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Report

Series

National Fire Data Center

16825 S. Seton Ave.

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usfa.fema.gov

Investigation of MODISDetected Fires in NFIRS

February 2021

Executive summary

Moderate Resolution Imaging Spectroradiometer (MODIS)1 is a satellite-based instrument used to collect data 

about features on the Earth’s surface. Scientists have developed algorithms to analyze that data to detect 

active fires. Researchers David T. Butry and Douglas S. Thomas published a paper in 20172 that compared 

the MODIS active fire data for California from 2003 to 2014 to wildfire incident data collected by the U.S. 

Fire Administration’s (USFA’s) National Fire Incident Reporting System (NFIRS) and found that only 32% of 

the MODIS-detected fires could be matched to an NFIRS incident. (Butry and Thomas’ criteria for identifying 

wildfires in NFIRS and for matching them to MODIS active fire data are discussed on page 2.)

In conducting this analysis, USFA’s goal was to apply a variation of Butry and Thomas’ MODIS/NFIRS fire 

incident matching process at the national level to determine if the same proportion of data could be matched 

in the rest of the U.S. Additionally, as a path to improving NFIRS reporting, it was thought that this could be 

a first step in determining the feasibility of using MODIS data as a means for identifying wildfire incidents 

that may be missing from NFIRS. 

Using geocoded 2017 NFIRS data for all fire incidents in the U.S., USFA found that only 1.1% of the MODIS 

observations (or 1.6% of MODIS-identified incidents) occurred within 1 kilometer and 24 hours of any NFIRSreported incident. It was determined that 6.4% of MODIS-identified incidents occurred within national parks 

and national forests, grasslands, and wilderness areas, but only a handful of these incidents appear in NFIRS 

data. As for the remaining unmatched MODIS-identified incidents, it is uncertain whether they occurred in 

other public lands; were small, controlled unreported fires; or were false positives.

MODIS

MODIS is an observational instrument operated by the National Aeronautics and Space Administration. It is the 

name of the sensor aboard two satellites, Terra and Aqua, that were launched in 1999 and 2002 respectively. 

Terra and Aqua follow a sun-synchronous near polar orbit, approximately 705 kilometers above the surface of 

the Earth. Collectively, the satellites observe each point on the Earth’s surface three to four times per day, though 

the interval between passes varies. Instrument data is used to monitor and process trends in land vegetation, 

ocean phytoplankton, and cloud temperature and altitude, among other features.3 

One of the uses of MODIS data is the detection of active fires. The fire detection strategy is based on absolute 

detection of a fire (when the fire strength is sufficient to detect) and on detection relative to its background (to 

account for variability of the surface temperature and reflection by sunlight).4 Scientists at the University of 

Maryland developed the algorithm to identify areas where the infrared radiation being emitted is significantly 

different from that of surrounding areas. MODIS can routinely detect both flaming and smoldering fires 

1

National Aeronautics and Space Administration (NASA). (n.d.). About. MODIS: Moderate Resolution Imaging Spectroradiometer. Retrieved 

December 16, 2020 from https://modis.gsfc.nasa.gov/about/index.php 2Butry, D. T., & Thomas, D. S. (2017, August 8). Underreporting of wildland fires in the US Fire Reporting System NFIRS: California. International 

Journal of Wildland Fire, 26(8), 732–743. https://doi.org/10.1071/WF17004 3NASA. (n.d.). Data. MODIS: Moderate Resolution Imaging Spectroradiometer. Retrieved December 16, 2020 from https://modis.gsfc.nasa.

gov/data/

4NASA. (n.d.). MODIS thermal anomalies/fire. MODIS: Moderate Resolution Imaging Spectroradiometer. Retrieved December 16, 2020 from 

https://modis.gsfc.nasa.gov/data/dataprod/mod14.php
Investigation of MODIS-Detected Fires in NFIRS 2

approximately 1,000 square meters in size. Under very good observing conditions (e.g., near nadir, little or no smoke, 

relatively homogeneous land surface, etc.), flaming fires one-tenth this size can be detected. Under pristine (and 

extremely rare) observing conditions, even smaller flaming fires approximately 50 square meters can be detected.5

The Butry/Thomas analysis: Matching selected NFIRS fires to MODIS observations by county 

and date in California

Summary of approach and findings

Butry and Thomas examined MODIS-detected fires within areas of local jurisdiction in California from 2003 to 2014 

and found that only 32% of them were present in NFIRS. However, their analysis did not use geocoded NFIRS data, 

and they were only able to attempt to match NFIRS fires with MODIS-detected fires by county and date. In addition, 

the criteria they used to select NFIRS incidents may have omitted some fires that may have been detected by MODIS. 

