A PRECAUTION REGARDING CIRRUS CLOUD DETECTION FROM AIRBORNE IMAGING SPECTROMETER DATA USING THE 1.38-MU-M WATER-VAPOR BAND

A case study thai shows a malfunction of the water vapor channel at 1.38 mu m to detect cirrus clouds is presented in this article. A combination of elevation, vegetation coverage, water vapor content, and albedo characteristics (mostly governed by the terrain) are the major factors affecting cirrus cloud detection. Using the criteria of relative low radiance and high signal-to-noise ratio amongst several targets and across the 1.84-1.92 mu m spectral region, the 1.8489-mu m channel was found to more effectively mask ground signals than the 1.3827-mu m channel. Over targets having moderate elevation, dry conditions, minimal vegetation, and high albedos, both spectra regions present significant ground signals that can mistakenly be attributed to cirrus cloud particles. It is strongly recommended that for accurate cirrus cloud detection, both spectral regions around 1.38 mu m and 1.88 mu m be examined along with the above-mentioned factors.