Prior to use in operational systems, it is essential to validate ionospheric models in a manner relevant to their intended application to ensure satisfactory performance. For Over-the-Horizon radars (OTHR) operating in the high-frequency (HF) band (3-30 MHz), the problem of model validation is severe when used in Coordinate Registration (CR) and Frequency Management Systems (FMS). It is imperative that the full error characteristics of models is well understood in these applications due to the critical relationship they impose on system performance. To better understand model performance in the context of OTHR, we introduce an ionospheric model validation technique using the oblique ground backscatter measurements in soundings from the Super Dual Auroral Radar Network (SuperDARN). Analysis is performed in terms of the F-region leading edge (LE) errors and assessment of range-elevation distributions using calibrated interferometer data. This technique is demonstrated by validating the International Reference Ionosphere (IRI) 2016 for January and June in both 2014 and 2018. LE RMS errors of 100-400 km and 400-800 km are observed for winter and summer months, respectively. Evening errors regularly exceeding 1,000 km across all months are identified. Ionosonde driven corrections to the IRI-2016 peak parameters provide improvements of 200-800 km to the LE, with the greatest improvements observed during the nighttime. Diagnostics of echo distributions indicate consistent underestimates in model NmF2 during the daytime hours of June 2014 due to offsets of -8° being observed in modelled elevation angles at 18:00 and 21:00 UT.

Over-the-horizon radar (OTHR) systems operating in the high-frequency (HF) band (3-30MHz) are unique in their ability to detect targets at extreme ranges, offering cost-effective large area surveillance. Due to their reliance on the reflective nature of the ionosphere in this band, OTHR systems are extremely sensitive to ionospheric conditions and can expect significant variations in operational performance. At high latitudes, the presence of auroral enhancements in the E-Region electron density can substantially modify the coverage area and frequency management of OTHR systems. In this study, HF raytracing is utilized to investigate these impacts for a hypothetical radar under different auroral conditions simulated using the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM). Aurora were seen to increase maximum useable frequency (MUF) from 8.5 MHz to 26 MHz whilst also reducing median available target range from 2541 km to 1226 km, for the greatest differences. Target interception showed large variations in path coverage of between 33-115% and 0-107% for two flight paths tested with precipitation toggled. Two distinct propagation modes were observed with aurora, noted as the F-E ducted and Auroral E-modes. Long-range coverage provided by the auroral F-E ducted mode was of limited capacity with low solar activity due to the reduced NmF2. F-mode propagation transitioned to the dominating Auroral E-mode between Auroral Electrojet (AE) index values of 50- and 200-nT. The significant variations in both frequency and coverage observed within this study highlight some aspects of the importance of considering aurora in OTHR modelling and design.