Working with Jules Jaffe of Scripps, we have developed a novel two-dimensional imaging fluorometer. This system uses a sheet of laser light to induce chlorophyll a fluorescence of phytoplankton, which is imaged using a sensitive CCD camera. The laser sheet is angled downward at 45 degrees to extend below the platform as it sinks. This permits imaging of plankton that are undisturbed by the instrument itself.
In July of 2001 we deployed a second-generation imaging fluorometer off San Diego, CA, on an untethered free-falling platform. We could regulate the buoyancy to set the fall speed, typically 3-15 cm/s. Below are some sample images obtained from the system.
One striking feature of the images is the discrete nature of the phytoplankton. Rather than forming a continuous sheet of fluorescent material, we clearly see the individual cells, with considerable empty space between them. The camera system (imaging 35 x 35 cm with 300 micron resolution) can distinguish between single dinoflagellates and diatom chains.
The images below have not been processed: they must have the camera's dark current removed, and then be corrected for the pattern of excitation illumination. Once corrected they can be analyzed for the details of the microscale distribution patterns of the plankton.
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