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Estimates of Active Fire Properties using AVIRIS, ASTER and MODIS
D.A. RobertsDepartment of GeographyU.C. Santa Barbara
Photograph of the Station Fire behind the Jet Propulsion Laboratoryfrom Philipp Schneider
• Introduction– Remote Sensing of Wildfire– Why Fire Temperature and Area
• Multiple Endmember Spectral Mixture Analysis and Fire– AVIRIS Examples from Simi– MODIS– ASTER
• Early Detection using AVIRIS• Summary
Estimates of Active Fire Properties
• Major Contributors– Phil Dennison and Ted Eckmann
• Agency Support– NASA Solid Earth and Natural Hazards– NASA Regional Earth Science and Applications– NASA EO-1 Science Validation Team– Joint Fire Science Program– NASA Earth System Science Program MODIS: 9-5-2009
Remote Sensing of Wildfire• Pre-fire Conditions
– Fuel Types (Fuel models)– Fuel Condition (live to dead fuels)– Live Fuel Moisture
• Fire Danger (current conditions)– Incorporates measures of fuel properties and weather– Fire Danger Indices
• Active fire– Fire temperature, fire area and perimeters– Fire spread modeling– Emission modeling and suppression
• Post-fire conditions– Burned area– Fire effects– Post-fire recovery
Why Active Fire Properties?
• Improved measures of fire temperature and area may aid in fire suppression efforts
• Fire temperature and burned area are critical for an improved understanding of emissions
• Fire intensity (temperature) impacts post-fire recovery, soil properties
• While the TIR is widely considered the preferred part of the spectrum, the VNIR-SWIR also has considerable potential
0.000E+00
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400 1400 2400 3400 4400 5400 6400
Wavelength (nm)
Rad
ianc
e (W
m-2μm
-1sr
-1)
Solar*50
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1400K
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Hot Object Emission
• Hot objects emit strongly in the VNIR-SWIR
• As objects cool, peak emission shifts to the TIR and the area under the curve declines
• The spectral shape provides temperature, area under the curve size
AVIRIS
ASTER (6 bands) MODIS(3 SWIR, 1 MID-IR, 3TIR)
Fire Temperature and Area
• Spectral shape is unique to a specific temperature• The area under the curve varies with area and temperature
– Single band estimates of fire properties are under-determined
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400 1400 2400 3400 4400 5400 6400
Wavelength (nm)
Rad
ianc
e (W
m-2μm
-1sr
-1)
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1000K
1600K (0.1)
1000K (0.5)
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Multiple Endmember Spectral Mixture Analysis (MESMA)
• Extension of a Simple Mixture Model
– Riλ' = + εiλ
– RMS =
• Number and Types of Endmembers Vary Per Pixel• For fires mixed radiance is a product of modeled
radiance of hot objects and a background– The endmember selected provides temperature– The fraction of hot and cold endmembers provides area
f Pk 1
N
k i k* λ=∑
iλε2
k=1
N
N
∑-1
AVIRIS Fire Temperature and Area (Dennison et al., 2006)
• Multiple Endmember Spectral Mixture Analysis (MESMA) was used to model each pixel in the AVIRIS image
• Tested on the 2003 Simi Fire• Each pixel was modeled as a combination of:
– 1 emitted thermal radiance endmember– 1 reflected solar radiance endmember– Shade (zero radiance)
• Emitted thermal radiance endmembers were modeled using MODTRAN– Ranged from 400-1500 K (260°-2240°F) at increments of 10 K
• Reflected solar radiance endmembers were selected from the image using Endmember Average RMSE (EAR)– Six possible endmembers: riparian, dense chaparral, sparse
chaparral/sagescrub, grass, soil and ash
Reflected Solar Radiance Endmembers
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400 900 1400 1900 2400Wavelength (nm)
Rad
ianc
e (W
m2 nm
-1sr
-1) Dense Chap
Sparse ChapRiparianGrassSoilAsh
Dennison et al., 2006
Subset of Emitted Thermal Radiance Endmembers
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400 900 1400 1900 2400Wavelength (nm)
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ianc
e (W
m-2
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Dennison et al., 2006
Example: Mixed Radiance
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400 900 1400 1900 2400Wavelength (nm)
Rad
ianc
e (W
m-2
nm-1
sr-1
) Soil1000KCombined Radiance
Dennison et al., 2006
MODIS Fire Temperature and Area(Eckmann et al., 2008)
• MODIS provides far greater spatial and temporal coverage
• Applied Basic Principles to MODIS data– Utilized a subset of MODIS
bands• Applied to a daytime fire
from Ukraine• “Validated” using ASTER
Pixel Counts (band 9 > 2 Wm-1μm-1sr-1)
MODIS Endmembers
*Modtran Hot EMs500-1500K @ 10K
*Convolved to MODIS bands* 7 MODIS bands used in models
Eckmann et al., 2008
MODIS Endmembers
• Also required background spectra– Systematically sampled from MODIS, screened for fires
• Also required “shade” endmember– The equivalent of atmospheric emission– Generated using Modtran with a cold (10K) background
Eckmann et al., 2008
MODIS Fire Pixels(Eckmann et al., 2008)
19 pixels identified with 0 to 2.55% fireFire temperatures tended to be bimodal, most likely due to solar
contamination. This impacts fire area.
