GB2105464A

GB2105464A - Sound source location system

Info

Publication number: GB2105464A
Application number: GB08126688A
Authority: GB
Inventors: Alan Eusebius John Poultney; Peter William Gould
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1981-09-03
Filing date: 1981-09-03
Publication date: 1983-03-23
Also published as: GB2105464B

Abstract

A sound source location system comprises two spaced groups A1, A2 of transducers the groups each having their transducers 1, 2, 3 etc mutually spaced by a distance less than the distance travelled by sound in the minimum expected interval between sound occurrences. For each group, means is provided for determining signals representative of the direction of sounds received by all transducers, in dependence upon the receipt time of the sounds. Means is provided for deriving, from the signals representative of direction, signals representative of sound source locations the validity of which is confirmed in dependence upon the time interval between receipt of the sound by each transducer group. <IMAGE>

Description

SPECIFICATION Sound source location system This invention relates to sound source detection and more particularly to the detection of one sound source in the presence of other similar sound sources.

In a gun location system known to us, the position of the gun is determined from measurements of times of arrival of the gun sound at a line array of microphones whose positions are known accurately. The microphones in such an array are spaced apart one to the next by several kilometres in order to provide accurate location of the sound source in dependence upon the relative time of receipt of a sound by each microphone in the array. Such a system is accurate and satisfactory in the case of an isolated sound. However, ambiguity can arise when several sounds occur within close time intervals e.g. firing of several guns. This is because the spacing results in a delay in sound reception and any other gun fired within that time delay can provide a masking value.

The present invention seeks to provide a sound location system which is less susceptible to ambiguity of measurement when several sound sources are emitting sounds close together in time.

According to the invention there is provided, a sound source location system, comprising two spaced groups of transducers the groups each having their transducers mutually spaced by a distance less than the distance travelled by sound in the minimum expected interval between sound occurrences, means for determining, for each group, signals representative of direction of sounds received by all transducers, within time periods defined by the maximum time for sound to travel between each transducer in the group, in dependence upon the receipt time of the sounds, means for determining, from the signals representative of direction, signals representative of sound locations the validity of which is confirmed in dependence upon the time interval between receipt of the signal by each transducer group.

The groups may comprise two or more transducers. In one advantageous configuration three transducers are employed arranged at the corners of a right angled or isoscelese triangle. The transducers in each group may be mutually spaced by a distance of between 10 and 300 metres, e.g.

50 metres.

In a refinement of the invention for providing particularly accurate bearing information relating to the source there is provided an array of additional transducers which are spaced apart one from the next by a distance greater than the mutual spacing of transducers in each of said groups, means for determining from each of said signals representative of sound locations an individual sampling interval for each transducer in the array during which interval sound from the source is expected at the transducer, means for sampling the output signals of the transducers in the array which occurs during the individual sampling intervals and means for determining the sound source location in dependence upon the relative times of receipt of the signal by the transducers in the array.

The transducers of the array may be disposed in line. The two spaced groups of transducers may be disposed in line with the transducers of the array or may be spaced from the array.

The outputs from each of the transducers may be stored prior to processing storage may be effected on magnetic tape.

The groups of transducers may be arranged in front of the array so that sounds are received thereby prior to receipt by the transducers in the array thereby permitting processing immediately upon receipt. Alternatively or additionaliy the signals from the array may be delayed to permit processing after receipt of a sound by the groups.

In one advantageous form the groups each have three transducers. The three transducers may be mutually displaced to define the vertexes of a right angled or isoscelese triangle.

The transducers in the array may be mutually spaced one from the next by a distance of between 0.5 and 5 Km conveniently 1 to 2 km.

In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a schematic illustration of a group of three transducers arranged in a triangular disposition receiving a sound, Figure 2 is a schematic diagram showing two groups of transducers of a sound location system constructed in accordance with the invention, Figure 3 is a schematic block diagram showing the processing functions carried out by the system of Figure 2, Figure 4 is a schematic diagram of a refinement of the invention which employs an array of additional transducers, Figure 5 is a schematic block diagram showing the additional processing functions for the system of Figure 3 and Figure 6 is a schematic diagram similar to Figure 2 and showing an alternative disposition of the two groups of transducers relative to the array of additional transducers.

