An open source InSAR processing package

Step 0:

Before you get started, you need the following 5 things:
• Orbit files (for ERS, you'll have to use the header files for JERS and RADARSAT). The PRC link may be dead, but the ODR orbits work great (except where they don't exist, and you have to use the HDR format).
• InSAR processing software (ROI_PAC, freely available at Open Channel Foundation). Help with installation is available here.

• Digital Elevation Model (Definately try SRTM if available)

• Viewing software: DGX is freely available but doesn't run on LINUX. A possible work around is suggested here. MDX does work on LINUX and must be licensed directly from JPL.
• Raw data (Available from WInSAR database; ASF database; directly from ESA; Commercial vendors) The most important raw data files are the DAT file (roughly 300 Mb) and the LDR (leader or header file, about 30 kilobytes). For ROI_PAC, you'll need to rename these IMAGERY and SARLEADER files.

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Step 1:

Create the proper directory structure (see the "Set-up" step)

Run make_raw.pl ORBIT_TYPE LEADER_FILE DATE details

There are different scripts if you are using JERS, RADARSAT, ENVISAT, or ERS data downloaded in CEOS format from ASF. Those that are not available in ROI_PAC are available here. However, once you've made raw, the following steps are more-or-less the same for all data types.

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Step 2:

Create the proper processing file called "date1-date2.proc"

Run process_2pass.pl "date1-date2.proc" START END (see table below for some possible START/END points)

process_2pass.pl is the most commonly run script, but others are sometimes needed.

If you are exceedingly lucky, process_2pass.pl can go from the raw data to making an interferogram to removing the orbital effects ("flattening") to removing the topographic effect to unwrapping to geocoding in a single run. More likely, you are going to start and stop this flow at various points to fix errors or otherwise change the paramters. There are numerous such "start" and "stop" points listed below, but we highlight (in bold*) the ones that you will use most frequently.

START/END point	Comments
raw*	Always start here after running make_raw.pl
roi_prep	Create input files for SAR processor
orbbase	Calculate baselines
slcs	Create single-look-complex interferograms
offsets	Co-register two slcs: Frequently restart here after (question #3 on this list)
resamp	Resample slave scene to master coordinates
flatorb	"flatten" scene and remove orbital ramp
full_res*	Good stopping point: have created interferograms and correlation files
done_sim_off	Calculate offsets between interferogram and DEM
done_sim_removal*	Good stopping point: have removed the topographic effects from the flattened interferogram
begin filt	filter the interferogram
filtered	done filtering
make_mask	create mask for unwrapping
unwrapped*	Good stopping point: Flattened interferogram with topography removed is unwrapped
redo_base	Empirically re-estimate the baselines
sim_removal_bsim	remove topo from newly re-flattened interferogram
unwrapped_bsim	unwrap newly re-flattened interferogram
done*	Final stopping point: Put flattened unwrapped interferogram with topography removed in geographic coordinates

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Step 3:

Troubleshooting solutions from Schmidt

Additional troubleshooting suggestions

What are all these files!?

Alternative unwrapping algorithim: SNAPHU

Interested in the technical details behind ROI_PAC? See Ph.D. thesis chapter by Sean Buckley (modified by Paul Rosen and Patricia Persaud).

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New technique development:

Sophisticated new techniques are being developed by a variety of research groups to make use of multiple SAR image acquisitions over a given area and are called "Permanent Scatterers, Persistent scatterers, Point Target Analysis, etc." These methods develop time histories of deformation at specific, possibly unconnected pixels within an interferogram. These methods have not yet been implemented in ROI_PAC, but may be in the next few years. For the time being, here is a partial list of commercial software packages that do these analyses (no open-source software yet exists):

Andy Hooper's Open Source manual for StaMPS (Stanford Method for PS)

Permanent scatters by Ferretti et al.

Point Target Analysis by GAMMA

Persistent Scatterer Interferometry (PSI) by NPA

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For more information, please contact: Matt Pritchard
e-mail: mp337-at-cornell.edu

Updated: 5/13/06