Clustering 101
During periods of intense fire activity, it's common to see a new WFS cluster appear very close to an existing fire.
The first reaction is often:
"Is this really a new wildfire, or is it just another part of the same fire?"
The short answer is:
At the moment the alert is created, WFS can only make a decision based on the satellite observations available at that time. As more satellite passes arrive, that interpretation can evolve.
First, what's a cluster?
A cluster is WFS' way of grouping satellite hotspot detections that are likely to belong to the same wildfire.
Think of it as a living object rather than a fixed incident.
As new satellite observations arrive, a cluster can:
- grow,
- receive new hotspot detections,
- merge with another cluster,
- or remain separate if the evidence suggests it is a different fire.
Why was a new cluster created?
A new cluster is created when the latest hotspot detections don't sufficiently match any currently active cluster.
To make that decision, WFS considers several factors, including:
- how close the new detections are,
- when they were detected,
- which satellite detected them,
- and nearby active clusters.
Sometimes, a single hotspot is enough to create a new cluster. This is intentional, an isolated hotspot may represent the very first detection of a new wildfire.
Why do clusters sometimes merge later?
Because WFS receives new satellite observations throughout the day.
Imagine this sequence:
09:15
Satellite detects a hotspot.
↓
A new cluster is created.
11:30
Another satellite passes over.
↓
Additional detections connect the new cluster to an existing fire.
↓
The clusters are merged.
Nothing "went wrong."
The system simply had more information available after the second satellite pass.
Does a new cluster always mean a new wildfire?
No.
A new cluster means:
"Based on the information currently available, this appears to be a separate fire object."
As more observations become available, that interpretation may change.
This is especially common during:
- very large fires,
- rapidly spreading fires,
- heavy smoke,
- or when multiple satellites observe different parts of the same fire.
Why can two satellites appear to detect the fire in different locations?
Every satellite has different:
- spatial resolution,
- viewing geometry,
- geolocation uncertainty.
As a result, two satellites observing the same fire may place the hotspot slightly differently.
This is expected behaviour and one of the reasons why clustering continues to evolve as additional observations become available.
What happens after two clusters merge?
When two clusters are merged:
- one Cluster ID is retained (typically the oldest),
- the second cluster becomes part of the first,
- all hotspot history is preserved.
The updated cluster is reflected in WFS.
Important: A cluster merge does not generate a new notification. The change is visible in the platform.
GEO vs LEO: why does it matter?
Not all satellites behave the same way.
LEO satellites provide:
- fewer observations,
- but higher spatial accuracy.
GEO satellites provide:
- very frequent observations,
- but lower spatial accuracy.
WFS accounts for these differences when evaluating whether detections belong to the same wildfire.
Operational tips
If you receive a new cluster close to an existing wildfire:
✅ Treat it as a potential new fire.
✅ Check the next satellite passes before assuming it will remain independent.
✅ Remember that clusters can evolve as new observations arrive.
If something looks counter-intuitive, we'd like to know. Real operational examples help us continuously improve the clustering algorithm.
Frequently asked questions
Why did I receive a notification for a cluster that later disappeared?
The cluster didn't disappear—it was merged into another cluster after additional satellite observations became available.
Why didn't WFS merge these two nearby fires?
The clustering algorithm evaluates more than distance alone. Time, satellite type, and other criteria are also considered to avoid merging two independent wildfires incorrectly.
Does one wildfire always equal one cluster?
No.
A cluster is a technical representation of satellite detections, not an operational incident. During large or rapidly evolving fires, one wildfire may temporarily be represented by multiple clusters.