Off the shelf, onto the beach: commercial GPS in amphibious combat vehicles

GPS World, April, 2004 by Stephanie Edwards, Marlin Gendron, Maura Lohrenz, Richard Mang

Seeking to take advantage of advances in GPS technology, naval researchers compared traditional waypoint navigation using a standard military GPS receiver and a moving map display with a commercial differential GPS receiver. Field trials showed that the moving map system produced better accuracy and reduced times in navigating test courses.

Operation of amphibious assault vehicles (AAVs) in combat operations is one of the most arduous land navigation challenges faced by military forces. The U.S. Marine Corps' landing craft currently lacks an integrated navigational system. Consequently, AAV drivers have only a small viewing portal, with a dangerous blind spot, through which to see where they are going and the terrain, personnel, obstacles, and perils surrounding them. Their ability to attend to outside visual cues, such as marker buoys, may be seriously diminished by physical barriers such as sea spray, darkness, fog, and other factors.

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Landing craft crew workload can be intense: the driver has numerous electronic devices to monitor, up to 18 infantry Marines to transport, and a relatively narrow lane in which to safely navigate and outside of which may be land mines. Thus, any new systems to be introduced must be very easy to interpret and understand.

Although equipped with radio capabilities, weather conditions do not always allow a crew member to give directions to the driver because of limited or nonexistent line of sight. In the near future, the Marine Corps plans to implement the Data Automated Communications System (DACT) in the AAV platform which would provide some electronic charting capability. However, not all vehicles are scheduled to receive this system. A digital navigation tool, such as a moving map, could aid an AAV driver in controlling the vehicle by displaying the vehicle's current location and track, along with upcoming waypoints and lane boundaries (for example, if the craft tends to drift left, then try to stay to the right side of the lane).

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The Office of Naval Research (ONR) funded the Naval Research Laboratory (NRL) Moving-Map Capabilities (MMC) team (Code 7440.1) Stennis Space Center in Mississippi to equip AAVs with differential GPS (DGPS) moving map systems to test for improvements in lane navigation. NRL planned to accomplish the following tasks:

* Determine what navigation information should be displayed;

* Combine this information with precise lane coordinates;

* Display the lane as an overlay on an electronic chart;

* Evaluate how AAV drivers respond to these displays.

To develop the most reliable and accurate demonstration product possible with the funding available, NRL decided to use commercial off-the shelf (COTS) GPS products. In addition, NRL has developed software to compress different map types and imagery into the Raster Product Format Military Standard (RPF, MIL-STD-2411) to allow bathymetry data, nautical charts, and satellite and acoustic imagery to be loaded on devices that display standard National Imagery and Mapping Agency (NIMA) (recently renamed National Geospatial-Intelligence Agency or NGA) RPF data. The RPF map can display mission specific overlays, such as threat rings, lane markings, possible mine-like objects, and waypoints, to provide enhanced situational awareness. This article describes the results of the DGPS moving map development program and results from associated field trials.

Background

Military GPS receivers have changed profoundly during the past decade, benefiting from the general trend in electronics that produce smaller, lighter, lower-power, and less expensive equipment. A case study performed by the Office of the Defense Standardization Program in 1996 indicated that the AN/PSN-8 Manpack (an Army-developed 17-pound GPS receiver) cost more than $40,000. A smaller, more recent version is the Small Lightweight GPS Receiver (SLGR). During the Manpack's development, commercial GPS receivers became available. The commercial version of SLGR most attractive to the military weighed about four pounds and cost only about $4,000 each. Meanwhile, reasonably priced commercial GPS systems appeared on the market and can now be found virtually anywhere in the United States.

With the May 2000 discontinuance of Selective Availability (SA) based on a March 1996 Presidential Decision Directive, commercial GPS users now have access to a highly accurate, stable system of satellite signals without limitation or degradation by the GPS system operators. This ensures reliability that, until recently, was available only for military use. Consequently, the federal government now can leverage the advances made by commercial producers. Many of the nation's military platforms, including fighter jets, tanks and AAVs, were not designed to support a GPS system. Integration of a commercial GPS product on these platforms may be more appropriate than a military GPS.

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System Components

NRL configured several AAVs with a moving map display connected to a small, portable computer temporarily installed in the rear of the vehicle. The computer is a standard 1.3 GHz PC running Windows 2000that accommodates the AAV's space restrictions. NRL configured the computer to run FalconView, which is the moving map component of the government-owned Portable Flight Planning Software (PFPS). FalconView accepts location input from any National Marine Electronics Association (NMEA) compliant GPS system, Precision Lightweight GPS Receiver (PLGR) data, and Predator unmanned airborne vehicle data. FalconView can display several different map data types, including RPF, standard NIMA charts, and standard National Oceanic and Atmospheric Administration (NOAA) charts.