Calibration and validation of remotely sensed observations of ocean color from a moored data buoy

Satellite remote sensing of ocean color has the potential to map global surface phytoplankton concentrations at rates of up to once per day, providing wide-area data on a number of fundamental ocean processes relating to biological production, air-sea exchange of biogenic greenhouse gases: climate change, and living resources. There remain a number of problems in the technique, including the possible decline of satellite-sensor sensitivity over time and the difficulty of correcting for light detected by the satellite sensor that originated from the atmosphere. To overcome these problems, the new generation of ocean-color sensors must be coupled with an extensive calibration and validation program. In this study, the authors report on progress to develop a methodology to measure water-leaving radiance and incident irradiance from a moored buoy in order to effect vicarious calibration and validation of ocean-color satellite data at a rate of up to twice daily. The Plymouth Marine Bio-Optical Data Buoy, which became operational on 19 April 1997, is assessed against rigorous specifications for surface and in-water radiometers and is shown to be capable of making high-quality optical measurements for a fraction of the cost associated with other calibration-validation projects.