Denied GPS
LOOKING FOR NAVIGATION AIDS THAT CAN SUPPLEMENT OR REPLACE GPS, ESPECIALLY IN SITUATIONS WHERE GPS CANNOT BE ACQUIRED.
Special forces often operate in areas where they cannot obtain accurate tracking information from Global Positioning System (GPS) satellites, whether because their signal cannot penetrate the theater of operations or because the enemy is jamming them.
No fewer than three agencies within DoD have begun programs to overcome the problem of denied GPS in recent months, with the Office of Naval Research (ONR) most recently closing its broad agency announcement for navigation in a GPS-denied environment on March 30.
ONR is attempting to develop a program specifically for use by the Marine Corps because the Marines are more frequently operating inside buildings or caves where no GPS signal is available, Nathan Smith, project officer in ONR Code 30, Expeditionary Warfare and Combating Terrorism, told Special Operations Technology. “It is what they refer to as the urban canyon problem,” Smith explained. “A GPS receiver depends on being able to see some number of satellites in the sky. When you are inside a city with large buildings on the sides, it blocks a considerable amount of sky. The GPS signals do not travel through buildings.”
So the goal of the ONR program is to develop a handheld device that uses something other than GPS for Marines to use to identify their locations.
According to the ONR solicitation, “Nominally, each Marine will carry a lightweight device capable of reporting its own location and the location of the other members of its clique—where a clique is defined as a group of devices/Marines that are operating together. These devices cooperate with each other in order to determine their relative positions.”
Even partial or temporary access to GPS, however, would aid the determination of relative positions in these scenarios, Smith stated. “We can use GPS for an initial fix to set an absolute position, but then after that what we are depending on is some product being able to tell us that a fire team has moved into position, say, on the other side of a building,” he said. “Then we can share positions inside fire teams and small groups as they operate in a dispersed manner, say, within a kilometer or so.”
ONR also hopes to obtain some limited ability to fix the relative locations of personnel underground, which is complicated by the fact that few signals will penetrate well in most underground environments, Smith said. ONR’s goal is to obtain a fix on locations within about 100 meters of an underground entrance.
The Defense Threat Reduction Agency (DTRA) also had issued a request for proposals on GPS-denied navigation and mapping for its SOF Venture Program. The DTRA solicitation spelled out the data warfighters require to fix their location in an environment without GPS.
“Within these environments, military personnel conduct missions that require them to have the capability to accurately maintain one’s position while moving, either in reference to absolute coordinates [latitude, longitude, altitude] or relative coordinates [x, y, and z axes]” the RFP reads. “They also require the capability to accurately determine and produce the three-dimensional spatial shape of the traversed environment referenced to the individual’s position.”
DTRA originally planned to issue up to two contract awards by May 1 for manportable navigation systems that could precisely navigate and map terrain over long distances for long periods of time with minimal errors where GPS is not available. As of this issue the contract(s) have not been awarded but were currently anticipated by the end of August.
In efforts dating back to at least 2004, the Defense Advanced Research Projects Agency (DARPA) had sought manufacturers for navigation-grade integrated micro gyroscopes that could yield inertial measurement units small enough to enable small platforms (including unmanned or underwater vehicles) or individual soldiers to track their locations without GPS.
Such an inertial unit could track the progress of a vehicle or soldier from an original fixed location. The entire world got a taste of what these units are currently capable of doing in the recent DARPA Grand Challenge, which pitted unmanned ground vehicles in a race over difficult terrain.
INERTIAL NAV
The 2005 Grand Challenge took place October 2005, the southwestern United States. Applanix Corp., based in Ontario, Canada, supplied its Position and Orientation System, Land Vehicles (POS LV) integrated inertial/GPS system to vehicles built by Carnegie Mellon University, which took second and third place in the race.
“DARPA tried to make it incredibly difficult for people to rely solely on GPS, so they put a bunch of obstacles, some manmade, some natural, to basically deny GPS in certain areas of the course. Some people fared miserably, but the top four teams were basically able to successfully navigate, and all of them had an inertial navigation system onboard,” said Louis Nastro, Applanix director of land products.