The drawing of Figure 1 shows three transducers e.g. microphones 1, 2, 3 disposed in a triangular grouping forming a right angled triangle. The microphone 2 is equidistantly spaced from microphones 1 and 3 by a distance d. The direction of approach of a sound is shown by a line bearing an arrow and this is inclined to side 1-2 of the triangle by an angle 0.

If V-velocity of sound, then the time difference between receipt of the sound by microphones 1 and 2 is: d cos 0 t12 V V and the time difference between the receipt of the sound by microphones 2 and 3 is: d sin 0 t23= V t23 0=tan-' t12 Accordingly the direction of a sound source can be established. If the distance d is large then when there are several sound sources emitting sounds close together in time, e.g. heavy gunfire conditions, it is difficult, to isolate related transient signals developed by the transducers. If d is made small e.g. 10 to 300 metres then this difficulty is reduced.

If d=50 m the maximum value oft is 50 =148 m sec.

337 Any transients spaced by greater than that time can be ignored as being unrelated.

Under heavy gunfire conditions there will be a continuous stream of transients. Bearings 0 can be calculated for all groups of three transients which occupy less than 1 50 m sec. time period.

If two groups of transducers as previously described are employed, which groups are spaced apart by a predetermined distance D as shown in Figure 2, then bearings a from each group 1, 2, 3 and 1', 2', 3' can be calculated for each complement of transients spaced by less than 1 50 m sec.

The bearing calculations could be carried out either at one of the group positions or at a remote Command Post (C.P.). A list of bearings and corresponding timings can be prepared for each group.

For any particular gun the difference between the times of arrival of the sound at the two groups will be proportional to the difference in distances between the groups and the gun. Thus by comparing the ranges to the intersection points of pairs of bearings with the time difference between the constituents of the pair a "best fit" condition can be reached for the gun location and a pair of bearings and corresponding times.

Referring now to Figure 3 the processing function blocks, for processing the signals received by the microphones 1, 2, 3, and 1', 2', 3', are shown.

Each group has each microphone coupled by a separate transient detector to a correlator 11 for the group. The correlators 11 determine for each group all combinations of three transients which occur within a time period of d/V where d is the length of the equilateral side of the triangle and V is the velocity of sound.Values of (3 and 0' for each of these combinations are calculated in blocks 12 by performing the calculation

The values of On and On' are used together with the known distance D separating the two groups to calculate in block 13 apparent distance values rn and rn' of sources for all of the combinations of transients by performing the calculations: : D cos 8,' D cos On and and and sin (8,-8,') sin (8,-8,') The values of rn and rn' are used to provide for all combinations of rn and rn' a range of differential distance values r,,-r ' This calculation is performed in block 14. The differential distance values are assessed in block 1 5 and only values less than the maximum possible value D are routed to divider 16 for further processing.

The divider 16 divides the differential distance values by V the velocity of sound in air, to provide differential time values for the combinations of r,--r,' to be assessed. The differential time values are routed to comparator 17.

The correlators 11 also provide output values tnl t,' which are the mean values of arrival time of sounds at the two groups. Difference values tntnt are calculated in block 1 8 and are compared in comparator 1 7 with the values rr ' n n V to establish values which are closely compatible. The value of rn and On corresponding to the established value is routed via selector 19 to block 20 where the x and y coordinates of the location of the sound source are calculated in accordance with the equations xn=rn sin On and yn=rn cos 8,.

The output coordinates can be employed to drive an x/y plotter, e.g. a calibrated cathode ray tube display, or a recorder.

