Tuesday 27 August 2013

Sounds of the seabed

Since reaching Pobie Bank Reef cSAC on Saturday lunchtime, we have been focusing on collecting acoustic data using sidescan sonar and a multibeam echosounder. These data provide information about the seabed; sidescan uses diagonal sound waves to identify features on the seabed, whereas multibeam measures the depth of the seabed and collects 'backscatter' data which give an indication of the hardness and roughness of the seafloor.

Multibeam data

The data are collected in ‘swathes’ using sensors that are fixed to the ship's hull or pulled behind it on a torpedo-like 'towfish'. The sidescan has been collecting some interesting data so far, the detail in the images has allowed us to make out rock formations, different sediment types and even underwater pipelines!

The towfish out of the water

The towfish being deployed

We’re currently in the first of three survey sections, which is a 50km long rectangle where a single tow can take up to five hours! We hope to complete the acoustic work for this section later today. After the data have been processed by our colleague from the British Geological Survey, we can use some of the outputs to help inform where to focus the groundtruthing work.

Today the clouds have lifted slightly, but it's still very grey! This afternoon we’re due to collect another of our Marine Scotland Science colleagues from Shetland so we may even get a rare glimpse of land...