Demonstration of Imaging Capabilities of an Optically-Sparse Mirror Consisting of Non-Uniform Sized Sub-Apertures Applicable in Lightweight Space-Based Electro-Optical Telescopes for Remote Sensing

In this work we present an experimental demonstration of the comparative study of imaging quality of one of the non-uniform sized (NUS) optically-sparse aperture (OSA) mirror configurations - the Taylor-ln design as proposed in [1] against that of a conventional segmented mirror having sub-apertures of equal size, in laboratory. The perfomance of the proposed NUS OSA mirrors are noted to be equivalent to those of uniform-sized segmented mirrors, using simulations in the ideal scenario of noiseless imaging systems. Therefore, it is of utmost importance to demonstrate the efficiency of such NUS OSA mirror configurations, in the laboratory frame at least, so that real-life applications of these designs can be surmised. Therefore, in this paper we design masks that mimic an uniform sized segmented mirror with each sub-aperture as large as 2 cm and a NUS OSA mirror whose aperture sizes vary as the coefficients of the Taylor expansion series for ln. We consider only the average intensity information of the images captured by these two types of segmented mirrors. Thereafter, simple deconvolution with respective Point Spread Functions (PSFs) results in nearly similar reconstructed images, at least by visual inspection. In case of the uniform sized segmented mirror the Peak Signal-to-Noise-Ratio (PSNR) is 7.8 dB alongwith the Structural Similarity Index Measure (SSIM) being 0.1. The respective values for the NUS system are similar (8.8 dB and 0.24, respectively). This explicitly demonstrates very little degradation of performance even though the fill factor for the NUS design is reduced to 31% of the uniform OSA mirror. However, we emphasize on the fact that this is a very basic experimental setup, demonstrating the efficiency of imaging for such NUS systems and suggest further improvement of the reconstructed image quality with better quality mirrors used for the purpose as well as incorporating advanced reconstruction algorithms coupled with a suitable denoising algorithm. The success of this kind of an experiment is a promising breakthrough to encourage implementation in real-life ultra-lightweight space-based telescopic systems, encompassing a wide plethora of scientific objectives viz., astronomy, natural resources as well as infrastructure monitoring, security and surveillance and even disaster prediction like earthquakes.