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Deep-water Archaeological AUV Surveys and Photo Capabilities Robert A. Church, Robert F. Westrick, and Daniel J. Warren, C & C Technologies, Inc.

Copyright 2011, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 25 May 2011. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract In January 2001, C & C Technologies, Inc. placed into full operation the first commercial deep-water Autonomous Underwater Vehicle (AUV) in the Gulf of Mexico. The application of this advanced technology was immediately beneficial to the survey industry as well as having a profound impact on deep-water archaeology. Over twenty-four shipwrecks and several additional potential wrecks have been discovered and/or investigated using C & Cs AUVs. Several of those surveys resulted in new discoveries and at least, thirteen of the wrecks have been confirmed to be historic vessels. The initial primary geophysical instrument payload of the HUGIN model AUV consisted of dual frequency side scan sonar, subbottom profiler, and multibeam bathymetry. In 2009, C & C added a digital still camera to the vehicle allowing relatively quick visual confirmation of seafloor targets. The photos and photo mosaics produced from the camera surveys have further advanced deepwater archaeological investigation and mapping. This paper focuses on the archaeological application of the AUVs and in particular the photographic capabilities and utilization of those photographs.

Introduction Autonomous Underwater Vehicles (AUVs) are built for a variety of purposes and come in many shapes and sizes with near limitless combinations of sensors and payloads. Camera systems are a relatively new addition to some of the deeper AUV systems. Currently, there are only a few companies, institutions, or government agencies (e.g. C & C Technologies Inc. (C & C), Kongsberg, Woods Hole Oceanographic Institution (WHOI), the United States Navy, etc.) that operate AUVs equipped with digital still cameras capable of survey to 1,000 meters or deeper. This paper will focus primarily on the C-Surveyor AUVs, which are HUGIN 1,000, 3,000, and 4,500 meter systems (Figure 1). All references to AUV in this paper refer to one of the C-Surveyor AUVs unless otherwise specifically stated. Four AUVs have been added to C & Cs fleet over the last decade as well as several payload and sensor upgrades. Although the sensor payload of each AUV may be slightly different, the basic payloads include an EM 2000 multibeam bathymetry system (Figure 2), Chip Edgtech subbottom profiler system (Figure 3), and duel frequency side scan sonar at 410 kHz and either a standard 120 kHz frequency or a 230 kHz dynamically focused sonar system (Figure 4). Three of C & Cs AUVs (the 3,000 and 4,500 meter systems) are equipped with digital still cameras (George 2009a). The navigation/positioning system for the AUVs utilize a Kalman filter algorithm, which uses input data from a Simrad High Precision Acoustic Positioning (HiPAP) System, inertial navigation, and Doppler velocity speed log. The post-processed positions for the AUV are accurate to within 5 meters at a depth of 3,000 meters.

Figure 1. AUV being launched (4,500 meter system).

In 2001, C & C began using the first commercial deepwater AUV in the Gulf of Mexico in an effort to meet industry demands for a more accurate deepwater survey system. C & C surveyed the first of several shipwrecks

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with their AUV in January of that year when the AUV passed by the SS Robert E. Lee during a survey for BP Exploration and Production Inc. and Shell International Exploration and Production Inc. The SS Robert E. Lee was a passenger freighter that became the last victim of the German submarine, U-166 during World War II. The extensive survey work for the BP and Shell project lasted several months and in March of 2001, lead to the startling discovery of the U-166 (Church et al. 2002; and Warren et al. 2008). During the course of the survey two other historic shipwrecks, the Mica Wreck and the later designated Mardi Gras Wreck were imaged as well as four of SS Robert E. Lees lifeboats, though many of those targets were not identified as historic (50 years or older) until several years later. Between January 2001 and January 2011, C & C has collected over 205,000 line kilometers of deepwater AUV data, which is far enough to circumnavigate the earth five times at the equator. These surveys have included numerous archaeological surveys and deepwater shipwreck site assessments including surveys of at least 24 deepwater shipwrecks of which more than half of the wrecks have been confirmed to be historically significant.

Figure 2. AUV Multibeam Bathymetry of the U-166 Site at 0.5 Meter Bin Resolution (2003).

Figure 3. AUV Subbottom Profiler Image of U-166 (2009).

