Document


Title

Seasonal and topographic effects on estimating fire severity from Landsat TM/ETM+ data
Document Type: Journal Article
Author(s): D. L. Verbyla; E. S. Kasischke; E. E. Hoy
Publication Year: 2008

Cataloging Information

Keyword(s):
  • black spruce
  • boreal forest
  • boreal forests
  • coniferous forests
  • elevation
  • fire case histories
  • fire intensity
  • fire management
  • fire severity
  • forest management
  • Landsat
  • Normalized Burn Ratio
  • phenology
  • Picea mariana
  • radiation
  • remote sensing
  • solar elevation
  • topography
  • topography
Topic(s):
Record Maintained By:
Record Last Modified: June 1, 2018
FRAMES Record Number: 47108
Tall Timbers Record Number: 22991
TTRS Location Status: In-file
TTRS Call Number: Journals-I
TTRS Abstract Status: Okay, Fair use, Reproduced by permission

This bibliographic record was either created or modified by the Tall Timbers Research Station and Land Conservancy and is provided without charge to promote research and education in Fire Ecology. The E.V. Komarek Fire Ecology Database is the intellectual property of the Tall Timbers Research Station and Land Conservancy.

Description

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. © IAWF 2008. Reproduced from the International Journal of Wildland Fire (David L. Verbyla, Eric S. Kasischke and Elizabeth E. Hoy, 2008) with the kind permission of CSIRO PUBLISHING on behalf of the International Association of Wildland Fire.

Online Link(s):
Citation:
Verbyla, D. L., E. S. Kasischke, and E. E. Hoy. 2008. Seasonal and topographic effects on estimating fire severity from Landsat TM/ETM+ data. International Journal of Wildland Fire, v. 17, no. 4, p. 527-534. 10.1071/.