This blog explains the considerations when using geostationary active fire data, and shows you how to use the SUB-DAILY data filtering option within the ADVANCED mode of the FIRMS viewer to help track fire progression throughout the day. These steps can also be used for the polar-orbiting satellites.

CONSIDERATIONS WHEN USING GEOSTATIONARY ACTIVE FIRE DATA

Geostationary active fire data are viewable in NASA’s Fire information for Resource Management System (FIRMS). These data are ingested from multiple sources including GOES (NOAA), Meteosat (EUMETSAT) and Himawari (JAXA). Geostationary satellite sensors view the same area of the Earth’s surface at all times and, therefore, many observations are available throughout the day. Polar-orbiting sensors, such as MODIS, VIIRS, and Landsat OLI, on the other hand, view the same area of Earth’s surface less frequently. For example, MODIS and VIIRS generally view the same area of Earth’s surface twice daily; Landsat 8 and Landsat 9 each view the same area of the Earth’s surface every 16 days at the mid latitudes. Towards the poles, polar-orbiting satellites, such as MODIS and VIIRS, view the same area more than twice daily, and up to six times a day, due to the convergence that occurs towards the poles.

The use of geostationary satellite sensors to generate active fire detections, and the development of associated algorithms, is not considered as reliable as those from polar-orbiting satellite sensors such as MODIS and VIIRS. Additionally, geostationary satellite pixels have a coarse spatial resolution. The spatial resolution directly below the satellite (known as the “sub-satellite point”) is 2km for GOES ABI and Himawari AHI, and 3km for Meteosat SEVIRI. The spatial resolution of the pixel (i.e., the pixel size) also systematically grows away from the sub-satellite point towards the edge of the disk. Therefore, the active fire data layers from geostationary satellites viewable in FIRMS should be used with caution. These layers are labeled a beta product as refinement of the algorithms is ongoing, and they are only viewable in the ADVANCED MODE of FIRMS Global and FIRMS US/Canada.

As geostationary satellite sensors view the same area of Earth’s surface at all times and provide repeated observations on a sub-hourly basis, active fire data from geostationary satellites can help track fire progression throughout the day. This can be useful to narrow down the ignition time of a wildfire event, to detect fires not detectable at longer observation intervals, and to track fires that advance quickly in a relatively short period of time.

HOW TO USE THE SUB-DAILY OPTION

The steps below use an example from the Smokehouse Creek Fire in March 2024 in Texas, USA .

  • Open the FIRMS US/Canada interactive Fire Map
  • Access the ADVANCED MODE by selecting the three horizontal lines in the main menu on the right and selecting ADVANCED MODE
  • Use the calendar feature of the TIMELINE to set the date to February 26 2024 (1 DAY)
  • Open the LOCATION TOOL and type Stinnett into the Find Location option; select Stinnett, TX, USA. 
  • Expand the GEOSTATIONARY accordion in Fires / Hotspots section of the FIRMS legend (click the ‘+’ icon to the right of GEOSTATIONARY)
  • Deselect all of the active fire layers under the POLAR ORBITING accordion.
  • Select the Filtered Geostationary (provisional) layer  (click the ‘i’ Info for information about each of the products listed); this layer includes the combined active fire detections from GOES-16 and GOES-18 for the entire day. Note: GOES-16 is the eastern satellite positioned at 75 degrees west longitude and GOES-18 is the western satellite positioned at 135 degrees west longitude.
  • To track the progression of a fire throughout the day, FIRMS includes capabilities to filter data using the SUB-DAILY tool. 
  • On the main menu, toggle on SUB-DAILY (above the calendar icon); note the TIMELINE at the bottom of the map has changed to hours within a given day instead of days. 
  • Use the clock icon in the main menu to set the time to 22:00 (the SUB-DAILY menu displays the time in UTC; this is 16:00 CST). Note that 04:00 HH:MM appears below the clock icon in blue, this shows all active fires for the previous four hours and is the default time span. Change this to 06:00 HH:MM. Now you are viewing all the filtered geostationary active fire detections for the Smokehouse Creek Fire on 26th February between 16:00-22:00 UTC or 11:00-16:00 CST.
    • Note: You can view all the active fire detections within the last 10 minutes (00:10), every 10 minutes up to 1 hour (01:00), and within the last two (02:00), three (03:00) four (04:00), six (06:00), eight (08:00), ten (10:00), twelve (12:00), 18 (18:00), and 24 (24:00) hours (You can also dynamically change the time by sliding the bar along in the TIMELINE at the bottom of the map viewer)

  • We would like to investigate when the wildfire was initially detected by the geostationary satellites. Toggle on Time Based under the Fires/Hotspots table of contents. This displays the active fire detections based on Time since detection. Most of these active fire detections (shown in deep red) occurred <1 HOUR earlier than 22:00 UTC (16:00 CST), but some detections (shown in bright red) occurred between 1-3 HOURS earlier than 22:00 (between 19:00-21:00 UTC (13:00-15:00 CST)). One active fire detection (shown in orange) occurred 3-6 HOURs earlier than 22:00 UTC (between 16:00-19:00 UTC (10:00-13:00 CST)).

  • When you click on an individual active fire detection, an attribute pop up appears that displays the acquisition time (ACQUIRE_TIME) of the detection (the attribute specifications default to Local Time). Click on the active fire detection that occurred 3-6 HOURS Time since detection (the orange pixel), and select the UTC option to match the UTC time displayed in the menu on the right).
  • The active fire detection occurred at 19:00 UTC (13:00 CST). Change the time to 20:00 UTC and set the time interval to 02:00. This will display all the active fire detections that occurred between 18:00-20:00 UTC (12:00-14:00 CST). Several additional active fire detections were observed during this time period.
  • Tighten the time span to help identify how the wildfire progressed by changing the time interval to 02:00, several of the active fire detections persist. Incrementally tighten down the time span to further examine the wildfire progression by sequentially selecting 01:00, 00:50, 00:40, 00:30, 00:20, and finally 00:10. Several active fire detections are still present at 00:10 (between 19:50-20:00 UTC (13:50-14:00 CST). Therefore, while the initial active fire detection was observed around 19:00 UTC (13:00 CST), the wildfire expanded rapidly between 19:50-20:00 UTC (13:50-14:00 CST). 
  • Click on some of these active fire detections to access the attribute pop up and note the acquisition time (ACQUIRE_TIME) of these detections
  • Change the time to 23:50 UTC (17:30 CST), change the time interval to 00:10 HH:MM, and use the +10 mins option to reach back in 10 minute increments; visually interpret how the Smokehouse Creek wildfire expanded during the afternoon of 26th February; between the initial active fire detection at 19:00 UTC (13:00 CST) to 23:50 UTC (17:50 CST). This figure includes snapshots from different time intervals  

The above example highlights how the geostationary active fire data, which are acquired at a finer temporal resolution, can be used to more tightly identify, for example, a wildfire fire ignition time.

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