scholarly journals Evaluating Gravimetric Polar Motion Excitation Estimates from the RL06 GRACE Monthly-Mean Gravity Field Models

2020 ◽  
Vol 12 (6) ◽  
pp. 930 ◽  
Author(s):  
Justyna Śliwińska ◽  
Jolanta Nastula ◽  
Henryk Dobslaw ◽  
Robert Dill
Keyword(s):  
Polar Motion ◽  
Temporal Variations ◽  
Spectral Bands ◽  
Mass Redistribution ◽  
Temporal Models ◽  
Gravity Recovery ◽  
Grace Mission ◽  
Gravity Field Models ◽  
Polar Motion Excitation ◽  
Level Of Agreement

Over the last 15 years, the Gravity Recovery and Climate Experiment (GRACE) mission has provided measurements of temporal changes in mass redistribution at and within the Earth that affect polar motion. The newest generation of GRACE temporal models, are evaluated by conversion into the equatorial components of hydrological polar motion excitation and compared with the residuals of observed polar motion excitation derived from geodetic measurements of the pole coordinates. We analyze temporal variations of hydrological excitation series and decompose them into linear trends and seasonal and non-seasonal changes, with a particular focus on the spectral bands with periods of 1000–3000, 450–1000, 100–450, and 60–100 days. Hydrological and reduced geodetic excitation series are also analyzed in four separated time periods which are characterized by different accuracy of GRACE measurements. The level of agreement between hydrological and reduced geodetic excitation depends on the frequency band considered and is highest for interannual changes with periods of 1000–3000 days. We find that the CSR RL06, ITSG 2018 and CNES RL04 GRACE solutions provide the best agreement with reduced geodetic excitation for most of the oscillations investigated.

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 Preliminary Estimation and Validation of Polar Motion Excitation from Different Types of the GRACE and GRACE Follow-On Missions Data

2020 ◽  
Vol 12 (21) ◽  
pp. 3490
Author(s):  
Justyna Śliwińska ◽  
Małgorzata Wińska ◽  
Jolanta Nastula
Keyword(s):  
Polar Motion ◽  
Initial Period ◽  
Terminal Phase ◽  
Data Series ◽  
Great Success ◽  
The Earth ◽  
Mass Redistribution ◽  
Different Types ◽  
Grace Mission ◽  
Polar Motion Excitation

The Gravity Recovery and Climate Experiment (GRACE) mission has provided global observations of temporal variations in the gravity field resulting from mass redistribution at the surface and within the Earth for the period 2002–2017. Although GRACE satellites are not able to realistically detect the second zonal parameter (ΔC20) of geopotential associated with the flattening of the Earth, they can accurately determine variations in degree-2 order-1 (ΔC21, ΔS21) coefficients that are proportional to variations in polar motion. Therefore, GRACE measurements are commonly exploited to interpret polar motion changes due to variations in the global mass redistribution, especially in the continental hydrosphere and cryosphere. Such impacts are usually examined by computing the so-called hydrological polar motion excitation (HAM) and cryospheric polar motion excitation (CAM), often analyzed together as HAM/CAM. 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 began in May 2018 and continues to the present. This study presents the first estimates of HAM/CAM computed from GRACE-FO data provided by three data centers: Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), and GeoForschungsZentrum (GFZ). In this paper, the data series is computed using different types of GRACE/GRACE-FO data: ΔC21, ΔS21 coefficients of geopotential, gridded terrestrial water storage anomalies, and mascon solutions. We compare and evaluate different methods of HAM/CAM estimation and examine the compatibility between CSR, JPL, and GFZ data. We also validate different HAM/CAM estimations using precise geodetic measurements and geophysical models. Analysis of data from the first 19 months of GRACE-FO shows that the consistency between GRACE-FO-based HAM/CAM and observed hydrological/cryospheric signals in polar motion is similar to the consistency obtained for the initial period of the GRACE mission, worse than the consistency received for the best GRACE period, and higher than the consistency obtained for the terminal phase of the GRACE mission. In general, the current quality of HAM/CAM from GRACE Follow-On meets expectations. In the following months, after full calibration of the instruments, this accuracy is expected to increase.

scholarly journals Prograde and Retrograde Terms of Gravimetric Polar Motion Excitation Estimates from the GRACE Monthly Gravity Field Models

2020 ◽  
Vol 12 (1) ◽  
pp. 138 ◽  
Author(s):  
Jolanta Nastula ◽  
Justyna Śliwińska
Keyword(s):  
Angular Momentum ◽  
Gravity Field ◽  
Polar Motion ◽  
Temporal Variations ◽  
Short Term ◽  
Grace Data ◽  
Hydrological Angular Momentum ◽  
Gravity Field Models ◽  
Polar Motion Excitation

