REMOTE MEASUREMENT OF ENERGY AND CARBON FLUX FROM

855

Ecological Applications, 14(3), 2004, pp. 855–872q 2004 by the Ecological Society of America

REMOTE MEASUREMENT OF ENERGY AND CARBON FLUX FROMWILDFIRES IN BRAZIL

PHILIP J. RIGGAN,1,7 ROBERT G. TISSELL,1 ROBERT N. LOCKWOOD,1 JAMES A. BRASS,2

JOAO ANTONIO RAPOSO PEREIRA,3 HELOISA S. MIRANDA,4 ANTONIO C. MIRANDA,4,8

TERESA CAMPOS,5 AND ROBERT HIGGINS6

1U.S. Forest Service, Pacific Southwest Research Station, Forest Fire Laboratory, 4955 Canyon Crest Drive, Riverside,California 92507 USA

2NASA Ames Research Center, Moffett Field, California 94035 USA3Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renovaveis, Brasılia DF Brasil

4Universidade de Brasılia, Departamento de Ecologia, Brasılia DF Brasil5National Center for Atmospheric Research, Atmospheric Technology Division, Boulder, Colorado 80307 USA

6Simco Electronics, Inc., Moffett Field, California 94035 USA

Abstract. Temperature, intensity, spread, and dimensions of fires burning in tropicalsavanna and slashed tropical forest in central Brazil were measured for the first time byremote sensing with an infrared imaging spectrometer that was designed to accommodatethe high radiances of wildland fires. Furthermore, the first in situ airborne measurementsof sensible heat and carbon fluxes in fire plumes were combined with remote measurementsof flame properties to provide consistent remote-sensing-based estimators of these fluxes.These estimators provide a means to determine rates of fuel consumption and carbonemission to the atmosphere by wildland fires as required for assessments of fire impactson regional air pollution or global emissions of greenhouse gases. Observed fires developedcomplex fire-line geometry and thermal structure, even as average whole-fire temperaturesvaried little. Flame temperatures sometimes exceeded 1600 K along the leading edge ofactively spreading fire lines, yet .90% of the radiant energy from observed fires wasassociated with temperatures of 830–1440 K. Fire in a partially slashed forest encompasseda high-intensity flaming front and a trailing reach of residual combustion extending 400m. Fire fronts in tropical savanna typically formed with little depth and a high proportionof their radiant flux density associated with high temperatures due to low levels of residualcombustion. Measured fires had such low and variable radiance compared with that of ablackbody of comparable temperature as to preclude the use of fire radiance at a singlewavelength as a measure of fire intensity or temperature. One-half of the radiant flux densityfrom a measured savanna fire was associated with values of a combined emissivity–frac-tional-area parameter ,0.091 m2/m2; for a slash fire this fraction was associated with values,0.37 m2/m2. Observations reported here show wildland fires to be so complex and dynamicas to require frequent high-resolution measurements over their course and duration in orderto specify their effects in the environment; an understanding of global fire impacts mayrequire such measurements over a large sample of individual fires.

Key words: carbon flux; Cerrado; extended-dynamic-range imaging spectrometer; fire temper-ature; heat flux; infrared imaging; radiant flux density; remote sensing; slash fire; tropical forest;tropical savanna; wildfire.

INTRODUCTION

Fire science and management today are criticallylimited by an inability to quantitatively measure andtrack the properties of wildland fires at their full scaleand as they occur. Wildfires are by nature shrouded insmoke, difficult and dangerous to approach, sometimesobscured by terrain, and often unpredictable as to lo-cation, velocity of propagation, energetics, and envi-ronmental impact.

Manuscript received 16 May 2002; revised 11 April 2003;accepted 9 June 2003; final version received 18 August 2003.Corresponding Editor: C. A. Wessman.

7 E-mail: [email protected] Deceased.

Knowledge of fire properties is needed at scales fromthe local to the global. Tactical fire suppression requireseither tracking or prediction of fire spread rates, inten-sity, and direction so as to keep personnel and resourcesfrom harm’s way and maximize their effectiveness.Mitigation of the ecological impacts of fire requireseither active monitoring of fire properties or a meansto deduce them from an assessment of the burned area,since the impacts may be substantially affected by fireenergy release rates or intensity. For example, in-creased intensity of burning can effect greater nitrogenvolatilization, nitrification in soil, and nitrogen flux instream water (Dunn and DeBano 1977, Riggan et al.1994), with potential effects on soil productivity andaquatic ecosystems; accelerated soil erosion due to fire-

856 PHILIP J. RIGGAN ET AL. Ecological ApplicationsVol. 14, No. 3

induced water repellency (DeBano et al. 1977, Wells1981); higher postfire flood peaks (Riggan et al. 1994);seed destruction or altered germination and postfire re-covery (Moreno and Oechel 1994); and altered foreststructure from higher rates of canopy consumption ortree mortality (Van Wagner 1973). Avoidance of severeimpacts requires strategic planning and an ecosystemanalysis that specifies the likely response of a wildfireregime to different levels of intervention by prescribedburning or other means of fuel management. At con-tinental to global scales, wildland fires and agriculturalburning are an important source of trace gases andaerosols that pollute the atmosphere and can contributeto global climate change (Crutzen and Andreae 1990).National policy and international protocols to mitigatethese impacts depend on reliable estimates of fire emis-sions including the flux of carbon to the atmosphere.

Here we describe the first applications of remotesensing to the quantitative estimation of fire-line in-tensity and geometry and the sensible heat and carbonfluxes in plumes from large wildland fires, thereby pro-viding a synoptic view of fire behavior and properties.Our approach has been to evaluate bulk flame temper-atures, radiant-energy flux, flaming-front geometry,and rate of areal spread with a specialized, airborne,imaging spectrometer and to estimate carbon and sen-sible-heat fluxes within fire plumes from in situ air-borne measurements of the vertical component of windvelocity, potential temperature, CO2 mixing ratio, andplume geometry. Such measurements were made fortwo fires burning in the Cerrado, which is tropical sa-vanna vegetation, and a large slash fire in tropical forestin central Brazil. A method for estimating plume sen-sible-heat flux from remote sensing measurements ofthe fire line was consistently and successfully appliedto the data from the three fires. Furthermore, we showthat plume carbon flux is linearly and well related tosensible-heat flux across a range of wildland and ag-ricultural fires and conditions, and that plume carbonflux, when combined with estimates of areal rate of firespread, provides useful estimates of fuel consumptionrate. From remote sensing alone, these techniques pro-vide a means to assess a number of important fire prop-erties required for fire-behavior modeling, understand-ing ecological fire effects, and the estimation of globalbiomass combustion rates and fire emissions to the at-mosphere.

