Accurate radiometric calibration of space borne ocean-colour sensors is essential for retrieving geophysical variables (concentration of water constituents, inherent optical properties, aerosol content, etc.) quantitatively in terms of absolute values. The accuracy requirements for absolute calibration are especially demanding in ocean colour remote sensing, because the extracted signal is relatively small compared with the measured signal. In-orbit calibration is essential to ensure valuable data through monitoring of sensor stability. This report provides a review of techniques developed and employed for the radiometric calibration of satellite ocean colour sensors while they operate in orbit. All the techniques are presented with their accuracy, advantages, and limitations and recommendations are given on how to proceed with the radiometric calibration of ocean colour sensors during operational phase, in order to generate and maintain quality retrievals of water-leaving radiance. |
