DORIS-based Precise Orbit Determination and its geodetic applications

DORIS (Doppler Orbitography Radio positioning Integrated by Satellite) is a space-based piggyback satellite system that when used as a terrestrial measurement system can provide an accuracy of 10 cm in the absolute position measurement and in the order of sub-cm accuracy in relative measurements. When it rides piggyback on any satellite system can provide an orbital accuracy up to cm level. Precise Orbit Determination (POD) is the process of accurately tracking the position and velocity of a satellite in orbit. DORIS is an excellent satellite tracking system supporting the precise orbit determination of satellites. The accuracy of the POD does not affect only the quality of the estimated orbit ephemerides, but also the quantities derived from a free-network solution, mainly the station coordinates and the Earth rotation parameters (ERP). The precisely determined orbit can be used in many altimetric applications including estimating the mean sea surface, marine geoid, and vertical land motion, to derive vertical deflection and mean dynamic topography. Apart from that, the gravity field variations can also be determined more precisely.  GNSS data observations alone have been used so far in India to study the plate tectonics movements and earthquake predictions in the Indian subcontinent. Since DORIS and GNSS both have homogeneous network distributions and are complementary to each other, the DORIS data observations can be combined with GNSS data observations to study plate tectonics movements and earthquake predictions more effectively. Not only that since in DORIS the signal is transmitted from the ground, but processing DORIS measurement residue helps us to better understand and model what occurs in between the layers of the atmosphere which can be used for precise tropospheric modeling.   This space-based geodetic measurement technique has been used for the past three decades the world over, for precise measurement on the ground as well as on all oceanographic and altimetric satellite missions, it has not been introduced in India so far. Since our Space Research Organization has been launching several satellite missions and DORIS is being used for computation of the precise orbits, this technique has come to stay for a long time. The National Centre for Geodesy was set up by the Department of Science and Technology at the IIT Kanpur has also plans to set up a Geodesy village, where the DORIS station is going to be established and our DORIS data will be used in defining ITRF.