Processing and validation of the ERS-1 radar altimeter data at the Italian PAF

In the frame of the realization of the Italian Processing and Archiving Facility (I-PAF), Nuova Telespazio developed, under ASI (Italian Space Agency) contract, a processing chain for ERS Radar Altimeter data based on new reconstruction algorithms of sea surface height corrected from geophysical effects, wind speed at nadir and significant wave height. As a result of this activity, the off-line product ERS-1.ALT.MPR (Mediterranean ERS-1 Radar Altimeter Product) has been defined. The brocedure used to extract the quantities stored in the MPR product is tailored for closed seas (like the Mediterranean Sea), where the occurrence of areas where the sea is almost flat is frequent: the algorithm used to exploit the altimetric data needs special care in the satellite-sea surface distance computation and in the SWH extraction. Moreover the weakness of the oceanographic signal to be detected implies a full exploitation of the spatial resolution of the Radar Altimeter measurement (20 Hz data). In order to validate this product different case studies have been defined using the Radar Altimeter data over the Mediterranean Sea in January 1993. In this paper we present the results obtained by the processing chain exploiting these data. Moreover the comparison of these data with the corresponding ones stored in the ERS-1.ALT.OPR altimetric product is shown. Finally the altimetric wind speed data have been compared with the collocated data provided by the ECMWF analysis and the altimetric significant wave height data have been compared with the collocated data provided by the WAM model developed at ECMWF.