METHODS

Measured fires

We observed two freely burning fires in natural Cer-rado vegetation: the Tapera prescribed fire in the lateafternoon of 21 September 1992 at the Reserva Ecol-ogica of the Instituto Brasileiro de Geographia e Es-tatıstica (IBGE; Ecological Reserve of the BrazilianInstitute of Geography and Statistics) in the BrazilianFederal District, as well as a set pasture fire on 15

September 1992 in the Serra do Maranhao, ;65 kmnorth of Brasılia. On 22 September 1992, we also mea-sured an active fire burning in partially slashed tropicalforest near Maraba, Para. The latter fire burned in se-lectively harvested, primary forest.

The Tapera fire burned within a watershed of lowrelief, ranging from 1040 to 1130 m elevation. Uplandvegetation there is comprised of three phases of theCerrado (campo cerrado, campo sujo, and campo lim-po) that are distributed in the order listed from higherto lower elevations. Evergreen shrubs along this plantcommunity gradient comprise a declining proportionof the plant cover in a grassland matrix. Biomass struc-ture in these communities has been described by Ottmaret al. (2001). The fire was ignited by hand-carried driptorches along a trail on the fire’s eastern perimeter andadjacent to a narrow gallery forest on the north (Fig.1). Firing then progressed along the southern firebreak,with ignition keeping apace of the wind-driven fire line.The fire was contained on the west by a narrow burnedstrip and on the south by a cleared firebreak. We maderemote sensing or in situ plume measurements of theTapera fire over ;45 min from first ignition throughthe end of active combustion.

The Serra do Maranhao fire was first observed inprogress at 1622 hours local time. Observations weremade across 80 minutes. The fire burned across ele-vations of ;800–950 m, with grassland uplands, sev-eral phases of Cerrado along some slopes, and galleryforest along stream courses.

The Maraba fire was observed in progress during1310–1317 hours local time, with a well-developedplume and a strong plume-capping cumulus. The firehad been ignited in selectively harvested primary forestwith standing trees and logging slash and in adjacentpasture that had been converted from forest. Localground elevation is ;250 m.

Airborne measurements

Remote sensing and atmospheric measurements weremade from the King Air B200t research aircraft of theNational Center for Atmospheric Research (NationalCenter for Atmospheric Research 1990). The aircraftwas instrumented for fast-response measurement of at-mospheric state variables, CO2 mixing ratio, concen-tration of cloud water droplets and aerosol particles,and components of air velocity in three dimensions(Lenschow and Spyers-Duran 1989). The CO2 mixingratio was measured with a closed-path Licor model6262 CO2 and water analyzer (LI-COR, Lincoln, Ne-braska, USA), with corrections applied for ambienttemperature and pressure. Sample flow rate was ;0.075L/s. The aircraft also carried a unique airborne ex-tended-dynamic-range imaging spectrometer (EDRIS)that had been optimized for the quantitative measure-ment of the high infrared radiances associated withwildfires (Riggan et al. 1993). The EDRIS instrumentis a line-scanning remote imager, which is part of an

June 2004 857REMOTE WILDFIRE MEASUREMENT

FIG. 1. Successive locations of fire lines for the 1992 Tapera fire, as determined by remote sensing with the extended-dynamic-range imaging spectrometer (EDRIS). Lines are color coded by time since first observation (hours : minutes : seconds[h:min:s]) and mapped on Universal Transverse Mercator (UTM) coordinates. Fire locations are shown on a color compositeEDRIS image at wavelengths of 3.9, 0.7, and 1.63 mm (red, green, blue) from 20 August 1994. In this image, areas sparselycovered with grasses appear as light magenta tones. Denser grasses in this rolling terrain appear gray-green, areas with agreater proportion of evergreen shrubs are bright green, and gallery forests appear dark green, as at the top and far left.Parallel light lines at the bottom are cleared firebreaks.

Airborne Infrared Disaster Assessment System devel-oped by NASA Ames Research Center and the U.S.Forest Service.

Fire remote sensing.—The EDRIS produces radi-ance measurements and imagery, digitized to 14 bits,at infrared wavelengths of 1.56–1.69 mm, 3.82–3.97mm, and 11.5–12.2 mm. These wavelengths were cho-sen to allow discrimination of flame properties in pixelsencompassing both flames and hot ash (Riggan et al.1993). Spatial resolution of the imager is ;2.6 m per1000 m of altitude above ground level. The infraredchannels of the spectrometer were calibrated in the lab-oratory over a target with estimated emissivity of 0.95 at1.6 mm and 0.85 at 3.9 mm wavelength and at temper-atures spanning 300–860 K. The maximum temperaturecorresponded to radiances of 347 J·m22·s21·sr21·mm21 ata wavelength of 1.63 mm, 1566 J·m22·s21·sr21·mm21 at 3.9mm, and 154 J·m22·s21·sr21·mm21 at 11.9 mm. Preampli-fiers on the infrared channels were designed with a dual-range response that is linear with high gain at radiancesassociated with typical terrestrial temperatures and lowgain at radiances expected at fire temperatures.

To estimate wildland fire properties by remote sens-ing, we assumed that the radiant emissions of flames,outside of wavelengths with strong molecular absorp-tion, are dominated by the radiation from glowing soot

particles that act as gray-body radiators with high emis-sivity. Such radiation is described by the Planck func-tion with parameters of temperature and emissivity, thelatter of which relates radiance to that of a perfectblackbody radiator. Flames in biomass fires can be op-tically thin so that upwelling radiation encompassesradiation from hot soil beneath the flames as well asfrom the entrained soot particles. For large flames orthose of high soot-particle volume, such as found inaviation fuel fires, upwelling radiation can originatefrom and reflect the temperature of upper flames alone(L. Gritzo, personal communication). Yet even withlong flame lengths, flaming zone turbulence can be sogreat as to dictate that high-temperature flames occupyonly a fraction of a remote-sensing pixel, even for pix-els that fall well within a flaming front. The remaindercan be composed of residual flaming combustion andsmoldering of larger biomass elements, cooling ash,and unburned vegetation. Thus, a parameter repre-senting the product of emissivity and the fractional areaof fire within a pixel must be estimated in order torepresent fire radiance, and any such pixel can encom-pass a variety of targets with differing temperatures.

