System and method for disambiguating shooter locations
View Patent ↗Systems and methods for locating the shooter of supersonic projectiles based on shockwave-only measurements are described. Muzzle blast signals are neither sought nor required. The system uses at least five, preferably seven, acoustic sensors that are spaced apart at least 1 meter. The sensor signals are acquired with a time resolution in the order of microseconds and processed to find and disambiguate the shockwave arrival angle unit vector. Two different Time-Difference-Of-Arrival (TDOA) measurement techniques are described, with one technique using counters in each signal channel and the other technique using cross-correlation between signal channels. A genetic algorithm can be used to efficiently disambiguate the results.
1. A method for disambiguating a projectile trajectory from shockwave-only signals, comprising:
measuring at least an initial portion of the shockwave-only signals at five or more spaced acoustic sensors forming an antenna;
determining from the measured initial portion of the shockwave-only signals Time-Differences-Of-Arrival (TDOA) for sensor pairs;
applying a genetic algorithm to an initial chromosome, that comprises projectile trajectory assumptions, for a predefined number of generations;
computing residuals for solutions obtained with the chromosomes from the genetic algorithm;
performing a gradient search on a solution having a smallest residual and on its ambiguous alternate solution; and
if a ratio of the solution having the smallest residual and its ambiguous alternate solution is greater than a predefined value, designating the solution having the smallest computed residual as the disambiguated projectile trajectory.
2. The method of claim 1 , wherein the predefined value of the ratio is approximately 2.
3. The method of claim 1 , wherein the chromosome comprises a 4-tuple having elements selected from the group consisting of shooter azimuth, shooter elevation, missed azimuth and missed elevation.
4. The method of claim 1 , wherein applying a genetic algorithm comprises applying crossover and mutation operators.
5. The method of claim 4 , wherein the crossover operator comprises crossover azimuth and crossover missed azimuth operators.
6. The method of claim 5 , wherein the crossover azimuth operator exchanges shooter and trajectory azimuth between two chromosomes.
7. The method of claim 5 , wherein the crossover missed azimuth operator exchanges missed azimuth and missed elevation between two chromosomes.
8. The method of claim 4 , wherein the mutation operator comprises field-mutation, incremental mutation, flip mutation, and no mutation.
9. The method of claim 8 , wherein the field-mutation operator replaces a chromosome field with a randomly selected value.
10. The method of claim 8 , wherein the incremental mutation operator induces small mutations in all fields of a chromosome.
11. The method of claim 10 , wherein the small mutation operator comprises changes in all fields of a chromosome of less than ±2° in shooter azimuth and elevation, and less than ±0.5° for missed azimuth and elevation.
12. The method of claim 10 , wherein the flip-mutation operator comprises changing the solution having a smallest residual into its ambiguous alternate solution.
13. The method of claim 10 , wherein the flip-mutation operator comprises leaving a chromosome unaltered.
14. The method of claim 1 , wherein determining a Time-Difference-Of-Arrival (TDOA) for a sensor pair comprises performing a cross-correlation between shockwave signals detected at the sensor pairs and selecting the TDOA that produces the smallest computed residual.