The Shortwave Infrared Channel
| Channel No. | Central Wavelength (µm) | Sample sub-point (E/W x N/S) Resolution (km) | Common Reference |
| 2 | 3.9 | 2.3 x 4.00 | shortwave infrared, shortwave IR |
The 3.9 µm channel is different from the other imaging channels, in that it responds to both emitted terrestrial radiation, and reflected solar radiation. Since the emissivity of water droplets at 3.9 µm is less than that for longer wavelengths, it is often easier to identify fog and stratiform cloudiness in the channel 2 imagery, and to discriminate between water and ice clouds. Many times fog can be identified on channel 2 imagery as cooler regions, though confusion can occur between stratus or fog, and cold ground. Combining this imagery with other channels resolves most of these problems (see COMBINED IMAGE PRODUCTS).
The 3.9 µm channel is also very sensitive to sub-pixel hot spots. Therefore, in cloud-free areas it can be used alone, or in combination with other channels, to identify fires when the fires are of large enough size or of great enough intensity.
The following 3.9 µm channel imagery examples (click upon them for enlargement) illustrate fog banks off the CA coast and wildfires in FL, respectively.
Coastal Fog
FL Wildfires
