VLF SURFACE-IMPEDANCE MEASUREMENTS FOR ICE-DEPTH MAPPING - AN ASSESSMENT OF SOME COMMONLY ENCOUNTERED INTERFERENCE EFFECTS

The effects on very low-frequency surface-impedance measurements of la teral variations commonly found in ice environments have been measured and modelled numerically using the quasi-static two-dimensional bound ary-element method. Results indicate that surface-impedance measuremen ts made in the vicinity of crevasses oriented perpendicular to the pla ne of incidence. and those made in the vicinity of moraines and melt s treams, can all show significant changes to the measured apparent resi stivity. it is, therefore, misleading to use such measurements in tile interpretation of ice depth.