Dual-satellite altimeter crossover measurements for precise orbit determination.

摘要

A technique for precision orbit determination of altimetric satellites using the differenced height measurements at the points where the ground tracks of two satellites intersect (dual satellite crossover measurements) has been developed and utilized. This technique is used to generate dual crossover measurements between any two altimetric satellite; although presented here, are the results for ERS-1-T/P and Geosat-T/P dual crossovers. The primary advantage of the dual crossover measurement occurs when one of the satellite orbits is much more accurately known than the other. Here, the T/P orbit is known to 2-3 cm rms, while ERS-1 and Geosat are known to 6-8 cm rms and 9-10 cm rms, respectively. Hence, the T/P orbit is fixed and used as a reference trajectory for the independent orbit determination of ERS-1 and Geosat. The ERS-1-T/P case addresses the issue of dual crossovers between two satellites orbiting the Earth and operating simultaneously, while the Geosat-T/P case investigates the possibility of using dual crossovers between two satellites with non overlapping mission times. Studies show that the time span between the two altimeter measurements used to create the dual crossovers can be on the order of one month or an integer number of years (including El Nino years) without absorbing oceanographic signals into the orbit. Analysis indicates that adjusting these orbits using the dual crossovers results in an improved satellite orbit as measured by an increase in the radial orbit accuracy and by better agreement of orbital arc-length overlaps. A secondary representation of the dual crossover measurement is also exploited. Results indicate that after proper editing, this representation provides equally good results. Finally, the ERS-1 orbits computed with dual crossovers are evaluated over Greenland where the limiting factor is the meter level single crossover residuals computed over the ice. However, it is demonstrated that even with these residuals, the sensitivity of the orbit to the dual crossovers is observed and additionally, it is shown that the meter level residuals are not dominated by satellite radial orbit error.