It’s not just noise… It’s fog!

Here are a few images displayed in AWIPS/D2d of the MODIS fog and low cloud product as well as a high-res topography centered on N. Alabama (i.e. Huntsville) and Tennessee Valley. The MODIS images are from 0815 UTC on 3/17 or about 3:15am. The yellow areas are where MODIS is indicating fog and/or low clouds at a 1km resolution. Some “striping” or doubling of pixels is occurring in this image because the data near N. Alabama are near the edge of the satellite view (referred to as a “bow-tie” effect).

MODIS fog and low cloud product on 17 March 2009 at 0815 UTC.

The topography is provided to show low lying river and creek valleys (light pink and purple colors) vs the higher elevations (dark to light blues) and how MODIS shows fog in great detail lying in these lower elevations. Without the topography image to highlight the variations in elevations, it would be easy to think that that MODIS fog product has lots of “noise”. Not so, and by using the topography to dig a little deeper, it becomes evident that MODIS is providing some very interesting information.

Topography of N. Alabama and the surrounding region.

A third image is provided that combines the previous 2 images to make it easier to align the fog and geography. Notice the yellow fog areas now appear an orange-like color and match well with the low lying topography. This early, night-time look at where fog and low clouds are forming are a valuable tool for aviation forecasting and updates to TAFs before the sun comes up and allows high res. visible imagery from GOES. In addition, the MODIS resolution (1km) is superior to that of GOES night-time imagery (4km) and can be used to help better interpret the features seen in the more coarse, and frequent GOES imagery.

Blending of topography and the MODIS fog product to highlight areas of fog within valleys and low lying areas.

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