Visible Images : Visible images are simply black and white pictures from space. They can be used to detect fires during daylight hours, at times when there is little or no cloud cover. Fires are detected by the plumes of smoke they produce. One can frequently trace large smoke plumes back to very small points of origin. The advantage to using visible imagery is that the resolution is about 1 km.

Infrared Fire Detection Product: The second method for fire detection uses a combination of information from the 10.7 and the 3.9 µm infrared channels. The 3.9 µm channel is extremely sensitive to hot spots such as fires, while the 10.7 µm channel is not. On the fire detection images, regions with fires appear as bright spots that sometimes "flicker." However, be careful. There are several ways that a point can appear relatively bright and be a "false alarm."

1. Certain kinds of soils can become very warm. For example, a hot desert area may completely saturate small regions on the infrared product. Such areas should be easy to identify, since they occur in the same place, day after day. They also occur in regions having little, if any, combustible material (such as trees). The best solution here is to become familiar with the "normal" appearance of the ground from day to day.

2. Instrument noise may also make a tiny spot unusually bright. This "false alarm" can be identified by viewing two or more images in time sequence. Noisy spots occur randomly, and will not appear in the same spot twice in a row. Therefore, look for bright spots that only appear bright at a single image time. These are probably false alarms.

3. The 3.9 µm channel is also sensitive to water clouds. Thus, if there is a large cumulus cloud in the viewing area, it can make a spot on the infrared fire detetection image look relatively bright. However, cumulus clouds are easy to identify during the day on visible imagery, so it is easy to check this for possibility. At night, you will have to depend on the fact that cumulus clouds typically live only about 10-30 minutes, and usually appear as a part of a larger cloud field. With some practice, you should quickly be able to distinguish between cumulus clouds and small fires.

For a more detailed discussion of GOES satellite capabilities, and the special characteristics of the 3.9 mm channel, refer to the GOES tutorial or the 3.9 mm channel tutorial.