High Altitude Radiometric Measurements of Cirrus

Abstract

Based on aircraft measurements of the radiant emittance of cirrus clouds and cloudless sky, the 8-13? infrared transmissivity of high cirrus clouds was calculated. The measurements and applied calculations were made for cirrus clouds up to 5 km thick at altitudes ranging from 25,000-42,000 ft. Results of the calculations of transmissivity ranged from 95% for high, thin cirrus to 53% for 5 km thick cirrus. The transmissivity results were applied to radiative transfer calculations in an attempt to reduce discrepancies between in situ measurements and calculations. The application of the measured transmissivities in the calculations did, in fact, reduce the discrepancies. This should provide one interim modification in the treatment of the radiative transfer equation in the presence of cirrus while awaiting a complete solution tocomplex cirrus transmissivity and scattering.