| dc.description.abstract | The Global Navigation Satellite System (GNSS) brings many conveniences to humanity. In addition to precise positioning and timing, GNSS can also be applied to Earth observation, such as atmospheric studies, space weather and phenomena above the sea surface. GNSS-R/RO (GNSS-Reflectometry/Radio Occultation) are satellite based remote sensing techniques that use GNSS measurement of reflected/direct navigation satellite signals by LEO (Low Earth Orbit) satellite. With analysis of the received signal, the characteristics of the medium along the signal track can be retrieved from signal differences. The applications of LEO satellites in GNSS-R/RO observation can greatly increase the amount of data points above the ocean area, obtaining information on the atmosphere and ionosphere, which provides data to be assimilated for numerical weather prediction, or to establishing ionosphere models for space weather monitoring.
In accordance with high demand on satellite remote sensing of atmosphere and sea surface around the world, the Taiwan Space Agency (TASA) leads the GNSS-RO program in Taiwan, along with international cooperation. With the success and experience in GNSS measurement from FORMOSAT-3/COSMIC and FORMOSAT-7/COSMIC-2, TASA started the next GNSS measurement project, TRITON, for GNSS-R technical verification and providing users with sea surface data. Considering the COSMIC-2 observation capacity and the evolution of the commercial SPIRE satellite constellation for Earth observation, TASA has decided to have discussions about the feasibility of the next generation GNSS-R/RO satellite.
This article collects information from contemporary GNSS-R/RO satellite programs, conferences and data user requirements. Under the condition of revisiting the Taiwan ground station, constellations are built following user requirements and designed as Walker constellations. Using GPS (Global Positioning System) as the navigation satellite constellation utilized for GNSS-R/RO event simulation, the article discusses the coverage Figure of Merit (FOM ) in cases and demonstrates results as well. CubeSats are also popular nowadays for Earth observation. Therefore, this thesis establishes two scenarios for CubeSats and MicroSats respectively in the GPS-R simulation. In the GNSS-R/RO event simulation process, STK (System Tool Kits) provides orbit propagation and the Vector Geometry Tool, which are helpful in reducing complexity in the calculations. With the capacity of GNSS-R/RO measurement and requirements of the end user, this paper will demonstrate simulation results, and provide probable future applications. | en_US |