Gamma ISP: Reference Manual

gcp_phase

NAME
gcp_phase - extract unwrapped interferometric phases at Ground Control Points (GCPs).

SYNOPSIS
gcp_phase <unw> <OFF_par> <gcp> <gcp_ph> [win_sz]

<unw>	(input) unwrapped interferometric phase
<OFF_par>	(input) ISP interferogram/offset parameter file
<gcp>	(input) ground control point data (text format)
<gcp_ph>	(output) ground control point data + extracted unwrapped phase (text format)
[win_sz]	window size for averaging phase for each gcp, must be odd (default=5)

EXAMPLE
gcp_phase 1352.unw 1352_1610.off 1352_1610.gcp 1352_1610.gcp_data 5

DESCRIPTION
gcp_phase extracts for the ground control points the corresponding unwrapped interferometric phase and writes it to the GCP data file. The phase should be from the unwrapped interferogram after adding back the topographic phase used to generate the differential interferograms and facilitate unwrapping.

There is the option in base_ls to a add back a phase trend that was subtracted when flattening the interferogram using ph_slope_base however this approach is now rarely used. This is because phase unwrapping is generally performed on a differential interferogram where the phase from a simulated interferogram calculated using phase_sim (in the DIFF/GEO package) , has been subtracted. This phase must be added back using sub_phase (in the DIFF/GEO package).

These unwrapped phase values are used by the program base_ls to estimate the corrections to the baseline. The window size used for the estimation of the unwrapped interferometric phase at the location of the ground control points can be selected (only odd values can be selected), the optimum value is typically 1 or 3 depending on how much smoothing has been performed.

SEE ALSO
typedef_ISP.h, base_ls, ph_slope_base, base_orbit.