A method and system providing updated distance information to a flying target

Abstract

A method and system for providing distance information from a sensor assembly to a flying target. The method comprises detecting the flying target and locking on the flying target by means of a tracking sensor. Directing a light beam at the detected flying target. Generating a movement pattern having a path around the detected flying target and controlling movements of the light beam so that the LOS of the light beam completes moving across the path of the selected movement pattern within a set timeframe. Generating distance information by measuring time- of-flight of the light beam, when being reflected from the flying target while moving the LOS of the light beam across the path of the movement pattern. The system comprises sensors and devices for performing the method.

Description

[0001] A METHOD AND SYSTEM PROVIDING UPDATED DISTANCE INFORMATION TO A FLYING TARGET

[0002] TECHNICAL FIELD

[0003] The invention relates to measuring distance to a target, and more specifically to a method and system for acquiring updated distance information to a flying target.

[0004] BACKGROUND

[0005] There are several ways of measuring distance between two points. For points relatively close to each other, manual measurements by using a ruler or a tape measure is one way of doing it.

[0006] Measuring distance between points that are farther apart from each other can be done in different way. One way is by transmitting sound waves, e.g. ultrasound, from a source at one point to the other point and measuring time lapsed before reflections of the sound waves are received at the source.

[0007] For points faraway from each other, distance can be measured by directing a light beam from a source at one point to the other point and measuring time lapsed before reflections of light are received at the source.

[0008] Measurements of distance between stationary points or objects will most likely be consistent over time. As such, updated distance measurements between stationary objects are normally not necessary, other than for reducing measurement uncertainties.

[0009] On the other hand, distance to a moving object will change over time and updated distance information may be crucial for several purposes. One example is to determine and update distance information to a flying enemy target. This may be essential for effective engagement and control.

[0010] To provide an updated distance measurement to a moving object, such as a flying target, the target must be tracked after first being located. There are several ways of locating and tracking flying targets.

[0011] One way is manual locating and tracking by visual means. This can be done by a person visually locating the target and then tracking it by observing its movements. Another way of locating and tracking of a flying object is by means of sensors and automated systems.

[0012] There are different kinds of detection and tracking devices used for tracking and following paths of specific objects both relatively close to and far away from a measuring point. Example of such are ultrasonic sensors, radars, GPS trackers, infrared sensors, lasers and optical tracking sensors such as cameras with image processing.

[0013] US 8,681,317 B2 describes a tracking method and measuring system having a laser tracker. An object is tracked in two different tracking modes, where a first mode uses a camera with a narrow field of view, and a second mode has a wider field of view. It is switched from the first mode to the second mode if the object is not detectable in the first mode. When the object has been detected in the second mode, it is switched back to first mode. To follow movements of small moving objects, frequent switching between the modes will be necessary since a small object easily will come out of view in the first mode. As such, reliable distance information will be hard to achieve.

[0014] There are also systems where expected location of a flying target is determined by extrapolating a detected current path of the target.

[0015] US 6,750,806 B2 describes a method and system for tracking a target moving in an airspace. A target tracking system comprises a search sensor and a tracking sensor. It involves using the search sensor to establish target information over time, and an expected path to be flown by the target is extrapolated. This information is used for aiming at the target even if it is not currently detected. Determining an expected future location of a target is feasible when the target moves relatively slow, is not too far away, or not too small.

[0016] If the target is small, such as for instance a small drone, tracking of the target may be hard. It follows that it will be hard to get reliable distance measurements.

[0017] For measuring distance to an object relatively far away, a Laser Range Finder (LRF) is suited for providing such measurements. A LRF provides distance measurements to a target when receiving reflections from the target. A beam transmitted from the LRF is narrow and it might be difficult to lock to an receive reflected light from a flying target. If tracking of a target is lost, a laser beam from a LRF will not be reflected, and distance information to the target while it is moving is not possible.

[0018] Directing a laser beam at a target at a distance such as a moving object, e.g. a plane, and tracking and receiving a reflected light is feasible if the target is not too small, not moving too fast or rapidly changing directions, or is too far away. To acquire distance measurement, the laser beam from the LRF must be locked to the target to receive reflected light from the target.

