The Development of the Joint NASA GSFC and the National Imagery and Mapping Agency (NIMA) Geopotential Model EGM96
01 Jul 1998-
TL;DR: The Earth Gravitational Model 1996 (EGM96) as discussed by the authors was developed by the NASA Goddard Space Flight Center (GSFC), the National Imagery and Mapping Agency (NIMA), and The Ohio State University (OSU) to develop an improved spherical harmonic model of the Earth's gravitational potential.
Abstract: The NASA Goddard Space Flight Center (GSFC), the National Imagery and Mapping Agency (NIMA), and The Ohio State University (OSU) have collaborated to develop an improved spherical harmonic model of the Earth's gravitational potential to degree 360. The new model, Earth Gravitational Model 1996 (EGM96), incorporates improved surface gravity data, altimeter-derived gravity anomalies from ERS-1 and from the GEOSAT Geodetic Mission (GM), extensive satellite tracking data-including new data from Satellite Laser Ranging (SLR), the Global Postioning System (GPS), NASA's Tracking and Data Relay Satellite System (TDRSS), the French DORIS system, and the US Navy TRANET Doppler tracking system-as well as direct altimeter ranges from TOPEX/POSEIDON (T/P), ERS-1, and GEOSAT. The final solution blends a low-degree combination model to degree 70, a block-diagonal solution from degree 71 to 359, and a quadrature solution at degree 360. The model was used to compute geoid undulations accurate to better than one meter (with the exception of areas void of dense and accurate surface gravity data) and realize WGS84 as a true three-dimensional reference system. Additional results from the EGM96 solution include models of the dynamic ocean topography to degree 20 from T/P and ERS-1 together, and GEOSAT separately, and improved orbit determination for Earth-orbiting satellites.
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TL;DR: The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth, using dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution.
Abstract: [1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.
5,019 citations
TL;DR: EGM2008 as mentioned in this paper is a spherical harmonic model of the Earth's gravitational potential, developed by a least squares combination of the ITG-GRACE03S gravitational model and its associated error covariance matrix, with the gravitational information obtained from a global set of area-mean free-air gravity anomalies defined on a 5 arc-minute equiangular grid.
Abstract: [1] EGM2008 is a spherical harmonic model of the Earth's gravitational potential, developed by a least squares combination of the ITG-GRACE03S gravitational model and its associated error covariance matrix, with the gravitational information obtained from a global set of area-mean free-air gravity anomalies defined on a 5 arc-minute equiangular grid This grid was formed by merging terrestrial, altimetry-derived, and airborne gravity data Over areas where only lower resolution gravity data were available, their spectral content was supplemented with gravitational information implied by the topography EGM2008 is complete to degree and order 2159, and contains additional coefficients up to degree 2190 and order 2159 Over areas covered with high quality gravity data, the discrepancies between EGM2008 geoid undulations and independent GPS/Leveling values are on the order of ±5 to ±10 cm EGM2008 vertical deflections over USA and Australia are within ±11 to ±13 arc-seconds of independent astrogeodetic values These results indicate that EGM2008 performs comparably with contemporary detailed regional geoid models EGM2008 performs equally well with other GRACE-based gravitational models in orbit computations Over EGM96, EGM2008 represents improvement by a factor of six in resolution, and by factors of three to six in accuracy, depending on gravitational quantity and geographic area EGM2008 represents a milestone and a new paradigm in global gravity field modeling, by demonstrating for the first time ever, that given accurate and detailed gravimetric data, asingle global model may satisfy the requirements of a very wide range of applications
1,755 citations
TL;DR: In this article, the amplitude of the GRACE signal was determined to 1.5 cm of water thickness when smoothed over 1000 km, and 30% better for a 1500 km smoothing radius, and 40% worse for a 750 km radius.
