Abstract
The GRACE mission will map the Earth's gravity fields and its variations with unprecedented accuracy during its 5-year lifetime. Unless ocean tide signals and their load upon the solid earth are removed from the GRACE data, their long period aliases obscure more subtle climate signals which GRACE aims at. In this analysis the results of Knudsen and Andersen (2002) have been verified using actual post-launch orbit parameter of the GRACE mission. The current ocean tide models are not accurate enough to correct GRACE data at harmonic degrees lower than 47. The accumulated tidal errors may affect the GRACE data up to harmonic degree 60. A study of the revised alias frequencies confirm that the ocean tide errors will not cancel in the GRACE monthly averaged temporal gravity fields. The S2 and the K2 terms have alias frequencies much longer than 30 days, so they remain almost unreduced in the monthly averages. Those results have been verified using a simulated 30 days GRACE orbit. The results show that the magnitudes of the monthly averaged values are slightly higher than the previous values. This may be caused by insufficient sampling to fully resolve and reduce the tidal signals at short wavelengths and close to the poles.
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References
Bettadpur, S., Gruber, Th., and Watkins, M.: 1999, ‘GRACE Science Data System Design’, Supplement to EOS Transactions, AGU Fall Meeting 80(46), F254.
Eanes, R., and Bettadpur, S.: 1995, ‘The CSR 3.0 global ocean tide model, CSR-TM-95-06’, Technical Memorandum, Center for Space Research, December 1995.
Kaula, W.M.: 1966, ‘Theory of Satellite Orbits’, Blaisdell Publishing Co., Waltham, Mass, 124 pp.
Knudsen, P.: 1994, ‘Separation of residual ocean tide signals in a collinear analysis of GEOSAT altimetry’, Bull. Geod. 68, 7-18.
Knudsen, P., and Andersen, O.: ‘Correcting GRACE gravity fields for ocean tide effects’, Geophys. Res. Let. 29(8), 19-1-19-4.
Knudsen, P., Andersen, O.B., Khan, S.A., and Høyer, J.L.: 2000, ‘Ocean Tide Effects on GRACE Gravimetry’, IAG Symposia, Gravity Geoid and Geodynamics 2000, Vol. 123, Springer-Verlag, pp. 159-164.
Matsumoto, K., Takanezawa, T., and Ooe, M.: 2000, ‘Ocean Tide Models Developed by Assimilating TOPEX/POSEIDON Altimeter Data into Hydrodynamical Model: A Global Model and a Regional Model Around Japan’, Journal of Oceanography 56, 567-581.
Ray, R.D., Eanes, R.J., Egbert, G.D., and Pavlis, N.K.: 2001, ‘Error spectrum for the global M2 ocean tide’, Geophys. Res. Lett. 28, 21-24.
Tapley, B.D.: 1997, ‘The gravity recovery and climate experiment (GRACE)’, Supplement to EOS Trans. AGU 78(46), pp. 163.
Telford, W.M., Geldart, L.P., Sheriff, R.E., Keys, D.A.: 1976, Applied Geophysics, Cambridge University Press.
Wahr, J., Molenaar, M., and Bryan, F.: 1998, ‘Time variablity of the Earth's gravity field: Hydrological and oceanic effects and their possible detection using GRACE’, J. Geophys. Res. 103(B12), 30205-30229.
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Knudsen, P. Ocean Tides in GRACE Monthly Averaged Gravity Fields. Space Science Reviews 108, 261–270 (2003). https://doi.org/10.1023/A:1026215124036
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DOI: https://doi.org/10.1023/A:1026215124036