From 2002 to 2017, the Gravity Recovery and Climate Experiment (GRACE) mission’s twin satellites measured variations in the mass redistribution of Earth’s superficial fluids, which disturb polar motion (PM). In this study, the PM excitation estimates were computed from two recent releases of GRACE monthly gravity field models, RL05 and RL06, and converted into prograde and retrograde circular terms by applying the complex Fourier transform. This is the first such analysis of circular parts in GRACE-based excitations. The obtained series were validated by comparison with the residuals of observed polar motion excitation (geodetic angular momentum (GAM)–atmospheric angular momentum (AAM)–oceanic angular momentum (OAM) (GAO)) determined from precise geodetic measurements of the pole coordinates. We examined temporal variations of hydrological excitation function series (or hydrological angular momentum, HAM) in four spectral bands: seasonal, non-seasonal, non-seasonal short-term, and non-seasonal long-term. The general conclusions arising from the conducted analyses of prograde and retrograde terms were consistent with the findings from the equatorial components of PM excitation studies drawn in previous research. In particular, we showed that the new GRACE RL06 data increased the consistency between different solutions and improved the agreement between GRACE-based excitation series and reference data. The level of agreement between HAM and GAO was dependent on the oscillation considered and was higher for long-term than short-term variations. For most of the oscillations considered, the highest agreement with GAO was obtained for CSR RL06 and ITSG-Grace2018 solutions. This study revealed that both prograde and retrograde circular terms of PM excitation can be determined by GRACE with similar levels of accuracy. The findings from this study may help in choosing the most appropriate GRACE solution for PM investigations and can be useful in future improvements to GRACE data processing.

Hydrological signals in polar motion excitation – Evidence after fifteen years of the GRACE mission

2019 ◽  
Vol 124 ◽  
pp. 119-132 ◽  
Author(s):  
Jolanta Nastula ◽  
Małgorzata Wińska ◽  
Justyna Śliwińska ◽  
David Salstein
Keyword(s):  
Polar Motion ◽  
Grace Mission ◽  
Polar Motion Excitation

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.

Preliminary hydrological polar motion excitation estimates from the GRACE Follow-On mission

2020 ◽  
Author(s):  
Justyna Śliwińska ◽  
Małgorzata Wińska ◽  
Jolanta Nastula
Keyword(s):  
Reference Frame ◽  
Polar Motion ◽  
Water Storage ◽  
Drought Event ◽  
Great Success ◽  
Change Analysis ◽  
Geopotential Models ◽  
Level 3 ◽  
Grace Mission ◽  
Polar Motion Excitation

<p>Over almost 20 last years, observations from the Gravity Recovery and Climate Experiment (GRACE) mission have become invaluable as means to examine Earth global mass change. Since 2002, the relative along track motions between two identical satellites have been used to derive Earth’s time variable gravity field. The great success and scientific sound of the mission, which ended in 2017, contributed to the launch of its successor, GRACE Follow-On (GFO) in May 2018. Until now, monthly time series of GFO-based geopotential models have been made available to the users by official GRACE data centres at Center for Space Research (CSR), Jet Propulsion Laboratory (JPL) and GeoForschungsZentrum (GFZ). This data enables the continuation of many researches which started with the beginning of the GRACE mission. Such applications included monitoring of land water storage changes, drought event identification, flood prediction, ice mass loss detection, groundwater level change analysis, and more.</p><p>In geodesy, a crucial application of GRACE/GFO mission observations is the study of polar motion (PM) changes due to mass redistribution of the Earth’s surficial fluids (atmosphere, ocean, land hydrosphere). PM represents two out of five Earth Orientation Parameters (EOP), that describe the rotation of our Planet and link the terrestrial reference frame with the corresponding celestial reference frame. The use of C<sub>21</sub>, S<sub>21</sub> coefficients of GRACE/GFO-based geopotential models is a common method for determining polar motion excitation.</p><p>In this study, we present the first estimates of hydrological polar motion excitation functions (Hydrological Angular Momentum, HAM) computed from GFO data which were provided by CSR, JPL and GFZ teams. The HAM are calculated using (1) C<sub>21</sub>, S<sub>21</sub> coefficients of geopotential (GFO Level-2 data) as well as (2) gridded terrestrial water storage (TWS) anomalies (GFO Level-3 data). We compare and evaluate the two methods of HAM estimation and examine the compatibility between CSR, JPL and GFZ solutions. We also validate different HAM estimations using precise geodetic measurements of the pole coordinates.</p><p>Our analyses show that the highest internal agreement between different GFO solutions can be obtained when comparing CSR and JPL. Notably, GFZ estimates differ slightly from the other GFO models. The highest agreement between different GFO-based HAM, and between GFO-based HAM and reference data is obtained when GFO Level-3 data are used. We also demonstrate that the current accuracy of HAM from GRACE Follow-On mission meets the expectations and is comparable with the accuracy of HAM from GRACE Release-6 (RL06) data.</p>

scholarly journals Determining and Evaluating the Hydrological Signal in Polar Motion Excitation from Gravity Field Models Obtained from Kinematic Orbits of LEO Satellites

