Last updated: June 12, 2024
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3D Laser and Sonar Scanning to Monitor Shipwrecks in the Gulf of Mexico
This is a transcript of a presentation at the Preserving U.S. Military Heritage: World War II to the Cold War, June 4-6, 2019, held in Fredericksburg, TX. Watch a non-audio described version of this presentation on YouTube.
Using 3D Laser and Sonar Scanning to Monitor Oil-Spill Impacts on Deepwater World War II Shipwrecks in the Gulf of Mexico
Presenter: Melanie Damour
Abstract
The U.S. Bureau of Ocean Energy Management (BOEM) oversees conventional and renewable energy development and marine minerals extraction in Federal waters of the Outer Continental Shelf. BOEM is required to consider the potential effects of bureau-permitted activities on cultural resources prior to issuing leases or permits, per the National Historic Preservation Act (1966).
After the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, multiple research consortia and natural resource damage assessments focused on studying the spill’s impacts; however, none of these studies addressed the spill’s impacts on historic shipwrecks. As a result, BOEM and study partners developed a multidisciplinary study to assess micro- to macro-scale impacts from the spill on deepwater shipwrecks ranging in age from the 19th century through World War II.
The Gulf of Mexico Shipwreck Corrosion, Hydrocarbon Exposure, Microbiology, and Archaeology Project, or GOM-SCHEMA, conducted a comparative analysis of wooden- and metal-hulled shipwrecks within and outside of the spill-impacted area through collection of microbiological, geochemical, and archaeological data (Damour et al. 2016).
Using 3D laser and 3D sonar scanning systems, the project documented the shipwrecks’ post-spill state of preservation for comparison with existing geophysical and visual data collected prior to the spill.
This paper will focus on results from two of the study sites: the oil tanker Halo, and the German U-boat U-166 (Mugge et al. 2019), both casualties of World War II in the Gulf of Mexico.While 3D imaging of archaeological sites using laser, lidar, and other scanning systems has been a growing trend in terrestrial archaeology, its application for documenting submerged archaeological resources has only recently emerged.
Marine archaeologists are taking advantage of innovations in 3D scanning systems and employing them as new tools for recording and interpreting shipwreck sites. These tools also enhance our capabilities for analyzing site formation processes in the marine environment. The GOM-SCHEMA project collected 3D sonar and 3D laser scans that will inform BOEM of the oil spill’s long-term impacts on deepwater shipwreck preservation. Repeated 3D scans will provide a time-series data set that can be used to identify and quantify areas of enhanced corrosion and inform long-term monitoring efforts.
National Park Service
Presentation Transcript
Melanie Damour: Alright, good morning everyone and thank you for being here. First of all, I'd like to thank Debbie and Mary for herding all of these cats and making this symposium happen. Having been in that movie before, I know what it's like putting a conference together. So thanks to all of you in the NCPTT staff for organizing this. On a more personal note, my father was an army veteran and one of his hobbies was restoring military vehicles. So he collected them. So I grew up surrounded by military history. It's not only important to me to preserve military history in my professional capacity as a marine archeologists, but it's also deeply personal as a lot of these vehicles were integral to my childhood. I learned how to drive an army jeep before I learned how to drive anything else. So this session is right up my alley and it certainly would have been right at my father's alley. So again, thank you for the opportunity to participate here today.
I'm going to give you a little bit of background on a project that my bureau was working on, and I want to put another date in your mind that will also live in infamy for Gulf Coast residents and that is April 20th of 2010. On this date, the mobile offshore drilling unit, deep water horizon was completing an exploratory well and more than 1500 meters of water off the mouth of the Mississippi river when it suddenly exploded and killed 11 men.
Two days later, deep water horizon sank, causing a massive oil spill that lasted for about 87 days in the Gulf of Mexico. Now estimates were about 4.9 million barrels of oil released into the Gulf and approximately 2 million gallons of chemical dispersant were used to help mitigate the spill, both at the sea surface, where the oil had risen and was moving in shore, as well as at the wellhead itself on the sea floor. Use of the chemical dispersant was used to help emulsify the oil to break it up into smaller droplets, so that the hydrocarbon degrading bacteria which are ubiquitous in the Gulf, could hopefully metabolize the oil faster and prevent it from getting on shore.
