This paper is a review which briefly describes a selection of acoustic observation techniques and certain aspects of underwater video technology suitable for observations in an underwater environment. The review is divided into two sections, one for each subject, where each section concludes with a discussion of the current challenges within the respective fields. The acoustic section of the review covers bathymetric and geometrical measurements, imaging sonars, subsurface penetrating profilers, positioning methods, acoustic underwater communication and sensor networks, and water speed measurements. The section ends by considering temperature measurements by ocean acoustic tomography and passive acoustic monitoring. The underwater video section initially deals with questions of acquisition including underwater visibility, the type of platform, and video formats, image sensors and specialized cameras. This is followed by notes on processing techniques including mosaicking, stereo video, structured light, recording and transmission, image enhancement techniques and ends with a short discussion of underwater holographic cameras.
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