Exploitation of the ENVISAT radar altimeter individual echoes and S-band data for ocean, coastal zone, land and ice/sea ice altimetry (RAIES). Task 6: Scientific applications of S-band data

Abstract

This report presents the results of Task 6 of the study led by the Southampton Oceanography Centre under ESRIN Contract No.17900/03/I-LG in response to AO/1-4539/03/I-LG on the Exploitation of the ENVISAT Radar Altimeter Individual Echoes and S Band Data for Ocean, Coastal Zone, Land and Ice/Sea-Ice Altimetry (RAIES). This report first reviews the findings relating to scientific applications of RA2 S-band data for the ocean and the coastal zone, including improved rain, wind and wave products. Using a combination of numerical waveform simulations and comparisons with ERS2 and buoy data, the added value provided by S-band measurements to estimate range, wave height and backscatter was examined. S-band measurements over the ocean and in the coastal zone appear much noisier than Ku-band and ERS measurements when validated against SWH buoy data. However, S-band σ⁰ values are found to be less affected by rain than Ku-band σ⁰. Ionospheric corrections based on RA-2 dual frequency data show good agreement with those obtained from the JPL Global Ionospheric Maps (GIM). Global analyses show that S-band anomalies occur globally, with slight preference over Indonesia and descent over South America, plus poles. No periodicity is evident, indicating a likely instrumental origin. A new approach to estimating sea state bias at S-band using theoretical and empirical formulations is proposed.

The second part of the report presents the scientific applications with S-band data over land and ice/sea ice surfaces. Overall, the use of S-band for land/ice surfaces sounds promising. Extremely good echo retrieval is achieved at S-band over land surfaces, attributed to the width of the S band range window. Over sea ice, intriguing variations in the complex echo shapes are seen between Ku and S-band. Unexpected temporal variations are observed in many categories of waveform shape at S-band, which are not mirrored at Ku-band. This strongly indicates that the information content at S band differs significantly from that at Ku band over land as well as ice surfaces. This makes S-band data a valuable addition for non-ocean studies, and fully justifies the need to include S-band in the analysis of RA-2 waveforms.

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