One of the interesting things that scientists learn during the response and during a lot of the studies that kicked off right after, was that a subsea plume of this dispersed oil actually got entrained within the deep water currents and spread primarily to the southwest of the spill origin, at the wellhead itself. So previous studies that we've done in the Gulf have demonstrated a number of deep water coral communities, as well as historic shipwrecks, are well within this acute footprint of the deep water horizon spill, this, the subsea footprint.
So my bureau is a part of the Department of the Interior and we are responsible for managing offshore oil and gas, renewable energy and marine minerals, a recovery from the federal waters of the outer continental shelf. This includes the Atlantic, Pacific, Gulf of Mexico and Alaska. So we are responsible for about 1.7 billion, and that's with a "B," acres of submerged bottom lands. We are a much larger land managing agency than BLM. No offense guys, you're DOI family too. After the deep water horizon spill, a number of studies commenced to try and understand the fate and effect of the spill and all the different natural resources that were being impacted. Unfortunately none of these research consortia or natural resource damage assessment studies, considered historic shipwrecks. As part of my bureaus responsibility, we require oil and gas operators to conduct geophysical surveys, to try and identify historic shipwrecks and other sites that may be within their area of potential effect, and help identify them. Over the course of more than 40 years of oil and gas surveys in the Gulf, we have a non- publicly available database of more than 2000 historic shipwrecks just in the northern Gulf alone. So we have quite a bit of submerged cultural resources out there that may have been impacted.
In 2011, I began collaborating with Enable Research Lab to develop an interdisciplinary study that would look specifically at the effects of deep water horizon on historic shipwrecks. Specifically, 19th century wooden hull vessels and World War II era steel hull vessels that we had previously studied. So we had pre-spill baseline data available in order to compare their post-spill state of preservation. I'm not going to get into the microbial communities and what we found in the sediments. There are some peer review publications available I can point you to. I'm going to focus mostly on the archeological component of the study. What we're looking at is how are these sites degrading and corroding over time? And because of this particular symposium, I'm only going to talk about the two World War II sites that we looked at.
Anybody who's seen the movie Jaws is certainly familiar with the story of Indianapolis, but how many people in the room knew about the German U-boat campaign in the Gulf of Mexico during World War II? A lot of Americans had no idea that Germany brought the war right to our back door. In 1942, 17 German U-boats entered the Gulf with the express mission to interrupt allied shipping as well as sink as many ally vessels as they could. In that summer they sank 56 ally vessels, 56 in just the span of several months, making the Gulf of Mexico one of the most dangerous water bodies in the world at that time. More than a dozen others were damaged but did not sink.
Here's kind of showing you where some of these sites were lost. My bureau and our predecessor bureaus, have investigated about a dozen of those sites so far and many more have never been found. The two sites that I'm going to talk about are U-166, it's the only German U-boat that was sunk in the Gulf during World War II, and the American oil tanker Halo, which was a casualty of the U-boat campaign. I don't have a laser pointer to point. Do you guys see that okay? You see where we're looking? You might also notice if you're familiar with offshore Louisiana, U-166 is very close to the proximity of the deep water horizon spill origin.
In putting this study together, as I mentioned before, we were looking at sites that we had pre-spill data on, and we wanted to collect additional data after the spill as sort of a comparative dataset. Six of the sites that we selected, were divided up into three different areas of spill impact. You have two that are closest to the Macondo wellhead, that's the black spot in the middle. Those included a 19th century World War, oh sorry, 19th century wooden hull sailing vessel, and U-166 of World War II casualty. To the northeast, we believed that was going to be a moderately impacted area. That included the vessel Anona. It sunk in 1944, not during wartime activities. Totally unrelated, so I'm not going to discuss her very much. But our other one was, our two sites were outside of the spill impacted area and we use those as references for what normal wood degradation and corrosion should look like in a marine environment. Those included the oil tanker Halo.
So how we collected our data; for the archeological component we relied primarily on 3D scanning systems. We wanted to get a good idea of what the sites looked like in 2014 when we went out, so four years after the spill. We wanted that to provide our new baseline data set moving forward. Our contractor, CNC Technologies, which is now Oceanaire Inc., anybody who's familiar with some of the underwater work that's going on has heard of these guys. They deployed their autonomous underwater vehicle to go collect geophysical data out on the shipwreck sites.
