Fishing Sonar For many years, the fishing industry has employed sonar technology to assist in positioning the mouth of trawl net in front of the oncoming shoal. This sonar would typically be a single beam device.
work, however, these smaller vehicles must endeavour to keep the payload as light as possible. Smaller devices typically consume less power than larger units, which is another important consideration.
The sonar head would mechanically rotate a fan-shaped acoustic beam. At each step of, say, 10deg, the head would capture an image before moving to the next step. This would continue until a full 360 deg was recorded.
“We have been successful in developing a range of equipment items for this new emerging market. ”
Later this year, Imagenex will launch a new multibeam device specifically aimed at the fishing industry. Instead of accumulating an image in steps, it will be able to instantaneously record an entire 360deg arc. The ability to see the target in real time will not only make it possible to position the mouth of the net more accurately in front of the fast moving shoal, potentially improving the fishing yield. As the sonar provides a 360 deg scan, it will also help steer the vessel zero towards the next shoal. “Years ago, the size of a typical multibeam sonar would make it impracticable to fit onto a trawl system,” said Gordon Kristensen, Managing Director of Imagenex. “The design of the new sonar, however, is the latest manifestation of a drive we started many years ago, to try and decrease the size of our equipment while still enhancing the functionality. “At our disposal, we have a range of patented technologies that have allowed us to minimise the footprint of not only our sonars, but also other subsea equipment items. This has opened up an extensive range of markets.” “The evolution of many subsea vehicles, for example, has resulted in a generation of smaller, lighter vessels which can be offered by manufacturers alongside larger units. These smaller devices are generally cheaper to purchase and operate, and can, consequently, be used by research institutions with smaller budgets. In order to carry out the
UT2 August 2012
A recent example is the development and incorporation of a modified compact Imagenex Model 853 echo sounder for the iRobot 1KA Seaglider unmanned underwater vehicle (UUV). It will be used to support Antarctic research conducted by the University of East Anglia (UEA). The iRobot Seaglider is designed for missions lasting many months and covering thousands of miles. It is the first UUV to complete a greater than nine month mission without needing to recharge its battery and the first to complete a mission of greater than 3800km. “We plan to calibrate the Imagenex echo sounder on the iRobot Seaglider for krill biomass estimation,” said Professor Karen Heywood from the University of East Anglia. “Working with British Antarctic Survey colleagues, we aim to show that this system could enable long-term measurements of krill abundance in Antarctic water. This would help us to better understand the basis of the food chain supporting cetaceans and penguins.” Imagenex developed the 120 kHz Model 853 echo sounder along with an onboard self-logging processor and interface to Seaglider’s open serial interface protocol. The onboard processor supports a “glider mode”, which allows sample data profiles and statistics to be transmitted via Seaglider’s Iridium satellite phone each time it surfaces. The echo sounder is also able to store up to 200 days of raw data on its flash memory for download upon recovery. Its small size and low power consumption is ideal for long-range, high endurance missions supported by Seaglider.
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Sonar view showing trawl net and ocean bottom