A Method to Extrapolate the Diffuse Upwelling Radiance Attenuation Coefficient to the Surface as Applied to the Marine Optical Buoy (MOBY)

Abstract

The upwelling radiance attenuation coefficient (<i>K</i>_Lu) in the upper 10 m of the water column can be significantly influenced by inelastic scattering processes, and thus will vary even with homogeneous water properties. The Marine Optical BuoY (MOBY), the primary vicarious calibration site for many ocean color sensors, makes measurements of the upwelling radiance (<i>L</i>_u) at 1 m, 5 m, and 9 m and uses these values to determine <i>K</i>_Lu and propagate the upwelling radiance directed toward the zenith, <i>L</i>_u, at 1 m to and through the surface. Inelastic scattering causes the <i>K</i>_Lu derived from the arm measurements to be an underestimate of the true <i>K</i>_Lu from 1 m to the surface at wavelengths greater than 575 nm, thus the derived water leaving radiance is underestimated at wavelengths longer than 575 nm. A method to correct this <i>K</i>_Lu, based on a model of the upwelling radiance including Raman scattering and chlorophyll fluorescence has been developed which corrects this bias. The model has been experimentally validated, and this technique can be applied to the MOBY data set to provide new, more accurate products at these wavelengths. When applied to a 4 month MOBY deployment, the corrected water leaving radiance, <i>L</i>_w, can increase by 5 % (600 nm), 10 % (650 nm) and 50 % (700 nm). This method will be used to provide additional more accurate products in the MOBY data set.