共查询到20条相似文献，搜索用时 31 毫秒
1.
大气湍流极大限制了地基大口径望远镜观测天文目标图像的空间分辨率.根据最大似然估计原理,提出了用实际光学带宽约束的可有效减小天文观测图像中大气湍流影响的盲反卷积方法,通过共轭梯度优化算法使卷积误差函数趋向最小.建立了望远镜光学系统参数和图像频域带宽的关系,采用变量正性约束、点扩散函数带宽有限约束,提高算法的收敛性.为避免图像处理中有效傅立叶变换频率超出截止频率,要求采集望远镜焦面图像时单个成像单元(如CCD像素单元)应小于四分之一衍射斑直径.算法中未用目标支持域约束,所提出的方法适用于全视场天文图像恢复.用计算机模拟和对实际天文目标双鱼座图像数据的恢复结果验证了所提出方法的有效性. 相似文献
2.
We present a method for retrieving the wavefront phase and estimating the point spread function using data from a single imaging
channel. The method involves a set of short exposures and its speckle reconstruction of the observed object, and a parameterized
point spread function model which is used in order to estimate the wavefront phase and the point spread function from the
data. Estimates of the wavefront phase and the point spread function are computed by minimizing an error function with the
method of simulated annealing. Results of tests with simulated data and with real data are shown. We conclude that the proposed
technique provides reliable estimates of the instantaneous point spread function and is robust against noise. 相似文献
3.
A measurement of the intensity distribution in an image of the solar disk will be corrupted by a spatial redistribution of the light that is caused by the Earth's atmosphere and the observing instrument. If the precise form of the spatial point spread function is known and can be modeled, then the observed image can be corrected for its effects. However, accurate modeling of the spatial point spread function, which can be considered as composed of a blurring component and a scattering component (Zwaan, 1965), is difficult and the correction for its effects is computationally expensive.We introduce a simple correction method that is applicable for solar p-mode intensity observations obtained over a period of time in which there is a significant change in the scattering component of the point spread function. The method circumvents the problems incurred with an accurate determination of the spatial point spread function and its subsequent deconvolution from the observations. The method only corrects the spherical harmonic coefficients that represent the spatial frequencies present in the image and does not correct the image itself. The method is computationally inexpensive and has the potential of being useful in correcting for changes in the blurring component of the point spread function and also for correcting velocity images. 相似文献
4.
太阳图像中存在各种不同尺度、亮度和结构的物理活动现象,由于太阳日冕高动态活动和传感器设备等因素的影响,太阳图像成像质量不佳。根据太阳动力学天文台(Solar Dynamic Observatory,SDO)的大气成像仪(Atmospheric Imaging Assenbly,AIA)拍摄不同波段数据结构的动态范围大、噪声大、结构相对模糊等特点,提出一种基于盲退卷积的图像增强方法。首先对图像进行去噪和降低动态范围的处理,基于图像功率谱的分布假设,从原图中估计点扩散函数(Point Spread Function,PSF)的功率谱;然后使用相位提取算法恢复点扩散函数的相位,再退卷积得出较高质量的目标图像;最后通过轮廓切片分析、功率谱分析以及点扩散函数分析对增强结果进行定量和定性评价。实验结果表明,相比现有的图像增强方法,该方法在有效增强太阳日冕图像细节结构的同时,能够复原原图中因模糊无法识别的结构。 相似文献
5.
V. M. Bogod P. M. Svidskiy E. A. Kurochkin A. V. Shendrik N. P. Everstov 《Astrophysical Bulletin》2018,73(4):478-486
We present the results of forecasting flare activity based on the data from microwave spectropolarimetric observations of active regions (ARs) obtained with the RATAN-600 radio telescope and the X-ray data from the GOES satellite as well as monitoring data. The method is designed for short-term (1–3-days) flare forecasts. Proton events are considered as part of the general flare problem. Obtaining a reliable forecast is a difficult process in view of the multi-parameter and multi-dimensional system of plasma parameter variations and multiple non-linear interconnections.We used a modified Tanaka–Enome criterion, as well a database of observational material collected over many years. The forecasting efficiency was analyzed depending on the threshold values of the criterion. We show that the quality of the radio astronomical forecast is determined by the level of sensitivity of the detector at short centimeterwavelengths and by the solar activity level. 相似文献
6.
