A MICROWAVE TECHNIQUE FOR MAPPING THIN SEA-ICE

A technique is presented for mapping the distribution of new, young an d first-year sea ice in seasonal sea ice zones that utilizes microwave spectral and polarization information from the Defense Meteorological Satellite Program Special Sensor Microwave/Imager. The motivation for this work stems from the need for accurate estimates of open water an d thin ice within the Arctic ice pack. The technique utilizes the micr owave polarization and spectral characteristics of these three ice typ es through two microwave radiance ratios: the 19.4 GHz polarization an d the spectral gradient ratio, which is a measure of the spectral diff erence between the 19.4-GHz and the 37.0-GHz vertically polarized radi ance components. The combined use of the spectral gradient ratio and p olarization reduces the low ice concentration bias generally associate d with the presence of thin ice types. The microwave polarization, whi ch is sensitive to changes in ice thickness and ice surface characteri stics, is used to classify new, young, and first-year ice types. The p olarization varies from about 0.3 for calm ice-free water, to about 0. 15 for new ice, and to 0.03 for thick first-year ice. On the basis of this parameterization, improved sea ice concentration maps and maps of new, young and first-year ice type distributions are derived. Example s from the Bering Sea are presented and comparisons are made with anal yzed NOAA AVHRR imagery.