USING GROUND PENETRATING RADAR TO CHARACTERIZE SOIL FROST

Abstract

Seasonal soil freezing is an important natural perturbation common in cold regions around the world. A thorough evaluation of ecological responses to seasonally frozen ground is hampered by our inability to adequately characterize the frequency, depth, duration and intensity of soil frost events. When soil freezes, its dielectric value drops creating a detectable interface. Ground penetrating radar (GPR) has the potential to nondestructively quantify seasonal soil freezing in forests, though it requires further evaluation before it can be used in ecological applications. A series of test plots were established at sites in Vermont (2) and New Hampshire (1). Each site was fitted with frost tubes (30) to make direct comparisons with GPR estimates of frost depth using a SIR-3000 GPR system equipped with a 900 MHz antenna (Geophysical Survey Systems, Salem, NH) during winter 2011-2012. Half of the experimental plots were shoveled free of snow every other week to increase frost penetration. GPR was able to reliably detect and delineate frost at depths greater than 10 cm. Favorable conditions for GPR include bare soil or shallow snow; while standing water, wet snow and surface thawing interfered with detection. Soil frost was detectable through snow 50cm. The best use of GPR would be intensive campaigns where capturing spatial variability is valuable.