Frequency Management System (FMS) for Over-the-Horizon Radar (OTHR) Using a Near-Real-Time Ionospheric Model

Abstract

Sky-wave over-the-horizon radar (OTHR) propagates radio waves off the ionosphere to provide long-range surveillance around the Earth's curvature. Frequency selection for high-latitude and polar OTHRs is challenging unless there is an environmental monitor that addresses the significant ionospheric variability in high-latitude regions, a spectrum monitor that finds unoccupied frequencies in the high-frequency (HF) radio waveband, and a frequency management system (FMS) that selects an optimal frequency from the merged results of the environmental monitor and spectrum monitor. This article describes the first FMS for high-latitude OTHR that merges results from the environmental monitor and spectrum monitor in realtime. The environmental monitor uses the assimilative Canadian high-arctic ionospheric model (A-CHAIM), which assimilates near-real-time data and is, to date, the most advanced ionospheric model for high-latitude regions. Despite remaining limitations, demonstrations of this real-time FMS between a transmitter and four targets during the day and night and during fall and summer show that it could be one of the tools for selecting frequencies for operational scenarios.

High‐Latitude Off‐Great Circle Propagation Associated With the Solar Terminator

“…As these ray tracing methods strictly do not consider off-great circle propagation, deviations in the angle of arrival and time-of-flight associated with off-great circle propagation are likely to manifest significant target positioning errors. Frequency management, the process of determining which frequencies and elevations are expected to reach a position being surveilled (Thayaparan, Marchioni, et al, 2020;Thayaparan et al, 2019Thayaparan et al, , 2022, can also be impacted by off-great circle propagation. If propagation is assumed to be entirely on-great circle, or if a too limited azimuthal range of rays are traced, a frequency management system could miss valid propagation paths with a significant off-great circle component.…”