With most sources of satellite remote sensing data, spatial resolution and temporal resolution are inversely related. In other words, as spatial resolution increases, temporal resolution decreases and vice versa. For example, the VIIRS sensor onboard S-NPP and NOAA-20 has a swath width of 3,000 kilometers and each instrument images the entire surface of the Earth at least once daily. The swath width of MODIS onboard Terra and Aqua is narrower at 2,330 km providing slightly less than daily global coverage. However, the finest spatial resolution of active fire detection data that can be gleaned from VIIRS and MODIS at 375 meters and 1 kilometer, respectively, are considered coarse resolution data by most definitions.
In comparison to VIIRS and MODIS, the Operational Land Imager (OLI) onboard both Landsat 8 and Landsat 9 provides active fire detections at relatively finer spatial resolution (30 meters) (please see the related NASA FIRMS blog entry that introduces the Landsat active fire product). Unlike VIIRS and MODIS, OLI has a much narrower swath width of 185 kilometers. The swath of OLI is less than 1/10th the width of a MODIS swath and provides much lower temporal resolution/sampling by comparison (Fig 1).
Figure 1 - Example of a 185 km Landsat 9 OLI swath (red) compared to a 2,330 km Terra MODIS swath (orange). Terra MODIS can easily image the entire continental US daily in three consecutive orbits. However, Landsat 8 and Landsat 9 OLI each require multiple orbits over 16 days to provide the same coverage.
How do these characteristics affect the daily availability of active fire data?
The relatively large swath widths of VIIRS and MODIS sensors provide comprehensive satellite observations and derived active fire detection data for the entire globe on a daily basis. Additionally, both sensors provide multiple observations daily within a relatively short period of time where consecutive swaths may overlap, more so at higher latitudes (Fig 2).
Figure 2 - Example of MODIS and VIIRS orbit tracks showing overlap between tracks, especially at higher latitudes.
Conversely, each Landsat OLI sensor requires 16 days to completely image the surface of the Earth. So, OLI cannot fully image large geographic areas in one day, such as the continental United States, and can only provide partial coverage. However, since the orbits of the two Landsat satellites are 8 days out of phase, the combined temporal resolution of the two OLI sensors enables complete coverage once every 8 days (Fig 3).
Figure 3 – The top graphic provides an example of the swath coverage for the continental US by OLI onboard Landsat 8 (orange) and Landsat 9 (red) on July 13, 2022. Orbits for each satellite move to the east and west daily and complete a full cycle of coverage every 16 days. The bottom graphic displays the HLS imagery product in FIRMS for July 13, 2022, which contains the acquired Landsat 8 and Landsat 9 imagery over land. Areas along each swath that exceed the predetermined cloud cover threshold are excluded from HLS product in FIRMS. The combined daily coverage of OLI on both Landsat satellites can image the entire continental US, and the globe, every 8 days.
When viewing daily active fire detection data in FIRMS, users should be aware of the high temporal resolution characteristics of VIIRS and MODIS versus Landsat. In Figure 4, active fires detected by Terra MODIS and Landsat on September 10, 2022, for the Pacific Northwest are provided. Landsat active fire detection data, displayed as yellow points, is only available within the 185-kilometer OLI swath. However, MODIS active fire detection data, displayed as red points, is available for the entire region within and outside of the OLI swath. Consequently, updates to the finer resolution Landsat active fire detection data for the entire Earth cannot be provided daily.
Figure 4 - Active fires detected in the Pacific Northwest on September 10, 2022. 1 kilometer MODIS active fire detections (red) are available for the entire region while 30-meter Landsat 9 active fire detections (yellow) are limited to the 185-kilometer swath (WRS-2 Path 42) acquired on this date.
The NASA Worldview Snapshots tool enables users to easily create satellite imagery subsets for anywhere in the world. The tool provides access to current and historical imagery captured by Terra and Aqua MODIS and S-NPP and NOAA-20 VIIRS. By simply selecting the desired image product, acquisition date, spatial resolution, output file type as well as entering the latitude/longitude bounding box, users can quickly generate an imagery subset to use for visualization in a GIS or as a graphic in a presentation or document.
For the convenience of users who need to create satellite imagery subsets of geopolitical units, Snapshots has recently been enhanced to include predefined latitude/longitude bounding boxes for countries. After setting the basic parameters for an imagery subset, users can simply select their desired country of interest from the Countries dropdown list in Country/Region Presets box below the map. The red box that subsequently appears on the map indicates the bounding box of the subset to be generated. Users can also increase the default size of the subset boundary extent by 5% to 20% by selecting the desired 5% interval under the Padding dropdown list or manually edit the predefined coordinates as desired in the Bounding Box section of the interface.
Users can also generate imagery subsets for a US state or Canadian province or territory. After selecting either of these two countries, a user can select the State / Province / Region dropdown list to update the subset bounding box extent to the targeted state, province or territory.
A September 9, 2022 Aqua MODIS true color composite image for Oregon generated from NASA Worldview Snapshots. The subset bounding box is defined by the map extent of the state, predefined in Snapshots, and extended by an additional 5% in both dimensions.
A screenshot of the Worldview Snapshots definition for an imagery subset of the state or Oregon. The updated interface enables users to select a country (as well as a US state and Canadian province/territory) and use its associated map extent as the bounding box coordinates for the subset boundary. If desired, users can increase the size of the predefined bounding box in 5% intervals or edit manually edit the coordinates.
This blog shows you how to:
- change the colors of the fires/thermal anomalies
- change the fire pixel size
- show only day or night detections
- color code fires by Fire Radiative Power (FRP), Confidence or Time Since Detection
CHANGE FIRE COLOR BY INSTRUMENT
The default color for the MODIS and VIIRS thermal anomalies is red. There are times when it is useful to be able to distinguish between instruments (MODIS/VIIRS) or day/night detections. To do this Select ADVANCED MODE in the Layer List on the right of the map (see image below)
Select the "+" icon next to the fire detections you want to change.
Select the drop down arrow to the right of the color and a color wheel will appear. Select a color and press apply.
This step can be repeated for other fire detection categories.
CHANGE FIRE PIXEL SIZE
The fire pixel size defaults to the optimal display for the zoom level. When zoomed into the highest zoom levels, MODIS pixels maintain a size of approximately 1km and VIIRS approximately 375m
To change the pixel size, make sure ADVANCED MODE is selected (as shown above). Click the "+" icon and then click the drop down arrow next to the word "Auto"
Adjust the pixel size from the drop down list
SHOW ONLY DAY / NIGHT FIRES
By default, the map shows both Day time and night time fires, to view only day time fires, may sure ADVANCED MODE is selected (as shown above). Click the "+" icon then click on "Night" to deselect it and it is greyed out. To view only nighttime fires, click on "Night" to turn both back on and then click on "Day" so it is greyed out.
To view fires using Fire Radiative Power (FRP), Confidence or Time Since Detection, select "ADVANCED MODE" in the Layer List, then select the drop down arrow next to the word "Fires" for the fire detections you want to change.
Time Since Detection shows the fires < 1, 1-3, 3-6, 6-12, 12-24, and >24 Hours since the fires were detected by the satellite. Enable this by selecting "Time Based" in either Basic or Advanced Mode.
FIRMS recently integrated ultra real-time (URT) MODIS and VIIRS active fire data, within a minute of satellite observation, from multiple direct readout ground stations in the continental US (CONUS).
This is the first routine service provided by FIRMS for detecting wildfires over the continental United States from NASA and NOAA low-Earth orbit satellites with a latency of less than 60 seconds from Earth observation to wildfire detection. The ultra real-time processing has been made possible by the Space Science and Engineering Center (SSEC) at the University of Wisconsin-Madison with funding from NASA's WildFireSense program. Software systems enable the SSEC to stream direct broadcast data in real-time from each antenna to a central collection point at the University of Wisconsin–Madison, which then ingests and merges the data, including de-duplication of overlapping data, in real-time.
Currently URT data are received from Madison, Wisconsin (2 antennas), Hampton, Virginia and Mayaguez, Puerto Rico. In addition to the URT, Real-Time (RT) data are received from Honolulu, Hawaii and Monterey, California (after the pass is complete). Latency for RT data is 20—30 minutes. It is anticipated that the real-time data will be expanded to include additional CONUS stations and stations in Alaska and Hawaii.
Figure showing current and planned coverage of Direct Broadcast
stations collecting ultra real-time and real-time data
URT and RT thermal anomaly / fire detections are processed using the LANCE FIRMS active fire algorithms, so the data are comparable with the NRT data from LANCE.
- URT and RT data are available in both FIRMS and FIRMS US/Canada Fire maps and can be identified by the URT or RT suffix in the "version" - found by clicking on the fires to view the attributes.
- URT and RT data are also available in the WMS and WFS map services and KMZs.
- URT and RT data will roll off the system within six hours as the NRT data becomes available.
Screenshot showing URT fire detected on 2022/06/30.
The fire was observed at 12:17 CDT and displayed in FIRMS at 12:19 CDT
(as shown by computer time on top right of screen)
Users can see the real-time fire detections by selecting the Time Based option which color codes fires by Time Since Detection. However it is important to note that the URT and RT fires only show up within a minute of satellite fly-over so users need to know when the satellite passes overhead. To find our what time the satellite overpass is you can load the orbit tracks. (see next screenshot)
Screenshot showing descending overpass times from Suomi-NPP, NOAA-20, Aqua and Terra. These can be added by going to Advanced Mode and then selecting tracks from the Orbit Tracks and Overpass Times.
Once you have the Orbit tracks loaded, make sure the fires display using the "Time-Based" option and the look for the deep red colored squares.
FIRMS fire map users have always had the opportunity to compile a map view using desired layers and then capture a screenshot and save it as a JPG, PNG or GIF file to use or share. Users now have the option of capturing a FIRMS map view as a GeoTIFF image file. The GeoTIFF format includes spatial (georeferencing) information embedded in the .tif file so it can be integrated and viewed with other geospatial data. The GeoTIFF standard is in the public domain and can be readily imported and displayed in many GIS applications.
To create a GeoTIFF, click on the "screenshot" icon from the lower right of the FIRMS user interface and select "GeoTIFF" from the dropdown option in the screenshot window.
In collaboration with NASA's IMPACT project, dynamic false color imagery is now available through FIRMS to help better delineate burned areas.
A screenshot from FIRMS US/Canada displaying the Sentinel-2 Adjusted Reflectance Harmonized Landsat Sentinel (HLS) using bands 12-8a-4. It shows the Hermits Peak Fire in New Mexico, USA as captured on 3 May 2022. In this image, the burned areas appear in brick red and are overlain with active fire pixels from MODIS and VIIRS. (Link to view in FIRMS)
FIRMS has recently integrated an additional Harmonized Landsat/Sentinel-2 (HLS) Imagery product. The Reflectance (Bands 7-5-4) layer from Landsat 8/OLI and (Bands 12, 8a, 4) from Sentinel 2A and 2B are false color composite (FCC) images that allow us to visualize wavelengths that the human eye cannot see (i.e. short wave infrared and near infrared). Burned areas appear almost brick red making it easier to see fire affected areas and water is very dark, almost black, which makes it much easier to see lakes or flooded lands.
Unlike other satellite imagery layers in FIRMS, which are provided through NASA GIBS, the beta version HLS False Color Composite Imagery (Bands 7-5-4 for Landsat and Bands 12, 8a, 4 for Sentinel 2A and 2B), are provided dynamically through the NASA Interagency Implementation and Advanced Concepts Team (IMPACT), as such it may take slightly longer to display than the HLS True Color imagery through GIBS. HLS imagery is currently available approximately 2 -4 days after acquisition.
