GB2238441A

GB2238441A - Target acquisition apparatus

Info

Publication number: GB2238441A
Application number: GB9012932A
Authority: GB
Inventors: Frank-Lutz Dittmann
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1989-06-15
Filing date: 1990-06-11
Publication date: 1991-05-29
Anticipated expiration: 2010-06-11
Also published as: DE3919573A1; FR2649514B1; FR2649514A1; GB9012932D0; GB2238441B

Abstract

Apparatus for the acquisition from a steeply descending guided projectile 13 of a target point 14 situated centrally on the target object 12, no significant differences between target object 12 and surrounding ground (G) reflectivity being expected e.g. because the target object is an aircraft shelter with overgrown sloping side walls 20, enables the course correction (K) of the projectile to be determined as an angular-position mean value (wm) between two opposite scanning angular positions (wr, wl) for equal specific levels of the reflection (A) from a narrow range gate (FT) intersecting the target object (12). The value (wm) is preferably obtained from the resulting mean value (WM) of the central angular positions (wm) for different distance gates (22). <IMAGE>

Description

1 A METHOD AND APPARATUS FOR THE ACQUISITION OF A TARGET POINT This

invention relates to a method and apparatus for the acquisition of a target point which is approximately in a central plane of (or central of the top of) a target object.

It has been proposed, for example in GB-A-2 133 514, by means of an active detection instrument in the path of approach to a target object (and/or upon flying over the target object) to detect the height contour thereof by mutually offset distance measurements over the target object, in order then to compare this with a preset pattern and to determine therefrom the optimum target point in the projection geometry of the target object at which the target object is to be hit. Such a recording (pick-up) of a height profile of the target object that is to be combatted is, however, feasible with justifiable expenditure only when the target object differs sufficiently from its surroundings. Thus, said recording of the height profile is feasible only if significant differences, not only with respect to the elevation above the target terrain, but also with respect to the reflection properties, lead to sufficient information in the reflection energy received in detection.

This is, for example, the case with a hard-armoured vehicle on a flat, overgrown substrate. However, such conditions, for example, do not exist if the target object is a stationary protective structure/building which rises in a non-abrupt (gradual) manner from the surrounding terrain and which is possibly covered, for example overgrown, in the same way as the target surroundings. If such target objects are scanned with millimetre-wave or laser energy, there results, in the reception signal reflected to the transmitter, no 2 significant difference between reflections, for example, from the roof or top of the building (target object) and from the terrain adjoining inclined side walls of the building.

This tends to have a particularly aggravating effect if an airfield protective structure is to be attacked in steep diving flight with explosive or penetration munition. In this case, sufficient effect on the target object (in particular in the interior of the shelter against aircraft stationed there) is to be expected only when the hit target point lies approximately in the centre of the roof; whereas a hit point, f or example, on an inclined side wall of the structure may not promise an adequate result.

In recognition of these factors, an object of the present invention is to provide method and apparatus such that without unjustifiable extra sensor expenditure a central-line target-point position can be achieved, even in the case of target objects which (in the case of the applied seeker-head technology) do not differ significantly from their target-area surroundings.

According to the present invention there is provided a method for the acquisition of a target point on a central line at a target object, situated in surrounding ground, by scanning the target object, rising above the terrain by means of a reflection distance measuring instrument, characterised in that from at least one position approximately-above the target object a distance determination with regard to the ground and/or to the roof of the target object is effected, whereupon in the distance direction, at least two narrow distance windows are defined, one of said at least two distance windows covering the target object in the vicinity of the ground and a second distance window covering the target object 1 3 in the vicinity of its top or roof, in order to pick up reflection target location energy as a function of the instantaneous scanning swivel angle of the distance measuring instrument from these distance regions, and for predetermined amounts of the reflection power (energy) to obtain the mean value of two associated angular positions for obtaining an item of course correction information in the direction of a centrally situated hit target point.

Further according to the present invention there is provided apparatus for the acquisition of an approximately central hit target point on the roof or top of a target object rising from the surrounding target terrain, by means of a reflection distance measuring instrument on board a manoeuvrable projectile, characterised in that the distance measuring instrument has a swivellable seeker head for scanning the target object and the surrounding terrain and in that connected subsequently to the reflection distance measuring instrument is at least one distance gate for a narrow distance region in the plane of the target-object top or roof or of the ground surrounding the target object, which gate passes the reflection power (energy) selectively received from this distance region as a function of the instantaneous seeker-head angular position on to a storage and evaluation circuit, in which circuit an item of course correction information for a projectile control instrument or steering gear is obtainable from the communication of two angular positions of the seeker-head for identical reflection powers (energies).