It should be noted that NFIRS is not a census of all fire department-responded incidents, and it is not based on 

a statistically derived sample. Among other issues that prevent the NFIRS from being a complete source for fire 

department incident data are reporting deadlines, data access and budgetary considerations. For fire incidents, as 

with other NFIRS fire department-responded incidents, the NFIRS raw totals do not reflect the whole of the U.S. fire 

problem; NFIRS contains incident data derived from voluntary reporting of fire incidents in the U.S. 

The state of California is divided into distinct areas where either the local fire department, CAL FIRE or the agencies 

of the federal government have primary responsibility for wildfire incident management. The authors first identified 

MODIS-detected fires that occurred within local direct protection areas. They then retrieved a subset of California 

NFIRS incidents by selecting incidents where any of the following criteria was present:

ĵ Incident Type = 141: Forest, woods or wildland fire.

ĵ Incident Type in 100 series (Fire) or 561 (Unauthorized burning), 631 (Authorized controlled burning), or 632 

(Prescribed fire), and:

Ý Actions Taken includes 13: Establish fire lines (wildfire), or

Ý Actions Taken includes 14: Contain fire (wildland), or

Ý Actions Taken includes 15: Confine fire (wildland), or

Ý Actions Taken includes 16: Control fire (wildland).

ĵ Incident Type in 100 series (Fire), and:

Ý Area of Fire Origin = 95: Wildland, woods, or

Ý Suppression Factor includes 775: Urban-wildland interface area.

ĵ Wildland Fire Module: Was used for incidents where Incident Type was not 632 (Prescribed fire).

Finally, they found those NFIRS fires that occurred in the same county (using the county of the reporting fire 

department) and on the same day as any MODIS-detected fire in local direct protection areas (Figure 1). 

5University of Maryland. (n.d.). Active fire products. MODIS Active Fire and Burned Area Products. Retrieved November 6, 2019 from http://

modis-fire.umd.edu/af.html; Giglio, L., Schroeder, W., Hall, J. V., & Justice, C. O. (2018, December). MODIS collection 6 active fire product user’s guide 

revision B. NASA. http://modis-fire.umd.edu/files/MODIS_C6_Fire_User_Guide_B.pdf
Investigation of MODIS-Detected Fires in NFIRS 3

Figure 1: Subset of MODIS and NFIRS data examined for county-date matching

MODIS

observations

NFIRS

incidents

Selected NFIRS

incidents in Local

Direct Protection

Areas

Butry and Thomas found that 32% of the MODIS-detected fires in areas of local responsibility occurred in the same 

county and on the same day as an NFIRS-reported fire that met the criteria defined in the study to describe wildfires.

Discussion of approach

It is possible that some of the methods and assumptions used in this analysis are problematic. Butry and Thomas 

make an implicit assumption that all fires detected by MODIS are wildfires, but MODIS can on rare occasions detect 

fires as small as 50 square meters (4-meter radius) and routinely detects fires 1000 square meters in size (18-meter 

radius). The criteria Butry and Thomas used to identify wildfires in the NFIRS data potentially omits many other kinds 

of incidents that could match the MODIS observation. Moreover, the criteria used omits other factors that could 

identify additional wildland fires. Notably, the criteria do not include other outdoor incident types:

ĵ 140: Natural vegetation fire, other.

ĵ 142: Brush or brush-and-grass mixture fire.

ĵ 143: Grass fire.

ĵ 170: Cultivated vegetation, crop fire, other.

