TOGA, a prototype for an optimal orbiting GNSS-R instrument

Remotely sensing the Earth´s surface using GNSS (Global Navigation Satellite System) signals as bi-static radar sources is one of the most challenging applications for radiometric instrument design. As part of NASA´s Instrument Incubator Program, our group at JPL is building a prototype instrument, TOGA (Time-shifted, Orthometric, GNSS Array), to address a variety of GNSS science needs. Observing GNSS reflections is major focus of the design/development effort. The TOGA design features an electronically steered antenna (ESA) array which forms simultaneous high-gain beams in multiple directions. Multiple FPGAs provide flexible digital signal processing logic to process both GPS and Galileo reflections. A Linux operating system based science processor serves as experiment scheduler and data post-processor. This paper outlines the TOGA design approach as it applies specifically to observing science quality GNSS-R signals from low Earth orbit.