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20 Science Manual – Using Video Images for Fisheries Monitoring

3.6 Data storage

External USB hard drives are a flexible and simple way to collect, transport and, if

necessary, store data. A range of drives are available with up to two terabytes

capacity. Some makes were tested for the purposes of the project but it was not

possible to try everything, especially considering how quickly this area is expanding.

A good place to find information is on www.dabs.com

where you can read customer

reviews of some products. Most external hard drives are ‘plug and play’, meaning

that they can simply be connected to the USB port of the PC and will work without

having to install any drivers or software.

The majority of the larger capacity (above 250 GB) external hard drives require a

separate power supply, so are not suitable for sites with no mains power. There are,

however, drives available which are powered from the USB port and do not need a

separate power supply. These 2.5” hard drives, such as Freecom Toughdrive, are

designed to be used with laptop computers and work with the Mini-ITX system. The

maximum capacity of these low-power drives is currently 250 GB; however, this is

likely to increase rapidly.

3.7 Introduction to image processing software

Image processing is an important component of a video counting system, as it can

considerably reduce the amount of time taken to obtain a fish count from the raw

video data. Using an image processing system to handle the data, rather than

watching the video files, can make a video counting system viable where it may not

have been before. It can also mean that far more data can be analysed from a site,

increasing the amount of information that can be obtained.

3.7.1 Motion detection versus image analysis

A motion detection system produces a video clip of each event passing through a

user-defined region of interest. The video clip can subsequently be viewed and

interpreted by an operator. The criteria used to select which events to record can be

user-configured (minimum and maximum size, direction of travel, intensity and so

on). An image analysis system aims to produce a line of data for each event detected

and provide sufficient information on each event for an operator to eliminate non-

target species events. Each event is tracked as it passes through the region of

interest and again, the criteria for a track being accepted as a fish event can be user-

EXTERNAL USB HARD DRIVES

Mains-powered

Low-power drives

MOTION DETECTION VERSUS IMAGE TRACKING

• FISHTICK

• DIGITAL VIDEO MOTION DETECTOR (DVMD)

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