時間領域反射法による水中堆積土砂表面位の評価法  [in Japanese] Dielectric Approaches of Sediment-surface-level Estimation by Time Domain Reflectometry  [in Japanese]

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Abstract

河床や湖底における土砂堆積量の評価法を確立するために,実験用カラム内に沈降充填した粒径の異なる硅砂または玉砂利の表面位を時間領域反射法TDRにより測定した.水中に設置したTDRプローブのロッド先端からの土砂表面位<i>h</i><sub>sed</sub>は,ケーブルテスターから発信されるステップパルスの水-土砂境界面またはロッド先端における反射に基づいて評価される.前者の反射から水中部のみのパルス伝播に要する時間<i>t</i><sub>w</sub>を算出したところ,各土砂の<i>h</i><sub>sed</sub>は<i>t</i><sub>w</sub>の1次関数モデル(部分伝播法)に基づき高精度で評価できた.一方,ロッド先端での反射から水中と土砂層の全伝播時間<i>t</i><sub>t</sub>を求め,<i>t</i><sub>t</sub>と土砂層の比誘電率ε<sub>sed</sub>に基づくモデルで<i>h</i><sub>sed</sub>を評価したところ(全伝播法),平均粒径が大きい土砂ほど<i>h</i><sub>sed</sub>の誤差が増大した.しかし,その誤差は,ε<sub>sed</sub>に土砂の最大粒径と最小粒径の平均値の1次式に基づく補正を加えることで修正できることを明らかにした.

To establish a method for monitoring the fluctuations of river or lake sedimentary volume by means of time domain reflectometry (TDR), the surface levels of sediments composed of sand or gravel were measured using a 48cm-length TDR probe in laboratory and compared with two dielectric estimation approaches. In the experiments, the probe was vertically set under water surface to be across two layers of water and sediment. Giving microwave step-pulse to the probe, we could obtain the TDR waveform which contained the pulse reflections at the water-sediment interface and the end of probe. The sediment surface level <i>h</i><sub>sed</sub> estimated by partial-range propagation method PPM, where a linear function of the travel time (<i>t</i><sub>w</sub>) determined from the former reflection is employed, was in good agreement with the actual level. In whole-range propagation method WPM based on the travel time (<i>t</i><sub>t</sub>) given from the latter reflection and the sediment relative permittivity <i>ε</i><sub>sed</sub>, the estimation error of <i>ε</i><sub>sed</sub> augmented with increase in grain size of the sand or gravel resulted in low accuracy of <i>h</i><sub>sed</sub>. The inaccuracy, however, was improved by modifying <i>ε</i><sub>sed</sub> with the correction coefficient (<i>C</i><sub>g</sub>) expressed as a linear function of the middle grain size (<i>D</i><sub>mid</sub>). PPM and WPM could be reasonably used for the <i>h</i><sub>sed</sub>-estimation with TDR.

Journal

  • Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering

    Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering 77(4), 403-409, 2009-08-25

    The Japanese Society of Irrigation, Drainage and Rural Engineering

References:  15

Cited by:  2

Codes

  • NII Article ID (NAID)
    10025641638
  • NII NACSIS-CAT ID (NCID)
    AA12240517
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    18822789
  • NDL Article ID
    10423408
  • NDL Source Classification
    ZR7(科学技術--農林水産--農産)
  • NDL Call No.
    Z18-365
  • Data Source
    CJP  CJPref  NDL  J-STAGE 
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