Integration Tide Gauge and Satellite Altimetry for Storm Surge and Sea Level change prediction.

1. Integration Tide Gauge and Satellite Altimetry for Storm Surge and Sea Level change prediction. Ole B. Andersen,Y. Cheng (DTU, Denmark) X. Deng, M. Steward, N. Idris and Z. Gharineiat (Uni NewCastle, Australia)

2. Overview Satellite altimetry for sea level and storm surge/cyclones Crital issues for surge/cyclone monitoring: Spatio-temporal sampling vs surge/cyclone Availability and accuracy Accuracy degradation (Coastal and rain). Reliability of surge capturing Importance of residual range corr errors: Ocean tide correction spatio-temporal correlation Merging with tide gauges Hindcast / forecast modelling Conclusions. Queenland surge

3. Satellite altimetry is well Esablished for linear sea level change

4. Typical Surges / Cyclones North sea has mainly external surges generated by wind forcing. GBR has numerous tropical cyclones (near seasonal) Crosscorrelation = Water level recorders

5. Current SatelliteSampling: 3-4 ongoing missions Jason-2 Cryosat-2 (SAR)* AltiKa (French-India)* *>10% data affected. HY-2 (China) Sentinel-3 (SAR) Near Real time data J2+C2: 4-6 hours Accurcy: 4-6 cm

6. Sea Level and Storm Surges Critial issues: √ Spatio-temporal sampling vs surge/cyclone √ Availability and accuracy Accuracy degradation (Coastal and rain). Reliability of surge capturing Importance of residual range corr errors: Ocean tide correction Merging with tide gauges (spatial temporal correlation) Hindcast / forecast modelling

7. Heavy Rain + Coastal problems

8. Last devastating storm surge in Britain – 1953 ”Data for validation?”

9. High Water in Hvide Sande Simple 2 and 3 std. deviation test on ”high water”

10. Satellite Obs One versus two satellite (Jason/Envisat) Key to succes is two satellites

11. Seasonal Cyclones in NE Australia Cyclone Helen (4 January, 2008) Cyclone Larry (20 March 2006)

12. Sea Level and Storm Surges Critial issues: √Spatio-temporal sampling vs surge/cyclone √ Availability and accuracy √ Accuracy degradation (Coastal and rain). √ Reliability of surge capturing Importance of residual range corr errors: Ocean tide correction Spatial temporal correlation Merging with tide gauges Hindcast / forecast modelling

13. Combining satellite altimetry and tide gauge information Importance of de-tiding procedure.

14. Spatio-temporal Correlation Non-tidal (surge) Sea Level variation GOT4.7 Pointwise Ocean Tide model • TOPEX / JASON (17 years) ERS / ENVISAT (12 years)

15. Combing Tide gauges and Altimetry Small time scale, Large spatial scales, high correlation T/P + Gauges Regression Model Least squares fit in every T/P observation Previously shown better accuracy For Hvide Sande sea level prediction Than from DMI 2003 ”existing” storm surge model(Hoyer and Andersen, GRL)

16. Model Prediction. Cyclone Helen (January, 04, 2008) Cyclone Larry (March 19th, 2006) Blue=Tide gauge obs Green=Tide gauge alone Red=Altimetery + TG

17. Conclusions • Satellite altimetry has proven very valuable t • North Sea ”surge/high water” detection capturing all high water scenarios. • Cyclone mapping in north East Australia (unmapped by tide gauges) • Importance of re-tracking of satellite altimetry (increse nb of obs) • For North Sea surges two satellites were proven to be fundamental. • Analysis in Eastern Australia is still ongoing. • Future: • Cryosat-2 has non systematic ground track pattern. • AltiKa has potential problem with rain. This is currently under investigation. • Sentinel-3 (2014) will offer systematic ground track pattern and additional information.