A comparison of satellite and shipboard gravity measurements in the Gulf of Mexico

Geophysics ◽  
1992 ◽  
Vol 57 (7) ◽  
pp. 885-893 ◽  
Author(s):  
Christopher Small ◽  
David T. Sandwell
Keyword(s):  
Gulf Of Mexico ◽  
Gravity Field ◽  
Short Wavelength ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Reference Field ◽  
Satellite Gravity ◽  
Spherical Harmonic Degree ◽  
Transform Method ◽  
Full Resolution

Satellite altimeters have mapped the marine geoid over virtually all of the world’s oceans. These geoid height measurements may be used to compute free air gravity anomalies in areas where shipboard measurements are scarce. Two‐dimensional (2-D) transformations of geoid height to gravity are limited by currently available satellite track spacing and usually sacrifice short wavelength resolution. Full resolution may be retained along widely spaced satellite tracks if a one dimensional (1-D) transformation is used. Although the 1-D transform retains full resolution, it assumes that the gravity field is lineated perpendicular to the profile and is therefore limited by the orientation of the profile relative to the field. We investigate the resolution and accuracy of the 1-D transform method in the Northern Gulf of Mexico by comparing satellite gravity profiles with high quality shipboard data provided by Edcon Inc. The long wavelength components of the gravity field are constrained by a low degree reference field while the short wavelength components are computed from altimeter profiles. We find that rms misfit decreases with increasing spherical harmonic degree of the reference field up to 180 degrees (λ > 220 km) with negligible improvement for higher degrees. The average rms misfit for the 17 profiles used in this study was 6.5 mGal with a 180 degree reference field. Spectral coherence estimates indicate that the satellite data resolve features with wavelengths as short as 25 km.

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

2020 ◽  
Author(s):  
Américo Ambrózio ◽  
Marco Restano ◽  
Jérôme Benveniste
Keyword(s):  
Gravity Field ◽  
Ad Hoc ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Gravity Models ◽  
Gravity Gradient ◽  
Data Set ◽  
Radar Altimetry ◽  
Isostatic Gravity ◽  
L1 And L2

<p>The scope of this work is to showcase the BRAT (Broadview Radar Altimetry Toolbox) and GUT (GOCE User Toolbox) toolboxes.</p><p>The Broadview Radar Altimetry Toolbox (BRAT) is a collection of tools designed to facilitate the processing of radar altimetry data from all previous and current altimetry missions, including Sentinel-3A L1 and L2 products. A tutorial is included providing plenty of use cases on Geodesy & Geophysics, Oceanography, Coastal Zone, Atmosphere, Wind & Waves, Hydrology, Land, Ice and Climate, which can also be consulted in  http://www.altimetry.info/radar-altimetry-tutorial/.</p><p>BRAT's last version (4.2.1) was released in June 2018. Based on the community feedback, the front-end has been further improved and simplified whereas the capability to use BRAT in conjunction with MATLAB/IDL or C/C++/Python/Fortran, allowing users to obtain desired data bypassing the data-formatting hassle, remains unchanged. Several kinds of computations can be done within BRAT involving the combination of data fields, that can be saved for future uses, either by using embedded formulas including those from oceanographic altimetry, or by implementing ad-hoc Python modules created by users to meet their needs. BRAT can also be used to quickly visualise data, or to translate data into other formats, e.g. from NetCDF to raster images.</p><p>The GOCE User Toolbox (GUT) is a compilation of tools for the use and the analysis of GOCE gravity field models. It facilitates using, viewing and post-processing GOCE L2 data and allows gravity field data, in conjunction and consistently with any other auxiliary data set, to be pre-processed by beginners in gravity field processing, for oceanographic and hydrologic as well as for solid earth applications at both regional and global scales. Hence, GUT facilitates the extensive use of data acquired during GRACE and GOCE missions.</p><p>In the current version (3.2), GUT has been outfitted with a graphical user interface allowing users to visually program data processing workflows. Further enhancements aiming at facilitating the use of gradients, the anisotropic diffusive filtering, and the computation of Bouguer and isostatic gravity anomalies have been introduced. Packaged with GUT is also GUT's Variance/Covariance Matrix (VCM) tool, which enables non-experts to compute and study, with relative ease, the formal errors of quantities – such as geoid height, gravity anomaly/disturbance, radial gravity gradient, vertical deflections – that may be derived from the GOCE gravity models.</p><p>On our continuous endeavour to provide better and more useful tools, we intend to integrate BRAT into SNAP (Sentinel Application Platform). This will allow our users to easily explore the synergies between both toolboxes. During 2020 we will start going from separate toolboxes to a single one.</p><p>BRAT and GUT toolboxes can be freely downloaded, along with ancillary material, at https://earth.esa.int/brat and https://earth.esa.int/gut.</p>

