Absolute Calibration Of The SPOT-1 HRV Cameras

Abstract

The pre-flight and on-board in-flight absolute radiometric calibrations of the two HRV cameras on SPOT-1 are briefly described. The results of the in-flight calibrations at White Sands, New Mexico are presented in detail and compared to the other methods. The ratio of calibration coefficients for the two SPOT-1 HRVs was obtained from a histogram match of a scene, imaged simultaneously by the two cameras. This was compared to the ratio of the calibration coefficients from the White Sands results. The ratios are in good agreement, < 3% in three bands, the exception is multispectral band 2 which shows a 7% difference. The histogram result and a comparison with spectral radiances measured from an altitude of 3000 m indicate that, at the time and under the conditions that the calibrations were madelthe specification for a ± 10% RMS absolute calibration uncertainty for the SPOT-1 HRVs had been met. The White Sands and histogram ratio results were used to update the calibration of the on-board suncalibrator system for the HRVs.