Ordnance – Mounts – Training mechanisms
Reexamination Certificate
1999-04-02
2001-07-17
Johnson, Stephen M. (Department: 3641)
Ordnance
Mounts
Training mechanisms
C089S041050, C089S041030
Reexamination Certificate
active
06260466
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to target aiming systems.
BACKGROUND OF THE INVENTION
In a battle situation it is necessary for a gun crew to be able to assess the accuracy with which rounds fired by their gun are hitting intended targets. Conventionally, this assessment has been carried out visually with the aid of binoculars or a telescope. However, visual assessment of this type is of limited use because of the momentary nature of the event being observed and because the resulting cloud of smoke and dust which is raised by the resultant explosion can easily obscure the point of impact. It is also often the case that when an incoming round has landed close to a target such as a tank, the tank crew will rapidly fire off smoke bombs to obscure them from the attacking gun, again obscuring the view of the observer. Furthermore, the observer's line-of-sight can be interrupted by smoke and dust thrown up by his own gun and by vibration produced on firing the gun.
It is known to use an image sensor (typically a thermal imager) mounted on a gun and directed at the target to record continuously while the gun is being fired. The video sequence recorded can be viewed subsequently in an attempt to assess the accuracy of fired round. The gun operator can then attempt to correct any gun targeting errors by realigning the gun barrel. However, the transient nature of the firing and impact events, as well as the relatively small size of a fired round, makes it extremely difficult for the operator to view the trajectory of the round and the point of impact. The subjective nature of this process leaves open the possibility of significant human errors being introduced in the realignment stage.
A further disadvantage if this system is that it generates a large amount of recorded data which must generally be stored on video tape, an unreliable storage medium under battlefield conditions. Whilst solid state memory may be used, this is expensive where it is required to store a long video sequence or a large number of sequences to be stored for later historical analysis. Furthermore, in order to identify that portion of the video sequence which shows the round passing or hitting the target, perhaps only one or two frames of the video sequence, the gun crew must review a relatively large number of frames. In a battle situation, the time wasted studying the sequence can be critical.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome or at least mitigate the disadvantages of known target aiming systems.
According to a first aspect of the present invention there is provided a method of correcting the alignment of a gun following the firing of a round at a target by the gun, the method comprising the steps of:
aiming the gun at the target and predicting an expected trajectory for a round to be fired
firing the gun and monitoring the target and its surrounding area with an image sensor;
predicting a plurality of alternative round trajectories which encompass possible variations from said expected trajectory;
analysing image data generated by the image sensor to determine which of said trajectories the fired round followed and, if it is determined that the fired round followed one of said alternative trajectories, determining a gun alignment correction factor (for use with a subsequent round) from a comparison of the followed trajectory and said expected trajectory.
In a preferred embodiment of the present invention, the image sensor provides a sequence of image frames which together form a video record of the travel of the fired round and said step of analysing the image data comprises normalising the frames to subtract stationery background therefrom and then for each said trajectory:
mapping the trajectory onto the two-dimensional plane of the image frames;
for each frame predicting the displacement of a round following the trajectory, relative to a fixed reference point;
translating the frames of the sequence relative to said fixed reference point by the respective predicted displacements;
summing the translated frames to generate a single cumulative frame;
identifying features present in the cumulative frame which exceed a threshold level and which have a form chosen to be indicative of a fired round.
Typically, for the cumulative frame corresponding to the actual round trajectory, the fired round will appear as a bright spot, having a gaussian intensity distribution.
If for one of the trajectories a feature is identified in the cumulative image which exceeds said predetermined threshold then that trajectory is identified as the trajectory followed by the round. If features are so identified for a number of different trajectories, then the feature having the strongest intensity is selected and the associated trajectory identified.
Said video record may contain any appropriate number of image frames and may encompass a part or all of the travel of the fired round from gun to target.
The preferred embodiment described above may be modified so that, instead of considering each frame in its entirety, only a portion or patch of each frame predicted to contain the round, is considered. This patch will be of the same extent for each frame and it is only necessary to translate and sum the identified patches, considerably reducing the complexity of the image processing operation.
It will be appreciated that the field of view of the image sensor should be arranged such that it encompasses all or at least a part of each of the possible trajectories of a fired round.
According to a second aspect of the present invention there is provided a method of determining the site of impact of a round fired by a gun at a target, the method comprising:
monitoring and recording the target and its surrounding area with an image sensor;
defining a threshold level of change in the output of the image sensor as being indicative of an impact of a round;
following the firing of a round, detecting a change in the output of the image sensor in excess of said defined threshold and identifying the region of change; and
determining the centroid of said region of change and identifying this centroid as the site of impact of the fired round.
The detected change in the output of the image sensor may be determined relative to the preceding image frame in a sequence of image frames. Alternatively, the change may be determined relative to an image recorded prior to firing of the round.
According to a third aspect of the present invention there is provided a target hit assessment method for enabling a gun crew to determine the accuracy of a round fired by a gun, the method comprising:
estimating prior to firing the time-to-impact of the round, with reference to the time of firing of the gun, from the properties of the round and the gun and the prevailing atmospheric conditions; and
following firing of the gun, commencing recording of a video sequence of the target shortly before the estimated time-to-impact of the round and subsequently stopping recording shortly after the estimated time-to-impact; and
playing back the recorded sequence in slow motion on a video display to allow the accuracy of the firing to be quantified.
The method of the above third aspect provides a method which presents only minimal data storage requirements which can be satisfied for example by a compact solid state memory and which, because the recorded video sequence represents only a relatively short time window around the estimated time-to-impact, allows the gun crew very quickly to quantify the accuracy of the round fired.
The length of the video sequence recorded is determined in part by the accuracy with which the time-to-impact of the round can be estimated. Typically however, the video sequence will comprise less than 50 frames and, more preferably, less than 10 frames. Given the relatively short length of the sequence, the sequence can be played back, slowed down by a factor or 20 or more.
It will be appreciated that elements of the above third aspect of the present invention may be incorporated into the met
Alston & Bird LLP
Barr & Stroud Limited
Johnson Stephen M.
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