Glitter Pattern Research Articles

Determination of the Sea Surface Slope Distribution and Wind Velocity using Sun Glitter Viewed from a Synchronous Satellite

This work demonstrates the feasibility of determining the east-west component of the sea surface slope distribution from a synchronous satellite, through quantitative analysis of the sun glitter. The Cox-Munk sun glitter technique, utilizing a single photograph of the whole-sun glitter pattern, taken from an aircraft altitude, is adapted to a much higher altitude. This is done by making a sequence of light intensity measurements, reflected from a single point on the ocean, as this fixed point scans the westward moving sun glitter pattern. Wind velocity is calculated from the slope variance, using the Cox-Munk empirical relation. Calculated wind velocities for three locations in the Pacific, on two separate days, are compared to direct wind measurements taken at these locations during the Line Islands Experiment. The agreement is within ±1 m sec−1.

Sun glitter viewd from space

Space photographs of sun glitter on the sea are presented to illustrate some surface oceanographic phenomena that are visible from about 200 km above the Earth when the sea is relatively calm. Wind and sea conditions seem to affect the shape and brightness of glitter patterns. In the Gulf of California, eddies in slicks may have been created by surface currents when wind speeds were very low. Off Socotra in the Indian Ocean, a series of long slick-like lines over an undersea shelf possibly are caused by internal waves. Slicks in the Formosa Strait appear as bright streaks near the horizontal specular point and as dark streaks outside this zone. Long swells and dark swaths in calm areas are also visible in the pictures.

Directional energy spectra of the sea from photographs

The image of the sun reflected by the sea surface is called sun glitter or sun glint. The relationship of the glitter pattern to the distribution of slopes on the surface is well known, but this effect is of little use in determining a wave spectrum because glitter does not provide a continuous representation of a wave parameter. A generalization of the glitter concept, in which the point image of the sun is replaced by a continuous skylight luminance function, is quite effective in providing a linear representation that can be recorded photographically. Then by the use of optical analysis it is possible to resolve the variations of density in the photographic emulsion into the components of the two-dimensional Fourier spectrum of the surface. When a transparency of a surface photograph is placed in one focal plane of a lens, the Fourier transform of the variations appears as light amplitude in the other focal plane. In the transform recording, density distribution represents slope distribution, wave direction is the azimuth angle, and wave number is proportional to the radius from the center. This information, in addition to the height and aspect angle of the camera, allows the energy spectrum of the surf are to be obtained.