Item

Abstract

We propose to establish a new mean sea level observing system that consists of a global array of thousands of drifting buoys tracked by a Global Navigation Satellite System. The recorded height of the sea surface along such Lagrangian trajectories, when averaged over geographical areas, will provide daily estimates of regional and global mean sea levels. This new system will be independent of existing systems, resilient, sustainable, and comparatively economical. Using the example of the historical trajectories of the drifters of the NOAA Global Drifter Program (GDP), we have demonstrated that with the current configuration of the GDP array, global-mean sea-level decadal linear trend estimates with an uncertainty less than 0.3 mm per year could be achieved with daily random error of 1.6 m or less in the vertical direction for each individual drifter daily estimate. To test this requirement, we conducted a pilot project by deploying drifters in a moored configuration at two coastal locations in close proximity of reference tide gauges. We found that a standard GDP drifter equipped with a single-frequency u-blox GPS chipset and onboard processing do not always meet the required vertical accuracy. In contrast, a gold standard drifter equipped with a geodetic-grade GPS chipset continuously recording its dual-frequency raw tracking data from four global navigation satellite systems achieves the required accuracy. As such, a pathway exists to deliver the envisioned new global mean sea-level observing system as an added value to the NOAA Global Drifter Program.