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====== 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 different scenes. 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. The program [[EOLISA]] is a great tool that pairs scenes that can be correlated. It allows you to search for various pairs based on their location, date, baseline (the perpendicular distance between the 2 passes) and other various parameters. You can purchase scene data directly through EOLISA, or if your institution is a member of the WInSAR Consortium you can download data for the western U.S. free of charge from the [[http://winsar.unavco.org|Winsar website]]. Links to detailed explanations: [[EOLISA|EOLISA]]; [[winsar|WInSAR]]. ===== 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 directly from SAR scenes. A detailed list of procedures that explain how to use an SRTM DEM can be found here: [[srtm|Using SRTM data]]. Details on how to use SAR data can be found here: [[sar_dem|Using SAR data]]. ===== ROI_PAC Processing ===== You are finally ready to use the program ROI_PAC to produce interferograms. You will need to be familiar with Unix commands in order to store data and perform tasks. - After you have downloaded your scene data, you will have to pre-process that data using the [[:roipac:process:makeraw|]] script. - You will then need to create a [[:roipac:process:parameter|parameter file]] that tells ROI_PAC where to obtain the input files, the processing parameters, and where to put the output files. - After you have downloaded your scene data, you will have to pre-process that data using the [[:roipac:process:makeraw|]] script. - You will then need to create a [[:roipac:process:parameter|parameter file]] that tells ROI_PAC where to obtain the input files, the processing parameters, and where to put the output files. - Finally, in order to process the data you will need to run the script called [[:roipac:process:process2pass|process_2pass]]. ''**process_2pass.pl**'' is the primary processing script that will run a long series of programs that eventually produces your differential interferogram. - Since this process involves many complicated steps, be prepared to encounter various types of problems. While you run process_2pass, **Log** files will be produced in the directory in which your data is stored. These files record what the program has done and are useful for [[:trouble|troubleshooting]] when something goes wrong. ===== 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). You can use a variety of external programs to view your results (i.e. mdx, dgx, Matlab, GMT, ENVI, or other program that is flexible enough to read a binary image file). Note that an image viewer is not distributed along with ROI_PAC. 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]].