This article was written and placed for the Canadian Hydrographic Service.
Canada's Multibeam Platform:
Advantages & Applications
More Accurate Hydrographic Charts for Geologists, Military Users--Plus Faster Survey Speeds--Prompted Move to Multibeam
By Andrew Safer
Halifax, Nova Scotia
Whereas the push to conduct deep-ocean multibeam surveys in the 1960s and early 1970s came from military interests and geologists, it was the need for more accurate hydrographic charts that moved multibeam into shallow water areas (less than 500 metres) in the 1980s. It is the ability to produce 100 per cent bottom coverage, coupled with dramatically faster survey speeds, that make this method far superior to the single-beam systems. Because of this, many hydrographic agencies around the world are currently exploring the use of the multibeam platform.
When the Canadian Hydrographic Service (CHS) began to implement multibeam technologies in 1987, the production of accurate nautical charts was the agency's sole objective. Identifying hazards to navigation and establishing minimum depth restrictions were the top priorities, and remain so today. But in the intervening years, a host of other multibeam applications have come to the fore, including coastal zone management, cable and pipeline routing, coastal defence, fisheries management and harvesting, ocean mining, and eco-tourism.
After examining the elements of CHS's platform and technologies, this article will explore a number of the leading multibeam applications.
Purchased in 1987, CHS's first system consisted of a Simrad EM100 installed on one ship and an EM100 installed (IN)on a DOLPHIN (a semi-submersible remotely-controlled vehicle). CHS soon began to notice technology gaps, such as in the area of motion sensing. For operations in water depths from 50 metres to 500 metres, the shipboard system required a greater accuracy in motion sensing than what was available at the time. "We had to develop the technology," recalls CHS Atlantic's Director Paul Bellemare, "and so we partnered with private industry."
Applied Analytics (Applanix) of Markham, Ontario developed a motion sensor that could ALLOW MAPPING TO CONTINUE under dynamic conditions while meeting International Hydrographic Organization standards.
Traditionally, the motion sensor measures roll, pitch and heave, a gyro measures heading, and a GPS receiver provides positioning. Applanix's Position and Orientation System/MV (Marine Vessel) has integrated GPS with an inertial navigation system to measure position, velocity, heave, roll, pitch and heading. The unit was installed on CHS's survey vessel FREDERICK G. CREED (a 20.4-metre Small Water-plane Area Twin Hull)SWATH VESSEL in September 1994.
Bellemare compares the Applanix sensor to what came before: "In the past, sensors had to be run for three to five minutes on a straight line before they became stable, which was not cost effective. Now we have a sensor that gives us continuous reliable readings, and it gives the exact direction and location of each beam."
In order to develop the capacity to clean and validate the huge data sets generated by multibeam, CHS has worked in partnership with the University of New Brunswick's (UNB's) Ocean Mapping Group, Universal Systems Ltd. of Fredericton, New Brunswick, and Sirius Solutions Ltd. of Dartmouth, Nova Scotia.
UNB's team developed algorithms to help locate and resolve errors in hydrographic data sets, and for generating 3D visualizations of data. The former algorithms were spun off to Universal Systems Ltd., which incorporated them into its CARIS software by developing the HIPS module for multibeam processing. CHS began using this system in the early 1990s. Sirius Solutions commercialized the algorithms for data visualization in its product See Bed, which allows massive hydrographic data sets to be viewed from any point in space in 3D. This software helps hydrographers discriminate between outliers, or erroneous data points, and true bathymetry (such as a shipwreck mast). CHS started using See Bed in 1995.
A relational database management tool developed by Oracle Corp. in partnership with CHS_Oracle SDO_is also being implemented by CHS to manage the tremendous volumes of data that are accumulated during multibeam surveys.
The high ship costs associated with multibeam surveys motivated a Newfoundland survey firm to adapt the remotely-operated vehicle, DOLPHIN, to hydrographic duty. By 1992, Geo-Resources Inc. of St. John's had integrated multibeam sounder and GPS technology into the CHS-owned DOLPHIN vehicle, originally developed and engineered by International Submarine Engineering of Coquitlam, British Columbia.
Operating quietly beneath the surface, the remotely controlled and dIEsel-powered DOLPHIN can transmit data to either the mother ship or to shore, running for 27 consecutive hours on one fuelling.
Geo-Resources President E.C. (Carl) Granter reports that one DOLPHIN on either side of the mother ship will triple the area that can be surveyed in a day, and the survey can be completed for one-sixth the cost that would be incurred by operating only the mother ship.
It was a Dartmouth, Nova Scotia company that tackled the challenging task of launching and recovering the DOLPHIN at sea. Brooke Ocean Technology developed the Atlantic Arm, which has demonstrated performance in a sea state of four. (BEAUFORT SIDE?)
In June 1996, Brooke introduced a new product at the Canadian Hydrographic Conference in Halifax, Nova Scotia. The moving vessel sound velocity profiler is believed to be the first instrument capable of measuring the velocity of sound in water from a small moving vessel. Since multibeam bathymetry is dependent on acoustics, a proper interpretation of the acoustical signals that return from the seafloor is critical. Since the speed of sound in water is affected by changes in temperature and salinity, measurements must be taken during the surveyparticularly in areas where freshwater and saltwater mix and where there is a major current. This piece of equipment makes it possible to do so without even slowing down the vessel.
