====== ROI_PAC Overview ====== Here is a list of procedures you will need to perform as you produce your interferograms. Each section corresponds to a major step involved in processing your data. Follow the links in each numbered step to view more detailed instructions. If you are using ROI_PAC for the first time, go to the [[install|installation page]] to install and test the software. ===== Choosing a Region of Study ===== You first, obviously, need to locate your area of interest. You must make sure that it is in an area that will be coherent (e.g. not a lot of vegetation or atmospheric disturbance). It is helpful to research the geology of the area as well as what type of natural and man-made processes have happened in the past that could have produced ground displacement. For example, if you want to map out a landslide in an area that is tectonically active, you will want to make sure you understand the earthquake history in the area so that you don't confuse coseismic surface displacements with landslide displacements. ===== Obtaining SAR data ===== Next, it is time to actually download your SAR data. You will likely need to produce many interferograms in order to fully investigate an area, and for each interferogram you will need two SAR scenes. There are various [[sar|online catalogues]] where you can search for interferometric pairs based on the location, date, and baseline. If your institution is a member of the [[sar#WInSAR|WInSAR Consortium]], you can download SAR data for the western U.S. from their website. ===== Downloading Orbit Files ===== There exist two sources for obtaining accurate orbits for the ERS satellites. The [[http://www.deos.tudelft.nl/|Delft Institute for Space-Oriented Space Research]] (DEOS) provides orbit information for both [[http://www.deos.tudelft.nl/ers/precorbs/|ERS and ENVISAT]]. An alternative source is the [[http://earth1.esrin.esa.it/f/eeo2.400/pgersorbprc|Precise Orbit Product]] through the [[http://www.esa.int/|European Space Agency]] (ESA). Download instructions are posted [[orbits|here]]. This step does not have to be repeated once the orbit files are downloaded for a given scene. ===== DEM Preparation ===== In order to use the two-pass method, a Digital Elevation Model (DEM) is necessary to subtract out the topographic contribution from the interferogram. Global DEM data can be obtained from the [[http://srtm.usgs.gov/|Shuttle Radar Topography Mission (SRTM)]]. It can also be obtained indirectly from the SAR scenes using the three-pass method. A detailed list of procedures that explain how to use SRTM data can be found here: [[srtm|Using SRTM data]]. This step does not have to be repeated once the DEM is created. ===== ROI_PAC Processing ===== You are finally ready to use the program ROI_PAC to produce interferograms. You will need to be familiar with [[:links#Unix|Unix commands]] in order to navigate through the file system and perform tasks. **1)** After you have downloaded your SAR data and [[:roipac:process:process#File Management|renamed]] the files appropriately, you will have to pre-process that data using the [[:roipac:process:process#make_raw.pl|make_raw.pl]] script. **2)** Create a [[:roipac:process:process#Parameter File Setup|parameter file]] that tells ROI_PAC the location of the SAR data files, the various processing parameters, and where to place the output files. **3)** Finally, start the processing by running the script [[:roipac:process:process#process_2pass.pl|process_2pass.pl]]. This perl script runs a sequence of programs that eventually produces your differential interferogram. ===== Viewing Your Results ===== It's now time to interpret your data! ROI_PAC produces a long list of intermediate and final [[:output|output files]]. Typically, the final product is a geocoded unwrapped interferogram (geo_//date1-date2//.unw). An image viewer is not distributed along with ROI_PAC. You can use a variety of external programs to view your results (i.e. mdx, dgx, [[:matlab|Matlab]], GMT, ENVI, or other program that is flexible enough to read a binary image file). After you view your results, you may choose to re-process your data with different initial [[:roipac:process:parameter|parameters]] or experiment with some [[:advanced|advanced techniques]].