THE FEASIBILITY OF ESTIMATING OCEAN SURFACE CURRENTS ON AN OPERATIONAL BASIS USING SATELLITE FEATURE TRACKING METHODS

The feasibility of using a relatively new technique, often referred to as satellite feature tracking, for estimating ocean surface currents is described. sequential satellite imagery is used to determine the di splacements of selected ocean features over the time intervals between successive images. Both thermal infrared (IR) imagery from the Advanc ed Very High Resolution Radiometer (AVHRR) and ocean color imagery hav e been used to conduct feature tracking. Both subjective and objective techniques related to feature tracking exist to estimate surface flow fields. Because of the requirement for accurate earth location and co registration of the imagery used in feature tracking, the technique ha s been primarily restricted to coastal regions where landmarks are ava ilable to renavigate the satellite data. The technique is identical in concept to the approach that has been used in meteorology for the pas t 25 years to estimate low-level winds from geostationary satellite da ta. Initially, a description of the feature tracking technique is give n, followed by the history of satellite feature tracking in oceanograp hy. Next, the limitations associated with this technique are discussed . Also, only a few validation studies have been conducted to Verify th e results of satellite feature tracking. These studies are summarized together with some new results. Although this technique produces surfa ce flow patterns that generally agree with the expected patterns of fl ow, discrepancies in speed and direction are often found when detailed comparisons with in situ observations are made. With respect to curre nt speeds in particular, serious underestimates have occasionally been observed. A case study is given illustrating the technique for the sl ope water region off the U.S. East Coast. Finally, an example of a sur face current analysis that is being produced experimentally for one re gion off the East Coast is presented. In spite of certain limitations, this technique offers the potential for acquiring synoptic-scale cove rage of the surf ace circulation in coastal areas on a quasi-continuou s basis. Such information will be vital in supporting hydrodynamic cir culation models that are currently being developed for U.S. coastal wa ters.