Although several historic shipwrecks have been discovered during AUV surveys such as the WWII British aircraft craft carrier Ark Royal in the Mediterranean Sea and the nineteenth century sailing vessel Ewing Banks Wreck in the Gulf of Mexico, possibly the greater benefit to underwater archeology is the potential for investigating deepwater wrecks sites after their discovery. High-resolution site-specific investigation data is of immense benefit in analyzing and planning additional

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fieldwork at deep-water archaeological sites (Church et al. 2008). The AUV surveys of the Robert E. Lee and U-166 were invaluable in planning the 2003 long base line mapping project sponsored by NOAAs office of Ocean Exploration and Research (OER) (Warren et al. 2004). In 2004, the AUV surveys of the World War II tanker Alcoa Puritan as well as Robert E. Lee and U-166 were essential in planning the ROV dives during the archaeological and biological analysis of those sites sponsored by the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), NOAA OER, and the National Oceanographic Partnership Program (NOPP) (Church et al. 2007). The detailed AUV survey of the early nineteenth century Mardi Gras Wreck was valued data prior to Texas A&Ms excavation of that shipwreck. The AUV surveys were instrumental in planning and conducting the 2008, 2009, 2010 Reefs, Rigs, and Wrecks investigation (sponsored by the BOEMRE, NOAA OER, and NOPP) of the historical sailing vessels the Ewing Banks Wreck, the Viosca Knoll Wreck, the Green Lantern Wreck, and the WWII tanker Gulfoil (Church et al. 2010).

Figure 4. AUV 410 kHz Sides Can Sonar Image of U-166 (2009).

Integration of digital still camera

In 2009, C & C began integrating digital cameras into their AUV fleet. The AUV photography system provides black and white still photographs of the seafloor while the vehicle travels at a speed of 3.7 knots. Typically, an image is taken approximately every 1.75 seconds which equates to one photo every 3.5 meters of travel at normal survey speeds (George 2009b). The length of the camera footprint is equal to 0.75 times the AUV altitude and the aspect ratio is 4:3 (Figure 5). The AUV typically operated at 6 to 10 meters altitude during camera surveys with a typical tracklines spacing of 5 meter or less allowing for overlap of photos along track and cross track.

The first shipwreck imaged with the C & C AUV camera was the Ewing Banks Wreck (Figure 6). The near immediate success of the camera provided archaeologists and other researchers with yet another tool to quickly assess and ground truth archaeological sites or potential archaeological sites in deepwater. Soon other wrecks were imaged with the AUV camera including the Mardi Gras Wreck and the U-166.

Figure 5. AUV Photo Image Ratio Relative to Altitude.

Advantages and Challenges Three of the greatest advantages of the AUV camera system are the ability to take the collected images and efficiently mosaic the photos into larger geo-referenced images, the ability to combine those images with the other geophysical data to aid in interpretation and analysis of a site, and the ability to quickly ground truth targets detected with the side scan sonar and multibeam sensors during the AUV geophysical survey.

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Geo-referencing & Photo Correction. Several hundred photographs are collected during a typical camera survey and in order to produce a good quality and geo-

referenced photo mosaic, two obstacles have to be over come: 1) how to associate the photographs to real world positions and 2) how to resolve the typical lighting/shadowing issues that occurs during underwater flash photography, which tends to considerably distorts a photo mosaic. To resolve the first issue, C & C developed a software application to scenic the photos with the AUV position and convert each photograph to a geo-referenced image. The second issues was resolved by developing a post processing routine to equalize the repetitive flash pattern produced on each photograph, adjust for spherical light spreading, linear attenuation, and flash scattering resulting from particulates in the water column between the camera and the subject. The combined results of these software applications are nice evenly lighted geo-referenced images that could then be more easily and accurately mosaic together and imported into a GIS system of choice. Figure 6 shows the Ewing Banks Wrecks mosaic produced with processed images and Figure 7 shows an early version of the Ewing Banks Wrecks mosaic without image correction.

Figure 6. AUV Photo Mosaic of the Ewing Banks Wreck with Processed Images (2009).

Figure 7. AUV Photo Mosaic of the Ewing Banks Wreck without Processed Images (2009).

In 2004, archaeologists at C & C assembled a photo mosaic of U-166s bow. The imagery was collected with a Remotely Operated Vehicle (ROV). The mosaic included 46 images and required several days to assemble and correct the lighting issues during post processing (Figure 8). In 2009, the AUV was flown over the U-166s bow to take photographs of the site. The processed images were assembled into an accurate photomosaic within a few hours (Figure 9).

Combined Analysis of Georeferenced Data Having the photo mosaic and geophysical data (i.e. side scan sonar, multibeam bathymetry, and subbottom profiler)

collected simultaneously and location allows all the site data to be analyzed in conjunction (e.g. surface, subsurface, and three dimensional space). The photo mosaic in many cases can also be draped over the bathymetry to provide a three dimensional photographic perspective, which allows researchers another avenue to study a shipwreck or other types of sites (Figure 10). Although individual photographs and ROV investigation may be required for detailed analyses of specific areas of features of a wreck site, being able to see the bigger picture along with the sonar and other data offers a larger perspective of a site that is necessary for assessing site formation, artifact distribution, and other special related aspect of the site.

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Figure 8. Photo Mosaic of the U-166s Bow Produced from ROV Footage. Courtesy of the DeepWrecks Study - MMS 2007-015.

Figure 9. Photo Mosaic of the U-166s Bow Produced from AUV Photographs (2009).

Figure 10. Photo Mosaic of the Ewing Banks Wreck Draped Over the AUV Multibeam Bathymetry.

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Ground Truth Targets The AUV camera is also an excellent tool for ground truthing unidentified targets during a survey. Often potentially

significant targets are detected with side scan sonar during an archaeological and hazard survey and an archaeological recommendation has to be made based solely on the geophysical data. Having the option to run the AUV camera over select targets and other features at the end of a survey, removes most of the ambiguity in the interpretation. The BOEMRE, which regulates the offshore oil and gas industry, often requires potentially significant targets to be investigated or avoided as a condition of permitting an oil and gas project. Some times these targets have been found to be significant archeological resources, such as the Margi Gras Wreck, the steam yacht Anona, or the life boats from the Robert E. Lee, but more often these targets are modern debris or geological in origin. In that case, a target that might otherwise require avoidance or investigation could be shown to be merely modern debris using the AUV photographic data. Figures 11 and 12 show a sonar image and AUV photo mosaic of a modern shipping container. The BOEMRE have required oil and gas operators to investigate similar targets on previous project. Investigating such targets during the survey phase of the project can and has shown such unidentified targets as modern objects and of no archaeological significance, therefore saving time during the proceeding phases of a project.

Figure 11. Side Scan Sonar Target (Shipping Container), Initially Unidentified Contact (Courtesy of Shell Exploration and Production Company).

Figure 12. Photo Mosaic of a Shipping Container, Same Target Image in Figure 11, (Courtesy of Shell Exploration and Production Company).

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Likewise some targets originally thought to be potentially significant archeologically, were unequivocally proven to be archeologically significant as a result of AUV camera surveys. In 2009, a group of scientists investigated five deepwater shipwrecks as part the Reefs, Rigs, and Wrecks Project using Woods Hole Oceanographic Institutes (WHOI) ROV Jason II. One of the shipwrecks investigated is referred to as the 7,000-Foot Wreck. Resting in 2,271 meters (7,450 feet) of water this site is currently the deepest historic shipwreck scientifically investigated in the Gulf of Mexico. BOEMRE records indicate the shipwreck was discovered during an oil and gas survey, but it was not known for certain whether the wreck was modern or historic. Prior to the ROV investigation WHOI conducted a camera and multibeam survey of the site using the Sentry AUV (Figure 13). The AUV photo mosaic revealed the wreck was possibly a mid to late nineteenth century sailing vessel. The ships anchors, windlass, steering machinery, rigging remnants, and other remains were identifiable from the Sentry photo mosaic. Had the Sentry camera survey revealed a modern shipwreck, the expedition time planned to be devote to that site could have been allocated to other portions of the field project. As it turned out, the Sentry photo mosaic was instrumental in fine-tuning the planned site investigation.

Figure 13. Sentry Photo Mosaic of the 7,000-Foot Wreck. Courtesy of the Rigs, Reefs, and Wrecks Study - BOEMRE, NOAA OER, and NOPP.

In addition to archaeological sites and potential archaeological targets, the AUV cameras are beneficial for investigating

and ground truthing many other types of targets. AUV cameras can be used to inspect pipelines or various types of seafloor infrastructure (Figure 14). C & C has inspected several pipelines, matting, communication cables, and other debris using the AUV camera. AUV cameras can be used to ground truth otherwise unidentified targets for possible chemosynthetic community significances (Figure 15), or possible unexploded ordinance (UXO), and/or other possible military or industrial debris. Figures 16 shows two 6-packs of paint cans image with the AUV Camera during a survey for LLOG Exploration Offshore, Inc. These are just two of many sonar targets within a debris zone investigated during that project. Each of these two targets consists of six one-gallon paint cans used by the U.S. Navy to seal the hulls of ships for protection against rust. The U.S. Navy only used this type of six-unit packaging during the 1940s. These containers were often discarded by the U.S. military in designated offshore dumping zones along with other types of debris and ordnance from 1946 through 1970 (Samuel and Herbert 2007; and Herbert 2010).

