Research On Wavefront Detection Algorithms For Artificial Sodium Beacon

The artificial beacon improves the sky coverage of the adaptive optics telescope system, and makes up the shortage of the natural beacon. The artificial sodium beacon has a better performance compared with the Rayleigh beacon, it is much more suitable for large aperture telescope system, which is the future direction of the development of artificial beacon. Due to the influence of atmospheric turbulence, noise and the geometric position of factors, the artificial sodium beacon spot detected by the system will be extended, elongated or low signal to noise ratio, which will reduce the wave front sensing accuracy. Therefore, it is of great significance to study how to improve the accuracy of the wave front detection of the artificial sodium beacon.Based on the adaptive optics telescope system, the mechanism of artificial sodium beacon and the process of wave front detection using shack Hartmann wave front sensor is introduced in this paper. It analyzes the causes of the expansion and extension of the beam spot, and the influence of the different signal to noise ratio, the length and the length of the beam on the wave front detection. It is introduced by a variety of methods to improve the accuracy of the system, which is an efficient and convenient method to improve the extraction accuracy of the spot centroid.The focus of this paper is to explore the accuracy of the centroid extraction algorithm in different spot cases. Therefore, this article selected the five algorithms,namely, Centre of Gravity, Weighted Centre of Gravity, Intensity Weighted Centroiding(divided into P-IWC, A-IWC, M-IWC), Threshold Centre of Gravity and Distance Centre of Gravity. At first, three kinds of spot(different signal to noise ratio,different extend and pull degree) are simulated, and the five algorithms are used to extract the center of mass. The preliminary conclusion can be obtained by comparing the extraction error of each algorithm. Then the process of further repeatability of simulation, through the statistical data can be concluded that for good signal to noise than with non-extended elongated spot, the accuracy of the algorithm is higher; for expansion and elongate spot, weighted centroid method is better than other algorithms;for the noise of the spot and need to according to different signal to noise ratio select appropriate parameters and algorithm. Finally, taking into account the actual situation is the noise, the expansion and the coexistence of multiple factors, the coexistence ofthe three kinds of light spot centroid extraction algorithm, in order to get more in line with the actual situation of the conclusion.In order to verify the accuracy of the simulation results, an experimental study is made on the different signal to noise ratio and the different degree of extension. Five kinds of algorithms are used to recover the wave front and the precision of the reconstruction. The simulation results are basically consistent with the experimental results.Through theory, simulation and experiment study, for different signal to noise ratio, extended, elongated spot, choose weighted centroid method(Weighted Centre of Gravity and Intensity Weighted Centroiding) can improve the detection accuracy of centroid. Finally, it is prospected that the future of centroid extraction can be aimed at the same spot array, with different types of spot types of the situation using different algorithms to improve the system’s wave front sensing accuracy.