations of the topography, gravity field, orientation, and tides of Mercury, which helped constrain its surface and deep interior structure. X-band radio tracking data collected by the NASA Deep Space Network (DSN) allowed the determination of Mercury's gravity field to spherical harmonic degree and order 100, as well as refinement of the planet's obliquity and estimation of the tidal Love number k2. These geophysical parameters are derived from the range-rate observables that measure precisely the motion of the spacecraft in orbit around the planet. However, the DSN stations acquired two other kinds of radio tracking data, range and delta-differential one-way ranging, which also provided precise measurements of Mercury's ephemeris. The proximity of Mercury's orbit to the Sun leads to a significant perihelion precession, which was used by Einstein as confirmation of general relativity (GR) because of its inconsistency with the effects predicted from classical Newtonian theory. MESSENGER data allow the estimation of the GR parameterized post-Newtonian (PPN) coefficients γ and β. Furthermore, determination of Mercury's orbit also allows estimation of the gravitational parameter (GM) and the flattening (J2) of the Sun. We modified our orbit determination software, NASA GSFC's GEODYN II, to enable simultaneous orbit integration of both MESSENGER and the planet Mercury. The combined estimation of both orbits leads to a more accurate estimation of Mercury's gravity field, orientation, and tides. Results for these geophysical parameters, GM and J2 for the Sun, and the PPN parameters constitute updates for all of these quantities.

Compensation of Horizontal Gravity Disturbances for High Precision Inertial Navigation

PubMed Central

Cao, Juliang; Wu, Meiping; Lian, Junxiang; Cai, Shaokun; Wang, Lin

2018-01-01

Horizontal gravity disturbances are an important factor that affects the accuracy of inertial navigation systems in long-duration ship navigation. In this paper, from the perspective of the coordinate system and vector calculation, the effects of horizontal gravity disturbance on the initial alignment and navigation calculation are simultaneously analyzed. Horizontal gravity disturbances cause the navigation coordinate frame built in initial alignment to not be consistent with the navigation coordinate frame in which the navigation calculation is implemented. The mismatching of coordinate frame violates the vector calculation law, which will have an adverse effect on the precision of the inertial navigation system. To address this issue, two compensation methods suitable for two different navigation coordinate frames are proposed, one of the methods implements the compensation in velocity calculation, and the other does the compensation in attitude calculation. Finally, simulations and ship navigation experiments confirm the effectiveness of the proposed methods. PMID:29562653

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.

Trajectory Design Employing Convex Optimization for Landing on Irregularly Shaped Asteroids

NASA Technical Reports Server (NTRS)

Pinson, Robin M.; Lu, Ping

2016-01-01

Mission proposals that land spacecraft on asteroids are becoming increasingly popular. However, in order to have a successful mission the spacecraft must reliably and softly land at the intended landing site with pinpoint precision. The problem under investigation is how to design a propellant optimal powered descent trajectory that can be quickly computed onboard the spacecraft, without interaction from the ground control. The propellant optimal control problem in this work is to determine the optimal finite thrust vector to land the spacecraft at a specified location, in the presence of a highly nonlinear gravity field, subject to various mission and operational constraints. The proposed solution uses convex optimization, a gravity model with higher fidelity than Newtonian, and an iterative solution process for a fixed final time problem. In addition, a second optimization method is wrapped around the convex optimization problem to determine the optimal flight time that yields the lowest propellant usage over all flight times. Gravity models designed for irregularly shaped asteroids are investigated. Success of the algorithm is demonstrated by designing powered descent trajectories for the elongated binary asteroid Castalia.

Joint Tomographic Imaging of 3-­-D Density Structure Using Cosmic Ray Muons and High-­-Precision Gravity Data

NASA Astrophysics Data System (ADS)

Rowe, C. A.; Guardincerri, E.; Roy, M.; Dichter, M.

2015-12-01

As part of the CO2 reservoir muon imaging project headed by the Pacific Northwest National Laboraory (PNNL) under the U.S. Department of Energy Subsurface Technology and Engineering Research, Development, and Demonstration (SubTER) iniative, Los Alamos National Laboratory (LANL) and the University of New Mexico (UNM) plan to leverage the recently decommissioned and easily accessible Tunnel Vault on LANL property to test the complementary modeling strengths of muon radiography and high-precision gravity surveys. This tunnel extends roughly 300 feet into the hillside, with a maximum depth below the surface of approximately 300 feet. We will deploy LANL's Mini Muon Tracker (MMT), a detector consisting of 576 drift tubes arranged in alternating parallel planes of orthogonally oriented tubes. This detector is capable of precise determination of trajectories for incoming muons with angular resolution of a few milliradians. We will deploy the MMT at several locations within the tunnel, to obtain numerous crossing muon trajectories and permit a 3D tomographic image of the overburden to be built. In the same project, UNM will use a Scintrex digital gravimeter to collect high-precision gravity data from a dense grid on the hill slope above the tunnel as well as within the tunnel itself. This will provide both direct and differential gravity readings for density modeling of the overburden. By leveraging detailed geologic knowledge of the canyon and the lithology overlying the tunnel, as well as the structural elements, elevations and blueprints of the tunnel itself, we will evaluate the muon and gravity data both independently and in a simultaneous, joint inversion to build a combined 3D density model of the overburden.

Radio science investigations with Mars Observer

NASA Technical Reports Server (NTRS)

Tyler, G. L.; Balmino, Georges; Hinson, David P.; Sjogren, William L.; Smith, David E.; Woo, Richard; Asmar, Sami W.; Connally, Michael J.; Hamilton, Carole L.; Simpson, Richard A.

1992-01-01

Mars Observer radio science investigations focus on two major areas of study: the gravity field and the atmosphere of Mars. Measurement accuracies expressed as an equivalent spacecraft velocity are expected to be of the order of 100 microns/s (for both types of investigations) from use of an improved radio transponder for two-way spacecraft tracking and a highly stable on-board oscillator for atmospheric occultation measurements. Planned gravity investigations include a combination of classical and modern elements. A spherical harmonic (or equivalent) field model of degree and order in the range 30-50 will be obtained, while interpretation will be in terms of internal stress and density models for the planet, using the topography to be obtained from the Mars Observer laser altimeter. Atmospheric investigations will emphasize precision measurement of the thermal structure and dynamics in the polar regions, which are regularly accessible as a result of the highly inclined orbit. Studies based on the measurements will include polar processes, cycling of the atmosphere between the poles, traveling baroclinic disturbances, small-scale waves and turbulence, the planetary boundary layer, and (possibly) the variability and altitude of the ionosphere.

Quantizing higher-spin gravity in free-field variables

NASA Astrophysics Data System (ADS)

Campoleoni, Andrea; Fredenhagen, Stefan; Raeymaekers, Joris

2018-02-01

We study the formulation of massless higher-spin gravity on AdS3 in a gauge in which the fundamental variables satisfy free field Poisson brackets. This gauge choice leaves a small portion of the gauge freedom unfixed, which should be further quotiented out. We show that doing so leads to a bulk version of the Coulomb gas formalism for W N CFT's: the generators of the residual gauge symmetries are the classical limits of screening charges, while the gauge-invariant observables are classical W N charges. Quantization in these variables can be carried out using standard techniques and makes manifest a remnant of the triality symmetry of W ∞[λ]. This symmetry can be used to argue that the theory should be supplemented with additional matter content which is precisely that of the Prokushkin-Vasiliev theory. As a further application, we use our formulation to quantize a class of conical surplus solutions and confirm the conjecture that these are dual to specific degenerate W N primaries, to all orders in the large central charge expansion.

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.

The Mystery of the Mars North Polar Gravity-Topography Correlation(Or Lack Thereof)

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Sjogren, W. L.; Johnson, C. L.

1999-01-01

Maps of moderately high resolution gravity data obtained from the Mars Global Surveyor (MGS) gravity calibration orbit campaign and high precision topography obtained from the Mars Orbiter Laser Altimeter (MOLA) experiment reveal relationships between gravity and topography in high northern latitudes of Mars. Figure 1 shows the results of a JPL spherical harmonic gravity model bandpass filtered between degrees 6 and 50 contoured over a MOLA topographic image. A positive gravity anomaly exists over the main North Polar cap, but there are at least six additional positive gravity anomalies, as well as a number of smaller negative anomalies, with no obvious correlation to topography. Additional information is contained in the original extended abstract.

Gravity data from the San Pedro River Basin, Cochise County, Arizona

USGS Publications Warehouse

Kennedy, Jeffrey R.; Winester, Daniel

2011-01-01

The U.S. Geological Survey, Arizona Water Science Center in cooperation with the National Oceanic and Atmospheric Administration, National Geodetic Survey has collected relative and absolute gravity data at 321 stations in the San Pedro River Basin of southeastern Arizona since 2000. Data are of three types: observed gravity values and associated free-air, simple Bouguer, and complete Bouguer anomaly values, useful for subsurface-density modeling; high-precision relative-gravity surveys repeated over time, useful for aquifer-storage-change monitoring; and absolute-gravity values, useful as base stations for relative-gravity surveys and for monitoring gravity change over time. The data are compiled, without interpretation, in three spreadsheet files. Gravity values, GPS locations, and driving directions for absolute-gravity base stations are presented as National Geodetic Survey site descriptions.

Overview: Parity Violation and Fundamental Symmetries

NASA Astrophysics Data System (ADS)

Carlini, Roger

2017-09-01

The fields of nuclear and particle physics have undertaken extensive programs of research to search for evidence of new phenomena via the precision measurement of observables that are well predicted within the standard model of electroweak interaction. It is already known that the standard model is incomplete as it does not include gravity and dark matter/energy and therefore likely the low energy approximation of a more complex theory. This talk will be an overview of the motivation, experimental methods and status of some of these efforts (past and future) related to precision in-direct searches that are complementary to the direct searches underway at the Large Hadron Collider. This abstract is for the invited talk associated with the Mini-symposium titled ``Electro-weak Physics and Fundamental Symmetries'' organized by Julie Roche.

Value of the Cosmological Constant in Emergent Quantum Gravity

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

Hogan, Craig

It is suggested that the exact value of the cosmological constant could be derived from first principles, based on entanglement of the Standard Model field vacuum with emergent holographic quantum geometry. For the observed value of the cosmological constant, geometrical information is shown to agree closely with the spatial information density of the QCD vacuum, estimated in a free-field approximation. The comparison is motivated by a model of exotic rotational fluctuations in the inertial frame that can be precisely tested in laboratory experiments. Cosmic acceleration in this model is always positive, but fluctuates with characteristic coherence lengthmore » $$\\approx 100$$km and bandwidth $$\\approx 3000$$ Hz.« less

The Gravity Recovery and Interior Laboratory mission

NASA Astrophysics Data System (ADS)

Lehman, D. H.; Hoffman, T. L.; Havens, G. G.

The Gravity Recovery and Interior Laboratory (GRAIL) mission, launched in September 2011, successfully completed its Primary Science Mission in June 2012 and Extended Mission in December 2012. Competitively selected under a NASA Announcement of Opportunity in December 2007, GRAIL is a Discovery Program mission subject to a mandatory project cost cap. The purpose of the mission is to precisely map the gravitational field of the Moon to reveal its internal structure from crust to core, determine its thermal evolution, and extend this knowledge to other planets. The mission used twin spacecraft flying in tandem to provide the gravity map. The GRAIL Flight System, consisting of the spacecraft and payload, was developed based on significant heritage from previous missions such as an experimental U.S. Air Force satellite, the Mars Reconnaissance Orbiter (MRO) mission, and the Gravity Recovery and Climate Experiment (GRACE) mission. The Mission Operations System (MOS) was based on high-heritage multimission operations developed by NASA's Jet Propulsion Laboratory and Lockheed Martin. Both the Flight System and MOS were adapted to meet the unique challenges posed by the GRAIL mission design. This paper summarizes the implementation challenges and accomplishments of getting GRAIL ready for launch. It also discusses the in-flight challenges and experiences of operating two spacecraft, and mission results.

The Gravity Recovery and Interior Laboratory Mission

NASA Technical Reports Server (NTRS)

Lehman, David H.; Hoffman, Tom L.; Havens, Glen G.

2013-01-01

The Gravity Recovery and Interior Laboratory (GRAIL) mission, launched in September 2011, successfully completed its Primary Science Mission in June 2012 and is currently in Extended Mission operations. Competitively selected under a NASA Announcement of Opportunity in December 2007, GRAIL is a Discovery Program mission subject to a mandatory project cost cap. The purpose of the mission is to precisely map the gravitational field of the Moon to reveal its internal structure from crust to core, determine its thermal evolution, and extend this knowledge to other planets. The mission uses twin spacecraft flying in tandem to provide the gravity map. The GRAIL Flight System, consisting of the spacecraft and payload, was developed based on significant heritage from previous missions such an experimental U.S. Air Force satellite, the Mars Reconnaissance Orbiter (MRO) mission, and the Gravity Recovery and Climate Experiment (GRACE) mission. The Mission Operations System (MOS) was based on high-heritage multimission operations developed by NASA's Jet Propulsion Laboratory and Lockheed Martin. Both the Flight System and MOS were adapted to meet the unique challenges posed by the GRAIL mission design. This paper summarizes the implementation challenges and accomplishments of getting GRAIL ready for launch. It also discusses the in-flight challenges and experiences of operating two spacecraft, and mission results.

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.

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.

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.

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.

Satellite-tracking and Earth dynamics research programs

NASA Technical Reports Server (NTRS)

1981-01-01

The major focus for operations during this period was the preliminary MERIT Campaign and its intensive tracking of LAGEOS for polar motion and Earth rotation studies. The data acquired from LAGEOS were used for other geophysical investigations, including studies of crustal dynamics, and Earth and ocean tides, and for the general development of precision orbit determination. The network performed regular tracking of several other retroreflector satellites including GEOS-1, GEOS-3, BE-C, and Starlette for refined determinations of station coordinates and Earth's gravity field and for studies of solid Earth dynamics.

Ocean gravity and geoid determination

NASA Technical Reports Server (NTRS)

Kahn, W. D.; Siry, J. W.; Brown, R. D.; Wells, W. T.

1977-01-01

Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mgals for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 meters.

Gravity field of the Western Weddell Sea: Comparison of airborne gravity and Geosat derived gravity

NASA Technical Reports Server (NTRS)

Bell, R. E.; Brozena, J. M.; Haxby, W. F.; Labrecque, J. L.

1989-01-01

Marine gravity surveying in polar regions was typically difficult and costly, requiring expensive long range research vessels and ice-breakers. Satellite altimetry can recover the gravity field in these regions where it is feasible to survey with a surface vessel. Unfortunately, the data collected by the first global altimetry mission, Seasat, was collected only during the austral winter, producing a very poor quality gravitational filed for the southern oceans, particularly in the circum-Antarctic regions. The advent of high quality airborne gravity (Brozena, 1984; Brozena and Peters, 1988; Bell, 1988) and the availability of satellite altimetry data during the austral summer (Sandwell and McAdoo, 1988) has allowed the recovery of a free air gravity field for most of the Weddell Sea. The derivation of the gravity field from both aircraft and satellite measurements are briefly reviewed, before presenting along track comparisons and shaded relief maps of the Weddell Sea gravity field based on these two data sets.

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.

ASTROPHYSICS. Atom-interferometry constraints on dark energy.

PubMed

Hamilton, P; Jaffe, M; Haslinger, P; Simmons, Q; Müller, H; Khoury, J

2015-08-21

If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultrahigh-vacuum chamber, we reduced the screening mechanism by probing the field with individual atoms rather than with bulk matter. We thereby constrained a wide class of dark energy theories, including a range of chameleon and other theories that reproduce the observed cosmic acceleration. Copyright © 2015, American Association for the Advancement of Science.

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.

The Confrontation between General Relativity and Experiment.

