| 1. |
- Abrehdary, Majid
(författare)
-
Recovering Moho parameters using gravimetric and seismic data
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Isostasy is a key concept in geoscience to interpret the state of mass balance between the Earth’s crust and mantle. There are four well-known isostatic models: the classical models of Airy/Heiskanen (A/H), Pratt/Hayford (P/H), and Vening Meinesz (VM) and the modern model of Vening Meinesz-Moritz (VMM). The first three models assume a local and regional isostatic compensation, whereas the latter one supposes a global isostatic compensation scheme.A more satisfactory test of isostasy is to determine the Moho interface. The Moho discontinuity (or Moho) is the surface, which marks the boundary between the Earth’s crust and upper mantle. Generally, the Moho interface can be mapped accurately by seismic observations, but limited coverage of seismic data and economic considerations make gravimetric or combined gravimetric-seismic methods a more realistic technique for imaging the Moho interface either regional or global scales.It is the main purpose of this dissertation to investigate an isostatic model with respect to its feasibility to use in recovering the Moho parameters (i.e. Moho depth and Moho density contrast). The study is mostly limited to the VMM model and to the combined approach on regional and global scales. The thesis briefly includes various investigations with the following specific subjects:1) to investigate the applicability and quality of satellite altimetry data (i.e. marine gravity data) in Moho determination over the oceans using the VMM model, 2) to investigate the need for methodologies using gravimetric data jointly with seismic data (i.e. combined approach) to estimate both the Moho depth and Moho density contrast over regional and global scales, 3) to investigate the spherical terrain correction and its effect on the VMM Moho determination, 4) to investigate the residual isostatic topography (RIT, i.e. difference between actual topography and isostatic topography) and its effect in the VMM Moho estimation, 5) to investigate the application of the lithospheric thermal-pressure correction and its effect on the Moho geometry using the VMM model, 6) Finally, the thesis ends with the application of the classical isostatic models for predicting the geoid height.The main input data used in the VMM model for a Moho recovery is the gravity anomaly/disturbance corrected for the gravitational contributions of mass density variation due in different layers of the Earth’s crust (i.e. stripping gravity corrections) and for the gravity contribution from deeper masses below the crust (i.e. non-isostatic effects). The corrections are computed using the recent seismic crustal model CRUST1.0.Our numerical investigations presented in this thesis demonstrate that 1) the VMM approach is applicable for estimating Moho geometry using a global marine gravity field derived by satellite altimetry and that the possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination, 2) the combined approach could help in filling-in the gaps in the seismic models and it also provides good fit to other global and regional models more than 90 per cent of the locations, 3) despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the Moho result most significantly in many areas, 4) the application of the RIT correction improves the agreement of our Moho result with some published global Moho models, 5) the application of the lithospheric thermal-pressure correction improves the agreement of VMM Moho model with some other global Moho models, 6) the geoid height cannot be successfully represented by the classical models due to many other gravitational signals from various mass variations within the Earth that affects the geoid.
