Correction of thin cirrus effects in the 0.4- to 1.0-um region using the 1.375-um cirrus-detecting channel

Abstract

Using spectral imaging data acquired with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) from an ER-2 aircraft at 20 km altitude during various field programs, it was found that narrow channels near the center of the strong 1 .38-jim water vapor band arevery effective in detecting thin cirrus clouds. Based on this observation from AVIRIS data, a channel centered at 1 .375im with a width of 30 nm was selected for the Moderate Resolution Imaging Spectrometer (MODIS) for remote sensing of cirrus clouds from space. The sensitivity of the 1 .375-jim MODIS channel to detect thin cirrus clouds during the day time is expected to be one to two orders of magnitude better than the current infrared emission techniques. As a result, much larger fraction of the satellite data is expected to be identified as being covered by cirrus clouds. In order to make better studies of surface reflectance properties, thin cirrus effects must be removed from satellite images. We have developed an empirical approach for removing/correcting thin cirrus effects in the 0.4 - 1.0 j.tm region using channels near 1 .375 tim. This represents a step beyond the detection of cirrus clouds using water vapor absorption channels.