Marine Produce Australia: Cone Bay Barramundi Aquaculture ...

2.3. Equipment
2.3.1. Topside Control Unit
The towed camera system was powered and controlled by a Topside Control Unit
(TCU) and laptop computer that were mounted on the vessel. The TCU combined
the GPS and depth data into one NMEA data stream then encoded the (GPS and
depth) data to the audio and video tracks of the video footage. The TCU streamed
the video footage and data to a laptop computer (in real-time) for recording and
video analysis. The video footage was captured on the laptop computer at a
resolution of 720 x 576 (lines) at 30 frames per second. The GPS and depth data
(NMEA stream) were captured to the laptop using the ‘GO Video’ software (see
section 2.4)
2.3.2. Spatial positioning
The video footage and video analysis data was geo-referenced with latitude and
longitude coordinates from a Furuno GP 37 differential GPS system (accuracy of 10 m.
Depth was recorded throughout the day during the period 22/10/2011 to 24/10/2011,
at tide heights ranging from 2.97 to 9.24 metres above lowest astronomical tide
(LAT). The depths were corrected to LAT using the tide predictions for Derby, WA
minus 41 minutes (Point Usborne) (Table 2), using a method based closely on the
‘Rule of Twelfths’, a tool commonly used in yachting to adjust depth for tides (see
http://en.wikipedia.org/wiki/Rule_of_twelfths). This rule assumes that the rate of
flow of a tide increases smoothly to a maximum halfway between high and low tide
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