The present invention is based on the surprising realisation that, despite target objects which are blended in a well camouflaged manner into the surroundings and which rise sufficiently from the surrounding terrain, highly accurate items of position 4 information result if the items of reflection distance information of the target object and its surroundings as such are not evaluated, but there is needed only a superimposition of items of distance information from at least two defined or specific, mutually offset distance regions. These two regions are to a certain extent so placed as flat or shallow generally horizontal sections; the one region covers the ground region of the target object (and, thus, also the more immediate surroundings thereof) whilst the other region covers an upper region of the target object. In this way, there results for each distance region over the scanning swivel angle of the seeker head a significant course of reflection reception power (energy). For predetermined power or performance levels, then, from the two associated seekerhead swivel angles of the power (energy) curve of a distance region, mean angle values can be formed; and that resulting mean value which emerges from the aforesaid mean values (more especially if they are obtained from different distance regions) is in good approximation a measure of the position of the target point instantaneously sighted on the target object, or of the displacement of the seeker head from the central point of the target, and can thus be utilised as control correction information for the end-phase steering of the projectile.

Additional alternatives and further developments as well as further features and advantages of the present invention will become apparent from the following description.

An embodiment of a method of target acquisition and apparatus for acquiring a target in accordance with the present invention will now be described, by way of example only, with reference to the accompanying much simplified diagrammatic drawings in which:- 1 FIGURE 1 shows in side-view, sectional representation the typical scenario for the use of the present invention; FIGURE 2 shows a block circuit diagram of the technical 5 detection apparatus of the projectile in accordance with FIGURE 1; FIGURE 3 (3a to 3c) shows, in an idealised qualitative sketch, the reception power (energies) dependent upon the instantaneous swivel angles of a seeker head, in distance regions evaluated separately from one another in accordance with FIGURE 2; and FIGURE 4 shows the ltarget-point determination by mean valueformation from the superimposition of the swivel- angle-dependent reception energies in the distance regions in accordance with FIGURE 3b and FIGURE 3c.

From a target terrain 11 (FIGURE 1) there rises a 20 target object 12 of trapeze-like cross-section such as, in particular, a concreted shelter for aircraft and/or working or combat materials (fuels or chemical warfare agents) on an airfield. This target object 12 is to be acquired (detected and hit) by means of a projectile 13 which is manoeuvrable at least in its end approach phase (continuously guidable or discontinuously correctable in its flight orientation) in the steepest possible descent, for which(in the interests of high attack effectiveness on the target object 12), a hit target point 14 which is as central as possible at least in its cross-sectional plane is striven after here to thus obtain an impact approximately in the centre of the shelter roof 15. To this end, the guided projectile 13 (shown unrealistically large in FIGURE 1) is equipped with a seeker head 17 which is directed ahead in the direction of the longitudinal axis 16 of the projectile and which is swivellable in at least one plane. The seeker head is 6 substantially the transmission/reception transducer antenna of a reflection distance measuring instrument (range finder) 18 (radar, Lidar). Thus, in known manner the instantaneous distance E of the measuring instrument 18 and, thus, of the _projectile 13 in instantaneous flight orientation 19 above the ground G (target terrain 11) can be determined from the travel time of the echo of impulses sent out, or from the reception frequency in the case of a frequency-modulated continuous-wave- signal transmitter.

In the case of a target object 12 (the roof T of which merges along side walls 20 - which are inclined and frequently covered with soil or ground vegetation - into the surrounding terrain 11) upon sweeping-over the ground G and the side walls 20 and the roof T, the recept-Jon powers (energies) in the distance measuring instrument 18 on board the projectile 13 do not differ sufficiently significantly in order to be able to obtain a projection geometry (in the sectional plane of the seeker-head swivel direction) for the geometric extrapolation of the roof central point to be homed-in on as target point 14. This fundamental difficulty is, however, circumvented in accordance with the present invention by the simple additional measures of a distance-window staggering (over the previously known or typical height of the target object 12 between ground G and roof T), so that in the individual, defined distance regions, upon swivelling the seeker head, significantly fluctuating reception powers (energies) can be evaluated. Geometrically, the distance windows F can be represented as radially narrow ring segments, which are staggered concentrically to the swivel point 21 of the seeker head 17 (FIGURE 1). In circuitry respects, gate circuits (distance gates 22) are connected subsequently to the range finder 18 which allow only items of reception information (reflection power A) from a predetermined distance region (window F) - j 1 7 1 substantially not overlapping with an adjacent one - to pass. A distance window FO (FIGURE 1) which extends such a short distance from the projectile 13 that it reaches neither the ground G nor even only the target roof T, supplies practically no reflection reception power AC, (FIGURE 3a), irrespective of what angular position w the seeker head 17 is swung relative to the longitudinal axis 16 of the flying body.

