REMOTE SENSING GUIDE
Understanding a hotspot
Active fire / thermal anomaly
NASA FIRMS distributes satellite observations from instruments including MODIS and VIIRS. A detection identifies a pixel with a thermal anomaly at satellite overpass time; its coordinates represent a satellite observation, not a surveyed fire perimeter.
Sensor characteristics
VIIRS active fire products use nominal 375 m pixels; MODIS active fire products use nominal 1 km pixels. Pixel size changes with viewing geometry. Different products and overpasses should not be interpreted as interchangeable sampling.
Fire radiative power
FRP, when available, is reported in megawatts and estimates radiative energy release. Brightness temperature is stored in kelvin where supplied. Raw VIIRS thermal bands remain in source fields. Neither measurement is a direct PM2.5 or haze concentration reading.
Detection limitations
Cloud, smoke, small or short-lived fires, scan angle and timing can affect detections. Confidence measures algorithmic detection quality. Missing detections do not establish the absence of fire, and repeated detections do not necessarily mean separate fires.
Temporal availability
Near-real-time products are subject to processing latency and provider availability. GeoHaze preserves acquisition and retrieval timestamps and displays only imported observations.