Application of satellite visible band data to high latitude oceans

Abstract

Remote sensing of high latitude oceans differs from oceans of tropical and subtropical latitudes because of the decoupling of the water's temperature structure from the flow dynamics at low water temperatures. Sea surface thermal patterns are useful here as tracers of the flow only, without a direct link to the circulation dynamics. Oceanic flow responds to water density contrasts and at high latitudes the density is controlled by salinity distributions. Though density contrasts are not ordinarily detectable with remote sensors, freshwater discharge in the Northeast Pacific contains very fine sediments (glacial flour) that can be detected using Landsat Thematic Mapper (TM) and Multi Spectral Scanner (MSS) imagery. From the TM data we have discovered several new coastal circulation features in the northern Gulf of Alaska. Flow around a coastal island produces a myriad of dipole eddies which are important to the cross-shelf transport of salt and heat. They also serve as sites to test numerical models to allow a better understanding of coastal flows and eddy formation elsewhere. Detection of these dipole eddies from their sediment distributions has allowed the comparison of different spectral bands from six imaging satellite sensors for their abilities to describe these features. We conclude that, in addition to the TM sensor's capability, the sediments can be detected with the MSS and Coastal Zone Color Scanner (CZCS) sensors, but not with AVHRR or Defense Meteorological Satellite Program (DMSP). As a consequence of this comparison of satellite visible data, we have confirmed that the dipole eddies here exist under low flow conditions ( < 1000 m 3/s).