GAMMA DIFF/GEO Software: Reference Manual

SLC co-registration and resampling using a lookup table (SLC_resamp_lt_all)

Perl script: SLC_resamp_lt_all

Description

This is a Quickstart guide on how to use the script SLC_resamp_lt_all to resample a set of SLC images to a common reference SLC scene using a lookup table. The lookup table is derived using a DEM in the radar geometry.
The SLC_resamp_lt_all script helps guide you through the different processing steps. As input data the following inputs are required:

1. SLC image data with the ISP image parameter files
2. A table of the SLC images to be resampled and the reference scene in the form of an SLC_tab. The SLC tab has two columns, one line per SLC. In the first column is the SLC file name including the absolute or relative
path to the SLC. In the second column is the SLC parameter file name including the absolute or relative path to the SLC parameter file

An example SLC_tab is shown below for 2 SLC images with relative paths:

slc/19990915.slc slc/19990915.slc.par
slc/19991020.slc slc/19991020.slc.par

This can be created using the mk_tab script:

*** Copyright 2011, Gamma Remote Sensing, v1.1
  13-Apr-2011 clw ***

  *** Generate SLC_tab, MLI_tab, or RAW_list for processing 
  ***

  

  usage: mk_tab <dir> <ext-1> <ext-2>
  <tab>

      dir   (input) directory including
  paths that contain the data files

      ext-1 (input) pattern to select data files
  (examples: slc, raw...)

      ext-2 (input) pattern to select parameter
  files that match the data (examples: slc.par, raw_par,
  raw.par)

      tab   (output) two column list of
  data filenames and data parameter filenames (including paths)
  (text)

  

      NOTE: The current directory is denoted using
  .

  

  mk_tab slc slc slc.par SLC_tab

3. A multi-look intensity MLI image of the scene and the associated ISP image parameter file
4. A DEM in range-Doppler coordinates with the same pixel spacing as the MLI image

Either include $DIFF_HOME/scripts in the PATH environment variable or Copy the SLC_resamp_lt_all script to the directory above where the SLCs are located. The SLC images should all be in one directory. Next, run the script without arguments to see the command line arguments:

*** ./SLC_resamp_lt_all
*** Copyright 2011, Gamma Remote Sensing, v4.3 28-Apr-2011 clw ***
*** Resample a set of SLCs to a common reference SLC using a lookup table and DEM ***

usage: ./SLC_resamp_lt_all <SLC_tab> <ref_SLC> <ref_SLC_par> <ref_MLI_par> <DEM_rdc> <MLI_dir> <RSLC_dir> <RSLC_tab> <mode> [rflag] [rlks] [azlks] [rpos] [azpos]

    SLC_tab      (input) two column list of SLC filenames and SLC parameter filenames (including paths) (ascii)
    ref_SLC      (input) reference SLC (including path)
    ref_SLC_par (input) ISP image parameter file of the reference SLC (including path)
    ref_MLI_par (input) ISP image parameter file of the reference MLI (including path)
    DEM_rdc      (input) DEM in Range-Doppler Coordinates with width and height as described in the MLI_par
    MLI_dir      (input) directory containing MLI parameter files, same the same width and height as DEM_rdc.
    RSLC_dir     directory to contain the resampled SLCs, lookup tables, ISP image parameter files, and log files
    RSLC_tab     (output) RSLC_tab file for the resampled SLC files
    mode         processing modes:
                   0: generate lookup table and resample MLI-1 image into the geometry of MLI-2
                   1: refine lookup table based on measured offsets between MLI-1 resampled to the geometry of MLI-2
                   2: resample SLC-2 to the geometry of the reference SLC using lookup table
                   3: create offset parameter files for SLC resampling refinement, measure offsets, and calculate the SLC offset fit polynomials
               4: resample SLC images using lookup table offsets determined in mode 3 and generate RSLC_tab
    rflag        flag for interative refinement of the resampled SLC:
                   0: resample and measure residual range and azimuth offsets (no interation, default)
                   1: interatively improve range and azimuth offset polynomials then measure residual offsets
    rlks         number of range looks for initial offset estimation (enter - for default: 1)
    azlks        number of azimuth looks for initial offset estimation (enter - for default: 1)
    rpos         center of patch for initial offset estimation in range (samples) (enter - for default: image center)
    azpos        center of patch for initial offset estimation in azimuth (lines) (enter - for default: image center)

The different modes represent steps in the processing that must be performed sequentially.