Estimation of the temperature (T) of a gray-bodyradiator and the product of its emissivity («) and frac-tional area (Af) within a pixel requires measurement of


the emitted energy from at least two wavelengths, l1

and l2 (Riggan et al. 1993, Matson and Dozier 1981).With high spatial resolution in relation to the dimen-sions of the fire front, it may be assumed that the back-ground radiance from vegetation or ash within a pixelis negligible in relation to that from the flames, so thebackground can be ignored (Riggan et al. 2000). Planckfunctions for the apparent flame radiances (B1 and B2)at two wavelengths can then be solved simultaneouslyto yield the following relations:

hcT 5 (1)

5B l hc2 2kl ln exp 2 1 1 11 551 21 2 1 2 6[ ]B l kl T1 1 2

hc5B l exp 2 1i i 1 2[ ]kl Ti

«A 5 (2)f 26 22 3 10 hc

where h is the Planck constant (6.63 3 10234 J·s), cis the speed of light (3.00 3 108 m/s), k is the Boltz-mann constant (1.38 3 10223 J/K), T is specified inKelvin, l is in meters, Bl has units of joules per squaremeter per second per steradian per micrometer(J·m22·s21·sr21·mm21), and radiances are corrected foratmospheric transmittance. Eq. 1 can be solved iter-atively to yield T, and the product «Af can be computedfrom either wavelength via Eq. 2. Note that temper-ature estimation is independent of emissivity and frac-tional area. The wavelength-integrated radiant fluxdensity, Fd (J·m22·s21), which is a measure of fire in-tensity, is given by

4F 5 «A sTd f (3)

where s is the Stefan-Boltzmann constant (5.67 3 1028

J·m22·s21·K24; Liou 1980). We simulated atmospherictransmittance over measured fires with a medium-res-olution spectral model, MODTRAN, using measuredatmospheric water vapor, temperature, and pressure. Nocorrections for smoke aerosols were made, since theseare expected to have little impact on transmittance atthese infrared wavelengths (Riggan et al. 1993), andthe observation geometry here was such that flamingfronts were generally observed to the side of inclinedsmoke plumes.

Areal fire growth.—Multispectral eight-bit imageryof the fires was registered to a common base using theMicroImage software of TerraMar Resources. For theTapera fire, this base consisted of a 1:10 000-scale to-pographic survey of the Reserva Ecologica providedby IBGE. For the Maraba slash fire, we used as a basea prefire Landsat Thematic Mapper scene from 10 Au-gust 1992. For the Serra do Maranhao fire, we useddigital aerial photography collected in August 2000.Geo-referenced locations of the original 14-bit fire ra-diance data were determined by applying transforma-tion equations from the initial registrations to line and

sample numbers in the original data sets. Sizes for eachhigh-temperature pixel were determined from the trans-formation equations by calculating differences in Uni-versal Transverse Mercator (UTM) coordinates be-tween that pixel and offsets of a single line and samplenumber. Areal growth of the fire was estimated by pla-nimeter for areas between the registered images of suc-cessive fire-line observations. Times for successive re-mote-sensing passes were taken from times of closestapproach to the fire, as recorded by the aircraft navi-gation system.

In situ measurement of heat and carbon flux in fireplumes.—Fluxes of sensible heat and CO2 were con-currently estimated in cross sections through upwellingportions of each fire plume. Plume measurement tran-sects during the Tapera and Maraba fires were generallyflown with the ambient wind field; transects throughthe Serra do Maranhao plume were largely perpendic-ular to the ambient wind. We analyzed 25-Hz data forthe vertical component of wind velocity, potential tem-perature, and CO2 mixing ratio to estimate plume sen-sible heat and carbon fluxes. Carbon dioxide data wereoffset in time to account for a 1.76-s lag behind thevertical wind measurements.

Instantaneous fluxes, Fs, at a given height in theplume above ground, were defined as

F [ rw9s9s (4)

where r is the dry-air density, w is the vertical com-ponent of air velocity, s represents the mass mixingratio with respect to dry air for fluxes of substancessuch as water or CO2, and the prime denotes an in-stantaneous deviation from mean ambient values. Heatflux was similarly given as

Q [ r C w9u9s air p (5)

where u is potential temperature of the air, and rair isthe density and Cp is the specific heat of moist air. Weestimated the whole-plume fluxes from the product ofplume cross-sectional area and mean values of andFCO2

Qs from transects within the plume. The mean ambient-air vertical velocity was assumed to be zero, and meanambient-air CO2 mixing ratio and potential temperaturewere taken as the mean from a flight segment imme-diately preceding plume entry. Aircraft sensors esti-mate the flux at the altitude of the aircraft, so transectswere made as low as practicable to approximate thesurface fluxes. This approximation should be adequate,especially for fires with nearly steady rates of spreadand plumes with limited low-level divergence and highvertical velocities. Sampling altitudes above groundlevel were ;180–250 m at the Tapera fire, 1200–1340m at the Serra do Maranhao fire, and 500–1830 m atthe Maraba fire.

Estimates of areal fuel consumption.—For fire com-plexes with short residence times spreading at a nearlysteady state, as in tropical savanna, energy or carbonflux per unit area burned can be estimated for intervals


FIG. 2. Rates of areal spread for the 1992 Tapera fire, ascomputed from fire-line position during successive remote-sensing observations as in Fig. 1. The approximate time atwhich the final fire size was obtained was estimated by ex-trapolation (arrow). The final observation of the fire area wasat 16:30 in the afternoon, local time.

TABLE 1. Progression of radiometric flame temperature withtime during the Tapera fire.

Time since firstobservation

Flame temperature (K)

Mean 1 SD

0:00:000:07:150:22:290:26:050:34:190:38:21

110711221114109711241125

139135142164127184

Note: The first observation was at 15:35:11 local time,where time units are given in terms of hour: minutes: seconds(h:min:s).

of minutes to hours from the ratio of the correspondingwhole-fire rates and the associated areal progression ofthe fire over the interval. That is,

˜dC FC5 (6)dA dA /dt

where dC/dA (in units of kilograms per square meter)is the fuel carbon consumption rate, FC is the instan-taneous whole-plume carbon flux rate (in kilograms persecond), and dA/dt (in square meters per second) is theareal spread rate of the fire. Here we considered thecarbon flux from that of CO2 alone. Areal progressionis readily estimated from the growth of the ash layerfrom successive, geo-referenced images. Estimates ofconsumption rate for fires with residence time longerthan the interval between successive observations, asexpected for fires in slashed forest or organic soils,require integration of a time course of carbon or energyflux over the life of the fire.

Ground-level measurements at the Tapera fire

Air temperatures were measured with unshielded 30AWG chromel/alumel thermocouples (Omega Engi-neering, Stamford, Connecticut, USA) at heights of 1,30, 60, and 160 cm above the soil surface at two lo-cations within the fire area. Campbell CR-213 dataloggers (Campbell Scientific, Logan, Utah, USA) re-corded observations at a frequency of 1 Hz during burn-ing. Consumable fuel in the campo limpo plant com-munity was estimated before burning by clipping, dry-ing, and weighing biomass in 25, 0.25-m2 plots (Dias1994). Ground-level measurements were not possibleat either the Serra do Maranhao fire or Maraba slashfire, since these were observed as targets of opportunityand were not planned research fires.

