Our capabilities for exploring the seafloor have undergone a revolution in the last few decades. Depending on the scientific problem we need to solve, we can image from the ship and see large-scale features like mountains, or get very close to the seafloor in a submersible or remotely operated vehicle, and see tiny animals up close with human eyes or high-resolution cameras. AUV Sentry provides a level of detail between these two extremes that is very useful for all types of scientists like biologists, chemists, geologists, and geophysicists. Most long-term scientific campaigns utilize each type of vehicle for its particular strengths.
The “big gun” for mapping the seafloor are the sonars carried by a research vessel like Falkor. They can map swaths up to miles wide as the vessel moves at speeds up to 10 miles/hour. These systems have given us a fantastic capability for understanding the shape of the seafloor. Our Autonomous Underwater Vehicle Sentry can get even closer to the sea floor, descending down to 6000m or about 4 miles.Sentry can see fine levels of detail; about 100 times smaller than most ships. After mapping with its sonars, we often program Sentry to fly very close to the seafloor (about 5 meters height) to take digital photographs. At the same time, Sentry measures properties of the seawater (temperature, chemical activity, etc.), which allows us to spot places where hot “hydrothermal” fluids are emerging from the seafloor.
We call Sentry an Autonomous Underwater Vehicle because it is not connected to the vessel by a cable, meaning it swims completely free.Sentry maps a preprogrammed survey grid under control of its onboard computers using energy from its batteries. It follows the grid while “flying” above the seafloor at the height required for its sensors. Sentrydoes this in a relentless fashion. It doesn’t get bored or tired, at least until its batteries are nearly out of “juice” after which it drops weights and returns to the surface.
But Sentry is not quite autonomous, as we have a device called an acoustic link. This is a kind of underwater text-messaging system. About once a minute, we can exchange short messages that we send each other using our phones. Like teenagers, we have a compact shorthand that allows us to pack a lot of information into short messages (lol!). Sentry sends us data on its “state”, which includes its depth, heading, height off the bottom, speed, its battery level, and readings from the onboard scientific sensors. We can make changes to the programmed grid, and on occasion we have had to coax Sentry out of a predicament, like the time it got stuck in rough terrain. So I guess Sentry is really a mostly Autonomous Underwater Vehicle as it executes a preprogrammed plan, but the plan can be changed if we choose. Sometimes, we see details in the scientific data (hot water would be an example), in which case we could have Sentry investigate that particular spot in more detail.
Finally, scientists usually follow up their Sentrydives with visits from a Human-Occupied Vehicle or Remotely Operated Vehicles. They use Sentrymaps as a guide, allowing them to proceed directly to the most interesting spots where they make close-up observations, deploy experiments, and take samples. Like so many things in life, teamwork is the key to success.
