Atmospheric Stability-Dependent Performance of Evaporation Duct Models: Experimental Validation Through Over-the-Horizon Propagation in the South China Sea

An evaporation duct is a physical atmospheric phenomenon, caused by evaporation of seawater, which leads to anomalous propagation of electromagnetic (EM) waves over maritime regimes. Comprehensive understanding of the characteristics of evaporation duct is of great importance. However, evaporation duct models exhibit strong atmospheric stability-dependent performance. Besides, the performance varies considerably among different models. Consequently, under different stability conditions, path loss (PL) predictions can vary significantly across models, with errors reaching tens of decibels. In this case, the performance of evaporation duct models in terms of PL prediction needs to be carefully evaluated. In this study, the PL prediction capabilities of four evaporation duct models were evaluated through two over-the-horizon EM propagation link measurements conducted under different atmospheric conditions. Signal levels and meteorological data were recorded continuously at distances of 16.4–88.3 km (unstable conditions) and 45–105 km (stable conditions). By comparing the model-predicted PL with the measured PL, the performance of four models navy atmospheric vertical surface layer model (NAVSLaM), Paulus–Jeske (PJ), Babin–Young–Carton (BYC), and Russian State Hydrometeorological University (RSHMU) models) was evaluated. Comparative analysis revealed that NAVSLaM performs optimally under unstable conditions root mean square error (RMSE) (RMSE: 7.9 dB), with the PJ model ranking second (RMSE: 24 dB); conversely, the PJ model showed superior performance under stable conditions (RMSE: 13.3 dB), followed by NAVSLaM (RMSE; 45.9 dB). Furthermore, the modified NAVSLaM, incorporating near-neutral stability functions, yielded superior performance under stable conditions, representing 83.9% and 44.2% improvement over NAVSLaM and the PJ model, respectively. This advancement establishes an improved channel estimation methodology in marine environments.