| As is known to all,sand and dust is a common disastrous weather phenomenon in China.March of this year,the sand and dust weather was spread from Mongolia into the northern part of China.The accurate transmission of millimeter wave signal in sand and dust weather affects the performance of millimeter wave communication and radar.When dust particles moving in dust weather,they are usually charged.There have been many studies on the transmission characteristics of millimeter wave in sand and dust weather,but the electrification of sand and dust is usually not considered in the previous research.Therefore,it is very necessary to do research on the transmission characteristics of millimeter wave in charged dust weather.In order to solve this problem which mentioned above,the first thing we need to do is to study the attenuation characteristics of millimeter wave in charged dust and the echo power of millimeter wave radar.Because of the irregular shape for the dust particles,the net charge on the dust particles tends to be concentrated in the tip of the particles.Therefore,in addition to spherical and ellipsoidal dust particles,we also construct dust particles with rough surfaces.Based on these models,the discrete dipole approximation has been used to calculate the scattering characteristics of a single particle.In order to obtain the extinction factor and the backscattering factor,we need to take 42 incident angles from-180° to 180° for the particles with rough surface and then take their average value.For ellipsoidal particles,21 angles of incidence are taken between 0° and 180° to obtain the average values of the extinction factor and backscattering factor.The extinction factor and backscattering factor of spherical dust particles calculated by discrete dipole approximation are in good agreement with the results of Mie theory.The effects of dust particle shape,equivalent radius,charge and frequency on the polarization characteristics of dust particles were also studied in this paper.For dust particles,when their charge-to-mass ratios are 0 ?C/kg,250 ?C/kg,500 ?C/kg,800 ?C/kg,respectively,the extinction factor under millimeter waves(26GHz,38 GHz,72GHz,and 93GHz)is calculated using charged discrete dipoles.These extinction factors are used to calculate the characteristic attenuation under the distribution of loess,Maowusu desert,Taklimakan desert and Tengger desert.We can draw a conclusion that the characteristic attenuation decreases with the increase of visibility,increases with the increase of frequency and charge-mass ratio.In addition,under the larger particle size distribution,such as Taklimakan Desert and Tengger Desert,it is not obviously for characteristic attenuation between different electric charge.However,under the same charge and frequency,the attenuation of these two distributions is larger than that of Maowusu Desert and Loess.At the same charge-mass ratio,the characteristic attenuation of dust particles with rough surface is larger than that of ellipsoidal dust particles with smooth surface,but the difference between the two kinds of ellipsoidal particles is not obvious.The extinction factor and backscattering factor which is calculated by the dust particles with rough surface are used to study the radar echo power under different dust particle size distributions(loess distribution,Maowusu desert distribution,Taklimakan desert and Tengger desert)according to the meteorological radar equation.In the control of other conditions being the same,the results show that the radar echo power decreases with the increase of propagation distance,charge-to-mass ratio,and visibility,and increases with the increase of frequency.It is more likely to be affected by electric charge for radar echo power in low visibility.In the short distance,especially when the propagation distance is within 5km,the echo power decreases rapidly with the increase of the distance.When the propagation distance is greater than 5 km,the echo power decreases relatively gently. |
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