HK1022019B - Method and system for determining an impact point of a fired projectile relative to the target - Google Patents

Description

Method and system for determining the impact point of a projectile relative to a target

Technical Field

The present invention relates to a method for determining the impact point of a projectile relative to a target; and more particularly to the gun projectile aspect.

Background

When shooting projectiles, it is important to determine the location of the projectile's fall or hit in order to compare this location, for example, to a previously predicted point, i.e., Predicted Hit Point (PHP). The firing direction of the next projectile can then be adjusted, a method called "calibration in operation" (IAC). Furthermore, it is often important to provide an indication of the distance the projectile has left the target, so-called "miss distance indication" (MDI).

The impact point is typically determined by means of a search radar system. Particularly in the case of marine environmental applications such as the ocean, the location of the projectile is determined at the moment it hits the water and explodes. This creates a water column or spray in an upward direction. On land, the detonation of projectiles can produce a cloud of dust. The spray or dust cloud can be displayed with a search radar so that the impact point can be determined.

Such a method has the disadvantage of poor visibility of the spray on the radar display. Because the target typically produces a strong echo compared to the sputtering, the radar echo produced by the sputtering is sometimes even obscured by the radar echo produced by the target. If the projectile impact point is close to the target, it is impossible to distinguish between target and spray, and between spray and spray, due to limitations in radar resolution and limited dynamic range of the radar system. In addition, modern search radars equipped with TWT (traveling wave tube) transmitters emit long pulses. This causes time side lobes when processing the received echoes, thereby exhibiting reduced range resolution. A second disadvantage of search radar systems is that the update rate of the target and the spatter measurement is relatively low. Furthermore, in the case where several individual projectiles cause multiple splashes, it is difficult to coordinate each search radar resolution with the measurements on each individual splash, due in part to: not all splashes produce radar returns of equal intensity.

However, warships are also typically equipped with tracking radar systems, which typically incorporate transmitters for generating short pulses, particularly suited for airborne target tracking. This ensures good resolution and the tracking radar has a much higher update rate. The method according to the invention aims at utilizing existing tracking radar systems to eliminate the above-mentioned disadvantages.

Disclosure of Invention

The method is characterized in that:

tracking the target by means of a first radar beam;

directing a second radar beam over the target;

waiting for the projectile to appear in the second radar beam; and

the impact point is determined from the measurement data of the second radar beam.

An advantageous embodiment of the method according to the invention is characterized in that: the second radar beam is narrower than the first radar beam, since for example higher transmission frequencies can be used with the same antenna size. This may reduce the sensitivity of the second beam to well-known mirror effects on the echo of the projectile. When the ground reflects the echo of the target and the reflected echo is received in the radar antenna, a mirror effect occurs, disturbing the true target echo. As a result, the height measurement of the projectile is disturbed and even rendered useless. The method has the other advantages that: the azimuth angle, height and distance of the cannonball can be determined more accurately. Still another advantage resides in: it is thus possible to arrange for the projectile to be irradiated by the second radar beam without the target being irradiated by this beam, so that no disturbing echoes are produced by the target.

The invention will now be explained in more detail with reference to the following figures. In these figures:

drawings

FIG. 1 shows an arrangement in which the present method can be used;

FIG. 2 schematically shows a tracking computer in which the described method is implemented; and

FIG. 3 provides a detailed description of the target location of the configuration of FIG. 1.

Detailed Description

Fig. 1 shows a ship 1 on which a tracking radar device 2 with an antenna 3 and a gun system 4 are installed. The cannon system 4 fires a cannonball 5 in the direction of a surface target 6. The shell 5 follows a ballistic parabola 7. The gun system 4 may be, for example, a 76mm caliber. The gun system is controlled by a fire control computer 8, which computer 8 may receive data from a tracking computer 9 connected to the tracking radar equipment 2, although this is not absolutely necessary. The tracking radar device 2, equipped with an antenna 3, generates a first radar beam 10 and a second radar beam 11 and is directed at the surface target 6. The second radar beam 11 is preferably operated in a higher frequency band than the first radar beam 10, so that the frequency band is narrower. This almost eliminates the sensitivity to the mirror effect in the second beam. The most suitable band selection is: the beam width is about 8mrad for the first beam 10 in the I-band (8GHz-9.5GHz) and for the second beam 11 in the Ka-band (34.5GHz-35.5GHz), which makes the second radar beam 11 almost insensitive to echoes produced by surface targets. Since the first and second radar beams are generated by a single antenna 3, their movements are coupled. However, the antenna may also be designed such that the second beam can be rotated relative to the first beam, thereby allowing some independent measurement, although this is not absolutely necessary. Instead of the preferred embodiment of mounting one single antenna, two independently operating tracking radars, one for generating the first radar beam and the other for generating the second radar beam, may be used. However, this preferred embodiment provides a saving because it has only one antenna.

