(INVITED) GROUND PENETRATING RADAR INVESTIGATION OF ACTIVE LAYER IN CONTINUOUS- AND DISCONTINUOUS- PERMAFROST

摘要

The seasonally thawed soils and sediment in permafrost regions known as the active layer play an important roie in ecology, hydrology, and carbon cycling. Although the active layer is only typically 0.5 m to 2 m thick in Arctic permafrost regions, it nonetheless is the primary locations of hydrologic processes due to the presence of liquid water for at least part of the year. Although direct probe measurements of the active layer are reliable, they are still limited in space as point measurements, and therefore we use ground penetrating radar to obtain high-resolution maps of active layer thickness and water content. By co-locating sporadic probe measurements with ground penetrating radar travel time measurements we obtain velocities to accurately calculate depth, as well as velocity that can be converted to water content using rock physics transforms. Making probe measurement could be limited or restricted due to length of the probe, which is typically 1 m deep, then GPR measurements could be extremely helpful and could give a good idea in frozen ground distribution at greater depth. The GPR measurements is critically important for modeling 2D and 3D transects of a small watershed regions. Using ground penetrating radar, we find that active layer thickness varies considerably even over short distances of several meters indicating feedbacks with surface processes. It is possible to measure thousands of active layer thickness points distributed over kilometers of transect spaced tens-of-centimeters apart in only a few days. Large datasets enable robust statistical comparisons relative to surface vegetation communities and disturbance such as fire. Datasets of this size are also useful for calibrating satellite remote sensing products and making regional-scale comparisons of active layer properties. Here we show comparisons between results from continuous permafrost on the North Slope of Alaska and discontinuous permafrost in the Yukon-Kuskokwim Delta, Alaska.