3-D camera to reveal sea life

September 22, 2000

A new camera that captures 3-D images for display as holograms was unveiled on Monday at the University of Loughborough.

The Holocam will benefit marine biologists, divers surveying damage to sub-sea pipelines and oil rig structures, and marine archaeologists investigating shipwrecks.

Physicists from the universities of Aberdeen and Brunel at the Institute of Physics Applied Optics and Opto-Electronics explained that the camera operates to a depth of 100m and on each trip takes 45 holograms on photographic plates. When the plates have been processed, the holograms are displayed in a laboratory. A high level of detail is recorded, and during replay each 3-D image hovers in space.

The Holocam will first be used to record the numbers and positions of plankton in the oceans. Plankton are a very sensitive indicator of the environment, not least because they provide the staple diet for many species of fish. Until now, the method of working out the numbers of plankton in a particular area was to scoop up a container of sea water and count the plankton using a microscope.

This method destroys any information as to where the different kinds of plankton are in relation to each other, so biologists have no way of telling if some organisms are close enough to interact, breed or to eat one another.

By contrast, Holocam takes a3-D snapshot of about 100 litres of ocean, perfectly preserving the positions of the marine organisms for study.

Holograms are created using a laser beam. In the off-axis hologram, the beam is split in two, and while one half is reflected by a mirror straight onto a photographic plate, the other falls onto the subject, which, in turn, reflects it on to the plate. When the two beams meet, a pattern of light and dark is produced. This shows how bright the light from different parts of the subject is and also the distance travelled by each part of this light. Recording these distances provides the information needed for a 3-D image.

Once the plate is developed, shining another laser beam onto it at a specific angle produces the hologram. The test holograms taken so far in a water tank in the laboratory give a realistic picture.

As well as recording dense concentrations of organisms, Holocam can also show smaller, transparent organisms in lower concentrations. The ability to record both types makes Holocam unique, and means that no plankton can escape its gaze.

The camera was conceived to measure damage to underwater pipelines and oil rigs, but the researchers hope it will also prove useful to marine archaeologists. When removing sensitive finds from shipwrecks, or if large objects are tricky to raise, the level of detail it can record could provide an alternative to salvage.

The camera is scheduled to start sea trials at the Southampton Oceanography Centre on September 26.

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