Introducing EGM2020

2020 ◽  
Author(s):  
Daniel Barnes ◽  
Daniel Barnes ◽  
James Beale ◽  
Howard Small ◽  
Sarah Ingalls
Keyword(s):  
Gravity Models ◽  
Harmonic Model ◽  
Satellite Gravity ◽  
Intelligence Agency ◽  
Ellipsoidal Harmonic ◽  
Marine Gravity ◽  
Gravitational Model ◽  
Gravimetric Data ◽  
Global Coverage ◽  
Grace Mission

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 Outdated data gridding procedures have been replaced with improved approaches.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

scholarly journals DETERMINISTICALLY-MODIFIED INTEGRAL ESTIMATORS OF GRAVITATIONAL TENSOR

2015 ◽  
Vol 21 (1) ◽  
pp. 189-212 ◽  
Author(s):  
Mohsen Romeshkani ◽  
Mehdi Eshagh
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Physical Geodesy ◽  
Gravity Models ◽  
Satellite Mission ◽  
Satellite Gravity ◽  
Global Gravity ◽  
Gravimetric Data ◽  
Derivatives Of ◽  
Terrestrial Data

The Earth's global gravity field modelling is an important subject in Physical Geodesy. For this purpose different satellite gravimetry missions have been designed and launched. Satellite gravity gradiometry (SGG) is a technique to measure the second-order derivatives of the gravity field. The gravity field and steady state ocean circulation explorer (GOCE) is the first satellite mission which uses this technique and is dedicated to recover Earth's gravity models (EGMs) up to medium wavelengths. The existing terrestrial gravimetric data and EGM scan be used for validation of the GOCE data prior to their use. In this research, the tensor of gravitation in the local north-oriented frame is generated using deterministically-modified integral estimators involving terrestrial data and EGMs. The paper presents that the SGG data is assessable with an accuracy of 1-2 mE in Fennoscandia using a modified integral estimatorby the Molodensky method. A degree of modification of 100 and an integration cap size of for integrating terrestrial data are proper parameters for the estimator.

scholarly journals LOCAL EVALUATION OF EARTH GRAVITATIONAL MODELS, CASE STUDY: IRAN

2017 ◽  
Vol 43 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Ismael FOROUGHI ◽  
Yosra AFRASTEH ◽  
Sabah RAMOUZ ◽  
Abdolreza SAFARI
Keyword(s):  
Gravity Data ◽  
Low Frequency ◽  
Gravity Anomalies ◽  
Gravity Models ◽  
Data Sets ◽  
Observation Data ◽  
Satellite Gravity ◽  
Global Gravity ◽  
Marine Gravity ◽  
Global Gravity Models

Global gravity models are being developed according to new data sets available from satellite gravity missions and terrestrial/marine gravity data which are provided by different countries. Some countries do not provide all their available data and the global gravity models have many vague computational methods. Therefore, the models need to be evaluated locally before using. It is generally understood that the accuracy of global gravity models is enough for local (civil, mining, construction, etc.) projects, however, our results in Iran show that the differences between synthesized values and observation data reach up to ∼300 mGal for gravity anomalies and ∼2 m for geoid heights. Even by applying the residual topographical correction to synthetized gravity anomalies, the differences are still notable. The accuracy of global gravity models for predicting marine gravity anomalies is also investigated in Persian Gulf and the results show differences of ∼140 mGal in coastal areas. The results of evaluating selected global gravity models in Iran indicate that the EIGEN-6C4 achieves the lowest RMS for estimating the geoid heights. EGM08 predicts the closest results to terrestrial gravity anomalies. DIR-R5 GOCE satellite-only model estimates the low-frequency part of gravity field more accurately. The best prediction of marine gravity anomalies is also achieved by EGM08.

scholarly journals Study of water storage variations at the Pantanal wetlands area from GRACE monthly mass grids

2019 ◽  
Vol 9 (1) ◽  
pp. 133-143
Author(s):  
Ayelen Pereira ◽  
Cecilia Cornero ◽  
Ana C. O. C. Matos ◽  
M. Cristina Pacino ◽  
Denizar Blitzkow
Keyword(s):  
Water Mass ◽  
Spatial Scales ◽  
Water Storage ◽  
Transport Processes ◽  
Satellite Gravity ◽  
The North ◽  
Paraguay River ◽  
Gravity Recovery ◽  
Grace Mission ◽  
Phase Differences

