An optoelectronic sensor of mesoplankton as an addition to CTD-probes and towed vehicle

A new optoelectronic sensor TRAP-6 was designed at VNIRO and intended for assessment of size-quantitative characteristics of mesoplankton “in situ”. Its main difference from all previous designs is the use of principal new optical scheme which allows the measuring volume to be determined only by means of an optical method. The plankton is measured in a practically non-disturbed medium. At a speed of probing equal to 0.5 m/s the water volume observed per second will contain about 0.05 m³. As a result of using the new optical scheme one can succeed in making the emitter and photoreceiver as a single unit and to place the whole device in a cylindrical case with a diameter of 90 mm and the length of 140 mm. The absence of concentrating plankton net and the small size of the metering device allows it to be used as an additional sensor on a probe or vehicle towed. At the present time TRAP-6 is installed on the CTD-probe “MARK 3B” with a cassette of water bottle. The use of such a vehicle together with the parameters measured by probe gives the possibility for obtaining the approximate estimation of biomass. Simultaneously the measuring device plays the role of a stratificator of vertical plankton distribution and aim-pointer for´ sampling. Besides that the device modification was developed specially for installing on the towed undulating vehicle “AQUASHUTTLE”