Threshold Values for Weather Filters in AMSR2 Sea Ice Concentration Retrieval Algorithms

The performance of weather filters in satellite passive microwave sea ice concentration retrieval algorithms is analyzed under conditions of high winds. The analysis is based both on numerical modeling results and on the measurements of the Advanced Microwave Scanning Radiometer 2 (AMSR2) over high wind areas. It is shown that when the threshold values for the gradient ratios are used to classify measurements as being taken over open water, sea surface wind speed geophysical model function (GMF) uncertainty plays an important role in such weather filtering. The GMF uncertainty at higher AMSR2 frequencies is mostly pronounced at high winds. The gradient ratios are calculated using the radiative transfer modeling for the conditions of non-precipitating atmosphere and an ensemble of atmospheric meteorological profiles combined with ocean parameter data. The threshold values for the gradient ratios are set up basing on numerical calculations.