Patent Application
20150301169
The present invention relates to a method and to a device for determining the trajectory of a bullet, shot by a small firearm after a low-arched or direct shot (small arm weapon) and travelling at a supersonic or subsonic speed, indicating the direction from which the bullet is coming.
The invention enables protection actions and/or response reactions by an operator in real time after the shot.
In particular, the invention relates to a method and to a device for localizing the position from which the bullet has been shot.
For decades, army and police forces have been more and more frequently facing asymmetric warfare situations. In particular, operations in urban places, where snipers and/or occasional fighters are hidden, are quite recurrent.
Such fighters have normally inferior technology, but in the combat scenario they can conceal in more advantageous positions than the regular forces. In fact, they can easily dissimulate in the crowd, shoot from hiding places or from normal vehicles, and then disappear in the traffic or in the crowd. This makes it difficult distinguishing the fighters from the civilians, in such a way that regular forces can be vulnerable to sniper shots from hidden and/or unattended locations.
For this reason, it is always more difficult and risky to carry out recognition missions in adverse territories even on armoured/armed vehicles, missions of defence of the territory and of military bases, of airports, of movable posts such as checkpoints and other structures, missions of protection of persons in an unpredictably adverse environment, missions of protection of military convoys or of humanitarian aids delivery means.
Therefore, the need is felt of systems for increasing the protection of such objects against shooters such as snipers, guerrilla fighters and occasional fighters.
Devices are known for localizing snipers that comprise acoustic sensors. Their performances strongly depend on sniper's camouflage. For instance, the acoustic devices are not much effective for localizing a bullet fired through a hole of a wall of a reconstructing. Furthermore, the acoustic devices are influenced by particular and temporary conditions like echoes caused by the structures of the urban environments, for example by buildings.
It is also known that the acoustic sensors are substantially unable to localize bullets travelling at a subsonic speed as in the case of shots from RPG (Reaktivnyj Protivotankovyj Granatomët, reaction anti-tank grenade launcher), or by silencer-equipped weapons.
Radar systems are also known for measuring and tracing indirect shots like those fired by mortars. Such radar systems do not allow tracing too close and small objects, i.e. objects having size of about 1 cm, and/or objects having an RCS (Radar Cross Section) reflectivity less than 1 cm2. Furthermore, such radar systems are capable of localizing a target only outside of a blind zone about the device itself. The amplitude of the blind zone depends on the duration of the pulses of the radar signal, and is typically about one hundred metres.
In summary,
Allen et al. describe a method for determining the direction of a bullet by a radar system comprising three radar devices arranged in predetermined positions, where each radar emits a continuous-wave (CW) radar signal for carrying out a Doppler measurement on a bullet. The Doppler measurement data are used to determine bullet parameters such as the miss-distance, i.e. the minimum distance from the respective radar at which the object passes through, the speed of the bullet and the instant when the bullet passes through the miss-distance. The speed can be used for localizing the shooter position. Through a process of fusing the data obtained by the three radar devices, i.e. through a triangulation process, it is possible to estimate the points of the bullet trajectory.
DE 2011 012 620 B3 describes a method for determining the trajectory of bullets comprising an electronic scan interferometric radar apparatus performing a succession of detections of the bullet in successive instants from a single radar site, and where each detection provides the radial speed of the bullet and an azimuth angle of the bullet with respect to the radar apparatus. The position of the points is calculated indirectly, evaluating at first the so-called “miss distance” (or POCA) of the bullet trajectory, and then the trajectory. Both these systems carry out an estimation of the position of the points indirectly, by measurements that limit the precision of such estimate.
It is therefore a feature of the invention to provide a method and a device for detecting small size bullets in direct shots that travel at a subsonic or supersonic speed, in a time and with a precision in which a real time protection and/or response actions are permitted.
It is also a feature of the invention to provide a method and a device for determining the trajectory of bullets, in particular, of bullets shot by small guns or by subsonic weapons like RPG.
