====== Why would you use InSAR (Interferometric Synthetic Aperture Radar)? ====== InSAR is a tool that can be used to measure surface deformation of the Earth at a very fine level of precision. SAR satellites image the Earth's surface by transmitting and receiving electromagnetic radiation with wavelengths of a few centimeters. Satellite interferometry entails the input of 2 satellite images of a specific location on the Earth's surface into one output image. The output image represents the difference in received phase between the first satellite image (master SAR scene) and the second satellite image (slave SAR scene), given that the two passes occurred at different times (weeks to years). If any surface displacement occurred in the interim at that given location, the received electromagnetic wave phase of the second pass would differ from the phase of the first pass, and surface displacement can be calculated from this phase shift. InSAR is most useful for detecting and measuring the effects of events such as: shallow earthquakes; magma intrusions and their affect on the surface (volcanoes); subsurface fluid extraction/injection; movement of ice sheets; slow landslides; or any natural or man-made geologic event that produces small surface displacements (on the order of centimeters) over time. InSAR can be a time consuming procedure as many errors can arise as a product of the type of surface you are investigating as well as errors within the production of interferograms themselves. It is important to point out that heavily vegetated areas usually produce incoherent images since plants grow and change over time quite rapidly compared to geologic processes. Permanent structures such as buildings or rock faces usually produce the most coherent images. This wiki is designed to aid the processing of interferograms using the software ROI_PAC. In order to use ROI_PAC, it is critical that the user is comfortable in the UNIX operating environment. All scripts are run from the command line. Unix beginners may find a tutorial of basic Unix commands such as [[http://mally.stanford.edu/~sr/computing/basic-unix.html|this one]] helpful. Most of the code is written in Perl, C, and Fortran. Hopefully this documentation will help you in your quest to produce coherent interferograms. We encourage addition to this wiki to advance the use of interferometry in the future. So far there are satellites flying for the European Space Agency, the Japanese Space Agency, and the Canadian Space Agency designed for InSAR. Hopefully, with the advance of interferometry, we will be able to push NASA to develop a United States InSAR satellite. Do what you can to advance this existing technology so that its uses can be expanded to many other fields of research and industry. **Table of Past and Present InSAR Satellites** ^Agency ^Satellite ^Years of Operation ^ |ESA | ERS-1 | 1991-1996 | | | ERS-2 | 1995-present | | | Envisat | 2002-present | |JSA | JERS-1 | 1992-1998 | | | ALOS | 2006-present | |CSA | RADARSAT-1 | 1995-present | | | RADARSAT-2 | planned launch 2007 | To see an overview of how to use Roi_Pac, go to the [[overview|overview]].