Mobile version

Aviso Newsletter 4

February 1996

Editorial

Barely a year after the launch of TOPEX/POSEIDON, the oceanographic community was producing excellent work from Geophysical Data Records. "No special knowledge in areas of […] orbit mechanics was needed", said Cheney et al. in “TOPEX/POSEIDON, the 2-cm solution”, JGR vol. 99, # C12, page 24, 562. The authors were certainly not saying there was nothing left to achieve in orbitography. They were simply stressing the fact that the high-quality results from the Precise Orbit Determination (POD) people at NASA and CNES were enhancing the initial specifications. What’s happening now, three years after the launch, at the start of the T/P Follow-On mission?

The initial analyses showed that the dynamic orbits supplied by the PODs have comparable error spectra. At the same time, GPS experiments and analyses of the data showed geographical areas where the orbital errors appeared to be correlated. Also, the closer the initial dynamic orbits were to reality, the better the processing using the reduced dynamics technique. In the long term, however, laser and DORIS remained the sole nominal systems for calculating T/P trajectories.

These realizations led to a lot of work by U.S. and French orbitography specialists. First, there have been two particularly important developments. We have a new gravity model, JGM3, to which GPS has made an unmistakeable contribution. Similarly, an impressive number of ocean tide models are now available for the NASA and CNES PODs. Second, DORIS is undeniably essential as a tracking system for T/P, in terms of continuity and availability. An adapted reduced dynamics approach, based on the way DORIS works, has been developed and has led to the production of the ELFE orbit. Both POD orbits should provide higher and comparable quality than previous orbits, but will have different error spectra, offering users two statistically independent samples. In any case, that is our aim.

To maintain continuity, all the T/P cycles have been reprocessed and are available both as dynamic orbits from the NASA POD and as ELFE reduced dynamic orbits from the CNES POD. This is a lot of work and will call for a corresponding contribution from the oceanographic user community. The payoff we hope for in this exciting adventure is centimetre-by-centimetre improvement.

F. Nouel (CNES, France)

 

Editor : Patrick Vincent

Editorial board : Frédérique Blanc

Authors and other contributors : N. Ayoub, J. Barckicke, B. Barotto, S. Barstow, J.-P. Berthias, E. Blayo, P. Brasseur, N. J. Bravo, C. Brossier, P. De Mey, D. B. Enfield, L.L. Fu, J. E. Harris, G. Larnicol, P. Lasnier, P.-Y. Le Traon, S. Loeul, Y. Ménard, J.-F. Minster, F. Nouel, G. Pihos, R. D. Smith, J. Verron, R. Zaharia.

English adaptation : N. Greenwood

Design : D. Ducros

EnglishFrançais
Rss feedsContactPartnersFAQLexiconLegal noticePersonal Data Protection PolicyMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso+ features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

This home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!