An Improved Advanced Propagation Model Considering Free-Space Propagation in Evaporation Duct Environment

The evaporation duct (ED) environment has a significant impact on the path losses (PLs) of electromagnetic (EM) wave propagation over sea surface. However, the existing advanced propagation model (APM) does not sufficiently account for the free-space propagation within line-of-sight (LOS) range, leading to larger evaluated PLs compared with the observed data. Motivated by this, we propose an improved APM model considering free-space propagation (IAPMFS). Within LOS range, IAPMFS utilizes the free-space propagation model to evaluate the PLs of EM wave propagation, and then invokes APM to evaluate the PLs under ED environment in over-the-horizon (OTH) range based on the results of LOS range. By the observed data of both C-band and X-band obtained from multiple OTH links in the northern South China Sea (SCS), the accuracy of IAPMFS is validated. The results demonstrate that the PLs evaluated by IAPMFS are much closer to observed data compared with those by APM. Moreover, in an OTH link of 53.435 km, the percentages of absolute errors of PLs evaluated by IAPMFS not exceeding 5 dB and 10 dB are respectively 70.73% and 93.18%, while those by APM are only 12.19% and 50.45%, respectively. Therefore, IAPMFS can provide key technical supports for the development, upgrade and accurate performance evaluation of marine communication as well as radar systems.