The future of altimetry in measuring ocean surface waves from space

1. “15 years of altimetry” Venice, 12-16 March 2006 The future of altimetry in measuring ocean surface waves from space Jean-Michel Lefèvre Meteo-France With contributions of: M. Ablain, L. Aouf, J. Li, P.Janssen, P. Queffeulou, Y. Quilfen, C. Skandrani, N. Steunou, A. Toffoli, D. Vandemark. Jean-michel.lefevre@meteo.fr

2. Accidents due to heavy weather and Freak waves are a likely cause Toffoli et al, 2003

3. Maritime Security Warnings (winds, wave, tsunami) Structure design Rescue Maritime and Coastal Environement Management Shore and Off shore Fisheries Ship routing Naval operations Consultancy Accident reports Observations In situ Satellite Modelling/ Data assimilation Climatology Needs Means

4. Monitoring sea conditions • Buoy observations: everywhere but not anytime • Altimeters: anytime but in few places (mainly coastal) • Optimistic view: complementarity • However collocated data sets are required (with model data too) in order to : • Monitor the ocean conditions • Validate each data source, because all data have errors • (Janssen et al., 2003, Cotton et al., 2004)

5. Monitoring sea conditions • Use of several data sources also for: • -Classification of wave steepness using model and altimeter data with application tosea state bias work, Vandemark et al. • (see posters) • Potential utility in other synergistic satellite+model efforts (breaking wave detection, wave/current, salinity, etc…) older seas – low sea state mixed seas – low sea state young seas – low sea state mixed seas – mod sea state steep seas – mod. sea state high seas

6. Improving the prediction system Today, SWHand U10, Tomorrow Wave Period, according to Quilfen et al., Gommenginger et al. Wave Period is important for model validation, may be relevant for data assimilation, but is crucial for Ship design (Steepness calculation)

7. Improving the models From Holt and Li Altimeter data are important because model performance at buoy locations (close to the coast) may be different than in open sea F. Ardhuin, L. Bertotti, J. Bidlot, V. Filipetto, J.M Lefevre and P. Wittmann 2006, to be published in Ocean Engineering

8. Towards 2km resolution AltiKa (STEUNOU et al.) : For coastal application because of higher spatial resolution+ better accuracy (detection of low high swell). Today, operational NWP have at most 10km resolution Target is 2-3 km (regional model only) in 2008 (AROME project) Altika : STEUNOU et al.

9. Improving the prediction system Assimilation of ASAR + Altimeters+… Aouf et al., larger impact, longer

10. Extreme waves / Climate variability 50-year Return Value Investigating Seasonal Variabilities, climate change with satellite Hs, Tm in relation with the NAO, Regression of Tm on the NAO Challenor et al. Longer period 100-yearMore satellites better accuracy

11. Wind/Wave Atlas Satellites data are unique source of data to correct model fields for climatological purpose (Cavaleri et al. )

12. Data corrections Calibration of SWH data from the various altimeter is crucial P. Queffeulou Direct computation of statistics along tracks over 13 years with TOPEX and Jason

13. Tsunami Detection The Indian Ocean tsunami 26, 2004 observed by high resolution altimetry, Ablain et al. • For the first time, tsunami waves in the open ocean were clearly measured by all the satellite altimetry. • All these precise and unique observations show the unique contribution of satellite altimetry is to better understand and to improve the modeling of tsunami propagation and dissipation. Jason-1 Pass 129 20 Hz measurements Tsunami wave front

14. Meteo centers just agreed that wave conditions should be mandatory in marine bulletins and the possibility to issue warnings for severe conditions (e.g. risk of abnormal waves) has been added. Wave forecast supplies significant wave height, wave period and wave direction both for wind sea and swell conditions Abnormal waves http://tv-antenna.com/heavy-seas/

15. Freak Waves The combination of Waves + Ocean currents will be one step forwards the identification of dangerous areas, while investigations must going on in order to link some parameters potentially derivable from models or observations (Kurtosis, steepness, dir. Spreading). Acknowledgements http://www.seafriends.org.nz/oceano/currents.htm#surface

16. How many altimeters would we like to have for operational applications (one is not enough), wave climate…? (Gamble, Cotton et al., T. Allan) Choice of the orbit? (insure continuity) Can we benefit of a faster data delivery (less than 3h)? Are wind/wave data accurate enough? (seems to be already the most accurate data for SWH)? Is the spatial resolution enough? (Alti-Ka, for High resolution (2-3 km) wind/wave modeling) Is there strong limitation of Ka band to derive wave climate (7% of data affected by rain!)? How better combine altimeter data with other sources of data? Can we derive other parameters (Kurtosis of the PDF from wave forms for freak wave detection, according to Janssen theory?) Questions