A Reassessment of the In-Situ Dielectric Constant of Polar Firn

• Main Authors: Kovacs, Austin, Gow, Anthony J., Morey, Rexford M.
• Other Authors: COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
• Format: Text
• Language: English
• Published: 1993
• Subjects: Snow; Ice and Permafrost; Radiofrequency Wave Propagation; *POLAR REGIONS; *ICE FORMATION; *ICE; VELOCITY; DENSITY; MEASUREMENT; ECHOES; REFRACTION; ULTRAHIGH FREQUENCY; RADIO SCANNING; SPECIFIC GRAVITY; SOUNDING; VERY HIGH FREQUENCY; WIDE ANGLES; GRAVITY; GLACIOLOGY; UNCERTAINTY; DIELECTRICS; ELECTROMAGNETIC WAVE PROPAGATION; RADAR; FIRN ICE; ICE SHELVES; McMurdo Ice Shelf; Rho; Antarc*; Antarctica; Ice; Ice Shelf; Ice Shelves; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA276999; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA276999

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 Epsilon'=(1 + 0.851 rho)sq. However, this expression has met with uncertainty because wide-angle radar refraction sounding techniques have produced values of Epsilon' that are lower than Robin's equation predicts. This report discusses radar soundings made on the McMurdo Ice Shelf, Antarctica, and compares the resulting Epsilon' values with Robin's equation, laboratory measurements on firn and ice and other expressions given in the literature for determining Epsilon'vs. the specific gravity of dry firn and ice. Our findings indicate that the form of Robin's equation is valid. However, our analysis also indicates the expression could be slightly improved to read Epsilon' = (1 + 0. 845 rho)sq. Reasons are suggested as to why previous wide-angle radar sounding studies did not reproduce Robin's findings. Glaciology, Antarctica, Firn, Ice shelves, Dielectric constant, Glacial sounding Radio echo sounding.