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 sur face phytoplankton concentrations at rates of up to once per day, providing wide-area data on a number of fundamental ocean processes relating to biol ogical production, air-sea exchange of biogenic greenhouse gases: climate c hange, and living resources. There remain a number of problems in the techn ique, including the possible decline of satellite-sensor sensitivity over t ime and the difficulty of correcting for light detected by the satellite se nsor that originated from the atmosphere. To overcome these problems, the n ew generation of ocean-color sensors must be coupled with an extensive cali bration and validation program. In this study, the authors report on progre ss 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. Th e Plymouth Marine Bio-Optical Data Buoy, which became operational on 19 Apr il 1997, is assessed against rigorous specifications for surface and in-wat er radiometers and is shown to be capable of making high-quality optical me asurements for a fraction of the cost associated with other calibration-val idation projects.