scholarly journals GRAVITY ANOMALY ASSESSMENT USING GGMS AND AIRBORNE GRAVITY DATA TOWARDS BATHYMETRY ESTIMATION

2016 ◽  
Vol XLII-4/W1 ◽  
pp. 287-297
Author(s):  
A. Tugi ◽  
A. H. M. Din ◽  
K. M. Omar ◽  
A. S. Mardi ◽  
Z. A. M. Som ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Airborne Gravity ◽  
Satellite Gravity ◽  
Earth’S Gravity Field ◽  
Explorer Mission ◽  
Satellite Gravity Missions

The Earth’s potential information is important for exploration of the Earth’s gravity field. The techniques of measuring the Earth’s gravity using the terrestrial and ship borne technique are time consuming and have limitation on the vast area. With the space-based measuring technique, these limitations can be overcome. The satellite gravity missions such as Challenging Mini-satellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), and Gravity-Field and Steady-State Ocean Circulation Explorer Mission (GOCE) has introduced a better way in providing the information on the Earth’s gravity field. From these satellite gravity missions, the Global Geopotential Models (GGMs) has been produced from the spherical harmonics coefficient data type. The information of the gravity anomaly can be used to predict the bathymetry because the gravity anomaly and bathymetry have relationships between each other. There are many GGMs that have been published and each of the models gives a different value of the Earth’s gravity field information. Therefore, this study is conducted to assess the most reliable GGM for the Malaysian Seas. This study covered the area of the marine area on the South China Sea at Sabah extent. Seven GGMs have been selected from the three satellite gravity missions. The gravity anomalies derived from the GGMs are compared with the airborne gravity anomaly, in order to figure out the correlation (R<sup>2</sup>) and the root mean square error (RMSE) of the data. From these assessments, the most suitable GGMs for the study area is GOCE model, GO_CONS_GCF_2_TIMR4 with the R<sup>2</sup> and RMSE value of 0.7899 and 9.886 mGal, respectively. This selected model will be used in the estimating the bathymetry for Malaysian Seas in future.

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

2014 ◽  
Vol 63 (1) ◽  
pp. 3-24 ◽  
Author(s):  
Walyeldeen Godah ◽  
Malgorzata Szelachowska ◽  
Jan Krynski
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Accuracy Assessment ◽  
Gravity Anomalies ◽  
Geopotential Model ◽  
Satellite Gravity ◽  
Earth Gravity ◽  
Geopotential Models ◽  
Gravimetric Quasigeoid ◽  
Gravity Signal

Abstract 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.

scholarly journals An Improved Model of the Earth’s Static Gravity Field Solely Derived from Reprocessed GOCE Data

2021 ◽  
Author(s):  
Jan Martin Brockmann ◽  
Till Schubert ◽  
Wolf-Dieter Schuh
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Gravity Gradients ◽  
Data Set ◽  
Gravity Field Recovery ◽  
Global Gravity ◽  
The Impact ◽  
Goce Satellite

AbstractAfter it was found that the gravity gradients observed by the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite could be significantly improved by an advanced calibration, a reprocessing project for the entire mission data set was initiated by ESA and performed by the GOCE High-level processing facility (GOCE HPF). One part of the activity was delivering the gravity field solutions, where the improved level 1b and level 2 data serve as an input for global gravity field recovery. One well-established approach for the analysis of GOCE observations is the so-called time-wise approach. Basic characteristics of the GOCE time-wise solutions is that only GOCE observations are included to remain independent of any other gravity field observables and that emphasis is put on the stochastic modeling of the observations’ uncertainties. As a consequence, the time-wise solutions provide a GOCE-only model and a realistic uncertainty description of the model in terms of the full covariance matrix of the model coefficients. Within this contribution, we review the GOCE time-wise approach and discuss the impact of the improved data and modeling applied in the computation of the new GO_CONS_EGM_TIM_RL06 solution. The model reflects the Earth’s static gravity field as observed by the GOCE satellite during its operation. As nearly all global gravity field models, it is represented as a spherical harmonic expansion, with maximum degree 300. The characteristics of the model and the contributing data are presented, and the internal consistency is demonstrated. The updated solution nicely meets the official GOCE mission requirements with a global mean accuracy of about 2 cm in terms of geoid height and 0.6 mGal in terms of gravity anomalies at ESA’s target spatial resolution of 100 km. Compared to its RL05 predecessor, three kinds of improvements are shown, i.e., (1) the mean global accuracy increases by 10–25%, (2) a more realistic uncertainty description and (3) a local reduction of systematic errors in the order of centimeters.

