page_title: Long baseline acoustic positioning system
section_title: Examples
hierarchical_section_title: Long baseline acoustic positioning system / Examples
caption_attribution_description: Ohio-class submarine launches Tomahawk Cruise missiles (artist concept) original image caption: 030606-N-0000X-005 Washington, D.C. (Jun. 6, 2003) -- Artist concept of the SSGN conversion program. Four Ohio-class strategic missile submarines USS Ohio (SSBN 726), USS Michigan (SSBN 727) USS Florida (SSBN 728), and USS Georgia (SSBN 729) have been selected for transformation into a new platform, designated SSGN or Tactical Trident. The SSGNs will have the capability to support and launch up to 154 Tomahawk missiles, a significant increase in capacity as compared to other platforms. The 22 missile tubes will also provide the capability to carry other payloads, such as unmanned underwater vehicles (UUVs), unmanned aerial vehicles (UAVs) and special forces equipment. This new platform will also have the capability to carry and support more than 66 Navy SEALs (Sea, Air and Land) and insert them clandestinely into potential conflict areas. U.S. Navy graphic. (RELEASED)
context_page_description: A long baseline acoustic positioning system is one of three broad classes of underwater acoustic positioning systems that are used to track underwater vehicles and divers. The other two classes are ultra short baseline systems and short baseline systems. LBL systems are unique in that they use networks of sea-floor mounted baseline transponders as reference points for navigation. These are generally deployed around the perimeter of a work site. The LBL technique results in very high positioning accuracy and position stability that is independent of water depth. It is generally better than 1-meter and can reach a few centimeters accuracy. LBL systems are generally employed for precision underwater survey work where the accuracy or position stability of ship-based positioning systems does not suffice.
context_section_description: By the mid-1960s and possibly earlier, the Soviets were developing underwater navigation systems including seafloor transponders to allow nuclear submarines to operate precisely while staying submerged. Besides navigating through canyons and other difficult underwater terrain, there was also a need to establish the position of the submarine prior to the launch of a nuclear missile (ICBM).  In 1981, acoustic positioning was proposed as part of the U.S. military's MX missile system.  A network of 150 covert transponder fields was envisioned.  Submarines typically are guided by inertial navigation systems, but these dead reckoning systems develop position drift which must be corrected by occasional position fixes from a GNSS system.  If the enemy were to knock out the GNSS satellites, the submarine could rely on the covert transponder network to establish its position and program the missile's own inertial navigation system for launch.
caption: Figure 3: Precisely establishing the position of nuclear submarines prior to missile launches was an early application of long baseline acoustic positioning systems. Covert networks of sea floor transponders could survive and provide a precision navigation capability even after GPS satellites had been knocked out.
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