It is then a particular feature of the invention to provide a method and a device for localizing a shooter position, even if it is located outside of the observation zone of the radar.
It is a further feature of the invention to provide a method and a device for localizing a bullet in a zone close to an observation point.
These and other objects are achieved by a method for determining a trajectory of a bullet shot by a firearm, the method comprising the steps of:
This way, an advantageous trade-off is obtained between the signal detection capacity, in terms of signal/noise ratio, and the signal Doppler filtering. In fact, as well known in the radar technique, at each time TIC a Doppler analysis is carried out on the return signal, in order to detect travelling bullets. The TIC value according to the invention depends upon the very low size and RCS of the target, with respect to conventional radar targets. In fact, radar targets normally have an RCS larger than 10 m2, which is a value more than 106 times higher than 0.1 cm2. This way:
By choosing a sampling rate value and a coherent integration time as indicated above, an extension of the radar technique is possible to the detection of objects much smaller than the conventional targets, i.e. to the detection of objects having a size of about one centimetre, in particular to the detection of bullets shot by direct fire weapons. Moreover, the detection it is possible for bullets of this size that travel both at a supersonic and a subsonic speed.
A further advantage of the invention is that it makes it possible to localize a bullet close to the observation point. Besides the case of a bullet, the invention is surprisingly capable of detecting even indirectly fired bullets, like in the case of a mortar shot, in the last phase of their trajectory, before they fall to the ground. In fact, the trajectory can be precisely determined, in order to possibly take countermeasures or to calculate the shooter position precisely enough. In order to carry out such a measurement, the elevation angle has only to be added to the measured plot.
In particular, the lower limit value fc,min of the sampling rate fc is 54 kHz at a signal frequency of 4 GHz, and is 240 kHz at a signal frequency of 18 GHz, and the lower limit value is expressed by the formula:
f
c,min=(40/3)v,
wherein v is the signal frequency expressed in GHz, and fc,min is expressed in kHz.
In an exemplary embodiment, the step of emitting the radar signal is carried out permanently during the step of scanning. In particular, the radar signal is a continuous-wave radar signal CW. A continuous-wave radar signal, modulated or not, makes tit possible to see a target at a distance as short as a few metres or a few tenths of metres, which is required for an effective detection of a direct shot.
In particular, the continuous-wave radar signal comprises two waveforms that have respective distinct frequencies. Such a radar signal allows directly measuring the range of the bullet at a point of the trace, according to a process described hereinafter, as an example. In particular, the radar signal comprises two continuous sinusoidal tones.
In an exemplary embodiment, the radar signal comprises a continuous non-modulated waveform (CW). As an alternative, the radar signal comprises a frequency-modulated continuous waveform, in particular, a linearly modulated continuous waveform (LFMCW). This way, as described hereinafter, the range can be determined even before a threshold-detection step of the point, i.e. of the point, i.e. of the plot.
The sampling rate value, which is higher than a given lower limit value that depends on the signal frequency, and which is selected as specified above, makes it possible to determine the position, in particular it makes it possible to directly measure the range of high-speed moving objects, in particular of supersonic moving objects.
The TIC value, which is practically a time during which the target is observed, and which is selected as indicated above, causes the radar sensitivity to increase, and allows detecting small objects, in particular, it allows directly measuring their range. More in detail, such a coherent integration time makes it possible to detect objects that have a low RCS value, typically a reflectivity value lower than 1 cm2, down to a very low minimum value of about 0.1 cm2.
In particular, the coherent integration time, for a given wavelength λ of the signal, is set between 20λ½and 35λ½ more in particular, it is set between 22λ½and 32λ½.
In particular, in the observation zone a plurality of observation sectors is defined that have a common vertex at the radar site, and the step of computing the line as the trace of the bullet comprises a step of fusing traces the have been previously detected in the sectors of the observation zone, which are distinct from one another. The whole azimuth angle can be scanned by this electronic scan technique, in which a 360° azimuth scanning is obtained by electronically scanning a circular array of antennas, each of which covers one specific sector, while overcoming the speed restrictions of the mechanical rotation devices of the conventional radar systems.