|
|
| 2. |
- Bagherbandi, Mohammad, 1977-
(författare)
-
An Isostatic Earth Crustal Model : and Its Applications
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Mohorovičič discontinuity (Moho), which is the surface separating the Earth’s crust from the mantle, is of great interest among geoscientists. The Moho depth can be determined by seismic and gravimetric methods. The seismic methods are expensive, time-consuming and suffer from lack of global coverage of data, while the gravimetric methods use inexpensive and mostly already available global and regional data based on an isostatic model. The main reasons for studying an isostatic model are on one hand the gaps and uncertainties of the seismic models, and, on the other hand, the generous availability of gravity data from global models for the gravimetric-isostatic model. In this study, we present a new gravimetric-isostatic Moho model, called the Vening Meinesz-Moritz (VMM) model. Also, a combined Moho model based on seismic and gravimetric models is presented. Classical isostatic hypotheses assume that the topographic potential is fully compensated at all wavelengths, while is not the case in reality. We found that the maximum degree of compensation for the topographic potential based on the new Moho model is 60, corresponding to the resolution of about 330 km. Other (dynamic) isostatic effects (such as temporal compensation, plate tectonics, post-glacial rebound, etc) should be considered as well, which are disregarded in this thesis. Numerical results imply that the dynamic phenomena affect mostly the long-wavelengths. The VMM model is applied for different purposes. The Moho density contrast is an important parameter for estimating the Moho depth, and we present a technique to simultaneously estimate Moho depth and density contrast by the VMM and seismic models. Another application is the recovery of gravity anomaly from Satellite Gravity Gradiometry (SGG) data by a smoothing technique, and we show that the VMM model performs better than the Airy-Heiskanen isostatic model. We achieved an rms difference of 4 mGal for the gravity anomaly estimated from simulated GOCE data in comparison with EGM08, and this result is better than direct downward continuation of the data without smoothing. We also present a direct method to recover Moho depth from the SGG mission, and we show that the recovered Moho is more or less of the same quality as that obtained from terrestrial gravimetric data (with an rms error of 2 km). Moreover, a strategy is developed for creating substitutes for missing GOCE data in Antarctica, where there is a polar gap of such data. The VMM model is further used for constructing a Synthetic Earth Gravity Model (SEGM). The topographic-isostatic potential is simple to apply for the SEGM, and the latter can be an excellent tool to fill data gaps, extending the EGMs to higher degrees and validating a recovery technique of the gravity field from a satellite mission. Regional and global tests of the SEGM yield a relative error of less than 3 % vs. EGM08 to degree 2160.
|
|
| 3. |
- Gido, Nureldin A. A.
(författare)
-
Monitoring lithospheric motions by Satellite geodesy
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding of global and local Earth’s dynamic processes is of great importance to the Earth’s system knowledge, human life, and sustainability goals (e.g. climatic change and geo-hazard assessment, etc.). The processes are largely affected by the Earth's mass distribution and redistribution, which can be quantified and modelled using simultaneous and complementary data from various geoscience and environmental near earth-orbiting artificial satellites. In this thesis, which is based on five peer-reviewed papers, we study the lithospheric motion and the Earth’s mass change in terms of gravity variation, using a combination of geodetic satellite data and non-geodetic observations. The first paper is concerned with using of gravimetric approach to model sub-crustal horizontal stresses in the Earth’s mantle and their temporal changes using the Gravity Recovery and Climate Experiment (GRACE) data, caused by geodynamical processes such as mantle convection, in Fennoscandia region. We show that the determined horizontal stresses obtained by a gravimetric method are consistent with tectonics and seismic activities. In addition, the secular rate of change of the horizontal stress, which is within 95 kPa/year, is larger outside the uplift dome than inside in the study area. In the second paper, permafrost thawing and its associated gravity change, in terms of groundwater storage (GWS) anomalies changes is studied using the GRACE data and other satellites (e.g. AIRS) and ground-based observations in the northern high-latitude regions. The results of a preliminary numerical analysis reveal a high correlation between the secular trends of greenhouse gases (CO2), temperature, and the equivalent water thickness in the selected regions. Furthermore, the GRACE-based GWS estimates attributed to the permafrost thawing is increased at the annual rates of 3 to 4 cm/year in selected study areas. The third paper investigates the large-scale GRACE-based GWS changes together with different hydrological models over the major oil reservoirs in Sudan. The outcomes are correlated with the available oil wells production data. Moreover, using the freely available Sentinel-1 data, the ground surface deformation associated with oil and water depletion is studied. Our results show that there is a significant correlation between the GRACE-based GWS anomalies and the extracted oil and water volumes. The trend of GWS anomaly changes due to water and oil depletion varies from -18.5 ± 6.3 to -6.2 ± 1.3 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 Synthetic Aperture Radar (SAR) data analysis using Persistent Scatterer Interferometry (PSI) method shows high rate of subsidence, i.e. -24.5 ± 0.85, -23.8 ± 0.96, -14.2 ± 0.85 and -6 ± 0.88 mm/year, over the selected study area.In the fourth paper, a combined Moho model using seismic and gravity data is determined to investigate the relationship between the isostatic state of the lithosphere and seismic activities in the study area (which includes East Africa, Egypt, Congo and Saudi Arabia). Our results show that isostatic equilibrium and compensation state are closely correlated to the seismicity patterns in the study area. This paper presents a method to determine the crustal thickness and crust-mantle density contrast, and consequently one can detect low-density contrast (about 200 kg/m3) and thin crust (about 30 km) near the triple junction plate tectonics in East Africa (Afar triple junction), which confirms the state of over-compensation in the rift valley areas. Furthermore, the density contrast structure of the crust-mantle shows a large correlation with the earthquake activity, sub-crustal stress and volcanic distribution across East Africa. The fifth and last paper investigates the ground surface deformation of Gävle city in Sweden using Sentinel-1 data and PSI technique, as well as analyzing the historical leveling data. The PSI technique is used to map the location of risk zones, and their ongoing subsidence rate. Our PSI analysis reveals that the centre of Gävle city is relatively stable with minor deformation ranging between -2.0 mm/year and +2.0 mm/year in the vertical and East-West components. Furthermore, the land surface toward the northeast of the city is significantly subsiding with an annual rate of about -6 mm/year. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposit distribution was correlated with PSI results, and it shows that the subsidence areas are mostly located in zones where the sub-surface layer is marked by artificial fill materials.
