广角望远镜实时自动调焦的清晰度评价方法
|
摘要
SVOM天文卫星附属的地基广角相机阵(GWAC)含有36个广角望远镜,其短时标的高精度自动观测建立在实时自动调焦的基础上,本文将对广角望远镜实时自动调焦的图像清晰度评价方法进行研究和实现。文章首先比较研究了常用望远镜图像清晰度评价方法的原理及在GWAC系统上的适用性,得出基于星像能量集中度的两种方法:星像50%能量半径、PSF的FWHM值适用于GWAC系统。区别于常用天文软件包IRAF费时的算法,本文提出了基于点源强度分布进行PSF拟合计算FWHM的方法,并进一步探究了诸如拟合模型、选星标准、定心精度、拟合半径、插值方法、插值间隔、FWHM后处理等关键方法参数对FWHM计算精度与速度的影响。最终得到一套适用于GWAC实时自动调焦的清晰度评价方法,并用C++编程实现。本文中方法 FWHM计算误差为0.046pixel,精度与IRAF相当,计算焦点位置一致;单图(挑选后约300颗星)计算时间为0.67s,约为IRAF计算时间的1/20,满足GWAC系统自动调焦的精度与实时性需求。研究结果在GWAC系统中得到应用,并可为其他自动化望远镜观测系统提供参考。
Ground Wide Angle Cameras(GWAC)of the astronomy satellite SVOM contains 36 wideangle telescopes,and its high-precision automatic observation of short exposure is established on realtime auto-focusing,in this paper,we focus on the research and realization of image definition evaluation for real-time auto-focusing on GWAC.At first,principles of image definition evaluation methods of common telescope and applicability on GWAC system were researched,thus two kinds of methods based on encircled energy of star image were obtained,namely radius of 50%energy of stars and the full width of half maximum(FWHM)of point spread function(PSF),were suitable for GWAC system.Different from time-consuming algorithm of common astronomy software packageIRAF,method of calculating FWHM via PSF fitting calculation based on source intensity distribution was proposed,and further influence of key method parameters such as fitting model,star-choosing standard,centring precision,fitting radius,interpolation method,imterpolation interval,FWHM after-treatment,etc on calcu-lation precision and speed of FWHM was researched.A set of definition evaluation methods that are applicable to GWAC real-time automatic focusing were acquired in the last,and it is realized by C+ + programming.Calculation error of FWHM method in the paper is0.046 pixel,the precision is equal to IRAF approximately and calculated focus location is the same;calculation time of single graph(about 300 stars after selection)is 0.67 swhich is 1/20 of calculation time for IRAF.It satisfies precision and real-time requirements of automatic focusing for GWAC system.The research results havebeen applied in GWAC system and provide reference for other automatic observing system of telescope.
Ground Wide Angle Cameras(GWAC)of the astronomy satellite SVOM contains 36 wideangle telescopes,and its high-precision automatic observation of short exposure is established on realtime auto-focusing,in this paper,we focus on the research and realization of image definition evaluation for real-time auto-focusing on GWAC.At first,principles of image definition evaluation methods of common telescope and applicability on GWAC system were researched,thus two kinds of methods based on encircled energy of star image were obtained,namely radius of 50%energy of stars and the full width of half maximum(FWHM)of point spread function(PSF),were suitable for GWAC system.Different from time-consuming algorithm of common astronomy software packageIRAF,method of calculating FWHM via PSF fitting calculation based on source intensity distribution was proposed,and further influence of key method parameters such as fitting model,star-choosing standard,centring precision,fitting radius,interpolation method,imterpolation interval,FWHM after-treatment,etc on calcu-lation precision and speed of FWHM was researched.A set of definition evaluation methods that are applicable to GWAC real-time automatic focusing were acquired in the last,and it is realized by C+ + programming.Calculation error of FWHM method in the paper is0.046 pixel,the precision is equal to IRAF approximately and calculated focus location is the same;calculation time of single graph(about 300 stars after selection)is 0.67 swhich is 1/20 of calculation time for IRAF.It satisfies precision and real-time requirements of automatic focusing for GWAC system.The research results havebeen applied in GWAC system and provide reference for other automatic observing system of telescope.
引文
[1]PAUL J,WEI J,BASA S,et al..The ChineseFrench SVOM mission for gamma-ray burst studies[J].CRPhy,2011,12:298-308.
[2]WEI J,CORDIER B,ANTIER S,et al..The deep and transient universe in the SVOM Era:new challenges and opportunities-scientific prospects of the SVOM mission[J].arXiv,2016,arXiv:1610.06892.
