Journal oIG/aci%gy, Vol. 14, No. 7I, I975 INTERNAL REFLECTIONS IN POLAR ICE SHEETS
ABSTRACT. Internal refl ections a re due to changes in elec trical admittance b e tween adjacent d epositional layers. R eflection coeffi cients are given for discontinuous changes in either the p ermittivity or loss ta ngent. The observed strengths of internal ech oes rule out the p ossibility tha...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.458.2623 http://www.igsoc.org:8080/journal/14/71/igs_journal_vol14_issue071_pg251-259.pdf |
| Summary: | ABSTRACT. Internal refl ections a re due to changes in elec trical admittance b e tween adjacent d epositional layers. R eflection coeffi cients are given for discontinuous changes in either the p ermittivity or loss ta ngent. The observed strengths of internal ech oes rule out the p ossibility tha t they are caused by isolated layers contain ing " foreign " m a terial, but suggest instead that they are due to sys tematic fluctua tions of density, a niso tropy, or loss ta ngent. The electrical b ehaviour of ice from polar ice shee ts is reviewed and compa red with tha t of ice grown in controlled laboratory conditions. 'vVe suggest that the impurity distribution in polycrystalline ice is dependent on the impuri ty content and the temperature of freezing, and the conductivity is essentia lly determined by the intrinsic and impurity defects within the crysta l lattice. In a polar ice sh eet, dens ity fluctua tions d ecrease with depth, whereas I03S tangents (and hence their fluc tuations) increase since the ice becomes warmer towards bedrock. E cho strengths in centra l Antarct ica a re compared w ith those calculated for a boundary where either a ll bubbles disappear or the loss ta ngent ch anges by 50 %. Assu m ing a consta nt layering geometry to 2 700 m depth, dens ity flu ctuations account for ech oes above I 500 m, but d eep er echoes are b es t explained by variations in the ice conductivity. R EsuME. Rejlexiolls intemes dalls les calottes de glace /Jolaires. L es refl exions in ternes sont provoquees p ar des changements de resistivite electrique entre les couches d e d epots successives. Les coeffi cients de reflex ion |
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