GB2181547A

GB2181547A - Acoustic direction detector

Info

Publication number: GB2181547A
Application number: GB08525296A
Authority: GB
Inventors: John Arthur Glasgow
Original assignee: GEC Avionics Ltd
Current assignee: Allard Way Holdings Ltd
Priority date: 1985-10-14
Filing date: 1985-10-14
Publication date: 1987-04-23
Also published as: GB2181547B

Abstract

Signals from an array of four or more acoustic sensors A, B, C, D, E are inspected in pairs (at 7) to measure the delay in the time of arrival of a signal between each sensor of a pair. The validity of each delay measurement is then checked in logic circuit 13 by adding the measured delay values around different selections of three or more sensors. When the result of addition is zero, as it should be, all the appropriate delay measurements are assumed to be correct and are processed at 10. Any faulty measurements are repeated and the correct measurements alone are used to calculate the direction of the source of the signal. <IMAGE>

Description

SPECIFICATION Acoustic direction detector This invention relates to apparatus for detecting the direction of a target which emits or reflects sound.

Known systems for performing this function incorporate a great number of sensors but only three are essential in orderto determinethedirection ofthe target in a single plane (four in 3 dimensions). This invention arose from consideration ofthe possibility of building a detector having, for cost reasons, the minimum number of sensors: namely three.

A system having three sensors A, B and C is shown in Figure 1 and would operate by measuring the delay in arrival of a sound signal from atargetTat (i) B relative to A (positive in the illustrated example) (ii) C relative to B (negative in the illustrated example) (iii) A relative to C (negative in the illustrated example) From the above measurements, and from a knowledge of the spacing of the sensors and of the velocity ofsound; the direction ofthe target can be deduced.

Whilst such a system could be provided at an econ omic cost (relative to a known system incorporating say ten to a hundred or more sensors) it suffers from the disadvantage that one measurement made incorrectly will prevent satisfactory operation. This could be caused byfailure of one ofthe sensors orofthe mechanism made to produce the measurement.

The invention stemmed from the realisation that the correct operation of a system as shown in Figure 1 can be tested by adding the delays (i), (ii) and (iii) referred to and testing that the result is zero. Further more, if at least onefurthersensor is included, a numberof different such tests can be made so as to identify precisely which ofthe measurements are correct andwhich of any arefaulty.

Preferably at least two such further sensors, making a total of five, are included since this enables a series of tests to be carried out on the measurements to identify a failed element or a failure in a delay measuring mechanism, which will normallybeacor- relator.

One way in which the invention may be performed will now be described by way of example with referenceto Figures 2 and 3 of the accompanying drawings in which Figure2 shows a defence mechanism designed to detect a target and to launch a missile towards it; and Figure3shows in more detail a control unitofthe mechanism in Figure 1.

Figure 2 shows a launcher 1 containing a missile 2 and a control unit illustrated schematically to detect a threatening target3 and to launch the missile towards it.

The launcher 1 includes five acoustic sensors A,B,C,D and E, the term acoustic being used in this specification generically to include ultrasonic and subsonicaswell as audible sound. The outputsfrom the five sensors pass to a control unit shown in detail in Figure 3.

In the control unit the signals from the sensors pass along five respective channels containing amplifiers 4 and filters 5 to an interconnection unit 6 which serves to connect each of its various inputs a toe to those of its outputs denoted by the same refer ence letter.

Ten correlators 7 are arranged so that each receives a different pair of input signals. The result of each correlation reaches a maximum at a time, relat veto some reference, equaltothetime delay between the two inputs. Each correlator is followed by a processor8which produces a digital signal representing this time value and this signal is passed to a switching unit9 and then to a cosine law evaluator 10 which, for each input time value, calculates the direction angle Y of the target relative to the direction of the line joining the appropriate two sensors. This is done by using the equasion.

Cos Y = measured time delay/maximum time delay.

The maximum line delay is equal to the sensor spacing divided bythespeed of sound.

The circuit 10 rationalises each calculated value of Y by adding or subtracting an appropriate angleto make all the direction measurements relative to a single arbituary direction Z-Z (Figure 2). These rationalised direction values are averaged to pro duce the final direction measurement P.

The interconnection unit 6 also passes its five input signals to a target detector 11 which makes a judge ment asto the presence of a target based on: the average amplitude of its input; the presence of a significant signal on a majority of its input; and a spectrum analysis of the received signal. A launch control mechanism 12 launches the missile 2 (in re sponge to a signal from 11) in a direction determined by the signal from 10.

A logic circuit 13 receives input signals I toXfrom respective correlatorsthese representing time delays between respective pairs of sensors. For each possible selection ofthree or more of the sensors it adds together the three appropriate time delay values and noteswhetherthe resultofaddition is zero.

The logic circuit 13 has an output line associated with each time delay value (i.e. correlator output) and it produces a control signal on any output line associated with atime delay value belonging to at least one selection for which the result of addition was zero. An output signal on an output line from 13 closes the appropriate switch in 9 so that onlythose correlator outputs which are correct are processed at 10.