RESULTS

Tapera fire

The Tapera fire spread with two primary fire linesburning in similar vegetation: one parallel to the am-bient wind and spreading at only 0.1 m/s (the north fireline) and one with portions spreading largely downslope with the wind (the south fire line; Fig. 1). Flameson the north line were observed to lie over the fire lineitself, rather than over unburned fuel in the directionof spread. The south fire line, which accounted for mostof the area burned by the fire, initially consisted ofseveral lobed fronts; these eventually merged into asingle line running diagonally to the mean wind. Spec-ification of linear rates of spread for the south line issomewhat problematic because of its irregular shape.Once established, lobes of the south fire line traveledat 0.3–0.7 m/s in the direction of the mean wind (Fig.1). Areal rates of spread are more quantifiable: For thesouth fire line, these ranged from 65 m2/s during earlyobservations to a peak of 185 m2/s (Fig. 2). Arealspread rates declined as the fire encountered heavierbiomass loading near the watercourse at the westernboundary of the watershed and as the leading edge ofthe fire line reached the project boundary ;34 min afterfirst observation. The Tapera fire ultimately encom-passed 49 ha.

For the Tapera fire, estimates of atmospheric trans-mittance using MODTRAN were 0.97 at a wavelengthof 1.63 mm and 0.95 at 3.9 mm; radiance correctionsfor these values at a remote-sensing altitude of 1 kmabove ground level resulted in a fire temperature cor-rection of only 5 K.

Mean radiometric flame temperatures for the Taperafire as a whole varied little from early to late stages ofthe fire (Table 1), although there were strong temper-ature gradients across and along various portions of theline as they became active (Fig. 3). Flame temperaturesexceeded 1600 K along portions of the leading edgeof actively spreading fire lines. Fire temperatures at theinterior of active lines were commonly in the range900–1200 K. The trailing edge represented reaches ofresidual combustion with mean temperatures ,900 K.There were no consistent differences over time between


FIG. 3. Map of radiometric temperatures for wind-driven segments of fire line at the 1992 Tapera fire: (a) with pixelspacing of ;3.1 m, as remotely sensed from 1050 m above ground; and (b) with scan line spacing of 3.1 m and pixel spacingwithin lines of 0.8 m, as remotely sensed from 200 m above ground. Time after first observation is expressed as h:min:s.Fire spread is toward the (a) southwest and (b) west. The image background is as in Fig. 1.


FIG. 4. Distribution of radiant flux density by temperaturefor the Tapera fire at 16:09:30 (0:34:19 after first observation)and Serra do Maranhao fire at 16:22:15 (0:03:45 after firstobservation). The area of stippling in the figure shows overlapbetween the two histograms. The relatively high proportionof flux density at lower temperatures in the Serra do Maranhaofire reflects the importance there of large areas of residualcombustion, as shown in Fig. 8.

mean temperatures of the narrow north fire line, whichspread laterally to the wind, and the broader south line,which generally spread with the wind.

Ninety percent of the primary fire line’s radiant en-ergy flux at its peak (0:34:19 [h:min:s, i.e., hours :minutes : seconds] after first observation) was associ-ated with temperatures in the range 1004–1315 K (Fig.4). One-half of the radiant flux density occurred attemperatures ,1152 K.

The Tapera fire line was observed from different al-titudes only on successive passes, so no observationswere made in which sampling resolution was not con-founded with time. Nonetheless, there were similar pat-terns and gradients in temperature across the primaryfire line when it was observed from 1084 m altitude(for example, at 0:26:05 after first observation) andfrom 220 m altitude (at 0:38:21 after first observation;Fig. 3). Radiant flux density at temperatures .1150 Kwas equivalent (less than one percent difference) be-tween these two observations, but at the latter timeradiant flux density associated with temperatures,1150 K was approximately twice that from the earliertime.

Mean peak temperature registered by thermocouplesnear the ground surface within the area of the fire was827 K (1 SD 5 118, n 5 6); the greatest value recorded,1061 K, was well within the range of flame tempera-tures estimated by remote sensing.

The emissivity–fractional-area parameter from Eq. 2attained low values overall, even within the interior offire lines where it was generally the greatest. The lowestvalues of this parameter were associated with the high-est recorded temperatures at the leading edge of firelines and with the residual combustion at the trailing

side of fire lines (Fig. 5). At the leading edge this islikely due to heterogeneity in the wind-driven flamefront and the inclusion in the pixel of unburned groundahead of the fire. Ninety percent of the radiant fluxdensity for the rapidly spreading south line at its peakwas associated with values of «Af in the range 0.017–0.26 m2/m2. One-half of the radiant flux density wasassociated with values ,0.091 m2/m2.

There was little residual combustion behind the up-land fire lines of the Tapera fire, and after passage ofthe flaming front the soil surface radiated little energyat the short and intermediate infrared wavelengths mea-sured. Cooled ash and unburned ground showed radi-ances at 1.63 mm that were only one to two percent ofvalues observed in the flaming zone and thus contrib-uted insignificantly to the signal from any pixel en-compassing flaming combustion.

Combustion within the southern line of the Taperafire formed an inclined primary emission plume thatextended through the 1.6-km depth of the atmosphericboundary layer. The slowly propagating northern fireline and nearby residual burning formed a smaller sec-ondary plume near ground level that was not sampled.

Vertical air velocities (wi) within the primary plumewere readily discriminated from those in the ambientwind field; vertical wind sheer as great as 15 m/s inthe plume was measured over a horizontal distance of40 m (Fig. 6). Combined with a strong elevation of theCO2 mixing ratio, which peaked at 802 mL/L, thesevelocities produced a plume carbon flux as great as 2.73 1023 kg·m22·s21, more than three orders of magnitudegreater than local peak values typical of ambient air(Fig. 6). Potential air temperature in the plume at thealtitude sampled was as much as 4 K greater than thatof the ambient air (Fig. 6). This elevation, together withthe positive vertical air velocities, resulted in a strongheat flux signal. Carbon and sensible-heat fluxes werealso horizontally stratified in the lower plume, withhighest rates located on the upwind, eastern side (Fig.7).

