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The visible and infrared Moon And Jupiter Imaging Spectrometer (MAJIS), aboard the JUpiter ICy Moons Explorer (JUICE) spacecraft, will characterize the composition of the surfaces and atmospheres of the Jupiter system. Prior to the launch, a campaign was carried out to obtain the measurements needed to calibrate the instrument. The aim was not only to produce data for the calculation of the radiometric, spectral, and spatial transfer functions but also to evaluate MAJIS performance, such as signal-to-noise ratio and amount of straylight, under near-flight conditions. Here, we first describe the setup implemented to obtain these measurements, based on five optical channels. We notably emphasize the concepts used to mitigate thermal infrared emissions generated at ambient temperatures, since the MAJIS spectral range extends up to 5.6 µm. Then, we characterize the performance of the setup by detailing the validation measurements obtained before the campaign. In particular, the radiometric, geometric, and spectral properties of the setup needed for the inversion of collected data and the calculation of the instrument's calibration functions are presented and discussed. Finally, we provide an overview of conducted measurements with MAJIS, and we discuss unforeseen events encountered during the on-ground calibration campaign., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

The MAJIS (Moons and Jupiter Imaging Spectrometer) instrument is an imaging spectrometer on-board the JUICE (JUpiter ICy moons Explorer) spacecraft. MAJIS covers the spectral range from 0.5 to 5.54 μm with two channels [visible-near infrared (VISNIR) and IR]. A comprehensive campaign of on-ground MAJIS calibration was conducted in August and September 2021 in the IAS (Institut d'Astrophysique Spatiale, CNRS/Université Paris-Saclay) facilities. In this article, we present the results relevant for the radiometric calibration of MAJIS. Due to the specific characteristics of the MAJIS detectors (H1RG from Teledyne), an extensive detector characterization campaign was implemented for both the VISNIR and IR detectors before integration so as to validate readout procedures providing precision and accuracy. The characterization also provided critical information on linearity and operability as a function of the integration time and operating temperature. The radiometric calibration of the integrated MAJIS instrument focused on the determination of the instrument transfer function in terms of DN output per unit of radiance for each MAJIS data element as a function of its position in the field of view of MAJIS and its central wavelength. The radiometric calibration of the VISNIR channel required a specific procedure due to stray light at short wavelengths. Observations of an internal calibration source during calibration and after launch (April 14, 2023) showed that there were minor changes in both the VISNIR and IR channels. The instrument transfer functions to be used in flight have been updated on this basis., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

MAJIS (Moons and Jupiter Imaging Spectrometer) is the imaging spectrometer onboard ESA's JUICE (JUpiter and ICy Moons Explorer) spacecraft that operates in the visible and near/mid-infrared between 0.5 and 5.54 μm. Before the launch of JUICE in April 2023, MAJIS underwent a comprehensive on-ground calibration campaign in between August and September 2021 in the IAS (Institut d'Astrophysique Spatiale, Université Paris-Saclay) calibration facilities. Among all the operations, calibration sequences using a set of natural mineral samples and synthetic reference materials were acquired in order to characterize MAJIS performances under conditions assumed to be close to certain future observation configurations. Here, we analyze these calibration measurements using comparison with laboratory reference spectra to quantify MAJIS spectral and spatial performances while observing these solid surfaces. We first assess the MAJIS absolute spectral calibration of the visible and near-infrared channel covering half of the wavelength range. We then quantify spectral performances in terms of global spectral slopes, band detection, band shape, and depth retrievals, over most of the spectral range using six mineral samples. We conclude that for most configurations, the MAJIS instrument demonstrates excellent spectral performances compliant with the requirements. MAJIS can, however, be affected by stray light contributions, notably for wavelengths lower than about 1.2 μm, and some performances of the instrument may then be significantly impacted depending on viewing conditions. In particular, we have identified cases of spectral contrast reduction up to 40%, absolute spectral shifts up to 2-3 nm, and spectral smile variability by +/1 nm. Finally, we used the MAJIS internal scanning mirror to test its ability to construct hyperspectral images of a few samples: we present the first band depth maps derived with MAJIS while observing a serpentine/carbonate sample, as well as an evaluation of MAJIS spatial point spread function. Overall, the analysis of MAJIS behavior while observing samples confirms most MAJIS expected performance requirements, while revealing subtle spectral perturbations that may be related to stray light and viewing conditions. These differences will be further investigated in-flight during the cruise, with a solar reflected target such as the Moon, as well as Jupiter before the JUICE orbital insertion., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

MAJIS, Moons and Jupiter Imaging Spectrometer, is one of the scientific payloads aboard European Space Agency's Jupiter Icy Moons Explorer mission. This instrument underwent a comprehensive characterization and calibration campaign before integration on the spacecraft. In this work, we report on the measurements of the instrumental spatial responses, including the slit and pixel functions, the knife edge function, the ensquared energy, and the keystone aberration. The measurements were repeated in several positions of the field of view and within the range of MAJIS temperatures during science observations. The goal was to characterize the instrument's response under a wide set of conditions and at different visible-infrared wavelengths. The experimental setups employed to perform calibrations are described in detail, and the methodology applied to derive the instrumental spatial responses is discussed. After launch, minor changes in the instrument response and the coalignment between the two spectral channels were identified by comparing on-ground data with the first in-flight data returned by MAJIS., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

The Moons And Jupiter Imaging Spectrometer (MAJIS) is the visible and near-infrared imaging spectrometer onboard the European Space Agency (ESA)'s Jupiter Icy Moons Explorer mission. Before its integration into the spacecraft, the instrument undergoes an extensive ground calibration to establish its baseline performances. This process prepares the imaging spectrometer for flight operations by characterizing the behavior of the instrument under various operative conditions and uncovering instrumental distortions that may depend on instrumental commands. Two steps of the on-ground calibration campaigns were held at the instrument level to produce the data. Additional in-flight measurements have recently been obtained after launch during the Near-Earth Commissioning Phase. In this article, we present the analyses of these datasets, focusing on the characterization of the spectral performances. First, we describe and analyze the spectral calibration datasets obtained using both monochromatic sources and polychromatic sources coupled with solid and gas samples. Then, we derive the spectral sampling and the spectral response function over the entire field of view. These spectral characteristics are quantified for various operational parameters of MAJIS, such as temperature and spectral binning. The derived on-ground performances are then compared with in-flight measurements obtained after launch and presented in the framework of the MAJIS performance requirements., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)

Ab initio calculations of the shapes of pure CO2 infrared and Raman bands under (pressure) conditions for which line-mixing effects are important have been performed using requantized classical molecular dynamics simulations. This approach provides the autocorrelation functions of the dipole vector and isotropic polarizability whose Fourier-Laplace transforms yield the corresponding spectra. For that, the classical equations of dynamics are solved for each molecule among several millions treated as linear rigid rotors and interacting through an anisotropic intermolecular potential. Two of the approximations used in the previous studies have been corrected, allowing the consideration of line-mixing effects without use of any adjusted parameters. The comparisons between calculated and experimental spectra under various conditions of pressure and temperature demonstrate the quality of the theoretical model. This opens promising perspectives for first principle ab initio predictions of line-mixing effects in absorption and scattering spectra of various systems involving linear molecules.