Physics Background
Fire Light Detection Algorithm (FILDA-2) includes advances in fire detection and retrievals of radiative power (FRP), fire visible energy fraction (VEF), and fire modified combustion efficiency (MCE) at nighttime from the holistic use of multiple-spectral radiances measured by the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard Suomi-NPP (VNP) and NOAA-20/JPSS-1 (VJ1) satellites. The availability of the VEF, FRP, and MCE of FILDA-2 at the fire pixel level in near real-time provides new opportunities for using the satellite fire information to support tactical planning of wildfire control and the estimation of the chemical speciation of fire emission for air quality forecast and climate studies.
FILDA-2 essentially take advantage of three facts of the wildfire to achieve the fire detection and modify combustion efficiency estimation:
Wildfires emit light in the visible and near-infrared bands where terrestrial emissions are minimal.
Figure below shows the fact that the VIIRS DNB is sensitive to fire emitted light across smoldering and flaming. As there is almost no terrestrial emissions over this DNB spectrum range, consequently signal on the DNB could be a strong indicator of the occurence of a wildfire.
Biomass burning is a transient event and typically lasts only a short period of time at a specific location.
Figure below illustrates a comparison of the VIIRS DNB observation of the Caldor fire happened in California 2021 and the corresponding DNB climatology (3 month mean). Fires could be easily identified by contrasting with its climatology. This allows to add temporal test to identify the fire candicates.
The ratio between two fire-sensitive channels provides information about the combustion status.
Visible Energy Fraction (VEF)
\[ VEF = \frac{VLP}{FRP} \]
\[ VLP = \pi A (L_\mathrm{DNB} - L_\mathrm{DNB_{bg}}) \]
\[ FRP = \frac{A \sigma (L_\mathrm{4} - L_\mathrm{4bg})}{C} \]