Abstract: Eleven monthly GRACE gravity field solutions are now available for analyses. We show those fields can be used to recover monthly changes in water storage, both on land and in the ocean, to accuracies of 1.5 cm of water thickness when smoothed over 1000 km. The amplitude of the annually varying signal can be determined to 1.0 cm. Results are 30% better for a 1500 km smoothing radius, and 40% worse for a 750 km radius. We estimate the annually varying component of water storage for three large drainage basins (the Mississippi, the Amazon, and a region draining into the Bay of Bengal), to accuracies of 1.0–1.5 cm.
695 citations
TL;DR: In this article, three approaches are used to reduce the error in the satellite-derived marine gravity anomalies: retracking the raw waveforms from the ERS-1 and Geosat/GM missions resulting in improvements in range precision of 40% and 27%, respectively.
Abstract: [1] 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 of up to 20 mGal occur on the crests of narrow large seamounts. The global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate. For rates less than about 60 mm/a the typical ridge segment is 50–80 km long while it increases dramatically at higher rates (100–1000 km). This transition spreading rate of 60 mm/a also marks the transition from axial valley to axial high. We speculate that a single mechanism controls both transitions; candidates include both lithospheric and asthenospheric processes.
636 citations
TL;DR: The empirical model GPT (Global Pressure and Temperature), which is based on spherical harmonics up to degree and order nine, provides pressure and temperature at any site in the vicinity of the Earth's surface as mentioned in this paper.
Abstract: The empirical model GPT (Global Pressure and Temperature), which is based on spherical harmonics up to degree and order nine, provides pressure and temperature at any site in the vicinity of the Earth’s surface. It can be used for geodetic applications such as the determination of a priori hydrostatic zenith delays, reference pressure values for atmospheric loading, or thermal deformation of Very Long Baseline Interferometry (VLBI) radio telescopes. Input parameters of GPT are the station coordinates and the day of the year, thus also allowing one to model the annual variations of the parameters. As an improvement compared with previous models, it reproduces the large pressure anomaly over Antarctica, which can cause station height errors in the analysis of space-geodetic data of up to 1 cm if not considered properly in troposphere modelling. First tests at selected geodetic observing stations show that the pressure biases considerably decrease when using GPT instead of the very simple approaches applied to various Global Navigation Satellite Systems (GNSS) software packages so far. GPT also provides an appropriate model for the annual variability of global temperature.
569 citations
Cites methods from "The Development of the Joint NASA G..."
...To accommodate this the geoidal undulations N from the EGM96 model (Lemoine et al. 1998) have been expanded into spherical harmonics up to degree and order nine and are used to transform the ellipsoidal heights h to orthometric heights H (h = H + N)....
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References
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01 May 1974
TL;DR: In this paper, a new anomaly degree variance model is developed by considering potential coefficient information to degree 20, and updated values of the point anomaly variance, the 1 degree block variance, and the 5 degrees block variance.
Abstract: : A new anomaly degree variance model is developed by considering potential coefficient information to degree 20, and updated values of the point anomaly variance, the 1 degree block variance, and the 5 degrees block variance. This new model and several other models were used to develop closed expressions for the covariance and cross-covariance functions between gravity anomalies, geoid undulations (or height anomalies), and deflections of the vertical. (Modified author abstract)
424 citations
TL;DR: In this article, a quantitative model-data comparison is carried out for the global Parallel Ocean Climate Model (POCM), known also as the Semtner and Chervin model, with nominal lateral resolution of 1/4° The focus is on various aspects of the simulated largescale circulation and their relation to the TOPEX/POSEIDON sea surface height (SSH) observations and World Ocean Circulation Experiment (WOCE) hydrography.
