This paper discusses mountaintop-based GNSS radio occultation and reflection experiments conducted in April 2015 and May 2017 on the summit of Haleakala, Maui, and the experiment data processing results. The objective of these experiments was to study signatures of GNSS signal carrier waves traversing ionospheric and tropospheric structures and low grazing angle reflections scattered off the ocean surface. The purpose was to gain an understanding of the disturbances experienced by these signals to enable development of two classes of robust, accurate GNSS receiver signal processing algorithms. The first class aims to improve navigation under naturally-occurring, challenging conditions, while the second class is for remote sensing of the ionosphere, atmosphere, and Earth surface using GNSS measurements. This paper will summarize some of the findings from processing the data collected during the experiments. These findings include: (1) performance differences between open loop tracking and advanced close-loop carrier tracking; (2) separation of troposphere scintillation and ocean surface multipath reflection signatures to enable retrieval of the troposphere profiles and ocean surface condition characterization; (3) detection of the planetary boundary layer using the signal amplitude time sequences.
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