An accident at sea, such as an

Transcription

1 Littoral water survey and security Surveying by Claude Cazaoulou, ECA More than 90% of international commercial exchange and 70% of annual world oil consumption are transported by sea. Millions of people live in the coastal areas and the marine environment represents for them a major source of life. The financial stability and well-being of many countries depend on the sea and the marine environment in general. An accident at sea, such as an incident involving a tanker, is a serious factor that contributes to the risk of pollution of the marine environment especially in the coastal zone, which would dramatically affect the nation s activities. Nation cooperation There is today, a growing concern for the marine environment, for protecting it, keeping it clean and taking measures to safeguard the coastal area and in particular sensitive areas recognised by the International Convention for the Prevention of Pollution from Ships (MARPOL). Figs. 1 and 2: Artisan fishers and crude carriers two major actors at sea. In the past few decades, few important factors have emphasised the need for adequate hydrographic survey coverage and the production of up to date nautical charts: The advent of exceptionally deep draught Very Large Crude Carriers. The need to protect the marine environment. The changing maritime trade patterns. The growing importance of seabed resources. On 23 December 2003, the United Nations General Assembly adopted resolution A/RES/58/240 on Oceans and Law of the Sea that dealt, in large part, with safety of navigation. In this resolution, the general assembly encourages the International Hydrographic Organisation (IHO) and the International Maritime Organisation (IMO) as well as states and agencies to improve hydrographical services and the production of nautical charts especially in areas of international navigation and ports and where there are vulnerable or protected marine areas. Figs. 3 and 4: Navigation mistakes can lead to a dramatic situation (courtesy of French Navy). Many charts, which were adequate a decade ago, may have to be recompiled using new survey data, collected to a higher degree of accuracy and providing improved coverage. This deficiency may not be limited to sparsely surveyed waters of developing nations, but may also apply to the coastal waters of major industrial states. The advent of accurate satellite navigation has made poorly positioned historical data an even greater problem for navigators. Fortunately, new survey technologies have improved the precision to which modern hydrographical surveys can be conducted. Actors and missions Bad positioning of natural obstacles on charts could lead to a major navigation accident. This drives the hydrographical services in their increasing efforts and cooperation. But other dangers in the underwater environment can generate the same kind of disaster. Coast guards as well as the Mine Warfare Group of the Navies are also involved in sub sea survey and security. Through their missions of surveillance and controls of navigation channels and harbour approaches, prevention of illegal activities including terrorism and piracy and mine counter measuring, they work PositionIT October

2 imagery is generally accomplished by hull mounted or towed high frequency sides scan sonars. Mosaicking the pictures results in a complete mapping of the area. Analysis of these pictures and/or comparison with previous stored data leads to new obstacle detection but their classification and potential impact on navigation generally requires more data and a better knowledge in the third dimension. Fig. 5: Hydrographic and survey missions from very shallow water to deep sea. Even if shadow contrast analysis is useful this technique is limited by seafloor gradient. The most appropriate sensors for bathymetry are single and multibeam echo sounders and sub bottom profiler for buried obstacles. By post processing, the bathymetry data are combined with imagery and topographic inputs to generate 3D digital seafloor charts that provide accurate presentation of the underwater features. It is obvious that the more accurate the processed data are, the better and faster the classification and identification of seafloor objects. Depending on the result of this inspection phase, the ultimate activity in subsea protection will be initialised. The neutralisation consisting in recovery or destruction of objects classified as dangerous for navigation or people safety. This operation requires specialised tools and well trained operators. Advanced single survey platform Fig. 6: SIMBA concept a multi mission platform and dedicated vehicles. Up to 2005, specialised ships, such as hydrographical survey ships (HSS) or mine hunters (MCMV), fitted with hull-mounted or towed systems, were the only solution to carry out these missions. They are expensive, require manpower and are time consuming. Today a unique vessel using unmanned vehicles (AUV, USV and ROV) fitted with efficient sensors offers a cost effective alternative solution for accomplishing the more demanding maritime missions. Figs. 7 and 8: USV Inspector. to protect people against these threats and ensure that economic activities can be conducted safely. Activities and means Even if hydrographic survey, homeland security and mine counter measures could, at first glance look like very different missions conducted by specialised organisations, they mainly make use of same kind of sensors and processes. The first step is to collect the widest amount of pictures of the seafloor. The collection of acoustic The SIMBA concept (Ship for Imagery and Bathymetry) described in the following lines has been directly driven by this alternative. The use of optimised sensor carriers, according to the situation, definitively improves the performances and measure accuracy and thus in water depth varying from coastal line down to deep sea. Distant remotely controlled operations with the vehicles, relax the constraints on the vessel which stays outside the critical 26 PositionIT October 2010

