GRSPI, a Prototype for an Optimal Orbiting GNSS Science Instrument

Science-based instruments which use radio signals from Global Navigation Satellite Systems (GNSS) have been successfully deployed on several NASA missions. Applications range from Precise Orbit Determination (POD), limb sounding and formation flying. Remotely sensing the Earth's surface using reflected GNSS signals as a bi-static radar source (GNSS-R) is one of the most challenging applications of radiometric instrumentation. As part of NASA's Instrument Incubator Program, our group at JPL is building a prototype instrument, GRSPI (GNSS, Remote-Sensing, POD Instrument), to address a variety of GNSS science needs. Observing GNSS reflections is one focus of the design and development effort but technology for additional science needs will also be developed. GRSPI will process upcoming additions to the GPS signal structure which will improve accuracy for POD as well as limb sounding. This paper outlines the GRSPI design as it would apply to a next generation science instrument giving specific attention to observing science quality GNSS-R signals from low Earth orbit. Keywords; GNSS-R, GRSPI, Global Positioning System, BlackJack GPS, Galileo, Bi-static radarIntroduction