| The research on the scattering characteristics of rough objects has important academic value in the fields of national defense,aerospace and airborne lidar target detection.Based on the theory of laser scattering from rough objects,the second-order and fourth-order statistical characteristics of laser scattering from rough objects are calculated numerically.Using the basic theory of laser beam scattering,a theoretical model of rough surface multi-beam scattering is established.According to the basic theory of rough target synthetic aperture lidar(SAL),the working mode of multi-transmission and multiple-receiving synthetic aperture lidar is given.Using range Doppler imaging algorithm,the imaging simulation of simple rough target is obtained.The main work of this thesis includes:1.According to the Beckmann theory of rough surface and Gaussian moment theorem,the analytical expressions of two kinds of two-frequency cross-correlation functions for two-dimensional rough surface are derived,and the fourth-order moment of scattering field is calculated.The influence of incidence,observation conditions and rough surface characteristic parameters on dual-frequency cross-correlation function and fourth-order moment function is analyzed emphatically.Based on physical optics approximation,taking rough sphere and cone targets as examples,the variation of incoherent component ratio of rough target with physical size and target material is numerically calculated under plane wave laser incidence.2.Using Kirchhoff approximation,a double-surface and multi-beam scattering model of rough surface is established to discuss the surface multi-beam scattering characteristics,mainly taking three beams as an example.The expression of normalized correlation coefficient of double-beam and multi-beam scattering intensity is derived,and the influencing factors of the ratio of three-beam coherent scattering intensity are analyzed.The variation of diffuse intensity and scattering intensity correlation coefficient with angle difference,correlation length and roughness is calculated numerically,which provides theoretical basis for the later research on speckle problem of 3D rough target.3.The two-dimensional impulse response function of SAL system is obtained by using the impulse response characteristics,and the LFM signal is simulated.This article briefly introduces the basic principle of the forward side view strip mode SAL,establishes the system model of the multi-transmission and multi-receive SAL,and verifies the feasibility of the multi-transmission and multi-receive SAL system.Finally,the range Doppler algorithm is used to process the original echo signals to obtain the azimuth phase map and the two-dimensional and three-dimensional imaging maps of the SAL target imaging in the strip mode.Numerical results show:the wavelength difference and roughness have a significant effect on the fourth-order moment of the scattering field of the rough surface,and the peak height in the mirror reflection direction is inversely proportional to the change of the scattering angle.The radius,correlation length and roughness of the sphere have great influence on the incoherent component ratio.It can be found that the peak position of the incoherent component ratios of the corresponding curves of cone targets are different with different roughness,but they are all located in the mirror reflection direction.The gold-plated material has a smaller incoherent component ratio than the polished aluminum material,and the change in radius is proportional to the incoherent component ratio.In the three beams scattering on rough surface,the cases of equal incidence angle,equal azimuth angle and unequal time beam are discussed respectively.With the change of roughness,correlation length and other factors,it is inversely proportional to the diffusion intensity,and the correlation coefficient of double beam scattering intensity is not affected by the interference intensity and the backscattering effect occurs.The multi-transmitter and multi-receiver SAL mode takes the three-transmitter and three-receiver SAL mode as an example,and uses the echo data of three-transmitter and three-receiver in the azimuth direction to obtain large-bandwidth unambiguous data imaging,thus eliminating Doppler ambiguity.By comparing the azimuth phase simulation results of point targets and rectangular targets,it can be found that the azimuth phase diagram curve of point targets is smoother than that of rectangular target. |
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