Gamma DIFF/GEO: Reference Manual

WSS_interp_lt

ANSI-C program: WSS_interp_lt.c

NAME
WSS_interp_lt - ASAR Wide-Swath SLC complex image resampling via a lookup table and  2-D SINC interpolation

SYNOPSIS
 WSS_interp_lt <SLC-1> <SLC-2> <SLC1_par> <SLC2_par> <lookup_table> <MLI1_par> <MLI2_par> <DIFF_par> <SLC-2R> <SLC2R_par><DIFF_par2>

<SLC-1> (input) ASAR Wide-Swath SLC_1 reference image
<SLC-2> (input) ASAR Wide-Swath SLC-2 image to be resampled to the geometry of the WSS SLC-1 reference image
<SLC1_par> (input) ASAR Wide-Swath SLC-1 image parameter file
<SLC2_par> (input) ASAR Wide-Swath SLC-2 image parameter file
<lookup_table> (input) lookup_table relating MLI-2 to MLI-1 created from SLC-2 and SLC-1 respectively
<MLI1_par>  ISP image parameter file of reference MLI-1 (lookup table dimension)
<MLI2_par> ISP image parameter file of MLI-2 (lookup table values)
<DIFF_par>  (input) WSS DIFF/GEO offset parameter file used for refinement (enter - for none)
<SLC-2R>  (output) ASAR Wide-Swath SLC-2 resampled and co-registered to SLC-1
<SLC2R_par  (output) ASAR Wide-Swath image parameter file for the co-registered resampled image
<DIFF_par2  (output) DIFF/GEO offset parameter file for MLI-1, MLI-2 (enter - for none)

EXAMPLE

WSS_interp_lt_051103 20030921.VV.IS2.SLC 20040208.VV.IS2.SLC 20030921.VV.IS2.SLC.par 20040208.VV.IS2.SLC.par 20030921_20040228.VV.IS2.lt 20030921.VV.IS2.mli.par 20040208.VV.IS2.mli.par is2.diff  20040208.IS2.rslc 20040208.IS2.rslc.par diff_par2

Use the lookup table 20030921_20040228.VV.IS2.lt to resample 20040208.VV.IS2.SLC to the geometry of20030921.VV.IS2.SLC. The lookup table has geometry defined by 20030921.VV.IS2.mli.par and the values by 20040208.VV.IS2.mli.par. The DIFF parameter file is2.diff  is optionally provided for refinement of the lookup table indices. Output is in 20040208.IS2.rslc with parameter file 20040208.IS2.rslc.par. A DIFF/GEO offset parameter file is created for later use in estimation of residual offset model between the resampled SLC image and the reference

DESCRIPTION
WSS_interp_lt uses a lookup table generated using the program rdc_trans  to resample one ASAR Wide Swath SLC into the geometry of a reference ASAR Wide Swath 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 related to 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 as defined in the MLI-1.par. 

The Wide-Swath SLC data are produced from scan-sar data. Hence the format is different than strip-map mod SLC images. Each burst is processed into an SLC burst that is 48 lines long with 80 meter along-track azimuth pixel spacing with each point on the ground imaged by on average 3 bursts. The MLI-1 and MLI-2R files are calculated from the SLC-1 and SLC-2R files. Processing steps are as follows for co-registration and resampling of the ASAR Wide-Swath SLC data.
  1. Generate MLI images from the Wide-Swath SLC data using  the ISP program  multi_SLC_WSS.
  2. Terrain geocode the MLI image of the reference scene using  DIFF/GEO tools and calculate a DEM in the MLI SAR range doppler coordinates  (see DIFF users guide)
  3. Generate the lookup-table using program rdc_trans with the MLI parameter files created in Step 1 and a DEM in SAR coordinates.
  4. Refine lookup table values generated by rdc_trans:
    1. Use DIFF/GEO program geocode to use the lookup table from Step 3 to trasform MLI-2 into the geometry of MLI-1
    2. create DIFF/GEO offset parameter file DIFF_par using create_diff_par
    3. Measure offsets between resampled MLI-2 and MLI-1 using ( offset_pwrm)
    4. Estimate offset polynomial coefficients using (offset_fitm)
    5. update lookup table values using offset polynomials in the DIFF_par using gc_map_fine
  6. Calculate the  resampling of SLC-2 into SLC-1 reference geometry using WSS_interp_lt  (without using a DIFF_par file)
  7. (OPTIONAL) Confirm lookup table offset correction and goodness of fit: 
    1. Calculate an MLI image from the resample SLC-2R using the ISP program  multi_SLC_WSS  
    2. Create a new DIFF_par using  create_diff_par, Note that the DIFF_par must be created with the parameter files from the reference and the resampled MLI! 
    3. Measure new offsets btween the MLI-2R and MLI-1 using DIFF program offset_pwrm. (use a new DIFF_par file)
    4. Generate new range and azimuth offset polynomials using DIFF program  offset_fitm 
    5. Analyze the new residual range and azimuth offset polynomials to confirm goodness of fit
    6. Use dis2SLC to confirm goodness of fit between resampled SLCs and the reference. The number of pixels to use for the image width is number of image pixels +  24 bytes at the start of each line are use for the line header.
  9. (OPTIONAL) run WSS_interp_lt, but now including the DIFF_par secondary refinement offset model to generate the resampled SLC image. This should not be required if the residual offset is < .03 pixels. 

Note that WSS_interp_lt supports adding a DIFF parameter file (DIFF_par) that contains range and azimuth offset polynomials determined between MLI-1 and MLI-2R an initial resampling. There may be a slight offset between the resampled and reference SLCs may remain after an initial resampling due to a combination of inaccuracies in DEM, orbit state vectors, and geocoding that can be corrected using the secondary polynomial model.

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

SEE ALSO
rdc_trans, create_diff_par, offset_pwrm, offset_fitm

© Copyrights for DIFF/GEO Documentation, DIFF/GEO Users Guide and DIFF/GEO Reference Manual by Gamma Remote Sensing, 2006.
UW, CW, last change 1-Mar-2006.