Maximum downwind extent of the plume at the al-titude sampled, which we defined by substantial reach-es of carbon flux .5 3 1025 kg·m22·s21, was ;690 m.Plume width, measured as the width of the south lineperpendicular to the mean wind, was 265 m. An in-dependent estimate of 285 m at 250-m altitude wasderived from remote sensing of the plume with con-sideration of plume inclination and image distortionfrom line-of-sight projection of the elevated plume ontothe ground surface. By assuming an elliptical plumecross section parallel to the ground with major axis of690 m and minor axis of 275 m and applying averagemeasured fluxes across this area (as in Fig. 7), we es-timated an instantaneous carbon flux for the entiresouth line of the Tapera fire of 29 kg/s and a sensible-heat flux of 8.7 3 108 J/s (Table 2). Assuming thatcarbon makes up one-half of the consumed biomass,the carbon flux and average areal spread rate (54 m2/



FIG. 6. (a) Measured potential temperature, CO2 mixingratio, and vertical air velocity (wi) along a transect at ;180m altitude above ground within the plume of the Tapera fire.(b) Carbon and heat fluxes are estimated from variables shownin (a). Values on the x-axis indicate time since first obser-vation (h:min:s).

←

FIG. 5. Map of the emissivity–fractional-area parameter for segments of fire line at the 1992 Tapera fire, with distinctionsbetween parts (a) and (b) as in Fig. 3. This parameter obtained generally low values throughout the fire line even at highresolution; thus, fire radiant flux density appears low compared to that of a blackbody at comparable temperature.

s) from the latter period of plume sampling give anaverage fuel consumption estimate for the active southfire line of 1.1 kg/m2.

Serra do Maranhao fire

The Serra do Maranhao fire was first observed wellin progress as a complex of hot flaming fronts in grassesand large reaches of cooler, residual combustion inheavier woody fuels (Fig. 8). It produced a substantialcumulus-capped plume beneath a cover of stratocu-mulus. A wide range in fire activity was observed overthe course of 72 min of observation as fire fronts flared,spread and merged, or remained nearly stationary (Fig.9). The large, persistent reaches of residual combustionwere most remarkable in comparison with other fireswe have observed in the Cerrado region. Discernablelinear spread, at rates of 0.02 m/s perpendicular to thewind and of 0.03 m/s with the wind, was primarily ingrasses where fire lines were narrow, encompassing awidth of one to three pixels at 10-m2 resolution. Arealspread was only 37 m2/s (a total of 16 ha) over theperiod of observation. At last observation, the Serrado Maranhao fire had reached an area of 59 ha.

As with the Tapera fire, the spatially averaged ra-diometric flame temperatures of the Serra do Maranhaofire varied little across 72 min of observation (Table3), even though there were considerable local changesin activity as different fuel types became engaged.Overall, 90% of the fire radiant flux density (for ex-ample, at 0:03:45 after first observation) occurred with-in the temperature range 830–1383 K. One-half of theflux density occurred below a temperature of 1032 K.The greater fraction of overall fire radiance at relativelylow temperatures (Fig. 4), in comparison with the Tap-era fire, apparently resulted from the much greater areaof residual combustion in the Serra do Maranhao fire.

The Serra do Maranhao fire formed primary and sec-ondary plumes (Fig. 10); the primary plume was stableand persistent over the period of sampling. The primaryplume, which was inclined 298 from the vertical,reached through the 4300 m depth of the atmosphericboundary layer to form a capping cumulus that peakedat an altitude of 5100 m. The plume widths at 1280 mabove ground were 690 m crosswind and 790 m withthe wind, which yield an estimated cross-sectional areaof 4.3 3 105 m2. The peak vertical component of airvelocity within the plume was 8.8 m/s. As with theTapera fire, the highest carbon fluxes within the plumewere on the upwind side. Whole-plume carbon flux,estimated from the product of cross-sectional area and

average measured carbon flux for each of the primaryand secondary plumes, was 47 kg/s.

Maraba slash fire

The fire in partially felled tropical forest at Maraba(Fig. 11) was ignited along the northern and upwind,


FIG. 7. Plume carbon flux as mapped from cross-plume airborne measurements of the 1992 Tapera fire. Instantaneousmeasurements are color coded by flux rate and mapped on Universal Transverse Mercator coordinates derived from theaircraft navigation system. Also depicted is the direction of the average ambient wind at 300 m above ground and the positionof the fire line at the beginning of four lengthwise plume transects. The low bound of carbon flux progresses as follows: 223 1025, 0, 2 3 1025, 4 3 1025, 8 3 1025, 16 3 1025, 32 3 1025 kg·m22·s21.

TABLE 2. Comparison of sensible-heat flux (SHF) estimates, as derived from remotely sensedfire properties and from cross-plume airborne measurements.

Measurement or estimate

Cerrado

Tapera fireSerra do

Maranhao fire

Tropical forest

Maraba slash fire

Radiant flux density (J/s) from remote sensing measurementsT . 1100 KAll temperatures

4.1 3 107

5.1 3 1076.4 3 107

1.6 3 1082.8 3 108

2.4 3 109

Modeled from remote sensingSHF (J/s) from fire radiance 8.7 3 108 1.4 3 109 6.4 3 109

Plume measurementsSHF (J/s) 8.7 3 108 1.4 3 109 6.7 3 109

Notes: Radiant flux density is shown for comparison. The proportionality constant (kT; Eq.7 and text immediately following) was determined by setting the remote-sensing-based estimatefor the Tapera fire equal to that from airborne measurements; the resultant model was appliedto remote-sensing data from the Serra do Maranhao and Maraba fires (compare boldface anditalic entries).

eastern margins of the harvested area; most of the ob-served activity resulted from a wind-driven fire front(Fig. 12). The fire involved a wide reach of residualcombustion extending as far as 400 m behind the high-temperature front. This residual combustion apparentlyhad a strong effect on the overall distribution of radiantenergy flux with temperature. Thus, in comparison with

the Tapera fire in Cerrado vegetation, which showedlittle residual combustion and a narrow flaming front,a much greater proportion of the radiant flux densityfrom the slash fire was associated with low tempera-tures than high (Fig. 13). Specifically, 17% of the ra-diant flux density of the slash fire was associated withtemperatures .1075 K; only 17% of that from the Tap-


FIG. 8. Temperature map of a freely burning wildland fire in Cerrado vegetation in the Serra do Maranhao, FederalDistrict, Brazil (1992). Radiometric temperatures are at 0:03:45 after first observation. Fire pixels are color coded bytemperature class and shown on a background derived from an image of reflected red light at 0.65 mm and near-infraredlight at 0.85 mm wavelength that was collected 15 September 2000. Evergreen Cerrado vegetation is shown in light green;dry grassland and bare ground are depicted in magenta tones. Universal Transverse Mercator coordinates are shown. Thefire extends ;1.2 km from west to east. Note the extended regions of relatively cool residual combustion in the west of thefire and the hot, thin fire lines in grasses, for example, at center and in the northeast.

era fire was associated with temperatures below thatpoint. Ninety percent of the radiant flux density fromthe slash fire occurred within the range 857–1166 K.Nonetheless, that fire was marked by a highly energetic,high-temperature spreading front. When first observed,the fire had encompassed 43 ha; it further grew by 5.7ha over the ensuing 256 s.

