| As a new atmospheric wind field detection technology,ultraviolet lidar has caused extensive concern in recent years.Compared with Infrared wind lidar,the ultraviolet lidar is based on the Rayleigh scattering of air molecules,achieving short distance wind field measurement in the rare aerosol environment.It has the characteristics of confidentiality,omnidirectionality,and anti-interference and is an effective method for detecting under the radio silence condition.The current airborne ultraviolet wind lidar parameter setting mainly comes from the specific test in the experimental environment,and there is a lack of systematic theoretical research.However,the existing ultraviolet laser atmospheric transmission model has an extensive calculation and low calculation accuracy.And for specific application environments,it is challenging to obtain simulated echo signal data quickly.At the same time,the existing models lack the simulation of the ultraviolet light source,so that many research projects need to spend a lot of time in the selection and testing of the light source,which increases the purchase cost.Besides,the existing ultraviolet laser atmospheric transmission model lacks consideration of severe weather,such as atmospheric turbulence.The existing ultraviolet laser atmospheric transmission model lacks consideration of severe weather,such as turbulence.Turbulence will interfere with the echo stability of the ultraviolet laser signal and affect the accuracy of radar detection.In response to the urgent need to establish an airborne ultraviolet laser radar atmospheric transmission model,a systematic study on ultraviolet laser atmospheric transmission is carried out.A short-distance transmission model of airborne ultraviolet lidar based on the Monte Carlon next event estimation(MCNEE)is proposed.The influence of various system geometric parameters in the ultraviolet lidar system on the echo signal is studied.The relationship between the echo signal intensity and the geometric parameters of the system under different light intensity distribution of ultraviolet light sources is obtained.The simulation of the echo signal of the forward-looking wind lidar transceiver link in a turbulent environment is completed.The main research contents and contributions of the thesis are as follows:1.To further study the ultraviolet laser atmospheric measurement technology,the basic principles of the atmospheric propagation of ultraviolet laser radar signals have been studied.The atmospheric transmission theory of ultraviolet lidar signal and its existing shortcomings have been summarized and summarized.The research status of ultraviolet laser atmospheric scattering theory is introduced.Since the discrete coordinate method transforms the radiative transfer equation into a firstorder linear differential equation system,it is tough to solve it when calculating complex boundary conditions.In addition,the finite volume method approximates the scattering term in the radiation transmission equation through numerical integration,which has a large amount of calculation and a complicated model.The traditional Monte Carlo method counts the number of photons captured by the detector,and it isn't easy to obtain a convergent solution quickly.Therefore,this paper proposes an airborne ultraviolet lidar atmospheric transmission model based on Monte Carlo next event estimation.2.Due to an extensive calculation in the existing ultraviolet light atmospheric transmission model,it isn't easy to quickly obtain a convergent solution.Therefore,the Monte Carlo next event estimation was adopted,and single and multiple scattering models were established.For studying the atmospheric transmission problem of ultraviolet laser,the influence of different physical parameters(transceiving distance,non-coplanar off-axis angle of the transceiver,transceiver elevation angle,light source divergence angle,and detector field of view)on the echo signal is analyzed.The difference between single and multiple scattering is compared.The ultraviolet light atmospheric echo signal will be pulse broadened due to scattering,and the time delay of the echo signal will increase.In the single or multiple scattering model,the non-coplanar angle and the elevation angle of the transceiver,the divergence angle of the light source,and the field of view angle of the receiver will affect the radiation power density of the received light signal,the time delay of the pulse,and the pulse width.Due to the jitter of the aircraft,when the non-coplanar angle of the transmitting and receiving axis increases,the peak value of the power density of the ultraviolet echo signal decreases,and the pulse width becomes narrower.Specifically,under the condition of short-distance transmission and reception,the non-coplanar angle of the transmission and reception axis has an apparent influence on the echo.Still,the effect is weaker at a long distance.Multiple scattering cannot be ignored when the distance between receiving and sending is short,and the non-coplanar angle is large.Finally,the simulation results are compared with the traditional Monte Carlo model.The results show that the measurement results of the two models are consistent,which further demonstrates the correctness of the established model.The former can obtain the convergent solution more quickly in terms of the program operation time and has higher operation efficiency.3.As the existing ultraviolet light atmospheric transmission model lacks the consideration of the light intensity distribution of the light source,the random photon simulation method is adopted.The ultraviolet light source has been numerically mode.Using MCNEE,the influence of the characteristics of the light source on the ultraviolet echo signal is innovatively studied through simulation modeling.Under the conditions of the same geometric parameters of the transceiver and different light sources(different light source types,different laser working modes),the energy density distribution curve of the airborne ultraviolet lidar echo signal over time has been obtained.Calculations show that when the same non-coplanar angle is the same,the received light irradiance of a laser with a Gaussian distribution is one order of magnitude higher than that of a uniformly distributed light source.When the divergence half-angle of the laser light source is smaller,the transceiver system allows a larger maximum non-coplanar angle.From the calculation results of single and multiple scattering of the three light sources,it can be seen that when the distance between receiving and sending is small,multiple scattering has a significant influence on the maximum non-coplanar angle of the system.When the divergence angle of the light source is slight,multiple scattering contributes little to the return energy of the system.When the divergence angle of the light source is large,the contribution of multiple scattering in the echo signal is evident.4.As the existing airborne ultraviolet lidar atmospheric transmission model lacks the consideration of severe weather,the transmission problem of the airborne ultraviolet wind lidar transceiver link in a turbulent environment is get researched.Based on the existing coaxial ultraviolet transmission turbulence atmosphere model,a non-coaxial turbulence ultraviolet laser transmission model was established.The scintillation exponential probability density function of the echo signal of the noncoaxial ultraviolet laser link is calculated.The influence of the elevation angle of the transceiver under the turbulent environment on the ultraviolet light link is explored.The smaller the elevation angle,the weaker the turbulence flicker effect. |
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