Title:study On The Use Of Partical Image Velocimetry To Obtain Atmospheric Lateral Wind Speeds

Wireless optical communication has the advantages of large communication capacity,strong anti-interference and good confidentiality,which gradually becomes one of the hot spots of academic research.Laser light transmission in atmospheric turbulence produces a wavefront phase distortion phenomenon,in which transverse wind speed is an important factor affecting the wavefront phase.In the wireless optical communication system,the relationship between wavefront phase and transverse wind speed is combined to improve the effect of wavefront correction by using image processing techniques to obtain the transverse wind speed from the light spot at the receiving end and to explore the effect of transverse wind speed on the beam transmission process.The main work is as follows.1.A numerical simulation of the phase distortion wave front caused by atmospheric turbulence disturbances is carried out using Zernike polynomial and power spectrum inversion methods.Since the phase screen generated by the Zernike polynomial simulation can suffer from the deficiency of high frequency information,this paper applies the power spectrum inversion method to establish a multi-phase screen to simulate atmospheric turbulence.The simulation analyses the transmission of Gaussian beams under weak,moderate and strong turbulence.The results show that after the beam is modulated by the multi-phase screen turbulence,the spot generated at the receiving end will show spot scattering and centre-of-mass drift,and these phenomena will change more obviously as the turbulence intensity continues to increase.2.The intercorrelation algorithm is the core of particle image velocimetry(PIV),which is used to precisely match two consecutive frames of light spot particle images to obtain the scattering velocity as the spot morphology varies with time.The simulation analyses the implementation of dynamic phase screen to simulate the transverse wind speed.By setting the moving speed and moving angle of the phase screen,the effect of different sizes and positions of the transverse wind speed on the light spot particle images under weak turbulence,medium turbulence and strong turbulence is simulated.3.A wireless optical communication system was built and outfield experiments with transmission distances of 1.3,10.3 and 100 km were carried out,with the transmitter sending signal light in the atmospheric environment and the receiver collecting a large amount of light spot image data.The PIV particle velocimetry technique is applied to the spot images to obtain the transverse wind speed along the laser transmission path,and the exposure time of the wavefront correction process is adjusted according to the resulting transverse wind speed to obtain the compensated optical power value.The feasibility of the method to obtain the transverse wind speed in atmospheric turbulence using PIV particle image velocimetry is verified,and it is validated that the correction performance of the adaptive optics system can be effectively improved by wind speed compensation.In this paper,the lateral wind speed in atmospheric turbulence is determined by using a combination of simulation and experiment.The results show that the average lateral wind speed values obtained using this technique are 1.5739,1.7160 and 1.7688 m/s for transmission paths with transmission distances of 1.3,10.3 and 100 km respectively,with correlation coefficients of 0.9674,0.9346 and 0.91591 between them and the actual wind speed at that time.The calibration process for the three transmission links is The lateral wind speed compensation was obtained to improve the corrected optical power values from-25,-43 and-38 dBm to-16,-21 and-23 dBm,respectively.The feasibility of the method to obtain the lateral wind speed in atmospheric turbulence using PIV particle image velocimetry was verified,and the correction effect of the system by wind speed compensation was higher and converged faster than before the compensation.