GB2075789A

GB2075789A - Missile mounted scanner

Info

Publication number: GB2075789A
Application number: GB8113518A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1980-05-05
Filing date: 1981-05-01
Publication date: 1981-11-18
Also published as: FR2481794A1; DE3117421A1; FR2481794B1

Abstract

A missile mounted target location system comprises an optical objective 10 and an optical element with a portion 11, 12 which is rotatable about an axis of rotation XX' which is parallel to the optical axis of the objective so arranged that the focal plane of said optical system is perpendicular to the axis of rotation. The detection system comprises an array of stationary detectors 15 in said focal plane, which is the plane of the image of the field or means for scanning said image plane with the optical image of a stationary detector. <IMAGE>

Description

SPECIFICATION Optical scanner The present invention relates to an optical arrange ment for analysing a spatial field and for determin ing the angular location of a radiating object in said field, comprising an optical field scanning system and a system for detecting the image of said optical system.

The invention may be used for detecting and tracking an object emitting visible or invisible radia tion, hereinafter referred to as a target, and may be employed in an automatic infra-red tracking system in a missile which is automatically guided towards said target.

For this kind of use an optical receiver is associ ated with a photoelectric detector in order to focus and detect the radiation from the field of view with a specific aperture which is centred on the optical aiming axis. The radiation received contains the useful radiation from the target to be detected and located when said target is in the field being observed and spurious radiation produced by other sources present in said field. Without additional measures the target cannot be detected with a satisfactory signal-to-noise ratio. The flux received from the target is generally small in comparison with that of the spurious radiation coming from the background, that is the space observed exterior to the target.

It is known, for example, from French patent specification no. 2,420,144, to improve the signal-to noise ratio by spatially scanning the focussed field image by a movable mask provided with a grating.

The dimensions of said gratings being related to those of the image to be detected in order to obtain a spatial filtration for eliminating the other sources whose dimensions differ from those of the target.

These systems have the advantage of being simple and of performing satisfactorily when the target is the only one in the field of the system or when the background is substantially uniform and the contrast of the target relative to the background is satisfac tory. A drawback of these systems is that they give rise to incorrect locations when a plurality of targets of the same intensity are present in the field, for example artificial interference sources, in the case of the detection of military objects, or natural interfer ence sources in the scene, such as clouds, the horizon, ground obstacles, the distinction between said targets being no longer possible, the more so because said grating systems do not permit the image of the scene to be reconstructed by means of the signal supplied by the detector or detectors.

Other optical arrangements which may be used in conjunction with automatic aiming systems operate with a different principle. They are related to camer as with opto-mechanical scanning ortelevision cameras, wherein the field analysis is effected in two perpendicular directions. By means of these camer as it is possible to obtain the coordinates of random points in the field.Automatic aiming systems equip ped with said arrangmenets have certain advan tages: they enable the target to be selected in the image and to adapt the field analysis to the dimensions of said target, said field being very small, yielding a very effective spatial filtering of the field; the image can be processed by providing a processing window which is governed by the desired target, resulting in the elimination of natural interference in the scene (clouds, horizon, ground obstacles) or artificial interference. The system for scanning in two perpendicular directions of said arrangements is comparatively intricate and, in the case of a missile, employs separate mechanical means not present on the missile.

The invention proposes an arrangement which does not have the same drawbacks as the grating arrangements and which for scanning the field utilises the means which are generally present on a missile, more specifically the gyroscopic means for stabilizing the missile. The optical arrangement in accordance with the invention no longer scans the field in two perpendicular directions, but solely employs mechanical scanning in accordance with a circular path around an axis of rotation which, when the arrangement is mounted on a missile, may be the spin axis of a gyroscope with which said missile is equipped.The analysis system has the advantage that it is simple and has a reduced elemental analysis field adapted to the dimensions of the target to be detected, which results in a very effective spatial filtering by which natural interference of the scene or artificial interference is eliminated.

