Gravity Field Parameters Estimation and precise Geoid Modeling in Pakistan with additional study on the Data processing and combination of twin GRACE Satellites using SRTM Topography, EGM96 Model and Ground Gravity Data

Abstract

The main objective of this thesis is the gravity field and geoid modeling in Pakistan using the solution of Molodensky's geodetic boundary value problem. Based on basic principles of potential theory, a definition of the above mentioned geodetic boundary-value problem is presented, with its possible solutions both in gravity and geometrical spaces leading to practical solutions. For the application of these formulations, an appropriate procedure has been developed for the data management, evaluation and analysis that best suits for the establishment of gravimetric geoid model of Pakistan. To analyze the procedure, a high precision gravimetric geoid of Pakistan has been developed bounded by 23.50-37.0833330 N latitude and 60.50-780 E longitude with random data distribution. Different types of datasets, e.g., observed gravity, GETECH Bouguer anomalies, Shuttle Radar Topographic Mission (SRTM30) digital elevation model and observed GPSLevelling data WGre combined with global geopotential model EGM96 for the desired solution. The geoid model has been computed by applying high-frequency corrections from observed gravity and topography to the Earth's Global geopotential model EGM96 following the Remove-Restore scheme. Both least squares collocation (LSC) and Fast Fourier Transform (FFT) mathematical techniques have been explored to estimate the residual height anomalies. An optimum covariance model has been developed and analysis of the observed dataset using LSC was made for error study and its comparison was also made with FFT based covariance functions. Different Reference elevation grids generated from SRTM30 were tested for best possible statistics with least average value of the residual gravity anomaly in the remove step. The elevation grids with 30'1, 21 and 181 (arc minutes) resolutions gave best possible statistics in combination with the EGM96 reference field to order and degree 360. This study also covers the analysis of observed gravity data and GETECH Bouguer anomalies for gravity field modeling. The gravity field prediction error study was carried out using least square collocation at the data gaps and at GETECH locations for quality checks and outlier detection. The height system bias parameter No has been estimated using LSC and adjustment was made using GPS/leveling height anomalies for final fitting of the height anomaly/geoid with local vertical datum. A regional gravity field model has ' been established through the development of best possible residual terrain model for the Pakistan area and interpolation techniques, i.e., Spline & Lagrange interpolation with least squares adjustment. The model has an accuracy of 30 mgal with ±2a standard deviation. An additional study has been made during this research on the satellite data processing, for gravity field recovery. Full Precession-Nutation theory based on IAU2000 has been implemented in a software RR2POT.BAS for the processing of twin GRACE satellite's kinematics data. The least squares collocation solution for the combination and downward continuation of CHAMP, GRACE using ground gravity data at the Earth surface has been used for Pakistan's regional gravity modeling and gravity field recovery. Major tectonic structure identification has been made in Pakistan and surrounding area by the use of global gravity model EGM08 and monthly GRACE satellite solutions. The geoid slope reSolves more clearly the major tectonic structures (MBT, MMT, MKT, CHAMAN, PAMIR and H.[:R fl. -p.·fau./ts.. etc.) as compared to topography, free air anomaly and geoid itself.