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Documentation   
Processing Notes (version 2008_rel2)

TOPEX/Poseidon

The TOPEX/Poseidon (T/P) data are from the Merged Geophysical Data Records (MGDRs) and have been modified to include the Wallops internal calibration, new tide models, a new TMR path delay correction, and updated sea state bias models.
To make comparisons with Jason more compatible, we replaced the (M)GDR ocean and load tides with those from GOT00.1 model (Ray, 1999) and the equilibrium long-period ocean tides with those used for the Jason GDRs (P. Callahan, personal communication).
Keihm et al. (2000) discovered a drift in one channel of the TOPEX Microwave Radiometer (TMR), which caused a noticeable drift in comparisons between T/P SSH measurements and the global tide gauge network (Mitchum, 1998). We have applied the TOPEX Microwave Radiometer (TMR) replacement product. This new TMR correction removes the drift and yaw-state dependent errors that were in the TMR measurements on the original T/P MGDRs.
We applied parametric estimates of the sea state bias (SSB) produced by D. Chambers for each of the two different TOPEX altimeters (TOPEX-A and TOPEX-B) that have operated during TOPEX/POSEDION mission. A 0.24 mm bias between TOPEX-A and TOPEX-B determined from the tide gauge calibration has been applied. We have not applied any retracking corrections or corrections to the ionosphere path delay that result from changes to the SSB model.
The inverted barometer used is computed from both the local value from the TOPEX MGDR-B and the global values from the European Centre for Medium-Range Weather Forecasts (ECMWF), where the latter is given by

Inverted Barometer = -9.948*(1013.3 - global_average_pressure)

The global_average_pressure is interpolated from values determined at 6 hour intervals from CNES. The file containing the average values is obtained from CNES/CLS.  The inverted barometer does not have much apparent effect on the global mean sea level because the ocean as a whole is not compressible.

Jason-1

The Jason-1 data are from the Geophysical Data Records (GDRs); no Interim GDRs data are processed for these results. Jason-1 version-B GDRs (GDR-Bs) are used for cycles 1-177 (15 January 2002 - 25 October 2006) and cycles 179-211 (14 November 2006 - 29 September 2007).
GDR-Bs include the Jason Microwave Radiometer (JMR) replacement product. We divided the JMR path delay by 1.023, which is the scale difference between the new TMR path delay and the JMR path delay. The SSB provided on the GDR-Bs has been used.
An along-track relative bias has been removed from the Jason-1 SSH data to bring them into agreement with the T/P SSH data. This bias has a global average value of 131.8 mm and a standard deviation of 12.7 mm.

Global mean sea level

We chose to reference TOPEX and Jason SSH anomalies on the common ground-track to an along-track mean computed by the CLS_01 mean sea surface. Each cycle of T/P and Jason data are referenced to a standard set of locations using a cross-track gradient correction.
Spurious data have been removed with a restriction of SSH anomalies to be < 2 meter. Global mean sea level was computed from the corrected SSH anomalies using a simple equal-area weighted average (Wang and Rapp, 1994). See our calibration paper (Leuliette, E. W, R. S. Nerem, and G. T. Mitchum, 2004. Calibration of TOPEX/Poseidon and Jason altimeter data to construct a continuous record of mean sea level change. Marine Geodesy, 27(1-2), 79-94.) for more information.