scholarly journals Constrained Linear Deconvolution of GRACE Anomalies to Correct Spatial Leakage

2020 ◽  
Vol 12 (11) ◽  
pp. 1798
Author(s):  
Ki-Weon Seo ◽  
Seokhoon Oh ◽  
Jooyoung Eom ◽  
Jianli Chen ◽  
Clark R. Wilson
Keyword(s):  
Climate Forcing ◽  
Mass Change ◽  
Data Types ◽  
Surface Mass ◽  
Grace Data ◽  
Mass Redistribution ◽  
Grace Satellites ◽  
Earth’S Climate ◽  
Gravity Recovery ◽  
Mass Loads

Time-varying gravity observed by the Gravity Recovery and Climate Experiment (GRACE) satellites measures surface water and ice mass redistribution driven by weather and climate forcing and has emerged as one of the most important data types in measuring changes in Earth’s climate. However, spatial leakage of GRACE signals, especially in coastal areas, has been a recognized limitation in quantitatively assessing mass change. It is evident that larger terrestrial signals in coastal regions spread into the oceans and vice versa and various remedies have been developed to address this problem. An especially successful one has been Forward Modeling but it requires knowledge of geographical locations of mass change to be fully effective. In this study, we develop a new method to suppress leakage effects using a linear least squares operator applied to GRACE spherical harmonic data. The method is effectively a constrained deconvolution of smoothing inherent in GRACE data. It assumes that oceanic mass changes near the coast are negligible compared to terrestrial changes, with additional spatial regularization constraints. Some calibration of constraint weighting is required. We apply the method to estimate surface mass loads over Australia using both synthetic and real GRACE data. Leakage into the oceans is effectively suppressed and when compared with mascon solutions there is better performance over interior basins.

scholarly journals An ice flow modeling perspective on bedrock adjustment patterns of the Greenland ice sheet

2012 ◽  
Vol 6 (6) ◽  
pp. 1263-1274 ◽  
Author(s):  
M. Olaizola ◽  
R. S. W. van de Wal ◽  
M. M. Helsen ◽  
B. de Boer
Keyword(s):  
Mass Balance ◽  
Maximum Yield ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Elastic Response ◽  
Delayed Response ◽  
Surface Mass ◽  
Grace Data ◽  
Grace Satellites ◽  
Gravity Recovery

Abstract. Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland ice sheet (GrIS) have been produced. To obtain ice mass changes, the GRACE data need to be corrected for the effect of deformation changes of the Earth's crust. Recently, a new method has been proposed where ice mass changes and bedrock changes are simultaneously solved. Results show bedrock subsidence over almost the entirety of Greenland in combination with ice mass loss which is only half of the currently standing estimates. This subsidence can be an elastic response, but it may however also be a delayed response to past changes. In this study we test whether these subsidence patterns are consistent with ice dynamical modeling results. We use a 3-D ice sheet–bedrock model with a surface mass balance forcing based on a mass balance gradient approach to study the pattern and magnitude of bedrock changes in Greenland. Different mass balance forcings are used. Simulations since the Last Glacial Maximum yield a bedrock delay with respect to the mass balance forcing of nearly 3000 yr and an average uplift at present of 0.3 mm yr−1. The spatial pattern of bedrock changes shows a small central subsidence as well as more intense uplift in the south. These results are not compatible with the gravity based reconstructions showing a subsidence with a maximum in central Greenland, thereby questioning whether the claim of halving of the ice mass change is justified.

Statistical downscaling of GRACE products to improve spatial resolution

2021 ◽  
Author(s):  
Nico Sneeuw ◽  
Bramha Dutt Vishwakarma ◽  
Jinwei Zhang
Keyword(s):  
Spatial Resolution ◽  
Statistical Downscaling ◽  
Spatial Scales ◽  
Climate Forcing ◽  
Water Compartments ◽  
Grace Data ◽  
Physical Information ◽  
Physical Attributes ◽  
Spatio Temporal ◽  
Gravity Recovery