Figure 14. AUV Camera Images of a Pipeline, Fiber Optic Cable, and Matting.

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Figure 15. AUV Camera Image of a Chemosynthetic Community Site in the Gulf of Mexico.

Figure 16. AUV Camera Image of US Navy marine paint cans (Courtesy of LLOG Exploration Offshore, Inc.).

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Conclusion AUV cameras are advantageous to both the survey industry and the advancement of deepwater marine archaeology. Since the introduction of digital still camera systems into survey class AUVs, the technology has repeatedly proven its value, efficiency, and effectiveness. Although the technology is still in its relative infancy, it has immediately demonstrated its benefit for deep water AUV surveys in ground truthing targets detected during geophysical surveys, inspecting previously known sites, objects, or seafloor infrastructure, and creating photo mosaics to analyze historic shipwreck sites. Acknowledgments The authors acknowledge and express their appreciation to LLOG Exploration Offshore, Inc., and Shell Exploration and Production Company for the use of their data and for allowing that data to be displayed in this paper. The authors also thanks the BOEMRE, NOAA OER, NOPP, and TDI Brooks International for allowing the Sentry AUV imagery from the current Rigs, Reefs, and Wrecks Study to be included in this publication. All other images and survey data in this publication, except those noted, are courtesy of C & C Technologies, Inc. References Church, R. A., D. J. Warren, and R. F. Westrick. 2010. Reefs, Rigs, and Wrecks: The 2009 Field Season of Deep-water Archaeology in

the Gulf of Mexico. Paper presented at MTS/IEEE Oceans10, Seattle, WA (September). Church, Robert, and Daniel Warren. 2008. "Sound Methods: The Necessity of High-resolution Geophysical Data for Planning Deepwater

Archaeological Projects". International Journal of Historical Archaeology. 12 (2): 103-119. Church, R., D. Warren., R. Cullimore, L. Johnston, M. Kilgour, J. Moore, N. Morris, W. Patterson, W. Schroeder, and T. Shirley. 2007.

Archaeological and Biological Analysis of World War II Shipwrecks in the Gulf of Mexico: Artificial Reef Effect in Deepwater. U.S. Dept. of the Interior, Minerals Management Service, New Orleans, LA. OCS Study MMS 2007-015.

Church, R. A., D. J. Warren, A. W. Hill, and J. S. Smith. 2002. The Discovery of U-166: Rewriting History with New Technology. Paper OTC 14136 presented at the Offshore Technology Conference. Houston, Texas (May).

George A Robert. 2009a. Sensor Upgrades for Deepwater Survey AUVs. International Hydrographic and seismic Search, (August): 32-33.

George A Robert. 2009b. Integrated High Resolution Geophysical and Photographic AUV System. Oral presentation given at the IMCA Annual Seminar, Rio De Janeiro Copacabana, Brazil (November).

Herbert, E. John. 2010. Underwater Explosive Ordnance Mitigation for the LLOG Development Project, Gulf of Mexico (AUV Post Mission Analysis). Report prepared by Applied Marine Technology, Inc. for C & C Technologies on behalf of LLOG Exploration Offshore, Inc. (December).

Samuel, Lynn B., and John E. Herbert. 2007. Special Session: AUVs: Groundtruthing High-Resolution AUV Side Scan Sonar Contacts for Unexploded Ordnance in a Deepwater GeoHazard Assessment. Paper OTC 18844 presented at the Offshore Technology Conference. Houston, Texas (May).

Warren, Daniel J., Robert A. Church, and Robert F. Westrick. 2008. Using AUVs to Investigate Shipwrecks: Deepwater Archaeology in the Gulf. Sea Technology 49 (10): 15-18.

Warren, Daniel J., Robert A. Church, Roy Cullimore, Lori Johnston. 2004. ROV Investigations of The DKM U-166 Shipwreck Site to Document the Archaeological and Biological Aspects of the Wreck Site: Final Performance Report. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Office of Ocean Exploration. Silver Spring, Maryland.

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