Acoustic hit indicator

This invention discloses a method of indicating information related to the trajectory of a projectile traveling at a supersonic velocity, the trajectory intersecting a predefined target plane at a point of incidence and having an angle of incidence with the target plane, the method including sensing a shock wave generated by the projectile at a plurality of fixed locations in a vicinity of the target plane, not all of which locations lie on a single straight line, and providing a plurality of outputs responsive, respectively, to the shock wave sensed at the plurality of locations determining a time-delay for each of the plurality of locations, relative to a predefined, common, reference time, based on the plurality of outputs and determining at least one of the point of incidence, the angle of incidence and the supersonic velocity by at least estimating a solution to a set of time-delay equations, each equation providing an independent representation of only one of the time-delays as a function of the point of incidence, the angle of incidence and the supersonic velocity. A system for indicating information related to the trajectory of a projectile traveling at a supersonic velocity and intersecting a predefined target plane at a point of incidence, the trajectory having an angle of incidence with the target plane is also disclosed.

I claim:

1. A method of indicating information related to the trajectory of a projectile traveling at a supersonic velocity, the trajectory intersecting a predefined target plane at a point of incidence and having an angle of incidence with said target plane, the method comprising:

sensing a shock wave generated by the projectile at a plurality of fixed locations in a vicinity of said target plane, not all of which locations lie on a single straight line, and providing a plurality of outputs responsive, respectively, to the shock wave sensed at said plurality of locations;

determining a time-delay for each of said plurality of locations, relative to a predefined, common, reference time, based on said plurality of outputs; and

determining at least one of said point of incidence, said angle of incidence, said supersonic velocity and a time offset which represents said reference time, by at least estimating a solution to a set of time-delay equations of the form ##EQU17## wherein (x.sub.k,y.sub.k,h.sub.k), k=1, 2, . . . , N, represent the coordinates of N of said locations, respectively, t.sub.k represent the determined time-delays, C represents the velocity of sound, v represents said projectile supersonic velocity, .alpha. represents said angle of incidence, t.sub.offset represents the time offset, and x.sub.T and h represent coordinates of said trajectory on said target plane.

2. A method according to claim 1, wherein said plurality of locations comprise at least five separate locations in the vicinity of the target plane.

3. A method according to claim 1 and further comprising providing an output responsive to the estimated value of at least one of said point of incidence, said angle of incidence and said supersonic velocity.

4. A method according to claim 1 and comprising displaying the estimated value of at least one of said point of incidence, said angle of incidence and said supersonic velocity.

5. A method according to claim 1 wherein at least two of said locations are not at the same distance from said target plane.

6. A method according to claim 5, wherein said plurality of locations comprises a first group of locations positioned substantially along a line parallel to said target plane, and a second group of at least one additional location positioned at a different distance from said target plane than said first group of locations.

7. A method according to claim 1 wherein at least estimating a solution to said set of time-delay equations comprises applying a least-squares estimation algorithm.

8. A method according to claim 7 wherein applying a least-squares estimation algorithm comprises applying an iterative least-squares estimation algorithm.

9. A method according to claim 7 wherein applying a least-squares estimation algorithm comprises applying a variation of a Gauss-Newton solution.

10. A method according to claim 1 wherein said incidence angle lies on a predefined incidence plane substantially perpendicular to said target plane.

11. A method according to claim 10 wherein said incidence plane comprises a substantially horizontal plane.

12. A method according to claim 1 wherein said target plane comprises a substantially vertical plane.

13. A system for indicating information related to the trajectory of a projectile traveling at a supersonic velocity and intersecting a predefined target plane at a point of incidence, said trajectory having an angle of incidence with said target plane, the system comprising:

a plurality of acoustic sensors located at fixed positions in a vicinity of said target plane, not all of which positions lie on a single straight line, each sensor providing an output responsive to a shock wave generated by said projectile; and

a processor which determines a time-delay for each of said plurality of positions, relative to a predefined, common, reference time, based on the output of said sensors, and which determines at least one of said point of incidence, said angle of incidence, said supersonic velocity and a time offset which represents said reference time, by at least estimating a solution to a set of time-delay equations of the form ##EQU18## wherein (x.sub.k,y.sub.k, h.sub.k), k=1, 2, . . . , N, represent the coordinates of N of said locations, respectively, t.sub.k represent the determined time-delays, C represents the velocity of sound, v represents said projectile supersonic velocity, .alpha. represents said angle of incidence, t.sub.offset represents the time offset, and x.sub.T and h represent coordinates of said trajectory on said target plane.

14. A system according to claim 13, wherein said plurality of sensors comprises at least five sensors.

15. A system according to claim 13 and further comprising a display which displays the estimated value of at least one of said point of incidence, said angle of incidence and said supersonic velocity.

16. A system according to claim 13 wherein at least two of said sensors are not at the same distance from said target plane.

17. A system according to claim 16, wherein said plurality of sensors comprises a first group of sensors positioned substantially along a line parallel to said target plane, and a second group of at least one additional sensor positioned at a different distance from said target plane than said first group of sensors.

18. A system according to claim 13 wherein said processor at least estimates a solution to said set of time-delay equations by applying a least-squares estimation algorithm.

19. A system according to claim 18 wherein said least-squares estimation algorithm comprises an iterative least-squares estimation algorithm.

20. A system according to claim 18 wherein said least-squares estimation algorithm comprises a variation of a Gauss-Newton solution.

21. A system according to claim 13 wherein said target plane comprises a substantially vertical plane.

22. A system according to claim 13 wherein said angle of incidence lies on a predefined incidence plane substantially perpendicular to said target plane.

23. A system according to claim 22 wherein said incidence plane comprises a substantially horizontal plane.

24. A system according to claim 13 and comprising a control unit, wherein said processor provides said control unit with an output responsive to said estimated value of at least one of said point of incidence, said angle of incidence and said supersonic velocity.

25. A system according to claim 13 wherein said plurality of acoustic sensors comprises a plurality of acoustic transducers.

26. A system according to claim 13, wherein said processor is configured to ignore outlier time-delays.

27. A system according to claim 13, wherein the set of time-delay equations is an explicit scalar expression of the time-delays as a function of said point of incidence, said angle of incidence and said supersonic velocity, and an iterative algorithm, involving analytical expressions of the derivatives of said time-delays with respect to said point of incidence, said angle of incidence and said supersonic velocity, is utilized to solve the set of time-delay equations.