| When the laser beam propagates in the atmosphere,the randomly fluctuating refractive index causes a series of optical turbulence effects,such as beam wander,scintillation and wavefront aberration.These effects seriously restrict the development of remote sensing imaging system and laser communication.In order to evaluate the impact of atmospheric turbulence on optical imaging systems and laser communication systems,it is necessary to accurately measure the temporal and spatial distribution of optical turbulence.The atmospheric refractive index structure constant is generally used to measure the intensity of atmospheric turbulence,and its distribution with altitude is called atmospheric turbulence profile.The development of differential wavefront lidar monitoring atmospheric turbulence profile is conducive to accurately obtaining atmospheric turbulence information with high spatial resolution.Numerical simulation is the theoretical basis of modeling,which can provide optimization for the configuration of experimental system parameters.At the same time,it can be mutually verified with experimental results.This thesis analyzes the principle and method of differential wavefront lidar system monitoring atmospheric turbulence profile,and focuses on numerical simulation research.The feasibility and reliability of differential wavefront lidar for atmospheric turbulence profile detection are verified by simulation and experimental results.According to the theory of turbulent phase screen,the equation of lidar,the principle of incoherent imaging,and the grid sampling constraints,numerical simulation has obtained the two spots formed by two-apertures of the telescope of differential wavefront lidar.On the basis of difference motion variance of imaging spots at different heights,the atmospheric coherence length and the atmospheric refractive index structure constant at the corresponding height can be further retrieved.Under the condition of simulation test parameters in this thesis,the analysis of numerical simulation results can be divided into four parts:(1)As the intensity of turbulence increases,the variance of sharpness diameter of spots in the sky increases,that is,the degree of beam energy concentration changes greatly.(2)The sharpness diameter of the imaging spot decreases rapidly within 2 km and slowly decreases beyond 2 km.When the simulation height reaches 10 km,the sharpness diameter of the imaging spot decreases to 2.45×10-4 m.(3)The profiles of atmospheric turbulence are compared with the HV5/7(Hufnagel-Valley 5/7)model input by the simulation.The results show that the two have a good consistency in the overall trend.The reliability of differential wavefront lidar for detecting atmospheric turbulence is preliminarily proved.(4)In order to explore the influence of different parameters on the simulation results,simulation tests with different grid spacing and transmission times are designed.The results show that selecting small mesh spacing can reduce the error of simulation results.When conditions permit,obtaining as many samples as possible is conducive to accurately and effectively obtaining the atmospheric turbulence profiles.The preliminary detection experiments are carried out by using the self-developed differential wavefront lidar system.Through the comparison of the echo photon number profiles obtained by experimental detection and numerical simulation,it is found that they have a good consistency.The correlation analysis is carried out on the two,and the multiple correlation coefficient reaches 0.98.After processing the preliminary experimental results,the variation of atmospheric coherence length with time and the profiles of the atmospheric refractive index structure constant are obtained.Through the analysis of the experimental results,it is obtained that the differential wavefront lidar has reliable detection performance. |
PDF Full Text Request