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By Skyy Sumlin, STEMSEAS Student
While on board E/V Nautilus, I was granted the opportunity to assist the expedition lead, Renato Kane, with using the eXpendable BathyThermograph (XBT). The XBT was used to measure the sound of speed through our position on the water, and it does this by utilizing a probe that measures the temperature and conductivity of the water, as it falls through the depths of the water. The conductivity of the water is based on electrical resistivity, which is the measure of a material’s property to oppose the flow of electric current. So, if the water (or other material) has a high resistivity then it’s a poor conductor of electricity.
The data collected through the XBT is transmitted through a copper wire, to the deck box. There the team reads and inputs the data into a sound velocity profile, which is then input into the multibeam sonar on the vessel. Multibeam sonars are used to map the seafloor and discern objects in the water column.
The sound of speed is based on temperature, depth, and salinity. The XBT measured the temperature at various depths, while the salinity of the Pacific remained constant. This data collection enables the multibeam sonar to know how fast sound is traveling through the water at a specific location, which is critical for mapping the seafloor. So, essentially the XBT aids the multibeam sonar in determining the accurate depth of the water via a two-way travel time, which is pertinent for navigating waters safely.
The two-way travel time refers to the ping being sent out and received by the multibeam sonar. For example, the speed of sound travels 1500 meters per second through salt water, so if it takes 2 seconds for the sonar to receive a ping it sent out then the team on board will know that the depth of the ocean is 1500 meters. But, if the XBT was to malfunction (equipment or operator error), the data collected will be inaccurate and the depth of the ocean to the seafloor will be miscalculated.
I really enjoyed this experience and I’m grateful to be a participant in the STEMSEAS/A-STEP program.
