Effects of intermittent entrainment of air bubbles by breaking wind waves on ocean reflectance and underwater light field

Light-scattering properties of air bubbles suspended in water and observational evidence of bubble entrainment by breaking wind waves indicate that bubble clouds may influence ocean reflectance and in-water light field characteristics within the surface layer. We estimate potential changes in remote sensing reflectance and in-water light field associated with a bubble entrainment event observed at a wind speed of 10 m s(-1). Our approach combines acoustic measurements of bubble concentration as a function of time and depth and radiative transfer simulations of the light field within and leaving a water body. We show that the remote sensing reflectance can increase significantly (more than twofold) due to bubble entrainment, and these large variations occur over time periods on the order of minutes or less. The bubble clouds have a spectral effect on ocean reflectance such that the water patch containing bubbles will appear greener or more yellowish than the surrounding waters with no bubbles. These results are relevant to measurements of remote sensing reflectance made from just above the water surface with downlooking radiance meters whose spot size at the surface is of O(0.1-1) m. The light field characteristics within the bubble layer are also significantly affected, with most pronounced effects seen in the profiles of upwelling irradiance and upwelling radiance. Therefore the bubble entrainment can be a source of error in the estimation of reflectance from extrapolation of underwater measurements at a depth up to and across the surface. While our radiative transfer simulations were made using a model with a plane-parallel geometry, future efforts to examine the effects of spatial distribution of bubble clouds and their properties on ocean reflectance from spatially integrating [O(10-1000) m] satellite measurements will have to be based on a three-dimensional approach.