In the ERS-1 POD described in this Chapter, altimeter height measurements and crossover height differences have been used as tracking data or to monitor the radial orbit accuracy.
All altimeter data are retrieved from the ESA ERS-1 ``ocean product'' OPR02 (version 3.0) for repeat Cycle 9 of the Multi-disciplinary phase. This data set spans from 0:00 on 19 January till 0:00 on 24 February 1993 (36.0 days in total).
Before they are used in statistical analyses, the altimeter ranges are processed to relative sea heights based on the D-PAF or DUT orbits, subtracting the MSS93A mean sea surface model height provided on the OPR02 data set [Anzenhofer et al., 1994], and correcting for atmospheric delays, solid-earth and ocean tides, inverse barometric effect, and sea-state bias. Relative sea heights above a threshold of 5 m are rejected because they are expected to be erroneous. In addition, to avoid contamination by ocean tide model errors, data over shallow waters (depth less than 2251 m) are excluded. Remaining spurious data are removed by checking additional information (significant wave height, wind speed, peakiness of the waveforms, and measurement noise) on its merits. Afterwards, these relative sea heights are converted to crossover height differences and altimeter normal points.