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. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 2DTU Space, Technical University of Denmark 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. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 3DTU Space, Technical University of Denmark Satellite altimetry is well Esablished for linear sea level change

4. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 4DTU Space, Technical University of Denmark Typical Surges / Cyclones North sea has mainly external surges generated by wind forcing. GBR has numerous tropical cyclones (near seasonal) = Water level recorders Crosscorrelation

5. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 5DTU Space, Technical University of Denmark Current Satellite Sampling: Satellite Repeat Period Track spacing Inclination Coverage CryoSat-23698 km92°(+/-88°) AltiKa35 days80 km 98°(+/-82°) Jason-210 days315 km66.5° 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. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 6DTU Space, Technical University of Denmark 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. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 7DTU Space, Technical University of Denmark Heavy Rain + Coastal problems

8. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 8DTU Space, Technical University of Denmark Last devastating storm surge in Britain – 1953 ”Data for validation?”

9. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 9DTU Space, Technical University of Denmark High Water in Hvide Sande Simple 2 and 3 std. deviation test on ”high water”

10. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 10DTU Space, Technical University of Denmark Satellite Obs One versus two satellite (Jason/Envisat) Key to succes is two satellites

11. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 11DTU Space, Technical University of Denmark Seasonal Cyclones in NE Australia Cyclone Helen (4 January, 2008)Cyclone Larry (20 March 2006)

12. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 12DTU Space, Technical University of Denmark 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. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 13DTU Space, Technical University of Denmark Combining satellite altimetry and tide gauge information Importance of de-tiding procedure.

14. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 14DTU Space, Technical University of Denmark Spatio-temporal Correlation Non-tidal (surge) Sea Level variation TOPEX / JASON (17 years)ERS / ENVISAT (12 years) GOT4.7Pointwise Ocean Tide model

15. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 15DTU Space, Technical University of Denmark Combing Tide gauges and Altimetry Small time scale, Large spatial scales, high correlation T/P + Gauges Least squares fit in every T/P observation Regression Model Previously shown better accuracy For Hvide Sande sea level prediction Than from DMI 2003 ”existing” storm surge model(Hoyer and Andersen, GRL)

16. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 16DTU Space, Technical University of Denmark Model Prediction. Cyclone Helen (January, 04, 2008) Cyclone Larry (March 19th, 2006) Blue=Tide gauge obs Green=Tide gauge alone Red=Altimetery + TG

17. IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July, 2013 17DTU Space, Technical University of Denmark 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. Conclusions