I lucked out not too long ago and happened to be at the right place at the right time (usually it’s the other way around). I ran into Brian Kidd, our resident expert on Multibeam Echosounder systems (also known as a Swath system) and he said he just happened to have the multibeam components apart for servicing. I ran to get my camera and followed Brian around and asked all kinds of insightful questions (of course). Echosounders are a version of Sonar (which stands for SOund Navigation And Ranging) wherein a transmitter emits a sound pulse downward into the water and then the amount of time that the pulse takes to come back to the ship is measured. A single beam echosounder will shoot a beam straight down and and use a single receiver to receive the pulse that bounced back from the bottom of the body of water. This is used to determine how deep the water is beneath the ship. A multibeam echsounder will emit a broad pulse of sound into the water and then will use multiple receivers aimed at various angles to measure the reflected sound. These times are then processed by the computer to generate a “swath” beneath the ship and at some distance to either side which shows the height of the sea floor. Moving the ship forward will give a band of height information beneath the ships track, and by moving in parallel, overlapping tracks, an ever-growing patch of sea floor heights can be mapped.
Okay, I’ve exhausted my general knowledge of the subject. I’ll let Brian take the reigns and kick back and learn from the master…
At the 2009 RVTEC meeting, I sat in on the Swath/Multibeam workshop and updated the Swath/Multibeam section of OCEANIC’s International Research Vessels database for the UNOLS vessels. There were some huge swath transducer arrays being discussed at the workshop on some of the deep water vessels, so I was pretty surprised to see just how compact the shallow water multibeam systems can be. In the second part of the video, Brian shows us what the Reson Seabat 8101 transducer assembly looks like and how they mount the unit to the ship.
Many thanks to Brian for putting up with me and for taking time to share his knowledge of the Reson Seabat 8101 Multibeam System (PDF of specs here) onboard the RV Hugh R. Sharp.
Why two videos and not one? Apparently YouTube has a 10 minute max length for uploaded videos, so I broke the video into two parts. Part 1 covers the monitoring and display station and Part 2 covers the mounting infrastructure and the transducer assembly. This works well for me as I doubt that too many people are able to sit through a 20+ minute video anyways, so breaking it up into two more digestible chunks is better in my opinion.