ИСТИНА

The investigation of permafrost is one of the most important and significant fields of contemporary science. A specific type of ground ice are ice wedges, which exhibit a characteristic wedge-shaped geometrical structure and form in successive thaw- and freeze cycles during several years. Ice wedges are common in permafrost areas, where they build the typical polygonal patterned ground. Geophysical methods are widely used in permafrost areas since the late 1970s. Ground-penetrating radar is a non-destructive geophysical method, which uses reflected radio waves to probe the ground. It was designed specifically for shallow (rarely more than 10 m) subsurface investigations. The measurement consists of a transmitter and a receiver in a fixed geometry, which are moved over the surface to detect reflections from subsurface features. The high dielectric contrast between the electromagnetic properties of ice, water and sediments determines the possibility of identifying the boundaries between melt and frozen grounds on the ground-penetrating radar data (profiles), as well as local objects such as ice wedges. If radar waves meet a boundary between two materials with a different permittivity or a local object, a part of the energy is reflected. However, when investigating ice wedges, ground-penetrating radar data typically show complex reflection patterns. Despite the abundant occurrence of ice wedges in permafrost landscapes and the wide use of ground-penetrating radar in these environments, imaging of ice wedge geometry has not been well studied yet. The question is what features in field data can help to identify the location and the width of ice wedges? Numerical modeling, as a rather new technology, can help to examine different factors influencing wave propagation and the observed reflection patterns. However, synthetic models are not sufficient to display the features that could appear in a real field data – in these cases, the physical modeling can help scientists. Here we present the study, which focus was on the identifying the signs of ice within subsurface with the help of physical modeling. In conjunction with my colleagues from Potsdam University we constructed the 3D wedge from Styrofoam and put it into the water and into the sand – such host mediums were less complex than real field conditions, but it allowed us to detect even out-of-plane reflections, which are typically below signal-to-noise ratio. We wanted to confirm current assumptions (hyperbolic wave patterns) and find new features that can be used to evaluate the shape and size of ice body. Using classical survey system, we got high quality results, which we used to formulate the signs of the presence of ice in the medium according to the ground penetrating radar data. We used the PulseEkko Pro GPR system, comprising two separate 1 GHz antennas acting as transmitter and receiver for physical modeling. A modeling set was presented by plastic tank with a size of 1.1 m × 0.9 m × 0.5 m; the host medium and a wedge model were located in the tank, GPR data were collected above the tank. To ensure accurate and repeatable positioning of the antennas, we guide the antenna sledge by plastic tracks. Positioning data are measured by a self-tracking total station (TPS1200; Leica Geosystems). We thank Jens Tronicke (Universität Potsdam) and Mikhail Vladov (Lomonosov Moscow State University) for comments and discussion.