Dr. Avyarthana Ghosh Profile

Dr. Avyarthana Ghosh

at Tata Consultancy Services Ltd

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Publications (3)

Proceedings Article | 19 October 2023 Poster + Paper

Image restoration techniques for space-based lightweight optically sparse aperture Earth-observation telescopes in the longwave infrared domain

Avyarthana Ghosh, Pavan Reddy, Achanna Anil Kumar, Balamuralidhar P., Arpan Pal

Proceedings Volume 12733, 1273316 (2023) https://doi.org/10.1117/12.2687127

KEYWORDS: Image restoration, Imaging systems, Image filtering, Segmented mirrors, Convolutional neural networks, Point spread functions, Remote sensing, Lightweight mirrors

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Any high spatial resolution space-borne electro-optical sensing system operating in long wavelengths, like Earth-observation facilities operating in the longwave infrared are subjected to an inherent design and implementation challenge of deploying large monolithic primary aperture mirrors, to achieve a ground resolution distance of a few tens of cm. To outflank this issue, many present-date missions design and commission lightweight segmented mirrors, mostly with equal sized sub-apertures. One step ahead, these sub-apertures could be of particular non-uniform size distributions (One-by-Three, Taylor-ln and Taylor-invtan), thereby ensuring a smaller and even lighter primary and with marginal compromise in imaging quality due to significant sidelobe suppression. This is also confirmed by the fact that these particular non-uniform sized mirrors have very less loss of spatial frequencies with respect to that of equal-sized segmented mirrors. Therefore, under lossless conditions, there is hardly any degradation in imaging performance of these two configurations. However, in the presence of gaussian, impulse and shot noise, the situation worsens because of the compromised collecting area as well as noise contribution. A simple deconvolution technique for image restoration in presence of noise is no longer possible because of the lack of convergence. This calls upon for the use of iterative reconstruction algorithms with denoisers like Total Variation (TV), Block Matching and 3D Filtering (BM3D) or Convolutional Neural Networks (CNN) in the post-processing step to ensure better output images with high Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) along with good edge and texture preservation of the features. A comparison of these three kinds of denoisers, TV, BM3D and DnCNN implemented as a part of the Alternating Directions Method of Multipliers (ADMM) reconstruction technique is presented in this work. It is seen that in presence of some shot noise, random gaussian noise with σ= 0.03 and some impulse noise, the best performance is achieved for ADMM-BM3D technique with comparable performance from the ADMM-DnCNN method (except for Taylor-ln design). On the contrary, denoising with TV can perform well only in presence of shot noise. Additionally, this technique is nearly rejected for use in case of the Taylor-invtan model because of extremely low SSIM when all three noise types are incorporated.

Proceedings Article | 31 August 2022 Poster + Paper

The thermal filter for the Solar Ultraviolet Imaging Telescope (SUIT) on-board Aditya-L1

Avyarthana Ghosh, Ravi Kesharwani, Aafaque Khan, Sreejith Padinhatteeri, Durgesh Tripathi, A. Ramaprakash, Ketan Patel, Tayaramma D. P. V. Jalluri, G. R. Madhumalathi, R. Venkateshwaran, S. Elumalai, Kinshuk Gupta, J. P. Nair, H. Sparrow, R. S. Worlikar, Anit Gupta, Sanjoy Sen

Proceedings Volume 12181, 121813O (2022) https://doi.org/10.1117/12.2629760

KEYWORDS: Optical filters, Telescopes, Coating, Charge-coupled devices, Ultraviolet telescopes, Reflection, Ultraviolet radiation, Sun, Visible radiation, Space telescopes, Bandpass filters, Gamma radiation

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The solar ultraviolet imaging telescope (SUIT) is an imaging telescope on-board the Aditya-L1 satellite, which is India’s maiden space mission dedicated solely to solar observations. The spatially resolved, high cadence observations are designed to be taken in eleven science filters with full width half maxima ranging between 0.1–58 nm and spread over the near-ultraviolet (NUV) domain of the solar spectrum (200–400 nm). The huge incoming solar flux, limited by the linearity regime performance of the charge coupled device (CCD) as well as the thermal operational constraints, mandate the use of an entrance aperture filter, the thermal filter (TF), for SUIT. The design of this filter is, further, constrained by exposure time and enhanced emission of the sun during eruptive events. From performance perspective, the TF reflects ∼50% of the incident radiation and allows only 0.1–0.45% of the incoming flux to pass within 200–400 nm. The transmission on either side of the operational range is satisfactorily reduced, so as to ensure minimum unwanted light leaking into the imaging system. Therefore, the TF plays a significant role in increasing the photometric efficiency as well as maintaining the operational temperature of the telescope. To the best of our knowledge, this is the first time any attempt of designing and manufacturing any such rejection filter aiming optimized performance in the NUV range is being done for a space-based imaging solar telescope. The choice of materials for substrate and coating for the filter poses several challenges in terms of contamination, corrosion/ oxidation, durability during manufacturing process, long-term exposure to harsh space environment as well as formation of pinholes. The transmission and reflection profiles of the fabricated TF is satisfactory to meet our design and technical constraints. The TF is also qualified for various environmental and radiation conditions. The transmission of the TF is seen to be well within our allowed margins (±10% of the design value) even after being exposed to these qualification tests.

Proceedings Article | 18 July 2016 Paper

The Solar Ultraviolet Imaging Telescope onboard Aditya-L1

Avyarthana Ghosh, Subhamoy Chatterjee, Aafaque Khan, Durgesh Tripathi, A. Ramaprakash, Dipankar Banerjee, Pravin Chordia, Achim Gandorfer, Natalie Krivova, Dibyendu Nandy, Chaitanya Rajarshi, Sami Solanki, S. Sriram

Proceedings Volume 9905, 990503 (2016) https://doi.org/10.1117/12.2232266

KEYWORDS: Space operations, Ultraviolet radiation, Space telescopes, Telescopes, Space telescopes, Solar processes, Sensors, X-ray imaging, Plasma, Ions, Magnetosphere

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