Bass Strait, Southern Ocean (SOTS) and Great Barrier Reef (Davies Reef)

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 extends and expands the longstanding validation of nadir altimetry over 28+ years at the Bass Strait facility that is located within the SWOT 1-day repeat validation orbit.

The Bass Strait validation campaign focuses 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 includes 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 are 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 will allow the collection of observed SSH, current (U, V) and 3D wave spectra time series from numerous point locations in Bass Strait. These will be combined with outputs from a high-resolution regional ocean model. A flexible deployment approach will enable specific questions to be addressed during the validation phase. The Bass Strait campaign will contribute to achieving a robust understanding of SWOT measurements and the data products that will follow. 

The approach is also being 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 has 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 is in the process of having 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 will provide an additional consistency test for SWOT over a few thousand kilometers of the 1 day repeating orbit.

The Bass Strait validation facility is 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 ( (University of Tasmania), Benoit Legresy ( (CSIRO)

Surface currents (left panel) and relative vorticity ( ζ=vxuy) normalized by Coriolis frequency (f) (right panel) for the Bass Strait study site with SWOT grid overlaid (black lines). Images were generated using output from a high-resolution MITgcm simulation and are instantaneous snapshots from 1 July 2012.
Detailed view of the Bass Strait altimeter validation facility. Existing comparison points (CPs) for the Jason series (red), Sentinel-3A (cyan) and Sentinel-3B (blue) missions are shown as coloured dots. Mission ground tracks shown as coloured lines. The SWOT 1-day repeat fast sampling orbit is shown in yellow (swath limits shown as solid lines, centre nadir altimeter shown as a dashed line). The proposed activities focus on the left (western) swath. Note the red line indicates the Jason-series ground track also to be used for validation of Sentinel-6 Michael Freilich.