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====== Parameter File Setup ======
The parameters that ROI_PAC uses to create interferograms must be specified in a text file, which is then passed to the processing script.  This file can have any name but by convention it is called ''param.txt''.  Create ''param.txt'' in the directory which contains the directories for the master and slave SAR scenes (e.g. the 19970104-19991220/ directory created in the [[makeraw|previous step]]).

At the basic level, the ''param.txt'' file must list four parameters: the directories containing the master and slave SAR scenes, the main output directory (called ''INT'' by convention but may be named arbitrarily), and the location of the DEM file that will be used.  Below is an example of the layout of a parameter file:

<code>
SarDir1=19970104
SarDir2=19991220
IntDir=INT
DEM=/research/insar/dem/bayarea.dem
</code>
The ''SarDir1'', ''SarDir2'', ''IntDir'', and ''DEM'' parameters are always required.  Additional optional parameters include the preferred spatial resolution, the type of spatial filter, and other specialized modifications.  For a list of all the possible parameters, see [[parameter_details|Parameter File Details]].

  * **Go to the next step:** [[process2pass|Using process_2pass]]