Calibration and Validation of Multiple Ocean Color Sensors

The Coastal Zone Color Scanner (CZCS), launched in October 1978, was the first satellite-borne, visible imager developed for the purpose of investigating ocean color. The results showed that many ocean products can be generated from the remote sensing reflectance, the primary output of ocean color sensors, including chlorophyll, diffuse attenuation coefficient, particulate inorganic and organic carbon, water clarity, and sediment concentrations. Due to atmospheric absorption and scattering fewer than 10% of the photons reflected by the ocean reach space to be captured by orbiting ocean color sensors. The error budget for ocean color sensors is small and the calibration of these sensors is important for applications of the data. In order to generate useful ocean products, wavelengths around 412, 443, 488, 551, and 600 nanometers are suggested. Additional wavelengths in the shortwave infrared are required for quality atmospheric corrections. At present, the Naval Research Laboratory acquires data from five ocean color sensors. The Automated Processing System was developed to process, calibrate, and validate these sensors. Using in-situ data from the deep ocean Marine Optical Buoy and NASA’s Aerosol Robotic Network of ocean color sensors at various coastal locations, the satellite data are compared and calibrated. Additionally, the data from each satellite are compared to insure that data generated are consistent. The latter allows compositing sensor data from different satellites to generate quality weekly composites. Recently acquired morning coverage provides the capability for better cloud removal and daily compositing as well as showing potential ocean feature movement over a three hour period.