Validating a New GNSS-Based Sea Level Instrument (CalNaGeo) at Senetosa Cape

Abstract

The geodetic Corsica site was set up in 1998 in order to perform altimeter calibration of the TOPEX/Poseidon (T/P) mission and subsequently, Jason-1, OSTM/Jason-2, Jason-3 and more recently Sentinel-6 Michael Freilich (launched on November, 21 2020). The aim of the present study held in June 2015 is to validate a recently developed GNSS-based sea level instrument (called CalNaGeo) that is designed with the intention to map Sea Surface Heights (SSH) over large areas. This has been undertaken using the well-defined geodetic infrastructure deployed at Senetosa Cape, and involved the estimation of the stability of the waterline (and thus the instantaneous separation of a GNSS antenna from water level) as a function of the velocity at which the instrument is towed. The results show a largely linear relationship which is approximately 1 mm/(m/s) up to a maximum practical towing speed of ∼10 knots (∼5 m/s). By comparing to the existing “geoid” map, it is also demonstrated that CalNaGeo can measure a sea surface slope with a precision better than 1 mm/km (∼2.5% of the physical slope). Different processing techniques are used and compared including GNSS Precise Point Positioning (PPP, where the goal is to extend SSH mapping far from coastal GNSS reference stations) showing an agreement at the 1-2 cm level.

Keywords:

• Calibration and validation
• GNSS
• satellite altimetry
• marine geoid
• water level

Acknowledgements

This study has been conducted and financed thanks to Centre National d’Etudes Spatiales (CNES), Centre National de la Recherche Scientifique (CNRS), and French Ministry of Research. This work has also received technical support from CNRS UAR855, INSU Technical Division. Special thanks to Claude Gaillemin who takes care of all the instruments at Cape Senetosa since 1998 and performs the deployments of the GNSS-based systems for sea level measurements.

Data availability statement

The data that support the findings of this study are available from the corresponding author [PB], upon reasonable request.

Additional information

Funding

This work was supported by Centre National d’Etudes Spatiales.