ĵ 171: Cultivated grain or crop fire.

ĵ 172: Cultivated orchard or vineyard fire.

ĵ 173: Cultivated trees or nursery stock fire.

ĵ 561: Unauthorized burning.

ĵ 631: Authorized controlled burning.

ĵ 632: Prescribed fire.

The criteria do not consider property use: 

ĵ 655: Crops or orchard.

ĵ 659: Livestock production.

ĵ 669: Forest, timberland, woodland.

ĵ 931: Open land or field.

The criteria omit certain areas of origin: 

ĵ 94: Open area, outside; included are farmland, field.

Last, the criteria do not include other possible suppression factors: 

ĵ 434: Poor or no access for fire department apparatus.

ĵ 760: Unusual vegetation fuel loading. 
Investigation of MODIS-Detected Fires in NFIRS 4

Incidents defined under these categories would not be included in the analysis unless they also meet the criteria 

specified by Butry and Thomas.

The criteria Butry and Thomas use to identify potential wildfires rely upon values in the Basic, Fire and Wildland Fire 

Modules. Of these, only the first Action Taken value is required and is populated with useable data nearly all of the 

time (Table 1). Area of Fire Origin, in the Fire Module, contains usable data in 81% of the reports where a Fire Module 

is completed (Table 2). Suppression Factors, also in the Fire Module, are optional fields and are sparsely populated 

(Table 3). Finally, Butry and Thomas use the presence of the Wildland Fire Module to infer a wildfire, but the Wildland 

Fire Module is only used for 23% of the incidents where it is allowed (Table 4).

Action Taken is recorded in the NFIRS Basic Incident Module. In this module, up to three values may be entered. The 

first one is required for all values of aid, and the others are optional.

Table 1: Usability of primary actions taken (Basic Incident Module)

Action Taken 1 Action Taken 2 Action Taken 3

Primary1 Aid Given Total Primary Aid Given Total Primary Aid Given Total

Total basic incidents 1,073,284 227,128 1,300,412 1,073,284 227,128 1,300,412 1,073,284 227,128 1,300,412

Invalid values2 11,975 7,538 19,513 2,337 854 3,191 1,080 154 1,234

Null values 1 0 1 730,701 157,477 888,178 944,352 199,607 1,143,959

Usable values 1,061,308 219,590 1,280,898 340,246 68,797 409,043 127,852 27,367 155,219

Percent of incidents 99 97 98 32 30 31 12 12 12

1

Primary refers to incidents where Aid = 1 (Mutual Aid Received), 2 (Automatic Aid Received), 5 (Other Aid Given), or N (No Aid). Aid Given refers to incidents where Aid = 3 

(Mutual Aid Given) or 4 (Automatic Aid Given).

2Invalid Values are entered values that are not listed in the NFIRS Complete Reference Guide, including “-“, “00”, “0”, “6”, “18”, “25”, “59”, “68”, “95”, and “N.”

Area of Fire Origin and Suppression Factors are recorded in the NFIRS Fire Module, which is only required for certain 

incident types where the reporting department (primary) is not giving aid. Area of Fire Origin is required. Suppression 

Factors are optional, and up to three values may be recorded.

Table 2: Usability of area of fire origin (Fire Module)

Area of origin

Primary1 Aid Given Total

Total Fire Module reports 598,828 5,803 604,631

Null values 448 274 722

Undetermined (UU) 94,464 2,020 96,484

Other (0) 18,751 192 18,943

Usable values 485,165 3,317 488,482

Percent of incidents with Fire Module 81 57 81

1

Primary refers to incidents where Aid = 1, 2, 5, or N. Aid Given refers to incidents where Aid = 3 or 4.
Investigation of MODIS-Detected Fires in NFIRS 5

Table 3: Usability of suppression factors (Fire Module)

Suppression factor 1 Suppression factor 2 Suppression factor 3

Primary1 Aid Given Total Primary Aid Given Total Primary Aid Given Total

Total Fire Module 

reports

598,828 5,803 604,631 598,828 5,803 604,631 598,828 5,803 604,631

Null values 426,033 3,900 429,933 595,107 5,709 600,816 597,467 5,765 603,232

Undetermined 

(UUU)

1 0 1 2 0 2 0 0 0

Other (0) 1,567 28 1,595 55 2 57 31 0 31

None (NNN) 154,590 1,536 156,126 0 0 0 0 0 0

Usable values 16,637 339 16,976 3,664 92 3,756 1,330 38 1,368

Percent of incidents 

with Fire Module

4 9 4 1 2 1 0 1 0

1

Primary refers to incidents where Aid = 1, 2, 5, or N. Aid Given refers to incidents where Aid = 3 or 4.

