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====== Differences ====== This shows you the differences between two versions of the page.

--- faa [2010/03/04 23:47]
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 This error occurs when the scripts cannot determine the offsets between two files.  Offsets are found by preforming a cross correlation of common data windows within the two images.  Failure can occur if the images do not match up very easily (such as is the offsets are large), if the SAR images are not properly focused, or if there are too few discernable features (such as if the scene is dominated by water).  For most instances (but not all), this problem can be fixed by manually finding the offsets.
-Offsets are determined at two points in process_2pass.pl; first when matching up the master and slave slc's, and second when matching the interferogram to the DEM.  If the last files created in the directory have "ampcor" in the filenames, then the failure ocurred while determining the offsets between the slc's.  Otherwise, if "ampmag" is in the filenames, the the problem is with matching up the DEM.  The procedure to fix the problem is identical for both cases, but the syntax is slightly different.  In both situations, you should first display both of the images side-by-side and manually determine the range/azimuth (i.e. x/y) offsets by visually matching common features.  To get the sign correct, determine the offsets as follows:  (pixel position of slave scene)-(pixel position of master scene).  Follow the directions below depending on you situation.
+Offsets are determined at two points in process_2pass.pl; first when matching up the master and slave slc's, and second when matching the interferogram to the DEM.  If the last files created in the directory have "ampcor" in the filenames, then the failure ocurred while determining the offsets between the slc's.  Otherwise, if "ampmag" is in the filenames, the the problem is with matching up the DEM.  The procedure to fix the problem is identical for both cases, but the syntax is slightly different.  In both situations, you should first display both of the images side-by-side and manually determine the range/azimuth (i.e. x/y) offsets by visually matching common features.  To get the sign correct, determine the offsets as follows:  (pixel position of slave scene)-(pixel position of master scene).  Follow the directions below depending on your situation.
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 FIXME Instructions to be posted.
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 ===== Offsets between the interferogram and DEM =====
-Before progressing further, make sure that (1) the full path to the DEM file was correctly given in the process_2pass parameter file, (2) the binary DEM file was formatted correctly to be read by ROI_PAC, (3) the coordinate and pixel size are correct in the *dem.rsc file, and (4) that SIM/SIM_*.hgt (which is your cropped DEM) is the same general geographical region as your SAR scene.  If SIM_*.hgt looks correct, then you want to manually reproduce the work of the script //synth_offset.pl//.  You can check the log file to see the correct arguments that are passed to the command.
+Before progressing further, make sure that (1) the full path to the DEM file was correctly given in the process_2pass parameter file, (2) the binary DEM file was formatted correctly to be read by ROI_PAC, (3) the coordinate and pixel size are correct in the *dem.rsc file, and (4) that SIM/SIM_*.hgt (which is your cropped DEM) is the same general geographical region as your SAR scene.  If one of these is wrong, fix the problem and restart process_2pass.
+If SIM_*.hgt looks correct, then you want to manually reproduce the work of the script //synth_offset.pl//.  You can check the log file to see the correct arguments that are passed to the command.
 <code>
 offset.pl YYYYMMDD-YYYYMMDD_4rlks.cor SIM_4rlks.hgt ampmag_gross 2 rmg 0 0 1. 1. 20 20 64 300 no 1 no