Comparison of velocity estimates from advanced very high resolution radiometer in the Coastal Transition Zone

Two methods of estimating surface velocity vectors from advanced very high resolution radiometer (AVHRR) data were applied to the same set of images and the results were compared with in situ and altimeter measurements. The first method used an automated feature-tracking algorithm and the second method used an inversion of the heat equation. The 11 images were from 3 days in July 1988 during the Coastal Transition Zone field program and the in situ data included acoustic Doppler current profiler (ADCP) vectors and velocities from near-surface drifters. The two methods were comparable in their degree of agreement with the in situ data, yielding velocity magnitudes that were 30–50% less than drifter and ADCP velocities measured at 15–20 m depth, with rms directional differences of about 60°. These differences compared favorably with a baseline difference estimate between ADCP vectors interpolated to drifter locations within a well-sampled region. High correlations between the AVHRR estimates and the coincident Geosat geostrophic velocity profiles suggested that the AVHRR methods adequately resolved the important flow features. The flow field was determined to consist primarily of a meandering southward flowing current, interacting with several eddies, including a strong anticyclonic eddy to the north of the jet. Incorporation of sparse altimeter data into the AVHRR estimates gave a modest improvement in comparisons with in situ data.

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