PubMed

Will, Clifford M

2014-01-01

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein's equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

Accurate computation of gravitational field of a tesseroid

NASA Astrophysics Data System (ADS)

Fukushima, Toshio

2018-02-01

We developed an accurate method to compute the gravitational field of a tesseroid. The method numerically integrates a surface integral representation of the gravitational potential of the tesseroid by conditionally splitting its line integration intervals and by using the double exponential quadrature rule. Then, it evaluates the gravitational acceleration vector and the gravity gradient tensor by numerically differentiating the numerically integrated potential. The numerical differentiation is conducted by appropriately switching the central and the single-sided second-order difference formulas with a suitable choice of the test argument displacement. If necessary, the new method is extended to the case of a general tesseroid with the variable density profile, the variable surface height functions, and/or the variable intervals in longitude or in latitude. The new method is capable of computing the gravitational field of the tesseroid independently on the location of the evaluation point, namely whether outside, near the surface of, on the surface of, or inside the tesseroid. The achievable precision is 14-15 digits for the potential, 9-11 digits for the acceleration vector, and 6-8 digits for the gradient tensor in the double precision environment. The correct digits are roughly doubled if employing the quadruple precision computation. The new method provides a reliable procedure to compute the topographic gravitational field, especially that near, on, and below the surface. Also, it could potentially serve as a sure reference to complement and elaborate the existing approaches using the Gauss-Legendre quadrature or other standard methods of numerical integration.

Absolute Gravity Datum in the Age of Cold Atom Gravimeters

NASA Astrophysics Data System (ADS)

Childers, V. A.; Eckl, M. C.

2014-12-01

The international gravity datum is defined today by the International Gravity Standardization Net of 1971 (IGSN-71). The data supporting this network was measured in the 1950s and 60s using pendulum and spring-based gravimeter ties (plus some new ballistic absolute meters) to replace the prior protocol of referencing all gravity values to the earlier Potsdam value. Since this time, gravimeter technology has advanced significantly with the development and refinement of the FG-5 (the current standard of the industry) and again with the soon-to-be-available cold atom interferometric absolute gravimeters. This latest development is anticipated to provide improvement in the range of two orders of magnitude as compared to the measurement accuracy of technology utilized to develop ISGN-71. In this presentation, we will explore how the IGSN-71 might best be "modernized" given today's requirements and available instruments and resources. The National Geodetic Survey (NGS), along with other relevant US Government agencies, is concerned about establishing gravity control to establish and maintain high order geodetic networks as part of the nation's essential infrastructure. The need to modernize the nation's geodetic infrastructure was highlighted in "Precise Geodetic Infrastructure, National Requirements for a Shared Resource" National Academy of Science, 2010. The NGS mission, as dictated by Congress, is to establish and maintain the National Spatial Reference System, which includes gravity measurements. Absolute gravimeters measure the total gravity field directly and do not involve ties to other measurements. Periodic "intercomparisons" of multiple absolute gravimeters at reference gravity sites are used to constrain the behavior of the instruments to ensure that each would yield reasonably similar measurements of the same location (i.e. yield a sufficiently consistent datum when measured in disparate locales). New atomic interferometric gravimeters promise a significant increase in accuracy. Our presentation will also explore the impact of such an instrument on our theory of how to constrain the gravity datum and on how to ensure stability, repeatability, and reproducibility across different absolute gravimeter systems.

The Attraction of Gravity (Jean Dominique Cassini Medal Lecture)

NASA Astrophysics Data System (ADS)

Iess, Luciano

2017-04-01

The motion of planetary bodies, their interior structure, their shape, and ultimately their landscape, are all determined, more or less directly, by gravity. It is therefore not surprising that by measuring the orbital motion and the gravity field of planets and satellites we have been able to gather crucial information on the interior structure and evolution of those bodies, and at the same time to put the laws of gravity to the test. Planetary geodesy is now a fully developed discipline that uses methods and observable quantities adopted also in other fields, such as space navigation and telecommunications. Thanks to this winning synergy between science and engineering, we can now measure spacecraft velocities to 10-6 m/s and accelerations to 10-9 m/s2 over time scales as short as 1000 s, everywhere in the solar system. The past ten years have seen outstanding results in the scientific exploration of the deep space, with gravity investigations contributing to the success of many missions. Thanks to gravity measurements, MESSENGER was able to unveil the main features of Mercury's interior structure. GRAIL, the first planetary mission entirely devoted to gravity, recovered the structure of the lunar gravity anomalies to a spatial resolution and accuracy unmatched even for the Earth. The discovery and characterization of habitable environments in the Saturnian system, on Enceladus and Titan, were possible also by the radio science investigations of the mission Cassini. Thanks to a carefully designed orbit, with a pericenter just 3000 km above the cloud level, the spacecraft Juno is now carrying out precise gravity measurements at Jupiter to unveil the interior structure of the planet and the depth of its winds. With Cassini providing similar information at Saturn in the Grand Finale orbits, just before the final plunge into the planet, we will soon be able to reveal how similar or different the two gas giants are. But the interior structure of many planetary bodies remains elusive, and much remains to be explored. New missions and new tools are needed. In the next five years the planetary community will see the launch of BepiColombo and JUICE, two spacecraft equipped with a powerful suite of instruments devoted to the tomography of Mercury and Ganymede. Innovative instrumentation and probes are being conceived and designed. The Cassini Medal Lecture will review the past successes and future trends of planetary geodesy and radio science, from the peculiar perspective of someone whose attraction for gravity kept him at the ill-defined boundary between science and engineering, measuring angles, distances and velocities in the solar system.

Microgravimetry and the Measurement and Application of Gravity Gradients,

DTIC Science & Technology

1980-06-01

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

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

NASA Astrophysics Data System (ADS)

Pivetta, Tommaso; Braitenberg, Carla

2015-04-01

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

Gravity field information from Gravity Probe-B

NASA Technical Reports Server (NTRS)

Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.

1989-01-01

The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.

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.

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.

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

NASA Astrophysics Data System (ADS)

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

2011-12-01

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

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.

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.

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.

A proposal for a test of Weak Equivalence Principle with improved accuracy using a cryogenic differential accelerometer installed on a pendulum

NASA Astrophysics Data System (ADS)

Iafolla, V. A.; Fiorenza, E.; Lefevre, C.; Lucchesi, D. M.; Lucente, M.; Magnafico, C.; Nozzoli, S.; Peron, R.; Santoli, F.; Lorenzini, E. C.; Milyukov, V.; Shapiro, I. I.; Glashow, S.

2016-01-01

We present here the concept for a new experimental test of the Weak Equivalence Principle (WEP) carried out in the gravity field of the Sun. The WEP, stating the independence of the gravitational acceleration a body is subject to from its mass and composition, is at the basis of general relativity theory and more in general of metric theories of gravitation. It is therefore very important to test it to the precision allowable by current technology. The experiment here proposed aims at measuring the relative acceleration of two test masses in free fall, searching for a possible violation of the WEP, which would show up as a non-zero acceleration signal. The core of the experiment is constituted by a differential accelerometer with zero baseline, whose central elements are two test masses of different materials. This differential accelerometer is placed on a pendulum, in such a way as to make the common center of mass coincident with the center of mass of the pendulum itself. Ensuring a very precise centering, such a system should provide a high degree of attenuation of the local seismic noise, which - together with an integration time of the order of tens of days - would allow a test of the WEP with an accuracy improved by at least an order of magnitude with respect to the best measurements achieved so far. One of the strengths of this proposal is the know-how acquired from a previous study and technology development (GReAT: General Relativity Accuracy Test) that involved a test of the WEP in the gravity field of the Earth, in free fall inside a co-moving capsule released from a stratospheric balloon. The concept of the experiment is introduced, with particular attention to the differential accelerometer and its accommodation on the pendulum. A preliminary estimate of the attainable precision is given, along with a critical analysis of the associated challenges.

Optimally combined regional geoid models for the realization of height systems in developing countries - ORG4heights

NASA Astrophysics Data System (ADS)

Lieb, Verena; Schmidt, Michael; Willberg, Martin; Pail, Roland

2017-04-01

Precise height systems require high-resolution and high-quality gravity data. However, such data sets are sparse especially in developing or newly industrializing countries. Thus, we initiated the DFG-project "ORG4heights" for the formulation of a general scientific concept how to (1) optimally combine all available data sets and (2) estimate realistic errors. The resulting regional gravity field models then deliver the fundamental basis for (3) establishing physical national height systems. The innovative key aspects of the project incorporate the development of a method which links (low- up to mid-resolution) gravity satellite mission data and (high- down to low-quality) terrestrial data. Hereby, an optimal combination of the data utilizing their highest measure of information including uncertainty quantification and analyzing systematic omission errors is pursued. Regional gravity field modeling via Multi-Resolution Representation (MRR) and Least Squares Collocation (LSC) are studied in detail and compared based on their theoretical fundamentals. From the findings, MRR shall be further developed towards implementing a pyramid algorithm. Within the project, we investigate comprehensive case studies in Saudi Arabia and South America, i. e. regions with varying topography, by means of simulated data with heterogeneous distribution, resolution, quality and altitude. GPS and tide gauge records serve as complementary input or validation data. The resulting products include error propagation, internal and external validation. A generalized concept then is derived in order to establish physical height systems in developing countries. The recommendations may serve as guidelines for sciences and administration. We present the ideas and strategies of the project, which combines methodical development and practical applications with high socio-economic impact.

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

NASA Technical Reports Server (NTRS)

1984-01-01

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

Can Gravity Probe B usefully constrain torsion gravity theories?

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

Flanagan, Eanna E.; Rosenthal, Eran

2007-06-15

In most theories of gravity involving torsion, the source for torsion is the intrinsic spin of matter. Since the spins of fermions are normally randomly oriented in macroscopic bodies, the amount of torsion generated by macroscopic bodies is normally negligible. However, in a recent paper, Mao et al. (arXiv:gr-qc/0608121) point out that there is a class of theories, including the Hayashi-Shirafuji (1979) theory, in which the angular momentum of macroscopic spinning bodies generates a significant amount of torsion. They further argue that, by the principle of action equals reaction, one would expect the angular momentum of test bodies to couplemore » to a background torsion field, and therefore the precession of the Gravity Probe B gyroscopes should be affected in these theories by the torsion generated by the Earth. We show that in fact the principle of action equals reaction does not apply to these theories, essentially because the torsion is not an independent dynamical degree of freedom. We examine in detail a generalization of the Hayashi-Shirafuji theory suggested by Mao et al. called Einstein-Hayashi-Shirafuji theory. There are a variety of different versions of this theory, depending on the precise form of the coupling to matter chosen for the torsion. We show that, for any coupling to matter that is compatible with the spin transport equation postulated by Mao et al., the theory has either ghosts or an ill-posed initial-value formulation. These theoretical problems can be avoided by specializing the parameters of the theory and in addition choosing the standard minimal coupling to matter of the torsion tensor. This yields a consistent theory, but one in which the action equals reaction principle is violated, and in which the angular momentum of the gyroscopes does not couple to the Earth's torsion field. Thus, the Einstein-Hayashi-Shirafuji theory does not predict a detectable torsion signal for Gravity Probe B. There may be other torsion theories which do.« less

Moving-mass gravimeter calibration in the Mátyáshegy Gravity and Geodynamical Observatory (Budapest)

NASA Astrophysics Data System (ADS)

Kis, Márta; Koppán, Andras; Kovács, Péter; Merényi, László

2014-05-01

A gravimeter calibration facility exists in the Mátyáshegy Gravity and Geodynamical Observatory of Geological and Geophysical Institute in Hungary. During the calibration a cylindrical ring of 3200 kg mass is vertically moving around the equipment, generating gravity variations. The effect of the moving mass can be precisely calculated from the known mass and geometrical parameters. The main target of the calibration device was to reach a relative accuracy of 0.1-0.2% for the calibration of Earth-tide registering gravimeters. The maximum theoretical gravity variation produced by the vertical movement of the mass is ab. 110 microGal, so it provides excellent possibility for the fine calibration of gravimeters in the tidal range. The instrument was out of order for many years and in 2012 and 2013 it was renovated and automatized. The calibration process is aided by intelligent controller electronics. A new PLC-based system has been developed to allow easy control of the movement of the calibrating mass and to measure the mass position. It enables also programmed steps of movements (waiting positions and waiting times) for refined gravity changes. All parameters (position of the mass, CPI data, X/Y leveling positions) are recorded with 1/sec. sampling rate. The system can be controlled remotely through the internet. As it is well known that variations of the magnetic field can influence the measurements of metal-spring gravimeters, authors carried out magnetic experiments on the pillar of the calibration device as well, in order to analyze the magnetic effect of the moving stainless steel-mass. During the movements of the mass, the observed magnetic field has been changed significantly. According to the magnetic measurements, a correction for the magnetic effect was applied on the measured gravimetric data series. In this presentation authors show the facility in details and the numerical results of tests carried out by applying LCR G gravimeters.

Geodesy at Mercury with MESSENGER

NASA Technical Reports Server (NTRS)

Smith, David E.; Zuber, Maria t.; Peale, Stanley J.; Phillips, Roger J.; Solomon, Sean C.

2006-01-01

In 2011 the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft will enter Mercury orbit and begin the mapping phase of the mission. As part of its science objectives the MESSENGER mission will determine the shape and gravity field of Mercury. These observations will enable the topography and the crustal thickness to be derived for the planet and will determine the small libration of the planet about its axis, the latter critical to constraining the state of the core. These measurements require very precise positioning of the MESSENGER spacecraft in its eccentric orbit, which has a periapsis altitude as low as 200 km, an apoapsis altitude near 15,000 km, and a closest approach to the surface varying from latitude 60 to about 70 N. The X-band tracking of MESSENGER and the laser altimetry are the primary data that will be used to measure the planetary shape and gravity field. The laser altimeter, which has an expected range of 1000 to 1200 km, is expected to provide significant data only over the northern hemisphere because of MESSENGER's eccentric orbit. For the southern hemisphere, radio occultation measurements obtained as the spacecraft passes behind the planet as seen from Earth and images obtained with the imaging system will be used to provide the long-wavelength shape of the planet. Gravity, derived from the tracking data, will also have greater resolution in the northern hemisphere, but full global models for both topography and gravity will be obtained at low harmonic order and degree. The limiting factor for both gravity and topography is expected to be knowledge of the spacecraft location. Present estimations are that in a combined tracking, altimetry, and occultation solution the spacecraft position uncertainty is likely to be of order 10 m. This accuracy should be adequate for establishing an initial geodetic coordinate system for Mercury that will enable positioning of imaged features on the surface, determination of the planet's obliquity, and detection of the librational motion of the planet about its axis.

Testing the weak gravity-cosmic censorship connection

NASA Astrophysics Data System (ADS)

Crisford, Toby; Horowitz, Gary T.; Santos, Jorge E.

2018-03-01

A surprising connection between the weak gravity conjecture and cosmic censorship has recently been proposed. In particular, it was argued that a promising class of counterexamples to cosmic censorship in four-dimensional Einstein-Maxwell-Λ theory would be removed if charged particles (with sufficient charge) were present. We test this idea and find that indeed if the weak gravity conjecture is true, one cannot violate cosmic censorship this way. Remarkably, the minimum value of charge required to preserve cosmic censorship appears to agree precisely with that proposed by the weak gravity conjecture.

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.

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.

The Equivalence of Precession Phenomena in Metric Theories of Gravity

NASA Technical Reports Server (NTRS)

Krisher, Timothy P.

1997-01-01

The requirement of general covariance imparts to metric theories of gravity, such as general relavity, important structural features. A precise mathematical form results, ensuring that computation of observable physical effects in the theory gives the same answers independently of the chosen system of coordinates.

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.

(abstract) Venus Gravity Field

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Sjogren, W. L.

1995-01-01

A global gravity field model of Venus to degree and order 75 (5772 spherical harmonic coefficients) has been estimated from Doppler radio tracking of the orbiting spacecraft Pioneer Venus Orbiter (1979-1992) and Magellan (1990-1994). After the successful aerobraking of Magellan, a near circular polar orbit was attained and relatively uniform gravity field resolution (approximately 200 km) was obtained with formal uncertainties of a few milligals. Detailed gravity for several highland features are displayed as gravity contours overlaying colored topography. The positive correlation of typography with gravity is very high being unlike that of the Earth, Moon, and Mars. The amplitudes are Earth-like, but have significantly different gravity-topography ratios for different features. Global gravity, geoid, and isostatic anomaly maps as well as the admittance function are displayed.

