Rain and ice flagging of Envisat altimeter and MWR data

Altimetry range, wave height, and wind speed measurements are often corrupted by two effects over the ocean: rain and sea-ice. Radiometer measurements, which provide the altimetric wet troposphere correction, are similarly corrupted by the presence of rain or sea-ice in the instrument's footprint. To avoid contamination of sea surface height measurements, it is imperative that data influenced by either of these effects be edited out. The waveform “peakiness” parameter, available on the GDR data sets is effective at identifying sea-ice returns when stringent thresholds are applied. The mean relationship between backscatter (sigma0) at the two altimeter frequencies allows one to flag data impacted by both rain and sea-ice. We present here a new method for flagging rain or sea-ice contaminated data, based on two-dimensional histograms of sigma0.