The plume from the Maraba fire showed strong ver-tical air movement with a peak velocity of 15.4 m/sand a vertical sheer of 20.4 m/s over a distance of 63m. At last observation, the plume was capped by a deepcumulus. The peak value of the CO2 mixing ratio, 589mL/L, was nearly coincident with the maximum verticalair velocity encountered. The resultant maximum in-stantaneous carbon flux was 1.2 3 1023 kg·m22·s21.Potential air temperature in the plume at 526 m aboveground was as much as 2.4 K greater than in the am-bient air. Crosswind width of the plume, as determinedfrom remote sensing of the active fire line, was ;740m; aircraft penetration of the plume yielded a lengthof 1760 m in the direction of the wind. From thesevalues, we estimated an elliptical cross-sectional areafor the inclined plume of 9.3 3 105 m2, an instantaneouswhole-plume carbon flux of 234 kg/s, and sensible-heatflux of 6.7 3 109 J/s.

Flux estimates from remote sensing

We derived estimators of whole-plume sensible-heatflux and carbon flux by relating in situ plume mea-surements to remotely sensed fire properties. As givenin Eq. 5, the heat flux at the top of the combustion zonecan be estimated as the product of the kinematic heatflux, w9u9, and the density and specific heat of the air.Here we parameterized the kinematic heat flux as

]uw9u9 5 2K (7)H ]z

and assumed the scalar KH, the eddy diffusivity (Stull1988), to be proportional to flame temperature, i.e., KH

5 kTT; the potential temperature gradient, ]u/]z, wastaken as proportional to the difference between the tem-perature of flames and that of the overlying ambientair; and flame temperature and spatial dimensions wereestimated by remote sensing. We applied Eqs. 5 and 7,along with these assumptions, to the remotely sensedflame temperatures and emissivity–fractional-area pa-rameters from the south line of the Tapera fire to findthe value of the proportionality constant kT that obtainsa heat-flux estimate equivalent to that derived from insitu plume measurements. The estimate from remote


FIG. 9. Time sequence of radiant flux mapped from a portion of the 1992 Serra do Maranhao fire as in Fig. 8. Times aregiven as h:min:s since first observation at 16:18:30 local time. The distance across the graph is 400 m. Note the changes inenergy output or intensity of the fire as the line at the upper left spreads to the east and as two lines merge at the bottomcenter. The background image is the same as in Fig. 8.

TABLE 3. Progression of mean fire temperature with timeduring the Serra do Maranhao fire.

Time since firstobservation

Flame temperature (K)

Mean 1 SD

0:03:450:14:440:22:151:15:53

1007101110171006

163157149170

Note: The first observation was at 16:18:30 local time,where time units are given in terms of h:min:s.

sensing was limited to regions of intense flaming com-bustion by including in the summation only those pix-els with temperatures .1100 K. A value of kT 5 0.0026resulted.

We tested this model by applying it to remotelysensed temperatures and emissivity–fractional-area pa-rameters of both the Serra do Maranhao and Marabaslash fires. Heat flux estimates from the model, basedon remotely sensed properties alone and the propor-tionality constant derived from the Tapera fire, werenearly equivalent to estimates from in situ plume mea-surements (Table 2). Furthermore, for a series of air-craft transects through active fire plumes, we foundcarbon flux to be well and linearly related to sensible-heat flux (Fig. 14). Thus, we have a provisional yetpromising method for estimating both sensible-heat

flux and carbon flux to the atmosphere based solely onremotely sensed variables. For fire fronts in which flam-ing consumption of fuel within an observed pixel iscomplete within the period of successive observations,


FIG. 10. Map of vertical carbon flux (depicted as in Fig. 7) for the plume of the 1992 Serra do Maranhao fire. Theapproximate locations of the cores of primary and secondary plumes are indicated by circles. The low bound of carbon fluxprogresses as follows: 22 3 1025, 0, 2 3 1025, 4 3 1025, 8 3 1025, 16 3 1025 kg·m22·s21.

combination of the whole-fire carbon flux and arealspread rates as in Eq. 6 provides a useful estimate ofthe fuel consumption rate.

DISCUSSION

Results presented here are based on the first synoptic,quantitative, and high-resolution measurements of theradiances and temperatures associated with wildlandfires. Other multispectral remote-sensing systems, in-cluding the Landsat thematic mapper, the advancedvery-high resolution radiometer (AVHRR), and air-borne MODIS and thematic mapper simulators are crit-ically limited in their ability to make calibrated high-temperature measurements and will commonly saturateover high-temperature targets (Brustet et al. 1991; J.A. Brass, personal communication; A. Setzer, personalcommunication), which is to say that the instrumentsbecome unresponsive to increasing radiance abovesome threshold value.

Systems including the AVHRR, imagers of the geo-stationary operational environmental satellites, and themoderate-resolution imaging spectrometer (MODIS)

have poor resolution in comparison with our airbornemeasurements and are incapable of discriminating anyof the detail of fires depicted here. Furthermore, ourmeasurements of fires in the Cerrado show that averagewhole-fire flame temperatures vary little with time, de-spite large fluctuations in temperature and radiant fluxdensity spatially across fire lines, from one line to an-other, and temporally within specific locations. Thus,coarse-resolution sensors are unlikely to provide muchuseful detail of flame properties based on time trendsin estimated whole-fire temperature, especially whenderived from a single infrared wavelength. In the lattercase, one cannot estimate both the temperature andemissivity–fractional-area parameter, which we ob-served to be highly variable and to generally attainvalues much less than one. Blackbody temperaturesestimated from radiance at a single wavelength, re-gardless of spatial resolution, would be quite low inrelation to that of the fire, and critical information re-garding fire intensity would be lost. Even multispectraldata might be inadequate at resolution equivalent to orcoarser than 100 m, since fire radiance at shortwave-


FIG. 11. Sampled slash fire plume near Maraba, Para, as viewed from the northeast (corresponding to a view from theupper right in Fig. 12). Note the primary tropical forest in the left foreground and the pasture, which had been type convertedfrom tropical forest, on the right. The slashed area contained some standing trees, especially palms.

infrared wavelengths is then confounded with a largesignal from solar radiation reflected from the nonfirebackground. There is large inherent uncertainty as tothe background composition (whether ash or vegeta-tion) within a coarse-resolution fire pixel, and resultingtemperature estimates represent well neither fire norbackground (Riggan et al. 2000).

