1. - 1- Quality of real time altimeter products OSTST, Hobart, March 2007 Quality of real time altimeter products impact of the delay G.Larnicol, G. Dibarboure, C.Boone, CLS Space Oceanography Division Ananda Pascual, IMEDEA(CSIC-UIB), Spain Pierre-Yves Le Traon, IFREMER, Brest, France

2. - 2- Quality of real time altimeter products OSTST, Hobart, March 2007 Context Sampling : Along-trackGridded fields Content : sea level anomalyabsolute sea level (MDT+SLA) Global products Regional products: Mediterranean sea: standard processing refined for Med sea European Shelves: Products dedicated to regional applications provision of tide, inverse barometer, HF signals information Overview of SSALTO/DUACS products

3. - 3- Quality of real time altimeter products OSTST, Hobart, March 2007 Sampling : Along-trackGridded fields Content : sea level anomalyabsolute sea level Global products Regional products: Mediterranean sea: standard processing refined for Med sea European Shelves: Products dedicated to regional applications provision of tide, inverse barometer, HF signals information (Ducet et al. 2000) Research activities (science review) Context

4. - 4- Quality of real time altimeter products OSTST, Hobart, March 2007 Sampling : Along-trackGridded fields Content : sea level anomalyabsolute sea level Global products Regional products: Mediterranean sea: standard processing refined for Med sea European Shelves: Products dedicated to regional applications provision of tide, inverse barometer, HF signals information Operational activities (Dombrosky review) Context

5. - 5- Quality of real time altimeter products OSTST, Hobart, March 2007 Assess the quality of NRT altimeter observing system Main sources of errors in near real time: Orbit error (POE  MOE) minor error thanks to the long wave length error correction procedure

6. - 6- Quality of real time altimeter products OSTST, Hobart, March 2007 Theory real life !! June 21, 2006 Main sources of errors in near real time Orbit error (POE  MOE) minor error thanks to the long wave length error correction procedure Data availability delay in the data delivery number of missions available Assess the quality of NRT altimeter observing system

7. - 7- Quality of real time altimeter products OSTST, Hobart, March 2007 Main sources of errors in near real time Orbit error (POE  MOE) minor error thanks to the long wave length error correction procedure Data availability delay in the data delivery number of missions available Assess the quality of NRT altimeter observing system Anomalie IGDR IGDR Nominal ENVISAT : USO + SideB GFO : Problème batteries + WVR Jason : SHM + Problème lecture mémoire Livraison Météo (4 jours de retard sur toutes les missions) Délai > 15j : désactivation automatique d’une mission Délay IGDR Jan 06 Dec 06

8. - 8- Quality of real time altimeter products OSTST, Hobart, March 2007 Assess the quality of NRT altimeter observing system Main sources of errors in near real time Orbit error (POE  MOE) minor error thanks to the long wave length error correction procedure Data availability delay in the data delivery number of missions available Time window used for data selection in the mapping since we need maps as recent as possible in NRT

9. - 9- Quality of real time altimeter products OSTST, Hobart, March 2007 Assess the quality of NRT altimeter observing system Data and data processing AVISO products Period where 4 altimeters are available Oct 2002- Oct 2003 Main sources of errors in near real time Orbit error (POE  MOE) minor error thanks to the long wave length error correction procedure Data availability delay in the data delivery number of missions available Time window used for data selection in the mapping since we need maps as recent as possible in NRT

10. - 10- Quality of real time altimeter products OSTST, Hobart, March 2007 Impact of the satellite configuration (DT analysis) rms of sea level anomaly (SLA) estimated with 4 altimetric missions. rms of SLA differences between 4 and 2 satellites 0 10 20 (cm) 0 5 10 (cm) Presented last year in Venice Pascual et al. (GRL, 2006) - 2 DT satellite configuration is a minimum to provide a relatively good description of Mesoscale activity - 4 satellites configuration improved this description and could be indispensable for specific area (Med for instance)

11. - 11- Quality of real time altimeter products OSTST, Hobart, March 2007 Degradation of the NRT products (versus DT) 0cm10cm RMS of the differences between delayed and real time SLA Estimation done with 4 satellites configuration

12. - 12- Quality of real time altimeter products OSTST, Hobart, March 2007 Comparison with drifters data Delayed TimeReal Time 2 missions 4 missions 2 missions 4 missions U 26.624.231.026.9 V 33.128.141.233.4 Mean square differences between drifter and altimeter velocities (AVISO+ Ekman= SURCOUF) Units are % of drifter variance. 2 missions 4 missions Dealyed time Old corrections (GOT99+IB) 46.735.3 Delayed time new corrections (GOT00+DAC) 36.729.7 Real time Orbit error No-centring 45.237.1 Comparison with tide gauge data Mean square differences between tide gauge and altimeter sea level. Units are % of tide gauge variance. DAC = IB+MOG2D (Dynamic Atmos. Cor.)

13. - 13- Quality of real time altimeter products OSTST, Hobart, March 2007 Performance loss due to delay in the IGDR delivery On going work : tested for Indian ocean and Gulf- stream region Simulated NRT : DT with delay The NRT maps are compared to “optimal” DT maps. Results are the same for all areas and only the base variance is different. Impact of the delay shows linear trend 2 missions 1 unavailable 3 missions 2 unavailable 3 missions 1 unavailable 4 missions Best NRT available RMS of differences between “optimal” DT maps with degraded NRT maps (as a function of the number of days of delivery delay)

14. - 14- Quality of real time altimeter products OSTST, Hobart, March 2007 Definition of a performance Indicator for NRT applications The linear trend is used to define a NRT perfor-mance indicator. The RMS of the DT- NRT difference (additional NRT error) is normalized by the best and the poorest NRT results one could obtain in a nominal scenario. Performance loss due to delay in the IGDR delivery

15. - 15- Quality of real time altimeter products OSTST, Hobart, March 2007 Performance of 3 satellites conf = 72% Absence of GFO  loss of 25% performance For a two satellite configuration, there is a 5% error increase per day of missing data Only 4% for a three satellite configuration. 10% error increase with delay of 2 satellite Best NRT map (4 sat) Poorest NRT map (1sat) 3 satellites 2 satellites Performance loss due to delay in the IGDR delivery

16. - 16- Quality of real time altimeter products OSTST, Hobart, March 2007 Conclusions 2 DT satellites is the minimum to observe the mesoscale signal 4 NRT satellites give same results than 2 DT satellites  Need to have a at least 3 but preferably 4 satellites for operational applications Data gaps and delivery delay cause a significant loss of accuracy on NRT maps. The IGDR delivery delay is critical for NRT applications, especially with fewer satellites Being able to process Real Time (<24h) altimeter products with an IGDR-like accuracy could improve the NRT accuracy by up to 25%  Ongoing work on DUACS Continue the development of performance indicator. Refined the estimation by characterising the loss or the delay of Jason (reference mission) Improvements not only come from additional missions and reduction of delay. It is also important to continue to improve the processing (geophysical corrections, dynamic atmospheric correction,etc…)