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14 Science Manual – Using Video Images for Fisheries Monitoring

Deep red fluorescent tube light panels were used on Cardiff Bay fish pass. These

large light panels require a mains power supply and would not be suitable for a 12-

volt system. They are also expensive and require a lot of maintenance. Each tube is

powered separately, entailing a large number of underwater connections, and

problems were encountered with ensuring no water ingress at these connection

points.

The fish sizing method incorporated into the image processing systems (Section 3.7)

requires reference points within the camera field of view. These can be placed or

drawn on the light panel before it is installed. It is important to measure and record

the position of each marker.

3.3.2 Illuminators and LED lamps

If a light panel is not suitable or too expensive for the site, infrared lamps or

illuminators are a good second choice, although the light won’t be as even and the

images might not work as well with image processing software. Cheap red, or

infrared, underwater lighting is not an easy thing to find ‘off-the-shelf’. Pro-Optocam

has produced a prototype underwater 24-volt infrared LED illuminator (Figure 3.4 and

Table 3.4) which was lent to this project for testing. It draws approximately two amps

(Table 3.1) so would not be suitable for a stand-alone battery-powered site, but

would be suitable where installation of a light box was not possible. Pointing a lamp

or illuminator directly at a camera causes glare, so you need to reflect the light off a

light background and point the camera at, or across, this. Alternatively, the light can

be angled slightly away from the camera lens. Trial and error is usually necessary to

optimise the lighting and camera configuration.

Figure 3.4: An infrared LED illuminator

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