Our high-resolution measurements in Brazil with theextended-dynamic-range imaging spectrometer showthat spreading wildland fires can develop complex ther-mal environments, even in seemingly simple and rel-atively uniform fuels, such as those of the grassland-dominated Cerrado. The primary fire line of the Taperafire initially assumed a shape with several lobes, pos-sibly due to differences in terrain, fuel, or fire buildupnear the initial line of ignition. These lobes joined toform a continuous line, which was oriented diagonallyto the mean wind, yet the line maintained some historyfrom the earlier configuration with sections, runningmore perpendicular to the wind, that displayed higherline temperatures and energy release rates. The Serrado Maranhao fire, which was first observed well inprogress, also formed a complex of fire lines that waxedand waned with changes of an order of magnitude inradiant flux density or intensity. Of note was a region

of high fire intensity that developed where two fire linesburned together at an acute angle (Fig. 9). Neither theTapera nor Serra do Maranhao fires developed a clas-sical elliptical shape.

The fires described here represented two distinct andcommon classes of fire in Brazil: open burning in thedry Cerrado, and clearing fires in slashed forest. Theywere similar in that each exhibited a gradient of ra-diometric temperatures across active fire lines with thehighest temperatures at the leading edge of those lines.In each fire, there were substantial reaches of fire lineat temperatures in the range 1400–1600 K. A distin-guishing feature among the three fires was in the rel-ative importance of high-temperature flaming combus-tion to the overall radiant flux density. In the Serra doMaranhao fire, large and persistent areas of residualcombustion were predominant, especially at our ear-liest observation when only one-third of the radiantflux density was associated with temperatures .1100K; at the Tapera fire three-quarters of the radiant fluxdensity occurred at such temperatures. Residual com-bustion at the Serra do Maranhao fire appeared to bealigned with more continuous cover of woody Cerradovegetation or gallery forests and was coincident withemission rates of carbon monoxide, methane, and hy-


FIG. 12. The radiometric temperatures of the 1992 fire in partially slashed primary tropical forest near Maraba, Para, at13:10:27 local time. The background of the graphic is a prefire Landsat Thematic Mapper image with band 7 shown in red,band 5 in green, and band 3 in blue. The slash fire (right of center) is associated with a strong fire front and wide reach ofresidual combustion. Note the concurrent burning in pasture (left of center) with cooler fire lines and discontinuous residualcombustion. The most northerly edge of the fire at the top corresponds to the road visible in Fig. 11.

FIG. 13. Comparison of radiant flux density distributionwith temperature for the Tapera fire (0:34:19 after first ob-servation) in Cerrado vegetation and the Maraba slash fire(at 13:10:27). Stippling shows the overlap between the twohistograms. Energy flux in the Maraba fire is dominated bylower-temperature residual combustion, despite the presenceof a highly energetic, high-temperature fire front there.

drocarbons that were large relative to other Cerradofires we have monitored (Riggan et al., unpublishedmanuscript). The Maraba slash fire generated the great-est combustion-zone depth, ;400 m, with only one-

tenth of its radiant flux density associated with tem-peratures .1100 K, even though it was partly com-prised of a very energetic, high-temperature fire line.There, too, the long fire residence time was associatedwith high CO emission rates.

The emissivity–fractional-area parameter attainedsubstantially higher values in the Maraba slash fire thanobserved for the narrow fire lines of the Tapera fire.Although this parameter is expected to be sensitive tothe spatial resolution of remote sensing, increasing assampling scales are reduced in relation to the size andheterogeneity of the flaming front, the large and con-sistent difference between the fires must have been dueto different fire properties, since the Tapera fire, whichhad the lowest values, was viewed at very high reso-lution. Ninety-five percent of the radiant flux densityfrom the narrow lines of the Tapera fire was at valuesof the emissivity–fractional-area parameter ,0.26 m2/m2. In contrast, less than one-third of the radiant fluxdensity from the Maraba slash fire was associated withsuch values. Indeed, some areas there showed valuesof the parameter near 1.0, and approximately four per-cent of the radiance was associated with values .0.8.Such high values are possible only if the associatedhot targets have a very high emissivity, as expected forblack carbon or soot. Thus, we consider that bulk emis-sivity is likely very high for the combined system of


FIG. 14. Relation of carbon flux (FC) to sensible-heat flux(Qs) for a series of aircraft transects through fire plumes inthe Brazilian Federal District and State of Para. Included areobservations of the Tapera fire and Maraba slash fire, alongwith pasture and land-clearing fires observed on 22 Septem-ber 1992. The regression equation is given by FC 5 (3.83 3108)Qs; confidence limits for the regression coefficient aregiven by Pr{3.68 3 108 # b # 3.99 3 108} $ 0.95; R2 50.99.

flames and hot underlying surface, and in regions withlow emissivity–fractional-area, such as throughout theTapera fire, either the instantaneous area of flame with-in flaming zones is small or the flames have a smalloptical depth. The result is that, although the wildlandfire fronts are of high temperature, they are not espe-cially bright in comparison with a classic blackbodyradiator; the Tapera fire, for example, was only one-quarter as bright.

In each of the three fires sampled, plumes extendedat least through the depth of the atmospheric boundarylayer. Each of the fires was roughly comparable in size,ranging within 43–59 ha at last observation, and ourplume sampling was in lower reaches of each plume,at altitudes from approximately one-tenth to one-thirdof the plume height. Sensible heat and carbon fluxesand the radiant flux density at temperatures .1100 Kfrom the Serra do Maranhao fire were each 1.6 timesthose from the Tapera fire; fluxes from the Maraba slashfire were seven to eight times those from the Tapera.Thus, as expected, the slash fire consumed fuel at amuch greater rate than either of the Cerrado fires. Yetthe much greater sensible-heat flux in the Maraba firegenerated a peak vertical air velocity of 15.4 m/s inthe lower plume, which was comparable to the maxi-mum of 14.7 m/s observed low in the plume of theTapera fire. However, the high vertical velocities in theMaraba plume were sustained over a much larger areathan in the Tapera fire plume, and this allowed heatand carbon fluxes that were several-fold greater.

