CHIPS Articles: Positioning, Navigation and Timing

Safety of Navigation
Freedom of maneuver is an integral component of achieving superiority in battle, whether on land, on or under the sea, or in the air. Over the last decade, the advent of maritime electronic navigation systems has yielded dramatic improvements in our ability to exploit the battlespace. By integrating digital charts with navigation sensors, these enhancements provide real-time PNT information.

In 1998, the Chief of Naval Operations directed that all commissioned Navy vessels transition from navigating with hardcopy charts to an electronic navigation capability. By 2001, the standards for the Electronic Chart Display and Information System – Navy (ECDIS-N) were established, paving the way for the Navy transition from paper charts to state-of-the-art electronic navigation systems. ECDIS-N combines software and hardware that digitally displays navigation charts overlaid with automated, continuous positioning data, as well as data from ancillary equipment supporting navigation, such as radar, environmental sensors, ship performance parameters and the Automated Identification System. The result is an official, digital navigation plot with enhanced situational awareness tools that facilitate safety of navigation.

Since the first afloat ECDIS-N certification in 2005, the Navy has aggressively pursued the installation of electronic navigation systems across the fleet. Currently, about 78 percent of the surface force and 82 percent of the submarine force are navigating electronically. With the exception of those units scheduled for decommissioning, the remainder of the fleet is scheduled for ECDIS-N certification by the end of fiscal year 2016.

ECDIS-N uses the Digital Nautical Chart (DNC) library, which is produced by the National Geospatial-Intelligence Agency (NGA). DNC is a digital database supported by a portfolio of approximately 5,000 nautical charts covering the maritime domain worldwide. Global Positioning System fixes are automatically updated from shipboard sensors, eliminating the traditional delay inherent with manual plotting on hardcopy charts. DNCs display essential navigation data and can integrate higher resolution data. DNCs of a harbor, for instance, display topographic and bathymetric data, navigation lanes, established navigation aids and fixes, buoys and channels markers, as well as hazards to navigation. A follow-on ECDIS system will be interoperable with NATO vessels, and have the ability to provide both navigational and tactical data to the bridge. It will also include additional military layers of operationally important information such as mine warfare areas, weather warnings and ice extents.

In the aggregate, these capabilities represent a substantial improvement in the Navy’s safety of navigation, and greatly enhance our ability to dominate the maritime battlespace.

Precise Time and the Global Positioning System
Precise and synchronized time is critical for a wide array of services. These include accurate navigation and positioning, the alignment and transfer of digital data across the Internet, and the synchronization of distributed computer networks, communications systems, high-speed financial brokerage and trading networks, and large regional electric power grids.

For the U.S. military, precise timing translates into safer navigation, more accurate unit positioning, putting ordnance on target while minimizing collateral damage, and ensuring the security and bandwidth of communications systems and command and control networks. To make this a reality, time must be known and transferred at the nanosecond level (a nanosecond is one billionth of a second).

The U.S. Naval Observatory (USNO), in Washington, D.C., is responsible for maintaining precise time and making it available to Defense Department users. USNO’s realization of Coordinated Universal Time (UTC(USNO)) is the DoD standard and is the primary time reference for GPS and other military applications. The precision of the USNO’s Master Clock (MC) makes it a popular reference choice for the Internet’s Network Time Protocol (an Internet standard that facilitates the transfer of digital data). The MC is a major contributor to determining UTC, which is the primary international civil time reference.

The MC is an ensemble of dozens of independently operating atomic clocks, including cesium frequency standard clocks, hydrogen masers and rubidium fountains. Its principal backup is the Alternate Master Clock Facility located at Shriever Air Force Base in Colorado Springs, Colo. Most of the world’s timing laboratories do not run continuously, but DoD requires USNO to provide an uninterrupted time reference. No other continuously operating timing service maintains the precision of USNO’s Master Clock.

USNO’s primary means for disseminating Coordinated Universal Time is through GPS, over which more than 95 percent of military users rely for time transfer. USNO monitors the GPS constellation and provides system timing offsets and timing data for individual GPS satellites. There are two levels of GPS services:

• Standard Positioning Service (SPS) is a positioning and timing capability available to all [public] users on a continuous, worldwide basis with no user fees. SPS utilizes the single frequency GPS C/A (Coarse/Acquisition) code in the L1 band, delivering predictable positioning accuracy of 9 meters horizontally and 15 meters vertically, and time transfer accuracy to within 40 nanoseconds of UTC.
• Precise Positioning Service (PPS) is a highly accurate positioning, velocity, and timing capability which is available to authorized military users. PPS utilizes the dual frequency GPS P(Y) code in both the L1 and L2 bands, providing a more robust service than single frequency SPS. It delivers positioning accuracy of 2.7 meters horizontally and 4.9 meters vertically, and time transfer accuracy to better than 30 nanoseconds of UTC. PPS is denied to unauthorized users by the use of encryption.

