Research On Centroid Detection Of Laser Illumination Beacon

Artificial beacon improves the sky coverage of the adaptive optics telescope system,and makes up the shortage of natural beacon.Compared with sodium beacon and Rayleigh beacon,laser illumination beacon solves the focus anisoplanatic and overall tilt detection problem.However,due to the influence of atmospheric turbulence,noises and the geometric position of the system itself,the laser illumination beacon spot detected by the system will expand,which will reduce the accuracy of wavefront detection.Therefore,it is of great significance to study how to improve the accuracy of laser illumination beacon wavefront detection.Based on the adaptive optics telescope system,this paper introduces the limitations of sodium beacon and Rayleigh beacon theoretically,and shows the advantages of laser illumination beacon relative to sodium beacon and Rayleigh beacon.This paper introduces the working principle of Shack-Hartmann wavefront sensor,analyzes the causes of daylight background,CCD readout noise,photon noise and background darkness based on it.The effects of these noises on the spot centroid detection are also introduced.This paper introduces several methods to improve the spot centroid detection accuracy,such as window method,threshold method,weighted centroid method and Top-hat morphological filtering method.Finally,this paper uses different methods to detect the spot centroid under different noise,different signal-to-noise ratio and different atmosphere coherence length,compares the spot centroid detection accuracy of these methods.The main point of this paper is to explore which method has a higher accuracy under different conditions to laser illumination beacon spots,and prospect for a high-precision method.To do this,we first simulating the laser illumination beacon spots,using the window method,Otsu method,Otsu method within a window and Top-hat morphological filtering method to a single-aperture ideal spot which under different noise and different signal-to-noise ratio.We analyze the effects of these four methods in removing CCD readout noise,photon noise,background darkness and daylight background,then propose a new method which combines Top-hat morphological filtering and Otsu method within a window.Use window method,Otsu method,Otsu method within a window,Top-hat morphological filtering method and the new method to a single-aperture ideal spot,a single-aperture spread spot and the whole aperture spread spots array in different atmosphere coherence length under a variety of noises.Beyond that,to study the performance of the new method,we simulate the centroid detection of whole aperture spread spots array in different signal-to-noise under multi noises.Through the simulation experiments,we can get this: For the centroid detection of spread laser illumination beacon spots under multi noises,when coherence length is greater than or equal to 7cm,the centroid detection error of new method is smaller than the window method,Otsu method,Otsu method within a window and Top-hat morphological filtering method.The new method can effectively extract the laser illumination beacon spots,improve the detection accuracy of the centroid.The content of this paper provides a technical basis for the centroid detection of laser illumination beacon.