Study On Electromagnetic Scattering Of Charged Non-spherical Sand Particles And Its Applications

The sand particles are generally non spherical particles in the sand/dust system,such as wind-blown sand flow,sandstorm,dust aerosol,etc.During the transportation and sediment of these non-spherical sand particles in the atmospheric turbulence,the particles collide and contact with other substances frequently,which results in charges transfer between sand particles,to make sand particles carry some net charges.In addition,the orientation angles of sand particles cannot remain constant due to the turbulent wind.However,it is still unclear what the scattering of electromagnetic waves(EMWs)is by non-spherical particles carried net charges on the particle surface,and it is also still unclear whether the orientation angles of sand particles observably affect the scattering of EMWs by non-spherical charged particles.Accurately predicting the scattering characteristics of sand-dust system is not only the key to evaluating the monitoring results by radar and satellite technologies,but also a guarantee for assessing high-speed wireless communication.It is also of great significance for understanding the micro-physical/optical phenomena of dust aerosol and the balance of atmospheric radiation.Therefore,the scattering model of charged non spherical sand particles is established for the first time,focusing on the influence of the shape,orientation and surface charges on the scattering characteristics of EMWs by the non-spherical charged particle system,further to apply this model to the study of attenuation of EMWs by non-spherical charged particle system in turbulent wind.The main research works are as follows.Firstly,aiming at the scattering of EMW by charged non-spherical sand particles,a charged non-spherical scattering model is established based on the T-matrix theory,and an analytic expression of the scattering field of a charged non-spherical sand particle is derived as well,which is applied to study the scattering field of non-spherical charged sand particle.In case of a charged spheroidal sand particle,the scattering,extinction cross-section,attenuation coefficient of EMWs by such particles are numerically calculated.The results indicate that there is a significant difference in the extinction cross section of EMWs by a charged spheroidal sand particle from the one by a charged spherical sand particle.With the equal volume,the extinction ability of a sphere is greater than that of a prolate spheroid,while less than that of an oblate spheroid when the EMW is incident along the symmetry axis of spheroid particle;when the orientation angle is equal to 90°,the extinction cross section of prolate ellipsoid will reach its maximum,the oblate ellipsoid,the minimum.When the charged density of prolate ellipsoidal sand particle is-200?C/m~2and size parameter x?2e-4,the extinction enhancement can be as high as 3?4 times.Secondly,the differential attenuation,differential phase shift and cross-polarization discrimination rate(XPD)of EMWs by charged non-spherical sand-dust system are derived based on the transformation matrix model and the scattering model of charged non-spherical particle.The differential attenuation,differential phase shift and depolarization of EMW with the frequency 3-37GHz propagating in a charged non-spherical sand-dust system under different parameters are investigated.It is found that for a given polarized wave,the higher the frequency is,the greater the depolarization is;the depolarization of circularly polarized wave is greater than the one of linearly polarized wave with the same frequency.For example,the XPD of 37 GHz circularly polarized wave is 16d B/lower than that of linearly polarized wave,and 30d B/km smaller than that of 3GHz circularly polarized wave.The statistical relationship between co-polarization attenuation(CPA)and XPD of 3-37GHz microwave propagating in the dust system is studied for the first time,and the effect of surface charges on CPA-XPD is also considered,where the surface charges carried by sand particles can significantly enhance the depolarization effect of microwave in sand-dust system once the frequency is less than 15GHz,and when CPA=1dB and frequency ?=10GHz,XPD caused by sand particles is about 2.5 times lower than XPD caused by raindrops.Finally,the radiation transmission of EMWs by considering into the multiple scattering of electromagnetic signal propagating in long-distance and low-visibility sand-dust system is simulated by Mont Carlo method,and the transmittance and attenuation coefficient of EMWs are derived according to the Beer-Lambert law.It is also found that the visibility of dusty weather and the propagation distance of EMWs are the main factors that cause multiple scattering of EMWs,and charged non-spherical sand particles can significantly enhance multiple scattering effect.A visibility threshold of sand-dust system considering the multiple scattering effect of EMWs is presented.In addition,the transmittance and attenuation coefficient of EMWs in the near infrared(NIR)band and visible light(VIS)band are measured as well.The theoretical results predicted by considering multi scattering by the charged spheroid particles are much close to the experimental results,especially in the low visibility.It indicates that when the visibility is less than 100m,the multiple scattering of EMWs in NIR and VIS bands must be considered.