How do we get the images?

nice isiis3

Since the 1800’s, plankton has been studied and collected using simple nets with very fine mesh. The process of analysis of these plankton ‘samples’ is tedious, labor intensive, confined to laboratory, and can only be done on relatively small areas of the ocean. By sampling in this manner, it is difficult to get a good understanding of how planktonic organisms are distributed and how they interact with each other. Yet plankton represents a very important part of a global system feeding larger animals like fish, whales and many others. The In Situ Ichthyoplankton Imaging System (ISIIS) is one of a few systems in the world capable of improving the way we study plankton to better understand their life and function in the marine environment. Instead of using an actual net to capture plankton, ISIIS captures the images of the organisms and information about their immediate surroundings. ISIIS samples continuously, resulting in a collection of digital images that record the exact location of the various plankton organisms in relation to each other and the environment in which they live. Further, the images are recorded onto a simple hard drive instead of slurry of plankton all mixed together in a sample jar with formaldehyde (yech!).

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ISIIS is an underwater imaging system developed to capture real time images of plankton that are relatively rare, small, and fragile such as fish larvae and delicate gelatinous organisms (like jelly fish). ISIIS is composed not only of a macro-camera system with its own illumination but it also is integrated into an underwater vehicle with a variety of additional sensors to measure the depth, salinity and temperature of the water, as well as such properties as dissolved oxygen, light level, and even how much chlorophyll a (measure of primary production) is present. Together, the camera and sensors provide detailed profiles and tracks of what plankton are where and what the ocean environment around them is like.

isiis schematic

The vehicle, and associated imaging system and sensors, moves up and down through the water column using side-mounted, user-controlled dive fins (like an underwater glider) while being towed behind an oceanographic ship moving at 5 knots. The vehicle frame is divided into four compartmentalized enclosures with imaging and optical equipment seamlessly integrated into ISIIS’s ventral housings and environmental sensors and electronics in the dorsal housings. ISIIS is designed to undulate in a zigzag fashion between the surface and a maximum depth of 200 meters.

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The ISIIS system utilizes imaging technology very similar to an office scanner flipped on its side. The imaged parcel of water passes between the forward portions of two streamlined pods where it is “scanned” and transformed into a continuous image. The resulting very high-resolution image is of plankton in their natural position and orientation. When a sufficient volume of water is imaged this way, quantification of concentration (individuals per unit volume) and fine scale distribution is possible. ISIIS is capable of imaging a maximum of 162 Liters (43 gallons) of water per second (when moving at 5 knots) with a pixel resolution of 70 µm (the thickness of a human hair).

The imaging data and associated oceanographic data are sent to the surface ship via a fiber optic cable and recorder onto a main computer for later viewing and analysis.

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