MODIS-Aqua Calibration as seen by Alternative Statistical Methods over Natural Targets

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CONFERENCE: Conference on Characterization and Radiometric Calibration for Remote Sensing (CALCON)

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Fougnie, Bertrand; Henry, Patrice; Gamet, Philippe; Bruniquel, Véronique; Fontanilles, Guillaume
conference paper description
MODIS-AQUA launched in 2002 is a sensor which has not only provided a very significant archive of Earth reflectances, more than 11 years now, but is also considered as a strong radiometric reference in the space remote sensing field. For instance, MODIS is currently the reference LEO sensor for the reflective part of the spectrum for GEO inter-calibration in the framework of GSICS activities. Several analysis have shown the reliability of the in-flight calibration, particularly using a sophisticated on-board calibration device which includes solar diffusers, black bodies, spectroradiometric calibration, and lunar and space views.In this study, various calibration methods using a statistical approach over natural targets have been implemented for MODIS-AQUA. These methods which are operational in the SADE/MUSCLE environment have shown their potentialities for validation of the different aspect of the in-flight calibration for various sensors such as PARASOL, MERIS, Végétation, and more recently SEVIRI. Very useful information can be derived about the temporal trending correction, the variation inside the field of view or scan angle, the interband consistency for the full reflective spectral range, the check of the consistency with other sensors (through a cross-calibration), the validity for high or low radiances, the sensitivity to polarization, etc…Cross-calibration over desert sites was elaborated in the last years (Lachérade et al., 2013), and a refined evaluation of the temporal trending will be presented. A summary of cross-calibrations with several sensors will draw the radiometric consistency with MERIS, PARASOL, Vegetation, SEVIRI.Calibration over oceanic sites has been implemented in order to derive absolute calibration of visible bands over Rayleigh scattering as well as interband calibration of all reflective bands over the sunglint. Nevertheless, because some saturation may occur over bright targets (such as desert or sunglint), it was not allowed to obtained this result for some ocean color bands. Comparative results will be illustrated.The MODIS-AQUA calibration was found to be globally consistent within roughly +/- 1.5% for all bands providing a significant validation. If a good agreement of the interband calibration is observed for the full spectral range, it will be discussed the reliability of very small interband variations (about 1%). For that, a comparison with the vicarious adjustment proposed in the literature but also for ocean color processing (through the SeaDAS Data Analysis System) will also be considered.Other behaviours, for instance versus scan angle (so potentially polarization), viewing geometry or versus time, will be analysed and discussed.The presentation will highlight the interest to develop alternative calibration methods (for instance statistical approaches), in order to possibly improve, or if not validate, the knowledge of the instrumental behaviour, complementarily to robust on-board characterisation.