They also integrated a deep water 3D laser scanning system within their AUV and were able to collect laser scans of some of our lower relief sites. You can see in this image, that big gray rectangle, that's a high resolution black and white camera that they had on board, so that we could actually create photo mosaics of these sites after the fact. The blue, you may not be able to see it very well in the back, that's the footprint of the 3D laser scanner. It emits about 1400 points as it scans along the sea floor each time it fires, 1400 data points. So, as you can imagine as you're running your transects back and forth, you're collecting millions of data points just in that one particular area. We use that data for creating 3D point cloud models, and that allows us to create these textured surfaces that you can see in three dimensions what these shipwreck sites look like.
We use several different geophysical tools to collect this data beginning with a high resolution multi-beam bathymetry and that provided us with about 18 centimeters of resolution. Which, for deep water sites is really, really good. The 3D laser however, provides about five millimeters of resolution, so extremely tight resolution. This is phenomenal for us. We also had 3D sonar scanning, which we integrated onto a remotely operated vehicle when we investigated the sites in order to collect sediment cores and coral samples and other video footage of these sites. This is kind of showing you what it looks like using the multi beam data in grey as our basis, and then using each line of laser data sandwiched down on top of that to start creating these 3D point cloud models.
This is actually an image of Anona, the one I'm not going to talk about. But you'll notice that the image on top is actually a composite of the 3D laser data from the AUV, which is shooting top down so it's giving us a plan view of what the site looks like. We use the 3D sonar on the ROV so that we could fill in the areas that the laser missed. If you could see up on the bow, which is to the left, we actually have a nice profile of Anona's bow. We got that by using the 3D sonar scanner on the ROV. That had to remain stationary in order to do the profile sweeps back and forth.
Now on the bottom image you'll see back towards the stern, there's a lot of gray dots. While in flying the AUV, because it's going over these sites, and as it detects an obstruction the superstructure of the vessel here, it actually comes up higher in the water column in order to avoid it. Unfortunately, what that also does is it gets it out of the range of the 3D laser, which has to be in several meters proximity of what it's trying to scan. So, in that area we had a pretty big data gap, so the multi beam data was used to fill in those gaps. Now we're combining multi beam data with 3D laser data and 3D sonar data to try and get really good 3D composite images of these sites.
Now, focusing on our two World War II shipwrecks, U-166 was discovered in about 2001. It was confirmed as a Type 9C German U-boat. It was originally believed to have been lost over a hundred miles away based on the historical records. It was offshore the Mississippi River laying mines in July of 1942, hoping to take out some of the allied vessels that were coming in and out of the port of the New Orleans. When it spotted the passenger freighter Robert E. Lee, which was on its way to New Orleans with the US Navy patrol craft 566 in a convoy. U-166 spotted the vessel, torpedoed Robert E. Lee, Robert E. Lee began to sink, and the navy patrol craft saw what happened, turned around, tossed some depth charges and that was it. No one knew what happened. It wasn't until an oil and gas survey decades later that U-166 was found, and it's been visited a number of times since 2001, so we have quite a robust data set of ROV footage and photographs of his particular site over time.
Halo was also sunk in 1942. This was an American oil tanker. It was carrying hundreds of thousands of barrels of bunker oil when it was torpedoed and sank. It lies in about 150 meters of water, so it's our shallowest site. U-166 is in about 1500 meters of water. So it is quite a bit of a deep water site and very much of a challenge to get to. You can see on the photograph on the left, that's the conning tower of U-166. That's a feature I'm going to be talking about quite a bit.
On the bottom is a photo mosaic of the stern section of U-166. When it was hit by the depth charge from the patrol craft, the vessel actually exploded and the bowel separated. And as both pieces came down the water column, they left quite an extensive debris field in between the bow and stern sections. Including things like uniforms, Draeger lungs, which are the breathing apparatus used by the submariners, and a bunch of other artifacts that are now laying on sea floor. So yes, absolutely this is a war grave. Unfortunately it is closest to the deep water horizon spill origins. So, this is an incredibly important site for us monitoring as we move forward. What you can see in the photograph on the bottom is the conning tower and some of the deck guns. The stern is to your left, you can't really see it very well. But, as this part of the vessel came down and landed on the sea floor, it created a huge impact crater, which has created some sediment berms on either side of it. You get to see those in a minute.
