Remote sensing was long considered an obvious tool for studying the distribution of HAB organisms over larger spatial and shorter time scales than is possible with ship-based sampling [ Tester et al., 1991; Keafer and Anderson, 1993]. It has only recently lived up to its potential, however. Although multi-spectral scanners (e.g. Coastal Zone Color Scanner; CZCS) can be used to detect the reflectance of chlorophyll a and other pigments, these efforts have been constrained by the inability of the sensors to discriminate phytoplankton populations at the species level. This is, of course, a fundamental requirement of HAB programs. Instead, progress has been made by first linking specific water masses to HAB organisms and then identifying and tracking that water mass with an appropriate remote sensing technique. In particular, remotely-sensed sea surface temperatures (SST) have been used to follow the movement of fronts, water masses, or other physical features where HAB species accumulate. The coastal current discussed above that dominates PSP dynamics in the southwestern Gulf of Maine is easily identified by its temperature signature (Fig. 4). Likewise, the long-distance advection of Gymnodinium breve from Florida into the nearshore waters of North Carolina via the Gulf Stream was documented with this approach [ Tester et al., 1991].
A few years ago, remote sensing images were expensive and difficult to obtain in a timely manner for all but those closely linked to a satellite receiving station or processing center. The advent of the National Oceanic and Atmospheric Administration (NOAA) Coastwatch Program has since brought this technology on a near real-time basis to the small user at little or no cost [ Keafer and Anderson, 1993]), so the prospects are bright for an expansion in the application of remote sensing to HAB issues. In an offshoot of remote sensing technology, the same automated buoys that will someday be searching for HAB cells using molecular probe technology can also be measuring the physical and optical characteristics of the water column to provide the complementary information needed to make ``algal forecasts'' of impending toxicity.