Stray Light Correction Algorithm for High Performance Optical Instruments: The Case of Metop-3MI

Abstract

Stray light is a critical aspect for high performance optical instruments. When stray light control by design is insufficient to reach the performance requirement, correction by post-processing must be considered. This situation is encountered, for example, in the case of the Earth observation instrument 3MI, whose stray light properties are complex due to the presence of many ghosts distributed on the detector array. We implement an iterative correction method and discuss its convergence properties. Spatial and field binning can be employed to reduce the computation time but at the cost of a decreased performance. Interpolation of the stray light properties is required to achieve high performance correction. For that, two methods are proposed and tested. The first interpolate the stray light in the field domain while the second applies a scaling operation based on a local symmetry assumption. Ultimately, the scaling method is selected and a stray light reduction by a factor of 58 is obtained at 2σ (129 at 1σ) for an extended scene illumination.

Out-of-field stray light correction in optical instruments: the case of Metop-3MI

“…( 2)]. 5 Here, x; y ¼ ½1∶N are the spatial coordinates on the detector array, in units of pixels E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 1 ; 1 1 7 ; 8 8 I mes ðx; yÞ ¼ I nom ðx; yÞ þ I SL IF ðx; yÞ þ I SL OOF ðx; yÞ;…”

“…Previously, a scaling interpolation method was developed for IF SL in 3MI, where the SPST map at a given field is obtained by applying a rotation and scaling operation to the map calibrated at the closest field. 5 The rotation is the difference in azimuth angle between the field to interpolate and its closest neighbor. The scaling is the ratio between the radial distance of the nominal pixel of both fields.…”

“…For that purpose, an interpolation method was proposed for 3MI based on a local symmetry assumption. 5 Spatial and field binning can be applied to reduce the quantity of data, with consequences on the performance. 5 In most situations, correction algorithms only consider SL caused by sources located inside the FOV of the instrument, called in-field (IF) SL.…”

“…5 Spatial and field binning can be applied to reduce the quantity of data, with consequences on the performance. 5 In most situations, correction algorithms only consider SL caused by sources located inside the FOV of the instrument, called in-field (IF) SL. However, SL can also come from sources located outside the FOV, called out-of-field (OOF) SL.…”

A new paradigm in the field of stray light control and characterization enabled by ultrafast time-of-flight imaging

“…It is important to identify any stray light issue on ground so that appropriate actions can be taken if necessary. Furthermore, characterization can be done to be used as an input for stray light correction algorithms [4] [5][6] [7].…”