Using ground-penetrating radar to image previous years' summer surfaces for mass-balance measurements

In traditional mass-balance measurements one estimates winter snow accumulation by identifying the depth to the previous summer's snow or ice surface using a snow probe. This is labor-intensive and unreliable for inhomogeneous summer surfaces. Another method is to image internal reflection horizons using a ground-penetrating radar (GPR), which has advantages in speed and areal coverage over traditional probing. However, to obtain quantitative mass-balance measurements from GPR images one needs to convert the time scale to a depth scale, not a straightforward problem. We compare a GPR section with dielectric profiles and visual stratigraphy of three snow cores, manual probings, and previous mass-balance measurements. We relate changes in snow-core dielectric properties to changes in density and to the travel times of reflecting horizons in the GPR section, and correlate some of these reflecting horizons with previous summer surfaces. We conclude that GPR can be used as a complementary tool in mass-balance measurements, giving a wide areal survey of winter accumulation and net balance for preceding years. However, proper calibration is essential for identifying specific surfaces in the radar data.