GB1498843A - Acoustic camera apparatus - Google Patents

Abstract

1498843 Pulse-echo systems WESTINGHOUSE ELECTRIC CORP 7 March 1975 [29 March 1974 (3)] 9639/75 Heading G1G A target area 75 is imaged by transmitting a brief acoustic pulse to insonify a narrow strip 79 which is defined by the intersection of the acoustic wavefront with the area 75 and which thus sweeps the area in a range direction, focusing acoustic returns from adjacent strips Ri-Rn on to respective receiver transducers Ti-Tn, processing the resulting transducer output signals and displaying the processed signals. As shown the focusing device is an acoustic lens and the transducers are elongated. The lens and transducer configuration and spacing are such that the depth of focus extends from a minimum to a maximum target range (corresponding to a propogation time interval t 1 -t M ). The signal processing comprises amplifying range-gated transducer outputs with swept gain in respective signal channels, then sampling the channel signals in turn. The sampled signals intensity-modulate a CRT display whose vertical and horizontal timebase sweeps are synchronized with the pulse transmission and channel sampling respectively. In a typical system the pulses are transmitted at a 60Hz rate with a 3MHz carrier frequency and a 33À3 micro-second duration to give a one-inch slant range resolution; minimum and maximum short range to the 260 inch wide target area are 250 and 500 inches; and 200 receiver channels are used to give a similar resolution laterally and are all sampled within a 30 micro-second period. For use at greater ranges the transmission pulse rate is reduced and storage of echo data (e.g. in a CRT or on a magnetic disc) may be needed to avoid flicker problems in the display. Instead of elongated receiver transducers, point-form ones can be used, the lens then having a cylindrical or part-conical surface Figs. 2, 3, 4 (not shown). An acoustic reflector may be used instead of a lens to provide focusing Figs. 5 6, 7 (not shown). A marine sonar is described Fig. 10 (not shown) in which water-bottom target areas to port and starboard are scanned as described above, using two arrays of receiver transducers in conjunction with a single focusing element, and a third array is used to scan an area ahead of a vessel, thereby "filling-in" the gap between the other two areas.