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A COMPARISON OF IN SITU AND MODELLED ESTIMATES OF SELECTED APPARENT OPTICAL PROPERTIES IN RESPONSE TO CHL A AND CDOM VARIABILITY IN THE COASTAL WATERS OF SOUTHERN NEW ENGLAND DURING SUMMER 1999
Citation:
Keith, D J., J. A. Yoder, AND C. Beckmann. A COMPARISON OF IN SITU AND MODELLED ESTIMATES OF SELECTED APPARENT OPTICAL PROPERTIES IN RESPONSE TO CHL A AND CDOM VARIABILITY IN THE COASTAL WATERS OF SOUTHERN NEW ENGLAND DURING SUMMER 1999. American Geophysical Union 2000 Ocean Sciences Conference, San Antonio TX, January 24-28, 2000.
Description:
Chlorophyll a concentrations, colored dissolved organic matter (CDOM) absorption coefficients, and selected apparent optical properties (AOPs) of waters along the Western Passage of Narragansett Bay and adjoining Rhode Island Sound were determined from May -August 1999. Water samples were collected at 5 m depth at four stations from Rhode Island Sound to the entrance of the Providence River. Three AOPs: reflectance (R), diffuse attenuation (Kd), and remote sensing reflectance (RRS) were calculated at 412,443,490,510,555 and 665 nm from profile measurements of downwelling spectral irradiance and upwelling radiance using a profiling reflectance radiometer. To check for internal consistency of the observations, radiometer measurements were compared with simulations using HYDROLIGHT, a radiative transfer equation model, that uses inherent optical properties (lOPs) such as CDOM absorptions and chlorophyll a concentrations to predict AOPs.
Field measurements generally indicated that the bio-optical properties of lower Narragansett Bay are absorption-dominated. Chlorophyll a and CDOM concentrations were highly variable during the sampling period with values generally increasing from Rhode Island Sound northward into upper Narragansett Bay. A comparison of Kd coefficients measured in situ and predicted by HYDROLIGHT showed high statistical correlation (r2 = 0.82), with highest Kd in upper Narragansett Bay and steadily decreasing values toward Rhode Island Sound. Modeled and in situ estimates of R also indicated high correlation (r2 = 0.89) with the highest reflectance in the blue region of the spectrum occurring offshore in Rhode Island Sound. Conversely, highest reflectance in the green wavelengths occurred in the estuarine waters of the upper bay. The strong relationship between the modeled and measured AOPs indicated that HYDROLIGHT has accurately simulated the in situ optical and reflectance properties of waters along Western Passage. It is now possible to explore analytical relationships between these lOPs and AOPs during the development or tuning of an algorithm to retrieve phytoplankton chlorophyll a concentrations and CDOM absorptions from in situ bio-optical and remote sensing measurements of New England coastal and estuarine waters.