A comparison of experimental and theoretical values of atmospheric absorption at the longer millimeter wavelengths

Results of atmospheric absorption measurements made over very long slant paths at frequencies of 15 and 35 GHz are reported. The absorption was determined from a set of measurements using the Sun as a source. Fifty-eight sets of data were collected at sunrise and sunset during clear sky conditions for a set of elevation angles from near the horizon to 20 degrees . The surface absorption coefficient, zenith absorption, and effective height of the absorbing atmosphere were derived from these data. Regressions of both surface absorption coefficient and zenith absorption were performed as a function of surface absolute humidity; the results were compared with theoretical values obtained by several investigators. Zenith absorptions were found to be in good agreement with theory. However, experimental surface absorption coefficients were consistently lower than the calculated values.<>