The search for the most reliable long-term rain attenuation CDF of a slant path and the impact on prediction models

Many prediction methods of long term complementary distribution function (CDF) of rain attenuation based on rain intensity CDF, when tested against concurrent beacon measurements show very similar large errors. In our opinion, these tests may indicate that the real concurrency of rain attenuation and rain intensity CDFs is not sure. The scope of the paper is to show that this can happen even in a well designed and controlled experiment. To this end, we have used the measurements collected at Spino d´Adda of Italsat 18.7-GHz beacon in a 37.7° slant path, and the independent predictions of the synthetic storm technique (SST) for the same radio link, to search the most reliable long term rain attenuation CDF of the slant path, that we found given by the SST CDF. Since the search is based on concurrent and independent rain intensity measurements, we think that our conclusion is sound. We have also discussed how to complete, statistically, a rain attenuation data bank with the SST prediction (such as the large and valuable Italsat data bank) to provide a secure experimental set of concurrent rain attenuation and rain intensity statistics to test prediction methods under controlled conditions, like in a laboratory.