Abstract
Global Navigation Satellite System (GNSS)-equipped buoys have a fundamental role in the validation of satellite altimetry. Requirements to validate next generation altimeter missions are demanding and call for a greater understanding of the systematic errors associated with the buoy approach. In this paper, we assess the present-day buoy precision using archived data from the Bass Strait validation facility. We explore potential improvements in buoy precision by addressing two previously ignored issues: changes to buoyancy as a function of external forcing, and biases induced by platform dynamics. Our results indicate the precision of our buoy against in situ mooring data is ~15 mm, with a ~8.5 mm systematic noise floor. Investigation into the tether tension effect on buoyancy showed strong correlation between currents, wind stress and buoy-against-mooring residuals. Our initial empirical correction achieved a reduction of 5 mm in the standard deviation of the residuals, with a 51% decrease in variance over low frequency bands. Corrections associated with platform orientation from an Inertial Navigation System (INS) unit showed centimetre-level magnitude and are expected to be higher under rougher sea states. Finally, we conclude with further possible improvements to meet validation requirements for the future Surface Water Ocean Topography (SWOT) mission.
Highlights
With a record length approaching 30 years, satellite altimetry is an established observational tool central to the understanding of Earth’s ocean circulation and its response to a warming climate [1,2,3]
The deployment-wise mean differences between the mooring and buoy time series appears reasonably normally distributed with a median of −0.1 mm and a standard deviation of 9.2 mm, while the buoy minus mooring residual has an average 14.9 mm standard deviation, with 3.9 mm scatter within the deviation values
The deployment-wise mean differences between the mooring and buoy time series appears reasonably normally distributed with a median of −0.1 mm and a standard deviation of 9.2 mm, while the buoy minus mooring residual has an average 14.9 mm standard deviation, with 3.9 mm scatter withRienmottheeSednse. v20i2a0t,i1o2n, 30v0a1lues
Summary
With a record length approaching 30 years, satellite altimetry is an established observational tool central to the understanding of Earth’s ocean circulation and its response to a warming climate [1,2,3]. The societal importance of the altimeter sea level climate record underscores the requirement for a sustained and rigorous calibration and validation (cal/val) of the observational dataset. Bonnefond et al [20] installed two GNSS receivers on a catamaran to observe the marine geoid which was later used for validation of Jason-1 at the Corsica site operated by the Centre National D’Etudes Spatiales (CNES, the French Space Agency). The small RMS arguably benefitted from near shore calm sea states and short baseline GNSS processing. Their study obtained a larger RMS between the buoy and in situ mooring data of ~21 mm, yet they suggested the dominant driver of this variability was thought to originate from the buoy
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