1. Assessing GOCE Gravity Models using Altimetry and In-situ Ocean Current Observation.
Per Knudsen & Ole Andersen, DTU Space,
Jerome Benveniste, ESA/ESRIN,
Sean Bruinsma, CNES,
Johanna Honecker, TUM,
Nikolai Maximenko, ICPR-UH

2. New model - DTU13MDT: Similar to DTU12MDT updated with DTU13MSS
Eigen-6C3
Improved mainly in the Arctic and in the equatorial region..
20 year reference period
Consistent with the new
AVISO altimetry reference period.

3. Geostrophic Currents (DTU13MDT):
40-
cm/s 5-
Geostrophic Currents (DTU13MDT):

4. GV Speeds (DTU13MDT vs Maximenko):
40-
cm/s 5-
GV Speeds (DTU13MDT vs Maximenko):
DTU13MDT Maximenko

5. GV Directions (DTU13MDT vs Maximenko):
DTU13MDT Maximenko

6. North Atlantic Ocean:
DTU_EGU13_MDT Maximenko

7. North Pacific Ocean:
DTU_EGU13_MDT Maximenko

8. Assessment of GOCE models
A more quantitative assessment of GOCE gravity models is carried out using:
A MSS model based on satellite altimetry,
(In “quiet” areas the MSS is a really good approximation to the marine geoid)
A MSS model and mean drifter velocities.
(to make a link to the ocean circulation)

9. Assessment using DTU13MSS
In a “quiet” area in the Southeast Pacific, 17 models were used:
tim_r3
tim_r4
tim_r5
dir_r3
dir_r4
dir_r5
eigen6c
eigen6c2
eigen6c3
30x30 deg areas, 1/4x1/4 deg grids, up to Nmax, no filtering
goco02s
goco03s
gogra02s
gogra04s
itg-goce02
jyy_goce02s
jyy_goce04s
spw_r2

12. Use EOFs to detect common features
Use SVD to perform X=U∧V (only Tim + Dir + Eigen) EOF#1: Average.
EOF#1
Tim
Dir
Eigen6c

13. Use EOFs to detect common features
EOF#2 describes the progression/improvement of the releases – similar for Tim and Dir models Wavelengths: cy/deg (d/o )
Tim 5 4 3
Dir 5 4 3
Eigen6c
EOF#2

14. Use EOFs to detect common features
EOF#3 shows the special features of the Eigen models wrt the other modes. Wavelengths: cy/deg (d/o ) And meridional (d+o )
EOF#3
Eigen6c
Tim
Dir

15. Use EOFs to detect common features
EOF#4 show special feature of release 4 of both Tim and Dir
EOF#3 4
Tim 4
Dir
Eigen6c

16. RMS of residuals: RMS values vary around 16 – 19 cm.
A tendency of lower values for newer models.
RMS for the EIGEN-6C models are 10 cm.
MSS-geoid (left)
Power spectrum (below)
2D power spectrum (right)
Most signal >0.6 cy/deg (≈ d/o 220) have been removed.

17. Power Spectra of residuals:
RMS values vary around 16 – 19 cm.
A tendency of lower values for newer models.
Tim Dir
3, 4, , 4, 5
Improvements detected at cy/deg (≈ d/o )

18. Assessment using MSS and drifter velocities
An assessment of GOCE gravity models is carried out using a MSS model and
An MDT model (Maximenko) and
Mean drifter velocities.
¼ x ¼ deg. means, Ekman drift removed, no meso-scale correction.

19. Results – correlation spectra
Signals are nicely correlated at longer wavelength (to cy/deg, i.e km) Ongoing research !!!
MDT Vx Vy

20. Conclusions
We have
Shown good similarities between DTU13MDT and Maximenko et al. MDT
Described differences in GOCE models using EOFs.
Computed spectra of the residuals
Computed correlations.
We need to continue
Doing assessments in more areas - compare,
Study correlations.