High-resolution AVHRR IR imagery is used to detect and monitor volcanic activity. Ash from volcanoes poses a serious threat to aviation interests. This black-and-white 11-µm (Ch 4) infrared image was taken early during an energetic phase of the Mt. Spurr eruption on 18 September 1992.

Surrounding "weather" cloud cover was minimal at this time allowing for easy discrimination of the ash cloud. Had colder cloud tops been present nearby, the 11-µm channel data alone might not have been able to differentiate between ash and water clouds. Inspection of the color-enhanced 11-µm image shows the extent of the ash plume from the Mt. Spurr eruption on 19 September 1992 at 5:12 UTC (21:12 local time). Notice that the size, shape, and temperature of the plume could be mistaken as the top of an anvil cloud associated with a strong convective cell.

Could the use of multispectral processing techniques improve discrimination of ash from water clouds? Go to the next page for an example.