MODIS is an observational instrument operated by the National Aeronautics and Space Administration.
It is the name of the sensor aboard 2 satellites, Terra and Aqua, that were launched in 1999 and 2002 respectively. Terra and Aqua follow a sun-synchronous near polar orbit, approximately 705 kilometers above the surface of the earth. Collectively, the satellites observe each point on the Earth's surface 3 to 4 times per day, though the interval between passes varies. Instrument data is used to monitor and process trends in land vegetation, ocean phytoplankton, and cloud temperature and altitude, among other features.3
One of the uses of MODIS data is the detection of active fires. The fire detection strategy is based on absolute detection of a fire (when the fire strength is sufficient to detect) and on detection relative to its background (to account for variability of the surface temperature and reflection by sunlight).4 Scientists at the University of Maryland developed the algorithm to identify areas where the infrared radiation being emitted is significantly different from that of surrounding areas. MODIS can routinely detect both flaming and smoldering fires ∼1000 square meters in size. Under very good observing conditions (e.g., near nadir, little or no smoke, relatively homogeneous land surface, etc.), flaming fires one-tenth this size can be detected. Under pristine (and extremely rare) observing conditions, even smaller flaming fires ∼50 square meters can be detected.5
- 3 NASA. (n.d.). Data. MODIS: Moderate Resolution Imaging Spectroradiometer. Retrieved December 16, 2020 from https://modis.gsfc.nasa.gov/data/
- 4 NASA. (n.d.). MODIS thermal anomalies/fire. MODIS: Moderate Resolution Imaging Spectroradiometer. Retrieved December 16, 2020 from https://modis.gsfc.nasa.gov/data/dataprod/mod14.php
- 5 University of Maryland. (n.d.). Active fire products. MODIS Active Fire and Burned Area Products. Retrieved November 6, 2019 from http://modis-fire.umd.edu/af.html; Giglio, L., Schroeder, W., Hall, J. V., & Justice, C. O. (2018, December). MODIS collection 6 active fire product user’s guide revision B. NASA. http://modis-fire.umd.edu/files/MODIS_C6_Fire_User_Guide_B.pdf