Abstract:
To understand the subsurface properties of polygonal patterned ground (PPG) and to attempt to resolve competing theories of PPG activity, non-invasive, non-destructive geophysical methods were used to obtain three dimensional images of the subsurface beneath PPG at two sites in the Dry Valleys: Victoria Valley and Beacon Valley. In Victoria Valley an initial reconnaissance of the area was
... completed, two polygon sets and a long transect line was selected for surveys. The first polygon set was surveyed with 3D ground penetrating radar (GPR) and photogrammetry, then with time lapse electrical resistivity tomography (ERT). The second polygon was surveyed with ERT and photogrammetry and then with lapse 3D GPR. Detailed topography was acquired over the second polygon and each polygon set was finally surveyed with horizontal loop electromagnetic system (HLEM) for lateral electrical conductivity variations. The long transect ran from near the top of the ridge to the SW of the upper Victoria Valley to the other side of the narrows in the lower Lake Victoria. The transect was initially profiled using ERT, then a series of contiguous, sometimes overlapping time-domain EM soundings were acquired in the valley along the transect. A deep GPR profile was acquired and a total magnetic field survey line was completed. Finally, the topography of the transect was surveyed. These geophysical images target the deeper bedrock and massive ice targets. In Beacon Valley an initial reconnaissance of the area was completed and two polygons were selected for detailed geophysical imaging and a 1.2km transect running NW-SE across the valley was completed for large-scale deeper structure and stratigraphy. The two polygons were both surveyed using 3D GPR imaging, ERT, HLEM and detailed topography. Deep GPR and ERT profiles, as well as topographic surveys were acquired along the transect. 
