Stepping into finer scale in situ geometric calibration of higher resolution altimetry and linking the geodetic validation to finer scale processes.
Bass Strait separates mainland Australia from Tasmania – it is a coastal domain (30-80 m depth) with significant yet predictable ocean tides, reasonably high spatial variability of sea state, yet quiet ocean dynamics. The work proposed in this region extended and expanded the longstanding validation of nadir altimetry over 28+ years at the Bass Strait facility that was located within the SWOT 1-day repeat validation orbit.
The Bass Strait validation campaign focused on the further development of a geometric geodetic approach that includes Global Navigation Satellite System (GNSS) / Inertial Navigation System (INS) equipped buoys, an array of coastal oceanographic moorings (pressure, temperature, salinity and 5-beam ADCPs / current, wave, pressure inverted echo sounders – CWPIES), and enhancements to regional high-resolution oceanographic modelling over the Bass Strait domain. The project included preparatory studies with deployments along a Sentinel-3B track, followed by extended deployments along Sentinel-6 Michael Freilich Pass 088.
A series of deployment configurations for moorings and up to 9 surface buoys were under consideration for the SWOT fast sampling phase. These have the advantage of connecting SWOT validation to the heritage of the Bass Strait site given simultaneous sampling of the long-standing JAS comparison point.
The campaign allowed the collection of observed SSH, current (U, V) and 3D wave spectra time series from numerous point locations in Bass Strait. These were combined with outputs from a high-resolution regional ocean model. A flexible deployment approach enabled specific questions to be addressed during the validation phase. The Bass Strait campaign contributed to achieving a robust understanding of SWOT measurements and the data products that are following.
The approach was also extended to observations at the Southern Ocean Time Series (SOTS) mooring location (~47°S ~142°E) and within the Great Barrier Reef (Davies Reef, ~19°S, ~148°E, and potentially the Yongala Australian National Reference Station, ~19°S, ~147°E). The SOTS long term ocean observatory is located SSW from Tasmania in an energetic region of the sub-Antarctic Southern Ocean. The mooring here have been augmented with a GNSS unit which is successfully observing wave state in one of the harshest environments globally. Work has commenced to derive sea surface height from the GNSS in combination with the continuously observed water column sampling to enable a comparison of in situ data against satellite observations. The Davies Reef site had a radar tide gauge and GNSS augmented to the instrument tower. Davies Reef and Yongala are located in the coastal domain on the same fast sampling phase pass as the SOTS mooring – this provided an additional consistency test for SWOT over a few thousand kilometers of the 1 day repeating orbit.
The Bass Strait validation facility was supported by Australia’s Integrated Marine Observing System (IMOS) – IMOS is enabled by the National Collaborative Research Infrastructure Strategy (NCRIS). IMOS is operated by a consortium of institutions as an unincorporated joint venture, with the University of Tasmania as Lead Agent.
Principal Investigators: Christopher Watson (University of Tasmania), Benoit Legresy (CSIRO)
Contact point for the study site: Christopher Watson (cwatson@utas.edu.au) (University of Tasmania), Benoit Legresy (benoit.legresy@csiro.au) (CSIRO)
