Within the horizon propagation measurements over sea at 10.5 GHz

Results of a within-the-horizon propagation experiment at 10.5 GHz conducted along a 9.9-km low-altitude path in the Netherlands area of the North Sea are given. The objective was to investigate the effects of the evaporation duct on low-altitude propagation within the horizon region in order to validate the propagation model program RPE (radiation parabolic equation). This program predicts the path loss as a function of evaporation duct height for propagation over the sea within and beyond the horizon region. The experiment was performed in the period 7 June-11 July 1989. A one-month test period was chosen to get propagation data for a variety of weather conditions. The North Sea propagation experiment clearly demonstrated that the within-the-radio-horizon evaporation duct can have a significant impact on low-level propagation at X-band. It was found that the accuracy of the predictions improved considerably when the height of the sea level used in the propagation model RPE was adjusted for sea roughness. Predictions using the adjusted sea-level were, on the average, loss levels in the range from 128 to 152 dB.<>