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Dissertation Defense

Engineering Calibration and Physical Principles of GNSS-Reflectometry for Earth Remote Sensing

Tianlin Wang

The Cyclone Global Navigation Satellite System (CYGNSS) is a NASA Earth Venture mission that uses 32 Global Positioning System (GPS) satellites as active sources and 8 CYGNSS satellites as passive receivers to measure ocean surface roughness and wind speed, as well as soil moisture and flood inundation over land. This dissertation focuses on addressing two major engineering calibration aspects: (1) characterization of the GPS effective isotropic radiated power (EIRP); (2) development of an end-to-end Level 1 calibration approach. Four research projects are discussed: (1) A ground-based GPS constellation power monitor (GCPM) system is built to measure the direct GPS signals and then to estimate the GPS transmit power; (2) The gain pattern of each GPS satellite’s transmit antenna is determined from on-orbit measurements of signal strength received by CYGNSS zenith channels; (3) A dynamic EIRP calibration approach is developed to monitor GPS EIRP in real-time and address its variability due to the fluctuation of transmit power and azimuthal asymmetry of transmit antenna gain pattern; (4) A physics-based approach is proposed to examine potential calibration errors, e.g. the CYGNSS nadir receive antenna gain pattern, by using modeling and measurements of ocean surface mean square slope (MSS).

The engineering calibration methods presented in this dissertation make significant contributions to the spatial coverage, calibration quality of the measurement and the geophysical data products produced by the NASA CYGNSS mission. The research is also useful to the system design, science investigation and engineering calibration of future GNSS-reflectometry missions.

Chair: Professor Christopher S. Ruf