Abstract: Numerical high-resolution ocean general circulation models have experienced a revolutionary development during the last decade Today they are run globally in realistic configuration with realistic surface boundary forcing To fully use the results of those models in understanding various aspects of the ocean general circulation and to combine ocean observations with models (state estimation) in a manner consistent with the data and model dynamics, stringent model-data comparisons are a necessary first step In this paper a quantitative model-data comparison is carried out for the global Parallel Ocean Climate Model (POCM), known also as the Semtner and Chervin model, with nominal lateral resolution of 1/4° The focus is on various aspects of the simulated large-scale circulation and their relation to the TOPEX/POSEIDON sea surface height (SSH) observations and World Ocean Circulation Experiment (WOCE) hydrography Comparisons are made for (1) the global mean sea surface circulation and absolute slopes, (2) rms SSH variability and eddy kinetic energy, (3) the simulation of the observed seasonal cycle in SSH, (4) two-dimensional frequency-wavenumber spectra of the large-scale fluctuations, as well as (5) the hydrography for WOCE sections Recent improvements in external surface forcing fields including daily wind-stress fields and sea surface heat fluxes lead to a significant improvement in the overall agreement of the simulated and observed large-scale mean circulation and its variability However, simulated amplitudes of variability remain low by about a factor of 2 to 4 over a broad spectral range, including the long wavelengths and periods Both the causes and consequences of this low variability remain obscure
242 citations
"The Development of the Joint NASA G..." refers methods in this paper
...Stammer et al. [1996] describe the development of the Semtner–Chervin-type model, such as POCM–4B....
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TL;DR: In this paper, the authors compare results from 2 years (October 1992-October 1994) of the satellite observations to computer simulations for the same period using a state-of-the-art ocean general circulation model driven by realistic winds from an atmospheric weather-prediction model.
Abstract: The sea surface elevation relative to the geoid, a dynamic boundary condition for the three-dimensional oceanic pressure field, is being determined over the global ocean every 10 days by a precision radar altimeter aboard the TOPEX/POSEIDON satellite. This is the most accurate altimeter data stream to date for the study of the ocean general circulation and its variability. The authors compare results from 2 years (October 1992-October 1994) of the satellite observations to computer simulations for the same period using a state-of-the-art ocean general circulation model driven by realistic winds from an atmospheric weather-prediction model. The average horizontal resolution of the model is 1/5° (varying from 30 km at the equator to 6 kin at the polar latitudes), the highest for a global simulation performed to date. Comparisons of the mean circulation, the mesoscale variability, the amplitude, and phase of the annual cycle, as well as intraseasonal and interannual changes show that the simulations...
149 citations
TL;DR: In this article, a potential coefficient model of the Earth's gravitational potential was used to calculate height anomalies and then reduced to geoid undulations where such quantities are needed for orthometric height determination and vertical datum definition through potential coefficient realization of the geoid.
Abstract: This paper suggests that potential coefficient models of the Earth's gravitational potential be used to calculate height anomalies which are then reduced to geoid undulations where such quantities are needed for orthometric height determination and vertical datum definition through a potential coefficient realization of the geoid. The process of the conversion of the height anomaly into a geoid undulation is represented by a height anomaly gradient term and the usual N–ζ term that is dependent on elevation and the Bouguer anomaly. Using a degree 360 expansion of 30′ elevations and the OSU91A potential coefficient model, a degree 360 representation of the correction terms was computed. The magnitude of N–ζ reached –3.4 m in the Himalaya Mountains with smaller, but still significant, magnitudes in other mountainous regions.
143 citations
01 Sep 1978
TL;DR: In this article, the degree variances of the covariance function for gravity anomalies are represented according to the two-component model suggested by Moritz in an attempt to arrive at a low horizontal gradient variance (200 E squared).
Abstract: : Degree variances of the covariance function for gravity anomalies are represented according to the two-component model suggested by Moritz in an attempt to arrive at a low horizontal gradient variance (200 E squared). The parameters of the model are determined through a least squares adjustment to data consisting of GEM 9 anomaly degree variances, as well as empirical point and mean anomaly variances. Results show that this model can accommodate the given point and mean anomaly variances and degree variances, while also yielding the desired low gradient variance. A comparison of this and a similar one-component model investigated by Tscherning and Rapp indicates that the latter cannot produce a low gradient variance together with a satisfactory fit to the data. Also, it does not adapt as well to the observed (GEM 9) attenuation of the anomaly degree variances. (Author)
32 citations