GAMMA Interferometric Point Target Analysis Software (IPTA): Reference Manual

mcf_pt

ANSI-C program: mcf_pt.c

NAME
mcf_pt - Minimum Cost Flow phase unwrapping for point data stack (single record or all records)

SYNOPSIS
mcf_pt <plist> <pmask> <pint> <rec_num> <pwgt> <mask> <punw> [rps] [azps] [np_ref] [phref_flag] <rlks> <azlks>

<plist>	(input) point list (int)
<pmask>	(input) point data stack of mask values (uchar, set to - to accept all points)
<pint>	(input) point data stack of interferograms (fcomplex)
<rec_num>	record number to process (default -: all records)
<pwgt>	(input) point data stack of weight factors (float, value range 0 -> 1.0, enter - for uniform weight)
<mask>	(input) validity mask (SUN raster or BMP format, value 0 -> pixel not used, enter - for no mask)
<punw>	(output) point data stack of unwrapped phases (float)
[rps]	range pixel spacing (default= 1.0)
[azps]	azimuth pixel spacing (default = 1.0)
[np_ref]	phase reference point number (beginning from 0, default=0)
[phref_flag]	flag to set phase value at phase reference point 0: use initial value (default) 1: set phase to 0.0 at initial point)
<rlks>	mask file range looks relative to the point SLC coordinates, required if mask specified
<azlks>	mask file azimuth looks relative to the point SLC coordinates, required if mask specified

EXAMPLE
mcf_pt pt pmask3 pdiff4_sm 3 - diff4_sm_unw_mask.ras pdiff4_sm_unw 20 20 125677 1 1 5

Conducts MCF phase unwrapping for record 3 of the input stack of interferograms. Point masks (pmask3), and a mask in raster format (diff4_sm_unw_mask.ras) are considered. Uniform weights are used. The distances used in the cost calculations consider the indicated range and azimuth spacings. Point 125677 is used as reference and the phase at this reference point is the initial value is set to 0.0. The mask raster file has 1 range look and 5 azimuth looks relative to the SLC coordinates

mcf_pt pt pmask3 pdiff4_sm - - - pdiff4_sm_unw 20 20 125677 1

Conducts MCF phase unwrapping for all records of the input stack of interferograms. Point masks (pmask3) alone determines which points are considered. Uniform weights are used. The distances used in the cost calculations consider the indicated range and azimuth spacings. Point 125677 is used as reference and the phase at this reference point is the initial value is set to 0.0.

DESCRIPTION
mcf_pt conducts Minimum Cost flow (MCF) phase unwrapping for interferograms in point data format. This can be done for a single record of the stack of interferograms or all records.

The coordinates of the points considered are defined in the point list. The optional mask file (in point data format) indicates for each point if it is valid (1, i.e. considered) or not valid (0, excluded). In addition, a mask can be provided in 2-D raster format. Points in areas of 0 value are excluded.

The input interferograms are provided as a point data stack. This stack is of fcomplex type. The type of the output stack of unwrapped interferograms is of float format.

Unwrapped phases are calculated for each valid point of the point list. Valid points are points with a non-zero input interferogram value, a non-zero point mask value (if provided), and a non-zero raster mask value (if provided).

The unwrapping is conducted for the valid points of a single record. Delaunay triangulation is used to generate an optimized irregular triangular network of the points to be unwrapped.

The minimum cost flow (MCF) algorithm is used to minimize the total cost associated with phase discontinuities in the scene associated with noise, and layover. The user supplies weights (usually related to the spatial coherence) used to calculate where discontinuities (i.e. network flow) are preferred. Regions of low weight have low costs for phase jumps whereas areas of high cost tend to exclude such discontinuies in the unwrapped phase.

Each triangle is a node in the network. If integration of the phase around a triangle indicates a a positive phase disconituity (residue) then the node is marked as contributing flow to the network. A negative phase discontinuity at a node is marked as accepting flow from the network. The cost of flow in an arc connecting adjacent nodes is derived from the weight factors provided. In full 2-D interferograms typically, the interferometric correlation is used as weight file. For isolated points this maz not be an appropriate measure. The weight may also be set to a uniform factor.

The MCF algorithm solves for the flow in the arcs that minimizes the net cost. The implemented MCF solution is based on the successive shortest path (SSP) method.

The unwrapped phases are written to the output point data stack of unwrapped phases at the indicated record number.

If a new output stack name is indicated the stack is created. Indicating a record number larger than the highest record number of the indicated stack results in an increase of the stack size.

An alternative to the "spatial" unwrapping supported by mcf_pt is the unwrapping through the baseline-time-regression analysis as supported by def_mod_pt and multi_def_pt. The advantage of mcf_pt is that it is also feasible for small number of interferometric pairs. For very large stacks def_mod_pt and multi_def_pt are preferred.

The reliability of mcf_pt is improved if differential interferograms are unwrapped. The better the model subtracted the more robust the unwrapping. In the case that the interferogram is within PI/2 of the simulated phase (model) another alternative for the unwrapping is unw_model_pt.

To display the complex or real valued input or output interferograms contained in the point data stack the programs pt2data or pt2d can be used to convert the point data to raster data format which can then be displayed using conventional display programs.

SEE ALSO
unw_model_pt, def_mod_pt,multi_def_pt, pt2data,pt2d, ipta.h.