By 2015, one-third of all U.S. forces must operate autonomous platforms for use in particular missions, Nastro noted.
“Anytime we can automate the job of the special operations operative, keeping them out of harm’s way is what this is all about,” Nastro said. “A special operator is a high-value asset. Looking at some of the work that has already been done, special forces are already using autonomous vehicles to a great extent—for reconnaissance especially.”
In the Grand Challenge, competitors combined the longitude, latitude and altitude readings of GPS with technologies like laser sensors, which provided some information on orientation in addition to detecting obstacles in front of the vehicles.
“If you are going five miles per hour, orientation is not very important. It’s basically your position,” Nastro explained. “However, when you are going 40 or 50 miles per hour with an autonomous vehicle, orientation becomes very critical because that will give you your roll, pitch and heading. With the roll, pitch and heading, knowing it at a very robust rate, you can understand exactly what the vehicle dynamics are with respect to its position in real time.”
When GPS is unavailable, the Applanix inertial navigation system relies upon accelerometers and gyroscopes to provide information on rate of change and velocity. Those figures, computed in 6 degrees of freedom, can accurately reveal roll, pitch and heading. Using GPS or partial GPS provides a check against the initial navigation calculations, preventing the growth of any error rate from becoming too big.
In cases where GPS is completely unavailable, a distance-measuring instrument can provide a check against any margin of error in the inertial navigation system, Nastro added. In the Grand Challenge, for example, the Carnegie Mellon vehicles used a wheelmounted encoder, which measures pulses per revolution and feeds the data into a composite computer system.
Applanix has also manufactured some man-portable inertial navigation backpacks, used primarily for surveying sites where GPS was unavailable.
PENETROMETRY AND ALTIMETRY
The software algorithms that enable sensors to work together in a GPS-denied environment ensure accuracy in the developing data that substitute for GPS readings. L-3 Communications focuses on these algorithms as the key to successful navigation through its subsidiary Interstate Electronics Corp. (IEC), based in Anaheim, Calif.
IEC is a navigation company that works with a number of sensor technologies, including devices such as altimeters, Doppler velocimeters and some penetrometry applications, according to Steve Rounds, IEC senior director of advanced technology.
“So there are a variety of sensors out there, but what we think we have added to it is the ability, in a network environment, to really integrate all of the navigation data that is available across the network, so that in [an] environment where you have multiple warriors, all of whom have a little bit of navigation data, we are able to integrate that data together and provide accurate navigation for all of the individuals in the network,” Rounds explained.
An altimeter can measure altitude, providing one axis of the three axes required for successful navigation, Rounds added. A penetrometer coupled with a magnetometer or a digital compass would provide a dead reckoning solution, determining the direction and distance traveled from a specific fixed location. In addition, soldiers could use radio frequency ranging to detect their positions relative to one another.
Some of these solutions work well with access to one or two GPS satellites, which can contribute to a solution even when full access to GPS data is not available, Rounds said.
“The core technology that we bring to this is the algorithms that integrate all of this data together. We are putting that together with hardware,” Rounds said. “We have done demonstrations of this prototype equipment for various people, including, for example, JFCOM [Joint Forces Command]. We gave them a demonstration a short while ago. They are looking at special ops applications.” IEC has not developed a production package for a GPSdenied navigation system yet, but it does have prototypes that it has been able to demonstrate for interested parties, Rounds said. The company has been looking at recent RFPs with an eye toward fielding a production package—a goal that Rounds believes could be easily realized.
“We are targeting handheld devices or wearable devices for very near-term markets. They are battery-powered with battery lives of four to eight hours,” Rounds said. “All of the technology pieces are in hand. I think the solutions for these are not as far off as some people think they are.”
DEAD RECKONING
So important is GPS-denied navigation that its capabilities have been mandated for inclusion in larger systems. In the Army’s LandWarrior systems, being fielded for the first time this summer, every soldier will carry a “dead reckoning” system manufactured for inclusion in the system by Vectronix AG, headquartered in Switzerland.
