The European program Olympus of slant millimeter waves propagation studies uses three beacons on board an experimental satellite, the frequency of which is 12.5, 20, and 30 GHz. The objectives of the program require an accuracy of attenuation measurement lower than 0.1 dB. It is difficult to determine the no-attenuation level relative to which the atmospheric attenuation is measured because the transmitted signal shows daily variations caused by satellite movements and temperature changes. The problem is thus to separate the diurnal pattern of the satellite signal from propagation effects. The purpose of this paper is to analyze the calibration method of using a multifrequency radiometer. One attempt was made to deduce the absorption on the satellite-Earth line from the apparent sky temperature. We discuss some retrieval algorithms using radiometer measurements, keeping the Olympus experiment objectives in mind, and show a new inversion method. Retrieval algorithm and calibration method performances lead to a final accuracy of the method lower than 0.1 dB.
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