High-Resolution Widesweep Backscatter Ionograms

Introduction: High frequency (HF) over-the-horizon radar (OTHR) relies on the refraction of electromagnetic waves by the ionosphere to detect targets at very long ranges, typically more than 500 nmi (see Fig. 1). A fundamental aspect of successful target detection is the selection of an appropriate operating frequency to ensure a large amount of backscatter energy at the desired surveillance range. HF OTHR operates over four octaves of frequency (5 to 30 MHz) and highly variable (spatially and temporally) ionospheric conditions. For