Unusual Sun Glint Artifact in MODIS Imagery

Sun Glint is a common phenomenon seen in satellite imagery. It is an area of bright specular reflectance of sunlight over larger areas of smooth surfaces such as water bodies. Figure 1 shows histogram equalized MODIS L1 image in the visible bands with a large area of sunglint. The image also shows areas of interesting dark regions on the western side of several West Indian islands namely Guadaloupe, Dominica, Martinique, St. Lucia and St Vincent and Grenidines that can be attributed as artifacts of sun glint. It appears that these islands are influencing the sea state hence changing the surface reflectance. Asymmetric alteration of sun glint under varying wind conditions has been documented by McClain and Strong [1]. They document a phenomenon off the Galapagos Islands using Application Technology Satellites (ATS) in March 12 1968. The diagrammatic map of the phenomenon is shown in Figure 2. McClain and Strong hypothesize that with March air and water movement towards northwest, the island represents a disturbance in the wind’s and current’s path. Since the sea state is a complex function of several parameters such as the atmosphere above the surface, the fetch of the wind, duration of the wind and the stability of the marine boundary layer, a possible marine inversion is occurring downwind of the island. This inversion produces a streak of calm water seen as abnormal streak north-west of the Galapagos Islands. In the case presented here, the West Indian islands seem to be disturbing the wind and current’s preferred northwesterly movement and thereby producing a streak of calm water on the western side of these islands. These streaks of calm water produce the unusual sun glint artifact in the MODIS imagery. However, to substantiate this requires analysis of additional data sets.