|
|
| 4. |
- Joud, Seyed Mehdi Shafiei, 1980-
(författare)
-
Contributions of Satellite Geodesy to Post-Glacial Rebound Research
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glacial Isostatic Adjustment (GIA) is a global and long-term process in the Earth, which began 21.5 millennia ago, according to many ice history modellers. One way to understand the processes of the Earth’s interior, the crustal deformation, and a key correction to estimate the climatological parameters is obtained by studying GIA.Our main objectives are to improve the gravimetric GIA modelling by utilizing some of the satellite geodesy missions leading to the land uplift and geoid rate models and to determine the geoid depression due to GIA. The isostatic rebound of the solid Earth is observable in some regions, e.g. in Fennoscandia, North America and Greenland, using some geodetic techniques, such as GPS. In view of physical geodesy, the mantle mass flow in the GIA process perturbs the observed gravity from a hypothetic isostatic state, which can be measured using satellite gravimetry techniques. We will extract the static and temporal gravity signals due to GIA from satellite gravimetry and present a mathematical relation to determining the solid Earth vertical movement due to GIA leading to gravimetric and combined land uplift rate models.We use an Earth Gravitational Model (EGM) determined from a number of satellite missions to produce regional geoid models and remove the perturbing effect of the crustal variation and topography from the geoid height resulting in topographic-isostatic geoid models. Then the geoid height signal due to GIA will be extracted using a spectral window and a multiple regression analysis. In North America and Fennoscandia, we find that maximum depressions of 13.8 and 9.2 m of the topographic-isostatic geoid model, respectively, are due to GIA.Using some analysing methods, a number of high-resolution regional gravimetric modelling methods have been investigated with respect to their compatibility with the GPS data and the data from the GIA forward models. We determine the GIA signal of the temporal geoid change by exploiting the monthly gravity field from Gravity Recovery And Climate Experiment (GRACE) satellite mission and investigate the capability of three mathematical methods, namely regression, principal component, and independent component analysis (ICA) in extracting the secular trend of the GRACE monthly gravity data. One of the results of this investigation is the success of the ICA method relative to the other methods of gravimetric modelling.Finally, we present a least squares combined Land Uplift rate Model (LUM) by assimilating the data from GPS and the gravimetric model, determined using the ICA method, into the GIA forward model and compare it with a recent GIA forward model, namely ICE-6G_C (Peltier et al. 2015). Their discrepancies, for the whole areas subject to epeirogeny in North America and Fennoscandia, vary from -1.8 to +3.3, and -0.45 to +0.75 mm/a, respectively, while for the areas near the centre of the uplifting regions these two models are shown to be in a complete agreement.
|
|
| 5. |
- Agha Karimi, Armin, et al.
