Comparison of radiometer, radar and rain gauge attenuation predictions with Olympus beacon measurements

In the framework of the Olympus propagation experiment (OPEX) continuous measurements of 20 GHz beacon attenuation, 19 GHz sky noise temperature, rain rate, drop size distribution (distrometer), and further meteorological parameters like ambient temperature, humidity, and wind speed have been carried out at DLR. The path elevation was 27.6 degrees, the polarisation tilt angle with respect to the local horizon was 24.3 degrees. Yearly and monthly statistics of these data are presented for Sep. 1991- Aug. 1992. Of particular interest is the correlation of the slant path attenuation with rain rate and sky noise. The performance of different attenuation prediction methods is investigated by equiprobability statistics of rain rate, sky noise temperature, and measured beacon attenuation. Another useful instrument for propagation measurements is a polarimetric radar. The Olympus path had been scanned with the polarimetric C-band weather radar of DLR for several mainly convective events. The radar derived attenuations are compared with the real beacon attenuations in a statistical way. The basis for these radar predictions is the derivation of drop size distributions from the measured polarimetric radar observables. A similar algorithm has been developed for the derivation of path integrated drop size distributions from dual-polarisation radiometer measurements. The radiometer derived drop size distributions are in good agreement with distrometer measurements.