Lead retrieval using visible and thermal AVHRR imagery: testing theoretical atmospheric and geometric effects with LEADEX data

On the scale of tens to hundreds of meters the release of heat from sea ice leads is an important component of the Arctic heat budget. On regional scales, however, their effects are difficult to assess without information on their distribution in time and space. Medium-resolution visible and thermal sensors such as the Advanced Very High Resolution Radiometer (AVHRR) or Operational Line Scanner (OLS) provide perhaps the best combination of spatial coverage and spectral information for studies of leads. However, both the atmosphere and the geometrical aspects of the sensors play a significant role in the retrieval of lead characteristics. The present authors apply results from previous analyses of the effects of sensor spatial resolution and atmospheric attenuation on the retrieval of lead characteristics from satellite visible and thermal data (Key et al., 1994; Stone and Key, 1993). The attenuation of upwelling thermal radiation by ice crystal precipitation, aerosols, and clouds has been modeled and is discussed in the context of lead detectability. Statistical and empirical models of the effects of sensor resolution (i.e., pixel size) are presented in the context of lead width estimation. Data collected during IBADEX (Beaufort Sea, March-April 1992) are used for validation.