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MODIS-Detected Fires in NFIRS

The U.S. Fire Administration Analysis

Matching a Broader Base of More Precisely Located NFIRS Fires to MODIS Observations Within 1 Kilometer and 24 Hours at the National Level

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Consolidating MODIS Observations to Incidents

Since the Terra and Aqua satellites both pass each point on earth multiple times per day and since wildfires can have long durations, rules were developed to consolidate multiple MODIS observations to single MODIS incidents.

MODIS observations within 24 hours and 1 kilometer (0.62 miles) of any other MODIS observation were grouped together as a single incident. This technique may overestimate the number of incidents if intervening observations are not captured by the satellites due to cloud or smoke coverage. (For example, if a wildfire lasted 3 days but was only captured by MODIS on the first and last day, those observations will be classified as separate incidents. Similarly, if a fast-moving wildfire is observed in subsequent satellite passes but the distance between the observations is greater than 1 kilometer, they will be classified as separate incidents.)

As part of this analysis, it was determined there were 162,093 MODIS observations of fire in the U.S. in 2017. Of these, 85,039 observations occurred within 24 hours and 1 kilometer of another observation. There were 77,054 MODIS incidents of fire in the U.S. in 2017, consisting of the groupings shown in Table 6.

Table 6: Consolidation of MODIS Observations to MODIS Incidents

Number of observations per incidentNumber of observationsNumber of incidentsAverage duration of event (hr)Average distance (km)
156,21756,217n/an/a
2-544,00017,9122.80.6
6-1012,2091,68212.71.8
11-209,31365127.12.9
21-5011,13135049.64.6
51-1009,80314090.86.8
101-50021,80897165.612.0
501+4,5275368.025.4
map depicting the MODIS observations made during the Highline Fire

Figure 2: MODIS Observations in Payette National Forest, Idaho

The largest fire, with 1,388 observations between Aug. 16 and Sept. 8, 2017, was the Highline Fire in the Payette National Forest in Idaho. Figure 2 contains a map depicting the MODIS observations made during this fire.
Click on the map to enlarge.