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1,274,054. Acoustic Doppler determinaton of speed or course. FRIED KRUPP G.m.b.H. 18 Sept., 1969 [19 Sept., 1968], No. 46104/69. Heading H4D. In a system for determining the speed and/or course of a craft (e.g. water craft, land vehicle or hovercraft) by measuring the Doppler effect on a sound wave beam inclined from the horizontal, the transducer system comprises a phased array of transducer elements mounted with equal spacing in the bottom of the craft. It is shown that by energizing the array elements in fixed phase relationship by a polyphase generator, variation of the transmitted beam inclinationαwith variation of the sound wave velocity c compensates for variation of the Doppler shift with c whereby the speed measurement is independent of c. In the Fig. 4 embodiment, the required spacing of transducers 1 is less than their diameter so they are arranged in staggered rows. A forwardly and a rearwardly inclined beam are emitted simultaneously by energizing the transducers 1 in a cyclic order and the inverse of that order respectively. The energization may be intermittent or continuous. For energization oscillator 3a and ring counter 4a, 5a, 6a provide a three-phase supply at frequency f 1 to lines R, S, T, while oscillator 3b and ring counter 4b, 5b, 6b provide a threephase supply at frequency f 2 to lines R, S, T. The same or an additional array is used for reception of echoes and its output lines R, S, T are coupled to two scanners operating at scan frequencies f 1 , f 2 respectively (Fig. 8, not shown) for sampling the outputs on lines R, S, T in a cyclic order at frequency f 1 and the inverse of that order at frequency f 2 respectively. Due to the overlap of side-lobes of the f 1 beam with the main lobe of the f 2 beam and vice versa there will be mixing of f 1 , f 2 and their Doppler shifted received signals # f 1 , # f 2 ; a filter (9a) extracts the side-band # f 1 -f 2 from the second scanner output. These side-bands are analysed in frequency discriminators 14a, 14b respectively in the Fig. 9 circuit as follows. Frequencies f h /m and f h /n define upper and lower references for each discriminator, being derived from oscillator 16 by frequency dividers 15a, 15b and fed to mixers 17a, 17b whose outputs are low-pass filtered at 18a, 18b and rectified. If the side-band spectrum lies asymmetrically between the upper and lower reference frequencies the discriminator gives an output dependent on the asymmetry. The two discriminator outputs are combined at 19 and will cancel if the Doppler components are due to vertical motion of the craft but will add for horizontal motion. The combined output is integrated at 20 to provide a feedback control voltage for varying the oscillator 16 frequency f h so as to zero the control voltage. The locked frequency f h is thus made a function of the Doppler shift and its frequency-divided output from 21 is fed to computer 22 for extraction of forward or backward speed data which may be integrated to determine, in conjunction with sideways speed data similarly derived with duplicated apparatus, the course of the craft.
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