Abstract
Abstract. Underwater photogrammetry using consumer grade photographic equipment can be feasible for different applications, e.g. archaeology, biology, industrial inspections, etc. The use of a camera underwater can be very different from its terrestrial use due to the optical phenomena involved. The presence of the water and camera pressure housing in front of the camera act as additional optical elements. Spherical dome ports are difficult to manufacture and consequently expensive but at the same time they are the most useful for underwater photogrammetry as they keep the main geometric characteristics of the lens unchanged. Nevertheless, the manufacturing and alignment of dome port pressure housing components can be the source of unexpected changes of radial and decentring distortion, source of systematic errors that can influence the final 3D measurements. The paper provides a brief introduction of underwater optical phenomena involved in underwater photography, then presents the main differences between flat and dome ports to finally discuss the effect of manufacturing on 3D measurements in two case studies.
Highlights
As in case of more traditional aerial and terrestrial photogrammetry, in the field of underwater photogrammetry advances and progresses have gone hand in hand with improvements in photography
Stating the peculiarities of a hostile environment such as the underwater world, probably even more in air, an insight of the basic principles of underwater photography and equipment is fundamental for a successful approach to underwater photogrammetry
Despite being more complex to build and assemble to camera pressure housings when compared to flat ports, dome ports show numerous advantages from a photogrammetric point of view as they preserve the main geometrical characteristics that rule the image formation
Summary
As in case of more traditional aerial and terrestrial photogrammetry, in the field of underwater photogrammetry advances and progresses have gone hand in hand with improvements in photography. The knowledge about photographic equipment and its behaviour in different conditions is the first step to be investigated Moving from this consideration, in the first part of this contribution the main physical properties of water are explained in relation to how they affect underwater photography. The study is focused on the geometric and optic characterization of a consumer grade pressure housing with a dome port (NiMAR NI303D and NI320), in which a DSLR Nikon D300 with a Nikkor 24 mm is mounted. Both simulations and tests underwater are carried out and described. Other optical phenomena are to be accounted for underwater, all related to the so called inherent optical properties that govern propagation of light in water
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