Experience with satellite navigation

Abstract

ONGC acquired a fully equipped geophysical survey vessel 'Anweshak' from USA in 1975. The vessel is fitted with a Satellite Navigation System (SATNAV) and it is the first Indian Vessel with SATNAV. During the first five months of operation 'Anweshak' has completed 5500 km of seismic, gravity and magnetic surveys off Coromandel Coast and the west of India. The SATNAV system of Anweshak uses doppler sonar in conjunction with gyrocompass for dead reckoning between satellite fixes. The system has proved to be very useful for carrying out seismic profiling on round the clock, all seasons basis with a fair accuracy. The system performance was excellent. Problems were encountered when water depths were less than 15 m and more than 180 m, as the doppler sonar returns from sea bottom were not clear. Besides continuous navigation on a mobile ship, the SATNAV system has been successfully used for accurate positioning of offshore drill-ships by using the system in a 3-D mode