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FOR 435/535: Remote Sensing for Fire Management

FOR 435: Remote Sensing for Fire Management

4. Active Fire Behavior

• Thermal Properties of Fires

• Field Measures

• Remote Sensing

The amount of heat per unit area per unit time is called the heat flux or fire intensity. Typically, this value is reported in kW per meter.

FOR 435: Thermal Properties of Fires

The process of combustion has distinct phases beginning with pre-ignition of the fuel followed by dehydration and pyrolysis. These are followed by a transition stage of ignition which leads

Figure from http://learnline.cdu.edu.au/wip/fire2/fundamentals/dynamics.html

transition stage of ignition, which leads to flaming and smoldering combustion followed by extinction.

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Heat transfer is the movement of heat energy. This movement occurs whenever there is a heat difference between media. There are three primary modes of heat transfer conduction, convection and radiation. In fires, we also have latent heats of vaporization and condensation arising from phase changes.

FOR 435: Thermal Properties of Fires

The general form of the energy

Figure from http://eesc.columbia.edu/courses/ees/climate/lectures/atm_phys.html

transfer equation is:Flux = constant * (Final Gradient State –Initial Gradient State)

Conductive Heat Flux = k/L * (Final Temperature – Initial Temperature)

Convective Heat Flux = h * (Final Temperature – Initial Temperature)Radiation Heat Flux =εσ [Object T4 - Background T4]

Conduction: An object transfers its kinetic energy (i.e. Heat) to anotherobject by its molecules hitting the molecules (making them move around) ofthe colder object.

Convection: The kinetic energy of objects are moved from one location to another by physically moving the objects.

Wind

FOR 435: Thermal Properties of Fires

Hayman Fire Interim Report

Heated Burned Surface

Temperature Gradient

Radiation: The transfer of energy via electromagnetic waves (or photons) is the only way the energy can be transferred within a vacuum (i.e. in space between the sun and the Earth).

The Stefan-Boltzman Law provides a measure of the maximum energy emitted:E = εσ T4

FOR 435: Thermal Properties of Fires

E = εσ T4

[σ = 5.67 x 10-8 watts/m2/K4]ε = emissivity, 0 <= ε <= 1, and is the efficiency that surface emits energy when compared to a black body

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FOR 435: Thermal Properties of FiresIn fire remote sensing studies we make the assumption that the energy is apportioned into the conductive, radiative, and convective component at the same proportion regardless of the fuel loading.

Making this assumption allows you to infer convective and conductive (i.e. difficult to measure) components through direct measurement of the radiative energy, which is easy to gy ymeasure.

The validity of this assumption needs further research …

Via this assumption we can infer the fuel consumed through measures of the radiative energy.

If the heat of combustion, H, of fuels is known, then the fuel consumed within a pixel can be calculated by:

FOR 435: Thermal Properties of Fires

In the equation:• H can be calculated via using a bomb calorimeter• FRE is the fire radiative energy released• Fr is the fraction of the total energy release (per unit area) that is apportioned to radiation.

Wooster, M.J., et al. (2005) Retrieval of biomass combustion rates and totals from fire radiative power observations: FRP derivation and calibration relationships between biomass consumption and fire radiative energy release, JGR, 110, D24311, doi:10.1029/2005JD006318,

FOR 435: Thermal Properties of FiresTo get at FRE we use properties of the Stefan-Boltzman Law. In wildland fires, the T4 relationship within the law, ensures that the radiation from the hot fires (>900K) dominates over any cooler background emissions (Kremens et al 2010).

The trick is that we need to calculate the brightness or radiant temperature, T.

We can measure this by either using a full range (UV-TIR: 0.1-50 microns) spectroradiometer OR through using two or more radiometers.

The 2 (or more) detector method allows an estimation of the brightness or radiant temperature (T) via dual band thermometry.

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FOR 435: Thermal Properties of FiresTo get at FRE we use properties of the Stefan-Boltzman Law. In wildland fires, the T4 relationship within the law, ensures that the radiation from the hot fires (>900K) dominates over any cooler background emissions (Kremens et al 2010).

Step 1. Integrate the Stefan-Boltzman equation over the 2 bands

FOR 435: Thermal Properties of FiresTo get at FRE we use properties of the Stefan-Boltzman Law. In wildland fires, the T4 relationship within the law, ensures that the radiation from the hot fires (>900K) dominates over any cooler background emissions (Kremens et al 2010).

