Regional Spatiotemporal Statistical Database of Evaporation Ducts Over the South China Sea For Future Long-Range Radio Application

Abstract

To fully grasp the characteristics and provide a basis for establishing an evaporation duct communication system for the South China Sea (SCS), we constructed a regional statistical database based on remote sensing meteorological parameters and a numerical model. This database has the advantage of extensive spatiotemporal coverage and high resolution, which can provide accessibility and as a supplementary means for the maritime 6 th Generation communication network. Specifically, work has been completed in three areas. (1) The overall EDH in the central SCS varies periodically and remains intense throughout the day, decreasing only just before sunrise during 04:00-08:00. Moreover, a 20.0 m high channel appears at the "Golden edge" in the northern coastal area, which can expand as far as 300 km from the coast during May-July. (2) The characteristics of specific regions were analyzed, and the highest average EDH was determined as 18.4 m in the Taiwan Strait. The height in the central SCS fluctuates little with monthly and annual variation, and it is maintained between 10.0 and 12.0 m. (3) Based on the evaporation duct formation principle, we analyzed the spatiotemporal distributions of meteorological parameters. The Taiwan Strait maintains the highest EDH over the SCS, owing to the influence of the Kuroshio Current, and the average sea surface temperature (SST) reaches 28.41°C in June and 19.58°C in January. To the central SCS, high SST, low wind speed, and relative humidity of approximately 80% provide excellent conditions for maintaining an evaporation duct over the long term.

Revisiting Enhanced AIS Detection Range under Anomalous Propagation Conditions

“…In the tropospheric duct, the electromagnetic (EM) energy of certain frequencies is trapped and propagated over a long distance as in a waveguide. Recently, considerable efforts have been made in studying the propagation characteristics of tropospheric ducts and investigating the associated over-the-horizon maritime propagation for specific regions or seas [10,11,[15][16][17]. The evaporation duct attracted the attention of the authors of those papers because it is nearly permanently present above large bodies of water at lower and even moderate latitudes [18].…”

Research on Optimization Method of Evaporation Duct Prediction Model

“…Due to the influence of oceanic momentum and heat flux, as well as the effects of the interaction between maritime dry and hot air masses, wet and cold air masses, the atmospheric boundary layer over the sea is prone to the formation of atmospheric ducting phenomena, resulting in abnormal refraction of electromagnetic waves [1]. Under certain conditions, electromagnetic waves emitted by ship-borne radar and other radio frequency devices can be trapped within the ducting layer, which can achieve "beyond-line-of-sight" propagation with very low transmission losses [2]. At the same time, the trapping of electromagnetic waves within the ducting layer also leads to the disappearance of some echo regions, and creates "blind zones" [3].…”

“…The output of the evaporation duct prediction model includes the evaporation duct height and the modified refractivity profile. Current research primarily focuses on improving the accuracy of predicting evaporation duct height [2,[7][8][9][10]. There are relatively few studies on the modified refractivity profile.…”

Long-term over-the-horizon microwave channel measurements and statistical analysis in evaporation ducts over the Yellow Sea

“…The temporal and spatial distribution characteristics of evaporation duct show strong differences in different sea areas (Shi et al, 2015b;Sirkova, 2015;Yang et al, 2016;Zhang et al, 2016;Yang et al, 2022a;Huang et al, 2022). Lying between mainland China and the Korean Peninsula, the Yellow Sea is one of the largest areas of continental shelf shallow water that provides rich fishing grounds and oil resources.…”