Gamma DIFF&GEO: Reference Manual

dispmap_vec2

NAME
dispmap_vec2 - Calculation of displacement vector field from 2 measured components (asc./desc.).

SYNOPSIS
dispmap_vec2 <DEM_par> <DEM> <dispmap1> <lv_theta1> <lv_phi1> <dispmap2> <lv_theta2> <lv_phi2> <dv_norm> [dv_theta] [dv_phi] [dv_x] [dv_y] [dv_z] [mode] [ax_north] [ax_east]

<DEM_par>	(input) DEM/MAP parameter file
<DEM>	(input) DEM data file (or constant height value)
<dispmap1>	(input) 1. displacement observation (along look-vector 1) (file of float)
<lv_theta1>	(input) look-vector 1 elevation angle (file of float or constant value in deg.)
<lv_phi1>	(input) look-vector 1 orientation angle (file of float or constant value in deg.)
<dispmap2>	(input) 2. displacement observation (along look-vector 1) (file of float)
<lv_theta2>	(input) look-vector 2 elevation angle (file of float or constant value in deg.)
<lv_phi2>	(input) look-vector 2 orientation angle (file of float or constant value in deg.)
<dv_norm>	(output) norm of 3-dim displacement vector (file of float)
[dv_theta]	(output) elevation angle of 3-dim displacement vector (file of float)
[dv_phi]	(output) orientation angle of 3-dim displacement vector (file of float)
[dv_x]	(output) easting component of 3-dim displacement vector (file of float)
[dv_y]	(output) northing component of 3-dim displacement vector (file of float)
[dv_z]	(output) vertical component of 3-dim displacement vector (file of float)
[mask_angle]	cutoff angle in degrees between the look and normal vectors to mask inaccurate areas (default=2)
[mode]	displacement model mode 0: displacement along terrain surface (default) 1: displacement towards center axis
[ax_north]	displacement center axis northing/latitude
[ax_east]	displacement center axis easting/longitude

EXAMPLE
dispmap_vec2 aoi.dem_par aoi.dem aoi.disp1 aoi.lv_theta1 aoi.lv_phi1 aoi.disp2 aoi.lv_theta2 aoi.lv_phi2 aoi.disp_norm aoi.disp_theta aoi.disp_phi

Calculates the 3D displacement field based on the 2 indicated DINSAR based line-of-sight displacement component (from ascending and descending orbits) and the assumption that the displacement is along the terrain surface. The output displacement field is expressed through the norm, the elevation angle (theta) and the orientation angle (phi).

dispmap_vec2 aoi.dem_par aoi.dem aoi.disp1 aoi.lv_theta1 aoi.lv_phi1 aoi.disp2 aoi.lv_theta2 aoi.lv_phi2 aoi.disp_norm - - aoi.disp_x aoi.disp_y aoi.disp_z 2 1 186050 2465870

Calculates the 3D displacement field based on the 2 indicated DINSAR based line-of-sight displacement component (from ascending and descending orbits) and the assumption that the displacement is towards a vertical axis located at the coordinate (186050 2465870). The output displacement field is expressed through the easting (x), northing (y) and vertical (z) components.

DESCRIPTION
dispmap_vec2 calculates the displacement vector field based on two indicated DINSAR based components and an additional assumption on the displacement direction field.

The two indicated DINSAR based components correspond typically to an ascending and a descending orbit based result, so that the directions of the two observed compontents differ significantly. The use of two indipendent observations (two interferograms) acquired in the same satellite track is not adequate.

Based on the two motion components observed with interferometry the 3D motion vector field cannot be determined, an additional constraint is required. Two such additional constraints are supported by the program. The first one is thast the motion shall be in the terrain surface plain. This constraint seems adequate in the case of glacier motion. The second constraint is that the motion vector points towards a central axis. This is an adequate assumption for concentric deformation pattern as may occur under certain circumstances in the case of subsidence and for volcanic deformation.

The dimensions of the image files and the map projection which is the reference are defined in the DEM/map parameter file. The DEM is required for the caluclation of the terrain surface plain.

Differential interferometry permits to estimate the deformation component in the SAR look direction. This DINSAR based information is specified through the displacement component in the look direction and the direction angles (elevation theta and orientation phi) in the map geometry. The look vector direction angles can be determined using the program look_vector. DINSAR based information needs to be provided for two observations in different directions, typically corresponding to ascending and descending track acquisitions.

Apart from the two components (and related directions) provided the additional condition constraints one more dimension, permitting to calculate the 3D motioin field.

The output displacement vector is available as displacement norm, elevation and orientation angles, or as easting (x), northing (y) and vertical (up) components, stored in separate binary files (float).

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 radian.

Warning: the interferometric observation is only sensitive to motion in the SAR look vector directions. For other directions the sensitivity is reduced which will lead to higher errors. The ascending and descending components may be far from perpendicular to each other. In the case of ERS, for example, both observation directions will be at quite steep angles (about 23 deg. from the normal). As a result horizontal motion in East-West direction is measured at much more accurate than North-South motion.