DEM Metrics

DEM data is organized by the different Metrics from DEVISE (compound topographic index, heat load index, slope, solar radiation aspect index, topographic position index and topographic relief index) along with different aggregations (max, mean and median) by the Scale groups (e.g. different window sizes where appropriate; 90m, 330m, 510m, 990m, 1,530m). These data were obtained and derived from the SRTM 1 Arc-Second Global DEM. The available data are projected in epsg:5072 coordinate reference system.

Compound Topographic Index (CTI)

Using GRASS GIS 7.4 r.topidx function and a 3x3 window (90m), the steady state wetness index was calculated using ln(a/tan(beta)). Higher numbers would indicate greater potential wetness. Derived from SRTM, 30 m resolution DEM.

Heat Load Index (HLI)

Calculates the McCune & Keon (2002) Heat Load Index in a 3x3 window (90m). Describes A southwest facing slope should have warmer temperatures than a southeast facing slope, even though the amount of solar radiation they receive is equivalent. The McCune and Keon (2002) method accounts for this by "folding" the aspect so that the highest values are southwest and the lowest values are northeast. Additionally, this method account for steepness of slope, which is not addressed in most other aspect rescaling equations. HLI values range from 0 (coolest) to 1 (hottest). Derived from SRTM, 30 m resolution DEM.

Topographic Position Index (TPI)

Calculates topographic position using mean deviations in a 11x11 window (330m). The TPI is calculated by averaging a DEM over a user-specified moving window size and subtracting the original DEM from the averaged version to get the residual. This has the effect of extracting finer-scale landforms from regional-scale relief. Positive TPI values represent ridges or hills, and negative TPI values represent valleys or pits. Derived from SRTM, 30 m resolution DEM.

Topographic Relief Index (TRI)

Calculates the Riley et al (1999) Topographic Release Index in a 3x3 window (90m). The index represents the mean change in elevation between a grid cell and its neighbors, over a user-specified moving window size. Derived from SRTM, 30 m resolution DEM.

Solar Raditaion Aspect Index (TRASP)

Calculates the Roberts and Cooper (1989) Solar-radiation Aspect Index using a circular aspect transformation and a 3x3 window (90m). The metric is defined as: trasp = ( 1 - cos((pi/180)(a-30) ) / 2 where; a = aspect in degrees. The indexed values range between 0 (north ‐northeast) and 1 (south ‐ southwest). Derived from SRTM, 30 m resolution DEM.