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

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Elsaka, Basem

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

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)

High Sensitivity Gravity Measurements in the Adverse Environment of Oil Wells

NASA Astrophysics Data System (ADS)

Pfutzner, Harold

2014-03-01

Bulk density is a primary measurement within oil and gas reservoirs and is the basis of most reserves calculations by oil companies. The measurement is performed with a gamma-ray source and two scintillation gamma-ray detectors from within newly drilled exploration and production wells. This nuclear density measurement, while very precise is also very shallow and is therefore susceptible to errors due to any alteration of the formation and fluids in the vicinity of the borehole caused by the drilling process. Measuring acceleration due to gravity along a well provides a direct measure of bulk density with a very large depth of investigation that makes it practically immune to errors from near-borehole effects. Advances in gravity sensors and associated mechanics and electronics provide an opportunity for routine borehole gravity measurements with comparable density precision to the nuclear density measurement and with sufficient ruggedness to survive the rough handling and high temperatures experienced in oil well logging. We will describe a borehole gravity meter and its use under very realistic conditions in an oil well in Saudi Arabia. The density measurements will be presented. Alberto Marsala (2), Paul Wanjau (1), Olivier Moyal (1), and Justin Mlcak (1); (1) Schlumberger, (2) Saudi Aramco.

Fundamental Structure of Loop Quantum Gravity

NASA Astrophysics Data System (ADS)

Han, Muxin; Ma, Yongge; Huang, Weiming

In the recent twenty years, loop quantum gravity, a background independent approach to unify general relativity and quantum mechanics, has been widely investigated. The aim of loop quantum gravity is to construct a mathematically rigorous, background independent, non-perturbative quantum theory for a Lorentzian gravitational field on a four-dimensional manifold. In the approach, the principles of quantum mechanics are combined with those of general relativity naturally. Such a combination provides us a picture of, so-called, quantum Riemannian geometry, which is discrete on the fundamental scale. Imposing the quantum constraints in analogy from the classical ones, the quantum dynamics of gravity is being studied as one of the most important issues in loop quantum gravity. On the other hand, the semi-classical analysis is being carried out to test the classical limit of the quantum theory. In this review, the fundamental structure of loop quantum gravity is presented pedagogically. Our main aim is to help non-experts to understand the motivations, basic structures, as well as general results. It may also be beneficial to practitioners to gain insights from different perspectives on the theory. We will focus on the theoretical framework itself, rather than its applications, and do our best to write it in modern and precise langauge while keeping the presentation accessible for beginners. After reviewing the classical connection dynamical formalism of general relativity, as a foundation, the construction of the kinematical Ashtekar-Isham-Lewandowski representation is introduced in the content of quantum kinematics. The algebraic structure of quantum kinematics is also discussed. In the content of quantum dynamics, we mainly introduce the construction of a Hamiltonian constraint operator and the master constraint project. At last, some applications and recent advances are outlined. It should be noted that this strategy of quantizing gravity can also be extended to obtain other background-independent quantum gauge theories. There is no divergence within this background-independent and diffeomorphism-invariant quantization program of matter coupled to gravity.

VLTI/GRAVITY observations of the young star βPictoris

NASA Astrophysics Data System (ADS)

Defrère, D.

2017-12-01

The nearby young star β Pictoris is surrounded by the archetypal debris disc, which provides a unique window on the formation and early evolution of terrestrial planets. While the outer disc has been extensively studied since its discovery in 1984, very little is currently known about the inner planetary system (<4AU). Recently, accurate squared visibilities obtained with VLTI/PIONIER revealed the presence of resolved circumstellar emission with an integrated brightness amounting to approximately 1.4% of the stellar brightness in H band. However, it is not clear whether this excess emission originates from thermal emission, reflected light from hot dust grains located in the innermost regions of the planetary system, or is simply due to forward scattering by dust grains located further away (but still within the PIONIER field-of-view, i.e., close to the line of sight). In this paper, we present medium-resolution K-band observations of βPic obtained with VLTI/GRAVITY during science verification. The goals of these observations are to better constrain the temperature of the grains (and hence their location and chemical composition) and to showcase the high-precision capabilities of GRAVITY at detecting faint, close-in circumstellar emission.

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

Temperature, gravity, and bolometric correction scales for non-supergiant OB stars

NASA Astrophysics Data System (ADS)

Nieva, M.-F.

2013-02-01

Context. Precise and accurate determinations of the atmospheric parameters effective temperature and surface gravity are mandatory to derive reliable chemical abundances in OB stars. Furthermore, fundamental parameters like distances, masses, radii, luminosities can also be derived from the temperature and gravity of the stars. Aims: Atmospheric parameters recently determined at high precision with several independent spectroscopic indicators in non-local thermodynamic equilibrium, with typical uncertainties of ~300 K for temperature and of ~0.05 dex for gravity, are employed to calibrate photometric relationships. This is in order to investigate whether a faster tool to estimate atmospheric parameters can be provided. Methods: Temperatures and gravities of 30 calibrators, i.e. well-studied OB main sequence to giant stars in the solar neighbourhood, are compared to reddening-independent quantities of the Johnson and Strömgren photometric systems, assuming normal reddening. In addition, we examine the spectral and luminosity classification of the star sample and compute bolometric corrections. Results: Calibrations of temperatures and gravities are proposed for various photometric indices and spectral types. Once the luminosity of the stars is well known, effective temperatures can be determined at a precision of ~400 K for luminosity classes III/IV and ~800 K for luminosity class V. Furthermore, surface gravities can reach internal uncertainties as low as ~0.08 dex when using our calibration to the Johnson Q-parameter. Similar precision is achieved for gravities derived from the β-index and the precision is lower for both atmospheric parameters when using the Strömgren indices [c1] and [u - b] . In contrast, external uncertainties are larger for the Johnson than for the Strömgren calibrations. Our uncertainties are smaller than typical differences among other methods in the literature, reaching values up to ± 2000 K for temperature and ± 0.25 dex for gravity, and in extreme cases, + 6000 K and ± 0.4 dex, respectively. A parameter calibration for sub-spectral types is also proposed. Moreover, we present a new bolometric correction relation to temperature based on our empirical data, rather than on synthetic grids. Conclusions: The photometric calibrations presented here are useful tools to estimate effective temperatures and surface gravities of non-supergiant OB stars in a fast manner. This is also applicable to some single-line spectroscopic binaries, but caution has to be taken for undetected double-lined spectroscopic binaries and single objects with anomalous reddening-law, dubious photometric quantities and/or luminosity classes, for which the systematic uncertainties may increase significantly. We recommend to use these calibrations only as a first step of the parameter estimation, with subsequent refinements based on spectroscopy. A larger sample covering more uniformly the parameter space under consideration will allow refinements to the present calibrations. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max- Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2001-2.2-011 and H2005-2.2-016.Based on observations collected at the European Southern Observatory, Chile, ESO 074.B-0455(A) and from the ESO Archive.Based on spectral data retrieved from the ELODIE archive at Observatoire de Haute-Provence (OHP).Appendices A and B are available in electronic form at http://www.aanda.org

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.

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.

Inversion of Density Interfaces Using the Pseudo-Backpropagation Neural Network Method

NASA Astrophysics Data System (ADS)

Chen, Xiaohong; Du, Yukun; Liu, Zhan; Zhao, Wenju; Chen, Xiaocheng

2018-05-01

This paper presents a new pseudo-backpropagation (BP) neural network method that can invert multi-density interfaces at one time. The new method is based on the conventional forward modeling and inverse modeling theories in addition to conventional pseudo-BP neural network arithmetic. A 3D inversion model for gravity anomalies of multi-density interfaces using the pseudo-BP neural network method is constructed after analyzing the structure and function of the artificial neural network. The corresponding iterative inverse formula of the space field is presented at the same time. Based on trials of gravity anomalies and density noise, the influence of the two kinds of noise on the inverse result is discussed and the scale of noise requested for the stability of the arithmetic is analyzed. The effects of the initial model on the reduction of the ambiguity of the result and improvement of the precision of inversion are discussed. The correctness and validity of the method were verified by the 3D model of the three interfaces. 3D inversion was performed on the observed gravity anomaly data of the Okinawa trough using the program presented herein. The Tertiary basement and Moho depth were obtained from the inversion results, which also testify the adaptability of the method. This study has made a useful attempt for the inversion of gravity density interfaces.

The Earth Gravitational Observatory (EGO): Nanosat Constellations For Advanced Gravity Mapping

NASA Astrophysics Data System (ADS)

Yunck, T.; Saltman, A.; Bettadpur, S. V.; Nerem, R. S.; Abel, J.

2017-12-01

The trend to nanosats for space-based remote sensing is transforming system architectures: fleets of "cellular" craft scanning Earth with exceptional precision and economy. GeoOptics Inc has been selected by NASA to develop a vision for that transition with an initial focus on advanced gravity field mapping. Building on our spaceborne GNSS technology we introduce innovations that will improve gravity mapping roughly tenfold over previous missions at a fraction of the cost. The power of EGO is realized in its N-satellite form where all satellites in a cluster receive dual-frequency crosslinks from all other satellites, yielding N(N-1)/2 independent measurements. Twelve "cells" thus yield 66 independent links. Because the cells form a 2D arc with spacings ranging from 200 km to 3,000 km, EGO senses a wider range of gravity wavelengths and offers greater geometrical observing strength. The benefits are two-fold: Improved time resolution enables observation of sub-seasonal processes, as from hydro-meteorological phenomena; improved measurement quality enhances all gravity solutions. For the GRACE mission, key limitations arise from such spacecraft factors as long-term accelerometer error, attitude knowledge and thermal stability, which are largely independent from cell to cell. Data from a dozen cells reduces their impact by 3x, by the "root-n" averaging effect. Multi-cell closures improve on this further. The many closure paths among 12 cells provide strong constraints to correct for observed range changes not compatible with a gravity source, including accelerometer errors in measuring non-conservative forces. Perhaps more significantly from a science standpoint, system-level estimates with data from diverse orbits can attack the many scientifically limiting sources of temporal aliasing.

A new Ellipsoidal Gravimetric-Satellite Altimetry Boundary Value Problem; Case study: High Resolution Geoid of Iran

NASA Astrophysics Data System (ADS)

Ardalan, A.; Safari, A.; Grafarend, E.

2003-04-01

A new ellipsoidal gravimetric-satellite altimetry boundary value problem has been developed and successfully tested. This boundary value problem has been constructed for gravity observables of the type (i) gravity potential (ii) gravity intensity (iii) deflection of vertical and (iv) satellite altimetry data. The developed boundary value problem is enjoying the ellipsoidal nature and as such can take advantage of high precision GPS observations in the set-up of the problem. The highlights of the solution are as follows: begin{itemize} Application of ellipsoidal harmonic expansion up to degree/order and ellipsoidal centrifugal field for the reduction of global gravity and isostasy effects from the gravity observable at the surface of the Earth. Application of ellipsoidal Newton integral on the equal area map projection surface for the reduction of residual mass effects within a radius of 55 km around the computational point. Ellipsoidal harmonic downward continuation of the residual observables from the surface of the earth down to the surface of reference ellipsoid using the ellipsoidal height of the observation points derived from GPS. Restore of the removed effects at the application points on the surface of reference ellipsoid. Conversion of the satellite altimetry derived heights of the water bodies into potential. Combination of the downward continued gravity information with the potential equivalent of the satellite altimetry derived heights of the water bodies. Application of ellipsoidal Bruns formula for converting the potential values on the surface of the reference ellipsoid into the geoidal heights (i.e. ellipsoidal heights of the geoid) with respect to the reference ellipsoid. Computation of the high-resolution geoid of Iran has successfully tested this new methodology!

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.

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.

Test of Newtonian gravity at short range using pico-precision displacement sensor

NASA Astrophysics Data System (ADS)

Akiyama, Takashi; Hata, Maki; Ninomiya, Kazufumi; Nishio, Hironori; Ogawa, Naruya; Sekiguchi, Yuta; Watanabe, Kentaro; Murata, Jiro

2009-10-01

Recent theoretical models of physics beyond the standard model, including attempts to resolve the hierarchy problem, predict deviations from the Newtonian gravity at short distances below millimeters. Present NEWTON project aims an experimental test of the inverse-square law at the millimeter scale, using a torsion pendulum with a pico-precision displacement sensor, which was originally developed for the micron precision optical alignment system (OASys) for the PHENIX muon tracking chambers at RHIC, using digital image analysis technique. In order to examine the gravitational force at short range scale around micrometers, we have developed a new apparatus NEWTON-III, which can determine the local gravitational acceleration by measuring the motion of the torsion pendulum. In this presentation, the development status and the results of the NEWTON-experiment will be reported.

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.

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.

Geodesy and gravity experiment in earth orbit using a superconducting gravity gradiometer

NASA Technical Reports Server (NTRS)

Paik, H. J.

1985-01-01

A superconducting gravity gradiometer is under development with NASA support for space application. It is planned that a sensitive three-axis gravity gradiometer will be flown in a low-altitude (about 160 km) polar orbit in the 1990's for the purpose of obtaining a high-resolution gravity map of the earth. The large twice-an-orbit term in the harmonic expansion of gravity coming from the oblateness of the earth can be analyzed to obtain a precision test of the inverse square law at a distance of 100-1000 km. In this paper, the design, operating principle, and performance of the superconducting gravity gradiometer are described. The concept of a gravity-gradiometer mission (GGM), which is in an initial stage of development is discussed. In particular, requirements that such a mission imposes on the design of the cryogenic spacecraft will be addressed.

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.

Alaska/Yukon Geoid Improvement by a Data-Driven Stokes's Kernel Modification Approach

NASA Astrophysics Data System (ADS)

Li, Xiaopeng; Roman, Daniel R.

2015-04-01

Geoid modeling over Alaska of USA and Yukon Canada being a trans-national issue faces a great challenge primarily due to the inhomogeneous surface gravity data (Saleh et al, 2013) and the dynamic geology (Freymueller et al, 2008) as well as its complex geological rheology. Previous study (Roman and Li 2014) used updated satellite models (Bruinsma et al 2013) and newly acquired aerogravity data from the GRAV-D project (Smith 2007) to capture the gravity field changes in the targeting areas primarily in the middle-to-long wavelength. In CONUS, the geoid model was largely improved. However, the precision of the resulted geoid model in Alaska was still in the decimeter level, 19cm at the 32 tide bench marks and 24cm on the 202 GPS/Leveling bench marks that gives a total of 23.8cm at all of these calibrated surface control points, where the datum bias was removed. Conventional kernel modification methods in this area (Li and Wang 2011) had limited effects on improving the precision of the geoid models. To compensate the geoid miss fits, a new Stokes's kernel modification method based on a data-driven technique is presented in this study. First, the method was tested on simulated data sets (Fig. 1), where the geoid errors have been reduced by 2 orders of magnitude (Fig 2). For the real data sets, some iteration steps are required to overcome the rank deficiency problem caused by the limited control data that are irregularly distributed in the target area. For instance, after 3 iterations, the standard deviation dropped about 2.7cm (Fig 3). Modification at other critical degrees can further minimize the geoid model miss fits caused either by the gravity error or the remaining datum error in the control points.

Comparison between the Juno Earth flyby magnetic measurements and the magnetometer package on the IRIS solar observatory

NASA Astrophysics Data System (ADS)

Merayo, J. M.; Connerney, J. E.; Joergensen, J. L.; Dougherty, B.

2013-12-01

In October 2013 the NASA's Juno New Frontier spacecraft will perform an Earth Flyby Gravity Assist. During this flyby, Juno will reach an altitude of about 600 km and the magnetometer experiment will measure the magnetic field with very high precision. In June 2013 the NASA's IRIS solar observatory was successfully launched. IRIS uses a very fine guiding telescope in order to maintain a high pointing accuracy, assisted by a very high accuracy star tracker and a science grade vector magnetometer. IRIS was placed into a Sun-synchronous orbit at about 600 km altitude by a Pegasus rocket from the Vandenberg Air Force Base in California. This platform will also allow to performing measurements of the Earth's magnetic field with very high precision, since it carries similar instrumentation as on the Swarm satellites (star trackers and magnetometer). The data recorded by the Juno magnetic experiment and the IRIS magnetometer will bring a very exciting opportunity for comparing the two experiments as well as for determining current structures during the flyby.

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".

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.

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

CryoSat-2 altimetry derived Arctic bathymetry map: first results and validation

NASA Astrophysics Data System (ADS)

Andersen, O. B.; Abulaitijiang, A.; Cancet, M.; Knudsen, P.

2017-12-01

The Technical University of Denmark (DTU), DTU Space has been developing high quality high resolution gravity fields including the new highly accurate CryoSat-2 radar altimetry satellite data which extends the global coverage of altimetry data up to latitude 88°. With its exceptional Synthetic Aperture Radar (SAR) mode being operating throughout the Arctic Ocean, leads, i.e., the ocean surface heights, is used to retrieve the sea surface height with centimeter-level range precision. Combined with the long repeat cycle ( 369 days), i.e., dense cross-track coverage, the high-resolution Arctic marine gravity can be modelled using the CryoSat-2 altimetry. Further, the polar gap can be filled by the available ArcGP product, thus yielding the complete map of the Arctic bathymetry map. In this presentation, we will make use of the most recent DTU17 marine gravity, to derive the arctic bathymetry map using inversion based on best available hydrographic maps. Through the support of ESA a recent evaluation of existing hydrographic models of the Arctic Ocean Bathymetry models (RTOPO, GEBCO, IBCAO etc) and various inconsistencies have been identified and means to rectify these inconsistencies have been taken prior to perform the inversion using altimetry. Simultaneously DTU Space has been placing great effort on the Arctic data screening, filtering, and de-noising using various altimetry retracking solutions and classifications. All the pre-processing contributed to the fine modelling of Actic gravity map. Thereafter, the arctic marine gravity grids will eventually be translated (downward continuation operation) to a new altimetry enhanced Arctic bathymetry map using appropriate band-pass filtering.

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.

GNSS orbit determination by precise modeling of non-gravitational forces acting on satellite's body

NASA Astrophysics Data System (ADS)

Wielgosz, Agata; Kalarus, Maciej; Liwosz, Tomasz

2016-04-01

Satellites orbiting around Earth are affected by gravitational forces and non-gravitational perturbations (NGP). While the perturbations caused by gravitational forces, which are due to central body gravity (including high-precision geopotential field) and its changes (due to secular variations and tides), solar bodies attraction and relativistic effects are well-modeled, the perturbations caused by the non-gravitational forces are the most limiting factor in Precise Orbit Determination (POD). In this work we focused on very precise non-gravitational force modeling for medium Earth orbit satellites by applying the various models of solar radiation pressure including changes in solar irradiance and Earth/Moon shadow transition, Earth albedo and thermal radiation. For computing influence of aforementioned forces on spacecraft the analytical box-wing satellite model was applied. Smaller effects like antenna thrust or spacecraft thermal radiation were also included. In the process of orbit determination we compared the orbit with analytically computed NGP with the standard procedure in which CODE model is fitted for NGP recovery. We considered satellites from several systems and on different orbits and for different periods: when the satellite is all the time in full sunlight and when transits the umbra and penumbra regions.

A new theory of gravity

NASA Technical Reports Server (NTRS)

Ni, W.

1972-01-01

A new relativistic theory of gravity is presented. This theory agrees with all experiments to date. It is a metric theory, it is Lagrangian-based, and it possesses a preferred frame with conformally-flat space slices. With an appropriate choice of certain adjustable functions and parameters, this theory possesses precisely the same post-Newtonian limit as general relativity.

Monitoring groundwater variation by satellite and implications for in-situ gravity measurements.

PubMed

Fukuda, Yoichi; Yamamoto, Keiko; Hasegawa, Takashi; Nakaegawa, Toshiyuki; Nishijima, Jun; Taniguchi, Makoto

2009-04-15

In order to establish a new technique for monitoring groundwater variations in urban areas, the applicability of precise in-situ gravity measurements and extremely high precision satellite gravity data via GRACE (Gravity Recovery and Climate Experiment) was tested. Using the GRACE data, regional scale water mass variations in four major river basins of the Indochina Peninsula were estimated. The estimated variations were compared with Soil-Vegetation-Atmosphere Transfer Scheme (SVATS) models with a river flow model of 1) globally uniform river velocity, 2) river velocity tuned by each river basin, 3) globally uniform river velocity considering groundwater storage, and 4) river velocity tuned by each river basin considering groundwater storage. Model 3) attained the best fit to the GRACE data, and the model 4) yielded almost the same values. This implies that the groundwater plays an important role in estimating the variation of total terrestrial storage. It also indicates that tuning river velocity, which is based on the in-situ measurements, needs further investigations in combination with the GRACE data. The relationships among GRACE data, SVATS models, and in-situ measurements were also discussed briefly.

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.

Precision gravity measurement utilizing Accelerex vibrating beam accelerometer technology

NASA Astrophysics Data System (ADS)

Norling, Brian L.

Tests run using Sundstrand vibrating beam accelerometers to sense microgravity are described. Lunar-solar tidal effects were used as a highly predictable signal which varies by approximately 200 billionths of the full-scale gravitation level. Test runs of 48-h duration were used to evaluate stability, resolution, and noise. Test results on the Accelerex accelerometer show accuracies suitable for precision applications such as gravity mapping and gravity density logging. The test results indicate that Accelerex technology, even with an instrument design and signal processing approach not optimized for microgravity measurement, can achieve 48-nano-g (1 sigma) or better accuracy over a 48-h period. This value includes contributions from instrument noise and random walk, combined bias and scale factor drift, and thermal modeling errors as well as external contributions from sampling noise, test equipment inaccuracies, electrical noise, and cultural noise induced acceleration.

Gravity compensation in a Strapdown Inertial Navigation System to improve the attitude accuracy

NASA Astrophysics Data System (ADS)

Zhu, Jing; Wang, Jun; Wang, Xingshu; Yang, Shuai

2017-10-01

Attitude errors in a strapdown inertial navigation system due to gravity disturbances and system noises can be relatively large, although they are bound within the Schuler and the Earth rotation period. The principal objective of the investigation is to determine to what extent accurate gravity data can improve the attitude accuracy. The way the gravity disturbances affect the attitude were analyzed and compared with system noises by the analytic solution and simulation. The gravity disturbances affect the attitude accuracy by introducing the initial attitude error and the equivalent accelerometer bias. With the development of the high precision inertial devices and the application of the rotation modulation technology, the gravity disturbance cannot be neglected anymore. The gravity compensation was performed using the EGM2008 and simulations with and without accurate gravity compensation under varying navigation conditions were carried out. The results show that the gravity compensation improves the horizontal components of attitude accuracy evidently while the yaw angle is badly affected by the uncompensated gyro bias in vertical channel.

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.

GTOOLS: an Interactive Computer Program to Process Gravity Data for High-Resolution Applications

NASA Astrophysics Data System (ADS)

Battaglia, M.; Poland, M. P.; Kauahikaua, J. P.

2012-12-01

An interactive computer program, GTOOLS, has been developed to process gravity data acquired by the Scintrex CG-5 and LaCoste & Romberg EG, G and D gravity meters. The aim of GTOOLS is to provide a validated methodology for computing relative gravity values in a consistent way accounting for as many environmental factors as possible (e.g., tides, ocean loading, solar constraints, etc.), as well as instrument drift. The program has a modular architecture. Each processing step is implemented in a tool (function) that can be either run independently or within an automated task. The tools allow the user to (a) read the gravity data acquired during field surveys completed using different types of gravity meters; (b) compute Earth tides using an improved version of Longman's (1959) model; (c) compute ocean loading using the HARDISP code by Petit and Luzum (2010) and ocean loading harmonics from the TPXO7.2 ocean tide model; (d) estimate the instrument drift using linear functions as appropriate; and (e) compute the weighted least-square-adjusted gravity values and their errors. The corrections are performed up to microGal ( μGal) precision, in accordance with the specifications of high-resolution surveys. The program has the ability to incorporate calibration factors that allow for surveys done using different gravimeters to be compared. Two additional tools (functions) allow the user to (1) estimate the instrument calibration factor by processing data collected by a gravimeter on a calibration range; (2) plot gravity time-series at a chosen benchmark. The interactive procedures and the program output (jpeg plots and text files) have been designed to ease data handling and archiving, to provide useful information for future data interpretation or modeling, and facilitate comparison of gravity surveys conducted at different times. All formulas have been checked for typographical errors in the original reference. GTOOLS, developed using Matlab, is open source and machine independent. We will demonstrate program use and utility with data from multiple microgravity surveys at Kilauea volcano, Hawai'i.

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.

Gauge/Gravity Duality

ScienceCinema

Polchinski, Joseph

2017-12-22

Gauge theories, which describe the particle interactions, are well understood, while quantum gravity leads to many puzzles. Remarkably, in recent years we have learned that these are actually dual, the same system written in different variables. On the one hand, this provides our most precise description of quantum gravity, resolves some long-standing paradoxes, and points to new principles. On the other, it gives a new perspective on strong interactions, with surprising connections to other areas of physics. I describe these ideas, and discuss current and future directions.

Tidal Response of Jupiter and Saturn from CMS calculationsTidal Response of Jupiter and Saturn from CMS calculations

NASA Astrophysics Data System (ADS)

Wahl, Sean; Hubbard, William B.; Militzer, Burkhard

2016-10-01

The Juno gravity science system promises to provide observational data from Jupiter's gravitational field at an unprecedented precision. Meanwhile, recent ab-initio simulations on mixtures of hydrogen and helium allow for the construction of realistic interior models. The concentric Maclaurin spheroid (CMS) numerical method has been developed for efficient, non-perturbative, self-consistent calculations of shape and gravitational field of a rotating liquid body to this desired precision. Here we present a generalization of the CMS method to three dimensions and included the effect of tides from a satellite. We have identified a number of unexpected features of the static tidal response in the case where a planet's shape is dominated by the rotational bulge. In the general case, there is state mixing of the spherical-harmonic components of the response to the corresponding components of the rotational and tidal excitations. This breaks the degeneracy of the tidal love numbers knm with m, and introduces a dependence of knm on the orbital distance of the satellite. Notably for Jupiter and Saturn, the predicted value of k2 is significantly higher when the planet's high rotation rates are taken into account: k2=0.413 for Saturn and k2=0.590 for Jupiter, accounting for an ~13% and 10% increase over the non-rotating case respectively. We have also done preliminary estimates for the off-resonance dynamic response, which may lead to an additional significant increase in k2. Accurate models of tidal response will be essential for interpreting gravity observations from Juno and future studies, particularly for when filtering for signals from interior dynamics in the observed field. This work was supported by NASA's Juno project. Sean Wahl and Burkhard Militzer acknowledge the support of the National Science Foundation (astronomy and astrophysics research grant 1412646).

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

Delineating the Rattlesnake Springs, New Mexico Watershed Using Precision Gravity Techniques

NASA Astrophysics Data System (ADS)

Doser, D. I.; Boykov, N. D.; Baker, M. R.; Kaip, G. M.; Langford, R. P.

2009-12-01

Rattlesnake Springs serves as the sole domestic water source for Carlsbad Caverns National Park. The recent development of oil and gas leases and agricultural lands surrounding the springs has led to concern about contamination of the fracture controlled aquifer system. We have conducted a series of precision gravity surveys (station spacing 200 to 300 m in a 4 x 4 km area), combined with other geophysical studies and geologic mapping, to delineate possible fracture systems in the gypsum and carbonate bedrock that feed the spring system. Our combined results suggest several pathways for water to enter the springs. A series of WNW-ESE striking features are apparent in our gravity data that appear to align with relict spring valleys we have mapped to the west of the springs. A self potential survey indicates that water is entering the springs at a shallow level from the northwest direction. However, gravity data also indicate a north-south trending fracture system could be providing a pathway for water to enter from the south. This is consistent with drawdown tests conducted in the 1950’s and 1960’s on irrigation wells located to the south of the springs. The north-south fracture system appears related to a basin bounding fault system observed in the regional gravity data.

Effect of angular momentum alignment and strong magnetic fields on the formation of protostellar discs

NASA Astrophysics Data System (ADS)

Gray, William J.; McKee, Christopher F.; Klein, Richard I.

2018-01-01

Star-forming molecular clouds are observed to be both highly magnetized and turbulent. Consequently, the formation of protostellar discs is largely dependent on the complex interaction between gravity, magnetic fields, and turbulence. Studies of non-turbulent protostellar disc formation with realistic magnetic fields have shown that these fields are efficient in removing angular momentum from the forming discs, preventing their formation. However, once turbulence is included, discs can form in even highly magnetized clouds, although the precise mechanism remains uncertain. Here, we present several high-resolution simulations of turbulent, realistically magnetized, high-mass molecular clouds with both aligned and random turbulence to study the role that turbulence, misalignment, and magnetic fields have on the formation of protostellar discs. We find that when the turbulence is artificially aligned so that the angular momentum is parallel to the initial uniform field, no rotationally supported discs are formed, regardless of the initial turbulent energy. We conclude that turbulence and the associated misalignment between the angular momentum and the magnetic field are crucial in the formation of protostellar discs in the presence of realistic magnetic fields.

Dynamically controlled crystallization method and apparatus and crystals obtained thereby

NASA Technical Reports Server (NTRS)

Arnowitz, Leonard (Inventor); Steinberg, Emanuel (Inventor)

2003-01-01

A method and apparatus for dynamically controlling the crystallization of molecules including a crystallization chamber (14) or chambers for holding molecules in a precipitant solution, one or more precipitant solution reservoirs (16, 18), communication passages (17, 19) respectively coupling the crystallization chamber(s) with each of the precipitant solution reservoirs, and transfer mechanisms (20, 21, 22, 24, 26, 28) configured to respectively transfer precipitant solution between each of the precipitant solution reservoirs and the crystallization chamber(s). The transfer mechanisms are interlocked to maintain a constant volume of precipitant solution in the crystallization chamber(s). Precipitant solutions of different concentrations are transferred into and out of the crystallization chamber(s) to adjust the concentration of precipitant in the crystallization chamber(s) to achieve precise control of the crystallization process. The method and apparatus can be used effectively to grow crystals under reduced gravity conditions such as microgravity conditions of space, and under conditions of reduced or enhanced effective gravity as induced by a powerful magnetic field.

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

NASA Astrophysics Data System (ADS)

Godah, Walyeldeen; Szelachowska, Malgorzata; Krynski, Jan

2014-06-01

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

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.

Jupiter's interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft

NASA Astrophysics Data System (ADS)

Bolton, S. J.; Adriani, A.; Adumitroaie, V.; Allison, M.; Anderson, J.; Atreya, S.; Bloxham, J.; Brown, S.; Connerney, J. E. P.; DeJong, E.; Folkner, W.; Gautier, D.; Grassi, D.; Gulkis, S.; Guillot, T.; Hansen, C.; Hubbard, W. B.; Iess, L.; Ingersoll, A.; Janssen, M.; Jorgensen, J.; Kaspi, Y.; Levin, S. M.; Li, C.; Lunine, J.; Miguel, Y.; Mura, A.; Orton, G.; Owen, T.; Ravine, M.; Smith, E.; Steffes, P.; Stone, E.; Stevenson, D.; Thorne, R.; Waite, J.; Durante, D.; Ebert, R. W.; Greathouse, T. K.; Hue, V.; Parisi, M.; Szalay, J. R.; Wilson, R.

2017-05-01

On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter's poles show a chaotic scene, unlike Saturn's poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth's Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno's measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.

The tides of Titan.

PubMed

Iess, Luciano; Jacobson, Robert A; Ducci, Marco; Stevenson, David J; Lunine, Jonathan I; Armstrong, John W; Asmar, Sami W; Racioppa, Paolo; Rappaport, Nicole J; Tortora, Paolo

2012-07-27

We have detected in Cassini spacecraft data the signature of the periodic tidal stresses within Titan, driven by the eccentricity (e = 0.028) of its 16-day orbit around Saturn. Precise measurements of the acceleration of Cassini during six close flybys between 2006 and 2011 have revealed that Titan responds to the variable tidal field exerted by Saturn with periodic changes of its quadrupole gravity, at about 4% of the static value. Two independent determinations of the corresponding degree-2 Love number yield k(2) = 0.589 ± 0.150 and k(2) = 0.637 ± 0.224 (2σ). Such a large response to the tidal field requires that Titan's interior be deformable over time scales of the orbital period, in a way that is consistent with a global ocean at depth.

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.

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

NASA Astrophysics Data System (ADS)

Claessens, S. J.

2016-12-01

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

Duration of inflation and conditions at the bounce as a prediction of effective isotropic loop quantum cosmology

NASA Astrophysics Data System (ADS)

Linsefors, Linda; Barrau, Aurelien

2013-06-01

Loop quantum cosmology with a scalar field is known to be closely linked with an inflationary phase. In this article, we study probabilistic predictions for the duration of slow-roll inflation, by assuming a minimalist massive scalar field as the main content of the Universe. The phase of the field in its “prebounce” oscillatory state is taken as a natural random parameter. We find that the probability for a given number of inflationary e-folds is quite sharply peaked around 145, which is consistent with the most favored minimum values. In this precise sense, a satisfactory inflation is therefore a clear prediction of loop gravity. In addition, we derive an original and stringent upper limit on the Barbero-Immirzi parameter. The general picture of inflation, superinflation, deflation, and superdeflation is also much clarified in the framework of bouncing cosmologies.

FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME

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

Filippazzo, Joseph C.; Rice, Emily L.; Faherty, Jacqueline

We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L{sub bol})more » and radius estimates from evolutionary models give semi-empirical effective temperatures (T{sub eff}) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T{sub eff}, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T{sub eff} of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M{sub H} magnitude.« less

Curvature in Arabidopsis inflorescence stems is limited to the region of amyloplast displacement

NASA Technical Reports Server (NTRS)

Weise, S. E.; Kuznetsov, O. A.; Hasenstein, K. H.; Kiss, J. Z.

2000-01-01

Gravitropic sensing in stems and stem-like organs is hypothesized to occur in the endodermis. However, since the endodermis runs the entire length of the stem, the precise site of gravisensing has been difficult to define. In this investigation of gravisensitivity in inflorescence stems of Arabidopsis, we positioned stems in a high gradient magnetic field (HGMF) on a rotating clinostat. Approximately 40% of the young, wild-type (WT) inflorescences, for all positions tested, curved toward the HGMF in the vicinity of the stem exposed to the field. In contrast, when the wedge was placed in the basal region of older inflorescence stems, no curvature was observed. As a control, the HGMF was applied to a starchless mutant, and 5% of the stems curved toward the field. Microscopy of the endodermis in the WT showed amyloplast displacement in the vicinity of the HGMF. Additional structural studies demonstrated that the basal region of WT stems experienced amyloplast displacement and, therefore, suggest this region is capable of gravity perception. However, increased lignification likely prevented curvature in the basal region. The lack of apical curvature after basal amyloplast displacement indicates that gravity perception in the base is not transmitted to the apex. Thus, these results provide evidence that the signal (and thus, response) resulting from perception in Arabidopsis inflorescence stems is spatially restricted.

Mars' gravity field and upper atmosphere with MGS, Mars Odyssey, and MRO radio science data

NASA Astrophysics Data System (ADS)

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

2015-04-01

The Mars exploration program conducted by NASA during the last decade has enabled continuous observations of the planet from orbit with three different missions: the Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). These spacecraft were equipped with on board instrumentation dedicated to collect radio tracking data in the X-band. The analysis of these data has provided a high-resolution gravity field model of Mars. MGS and ODY were inserted into two separate frozen sun-synchronous, near-circular, polar orbits with different local times, with their periapsis altitude at ~370 km and ~390 km, respectively. MGS was in orbit around Mars between 1999 and 2006, whereas ODY has been orbiting the planet since January 2002. Using the radio science data of these two spacecraft, gravity models with a maximum resolution of degree and order 95 in spherical harmonics (spatial resolution of 112 km) have been determined. MRO has been orbiting Mars since August 2006 in a frozen sun-synchronous orbit with a periapsis at 255 km altitude. Therefore, its radio data helped significantly improve Mars' gravity field model, up to degree and order 110 (spatial resolution of 96 km). However, mismodeling of the atmospheric drag, which is the strongest non-conservative force acting on the spacecraft at MRO's low altitude, compromises the estimation of the temporal variations of the gravity field zonal harmonics that provide crucial information on the seasonal mass of carbon dioxide in the polar caps. For this reason, we implemented the Drag Temperature Model (DTM)-Mars model (Bruinsma and Lemoine 2002) into our Precise Orbit Determination (POD) program GEODYN-II. We estimated key model parameters to adequately reproduce variations in temperatures and (partial) density along the spacecraft trajectories. Our new model allows us to directly estimate the long-term periodicity of the major constituents at MGS, ODY, and MRO altitudes (~255-450 km). In this region of the Martian upper atmosphere, CO2, O, and He represent the dominant species. MRO data primarily determine the annual and semi-annual variability of CO2 and O since these two elements are the major constituents along its orbit. MGS and ODY sample altitudes where He is the most abundant species and thus they help constrain the long-term variations of O. We will present an update on the DTM-Mars model using MGS, ODY, and MRO radio science data. The improved atmospheric model provides a better prediction of the long-term 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 using MGS, ODY, and MRO radio tracking data. The solution will be especially based on 8 years of MRO data from August 2006 to June 2014.

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.

A geopotential model from satellite tracking, altimeter, and surface gravity data: GEM-T3

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Nerem, R. S.; Putney, B. H.; Felsentreger, T. L.; Sanchez, B. V.; Marshall, J. A.; Klosko, S. M.; Patel, G. B.; Williamson, R. G.; Chinn, D. S.

1994-01-01

An improved model of Earth's gravitational field, Goddard Earth Model T-3 (GEM-T3), has been developed from a combination of satellite tracking, satellite altimeter, and surface gravimetric data. GEM-T3 provides a significant improvement in the modeling of the gravity field at half wavelengths of 400 km and longer. This model, complete to degree and order 50, yields more accurate satellite orbits and an improved geoid representation than previous Goddard Earth Models. GEM-T3 uses altimeter data from GEOS 3 (1975-1976), Seasat (1978) and Geosat (1986-1987). Tracking information used in the solution includes more than 1300 arcs of data encompassing 31 different satellites. The recovery of the long-wavelength components of the solution relies mostly on highly precise satellite laser ranging (SLR) data, but also includes Tracking Network (TRANET) Doppler, optical, and satellite-to-satellite tracking acquired between the ATS 6 and GEOS 3 satellites. The main advances over GEM-T2 (beyond the inclusion of altimeter and surface gravity information which is essential for the resolution of the shorter wavelength geoid) are some improved tracking data analysis approaches and additional SLR data. Although the use of altimeter data has greatly enhanced the modeling of the ocean geoid between 65 deg N and 60 deg S latitudes in GEM-T3, the lack of accurate detailed surface gravimetry leaves poor geoid resolution over many continental regions of great tectonic interest (e.g., Himalayas, Andes). Estimates of polar motion, tracking station coordinates, and long-wavelength ocean tidal terms were also made (accounting for 6330 parameters). GEM-T3 has undergone error calibration using a technique based on subset solutions to produce reliable error estimates. The calibration is based on the condition that the expected mean square deviation of a subset gravity solution from the full set values is predicted by the solutions' error covariances. Data weights are iteratively adjusted until this condition for the error calibration is satisfied. In addition, gravity field tests were performed on strong satellite data sets withheld from the solution (thereby ensuring their independence). In these tests, the performance of the subset models on the withheld observations is compared to error projections based on their calibrated error covariances. These results demonstrate that orbit accuracy projections are reliable for new satellites which were not included in GEM-T3.

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

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.

Magma intrusion beneath long valley caldera confirmed by temporal changes in gravity

PubMed

Battaglia; Roberts; Segall

1999-09-24

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 +/- 6 microgals (1 microgal = 10(-8) meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 +/- 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 10(3) to 4.1 x 10(3) kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.

Magma intrusion beneath Long Valley caldera confirmed by temporal changes in gravity

USGS Publications Warehouse

Battaglia, Maurizio; Roberts, C.; Segall, P.

1999-01-01

Precise relative gravity measurements conducted in Long Valley (California) in 1982 and 1998 reveal a decrease in gravity of as much as -107 ?? 6 microgals (1 microgal = 10-8 meters per square second) centered on the uplifting resurgent dome. A positive residual gravity change of up to 64 ?? 15 microgals was found after correcting for the effects of uplift and water table fluctuations. Assuming a point source of intrusion, the density of the intruding material is 2.7 x 103 to 4.1 x 103 kilograms per cubic meter at 95 percent confidence. The gravity results require intrusion of silicate magma and exclude in situ thermal expansion or pressurization of the hydrothermal system as the cause of uplift and seismicity.

Gamma astrometric measurement experiment -science and implementation

NASA Astrophysics Data System (ADS)

Gai, Mario; Vecchiato, Alberto; Lattanzi, Mario G.; Ligori, Sebastiano; Loreggia, Davide; Fineschi, Silvano

GAME (Gamma Astrometric Measurement Experiment) is a mission concept taking advantage of astronomical techniques for high precision measurements of interest to Fundamental Physics, and in particular the γ parameter of the Parameterized Post-Newtonian formulation of gravi-tation theories modifying the General Relativity. A space based telescope, looking close to the Solar limb thanks to coronagraphic techniques, may implement astrometric measurements sim-ilar to those performed in the solar eclipse of 1919, when Dyson, Eddington and collaborators measured for the first time the gravitational bending of light. Simulations show that the final accuracy of GAME can reach the 10-7 level. GAME will be a decisive experiment for the understanding of gravity physics, cosmology and the Universe evolution. The observations leading to Dark Matter (e.g. galaxy rotation curves) and Dark Energy (accelerated expansion of the Universe) might be explained with a modified version of General Relativity, e.g. in which the curvature invariant R is no longer constant as in Einstein's equations, i.e. the f (R) gravity theories. A 10-7 level determination of γ will provide stringent constraints on acceptable theories. Also, high precision astrometry makes accessible other appealing measurements, e.g. the light deflection induced by the quadrupole moment of giant planets, like Jupiter or Saturn, and, by high precision determination of the orbits of Mercury and high elongation asteroids, the PPN parameter β. GAME may also carry out measurements on selected astrophysical targets, e.g. nearby, bright stars known to host companions with minimum masses in the planetary/brown dwarf regime, and orbital radii in the 3-7 AU range, which are observed by no other present or planned campaigns. GAME, also thanks to high-cadence, high-precision photometry on transit-ing exoplanet systems, will thus improve on our understanding of the actual mass distribution and multiplicity of sub-stellar companions. The GAME measurement principle is based on the differential astrometric signature on the stellar positions. Calibration is implemented by observation of stellar fields affected by neg-ligible deflection. The instrument concept is based on a dual field, multiple aperture Fizeau interferometer, observing simultaneously sky regions close to the Solar limb. Coronagraphic solutions are embedded in the astrometric telescope design, to achieve a rejection factor of the Sun disk and stray light of ˜ 10-9 . An array of apertures implemented by pupil masking on an underlying telescope with primary diameter below one meter, with long focal length, fulfills the mission specifications by providing individual photo-center precision better than 1 milli-arcsecond for source magnitude 15 or brighter.

Studies into the averaging problem: Macroscopic gravity and precision cosmology

NASA Astrophysics Data System (ADS)

Wijenayake, Tharake S.

2016-08-01

With the tremendous improvement in the precision of available astrophysical data in the recent past, it becomes increasingly important to examine some of the underlying assumptions behind the standard model of cosmology and take into consideration nonlinear and relativistic corrections which may affect it at percent precision level. Due to its mathematical rigor and fully covariant and exact nature, Zalaletdinov's macroscopic gravity (MG) is arguably one of the most promising frameworks to explore nonlinearities due to inhomogeneities in the real Universe. We study the application of MG to precision cosmology, focusing on developing a self-consistent cosmology model built on the averaging framework that adequately describes the large-scale Universe and can be used to study real data sets. We first implement an algorithmic procedure using computer algebra systems to explore new exact solutions to the MG field equations. After validating the process with an existing isotropic solution, we derive a new homogeneous, anisotropic and exact solution. Next, we use the simplest (and currently only) solvable homogeneous and isotropic model of MG and obtain an observable function for cosmological expansion using some reasonable assumptions on light propagation. We find that the principal modification to the angular diameter distance is through the change in the expansion history. We then linearize the MG field equations and derive a framework that contains large-scale structure, but the small scale inhomogeneities have been smoothed out and encapsulated into an additional cosmological parameter representing the averaging effect. We derive an expression for the evolution of the density contrast and peculiar velocities and integrate them to study the growth rate of large-scale structure. We find that increasing the magnitude of the averaging term leads to enhanced growth at late times. Thus, for the same matter content, the growth rate of large scale structure in the MG model is stronger than that of the standard model. Finally, we constrain the MG model using Cosmic Microwave Background temperature anisotropy data, the distance to supernovae data, the galaxy power spectrum, the weak lensing tomography shear-shear cross-correlations and the baryonic acoustic oscillations. We find that for this model the averaging density parameter is very small and does not cause any significant shift in the other cosmological parameters. However, it can lead to increased errors on some cosmological parameters such as the Hubble constant and the amplitude of the linear matter spectrum at the scale of 8h. {-1}Mpc. Further studiesare needed to explore other solutions and models of MG as well as their effects on precision cosmology.

Design of a cusped field thruster for drag-free flight

NASA Astrophysics Data System (ADS)

Liu, H.; Chen, P. B.; Sun, Q. Q.; Hu, P.; Meng, Y. C.; Mao, W.; Yu, D. R.

2016-09-01

Drag-free flight has played a more and more important role in many space missions. The thrust control system is the key unit to achieve drag-free flight by providing a precise compensation for the disturbing force except gravity. The cusped field thruster has shown a significant potential to be capable of the function due to its long life, high efficiency, and simplicity. This paper demonstrates a cusped field thruster's feasibility in drag-free flight based on its instinctive characteristics and describes a detailed design of a cusped field thruster made by Harbin Institute of Technology (HIT). Furthermore, the performance test is conducted, which shows that the cusped field thruster can achieve a continuously variable thrust from 1 to 20 mN with a low noise and high resolution below 650 W, and the specific impulse can achieve 1800 s under a thrust of 18 mN and discharge voltage of 1000 V. The thruster's overall performance indicates that the cusped field thruster is quite capable of achieving drag-free flight. With the further optimization, the cusped field thruster will exhibit a more extensive application value.

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.

The gravity fields of Ganymede, Callisto and Europa: how well can JUICE do?

NASA Astrophysics Data System (ADS)

Parisi, Marzia; Iess, Luciano; Finocchiaro, Stefano

2014-05-01

With 20 flybys of Callisto, 2 of Europa and an extended orbital phase around Ganymede, ESA's JUICE mission offers an excellent opportunity to investigate the interiors of the three Galilean satellites. All of these moons can host an internal ocean, but the evidence is compelling only for Europa, where Galileo's measurements of the induced magnetic field are not marred by an intrinsic field as for Ganymede. However, both Europa's and Ganymede's appear to be differentiated (Showman and Malhotra, 1999), and probably hosting a subsurface liquid water ocean underneath the icy surface (Khurana et al., 1998; Kivelson et al., 2002). But even for Callisto, which appears as an undifferentiated body of ice and rock (Showman and Malhotra, 1999), a global or partial subsurface ocean cannot be ruled out (Khurana et al., 1998). The determination of the interior structure of the Galilean satellites, one of the main goal of the JUICE mission, can be accomplished by a combination of gravity, altimetric and magnetic measurements. Gravity measurements are addressed by the 3GM (Geodesy and Geophysics of Jupiter and the Galilean Moons) by means of highly accurate Doppler tracking of the spacecraft from ground antennas. Precise range rate measurements are enabled by a dedicated Ka-band (32-34 GHz) transponder, heritage from the Juno and BepiColombo missions. The expected range rate accuracies are around 0.01 mm/s at 60 s integration time, at nearly all solar elongation angles. A complete cancellation of the interplanetary plasma noise is indeed possible by operating simultaneously the links at X and Ka band. The current mission profile envisages two, low altitude, orbital phases around Ganymede: a circular polar, orbit at an altitude of 500 km for the first 102 days, and circular polar orbit at an altitude of 200 km for the last 30 days. The low altitude will permit the determination of Ganymede's gravity field with a relative accuracy of about 10^-5 for both J2 and C22. The 18 tidal cycles of Ganymede observed by JUICE will allow the determination of the k2 Love number with an absolute accuracy of about 10^-3, both for the real and the imaginary part. The presence or absence of an internal ocean will be therefore assessed unambiguously. Numerical simulations of the gravity experiment show also an excellent sensitivity to the satellite's rotational state (obliquity and libration amplitude). Prior to the orbit insertion around Ganymede, the JUICE spacecraft will perform also 20 flybys of Callisto. The determination of the octupole gravity field appears certainly attainable. Since Callisto will be observed at different mean anomalies, its Love number k2 can be estimated with an accuracy of about 0.06, enough to provide evidence for an internal ocean. In the same mission phase, two Europa flybys will offer the opportunity to measure the static quadrupole field and test if the satellite is in hydrostatic equilibrium. References K.K. Khurana et al., Nature 395, 777 (1998). M.G. Kivelson et al., Icarus 157, 507 (2002). A.P. Showman and R. Malhotra, Science 286, 77 (1999).

