Abstract
The next generation of optical sparse aperture systems will provide high angular resolution for astronomical observations. Spatial modulation diversity (SMD) is a newly developed post-processing technique for such telescopes, faced with challenges of imaging faint objects, which are very attractive for astronomers but always make raw diversity images suffer serious photon noise. In this paper, we propose an improved SMD with denoising reprocessing embedded to address the problem. The blocking-matching and 3D filtering algorithm, a state-of-the-art denoising technique, is first employed to process the diversity images with low photon intensities generated by spatial modulation, specifically switching off each sub-aperture sequentially. SMD algorithm then can be applied to estimate wavefront and digitally restore images. It is demonstrated by both simulations and experiments that the proposed method outperforms the previous SMD in terms of reconstructions of wavefront and imagery from the raw images of faint objects corrupted seriously by photon noise. The reported method may provide an alternative approach to acquire high-quality images of faint objects for astronomical observations of the future segmented mirrors or telescope arrays.
Highlights
Due to the limits to the size and weight of monolithic primary mirrors, it’s difficult for modern ground-based and space-based telescopes to achieve the desired increases in angular resolution
Diversity images are generated by controlling the status of the transmittance of sub-apertures, which are required to be captured within a short time
We propose and demonstrate an improved Spatial modulation diversity (SMD) with a denoising preprocessing procedure using the blocking-matching and 3D filtering (BM3D) algorithm in this paper
Summary
Due to the limits to the size and weight of monolithic primary mirrors, it’s difficult for modern ground-based and space-based telescopes to achieve the desired increases in angular resolution. Based on the diversity raw images, an optimization process is performed to recover the aberrations and a high-quality image can be acquired with deconvolution It may provide an alternative solution for adaptive optics. Simulation results show that the proposed ISMD can achieve higher accuracy of wavefront reconstruction and better quality of recovered images compared with previous SMD. It is further presented by experimental study that the wavefront and image reconstructions using ISMD at high noise levels exhibit the similar quality to those using SMD at high photon levels By proposing such a useful strategy, SMD is developed to be capable of imaging faint objects, which are very attractive for astronomy. It is believable that the proposed ISMD may find wide applications in post processing of astronomical observations of the future segmented mirrors or telescope arrays
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