One of the limitations of the 3D laser, again shooting top down from the AUV, is that it creates data gaps in the sides of anything that's exhibiting relief. So you can see in the image on the left, the conning tower looks like it's kind of floating in the water column. Well we know that's not reality. Again, using the 3D sonar, which was mounted to our ROV, we were able to collect that profile view, that three 3D data, and make the conning tower look like it's supposed to look. That's kind of one of the benefits of these different types of tools that we have at our disposal.
Here, this is some of the laser data and you can kind of see the impact crater where the stern section went down. You can see the sediment berms that are building up on either side of it. But what we can also get with this laser data, is we can see that the stern section, and you're looking forward aft, is actually listing 14 degrees to starboard. So if that changes over time, we can monitor that using this dataset.
Another dataset that we've had since 2001, is a lot of high resolution photographs. The image on the left is from 2003. That red circle is around one of the hulls that was observed back then. These are some of the machine deck hulls that would have been used to help drain the deck as the U-boat was coming up and surfacing. On the right, this is a photograph from 2013 showing that same hull. What we found from our sediment core data as well as NC2 field experiments that we placed at U-166, and laboratory experiments in which we simulated steel exposure to oil and dispersant in a laboratory setting, is we found that metal corrosion actually enhanced. It sharply went up when exposed to oil and even dispersed oil. So what we're seeing here, is corrosion has actually elevated again. Now the site had maintained a sort of equilibrium over the past, you know, 70 some odd years that it's been down there, but after the spill event we started seeing corrosion increase again. This is not good.
Here is an image that's a photograph from 2003. That red area is areas of degradation and deterioration that we saw in 2013. So, these holes are starting to get larger. In just the four years after the spill, we saw more deterioration in that short period of time, that had been observed in the six years prior to deep water horizon. So what's going on here? We know from a lot of previous studies that microorganisms are incredibly key to many different functions in the Gulf of Mexico and in the water body. They are the largest biomass by far, the unseen majority. They play a key role in filming what's called a biofilm. On any surface that you put in the marine environment, they're the first ones there to help colonize that area and make it more habitable for other marine fauna to attach to. They are the basis of what eventually will become an artificial reef. That biofilm is key to slowing down the corrosion process in the marine environment. Steel and salt water do not mix. We all know that. What happens when you get an oil input, from something like deep water horizon? It affects the biofilm, and it's in essence like peeling a scab off and exposing all that metal to oil all over again. And so now we're starting to see corrosion amp right back up again.
Our other site is Halo. With this particular vessel, because it's so large, we were not able to get 3D laser data at this site. Again, there's a lot of hazards to the AUV. So instead, the multi beam was absolutely key to giving us a much better picture of what this site looks like. ROV investigations at this site, again, it's 150 meters of water, the visibility is terrible. You only see little bits of the site at a time. So the multi beam provided us with really our first good, comprehensive image of what the wreck site looks like.
As you can see, the photo on the top and the multi beam image on the bottom, they're both oriented with the bow to the right. You can see on the lower image and the multi beam where the hull had actually been breached and the stern broke off from the rest of the hull after it collided into the sea floor. The bow on the right basically buried itself as it was coming down in the water column, and the stern as it was up, ended up just collapsing downwards. Unfortunately, the site also has a lot of shrimp net on it. It's a popular fishing spot and fishermen love to dump their nets on known hangs. So unfortunately a lot of these World War II sites provide that very function for them. A lot of these sites are very dangerous to dive with an ROV, because of the entanglement hazard and also entangling your AUV if you get too close.
With Halo, we also used the 3D sonar to help get more of that profile view of Halo, and we specifically focused on the area of the breach. You can see that that data is in blue. We got some really good imagery penetrating inside the breach and we can actually see some of the internal structures of Halo. Now, this particular site is outside of the spill impacted area, so we did not see any evidence of enhanced corrosion, but this is a site that we're using as our reference site moving forward so that we can compare with those steel hulled sites that are within the spill impacted area moving forward.