[0019] There is a need for a method and system providing reliable updated distance information to an object such as a flying target, even if the target is small and / or moving fast. SUMMARY OF THE INVENTION

[0020] The present invention concerns a method and system providing updated distance information between one location with a sensor assembly and a flying target, even if the target is small or moving fast. The solution is defined by the appended claims and in the following.

[0021] In general terms and in a first aspect, the invention comprises a system providing distance information from a sensor assembly to a flying target. The system comprises a sensor assembly with one or more tracking sensors for detecting and locking on the flying target, and an image recording device capturing images of the tracked target. The image recording device may be digital video recorder.

[0022] In one embodiment, the sensor assembly comprises two or more cooperating sensors, being among digital picture sensor, IR-sensor, and radar to detect the flying target. One sensor may detect the flying target, while another sensor may zoom in on the detected flying target.

[0023] In one embodiment, the tracking sensor is an optical tracking sensor such as a camera connected to image processing means to track movement of objects.

[0024] The system further comprises a light effector producing a light beam, wherein a Line of Sight, LOS, of the light effector is directed at the detected target. In one embodiment, the light effector is a Laser Range Linder, LRE.

[0025] In one embodiment, the light effector is installed at a weapon having a Line of Bore, LOB, along an axis parallel to the LOS of the light effector, and wherein a calculation unit is configured to calculate the spherical position of the flying target relative to a muzzle of the weapon, based on the distance information, the polar angle 9 and the azimuth angle cp from the muzzle of the weapon.

[0026] The system comprises a pattern generating device generating a selected movement pattern having a path around the detected flying target.

[0027] The system comprises a controller configured to control movements of the light effector so that the LOS of the emitted light beam completes moving across the path of the generated movement pattern within a set timeframe.

[0028] In one embodiment, the image recording device is configured to apply picture stabilization of images and to correlate picture stabilization with movement of the LOS of the light effector when it is moved across the path of the selected movement pattern.

[0029] The system comprises a measuring device configured to provide the distance information, when the light effector detects light reflected from the flying target while moving the LOS of the light effector across the path of the selected movement pattern.

[0030] A second aspect of the invention comprises use of the system described above for keeping an aim of the weapon locked to a flying target, wherein light effector is installed at the weapon and wherein the LOS of the light effector producing the light beam is parallel to the LOB of the weapon.

[0031] In a third aspect of the invention, there is provided a method for providing updated distance information from a sensor assembly to a flying target. The method comprises different steps that are repeated.

[0032] The first step of the method is detecting the flying target and locking to the flying target by means of the sensor assembly which comprises one or more tracking sensors following the movements of the flying target and an image recording device recording images of the flying target.

[0033] The next step is directing a light beam at the detected flying target, the light beam is emitted from a light effector at the sensor assembly, having a Line of Sight, LOS, at the detected target. In one embodiment, a Laser Range Finder, LRF, is used as the light effector.

[0034] The next step is selecting a movement pattern having a path around the detected flying target. In one embodiment, the movement pattern is created as a spherical pattern starting from the position of the flying target. In another embodiment, the movement pattern is manually selected according to type of observed flying target. In yet another embodiment of the invention, the movement pattern around the flying target is automatically selected according to detected characteristic features of the flying target.

[0035] The next step is continuously controlling movements of the light effector so that the LOS of the emitted light beam completes moving across the path of the selected movement pattern within a set timeframe,

[0036] In one embodiment, picture stabilization is applied on recorded images of the detected flying target and the picture stabilization is correlated with the movements of LOS of the light effector when moving across the defined movement pattern.

[0037] In one embodiment, the method comprises using two or more cooperating sensors in the sensor assembly, being among digital picture sensor, IR-sensor, and radar to detect the flying target.

[0038] The next step is generating the distance information by measuring time-of-flight of the emitted light from the light effector, when being reflected from the flying target while moving the LOS of the light effector across the path of the selected movement pattern. The method steps above are repeated for providing updated distance information to the flying target.

