Airborne detection of oceanic turbidity cell structure using depth-resolved laser-induced water Raman backscatter.

Airborne depth-resolved laser-induced sea-water Raman-backscatter waveforms have been obtained along a flight line extending westward from a point approximately 30 km seaward of Assateague Island to a point where the beach was intersected at latitude 38.1 degrees N and longitude 75.2 degrees W. Pulses from a 337.1-nm nitrogen laser were repetitively transmitted vertically downward into the water column. The laser-induced water Raman backscatter pulse at 381-nm wavelength was depth (or time) resolved into forty bins having widths of -25 cm each. When converted to along-track profiles, the waveforms reveal cells of decreased Raman backscatter superimposed on an overall trend of monotonically decreasing water column optical transmission. This airborne lidar technique shows potential for (1) rapid, quantitative, synoptic study of the homogeneity of the oceanic water column and (2) measurement of the horizontal spatial distribution of the optical transmission of the upper mixed layer of the ocean. A multiple convolution model of a Gaussian transmitted pulse, Gaussian sea surface height, and slope probability density, together with an exponential-decay water-column impulse response, is shown to qualitatively account for the observed pulse shape.