The invention provides an arrangement for analysing a spatial field and determining the angular location of a radiating object in said field, comprising an optical field-scanning system and a system for detecting the image of the said optical system, the optical field-scanning system comprising a convergent objective and an optical element comprising a portion which rotates about an axis of rotation parallel to the optical axis of the objective, said optical element being constructed and arranged in such a way that the focal plane of the entire optical system is perpendicular to said axis of rotation and causes the image of the field to rotate in the focal plane, and the system for detecting the image of the optical system comprising a system of stationary detectors in the plane of the field image or means for scanning said field image with a moving image of a stationary detector.

In a first embodiment of the invention the optical axis of the objective and said axis of rotation coincide and said rotary portion is designed such that the image focal point of the optical system is situated on the axis of the objective and causes the image of the field to rotate about said focal point in the focal plane through an angle which is twice that of the rotation of said rotary portion. The system for detecting said image and for locating the object may comprise a stationary array of detectors in said focal plane, which detectors are arranged in accordance with one or a plurality of rows, one of the ends of said array coinciding with said focal point.As it rotates, the image of the field travels over the stationary detector array and the locations of the object to be detected is determined in polar coordinates (p,0), p being the distance between the image focal point and the detector(s) over which the image of the object travels, and e being the angle between the array and a direction of origin situated in the image plane.

In a first variant of said first embodiment the optical element with the rotary portion is arranged behind the objective and is constituted by a stationary reversing mirror, which is arranged perpendicularly to the axis of rotation or by a catadioptric reflecting element, the rotary portion being constituted by an assembly of plane reflecting mirrors forming a rectangular dihedral whose edge is perpendicularto the axis ofrotation, the mirrors having the same inclinations relative to said axis of rotation.

In a second variant the optical element with a rotary portion is an assembly of three mirrors which rotates about said axis of rotation, one of said mirrors being parallel to said axis of rotation, the two other mirrors having equal and opposite inclinations relative to the first mirror and relative to the axis of rotation.

In a third variant, the optical element with a rotary portion is a Pecan prism which rotates about an axis which is perpendicularto the plane entrance and exit surfaces of said Pecan prism.

In a fourth variant, the optical element with a rotary portion is a Wollaston prism arranged before the objective and rotating about an axis parallel to the reflecting surface of said prism.

In a second embodiment of the invention the opticaiSaxis of the objective does not coincide with the axis of rotation and the optical element with a rotary portion is the objective itself, whilst the system for detecting the image is a stationary array of detectors arranged in at least one row the length of said array being equal to the diameter of the field image and its centre being situated on the axis of rotation. As the objective rotates, the image of each point of the field describes an arc of circle in the image plane, in particular the image of the object to be detected, which object is located by means of linear and circular co-ordinates respectively.

In a third embodiment of the invention, in which simultaneously the field is scanned two times by means of the same rotary movement, the axis of the objective and the axis of rotation coinciding, the detection system comprises a rotary drum provided with reflecting surfaces, which drum is connected to the rotary portion of the optical field scanning system, the surfaces being regularly arranged around the axis of rotation of the drum and means for imaging a stationary detector in the image plane of said optical field scanning system via one of the surfaces of the drum, the drum and the imaging means being arranged in such a way that during rotation of the drum the image of the detector describes a curve which passes through the centre of the field image and which is symmetrical relative to said centre for each surface of the drum, the curves described having the same shape for all the drum surfaces, but being shifted from one surface to another.

Some embodiments of the arrangement in accordance with the invention, given by way of a nonlimitative example, will now be described with reference to the accompanying drawings in order thatthe invention be more fully understood, of which drawings: Figure 1: is a sectional view of a first embodiment of the invention through a plane of symmetry perpendicular to the edge of the rectangular dihedral angle of the rotary element.

Figure 2: is a perspectiveview of said embodiment, mounted on a missile.

Figure 3: represents the movement of the detector in said first embodiment relative to the scene being observed in the image plane.

Figure 4: is a sectional view, through the same plane of rotation, of a first variant of said first embodiment, equipped with a teleobjective.

Figure 5: is a sectional view of said first variant through the plane of symmetry parallel to the edge of the rectangular dihedral angle of the rotary element.

Figure 6: represents a second version of the rotary optical element.

Figure 7: represents a third version of said rotary optical element.

Figure 8: represents a fourth version of said rotary optical element.

