Geophysical experiments in periglacial environments: Devon Island, Nunavut
Carlos E. Nieto, Robert R. Stewart
In the summer of 2003, various 2D and 3D ground-penetrating radar surveys were acquired at two different locations around the NASA Haughton-Mars Project base camp on Devon Island, Nunavut. The objective of the project was to obtain high-resolution images to understand shallow subsurface structure periglacial environments. We used a Sensors and Software Systems NOGGIN 250 MHz GPR equipment to record the data. It has a constant antenna separation of 0.28 m and allows a real-time display of the data that has been acquired.
A calibration experiment using rebar as a point diffractor was used to define a velocity model of the thawed layer of the area. We found an average velocity of 0.065 m/ns for this layer, which correlates with standard velocities reported for this type of material. At the same site, a 3D GPR over a 10 m2 area shows the lateral distribution of the thawed-frozen ground interface. The thickness of this layer varies from 0.60 m to 0.78 m. Diffraction patterns at different locations are interpreted to be caused by the presence of ice lenses or cobbles at the permafrost top. An absence of data between adjacent lines in both direction of the 3D was solved by interpolation. A quasi-3D GPR was acquired at a site characterized by water saturation, which has the effect of supplying heat to the ground and is observed in this volume by a relatively deeper thawed-frozen ground interface. The depth values range from 0.7 m to 0.9 m.