A Preliminary Investigation of UAV-LSPIV for Measuring Water Surface Velocities

Velocity of river flow measurement technologies are divided into intrusive and nonintrusive methods. Intrusive method requires infield operations. The deployment of intrusive methods are time consuming, and likely to cause damages of operator and instrument. Nonintrusive methods is safe for operators and can reduce instrument damages from directly attaching to the flow. Nonintrusive measurements may use radar or image velocimetry to measure the velocities at the surface of water flow. The image velocimetry, such as large scale particle image velocimetry (LSPIV) accesses not only the point velocity but the flow velocities in an area simultaneously. Flow properties of an area hold the promise of providing spatially information of flow fields. This study attempts to construct a mobile system UAV-LSPIV by using an unmanned aerial vehicle (UAV) with LSPIV to measure flows in fields. The mobile system consists of a six-rotor UAV helicopter, a Sony nex5T camera, a gimbal, an image transfer device, a ground station and a remote control device. The activate gimbal helps maintain the camera lens orthogonal to the water surface and reduce the extent of images being distorted. Ground Reference Points (GRPs) are positioned with total station. The image transfer device can monitor the captured image instantly. The operator controls the UAV by remote control device through ground station. The mobile system was then applied to high flow and low flow condition of field experiments at Han River, Taichung Taiwan. The deviation of velocities in low flow condition measured by UAV-LSPIV of field experiments and handhold Acoustic Doppler Velocimeter (ADV) is under 8%. The deviation of velocities in high flow condition measured by UAV-LSPIV of field experiments and PTV(Particle Tracking Velocimetry) is under 4.37%.流速的現場觀測方式分為接觸式及非接觸式，接觸式方法主要倚靠觀測人員運用儀器接觸水面量測，不僅耗費時間亦可能造成儀器的損壞，且有觀測人員安全之疑慮。非接觸式方法中的大尺度影像質點量測方法(Large Scale Particle Image Velocimetry, LSPIV)由單次量測即可獲得流場面的資訊，且可減少操作人員並降低儀器的損壞。分析自然河道之流速時，相較於單點流速資料，流場面的資訊能夠分析河川整體之流速分佈。本研究建立出一套機動性觀測流場系統UAV-LSPIV，以無人飛行載具(Unmanned Aerial Vehicle, UAV)作為影像紀錄載具，擷取影像後以LSPIV技術分析流場。 本研究自行建置之UAV-LSPIV包含六旋翼飛行器、電子可調式雲台、Sony nex5T相機、影像傳輸模組及地面控制站，影像傳輸模組能即時於飛行中觀測水流影像，於地面控制戰的操作人員可調整雲台旋轉相機鏡頭角度，使UAV拍攝時能正攝水面減少影像之變形，再利用全測站經緯儀測量地面控制點做影像校正。 運用建置之UAV-LSPIV分別進行高、低流量之室外實驗，室外實驗區域於台中市旱溪積善橋下游河段，低流量試驗與手持式ADV量測流速相較差異低於8%，高流量試驗與PTV(Particle Tracking Velocimetry)量測平均差異為4.37%。目錄 摘要 i Abstract ii 目錄 iii 圖目錄 iv 表目錄 vi 第一章 前言 1 1.1 研究動機與目的 1 1.2 本文架構 2 第二章 文獻回顧 4 2.1 現地流速量測的方法 4 2.2 影像質點追蹤法(Particle tracking velocimetry, PTV)6 2.3 大尺度的影像質點量測法(Large-Scale Particle Image Velocimetry, LSPIV) 7 2.4 影像擷取設備載具UAV之探討 9 第三章 UAV-LSPIV系統之原理與建立 16 3.1 LSPIV處理 19 3.2 現地座標轉換 21 3.3 影像處理 22 3.4 UAV-LSPIV建立 29 第四章 研究材料與方法 30 4.1 室內實驗環境與設備 30 4.2 室內實驗流程 31 4.3 室外實驗環境與設備 39 4.4 室外實驗流程 52 第五章 結果與分析 58 5.1 室內實驗討論 58 5.2 室外實驗討論 71 第六章 結論與建議 86 6.1 結論 86 6.2 建議 87 參考文獻 8