Accession Number:

ADA199515

Title:

An Extension of the Split Window Technique for the Retrieval of Precipitable Water: Experimental Verification

Descriptive Note:

Corporate Author:

AIR FORCE GEOPHYSICS LAB HANSCOM AFB MA

Report Date:

1988-09-23

Pagination or Media Count:

7.0

Abstract:

The split window technique has been demonstrated to be a viable method of removing effects of atmospheric attenuation in order to make a more accurate estimate of surface properties. This technique has also been used to estimate low level water vapor fields. In this paper we make an extension to the split window technique such that it is possible to estimate total precipitable water. The essence of the split window technique is making observations of the earth in two differentially absorbing windows. We extend this technique by making observations in the split window under conditions where the atmospheric contribution to the upwelling radiance is essentially invariant, but the surface contribution changes markedly. Under these conditions it is possible to write a set of simultaneous equations and solve them for the transmittance at the two frequencies of the split window, and from those deduce the quantities of the primary absorber, water vapor. The conditions under which this extension is valid basically fall under two categories that of variation in time, and that of variation in space. Consecutive observations of a land surface from a geosynchronous satellite during the heating cycle of the day would be one example. Another would be observations from either a geosynchronous or polar orbiting satellite of immediately adjacent land and water surfaces with contrasting skin temperatures. This paper presents experimental verification of this extension to the split window technique utilizing the Visible Infrared Spin Scan Radiometer VAS and the Advanced Very High Resolution Radiometer AVHRR. Reprints.

Subject Categories:

  • Meteorology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE