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

Field estimation of ash and char colour-lightness using a standard grey scale

David P. Roy A E , Luigi Boschetti B , Stefan W. Maier C and Alistair M. S. Smith D
+ Author Affiliations
- Author Affiliations

A Geographic Information Science Center of Excellence, South Dakota State University, Brookings, SD 57007, USA.

B Department of Geography, University of Maryland, College Park, MD 20740, USA.

C School of Environmental and Life Sciences, Charles Darwin University, Darwin, NT 0909, Australia.

D Department of Forest Resources, University of Idaho, ID 83844, USA.

E Corresponding author. Email:

International Journal of Wildland Fire 19(6) 698-704
Submitted: 18 November 2009  Accepted: 17 April 2010   Published: 17 September 2010


Vegetation fires produce biomass combustion residues, with colour varying from dark black char to white mineral ash. The colour-lightness of char and ash combustion residues is a qualitative parameter describing the post-fire condition of burned areas, and has been correlated with the completeness of combustion, fire intensity, and fire duration. Researchers have suggested that visual comparison of combustion residue samples with a standard grey scale would enable reliable combustion residue colour-lightness estimation. This paper describes an experiment aimed at assessing if colour-lightness can be estimated using a standard grey scale. Fifteen combustion residue samples with colour-lightness ranging from black char to white mineral ash were collected in the Northern Territory, Australia, and visually evaluated by three individuals using a grey scale. The grey-scale scores (0–19) were compared with the mean visible (390 to 830 nm) wavelength combustion residue reflectance (0–1) measured with a portable spectroradiometer. A significant linear relationship between the grey-scale scores and the mean visible combustion residue reflectance was found (R2 = 0.816 with a linear fit, R2 = 0.936 with a logarithmic-transformed fit). This finding suggests that combustion residue colour-lightness can be assessed in the field using inexpensive grey scales, and that this technique is a suitable avenue for future research on the field assessment of fire characteristics and effects.


This work could not have been carried out without the support of WALFA project personnel, West Arnhem Land traditional owners, and the North Australian Indigenous Land and Sea Management Alliance (NAILSMA). This work was partly funded by NASA Earth System Science grant NNG04HZ18C and by NASA Earth Science Applications Feasibility Studies grant NNX09AO12G.


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