[0039] One embodiment of the method comprises updating the spherical position of the flying target relative to a muzzle of a weapon, having a Line of Bore, LOB, along an axis parallel to the LOS of the light effector installed at the weapon, based on the updated distance information, the polar angle 9 and the azimuth angle cp from the muzzle of the weapon.

[0040] In one embodiment, measurements from the sensors are filtered for separating background from the flying target. This may be done by analysing foreground and background objects and filter out background based on different parameters such as distances, movements, light intensity etc.

[0041] In one embodiment, Kalman filtering is combined with target discrimination and / or target type to improve detection of the flying target.

[0042] In one embodiment, travel path of the flying target is estimated based on current speed and direction, where this is used as input to the sensor assembly.

[0043] In one embodiment, the characteristic features detected includes at least one of: appearance, heat signature and sound.

[0044] SHORT DESCRIPTION OF THE FIGURES

[0045] The present invention will be explained in detail by reference to an example embodiment shown in the following figures, in which:

[0046] Figure 1 illustrates the system providing updated distance information to a flying target.

[0047] Figure 2 illustrates an example of use of a system providing distance information to a weapon locked to a target.

[0048] Figure 3 illustrates examples of movement patterns around a flying target.

[0049] Figure 4 illustrates distance measurements to several flying targets within a defined movement pattern.

[0050] Figure 5 is a flow chart illustrating the steps for providing distance information from a sensor assembly to a flying target. DETAILED DESCRIPTION OF THE INVENTION

[0051] As mentioned, providing updated distance information to targets such as small flying objects can be challenging. For automatic systems, the target must first be detected before being tracked. When detected, the Line of Sight of a distance measuring device must be locked to the target and follow its movements to be able to measure distance to the target.

[0052] The device for measuring distance to a flying target can be a Laser Range Finder (LRF) transmitting a narrow light beam at the target. Locking the Line of Sight (LOS) to the target may be hard. If lock is lost, the target must once again be detected before yet again locking to the target for tracking it. This means that the target may have moved for some time without providing distance information from the distance measuring device to the target.

[0053] The present invention addresses this problem by providing a method and system for providing updated distance measurements to a small flying target.

[0054] Figure 1 illustrates the concept of a system according to the invention. The system provides updated distance information from a sensor assembly to a flying target 130. The sensor assembly comprises one or more tracking sensors 144 for detecting and locking to the flying target 130, wherein the LOS of the tracking sensor 148 is directed at the flying target 130. An image recording device 146 is arranged to capture images of the tracked flying target 130.

[0055] The sensor assembly may comprise two or more cooperating sensors. In one embodiment, the cooperating sensors may be a camera recording images or video of the flying target 130 and an IR-camera providing information of the flying target 130 in dark environments. In another embodiment, the cooperating sensors may be a radar and a camera. Sensor area 100 is indicated by the dashed lines in the figure. This corresponds to the field of view of the camera. A stabilized operator’s view 110 is also indicated in the figure. This is the available field of view when applying picture stabilization. This is further described below with reference to figure 5 and the method performed to provide distance information from a sensor assembly to a flying target 130.

[0056] A light effector 150 produces a light beam with a Line of Sight, LOS, of the light effector 152 directed at the detected flying target 130. In one embodiment the light effector 150 is a Laser Range Finder, LRF, which operates by using a laser beam to measure the distance to an object. The laser beam is emitted from the LRF towards the object. The laser beam hits the object and is reflected back to the LRF. When the beam is reflected from the target, the distance from the LRF to the object is determined based on the travel time, i.e. the time it takes from transmitting the beam from the LRF to travel to the target and back to the LRF. The distance is calculated from the measured travel time multiplied with the speed of light of the laser beam. The resulting calculated distance is divided by two, since the beam first travels from the LRF to the target, and then back to the LRF.

[0057] A pattern generating device 154 is arranged to generate a selected movement pattern 140 having a path around the detected flying target 130. The movement pattern 140 can be automatically generated based on type of flying target 130 detected. Alternatively, the movement pattern 140 is manually selected by an operator. Examples of target points 142 for a LRF within the movement pattern 140 are indicated in the figure. Examples of movement patterns 140 are described below with reference to figure 3.

