Navigation is the process of determining the position of a vehicle or object with respect to some exterior reference system. Global navigation systems determine position with respect to world coordinates. Local navigation systems determine position with respect to a local object or a set of transducers that are not referenced to world coordinates. Integrated navigation systems measure the position of the vehicle with respect to a local reference, and then transform the output into global coordinates.
A common technique for navigating submersible and autonomous or remotely operated vehicles is to determine the position of the support ship using a global navigation system (such as GPS), simultaneously determining the position of the vehicle with respect to the ship, using an acoustic positioning system employing short or ultrashort baseline technology. These measurements can then be integrated to form a global position or used separately. Another common method is to calibrate a long baseline system with respect to ship position, and then to determine the position of the vehicle with respect to the long baseline. Other technologies can be used to increase the accuracy of navigation systems or to fill in the gaps during the periods of time that information is not available from other systems. These technologies include the use of acoustic Doppler to determine vehicle velocity, inertial motion reference systems to determine changes in position, and correlation sonar to determine changes in position with respect to the sea bottom. Another type of navigation is positioning with respect to a local environment. This is accomplished by using vision or sonar to sense objects in the local environment, then positioning the vehicle or manipulator with respect to those objects.
Acoustic positioning techniques of long baseline, short baseline, and ultrashort baseline are available and commonly used in the former Soviet Union (FSU), Western Europe, and the United States. Integration of acoustic positioning systems and GPS or similar systems are also commonly available. Technologies to fill in information to augment acoustic positioning are becoming available but are still expensive, large, and/or power hungry. Techniques applicable to submersibles, or ROVs or AUVs, for navigation using sensors of local terrain and integrated inertial navigation systems, are being researched.
. Several institutions in Russia and Ukraine are working on the development of transponders for subsea navigation. At the Andreev Institute there are several projects developing this technology (see Andreev Institute site report - Appendix B). The scientists' focus is on extending the duration of the transponders. This can be accomplished by increasing the efficiency of the power transfer from electrical energy to acoustical energy. It can also be accomplished by putting the transponder to sleep, waking it up only when power is needed. Another method is to focus on failure modes and to increase the mean time between failure of the transponder. Oceanpribor is developing low, medium, and high power transponders. A test facility is used there to test transponders and navigation systems. The company has developed long, short, and ultrashort baseline navigation systems, some of which have capabilities similar to the Honeywell and Simrad systems (see Oceanpribor site report - Appendix B). The Bureau of Oceanological Engineering is developing transponders for two systems: a long baseline system and an ultrashort baseline system (see Bureau of Oceanological Engineering site report - Appendix B). St. Petersburg State University has been working on ultrashort baseline underwater tracking systems and the corresponding transponders (see St. Petersburg State University site report - Appendix B). Transponder design (for navigation, communication, and sensing) is an area that was described to the WTEC team as an area of strength in the FSU. Russia and Ukraine have impressive test facilities and a large experience base to offer in this area.
The Andreev Institute is working on bottom referenced navigation (see Andreev Institute site report - Appendix B). This includes correlation sonar and multibeam sonar. These systems use multibeam transmitters to insonify a large area and then correlate the response with a reference image. Another system under development uses a multibeam receiver to track the position of a remote transponder.
At the Bauman Institute in Moscow, there is a research program to develop a low drift integrated inertial navigation system based on some very high accuracy accelerometers (see Bauman site report - Appendix B).
France. In France, several programs are focused on using locally sensed data in the navigation system of an undersea, or any robotic, vehicle. At LIFIA, in Grenoble, the French are using a multibeam sonar to sense the local environment (see LIFIA site report - Appendix D). This data is then matched to a world model. The position of the vehicle, as well as any new obstacles, can be determined from this data. A path on how to proceed to the objective can then be calculated. Figure 8.1 shows the output of the user interface showing the vehicle and the position that it has calculated with respect to the walls of the laboratory.
Figure 8.1. 2-D Local World Model and Vehicle From LIFIA System
IFREMER and INRIA are working on the use of video in navigation (see IFREMER and INRIA site reports - Appendix D). They use an image from a video camera to determine the position of a vehicle relative to a wellhead. They then use the signal to guide the vehicle to reenter the well. IFREMER has been involved in subsea navigation systems of various types for several years.
United Kingdom. There are several projects in the U.K. that focus on navigation in such man-made structures as oil rigs or nuclear power plants (see Marine Technology Directorate site report - Appendix E). At Strathclyde University a system is being developed that uses a model from a CAD drawing as a reference. It then correlates the actual sonar image with the expected image, which is calculated by simulating the projection of sonar on the CAD drawing. The information is used to determine a most likely position within the structure of the vehicle. Then this position is used to navigate the vehicle.
For newer vehicles, navigation systems are acquired internationally so that their performance is not limited to regional or national capabilities. Two vehicles that have been used extensively by the worldwide scientific community are the two Mir submersibles that were designed and built in Finland by Rauma Oceanics. The navigation and communications equipment onboard the Mir submersibles is built in Finland by a Rauma subcontractor (see Rauma site report - Appendix F).
In the area of navigation, research programs in the FSU, Western Europe, and the United States all use similar technologies (Figure 8.2). In Russia and Ukraine, there are: (1) a large number of engineers who are trained and working in this area; (2) an infrastructure for the development, testing, and evaluation of navigation technologies; and (3) a focus on the development of hardware, on the development of algorithms, and on testing and evaluating navigation technologies.
Availability of Navigation Technologies
C = Commonly available in science ROV submersibles
A = Available / under development
R = Research