The document summarizes a study that assessed the burn severity of the 2011 Bastrop County Complex Fire in Texas using satellite imagery and remote sensing indices. The study analyzed pre-fire and post-fire Landsat 5 imagery to calculate Normalized Burn Ratio (NBR) and difference Normalized Burn Ratio (dNBR) values. These were classified into 5 burn severity classes and assessed for accuracy, finding moderate agreement. The modified classification approach was determined to more accurately represent the full burn severity spectrum.

1. Bastrop County Complex
Fire
A Low Cost Burn Severity Estimate
Presented by:
Eric R. Maurer, Eric Putman, & Nicholas Stokes
ESSM 444 - 500
http://farm7.static.flickr.com/6069/6122579403_ce4e97e7a3.jpg

2. Outline
• Objectives
Assess the burn severity of the Bastrop County Complex Fire (BCCF) of 2011 by
utilizing the Normalized Burn Ratio (NBR) and difference Normalized Burn Ratio
(dNBR)
• Background/Study Area
Bastrop County Complex Fire (BCCF) of 2011
Bastrop County, TX. - Lost Pines Region
• Methods
Data
Flowchart
• Results
Burn severity maps
Review accuracy assessment
• Discussion/Conclusion

3. • Assess the burn severity of the Bastrop County Complex Fire (BCCF) of
2011 by utilizing the Normalized Burn Ratio (NBR) and difference
Normalized Burn Ratio (dNBR)
• Using the resultant dNBR calculations, classify the Bastrop County
Complex Fire into a range of 5 burn severity classes and delineate the
boundaries of the fire.
• Use the following methods learned in laboratory exercises:
band math, image preprocessing/statistics extraction, image classification,
and accuracy assessment.
Objectives

4. Background
• A wildfire started on Sep. 4, 2011 in Bastrop County, TX.
(East of Austin) in the Lost Pines area of the county,
approximately 34,000 acres burned and around 1,500
homes/buildings destroyed. (Pines Recovery Team, 2011)
• This wildfire was the most destructive wildland-urban
interface fire in Texas history. (Bastrop Complex Wildfire Case Study)
http://cravedfw.files.wordpress.com/2011/09/texas-fires.jpg?w=500

5. Study Area
• Bastrop County, TX.
(30̊ 6’0”N, 97˚18’36” W)
• Population: 74,763
(2012)
• Lost Pines Area
A population disjunction
of loblolly pines

6. Methods
Burn severity is defined as the measurement of
organic matter loss in or on the soil surface,
and in remote sensing operations the preferred
index used to identify the changes in the
vegetation and soil exposure is known as the
Normalized Burn Ratio (NBR) (Keeley, 2009;
Key & Benson, 2006).
NBR= (Band 4 - Band 7) / (Band 4 + Band 7).
dNBR=NBRprefire - NBRpostfire

7. Data
Post-Fire
10/13/2011
Pre-Fire
8/27/2011
• Using earthexplorer.usgs.org we attained pre & post fire LANDSAT 5 imagery.
• The LANDSAT 5 imagery consists of 7 spectral bands.
• Bands 1 to 5 along with 7 have a spatial resolution of 30 meters, while Band 6 (thermal
infrared) is 120 meters, but has been resampled to 30-meter pixels.
(http://landsat.usgs.gov/band_designations_landsat_satellites.php)
• Utilized band 4 (0.76-0.90µm) and band 7 (2.08-2.35µm)

8. Flowchart
Image Acquisition
(LANDSAT 5)
Pre-Fire (26 AUG 2011)
Post-Fire (13 OCT 2011)
Clipped Image in ENVI using Spatial
Subset for smaller study area
Calculated
Normalized Burn Ratio (NBR)
for Pre/Post Fire Images:
NBR =
(Band 4 − Band7)
(Band 4 + Band 7)
Calculated
Difference Normalized Burn Ratio
dNBR = (NBRprefire – NBRpostfire)
Manually digitized fire
perimeter using dNBR
image to create shapefile
Reclassified dNBR
values to 5 levels of Burn
Severity
Performed Accuracy
Assessment
Analyze Accuracy
Assessment

10. Severity Level dNBR Range
Unburned -500 to +99
Low Severity +100 to +269
Moderate-Low Severity +270 to +439
Moderate-High Severity +440 to +659
High Severity +660 to +1300
Severity Level dNBR Range
Unburned -500 to +24
Low Severity +25 to +194
Moderate-Low Severity +195 to +364
Moderate-High Severity +365 to +584
High Severity +585 to +1300
Results

12. Burn Severity Unburned Low Moderate-
Low
Moderate-
High
High User Accuracy
Unburned 24 21 7 0 0 52 46%
Low 14 35 43 1 1 94 37%
Moderate-Low 4 6 19 32 4 65 29%
Moderate-High 0 0 3 39 3 45 87%
High 0 0 1 3 67 71 94%
42 62 73 75 75 184
Overall Accuracy
Producer Accuracy 57% 56% 26% 52% 89% 56%
Burn Severity Unburned Low Moderate-
Low
Moderate-
High
High User Accuracy
Unburned 4 2 0 0 0 6 67%
Low 31 43 26 0 0 100 43%
Moderate-Low 7 17 36 10 3 73 49%
Moderate-High 0 0 10 57 4 71 80%
High 0 0 1 8 68 77 88%
42 62 73 75 75 327
Overall Accuracy
Producer Accuracy 10% 69% 49% 76% 91% 64%
Original Burn Severity Results
Modified Burn Severity Results
K-hat = 45.45% : Moderate Agreement
K-hat = 53.70% : Moderate Agreement
Accuracy Assessments

13. Unburned Low
Severity
Moderate-
High
Moderate-
Low
High
Severity
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
57% 56%
26%
52%
89%
10%
69%
49%
76%
91%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PRODUCER ACCURACY

14. 46%
37%
29%
87%
94%
67%
43%
49%
80%
88%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
USER ACCURACY
Unburned Low
Severity
Moderate-
High
Moderate-
Low
High
Severity
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR
- Original dNBR
- Modified dNBR

16. Discussion/Conclusion
• Assessment of the burn severity of the Bastrop County Complex Fire
(BCCF) utilizing the Normalized Burn Ratio (NBR) and Normalized
Difference Burn Ratio (dNBR) is a quick, inexpensive and accurate
alterative for estimating the burn severity of a wildfire.
• We believe our modified dNBR classes dataset to be more accurate and
useful, as it is more accurate over the entire spectrum of burn severity.
• Room For Improvement:
-possibly more accurate than statistics suggest, could modify accuracy
point placement system in the future.
Questions?