MESMA Compared to FRP
Fire Radiative Power (FRP) is estimated from the MODIS 4 μm bandFRP = 4.34x10-19Wm-2K-8*[(T4)8-(T4b)8]
ASTER fire counts match MESMA area better, although neither isperfect
Eckmann et al., 2008
ASTER Night Time ImageSawmill Fire (15 Sept 2006)
• ASTER has a finite field of view– Thus ASTER fire
counts represent mixtures
• MESMA was applied to ASTER imagery to estimate fire temperature and area
Eckmann et al., in press
ASTER Hot Endmembers
• Generated using Modtran4.3
• Parameterized for– Sept 15, 2006 5:54:21 UTC– Mid-latitude Summer– 5 km visibility– 0.503 cm water vapor– 385 ppm CO2– 37.77 N, 118.39 W 1985 m
Eckmann et al., in press
Fire Temperature and Area from ASTER
• Fire temperatures ranged 500 to 1500K, mostly around 1000K
• Fire sizes were generally small, less than 5%
Eckmann et al., in press
Modeled vs Measured Radiance
• Modeled and measured radiance match well
• Examples are given for 740, 910 and 1330 K with areas of 0.826, 0.313 and 0.0075%
Eckmann et al., in press
Early Fire Detection(Dennison and Roberts, 2009)
• MESMA works but is computationally intensive
• A Normalized Difference Index (NDI) was evaluated as a way of detecting fire emitted radiance
• Optimal bands were identified by developing band combinations that produced the highest accuracy compared to MESMA
• Optimal bands were all located in the SWIR
Kappa for fire detectionsHDFI= (Li-Lj)/(Li+Lj)
i
j
Wavelength Dependence of the HFDI
• Emission sources can be mapped by additional radiance in strong atmospheric absorption bands– HFDI= (L2429-
L2061)/(L2429+L2061)• By rapid location of
emission sources, MESMA can be implemented only where needed
Dennison and Roberts, 2009
Early Detection: Simi
• All combinations of AVIRIS bands were tested as an “NDVI”
• A combination of 2429 and 2061 nm produced the highest detection rates (highest kappa)
Dennison and Roberts, 2009
Early Detection: Indian Fire
• HFDI was compared to three other approaches– CO2 Index (Dennison, 2006)– K Emission Index (767, 770
nm)(Vodacek et al., 2002)– ASTER Fire Detection
• CO2 Index produced numerous false positives
• K Emission Index severely impacted by smoke
• HFDI and ASTER Fire count very similar
Dennison and Roberts, 2009
Summary
• MESMA has shown considerable promise applied to AVIRIS, ASTER and MODIS for estimating fire area and temperature
• New approaches can be developed to improve MESMA performance– HFDI, followed by MESMA applied to targeted pixels– Duel hot temperatures?
• Future potential is good– MESMA applied to Savanna fires from MODIS
• Shows temporal trends in fire behavior consistent with changes in emissions (Eckmann, in prep)
– Joint AVIRIS/MASTER data sets• HyspIRI precursor science
• But there are issues– Lack of validation data sets is a serious problem
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