利用微波侦测地下水位与河川变化

Detecting groundwater level and river elevation variation by microwave

论文探讨藉由电磁波照射地表 ,从反射讯号中去判断地下水水位与土石流移动观测之可行性 ,期能提供一新的土石流预警方法。电磁波在土壤中的行为受土壤的介电系数所控制。我们首先以地下水模式仿真出地层中的含水量分布状况 ,同时搜集过去关于土壤介电系数的实验资料和模型 ,将其运用于层状介质法来仿真电磁波照射在不同含水量剖面下之反射波 ,以建立含水量分布与反射讯号间的对比模块。最后则是以砂箱实验 ,量测含水量剖面后 ,藉由天线与网络分析仪来发射电磁波与记录反射波。由理论计算与实验测量结果之比较可知所选择的土壤介电系数模型可以仿真简单潮湿土壤的电磁行为 ;而由实验量测可知电磁波至少可以打进 5 0cm的微湿砂子。若以雷达扫瞄河道 ,可对土石流或洪水前锋的速度作准确之估计。

This study is to evaluate the feasibility of detecting the groundwater level and debris flow motion from the reflected signals by emitting electromagnetic waves to the ground. The propagation of electromagnetic wave in soil is controlled by the dielectric constant that varies according to the water content distribution. We first simulate the soil moisture profiles by the groundwater flow model. Then apply the results to the “layered media method' to simulate the reflective waves under different water content distribution. A sandbox experiment with a premeasured moisture profile was conducted. The recorded reflective signals by network analyzer system show good agreement with theoretical results. We can also use this kind of radar to detect the front of debris flow or flood.