Absolute Calibration in Bass Strait, Australia: TOPEX, Jason-1 and OSTM/Jason-2

Abstract

Updated absolute bias estimates are presented from the Bass Strait calibration site (Australia) for the TOPEX/Poseidon (T/P), Jason-1 and the Ocean Surface Topography Mission (OSTM/Jason-2) altimeter missions. Results from the TOPEX side A and side B data show biases insignificantly different from zero when assessed against our error budget (−15 ± 20 mm, and −6 ± 18 mm, respectively). Jason-1 shows a considerably higher absolute bias of +93 ± 15 mm, indicating that the observed sea surface is higher (or the range shorter), than truth. For OSTM/Jason-2, the absolute bias is further increased to +172 ± 18 mm (determined from T/GDR data, cycles 001–079). Enhancements made to the Jason-1 and OSTM/Jason-2 microwave radiometer derived products for correcting path delays induced by the wet troposphere are shown to benefit the bias estimate at the Bass Strait site through the reduction of land contamination. We note small shifts to bias estimates when using the enhanced products, changing the biases by +11 and +3 mm for Jason-1 and OSTM/Jason-2, respectively. The significant, and as yet poorly understood, absolute biases observed for both Jason series altimeters reinforces the continued need for further investigation of the measurement systems and ongoing monitoring via in situ calibration sites.

Keywords:

• Altimeter calibration
• absolute bias
• TOPEX
• Jason-1
• OSTM/Jason-2

Acknowledgements

Two anonymous reviewers are thanked for their constructive review of this manuscript. The contribution of this absolute bias data stream is supported by the Australian Integrated Marine Observing System (IMOS), established under the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS). The GPS data were computed on the Terrawulf II computational facility at the Research School of Earth Sciences, a facility supported through the NCRIS geoscience capability, AuScope Ltd. AuScope is also acknowledged for their support of regional CGPS installations used throughout this project. This paper is a contribution to the Centre for Australian Weather and Climate Research Climate Change Research Program. J.A.C. and N.J.W. were partly funded by the Australian Climate Change Science Program. The authors thank the International GNSS Service (IGS) and Geoscience Australia for making the raw GPS data publicly available, and the National Tidal Centre (NTC) for operating and maintaining the Burnie tide gauge with assistance from the Tasmanian Ports Corporation. The CSIRO Marine and Atmospheric Research coastal mooring group undertook the setup, deployment and retrieval of the mooring array. Neil Adams from the Australian Bureau of Meteorology provided atmospheric pressure information. Altimetry products were obtained from the Jet Propulsion Laboratory (JPL) PO.DAAC and Centre National d’Études Spatiales (CNES) AVISO archives. Members of the Ocean Surface Topography Science Team (OSTST) are thanked for providing ongoing technical assistance. Aspects of this work were supported under the Australian Research Council's Discovery Projects funding scheme (DP0877381).