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 37 of 72 June 2017 / st 37 G ravity has been used as a means to passively aid in- ertial navigation systems of both submarine and surface ships of the U.S. Navy. Most of this work was first done in the 1990s on an experimental basis using gravi- meter and the gradiometer sen- sors. The modern gradiometer, which measures the gradients of the gravity vector, has been in existence for decades. A version was developed in the 1980s to provide covert aid to submarine navigation as an independent position sensor. The navigation-aiding perfor- mance of the gradiometer was completely successful, but the technique is not used operation- ally in U.S. Navy ships, sub- marines or UUVs because the gradiometer used in the Navy experiments was large and rela- tively complex. Versions were subsequently developed for geophysical prospecting. The most recent development of the geophysical gradi- ometer is the Falcon-Plus version, which is mechanically less complex than the original Bell Aerospace full-tensor gradiometer (FTG) from which it was derived. It measures a subset of the full-tensor set of gravity gradients but is still a large, heavy, complicated sensor system unlikely to be con- sidered practical in a UUV, although it could be useful in a conventional manned submarine. To the best of my knowledge, there is no current opera- tional implementation of a gradiometer-aided navigation system in a submarine vehicle, either manned or unmanned. Most likely, this is because current operational gradiometers are still complex, large and expensive instruments, and the need for navigation covertness by the military has been met by near-covert acoustic fathometer sensors. However, new gravity gradient sensor concepts, gravity gradient map generation methods and navigation algorithms will provide new passive navigation options for deep-ocean UUV explo- ration and defense missions. New Gradiometers France's space agency, ONERA, developed the hugely successful electrostatic-accelerometer-based gradiometers used in the European Space Agency missions GRACE and GOCE, Earth-orbiting satellites that have been measuring the Earth's gravity field and its gradients since 1999. Passive Autonomous Navigation For Exploration, Defense Using Gravity to Aid INS on UUVs By Paul Madden This figure shows the bathymetry north of Palau in the Pacific and the UUV track. Only a short section is required for a posi- tion fix.

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