Silent Night
Posted by Sue on
19 December 2011
The weather is finally in our favour and we have successfully
completed the first of our survey areas in the Eastern English
Channel. The final Hamon grab was recovered and processed,
followed by a brief celebration (which involved the consumption of
rather a large amount of chocolate).
We then transited to our next survey area located in the outer
Thames. This survey has been designed to inform a long-term
study into both the physical and biological recovery of the seabed
following a period of marine aggregate extraction. Therefore,
the survey requires the collection of both multibeam bathymetry
data (see 'Sleigh Bells Pinging') and also sidescan sonar data (see
below). Overnight acoustic surveys are always welcomed
onboard by those taking their hours of rest as the peaceful motion
of the ship, steaming gently up and down the survey lines, quietly
rocks you to sleep!
The sidescan sonar is a 'towfish' (see below, left) which we tow
at an approximate altitude of 10-20m above the seabed. The sidescan
data allows us to assess the 'roughness' and 'hardness' of the
surface of the seabed (see below, right). This is
particularly useful when attempting to detect certain seabed
features, such as sand waves and ripples, and also boundaries
between different sediment types.
On completion of the acoustic and ground-truth sampling within
this survey area we will be transiting for a short distance to the
south to begin work on the second of our surveys designed to assess
the effects of a range of human activities on the seabed (see
'Multibeam Celebrations'). See the next blog to follow our
progress.
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