<title>Small static and dynamic target detection in nontransparent medium and opaque water</title>

Abstract

Target detection in water (or another liquid medium) is achieved by optical registration and measurement of the shape of the surface disturbance (hump") of liquid caused by radiation pressure of ultrasound waves passing by or reflected from the object. Two methods have been developed. In the first case, the effects of refraction and diffraction of a laser beam by the "hump" are used. This method is very sensitive for detection and observation of dynamic underwater objects. In the second case the Talbot effect is used (the self-reproduction of images of regular grating of images at distances z = 2dn/2, where d is the grating period, X is the wavelength, and n = 1,2,..). Both methods allow to detect and observe the dynamic objects inside a liquid. This report describes: the schemes and the equipment used for measuring the underwater objects; the results of the "hump's" 3D shape measurement and its usage for creating 'humped" ultrasound hologra.m; the image of a small target (..-1 . 5 cm2) produced by computer reconstruction of "humped" ultrasound hologram. This report also demonstrates the possibility of using Talbot effect for measurement of the shape and thickness of oil films on liquid and solid surfaces and for the wettability angle measurements.Keywords: target recognition in opaque media, Talbot effect, light refraction and diffraction on disturbed water, water disturbance by ultrasound.