GB1506700A - Apparatus for passive sonar target location - Google Patents

Abstract

1506700 Sonar system FRIED KRUPP GmbH 11 Oct 1971 [30 Oct 1970] 47313/71 Heading G1G Apparatus for passive sonar target location, comprises means for applying various target criteria to received signals in order to eliminate indication of false targets. The apparatus comprises a receiver array 1 and beam-former. The array 1 comprises groups 1a, 1b whose acoustical centres are spaced a distance s apart. A true target Zn (Fig. 2) gives rise to two signals U1(Zn), U2(Zn) related by ## is the angle between the Direction S of sound incidence and a main Direction H # is the sound wavelength A source of noise, Zsl, at 180‹ to the Direction of sensitivity of the apparatus (Fig. 3) gives rise to two signals U1(Zs1), U2(Zsl) related by which the apparatus "sees" as false target Zsl'. Similarly, reflections from surrounding surfaces 3 of the apparatus give rise to an apparent target Zs2' (Fig. 4). The apparatus is enabled to discriminate between the true and false targets by applying to the received signal waveform suitable criteria. A comparison of the waveforms of the correlation functions with zero axis crossing Kazv(Uzn) and Kazv (Uzs1,2) (Fig. 6, not shown) shows that the former goes positive on passing through zero, while the latter go negative. The difference quotient #Kazv/## thus gives a target discrimination criterion. Another criterion, is useful for eliminating large false targets proximate the apparatus. Signals Ul, U2 pass from the beam-former 2 via correlators 4 and 5 to target discriminators D1, ... D5 which apply the respective discrimination criteria: These discriminators output to a logic circuit 6 which yields a target signal when the criteria are fulfilled at least once in several successive scanning cycles for one bearing direction or, for a given bearing direction, in a given time interval. Control units 9, 10 allow selective introduction of evaluation criteria into the computor 7 of the apparatus. Thus, all or selected target criteria must be fulfilled simultaneously in any one bearing direction, or for a given time interval in a given bearing direction according to the discriminators selected by control unit 2. Control unit 10 can provide directionally independent variation in sensitivity of all or selected discriminators. The control units 9, 10 can be replaced by computors programmed to effect a prescribed coupling of different target and evaluation criteria.