scholarly journals Introducing an Improved GRACE Global Point-Mass Solution—A Case Study in Antarctica

2020 ◽  
Vol 12 (19) ◽  
pp. 3197 ◽  
Author(s):  
Vagner G. Ferreira ◽  
Bin Yong ◽  
Kurt Seitz ◽  
Bernhard Heck ◽  
Thomas Grombein
Keyword(s):  
Noise Level ◽  
Order Approximation ◽  
Statistical Tests ◽  
Taylor Series Expansion ◽  
Point Mass ◽  
Surface Integral ◽  
Goddard Space Flight Center ◽  
Gravity Recovery ◽  
Grace Mission ◽  
Level 2

In the so-called point-mass modeling, surface densities are represented by point masses, providing only an approximated solution of the surface integral for the gravitational potential. Here, we propose a refinement for the point-mass modeling based on Taylor series expansion in which the zeroth-order approximation is equivalent to the point-mass solution. Simulations show that adding higher-order terms neglected in the point-mass modeling reduces the error of inverted mass changes of up to 90% on global and Antarctica scales. The method provides an alternative to the processing of the Level-2 data from the Gravity Recovery and Climate Experiment (GRACE) mission. While the evaluation of the surface densities based on improved point-mass modeling using ITSG-Grace2018 Level-2 data as observations reveals noise level of approximately 5.77 mm, this figure is 5.02, 6.05, and 5.81 mm for Center for Space Research (CSR), Goddard Space Flight Center (GSFC), and Jet Propulsion Laboratory (JPL) mascon solutions, respectively. Statistical tests demonstrate that the four solutions are not significant different (95% confidence) over Antarctica Ice Sheet (AIS), despite the slight differences seen in the noises. Therefore, the estimated noise level for the four solutions indicates the quality of GRACE mass changes over AIS. Overall, AIS shows a mass loss of −7.58 mm/year during 2003–2015 based on the improved point-mass solution, which agrees with the values derived from mascon solutions.

scholarly journals The Intriguing Structure of Stripes in GRACE Geopotential Models

2021 ◽  
Vol 13 (21) ◽  
pp. 4362
Author(s):  
Spiros Pagiatakis ◽  
Athina Peidou
Keyword(s):  
Sampling Rate ◽  
Low Frequency ◽  
Disturbing Potential ◽  
Geopotential Models ◽  
Simple Simulation ◽  
Low Degree ◽  
Depth Analysis ◽  
Gravity Recovery ◽  
Grace Mission ◽  
Level 2

Geopotential models derived from Gravity Recovery and Climate Experiment (GRACE) mission measurements are significantly obscured by the presence of a systematic artifact, known as longitudinal stripes. Based on our previous work (Peidou and Pagiatakis, 2020) we provide an in-depth analysis of the latitudinal sampling characteristics of GRACE and we reveal the intriguing sampling mechanism that creates sub-Nyquist artifacts (stripes). Because the sub-Nyquist artifacts are poorly understood, we provide a simple simulation example to elucidate the mechanism of the sub-Nyquist artifact generation. Subsequently, we randomly select June 2009 daily GPS precise science orbits for GRACE-A to produce ground tracks to sample the low frequency disturbing potential (geoid) along the parallel of ϕ=10° N. The sampled geoid is then deinterlaced in space to produce a monthly data sequence whose detailed analysis shows that the sub-Nyquist artifacts (stripes) are produced from a critical sampling rate of the low degree gravitational field that is related to the ratio m/n of two mutually prime integers, where m is the number of days it takes to have a nearly repeat orbit and n is the number of complete orbits in one day. We perform extensive analyses of GRACE Level-2 data over a period of eight years to show the variability in the orbital characteristics that are directly linked to the orbit resonances (via integers m and n). It turns out that during short repeat cycle resonances the stripes are amplified. Finally, to minimize the presence of stripes in Level-2 data products, it is recommended that orbits of future missions should be designed to avoid the critical m/n ratios while appropriately monitoring and adjusting them during the mission. For completed missions, or missions that are already active, force modelling the latitudinal low frequency disturbing potential may be a viable and most preferred approach to filtering.

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.

