Satellite · thermal observation
A hotspot is an observation, not the fire boundary
Satellites provide a consistent view across large areas, but every detection carries the time, resolution, angle, cloud conditions and thresholds of the sensor that produced it.
- Published
- Revised
Four reading steps
Acquisition, footprint, anomaly and interpretation: keeping these steps separate prevents a thermal signal from becoming an official boundary.
Short answer
An algorithm compares thermal radiation measured in a pixel with its surroundings and flags an anomaly compatible with active fire. The point represents the sensor footprint and acquisition time; it can be displaced, combine several sources or miss a fire that is obscured, too small or active between passes. By itself it does not trace a burned-area perimeter.
Key points
The pixel is a footprint
The point symbol simplifies an observed area whose size and shape depend on sensor and viewing angle.
Time is essential
A detection describes an acquisition, not necessarily current conditions when the map is opened.
Absence remains ambiguous
Cloud, dense smoke, low intensity, revisit cadence or geometry can prevent detection.
The sensor measures radiation
Instruments do not visually identify a fire as a person would. They measure energy in several spectral bands. The algorithm searches for a thermal signature that is unusual relative to neighboring pixels and applies checks to reduce false positives.
Response depends on temperature, active area inside the pixel, atmosphere, view angle and sensor. A very hot but small source can be detected inside a pixel much larger than the source.
Revisit rate and detail are a tradeoff
Polar-orbiting satellites can provide finer observations but pass at set times. Geostationary satellites look at the same region much more frequently, generally with a coarser footprint.
Combining both families helps read change and location without confusing them. A frequent series does not become meter-accurate; a fine image does not become continuous between acquisitions.
Cloud, smoke and scan edge change detection
Opaque cloud can hide the ground in the bands being used. Dense smoke or moist atmosphere can weaken the signal. Near the edge of a scan, the ground-projected pixel stretches and location becomes less intuitive.
Industrial sources, volcanoes, flares or reflection can also produce anomalies. Products publish confidence and quality attributes that should remain attached to the point.
Active detection, burned area and perimeter are three objects
A thermal anomaly reports heat at an acquisition time. Burned-area mapping interprets change after fire passage. An operational perimeter is surveyed or validated through another process.
Connecting them can clarify a situation, but none should be silently renamed. Fire Maps separates observation, geometry and model so the reader knows what each layer claims.
Common questions
- Is the fire exactly at the center of the point?
- Not necessarily. The symbol represents a sensor footprint and estimated location. The hot source may occupy only part of the pixel, and the footprint widens with viewing angle.
- Does no hotspot mean there is no fire?
- No. Fire may be too small, too cool, obscured, outside the latest acquisition or below the product threshold. No detection is not proof of absence.
- Can the points be joined to draw the perimeter?
- Mechanically joining centers would create geometry the sensor did not measure. An estimate can be computed, but it must be published as an estimate with its method and limits.