應用聲波都卜勒流速儀之底追蹤功能量測動床速度

本研究應用聲波都卜勒流速儀之底追蹤功能量測動床速度，以等速全運移之動床水槽實驗評估底追蹤量測誤差，並探討脈衝長度、動床速度、與床面類型對底追蹤量測準度與精度之影響。研究結果顯示，床面顆粒之均質性與粒徑大小均爲影響底追蹤量測準確度之因素，床面顆粒愈均質、粒徑愈小時，床面不平聲性所造成之反射訊號變異性愈小，底追蹤之量測準確度愈高，增長量測時間以增加資料筆數，其平均效果能有效降低誤差，提高資料準確性。底追蹤量測之準度與精度均隨脈衝長度或動床速度增加而提升，對混合床面之提升效果尤爲顯著。本實驗在等速全運移之動床條件下，非均質床面之不平整性造成聲波反射狀態變異爲儀器雜訊之主要來源。底追蹤之整體量測水準隨脈衝長度增加而提高，但量測水準之提升有其上限，約爲85%。根據本研究結果，應用底追蹤量測砂、碟質之動床速度時，可以、30~60cm之脈衝度進行量測，以確保整體量測水準在80%以上，並配合現地懸浮載濃度再調整至最佳脈衝長度。

關鍵字

聲波都卜勒流速儀；底追蹤；脈衝長度；動床速度；床面類型；全運移

並列摘要

In this study we applied the Bottom Tracking (BT) of Acoustic Doppler current Profiler (ADP) to measure the bed velocity. Flume experiments were conducted with a mobile-bed carrier moving in a constant-velocity full-transport mode. The effects of pulse length, bed velocity, and bed type on the accuracy and precision of BT were investigated. The results indicated that the homogeneity and grain size of bed material affects the accuracy of BT. For homogeneous fine material, the variability of signal reflections induced by the irregularity of bed surface became less and thus raised the accuracy. The averaging effects associated with the increase of measurement time and data quantity would effectively reduce the BT error. The accuracy and precision of BT became higher as the pulse length or bed velocity increased, especially for mixed bed. For the current experiments in a constant-velocity full-transport mode, the instrument noises induced by the heterogeneous bed material were the primary source of error. The overall performance of BT improved with the increase of pulse length; however, there exists an upper limit of ~85%. According to our study, when BT is applied to measuring the apparent velocity of sand and gravel bed, the pulse length of 30~60 cm could be used to ensure an 80% overall performance, an optimal pulse length could be farther sought if adjusted to suit the in-situ condition of suspended material.

並列關鍵字

ADP ； Bottom Tracking ； Pulse length ； Bed velocity ； Bed type ； Full transport

國際替代計量

應用聲波都卜勒流速儀之底追蹤功能量測動床速度

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