Difference curvature (E) is a half-difference of horizontal and vertical curvatures*. The unit of measurement is m-1.
Once elevations are given by , where x and y are plane Cartesian co-ordinates, difference curvature is a function of the partial derivatives of z:
Two mechanisms of flow accumulation, convergence and deceleration, are controlled by horizontal and vertical curvatures, correspondingly. So, difference curvature shows to what extent flow deceleration is higher than flow convergence at the given point of the topographic surface.
Like other local morphometric variables, difference curvature can be derived from a digital elevation model (DEM) by finite-difference methods (e.g., IF-2009 method and IF-1998 method) as well as the universal spectral analytical method.
Example**. A model of difference curvature was derived from a DEM of Mount Ararat by the universal spectral analytical method. The model includes 779,401 points (the matrix 1081 x 721); the grid spacing is 1". To deal with the large dynamic range of this variable, its values were logarithmically transformed. The vertical exaggeration of the 3D model is 2x. The data processing and modelling were carried out using the software Matlab R2008b.
* Shary, P.A., 1995. Land surface in gravity points classification by a complete system of curvatures. Mathematical Geology, 27: 373–390.
** Florinsky, I.V., 2017. An illustrated introduction to general geomorphometry. Progress in Physical Geography, 41: 723–752. doi pdf
For details and other examples, see: