Roman Christopher N.

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Roman
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Christopher N.
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  • Article
    Variable morphologic expression of volcanic, tectonic, and hydrothermal processes at six hydrothermal vent fields in the Lau back-arc basin
    (American Geophysical Union, 2008-07-26) Ferrini, Vicki L. ; Tivey, Margaret K. ; Carbotte, Suzanne M. ; Martinez, Fernando ; Roman, Christopher N.
    Ultrahigh-resolution bathymetric maps (25 cm grid) are used to quantify the physical dimensions of and spatial relationships between tectonic, volcanic, and hydrothermal features at six hydrothermal vent fields in the Lau back-arc basin. Supplemented with near-bottom photos, and nested within regional DSL-120A side-scan sonar data, these maps provide insight into the nature of hydrothermal systems along the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR). Along-axis transitions evident in localized volcanic morphology and tectonic characteristics include a change from broad low-relief volcanic domes (hundreds of meters wide, <10 m tall) that are dominated by pillow and lobate lava morphologies and are cut by faults and fissures to higher aspect ratio volcanic domes (tens of meters wide, tens of meters tall) dominated by aa-type lava morphologies, with finger-like flows, and few tectonic structures. These along-axis differences in localized seafloor morphology suggest differences in hydrothermal circulation pathways within the shallow crust and correlate with regional transitions in a variety of ridge properties, including the large-scale morphology of the ridge axis (shallow axial valley to axial high), seafloor lava compositions, and seismic properties of the upper crust. Differences in morphologic characteristics of individual flows and lava types were also quantified, providing an important first step toward the remote characterization of complex terrains associated with hydrothermal vent fields.
  • Article
    Detection and quantification of oil under sea ice : the view from below
    (Elsevier, 2014-08-21) Wilkinson, Jeremy P. ; Boyd, Tim ; Hagen, Bernard ; Maksym, Ted ; Pegau, Scott ; Roman, Christopher N. ; Singh, Hanumant ; Zabilansky, Leonard
    Traditional measures for detecting oil spills in the open-ocean are both difficult to apply and less effective in ice-covered seas. In view of the increasing levels of commercial activity in the Arctic, there is a growing gap between the potential need to respond to an oil spill in Arctic ice-covered waters and the capability to do so. In particular, there is no robust operational capability to remotely locate oil spilt under or encapsulated within sea ice. To date, most research approaches the problem from on or above the sea ice, and thus they suffer from the need to ‘see’ through the ice and overlying snow. Here we present results from a large-scale tank experiment which demonstrate the detection of oil beneath sea ice, and the quantification of the oil layer thickness is achievable through the combined use of an upward-looking camera and sonar deployed in the water column below a covering of sea ice. This approach using acoustic and visible measurements from below is simple and effective, and potentially transformative with respect to the operational response to oil spills in the Arctic marine environment. These results open up a new direction of research into oil detection in ice-covered seas, as well as describing a new and important role for underwater vehicles as platforms for oil-detecting sensors under Arctic sea ice.
  • Preprint
    Toward extraplanetary under-ice exploration : robotic steps in the Arctic
    ( 2009-01-12) Kunz, Clayton G. ; Murphy, Christopher A. ; Singh, Hanumant ; Pontbriand, Claire W. ; Sohn, Robert A. ; Singh, Sandipa ; Sato, Taichi ; Roman, Christopher N. ; Nakamura, Ko-ichi ; Jakuba, Michael V. ; Eustice, Ryan M. ; Camilli, Richard ; Bailey, John
    This paper describes the design and use of two new autonomous underwater vehicles, Jaguar and Puma, which were deployed in the summer of 2007 at sites at 85°N latitude in the ice-covered Arctic Ocean to search for hydrothermal vents. These robots are the first to be deployed and recovered through ice to the deep ocean (> 3500m) for scientific research. We examine the mechanical design, software architecture, navigation considerations, sensor suite and issues with deployment and recovery in the ice based on the missions they carried out. Successful recoveries of vehicles deployed under the ice requires two-way acoustic communication, flexible navigation strategies, redundant localization hardware, and software that can cope with several different kinds of failure. The ability to direct an AUV via the low bandwidth and intermittently functional acoustic channel, is of particular importance. Based on our experiences, we also discuss the applicability of the technology and operational approaches of this expedition to the exploration of Jupiter's ice-covered moon Europa.
  • Preprint
    Characterizing the deep insular shelf coral reef habitat of the Hind Bank marine conservation district (US Virgin Islands) using the Seabed autonomous underwater vehicle
    ( 2005-10-26) Armstrong, Roy A. ; Singh, Hanumant ; Torres, Juan ; Nemeth, Richard S. ; Can, Ali ; Roman, Christopher N. ; Eustice, Ryan M. ; Riggs, Lauren ; Garcia-Moliner, Graciela
    The benthic communities of the deep insular shelf at the Hind Bank Marine Conservation District (MCD), an important spawning grouper aggregation site, were studied with the Seabed autonomous underwater vehicle (AUV) at depths between 32 to 54 m. Four digital phototransects provided data on benthic species composition and abundance of the insular shelf off St. Thomas, U.S. Virgin Islands. Within the western side of the MCD, well developed coral reefs with 43% mean living coral cover were found. The Montastrea annularis complex was dominant at all four sites between 33 to 47 m, the depth range where reefs were present. Maximum coral cover found was 70% at depths of 38 to 40 m. Quantitative determinations of sessile-benthic populations, as well as the presence of motile-megabenthic invertebrates and algae were obtained. The Seabed AUV provided new quantitative and descriptive information of a unique coral reef habitat found within this deeper insular shelf area.
