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 combin ation of elevation, vegetation coverage, water vapor content, and albe do characteristics (mostly governed by the terrain) are the major fact ors affecting cirrus cloud detection. Using the criteria of relative l ow 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 wa s found to more effectively mask ground signals than the 1.3827-mu m c hannel. Over targets having moderate elevation, dry conditions, minima l vegetation, and high albedos, both spectra regions present significa nt ground signals that can mistakenly be attributed to cirrus cloud pa rticles. It is strongly recommended that for accurate cirrus cloud det ection, both spectral regions around 1.38 mu m and 1.88 mu m be examin ed along with the above-mentioned factors.