Sadiq M.,National Engineering and Scientific Commission NESCOM Islamabad |
Ahmad Z.,Quaid-i-Azam University
Arabian Journal of Geosciences | Year: 2015
The gravimetric geoid model can be used as vertical reference in surveying and other related technologies. It is being developed by NESCOM in collaboration with the Department of Earth sciences QAU, Survey of Pakistan and Directorate General of Petroleum Concessions (DGPC). The data collection, selection, and analysis to make the data suitable for this purpose are being carried out. About 77,834 land gravity observations along with leveling and 11,787 Bouguer/free-air anomalies from GTECH are available and readily accessible. While GPS/leveling data for the whole Pakistan region is required and is being collected from different sources, though its density and quantity is not good enough for better calibration of gravimetric geoid. This study involves the feasibility and application of different datasets for the development of geoid model of Pakistan. The SRTM30 digital elevation model has been selected for topographic corrections and reductions due to its relatively better statistical comparison with local elevation data. Both least square collocation and FFT methods have been applied for this study. Two realistic studies have been carried out for global geopotential model selection based on statistical findings and evaluation of geoid-quasigeoid separation term in Pakistan. Geoid-quasigeoid separation term is an integral part of “Restore step” for geoid modeling with the utilization of the solution of the Molodensiky’s geodetic boundary value problem. The digital elevation model comparison with local leveling data shows that SRMT30 model is relatively better in accuracy (in terms of mean and standard deviation) than other counterparts such as Globe30, GTOPO30, and ETOPO2, etc. The results of geoid modeling have revealed that there exists a height bias of −70 cm between local vertical datum and global mean sea level. © 2014, Saudi Society for Geosciences.