We report results from the Eddy Experiment, where a synchronous GPS receiverpair was flown on an aircraft to collect sampled L1 signals and theirreflections from the sea surface to investigate the altimetric accuracy ofGNSS-R. During the experiment, surface wind speed (U10) was of the order of 10m/s, and significant wave heights of up to 2 m, as discussed further in acompanion paper. After software tracking of the two signals through despreadingof the GPS codes, a parametric waveform model containing the description of thesea surface conditions has been used to fit the waveforms (retracking) andestimate the temporal lapse between the direct GPS signals and theirreflections. The estimated lapses have then been used to estimate the seasurface height (SSH) along the aircraft track using a differential geometricmodel. As expected, the precision of GNSS-R ranges was of 3 m after 1 secondintegration. More importantly, the accuracy of the GNSS-R altimetric solutionwith respect to Jason-1 SSH and in situ GPS buoy measurements was of 10 cm,which was the target with the used experimental setup. This new result confirmsthe potential of GNSS-R for mesoscale altimetric monitoring of the ocean, andprovides an important milestone on the road to a space mission.
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