Development and application of GNSS remote sensing techniques for Earth Observation

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The radio occultation (RO) technique uses a space-based Low Earth Orbit (LEO) satellite receiver to receive GPS/GNSS signals and perform limb sounding on the Earth atmosphere and ionosphere. Due to the success of FormoSat-3/ Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) consisting of six micro-LEO satellites, the joint U.S. and Taiwan RO team, lead separately by the National Oceanic and Atmospheric Administration (NOAA) and Taiwan National Space Organization (NSPO), have decided to move forward with a COSMIC follow-on mission (called FS7/COSMIC2. The GNSS RO payload, named Tri-G GNSS Radio-occultation System (TGRS) will receive multi-channel GPS, GLONASS, and Galileo satellite signals and will be capable of tracking more than 10,000 RO observations per day after both low- and high-inclination constellations are fully deployed. It is expected that denser RO scintillation observations will be used to accurately structure and model the Earth atmosphere and ionosphere.In addition, the special kind of GNSS multi-path delay reflected from the Earth surface could be used to sense the Earth surface environments such as ocean altimetry and sea state. This has brought out the need of designing and developing appropriate receivers in order to track and process reflected and scattered GPS/GNSS signals in real-time to avoid the storage of huge volumes of raw data. We also propose to apply the Field Programmable Gate Array (FPGA) to the GPS/GNSS Reflectometer Instrument achieving a high synchronism and a most benefit of the available hardware resources. Using Simulink/Matlab, the FPGA can also compute complex Delay-Doppler Map (DDM) data in real-time by correlating the in-phase and quadrature components of the baseband signals. A real-time high resolution DDM reflectometer can be implemented at both GPS L1 and L2 frequency. This study will address new objectives and results of GNSS remote sensing in the atmosphere, ionosphere, ocean altimetry and sea state as well as new opportunities for the future FS7/COSMIC2 mission. The project will be accomplished at Institute of Geodesy and Geoinformation Science of Technische Universität Berlin (IGG TUBerlin) in close connection with scientists at Deutsches GeoForschungs Zentrum (GFZ) Potsdam and Taiwan GPS Science and Application Research Center (GPSARC) at National Central University (NCU).Objectives of the project can be summarized as:(1) using GPS/GNSS RO atmosphere data and developing advanced algorithms for the lower troposphere and climatological investigations,(2) retrieving and monitoring sporadic E (Es) layer, scintillations and related effects including vertical couplings, and(3) developing real-time FPGA based GPS/GNSS reflectometer for applications on ocean altimetry and sea state observations.