AUTOMATIC DETERMINATION OF SNIPER POSITION FROM A STATIONARY OR MOBILE PLATFORM

Abstract: A method is described to determine the position of one or more snipers when a listening station is located in the target area, and when the snipers are randomly located. The intelligent listening system can be located at a stationary or a mobile platform, consisting of a minimum of 2 microphones in the combination with a compass. The listening station registers shot sound from the sniper weapon and the shock wave from the projectile trajectory. These two signals are utilised to determine the north adjusted direction to the weapon and the shock wave. The position of the weapon is determined when utilising the speed of the projectile and the time difference between the shot sound from the weapon and the shock wave. The position is determined as the distance along the direction vector from the listening station and to the sniper weapon. Additionally the closest distance to the trajectory of the projectile is determined. A corresponding requirement can be satisfied in an open battlefield or for general surveillance when the time and the position of gunfire is of interest. Such information can be communicated over telephone or radio.

Description: Automatic determination of sniper position from a stationary or mobile platform The present invention relates to an automatic method of passive determination of sniper positions randomly located in the surroundings, utilising a simple stationary or mobile listening station, consisting of an intelligent listening system includmg two or more microphones together with a compass supporting the solution Such a method of surveillance of shooting activity is utmost important during unsafe conditions when snipers are especially active, as it may be during UN operations, and the importance of identifying the position of any shoot is vital The method is meant for stationary as well for mobile activities. The following shows areas for which a stationary solution can be useful Airports Official buildings Military facilities Private buildings, VIP's in governmental administration Unsafe areas The method can be utilised for mobile activities as follows Hand held in the battle field Mounted on a car when driving in unsafe areas Equipment that is utilising the present invention can be located to areas with shootmg activities, mounted on a car that is moved mto the area Remote monitoring by radio satisfies safe monitoring of the situation when gunfire is registered Various methods for the detection and positioning of sound sources have been patented, and these are as follows: GB-3.336.245, GB-2.062.864, GB-2.099.995. US-3.838.593 and US-3.626.750, GB- 1.349.120, NO-1.39.240, GB-1.174.048, GB-342.800, GB-1.452.788, GB-2.167.556, US-4.372.151, US-4.543.817, WO 82/00718. NO 169678, GB-A.2.181.238, US 4.333.170, EP-A.64.477, GB-A.2.191.580, US-5.070.484 and US-5.099.455 A majority of these patents deals with leakage in pipes, and expects that the sound moves through solid material. Thereby they are distinctly deviating from the present invention. Most methods are oriented towards leakage problems in situations where the positioning can be achieved along one line (one dimensional). EP-A.64.477, GB-A.2.181.238 and NO 169678 on the other hand, are utilised to detect, determine the direction to and the position of acoustic sound through air, all utilising more than one microphone cluster for such positioning, and have several microphones in each cluster for that purpose. EP-A.64.477 and GB-A.2.181.238 are related to weapons and gunfire. Most of these methods are using several intercepting directional vectors, with base in several microphones clusters in order to determine the position of sound origin. GB-A.2.191.580 is using an array of distributed microphones to determine the position of weapons by sound. The present invention relates to the determination of the position of weapons, utilising one cluster only with 2 or more microphones. The position calculations are made for weapons with projectiles that creates shock waves along the projectile trajectory. These shock waves are used together with the shot sound to determine the position of the weapon that fired the projectile. Both sound impressions have impulse features that makes it possible to distinguish the sound pattern from other existing sound. None of the above mentioned methods are using such a principle for the positioning of a weapon. The present invention is significantly different from the above mentioned methods. There are no known means for such automatic determination of sniper position, based upon a stationary or mobile listening station, requiring a compass for vehicle angular and speed corrections to the calculations considering also a variable projectile speed in the position calculations. The present invention is providing a tool for minimising the equipment for determination of sniper positions, facilitating a method for one person to achieve such determination without the need for any co-ordination with other persons or with an other mobile and fixed mounted listening equipment. The present invention provides a method for the determination of position of one or more active weapons when the projectiles from these weapons creates a shock waves along their trajectories. A listening station with 2 or more microphones in a cluster is required for the implementation of the method. These microphones picks up signals from all available acoustics within the frequency domain of the microphones for acoustic monitoring in the sound measuring system of the listening station. The sound measuring system measures, calculates and do the analysis of any existing environmental sound, received from the microphones. Amplitude/phase/frequency-data for each microphone is calculated along with a complete and continuos evaluation of the sound impulses received. A shock wave from a projectile has no pre warning. This sound is distinctly different from the shot sound as well as any other environmental sound. The direction to the shock wave is determined by a relative phase measurement, eventually also together with time measurement. A 2 or 3 dimensional vector can be calculated, depending only upon the number of microphones involved. A corresponding determination of the direction to the weapon is made when the shot sound reaches the sensor. The projectile follows a trajectory when it leaves the weapon, and this trajectory identifies one side of a triangle in which the two calculated velocity vectors represents the remaining two sides of the triangle. The position of the weapon can be determined along the directional vector with base in the position of the cluster, taking into consideration the speed of the projectile and the time utilised between the two corners of the triangle. The method is general by nature, and do not require any knowledge about the surroundings. This is achieved as the methods described in the following claims. The method makes it possible to estimate the position of a sniper when the sniper is positioned at a point K and shoots towards point S as shown in Fig. 1. The line (trajectory) K-S has a minimum distance 1 from the cluster M. The point P at the trajectory K-S has a minimum distance from the sensor. Point X is the so called "bang generation point". The following is one example on possible ways of calculating the sniper position: The speed of the projectile is known as: 1. v = v(t) The distance from the projectile to the closest point P on the trajectory K-S at time t is given by: See Fig. 1. The sound generated by the projectile in a position p reaches the sensor after a time τ , calculated from the point in time when the shot was fired. The shock wave reaches the sensor at a time given by the minimum of the above function. A corresponding value for t is t m» . This value is found by solving the following equation: This leads to the equation: At time t ™ ., the projectile was in the position X on the trajectory K-S. The position X is identified on the said trajectory at a distance given by the angle β in relation to perpendicular from the sensor to the trajectory. The angle β is defined as follows: This gives further as follows: n • / θ \ V(t mιn) 7. sιn(β = c The listening station is recording the shot sound from the weapon as well as the shock wave from the projectile when passing. With the basis in a reference line as shown in Fig. 1, the angles to the two sound impressions are measured as correspondingly angle di and angle di relative to the reference line. The distance h is thereafter calculated as the distance between the position K and P. The shot sound reaches the sensor at a time τ<> : c An it follows that: 10. Δτ = τ« - τ wn By means of the above equations, Λ and / can be determined numerically, and principally this is made by finding the solutions of the following equations: 11. θι - θ. = arctan( -J - β(λ,/)+σ ι The method gives an accuracy estimate for the distance h and 1, while σ. and σ: represents the measuring error for the measurements di - di and Δτ . The position calculations can be made when the listening station is stationary, or is transported with a person or mounted on a moving vehicle. A compass is utilised in order to compensate for north corrections in the angular calculations. A feature of the present invention is that counter mechanisms enables the calculation of shots, starting at any time. Such a calculation can be made for all weapons for whom positions are calculated as well as for those that have no shock wave related. The listening station is equipped with a compass, utilised to correct the north orientation of any angular calculation. Another feature of the present invention is that the listening station can be connected to a presentation unit, thereby providing the operator with available data for the various weapons being active in the area. A central feature of the invention is that the operator can have presented to him the position of the firing weapons, and the time for such firing. Another feature of the present invention is that the listening station includes automatic and continuos calibration of microphone characteristics. This is achieved by locating one or more sound generates in known positions within the reach of the listening station. This is a quality assurance for the detection and angular capabilities. Another feature of the present invention is that the listening station is self sufficient regarding power, thereby simplifying transportation and installation in an emergency. A feature of the present invention is that the listening station can be connected to a separate alarm & warning system, reached by radio or telephone.

