An optimal approach for the development of precise regional geoid in Pakistan through a comparative study with least square collocation and FFT techniques

摘要

This study attempts to develop a strategy of data management, processing, evaluation, and analysis that best suits for the regional gravimetric geoid in Pakistan where gravimetric data is sparse. A high-precision gravimetric geoid has been developed covering the Salt Range and Kohat-Potowar Plateau along with Punjab and KPK plain area south of it bounded by latitude 30-33N and longitude 70-73E and with random data distribution. The study also covers the analysis and comparison of observed gravity data with GETECH Bouguer anomalies. The gravity prediction error study was carried out using least square collocation (LSC) at the data gaps and at GETECH locations for data quality analysis. Covariance analysis of both datasets using LSC was made for error study and compared with covariance function by FFT technique. Variety of datasets, e.g., observed gravity; GETECH Bouguer anomalies, SRTM30 digital elevation model, and observed leveling data were combined with global geopotential model through LSC and FFT techniques. The geoid model was computed by applying high-frequency corrections from observed gravity and topography to the Earth Gravity Model 1996 global geopotential model in a remove-restore procedure. The elevation grids with 30aEuro(3) 5' and 18' resolutions gave a best possible statistics in combination with the EGM96 reference field to order and degree 360. The results of bias parameter N (o) estimation and adjustment were compared with draping of GPS/leveling height anomalies for final fitting of the geoid; LSC- and FFT-derived height anomalies were found to be comparable after the N (o) adjustment and draping with respect to GPS/leveling.