1. Towards improved GRACE de-aliasing - first results from dynamical and residual ocean tide analysis Wolfgang Bosch 1), Detlef Stammer 2), Frank Flechtner 3), Karl-Heinz Ilk 4), Torsten Mayer-Gürr 4), Christoph Dahle 3), Eifu Taguchi 2), R. Savcenko 1) E-mail: bosch@dgfi.badw.debosch@dgfi.badw.de 1)Deutsches Geodätische Forschungsinstitut (DGFI), München 2)Institut für Meereskunde (IfM), Hamburg 3)GeoForschungsZentrum (GFZ), Potsdam 4)Institut für Geodäsie und Geoinformatik (IGG), Bonn

2. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 2 Rationale and Objectives Rationale: Deficiencies of global ocean tide models over shelves and polar oceans known – errors map to GRACE gravity fields. Objectives: Improving GRACE de-aliasing by 1)Empirical residual tide analysis w.r.t. the state-of-the-art ocean tide model FES2004 by a)Solving for long wavelength residuals from GRACE data b)Solving short scale residual tides from altimeter data 2)Enhance hydrodynamic modelling by revising the HAMTIDE model

3. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 3 Sampling of K2, S2, and M2 by GRACE M2 S2 K2 [Tage]

4. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 4 Alias and Rayleigh Periods for GRACE 1825 d = 5 a: GRACE until now 2726 d = 7.5 a

5. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 5 GFZ RL04 COS 161dGFZ RL04 SIN 161d GRGS COS 161dGRGS SIN 161d CSR RL04 COS 161d CSR RL04 SIN 161d all excl. C20! Analysing the GRACE time series

6. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 6 Analysis of Residuals (Dec 2006) Gridding (2° x 2°, 4 years)

7. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 7 M2 Amplitude from Residuals

8. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 8 Empirical tide analysis with Altimetry data Altimeter satellites have their own alias periods (Smith 2000) Combination of mission with different sampling allows to overcome some of the obstacles of individual missions Harmonized and cross-calibrated (common multi-mission crossover analysis of all systems operating simultaneously) Common residual analysis with TOPEX, TOPEX-EM, Jason-1, ERS-1, ERS-2, ENVISAT, GFO (w.r.t. FES2004) Least Squares harmonic analysis on a global 15’x15’ grid Solving for mean, drift, seasonal signal ( Sa, Ssa), long period (Mm, Mf), diurnal(Q1, O1, P1, K1), semidiurnal (M2, S2, K2, N2) and shallow water (M4, MS4, M6)

9. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 9 Results for M2

10. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 10 Results for S2

11. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 11 Residual tides (w.r.t. FES2004) at NW European Shelf

12. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 12 Validation with BODC bottom pressure gauges Left: rms of sea surface heights (after FES2004 correction) Right: % gain in variance due to residual tide corrections

13. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 13 Clear indications that the ocean tide model presently used for GRACE processing can be considerably improved by – Long wavelength structure seen by GRACE data itself (residuals or time series analysis) – Short wavelength resulting from analysis of multi- mission altimeter data Ultimate goal is to combine both empirical approaches

14. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 14 HAMTIDE (Hamburg direct Assimilation Method for TIDE) HAMTIDE: direct minimization of model deficiency and the inaccuracy data in a least square sense, Assimilation of altimeter data, tide gauge, and bottom pressure recorder data Blue: indput data Red: 102 Pelagic Sites used as standard reference

15. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 15 HAMTIDE (Hamburg direct Assimilation Method for TIDE) HAMTIDE is run with three different spatial resolutions, i.e., 1°, 10’ and 5’. Right: 10’ run M2 Comparison with FES2004 (10’ resolution)

16. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 16 HAMTIDE applied to strongly nonlinear effects on the NW European Shelf Rms: 0.8 cm 7.7 cm Fig. 5 Fig. 6

17. SPP1257 Project DAROTA International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 17 See Posters for details of the project Taguchi, E., D. Stammer, W. Zahel, R. Savcenko, and W.Bosch: Toward high resolution dynamic modelling using HAMTIDE Savcenko, R. and W. Bosch: Assessment of errors in global ocean tide models and their impact on GRACE gravity fields