Solar image reconstruction method under atmospheric turbulence at Fuxian Lake Solar Observatory

Strong atmospheric turbulence reduces astronomical seeing,causing speckle images acquired by ground-based solar telescopes to become blurred and distorted.Severe distortion in speckle images impedes image phase deviation in the speckle masking reconstruction method,leading to the appearance of spurious imaging artifacts.Relying only on linear image degradation principles to reconstruct solar images is insufficient.To solve this problem,we propose the multiframe blind deconvolution combined with non-rigid alignment(MFBD-CNRA)method for solar image reconstruction.We consider image distortion caused by atmospheric turbulence and use non-rigid alignment to correct pixel-level distortion,thereby achieving nonlinear constraints to complement image intensity changes.After creating the corrected speckle image,we use the linear method to solve the wavefront phase,obtaining the target image.We verify the effectiveness of our method results,compared with others,using solar observation data from the 1 m new vacuum solar telescope(NVST).This new method successfully reconstructs high-resolution images of solar observations with a Fried parameter r0 of approximately 10 cm,and enhances images at high frequency.When r0 is approximately 5 cm,the new method is even more effective.It reconstructs the edges of solar graining and sunspots,and is greatly enhanced at mid and high frequency compared with other methods.Comparisons confirm the effectiveness of this method,with respect to both nonlinear and linear constraints in solar image reconstruction.This provides a suitable solution for image reconstruction in ground-based solar observations under strong atmospheric turbulence.

Automatic removal of false image stars in disk-resolved images of the Cassini Imaging Science Subsystem

Taking a large number of images,the Cassini Imaging Science Subsystem(ISS)has been routinely used in astrometry.In ISS images,disk-resolved objects often lead to false detection of stars that disturb the camera pointing correction.The aim of this study was to develop an automated processing method to remove the false image stars in disk-resolved objects in ISS images.The method included the following steps:extracting edges,segmenting boundary arcs,fitting circles and excluding false image stars.The proposed method was tested using 200 ISS images.Preliminary experimental results show that it can remove the false image stars in more than 95%of ISS images with disk-resolved objects in a fully automatic manner,i.e.,outperforming the traditional circle detection based on Circular Hough Transform(CHT)by 17%.In addition,its speed is more than twice as fast as that of the CHT method.It is also more robust(no manual parameter tuning is needed)when compared with CHT.The proposed method was also applied to a set of ISS images of Rhea to eliminate the mismatch in pointing correction in automatic procedure.Experiment results showed that the precision of final astrometry results can be improve by roughly 2 times that of automatic procedure without the method.It proved that the proposed method is helpful in the astrometry of ISS images in a fully automatic manner.

Reconstructing the landing trajectory of the CE-3 lunar probe by using images from the landing camera

An accurate determination of the landing trajectory of Chang＇e-3 （CE-3） is significant for verifying orbital control strategy, optimizing orbital planning, accu- rately determining the landing site of CE-3 and analyzing the geological background of the landing site. Due to complexities involved in the landing process, there are some differences between the planned trajectory and the actual trajectory of CE-3. The land- ing camera on CE-3 recorded a sequence of the landing process with a frequency of 10 frames per second. These images recorded by the landing camera and high-resolution images of the lunar surface are utilized to calculate the position of the probe, so as to reconstruct its precise trajectory. This paper proposes using the method of trajectory reconstruction by Single Image Space Resection to make a detailed study of the hov- ering stage at a height of 100 m above the lunar surface. Analysis of the data shows that the closer CE-3 came to the lunar surface, the higher the spatial resolution of im- ages that were acquired became, and the more accurately the horizontal and vertical position of CE-3 could be determined. The horizontal and vertical accuracies were 7.09 m and 4.27 m respectively during the hovering stage at a height of 100.02 m. The reconstructed trajectory can reflect the change in CE-3＇s position during the powered descent process. A slight movement in CE-3 during the hovering stage is also clearly demonstrated. These results will provide a basis for analysis of orbit control strategy, and it will be conducive to adjustment and optimization of orbit control strategy in follow-up missions.

Wavelet Analysis of Space Solar Telescope Images

The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job.

