Mapping ocean dynamic structure using optical spectroscopic measurements from space

Ocean circulation is an important element in many of the large scale experiments planned for the World Climate Program. Satellite infrared data, particularly that from polar oribiting NOAA weather satellites, have demonstrated a capability for showing flow patterns in the ocean in areas where western boundary currents or upwelling provide sufficient thermal contrast. Many areas, however, have thermal contrasts too low to be mapped reliably and other tracers are needed.Images showing variations in the colour (spectral reflectance) of the surface layers of the ocean, from the Coastal Zone Color Scanner on Nimbus 7, have provided excellent examples of flow patterns traced by movements of water bodies having different phytoplankton content. Examples are presented here which show coastal flow patterns off the British Columbia coast, Gulf Stream flow between the New England sea mounts and the form of the Alaskan Stream.Such imagery has only recently become available, and could contribute greatly to a more detailed understanding of ocean circulation. The CZCS was launched in 1978 and is slowly degrading in operation. It appears that a six-year gap in supply of ocean colour imagery may now occur before a replacement can be launched. A large back-log of data remains to be analysed. The CZCS was the first to make this type of measurement and it seems certain that improved sensor designs could increase the value of the data. One such design being developed in Canada makes use of two dimensional arrays of optical detectors to provide greatly increased spectral resolution, and improved sensitivity.