Unspecified Léa Scheveiler Profile

Léa Scheveiler

at Lab. Atmosphères, Milieux, Observations Spatiales

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Publications (2)

Proceedings Article | 12 July 2023 Open Access

Spectral contamination between diffraction orders of the NIR spectrometer (TGO) but possible solutions to overcome it

Abdanour Irbah, Jean-Loup Bertaux, Franck Montmessin, Léa Scheveiler, Gaetan Lacombe, Nicolas Rouanet, Alexander Trokhimovskiy, Oleg Korablev, Anna Fedorova

Proceedings Volume 12777, 127776Z (2023) https://doi.org/10.1117/12.2691362

KEYWORDS: Diffraction, Acoustooptic tunable filters, Contamination, Spectroscopy, Astronomical imaging, Sun, Calibration, Near infrared, Image processing, Stray light

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The ACS-NIR spectrometer aboard TGO is currently used to probe the atmosphere of Mars. ACS-NIR detects the spectral signature of atmospheric components along its line of sight as it passes through the atmosphere when the spectrometer points toward the Sun. The solar spectrum will be directly measured when the line of sight is above the atmosphere. Thus, observations were specifically requested to build the solar spectrum over the domain accessible by the ACS-NIR spectrometer but also to study its instrumental properties and their effects on the measurements. They consisted in recording all the images of the diffraction orders of ACS-NIR by continuously varying the frequency of its acousto-optical element, the AOTF. This second objective is the aim of this paper since the first has already been studied in detail in irbah et al. (2022). In particular, this previous paper presented the method and the different processing steps to avoid spectral contaminations between successive orders that occurs when constant AOTF frequencies are used for acquire them. This contamination is problematic in that it causes wavelengths to appear in a spectral band of a given diffraction order that actually come from its immediate neighbours. The constant AOTF frequencies are however used in the nominal mode of ACS-NIR during operations. They are chosen so that the orders are centred on the detector, i.e. in the image. The orders, however, present 2D intensity variations in particular along the x axis (wavelength) and, therefore, the spectral lines at the ends are poorly detected due to the low level of intensity. In this paper, we first recall the different processing steps to obtain the spectral bands associated with the diffraction orders. However, we have completed the original method by adding the correction of the diffraction orders of their 2D intensity variations, which improves the quality of the processing for obtaining the solar spectrum. We then present how to identify the spectral contributions of neighbouring orders to a given spectral band. Next, we present a new method that overcomes cross-order contamination by extracting two parts of images of the same diffraction order obtained with distinct AOTF frequencies. We show that this combination also brings a solution to the problem of the detection of spectral lines at the extremities where the intensity of the order is weak. Finally, we end by showing and discussing some promising results of the method obtained with the ACS-NIR order 101 taken as an example because it is likely to present spectral contamination. These results show that its neighbours no longer contaminate its spectral band. It is also of better quality compared to that calculated with the geometric method presented in the paper cited above. This method can be easily extended to all other orders, which will improve the solar spectrum obtained with ACS-NIR. It can also be used for ACS-NIR during operations without a noticeable increase in telemetry.

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Proceedings Article | 27 August 2022 Poster + Paper

Processing of ACS-NIR observations to build the solar spectrum with high spectral resolution in the 0.7-1.7 µm domain

Abdanour Irbah, Jean-Loup Bertaux, Franck Montmessin, Léa Scheveiler, Gaetan Lacombe, Alexander Trokhimovskiy, Oleg Korablev, Anna Fedorova, Andrey Patrakeev, Alexei Shakun

Proceedings Volume 12180, 121803H (2022) https://doi.org/10.1117/12.2629398

KEYWORDS: Diffraction, Spectroscopy, Sun, Stray light, Sensors, Image processing, Calibration, Spectral resolution, Solar processes, Diffraction gratings, Spectrum analysis, Near infrared

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