ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway A. Albertella, R. Rummel, R. Savcenko, W. Bosch, T. Janjic, J.Schroeter, T. Gruber, J. Bouman IAPG München, DGFI München, AWI Bremerhaven Dynamic Ocean Topography from GOCE Some Preparatory Attempts

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway GEOTOP project Deutschen Forschungsgemeinschaft German Priority Research Program SPP1257 IAPG München: geodesy IPG Dresden: geodesy DGFI München: altimetry AWI Bremerhaven: oceanography

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway To determine the ocean circulation and its mass and heat transport assimilation of geodetic data of the dynamic ocean topography and oceanographic in-situ data This objective is possible thank to the gravity missions GRACE + GOCE

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Computation of a “geodetic” DOT from GRACE/GOCE geoid models and multi-mission altimeter data Adaptation this geodetic DOT to an ocean circulation model Assimilation the geodetic DOT together in-situ oceanographic data into the ocean model Determination of the mass and heat transport Comparison and analysis of the geodetic DOT and the oceanographic DOT obtained from the ocean circulation model runs

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway H = h-N H = dynamic ocean topography ( ~ ±2 m) h = sea surface height (from altimetric measurements) N = geoid height (from recent geoid models)

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway EGM96 geoid model (Lmax = 360) Topex-Poseidon ground tracks Distribution of the geodetic data

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway SPECTRUM of the data GEOID: spherical harmonic representation

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Sea surface anomaly along one track of Topex-Poseidon mission: black lines tracks at different time red line on 2004/12/26 (tsunami event) ALTIMETRY: discrete data along ground tracks SPECTRUM of the data

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway long wavelength short spectral representation spatial represention global regional local long wavelength short spectral representation spatial represention global regional local geoid undulation sea surface height (altimetry) The data have different distribution and different spectral resolution

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway H = h-N the data are not consistent! Different distribution  different representation  different definition of their spectrum The high frequencies present in h contain dynamic ocean topography and a high frequency geoid part To have control on the error propagation it is necessary to have consistent data (= covering the same spectral range)  It is necessary to filter the data with minimum possible signal attenuation

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway

Our two different approaches for the DOT computation GLOBAL approach: make altimetric data, which have a local distribution, “global” extending the data also in the land areas (IAPG) PROFILE approach: filtering the altimetric data along the satellite tracks (DGFI)

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway First preliminary corrections Reference system (Topex or GRS80 ellipsoid) Tide system: zero tide, mean tide (altimetry) or tide free (ITG03) Coordinates: ellipsoidal (altimetry) or spherical (geodesy and oceanography)

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Global approach

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Global approach

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Global approach sea altimetry land synthesis joint SHA SHS

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Global approach Sea surface and geoid are expressed in series of spherical harmonic functions The same filter up to a certain degree can be applied Jekeli-Wahr filter

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Spectral filtering of geoid heights applying 2D JW (N sh ) 2. Spatial filtering of sea surface heights to achieve spectral consistency 1D(h i ) 3. Filter correction to consider differences between spectral and along track filtering (2D JW [N SH ]i-1D JW [N i ]) 4. Computation of filtered DOT  =1D(h i ) - 2D JW (N sh ) + (2D JW [N SH ]i-1D JW [N i ]) Profile approach

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway 422 nd cycle of TOPEX/Poseidon and 79 th cycle of Jason-1

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway data Geoid = ITG-Grace03 Gravity Field Model (TU Bonn) –data from 09/2002 to 04/2007 –no a-priori information –only satellite data –maximum degree L =180 –full Variance-Covariance matrix (VCM) Altimetry –2004 –Missions Topex and Jason

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Differences few cm open ocean ± 40 cm along coastline global approach profile approach

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway

Filter up L=60

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Filter up L=120

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway Data assimilation Assimilation is carried out column by column of ocean model (FEOM) using a type of ensemble Kalman filter algorithm (LSEIK). Only data in radius of 900 km are considered for each column assimilation. Observational increment is weighted by function that approximates Gaussian of 245 km. Result is DOT that reflects the influence of the geodetic DOT data used and ocean model parameterization.

ESA Living Planet Symposium 28 June - 2 July 2010, Bergen, Norway

Conclusions Differences between the global and profile approach Improve the filtering, specially along the coastline Full error propagation (geoid + altimetry) to DOT Spectral consistency of geodetic DOT and ocean model Comparative analysis of geodetic and oceanographic mean dynamic ocean topography