BACKGROUND RECTIFICATION AND FEATURE EXTRACTION OF IMAGE IN A SPOT WELD OF AL ALLOY X-RAY DETECTION

A primary study on Processing in X - ray inspection of spot weld for aluminum alloy spot welding,in- cluding for background simulation,acquisition of ideal binary image, and extraction and identifi- cation of defect features was presented.

Example-based super-resolution for single-image analysis from the Chang'e-1 Mission

Due to the low spatial resolution of images taken from the Chang＇e-1 （CE-I） orbiter, the details of the lunar surface are blurred and lost. Considering the limited spatial resolution of image data obtained by a CCD camera on CE-1, an example-based super-resolution （SR） algorithm is employed to obtain high- resolution （HR） images. SR reconstruction is important for the application of image data to increase the resolution of images. In this article, a novel example-based algorithm is proposed to implement SR reconstruction by single-image analysis, and the computational cost is reduced compared to other example-based SR methods. The results show that this method can enhance the resolution of images using SR and recover detailed information about the lunar surface. Thus it can be used for surveying HR terrain and geological features. Moreover, the algorithm is significant for the HR processing of remotely sensed images obtained by other imaging systems.

A super-high angular resolution principle for coded-mask X-ray imaging beyond the diffraction limit of a single pinhole

High angular resolution X-ray imaging is always useful in astrophysics and solar physics. In principle, it can be performed by using coded-mask imaging with a very long mask-detector distance. Previously, the diffraction-interference effect was thought to degrade coded-mask imaging performance dramatically at the low energy end with its very long mask-detector distance. The diffraction-interference effect is described with numerical calculations, and the diffraction-interference cross correlation reconstruction method （DICC） is developed in order to overcome the imaging performance degradation. Based on the DICC, a super-high angular resolution principle （SHARP） for coded-mask X-ray imaging is proposed. The feasibility of coded mask imaging beyond the diffraction limit of a single pinhole is demonstrated with simulations. With the specification that the mask element size is 50 × 50 μm^2 and the mask-detector distance is 50 m, the achieved angular resolution is 0.32arcsec above about 10keV and 0.36arcsec at 1.24keV （λ = 1 nm）, where diffraction cannot be neglected. The on-axis source location accuracy is better than 0.02 arcsec. Potential applications for solar observations and wide-field X-ray monitors are also briefly discussed.

Development of the super high angular resolution principle for X-ray imaging

Development of the Super High Angular Resolution Principle （SHARP） for coded-mask X-ray imaging is presented. We prove that SHARP can be considered as a generalized coded mask imaging method with a coding pattern comprised of diffraction-interference fringes in the mask pattern. The angular resolution of SHARP can be improved by detecting the fringes more precisely than the mask＇s element size, i.e. by using a detector with a pixel size smaller than the mask＇s element size. The proposed mission SHARP-X for solar X-ray observations is also briefly discussed.

散射光对准确CCD平场的影响-修改某些反光镜挡光筒的必要性

继前文之后,进一步说明,晨昏蒙影平场与夜天露光的差别主要由于存在散射光.像Grundahl和Sorensen那样,上海天文台1.56米和南京大学63厘米反光镜的针孔像也已获得,直观地显示了散射光的存在.1.56米和63厘米反光镜都有标准设计的挡光筒.所有标准设计的反光镜都只有两个挡光筒,分别置于主镜和付镜前面.为了在得出准确平场时CCD不受散射光影响,这样的挡光筒是不够的.这是所有标准设计的档光筒共同的弱点.为了得到更准确的平场改正,修改所有类似的反光镜主镜挡光筒是极其重要的.

