Report on the Topex/Poseidon & Jason-1 SWT
==========================================

November 15-17, 2000
Miami, Florida

Jason-1 launch and initial verification period
==============================================

The Jason-1 launch is now planned for 30th April 2001. No further
delays are expected, but noone was prepared to make a more definite
statement on this. Apparently if it is delayed further there may be
problems fitting it into the launch schedule. It could also cause
problems for our Burnie work because of CMR's mooring group's other
committments - some of the equipment we will be using for the current
meter array off Burnie is committed to other projects in early 2002.

The intensive verification period will now, presumably, be something like
early June -> early December 2001.

The plan is to have an initial CALVAL meeting in October 2001 and a final
CALVAL plus SWT meeting in January 2002.

TOPEX/Poseidon
==============

The satellite continues to perform well, and they hope to get 10 years
or more from it (it was launched in August, 1992). However, some of the
instruments are having problems because of the exposure of the electronics
to radiation. One of the tape recorders is having problems and there are
a few other things showing their age.

Steve Nerem gets a global sea-level-rise figure of 2.4 +/- 0.5 mm/year.
Data from global tide-gauge calibration calculations are used in this work.

Jason-1 Precise Orbit Determination (POD)
=========================================

The reference systems in use today need to be improved. The CSR model
(used by NASA) does not have good velocities and ITRF97 (used by CNES)
has a bias and drift in Z. A transition to ITRF2000 (by both NASA &
CNES) should take place early next year. Progress has been made toward
NASA/CNES orbit convergence (current offset is ~4mm). ITRF2000
will be released at the December 2000 AGU meeting.

The GPS data from CHAMP (which has a similar receiver to Jason-1) looks
good.

Development of the Jason POD production system is proceeding
satisfactorily. It is 95% complete and the GPS processing has been
validated. Orbits will be stochastically corrected or reduced-dynamic
orbits. Surface forces are going to be the largest error source. These
forces will be hard to model in a short time period, and the POD team
want at least four months of data for tuning of orbit computations.

Jason-1 data and algorithms
===========================

The following auxiliary data sets have been chosen:

Ocean tides: (1) GOT99 (empirical)
(2) FES99 (assimilation) for the IGDR (i.e. for the
verification period).

Mean Sea Surface: GSFC00 for the IGDR. This will be reconsidered for the GDR.

Geoid: EGM96

Bathymetry/topography: DTM2000.1 - this is a 6-state land/sea mask (based on
the data set distributed with the GMT
plotting package).

Aliasing of high frequency signals: There will be a correction for this on
the GDR, but probably not on the IGDR.
There are three potential sources

Sea-state bias: A non-parametric estimate will be used for the verification
phase.

Note: The IGDR is the Interim GDR product which will be used for
verification work during the first six months of the mission.
A GDR (Geophysical Data Record) product is the normal method
of distributing the data files to the science community.

Jason-1 CALVAL
==============

The accuracy goals are 1cm in Jason-1 sea-surface height bias and 5mm for
T/P - Jason-1 relative bias by the end of the verification phase. In
addition, measurement stability should be good to ~1mm/year.

NASA's main calibration site for Jason-1 is the Harvest oil platform off
California. CNES's main site is at Senetosa in Corsica. T/P biases
measured at these sites are in good agreement.

Anny Cazenave is trying to get some new Doris beacons installed and some
old ones moved. One of the suggestions is for a new beacon at Townsville.

T/P - Jason-1 tandem mission
============================

Initially T/P and Jason-1 will be flying along the same ground track
with one a few minutes behind the other ("formation flight"), then T/P will
be moved to an orbit part (probably half) way between its current ground
tracks (the "tandem mission"). The formation flight period will be very
important for cross-calibration of the two satellites.

There is a possible conflict between the requirements for:
- T/P - Jason-1 cross-calibration
- Jason-1 POD
- continuity of T/P quality GDR data
- a long enough (1 year or more) tandem mission.

People involved in verification work all feel that a 3 month formation flight
period is not long enough.

The POD people want one or possibly two complete beta-prime cycles (4
months per cycle) of formation flight.

Once T/P starts its move to the new orbit it will not produce useable
science data for a month or two. If Jason-1 is not ready to produce GDR
quality science data at this stage there will be a gap in the production
of this quality of data.

The tandem mission will be most useful if both satellites are working
together for one year or more. Given the ageing problems that T/P is
having this may not be possible!

Jason-2 and on
==============

Jason-2 is planned for launch at the end of 2004 (Jason-1 nominal
lifetime is 3 years and the goal 5 years). CNES have begun the
preliminary procurement phase pending a formal decision. The formal
decision will be made by the end of 2001/early 2002. CNES has
funds for 50% of Jason-2, they are looking to EUMETSAT for other resources.

There are plans to have a WSOA (Wide Swath Ocean Altimeter) on Jason-1.
WSOA would have two extra altimeter antennae separated from the main antenna
and mounted on a very rigid frame. This would allow interferometric
estimates of sea-surface height over a wide swath of ocean, rather than
along a single line. However, WSOA would not threaten the decision on
Jason-2. A preliminary accomodation study has been performed.
NASA is supportive of WSOA but are concerned about practicality.

There are also plans to launch an "Altika" (Ka band) altimeter to
accompany Jason-2. This would be complementary to WSOA. Focus for Altika
is for ocean circulation studies, in particular getting closer to
coastlines for coastal studies.

T/P weighs 2,500kg, Jason-1 500kg, and Altika would weigh 100kg.