Figure 9: is a sectional view through the plane of symmetry perpendicular to the edge of the dihedral angle of a second variant of said first embodiment.

Figure 10: is a sectional view of a first variant of a second embodiment of the invention comprising a rotary objective.

Figure 11: represents the relative movement of the detector in the image plane relative to the scene in said first variant of said second embodiment of the invention.

Figure 12: is a sectional view of a second embodiment of the invention with a rotary objective in accordance with a second variant.

Figure 13: is a perspective view of a third embodiment of the invention in which the image is scanned via the image of a stationary detector.

Figure 14: is a diagram representing the actual relative movement of the image and a singleelement detector in the arrangement shown in Figure 13.

Figure 15: is a diagram which schematically represents the said movement.

Figure 16: is a diagram representing said relative movement of the image, in the case of a detector comprising n elements arranged in series and disposed on a line perpendicular to the axis of rotation in Figure 13.

Figure 17: is a diagram representing said relative movement of the image in the case of a detector comprising n x N elements arranged in seriesparallel and forming N rows perpendicular to the axis of rotation and n columns parallel to said axis.

Figure 18: is a sectional view perpendicular to the edge of the rotating dihedral of a first variant of the third embodiment.

Figure 19: is a sectional view perpendicular to the edge of the rotating dihedral of a second variant of the third embodiment.

In Figure 1, which relates to a first embodiment of the invention, the axis of the optical system is designated X X' which system is shown in a sectional view through one of its planes of symmetry passing through said axis, which axis also forms the aiming axis of the automatic aiming device in the case that the arrangement is mounted on a missile.

Said optical system comprises the convergent system, which is schematically represented by the lens 10, the rectangular dihedral comprising the plane mirrors 11 and 12 and the plane mirror 13, The dihedral 11, 12 and the mirror 13, which may be replaced by a reflecting catadioptric system, directs every optical ray originating from the scene to a point in the focal plane through the focus F', of the system. For this purpose, the dihedral has a central aperture 16 for the passage of the beams. The references 14 and 14' refer to two of said rays parallel to the axis XX', which rays bound the half of the beam coming from the scene in the aiming direction. Said beam, which for reasons of clarity is only shown partly, converges in F'. The dihedral is subject to a rotary movement about the axis X X' and causes the image of the scene to rotate about the focus F'.Arranged in the focal plane is a stationary array 15 of N detectors, one of the ends of said array coinciding with the focus F'. The detectors are arranged in the array along one or along a plurality of parallel rows, the detectors of the different rows being for example staggered relative to each other. The detectors are for example connected in series, and their output signals are added to each other via delay lines.

Preferably, the optical system is rigidly connected to the object or missile with which it is associated via a gyroscope mounted on said missile, as is shown in Figure 2 by means of a gymbal suspension.

In said Figure the axes 21 and 22 of the gymbal suspension pass through the image focal point F' of the optical system. The axis 22 is fixed relative to the missile, whilst the axis 21 is movable about 22. The major dimension of the array of detectors 15 extends along the movable axis 21. Thus, the detection system is always situated in the focal plane of the optical system, even when the axis XX', which is common to the optical system and the spin axis of the gyroscope, does not coincide with the axis 23 of the missile. The lens 10 and the mirrors 11, 12, 13 are shown in perspective in Figure 2. The numeral 6 designates the beam coming from the scene in the direction of XX', said beam intersecting the dihedral 11, 12 in accordance with the section 7.When the dihedral rotates about the axis X X' through an angle a, the image of the scene formed on the detector array rotates about F' through an angle 2a. The detector on which said image is formed is more remote from F' as the scanning direction is more oblique relative to the aiming axis. Figure 3 represents the relative movement of the detector with respect to the image of the scene, in the focal plane of the optical system. Each detector of the array 15 scans a circular band of the scene image, such as the band 31, the location of the detected target 32 being expressed in its polar co-ordinates p and 6.

Suitably, the arrangement has a large image focal length. To this end, in accordance with a variant of the embodiment, the converging part of the optical system is constituted by a teleobjective, as a result of which the central opaque zone of the system is reduced for a given optical range. This variant is represented in Figures 4 and 5.

