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

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.