In-flight calibration of large field of view sensors at short wavelengths using Rayleigh scattering

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Abstract
Satellite observations over the ocean in the backscatter direction are dominated by Rayleigh scattering. We use this predictable radiance for in-flight calibration of the visible SPOT channels. Two methods are evaluated. The first method directly relates the measured numerical signal in a short wavelength channel to the predicted reflectance. In the second method, we use a second channel centred at a longer wavelength, to correct the short wavelength channel for the effect of the atmospheric aerosol contribution. These two methods are examined for channel B0 , centred at 045 μm planned for launch on SPOT-4 VEGETATION, and for channel B1 centred at 0-55 mu;mm, currently on-board SPOT-1 HRV. In both cases, the channel B3 , centred at 0-85 mu;mm is used for aerosol correction. Error analysis shows that accuracies of 3 and 5 per cent respectively can be achieved for B0 and B1. The last section of the paper is devoted to a validation of the error analysis using SPOT-1 HRV data.