The Fire Module is required for most incident types but may be substituted with the Wildland Fire Module for certain 

kinds of fires. The Fire Module is optional for certain incident types in the 100 series (fire incidents) but is not available 

for other kinds of incidents. Neither module is required if the department is assisting another department (where 

Aid = 3 or 4).

Table 4: Presence of Fire and Wildland Fire Module by module requirement1

Primary2 Aid Given Total

Incidents % Using 

Fire

% Using 

Wildland Incidents % Using Fire

% Using 

Wildland Incidents % Using Fire

% Using 

Wildland

Fire or Wildland 

required

216,979 73 27 45,852 3 3 262,831 61 23

Fire required 365,130 100 156,146 3 521,276 71

Fire optional 328,130 23 21,459 1 349,589 21

Wildland optional 163,045 1 3,671 1 166,716 1

Total 1,073,284 56 6 227,128 3 1 1,300,412 46 5

1 Either the Fire Module or the Wildland Fire Module is required for incident types 140-143, 160, and 170-173. The Fire Module is required for incident types 100, 111-112, 

120-123, 130-138, and 161-164. The Fire Module is optional for all other fire incident types, and the Wildland Fire Module is optional for incident types 561, 631, and 632. 

Both modules are optional for Aid Given.

2Primary refers to incidents where Aid = 1, 2, 5, or N. Aid Given refers to incidents where Aid = 3 or 4.

Butry and Thomas did not have geocoded NFIRS incident data and matched selected NFIRS and MODIS incidents 

based on county and date. In practice, this means that any qualifying NFIRS incident in the county could be matched 

to any MODIS observation in the local direct protection area, regardless of the actual distance between the points. 

Also, matching incidents solely by date does not allow the researchers to identify possible matches where the NFIRS 

and MODIS reports occurred on adjacent dates.
Investigation of MODIS-Detected Fires in NFIRS 6

USFA analysis: Matching a broader base of more precisely located NFIRS fires to MODIS 

observations within 1 kilometer and 24 hours at the national level 

Summary of approach and findings

In an attempt to reproduce Butry and Thomas’ results at the national level, this analysis used NFIRS and MODIS6 data 

from 2017 covering the entire U.S. The 2017 NFIRS data was geocoded, so it was possible to find matches at a much 

more granular level than by county. All fire incident types were included (rather than attempting to define “wildfires” 

with NFIRS criteria), as well as authorized and unauthorized fires (Incident Types 631 and 561) and prescribed fires 

(Incident Type 632). To eliminate issues related to time zones and to be able to compare incidents within a 24-hour 

window, date and time of all NFIRS incidents was standardized by converting the alarm time to Universal Coordinated 

Time. Nationwide, we found that about 1.1% of the MODIS observations and 1.6% of the MODIS incidents occurred 

within 1 kilometer and 24 hours of an NFIRS incident. 

The 2017 NFIRS data was geocoded using location information provided by reporting fire departments and the 

GEOCODE Procedure in SAS 9.4. The precision of geographical coordinates returned by the geocoder is limited by 

the quality of the input information and the sophistication of the geocoding algorithm. Overall, 72% of the NFIRS 

incidents examined (where Incident Type was in the 100 series or was equal to 561, 631 or 632) were geomatched to 

an address, 11% were geomatched to the center point of a named street and 17% were geomatched to the center point 

of a ZIP code. However, the geocoding precision varied by type of incident. Structure fires (those where Incident Type 

was between 110 and 123) were geocoded to an address 83% of the time, while fires in forests and grasses (Incident 

