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Station automatique de mesures pour l'étalonnage en vol des capteurs satellitaires : application à SPOT/HRV sur le site de La Crau

Abstract : Vicarious calibration of the SPOT-HRV cameras has been performed on the La Crau test site for more than ten years. Several scientific teams characterized the atmosphere and the surface reflectance in order to predict the signal measured by HRV. Our objective is to
achieve this calibration using an automatic ground-based station.

We recall the radiative transfer theory used to predict the satellite signal. We also present the SPOT satellites, particularly SPOT4. Then we present the different methods used for the SPOT calibration.

Our instrumentation consists of a prototype of an entirely in situ calibrated radiometer. The irradiance calibration is based on the Langley-Bouguer law. In radiance, it is realised at short wavelengths on the Rayleigh scattering. Then the calibration is propagated to greater wavelengths with an original method. We present the results of the radiometer calibration with an estimation of its precision.

The atmospheric effects are evaluated from the radiometer measurements, as well as the surface bidirectional reflectance. The aerosols are represented by their optical thickness and their size distribution by a Junge-power law. We calculate the reflectance in the satellite viewing geometry using a directional effects model.

The TOA radiance is then estimated. We calculate the gaseous transmission with the 6S code. The Successive Orders of Scattering code is used to compute the TOA signal. We obtained four sets of coefficients for SPOT4 and one for SPOT2. The comparison with the
CNES coefficients shows a difference greater than the estimated uncertainty of our method. The difference remains similar to these formerly obtained on the La Crau site. It does not seem to be a systematic bias, and could then be lowered by further data collection. Now operational, the radiometer will allow this collection, thus improving the quality of the SPOT coefficients.
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Contributor : Catherine Six <>
Submitted on : Monday, September 22, 2003 - 4:40:33 PM
Last modification on : Monday, December 7, 2020 - 10:24:23 AM
Long-term archiving on: : Friday, April 2, 2010 - 7:30:26 PM

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Catherine Six. Station automatique de mesures pour l'étalonnage en vol des capteurs satellitaires : application à SPOT/HRV sur le site de La Crau. Autre. Université du Littoral Côte d'Opale, 2002. Français. ⟨tel-00003404⟩

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