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

Abstract

Updated absolute calibration results from Bass Strait, Australia, are presented for the TOPEX/Poseidon (T/P) and Jason-1 altimeter missions. Data from an oceanographic mooring array and coastal tide gauge have been used in addition to the previously described episodic GPS buoy deployments. The results represent a significant improvement in absolute bias estimates for the Bass Strait site. The extended methodology has allowed comparison between the altimeter and in situ data on a cycle-by-cycle basis over the duration of the dedicated calibration phase (formation flight period) of the Jason-1 mission. In addition, it has allowed absolute bias results to be extended to include all cycles since the T/P launch, and all Jason-1 data up to cycle 60. Updated estimates and formal 1-sigma uncertainties of the absolute bias computed throughout the formation flight period are 0 ± 14 mm for T/P and +152 + 13 mm for Jason-1 (for the GDR POE orbits). When JPL GPS orbits are used for cycles 1 to 60, the Jason-1 bias estimate is 131 mm, virtually identical to the NASA estimate from the Harvest Platform off California calculated with the GPS orbits and not significantly different to the CNES estimate from Corsica. The inference of geographically correlated errors in the GDR POE orbits (estimated to be approximately 17 mm at Bass Strait) highlights the importance of maintaining globally distributed verification sites and makes it clear that further work is required to improve our understanding of the Jason-1 instrument and algorithm behavior.

Keywords:

• altimeter calibration
• GPS buoy
• Jason-1
• TOPEX/Poseidon

Acknowledgments

The CSIRO Earth Observation Centre (EOC) provided funding for this experiment. The first author is supported by an Australian Postgraduate Award and CSIRO scholarship. Geoscience Australia maintains the data from the BUR1 GPS installation and also operates the Australian Regional GPS Network (ARGN). The National Tidal Facility (NTF) operate and maintain the Burnie tide gauge with the assistance from the Burnie Ports Corporation. The CSIRO Marine Research 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. Bruce Haines, Phil Callahan, and other members of the TOPEX/Poseidon and Jason-1 SWT provided valuable responses to numerous technical questions. Michael and Bradley Hardy are thanked for operating the boat and providing assistance during the buoy deployment campaign.

Notes

*The SSH_Mooring error estimate assumes independent GPS buoy comparisons on a half hourly basis, therefore n = 26 over 5 buoy deployments.

**Uncertainties are per overlight, based on SWH < 1.5 m.

***n = 18 over the formation flight period.