The company's first sale was to CHS. Pending successful sea trials in August, CHS intends to begin using the system in October.
After 10 years of development, CHS's multibeam fleet is fully rigged for shallow water surveying (from two metres to 500 metres). It includes the FREDERICK G. CREED (20.4 metres, 150 gross tonnes, with a Simrad EM1000), CSS MATTHEW (51.25 metres, 856 gross tonnes, monohull, with a Simrad EM100), one DOLPHIN (with EM100), and three survey launches (9.75 metres, with Simrad EM3000). CHS commissioned the launches this summer and is encouraging the survey industry to discuss partnering arrangements for the use of two of the launches during periods when they are not in use.
CHS's principal use for this arsenal of ocean mapping equipment is to conduct surveys for the production of nautical information for safe and efficient navigation, which are then distributed as electronic charts through Nautical Data International of St. John's, Nfld., and as paper charts through CHS's distribution network. NDI holds an exclusive license as master distributor of CHS's electronic charts and data.
In consideration of the Government of Canada's substantial investment in multibeam equipment, technology and expertise, CHS was pleased to discover that there are many non-navigational uses for the seafloor map information. Among the fastest growing are applications for coastal transoceanic cable and pipeline routing.
Teleglobe Canada has made use of multibeam surveys since 1989, when a transatlantic fibre optic cable was laid to connect the United States and Canada to Spain, France and the UK. Since then, multibeam data has assisted Teleglobe in one transpacific and two transatlantic projects, a project linking Vancouver Island with the British Columbia mainland, and two resurveys.
"Multibeam enables us to see the entire corridor," says Mike Kennah, who is Vice President for International Business Development for it-International Telecom, a privately-owned company providing consultancy services to Teleglobe Canada. "If you have a seamount (underwater mountain), you can see the entire area. Before, you could just see the high areas." And it's far more cost effective than single beam. Kennah figures that one multibeam survey at the mid-Atlantic ridge that took only three days would have taken 20 days using single beam.
Kennah is impressed with the DOLPHIN, both for its accuracy and cost-effectiveness. "At that time, the EM 100 on the DOLPHIN was incredible," he says, recalling that CHS's DOLPHIN-based transatlantic cable survey conducted in 1992 saved 50 per cent of reroute survey costs. "The survey data which we have from the APOCS 2 job (in which the CREED surveyed a fibre optic cable route between Newfoundland and Cape Breton, Nova Scotia) was by far the most superior I've ever(X) seen. We were able to do part of the route engineering using 3D information and imaging tools. It enabled us to lay cable in the deep water portion with absolutely no problems."
Kennah says the international market is "huge", since approximately 200 small cable systems will be designed and installed over the next six years, as well as some large optically amplified systems. He cites the demand to convert from copper wire to fibre optic cable which is fuelled by increasing Internet and video television usage, as well as the demand for high-quality transmission via cable.
In a related multibeam application, in November, 1995, Nortech Surveys of St. John's, Nfld. and Jacques Whitford Environment Ltd. of Dartmouth, N.S. partnered with CHS to survey a section of the seafloor off Sable Island with the CREED. The multibeam survey was carried out to assist in the preparation of an engineering assessment of a pipeline route from mainland Nova Scotia to the Sable Island gas field.
"This is the direction most marine corridor surveys are headed for full bottom coverage," reports Nortech's Manager of Marine Services Mike Cole. Completed in June, a Phase two survey over a 1,000- kilometre area (500 metres wide) took just three days to complete. With the CREED's ability to travel at 15 knots, Cole figures a single-beam survey of the same area would have taken three times as long. Like Kennah, he is impressed with the visualization component of the complete multibeam platform_a high-density digital terrain model which aids the decision making process.
Developed jointly by the Human Computer Interaction Laboratory and the Ocean Mapping Group at the University of New Brunswick, and commercialized by Interactive Visualization Systems of Fredericton, the Fledermaus (flying mouse) system takes ocean mapping information that has been converted into 3D imagery and brings it to life through animation. The user, who controls the virtual fly-over, can also draw a proposed cable or pipeline route over the seafloor terrain. This simulation can then be used in real time aboard the cable or pipeline laying vessel to follow the progress of the plow in the 3D scene.
In 1994 and 1995, the CREED journeyed to Point Aconi, Nova Scotia to assist the Cape Breton Development Corporation in its efforts to maximize the safety of a coal mine located 200 metres below the ocean floor. The objective was to see if the excavation of coal resulted in the formation of a cavity on the sea floor. "There was a direct proportion," reports Gerard Costello, Project Manager in CHS's Atlantic Region. "The size of the cavity translated into a depression in the seabed, about one metre deep. The survey provided them with valuable information about the geological structure and the stability of the area, and it helped them in the design of the mine for safety purposes."
