Fractal laser glints from the ocean surface

Abstract

Time series of laser glint counts from the ocean surface exhibit fractal behavior. Glint-count histogram widths do not follow Gaussian statistics, and histogram shapes are approximately log normal. Fractal dimensions for the statistically self-similar glint-count time series are found from the power spectra, which have an inverse power-law form. Glint counts in one spatial dimension from a linearly scanning laser and glint counts in two spatial dimensions from a laser glint imager behave similarly. In both sets of data, spectral density peaks exist at frequencies corresponding to swell and long wind waves. This implies that the glint-count process contains information related to long-wave modulation of surface roughness.

Scanning-laser glint measurements of sea-surface slope statistics

“…If the spot size were to become larger than the glint correlation length, the PDF would be biased high. From video images of laser glints, 29 we found this correlation length to be of the order of 10 cm at ϳ3-m s Ϫ1 wind speed, decreasing with increasing surface roughness. For the current data set the maximum nadir angle from which we recovered statistically significant slopes was Ϯ45°, at which point the laser-spot size was 1.4 cm, comparable with the glint correlation length for the roughest surfaces observed.…”

Characterization of Sun Glitter Statistics in Ocean Video

“…Video images of the ocean surface were taken by [61] from an offshore platform and used to compute an ensemble-averaged space-time spectrum, extending the techniques from [11][12][13]20] to the time domain. Shaw and Churnside [62] calculated slope probability density functions from glint counts from a scanning laser over the Pacific Ocean, and in [63] described fractal behavior exhibited by the time series of the laser glint counts. Titov et al [64] and Titov, Zuikova, Luchinin, and Troitzkaya [65] studied spatial and temporal spectral behavior of surface waves over the Black Sea using an optical spectrum analyzer.…”

“…Shaw and Churnside [63] visualize glitter behavior in video by counting the number of glitter pixels that appear in each frame. They also compute histograms of these glitter counts.…”

“…The authors draw a connection between glitter count series and surface roughness variability, and go on to further examine the fractal behavior of glitter. The glitter studied in [63] was synthesized using scanning lasers and collected in open ocean from an overhead view. In contrast, the data collected for this work observes sun glitter in coastal waters at a very small viewing angle.…”

Blue sun reflected from water: optical lessons from observations of nature

“…Glitter patterns change shape depending on the water surface roughness and the solar elevation angle. 3,4 Because the water surface is roughened by small, wind-driven waves, 5,6,7 glitter pattern measurements can be used for remote sensing of wind patterns. 7,8,9 Under very light-wind conditions the number of sun glints decreases and interesting fun-house-mirror kind of reflections of the surroundings can be seen, as shown in Fig.…”