Orbit determination using dual crossing arc altimetry

Accurate knowledge of the position of an altimetric satellite is required for the altimeter range data to be effective in measuring ocean topography. This study addresses the use of high-precision altimeter data from NASA's TOPEX Mission in reducing the radial component of the orbit of the U.S. Navy's N-ROSS satellite. Simulated altimeter crossing arc residuals between the TOPEX and N-ROSS orbits are minimized using both geometric and dynamic techniques in an effort to reduce the N-ROSS radial error to a level comparable to that of TOPEX. Tracking of N-ROSS by the Navy's NAVSPASUR system is simulated, and crossover residuals are created from the TOPEX and N-ROSS orbits. A simple geometric fit is shown to reduce the radial component of the NAVSPASUR N-ROSS orbit error from 350 m RMS to below 10 m RMS. In comparison, the dynamic approach of estimating the initial conditions of the N-ROSS orbit using a twentieth degree and order gravity field and a combined data set of tracking and altimeter crossover data yields a 6 m RMS residual error. Sub-meter accuracy can be attained by geometrically fitting these residuals to remove long wavelength orbit error.