Scattering And Attenuation By Charged Sand And Dust Particles Affected By Relative Humidity

Dust&Sand(DUSA)weather is a kind of severe weather which frequently appears at the arid and semi-arid regions.With the rapid development of the radio technology and the improvement of living,people use radio technology more and more both in daily life and research events such as the wireless communications and detection in the DUSA weather.The signal quality and the detected results both rely on the scattering and attenuation of the electromagnetic waves(EMWs)propagating in the DUSA storms.Results have shown that the charge on sand particle surface and the relative humidity(RH)can affect the scattering and attenuation obviously.In fact,the occurrence and the progress of the DUSA weather is related to the RH,and the RH change greatly before and after the DUSA weather.Therefore,in this paper,the model of EMWs scattering by the charged sand which can take RH into consideration is proposed.An investigation of the effect of the surface charge and RH on EMWs scattering and attenuation in DUSA weather is made.The main research contents and the results are as following:Shairf measured the DUSA's dielectric constant under different RH.The effective dielectric constant to the Mie theory for charged particle is applied which first deduced by Bohren and Hunt,the new model can be used to calculated the attenuation and scattering of the EMws when the RH is lower than 60%.The new model is named the effective model.The attenuation of EMWs propagating through the DUSA storms is calculated.It is found that the absorption is still bigger than the scattering in the microwave band.And if the RH is lower than 60%,the effect of the charge carried on the particle is significant.When the incident EMWs frequency is 4 GHZ,considering the effect of charge carried on the sand surface and the RH,if the visibility is less than 300 m,the attenuation with the uniform particle size is bigger than attenuation with the nonuniform particle size.When the RH is higher than 60%,the water molecules can be absorbed and form a water layer on the sand surface.So a new scattering model is deduced which can both take the sand surface charge and the RH into consideration which is named water-sand double layers model.The attenuation of the EMWs in the DUSA storms on the horizontal path and the ground-space oblique path is calculated.Comparing with the measured the attenuation and the value given in the other literature,the charge carried by the particle and the RH can both increase the attenuation.When the RH is lower than 60%,the effective model should be chosen,otherwise,the double layers model is used.It is found that when the RH is higher than 60%,the effect of the charge carried by the particle on the attenuation can be negligible.The effect of the RH on the attenuation is significant.When the RH increase from 0% to 80%,the increase of attenuation on the horizontal path is 190%,which is 105% on the ground-space oblique path.On the ground-space oblique path,the attenuation of EMWs caused by dust storm will increase with the increase of measuring height.If the vertical height is 2km,the attenuation decreases with the increase of the elevation angle of ground antenna.The near-field and the far-field of the scattering and some parameters correlated to the far-field,such as the scattering intensity and single scattering albedo etc.are also investigated.The electric field and magnetic field of the near-field increase with the increase of the radius of the particles and the frequency of the incident EMWs.Even if the effect of charge carried on the sand's particle and the RH,the scattering intensity is still sensitive to the size parameter.When the RH is higher than 60%,the effect of the charge on the scattering intensity can be negligible.RH can increase the scattering intensity,but the distribution of the scattering intensity will not be effected.Then the single scattering albedo(SSA)of the sand particle,which represents the proportion of scattering of particle in total extinction effect is investigated.From S-band to W-band(3GHz-100GHz),it is found the scattering and absorption both increase when the frequency increase,and the SSA also increase with the frequency of EMWs.And the RH can affect the SSA,when the RH change from 0% to 80%,the SSA can increase by 1600%.When the RH is lower than 60%,the effect charge on the SSA is obvious,but the effect of the temperature on the SSA can be negligible.When the RH is higher than 60%,the effect charge on the SSA can be negligible,but the effect of the temperature on the SSA must be taken into consideration.Based on the effective model and the double layers model,using the first-order multiple scattering approximation method to solve the radiative transport equation,the transmittance of EMWs increases with the increase of the visibility.The RH can affect the transmittance,the higher the RH,the lower the transmittance.The charge carried by the particle can affect the transmittance when the RH is lower than 60%,but when the RH is higher than 60%,the effect of the charge on the transmittance can be negligible.When the distance of EMWs propagating through is 1km,the effect of the multiple scattering can be negligible if the optical thickness is short.The models mentioned above can be used to calculate the attenuation and transmittance.