International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

Seasonal and topographic effects on estimating fire severity from Landsat TM/ETM+ data

David L. Verbyla A C , Eric S. Kasischke B and Elizabeth E. Hoy B

A Department of Forest Sciences, University of Alaska, Fairbanks, AK 99775, USA.

B Department of Geography, University of Maryland, 2181 LeFrak Hall, College Park, MD 20742, USA.

C Corresponding author. Email: d.verbyla@uaf.edu

International Journal of Wildland Fire 17(4) 527-534 http://dx.doi.org/10.1071/WF08038
Submitted: 4 March 2008  Accepted: 16 June 2008   Published: 6 August 2008

Abstract

The maximum solar elevation is typically less than 50 degrees in the Alaskan boreal region and solar elevation varies substantially during the growing season. Because of the relatively low solar elevation at boreal latitudes, the effect of topography on spectral reflectance can influence fire severity indices derived from remotely sensed data. We used Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM) data to test the effect of changing solar elevation and topography on the Normalized Burn Ratio (NBR) and the differenced Normalized Burn Ratio (dNBR). When a time series of unburned pixels from black spruce forests was examined, we found that NBR values consistently decreased from June through September. At the stand level, dNBR-derived values from similar unburned and burned black spruce stands were substantially higher from September imagery relative to July or August imagery. Within the Boundary burn, we found mean post-fire NBR to consistently vary owing to topographic control of potential solar radiation. To minimise spectral response due to topographic control of vegetation and fire severity, we computed a dNBR using images from August and September immediately after a June–July wildfire. There was a negative bias in remotely sensed fire severity estimates as potential solar radiation decreased owing to topography. Thus fire severity would be underestimated for stands in valley bottoms dominated by topographic shading or on steep north-facing slopes oriented away from incoming solar radiation. This is especially important because highly flammable black spruce stands typically occur on such sites. We demonstrate the effect of changing pre- and post-fire image dates on fire severity estimates by using a fixed NBR threshold defining ‘high severity’. The actual fire severity was constant, but owing to changes in phenology and solar elevation, ‘high severity’ pixels within a burn ranged from 56 to 76%. Because spectral reflectance values vary substantially as solar elevation and plant phenology change, the use of reflectance-based indices to assess trends in burn severity across regions or years may be especially difficult in high-latitude areas such as the Alaskan boreal forest.

Additional keywords: boreal forest, fire severity, Normalized Burn Ratio, solar elevation, topography.


References

Bobbe T, Finco MV, Quayle B, Lannon K, Sohlberg R, Parsons A (2001) Field measurements for the training and validation of burn severity maps from spaceborne, remotely sensed imagery. USDA Forest Service, Remote Sensing Application Center, Joint Fire Science Report 2001–2. (Salt Lake City, UT)

Chander GMarkham B2003Revised Landsat-5 TM radiometric calibration procedures and post-calibration dynamic ranges.IEEE Transactions on Geoscience and Remote Sensing4126742677doi:10.1109/TGRS.2003.818464

Civco DL1989Topographic normalization of Landsat Thematic Mapper digital imagery.Photogrammetric Engineering and Remote Sensing5513031309

Ekstrand S1996Landsat-TM based forest damage assessment: correction for topographic effects.Photogrammetric Engineering and Remote Sensing62151161


Epting JVerbyla DSorbel B2005Evaluation of remotely sensed indices for assessing burn severity in interior Alaska using Landsat TM and ETM+.Remote Sensing of Environment96328339
doi:10.1016/J.RSE.2005.03.002

Fu PRich PM2002A geometric solar radiation model with applications in agriculture and forestry.Computers and Electronics in Agriculture372535doi:10.1016/S0168-1699(02)00115-1

Holben BJustice C1981An examination of spectral band ratioing to reduce the topographic effect on remotely sensed data.International Journal of Remote Sensing2115133doi:10.1080/01431168108948349

Howard SMLacasse JM2004An evaluation of gap-filled Landsat SLC-Off imagery for wildland fire burn severity mapping.Photogrammetric Engineering and Remote Sensing70877880

Hoy EEFrench NHFTuretsky MRTrigg SNKasischke ES2008Evaluating the potential of Landsat TM/ETM+ imagery for assessing fire severity in Alaskan black spruce forests.International Journal of Wildland Fire17500514
doi:10.1071/WF08107