Anticipating the effects of gravity when intercepting moving objects: differentiating up and down based on nonvisual cues.

PubMed

Senot, Patrice; Zago, Myrka; Lacquaniti, Francesco; McIntyre, Joseph

2005-12-01

Intercepting an object requires a precise estimate of its time of arrival at the interception point (time to contact or "TTC"). It has been proposed that knowledge about gravitational acceleration can be combined with first-order, visual-field information to provide a better estimate of TTC when catching falling objects. In this experiment, we investigated the relative role of visual and nonvisual information on motor-response timing in an interceptive task. Subjects were immersed in a stereoscopic virtual environment and asked to intercept with a virtual racket a ball falling from above or rising from below. The ball moved with different initial velocities and could accelerate, decelerate, or move at a constant speed. Depending on the direction of motion, the acceleration or deceleration of the ball could therefore be congruent or not with the acceleration that would be expected due to the force of gravity acting on the ball. Although the best success rate was observed for balls moving at a constant velocity, we systematically found a cross-effect of ball direction and acceleration on success rate and response timing. Racket motion was triggered on average 25 ms earlier when the ball fell from above than when it rose from below, whatever the ball's true acceleration. As visual-flow information was the same in both cases, this shift indicates an influence of the ball's direction relative to gravity on response timing, consistent with the anticipation of the effects of gravity on the flight of the ball.

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.

Gravity model development for TOPEX/POSEIDON: Joint gravity models 1 and 2

NASA Technical Reports Server (NTRS)

Nerem, R. S.; Lerch, F. J.; Marshall, J. A.; Pavlis, E. C.; Putney, B. H.; Tapley, B. D.; Eanes, R. J.; Ries, J. C.; Schutz, B. E.; Shum, C. K.

1994-01-01

The TOPEX/POSEIDON (T/P) prelaunch Joint Gravity Model-1 (JGM-1) and the postlaunch JGM-2 Earth gravitational models have been developed to support precision orbit determination for T/P. Each of these models is complete to degree 70 in spherical harmonics and was computed from a combination of satellite tracking data, satellite altimetry, and surface gravimetry. While improved orbit determination accuracies for T/P have driven the improvements in the models, the models are general in application and also provide an improved geoid for oceanographic computations. The postlaunch model, JGM-2, which includes T/P satellite laser ranging (SLR) and Doppler orbitography and radiopositioning integrated by satellite (DORIS) tracking data, introduces radial orbit errors for T/P that are only 2 cm RMS with the commission errors of the marine geoid for terms to degree 70 being +/- 25 cm. Errors in modeling the nonconservative forces acting on T/P increase the total radial errors to only 3-4 cm root mean square (RMS), a result much better than premission goals. While the orbit accuracy goal for T/P has been far surpassed geoid errors still prevent the absolute determination of the ocean dynamic topography for wavelengths shorter than about 2500 km. Only a dedicated gravitational field satellite mission will likely provide the necessary improvement in the geoid.

Gravity field and shape of Ceres from Dawn

NASA Astrophysics Data System (ADS)

Park, Ryan; Konopliv, Alexander; Vaughan, Andrew; Bills, Bruce; Castillo-Rogez, Julie; Ermakov, Anton; Fu, Roger; Raymond, Carol; Russell, Chris; Zuber, Maria

2017-04-01

The Dawn gravity science investigation utilizes the DSN radio tracking of the spacecraft and on-board framing camera images to determine the gravity field and global shape of Ceres. The gravity science data collected during Approach, Survey, High-Altitude Mapping Orbit, and Low-Altitude Mapping Orbit phases were processed. The final gravity science solution yielded a degree and order 18 gravity field, called CERES18C, which is globally accurate to degree and order 14. Also, the final Ceres shape using the stereo-photoclinometry method is available with the height uncertainty better than 30 meters. The degree-2 gravity harmonics show that the rotation of Ceres is very nearly about a principal axis. Combining the gravity field and topography gives the bulk density of 2162.6±2.0 kg/m3. The estimated spin pole vector yields RA=(291.42744±0.00022)° and Dec=(66.76065±0.00022)° with the prime meridian and rotation rate of (170.374±0.012)° and (952.1532638±0.0000019)°/day, respectively. The low Bouguer gravity at high topographic areas, and vice versa, indicates that the topography of Ceres is compensated, which can be explained by a low-viscosity layer at depth. Further studies on Ceres interior show that low gravity-topography admittances are consistent with Airy isostasy and finite-element modeling require a decrease of viscosity with depth.

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.

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.

Absolute marine gravimetry with matter-wave interferometry.

PubMed

Bidel, Y; Zahzam, N; Blanchard, C; Bonnin, A; Cadoret, M; Bresson, A; Rouxel, D; Lequentrec-Lalancette, M F

2018-02-12

Measuring gravity from an aircraft or a ship is essential in geodesy, geophysics, mineral and hydrocarbon exploration, and navigation. Today, only relative sensors are available for onboard gravimetry. This is a major drawback because of the calibration and drift estimation procedures which lead to important operational constraints. Atom interferometry is a promising technology to obtain onboard absolute gravimeter. But, despite high performances obtained in static condition, no precise measurements were reported in dynamic. Here, we present absolute gravity measurements from a ship with a sensor based on atom interferometry. Despite rough sea conditions, we obtained precision below 10 -5  m s -2 . The atom gravimeter was also compared with a commercial spring gravimeter and showed better performances. This demonstration opens the way to the next generation of inertial sensors (accelerometer, gyroscope) based on atom interferometry which should provide high-precision absolute measurements from a moving platform.

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.

The Equivalence of Precession Phenomena in Metric Theories of Gravity

NASA Technical Reports Server (NTRS)

Krisher, Timothy P.

1996-01-01

The requirement of general covariance imparts to metric theories of gravity, such as general relativity, important structural features. A precise mathematical form results, ensuring that computation of observable physical effects in the theory gives the same answers independently of the chosen system of coordinates. This coordinate independence property, in turn, can lead to an equivalence of apparently different physical effects.

Guidance and Control of a Man-Portable Precision Munition Concept

DTIC Science & Technology

2014-06-01

challenges posed by characteristics of spin-stabilized flight dynamics such as limit cycles, center -of- gravity swerve, instability, and practical...Control Line-of-sight rate and closing velocity estimates are used to form proportional navigation commands in classical guidance schemes...Accelerometers and gyroscopes often supply additional necessary feedback. The accelerometers ensure that the airframe is maneuvering the center of gravity

A new theory of gravity.

NASA Technical Reports Server (NTRS)

Ni, W.-T.

1973-01-01

A new relativistic theory of gravity is presented. This theory agrees with all experiments to date. It is a metric theory; it is Lagrangian-based; and it possesses a preferred frame with conformally flat space slices. With an appropriate choice of certain adjustable functions and parameters and of the cosmological model, this theory possesses precisely the same post-Newtonian limit as general relativity.

Characteristics of Marine Gravity Anomaly Reference Maps and Accuracy Analysis of Gravity Matching-Aided Navigation.

PubMed

Wang, Hubiao; Wu, Lin; Chai, Hua; Xiao, Yaofei; Hsu, Houtse; Wang, Yong

2017-08-10

The variation of a marine gravity anomaly reference map is one of the important factors that affect the location accuracy of INS/Gravity integrated navigation systems in underwater navigation. In this study, based on marine gravity anomaly reference maps, new characteristic parameters of the gravity anomaly were constructed. Those characteristic values were calculated for 13 zones (105°-145° E, 0°-40° N) in the Western Pacific area, and simulation experiments of gravity matching-aided navigation were run. The influence of gravity variations on the accuracy of gravity matching-aided navigation was analyzed, and location accuracy of gravity matching in different zones was determined. Studies indicate that the new parameters may better characterize the marine gravity anomaly. Given the precision of current gravimeters and the resolution and accuracy of reference maps, the location accuracy of gravity matching in China's Western Pacific area is ~1.0-4.0 nautical miles (n miles). In particular, accuracy in regions around the South China Sea and Sulu Sea was the highest, better than 1.5 n miles. The gravity characteristic parameters identified herein and characteristic values calculated in various zones provide a reference for the selection of navigation area and planning of sailing routes under conditions requiring certain navigational accuracy.

Characteristics of Marine Gravity Anomaly Reference Maps and Accuracy Analysis of Gravity Matching-Aided Navigation

PubMed Central

Wang, Hubiao; Chai, Hua; Xiao, Yaofei; Hsu, Houtse; Wang, Yong

2017-01-01

The variation of a marine gravity anomaly reference map is one of the important factors that affect the location accuracy of INS/Gravity integrated navigation systems in underwater navigation. In this study, based on marine gravity anomaly reference maps, new characteristic parameters of the gravity anomaly were constructed. Those characteristic values were calculated for 13 zones (105°–145° E, 0°–40° N) in the Western Pacific area, and simulation experiments of gravity matching-aided navigation were run. The influence of gravity variations on the accuracy of gravity matching-aided navigation was analyzed, and location accuracy of gravity matching in different zones was determined. Studies indicate that the new parameters may better characterize the marine gravity anomaly. Given the precision of current gravimeters and the resolution and accuracy of reference maps, the location accuracy of gravity matching in China’s Western Pacific area is ~1.0–4.0 nautical miles (n miles). In particular, accuracy in regions around the South China Sea and Sulu Sea was the highest, better than 1.5 n miles. The gravity characteristic parameters identified herein and characteristic values calculated in various zones provide a reference for the selection of navigation area and planning of sailing routes under conditions requiring certain navigational accuracy. PMID:28796158

Development of a Remote Sensing Small Satellite for Temperature Sounding in the Mesosphere/Lower Thermosphere by Measurement of the Oxygen Atmospheric Band Emission

NASA Astrophysics Data System (ADS)

Deiml, Michael; Kaufmann, Martin

2017-04-01

Coupling processes initiated by gravity waves in the middle atmosphere have increasing importance for the modeling of the climate system and represent one of the larger uncertainties in this field. To support new modeling efforts spatially resolved measurements of wave fields are very beneficial. This contribution proposes a new small satellite mission based on a three unit CubeSat form factor to observe the Oxygen Atmospheric Band emission around 762 nm for temperature derivation in a limb sounding configuration to characterize gravity waves. The satellite instrument resolves individual rotational lines whose intensities follow a Boltzmann law allowing for the derivation of temperature from the relative structure of these lines. The employed Spatial Heterodyne Spectrometer is characterized by its high throughput at a small form factor, allowing to perform scientific remote sensing measurements within a small satellite during day and night. The spectrometer consists of a thermally stabilized solid block and has no moving parts, which increases its reliability in orbit while allowing high precision measurements within a small volume. The instrument is verified in its precursor mission, the Atmospheric Heterodyne Interferometer Test (AtmoHIT), within the REXUS/BEXUS ballistic rocket flight campaign. The description of the flight campaign and the results thereof conclude this contribution.

Thermodynamics of new black hole solutions in the Einstein-Maxwell-dilaton gravity

NASA Astrophysics Data System (ADS)

Dehghani, M.

In the present work, thermodynamics of the new black hole solutions to the four-dimensional Einstein-Maxwell-dilaton gravity theory have been studied. The dilaton potential, as the solution to the scalar field equations, has been constructed out by a linear combination of three Liouville-type potentials. Three new classes of charged dilatonic black hole solutions, as the exact solutions to the coupled equations of gravitational, electromagnetic and scalar fields, have been introduced. The conserved charge and mass of the new black holes have been calculated by utilizing Gauss's electric law and Abbott-Deser mass proposal, respectively. Also, the temperature, entropy and the electric potential of these new classes of charged dilatonic black holes have been calculated, making use of the geometrical approaches. Through a Smarr-type mass formula, the intensive parameters of the black holes have been calculated and validity of the first law of black hole thermodynamics has been confirmed. A thermal stability or phase transition analysis has been performed, making use of the canonical ensemble method. The heat capacity of the new black holes has been calculated and the points of type one- and type two-phase transitions as well as the ranges at which the new charged dilatonic black holes are locally stable have been determined, precisely.

On the Inversion for Mass (Re)Distribution from Global (Time-Variable) Gravity Field

NASA Technical Reports Server (NTRS)

Chao, Benjamin F.

2004-01-01

The well-known non-uniqueness of the gravitational inverse problem states the following: The external gravity field, even if completely and exactly known, cannot Uniquely determine the density distribution of the body that produces the gravity field. This is an intrinsic property of a field that obeys the Laplace equation, as already treated in mathematical as well as geophysical literature. In this paper we provide conceptual insight by examining the problem in terms of spherical harmonic expansion of the global gravity field. By comparing the multipoles and the moments of the density function, we show that in 3-S the degree of knowledge deficiency in trying to inversely recover the density distribution from external gravity field is (n+l)(n+2)/2 - (2n+l) = n(n-1)/2 for each harmonic degree n. On the other hand, on a 2-D spherical shell we show via a simple relationship that the inverse solution of the surface density distribution is unique. The latter applies quite readily in the inversion of time-variable gravity signals (such as those observed by the GRACE space mission) where the sources over a wide range of the scales largely come from the Earth's Surface.

Investigating Gravity Anomalies Associated with Underground Nuclear Explosions

NASA Astrophysics Data System (ADS)

Rowe, C. A.; Miller, E.; Musa, D.; Schultz-Fellenz, E. S.; Sussman, A. J.; Swanson, E.

2016-12-01

Detection of subsurface effects from underground nuclear explosions (UNEs) is an important aspect of the overall characterization of a site and UNE signatures, which is central to the mission of the National Nuclear Security Admistration's Office of Proliferation Detection, Defense Nuclear Non-Prolifeation Research and Development, Underground Nuclear Explosion Signatures Experiment (UNESE). We are conducting an experiment at the Nevada National Security Site (NNSS) that includes the acquisition of ground-based gravity data to contribute to a multi-disciplinary characterization of two UNEs located on Pahute Mesa. For one of the UNEs, the working point for the detonation was in zeolitic ash-flow tuff 600 m below the surface. For the other UNE, the detonation working point was also at a depth 600m below the surface and was located in flow breccias and lavas. No evidence of chimney collapse has been manifested for either of these UNEs, hence a cavity may still in place and may produce a detectable gravity anomaly. Each of the gravity surveys consist of 150 sites which were precisely located using a Trimble 5700 GPS receiver for lateral precision of 2 cm and vertical control of 3 cm. The readings were arranged in radial lines from Surface Ground Zero (SGZ), with spacing 10-20 m near the center, and increasing intervals for the distal portions of the lines, which extended to as much as 200 m from SGZ. Gravity were collected using a LaCoste-Romberg model G gravity meter at one location and a Scintrex G-5 at the other. We present a preliminary look at the gravity data in conjunction with forward modeling of the anticipated anomaly given a suite of possible post-explosion cavity and chimney features.

