Abstract
Rising sea levels pose one of the greatest threats to coastal zones. However, sea-level changes near the coast, particularly absolute sea-level changes, have been less well monitored than those in the open ocean. In this study, we aim to investigate the potential of Global Navigation Satellite Systems Interferometric Reflectometry (GNSS-IR) to measure coastal absolute sea-level changes and tie on-land (coastal GNSS) and offshore (satellite altimetry) observations into the same framework. We choose three coastal GNSS stations, one each in regions of subsidence, uplift and stable vertical land motions, to derive both relative sea levels and sea surface heights (SSH) above the satellite altimetry reference ellipsoid from 2008 to 2020. Our results show that the accuracy of daily mean sea levels from GNSS-IR is <1.5 cm compared with co-located tide-gauge records, and amplitudes of annual cycle and linear trends estimated from GNSS-IR measurements and tide-gauge data agree within uncertainty. We also find that the de-seasoned and de-trended SSH time series from GNSS-IR and collocated satellite altimetry are highly correlated and the estimated annual amplitudes and linear trends statistically agree well, indicating that GNSS-IR has the potential to monitor coastal absolute sea-level changes and provide valuable information for coastal sea-level and climate studies.
Highlights
IntroductionIt is increasingly important to monitor and quantify coastal sea-level rise, and to determine the potential impact of climate changes on coasts (e.g., from sea-level rise)
Rising seas due to global warming present a major threat to coastal zones [1,2,3,4].It is increasingly important to monitor and quantify coastal sea-level rise, and to determine the potential impact of climate changes on coasts.coastal zones, where most human interactions with the ocean occur, remain an observational gap in our sea-level knowledge [5]
Considering the aforementioned advantages of Global Navigation Satellite Systems Interferometric Reflectometry (GNSS-IR) compared with tide gauges and satellite altimetry, we aim to address in this study the following questions: (1) Can Global Navigation Satellite Systems (GNSS)-IR measure the seasonal cycle in sea level—one of the most important non-tidal components of sea-level records—and how well does it measure the seasonal cycle compared to co-located tide-gauge records? (2) Can coastal GNSS stations provide reliable geocentric sea-level changes to quantify long-term sea-level trends, one of the essential indicators of climate change? We investigate both relative sea-level changes from
Summary
It is increasingly important to monitor and quantify coastal sea-level rise, and to determine the potential impact of climate changes on coasts (e.g., from sea-level rise). Coastal zones, where most human interactions with the ocean occur, remain an observational gap in our sea-level knowledge [5]. The two most commonly used systems for directly measuring sea levels are land-based tide gauges and satellite altimetry. Tide gauges have been providing valuable information about sea-level changes at the coast since 1831, when the first operational automatic tide gauge was installed [6], whereas satellite altimetry has been continuously monitoring open-ocean sea surface heights since 1992, when the first satellite mission designed for sea-level studies was launched [7]. Sea-level observations from these two observing systems suffer from several limitations
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