| Summary: | Radio wave propagation over the ocean at frequencies above about 1 GHz differs from that over land due to the effect of a stratified layer just above the sea's surface known as the evaporation duct. The height and strength of this duct are the main factors affecting propagation. Bulk parameters have been developed to define duct height mainly in temperate zones; their applicability to the tropical region is as yet ambiguous as is the effect of wind speed on duct effective height in these regions. Significant previous work has been carried out on identifying duct height from atmospheric parameters, and thus behaviour by Babin et al [28]. The author contacted Dr Babin who made available his entire Thesis [39] which was most useful in our early research on duct height. In this work, measurements from sensor buoys are presented along with wind speed measurements and an equation for duct height postulated by Kulessa and Hermann is examined. The developmental algorithm appears to reasonably fit a series of wind speeds taken in the Gulf St. Vincent, South Australia, in a temperate climate and Southern Ocean. Data is presented and the equation discussed for the tropical zone, from this some duct height predictions are made. These duct heights are compared with those calculated using bulk parameters and conclusions are drawn for the tropical littoral zone. Radio wave propagation inside the duct is therefore considered to be anomalous with over the horizon paths producing near line of sight loss values. In this research the phenomenon is demonstrated in the results from one long distance experiment conducted over a one week period. Results from a 24 hour period are fully analysed along with analysis of another period in the campaign when the results were different from those expected. Other experiments over shorter paths using a ten-element receiver array are presented and the results used to make conclusions on the accuracy of the Parabolic Equation Models (PEM) in the tropical littoral zone. A design for a sixteen ...
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