Types 141 and 143) were geocoded to an address only 51% of the time. Some incidents (1,454) lacked sufficient location 

information to be geocoded and most (953) of these were natural vegetation fires (Incident Types 140-143). Even where 

the geocoding algorithm provided a geomatched address, it is possible that the location information was incorrectly 

reported or interpreted. The subsequent analysis is based on identifying NFIRS fires that occurred within 1 kilometer 

and 24 hours of a MODIS observation; bear in mind that this distance calculation may be based on imprecise NFIRS 

location information. A summary of the geocoding precision by NFIRS incident type is shown in Table 5.

Table 5. Geocoding precision of 2017 NFIRS data fire locations by fire incident type

Address % Street % ZIP % City % None %

Structure 405,952 83 14,264 3 66,125 14 13 0 247 0

Vehicle 87,615 55 31,747 20 40,733 25 9 0 78 0

Natural 18,881 66 4,673 16 5,204 18 1 0 48 0

Forest 13,694 51 5,185 19 7,569 28 6 0 297 1

Brush 58,860 60 17,133 17 21,900 22 5 0 295 0

Grass 45,726 51 17,863 20 25,803 29 3 0 313 0

Authorized, 

unauthorized, 

prescribed

127,998 77 18,940 11 19,730 12 3 0 45 0

Other 172,647 71 36,128 15 34,540 14 8 0 131 0

Total 931,373 72 145,933 11 221,604 17 48 0 1,454 0

We were unable to identify shapefiles designating local direct protection areas for all states, but shapefiles for national 

parks and national forests, grasslands, and wilderness areas to examine MODIS incidents in areas of federal control 

were used. This omits land under the management of the Bureau of Land Management, Bureau of Reclamation, 

Bureau of Indian Affairs, and Fish and Wildlife Service as well as state parks and state forests. However, we found 

that 6.4% of MODIS incidents occurred within national parks and national forests, grasslands, and wilderness areas.

6https://fsapps.nwcg.gov/afm/gisdata.php
Investigation of MODIS-Detected Fires in NFIRS 7

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 three 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 

incident

Number of

observations

Number of

incidents

Average duration 

of event (hr)

Average distance 

(km)

1 56,217 56,217 n/a n/a

2-5 44,000 17,912 2.8 0.6

6-10 12,209 1,682 12.7 1.8

11-20 9,313 651 27.1 2.9

21-50 11,131 350 49.6 4.6

51-100 9,803 140 90.8 6.8

101-500 21,808 97 165.6 12.0

501+ 4,527 5 368.0 25.4

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. A map depicting the MODIS observations made during this fire is shown below in Figure 2. 

Figure 2: MODIS Observations in Payette National Forest, Idaho
Investigation of MODIS-Detected Fires in NFIRS 8

Figure 2: MODIS observations in Payette National Forest, Idaho

Matching MODIS incidents to NFIRS incidents

Our analysis revealed that 1.1% of MODIS observations and 1.6% of MODIS incidents occurred within 24 hours 

and 1 kilometer of an NFIRS incident. We grouped MODIS observations and NFIRS incidents and found a total of 

1,212 fires consisting of 1,800 MODIS observations and 2,042 NFIRS incidents. Of these fires, 876 included only one 

MODIS observation apiece, and 1,345 NFIRS incidents in total. The remaining 336 fires included a total of 924 MODIS 

observations and 697 NFIRS incidents (Table 7).

Table 7: MODIS-NFIRS matches

MODIS 

observations NFIRS incidents Total fires

All grouped fires 1,800 2,042 1,212

Fires with a single MODIS observation 876 1,345 876

Fires with multiple MODIS observations 924 697 336

One thousand, eight hundred MODIS observations out of 162,093 matched at least one NFIRS incident, which 

produces a MODIS observation match rate of 1.1%. Another 1,212 MODIS incidents out of 77,054 matched at least 

one NFIRS incident, which produces a MODIS incident match rate of 1.6%.
Investigation of MODIS-Detected Fires in NFIRS 9

The 2,042 NFIRS incidents that matched at least one MODIS observation (in all grouped fires in Table 7) included several 

incident types, suggesting that a fire detected by MODIS may be recorded as something other than a wildfire incident. 

