Envisat ASAR
ROI_pac can process image mode (IM) (also called stripmap) raw (or Level 0) data from the ASAR instrument on Envisat. The distributed ROI_pac is not presently capable of processing the Alternating Polarization (AP) or Wide Swath (WS) modes, although there is an effort to develop a ScanSAR interferometry processor for the Envisat WS data and an alternative technique is described below. ROI_pac is not designed to process the SLC (Level 1) data products from Envisat (although it is possible with a lot of extra work).
Envisat ASAR Level 0 (raw) data is a single file (the standard ESA name for the stripmap data is in the form ASA_IM__0*.N1 or if you get data from WInSAR it will have the form ENV1*.baq) so you can just copy this to your computer.
The make_raw_envi.pl script is now included in the ROI_pac version 3.0.x releases, along with a program asa_im_decode written by SeanBuckley that actually reads the Envisat IM data. The script can use either the orbits from ESA (called the Doris orbits) or the Delft (ODR) orbits for Envisat. Note that the script extracts the orbit information from the ODR, POR or VOR orbits and stores them in a hdr_$date.rsc file with the raw data. For the rest of ROI_pac processing, you use $orbit_type=HDR. This script can concatenate or merge multiple scenes.
To use the ESA Doris orbits (contact the ESA Help Desk EOHelp@esa.int for information on where to get these) you need to set the environment variables POR_DIR and VOR_DIR to point to directories of the POR (preliminary orbits) and VOR (precise orbits), and give the DOR parameter to the make_raw_envi.pl call. The ESA Doris POR orbits are usually available within about three days after acquisition and the VOR orbits are available about six weeks after acquisition. The ROI_pac software will first look for a VOR orbit for the desired date, and if there is no VOR orbit then it looks for a POR orbit.
In addition to the data file and the orbit files, you also need to have the set of Envisat instrument calibration (INS) files on your computer. Create a INS directory and download all of the ASA_INS* files from http://envisat.esa.int/services/auxiliary_data/asar/ into the directory. Note that the INS files for older data (pre 2007) may be compressed, so you will have to gunzip or unzip them if they are. Then set the environment variable INS_DIR to point to that directory. The make_raw_envi.pl script will determine which of the INS files to use. Note that you need to update the INS files every year or when there is a change in the calibration of the Envisat ASAR instrument.
Another script make_raw_envi_subset.pl and associated programs are not part of the 3.0 release but here under ContribSoftware. This script is for extracting a subset of a long "floating pass" product of ASAR Level 0 data.
Envisat ScanSAR
A new set of code has been contributed by CunrenLiang at Peking University to process Envisat WS data in ROI_pac using the zero-pulse padding technique, see the ContribSoftware page to download it, and the EnvisatScanSar page for more details.
older information
There are also some older versions of the Perl scripts and a program to do the "make_raw" import into ROI_pac available at:
http://winsar.stanford.edu/software/envisat/
http://www.geo.cornell.edu/eas/PeoplePlaces/Faculty/matt/ROI_PAC4ENVISAT.tar (a slightly newer version)