ON ANOMALOUS DARK PATCHES IN SATELLITE-VIEWED SUNGLINT AREAS

Abstract

Irregularities in sea-surface sunglint patterns have been frequently noticed in photographs from earth-orbiting satellites. High-resolution color photographs from low-altitude manned spacecraft missions have shown small-scale detail in many of the sunglint pictures. At the much higher altitude of the Applications Technology Satellites (ATS) the reflection pattern of the sun is spread over such a large area that varying sea-surface conditions can be inferred in many areas within a single sunglint region. Of particular interest are patches or swaths of ocean surface that appear dark within the brighter sunglint region. Short-period time sequences of photographs from ATS III exhibit reversals in brightness when the horizontal specular point moves into the area of the anomalous dark feature. Modeling statistics of sea-surface slope for increasing near-surface wind velocities show 1) a rapid drop in maximum sunglint radiance and 2) an increase in the area covered by the total glint pattern. It is shown, by combining calm surface conditions with higher background sea states, that sunglint patterns can be obtained which are very similar to those observed from satellites. Consequently, anomalous dark swath observations from ESSA satellites can be used to infer sea-state variations. The streaklike anomalies in many cases correspond to calm waters beneath high-pressure ridges or, when paralleling coastlines, the seaward limit of local sea-breeze circulations.