Flat Plate Radiometer (FPR)

Description

The Flat Plate Radiometer (FPR) system was designed to provide a measurement of the global distribution of reflected solar and long-wave radiation leaving the earth. The FPR system was comprised of four infrared sensors, an analog-to-digital converter, a commutator, and a tape recorder. Two pairs of radiometers were mounted on opposite sides of the spacecraft. A cone shield was employed on two of the radiometers to isolate or reduce any response due to direct solar radiation. The field of view on the other two instruments was unrestricted. Both types of radiometers used a coated (either black or white) aluminum disk as the sensing element. The disk temperature was measured by two thermistors hung on the black surface of the disk. The black-coated disk responded to the sum of the reflected solar, direct solar, and emitted long-wave radiation. The white disk reflected in the visual range but absorbed in the infrared (7 to 30 micron) range. Identical experiments were flown on the ESSA 3, 5, and 7 spacecraft. For a full description of the ESSA flat plate radiometer, see 'Studies in Atmospheric Energetics Based on Aerospace Probings, Annual Report - 1966,' University of Wisconsin, pp 111-129, Mar. 1967. The radiometer performed normally, and good data were obtained from launch until April 4, 1970, when an electronic failure occurred in the temperature calibration circuitry. The experiment was turned off on May 21, 1970.