Improved Orbit Determination of the CYGNSS Satellites and its Application to GNSS-R Ocean Altimetry

摘要

The accuracy of spaceborne ocean surface altimetry depends on precise knowledge of the altimeter satellite orbit. Previous studies of the potential utility of CYGNSS GNSS Reflectometry (GNSS-R) measurements for ocean altimetry have identified its orbit error as a limiting factor. To address this, a recent firmware upgrade to the CYGNSS satellites has enabled the downlink of additional GPS raw measurements from the navigation receiver and increased numerical precision of open-loop GNSS-R tracking information. In this paper, we present improvements to the accuracy of both the orbit determination and the ocean surface height retrievals as a result of these recent upgrades. JPL's GipsyX software is used to process 170 days of GPS navigation measurements for one of the 8 CYGNSS satellites. Incorporating high fidelity dynamic models and antenna group delay corrections, daily orbit overlaps throughout the period show mean RMS differences of 2.5 cm in height, 5.9 cm in cross-track, and 10 cm in along-track. Applying these new orbits reduced the standard deviation of retrieved sea surface height anomalies from 2.2 m to 1.9 m using 4 second smoothed measurements. Further improvements are expected using new ionospheric corrections and re-tracking methods currently in development.