A window FG, the mean value of which corresponds to, or is somewhat greater than, the instantaneous distance of the flying- body E above the target terrain 11, supplies reflection power AG only in the angular position w in which an arc of a circle about the swivel point 21 of the seeker head 17 with this radius presently intersects the ground G - which (see FIGURE 1) is the case only on both sides of the target near the transition of the target side walls 20 into the target terrain 11. In this position there corresponds an angular-position- dependent course of the reflection radiation AG (FIGURE 3c) with two pronounced maxima, which move further apart the smaller the flying-body distance E above the ground G becomes. From this geometry, therefore, upon a scanning of mutually offset distance windows F a criterion can be obtained regarding how large the instantaneous ground distance E is, namely represented by the distance of that distance window F in the case of which this pronounced double maxima (FIGURE 3c) occurs. Naturally, however, the distance above ground G can also be derived in a conventional manner from the reflection location detection information (not filtered by way of distance windows F) or it could be obtained by way of a separate range f inder 23. This can, in the circumstances, also supply an item regarding the height H of the appropriate of information target object 8 12 above terrain ground G; or the typical height H of the target object 12 that is to be combatted is stored away in an input instrument 27.

Typical target objects 12 have typical heights H of their roof T above ground G, in the case of aircraft shelters, for example, in the order of magnitude of 10 m. If the instantaneous flyingbody height E above ground G has been ascertained, a further distance window FT with the mean distance value "E-H" can be set. In this narrow distance region a reflection reception power AT emerges only when the antenna characteristic of the seeker head 17 precisely sweeps over the surface of the roof T. From this there results a bell-shaped item of reception information AT, having only one maximum, over the seekerhead swivel angle w (FIGURE 3b).

In order to obtain from the paths or courses A(w) items of angular information wl, wr (FIGURE 4), advantageously, comparator enquiries or interrogations with respect to the exceeding or falling below of thresholds ST, SG, are effected in the storage and evaluation circuit 24 of the projectile 13. The positions of the thresholds S are primarily predetermined as a function of the typical-instrument transmission/reception characteristic of the seeker head 17 and of its swivel speed, but changes as a function of the instantaneous distance E (height) above the ground G and of the extreme values (minima, maxima) of the actual power course (energy path) A(w). The mean angular positions wm. are, advantageously, for the ground G upon dropping of the power (energy) curve AG(w) below such an adaptive ground threshold SG (FIGURE 4) and for the roof T upon rise above an adaptive roof threshold ST, determined from a mean-value formation as indicated symbolically in FIGURE 4).

1 9 If, in accordance with FIGURE 1, the flight orientation (scanning swivel angle w=o=wm) already corresponds approximately with the axis of symmetry through the target object 12, i.e. the longitudinal axis 16 of the flying body already extends approximately vertically through the striven-aftercentral target point 14 in the roof T, the curve courses A(w) result approximately symmetrical to the seeker-head central position wm. Upon a superimposition of the curve courses (traces) in accordance with FIGURE 3, therefore, (see FIGURE 4) the angular central positions wm for specific amplitude values (in accordance with specific identical deflections wl, wr to the left or respectively to the right) lie on a line which coincides all the more exactly with the ordinate of the superimposed amplitude courses, the more exactly the longitudinal axis 16 of the projectile coincides with the normal N through the ideal target point 14. In practice, however, the resulting mean value WM (the angle central positions wmT-wmG from the superimposition of the curve courses; FIGURE 4) lies offset by an amount K from the striven-after target poinz 14.

Circuitwise, the superimposition of the power 25 courses A(w) filtered out by the distance gates 22 is effected in a storage and evaluation circuit 24 for the ascertainment, to be carried out as described above, of the instantaneously resulting mean value WM and for the issuance of an item of course correction information K to a projectile control instrument (steering gear) 25, in the case of which it is, thus, a matter of the displacement of the instantaneous resulting mean value WM from the central -position or zero-position angle wm of the scanning seeker head 17. The control instrument 25 is now so controlled that, by appropriate control-surface deflections or transverse impulse triggerings, the course correction information K becomes seemingly as small as 1 possible and, thus, the striven-after target point 14 is aimed-at ahead as seemingly exactly as possible in the longitudinal axis 16 of the flying body.

