Autonomous Rover for Polar GPR Surveys
Abstract:We deployed Yeti, an 80-kg, 4WD battery-powered rover to conduct ground-penetrating radar (GPR) surveys over crevasse-ridden ice sheets in Antarctica and Greenland. The rover navigated using GPS waypoint following and had 3 – 4 hr endurance at 5 km/hr while towing 60 – 70 kg of GPR equipment. Yeti’s low ground pressure allowed it to cross thinly bridged crevasses without interrupting a survey.
In Feb – Mar 2014, Yeti executed 23 autonomous GPR surveys covering 94 km of terrain on the ice transition to the main ice sheet in northwest Greenland. This was the first robotic effort directly to support manual crevasse surveys to map a safe route for vehicle travel, in this case a resupply traverse to Summit Station. Yeti towed a radar controller, 400 MHz antenna, GPS receiver and battery pack. Radar scan rate was 16 scans/m and pulse timing allowed good spatial resolution to about 20-m depth. The resulting data allowed us to map hundreds of subsurface crevasses and provide the results nightly to the manual survey team to compliment its efforts. We met our objectives: (a) to enhance operational efficiency of the concurrent manual surveys, and (b) to create a geo-referenced database of crevasse signatures to validate aerial- and satellite-based crevasse-mapping platforms.
In Oct – Nov 2014, we deployed Yeti in Antarctica to conduct systematic GPR surveys across a crevasse-ridden section of the shear margin between the Ross and McMurdo ice shelves and thereby gain insight into its state of fracture and long-term stability. Yeti flawlessly executed a total of 613 km of autonomous GPR surveys at temperatures as low as – 33ºC. The rover towed a a radar controlling a 400 MHz and a 200 MHz antenna, the latter added to profile 160 m through the ice sheet. The main survey grid covered 5.7 km x 5.0 km, with survey lines at 50-m spacing oriented west-east across the Shear Zone (575 km total length). Yeti’s tracks normally deviated only 1 – 2 m from a straight line between the two end waypoints. Interpreted features include crevasses up to 16 m wide with snowbridges up to 10 m thick and at least the upper 16 m of stratified marine basal ice.
These autonomous GPR surveys could not have been conducted safely using manual methods owing to the numerous, thinly bridged crevasses. Such systematic, repetitious measurements can enhance other Polar research projects.