Research On Atmospheric Turbulence Laser Imaging Detection Technology Based On Cooperative Target

Light propagation in turbulent atmosphere involves not only the theory of wave propagation in random media,but also the complex properties of atmospheric turbulence.With the continuous development of high-resolution imaging technology and computer technology,Using a laser imaging method of atmospheric turbulence can more intuitively obtain the characteristics of the temporal and spatial distribution of atmospheric turbulence,and understand the laser atmospheric turbulence transmission effect and turbulence intensity.At present,the detection targets of this method are mostly optical turbulence characteristic quantities,but few dynamic turbulence characteristic quantities.Traditional atmospheric turbulence laser transmission imaging experiments often use the form of emitting laser at one end and receiving the laser spot with a diffuse reflection screen at the other end where sets high-speed camera to capture images.This method not only requires high-power lasers and field operators,but also has shortcomings such as difficult alignment of long-distance light,mountain and island terrain restrictions.However,we find that using a 3M reflective film and large-aperture telescope can integrate the laser transmitting and receiving system,and effectively overcome the above problems.Therefore,this article mainly use the atmospheric turbulence laser imaging detection system based on 3M reflective film,which integrates the transmitter and collection system in a single end to do some experimental study.Our detecting target are two-dimensional horizontal wind vector and sensible heat flux.The former can directly reflect the motion characteristics of atmospheric turbulence,and its accurate detection is of great significance in meteorological,maritime,railway,military and other aspects.The latter is helpful to understand the interaction between near-surface and near-surface atmosphere the diffusion of urban air pollutants and the change of weather conditions.Specific research contents can be divided into the following two aspects:(1)A method for detecting two-dimensional transverse wind vectors in atmospheric turbulence using laser shadow images is proposed,and the feasibility of this method is analyzed through numerical simulation and experimental research.Firstly,the transverse wind on the optical transmission path is simulated by moving the infinite phase screen and the whole pixel search algorithm based on the normalized cross-correlation principle is used to calculate the moving speed of the laser shadow.Secondly,the influence of the transverse wind and its nonuniform distribution on the moving speed of the laser shadow are analyzed.Then,a comparative verification experiment of laser shadow imaging detection on a 100 m path is carried out,and a linear fitting relationship between the shadow movement speed in the horizontal direction and the average lateral wind speed of the path is obtained.The results prove that it is completely feasible to obtain the average two-dimensional transverse wind vector of the path by using the short-exposure laser shadow image,which have a significant impact on the remote measurement of wind field in atmospheric turbulence and related engineering applications.(2)The turbulent atmosphere single-ended laser imaging detection system is used to measure the average sensible heat flux of the path.The experiment of laser propagation in turbulent atmosphere with transmission distance of 1km under different weather conditions is carried out,and the atmospheric coherence length meter and meteorological sensor are set up in the same path for synchronous acquisition to obtain turbulence intensity information and meteorological parameters.The diurnal variation of laser speckle moving characteristics and the morphological difference under different weather are qualitatively analyzed.The atmospheric refractive index structure constant is calculated from the scintillation index and the variance of the center of mass drift respectively.It is found that the results obtained from the scintillation index had the shortcoming of small dynamic range,while the result calculated from the variance of the center of mass drift is very close to the calculation result of the atmospheric coherence length meter.The article conducts a preliminary theoretical analysis of the reasons for the differences between the two methods,and choses the drift method to calculate the path average sensible heat flux with the meteorological parameters.So,we directly observe the temporal and spatial changes of the laser speckle shape,and use the laser speckle image to calculate the average sensible heat flux of the path under the unstable stratification.This is of great significance for understanding the interaction between the ground and the atmosphere,the diffusion and propagation of atmospheric pollutants,and weather changes,and further expands the application range of the turbulent atmosphere laser imaging detection system.