Note: This post was updated on 9/11/20 to include information about the GOES Live Fire Layer as well as the GOES Live Satellite Imagery. We also attempted to address some of the most frequent questions we’ve gotten over the last few weeks in our help forums.

With the increase in wildfires across the Western US in the last week we’ve seen a huge spike in usage on CalTopo as well as numerous questions. This post contains a LOT of information about imaging, data sources, and methods, some of which was previously covered in some older blog posts in 2017 and 2018 but is updated here.

First and foremost: If you’re in an area near a wildfire follow your local authorities for evacuation notices and up-to-the-minute information. If you are in a life-threatening situation CALL 911. While maps provide valuable insights into fire behavior and areas affected, a map is always just a representation of the best available data. Sometimes data is delayed or erroneous. Above all things, please stay safe and healthy.

Data Sources

CalTopo aggregates data from a large number of sources that provide insights for fire fighters, fire managers, and the general public. These features have been added over the years, unfortunately usually as a result of fire activity. One of the informative and currently relevant is the Fire Activity overlay.

CalTopo’s Fire Activity overlay combines data from 4 main sources: two satellite platforms, MODIS and VIIRS, NOAA’s Hazard Mapping System and the National Interagency Fire Center.

MODIS

The MODIS program consists of two satellites Aqua and Terra, that pass around the Earth covering the entire Earth once every 24hrs. As of 8/16/20 the Aqua satellite is not producing fire data consistently (reference here). MODIS satellites have a resolution of 1km, which means that they can differentiate down to a 1km square but within that km x km box the satellite cannot further differentiate where heat/smoke are. MODIS data is available as a standalone imagery layer (Daily or Nightly Low-Res in the base layer drop down).

VIIRS

The VIIRS program is a newer program and provides a higher resolution than MODIS (375m instead of 1km, more than two times better). VIIRS similarly provides multiple passes around the Earth every 24hrs with two different satellites and is a major part of the current fire activity layer. As with MODIS, VIIRS images from the NPP satellite are available as raw images. However unlike MODIS, in the fire activity layer both VIIRS Satellites (NPP and JPS-1) are labeled VIIRS on the map.

NIFC

When selected the current fire activity layer displays satellite data in conjunction with data from the National Interagency Fire Center on the map. NIFC maintains data from incident managers including specific incident mapping obtained using GPS tracks from group crews and information from firefighting aircraft.

NOAA Hazard Mapping

NOAA Hazard Mapping provides 3 levels of smoke polygons, from low to high smoke (lightest grey to black in the images). The data is displayed only when “with smoke” is selected. The polygons can be very large and overlap with a lot of other data. This provides some insight into smoke, although it doesn’t tell us how bad the air quality or smoke is in that path. We’re continuing to look at adding air quality information and other smoke forecast information in the future.

Note that a satellite has to pick up the hot spot, the image needs to be processed and then the data has to be pushed out publicly for a fire to appear on our maps. With the recent lightning fires in California and with the incredibly dry conditions, fires started quickly and spread very rapidly. We saw delays of 12+ hours after starting before fires would appear in mapping. Fires can start very rapidly and grow incredibly quickly and VIIRS and MODIS programs only pass over the Earth 1-2 times each day.

Using the Fire Activity Overlay

There is a drop down menu for the Current Fire Activity overlay that allows selection from All Satellites, with smoke, MODIS, VIIRS 375m, VIIRS Progression, and IR Progression. Each option provides a slightly different dataset or view. As you zoom in on maps additional information is revealed.

All Satellites, MODIS, VIIRS 375m

The infrared data from both MODIS and VIIRS contribute to hotspot detection, from which we can infer fire activity. As seen above (this image is from the 2020 LNU Lightning Complex Fire) the time and date of each hot spot along with the satellite that the data came from is always available. If you select just MODIS or VIIRS 375m from the dropdown menu you’re also able to see temperature and power (measured in megawatts) of that data point. This is shown below.

Each hot spot also has an error radius around the point based upon error reporting from the satellites. The location of the satellite in relation to the Earth, as well as the resolution of the instruments on the satellites feeds these error rings. The best view of the Earth from a satellite is from directly above, toward the edge of images the view becomes more oblique and can result in more error (MODIS satellites are especially prone to this), this would be represented by larger circles around hot spots. A good option may be to switch satellites to get a better vantage point. Additionally we see some “false positives” along or ahead of the edge of the fire, while the reasons for this are not exactly clear, it likely has to do with the satellites sensing heat from smoke and gases coming off the fire. Finally each hot spot is color coded based on time of the report. Red are most recent (less than 12 hours), then orange (12-24 hours), and finally yellow (24-48 hours). After 48 hours we remove the hot spot from the map.