The Precise Orbit and the Challenge of Long Term Stability

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Cerri, Luca; Otten, Michiel; Bertiger, William; Zelensky, Nikita; Willis, Pascal

2012-01-01

The computation of a precise orbit reference is a fundamental component of the altimetric measurement. Since the dawn of the modern altimeter age, orbit accuracy has been determined by the quality of the GPS, SLR, and DORIS tracking systems, the fidelity of the measurement and force models, and the choice of parameterization for the orbit solutions, and whether a dynamic or a reduced-dynamic strategy is used to calculate the orbits. At the start of the TOPEX mission, the inaccuracies in the modeling of static gravity, dynamic ocean tides, and the nonconservative forces dominated the orbit error budget. Much of the error due to dynamic mismodeling can be compensated by reduced-dynamic tracking techniques depending on the measurement system strength. In the last decade, the launch of the GRACE mission has eliminated the static gravity field as a concern, and the background force models and the terrestrial reference frame have been systematically refined. GPS systems have realized many improvements, including better modeling of the forces on the GPS spacecraft, large increases in the ground tracking network, and improved modeling of the GPS measurements. DORIS systems have achieved improvements through the use of new antennae, more stable monumentation, and of satellite receivers that can track multiple beacons, and as well as through improved modeling of the nonconservative forces. Many of these improvements have been applied in the new reprocessed time series of orbits produced for the ERS satellites, Envisat, TOPEX/Poseidon and the Jason satellites, and as well as for the most recent Cryosat-2 and HY2A. We now face the challenge of maintaining a stable orbit reference for these altimetric satellites. Changes in the time-variable gravity field of the Earth and how these are modelled have been shown to affect the orbit evolution, and the calibration of the altimetric data with tide gauges. The accuracy of the reference frame realizations, and their projection into the future remains a source of error. Other sources of omission error include the geocenter for which no consensus model is as of yet applied. Although progress has been made in nonconservative force modeling through the use of detailed satellite-specific models, radiation pressure modeling, and atmospheric density modeling remain a potential source of orbit error. The longer term influence of variations in the solar and terrestrial radiation fields over annual and solar cycles remains principally untested. Also the long term variation in optical and thermal properties of the space vehicle surfaces would contribute to biases in the orbital frame if ignored. We review the status of altimetric precision orbit determination as exemplified by the recent computations undertaken by the different analysis centers for ERS, Envisat, TOPEX/Poseidon, Jason, Cryosat2 and HY2A, and we provide a perspective on the challenges for future missions such as the Jason-3, SENTINEL-3 and SWOT.

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.

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.

Simulation and analysis of a geopotential research mission

NASA Technical Reports Server (NTRS)

Schutz, B. E.

1986-01-01

A computer simulation was performed for a Geopotential Research Mission (GRM) to enable study of the gravitational sensitivity of the range/rate measurement between two satellites and to provide a set of simulated measurements to assist in the evaluation of techniques developed for the determination of the gravity field. The simulation, identified as SGRM 8511, was conducted with two satellites in near circular, frozen orbits at 160 km altitude and separated by 300 km. High precision numerical integration of the polar orbits was used with a gravitational field complete to degree and order 180 coefficients and to degree 300 in orders 0 to 10. The set of simulated data for a mission duration of about 32 days was generated on a Cray X-MP computer. The characteristics of the simulation and the nature of the results are described.

Holographic heat engines

NASA Astrophysics Data System (ADS)

Johnson, Clifford V.

2014-10-01

It is shown that in theories of gravity where the cosmological constant is considered a thermodynamic variable, it is natural to use black holes as heat engines. Two examples are presented in detail using AdS charged black holes as the working substance. We notice that for static black holes, the maximally efficient traditional Carnot engine is also a Stirling engine. The case of negative cosmological constant supplies a natural realization of these engines in terms of the field theory description of the fluids to which they are holographically dual. We first propose a precise picture of how the traditional thermodynamic dictionary of holography is extended when the cosmological constant is dynamical and then conjecture that the engine cycles can be performed by using renormalization group flow. We speculate about the existence of a natural dual field theory counterpart to the gravitational thermodynamic volume.

MSSM-inspired multifield inflation

NASA Astrophysics Data System (ADS)

Dubinin, M. N.; Petrova, E. Yu.; Pozdeeva, E. O.; Sumin, M. V.; Vernov, S. Yu.

2017-12-01

Despite the fact that experimentally with a high degree of statistical significance only a single Standard Model-like Higgs boson is discovered at the LHC, extended Higgs sectors with multiple scalar fields not excluded by combined fits of the data are more preferable theoretically for internally consistent realistic models of particle physics. We analyze the inflationary scenarios which could be induced by the two-Higgs-doublet potential of the Minimal Supersymmetric Standard Model (MSSM) where five scalar fields have non-minimal couplings to gravity. Observables following from such MSSM-inspired multifield inflation are calculated and a number of consistent inflationary scenarios are constructed. Cosmological evolution with different initial conditions for the multifield system leads to consequences fully compatible with observational data on the spectral index and the tensor-to-scalar ratio. It is demonstrated that the strong coupling approximation is precise enough to describe such inflationary scenarios.

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

The beam combiners of Gravity VLTI instrument: concept, development, and performance in laboratory

NASA Astrophysics Data System (ADS)

Jocou, L.; Perraut, K.; Moulin, T.; Magnard, Y.; Labeye, P.; Lapras, V.; Nolot, A.; Perrin, G.; Eisenhauer, F.; Holmes, C.; Amorim, A.; Brandner, W.; Straubmeier, C.

2014-07-01

Gravity is one of the second-generation instruments of the Very Large Telescope Interferometer that operates in the near infrared range and that is designed for precision narrow-angle astrometry and interferometric imaging. With its infrared wavefront sensors, pupil stabilization, fringe tracker, and metrology, the instrument is tailored to provide a high sensitivity, imaging with 4-millisecond resolution, and astrometry with a 10μarcsec precision. It will probe physics close to the event horizon of the Galactic Centre black hole, and allow to study mass accretion and jets in young stellar objects and active galactic nuclei, planet formation in circumstellar discs, or detect and measure the masses of black holes in massive star clusters throughout the Milky Way. As the instrument required an outstanding level of precision and stability, integrated optics has been chosen to collect and combine the four VLTI beams in the K band. A dedicated integrated optics chip glued to a fiber array has been developed. Technology breakthroughs have been mandatory to fulfill all the specifications. This paper is focused on the interferometric beam combination system of Gravity. Once the combiner concept described, the paper details the developments that have been led, the integration and the performance of the assemblies.

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

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.

Too Fast to Measure: Network Adjustment of Rapidly Changing Gravity Fields

NASA Astrophysics Data System (ADS)

Kennedy, J.; Ferre, T. P. A.

2014-12-01

Measurements of spatially-variable gravity at the field scale are difficult; measurements of the time-varying field even more so. Every previous gravity survey using relative gravimeters—still the workhorse of gravity studies, despite their nearly 80 year history—has assumed a static gravity field during the course of a survey, which may last days to weeks. With recently-improved instrumentation, however, measurements of fields changing on the order of tens of nm/sec2 per day are now possible. In particular, the A-10 portable absolute gravimeter provides not only absolute control, but also the change in that control during the course of a survey. Using digitally-recording spring-based relative gravimeters (namely, the ZLS Burris meter and the Scintrex CG-5), with their more efficient data collection and lower drift than previous generations, many more data are collected in a day. We demonstrate a method for incorporating in the least-squares network adjustment of relative gravity data a relation between the rate of change of gravity, dg, and distance from an infiltration source, x. This relation accounts for the fact that gravity at stations adjacent to the infiltration source changes more rapidly than stations further away; if all measurements collected over several days are to be included in a single network-adjustment, consideration of this change is required. Two methods are used to simulate the dg(x) relation: a simple model where dg is a linear function of x, and a coupled-hydrogeophysical method where a groundwater flow model predicts the nonlinear spatial variation of dg. Then, the change in gravity between different, independently adjusted surveys is used to parameterize the groundwater model. Data from two recent field examples, an artificial recharge facility near Tucson, Arizona, USA, and from the 2014 Lower Colorado River pulse flow experiment, clearly show the need to account for gravity change during a survey; maximum rates of change for the two studies were up to 30 and 50 nm/sec2 per day, respectively.

The gravity field model IGGT_R1 based on the second invariant of the GOCE gravitational gradient tensor

NASA Astrophysics Data System (ADS)

Lu, Biao; Luo, Zhicai; Zhong, Bo; Zhou, Hao; Flechtner, Frank; Förste, Christoph; Barthelmes, Franz; Zhou, Rui

2017-11-01

Based on tensor theory, three invariants of the gravitational gradient tensor (IGGT) are independent of the gradiometer reference frame (GRF). Compared to traditional methods for calculation of gravity field models based on the gravity field and steady-state ocean circulation explorer (GOCE) data, which are affected by errors in the attitude indicator, using IGGT and least squares method avoids the problem of inaccurate rotation matrices. The IGGT approach as studied in this paper is a quadratic function of the gravity field model's spherical harmonic coefficients. The linearized observation equations for the least squares method are obtained using a Taylor expansion, and the weighting equation is derived using the law of error propagation. We also investigate the linearization errors using existing gravity field models and find that this error can be ignored since the used a-priori model EIGEN-5C is sufficiently accurate. One problem when using this approach is that it needs all six independent gravitational gradients (GGs), but the components V_{xy} and V_{yz} of GOCE are worse due to the non-sensitive axes of the GOCE gradiometer. Therefore, we use synthetic GGs for both inaccurate gravitational gradient components derived from the a-priori gravity field model EIGEN-5C. Another problem is that the GOCE GGs are measured in a band-limited manner. Therefore, a forward and backward finite impulse response band-pass filter is applied to the data, which can also eliminate filter caused phase change. The spherical cap regularization approach (SCRA) and the Kaula rule are then applied to solve the polar gap problem caused by GOCE's inclination of 96.7° . With the techniques described above, a degree/order 240 gravity field model called IGGT_R1 is computed. Since the synthetic components of V_{xy} and V_{yz} are not band-pass filtered, the signals outside the measurement bandwidth are replaced by the a-priori model EIGEN-5C. Therefore, this model is practically a combined gravity field model which contains GOCE GGs signals and long wavelength signals from the a-priori model EIGEN-5C. Finally, IGGT_R1's accuracy is evaluated by comparison with other gravity field models in terms of difference degree amplitudes, the geostrophic velocity in the Agulhas current area, gravity anomaly differences as well as by comparison to GNSS/leveling data.

High-fidelity gravity modeling applied to spacecraft trajectories and lunar interior analysis

NASA Astrophysics Data System (ADS)

Chappaz, Loic P. R.

As the complexity and boldness of emerging mission proposals increase, and with the rapid evolution of the available computational capabilities, high-accuracy and high-resolution gravity models and the tools to exploit such models are increasingly attractive within the context of spaceflight mechanics, mission design and analysis, and planetary science in general. First, in trajectory design applications, a gravity representation for the bodies of interest is, in general, assumed and exploited to determine the motion of a spacecraft in any given system. The focus is the exploration of trajectories in the vicinity of a system comprised of two small irregular bodies. Within this context, the primary bodies are initially modeled as massive ellipsoids and tools to construct third-body trajectories are developed. However, these dynamical models are idealized representations of the actual dynamical regime and do not account for any perturbing effects. Thus, a robust strategy to maintain a spacecraft near reference third-body trajectories is constructed. Further, it is important to assess the perturbing effect that dominates the dynamics of the spacecraft in such a region as a function of the baseline orbit. Alternatively, the motion of the spacecraft around a given body may be known to extreme precision enabling the derivation of a very high-accuracy gravity field for that body. Such knowledge can subsequently be exploited to gain insight into specific properties of the body. The success of the NASA's GRAIL mission ensures that the highest resolution and most accurate gravity data for the Moon is now available. In the GRAIL investigation, the focus is on the specific task of detecting the presence and extent of subsurface features, such as empty lava tubes beneath the mare surface. In addition to their importance for understanding the emplacement of the mare flood basalts, open lava tubes are of interest as possible habitation sites safe from cosmic radiation and micrometeorite impacts. Tools are developed to best exploit the rich gravity data toward the numerical detection of such small features.

Gravity for Detecting Caves: Airborne and Terrestrial Simulations Based on a Comprehensive Karstic Cave Benchmark

NASA Astrophysics Data System (ADS)

Braitenberg, Carla; Sampietro, Daniele; Pivetta, Tommaso; Zuliani, David; Barbagallo, Alfio; Fabris, Paolo; Rossi, Lorenzo; Fabbri, Julius; Mansi, Ahmed Hamdi

2016-04-01

Underground caves bear a natural hazard due to their possible evolution into a sink hole. Mapping of all existing caves could be useful for general civil usages as natural deposits or tourism and sports. Natural caves exist globally and are typical in karst areas. We investigate the resolution power of modern gravity campaigns to systematically detect all void caves of a minimum size in a given area. Both aerogravity and terrestrial acquisitions are considered. Positioning of the gravity station is fastest with GNSS methods the performance of which is investigated. The estimates are based on a benchmark cave of which the geometry is known precisely through a laser-scan survey. The cave is the Grotta Gigante cave in NE Italy in the classic karst. The gravity acquisition is discussed, where heights have been acquired with dual-frequency geodetic GNSS receivers and Total Station. Height acquisitions with non-geodetic low-cost receivers are shown to be useful, although the error on the gravity field is larger. The cave produces a signal of -1.5 × 10-5 m/s2, with a clear elliptic geometry. We analyze feasibility of airborne gravity acquisitions for the purpose of systematically mapping void caves. It is found that observations from fixed wing aircraft cannot resolve the caves, but observations from slower and low-flying helicopters or drones do. In order to detect the presence of caves the size of the benchmark cave, systematic terrestrial acquisitions require a density of three stations on square 500 by 500 m2 tiles. The question has a large impact on civil and environmental purposes, since it will allow planning of urban development at a safe distance from subsurface caves. The survey shows that a systematic coverage of the karst would have the benefit to recover the position of all of the greater existing void caves.

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.

30 CFR 1206.53 - How do I determine value for oil that I or my affiliate do(es) not sell under an arm's-length...

Code of Federal Regulations, 2011 CFR

2011-07-01

... sales to the same gravity as that of the oil produced from the lease. Use applicable gravity adjustment tables for the field (or the same general area for like-quality oil if you do not have gravity adjustment tables for the specific field) to normalize for gravity. Example to paragraph (b): 1. Assume that a...

30 CFR 1206.53 - How do I determine value for oil that I or my affiliate do(es) not sell under an arm's-length...

Code of Federal Regulations, 2012 CFR

2012-07-01

... sales to the same gravity as that of the oil produced from the lease. Use applicable gravity adjustment tables for the field (or the same general area for like-quality oil if you do not have gravity adjustment tables for the specific field) to normalize for gravity. Example to paragraph (b): 1. Assume that a...

30 CFR 1206.53 - How do I determine value for oil that I or my affiliate do(es) not sell under an arm's-length...

Code of Federal Regulations, 2013 CFR

2013-07-01

... sales to the same gravity as that of the oil produced from the lease. Use applicable gravity adjustment tables for the field (or the same general area for like-quality oil if you do not have gravity adjustment tables for the specific field) to normalize for gravity. Example to paragraph (b): 1. Assume that a...

30 CFR 1206.53 - How do I determine value for oil that I or my affiliate do(es) not sell under an arm's-length...

Code of Federal Regulations, 2014 CFR

2014-07-01

... sales to the same gravity as that of the oil produced from the lease. Use applicable gravity adjustment tables for the field (or the same general area for like-quality oil if you do not have gravity adjustment tables for the specific field) to normalize for gravity. Example to paragraph (b): 1. Assume that a...

Effects of Gravity on Ignition and Combustion Characteristics of Externally Heated Polyethylene Film

NASA Astrophysics Data System (ADS)

Ikeda, Mitsumasa

2018-04-01

The objective of this research is to investigate the effects of gravity on the ignition and the combustion characteristics of the Polyethylene (PE) film by outer heating. Combustion experiments of PE film were carried out in a normal gravity field and the microgravity field. In the microgravity experiments, it was carried out in 50 m-class drop facility. Here it can be realized 10- 4G microgravity field in about 2.5-3.0 second. The PE film is heated by the inserted high-temperature chamber. In the experiments, the PE was used film type. The chamber temperature was fixed at 900 K and 1000 K. In the case of microgravity field, the ignition delay period has become about 50 percent shorter than that in the case of the normal gravitational field. In the normal gravity field, since the PE surface layer is cooled by natural convection, the ignition delay period is considered to be longer than that in the microgravity field. The combustion time in the normal gravity was about 0.8 sec. In the microgravity field, the combustion time was more than 2 sec, and it could not be measured during the free fall period.