[0058] The light effector 150 is connected to a movable support structure 160. Movements of the support structure 160 are enabled by a connected motor 158 which is controlled by a movement controller 156 connected to the pattern generating device 154. The movements of the support structure 160 are controlled such that LOS of the light effector 150 completes moving across the path of the generated movement pattern 140 within a set timeframe. A measuring area 120 wherein the light effector 150 can receive reflections from the flying object is then within the movement pattern 140.

[0059] A measuring device 162 is connected to the light effector 150 and configured to operate in Continuous Measurement Mode (CMM) to provide the distance information when the light effector 150 detects light reflected from the flying target 130 while moving the LOS of the light effector 152 across the path of the selected movement pattern 140.

[0060] Eigure 2 illustrates an embodiment of the system described above, used for providing distance information to a weapon 180 locked to a target. The light effector 150 is installed at a weapon 180 with a muzzle 170 having a Line of Bore, LOB 175, along an axis parallel to the LOS of the light effector 152.

[0061] A calculation unit is configured to calculate the spherical position of the flying target 130 relative to the muzzle 170 of the weapon 180. The calculated spherical position is based on the distance information r to the flying target 130, which is provided by the measuring device 162 connected to the light effector 150, the polar angle 9 and the azimuth angle cp from the muzzle 170 of the weapon 180.

[0062] In one embodiment, the image recording device 146 capturing images of the flying target 130 is configured to apply picture stabilization of images and to correlate picture stabilization with movement of the LOS of the light effector 152 when its emitted light beam is moved across the path of the selected movement pattern 140.

[0063] Eigure 3 illustrates examples of movement patterns 140 around a flying target 130. Different types of movement pattern 140 can be applied according to the type of flying target 130 detected and depending on if it is a single target, or two or more targets, e.g. swarms of drones. A movement pattern 140 may for instance be Archimedean or spiral shaped as illustrated in the figure.

[0064] Figure 4 illustrates distance measurements to several flying targets 130 within a defined movement pattern 140. This is relevant for drone swarms, where two or more drones are flying as a group. The figure illustrates three drones within the movements pattern 140, and different target points 142 for a LRF. Reflections from drones provide distance information. In this example reflections from the drones indicate that there are three drones at three different distances, i.e. 403m, 474m and 666m. Based on different distances measured, the number of drones in the swarm can be determined.

[0065] Figure 5 is a flow chart illustrating the steps of the method for providing updated distance information 200 from a sensor assembly to a flying target 130.

[0066] The first step 210 is detecting and locking to the flying target 130 by means of a sensor assembly comprising one or more sensors and devices. When detected, the movements of the flying target 130 and distance to the target is determined by at least one sensor in the sensor assembly.

[0067] As described above, the sensor assembly may comprise a camera visually detecting and tracking the flying target 130. By zooming in on the target, the type of target can be determined. By using an infrared camera, heat signatures from the flying target 130 can be detected and locking to the target can be based on detected heat.

[0068] By combining information generated by different sensor technologies used in the sensor assembly, e.g. digital picture sensor, IR-sensor, radar, more precise detection and tracking of a flying target 130 can be achieved.

[0069] Tracking and detection of a flying target 130 can be improved by using predictive algorithms to predict a likely future position of the flying target 130 based on current speed and direction. Kalman filter is an example of an algorithm used to predict a future position based on its past positions and velocities.

[0070] When locked to the target, a light beam from a light effector 150 is directed at the flying target 130. The light effector 150 may in one embodiment be a Laser Range Finder (LRF) comprised in the sensor assembly, wherein the LRF has a Line of Sight, LOS, directed at the detected target. The LRF will provide distance measurements to the flying target 130 when receiving reflections from the target.

[0071] When the flying target 130 is detected and the LRF is locked to the target, a movement pattern 140 is selected 230. The type of movement pattern 140 selected can be done automatically by the system or manually by an operator. The movement pattern 140 has a path around and outwards from the detected flying target 130, starting from the current detected position of the flying 130 target. A movement pattern 140 may be created as a spherical pattern or an Archimedean spiral having a path around the flying target 130, the path starting from the position of the flying target 130.

