Channel 3b of the AVHRR is located within the part of the spectrum that receives emitted radiation at night and a nearly equal contribution of emitted and reflected solar radiation during the day. It is most sensitive to wavelengths between 3.5 um and 3.9 um.

• Detect cloud types (always use channels 4 and 5 to help determining cloud type).
• Use the differences of channel 3b and 4 to determine the temperature structure within the cloud.

  • See the section on emissivity for an explanation.
  • Clouds in temperature inversions (e.g., fog) have a different signal compared to clouds in other temperature profiles.

• Detect the existence of fires and volcanic eruptions.

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