Modeling of Long-Range Reverberation Signal for Rough Bottom Consisting of Polygon Facets

2018 ◽  
Vol 26 (04) ◽  
pp. 1850041
Author(s):  
Youngmin Choo ◽  
Woojae Seong
Keyword(s):  
Long Range ◽  
Order Approximation ◽  
Higher Order ◽  
Ocean Bottom ◽  
Analytic Surface ◽  
Surface Integral ◽  
Computational Burden ◽  
Analytic Integration ◽  
The Cost ◽  
Delay Difference

To acquire a stable reverberation signal from an irregular ocean bottom, we derive the analytic surface integral of a scattered signal using Stokes’ theorem while approximating the bottom using a combination of polygon facets. In this approach, the delay difference in the elemental scattering area is considered, while the representative delay is used for the elemental scattering area in the standard reverberation model. Two different reverberation models are applied to a randomly generated rough bottom, which is composed of triangular facets. Their results are compared, and the scheme using analytic integration shows a converged reverberation signal, even with a large elemental scattering area, at the cost of an additional computational burden caused by a higher order approximation in the surface integral of the scattered signals.

scholarly journals Statistical Tests for the Reciprocal of a Normal Mean with a Known Coefficient of Variation

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
Wararit Panichkitkosolkul
Keyword(s):  
Monte Carlo Simulation ◽  
Coefficient Of Variation ◽  
Statistical Tests ◽  
Taylor Series Expansion ◽  
Type I ◽  
Type I Errors ◽  
Monte Carlo Simulation Study ◽  
Asymptotic Test ◽  
Normal Mean ◽  
Simulation Results

An asymptotic test and an approximate test for the reciprocal of a normal mean with a known coefficient of variation were proposed in this paper. The asymptotic test was based on the expectation and variance of the estimator of the reciprocal of a normal mean. The approximate test used the approximate expectation and variance of the estimator by Taylor series expansion. A Monte Carlo simulation study was conducted to compare the performance of the two statistical tests. Simulation results showed that the two proposed tests performed well in terms of empirical type I errors and power. Nevertheless, the approximate test was easier to compute than the asymptotic test.

scholarly journals Automated Dynamic Mascon Generation for GRACE and GRACE-FO Harmonic Processing

2021 ◽  
Vol 13 (16) ◽  
pp. 3134
Author(s):  
Yara Mohajerani ◽  
David Shean ◽  
Anthony Arendt ◽  
Tyler C. Sutterley
Keyword(s):  
Degrees Of Freedom ◽  
Ad Hoc ◽  
Region Of Interest ◽  
Arbitrary Point ◽  
High Mountain ◽  
Regional Trends ◽  
Goddard Space Flight Center ◽  
Geophysical Signal ◽  
Range Rate ◽  
Gravity Recovery

Commonly used mass-concentration (mascon) solutions estimated from Level-1B Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On data, provided by processing centers such as the Jet Propulsion Laboratory (JPL) or the Goddard Space Flight Center (GSFC), do not give users control over the placement of mascons or inversion assumptions, such as regularization. While a few studies have focused on regional or global mascon optimization from spherical harmonics data, a global optimization based on the geometry of geophysical signal as a standardized product with user-defined points has not been addressed. Finding the optimal configuration with enough coverage to account for far-field leakage is not a trivial task and is often approached in an ad-hoc manner, if at all. Here, we present an automated approach to defining non-uniform, global mascon solutions that focus on a region of interest specified by the user, while maintaining few global degrees of freedom to minimize noise and leakage. We showcase our approach in High Mountain Asia (HMA) and Alaska, and compare the results with global uniform mascon solutions from range-rate data. We show that the custom mascon solutions can lead to improved regional trends due to a more careful sampling of geophysically distinct regions. In addition, the custom mascon solutions exhibit different seasonal variation compared to the regularized solutions. Our open-source pipeline will allow the community to quickly and efficiently develop optimized global mascon solutions for an arbitrary point or polygon anywhere on the surface of the Earth.

Comparing and evaluating GRACE and GRACE-FO mascon data in the study of polar motion excitation

2020 ◽  
Author(s):  
Justyna Śliwińska ◽  
Małgorzata Wińska ◽  
Jolanta Nastula
Keyword(s):  
Polar Motion ◽  
Temporal Variations ◽  
Great Success ◽  
Spectral Bands ◽  
The Earth ◽  
Hydrological Angular Momentum ◽  
High Consistency ◽  
Gravity Recovery ◽  
Grace Mission ◽  
Polar Motion Excitation

