A Study On The Atmospheric Duct Over Ocean And Its Prediction

The speed of a radio wave in the atmosphere is determined by the dielectric property of the air. This property depends on the pressure, temperature and humidity of the air. In general as we move upwards through the atmosphere the pressure decreases and temperature falls. This means that the dielectric property changes with height and allows a slight increase in the speed of a radio wave as it moves upwards through the atmosphere. This in turn means that if a radio wave moves away from the earth at an angle less than 90 degrees, then the upper part of the wave travels faster than the lower part. Therefore even under normal conditions this can in effect bend, or refract, then wave back down to earth.Atmospheric duct was divided into evaporation duct and elevated ducts by its mechanism on sea. The paper joins to research work which is an important scientific research project of navy. At first, analyzing Model A and Pseudo-refractivity model acquired the modified refractivity profile and evaporation duct height on the basis of meteorological and hydrologic data. The validity of the models was proved through the experiment data of Nanhai, Donghai and Huanghai. In the end, a modified model is acquired and meteorological and hydrologic database was established in the different sea area and query system of modified refractivity profile over ocean was formed. It built the better foundation for the study on the propagation of electromagnetic wave. Secondly, the relativity between detecting rang and weather conditions were in existence by the analysis of the meteorological data and the echo data of microwave radar. So we completed the neural network model of special season to predicate detecting rang of Radar. Accordingly, not only we got the detecting range of ship-borne and land-borne radar in the weather conditions quantitatively, but also we could know if the atmospheric duct exited and changed in the weather conditions. But if we can explore the meteorological and hydrologic conditions for a long time and grip the rules of the refractivity change for special sea area, the more correct prediction will be acquired. In this paper, the forecast of the atmospheric duct over ocean can meet the need of OTH detection through the atmospheric duct basically. This kind of approach is practical and applicable.