GPS as Signals-of-Opportunity for Remote Sensing of Ionosphere, Atmosphere, and Earth Surface
GPS has impacted nearly every aspect of our modern society. Yet, it relies on extremely low power signals traversing a vast space to reach receivers on the Earth surface. Numerous factors interfere with the signals along their propagation path, including ionosphere plasma, moisture in the lower troposphere, and multipath reflections from Earth surface. Understanding these effects on navigation signals is the pre-requisite for developing robust navigation technologies. Moreover, these effects enable satellite navigation signals to function as signals-of-opportunity for low cost, distributed, passive sensing of the signal propagation environments. This lecture will discuss the effects of the space and local environments on satellite navigation signals, followed by the latest technology development to mitigate these effects, and finally case studies demonstrating the powerful applications of the satellite navigation signals for space weather monitoring, atmospheric profiling, ocean wind speed mapping, and precision altimetry measurements over ocean, sea ice, inland water bodies, and land cover.