弱信號哈特曼波前探測算法的研究
發(fā)布時間：2018-07-18 15:47
【摘要】：自適應光學技術(shù)已經(jīng)廣泛應用于大口徑地基望遠鏡系統(tǒng)中,用于克服大氣湍流引起的波前畸變。波前校正效果直接受自適應系統(tǒng)的波前探測精度影響。本論文對液晶自適應光學系統(tǒng)中的弱信號哈特曼波前探測算法進行了深入研究。光斑質(zhì)心探測精度是哈特曼波前探測器最重要的性能指標,它決定了哈特曼波前探測器的探測能力。在進行弱信號探測時光子噪聲嚴重影響了質(zhì)心探測精度。考慮到光子噪聲在幾何位置上重疊于信號,利用足夠小的幾何區(qū)域內(nèi)光能量變化不大、而光子噪聲則起伏較大的預想,提出了基于局部均值技術(shù)和加權(quán)技術(shù)的局部均值加權(quán)算法抑制光子噪聲的影響。在子孔徑光子數(shù)為100(5.5星等)、大氣相干長度分別為10cm和5cm的觀測情況下,采用局部均值加權(quán)算法抑制光子噪聲后,使質(zhì)心探測誤差的RMS值分別由傳統(tǒng)重心法的0.142?和0.181?減少到0.112?和0.145?,均減少了???。?對于大氣湍流引起的波前畸變,Zernike模式系數(shù)并不是統(tǒng)計獨立的,因此并不是最有效的重構(gòu)模式。相比Zernike模式,利用系數(shù)統(tǒng)計獨立的K-L模式進行波前重構(gòu)能提高波前重構(gòu)精度。在子孔徑數(shù)20×20、大氣相干長度10cm、質(zhì)心探測誤差0.1?的情況下,波前重構(gòu)誤差RMS值可以由??????減小到??????,減小了???。不同觀測條件下最佳的重構(gòu)模式數(shù)不同,模式數(shù)過多或者過少都會導致波前重構(gòu)誤差增大。因此提出采用差分星點像運動法從哈特曼探測的光斑質(zhì)心陣列數(shù)據(jù)中同時統(tǒng)計出大氣相干長度和質(zhì)心探測誤差,繼而獲得最佳重構(gòu)模式數(shù)的方法。為了保證湍流的各態(tài)歷經(jīng),同時考慮計算量,將該估計方法中子孔徑中心間隔確定為1個子孔徑,將采樣時間長度和采樣時間間隔分別確定為5000ms和50ms。即使在質(zhì)心探測誤差0.25?的情況下,根據(jù)該方法統(tǒng)計的大氣相干長度和質(zhì)心探測誤差也能夠使波前重構(gòu)誤差達到最小。液晶自適應光學系統(tǒng)采用哈特曼探測器進行傾斜像差探測,省卻了專門的傾斜探測器,簡化自適應光學系統(tǒng)的同時也提高了系統(tǒng)的能量利用率。將所有有效光斑質(zhì)心偏移平均作為傾斜信號的小光斑法探測精度高,但動態(tài)范圍小,而將所有光斑的重心偏移作為傾斜信號的大光斑法雖然動態(tài)范圍可以擴大到整個CCD面板,但是探測誤差又太大。為了能夠?qū)Υ笳穹鶅A斜進行高精度校正,提出通過網(wǎng)格劃分識別出子光斑和通過模板匹配將子光斑與其對應的微透鏡進行關(guān)聯(lián)的方法。該方法動態(tài)范圍與大光斑法相同,而精度與小光斑法相同,即使在子孔徑光子數(shù)100(5.5星等)、大氣相干長度5cm的觀測條件下,該方法依然能夠保證傾斜回路閉環(huán),閉環(huán)后傾斜探測誤差PV值為0.07″�？傊�,本論文進行的弱信號哈特曼波前探測算法的研究不僅提升了自適應系統(tǒng)校正效果,而且使得自適應系統(tǒng)能夠在更加極端的觀測條件下工作。
[Abstract]:Adaptive optics has been widely used in large aperture ground-based telescope systems to overcome wavefront distortion caused by atmospheric turbulence. The effect of wavefront correction is directly affected by the detection accuracy of the adaptive system. In this paper, the weak signal Hartmann wavefront detection algorithm in liquid crystal adaptive optical system is studied. The accuracy of spot centroid detection is the most important performance index of Hartmann wavefront detector, which determines the detection ability of Hartmann wavefront detector. The accuracy of centroid detection is seriously affected by the noise at the time of weak signal detection. Considering that the photon noise overlaps the signal in a geometric position, the energy of light within a sufficiently small geometric region does not change much, while the photon noise is expected to fluctuate considerably, A local mean weighted algorithm based on local mean technique and weighted technique is proposed to suppress the influence of photon noise. When the photon number of sub-aperture is 100 (5.5 stars et al.) and the atmospheric coherent length is 10cm and 5cm respectively, the local mean weighted algorithm is used to suppress photon noise, and the RMSs of centroid detection error are changed from 0.142? And 0.181? Reduced to 0. 1 12? And 0.145? The Zernike model coefficients of wavefront distortion caused by atmospheric turbulence are not statistically independent and therefore are not the most effective reconstruction model. Compared with Zernike model, using K-L model, which is statistically independent, can improve the precision of wavefront reconstruction. At the subaperture number of 20 脳 20, the atmospheric coherence length is 10 cm, the centroid detection error is 0.1? The RMS value of the wavefront reconstruction error can be determined by? To reduce to a small, reduced. The optimal number of reconstructed modes is different under different observation conditions. Too many or too few modes will lead to the increase of wavefront reconstruction error. Therefore, the differential star image motion method is proposed to calculate the atmospheric coherent length and centroid detection error simultaneously from Hartmann's centroid array data, and then obtain the best reconstruction mode number. In order to ensure the ergodic states of turbulence and take into account the computational complexity, the central interval of neutron aperture is determined to be one sub-aperture, and the sampling time length and sampling time interval are determined to be 5000ms and 50ms, respectively. Even if the centroid detection error is 0. 25? The atmospheric coherence length and centroid detection error calculated by this method can also minimize the wavefront reconstruction error. In liquid crystal adaptive optical system, Hartmann detector is used to detect skew aberration, which saves the special tilting detector, simplifies the adaptive optical system and improves the energy efficiency of the system. The small spot method, which uses the average centroid migration of all effective light spots as tilting signals, has high detection accuracy but small dynamic range. However, the large spot method, which uses the center of gravity of all light spots as tilting signals, can be extended to the whole CCD panel, although the dynamic range can be extended to the whole CCD panel. But the detection error is too big. In order to correct the large amplitude tilt accurately, a method is proposed to identify the sub-spot by mesh division and to associate the sub-spot with the corresponding microlens by template matching. The dynamic range of the method is the same as that of the large spot method, and the precision is the same as that of the small spot method. Even under the condition of the photon number of sub-aperture 100 (5.5 stars, etc.) and the atmospheric coherent length 5cm, the method can still guarantee the closed loop of the tilt loop. The detection error PV is 0.07 ". In a word, the research of weak signal Hartmann wavefront detection algorithm in this paper not only improves the correction effect of adaptive system, but also enables the adaptive system to work under more extreme observation conditions.
