Calibration Strategies for Optical Underwater 3D-Sensors – a Comparison of Approaches

Precise three-dimensional reconstruction of underwater objects is required in many different applications. Optical 3D sensors are interesting due to their high accuracy potential and to their capability of simultaneous full-field measurements. Calibration of these systems for underwater use is becoming increasingly important to unfold their full potential. Because of the transition of the vision rays between the media air, glass, and water, the calibration of optical underwater 3D sensors is challenging. The presented calibration refinement strategies, including expanded advanced pinhole camera modeling, explicit ray modeling, and systematic error compensation by correction functions are described and discussed. The approaches presented are simple in the sense that they do not require explicit modeling of beam refraction at the media boundaries. Experimental evaluation of one of the proposed strategies using a water tank has demonstrated the potential for a reduction of systematic errors. Additionally, accuracy and robustness of the initial calibration may be improved by the refinement. Requirements, advantages and limitations of the different strategies are discussed.