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Ocean Surface Topography from Space
A New Method for Mapping Mesoscale Circulation over the Shelf: Retracking Altimetric Waveforms to Conform to Geostrophic Currents Inferred from Satellite Imagery
Altimetric SSH for Sep. 7-13, 2003.
Larger image with caption
William Emery
(University of Colorado at Boulder)

C.K. Shum
(Ohio State University)


A major challenge facing present day satellite altimetry is mapping the mesoscale circulation in coastal regions where the bottom topography shallows abruptly, and onboard water vapor corrections become contaminated by the land. Waveforms reflected from coastal oceans differ from open oceans, such that the onboard satellite-tracking algorithm cannot accurately compute the coastal sea surface heights (SSHs). Retracking takes advantage of the 10 or 20 Hz measurements available in the waveforms as opposed to the 1 Hz measurements used in the standard altimetric retrievals. We are retracking altimetric data off the U.S. west/east coast study regions using as "truth" synthetic dynamic heights inferred from coincident geostrophic currents computed from sequential infrared and ocean color images. This method performs well against standard altimetric tracking in the open ocean and we hypothesize that the method could be extended into the shallow coastal regions where the retracking becomes important. Thus we can design the optimal retracker. To be consistent with this higher spatial resolution retracked SSHs we will use all available atmospheric water vapor data (from models or radiometers) and the best available tidal models to correct our altimeter heights. It is anticipated that this method can be extended to the Gulf of Mexico, Australia and Europe. This project fulfills theme one in the OSTST call and contributes significantly to themes two and three of this call. It contributes important steps forward to NASA's ocean currents and coastal environment objectives by linking infrared and ocean color imagery directly to coastal ocean altimetry to depict coastal mesoscale circulation.

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