Mode 0: generate lookup table and resample MLI-1 image into the geometry of MLI-2

In this step a lookup table is generated that maps one SLC into the reference SLCimage. The sample spacing of the lookup table is the same as the MLI reference image. The table entries are interpolated to resample the SLC data. The DIFF/GEO program rdc_trans is used to generate the lookup table and the ISP program SLC_resamp_lt is used to perform the resampling .

SLC_resamp_lt_all
  SLC_tab1 slc/19960421.slc slc/19960421.slc.par
  mli_1_5/19960421.mli.par geo/lan_dem.rdc  mli_1_5 rslc_lt
  RSLC_lt_tab 0 0

generates the following commands:

`rdc_trans mli_1_5/19960421.mli.par geo/lan_dem.rdc mli_1_5/19960422.mli.par rslc_lt/19960421_19960422.lt0 geocode rslc_lt/19960421_19960422.lt0 mli_1_5//19960421.mli 2296 rslc_lt/19960421_lt0.mli 2296 1176 2 0 - - 4 raspwr rslc_lt/19960421_lt0.mli 2296 1 0 1 1 0.6 0.4`

The output lookup table has dimensions of the reference MLI image determined from the MLI parameter file of the reference scene, in this case 2296 samples

Mode 1: refine lookup table based on measured offsets between MLI-1 resampled to the geometry of MLI-2

In this step, the offsets between MLI-2 the reference MLI resampled into the geometry of MLI-2. Range and azimuth offset polynomials derived
from these offsets are used to correct the entries of the lookup table for orbit and timing errors.

Example:

SLC_resamp_lt_all
  SLC_tab1 slc/19960421.slc slc/19960421.slc.par
  mli_1_5/19960421.mli.par geo/lan_dem.rdc  mli_1_5 rslc_lt
  RSLC_lt_tab 1 0

This generates the following commands to measure the MLI offsets, calculate the polynomials, and correct the lookup table

create_diff_par
  mli_1_5/19960422.mli.par - rslc_lt/19960421_19960422_lt0.diff_par
  1 < .in

  init_offsetm rslc_lt/19960421_lt0.mli mli_1_5/19960422.mli
  rslc_lt/19960421_19960422_lt0.diff_par 1 1 1148 588

  offset_pwrm rslc_lt/19960421_lt0.mli mli_1_5/19960422.mli
  rslc_lt/19960421_19960422_lt0.diff_par
  rslc_lt/19960421_19960422_lt0.offs
  rslc_lt/19960421_19960422_lt0.snr

  offset_fitm rslc_lt/19960421_19960422_lt0.offs
  rslc_lt/19960421_19960422_lt0.snr
  rslc_lt/19960421_19960422_lt0.diff_par
  rslc_lt/19960421_19960422_lt0.coffs -  3

  gc_map_fine rslc_lt/19960421_19960422.lt0 2296
  rslc_lt/19960421_19960422_lt0.diff_par
  rslc_lt/19960421_19960422.lt1

The inputs to create_diff_par are determined from the image dimensions and the range and azimuth patch size (256x256).

Mode 2: resample SLC-2 to the geometry of the reference SLC using lookup table including the initial refinement

This step resamples SLC-2 into the geometry of the reference SLC. (SLC-1).

Example:

SLC_resamp_lt_all SLC_tab1
  slc/19960421.slc slc/19960421.slc.par mli_1_5/19960421.mli.par
  geo/lan_dem.rdc  mli_1_5 rslc_lt RSLC_lt_tab 2 0

This results in the following command:

SLC_interp_lt
  slc/19960422.slc slc/19960421.slc.par slc/19960422.slc.par
  rslc_lt/19960421_19960422.lt1 mli_1_5/19960421.mli.par
  mli_1_5/19960422.mli.par - rslc_lt/19960422.rslc
  rslc_lt/19960422.rslc.par

Mode 3: create offset parameter files for SLC resampling refinement, measure offsets, and calculate the SLC offset fit polynomials

In this step, the offsets between the SLC reference and initial resampled SLC are measured over a grid of points.
The values of these offsets are then used to estimate offset polynomial that is used as a correction for the offset estimation using the lookup table.

