CD179: Deep-sea biology of the Portguese canyons


Daily diary

Monday 17 April 2006

Teresa writes:

"In the morning we finished the multibeam seabed bathymetry (depth) survey. After some initial stage processing, we obtained the first map of the area around the heads of the Cascais and Lisbon canyons. You will find some impressions of the results attached below.

We arrived at the head of the Lisbon Canyon and prepared TOBI (Towed Ocean Bottom Instrumment) to be deployed. At 11 am, TOBI was put in the water but the engineers realized that the swivel was not working properly due to a short circuit. TOBI was picked up and the swivel was replaced by a new one. Finally at 11.30 TOBI was put in the water again and started recording data.

TOBI is another tool to map the seabed using acoustics. It is a sidescan sonar, which sends out a pulses of sound, after which it listens to the echo coming back from both port and starboard side. The change in echo strength with time is recorded for every ping, and when we do this for a long enough time, and put all the results the one after the other, finally we become a map of the seafloor, very similar to a radar image of the land taken from a plane.

During the rest of the day and night nothing else happened besides the transects for TOBI. For the moment, the biologists are quiet, but they are eager to put their hands in their mud!"

3D image showing the shape (topography) of the seafloor at the top
of the Lisbon Canyon

Bathymetric map of the Lisbon and Caiscais canyon area. 'Colder' colours = deeper water; 'hotter' colours = shallower water

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April 2006
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