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From a dark lab to the sky and space

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All experimental setups in aeronomy require the characterization of instrumentation. It allows converting instrument raw signals into useful scientific data, with optimal control of instrumental effects and uncertainties. The solar irradiance measurement or the use of its flux as a reference light source is a key point for measurements in aeronomy. The radiometry laboratories at BIRA-IASB are equipped accordingly, with recent involvement in projects such as MAJIS, ALTIUS, and PLIP.
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Purpose of the radiometry laboratory

BIRA-IASB activities cover both theoretical work (modeling) and associated data processing, as well as experimental activities.

Solar flux used as a reference light source

In the field of aeronomy, the main objective of radiometry laboratories is to characterize instrumentation dedicated to the measurement of photon flux, especially for solar irradiance determination. This activity requires absolute calibration and thorough characterization of measuring instruments. It contributes to both the UV radiation climatology and the radiative transfer in the atmosphere.

When the solar flux is used as a light source in relative units (limb measurements, study of trace species and planetary atmospheres), the preparation of instruments in the laboratory is essential. A fundamental metrological principle for a mission using an instrument consists in possessing its measurement equation and mastering the uncertainty margins in order to interpret accurately the conversion of raw electronic signals into useful scientific data.

Deep understanding of measurements

Consequently, constant efforts are made to equip laboratories and fulfill all requirements, concerning especially the spectral, angular and absolute responses of the instruments, their sensitivity, temperature dependencies, and the accurate characterization of the performance of the detectors. This is both a validation of the instrument operational modes and a deep understanding of all the coefficients appearing in the measurement equations.

Therefore, darkrooms in laboratories are equipped with stable, homogeneous, monochromatic or not, and calibrated light sources if necessary, to analyze responses of subsystems and instruments covering a wide spectral range extending from the vacuum ultraviolet (VUV) to near infrared (NIR). In addition, the equipment is compatible for ground-based measurements (including at high altitude), but also for space technologies with strict constraints (simulation of spatial conditions, cryogenics, use of clean rooms).

Example of achievement

In addition to the management of the ground-based global solar illumination measurement instruments, the radiometry laboratories have been involved in the following recent projects:

  • Characterization of the VIS-NIR flight model detector of the MAJIS/JUICE instrument (Figure 1).
  • Measurement of the quantum efficiency of UV and VIS detectors for the ALTIUS experiment (Figure 2).
  • Characterization of filters used for a polarimetric imaging experiment (PLIP).
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Figure 1. Test bench for the thermal vacuum, used for the MAJIS project.
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Figure 2. Laboratory equipment used for the characterization of the UV-VIS detector prototypes of the ALTIUS experiment
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