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SPOT4, The fourth satellite of the SPOT family remote sensing satellites, was launched on the 20th of march 1998. During the first months, we calibrate the two identical on-board cameras named HRVIR (because of the added Mid Infra-Red channel) and VEGETATION, a wide field of view radiometer providing 1.15 kilometers resolution measurements in the same designed channels as HRVIR (B2, B3 and MIR), and we evaluate the quality of the images. Radiometric calibration results are presented in this paper. Different methods are applied based on the experience gained with SPOT1, 2, 3 and POLDER:

pre-launch measurements,

on-board calibration system,

vicarious calibration over test sites,

inter-SPOT calibration over desert areas,

calibration over the molecular scattering,

inter-cameras calibration between HRVIR1 and HRVIR2

inter-cameras calibration between HRVIR and VEGETATION.

The accuracy of each calibration procedure is estimated. The measurements are combined in a model that minimizes errors and provides the camera sensitivity as a function of time.