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Weighing In

Research Associate John Lund of the WHOI Autonomous Systems Lab lowers a glider into a test tank to weigh it in water, part of the process of adjusting the ballast. Gliders are autonomous underwater vehicles (AUVs) that change their buoyancy, adjust their ballast, and use wings or fins to produce forward motion. The vehicles have to be neutrally buoyant so they can dive and climb properly as they slowly move in a saw-toothed pattern through the ocean. Gliders have no external moving propellers or motors; instead they change buoyancy to dive and rise by using a piston to pump water in and out of the vehicle. The pumping action changes the volume of the glider, making it denser or lighter than the surrounding water. Internal motors also shift batteries inside the hull to adjust the vehicle’s pitch motion (or trim). (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)