(författare)
-
Multidecadal sea level variability in the Baltic sea and its impact on acceleration estimations
- 2021
-
Ingår i: Frontiers in Marine Science. - : Frontiers. - 2296-7745. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Multidecadal sea level variation in the Baltic Sea is investigated from 1900 to 2020 deploying satellite and in situ datasets. As a part of this investigation, nearly 30 years of satellite altimetry data are used to compare with tide gauge data in terms of linear trend. This, in turn, leads to validation of the regional uplift model developed for the Fennoscandia. The role of North Atlantic Oscillation (NAO) in multidecadal variations of the Baltic Sea is also analyzed. Although NAO impacts the Baltic Sea level on seasonal to decadal time scales according to previous studies, it is not a pronounced factor in the multidecadal variations. The acceleration in the sea level rise of the basin is reported as statistically insignificant in recent studies or even decelerating in an investigation of the early 1990s. It is shown that the reason for these results relates to the global warming hiatus in the 1950s−1970s, which can be seen in all eight tide gauges used for this study. To account for the slowdown period, the acceleration in the basin is investigated by fitting linear trends to time spans of six to seven decades, which include the hiatus. These results imply that the sea level rise is accelerated in the Baltic Sea during the period 1900–2020.
|
|
| 6. |
- Amin, Hadi, et al.
(författare)
-
A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters
- 2019
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 93:10, s. 1943-1961
-
Tidskriftsartikel (refereegranskat)abstract
- The geoid, according to the classical Gauss–Listing definition, is, among infinite equipotential surfaces of the Earth’s gravity field, the equipotential surface that in a least squares sense best fits the undisturbed mean sea level. This equipotential surface, except for its zero-degree harmonic, can be characterized using the Earth’s global gravity models (GGM). Although, nowadays, satellite altimetry technique provides the absolute geoid height over oceans that can be used to calibrate the unknown zero-degree harmonic of the gravimetric geoid models, this technique cannot be utilized to estimate the geometric parameters of the mean Earth ellipsoid (MEE). The main objective of this study is to perform a joint estimation of W0, which defines the zero datum of vertical coordinates, and the MEE parameters relying on a new approach and on the newest gravity field, mean sea surface and mean dynamic topography models. As our approach utilizes both satellite altimetry observations and a GGM model, we consider different aspects of the input data to evaluate the sensitivity of our estimations to the input data. Unlike previous studies, our results show that it is not sufficient to use only the satellite-component of a quasi-stationary GGM to estimate W0. In addition, our results confirm a high sensitivity of the applied approach to the altimetry-based geoid heights, i.e., mean sea surface and mean dynamic topography models. Moreover, as W0 should be considered a quasi-stationary parameter, we quantify the effect of time-dependent Earth’s gravity field changes as well as the time-dependent sea level changes on the estimation of W0. Our computations resulted in the geoid potential W0 = 62636848.102 ± 0.004 m2 s−2 and the semi-major and minor axes of the MEE, a = 6378137.678 ± 0.0003 m and b = 6356752.964 ± 0.0005 m, which are 0.678 and 0.650 m larger than those axes of GRS80 reference ellipsoid, respectively. Moreover, a new estimation for the geocentric gravitational constant was obtained as GM = (398600460.55 ± 0.03) × 106 m3 s−2.
|
|
| 7. |
- Amin, Hadi, et al.
(författare)
-
A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters
- 2020
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- According to the classical Gauss–Listing definition, the geoid is the equipotential surface of the Earth’s gravity field that in a least-squares sense best fits the undisturbed mean sea level. This equipotential surface, except for its zero-degree harmonic, can be characterized using the Earth’s Global Gravity Models (GGM). Although nowadays, the satellite altimetry technique provides the absolute geoid height over oceans that can be used to calibrate the unknown zero-degree harmonic of the gravimetric geoid models, this technique cannot be utilized to estimate the geometric parameters of the Mean Earth Ellipsoid (MEE). In this study, we perform joint estimation of W0, which defines the zero datum of vertical coordinates, and the MEE parameters relying on a new approach and on the newest gravity field, mean sea surface, and mean dynamic topography models. As our approach utilizes both satellite altimetry observations and a GGM model, we consider different aspects of the input data to evaluate the sensitivity of our estimations to the input data. Unlike previous studies, our results show that it is not sufficient to use only the satellite componentof a quasi-stationary GGM to estimate W0. In addition, our results confirm a high sensitivity of the applied approach to the altimetry-based geoid heights, i.e. mean sea surface and mean dynamic topography models. Moreover, as W0 should be considered a quasi-stationary parameter, we quantify the effect of time-dependent Earth’s gravity field changes as well as the time-dependent sea-level changes on the estimation of W0. Our computations resulted in the geoid potential W0 = 62636848.102 ± 0.004 m2s-2 and the semi-major and –minor axes of the MEE,a = 6378137.678 ± 0.0003 m and b = 6356752.964 ± 0.0005 m, which are 0.678 and 0.650 m larger than those axes of the GRS80 reference ellipsoid, respectively. Moreover, a new estimation for the geocentric gravitational constant was obtained as GM = (398600460.55 ± 0.03) × 106 m3s-2.
|
|
| 8. |
- Amin, Hadi, et al.
