Evaluation of the Moderate Resolution Imaging Spectrometer special 3.95-μm fire channel and implications on fire channel selections for future satellite instruments

The 3.75-mu m and 11-mu m channels on the polar orbiting NOAA Advanced Very High Resolution Radiometer (AVHRR) sensors have saturation temperatures of approximately 325 K. They allowed limited successes in estimating the sub-pixel fire temperature and fractional area coverage. The saturation problem associated with the 3.75-mu m AVHRR channel greatly limited the ability for such estimates. In order to overcome this problem, the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the NASA Terra and Aqua spacecrafts have both been equipped with a special fire channel centered at 3.95 mu m with a specified saturation temperature of 500 K and a spatial resolution of 1 km. We have analyzed more than 40 sets of Terra and Aqua MODIS fire data acquired over different geographical regions, and found that very few fire pixels have the 3.95-mu m fire channel brightness temperatures greater than 450 K. We suggest that the saturation temperature of fire channels near 4 mu m for future satellite instruments with pixel sizes of about 1 km should be specified at about 450 K or even slightly lower in order to make the channels more useful for quantitative remote sensing of fires. A dual gain approach should also be considered for future satellite fire channels.