Abstract The continental water storage is significantly in-fluenced by wetlands, which are highly affected by climate change and anthropogenic influences. The Pantanal, located in the Paraguay river basin, is one of the world’s largest and most important wetlands because of the environmental biodiversity that represents. The satellite gravity mission GRACE (Gravity Recovery And Climate Experiment) provided until 2017 time-variable Earth’s gravity field models that reflected the variations due to mass transport processes-like continental water storage changes-which allowed to study environments such as wetlands, at large spatial scales. The water storage variations for the period 2002-2016, by using monthly land water mass grids of Total Water Storage (TWS) derived from GRACE solutions, were evaluated in the Pantanal area. The capability of the GRACE mission for monitoring this particular environment is analyzed, and the comparison of the water mass changes with rainfall and hydrometric heights data at different stations distributed over the Pantanal region was carried out. Additionally, the correlation between the TWS and river gauge measurements, and the phase differences for these variables, were also evaluated. Results show two distinct zones: high correlations and low phase shifts at the north, and smaller correlation values and consequently significant phase differences towards the south. This situation is mainly related to the hydrogeological domains of the area.

scholarly journals Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change

2013 ◽  
Vol 7 (4) ◽  
pp. 3497-3541 ◽  
Author(s):  
B. C. Gunter ◽  
O. Didova ◽  
R. E. M. Riva ◽  
S. R. M. Ligtenberg ◽  
J. T. M. Lenaerts ◽  
...  
Keyword(s):  
Time Frame ◽  
Gravity Models ◽  
Mass Change ◽  
Data Sets ◽  
Glacial Isostatic Adjustment ◽  
Empirical Estimation ◽  
Satellite Gravity ◽  
Amundsen Sea ◽  
Average Value ◽  
Isostatic Adjustment

Abstract. This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of time, and now include a firn densification model to account for firn compaction and surface processes. A range of different GRACE gravity models were evaluated, as well as a new ICESat surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in-situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than existing GIA models. In addition, the new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea and Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica. The total GIA mass change estimates for the entire Antarctic ice sheet ranged from 53 to 100 Gt yr−1, depending on the GRACE solution used, and with an estimated uncertainty of ±40 Gt yr−1. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr−1 (EA: 5 ± 38, WA: −105 ± 22), consistent with other recent estimates in the literature, with the mass loss mostly concentrated in West Antarctica. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present day GIA and ice mass change, particularly with respect to determining more reliable uncertainties.

Unconstrained global simulations of ocean tides up to degree 3 for satellite gravimetry

2021 ◽  
Author(s):  
Roman Sulzbach ◽  
Henryk Dobslaw ◽  
Maik Thomas
Keyword(s):  
Signal To Noise Ratio ◽  
Relative Accuracy ◽  
Ocean Tide ◽  
Groundwater Depletion ◽  
Altimetry Data ◽  
Satellite Gravity ◽  
Tidal Model ◽  
Rotation Scheme ◽  
Gravimetric Data ◽  
High Level

<p>Tidal de-aliasing of satellite gravimetric data is a critical task in order to correctly extract gravimetric signatures of climate signals like glacier melting or groundwater depletion and poses a high demand on the accuracy of the employed tidal solutions (Flechtner et al., 2016). Modern tidal atlases that are constrained by altimetry data possess a high level of accuracy, especially for partial tides exhibiting large open ocean signals (e.g. M2, K1). Since the achievable precision directly depends on the available density and quality of altimetry data, the accuracy relative to the tidal amplitude drops for minor tidal excitations (worse signal-to-noise ratio) as well as in polar latitudes (sparse satellite-data). In contrast, this drop in relative accuracy can be reduced by employing an unconstrained tidal model acting independently of altimetric data.<br>We will present recent results from the purely-hydrodynamic, barotropic tidal model TiME (Weis et al., 2008) that benefit from a set of recently implemented upgrades. Among others, these include a revised scheme for dynamic feedbacks of self-attraction and loading; energy-dissipation by parametrized internal wavedrag; partial tide excitations by the tide-generating potential up to degree 3; and a pole-rotation scheme allowing for simulations dedicated to polar areas. Benefiting from the recent updates, the obtained solutions for major tides are on the same level of accuracy as comparable modern unconstrained tidal models. Furthermore, we show that the relative accuracy level only drops moderately for tidal excitations with small excitation strength (e.g. for minor tides), thus narrowing down the accuracy gap to data-constrained tidal atlases. Exemplarily for this, we introduce solutions for minor tidal excitations of degrees 2 and 3 that represent valuable constraints for the expected ocean tide dynamics. While they are currently not considered for GRACE-FO de-aliasing we demonstrate that third-degree tides can lead to relevant aliasing of satellite gravity fields and correspond closely to recently published empirical solutions (Ray, 2020).</p>