  • Preprint
    Long-baseline acoustic navigation for under-ice autonomous underwater vehicle operations
    ( 2008-05-19) Jakuba, Michael V. ; Roman, Christopher N. ; Singh, Hanumant ; Murphy, Christopher A. ; Kunz, Clayton G. ; Willis, Claire ; Sato, Taichi ; Sohn, Robert A.
    The recent Arctic GAkkel Vents Expedition (AGAVE) to the Arctic Ocean’s Gakkel Ridge (July/August 2007) aboard the Swedish ice-breaker I/B Oden employed autonomous underwater vehicles (AUVs) for water-column and ocean bottom surveys. These surveys were unique among AUV operations to date in requiring georeferenced navigation in proximity to the seafloor beneath permanent and moving ice cover. We report results for long-baseline (LBL) acoustic navigation during autonomous under-ice surveys near the seafloor and adaptation of the LBL concept for several typical operational situations including navigation in proximity to the ship during vehicle recoveries. Fixed seafloor transponders were free-fall deployed from the ship for deep positioning. The ship’s helicopter collected acoustic travel times from several locations to geo-reference the transponders’ locations, subject to the availability of openings in the ice. Two shallow beacons suspended from the ship provided near-surface spherical navigation in ship-relative coordinates. During routine recoveries, we used this system to navigate the vehicles into open water near the ship before commanding them to surface. In cases where a vehicle was impaired, its position was still determined acoustically through some combination of its acoustic modem, the fixed seafloor transponders, the ship-deployed transponders, and an on-board backup relay transponder. The techniques employed included ranging adapted for a moving origin and hyperbolic navigation.
  • Article
    The 2005 Chios ancient shipwreck survey : new methods for underwater archaeology
    (American School of Classical Studies at Athens, 2009-04) Foley, Brendan P. ; Dellaporta, Katerina ; Sakellariou, Dimitris ; Bingham, Brian S. ; Camilli, Richard ; Eustice, Ryan M. ; Evagelistis, Dionysis ; Ferrini, Vicki L. ; Katsaros, Kostas ; Kourkoumelis, Dimitris ; Mallios, Angelos ; Micha, Paraskevi ; Mindell, David A. ; Roman, Christopher N. ; Singh, Hanumant ; Switzer, David S. ; Theodoulou, Theotokis
    In 2005 a Greek and American interdisciplinary team investigated two shipwrecks off the coast of Chios dating to the 4th-century b.c. and the 2nd/1st century. The project pioneered archaeological methods of precision acoustic, digital image, and chemical survey using an autonomous underwater vehicle (AUV) and in-situ sensors, increasing the speed of data acquisition while decreasing costs. The AUV recorded data revealing the physical dimensions, age, cargo, and preservation of the wrecks. The earlier wreck contained more than 350 amphoras, predominantly of Chian type, while the Hellenistic wreck contained about 40 Dressel 1C amphoras. Molecular biological analysis of two amphoras from the 4th-century wreck revealed ancient DNA of olive, oregano, and possibly mastic, part of a cargo outbound from Chios.
  • Thesis
    Self consistent bathymetric mapping from robotic vehicles in the deep ocean
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2005-06) Roman, Christopher N.
    Obtaining accurate and repeatable navigation for robotic vehicles in the deep ocean is difficult and consequently a limiting factor when constructing vehicle-based bathymetric maps. This thesis presents a methodology to produce self-consistent maps and simultaneously improve vehicle position estimation by exploiting accurate local navigation and utilizing terrain relative measurements. It is common for errors in the vehicle position estimate to far exceed the errors associated with the acoustic range sensor. This disparity creates inconsistency when an area is imaged multiple times and causes artifacts that distort map integrity. Our technique utilizes small terrain "submaps" that can be pairwise registered and used to additionally constrain the vehicle position estimates in accordance with actual bottom topography. A delayed state Kalman filter is used to incorporate these sub-map registrations as relative position measurements between previously visited vehicle locations. The archiving of previous positions in a filter state vector allows for continual adjustment of the sub-map locations. The terrain registration is accomplished using a two dimensional correlation and a six degree of freedom point cloud alignment method tailored for bathymetric data. The complete bathymetric map is then created from the union of all sub-maps that have been aligned in a consistent manner. Experimental results from the fully automated processing of a multibeam survey over the TAG hydrothermal structure at the Mid-Atlantic ridge are presented to validate the proposed method.