| 其他摘要 | The high-resolution imaging of stars is one of the important goals of astronomical observations, especially the high-resolution imaging of faint stars. However, due to the influence of atmospheric turbulence, stellar incident light wave front is degraded so that ground-based telescopes can’t achieve the diffraction -limit imaging. At present, the methods of eliminating the effect of atmospheric turbulence and achieve high resolution imaging are Adaptive Optics, High Resolution Statistical Reconstruction Methods and Lucky Imaging. But because of the high expensive instrument, Adaptive Optics is relatively difficult to implement, while the High-Resolution Statistical Reconstruction Methods and Lucky Imaging are relatively easy to implement. Both of High Resolution Statistical Reconstruction Methods and Lucky Imaging make statistics to the short-exposure images in some way so as to preserve the high –frequency information of object to reconstruct the high resolution image close to telescope diffraction limit. Achieving plenty of high quality short exposure images of object is the primary job, so the appropriate detector is the key. At present, the main detectors meeting the satisfaction of astronomical observations are conventional CCDs, Intensified CCDs(ICCD) and Electron Multiplying CCDs(EMCCD). But Conventional CCDs with tiny readout noise have slow readout speed, difficult to achieve short exposure images. Other types of conventional CCDs have faster readout speed, but their readout noise is too much, difficult to achieve higher SNR. Although ICCD have electron multiplier effect, the quantum is too low. Compared with conventional CCDs and ICCDs, EMCCD have features of high quantum, tiny readout noise, high readout speed, low light level detection capability, much more easier to achieve high quality short-exposure images, so they are successfully applied to high resolution imaging of faint objects. Although EMCCD can achieve short exposure images of higher SNR, additive noises of EMCCD are different from conventional CCDs and ICCDs. The effect of additive noises on high resolution imaging is the focus of this study. Firstly, this paper briefly introduced the High Resolution Statistics Reconstruction Methods and Lucky Imaging, and discussed the transfer functions of the High Resolution Statistics Methods in chapter I. In Chapter II, after detailed analysis of the generation mechanism and characteristics of the EMCCD additive noises, measure of additive noises were made through experiments. Secondly, Chapter III in-depth study the effects of additive noises of EMCCD on the High Resolution Statistics Methods in faint subject imaging by numerical simulation on the basis of theoretical analysis. Meanwhile, noise deviation was corrected. In Chapter Ⅳ, we proposed High Resolution Statistical Reconstruction Methods on the base of Selected Frame Technology，and study the factors affecting High Resolution Statistical Reconstruction in the faint object imaging, proposed the new method of shift-and-add and the method of improving the High-Resolution Statistical Reconstruction accuracy. The results of simulation and real data processing show our proposed method could improve detection accuracy of faint object imaging. Finally, chapter Ⅴ are work summary and future plan. |
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