By: Eloise Cole, 2025 FL HTC intern
Sean Beckwith, a physical oceanography doctoral student.
I met with Sean Beckwith, a physical oceanography doctoral student at the 四虎影视 College of Marine Science (CMS) who is researching sound speed to enhance seafloor mapping. I have spent this last semester working alongside him as a intern with CMS. In this Q&A, Sean shares background knowledge on sound speed data and updates on the Glider Sound Speed Project.
Eloise Cole: Could you explain what sound velocity is and why it鈥檚 important?
Sean Beckwith: Sound velocity is the measure of sound through the ocean in a direction. It is important to have this measurement for seafloor mapping because sound is what鈥檚 used to map the seafloor. An echo sounder sends out pings and listens for the return when it hits the sea floor and comes back. Knowing the speed of sound throughout the entire water column from the vessel to the sea floor is important because the speed changes as temperature, salinity, and density changes.
EC: What are gliders and how do you gather sound speed data with them? How do you analyze the data?
SB: Gliders are one form of Autonomous Underwater Vehicles (AUVs) shaped like torpedoes with wings and a tail fin. Instead of using propellers, they move by pumping fluid to change their buoyancy and by shifting weight to dive or climb. Their wings provide forward motion as they glide, which allows for low-energy travel. Because of this, gliders can be programmed and sent to specific waypoints and courses to gather data from exactly where you need. They can sample for various lengths of time, usually weeks, sometimes over a month.
Gliders can be equipped with a variety of sensors, allowing them to collect data throughout the entire water column. These sensors can measure parameters such as salinity, chlorophyll concentration, and acoustic signals, making gliders a powerful tool for long-term ocean observation with minimal energy use. You can analyze the data in multiple ways - in our case we use a CTD instrument which measures conductivity, temperature and depth to calculate sound speed for sea floor mapping.
EC: How do factors like temperature, salinity and depth influence sound speed in the ocean?
SB: Temperature has the biggest and most immediate effect on the speed of sound in water鈥攕ound speeds up in warmer water and slows down in cooler water. Salinity also plays a role鈥攈igher salinity generally means faster sound speed, though the effect isn鈥檛 as strong as temperature. Depth, or more precisely, pressure, also increases sound speed in a more linear way鈥攖he deeper you go, the higher the pressure, and the faster sound can travel.
Since all these factors can vary with depth, you need to know how sound speed changes throughout the whole water column to accurately calculate how long it takes for a sound wave to travel, like from a sonar to the seafloor. It鈥檚 really a combination of different speeds at different depths.
EC: What are some challenges you have faced collecting or analyzing the data?
SB: With the gliders, one of the biggest things is getting the data off the gliders in a format that is quality controlled. Data often comes off the glider in a format that requires some correction. It is also challenging to find the time periods you want for your analysis among the very long glider data sets. Sorting and filtering the data to get only what you need for your specific analysis can sometimes be a challenge.
EC: What are the next steps in your research?
SB: The next step in my research is the second chapter of my dissertation. It will focus on evaluating the accuracy of modeled sound velocity profiles by comparing them to directly measured profiles. The goal is to determine whether modeled data can reliably support seafloor mapping efforts. Modeled profiles offer broad spatial and temporal coverage, potentially reducing the need for time-consuming and equipment-dependent in-situ measurements. If effective, this approach could streamline mapping operations by allowing post-processed integration of model data. This work builds on my first chapter on glider-derived bathymetry and may lead into a third chapter focused on how internal waves affect sound velocity, possibly using glider data.
EC: What advice would you give to someone considering research in ocean acoustics or physical oceanography?
SB: Whether through internships or volunteering, staying active in the field you want to enter will strengthen your grad school applications and job prospects. Ocean acoustics can lead to good jobs through certifications or training without needing a grad degree, since it鈥檚 in high demand across science, industry, and government. Physical oceanography usually requires a Master鈥檚 or PhD, though some jobs offer on-the-job training if you bring in related skills. Either way, starting to learn the core concepts now is a smart move.