Incident Types 140-143 (Natural vegetation fire, other; Forest, woods or wildland fire; Brush or brush-and-grass mixture 

fire; Grass fire) and 561, 631 and 632 (Unauthorized burning; Authorized controlled burning; Prescribed fire) were more 

common among NFIRS incidents that matched MODIS observations than among all NFIRS incidents (Figure 3).

Figure 3: Distribution of NFIRS incident types for MODIS matches and for NFIRS, 2017

18%

3% 37%

12%

4%

2%

13%

2%

23%

8%

16%

7%

9%

19%

14% 13%

Matching Incidents NFIRS Incidents

143: Grass Fire

142: Brush or brush -and-grass

mixture fire

141: Forest, woods, or wildland fire

140: Natural vegetation fire, other

130-138: Vehicle fire

110-123: Structure fire, Fire in 

mobile property used as fixed 

structure

Incident Type 100% = 2,042 100% = 1,300,412

561: Unauthorized burning

631: Authorized controlled burning

632: Prescribed fire

150s, 160s, 170s: Outside 

rubbish, Special outside, and 

Cultivated vegetation fires

100: Fire, other

We also compared the NFIRS incidents that matched MODIS observations to the criteria that Butry and Thomas 

used to select their NFIRS incidents. Overall, only 701 of the 2,042 NFIRS incidents that matched one or more MODIS 

observations would have been included by Butry and Thomas’ criteria. The figure below shows the number of 

matching NFIRS incidents by each criterion and the total indicates that number of matching NFIRS incidents that 

match at least one of them (Figure 4). Of the 701 matching incidents, 37 incidents matched three criteria, 224 incidents 

matched two criteria, and 440 incidents matched one criterion.
Investigation of MODIS-Detected Fires in NFIRS 10

Figure 4: Number of matching NFIRS incidents that meet Butry and Thomas’ criteria

Wildland Overall

module

Suppression 

factors

Area of 

origin

Actions 

taken

Incident 

type

701

247

47

74

358

273

MODIS incidents in selected federal lands

Nearly all MODIS incidents have no counterpart in NFIRS. One explanation for this may be that many MODIS incidents 

are fires on state or federal lands and the responding departments are not NFIRS reporters. We did not compare 

MODIS incidents to all public land, but we were able to determine which MODIS incidents occurred in national parks, 

or in national forests, grasslands and wilderness areas. Overall (Table 8), 37% of MODIS observations occurred in 

these federal areas. This number only represents 6.4% of MODIS incidents, which suggests that these incidents were 

large-scale fires and each incident may have been identified separately with multiple satellite observations.

Table 8: MODIS observations and incidents in selected federal lands

Parks Forests Grasslands Wilderness Overall

Observations 3,544 55,676 120 24,208 59,755

Incidents 265 4,585 14 1,634 4,931

However, a small number of MODIS observations and incidents in these selected federal lands do match an NFIRS 

incident. These matches were reported for 20 MODIS incidents (74 observations) by 24 different fire departments 

(Table 9).

Table 9: MODIS observations and incidents in selected federal lands with NFIRS matches

Parks Forests Grasslands Wilderness Overall

Observations 3 71 0 0 74

Incidents 1 19 0 1 20

Hypotheses regarding nonmatching MODIS incidents 

There were 77,054 MODIS incidents in 2017. Of the MODIS incidents, 4,931 occurred in national parks or national 

forests, grasslands, or wilderness areas. Another 1,212 of them occurred within 24 hours and 1 kilometer of a fire 

that was reported in NFIRS (including 20 that included land in the selected federal areas). That leaves 70,931 MODIS 

incidents, 92% of the total, that are not accounted for in NFIRS data.
Investigation of MODIS-Detected Fires in NFIRS 11

Some of these remaining MODIS incidents may have occurred in other types of public land that we did not examine, 

such as areas controlled by the Bureau of Land Management or Bureau of Reclamation. Some may have occurred in 

state parks and forests, and some may have occurred in unpopulated, privately-owned land.