We have developed a method of stray-light correction which is applicable to filter-based magnetograph observations. Stray-light-corrected Stokes images are obtained by performing the deconvolution of observed Stokes images by the point spread function which is determined from the Stokes I image. For image deconvolution, the maximum entropy principle is used to guarantee that intensity should be positive and polarization degrees should be less than unity. We present an iterative algorithm for the maximum entropy method, which seeks the solution in Fourier space and thus accomplishes fast convergence. We find that our method is effective in correcting stray light which has a spread angle greater than the full width at half maximum of the point spread function. We also discuss the effect of stray light on magnetograph calibration. 相似文献
7.
Miura Noriaki Baba Naoshi Sakurai Takashi Ichimoto Kiyoshi Soltau Dirk Brandt Peter 《Solar physics》1999,187(2):347-356
A method for the improvement of resolution in an observed solar image is proposed. A blind deconvolution method is used for
restoration of an atmospherically-degraded solar image, and a super-resolution method is applied to its restored image to
improve the resolution. It is confirmed that a blind deconvolution process can restore fine structures that are blurred in
an observed image, and that the super-resolution process can make a cutoff frequency in a blind-deconvolved image higher.
A time series of super-resolved images of a sunspot observed with the 70-cm Vacuum Tower Telescope at Teide Observatory is
presented. 相似文献
8.
In Brans-Dicke theory of gravity, from the nature of the scalar field-potential considered, the dark energy, dark matter, radiation densities predicted by different observations and the closedness of the universe considered, we can fix our ω BD , the Brans-Dicke parameter, keeping only the thing in mind that from different solar system constrains it must be greater than 5×105. Once we have a value, satisfying the required lower boundary, in our hand we proceed for setting unknown parameters of the different dark energy models’ EoS parameter. In this paper we work with three well known red shift parametrizations of dark energy EoS. To constrain their free parameters for Brans Dicke theory of gravity we take twelve point red shift vs Hubble’s parameter data and perform χ 2 test. We present the observational data analysis mechanism for Stern, Stern+BAO and Stern+BAO+CMB observations. Minimising χ 2, we obtain the best fit values and draw different confidence contours. We analyze the contours physically. Also we examine the best fit of distance modulus for our theoretical models and the Supernovae Type Ia Union2 sample. For Brans Dicke theory of gravity the difference from the mainstream confidence contouring method of data analysis id that the confidence contours evolved are not at all closed contours like a circle or a ellipse. Rather they are found to be open contours allowing the free parameters to float inside a infinite region of parameter space. However, negative EoSs are likely to evolve from the best fit values. 相似文献
9.
本文介绍在怀柔６０ｃｍ多通道太阳望远镜上运用斑点干涉像复原方法所取得的一些初步结果,对用短暴光方法（暴光时间不大于１０毫秒）获得的一系列“冻结”大气后的目标像用斑点干涉像复原方法进行处理,即可获得消除了地球大气影响的目标复原像,斑点掩模法即为斑点干涉像复原方法的一种,我们用它对日面中心的宁静区米粒进行处理,复原出了分率不劣于０．〃５的白光米粒象。 相似文献
10.
明安图射电频谱日像仪(Mingantu Spectral Radioheliograph, MUSER)能够在0.4--15GHz超宽频带内实现高时间、高空间、高频率分辨率的太阳射电成像. 而射电亮温度是描述太阳物理过程的一个重要的参数, 在研究不同射电辐射机制、太阳磁场以及太阳爆发过程中非热粒子加速等问题上有着非常重要的作用, 因此必须对MUSER观测的图像进行亮温度定标. 将介绍一种适用于射电日像仪图像强度定标的方法. 太阳射电图像中包含着太阳圆盘的结构信息, 利用射电日像仪短基线的可视度函数拟合第一类贝塞尔函数, 可以得到图像中宁静太阳圆盘的射电半径和强度, 再利用瑞利-金斯定律和每天的太阳射电流量可以计算得到每天图像的定标因子$G_c$, 从而实现对MUSER图像强度的定标. 将该方法应用到MUSER的实际观测数据中, 包括宁静太阳和有太阳射电爆发等不同的情况, $G_c$的误差基本不超过10%, 得到的宁静太阳亮温度与其他宁静太阳的结果具有较高的相关性, 表明了此方法的可行性和有效性. 相似文献
11.
