calibration before the survey start

After leaving Scheveningen harbour and steaming up north for 2 days, fisheries research vessel R/V 'Tridens' spent the past 2 days anchored in Loch Eriboll in the north of Scotland to calibrate the acoustic equipment before the start of the survey next week.



R/V Tridens located in Loch Eriboll, north of Scotland

Calibration of the acoustic equipment involves taking measurements of a small metal sphere with known acoustic properties that is attached to thin lines and suspended below the ship inside the acoustic beam:

image showing a typical echosounder calibration setup: the metal calibration sphere is situated inside the acoustic beam below the ship 



Such a calibration requires a sheltered location with quiet water conditions and enough depth below the ship - hence the choice for Loch Eriboll north of Scotland close to the survey area.

 

After a recent refit, R/V 'Tridens' now has a range of new acoustic equipment for ecosystem survey purposes. The numerous transducers of these systems (7 in total) are located in a drop keel, which can be lowered below the ship's hull to avoid air-bubbles in surface waters that affect the quality of acoustic recordings.

 



The new drop keel of R'V 'Tridens' just before it is lowered 3 metres below the ships' hull



Acoustic transducers of the acoustic equipment installed in the drop keel

The new acoustic equipment includes the recently released wideband echosounder EK80 and the multibeam echosounder ME70 from Simrad.

The wideband system will allow us to more confidently identify marine organisms encountered in the acoustic data, while the scientific multibeam echosounder will give us a 3D picture of the organism aggregations encountered and map the seabed at the same time. These systems are the key for surveying the ecosystem.



impression of the multibeam system ME70 installed onboard R/V 'Tridens'

3D fish school and seafloor maps based on multibeam echosounder recordings

All these systems now had to be calibrated in order to use them for quantitative purposes during the upcoming survey.

Luckily we found very favourable conditions in Loch Eriboll with hardly any currents and no wind at all:

view from R/V 'Tridens' towards the entrance of Loch Eriboll in the north of Scotland. The beams and winch systems are installed on deck to be used during calibration to steer the calibration sphere through the various acoustic beams



very calm and perfect calibration conditions at Loch Eriboll.



screen showing the EK80 in progress during calibration. The system was only officially market released 1 month ago! Cameras kept the winches in the picture to observe smooth operation of the metal sphere kept 20 meters below the ship inside the echosounder beam.



Dirk performing the calibration of the multibeam echosounder

screen shot of the multibeam echosounder calibration: note the recorded detections of the calibration sphere (grey dots) throughout the 21 beams covering a fan of 81 degrees.

After successfully calibrating all acoustic systems, it was soon time to leave our sheltered location to get ready for the survey start next week. R/V 'Tridens' will start the survey after leaving Aberdeen harbour on Monday. Not long to go until the official start of the Herring and Pelagic Ecosystem Survey in the North Sea this year! Watch this space...

Last impressions of Loch Eriboll after a successful calibration!



Performing some seabed mapping trials during passage to Aberdeen