2. Object speed measurement

The propagation properties of acoustic or electromagnetic waves are commonly used to determine the speed of objects without material contact. In this field of application, we come across the propagation of spherical waves, whose main properties will be briefly recalled. It will be shown that, under certain circumstances, the propagation of a spherical wave assumes the properties of a one-dimensional wave, as encountered in the gas pipe illustrated in § 2.1.3 of [D 1 324] , or in lines meeting the criteria established above. These are referred to as quasi-planar waves.

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