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Norman B. Foster
and
Laurence W. Foskett
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Laurence W. Foskett
and
Norman B. Foster

A simple grating spectrophotometer is used in conjunction with a tungsten filament lamp and projector to measure directly the precipitable water in the atmosphere. Utilization is made of the 1.380 μ water vapor absorption band and the 1.250 μ region for a point of reference. Vacuum thermocouples and high sensitivity galvanometer are employed for energy measurement. Included is a discussion on the calibration and field tests made at the Laboratory of the Institute of the Aeronautical Sciences, Sands Point, Long Island, New York, August and September, 1942. Calibration tests were conducted over optical paths of from 1.5 meters to 52 meters; precipitable water paths were from 0.0023 centimeter to 0.083 centimeter.

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LAURENCE W. FOSKETT
,
NORMAN B. FOSTER
,
WILLIAM R. THICKSTUN
, and
REX C. WOOD

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 µ water vapor absorption band and a 1.24 µ reference band. Isolation is by means of transmission type interference band-pass light 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.

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