Densely scattered fires were observed by S-NPP VIIRS and Aqua MODIS on November 12, 2012 at approximately 0800 UTC (1330 local time) over the Punjab region. This area is one of primarily agriculture land use-land cover and thus these fires are likely related to seasonal burning of crop residues from Rice harvests (see Vadrevu et al., 2011). As can be seen in the comparison grid plot VIIRS detected many more fires, in some cases nearly double. This is likely a function of scan angle as VIIRS observed these fires near nadir and the average MODIS detection was observed at a scan angle of 34°.
Nearly ten fire complexes are currently burning in Idaho and on September 9th both Suomi-NPP VIIRS and Aqua-MODIS detected numerous hot spots. Given the close timing in overpass (Aqua was only 20 minutes behind S-NPP) and similar viewing angle, the agreement in detections is quite good, as evident in the grid plot.
Fires from California to Wyoming continue to burn across the western U.S. states. In the above images, Suomi NPP VIIRS detected fires in California, Oregon, Nevada, and Idaho, approximately 55 minutes before Aqua-MODIS detected the same ones. Despite nearly an hour difference in overpass time, the agreement in fires detected is fairly good, as evident in the grid plot. However, while VIIRS detected more fires in Idaho, MODIS detected more in California, Oregon, and Nevada; the discrepancy is clearly a function of the VIIRS’ off-nadir scan angle in these states.
The larger fires in California observed in the images include the Fort Complex, Bagley, North Pass, Chips, and Rush. In Oregon, the Waterfalls 2 fire can be seen near the top-left portion of the image. And to the east, in Idaho, the Trinity Ridge and Halstead fires can easily be seen.
The High Park fire in Colorado, just west of Fort Collins, fire started in early June due to a lightning strike (http://www.inciweb.org/state/6) and took off June 9th because of high winds and low humidity. VIIRS got it’s first good observation on June 11th and by June 22nd the NIFC incident report stated the burnt area was up to 68,200 acres.
The following images show a comparison of VIIRS and Aqua active fire detections on June 18th within a 5x5 degree window centered near the High Park.
A MODIS - VIIRS comparison of the Whitewater-Baldy Fire complex in New Mexico from May 25th, 2012. NPP VIIRS was overhead at approximately 1955 UTC while Aqua observed the same fire about 20 minutes later. The grid plot shows the strong agreement in the number of detections made by both sensors.
Near coincident overpass of VIIRS and Aqua over the Gulf coast of Texas and Louisiana on May 17, 2012 (~1900 UTC) resulted in several matching fire detections. However, as can be seen from the cloud movement and sun glint shift, timing and viewing angle were slightly different, resulting in a number of missed detections by both sensors; MODIS was trailing about 30 minutes behind VIIRS and observing at a greater scan angle. The grid plot shows the number of detections by each sensor, as well as the matched detections (see the FAQ page for more information about the grid plot).
Fires occurring in the southwest U.S., primarily Utah, were detected by VIIRS and MODIS on May 1st, 2012 around 1:45 local time. VIIRS detected more fires in this example, which may be a result of greater cloud obscuration, as MODIS was overhead 30 minutes after VIIRS, and scan angle.
Fires occurring in Minnesota and Wisconsin were detected on April 26th by Suomi-NPP VIIRS at approximately 1905 UTC. Aqua-MODIS was trailing about 20 minutes. However, despite the close proximity in overpass between the two satellites, this comparison highlights the ephemeral nature of fires, as well the influence of scene conditions as demonstrated by the cloud cover to the west in the VIIRS swath having moved out by the time MODIS was overhead.
Fire detections made by VIIRS (~1817 UTC) and MODIS-Aqua (~1848 UTC) of the “County Line fire” in the Osceola National Forest, Florida on April 7th, 2012.
A lightning-ignited fire, which started in the Pinhook Swamp, smoke from the “County Line” fire is clearly visible in the center of these 5-minute swaths. As of 4/10/2012, the fire had grown to roughly 11,000 acres (4,450 ha).
The grid plot shows numerous coincident fire detections between VIIRS and MODIS, both within this fire complex, and other fires in the swath, despite the nearly 30 minute difference in overpass.
Finally, a map of major cities and roads in Florida, with VIIRS and MODIS-Aqua detections for April 7th, 2012 overlaid, is presented. This map is similar to ones generated by the USFS Remote Sensing Applications Center (RSAC).