Step 2. Calculate the radiant (brightness temperature), T

Step 3. Determine the emissivity. Large hot flames ~0.15, warm soils ~ 0.85 (Kremens et al 2010). Alternatively, the product of eA can be calculated:

)()(

ns

nLWIR

TTCTWA+

=ε

C is a calibration parameter and Ts is the temperature of the sensor.

FOR 435: Thermal Properties of FiresTo get at FRE we use properties of the Stefan-Boltzman Law. In wildland fires, the T4 relationship within the law, ensures that the radiation from the hot fires (>900K) dominates over any cooler background emissions (Kremens et al 2010).

Step 4. FRE is then calculated through the Stefan-Boltzman Law

Af is the fraction of unit area (i.e. of a pixel) occupied by the fire

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FOR 435: Field Measures

Quantifying radiant energy released is also important for evaluating effectiveness of fire shelters (they are designed to reflect 95% of the radiant energy)

The system consists of the following components:

– Various sensor packages – Low cost multi-purpose data

FOR 435: Field Measures

p plogger

– Simple 6.2 m tower to get down looking view and distance from fire

FOR 435: Field Measures

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FOR 435: Remote Sensing Measures - Aerial

-0:00:00- -0:03:18- -0:06:02- -0:08:28- -0:11:14- -0:16:48- -0:19:57- -0:22:56- -0:26:08-

-0:29:02- -0:32:22- -0:35:43- -0:39:13- -0:42:21-

-0:45:56- -0:49:22- -0:52:42- -0:55:56- -1:03:11-

Time Elapsed: –h:mm:ss-

• Example: WASP-LT Tar Hollow DBNF, KY

-1:07:08- -1:10:24- -1:13:33- -1:17:27- -1:21:35-

-1:26:18- -1:30:09- -1:33:55- -1:38:16- -1:42:21-

Data From Kremens:• WASP Arch Rock, OH• Time integral (total energy) of

13 frames• FRE fuel consumption

based on 40 experimental plots

FOR 435: Remote Sensing Measures - Aerial

y = 3.1861x

y = 2.7174x

0

2

4

6

8

10

12

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

FRE

, MJ/

m2

Fuel Consumed, kg/m2

Fuel Consumption vs. Total Radiant Enegy Release (FRE)

VF DataWoosterLinear (VF Data)Linear (Wooster)

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FOR 435: Remote Sensing Measures - Aerial

FOR 435: Remote Sensing Measures - Aerial

MIR channel TIR channelMSG SEVIRI

FOR 435: Remote Sensing Measures - Satellite

MIR-TIR Fire Map

15 mins imaging frequency

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MODIS BIR3.9 μm channel images

MODIS andBIRD FRP data in

Boreal Forest

FRP dataMODIS BIRD‘false alarms’

Zhukov, B., et al. (2005) Spaceborne detection and characterization of fires during the Bi-spectral Infrared Detection (BIRD) experimental small satellite mission (2001-2004) Remote Sensing of Environment, 100, 29-51

FOR 435: Remote Sensing Measures - Satellite

0 3 6 9 11Day of Burn

FOR 435: Remote Sensing Measures - Satellite

Roberts, G., et al. (2005) Retrieval of biomass combustion rates and totals from fire radiative power observations: Application to southern Africa using geostationary SEVIRI Imagery, JGR, 110, D21111, doi: 10.1029/2005JD006018

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BiomassCombusted

= 3.2 million tonnes (1.5 Mtonnes C)(4.3-5.1 million tonnes adj. for cloud)

ect

FOR 435: Remote Sensing Measures - Satellite

Roberts, G., et al. (2005) Retrieval of biomass combustion rates and totals from fire radiative power observations: Application to southern Africa using geostationary SEVIRI Imagery, JGR, 110, D21111, doi: 10.1029/2005JD006018

Clo

ud e

ffe

Head and Backing Grassland Fires

FOR 435: Remote Sensing Measures - Satellite

Smith AMS, Wooster MJ (2005) Remote classification of head and backfire types from MODIS fire radiative power observations. International Journal of Wildland Fire 14, 249-254.

Field

FOR 435: Remote Sensing Measures - Satellite

Image

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Crown and Surface Boreal Forest Fires

FOR 435: Remote Sensing Measures - Satellite

Wooster M.J, Zhang YH (2004) Boreal forest fires burn less intensely in Russia than in North America. Geophysical Research Letters 31, L20505. doi:10.1029/2004GL020805

“Byram’s Fire Intensity equation contains about as much informationabout a fire’s behavior as can be crammed into one number.”

Van Wagner (1977)