<p>The satellite missions Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-On record the change in the gravity field, which is then related to water mass redistribution near the Earth's surface and disseminated as monthly fields of Total Water Storage Change (TWSC). GRACE products effectively carry signal information only above spatial scales of about 300 km, which limits their application in regional hydrological applications. At present, several GRACE products are available at 0.5° or 1° grid cells, but they are only an interpolated version of the coarse resolution GRACE products and do not offer additional physical information. </p><p>In this study we implement a statistical downscaling approach that assimilates high resolution TWSC fields from the WaterGAP hydrology model (WGHM), precipitation fields from 3 models, evapotranspiration and runoff from 2 models, with GRACE data to improve its resolution. The downscaled product exploits dominant common statistical modes between all the datasets to inform the estimates of TWSC. An improvement in the spatial resolution is obtained from using WGHM that incorporates the geometry of various water compartments and simulates spatio-temporal changes in TWSC due to climate forcing, land use land cover change, and human intervention. Therefore, the downscaled product at a 0.5° grid is able to capture physical attributes of water compartments at a spatial resolution better than the available GRACE products. </p>

scholarly journals Quantifying the resolution level where the GRACE satellites can separate Greenland's glacial mass balance from surface mass balance

2015 ◽  
Vol 9 (1) ◽  
pp. 1315-1343
Author(s):  
J. A. Bonin ◽  
D. P. Chambers
Keyword(s):  
Mass Balance ◽  
Gravity Measurement ◽  
Surface Mass Balance ◽  
Satellite Gravity ◽  
Surface Mass ◽  
Grace Data ◽  
Resolution Level ◽  
Grace Satellites ◽  
Grace Satellite ◽  
Gravity Mission

Abstract. Mass change over Greenland can be caused by either changes in the glacial mass balance (GMB) or the precipitation-based surface mass balance (SMB). The GRACE satellite gravity mission cannot directly separate the two physical causes because it measures the sum of the entire mass column with limited spatial resolution. We demonstrate one theoretical way to indirectly separate SMB from GMB with GRACE, using a least squares inversion technique with knowledge of the location of the glacier. However, we find that the limited 60 × 60 spherical harmonic representation of current GRACE data does not provide sufficient resolution to adequately accomplish the task. We determine that at a maximum degree/order of 90 × 90 or above, a noise-free gravity measurement could theoretically separate the SMB from GMB signals. However, current GRACE satellite errors are too large at present to separate the signals. A noise reduction of a factor of 9 at a resolution of 90 × 90 would provide the accuracy needed for the interannual SMB and GMB to be accurately separated.

scholarly journals Improved GRACE regional mass balance estimates of the Greenland ice sheet cross-validated with the input–output method

2016 ◽  
Vol 10 (2) ◽  
pp. 895-912 ◽  
Author(s):  
Zheng Xu ◽  
Ernst J. O. Schrama ◽  
Wouter van der Wal ◽  
Michiel van den Broeke ◽  
Ellyn M. Enderlin
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mass Change ◽  
Input Output ◽  
Surface Mass ◽  
Ice Cloud ◽  
The Difference ◽  
Gravity Recovery

Abstract. In this study, we use satellite gravimetry data from the Gravity Recovery and Climate Experiment (GRACE) to estimate regional mass change of the Greenland ice sheet (GrIS) and neighboring glaciated regions using a least squares inversion approach. We also consider results from the input–output method (IOM). The IOM quantifies the difference between the mass input and output of the GrIS by studying the surface mass balance (SMB) and the ice discharge (D). We use the Regional Atmospheric Climate Model version 2.3 (RACMO2.3) to model the SMB and derive the ice discharge from 12 years of high-precision ice velocity and thickness surveys. We use a simulation model to quantify and correct for GRACE approximation errors in mass change between different subregions of the GrIS, and investigate the reliability of pre-1990s ice discharge estimates, which are based on the modeled runoff. We find that the difference between the IOM and our improved GRACE mass change estimates is reduced in terms of the long-term mass change when using a reference discharge derived from runoff estimates in several subareas. In most regions our GRACE and IOM solutions are consistent with other studies, but differences remain in the northwestern GrIS. We validate the GRACE mass balance in that region by considering several different GIA models and mass change estimates derived from data obtained by the Ice, Cloud and land Elevation Satellite (ICESat). We conclude that the approximated mass balance between GRACE and IOM is consistent in most GrIS regions. The difference in the northwest is likely due to underestimated uncertainties in the IOM solutions.

