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

无线电波在冰盖中传播过程及冰盖内部结构研究。

基本信息

批准号：
11440136
负责人：
MAE Shinji
金额：
$ 8.06万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11440136/
关键词：
ice dielectric radio wave Antarctica ice sheet radar microwave 電気伝導度電波

项目摘要

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.

利用2503 m深冰孔进行无线电波传播实验，测量了南极冰的原位高频极限介电常数。利用179 mhz雷达的脉冲波从井眼垂直运动的目标散射，测量平均相速度，并利用平均相速度确定不同深度的高频介电常数。这使得在215-232 K和高达14 MPa的静水压力下，可以在冰上测量高频介电常数。这种介电常数总是小于对普通六边形水冰（冰Ih）的预测。300 ~ 400m深度的介电常数约为2.98（±0.04），比该深度温度下的普通冰Ih小0.15左右。介电常数随深度增大而增大，在800 m处达到最大值3.11（±0.04）。随后随深度的增加而减小，到1400 m时为3.06（±0.08）。密度降低、低温、晶体取向和典型的环境杂质的影响不能解释这些异常低的介电常数值。我们提出了低介电常数的两个原因：(1)理论上提出的深层冰中静水压力的抑制作用；(2)浅层冰中晶格结构的变化。对于(1)，我们使用回归分析将介电常数随压力线性下降的理论拟合到我们的数据中，从而提出静水压力对介电常数的影响为-3.6（±2.6）x 10-9 Pa-1。介电常数的最大异常出现在地表附近；因此，需要一个单独的机构，机构(2)，因为靠近表面的压力最低。