1. OSTST, Hobart, March 2007 - 1- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? P.Escudier, G.Dibarboure, J.Dorandeu, CLS, Space Oceanography Division

2. OSTST, Hobart, March 2007 - 2- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Overview Until recently, the exceptional longevity of T/P and GFO added to the performance of Jason and ENVISAT were hiding the risk of future data gaps. –The current missions are still performing well but exceeding designed lifetime With the current launch schedule (Jason2, CryoSat, AltiKa, Sentinel…) can we guarantee a sufficient mesoscale observability for new and developing applications and for operational oceanography ? Use a probabilistic model to better assess the odds of having an observing system (multiple altimeters) accurate enough : Minimum needed to monitor mesoscale structures : –2 satellites in delayed time (offline), –3 satellites or more in near real time (Pascual et al) Question asked in Venice meeting (2006)

3. OSTST, Hobart, March 2007 - 3- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? 50 350 EKE in the Mediterranean sea depending on the satellite configuration

4. OSTST, Hobart, March 2007 - 4- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Approach and model used Lifespan probability model of a satellite driven by platform and payload design. –Probability function approximated with a simple model fitted on lifespan computations from AAS Launch (100% success rate assumed) Lifespan (75% survival chance) Mission should not outlive 2.2 * nominal lifespan Probability function for Each mission based –launch date, –expected lifespan as announced –specific cases taken into account Cryosat considered as 50% operational on ocean : payload limitation, non- repetitive ground track Lifetime limitation –ie propellant limit for ENVISAT Missions grouped by ground track : –redundant measurements are not stacked, but likelihood to have the ground track covered increases Individual probability function combined to compute combinatorial probabilities Probability function used for an altimeter with a 5 year lifespan

5. OSTST, Hobart, March 2007 - 5- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Model validation The probability model is validated using historical datasets. –actual coverage on ocean taken into account : platform/payload events, … Agreement between model prediction and observed reality fairly good Most significant differences : –GFO post-launch anomalies –unexpected longevity of T/P In both cases, the event is against the base probability assumptions on the satellite : 100% success rate at launch, and 2.2 * lifespan max Model Reality ERS1 ERS2 T/P GFO Jason1 ENVISAT Data losses Number of Altimeters in operation

6. OSTST, Hobart, March 2007 - 6- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Will altimetry provide the input needed by near real time applications ? Probability to have the minimum observing system needed to monitor mesoscale : –2 satellites for delayed time applications (red), –3 satellites for near real time applications (blue) Critical situations –Probability less than 10% in 2008 for near real time applications, Probability less than 25% until CryoSat. –Odds fall down to 30% after the scheduled end of ENVISAT in 2010, and until both Sentinel-3 are operational Results are arguably optimistic: –altimeters assumed to be operational just after launch –100% launch success rate HY-2 to be added Jason-3 to be confirmed Launch dates to be tuned according to latest infos Jason -3 Probability to get 2 satellites available Probability to get 3 satellites available

7. OSTST, Hobart, March 2007 - 7- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Jason tandem phase The probabilistic model was used to explore alternate scenarios and to assess the impact of various decisions on the minimum observability needed for Near Real Time applications and operational oceanography As an illustration, shifting Jason-1 on a different orbit (tandem phase, similar to the Jason/TP phase in 2003/2005) would improve the NRT odds by 20% The cross-calibration of both Jasons is mandatory, but if the tandem phase does not start six months after launch, the odds of getting the minimum NRT data reach 0% Probability to have the minimum NRT observability without a Jason-1 tandem mission (green), or with a Jason-1 tandem phase 6 months (red) or 1 year (blue) after the launch of Jason-2

8. OSTST, Hobart, March 2007 - 8- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Exploiting CryoSat data Similarly, an additional 20% chances can be gained if CryoSat data are fully exploited with a complete coverage on ocean (ice + ocean as primary mission), and better geophysical corrections/references : –improved MSS to balance out the non-repetitive ground track, –Improved model for ionosphere correction –Improved model for wet troposphere correction 20% chance increase to get the minimum observation in NRT with perfect ocean coverage and optimized processing Probability to have the minimum NRT observability with opportunistic ocean data from an ice-oriented CryoSat (blue) and with perfect ocean coverage and improved geophysical corrections (green)

9. OSTST, Hobart, March 2007 - 9- Future altimeter systems : is mesoscale observability guaranteed for operational oceanography? Summary and Conclusions Minimum number of satellites in operations needed to monitor mesoscale structures : –2 satellites in delayed time (offline studies) –3 satellites or more in near real time Simple probability model used to assess the odds of having an observing system (multiple altimeters) accurate enough to provide the input measurements needed for offline and Near Real Time applications Validation with historical data : good consistency and global predictions but unexpected boolean events (T/P longevity, launch failure…)  Improvements possible on model Offline mesoscale observability is likely (P>60% after Jason-2) Odds of meeting the NRT requirements are very poor until Jason-3 + both Sentinel-3 (P<25% until 2010, and 40% until 2011). It is ironically when operational oceanography and NRT applications start to be fruitful that NRT altimeter data may be lacking. Odds can be improved with a Jason tandem phase or a better use of CryoSat on ocean One more reliable altimeter launched before 2013 would almost double the NRT odds