On Nov. 1, a new record was set for the time-honored Massachusetts to Bermuda ocean passage when the diminutive submersible Spray arrived at its island destination. Spray is an underwater glider, an autonomous underwater vehicle being used by oceanographers to study vast ocean areas for extended periods of time. It departed Massachusetts waters on Sept. 11, taking seven weeks to arrive in Bermuda.
Combining the durability to operate unattended for weeks with the mobility of manned or guided vehicles, gliders have opened new realms for oceanographers.
Gliders have no motors and no propellers. Instead, they sail through the water on hydrodynamic wings. Forward motion — on the order of 0.5 knots — is generated by flying through the water column as minute buoyancy changes cause the glider to alternately sink, then rise. The energy used to pump a small oil-filled bladder is trivial, thus, the glider’s ability to operate for weeks.
Onboard sensors monitor ocean characteristics, such as salinity and temperature, and record the glider’s depth throughout each sawtooth dive. After a series of dives, the glider surfaces, finds its position via GPS, then computes the heading to its destination. While on the surface it uses an Iridium satellite modem to report its current position and download data.
So the next time you’re staring off to the horizon with hundreds of miles to go, don’t be surprised if a brightly painted mechanical dolphin pops to the surface beside your boat, takes a deep breath, and dives again.
