Study of GNSS-R Techniques for FORMOSAT Mission

The use of global navigation satellite system (GNSS) for remote sensing and environmental monitoring has been an important research topic in recent years due to the omnipresence and performance of GNSS signals. The FORMOSAT-3 and the upcoming FORMOSAT-7 have exploited the potential of GNSS-based radio occultation for profiling the ionosphere and atmosphere so that better understanding of space weather and higher accuracy in numerical weather prediction are achieved. In addition to occultation through the refraction of GNSS signals, reflection of GNSS signals is becoming an important remote sensing tool in probing sea surface height, wind velocity, salinity, soil moisture, roughness, and snow depth. This paper presents a development plan of a space GNSS-R experiment. The design of the GNSS-R receiver payload for a FORMOSAT-7 satellite is discussed with emphasis on processing of satellite-based augmentation system (SBAS) and regional navigation satellite system (RNSS) signals. It is shown that SBAS/RNSS signals can enhance GNSS reflectometry mission in terms of the increase of reflection events and repetition of the reflection location. Evidences of SBAS reflection on UK TDS-1 are reported to show that the SBAS reflected signals can indeed be processed even though the SBAS satellites are located at a geostationary orbit.