2019 ◽  
Vol 11 (15) ◽  
pp. 1784 ◽  
Author(s):  
Justyna Śliwińska ◽  
Jolanta Nastula
Keyword(s):  
Gravity Field ◽  
Polar Motion ◽  
Low Earth Orbit ◽  
Data Sets ◽  
Leo Satellites ◽  
Hydrological Angular Momentum ◽  
Academy Of Sciences ◽  
Gravity Field Models ◽  
Polar Motion Excitation ◽  
Background Models

This study evaluates the gravity field solutions based on high-low satellite-to-satellite tracking (hl-SST) of low-Earth-orbit (LEO) satellites: GRACE, Swarm, TerraSAR-X, TanDEM-X, MetOp-A, MetOp-B, and Jason 2, by converting them into hydrological polar motion excitation functions (or hydrological angular momentum (HAM)). The resulting HAM series are compared with the residuals of observed polar motion excitation (geodetic residuals, GAO) derived from precise geodetic measurements, and the HAM obtained from the GRACE ITSG 2018 solution. The findings indicate a large impact of orbital altitude and inclination on the accuracy of derived HAM. The HAM series obtained from Swarm data are found to be the most consistent with GAO. Visible differences are found in HAM obtained from GRACE and Swarm orbits and provided by different processing centres. The main reasons for such differences are likely to be different processing approaches and background models. The findings of this study provide important information on alternative data sets that may be used to provide continuous polar motion excitation observations, of which the Swarm solution provided by the Astronomical Institute, Czech Academy of Sciences, is the most accurate. However, further analysis is needed to determine which processing algorithms are most appropriate to obtain the best correspondence with GAO.

scholarly journals Validation of GRACE and GRACE-FO Mascon Data for the Study of Polar Motion Excitation

2021 ◽  
Vol 13 (6) ◽  
pp. 1152
Author(s):  
Justyna Śliwińska ◽  
Małgorzata Wińska ◽  
Jolanta Nastula
Keyword(s):  
Land Surface ◽  
Polar Motion ◽  
Surface Discharge ◽  
Goddard Space Flight Center ◽  
Discharge Model ◽  
Motion Studies ◽  
Gravity Recovery ◽  
Polar Motion Excitation

In this study, we calculate the hydrological plus cryospheric excitation of polar motion (hydrological plus cryospheric angular momentum, HAM/CAM) using mascon solutions based on observations from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions. We compare and evaluate HAM/CAM computed from GRACE and GRACE-FO mascon data provided by the Jet Propulsion Laboratory (JPL), the Center for Space Research (CSR), and the Goddard Space Flight Center (GSFC). A comparison with HAM obtained from the Land Surface Discharge Model is also provided. An analysis of HAM/CAM and HAM is performed for overall variability, trends, and seasonal and non-seasonal variations. The HAM/CAM and HAM estimates are validated using the geodetic residual time series (GAO), which is an estimation of the hydrological plus cryospheric signal in geodetically observed polar motion excitation. In general, all mascon datasets are found to be equally suitable for the determination of overall, seasonal, and non-seasonal HAM/CAM oscillations, but some differences in trends remain. The use of an ellipsoidal correction, implemented in the newest solution from CSR, does not noticeably affect the consistency between HAM/CAM and GAO. Analysis of the data from the first two years of the GRACE-FO mission indicates that the current accuracy of HAM/CAM from GRACE-FO mascon data meets expectations, and the root mean square deviation of HAM/CAM components are between 5 and 6 milliarcseconds. The findings from this study can be helpful in assessing the role of satellite gravimetry in polar motion studies and may contribute towards future improvements to GRACE-FO data processing.

scholarly journals Hydrological Excitation of Polar Motion Derived from GRACE Gravity Field Solutions

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
L. Seoane ◽  
J. Nastula ◽  
C. Bizouard ◽  
D. Gambis
Keyword(s):  
Polar Motion ◽  
Water Storage ◽  
High Latitudes ◽  
The North ◽  
Grace Data ◽  
Influence Of Water ◽  
Grace Mission ◽  
Polar Motion Excitation ◽  
Good Agreement ◽  
Global Hydrology

The influence of the continental water storage on the polar motion is not well known. Different models have been developed to evaluate these effects and compared to geodetic observations. However, previous studies have shown large discrepancies mainly attributed to the lack of global measurements of related hydrological parameters. Now, from the observations of the GRACE mission, we can estimate the polar motion excitation due to the global hydrology. Data processing of GRACE data is carried out by several centers of analysis, we focus on the new solution computed by the Groupe de Recherche de Géodésie Spatiale. At annual scales, excitations derived from GRACE data are in better agreement with geodetic observations than models estimates. The main contribution to the hydrological excitation comes from the monsoon climates regions where GRACE and models estimates are in a very good agreement. Still, the effect of the north high latitudes regions, where the principal areas of snow cover are found, cannot be neglected. At these regions, GRACE and models estimated contributions to polar motion excitations show significant discrepancies. Finally, GRACE-based excitations reveal the possible influence of water storage variations in exciting polar motion around the frequency of 3 cycles per year.

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