I posted this inquiry in the grass-user list.
JAXA is providing free access to PALSAR 50m Orthorectified K & C Mosaic. According to the website, data are provided in:
Data files (Raw format) and image files (PNG format)
I'm looking for open source apps that can read and export this data to the more common raster formats like geotiff, etc.
The header file is described in this pdf: http://www.eorc.jaxa.jp/ALOS/en/kc_mosaic/map/PALSAR_MSC_dsc.pdf
UPDATE: I found a non-foss application that can directly read the kc_mosaic format. It is called MapReady developed by the Alaska Satellite Facility. It can convert to various image format including geotiff.
Another tool is the Next ESA SAR Toolbox (NEST). However testing with NEST4C-1.1, the data format is not recognized.