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2000 Fiscal Year Final Research Report Summary

Research on the radio wave propagation process in the ice sheets and internal structure of the ice sheets.

Research Project

Project/Area Number 11440136
Research Category

Grant-in-Aid for Scientific Research (B).

Allocation TypeSingle-year Grants
Section一般
Research Field Meteorology/Physical oceanography/Hydrology
Research InstitutionHOKKAIDO UNIVERSITY

Principal Investigator

MAE Shinji  Hokkaido Univ., Grad.School of Eng., Prof., 大学院・工学研究科, 教授 (80022672)

Co-Investigator(Kenkyū-buntansha) FUJITA Shuji  Hokkaido Univ., Grad.School of Eng., Inst., 大学院・工学研究科, 助手 (30250476)
GOHARA Kazutoshi  Hokkaido Univ., Grad.School of Eng., Asso.Prof., 大学院・工学研究科, 助教授 (40153746)
Project Period (FY) 1999 – 2000
Keywordsice / dielectric / radio wave / Antarctica / ice sheet / radar / microwave
Research Abstract

The in situ high-frequency limit permittivity of Antarctic ice was measured by a radio-wave propagation experiment using a 2503-m-deep ice borehole. The pulse wave of a 179-MHz radar was scattered from a target moving vertically along the borehole to measure the average phase velocity that was used to determine the high-frequency dielectric permittivity at various depths. This allowed the high-frequency permittivity to be measured on ice at 215-232 K and at hydrostatic pressures of up to 14 MPa. This permittivity was always less than that predicted for ordinary hexagonal water ice (ice Ih). At depths of 300-400m, the permittivity was about 2.98 (±0.04), which is about 0.15 smaller than ordinary ice Ih at the temperature for this depth. The permittivity increased with depth and reached a maximum value of 3.11 (±0.04) at a depth of 800 m. Then it decreased slightly with depth to 3.06 (±0.08) at 1400 m. The effects of reduced density, low temperature, crystal orientation, and typical environmental impurities cannot explain these anomalously low values of permittivity. We suggest two causes for the low permittivity : (1) the suppressing effect by hydrostatic pressure in deep ice that had been proposed theoretically and (2) a change in crystal lattice structure at shallow depths. For (1), we used regression analysis to fit a theorized linearly decreasing permittivity with pressure to our data, and thus propose that the effect of hydrostatic pressure on the permittivity is -3.6 (±2.6) x 10-9 Pa-1. The largest anomalies in permittivity are near the surface ; therefore, a separate mechanism, mechanism (2), is required because the pressure is lowest near the surface.

  • Research Products

    (12 results)

All Other

All Publications (12 results)

  • [Publications] Fujita,S.: "Nature of radio echo layering in the Antarctic ice sheet detected by a two-frequency experiment,"Journal of Geophysical Research, Solid Earth. 104(B6). 13013-13024 (1999)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Fujita,S: "A summary of the complex dielectric permittivity of ice in the megahertz range and its applications for radar sounding"Physics of Ice Core Records (edited by T.Hondoh, Hokkaido University Press). 185-212 (2000)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Sugiyama,K.: "Measurement on electrical conductance in ice cores by AC-ECM method"Physics of Ice Core Records (edited by T.Hondoh, Hokkaido University Press). 173-184 (2000)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 藤田秀二: "大陸氷と惑星氷のレーダーサウンディング-氷の高周波誘電物性からみた現状と将来展望-"日本雪氷学会誌「雪氷」. 62(1). 49-60 (2000)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 藤田秀二: "アイスレーダで読む氷床内部の構造"学術月報 2月号. 54(2). 42-46 (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Siegert,M.J.,Fujita,S: "Internal ice-sheet radar layer profiles and their relation to reflection mechanisms between Dome C and the Transantarctic Mountains"Journal of Glaciology. 未定(印刷中). (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Fujita, S., H.Maeno, S.Uratsuka, T.Furukawa, S.Mae, Y.Fujii, and O.Watanabe: "Nature of radio echo layering in the Antarctic ice sheet detected by a two-frequency experiment"Journal of Geophysical Research, Solid Earth. 104 (B6). 13013-13024 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Fujita, S., T.Matsuoka, T.Ishida, K.Matsuoka, and S.Mae: "A summary of the complex dielectric permittivity of ice in the megahertz range and its applications for radar sounding"Physics of Ice Core Records (edited by T.Hondoh, Hokkaido University Press). 185-212 (2000)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Sugiyama, K., S.Fujita, H.Narita, S.Mae, T.Hondoh, K.Goto-Azuma, D.A.Fisher, and R.M.Koerner: "Measurement on electrical conductance in ice cores by AC-ECM method"Physics of Ice Core Records (edited by T.Hondoh, Hokkaido University Press). 177-184 (2000)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Siegert, M.J., and S.Fujita: "Internal ice-sheet radar layer profiles and their relation to reflection mechanisms between Dome C and the Transantarctic Mountains"Journal of Glaciology. (In Press). (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] S.Fujita: "Radar sounding of ice sheets and ice in outer planets : possibilities and limitations considering the dielectric properties of ice crystals"Seppyo (Journal of the Japanese Society of Snow and Ice). 62 (1). 49-60 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] S.Fujita: "Internal structure of the ice sheet detected using ice radars"Gakujyutsu Geppo (Journal Scientific Monthly). 54 (2). 42-46 (2001)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 2002-03-26  

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