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Underwater Acoustic Imaging of the Sea

100%

Grelowska G. , Kozaczka E.

tom Vol. 39, No. 4

439--452

Acoustic waves are a carrier of information mainly in environments where the use of other types of waves, for example electromagnetic waves, is limited. The term acoustical imaging is widely used in the ultrasonic engineering to imaging areas in which the acoustic waves propagate. In particular, ultrasound is widely used in the visualization of human organs – ultrasonography (Nowicki, 2010). Expanding the concept, acoustical imaging can also be used to presentation (monitoring) the current state of sound intensity distribution leading to characterization of sources in observed underwater region. This can be represented in the form of an acoustic characteristic of the area, for example as a spectrogram. Knowledge of the underwater world which is built by analogy to the perception of the space on the Earth’s surface is to be systematize in the form of images. Those images arise as a result of graphical representation of processed acoustic signals. In this paper, it is explained why acoustic waves are used in underwater imaging. Furthermore, the passive and active systems for underwater observation are presented. The paper is illustrated by acoustic images, most of them originated from our own investigation.

Triangular 3D Laser Scanning in Underwater Photogrammetry

80%

Wojtowicz A. , Stolarczyk K.

nr 3

35-44

The use of triangular 3D laser scanning may significantly enhance the visual inspection of underwater objects. In these days of high demand for accurate information, exclusively photographic documentation is not enough, as it is geometrically flawed. The authors of this article are trying to present the rudiments of laser scanning, a modern means of measuring, which is reliable, relatively easy to use and works in accordance with basic good measurement practices. With the use of a laser beam, a point model of the measured object is generated with a resolution that is adapted to the requirements. A well performed scan will cover the entire surface of the measured object with no information gaps, as is often the case with photographic documentation which focuses solely on key details. Photographic documentation is now already being replaced by Structure from Motion technology, the latter being an alternative to laser scanning, which creates a textured 3D model from the collection of photographs of the object with similar accuracy, but with more time required.