Derivation of a threshold function for the Advanced Very High Resolution Radiometer 3.75 µm channel and its application in automatic cloud discrimination over snow/ice surfaces
Abstract:The distinct contrast between the reflectance of solar radiation in Advanced Very High Resolution Radiometer (AVHRR) channel 3 (3.75 µm) by clouds and by bright surfaces provides an effective means of cloud discrimination over snow/ice surfaces. A threshold function for the top-of-atmosphere (TOA) albedo in channel 3 (r3) is derived and used to develop an improved method for cloud discrimination over snow/ice surfaces that makes explicit use of TOA r3. Corrections for radiance anisotropy and temperature effects are required to derive accurate values of r3 from satellite measurements and to utilize the threshold function. It has been used to retrieve cloud cover fractions from National Oceanic and Atmospheric Administration (NOAA)-14 AVHRR data over the Arctic Ocean and over the North Slope of Alaska (NSA) Atmospheric Radiation Measurement (ARM) site in Barrow, Alaska. The retrieved cloud fractions are in good agreement with SHEBA (Surface HEat Budget of the Arctic Ocean) surface visual observations and with NSA cloud radar and lidar observations, respectively. This method can be utilized to improve cloud discrimination over snow/ice surfaces for any satellite sensor with a channel near 3.7 µm.
Document Type: Research Article
Affiliations: 1: QSS Group Inc., 4500 Forbes Blvd, Lanham, MD 20706, USA and Office of Research and Applications, National Environmental Satellite Data and Information Service, NOAA Camp Springs MD 20746 USA 2: Geophysical Institute University of Alaska Fairbanks Fairbanks AK 99775 USA 3: Steven Institute of Technology Hoboken NJ 07030 USA 4: Scripps Institution of Oceanography University of California La Jolla CA 92093 USA
Publication date: 2004-08-01