PASSIVE MICROWAVE ALGORITHMS FOR SEA-ICE CONCENTRATION - A COMPARISONOF 2 TECHNIQUES

The most comprehensive large-scale characterization of the global sea ice cover so far has been provided by satellite passive microwave data . Accurate retrieval of ice concentrations from these data is importan t because of the sensitivity of surface flux (e.g., heat, salt, and wa ter) calculations to small changes in the amount of open water (leads and polynyas) within the polar ice packs. Two algorithms that have bee n used for deriving ice concentrations from multichannel data are comp ared. One is the NASA Team algorithm and the other is the Bootstrap al gorithm, both of which were developed at NASA's Goddard Space Flight C enter. The two algorithms use different channel combinations, referenc e brightness temperatures, weather filters, and techniques. Analyses a re made to evaluate the sensitivity of algorithm results to variations of emissivity and temperature with space and time. To assess the diff erence in the performance of the two algorithms, analyses were perform ed with data from both hemispheres and for all seasons. The results sh ow only small differences in the central Arctic in winter but larger d isagreements in the seasonal regions and in summer. In some areas in t he Antarctic, the Bootstrap technique shows ice concentrations higher than those of the Team algorithm by as much as 25%; whereas, in other areas, it shows ice concentrations lower by as much as 30%. The differ ences in the results are caused by temperature effects, emissivity eff ects, and tie point differences. The Team and the Bootstrap results we re compared with available Landsat, advanced very high resolution radi ometer (AVHRR) and synthetic aperture radar (SAR) data. AVHRR, Landsat , and SAR data sets all yield higher concentrations than the passive m icrowave algorithms. Inconsistencies among results suggest the need fo r further validation studies. (C) Elsevier Science Inc., 1997.