GAMMA Questions

Hello,

The newest release of the Gamma software (20200713) has a new Python script that
automates the coregistration of a pair of Sentinel-1 SLCs.

$ ScanSAR_coreg.py

• ScanSAR_coreg.py: Script to coregister a ScanSAR or TOPS mode burst SLC to a
  reference burst SLC ***
• Copyright 2020 Gamma Remote Sensing, v2.8 23-Jun-2020 cm/uw ***

usage: ScanSAR_coreg.py <SLC1_tab> <SLC1_ID> <SLC2_tab> <SLC2_ID> <RSLC2_tab>
[hgt] [rlks] [azlks] [options]
    SLC1_tab      (input) SLC_tab of ScanSAR burst SLC reference (e.g.
20200208.SLC_tab)
    SLC1_ID       ID for reference files (e.g. 20200208)
    SLC2_tab      (input) SLC_tab of ScanSAR burst SLC slave (e.g.
20200224.SLC_tab)
    SLC2_ID       ID for slave files (e.g. 20200224)
    RSLC2_tab     (input) SLC_tab of co-registered S1 ScanSAR burst SLC slave
(e.g. 20200224.RSLC_tab)
                  NOTE: if RSLC2_tab does not yet exist, the file entries will
be created with names based on SLC2_tab
    hgt           (input) height map in RDC of MLI-1 mosaic (float, or constant
height value; enter - for default: 0.1)
    rlks          number of range looks in the output MLI image (enter - for
default: 10)
    azlks         number of azimuth looks in the output MLI image (enter - for
default: 2)

    --poly1 file        polygon file indicating area used for intensity
matching (relative to MLI reference)
    --poly2 file        polygon file indicating area used for spectral
diversity (relative to MLI reference)
    --cc value          coherence threshold used (default: 0.8)
    --fraction value    minimum valid fraction of unwrapped phase values used
(default: 0.01)=
    --ph_stdev value    phase standard deviation threshold (default: 0.8 radian)
    --it1 number        maximum number of iterations in intensity matching
method (enter 0 to skip method, default: 5)
    --it2 number        maximum number of iterations in spectral diversity
method (enter 0 to skip method, default: 5)
    --num_ovr number    maximum number of successful burst overlap measurements
per subswath (enter 0 for all, default: 10)
    --npoly number      number of model polynomial parameters (1, 3, 4 or 6,
default: 1)
    --nr number         number of offset estimates in range direction in
intensity matching (default: 64)
    --naz number        number of offset estimates in azimuth direction in
intensity matching (default: 64)
    --rwin number       range patch size in intensity matching (default: 256)
    --azwin number      azimuth patch size in intensity matching (default: 256)
    --RSLC3_tab file    (input) 3 column list of already co-registered ScanSAR
slave image to use for overlap interferograms
    --RSLC3_ID name     ID for already co-registered ScanSAR slave; an
interferogram between RSLC3 and RSLC2 is calculated
    --lt1 name          (input) modified lookup table (generated by adding an
offset field to the orbit based lookup table)
    --wdir path         path to working directory; the working directory will
be created if it doesn't exist (default: .)
    --no_check          do not check if slave data correspond to reference data
    --no_int            no interferogram will be generated at the end of the
coregistration process
    --no_cleaning       keep intermediate files
    --use_existing      use existing intermediate files
    --ignore_errors     continue processing when errors are detected

An important functionality is that a 3rd scene that has already been corgistered
with the geometric reference scene. This permits having a sliding reference to
form the double difference interferogram required for precision coregistration.
Given scenes A, B, C, D, E, F,  and C is the Reference scene. I would coregister
B and D with C, and then A with B,  E with D, and finally F with E.  At each
step, make sure that the coregistration is successful.  To do this:

check the *.coreg_quality file, if num_valid_weights = 0, it failed, if
num_valid_weights is very low, and/or sum_valid_weights is below 1, you should
check the interferogram to see if there are phase jumps between bursts.

The coregistration process generates an interferogram between the two scenes to
see if there are phase jumps between bursts.

For coregistration of the entire stack, this needs to be called multiple times,
but can done by calling this script from within another python script that you
can write using the py_gamma package. One of the script options

See the py_gamma_user_guide.pdf documentation on py_gamma located in the top
directory of the software distribution gamma.

A script as you suggest may added at some point, since it is very reasonable.

Charles

Hi Charles,

Thanks for your helpful response.
According to your suggestion, I ran ScanSAR_coreg.py_ script with S1 data only for one burst in each image. However, I find error (ERROR: insufficient valid offset points to determine offset polynomial, minimum number required: 3) in offset refinement using spectral diversity iteration 1. I am pasting the error log for reference.

offset refinement using spectral diversity iteration 1
cmd: /usr/local/GAMMA_SOFTWARE-20200713/DIFF/bin/SLC_interp_lt_ScanSAR 20200706.SLC_tab1 ./20200706.slc.par 20181102.SLC_tab ./20181102.rslc.par ./tmp_dir_coreg_20155749453/20200706.mli.lt.az_ovr ./20181102.rmli.par ./20200706.mli.par ./tmp_dir_coreg_20155749453/20181102_20200706.off.start 20200706.RSLC_tab ./20200706.rslc ./20200706.rslc.par

ERROR: insufficient valid offset points to determine offset polynomial, minimum number required: 3

ERROR in previous command

Eagerly seek your help on this issue.

Best regards,
Tapas

Hello,
Spectral diversity by definition requires multiple bursts because you are
looking at the double difference interferograms between the bursts. The very
high accuracy of spectral-diversity coregistration is not required for a single
burst in any case.

Best regards,
Charles