Example:

SLC_resamp_lt_all SLC_tab1
  slc/19960421.slc slc/19960421.slc.par mli_1_5/19960421.mli.par
  geo/lan_dem.rdc  mli_1_5 rslc_lt RSLC_lt_tab 3 0

This results in the following commands:

create_offset
  rslc_lt/19960421.rslc.par rslc_lt/19960422.rslc.par
  rslc_lt/19960421_19960422.off < create_offset.in

  offset_pwr rslc_lt/19960421.rslc rslc_lt/19960422.rslc
  rslc_lt/19960421.rslc.par rslc_lt/19960422.rslc.par
  rslc_lt/19960421_19960422.off rslc_lt/19960421_19960422.offs
  rslc_lt/19960421_19960422.snr

  offset_fit rslc_lt/19960421_19960422.offs
  rslc_lt/19960421_19960422.snr rslc_lt/19960421_19960422.off
  rslc_lt/19960421_19960422.coffs - - 3

Mode 4: resample SLC using offset polynomials from SLC refinement, repeat SLC offset polynomial estimation, resample SLC and measure residual offsets

The SLC is resampled to the reference and the range and azimuth offsets of the SLC to the reference scene is measured. If the rflag command line parameter is set to 1 (offset refinement) the residual polymials are added to the offset polynomials and the SLC is resampled using the updated offset polynomial correction. The offsets of the resampled SLC with respect to the reference SLC are measured again and range and azimuth offset polynomials from these new offsets are determined. Iteration of the offset model reduces the residual offsets

Example:
Resampling using the SLC offset correction polynomials.

SLC_resamp_lt_all SLC_tab1
  slc/19960421.slc slc/19960421.slc.par mli_1_5/19960421.mli.par
  geo/lan_dem.rdc  mli_1_5 rslc_lt RSLC_lt_tab 4
  0

This results in the following commands, first to resample the SLC using the offset polynomial corrections:

 SLC_interp_lt
  slc/19960422.slc rslc_lt/19960421.rslc.par slc/19960422.slc.par
  rslc_lt/19960421_19960422.lt1 mli_1_5/19960421.mli.par
  mli_1_5/19960422.mli.par rslc_lt/19960421_19960422.off
  rslc_lt/19960422.rslc rslc_lt/19960422.rslc.par

Then measure the residual offsets of the resampled SLC



  offset_pwr rslc_lt/19960421.rslc rslc_lt/19960422.rslc
  rslc_lt/19960421.rslc.par rslc_lt/19960422.rslc.par
  rslc_lt/19960421_19960422_2.off rslc_lt/19960421_19960422_2.offs
  rslc_lt/19960421_19960422_2.snr

  offset_fit rslc_lt/19960421_19960422_2.offs
  rslc_lt/19960421_19960422_2.snr rslc_lt/19960421_19960422_2.off
  rslc_lt/19960421_19960422_2.coffs - - 3

  

  range_offset_polynomial: 0.00259 -3.0636e-06 1.2147e-07
  0.0000e+00 0.0000e+00 0.0000e+00

  azimuth_offset_polynomial: -0.00852 3.9308e-06 -9.8217e-08
  0.0000e+00 0.0000e+00 0.0000e+00

In the case where rflag = 0, the script ends at this point. In the case where rflag = 1 these polynomial models of the residual offsets are added to the original SLC offset polyomials for range and azimuth and then replaced in the offset parameter file rslc_lt/19960421_19960422_2.off:



  set_value rslc_lt/19960421_19960422.off
  rslc_lt/19960421_19960422.off "range_offset_polynomial" 
  "0.02641 -2.90396e-05  9.12520e-07  0.00000e+00 
  0.00000e+00  0.00000e+00"

  set_value rslc_lt/19960421_19960422.off
  rslc_lt/19960421_19960422.off "azimuth_offset_polynomial"
  "-0.23748  1.09871e-04  6.01638e-06 
  0.00000e+00  0.00000e+00 
  0.00000e+00"

