Tuesday, 28 August 2012

A lesson in multibeam acoustics

Last time I mentioned that we were anticipating some bad weather. When it finally hit
we had to batten down the hatches and take shelter moored on the beautiful Isle of
Barra overnight. We managed to go ashore whilst the vessel took on fresh water,
stock up at the local shop, and make a visit to the local pub.

We are now back collecting multibeam data over the southern section of Stanton
Banks SCI (Site of Community Importance). Our BGS colleagues have written a
paragraph to explain a bit more about their work:

Hydrographic surveyors “look” into the ocean to see what the sea floor looks
like. A multibeam echosounder is a device typically used by hydrographic
surveyors to determine depth of water and the nature of the seabed. On the
Polestar, we use a Simrad EM3002D shallow water (0.5-160m) high resolution
multibeam system. This  system collects a swath of bathymetry data that is up to
10 times the water depth wide. By running survey lines correctly spaced apart,
very accurate 100% coverage of the water depth can be collected. Data is
processed onboard using Caris, taking into account position, ship motion etc.
The final product is displayed using 3D viewers to fly through the data as if
the water were not there. The images BGS produce can then be used to aid
JNCC and CEFAS scientists in determining the best locations for camera tows
and grab sampling.
Kirstin & Gillian

On a closing note, this morning we saw dozens of common dolphins jumping in the
wake of the ship and spied a pod of about 150 out in the distance. I also saw my first
ever minke whale this afternoon as well!

Becca Lowe