A 'GPS' for undersea vessels
May 23, 2016
by Mark Ollig

A concern exists with sending military submarines, deep-sea vessels, and autonomous underwater vehicles beneath the ocean’s surface.

They are unable to use the satellite GPS (Global Positioning System).

GPS satellites orbiting our planet at an altitude of approximately 12,600 miles transmit radio signals to the Earth’s surface at the speed of light.

These satellites provide the military (and us) with continuous ‘round-the-planet surface location coverage.

Unfortunately, a GPS radio signal is unable to travel through seawater to reach submerged vessels.

They occasionally need to rise to the surface in order to get an accurate GPS “fix” on their location.

One risk associated with an undersea vessel coming to the surface includes the opportunity for a potential enemy to detect it.

Even if it remains in shallow water and raises its mast or radio-signal receiver pole above the water’s surface to obtain GPS signaling, it still risks detection.

Another obstacle an undersea vessel may face when surfacing, is having its reception of satellite GPS signals intentionally blocked or jammed.

Underwater vessels are able to stay submerged while tracking their location using undersea navigational sensors, DVL (Doppler Velocity Log), and computing devices equipped with navigation grade IMU (Inertial Measurement Units).

Nevertheless, these methods will not reliably keep track of an undersea craft’s precise location over long periods.

Occasions arise when the location algorithmic guidance data being used as a reference needs to be “refreshed and updated” using the precise and accurate triangulated tracking information obtained by the satellite GPS.

The monetary costs, along with the internal power requirements an underwater vessel expends for using state-of-the art, undersea navigational sensors are, according to information I’ve read: “significant.”

To save time, money, and possible intentional attack upon underwater vessels, the US military wants to install a system similar to today’s satellite GPS network under the oceans’ surface.

The US Department of Defense solicited classified and unclassified research proposals for their Positioning System for Deep Ocean Navigation (POSYDON) program under DARPA (Defense Advanced Research Projects Agency).

POSYDON calls for an “omnipresent and robust” underwater location positioning system, using a number of “acoustic sources” or devices analogous to GPS satellites.

By having an array of underwater acoustic or sounding source-devices acting similar to the platform used with the current satellite GPS, undersea vessels will be able to maintain accurate location positioning without the need for surfacing.

The 48-month POSYDON program is modeled into three phases:

1. A preliminary design focused on signaling processing and ocean modeling.

2. Developing and validating a real-time acoustic ranging capability.

3. A demonstration of real-time positioning, an integrated system demonstration, and validation of all POSYDON components by US Government team members.

The first phase began 12 months ago.

DARPA states the implementation of the POSYDON program will comply with “all applicable laws and regulations protecting marine life, including Executive Order 12114, Endangered Species Act, and Marine Mammal Protection Act.”

For those who are curious, Executive Order 12114: Environmental Effects Abroad of Major Federal Actions, was signed on Jan. 4, 1979, by President Carter.

I, for one, am glad the government made GPS available to the public.

As yours truly wrote in February 2013; “Originally, GPS started out as being used exclusively for the US military.

That changed in May 2000, when President Clinton ordered the US military to stop scrambling the signals coming from the GPS satellite network. This allowed GPS navigational information to become available for all of us.”

As I conclude this week’s column, I acknowledge appreciation for having GPS in my car.

Without it, I would still be stopping at gas stations to ask directions.

I also value the time GPS saves me from trying to correctly refold the paper highway map so it can neatly fit back into the glove compartment.

Will a future underwater navigational system become available to the public, like the existing satellite GPS?

The official response given in the POSYDON research solicitation’s Q&A paper is: “Unknown at this point.”

The US Government informational GPS website is: http://www.gps.gov.

You can easily locate this above-the-water columnist on Twitter via my @bitsandbytes handle.

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