Abstruct-A melting layer model related to the physical constants and meteorological parameters is employed in this investigation. The specific phase shift, together with the specific attenuation, is computed at 1-100 GHz by using the Mie theory. The additional zenith attenuation, which is the difference between zenith attenuation due to the melting layer and attenuation due to the same thickness of the resulting rain, is comprehensively studied. The ratio of the difference to rain zenith attenuation may be over 1 at 1-5 GHz although the difference is much less than 1 dB. The difference can be over 1 dB at frequencies above 20 GHz. A minimum of the ratio is below 0.05 at frequencies about 40-60 GHz but the ratio can become a value of about 0.1 at 100 GHz. The additional attenuation should be taken into account in satellite-earth communications and radar remote sensing. The power law parameters of the average specific attenuation of the melting layer and rain specific attenuation are tabulated for three raindrop size distributions at rain rates of below 25 mm/h. The power law method could be utilized in the additional attenuation calculation. It is a good approximation of the Mie theory results at 1-50 GHz and a useful estimate at 50-100 GHz.

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Helsinki Unriversity of Technology and the Finnish P&T performed 12 GHz radiometer measurements on a satellite link at Kirkkonummi (in Finland) during eleven years 1979-1989. The experimental equipment, measurement theory and different calibrations, for instance the calibration of the effective medium temperature using the attenuation statistics measured with the OTS satellite, are explained. The average annual and worst-month cumulative distributions of atmospheric attenuation and the corresponding conversion factor Q are presented as the longterm results. The standard deviations of the average distributions are also given.

Melting layer has been described with two melting particle models. The specific attenuation of melting snow, the average specific attenuation and the excess attenuation of the melting layer have been calculated by using two melting particle models and an approximate method in a frequency range of 1-1000 GHz for the precipitation rate below 12.5 mm/h. Numerical calculations have been performed with four drop-size distributions. The parameters a and b of the power law relation aRb for the average specific attenuation of the melting layer have been given in the frequency range.