(författare)
-
Evaluation of the Closure of Global Mean Sea Level Rise Budget over January 2005 to August 2016
- 2019
-
Konferensbidrag (populärvet., debatt m.m.)abstract
- Sea level changes over time because of water mass exchange among the oceans and continents, ice sheets, and atmosphere. It fluctuates also due to variations of seawater salinity and temperature known as the steric contributor. GRACE-based Stokes coefficients provide a valuable source of information, about the water mass exchange as the main contributor to the Earth’s gravity field changes, within decadal scales. Moreover, measuring seawater temperature and salinity at different layers of ocean depth, Argo floats help to model the steric component of Global Mean Sea Level. In this study, we evaluate the Global Mean Sea Level (GMSL) budget closure using satellite altimetry, GRACE, and Argo products. Hereof, considering the most recent released GRACE monthly products (RL06), we examine an iterative remove-restore method to minimize the effect of artifact leaked large signal from ice sheets and land hydrology. In addition, the effect of errors and biases in geophysical model corrections, such as GIA, on the GMSL budget closure is estimated. Moreover, we quantify the influence of spatial and decorrelation filtering of GRACE data on the GMSL budget closure. In terms of the monthly fluctuations of sea level, our results confirm that closing the GMSL budget is highly dependent on the choice of the spatial averaging filter. In addition, comparing the trends and variations for both the global mean sea level time series and those estimated for mass and steric components, we find that spatial averaging functions play a significant role in the sea level budget closure.
|
|
| 9. |
- Amin, Hadi, et al.
(författare)
-
Quantifying barystatic sea-level change from satellite altimetry, GRACE and Argo observations over 2005–2016
- 2020
-
Ingår i: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 65:8, s. 1922-1940
-
Tidskriftsartikel (refereegranskat)abstract
- Time-varying spherical harmonic coefficients determined from the Gravity Recovery and Climate Experiment (GRACE) data provide a valuable source of information about the water mass exchange that is the main contributor to the Earth’s gravity field changes within a period of less than several hundred years. Moreover, by measuring seawater temperature and salinity at different layers of ocean depth, Argo floats help to measure the steric component of global mean sea level (GMSL). In this study, we quantify the rate of barystatic sea-level change using both GRACE RL05 and RL06 monthly gravity field models and compare the results with estimates achieved from a GMSL budget closure approach. Our satellite altimetry-based results show a trend of 3.90 ± 0.14 mm yr−1 for the GMSL rise. About 35% or 1.29 ± 0.07 mm yr−1 of this rate is caused by the thermosteric contribution, while the remainder is mainly due to the barystatic contribution. Our results confirm that the choice of decorrelation filters does not play a significant role in quantifying the global barystatic sea-level change, and spatial filtering may not be needed. GRACE RL05 and RL06 solutions result in the barystatic sea-level change trends of 2.19 ± 0.13 mm yr−1 and 2.25 ± 0.16 mm yr−1, respectively. Accordingly, the residual trend, defined as the difference between the altimetry-derived GMSL and sum of the steric and barystatic components, amounts to 0.51 ± 0.51 and 0.45 ± 0.44 mm yr−1 for RL05 and RL06-based barystatic sea-level changes, respectively, over January 2005 to December 2016. The exclusion of the halosteric component results in a lower residual trend of about 0.36 ± 0.46 mm yr−1 over the same period, which suggests a sea-level budget closed within the uncertainty. This could be a confirmation on a high level of salinity bias particularly after about 2015. Moreover, considering the assumption that the GRACE-based barystatic component includes all mass change signals, the rather large residual trend could be attributed to an additional contribution from the deep ocean, where salinity and temperature cannot be monitored by the current observing systems. The errors from various sources, including the model-based Glacial Isostatic Adjustment signal, independent estimation of geocenter motion that are not quantified in the GRACE solutions, as well as the uncertainty of the second degree of zonal spherical harmonic coefficients, are other possible contributors to the residual trend.
