Atmospheric Attenuation of Solar Millimeter Wave Radiation

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Abstract
A lumped attenuation figure for the solar millimeter wave radiation in the water vapor of the atmosphere was measured with a thermal detection apparatus. The corresponding theoretical attenuation figure was computed from the solar millimeter spectrum known from previous measurements of the authors and from the Van Vleck-Weisskopf equation and turned out smaller than the first experimental figure by a factor of about 3 in terms of decibels per kilometer. With the general structure of an absorption spectrum considered well traced by theory this disagreement can only mean a failure of the computation to yield the correct absolute absorption level in the window regions to which the experiment predominantly refers. The fault may lie either in the equation itself or in inadequately known constants required in the computation. Regardless, however, of the cause and magnitude of this discrepancy, the novel method of this paper lies in a combination of the above-mentioned experimental and computed figures to furnish a well-supported spectral attenuation function in the window region. This function, which constitutes the final result, turns out largely independent of the shortcomings in the computation part, inasmuch as theory was used to furnish merely its structure and experiment to provide its absolute level.