基于激光映射方法的天线面板变形重构技术研究

对大型射电望远镜主反射面的单块面板变形进行了研究,将机器人学六自由度姿态变化应用至大型射电望远镜反射面面板的变形研究当中,提出了一种基于刚体六自由度变形的面板变形表征方式。基于该刚体六自由度姿态变形理论,提出了一种基于光学方法的天线面板变形重构技术,该项技术通过固结于面板上的激光单元所呈现的光斑图像来快速高精度地重构出面板的变形。深入地探究了激光光斑与天线面板变形两者之间的映射关系,将天线面板空间变形问题转化为有限区域内的激光光斑位移问题;对该方案的光斑图像进行了研究,提供了有效的光斑图像处理算法;将图像差分方法与Canny边缘检测算法相结合,能够有效地解决传统Canny算法在处理小目标时的问题,还采用了高精度亚像素质心定位算法,能够对光斑点进行亚像素级别的定位。为天线面板的测量提供了一种新的、可靠的图像处理方法,也为提高天线面板测量的精度和效率提供了新思路和方法。

Optical fiber positioning based on four-quadrant detector with Gaussian fitting method

With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant（4Q） detector, a fiber positioning and real-time monitoring system based on the 4Q detector is proposed. The detection accuracy of this system is directly determined by the precision of the center of the spot. A Gaussian fitting algorithm based on the 4Q detector is studied and applied in the fiber positioning process to improve the calculated accuracy of the spot center. The relationship between the center position of the incident spot and the detector output signal is deduced. An experimental platform is built to complete the simulated experiment. Then we use the Gaussian fitting method to process experimental data, compare the fitting value with the theoretical one and calculate the corresponding error.

太阳X-EUV成像望远镜的图像优化处理

太阳X-EUV成像望远镜主要用来监测和预报影响空间天气变化的太阳活动,成像资料专门服务于空间天气预报研究.为了满足望远镜的空间适应性,望远镜获取的图像会受到其结构调制形成的噪声干扰.本文主要对望远镜所获取的图像进行优化处理,讨论了傅里叶变换的物理意义及其在图像处理中的应用.通过二维离散傅里叶变换,将图像变换到频率域空间;选用巴特沃思陷波滤波器滤波,通过程序设计,实际调试,在尽量减少图像失真的前提下,滤除图像中的周期性噪声.优化后的图像有利于进一步分析太阳活动现象.

Algorithm Design and Test of the Solar Guide Telescope

The Solar Guide Telescope (SGT), an important solar attitude sensor of theSST (Space Solar Telescope, a space solar observing instrument being developed in China), canaccurately produce pointing error signals of the SST for attitude control at high speed. We analyzein detail the error algorithm of the heliocentric coordinates and the edge judging of solar images.The measuring accuracy of +- 0.5 arcsec of the SGT is verified by experiments on the tracking of theSun and by testing a sun simulator. Some factors causing the pointing errors are examined.

LAMOST CCD camera-control system based on RTS2

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope（LAMOST） is the largest existing spectroscopic survey telescope, having 32 scientific charge-coupled-device（CCD） cameras for acquiring spectra. Stability and automation of the camera-control software are essential, but cannot be provided by the existing system. The Remote Telescope System 2 nd Version（RTS2） is an open-source and automatic observatory-control system. However, all previous RTS2 applications were developed for small telescopes. This paper focuses on implementation of an RTS2-based camera-control system for the 32 CCDs of LAMOST. A virtual camera module inherited from the RTS2 camera module is built as a device component working on the RTS2 framework. To improve the controllability and robustness, a virtualized layer is designed using the master-slave software paradigm, and the virtual camera module is mapped to the 32 real cameras of LAMOST. The new system is deployed in the actual environment and experimentally tested. Finally, multiple observations are conducted using this new RTS2-frameworkbased control system. The new camera-control system is found to satisfy the requirements for automatic camera control in LAMOST. This is the first time that RTS2 has been applied to a large telescope, and provides a referential solution for full RTS2 introduction to the LAMOST observatory control system.

DSC based Dual-Resunet for radio frequency interference identification

Radio frequency interference(RFI)will pollute the weak astronomical signals received by radio telescopes,which in return will seriously affect the time-domain astronomical observation and research.In this paper,we use a deep learning method to identify RFI in frequency spectrum data,and propose a neural network based on Unet that combines the principles of depthwise separable convolution and residual,named DSC Based Dual-Resunet.Compared with the existing Unet network,DSC Based Dual-Resunet performs better in terms of accuracy,F1 score,and MIoU,and is also better in terms of computation cost where the model size and parameter amount are 12.5%of Unet and the amount of computation is 38%of Unet.The experimental results show that the proposed network is a high-performance and lightweight network,and it is hopeful to be applied to RFI identification of radio telescopes on a large scale.

