Gamma DIFF&GEO: Reference Manual

dem_gradient

NAME
dem_gradient - Calculate elevation and orientation angles of the DEM normal or gradient vector magnitude

SYNOPSIS
dem_gradient <DEM/MAP_par> <DEM> <theta> <phi> <mag> [mode]

<DEM/MAP_par>	(input) DEM/MAP parameter file
<DEM>	(input) DEM data file (or constant height value)
<theta>	(output) elevation angle of DEM normal/gradient vector (float)
<phi>	(output) orientation angle of DEM normal/gradient vector (float)
<mag>	(output) magnitude of the gradient vector (float)
[mode]	normal/gradient vector selection mode (default=1: gradient vector, 0: normal vector

EXAMPLE
dem_gradient aoi.dem_par aoi.dem aoi.grad_theta aoi.grad_phi aoi_grad_mag 1

Calculate the DEM gradient vector elevation (theta) angle, orientation (phi) angle, and DEM gradient magnitude (in map geometry) .

dem_gradient aoi.dem_par aoi.dem aoi.norm_theta aoi.norm_phi aoi_grad_mag 0

Calculates the DEM normal vector elevation (theta) angle, orientation (phi) angle, and dem gradient magnitude.

DESCRIPTION
dem_gradient calculates the terrain height normal or gradient vector direction in map geometry. The magnitude of the DEM gradient is also calculated

Based on the DEM geometry the terrain height normal or gradient vector is calculated for each pixel of the DEM/map section specified in the DEM parameter file. The gradient direction vector is expressed in the local map coordinates through the elevation angle and the orientation angle, both calculated at each map pixel. The magnitude of the gradient vector is also calculated

The map projection is defined in the DEM/map prameter file.

The output direction (surface normal or gradient) vector elevation and orientation angles and DEM gradient magnitude are stored in separate binary files (float). The surface gradient vector is defined as the projection of the surface normal on the srface plane which corresponds to the local direction of steepest descent. In displacement mapping applicaions motion along this direction is an often used assumption (e.g. landslides, glaciers). The elevation angle is defined as the angle between the horizontal surface and the look vector with positive angles indicating sensor positions above the surface. The orientation angle is defined as the angle between the East direction and the projection of the look vector on the horizontal surface plan. The orientation angle increases towards north, with the North direction corresponding to PI/2 (and south to -PI/2). Both angles are expresed in radians.

An important use of DEM gradient expressed in map geometry is the interpretation of surface deformation - the DINSAR approach provides the deformation component in the look vector direction.

The look vector information as provided by the program dem_gradient and the (assumed) deformation direction fields as calculated by dem_gradient are used to calculate the 3D displacement fields from differential interferometric observations as supporrted by the program dispmap_vec.