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1

Misje satelitarne do badania zmian pola grawitacyjnego Ziemi

Gałdyn Filip

Przegląd Geodezyjny

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2024

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R. 96, nr 4

1--3

PL

Obserwacje zmian mas w skali globalnej przy użyciu satelitów odgrywają kluczową rolę w badaniach dotyczących zmian klimatu, cyrkulacji oceanów, wnętrza Ziemi oraz aktywności ludzkości. Dane te są pozyskiwane dzięki misjom satelitarnym, które skupiają się na badaniu zmian pola grawitacyjnego Ziemi, a co za tym idzie – zmian wysokości geoidy. Dzięki postępowi w dziedzinie geodezji satelitarnej, zwłaszcza systemów nawigacyjnych, misje te mogą dokonywać precyzyjnych pomiarów na skalę globalną, oferując wysoką rozdzielczość przestrzenną i czasową. W niniejszym artykule skupiamy się na przedstawieniu technik obserwacji potencjału grawitacyjnego oraz omówieniu informacji, które można dzięki nim uzyskać. Szczególny nacisk położony jest na misję GRACE i jej następcę, GRACE Follow-On oraz planowanej misji MAGIC.

EN

Observations of mass changes on a global scale using satellites play a crucial role in research related to climate change, ocean circulation, Earth's interior, and human activities. Data is acquired through satellite missions that focus on studying changes in Earth's gravity field, that is changes in geoid height. Thanks to advancements in satellite geodesy, especially in navigational systems, these missions can conduct precise measurements on a global scale, offering high spatial and temporal resolution. In this article, we focus on time-variable Earth’s gravity field observation techniques and discuss the information that can be obtained through them. Special emphasis is placed on the GRACE mission and its successor, GRACE Follow-On and future planned MAGIC mission.

2

Szabó Viktor, Osińska-Skotak Katarzyna

Artificial Satellites : Journal of Planetary Geodesy

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2023

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Vol. 58, No. 2

63--87

EN

The study presents a compatibility analysis of gravimetric observations with passive microwave observations. Monitoring the variability of soil water content is one of the essential issues in climate-related research. Total water storage changes (∆TWS) observed by Gravity Recovery and Climate Experiment (GRACE), enables the creation of many applications in hydrological monitoring. Soil moisture (SM) is a critical variable in hydrological studies. Advanced Microwave Scanning Radiometer (AMSR-E) satellite products provided unique observations on this variable in near-daily time resolutions. The study used maximum covariance analysis (MCA) to extract principal components for ∆TWS and SM signals. The analysis was carried out for the global area, dividing the discussion into individual continents. The amplitudes of gravimetric and microwave signals were computed via the complex empirical orthogonal function (EOF) and the complex conjugate EOF* to determine the regions for detailed comparison. Similarities and differences in signal convergence results were compared with land cover data describing soil conditions, vegetation cover, urbanization status, and cultivated land. Convergence was determined using Pearson correlation coefficients and cross-correlation. In order to compare ∆TWS and SM in individual seasons, ∆TWS observations were normalized. Results show that naturally forested areas and large open spaces used for agriculture support the compatibility between GRACE and AMSRE observations and are characterized by a good Pearson correlation coefficient >0.8. Subpolar regions with permafrost present constraints for AMSR-E observations and have little convergence with GRACE observations.

3

Analysis of the ITSG-GRACE daily models in the determination of polar motion excitation function

Partyka Aleksander, Nastula Jolanta, Śliwińska Justyna, Kur Tomasz, Wińska Małgorzata

Artificial Satellites : Journal of Planetary Geodesy

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2023

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Vol. 58, No. 3

105--121

EN

The main aim of this study is to evaluate the usefulness of Institute of Geodesy at Graz University of Technology (ITSG) daily gravity field models in the determination of hydrological angular momentum (HAM) at nonseasonal time scales. We compared the equatorial components (χ1 and χ2) of HAM calculated with the ITSG daily gravity field models (ITSG-Gravity Recovery and Climate Experiment [ITSG-GRACE] 2016 and ITSG-GRACE 2018) with HAM and sea-level angular momentum (SLAM) from hydrological land surface discharge model (LSDM) and the hydrological signal in the polar motion excitation (known as geodetic residuals [GAO]). Data from ITSG have a daily temporal resolution and allow us to determine oscillations with higher frequencies than the more commonly used monthly data. We limited our study to the period between 2004 and 2011 because of the gaps in GRACE observations before and after this period. We evaluated HAM obtained from ITSG GRACE models in spectral and time domains and determined the amplitude spectra of the analyzed series in the spectral range from 2 to 120 days. Our analyses confirm the existence of a sub-monthly signal in the HAM series determined from ITSG daily data. We observed a similar signal in LSDM-based HAM, but with notably weaker amplitudes. We also observed common peaks around 14 days in the amplitude spectra for the GAO- and ITSG-based series, which may be related to the Earth’s tides. ITSG daily gravity field models can be useful to determine the equatorial components of HAM at nonseasonal time scales.

4

Evaluation of Water Storage Changes in Southeastern Anatolia, Turkey, using GRACE and GLDAS

Öztürk Emel Zeray

Meteorology Hydrology and Water Management. Research and Operational Applications

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2022

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Vol. 10, Iss. 1

47--59

EN

With climatic changes, access to freshwater resources becomes more limited. Correspondingly, water monitoring methods in sensitive or critical areas in terms of groundwater amount are becoming increasingly important. The monitoring of the water levels in these regions, using appropriate methods and data sets, is highly effective in preventing possible future water crises. This paper aims estimated water storage changes with available tools and data in southeastern Anatolia, Turkey, where hydroclimatological studies are scarce due to limited observations. Data obtained from the Gravity Recovery and Climate Experiment satellite mission and the Global Land Data Assimilation System were used for the analysis of water storage changes in the study area. The results demonstrate that water storage shows a downward trend in all subareas, particularly in high-elevation regions. In addition, climatic changes have both short- and long-term impacts on water storage. Climatic variables (increasing temperature and decreasing precipitation) showed the highest correlation with water storage at 2-month lags. The monitoring of water storage is crucial for the region, and our results confirm the major role of such monitoring in decision-making processes and water resource management.

5

A short note on the natural and anthropogenic variations in the water storage changes at Visakhapatnam, Andhra Pradesh, India

Mathews Gathala Vinod, Rajesh Rekapalli, Begum Shaik Kareemunnisa

Acta Geophysica

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2022

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Vol. 70, no 4

1847--1854

EN

We analyze the periodic and stochastic/random dynamics in the water storage changes at Visakhapatnam, Andhra Pradesh, India. We used time-variable gravity data in terms of Equivalent Water Thickness (EWT) measured from Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellite missions for the period 2002 to 2021 along with average rainfall data to assess the natural and anthropogenic impacts on water storage changes. We employ Wavelet Spectrum and Singular Spectrum Analysis (SSA) methods to analyze the non-stationary variation of spectral power and principal components. The water storage in the study area shows a significant positive trend with a peak correlation of 0.52 with the rainfall data at a lag of 3 months. The first, second, third, fourth, and fifth principal components depicting the monotonic trend and oscillations together contribute 69.48% to the total water storage changes. The wavelet spectrum of the SSA reconstructed signal from the first four principal components revealed non-stationary annual and 1.3 to 8 years periodicities associated with natural solar and El-Nino Southern Oscillations (ENSO) respectively. The phase plot of the residual signal of ~ 30% variance suggests the random dynamics. Thus the study suggests: (i) an increasing groundwater trend in the study area, (ii) nearly 70% of the water storage changes are linked with natural solar and ENSO variations, and (iii) 30% of water storage changes are with random dynamics possibly linked with anthropogenic activities and catastrophic climatic episodes of shorter duration at Visakhapatnam, Andhra Pradesh, India.

6

Badanie wielkoskalowych zmian hydrosfery lądowej w kontekście najnowszych satelitarnych misji grawimetrycznych

Mikocki Jan, Leńczuk Artur, Bogusz Janusz

Biuletyn Wojskowej Akademii Technicznej

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2021

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Vol. 70, nr 4

147--159

PL

Analiza zmian pola ciężkości Ziemi należy do głównych zadań geodezji fizycznej, a znajomość wybranych charakterystyk tego pola stanowi m.in. podstawowy element wyznaczenia kształtu Ziemi i uwiarygodnienia wiedzy na temat redystrybucji jej masy. Od 2002 roku do tego celu wydatnie przyczynia się satelitarna misja grawimetryczna GRACE (ang. Gravity Recovery and Climate Experiment) oraz jej misja kontynuacyjna GRACE-FO (ang. GRACE Follow-On). Wyniki opracowanych obserwacji uzyskanych z misji GRACE/GRACE-FO prezentowane są m.in. w postaci maskonów, które dostarczane są przez trzy centra przetwarzania: 1) CSR (Center for Space Research, Austin, Stany Zjednoczone), 2) JPL (Jet Propulsion Laboratory, Pasadena, Stany Zjednoczone) oraz 3) GSFC (Goddard Space Flight Center, Maryland, Stany Zjednoczone). W pracy wykorzystano dane udostępniane przez centrum przetwarzania GSFC w postaci globalnego rozkładu zmian całkowitej zawartości wody w kontynentach (ang. Total Water Storage, TWS), wyrażonego w postaci wysokości słupa wody (ang. Equivalent Water Height, EWH). W badaniach skupiono się na zidentyfikowaniu obszarów o wyraźnych zmianach TWS. Fluktuacje TWS przeanalizowano pod kątem zmian krótkookresowych, tj. amplitudy oscylacji rocznej (najbardziej wyraźnej oscylacji w hydrosferze), oraz zmian długookresowych, tj. trendu (kluczowego parametru dla badań klimatycznych), wyznaczonych z wykorzystaniem metody najmniejszych kwadratów. W rezultacie wyselekcjonowano piętnaście obszarów charakteryzujących się ekstremalnymi zmianami, tj. jedenaście obszarów dla parametru amplitudy oscylacji rocznej i cztery obszary dla trendu. Otrzymano zmiany sezonowe większe niż 140 mm na obszarach w obrębie równika (głównie dorzecza rzek - Amazonka, Niger, Ganges, Brahmaputra) oraz obszarach pokrytych ogromnymi masami lodowymi (Alaska, Grenlandia). Największe tempo zmian zasobów wodnych na poziomie ±70 mm/rok obserwowane jest w okolicach Antarktydy Zachodniej, Patagonii czy Morza Kaspijskiego. Wyniki podkreślają również zauważalny wpływ człowieka na zmiany wód kontynentalnych (np. region Meksyku oraz dorzecza rzek Indus, Ganges).

EN

The analysis of Earth’s gravity field changes is the one of essential task of physical geodesy. So the knowledge about selected characteristics of gravity field is the basic element of the Earth shape determining process and help to find information about mass redistribution in the Earth system. Since 2002, the gravity field changes have been successfully observed by the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission and its continued GRACE-FO (GRACE Follow-On) mission. The results obtained from GRACE/GRACE-FO observations are presented, among other, in form of mascons and they are provid-ed by three processing centers: (1) Center for Space Research (CSR; Austin, United States), (2) Jet Propulsion Laboratory (JPL; Pasadena, United States), and (3) Goddard Space Flight Center (GSFC; Maryland, United States). In the following study, we used data provided by GSFC in form of the global distribution of Total Water Storage (TWS), which are expressed in terms of Equivalent Water Height (EWH). In our study, we focused on identifying areas with significant changes in TWS. We analysed TWS fluctuations in seasonal short-term changes, i.e., amplitude of annual oscillation (the most pronounced oscillation in the land hydro-sphere) and long-term changes, i.e., trend (a key parameter for climate studies) determined using the Least Squares Method. As a result, we selected 15 areas characterised by extreme TWS changes, i.e., 11 areas for annual amplitude and 4 areas for trend parameter. We obtained seasonal changes greater than 140 mm in areas within the equator (mainly Amazon, Niger, Ganges, Brahmaputra river basin regions) and areas covered by huge ice masses (Alaska, Greenland). The greatest rate of change in water storage at ±70 is observed around West Antarctica, Patagonia or the Caspian Sea. The results also emphasize the significant human impact in continental water masses (e.g. Mexico, Indus and Ganges river basins).

