A Study of MODIS Fire Detecting Channel Centered at 3.95-m

The 3.75-mum and 11-mum NOAA AVHRR channels have saturation temperatures of approximately 325 K. Although these channels allowed limited successes in estimating the sub-pixel fire temperature and fractional area coverage, the saturation problem associated with the 3.75-mum channel over hot surfaces greatly limited the ability for such estimates. In order to overcome this problem, the MODIS instruments on board the NASA Terra and Aqua spacecrafts have both been equipped with a special fire channel centered at 3.95 mum with a specified saturation temperature of 500 K and a nadir spatial resolution of 1 km. We have analyzed more than 30 sets of Terra and Aqua MODIS fire data sets acquired over different geographical regions, and found that very few fire pixels had the 3.95-mum fire channel brightness temperatures greater than 450 K. We suggest that the saturation temperature of fire channels near 4 mum 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.