Using global positioning system for orthometric height determination for gravity surveys in Ladakh Himalaya

Though GPS can be used for precise 3-D positioning, the height thus measure d is spheroidal which needs to be converted to the orthometric height for a ny practical use. This requires knowledge of the geoid undulation that can either be measured using GPS/levelling technique, or can be modelled from g ravity data. We carried out extensive field measurements along a 100 km lon g transect in Ladakh Himalaya to study the viability of using the GPS for o rthometric height determinations required for gravity surveys. Geoid of the study area was also predicted using global gravity models, e.g. OSU91 and EGM96. It is seen that even on high and difficult terrain like that of the Himalaya, GPS can be used for orthometric height determination with an abso lute accuracy of 1-2 m.