TOPEX/POSEIDON Science Working Team Meeting
and
Tidal Science 96 Meeting
UK, October 1996 (partially funded by EOC)
John Church and Neil White
CSIRO Division of Marine Research
Background
The USA/French TOPEX/POSEIDON satellite altimeter mission was launched in September 1992 and provides global sea surface height measurements for determining surface ocean currents and their variability, and for the determination of global sea-level change. TOPEX/POSEIDON is particularly valuable for climate research and is an essential component of the World Ocean Circulation Experiment of the World Climate Research Programme.
The satellite continues to perform well above specifications - TOPEX/POSEIDON sea-level measurements now have a single point accuracy of better than 4 cm (compared with the design specification of 13 cm). This accuracy can be improved further by spatial and temporal averaging. Continued improvement of the accuracy of TOPEX/POSEIDON sea-level measurements will continue throughout the mission. TOPEX/POSEIDON is expected to operate normally to the year 2000.
We have continued to attend TOPEX/POSEIDON Science Working Meetings with the most recent meeting occurring at the Southampton Oceanography Centre, UK (October 23-25, 1996).
1996 TOPEX/POSEIDON Science Working Team Meeting
An important meeting of the TOPEX/POSEIDON Science Working Team (SWT) was held at the Southampton Oceanographic Centre, Southampton, U.K., October 23-25, 1996. To bring us up to date with the new data processing stream for TOPEX/POSEIDON and the status of production for the new geophysical data records, the meeting was attended by Dr John Church and Dr Neil White (and Associate Professor Richard Coleman of the University of Tasmania).
The SWT meeting gave the opportunity for SWT members to present their latest results - in all, there were 20 oral presentations and 61 poster papers given during the 3 day meeting. The work done by our group on calibration of the T/P altimeter, using the Burnie site in northern Tasmania, was presented in the Altimeter Bias and Sea Level Variations section (see below).
The NASA/CNES Project Scientists also informed the SWT members about the current status of the T/P mission and gave details of future altimeter missions. The T/P mission is being extended - the T/P Extended Mission (TPEM) - for another 3 years.
Other important issues from the meeting are outlined below.
Apparent Sea-level Rise and the TOPEX/POSEIDON Bias Drift
TOPEX/POSEIDON is the only satellite with sufficient accuracy to adequately determine global sea-level rise, including that originating from anthropogenic climate change. During 1995 and 1996, there were a number of reports of higher rates of global sea-level rise than had been estimated from the historical tide gauge record. The increasing magnitude of these rates of sea-level rise generated considerable scientific, community and political interest. At the same time, we were carefully comparing the TOPEX/POSEIDON sea-level measurements with in situ sea-level measurements at our tide gauge validation site at Burnie (northern Tasmania) and several other sites. These comparisons, and comparisons done by overseas colleagues, revealed that the TOPEX altimeter was drifting with time in the sense as to give an apparent sea-level rise. These comparisons, comparisons to the Poseidon altimeter and the large offset in the TOPEX altimeter bias led to a careful re-examination of the complete data processing stream and the discovery of coding error in one of the algorithms for processing the TOPEX altimeter data. This coding error had actually occurred in earlier satellite altimeter missions but was only revealed by the unprecedented accuracy of the TOPEX/POSEIDON mission and the careful comparison of satellite and in situ observations.
The results of T/P validation projects (including our own) were reported at the Science Working Team Meeting in Southampton. There was strong agreement of the need to continue in situ observations, such as our Burnie validation site, and that these comparisons are critical to the determination of any remaining drift in the altimeter bias and thus to the determination of global sea-level rise.
TOPEX/POSEIDON Extended Mission
TOPEX/POSEIDON has surpassed its design specifications and the satellite is anticipated to continue to operate normally in an extended mission to the year 2000. Throughout this period there will be continuing improvements in the accuracy of the TOPEX/POSEIDON sea-level measurements. This will come from improved orbits and algorithms for various corrections, especially the EM Bias (sea state correction) and tidal correction. There will also be a continuing monitoring of the total measurement accuracy and of drifts in any of the instruments.
Early in 1996, there was a research announcement from NASA calling for proposals for the TOPEX/POSEIDON Extended Mission. We submitted a detailed proposal in June 1996. As a result of our previous research, a number of additional scientists have recognised the value of the TOPEX/POSEIDON altimeter data set. Our proposal considerably extends the original proposal that was approved by NASA in 1987 by including additional scientists at the CSIRO Division of Marine Research and the Antarctic Cooperative Research Centre. This new proposal includes research on:
Subsequent to the meeting, we heard that we were selected by NASA to be part of the TPEM Science Working Team (is one of 36 successful NASA proposals from a total of 62 submitted).
JASON - A new satellite altimeter mission
As a result of the outstanding success of the TOPEX/POSEIDON mission and its demonstrated importance for Climate Research, a follow-on to the TOPEX/POSEIDON Mission is being planned. This mission is to be called JASON-1 and the anticipated launch date is 1999.
The first Science Working Team Meeting for JASON will be held in the USA at the end of May. As a member of the TOPEX/POSEIDON Extended Mission we have been invited to attend this meeting. Associate Professor Richard Coleman will represent our team at this meeting.
The Announcements of Opportunity for thr JASON mission will be made in 1997. We anticipate submitting a proposal to be a member of the JASON team later this calendar year.
Next TOPEX/POSEIDON SWT Meeting
The next SWT meeting will be held in Biarritz, October 13-17, 1997. The theme of the meeting is ''Monitoring the Oceans in the 2000's: An Integrated Approach". We plan to present results of T/P altimeter and in-situ hydrographic comparisons along oceanographic transects in the Southern Ocean at this meeting.
Tidal Science 96 meeting
Immediately prior to the TOPEX/Poseidon Science working team meeting, the Tidal Science 96 Meeting was held at The Royal Society, London, U.K. Tidal science has experienced a resurgence with the high quality TOPEX/POSEIDON data allowing development of more accurate global tidal models and revealing new features of deep ocean tides. The meeting was attended by Dr John Church, Associate Professor Richard Coleman and Dr Neil White.
This meeting was held on the occasion of the 70th birthday of David E. Cartwright, F.R.S. to honour his scientific contributions. The 2-day meeting consisted of invited speakers giving talks on various aspects of tides and tidal dynamics, in particular those research areas that David Cartwright had made a contribution towards. There were 17 talks given together with 19 poster presentations during the meeting.
Highlights were the review given by Prof Walter Munk on the sources/sinks of tidal friction and the talk by Richard Ray on the detection of internal tides using TOPEX/Poseidon data.