Instantaneous frequency scaling of microwave attenuation through radar measurements

Reflectivity profiles collected during different rain events by a S band meteorological radar sited at Spino d’Adda 30 km east of Milan (Italy) along a 38 deg. slant path towards the Italsat satellite have been worked out together with the time series of attenuation at the satellite frequencies of 18, 40 and 50 GHz measured by the co-located Earth terminal. For each rain event, the relationship between specific attenuation a and reflectivity Z needed to estimate the fade levels from radar measurements has been obtained at the lowest operating frequency through a best fit procedure that forced the predicted values to agree with the measured ones. Each one of these relationships has been assumed to well describe the rain process of the corresponding event, on the average, both in time (event duration) and in space (satellite path) because of the quite high correlation coefficient found in the best fit. Consequently, it has to contain also information about the DSD of the event. In order to prove this last statement the a-Z relations derived at 18 GHz have been used to deduce the DSD parameters and, consequently, to derive the a-Z relation at the other two satellite frequencies. In this way we were able to obtain the radar-predicted time series of attenuation at 40 and 50 GHz to be compared with the satellite measurements. The results have shown the correctness of the starting hypothesis.