3 areas, reducing design, manufacturing and through life costs while increasing the crew safety. The vessel is designed for missions of 20 consecutive days at sea and endurance up to 3500 nautical miles. Operated by a basic crew of 15 persons, it accommodates an additional staff of 22 members. Its main characteristics are: Overall length: 55 m Max. beam: 9,4 m Full load draught: 1,8 m Max. weight: 480 T Its classic hull shape with chins offers volume, stability, reduced draught and high manoeuvrability from shore to blue sea. The hull is in high grade welded steel and the light superstructure is in aluminium alloy. The vessel is divided into independent, water-resistant compartments. It complies with commercial and military international ship regulations (BV 2000, SOLAS, and IMO A601). Particular care has been taken to thermal as well as noise insulation. Operational and living spaces are provided with conditioned air. Fig. 9: USV Inspector and its sensors for VSW hydrographical survey. Figs. 10 and 11: TSSS, MBES and SBES data fusion in coastal hydrographical survey Sanary Bay (France) (courtesy of Semantic TS). The redounded diesel electric hybrid propulsion (CODLAD) is optimised for the different operational phases: High speed capability from harbour to mission area transit. Long period of low speed for TSSS towing and pattern tracking. Dynamic positioning for vehicle launch and recovery. Adjacent to the main bridge fitted with Integrated Navigation and Security System (INSS), the Control and Information Centre (CIC) is specially designed and equipped with Multi Function Consoles (MFC) for: Mission planning Vehicles monitoring Data logging Real time and post-processing Thanks to a common design of the Man Machine Interface, these MFC can be used for the remote control of any kind of vehicles simplifying mission configuration, training and upgrade of the SIMBA platform. In complement to the CIC, a wide laboratory in the main deck is equipped with work stations and a post processing software suite to manage the different tasks of hydrographical data processing from Figs. 12 and 13: AUV Alister. raw information storage down to chart production and data base enhancement. The first third of the hull is acoustically optimised to receive sensors for seabed mapping: High resolution multi beam echo sounder (MBES) for seamless coverage from m depth (deeper on request). Dual frequency single beam echo sounder (SBES) also used for navigation purposes. Low frequency sub-bottom profiler (SBP). Acoustic doppler current profiler (ADCP) for water column speed acquisition. Ultra short base line (USBL) for vehicles tracking and guiding. The aft deck is large and modular for accommodating and handling the various equipment and vehicles: Towed side scan sonar (TSSS) Unmanned surface vehicle (USV) Autonomous underwater vehicle (AUV) Remotely operated vehicle (ROV) Bathythermograph Hyperbaric chamber for diver operations The vehicles fitted onboard will depend on the mission profile: PositionIT October

