Vicarious calibration of ocean color satellites involves accurate surface measurements of water-leaving radiance to update and improve the system calibration of ocean color satellite sensors. An experiment was performed to compare a free-fall technique with the established MOBY measurement. We found in the laboratory that the radiance and irradiance instruments compared well within their estimated uncertainties for various spectral sources. In the field, the sensors measuring the above surface downwelling irradiance performed as well as they had in the laboratory. However, the water-leaving radiance, Lw, calculated from each instrument had a relative bias, although on average quite small. Based on the analysis of one matchup, the same bias was observed in the measurement of Lu(1 m). Instrument self-shadowing could account for some of the difference between these measurements, however this was not addressed in the present study. While measurements from these systems had small differences, both between and within system classes, that deserve further investigation, the two approaches provided a comparable level of accuracy for deriving water-leaving radiances for comparison with satellite observations of the sea-surface, and well within the 5% uncertainties required for the derivation of chlorophyll pigment concentrations in the global ocean.
Citation: Journal of Atmospheric and Oceanic Technology
Pub Type: Journals
ocean color, radiometry, vicarious calibration