Analysis And Experimental Study Of Laser Scattering Characteristics Based On Kirchhoff Approximation

The laser incident wavelength,the surface roughness of the target and the optical constant of the target material have important influence on the laser scattering characteristics of the target.At present,laser scattering characteristics are quantitatively described by bidirectional reflection distribution function(BRDF).However,most of the existing BRDF mathematical models can only study the scattering characteristics in the case of single wavelength,and the experimental measurement device can not obtain BRDF data at any wavelength due to the frequency modulation range of the laser.In view of this limitation,this paper analyzed the influence of laser incident wavelength and target surface roughness on laser scattering characteristics based on the analytical theory of electromagnetic scattering,and verifies the results through experiments.On this basis,the calculation method of LRCS for 3D target element was established,and the factors affecting the intensity of lidar echo were analyzed based on lidar equation.Firstly,the definition of BRDF and two classical mathematical models of BRDF were introduced,and the functional relationship among BRDF,LRCS and LIDAR equation was studied.This paper introduces the derivation process of BRDF analytical theoretical model(Kirchhoff approximation)when the target roughness is larger than the incident wavelength and less than the incident wavelength.The Lorentz-Drude model describing the optical constant of target material is briefly introduced,and the variation of optical parameters of aluminum and copper with wavelength is analyzed.Secondly,the optical constant of the material was introduced into the Kirchhoff approximation method(divided into scalar approximation method and resident phase approximation method),and the BRDF of aluminum and copper targets under different incident wavelength ? and roughness ? was simulated to obtain the laser scattering characteristics of the target.The laser wavelength range was 0.3?1.55 ?m and the target surface roughness range was 0.1?10 ?m.The results show that the target BRDF has a strong dependence on the roughness and a small dependence on the incident wavelength at ???,and the change caused by the wavelength can be ignored at ??10?.When???,target BRDF of the incident wavelength and the dependence of the roughness are strong,especially in ???3,with the increase of wavelength target coherent scattering significantly enhanced.Thirdly,based on the BRDF mathematical model(FOI model and Cook-Torrance model),the scattering characteristics of the target were fitted,and the relationship between the model parameters as a function of the incident wavelength and the target surface roughness was studied.The wavelength parameters were introduced into the FOI model.Based on the lidar equation,the effects of laser incident wavelength,target surface roughness,target attitude and detection range on the echo intensity of typical targets were studied.The results show that the variation law of echo energy with incident wavelength and roughness is consistent with the variation law of BRDF with incident wavelength and roughness.In addition,the target attitude and detection distance also have a great influence on the target echo intensity,so it is necessary to take comprehensive consideration when detecting the target.Finally,the dual-wavelength lidar measurement system was introduced,and the BRDF of eight kinds of samples were measured experimentally,the simulation results were verified by the experimental data,and the calculation method of target BRDF at different wavelengths was modified.The results show that the experimental phenomenon is consistent with the simulation results,and the root mean square error of simulation data and experimental data is less than 0.5786 at different incident wavelengths.After the correction of the simulation data,the root mean square error is less than 0.3553.