In Figures 4 and 5 the system is represented in sectional view in accordance with its Rlane of symmetry, perpendicularly and parallel to the edge 8 of the dihedral respectively. Figure 4 shows the mirror 13 and the mirrors 11 and 12 of the rectangular dihedral arranged on the block 45. The teleobjective is constituted by the lenses 44 and 43, the image focal point of the entire system being situated at F' on the axis XX'. In order to simplify the drawing, only those bounding rays 41 and 42 are shown, which issue from the scene being observed at an angle y with the aiming axis X X' and which pass through the upper half of the objective. The image of the scene for this direction is formed in the point P of the focal plane situated in the planes of the Figure. In Figure 5 only one half of the system is shown.The bounding rays issuing from the scene being observed and making an angle y with the aiming axis X X' are 51 and 52. The image of the scene for this direction is formed in the plane of the Figure in point P' of the focal plane. It is to be noted that the image is inverted when the plane being observed is perpendicular to the edge of the dihedral, whilst said inversion is not produced in the case of a plane of observation parallel to said edge, which permits the system to rotate the image of the scene through an angle which is twice that of the rotation of the dihedral and thereby form said image on one of the detectors of the array. The rectangular dihedral formed by two plane mirrors is not the only system which may be used for rotating the image. Any rotary optical system may be used which produces an erected image relative to a plane.

Figures 6,7 and 8 each represent one of said systems in a sectional view.

In Figure 6 it is shown as the objective 10 whose optical axis coincides with the axis of rotation X X' and whose focal point F'. The element of the optical system which rotates about the axis X X' is constituted by the assembly of the mirrors 61,62,63, which are rigidly connected to each other. The mirror 61 is, for example, parallel to the axis XX'.

The mirrors 62 and 63 have for example the same inclinations relative to 61 and relative to the axis X X'.

Figure 6 represents the beam 6 and the path inside the rotary element of the optical ray which coincides with the optical axis of the objective, the image field being the circle with the diameter 60.

In Figure 7 the rotary element is a Wollaston element 71, whose reflecting surface is parallel to the axis XX', which axis is situated in a section normal to said surfaces. Because said Wollaston element functions with parallel light, it is arranged before the objective 10. The Figure 7 shows the path inside the Wollaston element of the beam 6 and of an optical ray which coincides with the axis XX'. The image field being scanned is the circle with the diameter 70.

In Figure 8 the rotary element is a Pecan prism 81, which rotates about the axis X X' perpendicular to its plane entrance and exit surfaces. This scanning field is the circle with the diameter 80, which is centred around the focal point F'. The Figure shows the path inside the Pecan prism of an optical ray which coincides with the axis XX'. Because of the layer 84 of a material with a refractive index which differs from that of the other parts of the prism, said ray emerges slightly shifted relative to XX'.

The optical systems described in the foregoing are partly catadioptric. It is evident that they may also be entirely dioptric. The selected combination of a converging system and an erecting system (rotary part) is adapted to the available volume and to the specific problems to be solved.

Figure 9 shows another variant in a sectional view through the plane of symmetry of the optical system which is perpendicular to the edge ofthe dihedral.

Both the opening of the dihedral and the central dark portion of the entire system are reduced. Said system comprises a primary objective 10, having such a focal length that the focal point F' of the system comprising the objective 10; the mirror 13 and the dihedral 11, 12 are situated in the opening 93 of the dihedral. A convergent system 92 forms an image of said focal plane. This image plane is perpendicular to the aiming axis X X' situated in A, and contains the detector array, one of the ends of said array being located in point A.

The first embodiment has the advantage that a scanning efficiency is obtained which is substantially equal to unity (having no dead time) and that few detectors are required. On the other hand, it has the drawback that the field is scanned with non-uniform speeds and that in consequence the radiation pulses issuing from the targets and received by the detectors become shorterfrom the centre towards the exterior, the central detector receiving a continuous flux.

In a second embodiment this non-uniformity of the field scanning speed is remedied. In this embodiment the rotary optical element is constituted by the objective itself. Said objective, which axis of rotation coincides with the mechanical spin axis of a gyroscope when the arrangement is installed in a missile, is aff-centred, its focal plane remaining perpendicularto said axis of rotation.

