Scattered solar radiance from cirrus clouds has traditionally been detected over land at 1.37 micrometer, a wavelength that is ordinarily opaque to the surface due to water vapor absorption. We describe a new pairwise regression method for spectral imagery that retrieves cloud signals in the vicinity of a partially transmitting band, such as the 1.13 micrometer band, over any type of spatially structured terrain. The method, which uses spatial filtering and linear regression to cancel the surface background, has been applied to several rural and urban AVIRIS scenes. With a single cloud or cloud layer in the scene, the 1.13 micrometer and 1.37 micrometer cloud signals are closely correlated. Since the two signals are absorbed differently by water vapor, the slope of the correlation plot indicates the column water vapor above the cloud and thus the approximate cloud altitude. The less strongly absorbed 1.13 micrometer signal is closely related to the cloud optical thickness and can be used by itself or in combination with the 1.37 micrometer signal to correct apparent surface reflectance spectra for cirrus cloud effects.

Date Published: 20 October 1999
PDF: 6 pages
Proc. SPIE 3756, Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research III, (20 October 1999); doi: 10.1117/12.366391

Published in SPIE Proceedings Vol. 3756:
Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research III
Allen M. Larar, Editor(s)