A satellite is not watching continuously
The polar-orbiting satellites used by the ThermalGlobe launch sources pass over different parts of Earth at particular times. They do not provide an uninterrupted video feed. A fire can ignite, change or be controlled between useful overpasses. “Near real time” describes a processing and delivery mode, not permanent observation of every location.
Higher latitudes may receive overlapping passes more often than equatorial areas, while the useful geometry and pixel footprint change away from the centre of a satellite swath. Multiple detections close together can therefore reflect separate observations of a changing heat source rather than multiple confirmed fires.
Cloud, smoke and the atmosphere intervene
Thermal infrared energy must travel from the ground or flame through the atmosphere to the instrument. Thick cloud can block the surface. Dense smoke, water vapour and other atmospheric conditions can reduce or alter the measured signal. The same wildfire may be detected on one pass and absent on another without the incident having ended.
Algorithms also use contextual comparisons with neighbouring pixels. A hot source that is too small, too cool relative to its surroundings or mixed with cloud and water may not pass every product test.
Resolution sets a practical floor
VIIRS active-fire observations have a nominal 375 metre pixel dimension at nadir, while the MODIS active-fire product is approximately one kilometre. Those dimensions describe observation footprints, not exact flame coordinates. Small, short-lived or partly obscured fires may contribute too little energy to the observed pixel.
At the edge of a scan, the footprint can become larger and more elongated. Mountain slopes, narrow valleys, coastlines and mixed land cover can further complicate the relationship between the displayed point and conditions on the ground.
Processing and publication take time
After observation, data must be transmitted, processed into a fire product, exposed by the source service, retrieved, validated and published by ThermalGlobe. Each stage can add delay or temporarily fail. The map therefore displays observation time separately from its own release time and source-check time.
ThermalGlobe retains the previous verified source state when a required source fails instead of silently replacing it with an empty result. A stale or partial status is a warning about data availability, not evidence that detections disappeared.
How to use an absence of detections
Treat absence as “no qualifying observation is displayed in this release and filter,” never as “no fire exists.” Check the selected time window, enabled sensors, source status and observation timestamps. For any consequential decision, use current information from local fire, police, civil-protection and emergency-management authorities.