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Improving our Sun knowledge while certifying our instruments

Research Topic Chapter
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Measuring the solar spectrum from above the atmosphere is the obvious approach for scientists who want to know the amount of solar energy reaching our planet before any extinction takes place. Nevertheless, with ground-based instruments and from renowned high-altitude observatories, we can approach the quality of space-based measurements with the added advantage of being able to follow the instrument’s performances. The assessment of the radiometric performances of both spatial and ground-based instruments is done in BIRA-IASB’s radiometric laboratories.
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Ground-based measurements

In the Near Infrared (NIR) regions of the solar spectrum (from 800 nm to 2.5 micron), the measurement of the respective irradiance from space can be a laborious task due to the low energy of the NIR photons and the inherent difficulty to track the instruments calibration and complex behaviour in a space environment.

For several atmospheric windows it is possible to measure the NIR irradiance from the ground and extrapolate it to the top of the atmosphere with great accuracy, and with the added benefit of a close tracking of the instrument’s calibration.

Our group carried out these high accuracy measurements at two high altitude world renowned observatories where the conditions of atmospheric stability are excellent:

  • Izaña Observatory (IZO) on Tenerife
  • Mauna Loa Observatory (MLO) on Hawaii

The results obtained in the NIR spectrum for both campaigns have contributed greatly to the definition of the absolute level of the Sun’s NIR spectrum.

Laboratory facilities

The BIRA-IASB radiometric laboratory experienced a significant growth in equipment and expertise in the early 2000’s during the development and characterization phase of the SOLAR/SOLSPEC instrument.

This expertise was successfully applied to the characterization of:

  • ground-based broadband NIR and UV instruments
  • space instruments such as: SPICAM LIGHT on board Mars Express, SODISM on board PICARD and NOMAD/UVIS on board ExoMars

The laboratory is nowadays dedicated to the characterization of the MAJIS instrument to be flown on board JUICE. New calibration units are regularly developed to allow specific radiometric characterization to new instruments such as ALTIUS.

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Figure 2 caption (legend)
Near Infrared instrument pointing to the Sun during the campaign at the Izaña Observatory on Tenerife.
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Figure 3 caption (legend)
Radiometric laboratory material in action