en ru 
Topographic
index (TI)* takes into account both a local slope geometry and site location
in the landscape combining data on slope gradient and catchment area: , where
CA and G are catchment area and slope gradient, respectively. Topographic
index is a measure of the extent of flow accumulation at the given point of
the topographic surface. As catchment area increases and slope gradient
decreases, topographic index increases. Like other combined morphometric
variables, topographic index can be derived from a digital elevation model (DEM)
by the sequential application of methods for local and nonlocal morphometric characteristics,
followed by an arithmetic combination of the results of these calculations. Example**. A model of topographic index was derived from a DEM of Mount Ararat. CA was
calculated by the Martz–de Jong method adapted to spheroidal equal angular grids; G was calculated by the universal spectral
analytical method. The
model includes 779,401 points
(the matrix 1081 x 721); the grid spacing is 1". The vertical
exaggeration of the 3D model is 2x. The data processing and modelling were carried out using the software Matlab R2008b and LandLord 4.0. References
* Beven,
K.J., and Kirkby, M.J., 1979. A physicallybased variable contributing area
model of basin hydrology. Hydrological Science, 24, 4369.
**^{ }Florinsky,
I.V., 2016. An illustrated introduction to geomorphometry. Almamac Space
and Time, 11 (1): 20 p. (in Russian, with English abstract). Article
at the journal website
For
details and other examples, see:
