結合線型雷射系統與立體視覺技術進行水下檢測之初步研究

THE PRELIMINARY STUDY OF UNDERWATER INSPECTION BYCOMBINING LASER-LINE SCAN SYSTEM AND THE STEREO VISIONTECHNIQUE

本研究擬開發一套水下觀測系統以進行水下物體檢測之研究，其配備主要搭載雙攝影機視覺系統和水下線型雷射技術。在本研究中，水下觀測系統係利用攝影機內外部校正參數所建立的雙影像視覺裝置搭配高功率之水下線型雷射，並藉由線雷射掃描（Laser Line Scan, LLS）技術獲得水下物體之影像資訊，研究結果也發現此方法可以有效減少水中散射所帶來的影響。在影像處理程序中，首先經由水下影像處理技術將二維影像資訊比對特徵點，再藉由雙極線幾何（Epipolar Geometry）方法重建出物體三維點雲資料以建構出精準的水下物體尺寸。在全文中，本研究將於成大系統系穩定性能水槽探討不同幾何形狀之物體在水下不同濁度和亮度的環境下進行點雲重建計算，並分析其重建誤差程度，未來將更進一步模擬出不同水下環境以測試該方法之限制程度。預期本研究所建構之水下觀測系統，將能改善在水下光線不足且濁度過高的環境下，利用雷射掃描技術去放大其目標物之特徵點以做影像擷取。並改善以往水下聲學儀器在短距離的丈量上，無法得到較精確解析度的問題。 This study aims to establish an underwater observation system for the purpose of underwater survey. In the experiments, we have tested an optical technique, which is more popular in air acquisition, based on the Laser Line Scan (LLS) accompanied with a stereo vision system. The LLS is one of the underwater optical imaging methods, which are capable of reducing the detrimental effects of backscatter and forward scatter. By means of epi-polar geometry method, a coordinate mapping relationship between 2D pixel coordinate and 3D world coordinate, which then can be used to reconstruct 3D objects from 2D scan data, is established. The experiments for the underwater tests have been conducted in the stability tank at National Cheng Kung University by considering different optical conditions. Whereby, the quality of point clouds for 3D reconstruction are tested by underwater image detection technique in different turbidities and illuminances. Later on, the underwater observation system will be also used to test limitations of our developed optical method. It is anticipated that the LLS-based stereo vision system can improve deviations of acquired data in the closerange than acoustic systems.