TECHNIQUES FOR ANALYZING LEAD CONDITION IN VISIBLE, INFRARED AND MICROWAVE SATELLITE IMAGERY

The condition of a lead or polynya, whether open, partially refrozen, or completely ice covered, is extremely important from many points of view. From a meteorological and climatological perspective the moistur e and heat flux resulting from air and sea interaction over leads duri ng cold weather periods is crucial. Enormous cloud plumes have been ob served emanating from relatively small openings in leads and polynyas. Modeling studies have shown that plume development is extremely sensi tive to changes in humidity, air temperature, and the nature of near-s urface atmospheric lapse rates. The studies indicate that plumes can e xist, even in the refreezing process, until the new ice becomes suffic iently thick so that its temperature approaches the temperature of the surrounding ice. Heat balance studies for modeling the arctic environ ment depend upon knowledge of such distinctions for accurate assessmen t of the radiation balance over the area at any given time. This paper describes a new visible channel differencing technique shown to have some capabilities in distinguishing between open and refrozen leads an d, in larger leads, distinguishing the part that is open from that whi ch is partially or newly refrozen. Output from this technique is corre lated with infrared data in two examples over the Beaufort Sea and in a polynya example with additional microwave data over the Laptev Sea. Although in situ evidence for direct documentation of lead condition i s limited, the existence of cloud plumes emanating from open leads pro vides some verification and establishment of remote sensing parameters indicative df an open or closed condition. A logical consistency of v alues from independent sensors over varying conditions of open water, mixed ice and water, new ice, and first or multiyear ice also provides contributing remote sensing evidence of lead condition.