Table 1 Definitions for the shape and topographic indices used to characterize unburned islands within fires in the Inland Pacific Northwest from 1984 to 2014. pij = perimeter (m) of patch ij. aij = area (m2) of patch ij. TPI and TRI were calculated with a seven by seven focal window (90 m in each direction). Aspect is azimuth in degrees
From: Characterizing persistent unburned islands within the Inland Northwest USA
Index | Abbreviation | Formula | Notes | Reference |
|---|---|---|---|---|
Fractal Dimension Index | FRAC | \( \frac{2\ln \left(0.25\ {p}_{\mathrm{ij}}\right)}{\ln \left({a}_{\mathrm{ij}}\right)} \) | Shape complexity, from less complex to more complex | McGarigal and Marks 1995 |
Topographic Position Index | TPI | Difference between the value of a cell and the mean elevation of the surrounding cells | Weiss 2001 | |
Topographic Wetness Index | TWI | \( \ln \frac{upslope\ drainage}{\tan (slope)} \) | Measure of hydrologic pooling potential | Beven and Kirkby 1979 |
Terrain Ruggedness Index | TRI | Mean of the absolute differences between the elevation of a cell and the elevation of the surrounding cells | Riley et al. 1999 | |
Slope | Slope | Slope in degrees | Steepness | Â |
Cosine of the aspect | CosAsp | cos(Aspect) | Gradient from north to south aspects | Â |
Transformed aspect | TRASP | \( \frac{-\cos \left( Aspect-30\right)+1}{2} \) | Gradient from northeastern to southwestern aspects | Roberts and Cooper 1989 |