NASA is interested in passive remote sensing of earth science parameters including biomass, soil moisture and ice properties, which are important for hydrology, climatology, and agriculture. Since Global Navigation Satellite System (GNSS) signals are scattered differently when reflected from ocean, land, or ice, they can be used to observe and study the changes induced by the reflecting surface. GNSS-Reflectometry (GNSS-R) based remote sensing can give environmental scientists a low-cost, wide-coverage measurement network to gain insight on the Earth’s environmental processes. IAI and collaborators are developing a GNSS Reflectometer Instrument for Bi-static Synthetic Aperture Radar (GRIBSAR) to measure earth science parameters. The full-time operation of radio navigation satellite 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. IAI's approach is modular and scalable, and meets NASA's goals of a multi-channel GNSS-R system to exploit GNSS-reflected signals as SOO. IAI will continue development of the complete GRIBSAR system. This phase of development includes a passive, highly sensitive GNSS-Rx instrument, GNSS antenna array, Delay-Doppler Map (DDM) and BSAR processing routines, as well as a flight integration and test plan. GRIBSAR will feature a real-time, high-resolution, data-logging and processing module, allowing for concurrent reception of multiple satellite systems.