Abstract
In-flight calibration of space sensors once in orbit is a decisive step to be able to fulfill the mission objectives. This presentation describes the methods processed during the commissioning phase of PLEIADES 1A and PLEIADES 1B to update the absolute calibration coefficients of the two instruments.
PLEIADES is a dual Earth observation system composed of two satellites, PLEIADES 1A and PLEIADES 1B, respectively launched at the end of 2011 and 2012. This imagery system, led by the French National Space Agency, CNES, is derived from the instrument developed for the SPOT programs. It is composed of four spectral bands, blue, green, red and near infrared, with a resolution of 2.8 m in vertical viewing and a panchromatic band with a resolution of 0.7 m in vertical viewing. Its swath is about 20 km. It is characterized by a very high level of agility which allows it to acquire terrestrial targets with different viewing angles in a very short time or extraterrestrial objects as stars and the Moon.
To achieve a very good confidence in the calibration results, four in-flight calibration methods were used, compared and analysed during the commissioning phase: absolute calibration, cross-calibration with reference sensors such as PARASOL or MERIS, multi-temporal monitoring and inter-bands calibration. These algorithms were based on acquisitions over natural targets such as African deserts, Antarctic sites, La Crau (Automatic calibration station) and Oceans (Calibration over molecular scattering) or also new extra-terrestrial sites such as the Moon and selected stars.
After an overview of the instrument and a description of the calibration sites, this presentation will point out how each method is able to address one or several aspects of the calibration. Every calibration method has its own limitation: for example efficiency regarding the spectral range, sensitivity to the knowledge of the instrumental behavior (i.e. spectral response, variation in the field-of-view, linearity…), or robustness with number of matchups. Consequently, be able to merge various methods having different limitations is an opportunity to improve the radiometric calibration and the confidence one can have on it. In addition, it also provides a realistic evaluation of the final accuracy.
We will focus on how these methods complete each other in their operational use for PLEIADES, and how they help building a coherent set of information that addresses all aspects of in-orbit calibration.
Improved Confidence on the PLEIADES In-flight Absolute Calibration Through the Merging of Different Vicarious Calibration Methods
In-flight calibration of space sensors once in orbit is a decisive step to be able to fulfill the mission objectives. This presentation describes the methods processed during the commissioning phase of PLEIADES 1A and PLEIADES 1B to update the absolute calibration coefficients of the two instruments.
PLEIADES is a dual Earth observation system composed of two satellites, PLEIADES 1A and PLEIADES 1B, respectively launched at the end of 2011 and 2012. This imagery system, led by the French National Space Agency, CNES, is derived from the instrument developed for the SPOT programs. It is composed of four spectral bands, blue, green, red and near infrared, with a resolution of 2.8 m in vertical viewing and a panchromatic band with a resolution of 0.7 m in vertical viewing. Its swath is about 20 km. It is characterized by a very high level of agility which allows it to acquire terrestrial targets with different viewing angles in a very short time or extraterrestrial objects as stars and the Moon.
To achieve a very good confidence in the calibration results, four in-flight calibration methods were used, compared and analysed during the commissioning phase: absolute calibration, cross-calibration with reference sensors such as PARASOL or MERIS, multi-temporal monitoring and inter-bands calibration. These algorithms were based on acquisitions over natural targets such as African deserts, Antarctic sites, La Crau (Automatic calibration station) and Oceans (Calibration over molecular scattering) or also new extra-terrestrial sites such as the Moon and selected stars.
After an overview of the instrument and a description of the calibration sites, this presentation will point out how each method is able to address one or several aspects of the calibration. Every calibration method has its own limitation: for example efficiency regarding the spectral range, sensitivity to the knowledge of the instrumental behavior (i.e. spectral response, variation in the field-of-view, linearity…), or robustness with number of matchups. Consequently, be able to merge various methods having different limitations is an opportunity to improve the radiometric calibration and the confidence one can have on it. In addition, it also provides a realistic evaluation of the final accuracy.
We will focus on how these methods complete each other in their operational use for PLEIADES, and how they help building a coherent set of information that addresses all aspects of in-orbit calibration.