7

Comparing variance of signal contained in the most recent GRACE solutions

Lenczuk Artur, Leszczuk Grzegorz, Klos Anna, Bogusz Janusz

Geodesy and Cartography

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2020

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Vol. 69, no. 1

19--37

EN

Gravity Recovery and Climate Experiment (GRACE) mission data is widely used in various fields of science. GRACE explored changes of the gravity field regularly from April 2002 to June 2017. In the following research, we examine variance of signal contained in two different formats of GRACE data: standard spherical harmonics and mass concentration blocks (so-called “mascons”) solutions, both provided in the most recent releases. For spherical harmonics-based solution, we use monthly gravity field solutions provided up to degree and order (d/o) 96 by three different computing centers, i.e. the NASA’s Jet Propulsion Laboratory (JPL), the German Research Center for Geosciences (GFZ) and the Center for Space Research (CSR). For the mass concentration blocks, we use values of total water storage provided by the CSR, JPL and the Goddard Space Flight Center (GSFC) computing centers, which we convert to spherical harmonic coefficients up to d/o 96. We show that using the anisotropic DDK3 filter to smooth the north-south stripes present in total wate storage obtained from standard spherical harmonics solution leaves more information than common isotropic Gaussian filter. In the case of mascons, GSFC solution contains much more information than the CSR and JPL releases, relevant for corresponding d/o. Differences in variance of signal arise from different background models as well as various shape and size of mascons used during processing of GRACE observations.

8

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

Szabó Viktor, Marjańska Dorota

Artificial Satellites : Journal of Planetary Geodesy

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2020

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Vol. 55, No. 3

100--117

EN

Global 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.

9

Terrestrial water storage variations and their effect on polar motion

Śliwińska Justyna, Wińska Małgorzata, Nastula Jolanta

Acta Geophysica

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2019

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Vol. 67, no. 1

17--39

EN

The role of continental water in polar motion excitation can be illustrated by determining Hydrological Angular Momentum calculated from terrestrial water storage (TWS). In this paper we compare global and regional changes in TWS computed using Coupled Model Intercomparison Project Phase 5 climate models, Global Land Data Assimilation System (GLDAS) land hydrology models and observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. We also compare hydrological excitation functions derived from models with those obtained from the GRACE mission and the hydrological signal in observed polar motion excitation (the so-called geodetic residuals). The results confirm that GLDAS models of seasonal and non-seasonal TWS change are more consistent with GRACE data than climate models; on the other hand, none of the considered models are fully consistent with GRACE data or geodetic residuals. In turn, GRACE observations are most consistent with the non-seasonal hydrological signal in observed excitation. A detailed study of the contribution of different TWS components to the hydrological excitation function shows that soil moisture dominates.

10

Testing the relationship between vertical crustal movement and geoid uplift for the Sudetes area

Kowalczyk K., Kuczynska-Siehien J.

Annales Societatis Geologorum Poloniae

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2018

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Vol. 88, No. 1

47--57

EN

The aim of this study was to examine the relationship between vertical movements of the Earth’s crust and variation in geoid height. Data from the Gravity Recovery and Climate Experiment (GRACE), precise levelling, tidal gauge observations and Global Navigation Satellite Systems (GNSS) stations for the Sudetes area were used. The GRACE data provided the possibility of the analysis of geopotential changes. The geoid heights were calculated for the period from April 2002 to March 2016, using data from GeoForschungsZentrum (GFZ) GRACE Level-2 Product Release 05 in the form of spherical harmonic coefficients, truncated at degree and order (d/o) 60. Different filters were used. The calculated geoid change over time has the approximate value of 0.16 mm/y. This value was compared to the expected change in geoid height, determined on the basis of the Earth’s crustal movements.

11

Climate-driven Seasonal Geocenter Motion during the GRACE Period

Zhang H., Sun Y.

