Optronic sensors for mesoplankton studying in the sea water

A number of optronic sensors are developed at VNIRO. The sensors are used in hydrobiological probes for studying the spatial plankton distribution. The sensor used in probe “TRAP-4” allows to record the mesoplankton particles with the size from 0.5 to 15 mm when they go through the measuring volume of the flow channel. IR-laser diode is used as a source of silhouette illumination. Classification of particles according to five size-groups is being realized directly by matrix photodiode. For vertical probing, the probe is connected to the cod end of the concentrating plankton net together with flowmeter. It is hung on a single cable-rope analogically to standard CTD-probes and may operate down to a 1000 m depth. All the probe information on plankton, depth and water consumption through the net is transmitted to the board device and processed by IBM personal computer. The comparative analysis of data obtained by probe and data on parallel studies by means of net, water bottles and acoustic methods showed positive results. However, the experimental studies of hydrodynamic characteristics of probe net as well as visual observations from the underwater vehicle showed discrepancy between natural plankton state and its size-quantitative characteristics in artificially formed measuring volume. At present the experiments with new designs of optronic sensors which do not need concentrating plankton nets and flow channels are carried out