Gamma ISP: Reference Manual

unw_model

ANSI-C program: unw_model.c

NAME
unw_model - Phase unwrapping using model of unwrapped phase.

SYNOPSIS
unw_model <interf> <unw_model> <unw> <width> [xinit] [yinit] [ref_ph]

<interf>	(input) complex interferogram
<unw_model>	(input) approximate unwrapped phase model (float)
<unw>	(output) unwrapped phase (float)
<width>	number of samples/row of the interferogram
[xinit]	offset to phase reference location range pixel (col)
[yinit]	offset to phase reference location azimuth pixel (row)
[ref_ph]	reference point phase (radians) (enter - for phase at the reference point ))
[width_model]	number of samples/row of the unwrapped phase model (default: interferogram width)

EXAMPLE
unw_model 01608_02109.flt 01608_02109.unw_model 01608_02109.unw 2456 800 400 0.0

Unwraps the complex valued interferogram assuming that the unwrapped phase is within the interval (-PI,PI) of the provided model. After completion of the unwrapping a phase constant is subtracted from all unwrapped phase values such that the unwrapped phase at the indicated reference location (800,400) will corresponds to the indicated reference phase value (0.0 in the above example).

DESCRIPTION
unw_model unwraps a complex-valued interferogram using a pre-existing unwrapped phase model. For each pixel the unwrapped phase value is set to the value which is within the interval (-PI,PI) of the provided model and which is consistant with the complex valued interferogram in the sense that re-wrapping of the unwrapped interferogram will result in the original interferogram phase value, except for a constant phase offset, originating from setting the unwrapped phase at a reference location to a reference value.

The pre-requisite for the model used is that it deviates from the true unwrapped phase by only a small value. For deviations larger than PI the unwrapped phase will be set on the wrong ambiguity, i.e. it will deviate from the correct unwrapping by a multiple of 2*PI.

Unwrapped phase models can be obtained in different ways:

a) From modeling of the different terms (topographic, deformation, path delay term) of the interferometric phase. It has to be kept in mind, though, that the uncertainty in the path delay or atmospheric distortion term can easily be outside the tolerable interval.

b) By scaling of an independent unwarpped interferogram as done in multi-pass differential interferometry. Again, the uncertainty in the path delay or atmospheric distortion term can be outside the tolerable interval.

c) By an unwrapping result which was obtained using multi-looking followed by interpolation of the unwrapped result to the original resoltion.

d) By an unwrapping result which was obtained using adaptive sampling reduction followed by interpolation of the unwrapped result to the original (full) sampling.

After completion of the model based unwrapping a phase constant can be subtracted from all unwrapped phase values such that the unwrapped phase at the indicated reference location (800,400) will corresponds to the indicated reference phase value (0.0 in the above example). This can be used, for example, in differential interferoemtry to set the deformation phase of a stable reference location to 0.0.

OPTIONS
The user can specify independently the line width of the model phase file. The need for this arises if multi_cpx and multi_real have been used to unwrap a multi-looked version of the interferogram. When working with full frame inteferograms a vialble approach is to unwrap as asingle patch, a multi-looked version of the interferogram. This smaller interferogram is then reexpanded with multi_real and used as a phase model. The expanded phase model may have a slightly different line width because the original interferogram line width is not a multiple of the scaling factor that was used.