Cloud detection over the Arctic region using airborne imaging spectrometerdata during the daytime

Detection of clouds over arctic regions from current satellite radiometric measurements in the visible and IR atmospheric window regions, such as thos e of Advanced Very High Resolution Radiometer and Landsat, is often difficu lt due to the high albedos of snow- and ice-covered surfaces in the visible and the nearly isothermal temperature profiles in the lower atmosphere. In this paper the authors show that the water vapor absorption channel at 1.3 8 mu m is effective in detecting high clouds over snow- and ice-covered sur faces in the Arctic. Low-level clouds can be detected from surface snow and sea ice using a narrow channel centered at 1.5 mu m with a width of approx imately 10 nm because of the dark background that results from strong absor ption by snow and sea ice. Imaging data with contiguous spectral coverage b etween 0.4 and 2.5 mu m acquired with the Airborne Visible/Infrared Imaging Spectrometer during the Arctic Radiation Measurements in Column Atmosphere -Surface System in Alaska in 1995 are analyzed. The authors have observed t hat as wavelength increases from 1.38 mu m the atmospheric water vapor abso rption becomes weaker and weaker and the low-level clouds and surface tundr a are increasingly seen. It is always possible to locate a narrow channel i n the spectral range of 1.38-1.50 mu m with appropriate water vapor absorpt ion strength to separate water and ice clouds from surface snow, sea ice, a nd tundra. The simple cloud-masking technique described here is directly ap plicable to cloud detection during the daytime from hyperspectral imaging d ata over arctic regions, which will be acquired with future satellite senso rs.