Unwrapping using selected reference point

Added by Justin Brandt about 5 years ago

I have a few questions regarding phase unwrapping using a selected reference point:

When using mcf, what is the difference between the roff and loff variables, and r_init and az_init?

If I want to choose a specific location as a reference point (for example, the location of a continuous GPS site), is it better to leave the roff and loff values as 0 (defaults), and change the r_init and az_init values to the row/column, or have roff = r_init and loff = az_init (similar to defaults)?

This brings up another question. What is a good way to determine the row/column (in SAR coordinates) of the reference point? I have a X-Y location (in UTM coords for example) of a GPS station, is there a program somewhat equivalent to geocode, but for a single latitude/longitude location?

Replies (1)

Unwrapping using selected reference point - Added by Charles Werner about 5 years ago

Hello,
roff and loff are the upper right corner of the region to be unwrapped.
r_init and az_init and the coordinates of the point where the phase unwrapping
starts.

For best results you should not have no-data around the edges of the region to
unwrap. mcf treats regions differently near the edges to reduce errors due to
the abrupt cut in the phase. I usually try to select a rectangular region that
is filled with interferogram values, not no-data.
The region is specified using the roff and loff and the number of samples and
number of lines.
Also, I suggest unwrapping the scene as a single patch. The multiple patches
approach, while faster, can have errors.
The best way to handle very large images is to get more RAM :), or average the
image to a smaller size, unwrap that, then interpolate the image and use that as
a model to unwrap the original scene. There is an example of this in the script
mk_unw_2d, using the nlks parameter
See the documentation in the mk_diff_all.html file:

gamma_doc mk_diff_2d

here is the usage of mk_unw_2d:

$ mk_unw_2d

./mk_unw_2d
Unwrap the phase of a stack of interferograms using Minimum Cost Flow (MCF)
algorithm ***

usage: ./mk_unw_2d <RSLC_tab> <itab> <rmli> <diff_dir> [cc_thres] [pwr_thres]
[nlks] [npat_r] [npat_az] [mode] [r_init] [az_init] [tri_mode] [unw_mask] [roff]
[loff] [nr] [nlines]

    RSLC_tab    (input) two column list of coregistered SLC filenames and SLC
parameter filenames (including paths)
                  1. SLC filename (includes path)
                  2. SLC parameter filename (includes path)
    itab        (input) table associating interferograms with pairs of SLCs
listed in the RSLC_tab
                  1. row number in SLC_tab of the reference SLC
                  2. row number in SLC_tab of SLC-2 of the interferogram
                  3. line number in the itab
                  4. flag used to indicate if this interferogram is to be
considered in time-series processing (0:not used 1:used)
    rmli        (input) MLI image derived from the coregistered SLCs with the
same pixel spacing and dimensions as the interferogram
    diff_dir    differential interferogram directory containing .diff
differential interferogram files
    cc_thres    threshold for correlation for creating the unwrapping mask (0.0
--> 1.0) (default: 0.4)
    pwr_thres   threshold for relative intensity for creating the unwrapping
mask (0.0 --> 1.0) (default: 0)
    nlks        number of looks in range and azimuth to scale before unwrapping
(default: 1)
    npat_r      number of patches in range (default: 1)
    npat_az     number of patches in azimuth (default: 1)
    mode        processing mode:
                  0: unwrap unfiltered data (.diff)
              1: (default) unwrap adf filtered data (.adf.diff) using adf
correlation (.adf.cc)
    r_init      phase reference range offset (default: )
    az_init     phase reference azimuth offset (default: -)
    tri_mode    MCF triangulation mode:
                  0: filled triangular mesh
                  1: Delaunay triangulation (default)
    unw_mask1   mask file to specify unwrap region rather than using a mask
generated using cc_thres and pwr_thres
                parameters (enter - for none) (8-bit/pixel Sun raster, BMP, or
TIFF format)
    roff        offset to starting range of region to unwrap (default: 0)
    loff        offset to starting line of region to unwrap (default: 0)
    nr          number of range samples of region to unwrap (default(): width
- roff)
    nlines      number of lines of region to unwrap (default(-): total number
of lines - loff)

    -b rmli_dir (option) use MLI2 as the background image for display rather
than MLI image specified on the command line
    -d diff_tab (option) output a DIFF_tab file containing 2 column list of
unwrapped diff. interferograms and delta_T values in decimal days
    -n          (option) only generate DIFF_tab only, no interferometric processing
    -r          (option) only generate raster images of the already unwrapped phase
    -s scale    (option) set image display scale factor (default: 0.7)
    -e exp      (option) set image display exponent (default: 0.35)
    -p pcycle   (option) unwrapped phase cycle for output display (default:
12.5663706)
    -x          (option) unwrapped phase color scale is non-cyclical, (default
min: 12.5663706/2   max: 12.5663706/2)
    -c cmap     (option) color map used for unwrapped phase default: hls.cm
    -m mask     (option) mask to apply to the unwrapped phase (Sun raster or
BMP format)
    -u          (option) update flag, unwrap only interferograms that have not
yet been unwrapped

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