Rapid underway monitoring

The advent of easy access to the satellite-based global positioning system (GPS) and availability of off-the-shelf portable probes and rapid analyzers for a number of water quality determinants have enabled the development of systems that can be carried on small survey vessels to map water quality conditions. Rapid data acquisition is now practical using probes and sondes for measuring temperature, conductivity, turbidity, pH, and dissolved oxygen fluorometric technologies for chlorophyll biomass and phytoplankton composition flow injection and loop flow analysis for some nutrient species and acoustic Doppler-based devices for current profiling. 

Chiorophyii-a fluorescence probe (major groups and photosynthetic capacity) 

Muitiparameter water quaiity probe (pH, DO, temperature, saiinity, turbidity, chiorophyii-a fluorescence) 

Schematic diagram of the Rapid Underway Monitoring system illustrating key components and required integration Diaphragm pump (a) used to deliver water to the onboard instrumentation (b-d), instruments mounted in the water column (e, f), and GPS unit and computer components (g). (Reproduced from Hodge, J., Longstaff, B., Steven, A., Thornton, P., EUis, P., and McKelvie, 1., Mar. Pol. Bull., 51,113,2005. With permission.) 

While the survey vessel is underway, subsurface water is pumped to the instrumentation using a diaphragm pump from an intake positioned approximately 1 m below the surface to avoid turbulence created by boat wash. Trials of the system have shown that it can be successfully used from vessels as small as 4 m, and depending on which instruments are deployed, data acquired at speeds of 25 knots or more. 

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The use of rapid underway monitoring systems offers the capacity to detect small-scale spatial variability in water quality parameters that might otherwise be missed by discrete sampling site methodologies. Potentially, a rapid underway system provides a detailed view of where problem areas originate and their spatial extent. 

In the future, RMC-instruments may find applications as low cost, wide-field monitors for spin stabilized microsatellites. The alternative techniques requires three-axis stabilized platforms to perform well, and much higher data rates as well. The WATCH experience have shown, that the performance of an RMC is adequate for providing the first alert for, and the initial positions of, transient sources like X-ray novae. Plans are also underway in several laboratories to establish ground-based optical telescopes with possibility for rapid follow up of satellite gamma-burst localizations. A spaceborne RMC detector would complement such concepts very weU. 

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