GPS Doesn't Work Underwater
So the U.S. Navy is developing a new kind of system—built specifically for drone submarines.To prepare for the possibility that it will one day deploy swarms of uncrewed drone submarines, the U.S. Navy is developing a system that will allow the global positioning system (GPS) to function deep below the ocean’s surface. If successful, the technology could start to appear as soon as the 2020s.
The global positioning system is a marvel of accurate clocks and simple physics. A GPS receiver, like the kind in smartphones or car navigation systems, is little more than a radio antenna tuned to satellites. It listens for signals from the three GPS satellites that happen to be closest (there are more than 50 satellites in total, all constantly broadcasting their time), then it triangulates its own location from where it knows those satellites to be. Though composed only of silent listeners and a constellation of passive beacons, GPS can tell someone where they are on or above the planet’s surface.
But take heed of the prepositions—on or above. Right now, GPS signals can barely go below.
“Radio signals do not propagate very far underwater,” says Joshua Niedzwiecki, the director of sensor processing at BAE Systems. BAE is researching and developing the new technology for the government. “If you put your cellphone in a waterproof case and went into the ocean, as you start getting deeper and deeper, you’d very soon lose connectivity.”
And since GPS radio signals don’t reach very far underwater, they’re basically useless for any submarine below the surface. The Navy solves this problem now by outfitting each sub with a “very large and very expensive inertial measurement unit,” says Niedzwiecki. (Imagine a tricked-out, military-grade version of the accelerometer in your phone.) By remembering the submarine’s last known surface position, as measured by GPS, then keeping close track of its forward movement and diving depth, these units can give a high-accuracy estimate of where the submarine is in space.
But they are still very expensive and very large. If the Navy wants to deploy dozens or even hundreds of them to drone submarines, then it will soon run out of both budget and available cargo space. It needs something closer to GPS, a set of lightweight passive beacons that can help something deduce location through triangulation alone. Hence the new BAE Systems project: the Positioning System for Deep Ocean Navigation, or POSYDON.
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http://www.theatlantic.com/technology/archive/2016/06/its-gps-underwater-for-robots/486656/Navy divers ascend to the surface after conducting an anti-terrorism and force protection dive during exercise Eager Lion 2016 in the Gulf of Aqaba, Jordan, May 14, 2016. Exercise Eager Lion is a recurring exercise designed to strengthen military-to-military relationships and enhance regional security and stability. Navy photo by Petty Officer 2nd Class Sean Furey
Undersea navigation and positioning system development to begin for U.S. Navy
16 May 2016
DARPA has selected BAE Systems for its POSYDON – Positioning System for Deep Ocean Navigation – program.
The U.S. Defense Advanced Research Projects Agency (DARPA) has selected BAE Systems to develop an undersea navigation system aimed at enhancing the U.S. Navy’s ability to provide precise, global positioning throughout the ocean basins. The contract will support a program called the Positioning System for Deep Ocean Navigation (POSYDON), which seeks to allow undersea vehicles to accurately navigate while remaining below the ocean’s surface.
POSYDON aims to replace current navigational methods that pose a detection risk for undersea vehicles forced to surface periodically to access the space-based Global Positioning System (GPS), which cannot sufficiently penetrate seawater. In addition, access to above-water GPS may be denied by hostile signal jamming. Under DARPA’s POSYDON program, a BAE Systems-led team will create a positioning, navigation, and timing system designed to permit vehicles to remain underwater by using multiple, integrated, long-range acoustic sources at fixed locations around the oceans.
“BAE Systems has more than 40 years of experience developing underwater active and passive acoustic systems,” said Joshua Niedzwiecki, director of Sensor Processing and Exploitation at BAE Systems. “We’ll use this same technology to revolutionize undersea navigation for the POSYDON program, by selecting and demonstrating acoustic underwater GPS sources and corresponding small-form factor receivers.”
The vehicle instrumentation needed to capture and process acoustic signals for accurate navigation will also be developed under this program. The company will leverage its expertise and capabilities in signal processing, acoustic communications, interference cancellation, and anti-jam/anti-spoof technologies for the program. Other members of BAE Systems’ POSYDON team are the University of Washington, the Massachusetts Institute of Technology, and the University of Texas at Austin.
http://www.baesystems.com/en-us/article/undersea-navigation-and-positioning-system-development-to-begin-for-u-s--navyPositioning System for Deep Ocean Navigation (POSYDON)
Solicitation Number: DARPA-BAA-15-30
https://www.fbo.gov/index?s=opportunity&mode=form&id=6797db962e007d18615c3f2e96db42a8&tab=core&_cview=1The guided-missile destroyer USS Gonzalez travels in the Gulf of Aden, May 14, 2016. The Gonzalez is supporting maritime security operations and theater security cooperation efforts in the U.S. 5th Fleet area of responsibility. Navy photo by Petty Officer 3rd Class Pasquale Sena
