EL CONSEJO DIRECTIVO DE LA CDA

The basis for an innovative means of vessel navigation in the world’s uncharted frontier involves original research in the progression and integration of three seemingly unrelated technologies: forward looking sonar, Virtual (non-AIS) AtoN, and georeferencing. The approach described is eminently suitable for Arctic service in terms of usefulness, ease of deployment and low cost for installation and maintenance.

6.1 3-dimensional Forward Looking Sonar

This research is based upon the assertion that own ship sensors should be adequate to detect soundings and bottom configuration both at its current position as well as forward of the vessel in the path of transit sufficient to ensure safe navigation. Such capability is especially appropriate where soundings and bottom configuration are inaccurate or not available due to poor or lack of accurate hydrographic survey. This is possible through the use of 3-dimensional Forward Looking Sonar (3D-FLS), which is a variation of the multibeam echo sounder that detects bottom features and objects within the water column forward of the bow. Despite its usefulness and the availability of this technology in the commercial marketplace for over two decades, it is rarely included within the ships’

13 R. Glenn Wright and Michael Baldauf complement of navigation sensors. Historically, this is likely due to a lack of suitable range, low vessel speed of use requirements and confusing 2-dimensional displays. There is also no IMO carriage requirement for 3D-FLS at present.

The detection of bottom features, objects and soundings by determining range, azimuth and elevation information uses methods that can generally be described as variations on transmitting a steerable sonar signal ahead along the path of the vessel or by transmitting a single ping from which snapshots of the environment are obtained. Through this process a mosaic of the bottom topography and specific targets is created as the vessel proceeds on its course. 3D-FLS systems have been developed with different capabilities supporting both unmanned undersea vehicle and vessel applications. Of those designed for use on vessels, most are intended for pleasure and small fishing boats. There are systems with range and resolution that make them suitable for use on larger vessels such as workboats, offshore service vessels, merchant and passenger vessels. However, operational constraints may create limitations on their usefulness. For example, effective range may be limited by tradeoffs in transducer design to minimize water resistance and drag.

At present, 3D-FLS is capable of detecting and displaying the underwater environment looking ahead as much as 1,000 meters forward of the bow at speeds up to 25 knots. In shallower waters the range of 3D-FLS can extend from eight to twenty times the depth ahead, depending on bottom and target conditions [49,50]. It is most effective when the bottom topography slopes upwards, and when targets are large and consist of hard rock and/or coral that provide good acoustic signatures.

The research focuses on the enhancement of 3D-FLS capability to survey the sea bottom as well as to detect hazards attached to the bottom and floating in the water column to aid in Arctic navigation, where soundings on charts rarely exist and the vast majority of hazards to navigation have yet to be discovered. The utility of this technology as a means to avoid such hazards has been explored in a simulation of the M/V Costa Concordia disaster [51]. Its use as a means to perform hydrographic survey has also been discussed in terms of International Hydrographic Office (IHO) standards [52,53]. The potential exists to accomplish complete survey coverage with 3D-FLS for the transit route with horizontal and vertical accuracies within IHO standards using this approach. Such data can supplement national hydrographic organizations’ efforts in the collection of survey data in remote parts of the world and in areas lacking recent survey.

6.2 Virtual Aids to Navigation

Virtual AtoN based upon AIS technology are rapidly being deployed on a worldwide basis as a supplement to physical AtoN. While this is a valuable technology, the use of AIS-based AtoN is severely restricted in the Arctic due to lack of existing infrastructure to provide power and communications for health monitoring, access for maintenance and VHF radio range limitations. The research focuses in the creation of (non-AIS) Virtual AtoN, defined by the International Association of Lighthouse Authorities (IALA) as something that “does not

Arctic Environment Preservation through Grounding Avoidance 14 physically exist but is a digital information object promulgated by an authorized service provider that can be presented on navigational systems” [54]. Methods used for the creation of Virtual AtoN have been described in a real-time, shipboard implementation of this technology [55,56].

Virtual AtoN technology represents a major step beyond the capabilities of existing AtoN, although critical limitations exist that are inherent in their design and implementation. Qualifying as short range AtoN, Virtual AtoN appear neither visually nor directly on radar. AIS-based virtual AtoN appear on an AIS radar overlay and also on ENC/ECDIS displays. However, verification techniques to ensure AIS and ENC/ECDIS positions coincide have yet to be developed. Virtual AtoN may appear only on ENC/ECDIS displays. Such implementations can result in a potential “single point of failure” scenario that may cause false conclusions and possible system failures that may go undetected. A comprehensive Virtual AtoN verification approach to help overcome this deficiency and ensure virtual AtoN (AIS and non-AIS) are watching properly after deployment is possible using georeferencing techniques.

6.3 Georeferencing

Georeferenced navigation using terrain features and manmade object recognition has been in use for many years as a means of cruise missile and other unmanned aerial vehicle (UAV) navigation across the landscape. This has been made possible through highly detailed millimeter-resolution radar and laser-surveys of the land areas from aircraft and satellites, whereas the ocean depths are presently surveyed to a maximum resolution of about 5 kilometers [57].

This research utilizes a novel implementation of georeferencing based upon the extraction of features from both multibeam sonar and 3D-FLS data represented in the ENC, and correlation between vessel position indications and physical environmental features to verify that Virtual (and physical and AIS) AtoN are watching properly. Comparison between ENC soundings and echo sounder depths along the path of transit can be performed even if precise positioning information normally acquired using GNSS, AIS and other sources are unavailable due to a variety of manmade and natural events. The techniques used to accomplish this have been discussed based upon the results of a series of experiments conducted at sea [53,58]. Environmental features are identified in terms of bottom depth soundings for the ENC and echo sounder as well as the difference between these two sources, differences in bottom slope and differences in the rate of change of bottom slope resulting in new capabilities to automatically detect discrepancies in either bottom conditions or GNSS positioning that may require additional caution.