Followed by the final resampling of the SLC data and measurement of the residual offsets:



  SLC_interp_lt
  slc/19960422.slc slc/19960421.slc.par slc/19960422.slc.par
  rslc_lt/19960421_19960422.lt1 mli_1_5/19960421.mli.par
  mli_1_5/19960422.mli.par rslc_lt/19960421_19960422.off
  rslc_lt/19960422.rslc rslc_lt/19960422.rslc.par

  offset_pwr rslc_lt/19960421.rslc rslc_lt/19960422.rslc
  rslc_lt/19960421.rslc.par rslc_lt/19960422.rslc.par
  rslc_lt/19960421_19960422_2.off rslc_lt/19960421_19960422_2.offs
  rslc_lt/19960421_19960422_2.snr

  offset_fit rslc_lt/19960421_19960422_2.offs
  rslc_lt/19960421_19960422_2.snr rslc_lt/19960421_19960422_2.off
  rslc_lt/19960421_19960422_2.coffs - - 3

These are the final residual polynomials for the range and azimuth offsets:

range_offset_polynomial: 0.00031
  -3.8896e-07 2.2640e-08 0.0000e+00 0.0000e+00 0.0000e+00

  azimuth_offset_polynomial: -0.00061 2.8074e-07 -2.0560e-08
  0.0000e+00 0.0000e+00 0.0000e+00

Offset Error Estimation:

It is essential to have estimates of the residual error in the resampling for each of the SLCs. A log file is created for each SLC pair and stored in the resampled SLC directory. The commands and complete output of each of the programs is recorded in the log file. In this particular example there is only one log file since only a single pair has been co-registered. In this example the SLC data were resampled 3 times and the residual offsets measured. The values of the standard deviation of the measurements relative to the model can be extracted from the log file using the Linux/Unix grep utility as follows:



  grep "final model fit std.
  dev."  rslc_lt/19960421_19960422_resamp_lt.log

  final model fit std. dev. (samples) range:  
  0.0419  azimuth:   0.0088  #MLI image offset
  estimation

  final model fit std. dev. (samples) range:  
  0.0046  azimuth:   0.0074

  final model fit std. dev. (samples) range:  
  0.0044  azimuth:   0.0066

  final model fit std. dev. (samples) range:  
  0.0044  azimuth:  
  0.0066

This indicates that the standard deviation of the offsets in range and azimuth were improved after the second resampling. The values of the offset polynomials in range and azimuth can also be extracted using grep :

grep "final range
  offset poly. coeff.:" 
  rslc_lt/19960421_19960422_resamp_lt.log

  final range offset poly.
  coeff.:            
  -0.45454   3.96654e-05   2.84578e-05 
  -2.60329e-08  #MLI offset from offset_fitm

  final range offset poly.
  coeff.:             
  0.02382  -2.59757e-05   7.91047e-07  
  #SLC range offset polynomials

  final range offset poly.
  coeff.:             
  0.00259  -3.06361e-06   1.21473e-07

  final range offset poly.
  coeff.:             
  0.00031  -3.88958e-07  
  2.26396e-08

$ grep
  "final azimuth offset poly. coeff.:" 
  rslc_lt/19960421_19960422_resamp_lt.log

  final azimuth offset poly.
  coeff.:            
  -0.01594  -1.32865e-05   1.18202e-06 
  -1.43720e-09  #MLI offset from offset_fitm

  final azimuth offset poly.
  coeff.:            
  -0.22896   1.05937e-04   6.11460e-06 
  #SLC azimuth offset polynomials

  final azimuth offset poly.
  coeff.:            
  -0.00852   3.93078e-06  -9.82174e-08

  final azimuth offset poly.
  coeff.:            
  -0.00061   2.80742e-07 
  -2.05605e-08