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Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth’s horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave ray-tracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient. [ABSTRACT FROM AUTHOR]

The article presents information on 2004 Antennas and Propagation Society's" Distinguished Achievement Award". The Distinguished Achievement Award was established in 1985 to recognize outstanding technical achievement and meritorious service to the Antennas and Propagation Society. The 2004 Award was presented to Allan W. Love for his many contributions in the field of antennas, and particularly for his creative development of the line source feed for the Arecibo spherical reflector antenna. He served as a radar officer in the Royal Air Force from 1941 to 1945 in the Middle East and Australia. He served the Antennas and Propagation Society for many years in a number of capacities, including the Presidency in 1984.