The step of computing a line can be carried out using an algorithm for computing a motion equation, i.e. a motion law of the bullet, starting from the plot data.
In particular, a step is provided of backtracking and localizing a shooter position at a point of the trajectory. In the case of a direct shot, the shooter position may be some hundreds of metres far from the position of the device, at most it may be at a distance of about one kilometre. Unlike the prior art methods, by the method of the invention, which is based on using a radar sensor, the place where shot was fired is not localized directly, but it is localized starting from the trajectory of the flying bullet. This makes it possible to localize position that have been masked by a masking technique and/or by environment conditions favourable to the snipers, such as particular lighting and/or noise conditions.
Advantageously, a step is provided of prearranging an acoustic sensor at the radar site, the acoustic sensor being configured for detecting a compression wave, i.e. a “muzzle blast”, caused by the shot and travelling towards the radar site, and the step of localizing the shooter position is discontinued as soon as the compression wave is detected by the acoustic sensor. This mates it possible to stop the backtracking, i.e. the step of reconstructing the trajectory of the bullet, even outside the observation zone, as soon as the acoustic sensor detects the incoming compression wave created by the shot. This way, the shooter position can be localized more precisely. This optional feature selection is particularly advantageous for bullets travelling at a supersonic speed.
In another exemplary embodiment, the radar signal is a range-gated signal, i.e. a signal in which the step of emitting the radar signal and the step of receiving the return signals, i.e. the echo provided by the targets that are present in the observation zone, are carried out in time-division with respect to each other, i.e. during distinct time intervals, which causes an attenuation of the return signals back from the observation zone. The duration of each step is predetermined, and is carried out according to a period, corresponding to a repetition frequency, that is much longer than the coherent integration time (TIC), wherein the cadence and the duration are selected so that the signal/noise ratio is the best possible at the maximum detection distance of the bullets. This causes a sensitivity decrease of the radar device at close ranges, i.e. at a small distance from itself. This makes it possible to reduce or substantially eliminate the noise due to electrostatic discharges at a short-very short distance. In fact, a radar system conceived for short distance detection, such as the system according to the invention, is conceived for being very sensitive. For this reason, this system is also particularly sensitive towards short-distance noise. This short distance noise can be caused by electrostatic discharges due to rain drops falling to the ground, or to electrostatically charged objects coming into contact with each other. The short distance noise can reduce the radar device sensitivity down to an extent of a few tenths of dB.
In particular, a third time interval, during which only the reception means of the antenna are working, is complementary to the first interval with respect to the whole interval, and the reception units of the antenna are turned on substantially immediately after turning off the emission means of the antenna unit.
As an alternative, a step is provided of waiting a separation time interval before turning on the reception means of the antenna unit, during which both the emission means and the reception means are inactive. In particular, the separation time interval lasts between 10 and 30 nanoseconds, more in particular, about 20 nanoseconds. This further reduces the local noise besides preventing an unwanted coupling between the emission and the reception means.
In a particular exemplary embodiment, the step of processing comprises determining the radial speed of the bullet, as a further item of the plot. The radial speed can be used for assisting the determination of the range, in order to improve the precision.
In a particular exemplary embodiment, the step of processing comprises, for each point, a step of determining an elevation angle of the bullet.
The above mentioned objects are also reached by an electronic-scan radar device for determining, from a radar site, a trajectory of a bullet shot from an unknown shooter position, the bullet crossing an observation zone arranged to be observed by the radar device, the radar device comprising:
In an exemplary embodiment, the signal processing means is configured for reconstructing, starting from the trace, a line that passes proximate to the points, so that this line can be assumed as the trajectory of the bullet.
In particular, the signal processing means is configured for carrying out a step of backtracking and localizing a shooter position at a point of the trajectory.
