Fire Data Questions

What do the fire hotspot symbols mean?
A fire symbol on the map indicates the approximate location of a “Hot Spot” detected by NASA’s MODIS or VIIRS satellites. A “Hot Spot“ is an area of the Earth’s surface that is radiating a large amount of heat, thus indicating a fire.
What do the different colors mean?
  • Yellow hotspots have been detected in the past 12 hours. Fires here are likely still burning strongly.
  • Bright orange hotspots were detected in the past 12-24 hours.
  • Dim orange-red hotspots were detected in the past 24-48 hours.
  • Dark red hotspots were detected in the past 2 – 7 days. Fires here are likely extinguished or smoldering.
Where does the hotpot data come from?
Hot Spots are detected by three NASA Earth Observing satellites. The Terra and Aqua satellites are equipped with MODIS sensors, while the Suomi NPP satellite carries the more modern VIIRS sensor. MODIS and VIIRS collect radiometric data about Earth’s surface, oceans, and atmosphere as they orbit the planet. Areas of intense heat are detected as Thermal Anomalies, i.e. fires.
What is MODIS?
“MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (originally known as EOS AM-1) and Aqua (originally known as EOS PM-1) satellites. Terra’s orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth’s surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see MODIS Technical Specifications).” Source: NASA
What is VIIRS?
VIIRS is a multi-disciplinary sensor providing data for the ocean, land, aerosol, and cloud research and operational users. VIIRS spectral coverage allows for data products similar to those from SeaWiFS as well as SST, a standard MODIS product. SST is an Essential Climate Variable (ECV) and, through validation with instruments traceable to NIST standards, is a Climate Data Record. Also, as with SeaWiFS and MODIS, the VIIRS scan and orbit geometries will provide global coverage every two days.” Source: Raytheon
How do I toggle between MODIS and VIIRS?
Click on the Legend Icon icon at the far left of the toolbar located in the blue section directly above the map. Click on “MODIS Hotspots” to toggle MODIS on and VIIRS off; click on “VIIRS Hotspots” to toggle VIIRS on and MODIS off.
How accurate is the hotspot data?
Hotspots on will always be near the approximate real-world location of fires. VIIRS Hot Spots are no more than approximately 300 meters away from real-world fire location, and MODIS Hot Spots are within approximately 800 meters of real-world fire location.
How current is the hotspot data?
Hotspots on will always be near the approximate real-world location of fires. VIIRS Hot Spots are no more than approximately 300 meters away from real-world fire location, and MODIS Hot Spots are within approximately 800 meters of real-world fire location.
Why is the fire near me not on the map?
The fire may not be big enough to be detected by MODIS or VIIRS. Alternatively, there may not have been a satellite pass over the location since the fire began.
Why are there so many small fires in agricultural areas?
Throughout the year, farmers will burn off their old crops in order to remove old vegetation and prepare the soil for new. If a single Hot Spot appears to be on or near cropland, it is likely nothing to be concerned about.
How do I find a specific fire?
If the fire has been assigned a GEOMac Perimeter:
Click on the Zoom Icon icon on the far right of the toolbar located on the blue strip above the map. A “Zoom to Perimeter” sidebar will appear. Simply scroll down the alphabetical list of current perimeters to find your targeted fire. Click the fire’s name to be zoomed to that perimeter. A GeoMAC sidebar will open with technical data about the selected fire.

If the fire has not been assigned a GEOMac Perimeter:
Use the zoom and pan tools to navigate to the approximate geographic location of the fire.

Where do the fire perimeters come from?
Fire perimeters are courtesy of GeoMAC, a USGS data service.
Why doesn’t the fire perimeter match the hotspots?
GeoMAC perimeters are usually updated once a day. Our hotspots are generally more current than the perimeters.
How do I use the wind layer?
While the wind layer is on, the bottom left area will display a readout of the wind speed and direction corresponding to wherever the mouse is pointing.  The intensity of the wind streaks indicates the strength of the wind visually.
How current is the wind data?
Wind data are no older than 6 hours, which is how often it is made available.  The wind overlay is generated from NOAA’s Global Forecast System, which considers a multitude of weather observations and uses them to model all facets of the weather at medium-fine scale.  We show the surface wind model as it is at the time it is generated.
Why are there old timestamps on some weather stations?
The networks we gather weather reports from include stations in harsh and remote environments, where it is not uncommon to have gaps in reporting.  We present only the latest readings, reporting nothing older than 1 month.
What does Wildfire Potential mean?
These layers correspond to forecasts created for upcoming months by the National Interagency Fire Center.  They represent areas where conditions such as weather patterns and fuel characteristics create the potential for large fire events that is higher than historic norms.
Why does Conterminous US have more and different layers than other maps?
The Wildfire Viewer maps provide all available data for their geographic extent.  Not all areas have the same data layers available.
Why does the fire record only go back to 2000?
This is when the GeoMAC program started collecting a national record of digital fire perimeters.
Where did the California fire perimeters come from?
These were compiled by multiple agencies from various sources and ultimately assembled by CAL FIRE as a single dataset.


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General Terms
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Tool Bar
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