Sun Glint
For many years, the orientation and the extent of sun glint, as seen with visible imagery, has been used to locate regions of smooth seas and weak surface winds. For instance, if the surface winds are calm and the water surface is smooth, reflection is strong when the sun-satellite geometry is optimized. The high quality VIS imagery from the new GOES gives users the opportunity to enhance the imagery to reveal greater detail in the sun glint region. There is very strong reflection of solar radiation at 3.9 um because of a difference in the refractive index of water at that wavelength. This causes sun glint to be very bright in the 3.9 um imagery and, at low solar angles, the sensor (and thus the image) becomes saturated.
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These four-frame sequences of coincident VIS, above, and 3.9 um (displayed as reflectivity), below, imagery show sun glint detected by GOES-9 on 11 Sept 1995, when the satellite was located at 90 W. The glint region is at the right-center portion of the images and progresses to the left (west) until it is barely detectable in the 4th frame of the sequence. Note the extensive glint area in the 3.9 um images as compared with that seen in the visible images.
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