Claims: Claims 1. A method for the passive automatic determination of the position of one or more sniper weapons in active use from on or more geographical positions, by utilising a stationary or mobile listening station consisting of an intelligent sound measuring system attached to a set of two or more microphones and a compass, characterised in that the listening station measures the sound signals from the use of sniper weapons within line of sight and the reach of the listening system through air, that the microphones have well defined inter distances, that the listening station is located within the target area of the sniper weapon, that the said weapon are utilising projectiles that creates characteristic shock waves, that a projectile from said weapon establishes a characteristic shot sound when the projectile leaves the weapon, that the microphone signal is continuously treated in the time domain, in the frequency domain or in a combination thereof, and that the time for the shock wave arrival and the shot sound arrival are both detected by their characteristics, that the time difference between the shock wave and the shot sound is calculated, that the direction to the characteristic shock wave is calculated, utilising phase measurement, time-/amplitude measurements and cross correlation of signals independently or in combinations, that the direction to the characteristic shot sound is calculated, utilising phase measurement, time-/amplitude measurements and cross correlation of signals independently or in combinations, that the direction to the shock wave and the shot sound is north adjusted by means of a compass, that the speed of the projectile is measured or is made available by other means, as the speed of the projectile, the time difference, the direction to the weapon and the direction to the shock wave are utilised to determine the position of the sniper weapon, measured along the north adjusted direction to the weapon from the listening station. 2. A method according to claim 1, characterised in that the listening system counts and register the number of detected shots for one or more directions and positions. 3. A method according to claim 1, characterised in that the listening system is connected to a display for the presentation of weapon characteristics. 4. A method according to claim 1 , characterised in that the listening system can provide the operator with the direction to and the position from where shoots are made, and the time for each shooting. 5. A method according to claim 1, characterised in that one or more sound generators are located in known positions for the automatic calibration of the characteristics of the microphones in the listening station. 6. A method according to claim 1 , characterised in that the listening station can easily be relocated, due to self sufficiency in power and other supplies. 7. A method according to claim 1, characterised in that the listening station can be connected to an alarm and warning function. 8. A method according to claim 1, characterised in that the listening system can be connected to a communication unit for the transmission of weapon characteristics.

Inventors: ENDRESEN TORE, GUSTAVSEN ARVE, OTTERLEI RAGNVALD, ENDRESEN, TORE, GUSTAVSEN, ARVE, OTTERLEI, RAGNVALD
Applicants: ENDRESEN TORE, GUSTAVSEN ARVE, OTTERLEI RAGNVALD, ENDRESEN, TORE, GUSTAVSEN, ARVE, OTTERLEI, RAGNVALD
Application year: 1996
Main classification: G01S3
IPC codes: G01S3, G01S5, G01S11