[3]黄垒,辛立平,韩旭辉,等.广角天文望远镜的自动调焦[J].光学精密工程,2015,23(1):174-183.HUANG L,XIN L P,HAN X H,et al..Auto-focusing of wide-angle astronomical telescope[J].Opt.Precision Eng.,2015,23(1):174-183(in Chinese)
[4]陈芳,张存继,韩延祥,等.简单图像的快速聚焦[J].光学精密工程,2014,22(1):220-227.CHEN F,ZHANG C J,HAN Y X,et al..Fast focus on simple images[J].Opt.Precision Eng.,2014,22(1):220-227.(in Chinese)
[5]洪裕珍,任国强,孙健.离焦模糊图像清晰度评价函数的分析与改进[J].光学精密工程,2014,22(12):3401-3408.HONG Y ZH,REN G Q,SUN J.Analysis and improvement on sharpness evaluation function of defocused image[J].Opt.Precision Eng.,2014,22(12):3401-3408.(in Chinese)
[6]丁健生,史国权,石广丰.基于图像清晰度检测的光栅刻划平台调平装置[J].光学精密工程,2016,24(4):819-825.DING J SH,SHI G Q,SHI G F.Grating ruling platform leveling device based on image clarity measurement[J].Opt.Precision Eng.,2016,24(4):819-825.(in Chinese)
[7]金雪,马卫红.图像调焦过程的清晰度评价函数研究[J].光学仪器,2012,34(1):59-64.JIN X,MA W H.Study on image definition evaluation function in auto-focusing process[J].Optical Instruments,2012,34(1):59-64.(in Chinese)
[8]郭玲华,丁晓青,方卯发.空间太阳望远镜在轨自动调焦的最小图像熵判据[J].光学技术,2003,29(4):391-393.GUO L H,DING X Q,FANG M F.Using the minimum entropy as a criterion for the in-orbit automatic focusing of space solar telescope[J].Optical Technique,2003,29(4):391-393.(in Chinese)
[9]李晓燕,朱庆生.一种基于图像清晰度评价的天文望远镜自动调焦系统[J].天文研究与技术,2008,5(3):294-298.LI X Y,ZHU Q SH.An automatic focusing system of astronomical telescope based on image definition evaluation[J].Astronomical Research&Technology,2008,5(3):294-298.(in Chinese)
[10]BERTIN E,ARNOUTS S.SExtractor:Software for source extraction[J].Astronomy&Astrophysics Supplement,1996,117:393-404.
[11]TANG P Y,LIU J J,ZHANG G Y,et al..Automatic focusing system of BSST in Antarctic[J].SPIE,2015,9678:16-21.
[12]施展,樊祥,程正东,等.关联成像的点扩散函数分析法[J].红外与激光工程,2016(11):339-344.SHI ZH,FAN X,CHENG ZH D,et al..PSF analysis of correlated imaging[J].Infrared and Laser Engineering,2016(11):339-344.(in Chinese)
[13]VALDES F.PSFMEASURE/STARFOCUS:PSF measuring algorithms[J].ASPC,1994(61):284-287.
[14]VALDES F.PSFMEASURE/STARFOCUS:Psfmeasure/starfocus:IRAF PSF measuring tasks[J].ASPC,1994(61):280-283.
[15]BENDINELLI O,PARMEGGIANI G,ZAVATTI F.CCD star images:on the determination of moffats PSF shape parameters[J].Journal of Astrophysics and Astronomy,1988(9):17-24.
[16]LI B SH,LI G L,CHENG J,et al..The point spread function reconstruction by using Moffatlets-Ⅰ[J].Research in Astronomy and Astrophysics,2016,16(9):139.
[17]FRASER W,ALEXANDERSEN M,SCHWAMB M E,et al..TRIPPy:trailed image photometry in python[J].The Astronomical Journal,2016,151(6):151-158.
[18]PUJOL J.The solution of nonlinear inverse problems and the Levenberg-Marquardt method[J].Geophysics,2007,72(4):W1.
[19]李鹏程,徐青,邢帅,等.全局收敛LM的激光雷达波形数据分解方法[J].红外与激光工程,2015,44(8):2262-2267.LI P CH,XU Q,XING SH,et al..Full-waveform LiDAR data decomposition method based on global convergent LM[J].Infrared and Laser Engineering,2015,44(8):2262-2267.(in Chinese)
[20]KHAMATNUROVA M Y,GRIBANOV K G.Levenberg-Marquardt method with simultaneous calculations of averaging kernels and errors for methane retrieval from IASI spectra[J].SPIE,2015,9680:71-77.
[2]WEI J,CORDIER B,ANTIER S,et al..The deep and transient universe in the SVOM Era:new challenges and opportunities-scientific prospects of the SVOM mission[J].arXiv,2016,arXiv:1610.06892.