In particular, the signal processing means and the detection means is configured for operating at a coherent integration time set between 20λ1/2 and 35λ1/2, more in particular, set between 22λ1/2 and 32λ1/2, for a determined wavelength λ of said signal.
In particular, the emission means is configured for permanently emitting the radar signal during a radar-scanning. In this case, the emission means can be configured for emitting a non-modulated continuous-wave signal (CW), or a linearly frequency-modulated continuous waveform (LFMCW).
As an alternative, the emission means is configured for emitting a range-gated signal, i.e. it is configured for emitting the radar signal during a predetermined emission time interval and with a cadence longer than the duration, where the cadence and the duration are selected in such a way that an observation zone is created that is centred at the radar site and that is defined by a predetermined maximum observation distance, the attenuation of the received power having a minimum value at the maximum observation distance.
In an exemplary embodiment, said device comprises an acoustic sensor configured for detecting a compression wave caused by the shot and travelling towards the radar site, wherein the radar device is configured for blocking the step of localizing said shooter position as soon as the compression wave is detected by the acoustic sensor.
The invention will be now shown with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings in which:
With reference to the block diagram of
The method comprises a step 100 of arranging a radar device 30 at a radar site 12 of an observation zone 10, as shown in
Sill with reference to
According to the invention, in order to determine the trajectory of a bullet shot by a small arm weapon, said bullet travelling at a supersonic or at a subsonic speed, the radar-scanning step, unlike what is made in DE 2011 012 620 B3, provides a combination of operations comprising a direct determination of a set of points (plots), by directly measuring the range and the azimuth angle of each point, using a very short coherent integration time (TIC), as described hereinafter, which is set between two values, i.e. between a minimum value and a maximum value, depending on the wavelength λ of the signal, and using a very high sampling rate fc, which is higher than a minimum value fc,min, which depends on the radar signal frequency.
This solution makes it possible to determinate the trajectory of the bullet with a higher precision, with respect to the known systems.
In the case of
In the case of
More in detail, radar unit 36 comprises a transceiver unit, i.e. a transceiver 33, a transception control unit 34 for controlling the operation modes, the generation of the waveform and the commutation, and an acquisition, control and processing unit 35, i.e. a drive unit for setting the operation mode and the waveform, and for processing the return signals. In other words, radar unit 36 comprises hardware and software modules for driving the apparatus, for generating the desired waveform, for selecting the predetermined operation mode, for displaying data and alarms and for communicating with the operators.
Transceiver 33 serves for amplifying the radar signal and sending it to antenna unit 31, and also serves for receiving, demodulating, and filtering the return signal coming back from the scenario, for making it fit for acquisition, control and processing unit 35, in particular, for the analog-to-digital conversion means included therein.
For time-division scanning sectors 13,14,15,16, antenna unit 31 comprises a plurality of sector-oriented antennas 31i, for example of the type shown in
Moreover, switching unit 32 is configured for selectively connecting transceiver 33 with at least one sector-oriented antenna 31i.
For instance, in the configuration of
Furthermore, transceiver control unit 34 comprises a program means for operating switching unit 32 according to a radar-scanning programme. The radar-scanning program may comprise a step of discovery, in which transceiver 33 is connected in turn, and for a predetermined time interval, with each sector-oriented antenna of antenna unit 31. In addition, the radar-scanning program can comprise a step of tracking a moving target, wherein transceiver 33 is connected to at least one sector that receives return signals from a given moving target, and a step is provided of switching from the step of discovery to the step of tracking the target, and vice-versa, in case of appearance/disappearance of a moving target, according to conventional radar technique.
The time during which a transceiver 33 remains at a given sector 13,14 and/or 15,16 is called coherent integration time (TIC).