Acta Geophysica

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2018

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Vol. 66, no. 2

223--232

EN

Annual cycles in the geocenter motion time series are primarily driven by mass changes in the Earth’s hydrologic system, which includes land hydrology, atmosphere, and oceans. Seasonal variations of the geocenter motion have been reliably determined according to Sun et al. (J Geophys Res Solid Earth 121(11):8352-8370, 2016) by combining the Gravity Recovery And Climate Experiment (GRACE) data with an ocean model output. In this study, we reconstructed the observed seasonal geocenter motion with geophysical model predictions of mass variations in the polar ice sheets, continental glaciers, terrestrial water storage (TWS), and atmosphere and dynamic ocean (AO). The reconstructed geocenter motion time series is shown to be in close agreement with the solution based on GRACE data supporting with an ocean bottom pressure model. Over 85% of the observed geocenter motion time series, variance can be explained by the reconstructed solution, which allows a further investigation of the driving mechanisms. We then demonstrated that AO component accounts for 54, 62, and 25% of the observed geocenter motion variances in the X, Y, and Z directions, respectively. The TWS component alone explains 42, 32, and 39% of the observed variances. The net mass changes over oceans together with self-attraction and loading effects also contribute significantly (about 30%) to the seasonal geocenter motion in the X and Z directions. Other contributing sources, on the other hand, have marginal (less than 10%) impact on the seasonal variations but introduce a linear trend in the time series.

12

On the estimation of physical height changes using GRACE satellite mission data – A case study of Central Europe

Godah W., Szelachowska M., Krynski J.

Geodesy and Cartography

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2017

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Vol. 66, no. 2

211--226

EN

The dedicated gravity satellite missions, in particular the GRACE (Gravity Recovery and Climate Experiment) mission launched in 2002, provide unique data for studying temporal variations of mass distribution in the Earth’s system, and thereby, the geometry and the gravity fi eld changes of the Earth. The main objective of this contribution is to estimate physical height (e.g. the orthometric/normal height) changes over Central Europe using GRACE satellite mission data as well as to analyse them and model over the selected study area. Physical height changes were estimated from temporal variations of height anomalies and vertical displacements of the Earth surface being determined over the investigated area. The release 5 (RL05) GRACE-based global geopotential models as well as load Love numbers from the Preliminary Reference Earth Model (PREM) were used as input data. Analysis of the estimated physical height changes and their modelling were performed using two methods: the seasonal decomposition method and the PCA/ EOF (Principal Component Analysis/Empirical Orthogonal Function) method and the differences obtained were discussed. The main fi ndings reveal that physical height changes over the selected study area reach up to 22.8 mm. The obtained physical height changes can be modelled with an accuracy of 1.4 mm using the seasonal decomposition method.

13

On the analysis of temporal geoid height variations obtained from GRACE-based GGMs over the area of Poland

Godah W., Szelachowska M., Kryński J.

Acta Geophysica

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2017

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Vol. 65, no. 4

713--725

EN

Temporal mass variations in the Earth system, which can be detected from the Gravity Recovery and Climate Experiment (GRACE) mission data, cause temporal variations of geoid heights. The main objective of this contribution is to analyze temporal variations of geoid heights over the area of Poland using global geopotential models (GGMs) developed on the basis of GRACE mission data. Time series of geoid height variations were calculated for the chosen subareas of the aforementioned area using those GGMs. Thereafter, these variations were analyzed using two different methods. On the basis of the analysis results, models of temporal geoid height variations were developed and discussed. The possibility of prediction of geoid height variations using GRACE mission data over the area of Poland was also investigated. The main findings reveal that the geoid height over the area of Poland vary within 1.1 cm which should be considered when defining the geoid model of 1 cm accuracy for this area.

14

Water Storage Changes over the Tibetan Plateau Revealed by GRACE Mission

Guo J., Mu D., Liu X., Yan H., Sun Z., Guo B.

