Supercavitating projectile tracking system and method
View Patent ↗A system for three-dimensional tracking of high speed undersea projectiles may utilize a distributed field of randomly positioned passive acoustic sensors. The system measures variables related to the pressure field generated by a supercavitating projectile in flight wherein the amplitude of the pressure generated at a point in space is related to the projectile dimensions, velocity, and trajectory. The system iteratively processes data from the sensors to measure launch velocity, flight direction (trajectory), ballistic coefficient (drag), and/or maximum range.
1. A system for tracking an underwater object comprising:
a plurality of randomly distributed passive pressure transducers at positions offset from a projected path of said underwater object, said plurality of randomly distributed passive pressure transducers comprising directional transducers, each said transducer being operable to detect a peak transient pressure;
a data flow path operatively connected to each of said plurality of passive pressure transducers for transferring data produced thereby; and
at least one processor joined to said data flow path and operable for utilizing said data produced by said plurality of randomly distributed passive pressure transducers to determine a trajectory of said underwater object wherein said at least one processor is programmed to iteratively determine the trajectory based on an initial estimate of a velocity and a trajectory.
2. The system of claim 1 , wherein said processor is programmed to utilize a time of occurrence of said peak transient pressure and an amplitude of said peak transient pressure to determine said trajectory.
3. The system of claim 2 , wherein said processor is also programmed to determine a ballistic coefficient of said underwater object.
4. The system of claim 2 , wherein said processor is programmed to distinguish peak pressure from a noise made during launch of the underwater object.
5. The system of claim 2 , wherein said processor is programmed to distinguish peak pressure from a cavity closure noise made during passage of the underwater object.
6. The system of claim 1 , wherein said plurality of randomly distributed passive pressure transducers are randomly positioned within one hundred feet of said path of said underwater object.
7. The system of claim 1 , wherein said plurality of randomly distributed passive pressure transducers comprises less than twenty but more than ten of said passive pressure transducers.
8. The system of claim 1 wherein said at least one processor iteratively produces a trajectory by:
determining an error of said initial estimate for each of said plurality of passive pressure transducers;
computing a sum of the determined errors;
producing a perturbed estimate by perturbing said initial estimate of velocity and trajectory with a random perturbation having a perturbation magnitude;
determining a perturbed error of said perturbed estimate for each of said plurality of passive pressure transducers;
computing a perturbed sum of the determined perturbed errors;
comparing said perturbed sum against said sum, replacing said original estimate with said perturbed estimate if said perturbed sum is less than said sum, and retaining said original estimate if said sum is less than said perturbed sum; and
iterating said steps of producing a perturbed estimate, determining a perturbed error, computing a perturbed sum and comparing with a lower perturbation magnitude until trajectory accuracy is within 0.1 degrees, and velocity accuracy is within 10 meters per second.
9. The system of claim 1 , wherein the processor is specifically programmed to determine the trajectory of the underwater object when the underwater object has a velocity greater than 0.3 Mach.
10. A method for detecting velocity and trajectory of an underwater object comprising:
supporting a plurality of passive pressure transducers in water at a plurality of depths, said plurality of passive pressure transducers being arranged in said water so as to extend along at least a portion of a projected underwater path of said underwater object wherein said plurality of passive pressure transducers are directional passive pressure transducers;
launching an underwater object;
producing acoustic signal data comprising peak transient pressures and times of arrival of said peak transient pressures with respect to times at which said underwater object passes a point of closest approach for each of said plurality of passive pressure transducers; and
determining said velocity and trajectory of said underwater object in real time utilizing said peak transient pressures and times of arrival of said peak transient pressures with respect to times at which said underwater object passes said point of closest approach for each of said plurality of passive pressure transducers, said step of determining further including formulating an initial estimate of said velocity and trajectory, and iteratively producing a solution for said velocity and said trajectory based on the initial estimate of said velocity and trajectory.
11. The method of claim 10 , further comprising providing that said plurality of passive pressure transducers are randomly positioned within one hundred feet of said projected path of said underwater object.
12. The method of claim 10 , further comprising determining a ballistic coefficient of said underwater object.
13. The method of claim 10 , further comprising utilizing less than twenty but more than ten of said passive pressure transducers.
14. The method of claim 10 , further comprising the step of distinguishing peak pressure from launch noise prior to said step of determining the velocity and trajectory.
15. The method of claim 10 , further comprising the step of distinguishing peak pressure from cavity closure noise prior to said step of determining the velocity and trajectory.
16. The method of claim 10 , where said step of determining said velocity and trajectory comprises:
determining an error of said initial estimate for each of said plurality of passive pressure transducers;
computing a sum of the determined errors;
producing a perturbed estimate by perturbing said initial estimate with a random perturbation having a perturbation magnitude;
determining a perturbed error of said perturbed estimate for each of said plurality of passive pressure transducers;
computing a perturbed sum of the determined perturbed errors;
comparing said perturbed sum against said sum, replacing said original estimate with said perturbed estimate if said perturbed sum is less than said sum, and retaining said original estimate if said sum is less than said perturbed sum; and
iterating said steps of producing a perturbed estimate, determining a perturbed error, computing a perturbed sum and comparing with a lower perturbation magnitude until trajectory accuracy is within 0.1 degrees, and velocity accuracy is within 10 meters per second.