John Davis, a director of Eco-Nova Corporation of Halifax, is using multibeam survey data for a different sort of mining_to locate shipwrecks. When Davis accompanies a CHS survey, he looks for a bottom feature that's incongruent with the surrounding bathymetry. He then follows up on anomalies with a towed magnetometer, which indicates if the object is iron-based (possibly, a ship's hull). Once ashore, he conducts historical research to see if any ships have gone down in the area.
According to David Flemming, Director of the Maritime Museum of the Atlantic, the waters off Nova Scotia conceal one of the highest densities of shipwrecks in North America, and Davis is using this strength to attract eco-tourist divers from Europe. "A major tourism industry can be developed around these shipwrecks," he says, adding that divers from the UK, Switzerland and Germany have come to investigate the wrecks. "They come over as eco-tourists and go to work for the Nova Scotia Museum and Parks Canada, helping them to survey sites and gather more information. It gives relevance to their vacation experience."
Stellwagen Bank National Marine Park in Massachusetts is planning to use the wealth of information captured in multibeam imagery during recent surveys to care for its marine resources. Acting on behalf of the marine sanctuary, in 1994 the United States Geological Survey requested the collaboration of CHS and the University of New Brunswick to perform a three-part survey of the 800 square-mile park located north of Cape Cod and east of Boston. The marine park is home to the right whalean endangered speciesas well as humpback whales, fin whales, dolphins, and porpoises. In addition to aiding the park in its efforts to protect sea mammals, the seafloor maps will also help gauge the effects of a new sewage outfall sited 10 miles outside Boston harbour, and they will shed light on storm-related sediment transport.
Asked to comment on the results of the survey, Page Valentine, a USGS geologist who was the Sanctuary's liaison for the project, answered with one word: "Excellent. The CREED has probably the most sophisticated mapping system for doing this job." Plans are under way to bring the CREED back for future projects in the New York Bight area_south of New York Cityand in Long Island Sound, pending funding approvals.
Together with side scan, multibeam systems are also being used to develop mine warfare countermeasures. Lieutenant Commander Jim Bradford, XX NOT CMDR.Commander of Maritime Forces Atlantic in Halifax, points out that combining the two marries side scan's high resolution values with multibeam's accuracy in depth and total bottom coverage. "One is weak and the other is strong. Tie the two together, and you come up with a vastly improved capability. You know where the obstacles are."
Perhaps the most recent application for multibeam is in fisheries harvesting and management. Although it is too early to say definitively, it is believed that seafloor maps produced by multibeam can be used to locate fish habitats. Gerard Costello, CHS's Project Manager, returned from a 700-square-kilometre exploratory survey of western Browns Bank off southeastern Nova Scotia in early July. This prime scallop and groundfish fishing site has plagued fishermen over the years because its rough bottom tends to destroy gear.
"Fishermen tell me they've dragged up boulders the size of a VW," reports Costello. Armed with the bathymetry and complete side scan coverage, Costello and his colleagues at the Atlantic Geoscience Centre in Dartmouth are now interpreting the sediment type. He says the first results indicate a strong possibility of sand dunes up to eight metres high. CHS will make these maps available through Nautical Data International by the fall.
Mike Pittman, who is Fleet Manager at Clearwater's Deep Sea Trawlers in Lunenburg, Nova Scotia, has nearly 25 years' experience in the fishing industry. "This, to me, is the biggest thing in the fishing industry since the hook," he says, adding that the new maps will help the fishing industry approach the resource in much the same way that farmers work the land. Pittman says that an experienced fisherman can do so on the basis of knowledge of the bottom type and depth. The scientific community is just now exploring the use of multibeam/side scan data to identify fishery habitats.
Knowing where the nurseries are, says Pittman, will enable fishermen to avoid those areas; knowing where boulders and other obstacles are will enable them to save their gear; and knowing where populations of particular species are will enable them to fish effectively and judiciously. Asked if he thinks this new method will give the industry a carte blanche to overfish, he said the industry has learned its lesson from the recent east-coast groundfish debacle. Adding that quotas, the Enterprise Allocation, and the reduced numbers of fishing vessels will safeguard against overfishing, he points to the healthy scallop sector at Georges Bank, which rebounded from 800 pounds a day in the early 1980s to 5,000 pounds a day today.
The next step is to classify the bottom type. Single-beam classification systems exist, such as RoxAnn (Marine Microsystems of Aberdeen, Scotland) and QTC View (Quester Tangent Corporation of Sidney, BC). CHS has now partnered with Quester Tangent Corporation and the University of New Brunswick to adapt single-beam bottom classification techniques to the multibeam platform. This technology measures the hardness and roughness of the ocean bottom and assists in the interpretation of grain size and sediment distribution. Because of this, it can be used to indicate probable marine habitats.
CHS will continue to explore opportunities for both private and public-sector applications for multibeam and bottom classification, and it will help the Canadian private sector to develop the capabilities to offer these services in the future.
Route survey here was conducted November 1995 to
February 1996 offshore (looking onshore) Nova Scotia.
Rock out-cropping areas shows 6:1 vertical exaggeration.
(Courtesy of Nortech Surveys Canada Inc.)