Isaev ASKorovin GNBartalev SAErshov DVJanetos AKasischke ESShugart HHFrench NHOrlick BEMurphy TL2002Using remote sensing to assess Russian forest fire carbon emissions.Climatic Change55235249doi:10.1023/A:1020221123884

Kane ESKasischke ESValentine DWTuretsky MRMcGuire AD2007Topographic influences on wildfire consumption of soil organic carbon in black spruce forests of interior Alaska: implications for black carbon accumulation.Journal of Geophysical Research112G03017doi:10.1029/2007JG000458

Kasischke ESFrench NHF1997Constraints on using AVHRR composite index imagery to study patterns of vegetation cover in boreal forests.International Journal of Remote Sensing1824032426doi:10.1080/014311697217684

Kasischke ESTuretsky MROttmar RDFrench NHFHoy EEKane ES2008Evaluation of the composite burn index for assessing fire severity in Alaskan black spruce forests.International Journal of Wildland Fire17515526doi:10.1071/WF08002

Key CH, Benson NC (2006) Landscape assessment: ground measure of severity, the Composite Burn Index, and remote sensing of severity, the Normalized Burn Index. In ‘FIREMON: Fire Effects Monitoring and Inventory System’. (Eds DC Lutes, RE Keane, JF Caratti, CH Key, NC Benson, S Sutherland, LJ Gangi) USDA Forest Service, Rocky Mountain Research Station, General Technical Report RMRS-GTR-164-CD: LA1–51. (Ogden, UT)

Kotliar NB, Haire SL, Key CH (2003) Lessons from the fires of 2000: post-fire heterogeneity in Ponderosa pine forests. In ‘Fire, Fuel Treatments, and Ecological Restoration: Conference Proceedings’, 16–18 April 2002, Fort Collins, CO. (Tech. Eds PN Omi, LA Joyce) USDA Forest Service, Rocky Mountain Research Station, Proceedings RMRS-P-29, pp. 277–280. (Fort Collins, CO)

Landmann T2003Charcterizing sub-pixel Landsat ETM+ fire severity on experimental fires in the Kruger National Park, South Africa.South African Journal of Science99357360

Miller JDThode AE2007Quantifying burn severity in a heterogeneous landscape with a relative version of the delta Normalized Burn Ratio (dNBR).Remote Sensing of Environment1096680
doi:10.1016/J.RSE.2006.12.006

NASA Goddard Space Flight Center (2003) ‘Landsat 7 Science Data Users Handbook.’ (Landsat Project Science Office: Greenbelt, MD) Accessed at http://landsathandbook.gsfc.nasa.gov/handbook.html [Verified 23 July 2008]

Patterson MWYool SR1998Mapping fire-induced vegetation mortality using Landsat Thematic Mapper data: a comparison of linear transformation techniques.Remote Sensing of Environment65132142doi:10.1016/S0034-4257(98)00018-2

Riano DChuvieco ESalas JAguado I2003Assessment of different topographic corrections in Landsat-TM data for mapping vegetation types.IEEE Transactions on Geoscience and Remote Sensing4110561061doi:10.1109/TGRS.2003.811693

Roy DPBoschetti LTrigg SN2006Remote sensing of fire severity: assessing the performance of the Normalized Burn Ratio.IEEE Geoscience and Remote Sensing Letters3112116doi:10.1109/LGRS.2005.858485

Short NM (1982) ‘The Landsat Tutorial Workbook: Basics of Satellite Remote Sensing.’ (NASA Scientific and Technical Information Branch: Washington, DC)

Trigg SFlasse S2000Characterizing the spectral-temporal response of burned savannah using in situ spectroradiometry and infrared thermometry.International Journal of Remote Sensing21(16)31613168doi:10.1080/01431160050145045

van Wagtendonk JWRoot RRKey C2004Comparison of AVIRIS and Landsat ETM+ detection capabilities for burn severity.Remote Sensing of Environment92397408doi:10.1016/J.RSE.2003.12.015

White JDRyan KKey CCRunning SW1996Remote sensing of forest fire severity and vegetation recovery.International Journal of Wildland Fire6125136doi:10.1071/WF9960125



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