Classification of sea ice types with single‐band (33.6 GHz) airborne passive microwave imagery

Abstract

During March 1983 extensive high‐quality airborne passive K a band (33.6 GHz) microwave imagery and coincident high‐resolution aerial photography were obtained of ice along a 378‐km flight line in the Beaufort Sea. Analysis of these data suggests that four classes of winter surfaces can be distinguished solely on the basis of 33.6‐GHz brightness temperature: open water, frazil, old ice, and young/first‐year ice. New ice (excluding frazil) and nilas display brightness temperatures that overlap the range of temperatures characteristic of old ice and, to a lesser extent, young/first‐year ice. Scenes in which a new ice or nilas are present in appreciable amounts are subject to substantial errors in classification if static measures of K a band radiometric brightness temperature alone are considered. Textural characteristics of nilas and new ice, however, differ significantly from textural features characteristic of other ice types and probably can be used with brightness temperature data to classify ice type in high‐resolution single‐band microwave images. In any case, open water is radiometrically the coldest surface observed in any scene. Lack of overlap between brightness temperatures characteristic of other surfaces indicates that estimates of the areal extent of open water based on only 33.6‐GHz brightness temperatures are accurate.