The Study On Measurement Of Slant Atmospheric Transmittance In Finite Distance

The transmission of laser in a turbid atmosphere causes the attenuation of laser energy due to the action of the atmospheric medium,and the degree of attenuation is generally evaluated using the atmospheric transmittance.In the current research work,the study on the transmittance of the whole layer of the atmosphere has been mature.The main research methods are solar(stellar)radiometer,laser heterodyne,etc.These instruments have played a certain role in the development of atmospheric science.The backscattering lidar is the main method for the measurement of atmospheric transmittance in finite distance.Accurate measurement of atmospheric transmission in finite distance is important for the application of various laser devices,laser communication,and aeronautical observations.However,the traditional backscattering lidar has the influence of blind zone and transition zone at the near end,which limits its application in the measurement of atmospheric transmittance in finite distance.This paper mainly studies the atmospheric transmittance in finite distance near the ground using the new imaging lidar system to compensate blind zone and transition zone data of backscattering lidar:1.The construction of the imaging lidar system was completed.According to the Scheimpflug imaging principle,in the situation where the object plane is nonparallel to the lens plane,sharp focus can be achieved by tilting the image sensor so that the image plane intersects both with the object-and lens-planes;the pixel-distance relationship is obtained according to the calibration formula;through the theoretical calculation,the scattering signal received by the new imaging lidar system is almost backscattering;the distance resolution of the atmospheric backscattering signal is performed,and the clear imaging and detection of the atmospheric backscattering signal from close range to long distance is realized.2.The image data obtained by the lidar system was pre-processed before inversion.By flattening the obtained CCD image,the error caused by the uneven pixel response was reduced;the flatting image was de-noised by using two-dimensional wavelet de-noising method to improve the signal-to-noise ratio of the image;one-dimensional lidar signal was extracted using Gaussian fitting method.3.The GA and Broyden algorithms were proposed to calculate the extinction coefficient boundary value in the horizontal direction,and the Klett algorithm was used to invert the horizontal extinction coefficient profile to obtain the horizontal atmospheric visibility and atmospheric transmittance.In this paper,it was also proposed that the GABP intelligent algorithm to obtain better results by predicting visibility through lidar signals.4.The GA-IMBR-Fernald algorithm was proposed to invert the extinction coefficient profile in the vertical direction.The focus of this algorithm is to obtain the extinction coefficient boundary value in the vertical detection range.The feasibility of the algorithm was first verified by simulation.The simulation study obtains a new extinction coefficient profile by inputting a simulated extinction coefficient profile and performing a series of forward modeling,noise addition,de-noising and inversion.The root mean square errors between the two profiles are all within 0.02km-1.After that,the extinction coefficient profile in the range of 600-1000m was compared with the traditional backscattered lidar,and the overall relative error was within the acceptable range.Finally,the atmospheric transmittance in finite distance in the vertical direction for several days is obtained.5.The atmospheric extinction coefficient profile and atmospheric transmittance in the slant range direction in the finite distance were measured.The result of single-angle slant path detection and direct vertical detection were compared and verified the feasibility.Then,multiple angles of the slant path detection were carried out,and the detection results of each slant angle and the vertical direction were compared and analyzed.Finally,the slant atmosphere at a certain angle was detected for a long time,and the two-dimensional evolution graph of the extinction coefficient with distance-time was obtained.Then the slant atmospheric transmittance was obtained.