Smart ROV for underwater archaeological operations - Background
Wreck site surveys using the Smart ROV LATIS with precision navigation and autopilot functionality offers advanced flight control, high resolution multibeam and sidescan sonar, and multiple camera systems for video surveying. These technology developments, which have been on-going for the past number of years in MMRRC at UL, allow for unprecedented accuracy in survey operations and enable the production of precise multibeam images of a wreck site (using an ROV mounted SeaBat 7125 Multibeam sonar) from very low altitudes in close quarter imaging of targets.
The survey put together for this cruise focused on high-resolution multibeam and video surveying of wreck sites in the waters surrounding North Donegal. The survey was of particular interest to the Underwater Archaeology Unit (UAU) in the Department of Arts, Heritage & the Gaeltacht (DAHG) as survey and investigation of deeper wrecks are generally far beyond UAU dive limits. DAHG thus need to draw on other technologies, such as robotics technology of MMRRC, to provide survey information on such sites. A number of wreck sites having significant historical and archaeological value were identified as targets (shown in Figure 1) and members of the UAU were registered to join the survey cruise.
Daughter-ROV for marine inner-hull survey work
ROV’s such as LATIS can handle a wide variety of precision survey tasks; however size can limit operations such as inner-hull wreck survey. A miniature daughter-ROV can greatly increase potential success of a ROV mission. A daughter-ROV can access space restricted regions far inside a wreck interior. They can also access areas outside a hull with tight space constraints, e.g. the sea floor scour of a ship’s hull (see Figure 2).
ROV LATIS already has control functionality appropriate for daughter-ROV operations such as station hold/dynamic positioning, essential while the daughter-ROV is deployed. However, in the months leading up to the cruise the focus of research was the retrofitting of a VideoRAY Pro3 & Pro 4 for daughter-ROV ops, design and build of a VideoRAY interface bottle, development of control algorithms and development of useable umbilical management system. Although initial tests using this system were completed in the test tank facilities of UL, the main proof of concept testing phases were to be completed offshore during the cruise.
Trialling/gathering of data set for low cost UUV navigation system
The research is investigating a novel implementation of terrain relative navigation. The approach, in simple terms, combines the following steps:
• acquire unmanned underwater vehicle (UV) altitude off bottom,
• acquire pressure depth of the vehicle (this data combined gives depth of water to the bottom at the vehicles location),
• correct this water depth for tidal height to yield water depth to chart datum.
Water depth can then be referenced – compared to DTM or charted depths. This data can be used for navigation/position estimation in areas where prior accurate bathymetric data are available for comparison to the depth data. Specifically, the intention is to implement an advanced real-time algorithm based on a traditional navigation method - line of soundings. When a depth measurement is made, a line or lines connecting each location in the known map that have that depth will be generated and stored (isobath1). When the UV has moved a known distance and direction (with navigation errors), from low cost sensors, course and distance (movement vector), a new isobath will be stored (isobath 2). We then transfer all the locations from isobath1 forward, using our movement vector. Where isobath1 intersects isobath2 are possible locations that will be used to start our position estimation. There are many possible sources of error and factors affecting outcome, for example compass error and variability of terrain. The main objective is to explore the use of low cost navigation system based on low cost sensors where we have good bathymetric data available.
Offshore operations as a demonstrator for collaboration and dissemination
The waters surrounding the north coast of Ireland has some of the best visibility found in the Europe. Additionally, some of the most astounding shipwrecks are also located in these waters such as the S.S. Empire heritage, R.M.S Justicia or H.M.S. Audacious.
The survey of these shipwreck sites gives the possibility of gathering visually astounding video data from on-board cameras as well as data from on-board sonar imaging devices. Additionally, the harsh environment and difficult terrain of a World War I or II wreck site were used to demonstrate the capabilities of ROV LATIS’ navigation, control and survey features. Visual and sonar images collected during the survey can ultimately be used as a showcase to industry and institutions for the technology developed throughout and with a view on future collaborations. Additionally, representatives from some of Ireland’s maritime institutions were on-board and were active in getting informed on LATIS systems. This included state bodies such as Irish Coast Guard and Irish Naval Service, semi-state bodies such as Commissioner of Irish Lights’ and industry such as IDS Monitoring and VideoRAY.
Furthermore, the shipwrecks of the north coast also pose a significant interest in the public domain. Prior to embarkation we were contacted by a television production company located in Derry (360Productions) who were interested in gathering video for a BBC documentary. One of the producers and a freelance cinematographer will join the cruise and remain on-board for the 5 days of the wrecks survey.
For some more info on the North Donegal expedition visit the Marine Institute account of the expedition here.