Sun Glitter over Canada, June 4, 1999

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This is a NOAA-15 3 AVHRR channel color composite image acquired on June 4, 1999 at 9:42 AM EDT.

The orbital geometery was favorable for imaging the reflection of the sun in eastern Canada's many lakes and streams. The sun was toward the east and near the east side of the satellite scanning area the sun's reflection could be seen. The pass map makes this more clear. On the pass map the NOAA-15 satellite passed directly over the central ground track, moving from north to south. At any point along this track the satellite would have seen the sun brightly reflected from a small, nearly circular, area of lakes. This bright area of reflected light would appear to move south on the ground as the satellite moved in its orbit. The image is not a snapsnot of what the satellite saw at a point in time, but is built up as scan lines. The thin diagonal streak in the image on the left shows such a scan line (it is actually a few missing lines due to signal dropout). The satellite motion and the geometry of the scan lines cause the reflection spot to be smeared out into a long region.

The region of bright reflection (specular reflection) is lost beneath clouds at the northern end but extends south into Lake Ontario on the New York border. Lake Ontario is brightly lit at the east end and several of New York's finger lakes also appear bright just to the south. The pattern of brightly lit lakes is fairly narrow, but fainter sun glitter is seen in the larger water bodies. Both the St. Lawrence River and the Atlantic Ocean are brightened somewhat from sun glitter. The difference in the extent of the glitter pattern for small lakes and large water bodies is due largely to the difference in the available distance (fetch) for wind waves to build up (also the lakes may be somewhat more sheltered from the wind). The surface of small lakes is smoother because their waves are smaller, so the reflection point is not smeared out very much and a more intense reflection occurs in a more narrow area. The larger ocean waves can pick up sun glitter much farther from the specular point so that point is smeared out over a much larger area and thus much less intense. At least some of the darker areas on the large water bodies may be from a smoother surface, which far from the glitter center would pick up less scattered sunlight and appear darker (perhaps from low winds in those areas). Images of glitter patterns such as this are not rare, some other examples are May 28, 1999, and June 6, 1999 (both show glitter near the upper right corner).

There are a number of interesting surface features in these images. Perhaps most obvious is the large ring at about 51.5 degrees north latitude, due north of Maine. This is Lake Manicouagan which fills an structure created by an asteroid impact in the distant past. It is best seen on the second image. On that same image, very close to the upper left corner, is a double circular feature. These are also asteroid impacts, a double impact, forming Clear Water Lakes. More images of these craters are available.