The projectile-13 thus enters in good approximation in the centre of the roof T into thetarget object 12, in order (depending on the design as an inertial projectile and/or as explosive projectile) upon impact on the roof T or upon entry into the interior of the target object 12, possibly additionally to bring an incendiary or explosive charge into action in an optimum manner.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may be replaced by any equivalent Or generic term where sensible. Further it is to be understood that individual features, method or functions related to the targez acquisition apparatus might be individually patentably

Claims

inventive. In particular, any disclosure in this specification of a range

for a variable or parameter shall be taken to include a disclosure of any selectable or derivable sub-range within that range and shall be taken to include a disclosure of any value for the variable or parameter lying within or at an end of the range. The singular. may include the plural and vice versa where sensible. The present invention may be that defined in the characterising clause of Claim 1 or Claim 5. It is to be understood that any word or phrase derived from the German language of the priority document may be replaced or supplemented by a different English meaning where appropriate.

Therefore, further according to the present invention there is provided a method of combatting a target with a steerable projectile, said target being of a type which is camouflaged or blended into the 4 11 surrounding terrain, said method comprising scanning a target area with a detector on the projectile and setting up at least two detecting windows or bands arranged at different distances from the detector, one of said detecting windows or bands being arranged or settable to detect the ground level or target at ground level and another of said at least two detecting windows or bands being arranged to detect an upper portion of the target, said method comprising correlating the information detected from said windows or bands in order to correct the flight path of the projectile, if required, on a more central line to the target.

Still further according to the present invention 15 there is provided apparatus for carrying out the above method according to the immediately preceding paragraph.

12 CLAIMS 1. A method for the acquisition of a target point on a central line of a target object, situated in surrounding ground, by scanning the target object, rising above the terrain, by means of a reflection distance measuring instrument, characterised in that from at least one position approximately above the target object a distance determination with regard to the ground and/or to the roof of the target object is effected, whereupon in the distance direction, at least two narrow distance windows are defined, one of said at least two distance windows covering the target object in the vicinity of the ground and a second distance window covering the target object in the vicinity of its top or roof, in order to pick up reflection target location energy as a function of the instantaneous scanning swivel angle of the distance measuring instrument from these distance regions, and for predetermined amounts of the reflection power (energy) to obtain the mean value of two associated angular positions for obtaining an item of course correction information in the direction of a centrally situated hit target point.
2. A method according to Claim 1, in which for the item of course correction information a resulting mean value is obtained from mean angular-position values for the reflection powers (energies) in different distance windows.
3. A method according to Claim 1 or 2, in which a roof distance window is obtained from a ground distance window determined by way of a distance measurement, in which method the predetermined typical height of a target object above ground is deducted from the ground distance measured on board the projectile.

-Q 1 1 13
4. A method according to Claim 1 or 2, in which on board the projectile, for the setting of the distance windows, distance measurements with regard to the targetobject roof and to the surrounding target terrain are 5 effected.
5. Apparatus for the acquisition of an approximately central hit target point on the roof or top of a target object rising from the surrounding target terrain, by means of a reflection distance measuring instrument on board a manoeuvrable projectile, characterised in that the distance measuring instrument has a swivellable seeker. head for scanning the target object and the surrounding terrain and in that connected subsequently to the reflection distance measuring instrument is at least one distance gate for a narrow distance region in the plane of the target object top or roof or of the ground surrounding the target object, which gate passes the reflection power (energy) selectively received from this distance region as a function of the instantaneous seeker-head angular position on to a storage and evaluation circuit, in which circuit an item of course correction information for a projectile control instrument or steering gear is obtainable from the communication of two angular positions of the seeker-head for identical reflection powers (energies).
6. Apparatus according to Claim 5, in which in the storage and evaluation circuit a resulting mean value is obtained from the angular-position mean values of different distance windows for the delivery of an item of course correction information.
7. Apparatus according to Claim 5 or 6, having an additional range finder for the instantaneous projectile distance above ground.

1 14
8. Apparatus according to any one of Claims 5 to 7, having an input instrument for the specification of a typical height of the target-object roof above ground for the definition of the shortest distance window.
9. Apparatus according to any one of Claims 6 to 8 J. in which distancedependent thresholds for the angle evaluation of the power courses are formed in the storage and evaluation circuit.
10. Apparatus substantially as herein described and illustrated with reference to FIGURES 1 and 2 of the accompanying drawings.
11. A method as claimed in Claim 1 and substantially as herein described with reference to the accompanying drawings.

1R Published 1991 at7be Patent Office. State House. 66/71 High Holborn. London WC11147P. Further copies Tnay be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmrelinfach. Cross Keys. NmWrt. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary CTay, Kent.