Aerial Measurement of Radiation Temperatures over Mt. Fuji and Tokyo Areas and Their Application to the Determination of Ground- and Water-Surface Temperatures

Abstract

A Barnes PRT-4 portable radiometer with a spectral response in the 8–14 μ range was used to determine the equivalent blackbody temperature of 1) the slope of Mt. Fuji, 2) Sagami Bay, and 3) the city of Tokyo. A twin-engine aircraft was used to fly over these areas at various altitudes up to 12,000 ft. Through mapping the slope temperatures of Mt. Fuji, it was learned that the rocky slope heats up under the morning sun very rapidly to 32C almost irrespective of the elevation. The distribution of measured temperatures explains the reasons for the rapid growth of cumulus clouds along the east slope in the early morning hours. The nadir angle and the height dependence of equivalent blackbody temperatures measured over Tokyo and Sagami Bay were examined. The measured temperatures were compared with those computed from the radiative transfer equation. It was found that the values over Tokyo are reproduced fairly well by the addition of a graybody smog filling the layers up to 910 mb. To express the effects of atmospheric radiation upon the reduction of the radiant emittance from the surface, a damping factor was introduced. The factor which designates the reduction of the amplitude of the surface temperature when measured from aircraft or satellites must be known to an accuracy of about 10% in order to estimate the true temperature variation or gradient from measured equivalent blackbody temperatures. Further investigation of the temperature damping is necessary to determine accurately the radiometric sea-surface temperature.