Thursday, April 26, 2012

Yeti at Old Pole: Part I

When last I posted, Yeti was off to a moonlighting gig at South Pole Station.  Here I'll talk a little bit about the history of the station, and about Yeti's great success there this past season.

South Pole Station

More formally called Amundsen-Scott South Pole Station, the site of American-owned scientific research stations is located at the southernmost latitude of the world — the Geographic South Pole.  As with most "box-sitting-on-snow" structures located in Polar regions, the original station, built in 1956 is now buried and partially demolished under the snow.  The new station, or "New Pole" was built in 2003 in a better location, this time sporting elevated building designs to prevent burial during accumulation seasons and from snow and ice advection.

Artist's rendition for plans of the original Amundsen-Scott South Pole Station in 1956.  Hervey Garrett Smith (© 1957, National Geographic Society), from

In 2010, the buried structures from "Old Pole" were demolished using explosives, in efforts to remove vacancies and voids that would be hazardous to vehicle traffic.  This need was determined after one situation in which a tractor meandered over the area resulted in a collapse of the overlying snow, requiring a rescue vehicle to retrieve the fallen.  As the rescue tractor approached, it too succumbed to an unknown void from buried passageways from the Old Pole structures.

Before they set the charges to blow 325 ft by 80 ft craters over the structures, a GPR survey was performed to locate them.  Subsequently after blasting, the accumulation season filled the crater to the surface.

More info on the Old Pole blast can be found on the Antarctic Sun.

Yeti at Old Pole

Yeti was called in to duty for this GPR survey because of his obvious prowess in these types of situations: requirements of low ground pressure, complex survey patterns, GPR towing, and of course, taking human risk completely out of the picture.   

Yeti arrived at Old Pole on Dec 3 2011, and performed his surveys according to pre-programmed GPR waypoint files.  Typically, the GPS received information from 10 - 12 satellites and reported position accuracies of 2 - 10 ft., excellent results for 90 deg south.   Yeti displayed excellent mobility over natural snow near the site and performed well, mechanically and electrically, after being left outside each night at temperatures ranging from -29C to -33C.

Yeti conducting his survey at Old Pole.  Courtesy of Jim Lever 2011

Yeti conducted his autonomous GPR surveys in grid patterns on three successive days. The first two grids crossed the site roughly north-south and the third grid crossed it east-west. He collected GPR and GPS-position data concurrently. The consistent speed of the rover (~ 2.7 mph) combined with GPR settings tuned for the site (including scan acquisition rate, snow dielectric permittivity, and pulse time window) produced high quality GPR data. Yeti's small footprint and turning ability allowed him to execute closely spaced transects more easily than a manually operated platform such as a Pisten Bully or Tucker tractor.

GPR data files and GPS track maps were transferred during early evening satellite passes for expert analysis by Allan Delaney (my mentor in Greenland), who was located in Texas. Limited evening satellite access set the day’s schedule to ensure that all data were available for off-site review before the next day’s surveys. In all, over 325MB of data were transmitted and reviewed remotely.

The GPR data files were reviewed to determine the effectiveness of last year’s blasting, and to identify whether any potential subsurface hazards remain. Knowledge and experience from crevasse detection during overland traverses played an important role in reviewing the GPR data, since Yeti was essentially searching for voids just as he does in the shear zones.

In the next post, I'll talk about what Yeti found, and how he was beneficial to this effort.