Investigating the Congruence between Gravimetric Geoid Models over India

Abstract

A major motivation of precise geoid computation is to adopt it as a national vertical datum or as an alternative vertical reference surface to aid surveyors in calculating physical heights using the Global Navigation Satellite System (GNSS). There exist several methods of geoid computation, and only one particular method is generally used to calculate the national geoid model irrespective of the size and topographical landforms of the country. The validation of the developed geoid models is done with the complete GNSS-leveling data set. In such a case, it is hard to claim the consistency in the precision of the developed geoid model throughout the country. This study aims to identify the consistency of the geoid models over India computed using the three approaches primarily followed in Curtin University of Technology (CUT), the University of New Brunswick (UNB), and the Royal Institute of Technology (KTH). Three analyses have been done on the calculated geoid models: (1) clusterwise validation with the GNSS-leveling data, (2) intermodel comparison for the whole study area, and (3) intermodel comparison for Indian states and Union Territories (UT) only. The GNSS-leveling validation results show that the standard deviations of differences for all the methods are within a range of ±0.01 m with the exception of Uttar Pradesh West with the UNB method. However, inter-model comparison shows that the mean (meters) and standard deviation (meters) of the differences between the pairs (CUT-UNB), (CUT-KTH), and (KTH-UNB) are 0.241±0.854, −0.133±0.498, and 0.374±1.239, respectively, with maximum difference sometimes exceeding 5 m. There is only one UT and four states for which the mean value is within (−0.20 m, 0.20 m) and standard deviation ≤±0.05 m for all the three pairs. Therefore, the analysis shows that it is difficult to calculate a precise national geoid model using any one method alone and a strategy is required to merge various regional precise geoid models or methods to develop a consistently precise national geoid model.