Thursday, November 1, 2012

Yeti at Old Pole: Part II

The Survey:

The figures below show a floor plan for the hazardous areas, and Yeti's survey tracks for exploring the sunken building.

Figure 1 shows a map of the area of interest surrounding Old Pole. It measures about 445’ x 200’ and includes the three blast craters from 2010 (~ 325 ft long x 80 ft wide) and surrounding border areas. The two 2010 vehicle penetrations were at the western (left) end of the site.
Following 2010 blasting operations, South Pole personnel flagged the site (blast crater and ~ 60-ft-wide boarders) and these flags were in place upon our arrival on 29 Nov 11 to delineate the survey area. We acquired the GPS coordinates of the corner flags and divided the boundaries into waypoints ~ 10-ft apart to generate the survey grids.

As seen in the above figure, coverage was comprehensive and more than adequate for site assessment, although not as rectilinear as desired. Simple improvements to the algorithm, such as adding waypoints outside of the survey area to align Yeti for the next pass, would certainly improve grid geometry. Our tight deployment window prevented us from implementing these improvements.

The GPR data files were reviewed by Alan Delaney in Texas to determine the effectiveness of last year’s blasting activities and to identify whether any potential subsurface hazards remain prior to planned backfill- hardening of the area. Familiarity with the 2010 GPR dataset and the Old Pole station layout greatly facilitated the review process. Knowledge and experience from crevasse detection during overland traverses also played an important role in reviewing the GPR data.

The Results:

1. Buildings A15 and A21 at the eastern perimeter of the site, outside of the blast crater, appear to be intact at depths approximately 10-15 ft below the surface.    Figure 4 shows a typical radar sequence across this area. These structures could pose hazards to vehicles.

2. Strong returns in an area approximately 20-ft x 20-ft near the expected location of building A10 suggest an intact building at 11 - 13 ft below the surface. The figure below shows a typical radar sequence. Although this area is just east of the map location of A10, uncertainties in map geo- registration could account for the difference.

The Conclusions:

1. Yeti was an effective platform to conduct GPR surveys over a potentially hazardous site. He operated reliably at temperatures below -30C and displayed excellent mobility over the natural, rough snow surface at South Pole. Simple improvements to his navigation algorithms and software for survey planning will increase his effectiveness at low cost. For specific local sites, such as South Pole and the McMurdo shear zone, adding a differential GPS base station would improve survey accuracy and repeatability. Long-endurance rovers, such as the solar-powered Cool Robot, could similarly perform useful GPR surveys over longer distances in Antarctica to develop safe routes for science and cargo traverses.

2. Off-site data transfer is a feasible way to access scarce GPR interpretation expertise. Data transfer rates from South Pole are adequate for daily analysis and feedback to field personnel. Besides the radar data, track maps (from autonomous or manual surveys) must also be transferred to allow the analyst to form a clear picture of survey conditions. A key advantage for the present study was that the off-site expert had previous experience with the Old Pole site, having conducted the 2010 GPR survey and assessment. However, access to extensive background information, such as drawings, maps, etc., is essential for anyone off-site to develop a clear understanding of the survey. To aid this, the off-site analyst should possess the same Geographic Information System (GIS) package used on-site to map the surveys.

3. Good communication tools, timely review of the data, and follow-up discussions via telephone are essential to ensure an effective survey with off-site analysis. About one day’s worth of review time is needed for each day of survey data collected.