PNT Fusion and Distribution Systems
The Navy is modernizing its shipboard PNT fusion and distribution systems. The system under development is the GPS-based PNT Services. GPNTS is designed to replace both Navigation Sensor System Interface suites and stand-alone military GPS receivers (WRN-6). GPNTS is scheduled for initial fielding in FY16 and will reach full operating capability in 2029. GPNTS will provide the fleet with more robust PNT in anti-access/area denial environments. Enhancements include the latest Selective Availability/Anti-Spoofing military GPS receivers; digital, nulling GPS anti-jam antennas, and redundant rubidium clocks for synchronized time and frequency. GPNTS is also the lead system for development and integration of maritime domain GPS receivers capable of receiving and using the new military only M-code signal. M-code capable GPNTS systems are expected to be available in 2020.

The Navy’s seven globally-distributed oceanographic survey ships (T-AGS) operate 365 days per year, contributing significantly to a variety of Navy and international maritime missions. Complemented by full-time crews of Naval Oceanographic Office (NAVO) surveyors and technicians, these military survey vessels operate around the world’s oceans gathering high-resolution information for inclusion in nautical charts and bathymetric databases. Their multibeam, wide-angle precision sonar systems make it possible to continuously survey broad strips of the ocean floor. This capability not only yields data for nautical charts, but can also assist in mine countermeasures through surveys to detect changes that may reflect the placement of mines. T-AGS [ships] also measure water, seabed and sediment characteristics to support anti-submarine sonar operations.

Carrying sophisticated equipment for a wide array of scientific disciplines, the capabilities of these versatile ships occasionally translate to humanitarian assistance and disaster relief missions. For example, after the devastating 2010 earthquake in Haiti, severe damage to airports and roads necessitated the use of maritime transport for much of the U.S. and international relief effort. Operating from the sea, however, had its own challenges, as seismic events can create navigation hazards such as collapsed infrastructure and seabed convulsions. For relief vessels to approach Haitian ports, updated hydrographic surveys and navigation charts were needed.

In the case of Haiti, NAVO quickly deployed assets to provide clearance surveys. The first to arrive was the Compact Hydrographic Airborne Rapid Total Survey (CHARTS) aircraft, which used airborne light detection and ranging (LIDAR) technology to survey Haiti’s ports. LIDAR uses narrow laser beams to map physical features at very high resolutions. Unfortunately, LIDAR measurements can be degraded by suspended sediment, water turbidity and underwater vegetation which limit the depth of its effectiveness.

NAVO next dispatched a six-person, rapid response Fleet Survey Team. Using a rigid-hulled inflatable boat from a Navy frigate and two personnel watercraft outfitted with GPS, single-beam echo sounder and sidescan sonar, this team conducted an anchorage survey to clear the way for the hospital ship USNS Mercy (T-AH-19). After that, the team surveyed the approaches and pier depths of nearby terminals.

Finally, USNS Henson (T-AGS 63) arrived on-scene. Henson installed two tide gauges in Port-au-Prince and surveyed the approaches while her hydrographic survey launch examined anchorages and channels. By identifying a narrow channel through a surrounding reef, rescue assets were able to navigate to a nearby beach to establish a landing spot for movement of heavy equipment. Even more recently in January 2013, USNS Bowditch (T-AGS 62) was the first ship to arrive on-scene in the Sulu Sea to assist USS Guardian (MCM 5) after her grounding on the Tubbataha Reef. Bowditch provided logistical support to the grounded vessel, and then conducted survey operations with its complement of scientists and technicians to accurately map the Tubbataha Reef and the surrounding waters. This bathymetric data will be used to update NGA’s nautical charts.

The latest T-AGS vessel, USNS Maury, was christened and launched March, 27, 2013. This ship includes a new feature, a moon pool, which allows access to the ocean from inside the ship and facilitates the launch and recovery of autonomous unmanned vehicles and ocean gliders. These deployable sensors carry sidescan sonars, multibeam sonars, sub-bottom profilers and various other sensors. They can operate in greater sea states than T-AGS ships, and they can operate away from the ship to keep manned vessels out of harm’s way.

Edited from the Information Dominance Corps April 2013 Newsletter.

FOR MORE INFORMATION
U.S. Naval Observatory