According to the time-sharing principle, the first beam and the second beam can be generated alternately, so that two beams can be generated by means of one transmitter and one antenna.

Fig. 2 depicts in more detail the warship firing control arrangement shown in fig. 1. A radar processing unit 12 adapted to detect moving targets receives target data from the tracking radar device 2 and, on the basis of these data, aims the tracking radar device 2 at the corrected position. The radar processing unit 12 is also connected to the tracking computer 9 in order to constitute a kind of tracking for each target. The tracking computer is designed to control a fire control computer 8. In other words, this firing control computer 8 can be controlled by the intervention of an operator, who controls it on the basis of data provided by the tracking computer.

Figure 3 provides a detailed description of the arrangement of figure 1 in the context of the position of the surface target 6. Also shown are the shots 7A and 7B between which the projectile track 7 may occur. The projectile enters the second radar beam 11 at point 13 and exits the beam at point 14. Starting from point 14, a point of impact is predicted based on the ballistic data and the locally measured three-dimensional location of the projectile. The ballistic data includes a ballistic angle 15, which is predicted, for example, from the firing schedule and the final velocity and final acceleration of the projectile. The miss distance relative to the target 6 is then determined based on the measured target position and the predicted impact point. In an example of embodiment. This impact point coincides with target 6 and the predicted miss distance is zero. Off-target distances for the potential projectile tracks 7A and 7B are indicated by range lines 16 and 17.

In the example of the embodiment, the tracking radar 2 is connected to a radar processing unit 12, which unit 12 is in turn connected to the tracking computer 9. Tracking the surface target 6 within the first tracking gate zone 18 using the first radar beam 10; in the example of the present embodiment, the gate zone length is 300 m. At the position of the surface target, the first radar beam has a width of 250 m. In this example, the distance between the surface target and the vessel is 8000 m. The second radar beam 11 is aimed above the surface target 6, for example, based on a trigger signal from the tracking computer 9; in the example of this embodiment, the angle is between 0.5 and 1.0 degrees, depending on the target distance. In the example of the present embodiment, the second radar beam has a width of about 60m at the position of the surface target 6. The first radar beam 10 is wide enough to continue tracking the surface target 6. At a given point in time, the previously fired projectile 5 is present in the second radar beam; in fig. 3, this is indicated by the dot 13. At this time, the final speed is, for example, about 300 to 500m/s, and the impact angle 15 is, for example, about 16 degrees. The radar processing unit 12, connected to the tracking computer 9, detects the projectiles by recording and selecting target echoes from the doppler spectrum components in a manner well known in the art, within a capture gate area 19 for the second radar beam 11, in the vicinity of a target on the water surface. In the example of this embodiment, the method of implementing this detection is: transmitting bursts of radar-transmitted pulses, and detecting possible echoes of each burst. If at least two successive echoes have at least substantially the same range and doppler spectral components as detected within the capture gate area 19, the cannonball will be detected with a sufficiently low false alarm rate. In an example, the capture gate area 19 has a length of about 1000 m. Thereafter, the projectile is tracked by determining the tracking gate area 20 of the location of the projectile echo over distance, i.e. the point 13, within the radar processing unit 12. Thus, the tracking gate region 20 moves along the echo of the projectile. In the example of the present embodiment, the radar processing unit 12 provides a measure of projectile position and velocity to the tracking computer 9. At this point, the location of the projectile is known in three dimensions; and the projectile is already within close proximity to the target. From the target echo of the second radar beam and the ballistic data about the projectile, a prediction can be made about the impact point of the projectile. At the moment 14 when no projectile measurement of sufficiently large signal-to-noise ratio is received in the tracking door zone, the radar processing unit 12 stops the measurement of the projectile. At this point, the projectile apparently breaks free from the second radar beam, typically 200 to 300m in front of the location where it will hit the target or water. In an advantageous embodiment which allows the detection of several shells fired in succession, the radar processing unit stops the measurement of a shell as soon as a subsequent shell has been detected twice with the same distance and doppler spectrum components, whereupon the entry of this shell is tracked. The tracking computer 9 then predicts the further trajectory of the projectile for which it is no longer being tracked. This can also be done if the tracking computer is arranged to track a plurality of projectiles at the same time.

