Blog entry by Luis Greiffenhagen
Hello back from Whittard Canyon! The weather has been great, flat ocean, no clouds and 25°C! Due to the great conditions, we have collected a lot of data. An incredible amount of it comes from our new autonomous underwater vehicle (AUV), the Autosub5, which is a type of robot submarine and the newest, high tech observation vehicle we have on board.
It has been operating every day since we arrived at Whittard Canyon – so here is a short summary about the AUV and what it does.
Autosub5 has only been in the ocean once and is probably one of the best AUVs in the world right now. It has been developed over the last years by the Marine Autonomous and Robotic Systems division (MARS) of NOC. As it is still kind of a prototype, the AUV engineering team onboard is constantly working on improving its performance. Due to their great work, it has already proven to be very reliable on our cruise.
What is the AUV doing?
While the ROV (remotely operated vehicle) is connected to the ship via a huge umbilical /wire and is better suited for taking samples and fine-scale videos, it needs a lot of people working on it when in water. In contrast, our AUV does its job just by itself when on mission. For each dive, the very complex missions are being programmed onto its computers (5 alone for board control), but after that, we just have to drop it into the ocean. It runs a predefined route at a speed of around 2m/s, constantly sensing the environment and reacting to it. Autosub5 already went 100km away from the ship on this cruise and can go down to 6000m depth!
Challenges running an AUV at Whittard Canyon
The biggest challenge for the AUV team here is that we are surveying in an area with boulders and rough terrain, e. g. sudden elevations – but we also want the AUV to be very close to the seabed for our surveys. To avoid a crash, all missions require very detailed planning of the route.
How do you know where the AUV is?
While underwater, the team can only communicate with the AUV when it is close to the ship via telemetry. On the surface, they can control the AUV through satellite and through AUV wi-fi up to a distance of 1km. Once the AUV surfaces after a dive, we usually go on the bridge and try to spot it. After we found it, the captain steams there for its recovery.
Mapping the Ocean
While previously the duration of one AUV mission was quite limited, the new Autosub5 is super efficient and has a range of 24 hours and is perfect for high-resolution ocean floor mapping of large areas.
Mapping the seafloor is very exciting. While mapping new terrain on land has been the challenge of cartographers hundreds of years ago and has been perfected by satellite images in the last decades – the ocean is a completely different story. Now we can actually say that we know more about the surface of the mars (!) than of the ocean floor.
Underwater, we rely on acoustics to understand what the seafloor looks like. Therefore, different frequencies of sound are pinged from Sonar equipment in the AUV. Depending on how much time it takes for the echo to come back, and on how strong that echo is, we understand the heterogeneity of the seafloor.
Onboard the Autosub5 is, amongst many other devices, a multibeam echosounder (MBES) that produces a topographic (3D) bathymetry map, e. g. of the terrain and depth. With a resolution of up to 0.5×0.5m (per pixel), the smallest changes in seabed topography can be mapped. Check out this video if you want to know more about how it works.
At the same time, we also have a Sidescan Sonar that gives us an image of what the composition of the ocean floor looks like (rocks, sediments, boulders, or even wrecks). It currently has an incredibly high resolution of around 15cm. Here is an example of an area that was mapped during an AUV survey from NOC and you can clearly see how different they look.
Mapping the deep Atlantic Ocean is crucial to understanding all geological, biological and oceanographic processes and how they interfere. Further, it is key to predict the distribution of important ecosystems.
So: Off to the next mission!
Many thanks to the AUV team and see you soon!!