Path attenuation statistics influenced by orientation of rain cells

The influence of path azimuth on fade and space diversity statistics associated with propagation along earth-satellite paths at a frequency of 18 GHz is examined. The approach utilizes the methods employed by Goldhirsh and Robison [1], and Goldhirsh [2], in which a radar rain reflectivity data base obtained during the summer of 1973 is injected into a modeling program and the attenuation along parallel earth-satellite paths are obtained for a conglomeration of azimuths. In this work the statistics are separated into two groupings: one pertaining to earth-satellite paths oriented in the northwest-southeast and the other in the northeast-southwest quadrants using a fixed elevation angle of . The latter case shows fading to be greater with a degraded space diversity suggesting rain cells to be elongated along this direction. Great circle distance intervals along which the path attenuations are greater than a fixed threshold level (i.e., 2 dB) are defined here as "attenuation cell sizes." These cell dimensions are analyzed for both sets of quadrants and are found to have average values which are larger by 2 km in the northeast-southwest quadrants; a result consistent with the fade and space diversity results. Examination of the wind direction for the 14 rain days of data analyzed shows good correlation of the average or median wind directions with the directions of maximum fading and degraded space diversity.