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 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.

Towards an updated, enhanced regional gravity field solution for Antarctica

2021 ◽  
Author(s):  
Mirko Scheinert ◽  
Philipp Zingerle ◽  
Theresa Schaller ◽  
Roland Pail ◽  
Martin Willberg
Keyword(s):  
Gravity Anomaly ◽  
Gravity Field ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Data Set ◽  
Gravity Field Model ◽  
Terrestrial Gravity ◽  
Field Solution ◽  
Gravity Disturbances ◽  
Regional Gravity

<p>In the frame of the IAG Subcommission 2.4f “Gravity and Geoid in Antarctica” (AntGG) a first Antarctic-wide grid of ground-based gravity anomalies was released in 2016 (Scheinert et al. 2016). That data set was provided with a grid space of 10 km and covered about 73% of the Antarctic continent. Since then a considerably amount of new data has been made available, mainly collected by means of airborne gravimetry. Regions which were formerly void of any terrestrial gravity observations and have now been surveyed include especially the polar data gap originating from GOCE satellite gravimetry. Thus, it is timely to come up with an updated and enhanced regional gravity field solution for Antarctica. For this, we aim to improve further aspects in comparison to the AntGG 2016 solution: The grid spacing will be enhanced to 5 km. Instead of providing gravity anomalies only for parts of Antarctica, now the entire continent should be covered. In addition to the gravity anomaly also a regional geoid solution should be provided along with further desirable functionals (e.g. gravity anomaly vs. disturbance, different height levels).</p><p>We will discuss the expanded AntGG data base which now includes terrestrial gravity data from Antarctic surveys conducted over the past 40 years. The methodology applied in the analysis is based on the remove-compute-restore technique. Here we utilize the newly developed combined spherical-harmonic gravity field model SATOP1 (Zingerle et al. 2019) which is based on the global satellite-only model GOCO05s and the high-resolution topographic model EARTH2014. We will demonstrate the feasibility to adequately reduce the original gravity data and, thus, to also cross-validate and evaluate the accuracy of the data especially where different data set overlap. For the compute step the recently developed partition-enhanced least-squares collocation (PE-LSC) has been used (Zingerle et al. 2021, in review; cf. the contribution of Zingerle et al. in the same session). This method allows to treat all data available in Antarctica in one single computation step in an efficient and fast way. Thus, it becomes feasible to iterate the computations within short time once any input data or parameters are changed, and to easily predict the desirable functionals also in regions void of terrestrial measurements as well as at any height level (e.g. gravity anomalies at the surface or gravity disturbances at constant height).</p><p>We will discuss the results and give an outlook on the data products which shall be finally provided to present the new regional gravity field solution for Antarctica. Furthermore, implications for further applications will be discussed e.g. with respect to geophysical modelling of the Earth’s interior (cf. the contribution of Schaller et al. in session G4.3).</p>

scholarly journals Long Periodic Variation of Orbital Elements of A Satellite Perturbed by Discrete Gravity Anomalies

1978 ◽  
Vol 41 ◽  
pp. 240-240
Author(s):  
M.P. Ananda
Keyword(s):  
Gravity Field ◽  
Gravity Anomalies ◽  
Large Data ◽  
Periodic Variation ◽  
Static Case ◽  
Orbital Elements ◽  
Disturbing Potential ◽  
Data Set ◽  
Simple Matrix ◽  
Derivatives Of

AbstractA method for generating long periodic variations in satellite orbital elements when perturbed by discrete gravity anomalies is presented. The method consists of developing a disturbing potential as a function of orbital and gravity anomaly parameters, and generating partial derivatives of the potential with respect to the orbital elements. The partials are averaged over the period of the satellite to eliminate the short periodic variations. The averaged partials are substituted into the variation of parameter equations to give the mean orbital rates. Classically orbital elements are used in generating gravity field and thus the method is dynamic in nature. The problem is extremely cumbersome and complex when multi-state parameters have to be estimated from a considerably large data set. However, when mean orbital rates are used, the problem reduces to a simple linear static case, where only the gravity parameters have to be estimated, and it is a simple matrix inversion problem. Thus the method developed here was utilized in reducing Appolo 15 and 16 subsatellite radio tracking data to produce a lunar gravity field represented by point masses.