Extrapolation may be used to predict the impact point from point 14. While the prediction is much more accurate than the prediction of the projectile trajectory data from the initial velocity at the time of firing, since the position of the projectile is known at the last stage of its trajectory. It is not necessary to track the projectile all the way through the ballistic duration. The tracking computer can now transmit the difference between the calculated impact point and the predicted impact point to the fire control computer 8 for calibration in operation, taking into account their different time validity, so-called IAC data. Based on this, the firing control computer can readjust the firing direction of subsequent rounds. As well as taking into account its relative time validity, the calculated impact point and the target 6 can also be presented on a display unit capable of off-target distance indication (MDI).

The application of the method according to the invention is in no way limited to the described configuration but is also applicable to other projectile calibrations, other radar beam transmission frequencies, or differently selected tracking and acquisition gate zones, etc. The projectile may comprise a missile. Although the method is also applicable to land-based configurations, examples of embodiments relate only to offshore configurations.

A first and a second radar device can also be used to generate the first and the second radar beam. The first beam is now used to track the target and the second beam is aimed just above the target. Thus, the second beam can be azimuthally controlled based on the tracking data about the first beam.

This enables the second beam to be generated by a relatively simple radar.

In a possible embodiment the first and second radar beams comprise a single radar beam, the main lobe of which is aimed above the target, so that at least the mirror effect with respect to the return of the shell is practically insignificant, or even absent. This can be achieved with a suitably chosen radar frequency. The target is still present in the lower or side lobe of the main lobe of the radar beam, enabling detection and tracking of the target. This is possible because the target typically produces a much stronger echo than the projectile. Thus, the same individual radar beam can be used to detect projectiles and predict the impact point in the manner described above.

Claims (14)

1. A method for determining the impact point of a fired projectile relative to a target, characterized by:

tracking the target with the first radar beam;

aiming the second radar beam above the target;

waiting for the projectile to appear in the second radar beam; and

the impact point is determined from the measurement data of the second radar beam.

2. A method as claimed in claim 1, characterized in that for determining the impact point the ballistic data of the projectile are used.

3. The method of claim 1, wherein the second radar beam is narrower than the first radar beam.

4. A method according to claim 1, characterized in that the first radar beam and the second radar beam are generated by a single antenna and radar means connected thereto.

5. The method of claim 1, wherein the first radar beam operates in an I-band and the second radar beam operates in a Ka-band.

6. The method of claim 1, wherein the projectiles are fired from a ship and the first and second radar beams are generated in the same ship.

7. The method of claim 1, wherein if the projectile is present in the second radar beam, the second radar beam first captures the projectile in a capture gate area and then tracks the projectile in a tracking gate area that is substantially smaller than the capture gate area.

8. The method of claim 2, wherein the second radar beam is narrower than the first radar beam.

9. A method according to claim 2 or 3, characterized in that the first radar beam and the second radar beam are generated by a single antenna and radar means connected thereto.

10. A method according to any one of claims 2 to 4, characterized in that the first radar beam operates in the I-band and the second radar beam operates in the Ka-band.

11. A method according to any one of claims 2 to 5, wherein the projectiles are fired from a ship and the first and second radar beams are generated in the same ship.

12. A method for fire control, comprising:

-determining a predetermined impact point of the fired projectile relative to the target, comprising the steps of:

tracking the target with the first radar beam;

aiming the second radar beam above the target;

waiting for the projectile to appear in the second radar beam;

determining an impact point according to the measurement data of the second radar beam;

-adjusting the firing direction of the projectile in dependence on the predetermined impact point.

13. A system for determining the impact point of a fired projectile relative to a target, comprising a radar processing unit, a first radar device for generating a first radar beam, and a second radar device for generating a second radar beam, characterized in that:

-the radar processing unit is connected to the first and second radar devices;

-the radar processing unit is designed to adjust the first radar device such that the target is within the first radar beam;

the radar processing unit is designed to adjust the second radar device such that the second radar beam is aimed directly above the target;

the radar processing unit is designed to detect the position of a projectile as soon as it enters the second radar beam; and

the radar processing unit is designed to predict the impact point of the projectile on the basis of the detected position of the projectile.

14. A system for determining the impact point of a fired projectile relative to a target, comprising a radar processing unit, and a radar apparatus for generating a first radar beam and a second radar beam, characterized in that:

-the radar processing unit is connected to the radar device;

the radar processing unit is designed to adjust the radar device such that the target is substantially within the first radar beam and the second radar beam is aimed just above the target;

the radar processing unit is designed to detect the position of a projectile as soon as it enters the second radar beam; and

the radar processing unit is designed to predict the impact point of the projectile on the basis of the detected position of the projectile.