SPOT5: first in-flight radiometric image quality results

The SPOT5 remote sensing satellite was launched in May 2002. It provides SPOT service continuity above and beyond SPOT4 operation but the SPOT5 system also significantly improves the SPOT service with the new characteristics of its two HRG (High Resolution Geometry) cameras and its HRS (High Resolution Stereo) camera. SPOT5's first two months of life in orbit were dedicated to instrument calibration and the assessment of image quality performances. During this period, the CNES team used specific target programming to compute image correction parameters and estimate the performance of the image processing chain, at system level. This paper focuses on the relative radiometric performances of the different spectral bands for the three instruments, deduced from in-flight measurements. For each spectral band, a radiometric model gives the ratio between detector response and input radiance. This model takes the architecture of the onboard image chain into account. Calibration provides the normalisation parameters (dark currents and relative inter-detector sensitivities) used to correct the images. The quality of the corrected images is quantified through several signal-to-noise ratio measurements based on different techniques. These methods are presented and their accuracy is discussed. Finally, a comparison is given between flight measurements and ground measurements.