New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure

Science ◽  
2014 ◽  
Vol 346 (6205) ◽  
pp. 65-67 ◽  
Author(s):  
David T. Sandwell ◽  
R. Dietmar Müller ◽  
Walter H. F. Smith ◽  
Emmanuel Garcia ◽  
Richard Francis
Keyword(s):  
Gravity Model ◽  
Deep Ocean ◽  
Gravity Models ◽  
Spreading Ridge ◽  
Radar Altimeter ◽  
Tectonic Structures ◽  
Tectonic Processes ◽  
Marine Gravity ◽  
Regional Tectonic ◽  
Slow Spreading

Gravity models are powerful tools for mapping tectonic structures, especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment. We combined new radar altimeter measurements from satellites CryoSat-2 and Jason-1 with existing data to construct a global marine gravity model that is two times more accurate than previous models. We found an extinct spreading ridge in the Gulf of Mexico, a major propagating rift in the South Atlantic Ocean, abyssal hill fabric on slow-spreading ridges, and thousands of previously uncharted seamounts. These discoveries allow us to understand regional tectonic processes and highlight the importance of satellite-derived gravity models as one of the primary tools for the investigation of remote ocean basins.

Magnetic and gravity views of crust and lithosphere heterogeneity in the Wilkes Subglacial Basin of East Antarctica

2020 ◽  
Author(s):  
Egidio Armadillo ◽  
Fausto Ferraccioli ◽  
Alessandro Ghirotto ◽  
Duncan Young ◽  
Donald Blankenship ◽  
...  
Keyword(s):  
Bulk Composition ◽  
East Antarctica ◽  
Gravity Models ◽  
Gravity Gradient ◽  
Geothermal Heat ◽  
Satellite Gravity ◽  
Aeromagnetic Anomaly ◽  
Cascading Effects ◽  
Continental Scale ◽  
Lithosphere Thickness

<p>The Wilkes Subglacial Basin (WSB) is a major intraplate tectonic feature in East Antarctica. It stretches for ca 1400 km from the edge of the Southern Ocean, where it is up to 600 km wide towards South Pole, where it is less than 100 km wide. Recent modelling of its subice topography (Paxman et al., 2019, JGR) lends support to a long-standing hypothesis predicting that the wide basin is linked to flexure of more rigid and mostly Precambrian cratonic lithosphere induced by the Cenozoic uplift of the adjacent Trasantarctic Mountains,. However, there is also mounting evidence from potential field and radar exploration that its narrower structurally controlled sub-basins may have formed in response to more localised Mesozoic to Cenozoic extension and transtension that preferentially steered glacial erosion (Paxman et al., 2018, GRL).  </p><p>Here we exploit recent advancements in regional aerogeophysical data compilations and continental scale satellite gravity gradient imaging with the overarching aim of helping unveil the degree of 4D heterogeneity in the crust and lithosphere beneath the WSB. New views of crustal and lithosphere thickness stem from 3D satellite gravity modelling (Pappa et al., 2019, JGR) and these can be compared with predictions from previous flexural modelling and seismological results. By stripping out the computed effects of crustal and lithosphere thickness variations we then obtain residual intra-crustal gravity anomalies. These are in turn compared with a suite of enhanced aeromagnetic anomaly images. We then calculate depth to magnetic and gravity source estimates and use these results to help constrain the first combined 2D magnetic and gravity models for two selected regions within the WSB.</p><p>One first model reveals a major lithospheric scale boundary along the eastern margin of the northern WSB. It separates the Cambro-Ordovician Ross Orogen from a newly defined composite Precambrian Wilkes Terrane that forms the unexposed crustal basement buried beneath partially exposed early Cambrian metasediments and more recent Devonian to Jurassic sediments.</p><p>Our second model investigates a sector of the WSB further south, where the proposed Precambrian basement is modelled as being both shallower and of more felsic bulk composition. Although the lack of drilling precludes direct sampling of this cryptic basement, aeromagnetic anomaly patterns suggest that it may be akin to late Paleoproterozoic to Mesoproterozoic igneous basement exposed in part of the Gawler and Curnamona cratons in South Australia. We conclude that these first order differences in basement depth, bulk composition and thickness of metasediment/sediment cover are a key and previously un-appreciated intra-crustal boundary condition, which is likely to affect geothermal heat flux variability beneath different sectors of the WSB, with potential cascading effects on subglacial hydrology and the flow of the overlying East Antarctic Ice Sheet.</p>

scholarly journals A New Model to Improve Gravity Models

Eos ◽  
2016 ◽  
Author(s):  
Shannon Hall
Keyword(s):  
Gravity Models ◽  
New Model ◽  
Gravity Recovery ◽  
Grace Mission

Data from the Gravity Recovery and Climate Experiment (GRACE) mission gets a new and improved look.

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