Data processing method and used corrections
The Topex/Poseidon, Jason-1, Jason-2, Geosat Follow on (GFO) and Envisat data have been reprocessed using the X-TRACK processing tool (Ref 0). Processing includes parameter from the GDR (Geophysical Data Record) products for each altimeter mission plus additional state-of-the-art corrections distributed by the CTOH, Details on selected corrections are given in tables below.
The range and its associated corrections are provided in Ku-band for each satellite.
Topex/Poseidon | Jason-1 | Jason-2 | GFO | Envisat | |
---|---|---|---|---|---|
Range |
From altimeter measurement | From altimeter measurement | From altimeter measurement | From altimeter measurement | From altimeter measurement |
The altimetric radar wave undergoes several disturbances during the crossing of the atmopshere. We must therefore apply several corrections to this measured range according to the layer of the atmosphere which is crossed. Then we must also consider the sea state that will influence the return of the radar wave to the altimeter.
Once corrected from the satellite altitude above its reference ellipsoid, this gives a corrected range which corresponds to the Sea Surface Height (SSH) :
Corrections | Topex/Poseidon | Jason-1 | Jason-2 | GFO | Envisat |
---|---|---|---|---|---|
Ionosphere | From dual-frequency estimation + GCP (GDR Correction Product) correction |
From dual-frequency estimation |
From dual-frequency estimation |
From the GIM model | From the GIM model |
Dry troposhere |
From the ECMWF model |
From the ECMWF model |
From the ECMWF model |
From the NCEP model |
From the ECMWF model |
Wet troposhere |
From radiometer measurement + GCP correction of radiometer drift effects + GCP correction of yaw effects |
From radiometer measurement | From radiometer measurement | From radiometer measurement |
From radiometer measurement |
Sea state bias |
From BM4 model (Ref 9) + GCP correction (Ref 8) + GCP correction of non parametric electromagnetic bias (REF) |
From non parametric emperical model (Ref 10) |
From non parametric emperical model (Ref 10) |
From non parametric empirical model | From non parametric emperical model (Ref 11) |
Then, others geophysical corrections are applied to this SSH accounting for tides and dynamic atmopheric effects :
Corrections | For all missions |
---|---|
Solid tides |
From tide potential model (Ref 1) |
Pole tides |
From Wahr formula (Ref 2) |
Loading effect |
From FES1999 model (Ref 3) |
Atmospheric forcing |
From T-UGOm 2D global configuration (Ref 4), for periods smaller than 20 days + Inverted barometer for periods greater than 20 days, derived from ECMWF pressure |
Ocean tide |
From FES2012 model (Ref 6) |
After, the corrected SSH temporal average (Mean Sea Surface Height, MSSH) is removed at each point along the ground track, we obtain the Sea Level Anomaly (SLA).
References:
(Ref 0) Roblou L., F. Lyard, M. Le Hénaff, and C. Maraldi (2007): X-TRACK, A new processing tool for altimetry in coastal oceans, Proc. ENVISAT Symposium, Montreux, Switzerland
Roblou L., J. Lamouroux, J. Bouffard, F. Lyard, M. Le Hénaff, A. Lombard, P. Marsalaix, P. De Mey and F. Birol (2011) : Post-processing altimiter data towardcoastal apllications and integration into coastal models. Chapter 9 in
S. Vignudelli, A.G.
Kostianoy, P. Cipollini, J. Benveniste (eds.), Coastal Altimetry, Springer Berlin Heidelberg.
(Ref 1) Cartwright D. E. and R. J. Tayler (1971) : New computations of the tide-genereting potential, Geophys. J. R. Astr. Soc., 23, 45-74.
Cartwright D. E. and A. C. Edden (1973) : Corrected tables of tidal harmonics, Geophys. J. R. Astr. Soc., 33, 253-264.
(Ref 2) Wahr J. M. (1985) : Deformation induced by polar motion, J. Geophys. Res., 90(B11), 9363–9368.
(Ref 3) Lefèvre F., F. Lyard, C. Le Provost and E.J.O. Schrama (2002) : FES99: A Global Tide Finite Elemnet Solution assimilating Tide Gauge and Altimetric Information, Journal of Atmospheric and Oceanic Technology, 19, 1345-1356.
(Ref 4) Carrère L. and F. Lyard (2003) : Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing - Comparisons with observations, Geophysical Research Letters, 30, 6, 1275
(Ref 5) Roblou L. (2004) : Validation des solutions de marée en Mer Méditerranée: comparaisons aux observations, Technical Report, POC-TR-02-04, 67pp, Pôle d’Océanographie Côtière, Toulouse, France
Maraldi C. , B. G. Alton-Fenzi , F. Lyard , C. E. Testut , R. Coleman (2007) : Barotropic tides of the Southern Indian Ocean and the Amery Ice Shelf cavity. Geophys. Res. Let. , 34, XX. 10.1029/2007GL030900.
Pairaud I.L., F. Lyard, F. Auclair, T. Letellier, P. Marsalaix (2008), Dynamics of the semi-diurnal and quarter-diurnal internal tides in the Bay of Biscay. Part1: Barotropic tides, Continental Shelf Research, 28, 1294-1315.
(Ref 6) Lyard F., F. Lefèvre, T. L etellier, O. F rancis (2006) : Modelling the global ocean tides: modern insights from FES2004, Ocean Dynamics, xxx. 10.1007/s10236-006-0086-x.
(Ref 7) Ray R.D. (2008) : Thoughts on Sahllow-Water Tides ans Altimetry, Coastal Altimetry Workshop, Silver Spring, Maryland February 5-7.
(Ref 8) Chambers D. P., S. A. Hayes, J. C. Ries, and T. J. Urban (2003) : New TOPEX sea state bias models and their effect on global mean sea level, J. Geophys. Res., 108(C10), 3305, doi:10.1029/2003JC001839.
(Ref 9) Gaspar P., F. Ogor, P.Y. Le Traon, and O.Z. Zanife (1994) : Estimating the sea state bias of the TOPEX and POSEIDON altimeters from crossover differences, J.Geophys. Res., 99(C12), 24,981–24,994.
(Ref 10) Labroue S., P. Gaspar, J. Dorandeu, O.Z. Zanife, F. Mertz, P. Vincent and D. Cochet (2004) : Non parametrics estimates of the sea state bias for Jason-1 radar altimeter. Marine Geodesy 27 (3-4), 453-481.
(Ref 11) Labroue S. (2004) : RA-2 Ocean and MWR measurement long term monitoring. Final report for WP3. task 2. SSb estimation for RA-2 altimeter. Technical Note, CLS-DOS-NT-04-284.
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