The accuracy of the determination of the sound source location can be improved by employing an 'additional transducer array as shown in Figure 4. In this system a line array of transducers, in the illustrated example seven transducers M1 to M7, are spaced apart with the groups 1,2,3 and 1', 2', 3', of transducers located to one side. The transducers M1 to M7 are spaced apart by a distance of between 0.5 and 5 km one to the next. A spacing of 1 to 2 km is particularly suitable. The known position of each transducer is defined by x/y coordinates x1y1-x7y7. Referring now to Figure 5 the additional processing steps over those shown in Figure 3 are illustrated.

The values of xn and yn previously determined in block 20 are routed to block 21 where values +h are added to each. The value A corresponds to the maximum expected error in the values of xn and y, previously determined.

The summed values are routed to block 22 where maximum and minimum time arrival values t, max and t, min are calculated for each transducer M1 to M7 in the array. These values are fed to selector 23 where transient signals which occur during the calculated time between t, max and t, min for each transducer are detected. These seven values are used to calculate new values for xn, y, in block 24. Again the values of xn, y, can be used to drive an xly plotter or a recorder.

The embodiment of Figure 6 is similar to the embodiment of Figure 4 but has the two groups of transducers MP3 and MP5 provided in the line array as opposed to being located to one side of it. In this particular case the groups have a 50 m spacing and two non directional transducers are provided at advance posts AP 1 and AP2 to one side of the line array.

Although the embodiments described con leniently employ three transducers in each group it should be appreciated that the invention is not r^tricted to this configuration. The groups could comprise two or more than three transducers with appropriate modification of the processing which will be apparent to those skilled in the art.

Although it is envisaged that continuous processing of signals is possible it is possible that the outputs of all of the transducers may be recorded simultaneously to enable subsequent processing with expanded processing time.

It will be appreciated that although the diagrams of Figures 3 and 5 show separate processing blocks to indicate specific mathematical functions, processing will normally be effected by suitable programming of a computer to perform the illustrated mathematical steps or to perform equivalent processing steps.

Although the invention has been devised for gun location it will be appreciated that it will also find application where detection of the location of a sound source is required in the presence of other interfering sound sources occurring closely spaced in time from the wanted sound e.g. seismic and sonar detection techniques.

Claims (filed on 30 July 1982) 1. A sound source location system, comprising two spaced groups of transducers the groups each having their transducers mutually spaced by a distance less than the distance travelled by sound in the minimum expected interval between sound occurrences, means for determining, for each group, signals representative of direction of sounds received by all transducers, within time periods defined by the maximum time for sound to travel between each transducer in the group, in dependence upon the receipt time of the sounds, means for determining, from the signals representative of direction, signals representative of sound locations the validity of which is confirmed in dependence upon the time interval between receipt of the signal by each transducer group.

2. A system as claimed in claim 1 , wherein the groups each comprise three transducers arranged at the corners of a right angled or isoscelese triangle.

3. A system as claimed in claim 1 or 2, wherein the transducers in each group are mutually spaced by a distance of between 10 and 300 metres.

