Measurements of Atmospheric Attenuation on an Earth-Space Path at 90 GHz Using a Sun Tracker

Absorption in the atmospheric window between the 60-GHz oxygen absorption band and an oxygen absorption line at 118.75 GHz is due to absorption by the tails of atmospheric oxygen and water vapor features. Liquid water, when present in the form of rain, cloud and fog, also causes much attenuation in this atmospheric window. Measurements of attentuation through the total atmosphere are of importance in helping to decide the feasibility of earth-satellite communications in this frequency region. Measurements of attenuation through the clear atmosphere as a function of atmospheric water vapor content have been made by F. I. Shimabukuro 1 on an earth-space path at 90 GHz. The results are in fair agreement with theory. A. W. Straiton and C. W. Tolbert 2 and D. C. Hogg and R. H. Turrin 8 have measured propagation loss through the clear atmosphere along ground-based paths at frequencies near 94 GHz. Their results agree satisfactorily with theoretical predictions provided suitable values are taken for the pressure broadening constants of the oxygen and water-vapor lines.4 Hogg and Turrin 3 have also measured attenuation due to rain at 70 GHz along groundbased paths, and the results again show reasonably good agreement with theory. 4 103