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.

You can use this imagery during the night to:

- 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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