TOPEX/POSEIDON Altimeter Gridded Sea Level Anomalies and Deviations

Bob Cheney
Russ Agreen
John Lillibridge
Nancy Doyle
Laury Miller

National Ocean Service, NOAA (N/OES11)
Silver Spring, MD 20910

The data are here.


The gridded sea level deviations and anomalies are derived from T/P altimeter data. For the deviations, all sea heights are relative to the 1993/1994 mean. For the anomalies, Annual and semi-annual harmonics have been removed, leaving only the interannual change relative to the 1993/1994 mean. A separate file is given for each month. These data are used, after additional spatial filtering, to produce the maps published quarterly in the NOAA Climate Diagnostics Bulletin.


The data were processed in the following way using collinear differences:

Standard corrections were applied (troposphere, ionosphere, tides--using the Cartwright-Ray ocean tide model, inverse barometer, and sea state bias). In addition, corrections to the M2, K1, S2, and O1 tide model constituents were made based on an analysis of Topex collinear differences by Carl Wagner of NOAA. The Rapp geoid OSU91A was removed to reduce errors resulting from slight cross-track gradients within the 2-km collinear band. Both Topex and Poseidon altimeter data were used, with a height bias of 21.5 cm applied to correct for the relative difference in calibration between the two. Data are excluded if the satellite attitude was greater than 0.3 degrees for Topex, 0.4 degrees for Poseidon.

NO ADJUSTMENT WAS MADE FOR ORBIT ERROR. Altimeter observations were simply averaged in 4x1 cells.

For the anomalies, annual and semiannual harmonics computed for each 4x1 cell were removed from the total signal to convert the data from sea level deviations to sea level anomalies. All time series have zero mean over the 2-year period Jan - Dec 1994.