[1] Satellite and hydrographic observations of oceanographic conditions in the northwestern Gulf of Alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and, in doing so, influence the shelf-slope exchange of biota and water mass properties. Eddies typically form in the northern Gulf of Alaska during fall and winter and propagate southwestward within an $200 km wide corridor along and above the continental slope. Eddy activity within this corridor diminishes in the downstream direction. The trajectories of faster propagating (>4 km/day) eddies tend to lie closer to the shelf break than do the trajectories of slower propagating ($1.5 km/day) eddies. The interaction between azimuthal eddy currents and the shelf break frontal jet (1) establishes an upwelling zone, associated with the leading flank of the eddy, that strengthens cross-slope gradients, (2) weakens cross-slope gradients and promotes shelf-slope exchange where the eddy is adjacent to the shelf, and (3) reestablishes a weak upwelling zone associated with the trailing flank of the eddy.
We present an overview of the calibration of the Sea-viewing Wide Field-of View Sensor (SeaWiFS) from its performance verification at the manufacturer's facility to the completion of its third year of on-orbit measurements. These calibration procedures have three principal parts: a prelaunch radiometric calibration that is traceable to the National Institute of Standards and Technology; the Transfer-to-Orbit Experiment, a set of measurements that determine changes in the instrument's calibration from its manufacture to the start of on-orbit operations; and measurements of the sun and the moon to determine radiometric changes on orbit. To our knowledge, SeaWiFS is the only instrument that uses routine lunar measurements to determine changes in its radiometric sensitivity. On the basis of these methods, the overall uncertainty in the SeaWiFS top-of-the-atmosphere radiances is estimated to be 4-5%. We also show the results of comparison campaigns with aircraft- and ground-based measurements, plus the results of an experiment, called the Southern Ocean Band 8 Gain Study. These results are used to check the calibration of the SeaWiFS bands. To date, they have not been used to change the instrument's prelaunch calibration coefficients. In addition to these procedures, SeaWiFS is a vicariously calibrated instrument for ocean-color measurements. In the vicarious calibration of the SeaWiFS visible bands, the calibration coefficients are modified to force agreement with surface truth measurements from the Marine Optical Buoy, which is moored off the Hawaiian Island of Lanai. This vicarious calibration is described in a companion paper.
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