Global Navigation Satellite System (GNSS) signals scattered from ocean, land and ice are affected by the reflecting surface, and hence the changes induced by the surface can be observed. The full-time operation of radio navigation satellites system, abundant global signal coverage and spread spectrum communication for flexible signal processing makes GNSS reflected signals a viable candidate for Signal-Of-Opportunity (SOO) passive sensing. Existing research has shown that GNSS-Reflectometry (GNSS-R) based remote sensing has the potential to give environmental scientists a low-cost, wide-coverage measurement network that will greatly increase our knowledge of the Earth's environmental processes. The Intelligent Automation, Inc. (IAI) team proposes to develop a GNSS Reflectometer Instrument for Bi-static Synthetic Aperture Radar (GRIBSAR) for measuring earth science parameters. Our proposed approach is modular, scalable and meets the NASA goals of multi-channel, GNSS-R system to exploit GNSS reflected signals as SOO.