Seventy-three percent of MODIS incidents were observed once and at one location. MODIS generally detects fires 

that have a radius of 18 meters and can detect fires with a radius as small as 4 meters. These could be examples of 

authorized or unauthorized fires that are set to clear crop land or burn trash that are quickly extinguished, so no fire 

department intervention is needed.

We examined three MODIS observations for Frederick County, Maryland, and were surprised to see that they were 

of solar farms (Figure 5). MODIS’ detection algorithm relies on the heat signature emanating from an area, and it is 

possible that these objects created a false positive under the right conditions.

Figure 5. MODIS observations in Frederick County, Maryland

Umatched MODIS observations, Frederick County, Maryland

4/4/172

10/17/17, 10/20/171

Note: The data for the figure is based on MODIS data retrieved from https://firms2.modaps.eosdis.nasa.gov/download/ and excludes incidents where the Type is “other 

static land source.” 

1

Imagery ©2021 Maxar Technologies, U.S. Geological Survey (USGS), U.S. Department of Agriculture (USDA) Farm Service Agency. Map data ©2021.

2Imagery ©2021 Commonwealth of Virginia, Maxar Technologies, USGS, USDA Farm Service Agency. Map data ©2021.

Conclusion

Our examination of MODIS-detected fires supports Butry and Thomas’ hypothesis that few of these incidents are 

reported in NFIRS. Butry and Thomas assumed that MODIS observations were wildfires and those that occurred in 

local direct protection areas should be recorded in NFIRS as wildfires. Since NFIRS does not have an incident type for 

“wildfires,” Butry and Thomas developed criteria using incident type, actions taken, area of origin and suppression 

factors to identify NFIRS fires that were candidates for MODIS matching and matched them based on the county 
Investigation of MODIS-Detected Fires in NFIRS 12

and date. They found that 32% of the MODIS observations occurred on the same date and in the same county as a 

fire from their NFIRS subset. USFA analysis used geocoded NFIRS data and looked for any NFIRS incident (including 

unauthorized and prescribed fires) and found that only 1.6% of MODIS incidents occurred within 1 kilometer and 24 

hours of any NFIRS incident. A summary is provided in Table 10.

Table 10. Comparison of approaches and conclusions

Factor Butry/Thomas analysis This analysis

Timeframe 2003-2014 2017

MODIS observations used Only those located in California 

Local Direct Protection Areas

Entire U.S.

Consolidated multiple MODIS 

observations to single incidents

Not done Grouped MODIS observations within 

24 hours and 1 kilometer

NFIRS incidents used for comparison Incident Type 141

Actions Taken 13-16

Area of Origin 95

Suppression Factor 775

Use of Wildland Module

Incident Type in 100 series or 561, 

631, 632

MODIS-NFIRS matching technique Whether a fire department in 

the same county as a MODIS 

observation reported an NFIRS 

incident (meeting criteria above) on 

the same day

Whether a MODIS observation 

occurred within 24 hours and 1 

kilometer of an NFIRS incident

Conclusion 32% of MODIS observations are 

reported in NFIRS

1.6% of MODIS incidents (1.1% of 

MODIS observations) are reported 

in NFIRS

We distinguish between individual MODIS observations and MODIS incidents by grouping all MODIS observations 

that occurred within 1 kilometer and 24 hours together as a single incident. Slightly over half of MODIS observations 

(52%) can be grouped with another observation to create an incident, which suggests that MODIS can be useful for 

identifying fires with large burn areas and lengthy durations, likely large named wildfires. We also found that 6.4% 

of MODIS incidents occur within national parks and national forests, grasslands, and wilderness areas. However, the 

vast majority of MODIS incidents involve a single observation and most of these are not reported in NFIRS. Additional 

research should be done to determine whether these are fires in public or nonpublic lands, instances of crop or trash 

burning, or false positives.

This report is submitted to the U.S. Fire Administration National Fire Data Center by PG Public Services, LLC in 

accordance with the Performance Work Statement under contract HSFE20-17-P-0068.