In particular,
Antenna module 31i can comprise a component such as a hybrid coupler 45 that is functionally connected to antennas 42′,42″ and is configured for distributing incoming return signals 44+,44″ to a couple of RX channels Σi and Δi;
In the exemplary embodiments of
According to the invention, transceiver control unit 34 can be configured for operating with a coherent integration time TIC set between two values, i.e. between a minimum value and a maximum value, which depend on the signal wavelength λ. These minimum and maximum values can be expressed as k1λ1/2 and k2λ1/2, respectively, wherein, for example, k1=10 and k2=40. For instance, in the case of a 9 GHz frequency signal, which corresponds to a λ value of about 0.033 m, the coherent integration time is set between 1.8 and 7.3 ms. Preferably, the coherent integration time is set between 3.7 and 5.4 ms, more preferably between 4.7 and 5.1 ms, in particular, it is about 5 ms. For instance, in another exemplary embodiment, k1 and k2 values may be 30 and 35 or 22 and 32, respectively, which correspond to TIC narrower ranges.
According to the invention, radar unit 36 can be configured for carrying out reception step 140 (
In an exemplary embodiment, fc,min is 54 kHz for a signal frequency v of 4 GHz, and is 240 kHz for v equal to 18 GHz. For intermediate frequencies v set between 4 GHz and 18 GHz, minimum value fc,min can be obtained by interpolation of the above-mentioned minimum values for 4 GHz and 18 GHz. For instance, minimum values fc,min at intermediate frequencies can be obtained by a linear interpolation procedure, i.e. through the formula fc,min=(40/3)v, where v is expressed in GHz, and fc,min is expressed in kHz.
With reference to
In an exemplary embodiment, step 130 of emitting radar signal 43 is carried out permanently during scanning step 125.
In particular, radar unit 36 is configured for causing transceiver 33 to work with a double-frequency CW waveform. For example, radar signal 43 comprises two continuous sinusoidal tones.
Radar unit 36 performs step 130 of emitting signal 43 that has a waveform advantageously generated after a step of amplifying signal 43. Radar unit 36 performs reception and demodulation steps 140 of return signals 44′,44″, which operation zone 10 returns in response to signal 43 through one of the sector-oriented antennas of antenna unit 31.
Reception and demodulation steps 140 can be carried out according to conventional radar reception and demodulation techniques. In particular, the demodulation step comprises a step of filtering and conditioning the received signal in order to make it fit for the working voltage of an analog-to-digital conversion module 35′ (ADC), according to a conventional technique.
Signal acquisition, control and processing unit 35 (
With reference to
Doppler filtering steps 152 can be carried out, for instance, by a Fast Fourier Transform (FFT).
In a channels generation step 153, Doppler filtered signal 58, as obtained by Doppler filtering step 152, is distributed to three channels, i.e. to a detection channel 59′, to a monopulse angular measure channel 59″ and to a range channel 59′″.
In the exemplary embodiment of
Plot data generation step 154 comprises a threshold detection step 155, a step 156 of monopulse measurement and computing the azimuth angle, and a range computation and calibration step 157. Embodiments of steps 155,156 and 157 are shown more in detail in
As diagrammatically shown still in
In the exemplary embodiment of
a step 263 of computing azimuth angle φAZ as arcsin({circumflex over (θ)}); and comprising an offset calibration step 265, by means of a calibration table 264.
During threshold detection step 155, a signal 63 is generated that is used in steps 156 and 157 of computing the range and the azimuth angle, respectively, in order to associate only significant calculated range and azimuth values, i.e. the values that correspond to the events revealed as plots at threshold detection step 155, to plot 71j.
With reference to the sequence diagram of
In an exemplary embodiment, when a bullet 1 is revealed, acquisition, control and processing unit 35 of radar unit 36 (
By so-called backtracking algorithms, the direction of provenience of bullet 1 and shooter position 19 are determined.
In other words, the algorithms for reconstructing the trajectory use range and azimuth measurements (
More in detail, tracking step 160 includes:
On this basis, a trace updating step 164 is provided, in which the parameters of each trace/hypothesis of trace are changed in the light of the plot associated to it, or considering that no plot has been associated with the trace/hypothesis of trace. This step is a requirement for a
Starting from each trace/hypothesis of trace, it is possible to extract, by a
In a subsequent data-fusion step 170 (
The reconstruction of the line can be carried out also by a technique of computing a motion law of bullet 1, on the basis of the data obtained from step 154 of generating plot 71j.