F. P. Pijpers 《Monthly notices of the Royal Astronomical Society》1999,307(3):659-668
An unbiased method for improving the resolution of astronomical images is presented. The strategy at the core of this method is to establish a linear transformation between the recorded image and an improved image at some desirable resolution. In order to establish this transformation only the actual point spread function and a desired point spread function need be known. No image actually recorded is used in establishing the linear transformation between the recorded and improved image.
This method has a number of advantages over other methods currently in use. It is not iterative, which means it is not necessary to impose any criteria, objective or otherwise, to stop the iterations. The method does not require an artificial separation of the image into 'smooth' and 'point-like' components, and thus is unbiased with respect to the character of structures present in the image. The method produces a linear transformation between the recorded image and the deconvolved image, and therefore the propagation of pixel-by-pixel flux error estimates into the deconvolved image is trivial. It is explicitly constrained to preserve photometry and should be robust against random errors. 相似文献
This method has a number of advantages over other methods currently in use. It is not iterative, which means it is not necessary to impose any criteria, objective or otherwise, to stop the iterations. The method does not require an artificial separation of the image into 'smooth' and 'point-like' components, and thus is unbiased with respect to the character of structures present in the image. The method produces a linear transformation between the recorded image and the deconvolved image, and therefore the propagation of pixel-by-pixel flux error estimates into the deconvolved image is trivial. It is explicitly constrained to preserve photometry and should be robust against random errors. 相似文献
12.
The optical and technical characteristics of the tie-in between the chromospheric AFR-2 telescope and the digital camera Sony DSC-S85 are determined by computer simulation. The optimal layout of the camera, telescope optics, and collective lens is established. The modulation transfer function is used as an optimization parameter (quality criterion for the solar disk image in Hα). 相似文献
13.
Kh. I. Abdusamatov 《Kinematics and Physics of Celestial Bodies》2012,28(1):35-38
We propose a minimum level of the smoothed values for the solar constant during a period of low sunspot activity as a new
additional criterion for determining the time of a minimum between solar cycles. An indicator for the time of a minimum between
cycles is the time at which a minimum level in the average monthly values of the integral flux of solar radiation smoothed
over thirteen months (when the last four values of the flux are greater than the previous minimum point) is achieved. We successfully
tested the new criterion to determine the time of the previous minima between cycles 21 and 22, 22 and 23, and 23 and 24. 相似文献
14.
We show that daily sunspot areas can be used in a simple, single parameter model to reconstruct daily variations in several
other solar parameters, including solar spectral irradiance and total magnetic flux. The model assumes that changes in any
given parameter can be treated mathematically as the response of the system to the emergence of a sunspot. Using cotemporal
observational data, we compute the finite impulse response (FIR) function that describes that response in detail, and show
that the response function has been approximately stationary over the time period for which data exist. For each parameter,
the impulse response function describes the physical evolution of that part of a solar active region that is the source of
the measured variability. We show that the impulse response functions are relatively narrow functions, no more than 3 years
wide overall. Each exhibits a pre-active, active, and post-active region component; the active region component dominates
the variability of most of the parameters studied. 相似文献
15.
To restore an atmospherically degraded image of solar granulation the shift-and-add (SAA) method is applied to its specklegrams. It is the first time, to the best of our knowledge, that such a technique has been used for image reconstruction of solar granulation, a largely extended target. SAA, therefore, enables us to monitor restored images of solar granulation in a simple and fast way. 相似文献
16.
A principle of restoration methods based on multichannel blind deconvolution (MBD) is introduced. The methods assume that
for every un-degraded unobservable image several degraded observed images are available. It is better conditioned than classical
single channel approach. The first algorithm represents a generalization of iterative deconvolution scheme introduced for
single images. The second MBD algorithm is based on so-called subspace technique. The subspace method is not iterative and
this possibly implies an implementation that can be computationally more efficient. Both methods are presented in applications
to artificial image data (computer-generated multichannel degraded data) with known ideal image to get a comparison with restored
one. Performance in a real situation on solar photosphere images is shown. 相似文献
17.
Active or adaptive optics often require the ability to characterize wavefront aberrations using natural extended sources.
The task becomes especially challenging when dealing with widely extended sources such as the solar granulation. We propose
a new approach based on the processing of oppositely defocused images. This method, which is a generalization of a technique
known as curvature sensing, derives the wavefront curvature from the difference between two oppositely defocused images and
determines the second momenta of the point spread function. The proposed method measures the wavefront aberration from the
images themselves, requires little computational resources, is fast enough to be used in a real-time adaptive optics system
and is particularly adapted to random patterns such as solar granulation or spot penumbras whose morphology evolves during
the observation. We envision the application of the method to real-time seeing compensation in solar astronomical telescopes,
and to the correction of optical system aberrations in remote sensing instrumentation. This effort is directed towards building
a curvature sensor for the real-time applications. 相似文献
18.