|
|
| 10. |
- Amin, Hadi
(författare)
-
Study on the Earth’s Surface Mass Variations using Satellite Gravimetry Observations
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our complex planet is continuously undergoing temporal and spatial changes. In this context, ongoing processes in the Earth subsystems (geosphere, biosphere, cryosphere, hydrosphere, and atmosphere) cause changes in the gravity field of the Earth across a wide range of temporal and spatial scales. Accordingly, by both spatially and temporally tracing our planet’s ever-changing gravity field, scientists can better constrain the underlying processes contributing to such dynamic changes of mass distribution within the Earth system. Monitoring the Earth’s gravity field and its temporal variations is essential, among others, for tracking disasters and specifying land areas with a high risk of flooding, earthquakes, and droughts, movements of tectonic plates, and providing accurate positioning through satellite positioning technology. On short-term timescales, temporal variations in the Earth’s gravity field are mainly caused by the movement of water in its various forms. Accordingly, sea-level variations and ice-sheet and glacier changes, which are known as critical indicators of global warming and climate change, can be accurately monitored by tracking the Earth’s gravity field changes. Since there is a close link between water redistribution and the Earth’s energy cycle, climate system, food security, human and ecosystem health, energy generation, economic and societal development, and climate extremes (droughts and floods), it is essential to accurately monitor water mass exchange between the Earth system components. Among all observational techniques, satellite gravimetry has provided an integrated global view of ongoing processes within the Earth system. The current generation of satellite gravimetry missions (the Gravity Recovery and Climate Experiment (GRACE) mission and its successor, GRACE Follow-On) has dramatically revolutionized our understanding of dynamic processes in the Earth’s surface and, consequently, has significantly improved our understanding of the Earth’s climate system. By considering different aspects of studying the Earth’s gravity field, this thesis brings new insights to the determination and analysis of the mass change in the Earth system. First, by studying the shortcomings of the common techniques of estimating the geoid potential, a new approach is examined that simultaneously estimates the geoid potential, W0, and the geometrical parameters of the reference Mean Earth Ellipsoid (MEE). In this regard, as the geoid needs to be considered as a static equipotential surface, the sensitivity of the estimations to the time dependent Earth’s gravity field changes is studied. Secondly, relying on the GRACE monthly gravity fields and the complementary observational techniques, and by pushing the limit of GRACE, mass redistribution over land and ocean is investigated. Within the ocean, satellite altimetry and Argo products are utilized along with the GRACE monthly solutions for quantifying the global barystatic sea-level change and assessing the closure of the global mean sea level budget. Over land, a region with relatively high temporal mass change (oil and water extraction) is chosen in which by taking advantage of having in-situ observations and hydrological models, the ability of GRACE products in quantifying the changes in groundwater storage is studied. In this frame, for both the ocean and land studies, different aspects of the processing of GRACE monthly gravity fields are investigated and GRACE inherent errors are addressed appropriately to arrive at reliable and accurate estimates of the Earth’s surface mass change. As the final contribution in this thesis, a rigorous analytical model for detecting surface mass change from the time-variable gravity solutions is proposed and examined in different case studies of surface mass change. Since the launch of the GRACE twin satellites, the GRACE(-FO) time-varying gravity fields are conventionally converted into the surface mass change using a spherical analytical model that approximates the Earth by a sphere. More recently, the analytical mass change detection model has been improved by considering an ellipsoid as the shape of the Earth, which improved the previous estimations of surface mass change, especially over high latitudes with relatively large mass change signals. However, by taking into account the real shape of the Earth and considering more realistic assumptions, a new analytical solution for the problem of surface mass change detection from the time-varying gravity fields is proposed in this thesis. It is shown that the simplistic spherical and ellipsoidal geometries are no longer tenable and the new model surpasses the common spherical approach and its ellipsoidal version.
|
|
