X-Band Propagation in Laterally Heterogeneous Evaporation Ducts and Its Implications for Refractivity Inversions

Evaporation ducts (EDs) are an atmospheric phenomenon that can cause anomalies in X-band radar systems (8–12 GHz) by extending their range beyond the geometric horizon, potentially leading to positioning uncertainties. Additionally, the lateral spatial variations of the ED over ~60 km may cause further effects. However, the extent to which these lateral variations need to be incorporated for accurate propagation predictions, and whether such effects need to be accounted for in related applications such as refractivity inversion techniques, remains unclear. In addition, few studies have discussed the impacts of heterogeneous EDs on X-band propagation loss relative to a homogeneous ED. To address these questions, this article explores the impact of linear variations of ED height and duct shape over range on X-band propagation loss relative to a laterally homogeneous ED. It is found that significant differences in X-band propagation are likely to occur when horizontal variations of ED height or shape transition the environment’s trapping conditions downrange of the radar transmitter. Furthermore, it is shown that during such transitional trapping environments, heterogeneous refractivity inversions perform more accurately, on average, than homogeneous refractivity inversions. However, utilizing heterogeneous inversion methods when the true environment is homogeneous can lead to less accurate inversely determined refractivity.