Abstract
Ground-based GNSS-R (global navigation satellite system reflectometry) can provide the absolute vertical distance from a GNSS antenna to the reflective surface of the ocean in a common height reference frame, given that vertical crustal motion at a GNSS station can be determined using direct GNSS signals. This technique offers the advantage of enabling ground-based sea level measurements to be more accurately determined compared with traditional tide gauges. Sea level changes can be retrieved from multipath effects on GNSS, which is caused by interference of the GNSS L-band microwave signals (directly from satellites) with reflections from the environment that occur before reaching the antenna. Most of the GNSS observation types, such as pseudo-range, carrier-phase and signal-to-noise ratio (SNR), suffer from this multipath effect. In this paper, sea level altimetry determinations are presented for the first time based on geometry-free linear combinations of the carrier phase at low elevation angles from a fixed global positioning system (GPS) station. The precision of the altimetry solutions are similar to those derived from GNSS SNR data. There are different types of observation and reflector height retrieval methods used in the data processing, and to analyze the performance of the different methods, five sea level determination strategies are adopted. The solutions from the five strategies are compared with tide gauge measurements near the GPS station, and the results show that sea level changes determined from GPS SNR and carrier phase combinations for the five strategies show good agreement (correlation coefficient of 0.97–0.98 and root-mean-square error values of <0.2 m).
Highlights
As of 1997, about 37% of the global population was living within 100 km of a coastline [1] and that number is still increasing
Tide gauges (TG) have been used to measure global sea level changes by providing a relative measure with respect to land [2], but land motions around a land-based tide gauges (TG) can result in inaccuracies in sea level measurements
In order to verify the possibility of sea level retrieval using the L4 method, we adopted this station as our test site [34].The aim of this paper is to present a method for retrieving sea level change data based on geometry-free linear combinations of dual-frequency carrier
Summary
As of 1997, about 37% of the global population was living within 100 km of a coastline [1] and that number is still increasing. Climate change and related global warming are expected to cause sea levels to rise, forcing people to abandon certain coastal areas that may become submerged. Accurate and effective monitoring of sea level change and its impact on social development is of vital importance. There is a decreasing number of TGs, limiting extensive sea level measurements. There is a need for additional sea level monitoring techniques. Satellite radar altimetry is a powerful technique used for monitoring sea level changes [3] and studying circulation [4] in the open ocean. Radar altimetry provides high-precision sea surface topography data, but it often has poor precision in near-shore regions because of the complex and fast changing dynamics of the ocean in these areas [5,6]. It is unable to provide information on mesoscale phenomena, such as swell and waves, which need better spatiotemporal sampling [7]
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