Additionally we display the active fire perimeter from the National Interagency Fire Center (formerly GeoMAC) on all the satellite views. These perimeters are updated 1-2 times daily typically and come directly from incident management teams. They are based on a combination of reports from fire crews, satellite information and fire aircraft doing infrared flights or firefighting. If the fire has been named that name is also displayed on the perimeter polygon. This is shown below with the perimeters for the Loyalton Fire in Northern California (below left). When zoomed further out these perimeters become a small flame icon instead (Northern California/Nevada in August 2020 is shown below right)

With Smoke

The “with smoke” option adds the NOAA Hazard Mapping System smoke data. The smoke is designated with gray to black crosshatched polygons, the lighter the polygon the lighter the smoke (light gray is low, grey is medium, black is high). (Smoke over California and Nevada in August 2020 are shown below).

VIIRS Progression and IR Progression

The other options in the dropdown are progression layers that show a color coded progression over longer periods of time. The VIIRS progression layer shows VIIRS hotspots for more than just the 48hrs the baser layer does (a legend is under Fire Info in the top right of the page). The IR Progression layer is currently disabled due to changes in the way data was reported, we plan to update and bring it back online in the coming months.

GOES Live Fire Detection (Experimental)

GOES 16 and 17 are geostationary satellites positioned over the eastern US (16) and western US (17), streaming images back to Earth on a near-real-time basis (within 10 minutes, as compared to the above discussed VIIRS and MODIS satellites). The imagery from these satellites is frequently used for animated loops of hurricanes and other large-scale weather events. In addition to raw multi-spectral imagery, NOAA also releases a number of derived datasets, one of which is active fire detections. In the daytime, these fire detections are reported at 5 minute intervals.

CalTopo has incorporated the active fire detection information on our maps, seen right. The layer is found right below the Fire Activity Layer checkbox and is called “GOES Live Fire Detection”. The colors of pixels correspond to the time of the fire detection, the legend is available the top right corner and there is no information about temperature available in this layer, Active Fire Overlay provides that information.

This layer is updated live (new information within 10minutes at the longest). In addition to the satellite’s rapid update interval, the CalTopo map layer will auto-refresh to ensure you are always looking at the most current information, and the time of the last satellite image is displayed on the layer. For new or rapidly moving fires, this can be useful information to supplement between MODIS and VIIRS satellites passes from the “fire activity” layer.

However, each pixel is roughly 2km by 2km, so this layer will only show larger fire activity. An error of a single pixel is enough to place a fire over a mile off from its true location – this is not a layer that will give you insight down to the level of whether a specific neighborhood has burned. The “fire activity” layer is better for that use case, although even that is still an imprecise tool that only reports approximate locations and is easy to over-interpret as having more precision than it does.

Using Other Overlays for Fire Information

There are a number of other live data overlays available in CalTopo that can help inform fire behaviors. Both live temperature and wind layers can be useful and are found listed under Weather Forecast. Both are based on live NOAA data. The wind plot shows current wind direction (indicated by arrows) and speed (indicated by color with a legend on the page in the top right corner). There are dropdown menus to select speed versus gust speed and for time (from now all the way out to 36 hour forecast speeds). We also maintain a fire history layer with about 20 years of fire history also from the National Interagency Fire Center (image far right). While this isn’t much “history” it’s the best source of data we’ve found to date. Perimeters are colored by age, with name and year the fire occurred listed as you zoom in (here, red again is most recent)

CalTopo has also incorporated the. realtime imagery from GOES 16 and 17 which can be found as a base layer called GOES Live (seen right). The realtime imagery is kept up to date and automatically refreshes just like the Realtime fire layer. Images will be delayed no more than 10minutes from time of acquisition and typically smoke is visible from this layer, as are other large scale meteorological events (such as hurricanes, storms, etc).

Because the GOES satellites are geostationary and far from the Earth resolution of this layer is limited (around 1000m resolution), you won’t be able to see your house or van from the images. The Global Satellite Imagery layer, NAIP Aerial Imagery, or the Google Maps Satellite layers all provide much higher resolution (as high as 0.5m in places, though mostly between 1-5m resolution) , however they are only updated every few years, not in minutes. The Sentinel Weekly imagery is a happy medium providing a high resolution layer updated every 5 days that displays approximately 10m resolution images that can be used for things like snowpack detection as well as some evaluation after fires. Sentinal imagery requires a Pro subscription to use.

Other Data Sources

There are a variety of other data sources to inform decision making about fires. Local sheriffs’ offices, fire departments, and emergency management agencies provide a huge amount of information about fires nearby, and are proactive with pre-evacuation notices and evacuation notices. Additionally inciweb is a huge source of information with contact numbers, resources, fire size, containment, and evacuations. NIFC provides more general wildfire information and has links back to inciweb for further details about specific fires.

Stay safe.