<p>The Gravity Recovery and Climate Experiment (GRACE) mission has provided global observations of temporal variations in mass redistribution at the surface and within the Earth for the period 2002–2017. Such measurements are commonly exploited to interpret polar motion changes due to variations in the Earth’s surficial fluids, especially in the continental hydrosphere. Such impacts are usually examined by computing the so-called hydrological polar motion excitation (Hydrological Angular Momentum, HAM). The great success of the GRACE mission and the scientific robustness of its data contributed to the launch of its successor, GRACE Follow-On (GRACE-FO), which begun in May 2018 and continues to the present.</p> <p>This study compares the estimates of HAM computed from GRACE and GRACE-FO mascon data provided by three data centers: Jet Propulsion Laboratory (JPL), Center for Space Research (CSR), and Goddard Space Flight Center (GSFC). The analysis of HAM is performed for different spectral bands. A validation of different HAM estimates is conducted here using precise geodetic measurements of the pole coordinates and geophysical models (so-called geodetic residuals or GAO).</p> <p>Comparison of HAM computed from different mascon data sources indicates high consistency between the solutions provided by JPL and CSR, and low consistency between the GSFC solution and other data. The reason for this may be that the strategy used for GSFC mascons computation is different than methodology exploited by CSR and JPL teams. This study also indicates that HAM computed using CSR and JPL solutions are characterized by the highest consistency with GAO in all considered spectral bands.</p>

scholarly journals Time-variations of equivalent water heights'from Grace Mission and in-situ river stages in the Amazon basin

2012 ◽  
Vol 42 (1) ◽  
pp. 125-134 ◽  
Author(s):  
Flavio Guilherme Vaz de Almeida ◽  
Stephane Calmant ◽  
Frédérique Seyler ◽  
Guillaume Ramillien ◽  
Denizar Blitzkow ◽  
...  
Keyword(s):  
Time Series ◽  
Amazon Basin ◽  
Temporal Variations ◽  
Regression Coefficients ◽  
Linear Relationships ◽  
Time Variations ◽  
Gravity Recovery ◽  
Grace Mission

Gravity Recovery and Climate Experiment (GRACE) mission is dedicated to measuring temporal variations of the Earth's gravity field. In this study, the Stokes coefficients made available by Groupe de Recherche en Géodésie Spatiale (GRGS) at a 10-day interval were converted into equivalent water height (EWH) for a ~4-year period in the Amazon basin (from July-2002 to May-2006). The seasonal amplitudes of EWH signal are the largest on the surface of Earth and reach ~ 1250mm at that basin's center. Error budget represents ~130 mm of EWH, including formal errors on Stokes coefficient, leakage errors (12 ~ 21 mm) and spectrum truncation (10 ~ 15 mm). Comparison between in situ river level time series measured at 233 ground-based hydrometric stations (HS) in the Amazon basin and vertically-integrated EWH derived from GRACE is carried out in this paper. Although EWH and HS measure different water bodies, in most of the cases a high correlation (up to ~80%) is detected between the HS series and EWH series at the same site. This correlation allows adjusting linear relationships between in situ and GRACE-based series for the major tributaries of the Amazon river. The regression coefficients decrease from up to down stream along the rivers reaching the theoretical value 1 at the Amazon's mouth in the Atlantic Ocean. The variation of the regression coefficients versus the distance from estuary is analysed for the largest rivers in the basin. In a second step, a classification of the proportionality between in situ and GRACE time-series is proposed.

scholarly journals Uncertainty Assessments of Load Deformation from Different GPS Time Series Products, GRACE Estimates and Model Predictions: A Case Study over Europe

2021 ◽  
Vol 13 (14) ◽  
pp. 2765
Author(s):  
Song-Yun Wang ◽  
Jin Li ◽  
Jianli Chen ◽  
Xiao-Gong Hu
Keyword(s):  
Time Series ◽  
Noise Level ◽  
Climate Models ◽  
Linear Trend ◽  
Vertical Component ◽  
Deformation Analysis ◽  
Surface Displacements ◽  
Gravity Measurements ◽  
Gps Time Series ◽  
Gravity Recovery

A good understanding of the accuracy of the Global Positioning System (GPS) surface displacements provided by different processing centers plays an important role in load deformation analysis. We estimate the noise level in both vertical and horizontal directions for four representative GPS time series products, and compare GPS results with load deformation derived from the Gravity Recovery and Climate Experiment (GRACE) gravity measurements and climate models in Europe. For the extracted linear trend signals, the differences among different GPS series are small in all the three (east, north, and up) directions, while for the annual signals the differences are large. The mean standard deviations of annual amplitudes retrieved from the four GPS series are 3.54 mm in the vertical component (69% of the signal itself) and ~ 0.3 mm in the horizontal component (30% of the signal itself). The Scripps Orbit and Permanent Array Center (SOPAC) and MEaSUREs series have the lowest noise level in vertical and horizontal directions, respectively. Through consistency/discrepancy analysis among GPS, GRACE, and model vertical series, we find that the Jet Propulsion Laboratory (JPL) and Nevada Geodetic Laboratory (NGL) series show good consistency, the SOPAC series show good agreements in annual signal with the GRACE and model, and the MEaSUREs series show substantially large annual amplitude. We discuss the possible reasons for the notable differences among GPS time series products.

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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