Arctic leads (open or refrozen fractures in sea ice) provide for the exchange of heat between the ice/ocean surface and the atmosphere. Their influence on the energy budget is not easy to quantify, however, because little is known about their spatial and temporal distributions due to the difficulty in detecting and mapping leads using remote sensing techniques. The way in which thermal contrast between leads of varying widths and thicknesses can be distinguished from the background multiyear ice surface under varying atmospheric conditions is examined. The normalized brightness temperature difference between image pixels that include lead fractions and of the background ice is used in an attempt to determine thresholds of detection accounting for sensor field-of-view and various atmospheric phenomena that influence the Arctic radiation balance during winter. Brightness temperatures are derived from modeled top-of-the-atmosphere radiances for three thermal channels (3, 4 and 5) of the Advanced Very High Resolution Radiometer. Surface temperatures are prescribed as a function of ice thickness and the effects of the intervening atmosphere are simulated by varying the optical depths of hypothetical cloud or haze layers varying in microphysical characteristics. Results indicate that the limits of lead detection may be determined as a function of pixel lead fraction and atmospheric optical depth if suitable values of normalized contrast are used as detection criteria.

For example, given a pixel resolution of 1.0 km and the presence of a layer of ice crystals having a visible optical depth of 0.6 just above the surface, the minimum detectable lead width is estimated to be between 400 m and 750 m depending on what threshold criteria are used which, in turn, depends on the homogeneity of the multiyear ice surface. For the same conditions and range of threshold criteria but assuming a layer optical depth of 0.3, the minimum detectable lead width decreases to between 290 m and 560 m. Minimum detectable lead widths are also found to depend on the microphysical and physical properties of any intervening atmospheric layer. Our simulations indicate that narrower leads are detectable when hazy conditions exist than when stratiform water or ice clouds are present for any given layer optical depth. ¿ American Geophysical Union 1993