The results reported here are internally consistent.There was good correspondence between the plume-

based and remote sensing-based estimate of fuel con-sumption rate for the Tapera fire (1.1 kg/m2) and themean ground-based estimate of biomass loss duringburning (1.2 kg/m2; Dias 1994). There was also goodcorrespondence between estimated heat and carbonfluxes for the Tapera fire. Specifically, the sum of sen-sible- and radiant-heat fluxes, as estimated from plumetemperature measurements and remote sensing (Table2), was 90% of that estimated from the carbon flux andan assumed heat of combustion of 1.55 3 107 J/kg, assuggested for tropical savanna vegetation by Griffinand Friedel (1984). The maximum near-ground ther-mocouple temperature recorded was in the lower rangeof remotely sensed flame temperatures, but a strict com-parison was not possible because the thermocouple re-sponds to its own energy balance and this must differmarkedly from that of radiating soot particles in flames.

High-temperature regions within observed fire linesoften encompassed several contiguous pixels and wereat or near the leading edge, but not uniquely locatedwith respect to remote sensing scan lines. Thus, theydo not appear to be related to high noise levels ormeasurement artifacts in the remote-sensing signal. Al-though we have no concurrent measurements of a firefrom two altitudes, there is an indication that samplingaltitude did have some effect on estimated fire tem-peratures. Higher altitudes tended to map smaller re-gions of high temperature within fire lines, as mightbe expected if heterogeneous, multiple-temperature re-gions are included in the resultant, larger pixels.

The remote-sensing methodology described hereprovides synoptic measures of fuel consumption, en-ergy release, and rates of spread by active wildlandfires that could be important in fire modeling and un-derstanding fire behavior. Currently operational firemodels including the two-dimensional FARSITE (Fin-ney 1998) are largely based on laboratory-scale ex-periments (Rothermel 1972) with narrow fuel beds andflame lengths on the order of one meter; their appli-cation to fires with high rates of energy release andconditions producing flames many meters in length re-quires a wide and questionable extrapolation. Morecomplex models have been developed to describe trans-port of mass, momentum, and energy in a fire envi-ronment (Linn 1997). These explicitly describe inter-actions of fire with the atmosphere, including fire-gen-erated winds, and provide a means to simulate fire be-havior in nonhomogeneous fuels and terrain andrapidly changing weather. Application and improve-ment of both classes of models requires initiation withrealistic fuel consumption data and validation with spa-tially resolved observations of wildfires under realisticsettings and scales.

Fire remote sensing provides an efficient and prac-tical means to document actual response of wildfiresto applied fuel treatments by contrasting, for example,the rate of spread by a single wildfire and its intensitythrough different age classes in chaparral or managed


and unmanaged forest fuels. Such information is need-ed to explain observed fire ecological effects and instrategic planning to define appropriate levels of fuelmanagement to reduce ecological and societal lossesfrom catastrophic fire.

Our methodology can contribute to estimates of fireemissions, which especially in the tropics might be astrong source of greenhouse gases that are importantin the global radiation balance (Crutzen and Andreae1990). At both local and regional scales, emissions canbe estimated from the time-integrated product of theareal rate of fire occurrence, the biomass consumptionrate per area of land burned, and trace gas or particulateemissions per unit of biomass consumed.

Here, we have shown the efficacy of remote sensingfor estimating the second factor in this product: theareal biomass consumption rate. For the disparateclasses of fires measured here, remote-sensing esti-mates of fire geometry, the emissivity–fractional-areaparameter, and temperature provided a useful and con-sistent estimator of sensible-heat flux from flamingcombustion. Carbon flux was linearly related to sen-sible-heat flux, so carbon flux could be similarly es-timated by remote sensing. Furthermore, remote sens-ing can meet an important requirement for large-scaleemissions estimates, i.e., an ability to efficiently samplea large number of fires over the extant and complexrange of fire conditions, which includes a variety ofecosystem types, fuel loading, and fuel moisture. Intropical ecosystems, this range would necessarily in-clude burning in wetlands, standing tropical forest, pas-ture, and logging slash. In many of these situations,the fuel consumption rate would be difficult to establishby ground-based methods that estimate mass loss dur-ing burning, since fuel loading and consumption canhave an inherently large spatial variance, and ground-based sampling is labor-intensive and limited in scopeand can ignore potentially important fuels by a prioriassumptions about what will be burned under a givenset of conditions. Remote sensing of fuel consumptionby active fires appears to be the most advantageousmeans to make the required large-scale estimates.

CONCLUSION

We have made synoptic, high-resolution measure-ments by airborne remote sensing of radiances and in-tensity of wildland fires in tropical savanna and forestof Brazil and combined these with in situ plume mea-surements to develop estimators for fire energy andcarbon fluxes and fuel consumption. The methodologyprovides a means to understand the ecological and en-vironmental effects of wildland fires, which can de-velop complex thermal environments. Even in rela-tively simple savanna fuels, radiant flux density, whichis a measure of intensity, ranged over an order of mag-nitude. Fire lines showed gradients of temperature withsubstantial reaches .1400 K. A fire in partially slashedtropical forest developed both a high-intensity fire front

and an extensive reach of residual combustion. Thedistribution of radiant flux density with temperatureprovided a whole-fire measure that reflected the relativeimportance to overall energy flux of high-intensityflaming and residual combustion. Observed fire linesattained high temperatures, but generally low values ofa computed emissivity–fractional-area parameter; thus,at short-wave infrared wavelengths, they were not es-pecially bright in comparison with a blackbody model.The methodology is expected to have wide applicationfor understanding and modeling fire behavior, in tac-tical fire operations (especially by showing the relationof fire fighters to areas of critical fire behavior), instrategic planning to manage fire environmental im-pacts, and in understanding the potentially global roleof fire emissions in climate change.

ACKNOWLEDGMENTS

This research has been supported by the Instituto Brasileirodo Meio Ambiente e dos Recursos Naturais Renovaveis; theU.S. Forest Service, International Programs and GlobalChange Research Program; the U.S Agency for InternationalDevelopment, Global Change Program; the USDA ForeignAgricultural Service, Research and Scientific Exchange Di-vision; the NASA Process Studies Program; the National Cen-ter for Atmospheric Research; and the Instituto Brasileiro deGeographia e Estatıstica. The research was made possible bycontributions from James Allen, John Arvesen, Diane Bellis,Edward Hildum, Brad Lobitz, Larry Radke, and Captain JoseRamos. For their personal support, we wish to thank espe-cially Enoch Bell, Braulio F. S. Dias, Iracema Gonzales, He-lena Lucarelli, Eduardo Martins, Valdis Mezainis, WhettenReed, Jeff Sirmon, and Eric Stoner.

Trade names, commercial products, and enterprises arementioned solely for information. No endorsement by theU.S. Government is implied.

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REMOTE MEASUREMENT OF ENERGY AND CARBON FLUX FROM