Leap-frogging is a method for team ground navigation that allows for long-distance movements into GPS-denied regions with the potential for high positional tracking accuracy, and in practice is a simple and straightforward concept. Leap-frogging is a dead-reckoning technique that might best be understood as a hybrid navigation method combining various features of orienteering, field surveying, and coordinated positioning. In its simplest scheme, two people are necessary, plus a way to measure distances and directions/heading. Starting from a known position, one person remains stationary while the other person walks some distance (e.g. 25 to 75 meters) into the region of interest, before stopping to serve as a temporary target or waypoint. From the starting position, the far person’s distance and bearing are measured. These measurements provide a vector relative to the starting position, thus giving a high-precision estimate of the new position. Once the data is recorded, the person at the start is released to move forward to the same position as the other, who remains immobile until overtaken by the walker. The walker can leap farther ahead, or trade places, and this measurement process is repeatedly indefinitely for each segment of the journey. The key is that all times, one node is immobile during any movement of the other (i.e., serving as a temporary anchor), which preserves and then propagates the positional estimate for each measured segment of the journey. This approach is scalable and can be extended to more than 2 persons as shown below as an example for 4 persons. Leap-frogging provides a way to propagate a known position far forward into GPS-denied territory. Bearings or directions could be measured using a mechanical sighting compass, a digital compass, or using a theodolite or total-station type of portable protractor device. Distances can be measured using step-counting tech, laser ranging, acoustics, Ultra-Wide Band (UWB) radios, or other suitable ranging method. The higher precision (and ease) offered by the distance and/or direction measurements, the better. To assess the operational performance of collaborative localization (coordinated leap-frogging), experimental 2-person and 6-person leap-frogging exercises were carried out.
For the 2-person method, a military grade laser rangefinder with inbuilt digital compass was used to provide distance measurement between 2 nodes. This 2-person laser ranging leap-frogging was performed with assistance of a mobile application which computed the updated position vector automatically. See figure below for a screen capture of the mobile device during the experiment. Each blue arrow represents a captured vector for the leap-frog. At the end of the journey, the GPS coordinate at the end point was used to determine the error and the error was 1.8% and 2.9% at two different locations.
For the 4/6-person leap-frog, UWB nodes were used to automatically log the inter-nodal distances and using trilateration, the moving nodes were computed from the stationary nodes. Hence each person needs to carry a special vest and cap that contains the UWB and supporting electronics. In the experiment performed in Eastwood Metro Park in Dayton, Ohio as shown below, the final error (3m) was an impressive 0.65% over 470m.
About SUSTAIN Challenge
The Singapore-U.S. Tactical All-Inclusive Navigation (SUSTAIN) was a one-year effort with military scientists from both Singapore and the United States tackling the problem of navigation for dismounted war fighters when operating in situations in which information from Global Navigation Satellite Systems (GNSS) is degraded or denied. The nine members of the SUSTAIN had a diverse technical background, from psychology to autonomous robotics (I was one of the members). Under the guidance from several technical mentors, the team was tasked to work as a single team rather than a group of distributed teams. The team performed ideation, concept selection, concept testing, prototype development, and field testing, which culminated in a final demonstration of their products. The developed products included cell phone apps for performing orienteering functions; a man-portable relative positioning system using lasers or radio ranging combined with movement schemes of team members; an infrasound detection and direction-finding positioning system for tactical use; and a custom sextant attachment that turns a smart phone into a stellar positioning device. Both absolute and relative innovative navigation concepts were explored, tested, developed, and demonstrated. Outputs from the effort included six invention disclosures, several technical conference papers and presentations, and a final technology field demonstration.
- Wright-Patterson Air Force Base News, “SUSTAIN project tasks AFRL, Singaporean scientists to solve complex challenge,” 20 Sep 2016.
- J. P. McIntire, F. C. Webber, D. K. Nguyen, Y. Li, S. Foong, K. L. Schafer, W. Y. Chue, K. Ang, E. T. Vinande and M. M. Miller, “LeapFrogging: A Technique for Accurate Long-Distance Ground Navigation and Positioning Without GPS,” NAVIGATION, Journal of the Institute of Navigation, 2018.
- F. C. Webber, K. H. Schafer, E. T. Vinande, J. P. McIntire, D. D. Jensen, S. Foong, W. Y. Chue, Y. Li, K. Ang, R. H. Crawford and G. H. Wong, “Singapore-U.S. Tactical All-Inclusive Navigation (SUSTAIN) collaborative innovation,” 2016 ASEE International Forum, New Orleans, Louisiana. https://peer.asee.org/27256
- J. P. McIntire, F. C. Webber, D. K. Nguyen, Y. Li, S. Foong, K. L. Schafer, W. Y. Chue, K. Ang, E. T. Vinande and M. M. Miller, “LeapFrogging: A Technique for Accurate Long-Distance Ground Navigation and Positioning Without GPS”, ION Pacific PNT 2017, Honolulu, Hawaii.