Aviso has supplied users with Topex/Poseidon data and products since the satellite's launch. In addition to its initial role distributing data, Aviso has continually improved the service it provides by ensuring close and regular quality control of data and by forging close links with users, for whom it is a valued and efficient source of general, technical, and scientific information. This article reviews Aviso activities in 1999, concluding with a brief look at the developments planned for the years ahead.

Operational distribution and validation of Topex/Poseidon GDR-M data.

Ever since the Topex/Poseidon satellite was launched, Aviso has worked to nurture a close relationship between project teams and mission product users.  Aviso's core mission was initially to manage operational distribution of Topex/Poseidon data and products.  Routine distribution of off-line Merged Geophysical Data Records (GDR-M) is part of this mission.  Near-off-line products are also distributed on a regular basis, often much faster than initially specified for the Topex/Poseidon science mission: Interim Geophysical Data Records (IGDR-T and IGDR-P) and Doris precise orbit determination products are delivered to users in under 48 hours.

Aviso soon extended the scope of its core responsibilities to intensive validation of Topex/Poseidon data.  These calibration and validation activities (Calval) have ensured continuous quality control, providing scientists with the data they need to pursue research, from a validated and proven system.  Also in this newsletter, Dorandeu et al. [1999] review Calval efforts concerning systematic validation and long-term monitoring of data, intended in particular to detect instrument drift.  The latest Aviso/Calval yearly report details results obtained from the first six years of Topex/Poseidon operation [Aviso, 1999a].  The altimetry expertise the Aviso Calval team has developed and maintained proved especially valuable during calibration and validation of the backup Side B Topex altimeter, which came on stream in cycle 236.  Dorandeu et al. [1999] present some major results that offer new insight into those already obtained by the Side B evaluation project [1999b].  The switch from instrument A to instrument B has had little impact on operational distribution of Topex/Poseidon data: GDR-M data acquired with the B altimeter and distributed by AVISO integrate seamlessly with data from other missions.

Multi-satellite data processing

To complement its Topex/Poseidon mission activities, Aviso is leveraging its altimetry expertise to process altimetric data and distribute corresponding products from other satellites.  Its aim here is to encourage the uptake of satellite altimetry solutions by a wider audience of non-expert users.  CLS, as a member of the Ocean, Altimetry and Climate Group (POAC, formed by Cerfacs; CLS; the French space agency Cnes; Insu, the French national institute of universe sciences, and Toulouse University through the Legos research laboratory; the Météo-France weather service; and SHOM, the French navy’s hydrography and oceanography department) is contributing to these efforts by regularly generating CorSSH (CORrected Sea-Surface Height) and SLA (Sea Level Anomaly) products, distributed by Aviso.  In 1999, CORSSH and SLA products were derived from the sixth year of Topex/Poseidon data and the third year of ERS-2 data.  Aviso also widely distributed map products on CD-ROM showing SLAs derived from Topex/Poseidon, ERS-1 and ERS-2.

New catalogue of standard and high-level altimetry products

A brand new Aviso Catalogue came on line during the first quarter of 1999.  This catalogue now offers all users worldwide easier access to altimetry products from all the members of POAC.

The new catalogue's main objectives are to:

-        inform altimetry experts and lay users about ongoing missions, data produced, main technical and scientific results, and altimetry activities pursued by each POAC member;

-        provide access to altimetry data and products from POAC members for the international community; users can browse through the catalogue via the Internet to select products of interest and request geographic data covering a specific area and/or particular time period; they can then order products, which AVISO will deliver as soon as is practicable given the nature of the order.

The AVISO catalogue offers various categories of data and products:

-        All Topex/Poseidon level 2 products, i.e., GDR-M and orbit ephemeris data.  Products generated by Aviso/Calval for the purposes of validating Topex/Poseidon data are also available.  Higher-level data include CorSSH and SLA products, which CLS currently generates on a yearly basis.

-        Various high-level geophysical and oceanography products derived from level 2 data are accessible for other altimetry missions.  These are mostly multi-satellite products that offer the combined benefits in terms of performance and sampling rate of different missions.  For example, a wide range of oceanography products is now available for direct assimilation by numerical ocean circulation models.  These products are generated by CLS or UMR5566 at its Ocean Topography Centre (CTO).

-        Software is provided with accompanying user documentation for all products distributed.

-        Lastly, users can also access data and product user guides, various other documentation, promotional literature concerning altimetry missions, and so on.

The catalogue provides access to general information for the general public.  Users can browse through the product and data inventory, then select products to order after logging on and entering a password in the customary fashion.  Users ordering through the Aviso catalogue for the first time must register (they only need to register once) to receive a user ID and password, which they then use for subsequent orders.  Products may be delivered on physical storage media or over the Internet, depending on their nature and volume.

To enhance the services briefly described above, AVISO is pursuing its efforts to set up a user office aimed at providing a quick and efficient response to the scientific and technical needs of altimetry user communities.

Aviso and promotion of ocean altimetry

The foundation of the Topex/Poseidon mission's success is its scientific achievements, which have been made possible by the close partnerships established between the project and science teams.  However, we would have missed an opportunity had this success only benefited a small community of experts.  For this reason the Topex/Poseidon Science Working Team (SWT) is driving efforts to promote mission results to the wider scientific community, decision-makers and the general public, in particular in education.  What is the impact of these new objectives for AVISO?  One of the first steps has been to foster closer coordination between Aviso, Po.Daac and science teams defining and contributing to Topex/Poseidon promotional activities, particularly through the SWT's Outreach sub-group.  In recent months, for example, Aviso has established very close ties with Po.Daac to ensure the highest possible degree of compatibility between data and products distributed over the Internet.  Further, Aviso and Po.Daac have defined together an initiative to compile image banks and a wide range of presentation materials for use by SWT scientists at seminars and conferences.  Production of fact sheets has also continued with a new sheet on El Niño and La Niña.  Lastly, the Aviso team has taken an active part in many public and educational exhibitions and conferences to promote space oceanography and altimetry in particular.

Aviso and Jason-1

All the activities described above, developed mostly during the Topex/Poseidon project, will continue as part of the Jason-1 follow-on mission.  The aim will be to provide users with an even better service than before.  Work is already under way to define how real-time and off-line Jason-1 products will be distributed.  Consideration is also being given to developing and distributing Jason-1 products processed to a higher level than standard GDR products, i.e., the CorSSH and SLA products widely used today by the Topex/Poseidon community.  Such products could be distributed on a regular basis (for example, every orbit cycle).

As a key element of the new Ssalto multi-mission ground segment currently under development by Cnes [Coutin-Faye et al., 1999], Aviso is gearing up to ensure continued quality of service for altimetry users in the years ahead.

References:

• Aviso, 1999a: Aviso/Calval yearly report: 6 years of Topex/Poseidon data, Technical note AVI-NT-011-316-CN
• Aviso, 1999b: Aviso/Calval: Side B Topex altimeter evaluation, Technical note AVI-NT-011-317-CN
• Coutin-Faye S., J. Noubel, G. Boutonnet, 1999: Ssalto: a new ground segment for a new generation of altimetry satellites, Aviso Newsletter 7.
• Dorandeu J., M.H. de Launay, F. Mertz, 1999: Aviso Calval activities, Aviso Newsletter 7.