Gamma DIFF/GEO: Reference Manual

SLC_interp_lt

ANSI-C program: SLC_interp_lt.c

NAME
SLC_interp_lt - SLC image resampling via a lookup table and SINC interpolation 

SYNOPSIS
SLC_interp_lt <SLC-2> <SLC1_par> <SLC2_par> <lookup_table> <MLI1_par> <MLI2_par> <OFF_par> <SLC-2R> <SLC2R_par>

<SLC-2> (input) SLC-2 image to be resampled to the geometry of the SLC-1 reference image
<SLC1_par> (input) SLC/MLI ISP image parameter file of the SLC-1 reference
<SLC2_par> (input) SLC/MLI ISP image parameter file of SLC-2
<lookup_table> (input) lookup_table relating MLI-2 to MLI-1
<MLI1_par>  (input) SLC/MLI ISP image parameter file of reference MLI (lookup table dimension)
<MLI2_par>  (input) SLC/MLI ISP image parameter file of MLI2 (lookup table values)
<OFF_par>  (input) ISP offset/interferogram parameter file used for refinement (enter - for none)
<SLC-2R>  (output) single-look complex image 2 coregistered to SLC-1
<SLC2R_par  (output) SLC-2R ISP image parameter file for coregistered image

EXAMPLE
SLC_interp_lt 24936.slc 05263.slc.par 24936.slc.par lt1 05263.mli.par 24936.mli.par off.par rslc rslc.par

Use the lookup table lt1 to resample 24936.slc to the geometry of 05263.slc. The lookup table has geometry defined by 24936.mli.par. File off.par is provided for refinement of the lookup table indices. Output is in the rslc with parameter file rslc.par.

DESCRIPTION
SLC_interp_lt uses a lookup table generated using the program rdc_trans  to resample one SLC into the geometry of a reference SLC. The lookup table generated by rdc_trans can be smaller than the SLC because values in the lookup table are interpolated to obtain the offsets for each SLC point. Lookup-table geometry is defined by the MLI1_par and the values within the lookup table are coordinates as defined in the  MLI2_par file of the second image. The lookup table is generated in rdc_trans using DEM data resampled to Radar range-doppler coordinates  (RDC) as defined in the MLI-1.par. 

A slight offset between the resampled and reference SLCs usually remains after an initial resampling due to a combination of inaccuracies in DEM, orbit state vectors, and geocoding.  Hence SLC_interp_lt supports adding a offset parameter file  (OFF_par) that contains range and azimuth offset polynomials determined between SLC1 and SLC-2R in  the initial resampling. The processing steps are as follows:

1. Generate a DEM in SLC range-Doppler coordinates using the DIFF/GEO tools (see DIFF users guide)
2. Generate the lookup-table using DIFF/GEO program rdc_trans
3. Refine lookup table values generated by rdc_trans:
  1. Use DIFF/GEO program geocode to use the lookup table to resample  MLI-1 into the geometry of MLI-2
  2. create DIFF/GEO offset parameter file DIFF_par using create_diff_par
  3. Measure offsets between resampled MLI-1and MLI-2 (offset_pwrm)
  4. Estimate offset polynomial coefficients (offset_fitm)
  5. update lookup table values using offset polynomials in the DIFF_par using gc_map_fine
4. Calculate the initial resampling of SLC-2 into SLC-1 reference geometry using SLC_interp_lt (without the OFF_par secondary refinement data)
5. Estimate lookup-table offsets by the following steps:
  1. Measure offsets between SLC-2R and SLC-1 using  ISP program offset_pwr. (create OFF_par first using create_offset)
  2. Calculate range and azimuth offset polynomials using ISP program offset_fit from offset data
6. Rerun SLC_interp_lt, now including the OFF_par polynomial model refinement data
7. Confirm lookup table offset correction and goodness of fit::
  1. Measure new offsets btween the SLC-2R and SLC-1 using offset_pwr (use new OFF_par file)
  2. Generate new range and azimuth offset polynomials using offset_fit
  3. Analyze the new residual range and azimuth offset polynomials to confirm goodness of fit
  4. Use dis2SLC to confirm goodness of fit between resampled SLC and the reference

The programs create_offset, offset_pwr, and offset_fit are part of the ISP software package. 

