Calibration of MAJIS (Moons and Jupiter Imaging Spectrometer). IV. Radiometric calibration (invited).

This article focuses on the radiometric calibration of MAJIS (Moons and Jupiter Imaging Spectrometer), an imaging spectrometer aboard the JUICE (JUpiter ICy moons Explorer) spacecraft designed to study Jupiter and its icy moons across the 0.5–5.54 μm spectral range via two channels: visible–near infrared (VISNIR) and infrared (IR). The calibration involved a two-step process: detailed characterization of the flight detectors (H1RG from Teledyne) to validate readout procedures, linearity corrections, conversion efficiency, noise, and operability; followed by radiometric calibration of the integrated instrument using calibrated sources to determine instrument transfer functions (ITFs) for converting digital numbers (DNs) into physical radiances. Key findings include the identification and modeling of stray light contributions affecting the VISNIR channel at wavelengths below 1300 nm and near its upper spectral limit, necessitating specific correction procedures to isolate legitimate signals. Post-launch observations revealed minor spatial and spectral shifts requiring adjustments to the ITFs implemented in the MAJIS data pipeline. Overall, the calibration confirms that MAJIS meets or exceeds performance requirements, enabling reliable radiance measurements critical for the mission’s scientific objectives.