The height of the intersection between the free surface and a ship hull is of interest for many naval architecture applications. For example, wave height at a station influences the probability of water on deck, and wetted elevation at a buttock on a transom influences resistance forces. Determining this parameter through testing (either model- or full-scale) can be accomplished through various methods, many of which involve placing one or more measurement instruments in the flow field (e.g. resistance or capacitance probes or wires). However, the presence of these elements in the system can affect the flow itself. Non-invasive techniques, including sonic methods and laser-enabled technologies, avoid this issue, though there are benefits and drawbacks associated with these techniques as well. Measurement system complexity, in particular, can drive experimental cost and schedule. Some proven methods may provide more spatial resolution than is necessary to meet experimental objectives, providing extraneous information at additional cost. Image processing of digital camera video frames can be an effective non-invasive technique, though many commercially-available image processing tools are not designed specifically for this application. Though quite robust, these tools can add unnecessary time and cost to data processing for the waterline elevation problem. This paper lays out computationally-efficient image processing software methods which can be implemented in Matlab (without requiring additional toolboxes) to determine free surface elevation along a ship hull at a station or buttock using video files generated by cameras trained on the hull in the area of interest.

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