Evaporation Duct Propagation Research Articles

Deep Learning Method for Evaporation Duct Inversion Based on GPS Signal

Accurate evaporation duct prediction is one of the critical technologies for realizing the over-the-horizon impact of marine communication, ship radar, and other systems. Using GPS signals to invert evaporation ducts provides more benefits in terms of method realization and ease. In order to invert the evaporation duct from GPS-received power data, a deep learning technique based on Bayesian optimization is proposed to increase the prediction accuracy of evaporation ducts. The evaporation duct propagation mechanism of the GPS signal is explored. The GPS-received power is estimated using the two-parameter evaporation duct model, and a better neural network structure is built using Bayesian optimization. The study results show that the Bayesian optimization model has a smaller root mean square error (RMSE) than the human empirical model, which allows for rapid and accurate inversion of duct parameters even in noisy interference.

The Effects of Rainfall on Over-the-Horizon Propagation in the Evaporation Duct over the South China Sea

The evaporation duct (ED) is generated by the evaporation of seawater and can be an influential factor of electromagnetic (EM)-wave propagation. Rainfall also affects atmospheric factors and EM-wave propagation. However, the distribution of the ED and path loss (PL) during rainfall has rarely been reported. This paper analyzes the distribution of the atmospheric factors and ED in the South China Sea (SCS). The results show that the evaporation duct height (EDH) in the area of rainfall is generally lower. The effect of the ED on the over-the-horizon (OTH) propagation reaches 0.69 dB km−1 on average, which is 4.3 times stronger than the maximum rain attenuation (0.16 dB km−1) when the rainfall is less than 5 mm h−1. In the SCS, a 53 km long OTH link was established between Donghai Island and Jizhao Bay to observe the PL. The measurement results show that the nearly saturated relative humidity (RH) leads to a high PL. The results also show that the change in the direction of the sea–land breeze causes a 42.4 dB decrease of PL by transferring the moist patches. Rainfall has an attenuation effect on OTH propagation in ED, mainly owing to the high RH.

A Novel 3D Non-Stationary Maritime Wireless Channel Model

In this paper, a novel 3-dimensional (3D) non-stationary geometry-based stochastic model (GBSM) is proposed to mimic the ship-to-ship multiple-input multiple-output (MIMO) communication channels. To reflect the realistic maritime propagation environment, the effects of rough sea surface scattering and evaporation duct propagation are investigated in the proposed channel model. The model considers the movements of transmitter (Tx), receiver (Rx), and scatterers, and is capable of capturing the channel characteristics, including non-stationary characteristics, spatial consistency, location-dependent property, etc. Through taking the array cluster evolution into account, the proposed channel model can describe massive MIMO channels and can easily switch to conventional MIMO channel model by adjusting corresponding parameters. Based on the proposed model, key statistical properties like delay/angular/Doppler power spectrum density (PSD), space-time correlation function (STCF), stationary interval, and root mean square (RMS) Doppler/delay spreads in multi-scenarios are derived. The usefulness and accuracy of the proposed model are demonstrated by comparing theoretical results, simulation results, and corresponding measurement results.

C band transhorizon signal characterisations in evaporation duct propagation environment over Bohai Sea of China

Evaporation duct is an anomalous mechanism of transhorizon propagation in marine and coastal regions. In order to better understand the characteristics of signal fading, a C band signal transhorizon propagation experiment was carried out with a 107km path length over the Bohai Sea of China. Using an iron tower with meteorological and oceanographic (METOC) sensors at multiple altitudes, a direct diagnostic method of evaporation duct is presented. The dependence of signal strength on evaporation duct height, antenna height, and METOC parameters is analysed. The experimental results indicate that the signal strength tends to be linearly dependent on the evaporation duct height when the transmitter and receiver antennas are submerged within the duct layer. Normally, the signal strength is stronger when the relative humidity is lower. Stronger signal strength tends to occur under near-neutral or stable atmospheric conditions or when the air-sea temperature difference is higher. The results indicate that the signal strength distribution of fast fading is close to Rayleigh distribution, and the probability density of fade slope is symmetric at 0dB/s. These results have important implications for the design of ducting communications system.

Influence of obstacle on electromagnetic wave propagation in evaporation duct with experiment verification**Project supported by the National Natural Science Foundation of China (Grant No. 11174235) and the Fundamental Research Funds for the Central Universities of China (Grant No. 3102014JC02010301).

In this paper, the influence of obstacle on electromagnetic wave propagation in an evaporation duct is investigated, both from numerical simulation and experimental observation. A comparison of electromagnetic wave propagation in evaporation duct with and without obstacle for a typical case is presented. The presence of obstacle causes a significant increase in path loss. The obstacle has significant impact on electromagnetic wave propagation when the frequency is higher than 5 GHz and when the evaporation duct height is higher than 10 m. The influence of an island on electromagnetic wave propagation was observed in the experiment held in the South China Sea, October 2012. The experiment result shows that the island causes about 30–40 dB increase in path loss. The discrepancy between model and measurement is analyzed and the errors of transmitting antenna height and relative humidity are the possible causes of the discrepancy.

Long-term statistics related to evaporation duct propagation of 2 GHz radio waves in the English Channel

[1] This paper presents long‐term statistics additional to those previously published pertaining to evaporation duct propagation of UHF radio waves in the British Channel Islands, with particular focus on a completely over‐sea 50 km transhorizon path. The importance of the evaporation duct as an anomalous propagation mechanism in marine and coastal regions is highlighted. In particular, the influence of various atmospheric parameters on the performance of a popular operational evaporation duct model is examined. The strengths and weaknesses of this model are evaluated under specific atmospheric conditions. The relationship between the continually varying evaporation duct height and transmitter‐receiver antenna geometries is analyzed, and a range of statistics related to the implications of this relationship on the received signal strength is presented. The various issues under investigation are of direct relevance in the planning of long‐range, over‐sea radio systems operating in the UHF band, and have implications for the radio regulatory work carried out by organizations such as the International Telecommunication Union. Citation: Gunashekar, S. D., E. M. Warrington, and D. R. Siddle (2010), Long‐term statistics related to evaporation duct propagation of 2 GHz radio waves in the English Channel, Radio Sci., 45, RS6010, doi:10.1029/2009RS004339.

Statistical assessment of evaporation duct propagation

Over-the-horizon propagation from 0.6 to 18 GHz is presented in the form of accumulated frequency distributions of path loss, showing the comparisons between theory and two measurement programs. The path-loss theory is based on waveguide solutions for a family of refractivity/height profiles characterized by evaporation duct height in the range of 1 to 40 m. Annual frequency distributions of evaporation duct height have been prepared based on 15 years of marine surface meteorological observations and are combined with the waveguide path loss/duct height results to give accumulated frequency distributions from experiments performed in the Aegean Sea and the North Sea. Excellent agreement of theory and observation is noted in most cases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency diversity effects of evaporation duct propagation

A comparison of 3, 9.6, and 18-GHz low-altitude over-the-horizon propagation (as influenced by the evaporation duct) is presented. Theoretical and experimental results are given for a 35-km over-water path, where the transmitters were located about 5 m above mean sea level and the receivers were located either 4-5 m or 18-19 m above sea level. Results are presented in terms of the one-way propagation factor in decibels at each frequency. Long-term cumulative frequency distributions of calculated and observed propagation factors are presented. Particular attention is given to the relative performance of each radio frequency to investigate frequency-diversity improvements that may be available on such paths. In most cases presented, there is a close agreement between theory and observations. It is concluded that substantial improvements in received signal levels are likely to be achieved in most areas of the world by a suitable choice of two frequencies in the 10-20-GHz range. >