Manifestations of bright points observed in G-band and CaⅡH by Hinode/SOT

An algorithm was developed for identifying and tracking a magnetic bright point, or bright point （BP） for short, observed in both the photosphere （G-band） and chromosphere （Ca II H）, as well as for pairing a photospheric BP （PBP） with its conjugate chromospheric BP （CBP）. Two sets of data observed by Hinode/SOT in the quiet Sun near the disk center were analyzed. About 278 PBP-CBP pairs were identified and tracked. Lifetimes of both the PBPs and CBPs follow an exponential distribution with average lifetimes of 174 s and 163 s, respectively. We found that the differences in appearance time, in disappearance time and in lifetime of the two kinds of BPs all follow Gaussian distributions,which may indicate that the mechanisms of PBP and CBP formation/disintegration are different. However, the lifetimes of PBPs and CBPs are positively correlated with one another, with a correlation coefficient of 0.8. Furthermore, we calculated the horizontal displacement between the PBP and its conjugate CBP, which follows a Gaussian function with an average and standard deviation of （67.7 ± 38.5）km. We also calculated the amplitude of the flux tube shape change which might be caused by MHD waves propagating along the flux tube, and found that it follows an exponential distribution very well.

基于实时波前信息的图像复原

提出了一种基于PIX总线的千单元可扩展波前探测图像恢复技术。采用波前探测与图像恢复相结合的方式来克服大气扰动和系统像差对图像分辨率的影响,满足大型地基望远镜高分辨率成像的需求。首先利用波前探测的方法得到波前相位畸变量,再由此恢复退化图像。其核心部件-波前处理器则采用波前处理主板和可扩展的波前处理子板相结合的方式来满足不同光学系统对波前处理规模的需求,波前空间采样数可扩展至千单元数量级。系统在室内进行了激光光源图像恢复实验,使激光光源的能量集中度提高50%左右;在室外对恒星和0.6″的双星图像进行了恢复,其半高全宽下降了约80%。系统采用大规模现场可编程门阵列(FPGA)作为波前处理的核心器件,实现了波前探测的实时处理和透过大气成像的退化图像的高分辨率图像恢复。

天文仪器中图像跟踪定位算法的比较研究

天文光学观测中采用快速图像跟踪定位可以降低大气视宁度和望远镜跟踪误差的影响,提高观测效率.针对天文仪器观测的需要选择了两类共5种算法,通过数值实验和实验室实测对这两类算法在不同噪声背景下的精度和稳定性进行了比较研究,数值实验和实验室测试的结果表明归一化互相关法和重心法既有较高的精度,又有较好的抗干扰可靠性,将分别被应用于2.16 m望远镜的高色散光谱仪前置系统和SONG(Stellar Observations Network Group)项目的科学仪器.

基于计算机视觉的胡萝卜外观品质分级系统与装备

为了实现胡萝卜的自动化分级分选,在前期胡萝卜青头、须根、开裂检测算法研究的基础上,参照国家标准需求,进一步提出了胡萝卜外观等级规格,如弯曲、断折等缺陷,以及衡量异品种的锥形度参数的检测方法,并以此为基础设计了基于计算机视觉的胡萝卜外观品质实时分选生产线。该生产线由下位机控制系统、上位机软件系统和机械分级装置组成。通过对软硬件环境和机械系统性能的测试表明:该分选生产线每秒钟可检测20个胡萝卜的等级;对520个胡萝卜含有不同种类缺陷和异品种的胡萝卜进行分级检测,分级正确率达到了93.5%,能够满足胡萝卜外观品质分选实时检测的要求。该分选线能够同步实现胡萝卜等级规格、质量、各种缺陷的实时检测与在线分选。

1.2米地平式望远镜指向模型的研究(1.全天指向模型的建立)

介绍了云南天文台1.2米地平式望远镜用于天文观测和图像采集处理的方法,建立了新的、独特的全天指向模型,大大提高了该望远镜的指向精度,达到1″,并在多年的实际应用中得到验证。