4 Inspector's main characteristics are: Overall length: 8,3 m Max. beam: 3,1 m Full load draught: 0,5 m Weight: 3000 kg Propulsion: 2 turbo diesel with hydro jets Max. speed: 22 knots Endurance: up to 20 h at 6 knots In standard configuration inspector is fitted with: High-resolution towed side scan sonar (SSS) Multi-beam echo sounder (MBES) Single beam echo sounder (SBES) Fig. 14, 15 and 16: AUV Alister and its sensors for accurate seafloor survey. Data, corrected with integrated motion unit output, are time and georeferenced with the GPS-RTK receiver and transmitted to the mother ship (or ground when used from shore station) for real-time processing. AUV: Through its position a few metres over the seabed, its stability and its very low acoustic signature, this underwater vehicle is the best carrier for subsea sensors. Alister main characteristics are: Overall length: 5 m Max. body diameter: 0,7 m Weight: 960 kg Max speed: 8 knots Endurance: up to 20 h at 4 knots Figs. 17 and 18: Seafloor images with AUV Alister (courtesy of SHOM). Operational depth: 0 to -300 m For measuring and recording the physical characteristics of the seabed and water column, ECA proposes Alister with a complete set of sensors: High-resolution side scan sonar (SSS) Multi-beam echo sounder (MBES) Single beam echo sounder (SBES) Sub-bottom profiler (SBP) Video camera and two search lights CTD and sound velocity probes Figs. 19 and 20: ROV H300 with and without accessories. USV for very shallow water and inland hydrographical survey or MCM operations. AUV for high accuracy seafloor management. ROV for seafloor and wreck inspection in very deep water. MDS for mine inspection and destruction. USV: With its very low draught, Inspector is the perfect carrier for shallow and very shallow water imagery and bathymetry operations as well as detection and object classification. All sensors are working simultaneously and data are georeferenced using inertial navigation reference; time stamped, logged-in vehicle memory and transmitted to the ship as soon as Alister establishes the high data rate communication link. Flying a few metres over the sea bed, centimetre accuracy on details is now accessible. In use in the French hydrographical organisation (SHOM) since July 2008 under the name Daurade, this 28 PositionIT October 2010

5 vehicle and associated sensors have already revealed new details of what have been considered up to now well known areas. H300 ROV: Mainly used for precise identification and reporting on subsea objects such as wrecks, piers, buildings, pipelines and structures. Its video system enables the acquisition and recording of very high definition images in real time. It is particularly suited for inspection and divers' support tasks. An optional manipulator arm can be used to recover small objects. It is handled and operated by two men and can be deployed either from a pier or from the ship. H300's main characteristics are: Length: 0,9 m Width: 0,6 m Height: 0,47 to 0,7 m Weight: 65 kg in air Speed: up to 2,5 knots Endurance: unlimited Operating depth: down to -300 m In standard configuration H300 is delivered with: One fixed video camera used for navigation (low light BW 570 TV lines, 0,01 lux), associated with two 75 W headlights. One "mission" video system using a high-resolution colour camera fitted with pan, tilt and zoom (PTZ). One navigation sonar for harsh environment approach (turbid water). Conclusion Protection of people and economical activities requires suitable means. It appears inevitable that unmanned vehicles will play a fundamental role in the surveillance of coastal waters in the coming years. Thanks to them, it is now possible that a single platform provides hydrographic, mine counter measure and patrol capability as well. This concept offers rationalised operation and maintenance approach, plus efficient and easy upgrading. The vessel is operated and maintained by a reduced crew, while additional specialists are embarked to operate and manage vehicles as well as process the acquired data. Modules fitted with appropriated sensors drastically improve mission efficiency and performances. Resulting in: Better accuracy Faster operation Wider coverage Covert operations Unused equipment remains ashore for storage, training or maintenance, thus the overall availability of both equipment and crew is optimised. For MCM and other dangerous operations the vessel has less stringent signature To advertise in PositionIT contact: Tsholofelo Nakedi Tel tsholo.nakedi@ee.co.za Fig. 21: Pipe inspection with the ROV H300. requirements as it is kept in a clear area, while USV, AUV and MDS perform detection, localisation, classification and when necessary neutralisation. Through its tethered cable the ROV is directly remotely controlled from one console of the CIC. The video and sonar data are real-time transmitted onboard and processed. Acknowledgement This article was presented at Hydro 09 and is republished here with permission. Contact Claude Cazaoulou, ECA, cazaoulou.c@ecagroup.com PositionIT October