Calibration of broadband sonar systems using multiple standard targets

Abstract

A seven-octave active sonar system spanning the nominal frequency range 25-3200 kHz was deployed in Norwegian waters for the purpose of measuring the acoustic scattering characteristics of a range of marine organisms. This system transmitted linear frequency-modulated (LFM) signals in order to achieve good range resolution and to obtain spectral information on resolved targets. Total system performance was variously measured in situ and ex situ, depending on the particular octave band, using standard-target spheres. This enabled the frequency response of the entire system to be determined and the sidelobe level of the matched-filter receiver to be reduced. The effects of the deep nulls encountered in the backscattered spectrum of target spheres were partially reduced by using a string of up to six spheres of different sizes and material properties. Typical results will be presented showing that such calibration procedures are sensitive to the relative alignment of the sonar-target and to sound-speed profile changes over the length of the string.

Phase calibration of sonar systems using standard targets and dual-frequency transmission pulses

“…In order to minimize their detrimental effects the idea of separating the specular and resonant parts in the echo has been developed, 31 as well as the use of the joint response of multiple spheres. 44 In both approaches sensitivity to resonances is reduced. Other factors that can degrade the precision of amplitude calibration for broad band active sonar systems are mainly related to the level of knowledge and control of experimental conditions, as well as of the physical composition of the target.…”

Determination of Optimal Acoustic Passive Reflectors to Reduce Bycatch of Odontocetes in Gillnets

“…As spheres meet the demand of omnidirectionality, we concentrated on simulating spherical targets. Spheres are also used as standard targets in many sonar applications (MacLennan, 1981;Foote, 1982Foote, , 1983Sheng and Hay, 1993;Atkins et al, 2008). In his consideration of spherical acoustic targets as passive reflectors to decrease bycatch of odontocetes, Goodson (1997) remarks that, as a consequence of Rayleigh scattering, any sphere as a passive reflector would have to be several centimeters in size.…”

Development of an Autonomous Broadband Acoustic Scattering System for Remote Characterization of Zooplankton

“…Software has been developed to visualize the acoustic data, for performing multiplestandard target calibrations (Atkins et al, 2008), pulse compression processing, and for spectral analysis of the broadband data.…”