Fog Around San Francisco Bay
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Fog Around San Francisco Bay

January 31, 2005

Seemingly endless cities surround northern California's San Francisco Bay in this true-color Aqua MODIS image from January 22, 2005. Remnants of the morning's fog linger to the north and south, while an extremely large, persistent fog and cloud bank covers the entire San Joaquin Valley to the east. In the underlying Terra MODIS image, the morning fog stretches over much more of the scene, and almost entirely obscures the southern part of the Bay Area commonly referred to as the "Silicon Valley."

The Bay's waters also appear to change over the few hours between when the Aqua and Terra MODIS images were acquired. In the earlier, underlying Aqua MODIS image, sediments in the bay waters appear more convoluted, while the later Terra MODIS images show the sediments streaming in a more linear fashion to and from the bay's mouth. This may be due to the tide changing the flow of water, or other turbulence at the surface of the water.

At the southern end of the Bay, bright pink spots mark tidal salt flats. These marshy salt flats have been in use for centuries - first by the Ohlone Native Americans, then by Spanish missionaries, and later in commercial endeavors. As the salt dries, it takes on a pink tinge that is visible both at ground level and in satellite imagery. Today, 13,000 acres of these salt flats are part of the Don Edwards San Francisco Bay National Wildlife Refuge, though the salt is still collected for commercial purposes. The Refuge itself spans over 30,000 acres, and is a haven for shorebirds, waterfowl, and a number of endangered species.

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