The NOAA Thunder Bay National Marine Sanctuary is a large national sanctuary — 448 square miles (sq mi) — which includes all of Thunder Bay and a part of Lake Huron. It is the site of hundreds of well-preserved shipwrecks. The locations of numerous wrecks are known, but many others have yet to be found. NOAA is charged with maintaining and surveying this area, and they are always looking for new approaches to survey this large area with efficiency. The problem is compounded since the sanctuary may be expanded to over 2,000 sq mi.
Back in 2008, NOAA and the Applied Research Laboratories with the University of Texas at Austin (ARL:UT) felt that the ATLAS-AUV (autonomous underwater vehicle) would be a good sensor system to survey this area for known and unknown shipwrecks sites. Since the time when the project was originally proposed, Russ Green (Thunder Bay’s Deputy Superintendent/Research Coordinator) decided to expand the role of ATLAS to do more than just finding shipwrecks. He wanted to try using it to identify bottom characteristics, locate marine habitats, and survey prehistoric archeological sites.
During the Thunder Bay 2010 expedition, the team of NOAA and ARL:UT scientists had 10-and-1/2 days to run surveys. Due to the weather, missions were run on 7 days for a total of 52-and-1/2 mission hours in shallow- and deep-water areas. We surveyed approximately 104 sq mi for an average rate of 2 sq mi per hour (sq mi/hr). In deep areas, the rate increased to 3 sq mi/hr. While in the shallow areas, where the SVP limited the sonar’s operating range, the rate was 0.4 sq mi/hr (which is still higher that many other survey methods).
The whole team was pleased with the area covered, the discoveries, and the quality of the maps. We’ve all realized that there are many applications for this sensor and/or AUV technology, including large surveys of shipwreck sites, bottom characterizations, archeological sites, and for environmental evaluation.
Ultimately, it was truly a successful test. The AUV, sonar, and processing ran without any incidents. (There were no software crashes, and no AUV crashes into the lake floor or the shipwrecks). The weather was unusually poor, and we did not get out to the deep-water area as much as we would have liked, but we still covered a lot of area.
The deep-water area is difficult for NOAA to survey at this time, but even with our limited on-site time, we did survey a larger area than they had ever covered before. In the shallow area, we surveyed nearly half of Thunder Bay and the ATLAS maps revealed unexpected features and human activities.
Discoveries and Results
These discoveries have renewed NOAA’s interest in the region within the bay. For example, there are hundreds of 15-m (49-ft) diameter circular piles throughout the bay. A dive-team inspected one of them during our second week and discovered that they contain piles of large hunks of coal. There are also numerous manmade features that look like snowmobile tracks in the approach area to Alpena. Some are raised a few meters and some are depressed. All are roughly 17 m (56-ft) wide. There is quite a bit of speculation on their origins. In the deep-water areas, one of the dominant visible features are possibly glacial scrapings, which looked like “brush strokes” on the maps.
In addition to the amount of area surveyed, there were a number of other results from the test.
- We realized and developed a back-up safety plan for mission planning. Since the AUV had a second battery pack, it could be programmed to swim back into the protected waters of the bay on its own, which eliminated any AUV recoveries in high wind and waves. It is now part of ARL:UT’s standard planning procedure to include a safety back-up transit to safe waters for the AUV.
- We used a new method to get the AUV into the water after assembly by simply launching it from a boat trailer.
- ARL:UT collected terabytes of data in the deeper depths and at higher speeds than ever before for this system. This data will be used to develop improved sonar data processing schemes (i.e., computer programs).
- New techniques to pull data off of the AUV during a mission were successfully tested. This is used to immediately evaluate the performance of the sonar and to provide an early glance at any potential discoveries.
- Additional challenges with strongly refracting sound velocity profile were observed and will need to be solved with new processing schemes.
- A method to launch and recover the AUV from the R/V Storm was developed and tested.
- The ATLAS maps were used to locate interesting objects and features on the lake-floor, then divers and a small side scan sonar were sent to those specified locations to inspect them.
- NOAA’s Thunder Bay facility and sanctuary have been realized as a good location to operate, test, and develop AUV systems.
All of these results will help us develop or define a more robust AUV system to run increasingly independent missions, and will help us determine better ways to use AUVs to survey for objects, like those in the Thunder Bay National Marine Sanctuary.
One “result” that was personally satisfying for the ARL:UT scientists was the ease at which the ATLAS maps were understood and interpreted by the NOAA staff and other non-engineering visitors. Everyone who came into the mapping work area would study the maps for just a couple of minutes to get oriented, then ask a few questions and begin talking about the geology of the seafloor and not about anomalies due to the sonar or processing. This group included maritime historians, archeologists, SLS operators, and divers. Everyone seemed to understand the data.