A 2D SINC interpolator is used in the resampling of the complex valued data. The interporation takes into account  changes in the Doppler centroid both along-track and in slant range.  

As an example here is the annotated processing sequence for an interferometry pair of ERS data from ERS-2 orbit 05263 and ERS-1 orbit 24936 using rdc_trans and SLC_interp_lt..

#generate MLI images from 05263 and 24936 with 2 range looks and 10 azimuth looks
multi_look 05263.slc 05263.slc.par 05263.mli 05263.mli.par 2 10
multi_look 24936.slc 24936.slc.par 24936.mli 24936.mli.par 2 10

#geocode 05263.mli using DIFF/GEO tools, generate DEM in Radar coordinates using DIFF/.GEO program geocode

#generate initial lookup table lt0  using DEM lan_rdc.dem resampled in range-Doppler coordinates of 05263.mli. DEM was the result of terrain
#geocoding of 05263.mli. with 2 range looks and 10 azimuth looks. The MLI images are 1148 range pixels by 610 azimuth pixels.

rdc_trans 05263.mli.par lan_rdc.dem 24936.mli.par lt0

#lookup table refinement generated by rdc_trans. resample 24036.mli into geometry of 05263.mli, file is called mli0
geocode lt 05263.mli 1148 mli0 1148 610 2 0

#measure offset and estimate offset polynomials between mli0 and 24936.mli, refine lookup table
create_diff_par 24936.mli.par 24936.mli.par diff0 1
init_offsetm mli0 24936.mli diff0 1 1
offset_pwrm mli0 24936.mli diff0 offs0 snr0 - - - 2
offset_fitm offs0 snr0 diff0 coffs0 - - 4
gc_map_fine lt0 1148 diff0 lt1

#resample SLC-2 into geometry of SLC-1 and display, output data are rslc1 and the iamge parameter file rslc1.par
SLC_interp_lt 24936.slc 05263.slc.par 24936.slc.par lt1 05263.mli.par 24936.mli.par - rslc1 rslc1.par
dis2SLC 05263.slc rslc1 2296 2296 1 6000

#measure offsets for second refinement of lookup table coordinates using initially resampled SLC. Offset polynomials in OFF_par offt1
create_offset 05263.slc.par rslc1.par off1
offset_pwr 05263.slc rslc1 05263.slc.par rslc1.par off1 offs1 snr1 - - offsets1 2
offset_fit offs1 snr1 off1 - coffsets1 - 4

#resample SLC-2 again using offset information in OFF_par off1, output is rslc2 and rslc2.par
SLC_interp_lt 24936.slc 05263.slc.par 24936.slc.par lt1 05263.mli.par 24936.mli.par off1 rslc2 rslc2.par

#check coregistration using display and finding residual SLC offsets
dis2SLC 05263.slc rslc2 2296 2296 1 6000
create_offset 05263.slc.par rslc2.par off2
offset_pwr 05263.slc rslc2 05263.slc.par rslc2.par off2 offs2 snr2 - - offsets2 2
offset_fit offs2 snr2 off2 - coffsets2 - 4

final range offset poly. coeff.:          -7.106e-03  5.252e-06  1.826e-06 -1.223e-09
final azimuth offset poly. coeff.:        -2.603e-02  3.605e-06  1.197e-06 -2.498e-10
final model fit std. dev. (samples) range:   0.0128  azimuth:   0.0199

dis2SLC 05263.slc rslc2 2296 2296 1 6000

#generate interferogram

SLC_intf 05263.slc rslc2 05263.slc.par rslc2.par off1 int2 2 10

SEE ALSO
rdc_trans 

© Copyrights for DIFF/GEO Documentation, DIFF/GEO Users Guide and DIFF/GEO Reference Manual by Gamma Remote Sensing, 2008 UW, CW, last change 6-May-2008.