Three-dimensional modelling of inherent optical properties in a coastal environment: coupling ocean colour imagery and in situ measurements

Three-dimensional distributions of inherent optical properties (absorption, a, scattering, b, and single-scattering albedo, omega(0)) were defined for a coastal region in the north-eastern Gulf of Mexico by coupling surface ocean colour aircraft imagery and models of vertical optical profiles. The study area encompassed the surf zone region and offshore sand bar of an open beach environment to a depth of 10 m. During the aircraft overflights, concurrent in situ depth profiles of a and b were collected along an offshore transect, modelled, and assigned to each image pixel based on water depth. The modelled a and b profiles were subsequently integrated over depth (weighted by the diffuse attenuation coefficient) to provide a 'remote sensing' estimate comparable to what the aircraft sensor would see. At each pixel in the image, these initial optical depth profiles were then iteratively adjusted until the integrated values agreed to within +/-5% of the estimates derived from a bio-optical model using the aircraft-measured water-leaving radiances. Thus, unique vertical distributions of the optical fields were defined at each pixel from the corresponding profile when convergence was achieved. The modelled optical profiles compared favourably both spatially and spectrally with measured values. The 3-D visualization of the optical fields provided insight into the biological and physical processes affecting coloured dissolved organic matter (CDOM) and particle distributions in this coastal area.