Satellites get a pretty good image of the surface of the ocean - they produce amazingly accurate images of the surface of the planet - but they cannot see through water, below the waves.
Lily, a student from Oxford University, is using the data of the Multibeam Swath (an instrument attached to the keel of the ship which sends many beams of sound in the water column and gets back the echoes after they bounce off the seafloor) to compile a map of the seafloor in the seamount’s area.
In the old times, measurements of water depth were made with a sounding machine. It consisted of piano wires with a plumb bomb at the end deployed until the weight touched the seabed and then the length of the wire was measured. It was a very long process; the ship had to stop!
Around World War II, the echosounder was invented and it enabled us to measure the depth of the seabed while the ship was moving. These echosounders had a single sound beam only, and would measure the depth along the ship’s track. Multibeam echosounders are essentially doing the same thing but with a fan of sound beams that survey a whole swathe of seabed, sometimes kilometres to the left and right of the ship’s track.
Once this data has been collected, it has to be processed to get rid of errors, otherwise you may end up with 100m tall spires which are impressive but not actually there! The bathymetry from this trip will be compared with previous maps to determine whether there may have been submarine landslides or underwater eruptions in the past two years.
|Coral seamount; 2009 data collected aboard the R/V Fridtjof Nansen, hopefully we will fill some of the holes!|