Acquisition, control and processing unit 35 (
In another exemplary embodiment, transceiver 33 comprises radar unit 36 configured to generate an LFMCW continuous waveform. In other words, radar unit 36 is configured to generate a linearly frequency-modulated waveform.
With reference to
On the other hand, threshold detection step 155, for example a threshold detection step that uses the CFAR technique and monopulse measuring and computation step 156 can be carried out as they are carried out in the case of a radar signal comprising a double-frequency CW waveform, according to the description of
Also trajectory tracking and computing step 160, and step 180 of backtracking and localizing shooter position 19, may be carried out as they are in the case of a radar signal comprising a double-frequency CW waveform, according to the description of
With reference to
After turning off the emission means, radar unit 36 turns on reception means RX of antenna unit 31. Reception means RX remains active during a reception time interval 62″, during which the reception step is carried out, and during which emission means TX are inactive.
This way, the signals coming from the nearest zones, i.e. from zones that have the shortest range, are attenuated more than the signals coming from the farthest zones, i.e. from zones that have the longest range.
In particular, if duration 62′ of the emission step and duration 62″ of the reception step are equal to each other, as In the case of
As shown still in
Besides separating the emission instant from the reception instant and limiting the effects of the coupling between emission means TX and reception means RX, range-gated signal 43 makes it possible to reduce any noise arising close to the radar device. For instance, this noise can be an electrostatic noise, such as the noise due to rain drops falling to the ground, or to metal or electrostatically charged objects coming occasionally into contact with each other. By the range-gating technique, the saturation and the subsequent sensitivity loss of the receiver due to local noise can be prevented.
In summary, at a short distance, the attenuation or sensitivity decrease of the contribution of the approaching bullet can be tolerated, while the contribution of the local electrostatic noise is substantially eliminated.
In particular, reception duration 62″, during which only reception means RX of antenna unit 31 are active, is complementary of emission time interval 62′ with respect to the overall duration of cycle 61, in other words, reception means RX is turned on immediately after emission means TX of antenna unit 31 are turned off.
As an alternative, once emission time interval 62′ has elapsed in each cycle, i.e. once emission means TX have been turned off, and before turning on reception means RX of antenna unit 31, a separation time interval, not shown, can be awaited, during which both emission means TX and reception means RX are inactive. A separation time interval of a few nanoseconds makes it possible to further reduce the local noise and to eliminate the unwanted coupling of emission means TX and reception means RX, further dumping sudden changes with respect to the mode CW. As well known, by awaiting a separation time interval before turning on the reception means, a blind zone is created about radar site 12, from which no return signal is received. However, the extension of this blind zone, with a separation time interval as indicated above, is very small, with respect to the safety distance at which the bullets are detected effectively so that an operator can protect himself and/or react. For instance, with a separation time interval of 20 nanoseconds, the extension of the blind zone is about 3 metres, which is a distance much shorter than the safety distance at which a bullet should be detected.
Signal processing step 150, up to extraction 154 of plot data 71j (FIGS. 8,14), bullet tracking and trajectory computing step 160 (
Still with reference to the block diagram of
In an exemplary embodiment, the portable equipment can be used for protecting a vehicle 2, as shown in
The above description relates to one of the possible embodiments of the present invention. Other embodiments can differ from what is described, even if they fall within the scope of invention, in some specific aspects such as the waveform, the way the signal is processed, the decision logic means, the way different detection system are integrated, in order to improve the localizaion of the shooter position and the like.
The description as above, of exemplary specific embodiments will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiments without further research and without parting from the invention, and, accordingly, it is to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the scope of the invention. It is meant that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| PI2012A000110 | Nov 2012 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2013/059921 | 11/5/2013 | WO | 00 |