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.

scholarly journals Height unification using GOCE

2012 ◽  
Vol 2 (4) ◽  
pp. 355-362 ◽  
Author(s):  
R. Rummel
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
European Space Agency ◽  
Direct Determination ◽  
Gravity Anomalies ◽  
Satellite System ◽  
Future Trend ◽  
Reference Points ◽  
Gravity Models ◽  
Geoid Model

AbstractWith 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.

scholarly journals Understanding the Geology of the Philippines through Gravity Anomalies

2021 ◽  
Author(s):  
Mel Anthony Asis Casulla ◽  
Hideki Mizunaga ◽  
Toshiaki Tanaka ◽  
Carla Dimalanta
Keyword(s):  
Gravity Anomaly ◽  
Gravity Anomalies ◽  
Sedimentary Basins ◽  
The Philippines ◽  
Island Arc ◽  
Gravity Gradient ◽  
Mobile Belt ◽  
Upward Continuation ◽  
Basement Rocks ◽  
Isostatic Gravity

Abstract The Philippine Archipelago is a complex island arc system, where many regions still lack geopotential studies. This study aims to present a general discussion of the Philippine gravity anomaly distribution. The high-resolution isostatic anomaly digital grid from the World Gravity Map (WGM) was processed and correlated with the Philippines’ established geology and tectonics. This study also investigated the gravity signatures that correspond to the regional features, e.g., geology, structures, sedimentary basins, and basement rocks of the study area. Upward continuation, high-pass, and gradient filters (i.e., first vertical derivative, horizontal gradient) were applied using the Geosoft Oasis Montaj software. The interpreted gravity maps’ results highlighted the known geologic features (e.g., trench manifestation, ophiolite distribution, basin thickness). They revealed new gravity anomalies with tectonic significance (e.g., basement characterization). The isostatic gravity anomaly map delineates the negative zones. These zones represent the thick sedimentary accumulations along the trenches surrounding the Philippine Mobile Belt (PMB). The Philippine island arc system is characterized by different gravity anomaly signatures, which signify the density contrast of subsurface geology. The negative anomalies (< 0 mGal) represent the thick sedimentary basins, and the moderate signatures (0 to 80 mGal) correspond to the metamorphic belts. The distinct very high gravity anomalies (> 80 mGal) typify the ophiolitic basement rocks. The gravity data’s upward continuation revealed contrasting deep gravity signatures; the central Philippines of continental affinity (20 – 35 mGal) was distinguished from the remaining regions of oceanic affinity (45 – 200 mGal). Local geologic features (e.g., limestone, ophiolitic rocks) and structures (e.g., North Bohol Fault, East Bohol Fault) were also delineated downward continuation and gravity gradient maps of Bohol Island. The WGM dataset’s effectiveness for geologic investigation was achieved by comparing the established geologic features and interpreted gravity anomalies. The processed gravity digital grids provided an efficient and innovative way of investigating the Philippines’ regional geology and tectonics.

scholarly journals GOCE-Derived Coseismic Gravity Gradient Changes Caused by the 2011 Tohoku-Oki Earthquake

2019 ◽  
Vol 11 (11) ◽  
pp. 1295
Author(s):  
Xinyu Xu ◽  
Hao Ding ◽  
Yongqi Zhao ◽  
Jin Li ◽  
Minzhang Hu
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Spherical Harmonic ◽  
Least Squares Method ◽  
Time Variable ◽  
Gravity Models ◽  
Gravity Gradient ◽  
Gravity Field Recovery ◽  
Before And After ◽  
Gravity Field Models

In contrast to most of the coseismic gravity change studies, which are generally based on data from the Gravity field Recovery and Climate Experiment (GRACE) satellite mission, we use observations from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) Satellite Gravity Gradient (SGG) mission to estimate the coseismic gravity and gravity gradient changes caused by the 2011 Tohoku-Oki Mw 9.0 earthquake. We first construct two global gravity field models up to degree and order 220, before and after the earthquake, based on the least-squares method, with a bandpass Auto Regression Moving Average (ARMA) filter applied to the SGG data along the orbit. In addition, to reduce the influences of colored noise in the SGG data and the polar gap problem on the recovered model, we propose a tailored spherical harmonic (TSH) approach, which only uses the spherical harmonic (SH) coefficients with the degree range 30–95 to compute the coseismic gravity changes in the spatial domain. Then, both the results from the GOCE observations and the GRACE temporal gravity field models (with the same TSH degrees and orders) are simultaneously compared with the forward-modeled signals that are estimated based on the fault slip model of the earthquake event. Although there are considerable misfits between GOCE-derived and modeled gravity gradient changes (ΔVxx, ΔVyy, ΔVzz, and ΔVxz), we find analogous spatial patterns and a significant change (greater than 3σ) in gravity gradients before and after the earthquake. Moreover, we estimate the radial gravity gradient changes from the GOCE-derived monthly time-variable gravity field models before and after the earthquake, whose amplitudes are at a level over three times that of their corresponding uncertainties, and are thus significant. Additionally, the results show that the recovered coseismic gravity signals in the west-to-east direction from GOCE are closer to the modeled signals than those from GRACE in the TSH degree range 30–95. This indicates that the GOCE-derived gravity models might be used as additional observations to infer/explain some time-variable geophysical signals of interest.