Acta Geophysica

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2016

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Vol. 64, no. 2

463--476

EN

We use GRACE gravity data released by the Center for Space Research (CSR) and the Groupe de Recherches en Geodesie Spatiale (GRGS) to detect the water storage changes over the Tibetan Plateau (TP). A combined filter strategy is put forward to process CSR RL05 data to remove the effect of striping errors. After the correction for GRACE by GLDAS and ICE-5G, we find that TP has been overall experiencing the water storage increase during 2003-2012. During the same time, the glacier over the Himalayas was sharply retreating. Interms of linear trends, CSR’s results derived by the combined filter are close to GRGS RL03 with the Gaussian filter of 300-km window. The water storage increasing rates determined from CSR’s RL05 products in the interior TP, Karakoram Mountain, Qaidam Basin, Hengduan Mountain, and middle Himalayas are 9.7, 6.2, 9.1, –18.6, and –20.2 mm/yr, respectively. These rates from GRGS’s RL03 products are 8.6, 5.8, 10.5, –19.3 and –21.4 mm/yr, respectively.

15

Local Recovery of Sub-Crustal Stress Due to Mantle Convection from Satellite-to-Satellite Tracking Data

Šprlák M., Eshagh M.

Acta Geophysica

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2016

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Vol. 64, no. 4

904--929

EN

Two integral transformations between the stress function, differentiation of which gives the meridian and prime vertical components of the sub-crustal stress due to mantle convection, and the satellite-to-satellite tracking (SST) data are presented in this article. In the first one, the SST data are the disturbing potential differences between twin-satellites and in the second one the line-of-sight (LOS) gravity disturbances. It is shown that the corresponding integral kernels are well-behaving and therefore suitable for inversion and recovery of the stress function from the SST data. Recovery of the stress function and the stress components is also tested in numerical experiments using simulated SST data. Numerical studies over the Himalayas show that inverting the disturbing potential differences leads to a smoother stress function than from inverting LOS gravity disturbances. Application of the presented integral formulae allows for recovery of the stress from the satellite mission GRACE and its planned successor.

16

Correction of Hydrological and Oceanic Effects from GRACE Data by Combination of the Steric Sea Level, Altimetry Data and GLDAS Model

Fatolazadeh F., Voosoghi B, Raoofian Naeeni M.

Acta Geophysica

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2016

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Vol. 64, no. 4

1193--1210

EN

In this study, a scheme to estimate oceanic and hydrological effects in the GRACE (Gravity Recovery and Climate Experiment) data is presented. The aim is to reveal tectonic signals for the case of the Sumatra earthquake on 26 December 2004. The variations of hydrological and oceanic effects are estimated with the aid of data set of GRACE, altimetry, World Ocean Atlas, and the GLDAS model for a period of January 2003 to December 2006. The time series of computed gravity changes over Sumatra region show some correlations to the deformation resulting from the earthquake occurred in December 2004. The maximum and minimum impacts of hydrological and oceanic effects on gravity changes are about 3 μGal in radial direction and –5 μGal in northward direction. The maximum and minimum amounts of gravitational gradient changes after the correction are 0.2 and –0.25 mE, which indicates the significant influences of hydrological and oceanic sources on the desired signal.

17

Assessment of the Global and Regional Land Hydrosphere and Its Impact on the Balance of the Geophysical Excitation Function of Polar Motion

Wińska M., Nastula J., Kołaczek B.

Acta Geophysica

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2016

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Vol. 64, no. 1

270--292

EN

The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones.

18

On the selection of GRACE-based GGMs and a filtering method for estimating mass variations in the Earth system over Poland

Godah W., Szelachowska M., Krynski J.

Geoinformation Issues

|

2015

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Vol. 7, no. 1(7)

5--14

EN

Since the launch of the GRACE (Gravity Recovery And Climate Experiment) satellite mission in 2002, significant progress in the knowledge regarding the temporal variations of the Earth’s gravity field has been achieved. The main objectives of this contribution are to define a suitable filter to reduce the noise contained in the latest release, i.e. RL05, of GRACE-based GGMs as well as to select the most suitable GRACE-based GGM time series for estimating mass variations in the Earth system over Poland. The performance of the Gaussian filter with different radii and the de-correlation filters (DDK1–DDK5) applied to reduce the noise contained in those GGMs was examined. First, they were investigated globally. Then, they were examined over the area of Poland, in particular, over two basins, i.e. the Vistula river basin and the Odra river basin. Moreover, both the internal and external accuracy of RL05 GRACE-based GGMs were assessed. Error degree variances of geoid heights were calculated on the basis of these models. Equivalent water thickness variations obtained from GRACE-based GGMs were compared with the corresponding ones obtained from the hydrology model. The obtained results were analysed and discussed. Finally the filtering method and the GGM time series most suitable for estimating mass variations in the Earth system over Poland were selected.