【學位授予單位】：中國科學院研究生院(長春光學精密機械與物理研究所)
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O439
本文編號：2132385
[Abstract]:Adaptive optics has been widely used in large aperture ground-based telescope systems to overcome wavefront distortion caused by atmospheric turbulence. The effect of wavefront correction is directly affected by the detection accuracy of the adaptive system. In this paper, the weak signal Hartmann wavefront detection algorithm in liquid crystal adaptive optical system is studied. The accuracy of spot centroid detection is the most important performance index of Hartmann wavefront detector, which determines the detection ability of Hartmann wavefront detector. The accuracy of centroid detection is seriously affected by the noise at the time of weak signal detection. Considering that the photon noise overlaps the signal in a geometric position, the energy of light within a sufficiently small geometric region does not change much, while the photon noise is expected to fluctuate considerably, A local mean weighted algorithm based on local mean technique and weighted technique is proposed to suppress the influence of photon noise. When the photon number of sub-aperture is 100 (5.5 stars et al.) and the atmospheric coherent length is 10cm and 5cm respectively, the local mean weighted algorithm is used to suppress photon noise, and the RMSs of centroid detection error are changed from 0.142? And 0.181? Reduced to 0. 1 12? And 0.145? The Zernike model coefficients of wavefront distortion caused by atmospheric turbulence are not statistically independent and therefore are not the most effective reconstruction model. Compared with Zernike model, using K-L model, which is statistically independent, can improve the precision of wavefront reconstruction. At the subaperture number of 20 脳 20, the atmospheric coherence length is 10 cm, the centroid detection error is 0.1? The RMS value of the wavefront reconstruction error can be determined by? To reduce to a small, reduced. The optimal number of reconstructed modes is different under different observation conditions. Too many or too few modes will lead to the increase of wavefront reconstruction error. Therefore, the differential star image motion method is proposed to calculate the atmospheric coherent length and centroid detection error simultaneously from Hartmann's centroid array data, and then obtain the best reconstruction mode number. In order to ensure the ergodic states of turbulence and take into account the computational complexity, the central interval of neutron aperture is determined to be one sub-aperture, and the sampling time length and sampling time interval are determined to be 5000ms and 50ms, respectively. Even if the centroid detection error is 0. 25? The atmospheric coherence length and centroid detection error calculated by this method can also minimize the wavefront reconstruction error. In liquid crystal adaptive optical system, Hartmann detector is used to detect skew aberration, which saves the special tilting detector, simplifies the adaptive optical system and improves the energy efficiency of the system. The small spot method, which uses the average centroid migration of all effective light spots as tilting signals, has high detection accuracy but small dynamic range. However, the large spot method, which uses the center of gravity of all light spots as tilting signals, can be extended to the whole CCD panel, although the dynamic range can be extended to the whole CCD panel. But the detection error is too big. In order to correct the large amplitude tilt accurately, a method is proposed to identify the sub-spot by mesh division and to associate the sub-spot with the corresponding microlens by template matching. The dynamic range of the method is the same as that of the large spot method, and the precision is the same as that of the small spot method. Even under the condition of the photon number of sub-aperture 100 (5.5 stars, etc.) and the atmospheric coherent length 5cm, the method can still guarantee the closed loop of the tilt loop. The detection error PV is 0.07 ". In a word, the research of weak signal Hartmann wavefront detection algorithm in this paper not only improves the correction effect of adaptive system, but also enables the adaptive system to work under more extreme observation conditions.
【學位授予單位】：中國科學院研究生院(長春光學精密機械與物理研究所)
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O439
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