A comparison of seismic and radar methods to establish the thickness and density of glacier snow cover

Abstract

AbstractWe show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciären, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from ∼120 to ∼500 kg m–3(with a +50 kg m–3anomaly between 0.73 and 0.83 m depth). Depths estimated for two detectable GPR reflectors, 0.76 ±0.02 and 1.71 ± 0.03 m, correlate extremely well with ground-truth observations. Refraction seismic predicts an interface at 1.90 ± 0.31 m depth, with a refraction velocity (3730 ± 190 ms–1) indicative of underlying glacier ice. For density estimates, several standard velocity-density relationships are trialled. In the best case, GPR delivers an excellent density estimate for the upper snow layer (observed = 321 ± 74 kg m–3, estimated = 319 ± 10 kgm–3) but overestimates the density of the lower layer by 20%. Refraction seismic delivers a bulk density of 404 ±22 kgm–3compared with a ground-truth average of 356 ± 22 kg m–3. We suggest that geophysical surveys are an effective complement to mass-balance measurements (particularly for controlling estimates of snow thickness between pits) but should always be validated against ground-truth observations.