Evidence of Long-Term Correlation Between Clear-Air Attenuation and Scintillation in Microwave and Millimeter-Wave Satellite Links

Long-term correlation between microwave scintil-lation and path attenuation in clear-air troposphere is quanti-tatively evaluated carrying out a numerical and experimental analysis on a monthly basis. Amplitude scintillation variance is simulated by means of a weak-fluctuation propagation model, while path attenuation is obtained from ground-based brightness temperature data using a radiative transfer model. Both the scintillation and radiative transfer models are applied to a set of radiosounding observations, performed in Milan, Italy, during 1989. Regression formulas relating clear-air mean radiative tem-perature to meteorological quantities and slant-path attenuation to amplitude scintillation variance are derived from numeri-cal simulations. Their validity should be restricted, in general, to mid-latitude subcontinental climates. Monthly predictions of radiometer-derived path attenuation and correlation between attenuation and scintillation are tested using both multichannel radiometric data and Italsat beacon measurements at 18.7, 39.6, and 49.5 GHz, acquired at Spino d’Adda, Italy, ground station in 1995. A fairly good agreement is found by performing a comparison between estimates and measurements.