PL

Satelitarna misja GRACE (Gravity Recovery And Climate Experiment zapoczątkowana w 2002 roku znacząco przyczyniła się do rozwoju wiedzy o zmianach w czasie pola siły ciężkości Ziemi. Głównym celem niniejszego opracowania jest zdefiniowanie odpowiedniego filtru do redukcji szumu zawartego w ostatniej wersji, tj. wersji 5. globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE, jak również wybór najbardziej odpowiedniego szeregu czasowego globalnych modeli geopotencjału wyznaczonych na podstawie danych z misji GRACE, do określenia zmian rozkładu mas w systemie Ziemia dla obszaru Polski. W szczególności badano wpływ filtrów Gaussa o różnych promieniach oraz filtrów dekorelacyjnych (DDK1–DDK5) na redukcję szumu zawartego w globalnych modelach geopotencjału. Na początku wpływ użycia filtru był badany w ujęciu globalnym. Następnie wpływ ten został zbadany dla obszaru Polski – oddzielnie dla dorzeczy Wisły i Odry. Ponadto, została oszacowana zarówno wewnętrzna, jak i zewnętrzna dokładność wersji 5. globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE. Obliczono wariancje błędów wysokości geoidy dla poszczególnych stopni badanych modeli. Zmiany ekwiwalentnej warstwy wody wyznaczone z globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE zostały porównane z odpowiednimi zmianami otrzymanymi z modelu hydrologicznego. Wyniki poddano analizie i dyskusji. Ostatecznie wybrano metodę filtracji oraz szereg czasowy globalnych modeli geopotencjału najbardziej odpowiednie do oszacowania zmian rozkładu mas w systemie Ziemia dla obszaru Polski.

19

Equivalent water height extracted from GRACE gravity field model with robust independent component analysis

Guo J., Mu D., Yan H., Dai H.

Acta Geophysica

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2014

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Vol. 62, no. 4

953--972

EN

The Level-2 monthly GRACE gravity field models issued by Center for Space Research (CSR), GeoForschungs Zentrum (GFZ), and Jet Propulsion Laboratory (JPL) are treated as observations used to extract the equivalent water height (EWH) with the robust independent component analysis (RICA). The smoothing radii of 300, 400, and 500 km are tested, respectively, in the Gaussian smoothing kernel function to reduce the observation Gaussianity. Three independent components are obtained by RICA in the spatial domain; the first component matches the geophysical signal, and the other two match the north-south strip and the other noises. The first mode is used to estimate EWHs of CSR, JPL, and GFZ, and compared with the classical empirical decorrelation method (EDM). The EWH STDs for 12 months in 2010 extracted by RICA and EDM show the obvious fluctuation. The results indicate that the sharp EWH changes in some areas have an important global effect, like in Amazon, Mekong, and Zambezi basins.

20

Comparison of gravimetric excitation functions derived from equivalent water thickness, based on ﬁltered GRACE data sets

Nagalski T.

Reports on Geodesy

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2012

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z. 1/92

201--211

EN

We can estimate the Equivalent Water Thickness (EWT) from results of observations of the Earth gravity field from the Gravity Recovery and Climate Experiment (GRACE) gravimetric mission. However the maps of EWT obtained from raw gravimetric data contain typical stripes. To eliminate these disturbances we need to filter the raw data to improve the signal to noise ratio. The distribution of EWT obtained from the GRACE mission can be used to determine the gravimetric excitation function. In this paper it was investigated the filter influence on the EWT distribution and the amplitude of the gravimetric excitation functions. We use the EWT data sets derived from Stokes coefficients made accessible and filtered by the International Centre for Global Earth Models (ICGEM). The data sets available on ICGEM website were imported from three research centers GFZ, JPL and CSR. The anisotropic filter, with three degrees of smoothing DDK3, DDK2 and DDK1 is described in (Kusche et al., 2009).