Towards improved GRACE de-aliasing - first Towards improved GRACE de-aliasing - first results from dynamical andresults from dynamical andresidual ocean tide analysisresidual ocean tide analysis

Towards improved GRACE de-aliasing - first Towards improved GRACE de-aliasing - first results from dynamical andresults from dynamical andresidual ocean tide analysisresidual ocean tide analysis

Wolfgang Bosch1), Detlef Stammer2), Frank Flechtner3), Karl-Heinz Ilk4), Torsten Mayer-Gürr4), Christoph Dahle3), Eifu Taguchi2), R. Savcenko1)

E-mail: bosch@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

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 2SPP1257

Project DAROTA

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

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 3SPP1257

Project DAROTA

Sampling of K2, S2, and M2 by GRACE

M2

S2

K2

[Tage][Tage]

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 4SPP1257

Project DAROTA

Alias and Rayleigh Periods for GRACE

Sa Ssa Mm Mf Mtm Msq Q1 O1 P1 K1 2N2 N2 M2 S2 K2 M4

Sa 365 365 30 14 9 7 9 14 322 422 7 9 14 288 499 7

Ssa 183 32 15 10 7 10 15 2726 196 7 10 15 1363 211 7

Mm 28 27 14 10 14 27 33 28 9 14 27 33 28 9

Mf 14 28 15 27 2726 15 14 14 27 1363 15 14 13

Mtm 9 32 2726 28 10 9 27 1363 28 10 9 26

Msq 7 32 15 7 7 179 33 15 7 7 144

Q1 9 28 10 9 27 2726 28 10 9 26

O1 14 15 14 14 27 2726 15 14 13

P1 171 183 7 10 15 2726 196 7

K1 2726 7 9 14 171 2726 7

2N2 7 28 14 7 7 739

N2 9 28 10 9 27

M2 14 15 14 14

S2 161 183 7

K2 1363 7

M4 7

1825 d = 5 a: GRACE until now

2726 d = 7.5 a

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 5SPP1257

Project DAROTA

GFZ RL04 COS 161d GFZ RL04 SIN 161d

GRGS COS 161d GRGS SIN 161d

CSR RL04 COS 161d CSR RL04 SIN 161d

all excl. C20!

Analysing the GRACE time series

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 6SPP1257

Project DAROTA

Analysis of Residuals (Dec 2006)

Gridding (2° x 2°, 4 years)Gridding (2° x 2°, 4 years)

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 7SPP1257

Project DAROTA

M2 Amplitude from Residuals

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 8SPP1257

Project DAROTA

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)

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 9SPP1257

Project DAROTA

Results for M2

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 10SPP1257

Project DAROTA

Results for S2

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 11SPP1257

Project DAROTA

Residual tides (w.r.t. FES2004) at NW European Shelf

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 12SPP1257

Project DAROTA

Validation with BODC bottom pressure gauges

• Left: rms of sea surface heights (after FES2004 correction)

• Right: % gain in variance due to residual tide corrections

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 13SPP1257

Project DAROTA

• 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

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 14SPP1257

Project DAROTA

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

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 15SPP1257

Project DAROTA

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)

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 16SPP1257

Project DAROTA

HAMTIDE applied to strongly nonlinear effects on the NW European Shelf

• Rms: 0.8 cm 7.7 cm

Fig. 5Fig. 6

International GSTM+SPP Symposium, Potsdam, 2007 Oct. 15-17 17SPP1257

Project DAROTA

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