A Reassessment of the In-Situ Dielectric Constant of Polar Firn
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
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The success in using VHF and UHF frequency systems for sounding polar ice sheets has been tempered by an uncertainty in the in-situ dielectric constant Epsilon which controls the effective velocity V sub e of an electromagnetic wave propagating in an air-ice mixture. An empirical equation for determining Epsilon vs. density specific gravity, p was proposed in 1968 by Robin et al. where Epsilon1 0.851 rhosq. However, this expression has met with uncertainty because wide-angle radar refraction sounding techniques have produced values of Epsilon that are lower than Robins equation predicts. This report discusses radar soundings made on the McMurdo Ice Shelf, Antarctica, and compares the resulting Epsilon values with Robins equation, laboratory measurements on firn and ice and other expressions given in the literature for determining Epsilonvs. the specific gravity of dry firn and ice. Our findings indicate that the form of Robins equation is valid. However, our analysis also indicates the expression could be slightly improved to read Epsilon 1 0. 845 rhosq. Reasons are suggested as to why previous wide-angle radar sounding studies did not reproduce Robins findings. Glaciology, Antarctica, Firn, Ice shelves, Dielectric constant, Glacial sounding Radio echo sounding.
- Snow, Ice and Permafrost
- Radiofrequency Wave Propagation