Research On Characteristics And Retrieval Of Millimeter Wave Radar In Sand And Dust Weather

About a quarter of the world's land is now desertification,and China is one of the most desertification countries.The attenuation of millimeter wave transmission in sand and dust weather will become an important research topic.In order to study the impact of sand and dust weather on millimeter wave transmission,it is necessary to study the attenuation of electromagnetic waves in sand and dust weather and the retrieval of sand and dust weather types.The main research results of this article are as follows:1.Based on the sand particle models of different shapes,the paper uses the DDA method to calculate and analyze the scattering characteristics of individual sand particles.Since the sand particles are randomly and unevenly distributed in space,and the shape and size of the sand particles are different,this paper uses the DDA method to calculate the extinction cross-section and backscattering cross-section of sand particles of different shapes under different incident angles,and compare the calculation results with the Mie theory calculation results.It is found through comparison that when the sand particles are approximately spherical,the calculation results of the DDA method are consistent with the calculation results of the equivalent spherical Mie theory.As the shape of the sand particles changes,the DDA method deviates from the calculation results of the Mie theory.2.Based on the extinction cross section of a single sand particle calculated by the DDA method and the particle size distribution under different sand and dust weather conditions,the unit distance attenuation(specific attenuation)of millimeter waves(3.9GHz,26 GHz,38GHz,60 GHz,and 100GHz)under floating dust weather,dust weather,and sandstorm weather in different desert areas were calculated respectively.Comparing the calculation results with the empirical formula,when the sand particles are spherical,the calculation results using the Mie theory and the DDA method are consistent with the calculation results of the empirical formula.On this basis,the paper uses the DDA method to study the specific attenuation of cluster dust particles and ellipsoidal dust particles.In the same kind of sand and dust weather,as the frequency of electromagnetic waves increases,the specific attenuation is greater;in the same frequency band,as the visibility of sand and dust weather increases,the specific attenuation of electromagnetic waves is smaller.The calculation results of electromagnetic wave specific attenuation under different sand and dust weathers show that electromagnetic waves have less attenuation in floating dust weather and sand raising weather,and more attenuation in sand and dust storm weather,which can't be ignored in the project.3.Based on the backscattering cross section of a single sand and dust particle calculated by the DDA method and the meteorological radar equation,the echo power of the millimeter wave radar in different sand and dust weather conditions was calculated and analyzed.The calculation results show that the radar echo power is smaller in floating dust weather and sandy weather,and the radar echo power is larger in sand storm weather.In the same weather,the radar echo power decreases as the radar wave propagation distance increases.As the visibility of sand and dust weather increases,the radar echo power decreases.The calculation found that in the same dust environment,when the propagation distance is short,the echo power of the high-frequency radar wave is large,and when the propagation distance is long,the echo power of the low-frequency radar wave is large.4.Based on the specific attenuation of electromagnetic wave,radar echoes,wind speed and sand and dust visibility in different types of sand and dust weather,the use of attenuation –fuzzy logic algorithm,radar–fuzzy logic algorithm and support vector machine to predict the sand and dust weather type is proposed.Through the comparison of different retrieval methods,it is found that the support vector machine trains the data based on the measured data,which can accurately predict the type of sand and dust weather.The statistical relationship between radar observation data in sand and dust weather and dust weather grades in weather forecast is established,which provides support for sand and dust weather forecasters to quantitatively apply sand and dust numerical products.