Correcting Etaloning Fringes in Hyperspectral Image Cubes of Jupiter Using Sensor Thickness Modeling with Flat-Field Data Fitting
Journal of astronomical telescopes, instruments, and systems(2020)
Abstract
Evidence of "fringing" due to optical etaloning was observed in narrowband hyperspectral image cubes of Jupiter collected prior to 2018 at the Apache Point Observatory 3.5-m telescope with the New Mexico State University Acousto-optic Imaging Camera. The etaloning resulted from the use of a back-illuminated, high quantum efficiency CCD. Otherwise successful flat-field correction was ineffective in removing fringes at some wavelengths associated with Jupiter's absorption regions. We describe an etaloning correction method based on a mathematical interference model that assumes a single detection layer. A two-dimensional thickness function for the sensor layer was derived and found to have an overall "dish-shaped" variation along with some finely spaced surface polishing marks. Synthetic fringe frames corresponding to the flat-field and science images were created using the thickness function. Optimized contrast values were found for the synthetic frames and defringed images of Jupiter were generated by separately correcting flat-field and science images using the synthetic fringe frames before applying the final flat-field division. Quantitative analyses of defringed flat-field images showed fringe contrast reductions by factors of 2 to 8 on average and a disk-averaged spectrum of defringed Jupiter data compared favorably with an established spectrum. This defringing approach is applicable to other detectors that can be modeled with a single detection layer and where a sequence of spectral images with adequate wavelength resolution is available. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.
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Key words
optical etaloning,fringing,image processing,Jupiter,focal-plane arrays,telescopes
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