[0072] A timeframe is set 240, determining a time to be used for moving the LOS of the emitted laser beam of the LRF to complete moving across the path of the selected movement pattern 140 within the set timeframe.

[0073] The movements of the LRF are then controlled 250 so that the LOS of the emitted laser beam of the LRF completes moving across the path of the selected movement pattern 140 within the set timeframe while tracking the movements of the detected flying target 130. This means controlling the movements of a support structure holding the LRF according to the selected movement pattern 140 around the flying target 130 and the movements of the tracked target. When completing moving the light beam across the path and outwards from the detected target within the set timeframe, the movements of the support structure are controlled such that the LOS of the LRF follows the path inwards to the current position of the detected target. According to type of objects detected, different timeframes may be used, e.g. a timeframe of 0.5s, Is or 3s.

[0074] During the movements of the LRF across the path of the movement pattern 140 within the set timeframe, distance information is generated 260 by measuring time- of-flight of the emitted light from the LRF, when the light is being reflected from the flying target 130 while moving the LOS of the light effector 150 across the path of the selected movement pattern 140.

[0075] The steps above are repeated for providing updated distance information to the flying target 130.

[0076] There are several ways of improving accuracy of measurements. In one embodiment, picture stabilization is used for improving accuracy of the detection and tracking of the flying target 130. Optical picture stabilization of recorded images of the flying target 130 is correlated with movements of LOS of the light effector 152, e.g. LOS of the LRF, when moving across the defined movement pattern 140.

[0077] The movement pattern 140 selected is in one embodiment adapted to type of flying object detected and / or characteristic features detected. Examples of characteristic features are appearance, heat signature and sound signature.

[0078] In one embodiment, filtering of measurements from the tracking sensors 144 is applied for separating background from the flying target 130. In one embodiment, the travel path of the flying target 130 is estimated based on current speed and direction, and where this is used as input to the sensor assembly. Kalman filtering may in one embodiment be applied combined with target discrimination and / or target type to improve detection of the flying target 130. In one embodiment, the method described above is used for a weapon 180 locked to a flying target 130 by updating the spherical position of the flying target 130 relative to a muzzle 170 of a weapon 180, having a Line of Bore, LOB 175, along an axis parallel to the LOS of the light effector 152 installed at the weapon 180. Current spherical position of the flying target 130 is based on the updated distance information provided by the CMM measuring device 162, the polar angle Q and the azimuth angle (p from the muzzle 170 of the weapon 180.

[0079] By applying the system and method described herein, the chances of hitting the flying target 130 will increase based on the updated distance information, spherical position of flying target 130 and ballistic properties of ammunition used.

[0080] List of references

[0081] 100 - sensor area

[0082] 110 - stabilized operator’s view

[0083] 120 - measuring area

[0084] 130 - flying target

[0085] 140 - movement pattern

[0086] 142 - target points

[0087] 144 - tracking sensors

[0088] 146 - image recording device

[0089] 148 - LOS of the tracking sensor

[0090] 150 - light effector

[0091] 152 - LOS of the light effector

[0092] 154 - pattern generating device

[0093] 156 - movement controller

[0094] 158 - motor

[0095] 160 - support structure

[0096] 162 - measuring device

[0097] 170 - muzzle

[0098] 175 - Line of Bore (LOB)

[0099] 180 - weapon

Claims

1. CLAIMS1. A system providing distance information from a sensor assembly to a flying target (130), comprising: the sensor assembly comprises one or more tracking sensors (144) for detecting and locking on the flying target (130), and an image recording device (146) capturing images of the tracked flying target (130), a light effector (150) producing a light beam with a Line of Sight, LOS, of the light effector (152) directed at the detected flying target (130), a pattern generating device (154) generating a selected movement pattern (140) having a path around the detected flying target (130), a movement controller (156) connected to a motor (158) configured to control movements of a support structure (160) of the light effector (150) so that the LOS of the light effector (152) completes moving across the path of the generated movement pattern (140) within a set timeframe, a measuring device (162) configured for providing the distance information, when the light effector (150) detects light reflected from the flying target (130) while moving the LOS of the light effector (152) across the path of the selected movement pattern (140).

