Thursday, 13 February 2003
Improvements and Validation of the Gaussian Jet Model for Deriving Absolute Geostrophic Velocities from Satellite Altimetry
We improve key aspects of a Gaussian jet model for deriving absolute geostrophic velocity from TOPEX/Poseidon altimeter data. Velocities are obtained by synthesizing Gaussian-fits to cross-stream velocity anomaly profiles of the Kuroshio and its Extension for the 3-year period from October 1992. Significant meanders in the Kuroshio Extension are fitted using supplementary information on the jet position obtained from temperature frontal data. Contrary to the findings of earlier studies, the performance of the Gaussian jet model is sensitive to the details of the filter employed in pre-smoothing the altimeter data. We find that a Gaussian filter with a full-width at half maximum of 63 km is optimal for minimizing the difference in the mean sea surface height between the model and observations. When compared with simultaneous measurements from a shipboard acoustic Doppler current profiler (ADCP) at two intersection points, the altimetric and ADCP absolute velocities correlate well with the correlation of 0.55 to 0.74. The time-mean velocity is accurate to 1 cm s-1 to 5 cm s-1. The errors in the absolute and the mean velocities are similar to those reported previously for other currents. The comparable performance suggests the Gaussian jet model is a promising methodology for determining absolute geostrophic velocities, noting that in this region the Kuroshio does not meander sufficiently enough to guarantee the successful performance of the Gaussian model.
Supplementary URL: http://satrec.kaist.ac.kr/~sbkim/