Autonomous GPR Surveys using the Polar Rover Yeti • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • J. H. Lever and A. J. Delaney U. S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755 L. E Ray Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755 E. Trautmann Neuroscience Program, Stanford University, Stanford, California 94305 L. A. Barna and A. M Burzynski U. S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755 Received 29 May 2012; accepted 29 October 2012 The National Science Foundation operates stations on the ice sheets of Antarctica and Greenland to investigate Earth’s climate history, life in extreme environments, and the evolution of the cosmos. Understandably, logistics costs predominate budgets due to the remote locations and harsh environments involved. Currently, manual ground-penetrating radar (GPR) surveys must preceed vehicle travel across polar ice sheets to detect subsurface crevasses or other voids. This exposes the crew to the risks of undetected hazards. We have developed an autonomous rover, Yeti, specifically to conduct GPR surveys across polar ice sheets. It is a simple four-wheel- drive, battery-powered vehicle that executes autonomous surveys via GPS waypoint following. We describe here three recent Yeti deployments, two in Antarctica and one in Greenland. Our key objective was to demonstrate the operational value of a rover to locate subsurface hazards. Yeti operated reliably at −30 ◦ C, and it has has good oversnow mobility and adequate GPS accuracy for waypoint-following and hazard georeferencing. It has acquired data on hundreds of crevasse encounters to improve our understanding of heavily crevassed traverse routes and to develop automated crevasse-detection algorithms. Importantly, it helped to locate a previously undetected buried building at the South Pole. Yeti can improve safety by decoupling survey personnel from the consequences of undetected hazards. It also enables higher-quality systematic surveys to improve hazard- detection probabilities, increase assessment confidence, and build datasets to understand the evolution of these regions. Yeti has demonstrated that autonomous vehicles have great potential to improve the safety and efficiency of polar logistics. C  2012 Wiley Periodicals, Inc. 1. INTRODUCTION The National Science Foundation, Office of Polar Programs (NSF-OPP) operates stations on the ice sheets of Antarctica and Greenland to investigate Earth’s climate history, life in extreme environments, and the evolution of the cosmos. Understandably, logistics costs predominate budgets due to the remote locations involved and the need to ensure safety in these demanding environments. Recently, NSF-OPP has implemented oversnow tra- verses to resupply its polar science stations to reduce costs and air emissions compared with airlift operations (Lever & Weale, 2011). The South Pole traverse (SPoT) and the Green- land Inland traverse (GrIT) each consist of large, rubber- tracked tractors towing sled trains directly over natural snow surfaces (Lever & Weale, 2012). Both traverses cross glacial ice fields where ice movement creates crevasses (ver- tical fractures) in the ice but frequent snow storms bridge the crevasses as they slowly open. The surface snowfields Direct correspondence to: J. H. Lever, e-mail: james.lever@us .army.mil; L. E Ray, laura.e.ray@dartmouth.edu. can thus show no visual signs of underlying crevasses large enough to pose hazards to vehicles and people (2–10 m width, 20–50 m depth). Surface-deployed ground penetrating radar (GPR) has provided an effective tool to detect hidden crevasses and other voids in glacial ice for the past 20 years (Arcone & Delaney, 2000; Delaney, Arcone, & Blaisdell, 1996; Delaney, Arcone, O’Bannon, & Wright, 2004). Typically, a manually driven vehicle pushes a GPR antenna, and the GPR op- erator interprets the real-time sequence of radar returns to identify approaching hazards. The operator must command the driver to stop within a 2–3 s window if the approach- ing hazard is not clearly safe to cross. Needless to say, this places great stress on the crew and caution must prevail, increasing survey time in heavily crevassed areas. Hazards can also go undetected, especially if they present unusual GPR signatures in complex terrain (Figure 1). We have developed an autonomous rover, Yeti, specifi- cally to conduct GPR surveys to detect subsurface hazards in polar ice sheets (Trautmann, Ray, & Lever, 2009). It is a simple four-wheel-drive vehicle equiped with the same GPR system as used manually for SPoT and GrIT (Figure 2). Journal of Field Robotics 30(2), 194–215 (2013) C  2012 Wiley Periodicals, Inc. View this article online at wileyonlinelibrary.com • DOI: 10.1002/rob.21445