Also another benefit of the laser data and the sonar data as well as the multi beam, is that we are able to create much better and more accurate archeological site plans. That five millimeters of resolution is phenomenal. I mean terrestrial folks are like, "Eh, that's nothing." But, in the underwater environment, where divers cannot actually touch our site and we cannot draw our tape measure and measure it and actually touch it, we have to use robotics and expensive tools, this is, it's phenomenal. It's above and beyond anything we've been able to get before. U-166 on the left, Halo was on the right, and with that ...
If anybody's interested in some of the other aspects of this study, I can point you in the direction of some of the peer review articles. Just because the government loves acronyms, I'll tell you that the project title, it's the Gulf of Mexico, Shipwreck Corrosion, Hydrocarbon Exposure, Microbiology and Archeology Project or SCHEMA. We love our acronyms. So, with that, if anyone has any questions?
Questions
Mary Striegel: Who has the first question?
Speaker 1: Thanks Melanie. I mean, it's amazing. It's amazing what you can get from those systems. But, you mentioned the Naval Research Lab. Are they contributing corrosion scientists or something to interpretthis data for you, and what are they recommending?
Melanie Damour: Well, unfortunately there's not really a lot that we can do to mitigate the damage that's been done. We can't stop the corrosion processes that have been enhanced. What we can do right now, and what we hope to do is, is you know, engage in long-term monitoring. So what these 3D data sets are providing for us, is preserving the archeological information. There's not much that we can do until that biofilm reforms, and that means that the hydrocarbons that are in that area need to be gone. They need to have been degraded by the bacteria that are involved in that particular function. Once that happens, in these microbial communities that were more cosmopolitan prior to the spill could start to return to that level. We can start seeing, hopefully that biofilm will reform and can start slowing down that corrosion process again. But, in essence there's really no way for us to mitigate the damage that's been done. All we can do is just keep going back and collect as much archeological information over time as we can.
Speaker 2: In addition to the microbial loss of microbial communities, do you see any increased risk to corrosion on shipwrecks from increasing ocean temperatures and changing pH of the water?
Melanie Damour: We weren't looking at those components specifically. It was primarily looking at exposure to hydrocarbons and dispersant. But I mean, you know, I'm not a chemist, but I would assume that changes in pH and things like temperature, would affect the resident microbial communities. And that in turn could certainly affect what's happening preservation wise. You know, with these microorganisms, they perform a very specific function that they've evolved over millions of years to do. Whether it's hydrocarbon degradation, iron sulfate reduction, whatever. They all play a role in carbon and other nutrients cycling in the marine environment. So when you change things like that, certainly there's going to be some sort of domino effect down the road. But, specifically in terms of pH and water temperature, that's not my wheelhouse. I'm not exactly sure how that would look.
Speaker 3: You mentioned initially when, especially with U-boat 166, that you also found smaller ephemera that indicated that it [is 00:22:44] war graves. My question is, I know you're focused more on the ship, but have you also taken a look at some of that smaller ephemera and has the oil spill affected their deterioration?
Melanie Damour: So when we were out there in 2014, we visited both the bow section and the stern section. We placed our experiments near the bow section and collected some sediment cores to try and understand what the physical properties were of the sediment that was in that area. We did not go back and look at each of the individual artifacts. There are over a thousand that had been documented by previous archeological investigations. As we hopefully get to return to the site time and time again, we hope to be able to go visit maybe some of those smaller artifacts. But yes, it's definitely a war grave. No one, no one walked away from that.
Speaker Bio
Melanie Damour is a Marine Archaeologist and the Environmental Studies Coordinator for the Bureau of Ocean Energy Management’s (BOEM) Gulf of Mexico Region office in New Orleans, Louisiana. Melanie earned BS (1998) and MA (2002) degrees from Florida State University, both focusing in marine archaeology. Melanie’s primary interest and area of expertise is historic shipwrecks. She has worked on shipwrecks ranging in depth from Florida’s shallow rivers and bays to several thousand feet in the Gulf of Mexico.
Read other articles from this symposium, Preserving U.S. Military Heritage World War II to the Cold War, or learn more about the National Center for Preservation Technology and Training.