[3]黄垒,辛立平,韩旭辉,等.广角天文望远镜的自动调焦[J].光学精密工程,2015,23(1):174-183.HUANG L,XIN L P,HAN X H,et al..Auto-focusing of wide-angle astronomical telescope[J].Opt.Precision Eng.,2015,23(1):174-183(in Chinese)
[4]陈芳,张存继,韩延祥,等.简单图像的快速聚焦[J].光学精密工程,2014,22(1):220-227.CHEN F,ZHANG C J,HAN Y X,et al..Fast focus on simple images[J].Opt.Precision Eng.,2014,22(1):220-227.(in Chinese)
[5]洪裕珍,任国强,孙健.离焦模糊图像清晰度评价函数的分析与改进[J].光学精密工程,2014,22(12):3401-3408.HONG Y ZH,REN G Q,SUN J.Analysis and improvement on sharpness evaluation function of defocused image[J].Opt.Precision Eng.,2014,22(12):3401-3408.(in Chinese)
[6]丁健生,史国权,石广丰.基于图像清晰度检测的光栅刻划平台调平装置[J].光学精密工程,2016,24(4):819-825.DING J SH,SHI G Q,SHI G F.Grating ruling platform leveling device based on image clarity measurement[J].Opt.Precision Eng.,2016,24(4):819-825.(in Chinese)
[7]金雪,马卫红.图像调焦过程的清晰度评价函数研究[J].光学仪器,2012,34(1):59-64.JIN X,MA W H.Study on image definition evaluation function in auto-focusing process[J].Optical Instruments,2012,34(1):59-64.(in Chinese)
[8]郭玲华,丁晓青,方卯发.空间太阳望远镜在轨自动调焦的最小图像熵判据[J].光学技术,2003,29(4):391-393.GUO L H,DING X Q,FANG M F.Using the minimum entropy as a criterion for the in-orbit automatic focusing of space solar telescope[J].Optical Technique,2003,29(4):391-393.(in Chinese)
[9]李晓燕,朱庆生.一种基于图像清晰度评价的天文望远镜自动调焦系统[J].天文研究与技术,2008,5(3):294-298.LI X Y,ZHU Q SH.An automatic focusing system of astronomical telescope based on image definition evaluation[J].Astronomical Research&Technology,2008,5(3):294-298.(in Chinese)
[10]BERTIN E,ARNOUTS S.SExtractor:Software for source extraction[J].Astronomy&Astrophysics Supplement,1996,117:393-404.
[11]TANG P Y,LIU J J,ZHANG G Y,et al..Automatic focusing system of BSST in Antarctic[J].SPIE,2015,9678:16-21.
[12]施展,樊祥,程正东,等.关联成像的点扩散函数分析法[J].红外与激光工程,2016(11):339-344.SHI ZH,FAN X,CHENG ZH D,et al..PSF analysis of correlated imaging[J].Infrared and Laser Engineering,2016(11):339-344.(in Chinese)
[13]VALDES F.PSFMEASURE/STARFOCUS:PSF measuring algorithms[J].ASPC,1994(61):284-287.
[14]VALDES F.PSFMEASURE/STARFOCUS:Psfmeasure/starfocus:IRAF PSF measuring tasks[J].ASPC,1994(61):280-283.
[15]BENDINELLI O,PARMEGGIANI G,ZAVATTI F.CCD star images:on the determination of moffats PSF shape parameters[J].Journal of Astrophysics and Astronomy,1988(9):17-24.
[16]LI B SH,LI G L,CHENG J,et al..The point spread function reconstruction by using Moffatlets-Ⅰ[J].Research in Astronomy and Astrophysics,2016,16(9):139.
[17]FRASER W,ALEXANDERSEN M,SCHWAMB M E,et al..TRIPPy:trailed image photometry in python[J].The Astronomical Journal,2016,151(6):151-158.
[18]PUJOL J.The solution of nonlinear inverse problems and the Levenberg-Marquardt method[J].Geophysics,2007,72(4):W1.
[19]李鹏程,徐青,邢帅,等.全局收敛LM的激光雷达波形数据分解方法[J].红外与激光工程,2015,44(8):2262-2267.LI P CH,XU Q,XING SH,et al..Full-waveform LiDAR data decomposition method based on global convergent LM[J].Infrared and Laser Engineering,2015,44(8):2262-2267.(in Chinese)
[20]KHAMATNUROVA M Y,GRIBANOV K G.Levenberg-Marquardt method with simultaneous calculations of averaging kernels and errors for methane retrieval from IASI spectra[J].SPIE,2015,9680:71-77.