Measuring, modeling and removing optical straylight from venμs super spectral camera images

Abstract

The Venμs Super Spectral Camera suffers from high level of optical straylight. The probable causes of this defect will be discussed. Two types of straylight are observed: local ghost is caused by scattering of optical surfaces of the instrument, and multiple reflexions between detector and filter or filter window, or lenses. Cross-talk ghost is constituted of light going through the filter of one band, and impacting another band on the same detector. It is caused by multiple reflexions between detectors and filter.The optical set-up used to evaluate the straylight patterns will be presented, and then, the approach used to characterize and model the observed phenomena will be detailed:Local straylight model is computed as a global system MTF that includes the local straylight. The assumption is made that the phenomenon can be modeled by a convolution, and that it is slowly variable within the instrument field of view. Crosstalk straylight is modeled from a pinhole, used to extract the impulsive response of the cross-talk. The cross-talk pattern is observed through the ghost generated by a saturated input signal. The cross-talk signals for all contributing bands of the same tri-detector are substracted from the image of each band.The performances of the correction model are presented: on the ground over test pattern images, and then in-flight during the image quality commissioning phase, over specific targets: moon, sand/water transitions.

VENμS: Mission Characteristics, Final Evaluation of the First Phase and Data Production

“…Cross-talk ghosts are caused by reflections of light from a band to another band and it generates a blurring replication of the landscape. Filters were developed to correct these artifacts [15].…”

“…2022, 14, 3281 10 of 4 the scattering of surfaces of the instrument and multiple reflections on detectors, filters o lenses and generates a large blurring effect. Cross-talk ghosts are caused by reflections o light from a band to another band and it generates a blurring replication of the landscape Filters were developed to correct these artifacts [15].…”

Ghost reflection simulation, analysis, and correction in a multispectral imaging system

“…This model is used to develop a calibration and compensation method, which establishes the model's parameters for compensating for ghost reflections. Another research 6 goes into discussing several sorts of straylight that might occur: Scattering of the instrument's optical surfaces, repeated reflections between the detector and the filter or filter window, or lens surface, generating local ghosting. It also discusses about cross-talk ghost, i.e.…”