Internal Reflections in Polar Ice Sheets
Internal reflections are due to changes in electrical admittance between adjacent depositional layers. Reflection coefficients are given for discontinuous changes in either the permittivity or loss tangent. The observed strengths of internal echoes rule out the possibility that they are caused by is...
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Language: | English |
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Cambridge University Press (CUP)
1975
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Online Access: | http://dx.doi.org/10.1017/s0022143000021730 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021730 |
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crcambridgeupr:10.1017/s0022143000021730 2024-03-03T08:38:48+00:00 Internal Reflections in Polar Ice Sheets Paren, J. G. Robin, G. de. Q. 1975 http://dx.doi.org/10.1017/s0022143000021730 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021730 en eng Cambridge University Press (CUP) Journal of Glaciology volume 14, issue 71, page 251-259 ISSN 0022-1430 1727-5652 Earth-Surface Processes journal-article 1975 crcambridgeupr https://doi.org/10.1017/s0022143000021730 2024-02-08T08:34:04Z Internal reflections are due to changes in electrical admittance between adjacent depositional layers. Reflection coefficients are given for discontinuous changes in either the permittivity or loss tangent. The observed strengths of internal echoes rule out the possibility that they are caused by isolated layers containing “foreign” material, but suggest instead that they are due to systematic fluctuations of density, anisotropy, or loss tangent. The electrical behaviour of ice from polar ice sheets is reviewed and compared with that of ice grown in controlled laboratory conditions. We suggest that the impurity distribution in polycrystalline ice is dependent on the impurity content and the temperature of freezing, and the conductivity is essentially determined by the intrinsic and impurity defects within the crystal lattice. In a polar ice sheet, density fluctuations decrease with depth, whereas loss tangents (and hence their fluctuations) increase since the ice becomes warmer towards bedrock. Echo strengths in central Antarctica are compared with those calculated for a boundary where either all bubbles disappear or the loss tangent changes by 50%. Assuming a constant layering geometry to 2 700 m depth, density fluctuations account for echoes above 1 500 m, but deeper echoes are best explained by variations in the ice conductivity. Article in Journal/Newspaper Antarc* Antarctica Ice Sheet Journal of Glaciology Cambridge University Press Journal of Glaciology 14 71 251 259 |
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Open Polar |
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Cambridge University Press |
op_collection_id |
crcambridgeupr |
language |
English |
topic |
Earth-Surface Processes |
spellingShingle |
Earth-Surface Processes Paren, J. G. Robin, G. de. Q. Internal Reflections in Polar Ice Sheets |
topic_facet |
Earth-Surface Processes |
description |
Internal reflections are due to changes in electrical admittance between adjacent depositional layers. Reflection coefficients are given for discontinuous changes in either the permittivity or loss tangent. The observed strengths of internal echoes rule out the possibility that they are caused by isolated layers containing “foreign” material, but suggest instead that they are due to systematic fluctuations of density, anisotropy, or loss tangent. The electrical behaviour of ice from polar ice sheets is reviewed and compared with that of ice grown in controlled laboratory conditions. We suggest that the impurity distribution in polycrystalline ice is dependent on the impurity content and the temperature of freezing, and the conductivity is essentially determined by the intrinsic and impurity defects within the crystal lattice. In a polar ice sheet, density fluctuations decrease with depth, whereas loss tangents (and hence their fluctuations) increase since the ice becomes warmer towards bedrock. Echo strengths in central Antarctica are compared with those calculated for a boundary where either all bubbles disappear or the loss tangent changes by 50%. Assuming a constant layering geometry to 2 700 m depth, density fluctuations account for echoes above 1 500 m, but deeper echoes are best explained by variations in the ice conductivity. |
format |
Article in Journal/Newspaper |
author |
Paren, J. G. Robin, G. de. Q. |
author_facet |
Paren, J. G. Robin, G. de. Q. |
author_sort |
Paren, J. G. |
title |
Internal Reflections in Polar Ice Sheets |
title_short |
Internal Reflections in Polar Ice Sheets |
title_full |
Internal Reflections in Polar Ice Sheets |
title_fullStr |
Internal Reflections in Polar Ice Sheets |
title_full_unstemmed |
Internal Reflections in Polar Ice Sheets |
title_sort |
internal reflections in polar ice sheets |
publisher |
Cambridge University Press (CUP) |
publishDate |
1975 |
url |
http://dx.doi.org/10.1017/s0022143000021730 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021730 |
genre |
Antarc* Antarctica Ice Sheet Journal of Glaciology |
genre_facet |
Antarc* Antarctica Ice Sheet Journal of Glaciology |
op_source |
Journal of Glaciology volume 14, issue 71, page 251-259 ISSN 0022-1430 1727-5652 |
op_doi |
https://doi.org/10.1017/s0022143000021730 |
container_title |
Journal of Glaciology |
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14 |
container_issue |
71 |
container_start_page |
251 |
op_container_end_page |
259 |
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1792507252524974080 |