2. The system according to claim 1, wherein the sensor assembly comprises two or more cooperating sensors, being among digital picture sensor, IR- sensor, and radar.

3. The system according to claim 1, wherein the light effector ( 150) is a Laser Range Finder, LRF.

4. The system according to any one of claims 1 to 3, wherein the light effector (150) is installed at a weapon (180) with a muzzle (170) having a Line of Bore, LOB (175), along an axis parallel to the LOS of the light effector (152), and wherein a calculation unit is configured to calculate the spherical position of the flying target (130) relative to the muzzle (170) of the weapon (180), based on the distance information, the polar angle 9 and the azimuth angle cp from the muzzle (170) of the weapon (180).

5. The system according to any one of claims 1 to 4, wherein the image recording device (146) is configured to apply picture stabilization of images and to correlate picture stabilization with movement of the LOS of the light effector (152) when the light beam is moved across the path of the selected movement pattern (140).

6. Use of a system according to any of the claims 1 to 5, for keeping an aim of a weapon (180) locked to a flying target (130), wherein the light effector (150) is installed at the weapon (180) and wherein the LOS of the light effector (152) is parallel to the LOB (175) of the weapon (180).

7. A method providing distance information from a sensor assembly to a flying target (130) by performing the following steps: a) detecting the flying target (130) and locking on the flying target (130) by means of the sensor assembly comprising one or more tracking sensors (144) and an image recording device (146), b) directing a light beam at the detected flying target (130), the light beam is emitted from a light effector (150) at the sensor assembly, wherein the Line of Sight, LOS, of the light effector (152) is directed at the flying target (130), c) selecting a movement pattern (140) generated by a pattern generating device (154) having a path around the detected flying target (130), d) continuously controlling movements of the light effector (150) so that the LOS of the light effector (152) completes moving across the path of the selected movement pattern (140) within a set timeframe, e) generating the distance information by measuring time-of-flight of the emitted light from the light effector (150), when being reflected from the flying target (130) while moving the LOS of the light effector (152) across the path of the selected movement pattern (140), f) repeating steps a) to f) to provide updated distance information.

8. The method according to claim 7, by using a Laser Range Finder, LRF, as the light effector (150).

9. The method according to claims 7 or 8, by applying picture stabilization on images of the detected flying target (130) and correlating the picture stabilization with the movements of LOS of the light effector (152) whenmoving across the defined movement pattern (140).

10. The method according to any one of claims 7 to 9, by using two or more cooperating sensors, being among digital picture sensor, IR-sensor, and radar to detect the flying target (130).

11. The method according to any one of claims 7 to 10, by updating the spherical position of the flying target (130) relative to a muzzle of a weapon (180), having a Line of Bore, LOB, along an axis parallel to the LOS of the light effector (152) installed at the weapon (180), based on the updated distance information, the polar angle 9 and the azimuth angle cp from the muzzle of the weapon (180).

12. The method according to any one of claims 7 to 11, by filtering measurements from the tracking sensors (144) for separating background from the flying target (130).

13. The method according to any one of claims 7 to 12, by estimating travel path of the flying target (130) based on current speed and direction, and using this as input to the sensor assembly.

14. The method according to any one of claims 7 to 13, by applying Kalman filtering combined with target discrimination and / or target type to improve detection of the flying target (130).

15. The method according to any one of claims 7 to 14, by creating the movement pattern (140) with a path around the flying target (130) as a spherical pattern starting from the position of the flying target ( 130).

16. The method according to any one of claims 7 to 15, by manually selecting the movement pattern (140) around the flying target (130) according to type of observed flying target (130).

17. The method according to any of the claims 7 to 15, by automatically selecting the movement pattern (140) around the flying target (130) according to detected characteristic features of the flying target ( 130).

18. The method according to claim 17, wherein characteristic features detected includes at least one of: appearance, heat signature and sound.

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