We are interested in sampling effluent plumes underwater that might be both warm (hydrothermal plumes) and/or have contaminants in them (effluent plumes). I've done some preliminary research on sampling techniques based on towing monitoring devices behind boats.
Generally, you need to pair your monitoring device of interest (sampling jar, thermostat, nephelometer [measures concentration of suspended particulates], conductivity, camera) with something that measures depth.
Many papers on the topic of hydroplumes indicate that having multiple depths covered is important, rather than trawling/towing/planting a sensor at one depth. Three methods are outlined here:
1: A basic sampling strategy is simply vertical casts widely spaced along the ridge axis. Ensure each cast goes to a specific depth and remains there for long enough that the temperature or other measurement registers.
2: "Tow-yos" (tow yo-yo): Continual raisings and lowerings of the instrumentation through the plume while slowly steaming. Experience shows that a typical monitoring package can be towed with standard electromechanical cable at a rate of about 3-4 km hr-1, resulting in a complete up-down cycle through a 400-m plume layer about every 1 km along track using a winch speed of ~1 m s-1.
3: "Dynamic Hydrocast": This system comprises four sets of water sampling rosettes, each with a sensor package and data logger that are clamped to a cable and towed at different, known heights above the seafloor.
Finally, many studies use sonar to map plumes-- the different temperature changes salinity, and some plumes have enough dissolved particles in them that they show up with sonar. We will try some regular, fine tuned fishing sonar and post results.
Methods via NOAA: http://www.pmel.noaa.gov/pubs/outstand/bake1538/observational.shtml
A paper with an overview of hydrothermal plumes from natural sources that has a great catalogue of data visualization techniques: http://www.agu.org/books/gm/v091/GM091p0317/GM091p0317.pdf