FIELD: underwater acoustics, detection, identification and determination of spatial coordinates of stocks of fish with gas bladders employed in fishing industry. SUBSTANCE: unit of parametric radiation of low-frequency signals is positioned on one side of controlled boundary and unit of parametric reception of low-frequency signals is located on opposite side of boundary. Parametric radiation unit of low-frequency signals forms, amplifies and emits high-frequency pumping waves at frequencies ω1 and ω2 close to resonance frequency ω0 of air bubbles present in surface layer of water in direction of unit of parametric reception of low-frequency signals and executes nonlinear interaction of high-frequency pumping waves with formation of low-frequency wave of resonance frequency Ω = ω1-ω2 directionally propagating in aqueous medium. Unit of parametric reception of low-frequency signals forms, amplifies and omnidirectionally emits high-frequency pumping signal on frequency ω3 which scatters across inhomogeneities of aqueous medium, interacts with low-frequency wave of resonance frequency Ω′ reflected from stocks of fish with gas bladder as well as with low-frequency wave of inherent radiation of fish on frequency Ω″ with formation of high-frequency wave of combination frequencies ω3±Ω′ and ω3±Ω″ propagating towards unit of parametric reception of low- frequency signals where low-frequency signals on frequencies Ω′ and Ω″ are extracted from high modulation frequencies ω3±Ω′ and ω3±Ω″. Then spectral analysis of low-frequency signals is conducted, signals are compared with reference signals and decision on detection of stocks of fish is made. EFFECT: enlarged area of examination of water area, potential for detection of rarefied stocks of fish with simplified identification of their kinds. 5 dwg
