Sea Technology

JUN 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 40 of 72

40 st / June 2017 promise new flexibility for the source of the critical onboard gravity-gradient maps required for the map-matching navi- gation task. The maps can derive from original gradiometer measurement data, or they can be generated using forward modeling methods based upon new ocean bathymetric da- tabases. Use of the latter techniques for navigation aiding must still be demonstrated in practice, but simulation of new algorithms show tolerance to significant inherent map errors of certain types. What is unknown is the complete nature of map error types to be expected using the synthetic map-generation methods. Vast improvements in technology and navigation tech- niques have been made since the first demonstrations of gravity-aided inertial navigation of undersea vehicles two decades ago. New gravity gradiometer sensors are in the experimental stage and promise to demonstrate equivalent sensitivity to the original gradiometers but with much re- duced complexity and bulk. They will be suitable for mili- tary submarines and UUVs, as well as the new deep-ocean class of UUVs for geophysical applications. References For a list of references, contact Paul Madden at pmad ST Paul Madden spent much of his career at the Draper Laboratory (formerly the MIT Instrumentation Laboratory). He participated in diverse projects involv- ing missile, submarine and aerospace vehicle guidance, navigation and control. Those projects included the Deep Submergence Rescue Vehicle, the NASA Space Shuttle and the first fly-by-wire aircraft. He is presently a navigation con- sultant based in the Boston area. 6 arc-seconds, that is, 90 and 180 m, respectively. A good position fix was achieved in 6 hours, while little improve- ment was seen after 24 hours. After leaving a position fix location, the UUV navigation performance is entirely dependent upon the intrinsic perfor- mance of the velocity-aided INS that, in turn, depends upon the navigation capability of the particular INS employed and the mode of operation of the velocity aiding (either bottom- tracking or water-tracking). The particular mission of the UUV or manned submers- ible most likely will specify the maximum allowable naviga- tion position error. When this error threshold is approached, the vehicle will either have to seek out a new (or previously used) position fix location or surface momentarily to obtain a GPS position fix. The simulation results demonstrate that gravity-aided navigation algorithms have improved significantly and "Vast improvements in technology and navigation techniques have been made since the first demonstrations of gravi- ty-aided inertial navigation of undersea vehicles two decades ago." More powerful, yet easier to use • Full support for swath bathymetry • Advanced seabed characterization • New faster, integrated 3D viewer • Powerful visualization tools COMING SOON: 7

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