Near Infrared Channel - 3.9 microns - Summary

• Wavelength band is 3.78-40.3 microns
• 4 km resolution
• Detects both reflected solar and emitted longwave radiation
• little atmospheric attenuation
• sees earth's surface and low clouds
• less sensitive to subpixal clouds than the 10.7 micron channel - clouds appear to be warmer at 3.9 microns
• noisy data at cold temperatures
• sensitive to fires and other "hot spots" such as cities

• detects fog/low clouds at night when used with 10.7 micron channel.
• Take advantage of the emissivity differences between 3.9 and 10.7 microns.
• Can distinguish between water and ice clouds during the daytime hours.  Reflection at this channel depends on size and phase of particles.  Small water drops are most reflective.

Also, Check out the 3.9 micron Channel Tutorial.  It has much more discussion about how to interpret the data and more practical applications