1. Appa ratus for detecting the direction ofa targetwhich emits or reflects sound comprising at least four sensors, means for each pair of the sensors for measuring the delay in arrival of sound from the target at one relative to the other, means for adding groups ofthree or more delays around corresponding groups of three or more ofthe sensors and noting forwhich groups of delays the result is substantially zero, means for selecting from the measured delays those which belong to a group forwhich the result was zero and which can therefore be assumed to be

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Acoustic direction detector This invention relates to apparatus for detecting the direction of a target which emits or reflects sound. Known systems for performing this function incorporate a great number of sensors but only three are essential in orderto determinethedirection ofthe target in a single plane (four in 3 dimensions). This invention arose from consideration ofthe possibility of building a detector having, for cost reasons, the minimum number of sensors: namely three. A system having three sensors A, B and C is shown in Figure 1 and would operate by measuring the delay in arrival of a sound signal from atargetTat (i) B relative to A (positive in the illustrated example) (ii) C relative to B (negative in the illustrated example) (iii) A relative to C (negative in the illustrated example) From the above measurements, and from a knowledge of the spacing of the sensors and of the velocity ofsound; the direction ofthe target can be deduced. Whilst such a system could be provided at an econ omic cost (relative to a known system incorporating say ten to a hundred or more sensors) it suffers from the disadvantage that one measurement made incorrectly will prevent satisfactory operation. This could be caused byfailure of one ofthe sensors orofthe mechanism made to produce the measurement. The invention stemmed from the realisation that the correct operation of a system as shown in Figure 1 can be tested by adding the delays (i), (ii) and (iii) referred to and testing that the result is zero. Further more, if at least onefurthersensor is included, a numberof different such tests can be made so as to identify precisely which ofthe measurements are correct andwhich of any arefaulty. Preferably at least two such further sensors, making a total of five, are included since this enables a series of tests to be carried out on the measurements to identify a failed element or a failure in a delay measuring mechanism, which will normallybeacor- relator. One way in which the invention may be performed will now be described by way of example with referenceto Figures 2 and 3 of the accompanying drawings in which Figure2 shows a defence mechanism designed to detect a target and to launch a missile towards it; and Figure3shows in more detail a control unitofthe mechanism in Figure 1. Figure 2 shows a launcher 1 containing a missile 2 and a control unit illustrated schematically to detect a threatening target3 and to launch the missile towards it. The launcher 1 includes five acoustic sensors A,B,C,D and E, the term acoustic being used in this specification generically to include ultrasonic and subsonicaswell as audible sound. The outputsfrom the five sensors pass to a control unit shown in detail in Figure 3. In the control unit the signals from the sensors pass along five respective channels containing amplifiers 4 and filters 5 to an interconnection unit 6 which serves to connect each of its various inputs a toe to those of its outputs denoted by the same refer ence letter. Ten correlators 7 are arranged so that each receives a different pair of input signals. The result of each correlation reaches a maximum at a time, relat veto some reference, equaltothetime delay between the two inputs. Each correlator is followed by a processor8which produces a digital signal representing this time value and this signal is passed to a switching unit9 and then to a cosine law evaluator 10 which, for each input time value, calculates the direction angle Y of the target relative to the direction of the line joining the appropriate two sensors. This is done by using the equasion. Cos Y = measured time delay/maximum time delay. The maximum line delay is equal to the sensor spacing divided bythespeed of sound. The circuit 10 rationalises each calculated value of Y by adding or subtracting an appropriate angleto make all the direction measurements relative to a single arbituary direction Z-Z (Figure 2). These rationalised direction values are averaged to pro duce the final direction measurement P. The interconnection unit 6 also passes its five input signals to a target detector 11 which makes a judge ment asto the presence of a target based on: the average amplitude of its input; the presence of a significant signal on a majority of its input; and a spectrum analysis of the received signal. A launch control mechanism 12 launches the missile 2 (in re sponge to a signal from 11) in a direction determined by the signal from 10. A logic circuit 13 receives input signals I toXfrom respective correlatorsthese representing time delays between respective pairs of sensors. For each possible selection ofthree or more of the sensors it adds together the three appropriate time delay values and noteswhetherthe resultofaddition is zero. The logic circuit 13 has an output line associated with each time delay value (i.e. correlator output) and it produces a control signal on any output line associated with atime delay value belonging to at least one selection for which the result of addition was zero. An output signal on an output line from 13 closes the appropriate switch in 9 so that onlythose correlator outputs which are correct are processed at 10. CLAIMS

1. Appa ratus for detecting the direction ofa targetwhich emits or reflects sound comprising at least four sensors, means for each pair of the sensors for measuring the delay in arrival of sound from the target at one relative to the other, means for adding groups ofthree or more delays around corresponding groups of three or more ofthe sensors and noting forwhich groups of delays the result is substantially zero, means for selecting from the measured delays those which belong to a group forwhich the result was zero and which can therefore be assumed to be measured correctly, and means for using the selected delays to calculate the direction ofthe target.

2. Apparatus according to claim 1 including at least five sensors.

3. Apparatus substantially as described with re ferenceto the accompanying drawing and substantially as illustrated therein.