Active Fires

Active Fires

Overview

The active fires indicator detects and visualises fire events that occurred during the analysis period in the area surrounding the site, showing their intensity and distance from the site. Information is presented via an interactive map: the size of the dots indicates the extent of the area affected by fire, while the colour represents the intensity level (FRP, Fire Radiative Power). A greater number of fires with high intensity indicates an area with high fire risk, with potential impacts on biodiversity, air quality, and human safety.

Detection is based on satellite thermal anomalies (hotspots) detected by VIIRS (Visible Infrared Imaging Radiometer Suite) sensors aboard the Suomi-NPP (NOAA/NASA) and NOAA-20 satellites, with near-real-time updates (latency of a few hours).

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Calculation Methodology

Active fire detection is based on the identification of thermal anomalies in the SWIR (Short-Wave Infrared) band of the VIIRS sensor (Schroeder et al., 2014). The algorithm compares the temperature of each pixel with neighbouring pixels; if the difference exceeds an adaptive threshold, the pixel is classified as a hotspot (potential active fire).

Variables recorded for each hotspot:

• FRP (Fire Radiative Power, MW) — fire intensity; correlates with combustible biomass and emission rate
• Confidence — detection reliability (low, nominal, high)
• Estimated area — surface area affected by the thermal anomaly
• Distance from site — Euclidean distance from the study area

Visualisation:

• Dot size ∝ fire area
• Colour ∝ intensity (FRP): from yellow (low) to dark red (high)

Visibility logic: the KPI is visible only if at least one fire has been detected in the selected period in the "Active Fires" maps. In the absence of events, the KPI is not displayed.

Data sources:

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Nature of the KPI: Presence/Absence Indicator

Unlike other KPIs, Active Fires does not have graded quality levels (A–E) because it is a binary risk indicator: the mere presence of active fires in the analysis period and area constitutes a signal of concern, independent of a numerical scale. Severity is communicated visually through intensity (FRP) and the number of events on the map.

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Technical Notes

• The KPI is visible only if at least one fire has been detected in the selected period
• The VIIRS algorithm can generate false positives from hot surfaces (e.g. industrial plants, gas flaring)
• "Nominal" and "high" confidence thresholds reduce but do not eliminate false positives
• The 375 m resolution enables detection of small-scale fires compared to previous MODIS sensors (1 km)
• Near-real-time updates with typical latency of 3–6 hours from satellite overpass

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References

1. Schroeder, W., Oliva, P., Giglio, L., Csiszar, I.A. (2014). "The New VIIRS 375 m active fire detection data product: Algorithm description and initial assessment". Remote Sensing of Environment, 143, 85–96.
2. Giglio, L., Schroeder, W., Justice, C.O. (2016). "The collection 6 MODIS active fire detection algorithm and fire products". Remote Sensing of Environment, 178, 31–41.

Responsible: Claudio Barbieri