Abstract
Calibration of a camera system is essential to ensure that image measurements result in accurate estimates of locations and dimensions within the object space. In the underwater environment, the calibration must implicitly or explicitly model and compensate for the refractive effects of waterproof housings and the water medium. This paper reviews the different approaches to the calibration of underwater camera systems in theoretical and practical terms. The accuracy, reliability, validation and stability of underwater camera system calibration are also discussed. Samples of results from published reports are provided to demonstrate the range of possible accuracies for the measurements produced by underwater camera systems.
Highlights
A recent report by the World Wildlife Fund [1] notes a sharp decline in marine biodiversity, caused by overfishing, coastal development and climate change
The analysis demonstrates that perspective camera models incur increasing errors with increasing distance and tilt of the refractive surfaces, and only the physical model of refraction correction permits a complete theoretical compensation
Testing and validation has shown that the camera calibration is only reliable if the cameras in the housings are mounted on a rigid connection to the camera port [74]
Summary
A recent report by the World Wildlife Fund [1] notes a sharp decline in marine biodiversity, caused by overfishing, coastal development and climate change. Underwater stereo-video systems have been used in the assessment of wild fish stocks with a variety of cameras and modes of operation [13,14,15,16], in pilot studies to monitor length frequencies of fish in aquaculture cages [6,17,18] and in fish nets during capture [19]. Any inaccuracy will lead to significant errors in the estimated biomass [41] or a bias in the population distribution [12] Other applications such as structural monitoring or seabed mapping must achieve a certain level of accuracy for the surface shape. Experience demonstrates that, because of these effects, underwater calibration is more likely to result in scale errors in the measurements
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