Steps to view the HLS FCC layers:
The HLS layers are only available in Advanced Mode (basic mode has reduced functionality to minimize the complexity of the interface).
• Go to https://firms.modaps.eosdis.nasa.gov/usfs/map/ or https://firms.modaps.eosdis.nasa.gov/map/
• Toggle the “Advanced Mode” button in the upper right .
• Toggle the “Historical” button in the upper right.
• The HLS Landsat and Sentinel 2 imagery are in the “Harmonized Landsat/Sentinel-2” grouping in the table of contents.
• Use the tools/prompts to access and view the imagery.
• Toggle on the True Color imagery first to get a good idea of where the FCC data can be expected on a given day.
Use the screenshot tool to create a GeoTIFF of the image to enable the image to be imported in to a GIS.
Some things to note:
• The HLS imagery is not near real-time data. It is currently available about 2 -4 days after acquisition.
• The reach back on this service goes back to March 15, 2022.
• As the FCC is dynamically generated, it may take slightly longer to display than the True Color imagery through GIBS. We are monitoring the performance of the HLS FCC imagery and welcome feedback.
• Zoom scale to display the false color composite data is currently set to 11 through 14, but true color can be viewed at smaller scales. The zoom level is indicated at the very end of the URL (e.g., 11z).
• Orbit tracks for Landsat 8 and Sentinel 2A and 2B are available as layers in the table of contents.
• Landsat 9 data is anticipated to be incorporated into the HLS product in late April. At that time, or soon thereafter, it will be part of the HLS service in FIRMS.
FIRMS recently added a location tool to enable users to easily find and save places of interest.
- Enter the location or coordinates to search in the "Find Location" tab, checking the box to "allow multiple location selection".
- Click on the "Current Location" to find out what location you are viewing.
- Any locations you store for future visits will be saved under the "Saved Locations" tab.
Get information and zoom to extent of wildland fires
The new FIRMS US/Canada fire map includes the location and details of wildland and prescribed fires. Locations of currently/recently active incidents larger than 100 acres (40.5 hectares) are displayed as fire icons when you open the US & Canada Fire Map. Click USA Active Fires and Canada Active Fires layers to toggle them off.
Click on a fire location to view the name, discovery date/time and current size of the fire. This information is routinely updated and maintained in systems of record managed by US and Canadian wildland fire management agencies. Clicking the View Situation Report link spawns a national situation report which may contain specific reporting information about the fire of interest. Additionally, by clicking the ZOOM TO LOCATION button, your map extent will automatically zoom to the extent of that fire.
Clicking on a fire location provides information about the fire and the option to zoom to the map extent of the selected fire.
Perimeters for current US wildland fires
For wildland fires currently occurring in the US larger than 100 acres in size, fire perimeters are provided for context. These data are typically compiled by federal, state and local fire management agencies on a routine basis during the life of an incident, however, they may not be available for all incidents. These data are typically updated daily from multiple sources and indicate the current extent of the fire and containment lines. Click on USA Fire Perimeter layer to display the fire perimeter data in the FIRMS US/Canada Fire Map.
When using perimeters in the context of satellite active fire detection data, this can indicate where a fire is active within the perimeter and if it is growing outside of it. Additionally, if the fire perimeter is not fully covered by cumulative active fire detections, gaps in that coverage may indicate where the fire has grown in between observations by polar-orbiting satellite sensors like MODIS and VIIRS, cloud cover at the time of satellite overpass occluded observations when the fire was actively burning, or fire activity was smaller and/or less intense at the time of satellite overpass or was not detectable under the vegetation canopy. Isolated active fire detection pixels outside of the perimeter can be indicative of detections occuring towards the edge of a swath which results geolocational errors due to the increasingly distorted field of view in the scan track direction, particularly for MODIS.
Visualization of MODIS and VIIRS active fire detection data in the context of a current perimeter for a wildland fire.