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MODIS/VIIRS Land Product Quality Assessment

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Opening Date: 2018-08-03 Last update: 2020-07-17 Status: Note

False fire is observed outside wildfire perimeters in some cases when a super heated smoke plume can set off false fire during nighttime detection. This false fire artifact has been observed in the past, particularly at night in VNP14IMG. In these cases a hot plume is detected, which carries a signature that is easily confused with that of the "real" fire perimeter. The tall heat plume combined with the high view angle will be projected laterally on the surface, generating a false fire artifact. The artifacts are usually observed in the nighttime data as typically these super plumes tend to be flagged as clouds in the daytime scenes which prevents this detection. Users are advised to reference the VNP14 user guide in this LINK for more details. This issue has also been found to impact the fire product in the NOAA-20 (J1) VIIRS instrument.

The first image below is an example image from the FIRMS website, which shows the NPP VIIRS active fire product reporting a fire detected on July 26th, 2018 (2018.207) over Northern California's Whiskey Bottom lake. This is the projection of the false fire that is being detected by the active fire algorithm in the presence of a hot plume at high altitude over the true fire on the ground, which could be several kilometers away from the lake. The second image is section 5, the FREQUENTLY ASKED QUESTIONS of the VNP14 user guide, which explains this fire artifact in greater detail.

FIRMS Image example of SNPP false fire plume over lake
2018.207

VNP14 User Guide Section 5. FREQUENTLY ASKED QUESTIONS.

The second example below shows USGSs GeoMAC perimeter of the California Holy fire from August 8th, 2018. Fire detected by the VIIRS AF process on NRT was acquired from the FIRMS archive for 08.08.18 and overlaid with the Holy fire perimeter. Review of the S-NPP orbit map and L2 fire data both confirmed the fire pixels are located at the edge of the swath, i.e. off nadir. This example shows spurious fire projected outside of the fire perimeter due to the combination of high altitude heat plume and high view angle.

California Holy fire perimeter and FIRMS VIIRS Active Fire NRT product 08.08.2018

The third example below shows an image from the FIRMS website, which shows the NPP VIIRS active fire product reporting a fire detected on July 21st, 2019 (2019.202) in the mountainous region North of Flagstaff Arizona. In this example, false fire is observed down in the Northeastern jurisdiction of the city crossing HWY89. This is due to the tall heat plume combined with the high view angle of the sensor, which causes false fire to be projected laterally on the surface.

FIRMS Image example of SNPP false fire plume over Flagstaff AZ
2019.202 (07.21.19)

The fourth example below is the Kincade Fire, which stared in Sonoma County, CA, on October 23, 2019. The map provided from the VIIRS Land Science Team, shows the SNPP VIIRS night time (red) and day time (orange) active fire product overlaid onto the NIROPS fire perimeter map for October 27th and 28th. There is an observed large number of night fire pixels, some of which deviate outside the fire perimeter. This is most likely caused from plume detection as further review of sequential observations indicates that explosive fire behavior was taking place during this time period and this is conducive to plume detection during night time observations.