4. A system as claimed in claim 3, wherein the transducers are mutually spaced by a distance of 50 metres.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The divider 16 divides the differential distance values by V the velocity of sound in air, to provide differential time values for the combinations of r,--r,' to be assessed. The differential time values are routed to comparator 17. The correlators 11 also provide output values tnl t,' which are the mean values of arrival time of sounds at the two groups. Difference values tntnt are calculated in block 1 8 and are compared in comparator 1 7 with the values rr ' n n V to establish values which are closely compatible. The value of rn and On corresponding to the established value is routed via selector 19 to block 20 where the x and y coordinates of the location of the sound source are calculated in accordance with the equations xn=rn sin On and yn=rn cos 8,. The output coordinates can be employed to drive an x/y plotter, e.g. a calibrated cathode ray tube display, or a recorder. The accuracy of the determination of the sound source location can be improved by employing an 'additional transducer array as shown in Figure 4. In this system a line array of transducers, in the illustrated example seven transducers M1 to M7, are spaced apart with the groups 1,2,3 and 1', 2', 3', of transducers located to one side. The transducers M1 to M7 are spaced apart by a distance of between 0.5 and 5 km one to the next. A spacing of 1 to 2 km is particularly suitable. The known position of each transducer is defined by x/y coordinates x1y1-x7y7. Referring now to Figure 5 the additional processing steps over those shown in Figure 3 are illustrated. The values of xn and yn previously determined in block 20 are routed to block 21 where values +h are added to each. The value A corresponds to the maximum expected error in the values of xn and y, previously determined. The summed values are routed to block 22 where maximum and minimum time arrival values t, max and t, min are calculated for each transducer M1 to M7 in the array. These values are fed to selector 23 where transient signals which occur during the calculated time between t, max and t, min for each transducer are detected. These seven values are used to calculate new values for xn, y, in block 24. Again the values of xn, y, can be used to drive an xly plotter or a recorder. The embodiment of Figure 6 is similar to the embodiment of Figure 4 but has the two groups of transducers MP3 and MP5 provided in the line array as opposed to being located to one side of it. In this particular case the groups have a 50 m spacing and two non directional transducers are provided at advance posts AP 1 and AP2 to one side of the line array. Although the embodiments described con leniently employ three transducers in each group it should be appreciated that the invention is not r^tricted to this configuration. The groups could comprise two or more than three transducers with appropriate modification of the processing which will be apparent to those skilled in the art. Although it is envisaged that continuous processing of signals is possible it is possible that the outputs of all of the transducers may be recorded simultaneously to enable subsequent processing with expanded processing time. It will be appreciated that although the diagrams of Figures 3 and 5 show separate processing blocks to indicate specific mathematical functions, processing will normally be effected by suitable programming of a computer to perform the illustrated mathematical steps or to perform equivalent processing steps. Although the invention has been devised for gun location it will be appreciated that it will also find application where detection of the location of a sound source is required in the presence of other interfering sound sources occurring closely spaced in time from the wanted sound e.g. seismic and sonar detection techniques. Claims (filed on 30 July 1982)

1. A sound source location system, comprising two spaced groups of transducers the groups each having their transducers mutually spaced by a distance less than the distance travelled by sound in the minimum expected interval between sound occurrences, means for determining, for each group, signals representative of direction of sounds received by all transducers, within time periods defined by the maximum time for sound to travel between each transducer in the group, in dependence upon the receipt time of the sounds, means for determining, from the signals representative of direction, signals representative of sound locations the validity of which is confirmed in dependence upon the time interval between receipt of the signal by each transducer group.

5. A system as claimed in any one of the preceding claims, comprising an array of additional

transducers which are spaced apart one from the next by a distance greater than the mutual spacing of transducers in each of said groups, means for determining from each of said signals representative of sound locations an individual sampling interval for each transducer in the array during which interval sound from the source is expected at the transducer, means for sampling the output signals of the transducers in the array which occurs during the individual sampling intervals and means for determining the sound source location in dependence upon the relative times of receipt of the signal by the transducers in the array.

6. A system as claimed in claim 5, wherein the transducers of the array are disposed in line.

7. A system as claimed in claim 6, wherein the two spaced groups of transducers are disposed in line with the transducers of the array.

8. A system as claimed in claim 6, wherein the two spaced groups of transducers are spaced from the array.

9. A system as claimed in any one of claims 5 to 8, wherein the outputs from each of the transducers are stored prior to processing.

10. A system as claimed in any one of claims 5 to 9, wherein the groups of transducers are arranged in front of the array so that sounds are received thereby prior to receipt by the transducers in the array thereby permitting processing immediately upon receipt.

1 A system as claimed in any one of claims 5 to 10, wherein the signals from the array are delayed to permit processing after receipt of a sound by the groups.

1 2. A system as claimed in any one of claims 5 to 11, wherein the transducers in the array are mutually spaced one from the next by a distance of between 0.5 and 5 km.

1 3. A system substantially as described herein with reference to the drawings.