Inversions of the Evaporation Duct Heights Utilizing Opportunistic Signals of Navigation Radar

Evaporation ducts (EDs) can significantly impact marine communications and radar detections. Observations of ED height (EDH) are crucial for the remote sensing of anomalous propagation in different weather conditions. However, there are limitations in existing methods for remote sensing of EDs in large areas and long terms. This article first reports on an over-the-horizon (OTH) propagation measurement campaign lasted for five days over the South China Sea (SCS) to invert EDHs using opportunistic signals of a navigation radar. The results of different measurement systems show good consistency in their measured path loss (PL) and the inverted EDHs. For verifications, results that are predicted by the naval atmospheric vertical surface layer model (NAVSLaM) with observations of air-sea parameters were analyzed. The root-mean-square error (RMSE) between the EDHs inverted from the navigation radar signals and the predicted EDHs was 0.97 m. Based on the opportunistic signals of navigation radar, an EDH inversion method is proposed and verified by the predicted results. This method shows good potential in long-term EDH inversion of OTH propagation links via the opportunistic signals generated from navigation radar widely used on marine vessels.