Jos Van Seeters, Vectronix business development manager for OEM modules, told SOTECH, “The unit they are using is our Dead Reckoning Compass, or DRC. It provides the soldier with position location information in case GPS is not available. This unit is the most basic that we have is based on a compass and accelerometer only. The compass function provides the direction and the accelerometer provides the distance traveled, which allows you to calculate a new position from the previous position.”
The DRC is very small, intended for use in systems like the portable LandWarrior suite, which is designed for a dismounted soldier. The DRC module is about 1.25 inches square and about half an inch thick.
Vectronix also has a more advanced product called the Core Navigation Module (CNM), which builds on the DRC through the addition of a gryo that can support the determination of directions when the compass becomes unavailable due to a magnetic disturbance of some kind. A simple magnetic disturbance can occur around a compass simply by standing next to a tank or some other large piece of equipment that contains metal or generates electrical fields. The CNM also is very small—about oneinch square on all sides as a cube. It also has input for GPS in the event that it is available.
“The goal of the system is to stay low cost,” Van Seeters explained. “You do not work with the highest grade components on the market. That would increase the price tremendously. So that only allows you a medium-grade gyro to work for a small amount of time in a magnetically disturbed environment.”
Lou Shadle, Vectronix public relations director, added that the company is very experienced with working with the small components that make up these man-portable systems. “One of the core competencies of the company is the ability to work with sensors of such small size to integrate those into a package that has the kind of flexibility that we deliver with this platform,” Shadle said.
The industrial base of companies manufacturing GPS-denied navigation is very small, Shadle noted, placing a highly concentrated amount of expertise within a few programs. “Think about operating in caves in Afghanistan or jungle environments or urban environments, where GPS is not visible,” Shadle said. “So the military side is very important, but also think about first responders, where literally thousands of firefighters and HAZMAT teams go into urban environments or inside of buildings in crisis situations and the incident commander needs to know where these people are and GPS is not available.
“This is the kind of technology that we are working on, that helps that incident commander identify where his people are so that he can get them out if necessary or understand how long a person has been in a location,” he concluded.
PHOTOGRAMMETRY?
Vexcel Corp., based in Boulder, Colo., is an industry leader in photogrammetry, which involves making quantitative measurements from photographs.
“With any camera, you are going to get some lens distortions,” Bill Gale, marketing manager for Vexcel, told SOTECH. “You know this by the fact that in a typical picture where the alignment should be straight, but it has a curve in it. So if you are going to make measurements from those images, you have to first take out the lens distortion. Then you have to somehow relate the image to some sort of quantitative reference frame.”
In the past, an airplane could fly over a city for the purpose of urban mapping and would snap one or two thousand frames. Someone could spread those pictures out and they wouldn’t line up due to distortions, but Vexcel’s software for its UltraCam solves that problem.
Vexcel would like to engineer a solution that enables warfighters to use photogrammetry to calculate their positions in GPSdenied environments. “Essentially, we wanted to use image data and use photogrammetry with the proper engineering skills and knowledge to allow you extract altitude and heading information from the imagery if you start with some sort of geospatial reference,” Gale explained. “So if you start with a GPS fix and then you move out of GPS range, you could use that imagery to propagate your navigation solution for some length of time.”
Vexcel has used its UltraCam photogrammetric mapping camera for both aerial and close-range applications, Gale added. The company feels that it could explore navigation applications as well with a partner that had experience in internal navigation systems.
“We can provide an assessment of orientation and speed, those sorts of things, based on sequential images,” Gale said.
The UltraCam is one of three large-format aerial cameras available globally, he said. Vexcel is in the process of automating the software that aligns photogrammetric images. Currently, photogrammetric specialists must match up thousands of images to provide services such as urban mapping, but the new software would automate that process and thus revolutionize photogrammetry.
“That is one of the things that would allow us to do it from, say, a UAV if you are trying to do GPS-denied navigation,” Gale said. ♦