A Two-Path, Two-Wavelength Ultraviolet Hygrometer

Abstract

An ultraviolet-absorption hygrometer for airborne use was designed and tested. Here the principles of operation, the design, and the results of the first test flights are presented. The motivation for the new design is to overcome the shortcomings of existing Lyman-α devices. To solve the problem of source drift, a second optical path is employed as a reference. To address the problem of window contamination, a second ultraviolet wavelength is used. In addition, detector offsets are measured and subtracted from the signals. The flight data clearly demonstrate the value of both the reference detector and the second wavelength.