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

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.


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