A gravity study of the Saguenay area, Quebec

1977 ◽  
Vol 14 (2) ◽  
pp. 145-152 ◽  
Author(s):  
P. M. Duncan ◽  
G. D. Garland
Keyword(s):  
Gravity Field ◽  
Short Wavelength ◽  
Gravity Anomalies ◽  
Negative Anomaly ◽  
Gravity Survey ◽  
Downward Displacement ◽  
Mohorovičić Discontinuity

Results are presented of a detailed gravity survey over the Saguenay valley and adjacent areas. Gravity anomalies have been separated into features of long and short wavelength by the method of upward projection, and interpreted in terms of crustal models. A negative anomaly over the lowlands can be explained by downfaulting of denser units within the crust, giving support to the hypothesis of a graben structure. Downward displacement of the Mohorovicic discontinuity would be compatible with the observations, but cannot be verified by the gravity field alone.

Effect of Ocean Tide on Recovery of Satellite Gravity Field

2007 ◽  
Vol 50 (1) ◽  
pp. 116-123 ◽  
Author(s):  
Jiang-Cun ZHOU ◽  
He-Ping SUN
Keyword(s):  
Gravity Field ◽  
Ocean Tide ◽  
Satellite Gravity

scholarly journals On the earthquake detectability by the Next Generation Gravity Mission (NGGM)

2020 ◽  
Author(s):  
Gabriele Cambiotti ◽  
Karim Douch ◽  
Stefano Cesare ◽  
Alberto Anselmi ◽  
Nico Sneeuw ◽  
...  
Keyword(s):  
Gravity Field ◽  
Synthetic Data ◽  
Gravity Anomalies ◽  
Time Dependent ◽  
Induced Gravity ◽  
Earthquake Scenarios ◽  
Isostatic Adjustment ◽  
Geophysical Processes ◽  
Earthquake Characteristics ◽  
Gravity Mission

&lt;p&gt;We perform Next Gerataion Gravity Mission (NGGM) simulations over a 12-year operational period by including in the background gravity field the time-dependent gravity anomalies caused by different earthquake scenarios and considering different sources of error on 28-day mean gravity field solutions: the instrumental errors of the interferometer and accelerometers, the time depenendent background model and the atmosphere-ocean dealiasing. In order to assess whether the observational errors mask or not the earthquake-induced gravity signals, we assume known the background gravity field and the spatial and temporal pattern of the earthquake-induced gravity anomalies. Then, for each earthquake, we estimate the amplitude of its gravity anomaly by inverting the NGGM synthetic data time series and we check its consistency with the expected amplitude, as well as with the null hypothesis. In order to investigate case studies representative of the main earthquake characteristics and their compliance with the NGGM specifications, we have considered normal, inverse and strike-slip focal mechanisms striking with different angles with respect to the polar orbit, reaching the Earth surface and in depth, occurring inland, off-shore and close to the coastlines and at the beginning (2-4 years), at the middle (5-7 years) and at the end (8-10 years) of the 12-year operational period. The fault dimensions and slip distribution vary with the seismic moment magnitude and are prescribed according to the circular fault model by Eshelby (1957). Furthermore, we also consider two different rheological stratifications with asthenospheric viscosity of 10&amp;#185;&amp;#8312; and 10&amp;#185;&amp;#8313; Pa s. In order to discuss whether the earthquake signal can be discriminated from other geophysical processes (like atmosphere, ocean, hydrology and glacial isostatic adjustment), we also perform the same inversion but, this time, its amplitude is estimated jointly with the time dependent background gravity field, which we simply model using static values, trends and periodical functions.&lt;/p&gt;

scholarly journals New insights on the dynamics of the Sumatra and Mariana complexes inferred from the comparative analysis of gravity data and model predictions

