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Séminaire du département Images et Signal du 13/06/2019 à 14h00

 

Standard-target method of calibrating active sonars, with applications to the quantitative imaging and measurement of scattering

Intervenant : Kenneth G. FOOTE, Woods Hole Oceanographic Institution Woods Hole, Massachusetts, USA

Lieu : Salle Chartreuse

 

Résumé :

Active sonars are widely used in industry, medicine, and science for quantitative imaging and measurement of scattering. Sometimes, the sonar uses a single transmitting and receiving transducer; this defines the monostatic configuration. More generally, the transmitting and receiving transducers are physically separated, which defines the bistatic configuration. Either of these configurations is susceptible to calibration by the standard-target method, which is arguably the simplest, most accurate and rapid method, hence most cost-effective.

 

In this talk, the standard target is defined and illustrated.  The theoretical basis of the method, which aims to express echo data in absolute physical units of scattering, is developed, with reference to the volume scattering coefficient sVand physical effects intrinsic to operational sonars.  The generally bistatic acoustic sampling volume, which is a constituent of sV, is elaborated.  Formulas are derived for the calibration constant in the energy domain, and the combined transmit-receive frequency response function in the spectral domain. Practical elements of a calibration are elaborated in terms of the sonar specification, candidate calibration venue, environmental state, and calibration exercise design, with an approach that distinguishes reference and non-reference beams. These elements are illustrated through the example of a standard-target calibration of a multibeam sonar used in oceanographic applications, with execution at a land-based facility.  Preparations and protocols for the calibration exercise are described.


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