scholarly journals Reduced misclosure of global sea-level budget with updated Tongji-Grace2018 solution

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fengwei Wang ◽  
Yunzhong Shen ◽  
Qiujie Chen ◽  
Yu Sun
Keyword(s):  
Sea Level ◽  
Spherical Harmonic ◽  
Mass Change ◽  
Global Ocean ◽  
Argo Data ◽  
Ocean Mass ◽  
Grace Data ◽  
Budget Equation ◽  
Global Sea Level ◽  
Gravity Recovery

AbstractThe global sea-level budget is studied using the Gravity Recovery and Climate Experiment (GRACE) solutions, Satellite Altimetry and Argo observations based on the updated budget equation. When the global ocean mass change is estimated with the updated Tongji-Grace2018 solution, the misclosure of the global sea-level budget can be reduced by 0.11–0.22 mm/year compared to four other recent solutions (i.e. CSR RL06, GFZ RL06, JPL RL06 and ITSG-Grace2018) over the period January 2005 to December 2016. When the same missing months as the GRACE solution are deleted from altimetry and Argo data, the misclosure will be reduced by 0.06 mm/year. Once retained the GRACE C20 term, the linear trends of Tongji-Grace2018 and ITSG-Grace2018 solutions are 2.60 ± 0.16 and 2.54 ± 0.16 mm/year, closer to 2.60 ± 0.14 mm/year from Altimetry–Argo than the three RL06 official solutions. Therefore, the Tongji-Grace2018 solution can reduce the misclosure between altimetry, Argo and GRACE data, regardless of whether the C20 term is replaced or not, since the low-degree spherical harmonic coefficients of the Tongji-Grace2018 solution can capture more ocean signals, which are confirmed by the statistical results of the time series of global mean ocean mass change derived from five GRACE solutions with the spherical harmonic coefficients truncated to different degrees and orders.

scholarly journals Determination of ellipsoidal surface mass change from GRACE time-variable gravity data

2019 ◽  
Vol 219 (1) ◽  
pp. 248-259
Author(s):  
Khosro Ghobadi-Far ◽  
Michal Šprlák ◽  
Shin-Chan Han
Keyword(s):  
Time Variable ◽  
Mass Change ◽  
Lower Latitude ◽  
Spherical Approximation ◽  
Polar Regions ◽  
Surface Mass ◽  
Time Variable Gravity ◽  
The Earth ◽  
Mass Redistribution ◽  
Variable Gravity

SUMMARY The problem of determining mass redistribution within the Earth system from time-variable gravity (TVG) data is non-unique. Over seasonal and decadal time-scales, mass redistribution likely takes place on the Earth’s surface. By approximating the Earth’s surface by a sphere, surface mass variation can be uniquely determined from TVG data. Recently, using the improved GRACE TVG data, Li et al. and Ditmar found that such spherical approximation is no longer tenable and suggested practical approaches to accommodate the elliptical shape of the Earth. In this study, we develop a rigorous method of determining surface mass change on the Earth’s reference ellipsoid. We derive a unique one-to-one relationship between ellipsoidal spectra of surface mass and gravitational potential for the ellipsoidal geometry. In conjunction with our ellipsoidal formulation, the linear transformation between spherical and ellipsoidal harmonic coefficients of the geopotential field enables us to determine mass redistribution on the ellipsoid from GRACE TVG data. Using the Release 6 of GRACE TVG data to degree 60, we show that the ellipsoidal approach reconciles surface mass change rate significantly better than the spherical computation by 3–4 cm yr−1, equivalent to 10–15  per cent increase of total signal, in Greenland and West Antarctica. We quantify the spherical approximation error over the polar regions using GRACE Level-2 TVG data as well as mascon solutions, and demonstrate that the systematic error increases linearly with the maximum degree used for the synthesis. The terrestrial water storage computation is less affected by the spherical approximation because of geographic location of major river basins (lower latitude) and signal characteristics. The improvement of TVG data from GRACE and its Follow-On necessitates the ellipsoidal computation, particularly for quantifying mass change in polar regions.

scholarly journals Geophysical interpretation of GPS loading deformation over western Europe using GRACE measurements

