STRATUS AND FOG PRODUCTS USING GOES-8-9 3.9-MU-M DATA

Using data from the GOES-8-9 imager, this paper discusses the potentia l for consistent, around-the-clock image products that can trace the m ovement and evolution of low, stratiform clouds. In particular, the pa per discusses how bispectral image sequences based on the shortwave (3 .9 mu m) and longwave (10.7 mu m) infrared channels can be developed f or this purpose. These sequences can be animated to produce useful loo ps. The techniques address several problems faced by operational forec asters in the tracking of low clouds. Low clouds are often difficult o r impossible to detect at night because of the poor thermal contrast w ith the background on infrared images. During the day, although solar reflection makes low, stratiform clouds bright on GOES visible images, it is difficult to distinguish low clouds from adjacent ground snowco ver or dense cirrus overcasts. The shortwave infrared channel often gi ves a superior delineation of low clouds on images because water dropl ets produce much higher reflectances than ice clouds or ground snowcov er. Combined with the longwave channel, the shortwave channel can be u sed to derive products that can distinguish low clouds from the backgr ound at any time of day or night. The first case study discusses cloud properties as observed from the shortwave channels from the polar-orb iting Advanced Very High Resolution Radiometer. as well as GOES-9, and applies a correction to produce shortwave reflectance. A second case study illustrates the use of the GOES-8 shortwave channel to observe t he aftermath of a spring snowstorm in the Ohio Valley, Finally, the pa per discusses a red-blue-green color combination technique to build us eful forecaster products.