X-band transhorizon measurements of CW transmissions over the sea-Part I: path loss, duration of events, and their modelling

This article presents measurements, analysis, and modelling of path loss and duration of events obtained in a transhorizon experiment over the English Channel (La Manche, operated from 1987 to 1991, totalling 3708 valid data days and using five paths with three radiofrequencies at X-band. An overview of the equipment, operation and data acquisition, and processing is first given. The study reveals that the decibel path loss is normally distributed but exhibits three distinct regions of normality: path losses with probability of occurrence greater than about 1% reflect propagation dominated by several propagation mechanism. The second region, which can be clearly identified with probabilities of path loss below about 1%, reflects the various anomalous propagation mechanisms, and these are identified and discussed. The experimental median is compared with the value derived using several prediction methods, one of which is found to agree well with only a few decibels of difference. On the other hand, the existing CCIR prediction for small time percentages under values the strongest enhancements found. The continuous reduction of path loss below a given threshold L (decibels) constitutes an event with some duration. The analysis has shown that the conditional distribution Prob (D´⩾D/L´⩽L) that events last longer than D minutes is log-normal, is very skewed, and is the same for all types of propagation conditions. It is found that the signal level can rise from the troposcatter median to above the free space value and stay there continuously for periods of time which can range from a few minutes to well over one hour. The data base and modelling of L and D are given in detail