Jack Ireland 《Solar physics》2007,243(2):237-252
Spectral-line fitting problems are extremely common in all remote-sensing disciplines, solar physics included. Spectra in
solar physics are frequently parameterized by using a model for the background and the emission lines, and various computational
techniques are used to find values to the parameters given the data. However, the most commonly-used techniques, such as least-squares
fitting, are highly dependent on the initial parameter values used and are therefore biased. In addition, these routines occasionally
fail because of ill-conditioning. Simulated annealing and Bayesian posterior distribution analysis offer different approaches
to finding parameter values through a directed, but random, search of the parameter space. The algorithms proposed here easily
incorporate any other available information about the emission spectrum, which is shown to improve the fit. Example algorithms
are given and their performance is compared to a least-squares algorithm for test data – a single emission line, a blended
line, and very low signal-to-noise-ratio data. It is found that the algorithms proposed here perform at least as well or better
than standard fitting practices, particularly in the case of very low signal-to-noise ratio data. A hybrid simulated annealing
and Bayesian posterior algorithm is used to analyze a Mg x line contaminated by an O IV triplet, as observed by the Coronal
Diagnostic Spectrometer onboard SOHO. The benefits of these algorithms are also discussed. 相似文献
19.
太阳磁像仪是开展太阳磁场观测研究的核心仪器,其中的稳像系统是空间太阳磁像仪的关键技术之一,针对深空探测卫星系统对载荷重量、尺寸限制严苛的要求,设计了基于图像自校正方法的稳像观测系统.介绍了一套基于现场可编程门阵列(Field-Programmable Gate Array, FPGA)和数字信号处理器(Digital Signal Processor, DSP),通过基于自相关算法的高精度稳像方法设计,并结合精确偏振调制、准确交替采样控制等系统软硬件设计,克服由于卫星平台抖动、指向误差等因素造成的图像模糊,实现实时相关、校正、深积分的稳像观测系统.针对像素尺寸为1 K×1 K、帧频为20 fps的CMOS (Complementary Metal Oxide Semiconductor)探测器,实现了1像元以内的实时稳像观测精度.在完成实验室测试后, 2021年6月18日在国家天文台怀柔太阳观测基地35 cm太阳磁场望远镜上开展了实测验证,结果表明该系统能够有效地完成太阳磁像仪自校正稳像观测,获得了更高分辨率的太阳磁场数据.稳像系统的成功研制不仅可以为深空太阳磁像仪的研制提供轻量化、高... 相似文献
20.
光度特性测量是获取空间目标的物理特性的重要技术手段之一,无论是光变曲线的事后分析还是建立光度变化的仿真模型,都离不开一个重要的参数——太阳相位角（太阳-空间目标-测站的空间夹角）.目前空间目标的位置通常是通过双行根数（TLE）外推获得,存在一定误差,且随外推时间的延长而变大,因而有必要对其计算所得的太阳相位角的精度进行评估.以典型的不同高度的激光测距卫星LAGEOS1、AJISAI、STELLA为研究对象,以全球激光测距资料解算所得的高精度轨道作为参考轨道,对2012年全年利用双行根数计算所得的太阳相位角数据进行了比对分析,结果表明对于LAGEOS1、AJISAI这样的中高轨卫星,由于轨道较高,表征阻力的B＊恒定,计算所得的太阳相位角偏差较小,角分量级,且随外推时间的延长不会导致偏差明显增大;而对于STELLA这样的低轨卫星,因轨道较低、受变化的大气的影响显著,计算所得的太阳相位角偏差较大,尤其是当B＊比较大、变化较快时,偏差显著变大,且随外推时间的延长显著增大,在最差情况下：外推1d约为13＇,外推3d约为50＇,外推7d约为251＇,已超出目前的精度要求.因此,在事后分析中应尽可能使用1d之内的TLE计算太阳相位角,对于B＊较大且变化较快情况尤其需要注意.另外,针对UTC闰秒的情况,提出了一种处理方法,即在双行根数外推时判断外推时段是否跨越了闰秒时刻,若跨越了则进行修正：增加或减少1s,相应地需要修改结果对应的时间戳计算方法. 相似文献