Evaluation of using a CCD camera as a versatile measurement system for flume tank observation

A plane-based camera calibration method which substantially reduces the complexity of the procedure is presented in this paper. With the proposed method, camera array can be installed as a basic facility for wave flume tank experiment. Wave flume tank experiment is a methodology commonly used for ocean engineering research. Various parameters, such as wave properties on the surface (height, wave form, average level), current in the water (velocity field, vorticity and particle trace), bottom profile and sub-bottom layer thickness are measured with different apparatuses. Still image camera is one of the sensors widely used to extract information, such as waveform, bedform and velocity field (particle image velocimetry). The accuracy of image-based measurements mainly relies on the quality of the camera calibration which is a time-consuming process especially in field work. For the phenomena of interest observable on the flume tank window glasses, the features are planar in nature. Therefore, the camera calibration can be simplified as a map projection problem such that the time and efforts needed are reduced significantly while maintaining the desired accuracy. We studied the performance of the plane-based method by comparing the measurements with the theoretical values of a known curve which mimics a sandslope. The robustness of the method is examined by comparing the results acquired under the condition that the camera tripod and the quick-release are dissembled, assembled and repositioned during the experiments. According to the error analysis, the measurement can be accurate to less than 1. mm for static feature and 1 to 2 mm for dynamic feature.