Infrared Absorption Hygrometer

Abstract

A recording infrared absorption hygrometer which measures the absolute humidity in a 1-meter light path is described. Record is obtained on a remote self-balancing potentiometer. Use is made of the 1.37 p water vapor absorption band and a 1.24 reference band. Isolation is by means of transmission type interference band-pass liglit ' filters. Infrared detection is by means of a lead sulfide photocell and amplifier. Isolation filters are contained on a sector wheel which is rotated to chop an infrared beam. A self-balancing null system is employed whereby the energy in the absorption band is kept equal to the energy in the reference band at all times. Balance is maintained by automatically varying the temperature of the lamp supplying the infrared energy, and the temperature of the lamp is a measure of the water vapor in the sensing path. An index of the lamp temperature is obtained by means of a monitor photocell, and meter or recorder. Included is a discussion on the calibration and field tests made on the instrument at the Weather Bureau Laboratories, Washington, D. C.

Some studies of atmospheric transmittance on mauna loa

“…However, its use in routine studies has been greatly neglected until recent years when the U. S. Weather Bureau [12][13][14][15][16][17] and others l18, 19] have set up various types of hygrometers, filter radiometers, and spectl'oradiometers for water-vapor studies.…”

The 1956 Tornado Research Airplane Project Data

“…The instrumentation of the airplane included a Naval Research Laboratories axial-flow vortex thermometer [1] loaned by the Navy, a modified version of the Weather Bureau's infra-red hygrometer [2], a modified version of the VGH (velocity, gust, height) recorder [3] furnished by the National Advisory Committee for Aeronautics, a Kollsman recording pressure altimeter, several cameras, an Ampex tape (voice) recorder, an electric field meter, two two-channel Brown recorders, and the required associated gear. All instruments were checked and calibrated on the ground.…”