A different sort of cleaning...

Hi Guys,

Sorry I haven't written anything for a couple of days, I have been snowed under with processing and cleaning up the swath data for the seismic runs the ship has conducted so far... what is that I hear you ask? Well OK probably not but I'm going to tell you anyway because my life has consisted of little else this week and as I have been bored silly I think it only fair to share it around ;-)

Multibeam is an acoustic technique used for the production of bathymetric and sediment classification maps. Different sonar models are classified according to the following parameters:

• acoustic frequency
• depth
• number of beams
• size of beams
• angleof entry of each beam
• rate and duration of pulse

How does it work?

A transducer emits a signal composed of several straight beams (191 on James Cook) forming a band perpendicular to the ship's axis. This allows for the coverage of a large area over a relatively short period of time. An elevated sonar emission frequency decreases the range, however, it increases the resolution of the data. After a delay, the sonar waves are reverberated from the seafloor and received by the transducer. The depth of the seafloor and the presence of obstacles can be determined by the time elapsed between emission and reception of the signals. The average depths is obtained from the first beam directly beneath the axis of the ship. The exact position of the ship is determined using a GPS, this is important in creating representative bathymetric maps. Also, the rolling, pitching, and heave of the ship must be taken into account. Detectors are used so that the influence these have on the results can be measured.

A C-View Bathy 3D swath bathymetry image showing clearly a gas pipeline draped over reef

C-View Bathy detailed swath bathymetry sun-illuminated image of the Hong Kong Harbour showing the across harbour tunnel

Once all this data has been processed and cleaned it is combined with the data from the gun firing systems, the gps, magnetometer and gravity data and the data recovered from the OBS to give our scientific colleagues a highly accurate picture of the seabed and its composition.

Tomorrow, weather and workload permitting we are hoping to have a Bar-B-Cue, hopefully I should have something a bit more fun to write about...

Oh and one last thing... in my previous post I may have implied that I didn't really miss emails and telephones calls home... I apologise unreservedly if anyone mistakenly got that impression ;-)

Mick