Gamma ISP: Reference Manual

SLC_interp_map

ANSI-C program: SLC_interp_map.c

NAME
SLC_interp_map - SLC resampling using 2-D SINC interpolation. Resampling offsets include non-linear terms.

SYNOPSIS
SLC_interp <SLC-2> <SLC1_par> <SLC2_par> <OFF_par> <SLC-2R> <SLC2R_par> <OFF_par2> <coffs_sm> [loff] [nlines]

<SLC-2>	(input) SLC-2 image to be resampled to the geometry of the reference SLC-1 image
<SLC1_par>	(input) SLC-1 ISP image parameter file
<SLC2_par>	(input) SLC-2 ISP image parameter file
<OFF_par>	(input) ISP offset/interferogram parameter file
<SLC-2R>	(output) SLC-2 resampled into the reference geometry of SLC-1 (fcomplex)
<SLC2R_par>	(output) ISP image parameter file for resampled SLC-2R
<OFF_par2>	(input) ISP offset/interferogram parameter file used to measure residual range and azimuth offsets
<coffs_sm>	(input) smoothed residual range and azimuth offsets (fcomplex) between the resampled SLC-2 and the SLC-1
[loff]	offset to starting line of interferogram (relative to SLC-1) (default=0)
[nlines]	number of SLC lines to process (default=to end of file)

EXAMPLE
SLC_interp_map 1610.slc 1352.slc.par 1610.slc.par 1352_1610.off 1610.rslc 1610.rslc.par refine.off refine.coffs_sm

DESCRIPTION
SLC_interp_map registers SLC-2 to the reference SLC-1 geometry. The range and azimuth offsets are calculated as the sum of the contributions from the polynomials stored in the ISP OFF_par and the local residual offsets in the coffs file. These residual offsets are measured between the reference SLC and SLC-2 that has been resampled to the geometry of SLC-1 using the polynomials alone. This map contains the non-linear residual offsets between SLC-1 and SLC-2. The sum of these residual offsets and the offset contribution determined from the polynomials are the offsets used to resample the SLC-2. This program is needed only in situations were there are non-linear deformations in the scene such as due to glacier motion, or large earthquakes.

Processing of data using SLC_interp_map requires first generating an SLC resampled to the reference geometry of SLC-1 using SLC_interp. Offsets are then measured using a dense grid between the resampled SLC and SLC-1. These measurements contain information on the non-linear offset function between the SLCs due to scene deformation (e.g. earthquake or glacier motion). Taking this deformation into account when forming the interferogram improves the interferometric correlation.

A new offset parameter file for the refinement has to be created using create_offset with 0 initial offsets. The typical number of offset measurements in range and azimuth for the residual map is 700 x 700. These offsets must then be culled using offset_fit. The range size of the search window should be between 32 to 64 and the azimuth window size in the range of 64 to 128. Later culling of the offsets in offset_fit should limit the range of the residual range and azimuth offsets to the level of the maximum expected deformation. The threshold SNR should be set in the range between 5 and 7.

SLC_interp_map has been updated to adapt to changes in the Doppler centroid along-track. This is especially applicable to the processing of long strips (>200 km) of Radarsat data where the Doppler centroid changes by more than 100 Hz/frame.

After processing with offset_fit, the culled offset file (coffs) should be smoothed and filled using program interp_ad. This program fills the holes in the offset map by adaptive interpolation and smooths the data to reduce noise.

An 2D SINC interpolator is used in resampling the complex valued data. The registration uses the bilinear coregistration offset polynomials for range and azimuth offset (as a function of range and azimuth) of the ISP offset/processing parameter file. To determine the offset polynomials use the programs offset_pwr, offset_SLC, and offset_fit are used. No spectral filtering is applied during the registration. Such filtering is applied during calculation of the interferogram with program SLC_intf.

No multi-look intensity images are produced from the two SLC images. Coregistered multi-look intensity images in the identical geometry as the interferogram can be generated from the co-registered SLC images using the program multi_look. The parameters [lbegin] and [nltot] should nominally not be changed from the default values since the starting line and number of lines are not recorded in the SLC-1 parameter file. The primary intent of SLC_interp is to resample the SLC-2 image to the geometry of SLC-1. If a only an interferogram from a segment of the SLC images is desired, then use the program SLC_copy to extract the segment from SLC-1, before using processing.