2016 ◽  
Vol 59 (5) ◽  
Author(s):  
Songyun Wang ◽  
Jianli Chen ◽  
Jin Li ◽  
Xiaogong Hu ◽  
Shengnan Ni
Keyword(s):  
Western Europe ◽  
International Gnss Service ◽  
Satellite Gravity ◽  
Surface Mass ◽  
Grace Data ◽  
Surface Displacements ◽  
Residual Series ◽  
Vertical Displacements ◽  
Gravity Recovery ◽  
Improved Accuracy

<p>We analyze more than 10 years of Global Positioning System (GPS) height residuals and vertical displacements predicted from surface mass loading observed by the Gravity Recovery and Climate Experiment (GRACE) for 36 International GNSS Service (IGS) stations over Europe. Seasonal surface displacements, mostly due to atmospheric and hydrological loading, are significant in both GPS and GRACE measurements. With an extended time period, our new analysis based on release 05 GRACE data from Center for Space Research (CSR) shows considerably improved agreement between GPS and GRACE than that from previous studies, for not only annual but also interannual signals. The GPS height residual series at most stations exhibit reduced weighted root-mean-squares (WRMS) after removing GRACE-derived vertical displacements, which is attributed to improved accuracy of both GPS and GRACE data products. Furthermore, we demonstrate the necessity of reducing leakage bias in GRACE estimates for the study of surface loading deformation using GRACE satellite gravity observations.</p>

scholarly journals Quantifying the resolution level where the GRACE satellites can separate Greenland's glacial mass balance from surface mass balance

2015 ◽  
Vol 9 (5) ◽  
pp. 1761-1772 ◽  
Author(s):  
J. A. Bonin ◽  
D. P. Chambers
Keyword(s):  
Mass Balance ◽  
Gravity Measurement ◽  
Surface Mass Balance ◽  
Satellite Gravity ◽  
Surface Mass ◽  
Grace Data ◽  
Resolution Level ◽  
Grace Satellites ◽  
Grace Satellite ◽  
Gravity Mission

Abstract. Mass change over Greenland can be caused by either changes in the glacial dynamic mass balance (DMB) or the surface mass balance (SMB). The GRACE satellite gravity mission cannot directly separate the two physical causes because it measures the sum of the entire mass column with limited spatial resolution. We demonstrate one theoretical way to indirectly separate cumulative SMB from DMB with GRACE, using a least squares inversion technique with knowledge of the location of the glaciers. However, we find that the limited 60 × 60 spherical harmonic representation of current GRACE data does not provide sufficient resolution to adequately accomplish the task. We determine that at a maximum degree/order of 90 × 90 or above, a noise-free gravity measurement could theoretically separate the SMB from DMB signals. However, current GRACE satellite errors are too large at present to separate the signals. A noise reduction of a factor of 10 at a resolution of 90 × 90 would provide the accuracy needed for the interannual cumulative SMB and DMB to be accurately separated.

scholarly journals Using satellite laser ranging to measure ice mass change in Greenland and Antarctica

2018 ◽  
Vol 12 (1) ◽  
pp. 71-79 ◽  
Author(s):  
Jennifer A. Bonin ◽  
Don P. Chambers ◽  
Minkang Cheng
Keyword(s):  
Time Series ◽  
Mass Loss ◽  
Time Frame ◽  
Satellite Laser Ranging ◽  
Mass Change ◽  
Laser Ranging ◽  
Data Types ◽  
Gravity Recovery ◽  
Loss Estimate

Abstract. A least squares inversion of satellite laser ranging (SLR) data over Greenland and Antarctica could extend gravimetry-based estimates of mass loss back to the early 1990s and fill any future gap between the current Gravity Recovery and Climate Experiment (GRACE) and the future GRACE Follow-On mission. The results of a simulation suggest that, while separating the mass change between Greenland and Antarctica is not possible at the limited spatial resolution of the SLR data, estimating the total combined mass change of the two areas is feasible. When the method is applied to real SLR and GRACE gravity series, we find significantly different estimates of inverted mass loss. There are large, unpredictable, interannual differences between the two inverted data types, making us conclude that the current 5×5 spherical harmonic SLR series cannot be used to stand in for GRACE. However, a comparison with the longer IMBIE time series suggests that on a 20-year time frame, the inverted SLR series' interannual excursions may average out, and the long-term mass loss estimate may be reasonable.

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