2020 ◽  
Author(s):  
Arcangela Bollino ◽  
Anna Maria Marotta ◽  
Federica Restelli ◽  
Alessandro Regorda ◽  
Roberto Sabadini
Keyword(s):  
Comparative Analysis ◽  
Gravity Field ◽  
Wide Spectrum ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Phase Changes ◽  
Wide Range ◽  
Model Predictions ◽  
Dip Angle ◽  
The Masses

&lt;p&gt;Subduction is responsible for surface displacements and deep mass redistribution. This rearrangement generates density anomalies in a wide spectrum of wavelengths which, in turn, causes important anomalies in the Earth's gravity field that are visible as lineaments parallel to the arc-trench systems. In these areas, when the traditional analysis of the deformation and stress fields is combined with the analysis of the perturbation of the gravity field and its slow time variation, new information on the background environment controlling the tectonic loading phase can be disclosed.&lt;/p&gt;&lt;p&gt;Here we present the results of a comparative analysis between the geodetically retrieved gravitational anomalies, based on the EIGEN-6C4 model, and those predicted by a 2D thermo-chemical mechanical modeling of the Sumatra and Mariana complexes.&lt;/p&gt;&lt;p&gt;The 2D model accounts for a wide range of parameters, such as the convergence velocity, the shallow dip angle, the different degrees of coupling between the facing plates. The marker in cell technique is used to compositionally differentiate the system. Phase changes in the crust and in the mantle and mantle hydration are also allowed. To be compliant with the geodetic EIGEN-6C4 gravity data, we define a model normal Earth considering the vertical density distribution at the margins of the model domain, where the masses are not perturbed by the subduction process.&lt;/p&gt;&lt;p&gt;Model predictions are in good agreement with data, both in terms of wavelengths and magnitude of the gravity anomalies measured in the surroundings of the Sumatra and Marina subductions. Furthermore, our modeling supports that the differences in the style of the gravity anomaly observed in the two areas are attributable to the different environments &amp;#8211; ocean-ocean or ocean-continental subduction &amp;#8211; that drives a significantly different dynamic in the wedge area.&lt;/p&gt;

scholarly journals Accuracy Analysis of Gravity Field Changes from Grace RL06 and RL05 Data Compared to in Situ Gravimetric Measurements in the Context of Choosing Optimal Filtering Type

2020 ◽  
Vol 55 (3) ◽  
pp. 100-117
Author(s):  
Viktor Szabó ◽  
Dorota Marjańska
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Data ◽  
The Other ◽  
Subsurface Water ◽  
Satellite Gravity ◽  
Absolute Gravimetry ◽  
The Earth ◽  
Gravity Measurements ◽  
Gravity Recovery

AbstractGlobal satellite gravity measurements provide unique information regarding gravity field distribution and its variability on the Earth. The main cause of gravity changes is the mass transportation within the Earth, appearing as, e.g. dynamic fluctuations in hydrology, glaciology, oceanology, meteorology and the lithosphere. This phenomenon has become more comprehensible thanks to the dedicated gravimetric missions such as Gravity Recovery and Climate Experiment (GRACE), Challenging Minisatellite Payload (CHAMP) and Gravity Field and Steady-State Ocean Circulation Explorer (GOCE). From among these missions, GRACE seems to be the most dominating source of gravity data, sharing a unique set of observations from over 15 years. The results of this experiment are often of interest to geodesists and geophysicists due to its high compatibility with the other methods of gravity measurements, especially absolute gravimetry. Direct validation of gravity field solutions is crucial as it can provide conclusions concerning forecasts of subsurface water changes. The aim of this work is to present the issue of selection of filtration parameters for monthly gravity field solutions in RL06 and RL05 releases and then to compare them to a time series of absolute gravimetric data conducted in quasi-monthly measurements in Astro-Geodetic Observatory in Józefosław (Poland). The other purpose of this study is to estimate the accuracy of GRACE temporal solutions in comparison with absolute terrestrial gravimetry data and making an attempt to indicate the significance of differences between solutions using various types of filtration (DDK, Gaussian) from selected research centres.

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