scholarly journals Signal and error assessment of GOCE-based high resolution gravity field models

2019 ◽  
Vol 9 (1) ◽  
pp. 71-86 ◽  
Author(s):  
T. Gruber ◽  
M. Willberg
Keyword(s):  
High Resolution ◽  
Gravity Field ◽  
Gravity Data ◽  
Geoid Height ◽  
Harmonic Series ◽  
Regional Data ◽  
Data Set ◽  
Global Models ◽  
The Impact ◽  
Gravity Field Models

Abstract The signal content and error level of recent GOCE-based high resolution gravity field models is assessed by means of signal degree variances and comparisons to independent GNSS-levelling geoid heights. The signal of the spherical harmonic series of these models is compared to the pre-GOCE EGM2008 model in order to identify the impact of GOCE data, of improved surface and altimetric gravity data and of modelling approaches. Results of the signal analysis show that in a global average roughly 80% of the differences are due to the inclusion of GOCE satellite information, while the remaining 20% are contributed by improved surface data. Comparisons of the global models to GNSS-levelling derived geoid heights demonstrate that a 1 cm geoid from the global model is feasible, if there is a high quality terrestrial gravity data set available. For areas with less good coverage an accuracy of several centimetres to a decimetre is feasible taking into account that GOCE provides now the geoid with a centimetre accuracy at spatial scales of 80 to 100 km. Comparisons with GNSS-levelling geoid heights also are a good tool to investigate possible systematic errors in the global models, in the spirit levelling and in the GNSS height observations. By means of geoid height differences and geoid slope differences one can draw conclusions for each regional data set separately. These conclusions need to be considered for a refined analysis e.g. to eliminate suspicious GNSS-levelling data, to improve the global modelling by using full variance-covariance matrices and by consistently weighting the various data sources used for high resolution gravity field models. The paper describes the applied procedures, shows results for these geoid height and geoid slope differences for some regional data sets and draws conclusions about possible error sources and future work to be done in this context.

Joint estimation of gravity anomalies using second and third order potential derivatives

2019 ◽  
Author(s):  
Mohsen Romeshkani ◽  
Mohammad A Sharifi ◽  
Dimitrios Tsoulis
Keyword(s):  
Gravity Field ◽  
Gravity Model ◽  
Variance Component ◽  
Gravity Anomalies ◽  
Variance Component Estimation ◽  
Third Order ◽  
Global Gravity ◽  
Isostatic Gravity ◽  
Component Estimation ◽  
Global Gravity Model

Abstract Satellite gradiometry data provide the framework for estimating and validating Earth's gravity field from second and third order derivatives of the Earth's gravitational potential. Such procedures are especially useful when applied locally, as they relate to local and regional characteristics of the real gravity field. In the present study a joint inversion procedure is proposed for the estimation of gravity anomalies at sea surface level from second and third order potential derivatives, based on a standard Gauss-Markov estimation model. The estimation procedure is applied for a test area stretching over Iran involving simulated grids from GOCE-only model GGM_TIM_R05 at GOCE altitude and gravity anomalies recovered at sea level. In order to validate the proposed estimation three different reductions have been considered independently, namely the removal of the long-wavelength part of the observed field through a global gravity model, the removal of the high-frequency part of the field through the incorporation of a topographic/isostatic gravity model and the application of variance component estimation. The application of a global gravity model leads to an improvement in the individual component estimation of the order of magnitude 3 per cent to 73 per cent, with a significant reduction in bias to 4 mGal. Smoother gradient components can come out according to removing the topography and taking into account for isostasy that improved up results of recovery to 25 per cent for the radial second order derivative. Finally, the implementation of variance component estimation leads to no significant improvement in results of recovered gravity anomalies.

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