Time-variable and static gravity field of Mars from MGS, Mars Odyssey, and MRO

NASA Astrophysics Data System (ADS)

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

2016-04-01

The Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) missions have significantly contributed to the determination of global high-resolution global gravity fields of Mars for the last 16 years. All three spacecraft were located in sun-synchronous, near-circular polar mapping orbits for their primary mission phases at different altitudes and Local Solar Time (LST). X-Band tracking data have been acquired from the NASA Deep Space Network (DSN) providing information on the time-variable and static gravity field of Mars. MGS operated between 1999 and 2006 at 390 km altitude. ODY and MRO are still orbiting Mars with periapsis altitudes of 400 km and 255 km, respectively. Before entering these mapping phases, all three spacecraft collected radio tracking data at lower altitudes (˜170-200 km) that help improve the resolution of the gravity field of Mars in specific regions. We analyzed the entire MGS radio tracking data set, and ODY and MRO radio data until 2015. These observations were processed using a batch least-squares filter through the NASA GSFC GEODYN II software. We combined all 2- and 3-way range rate data to estimate the global gravity field of Mars to degree and order 120, the seasonal variations of gravity harmonic coefficients C20, C30, C40 and C50 and the Love number k2. The gravity contribution of Mars atmospheric pressures on the surface of the planet has been discerned from the time-varying and static gravity harmonic coefficients. Surface pressure grids computed using the Mars-GRAM 2010 atmospheric model, with 2.5° x2.5° spatial and 2-h resolution, are converted into gravity spherical harmonic coefficients. Consequently, the estimated gravity and tides provide direct information on the solid planet. We will present the new Goddard Mars Model (GMM-3) of Mars gravity field in spherical harmonics to degree and order 120. The solution includes the Love number k2 and the 3-frequencies (annual, semi-annual, and tri-annual) time-variable coefficients of the gravity zonal harmonics C20, C30, C40 and C50. The seasonal gravity coefficients led us to determine the inter-annual mass exchange between the polar caps over ˜11 years from October 2002 to November 2014.

Lifshitz gravity for Lifshitz holography.

PubMed

Griffin, Tom; Hořava, Petr; Melby-Thompson, Charles M

2013-02-22

We argue that Hořava-Lifshitz (HL) gravity provides the minimal holographic dual for Lifshitz-type field theories with anisotropic scaling and a dynamical exponent z. First we show that Lifshitz spacetimes are vacuum solutions of HL gravity, without need for additional matter. Then we perform holographic renormalization of HL gravity, and show how it reproduces the full structure of the z=2 anisotropic Weyl anomaly in dual field theories in 2+1 dimensions, while its minimal relativistic gravity counterpart yields only one of two independent central charges in the anomaly.

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.

Venus gravity - Analysis of Beta Regio

NASA Technical Reports Server (NTRS)

Esposito, P. B.; Sjogren, W. L.; Mottinger, N. A.; Bills, B. G.; Abbott, E.

1982-01-01

Radio tracking data acquired over Beta Regio were analyzed to obtain a surface mass distribution from which a detailed vertical gravity field was derived. In addition, a corresponding vertical gravity field was evaluated solely from the topography of the Beta region. A comparison of these two maps confirms the strong correlation between gravity and topography which was previously seen in line-of-sight gravity maps. It also demonstrates that the observed gravity is a significant fraction of that predicted from the topography alone. The effective depth of complete isostatic compensation for the Beta region is estimated to be 330 km, which is somewhat deeper than that found for other areas of Venus.

^4He experiments near T_λ with a heat current and reduced gravity in a low-gravity simulator

NASA Astrophysics Data System (ADS)

Liu, Yuanming; Larson, Melora; Israelsson, Ulf

1998-03-01

Conventional ground-based helium experiments experience limitations due to a variation of the superfluid transition temperature (T_λ) caused by the gravity-induced hydrostatic pressure in a ^4He sample cell. A low-gravity simulator consisting a high field superconducting magnet has been built in our laboratory and the preliminary measurements demonstrated a reduction of gravity in the sample cell. (Melora Larson, Feng-Chuan Liu, and Ulf Israelsson, Czech. J. of Phys. 46, 179 (1996).) We report our latest improvements on the simulator and measurements with a new sample cell which had copper end plates, Vepsel sidewalls, and sidewall probes. The measurements showed that gravity can be canceled with a field-field gradient product of 20.7 T^2/cm (or B=15.5 Tesla), in excellent agreement with the theoretical prediction. The measurements also revealed that the boundary resistance between the thermometers and liquid helium increased from 1.6 cm^2 K/W at zero field to 2.0 cm^2 K/W at B=13.8 Tesla. The preliminary dynamic measurements near T_λ with a heat current and reduced gravity will also be presented. This research was supported by NASA.

Gravity investigation of the Manson impact structure, Iowa

NASA Technical Reports Server (NTRS)

Plescia, J. B.

1993-01-01

The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater is characterized by two positive anomalies having amplitudes of about plus 4 mGal separated by a gentle saddle located approximately at the crater center.

On the role of covariance information for GRACE K-band observations in the Celestial Mechanics Approach

NASA Astrophysics Data System (ADS)

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

2017-04-01

The Astronomical Institute at the University of Bern (AIUB) derives static and time-variable gravity fields by means of the Celestial Mechanics Approach (CMA) from GRACE (level 1B) data. This approach makes use of the close link between orbit and gravity field determination. GPS-derived kinematic GRACE orbit positions, inter-satellite K-band observations, which are the core observations of GRACE, and accelerometer data are combined to rigorously estimate orbit and spherical harmonic gravity field coefficients in one adjustment step. Pseudo-stochastic orbit parameters are set up to absorb unmodeled noise. The K-band range measurements in along-track direction lead to a much higher correlation of the observations in this direction compared to the other directions and thus, to north-south stripes in the unconstrained gravity field solutions, so-called correlated errors. By using a full covariance matrix for the K-band observations the correlation can be taken into account. One possibility is to derive correlation information from post-processing K-band residuals. This is then used in a second iteration step to derive an improved gravity field solution. We study the effects of pre-defined covariance matrices and residual-derived covariance matrices on the final gravity field product with the CMA.

Teleparallel theories of gravity as analogue of nonlinear electrodynamics

NASA Astrophysics Data System (ADS)

Hohmann, Manuel; Järv, Laur; Krššák, Martin; Pfeifer, Christian

2018-05-01

The teleparallel formulation of gravity theories reveals close structural analogies to electrodynamics, which are more hidden in their usual formulation in terms of the curvature of spacetime. We show how every locally Lorentz invariant teleparallel theory of gravity with second-order field equations can be understood as built from a gravitational field strength and excitation tensor which are related to each other by a constitutive relation, analogous to the premetric construction of theories of electrodynamics. We demonstrate how the previously studied models of f (T ) and f (Tax,Tten,Tvec) gravity as well as teleparallel dark energy can be formulated in this language. The advantage of this approach to gravity is that the field equations for different models all take the same compact form and general results can be obtained. An important new such result we find is a constraint which relates the field equations of the tetrad and the spin connection.

Development and Release of a GRACE-FO "Grand Simulation" Data Set by JPL

NASA Astrophysics Data System (ADS)

Fahnestock, E.; Yuan, D. N.; Wiese, D. N.; McCullough, C. M.; Harvey, N.; Sakumura, C.; Paik, M.; Bertiger, W. I.; Wen, H. Y.; Kruizinga, G. L. H.

2017-12-01

The GRACE-FO mission, to be launched early in 2018, will require several stages of data processing to be performed within its Science Data System (SDS). In an effort to demonstrate effective implementation and inter-operation of this level 1, 2, and 3 data processing, and to verify its combined ability to recover a truth Earth gravity field to within top-level requirements, the SDS team has performed a system test which it has termed the "Grand Simulation". This process starts with iteration to converge on a mutually consistent integrated truth orbit, non-gravitational acceleration time history, and spacecraft attitude time history, generated with the truth models for all elements of the integrated system (geopotential, both GRACE-FO spacecraft, constellation of GPS spacecraft, etc.). Level 1A data products are generated and then the GPS time to onboard receiver time clock error is introduced into those products according to a realistic truth clock offset model. The various data products are noised according to current best estimate noise models, and then some are used within a precision orbit determination and clock offset estimation/recovery process. Processing from level 1A to level 1B data products uses the recovered clock offset to correct back to GPS time, and performs gap-filling, compression, etc. This exercises nearly all software pathways intended for processing actual GRACE-FO science data. Finally, a monthly gravity field is recovered and compared against the truth background field. In this talk we briefly summarize the resulting performance vs. requirements, and lessons learned in the system test process. Finally, we provide information for use of the level 1B data set by the general community for gravity solution studies and software trials in anticipation of operational GRACE-FO data. ©2016 California Institute of Technology. Government sponsorship acknowledged.

Modeling of micro thrusters for gravity probe B

NASA Technical Reports Server (NTRS)

Jones, Kenneth M.

1996-01-01

The concept of testing Einstein's general theory of relativity by means of orbiting gyroscopes was first proposed in 1959, which lead to the development of the Gravity Probe B experiment. Einstein's theory concerns the predictions of the relativistic precession of a gyroscope in orbit around earth. According to his theory, there will be two precessions due to the warping of space-time by the earth's gravitational field: the geodetic precession in the plane of the orbit, and the frame-dragging effect, in the direction of earth rotation. For a polar orbit, these components are orthogonal. In order to simplify the measurement of the precessions, Gravity Probe B (GP-B) will be placed in a circular polar orbit at 650 km, for which the predicted precessions will be 6.6 arcsec/year (geodetic) and 42 milli-arcsec/year (frame-dragging). As the gyroscope precesses, the orientation of its spin-axis will be measured with respect to the line-of-sight to Rigel, a star whose proper motion is known to be within the required accuracy. The line-of-sight to Rigel will be established using a telescope, and the orientation of the gyroscope spin axis will be measured using very sensitive SQUID (Superconducting Quantum Interference Device) magnetometers. The four gyroscopes will be coated with niobium. Below 2K, the niobium becomes superconducting and a dipole field will be generated which is precisely aligned with the gyroscope spin-axis. The change in orientation of these fields, as well as the spin-axis, is sensed by the SQUID magnetometers. In order to attain the superconducting temperatures for the gyroscopes and the SQUID's, the experiment package will be housed in a dewar filled with liquid helium. The helium flow through a GP-B micro thruster and into a vacuum is investigated using the Direct Simulation Monte Carlo method.

Modeling of the Earth's gravity field using the New Global Earth Model (NEWGEM)

NASA Technical Reports Server (NTRS)

Kim, Yeong E.; Braswell, W. Danny

1989-01-01

Traditionally, the global gravity field was described by representations based on the spherical harmonics (SH) expansion of the geopotential. The SH expansion coefficients were determined by fitting the Earth's gravity data as measured by many different methods including the use of artificial satellites. As gravity data have accumulated with increasingly better accuracies, more of the higher order SH expansion coefficients were determined. The SH representation is useful for describing the gravity field exterior to the Earth but is theoretically invalid on the Earth's surface and in the Earth's interior. A new global Earth model (NEWGEM) (KIM, 1987 and 1988a) was recently proposed to provide a unified description of the Earth's gravity field inside, on, and outside the Earth's surface using the Earth's mass density profile as deduced from seismic studies, elevation and bathymetric information, and local and global gravity data. Using NEWGEM, it is possible to determine the constraints on the mass distribution of the Earth imposed by gravity, topography, and seismic data. NEWGEM is useful in investigating a variety of geophysical phenomena. It is currently being utilized to develop a geophysical interpretation of Kaula's rule. The zeroth order NEWGEM is being used to numerically integrate spherical harmonic expansion coefficients and simultaneously determine the contribution of each layer in the model to a given coefficient. The numerically determined SH expansion coefficients are also being used to test the validity of SH expansions at the surface of the Earth by comparing the resulting SH expansion gravity model with exact calculations of the gravity at the Earth's surface.

Figuring large optics at the sub-nanometer level: compensation for coating and gravity distortions.

PubMed

Gensemer, Stephen; Gross, Mark

2015-11-30

Large, precision optics can now be manufactured with surface figures specified at the sub-nanometer level. However, coatings and gravity deform large optics, and there are limits to what can be corrected by clever compensation. Instead, deformations caused by stress from optical mounts and deposited coatings must be incorporated into the optical design. We demonstrate compensation of coating stress on a 370mm substrate to λ/200 by a process of coating and annealing. We also model the same process and identify the leading effects that must be anticipated in fabrication of optics for future gravitational wave detectors and other applications of large, precisely figured optics, and identify the limitations inherent in using coatings to compensate for these deformations.

Quantum light in coupled interferometers for quantum gravity tests.

PubMed

Ruo Berchera, I; Degiovanni, I P; Olivares, S; Genovese, M

2013-05-24

In recent years quantum correlations have received a lot of attention as a key ingredient in advanced quantum metrology protocols. In this Letter we show that they provide even larger advantages when considering multiple-interferometer setups. In particular, we demonstrate that the use of quantum correlated light beams in coupled interferometers leads to substantial advantages with respect to classical light, up to a noise-free scenario for the ideal lossless case. On the one hand, our results prompt the possibility of testing quantum gravity in experimental configurations affordable in current quantum optics laboratories and strongly improve the precision in "larger size experiments" such as the Fermilab holometer; on the other hand, they pave the way for future applications to high precision measurements and quantum metrology.

POPULATION PROPERTIES OF BROWN DWARF ANALOGS TO EXOPLANETS

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

Faherty, Jacqueline K.; Gagne, Jonathan; Weinberger, Alycia

2016-07-01

We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 18 new parallaxes (including 10 for comparative field objects), 38 new radial velocities, and 19 new proper motions. We also add low- or moderate-resolution near-infrared spectra for 43 sources confirming their low surface gravity features. Among the full sample, we find 39 objects to be high-likelihood or new bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. Using this age-calibrated sample, we investigate trends in gravity classification, photometric color, absolute magnitude, color–magnitude, luminosity, and effective temperature.more » We find that gravity classification and photometric color clearly separate 5–130 Myr sources from >3 Gyr field objects, but they do not correlate one to one with the narrower 5–130 Myr age range. Sources with the same spectral subtype in the same group have systematically redder colors, but they are distributed between 1 and 4 σ from the field sequences and the most extreme outlier switches between intermediate- and low-gravity sources either confirmed in a group or not. The absolute magnitudes of low-gravity sources from the J band through W 3 show a flux redistribution when compared to equivalently typed field brown dwarfs that is correlated with spectral subtype. Low-gravity, late-type L dwarfs are fainter at J than the field sequence but brighter by W 3. Low-gravity M dwarfs are >1 mag brighter than field dwarfs in all bands from J through W 3. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On color–magnitude diagrams, the latest-type, low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M{sub J} but are consistent with or brighter than the elbow at M{sub W1} and M{sub W2}. We conclude that low-gravity dwarfs carry an extreme version of the cloud conditions of field objects to lower temperatures, which logically extends into the lowest-mass, directly imaged exoplanets. Furthermore, there is an indication on color-magnitude diagrams (CMDs; such as M{sub J} versus (J – W 2)) of increasingly redder sequences separated by gravity classification, although it is not consistent across all CMD combinations. Examining bolometric luminosities for planets and low-gravity objects, we confirm that (in general) young M dwarfs are overluminous while young L dwarfs are normal compared to the field. Using model extracted radii, this translates into normal to slightly warmer M dwarf temperatures compared to the field sequence and lower temperatures for L dwarfs with no obvious correlation with the assigned moving group.« less

Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory

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

Chan, H.A.; Paik, H.J.

1987-06-15

Because of the equivalence principle, a global measurement is necessary to distinguish gravity from acceleration of the reference frame. A gravity gradiometer is therefore an essential instrument needed for precision tests of gravity laws and for applications in gravity survey and inertial navigation. Superconductivity and SQUID (superconducting quantum interference device) technology can be used to obtain a gravity gradiometer with very high sensitivity and stability. A superconducting gravity gradiometer has been developed for a null test of the gravitational inverse-square law and space-borne geodesy. Here we present a complete theoretical model of this instrument. Starting from dynamical equations for themore » device, we derive transfer functions, a common mode rejection characteristic, and an error model of the superconducting instrument. Since a gradiometer must detect a very weak differential gravity signal in the midst of large platform accelerations and other environmental disturbances, the scale factor and common mode rejection stability of the instrument are extremely important in addition to its immunity to temperature and electromagnetic fluctuations. We show how flux quantization, the Meissner effect, and properties of liquid helium can be utilized to meet these challenges.« less

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.