Measurement Validation for Ocean Color

On August 4–5, 2010, members of the satellite remote sensing community, including NIST’s Optical Technology Division, participated in a workshop off the coast of Long Island, New York. Their objectives were to interpret and implement recently published protocols for measuring normalized, water-leaving spectral radiances by above-water in situ radiometry, and to compare the results.

Each research team applied the measurement protocols to the water’s surface and three reflectance standard targets supplied by NIST—a white and a gray diffuse reflectance target and a blue ground-glass target. The reflectance values of the water’s surface and the test targets were determined and analyzed by each team.

The workshop participants included researchers from NIST, Naval Research Laboratory (team lead), City University of New York, Mississippi State University at Stennis Space Center, NOAA’s National Ocean Service and the National Environmental Satellite, Data, and Information Service, and the Center for Hydro-Optics and Remote Sensing at San Diego State University. A report on the workshop will be prepared detailing the methods for comparison of the participant’s results, methods of analysis, and data reduction.

This workshop served as preparation for the validation activities that will follow the launch of Visible Infrared Imager Radiometer Suite (VIIRS). Above water, in situ radiometric measurements will be one method to validate the data products, such as chlorophyll concentration, that are derived from ocean color sensors on VIIRS.

NIST’s role in the upcoming validation activities of VIIRS includes addressing the uncertainty budget, completing characterization of selected sun photometers, and observing the implementation of the measurement protocols. NIST’s first characterizations of the sun photometers, planned for September 2010, will involve their spectral characterization using the Spectral Irradiance and Radiance Responsivity using Uniform Sources (SIRCUS) facility in Optical Technology Division.