Evaluation of a Relative Bias between TOPEX and POSEIDON Altimeter Data.

TOPEX and POSEIDON altimeters are on board the same satellite and measure the sea surface topography, alternatively. Here the relative bias between the two altimeters is estimated. Data for five orbits over the North Pacific are analyzed. The relative bias is found to be about 22cm and considerably stable, not depending on the orbit and the observation time. The value is consistent with that indicated by the calibration by in situ data. The effectiveness of adding the constant relative bias to the POSEIDON altimeter data is demonstrated by the comparison with in situ sea level data. Corrected POSEIDON altimeter data are also obtained by linearly interpolating the TOPEX altimeter data closed in time instead of adding the constant value. In comparison of both results with in situ sea level data, the correlation is higher for the latter corrected data.