Figure 10 represents a first variant of this embodiment. X X' is the axis of rotation. The numeral 107 designates the optical axis of the objective. During its rotation about X X' 107 is at a constant distance from XX'. The focal point is F'. The image of the field being analysed, is a circle which is centred around X X' and has a diameter F' F". Detection is effected by means of a detector array of a length equal to said diameter. Said array is stationary in the image plane.

It is arranged on the axis 21 of the gymbal suspension as shown in Figure 2, its centre being the point of intersection of 21 and 22.

Figure 11 represents the relative movement, in the focal plane of the optical system, of the detectors with respect to the scene. The circle 102 is the image field being analysed. Detector no. 1 follows the circumference of the circuit 102, whilst detector no. n follows the circumference of the circle 101, which is derived from 102 by a translation in a direction parallel to the array and over a distance equal to the diameter of the image field.

The array 100, comprising twice the number of detectors in the first embodiment, moves relative to the imagefrom position 103 to position 104, whilst remaining parallel to itself, its ends fo!lowing the circumferences of the circles 101 and 102. Each detector scans a band of the scene image in the form of an arc of circle such as 105. When the position of a target 106 is defined in accordance with curvilinear co-ordinates, said co-ordinates may be converted into rectangular co-ordinates by calculation.This system has the advantage of having a pass-band which is the same for all detectors, but has the drawback that its scanning efficiency is smaller than unity, because the surface of the scanning field is the peripheral surface LMNOPQ with semi-circular boundaries, whilst the effective field surface is the circle 102. On the other hand, the detector comprises double the number of elements with constant angular resolution.

In a variant of this embodiment shown in Figure 12, the objective 10 is no longer rotationally symmetrical and instead of purely dioptric it is catadioptric.

The objective comprises the dioptric part 110,whose optical axis coincides with the axis of rotation XX', and the assembly of mirrors which folds back the beam 99 entering the system parallel to X X' and focusses said beam in F' outside XX'. When the mirror 110 rotates about X X' the objective analyses a field with an image diameter F'F".

Figure 13 shows a third embodiment in which the scanning of the image field is far more intricate.

Analysis of said field is effected in two directions, using the same rotational movement. Said Figure shows, arranged around the axis XX', the objective 10 and a dihedral 11, 12 identical to that of the first embodiment, whose edge is assumed to be vertical in the plane of the Figure, the elements bearing the same references as in Figure 2. The elements are arranged within a mount 11 1,which is connected to the drum 112 comprising a number of mirrors. In Figure 13 the mirrors are situated in the interior of the drum. The mirrors may alternatively be exterior mirrors. One of said mirror bears the numeral 113.

inside the drum a certain number of stationary optical elements are situated, which in conjunction with one of the reflecting surfaces of said drum form the image of a detector 114 in the circular field 115 which field is analysed by the objective 10 and the movable dihedral 11, 12. Said elements are the reversing mirror 116, the converging element 117 with the focus 114, the converging element 118 with the focus 119, and the mirror 120, the mirrors 116 and 120 being perpendicular to the plane of the Figure. The numeral 121 designates abeam pro ceedingfrom 119to 114 via a reflection at the surface 113 of the drum, the optical path of said beam being contained in a vertical plane comprising the axis XX' and the edge of the dihedral 11, 12.

Upon each revolution of the optical block 111 the image of the scene makes two revolutions in the plane of the image field 115 and the image 1 19 of the detector 114 describes a plurality of identical arcs of curve in the circular field 115, which curves pass through the centre of the field 115, one arc of curve being produced by each mirror of the drum. Some of said arcs of curve are represented in Figure 14. One tf said arcs is for example the arc 201. In order to facilitate the description and the graphical representation the radius of said arcs of curve is set equal to the diameter of the circle 115 in Figures 13, 15, 16, 17. For example, in Figure 13 the image of the detector follows the diameter 122, whilst the beam 121 is reflected by the mirror 113. Figures 15 represents the scanning in the image field 115.When taking into account the direction of rotation of the optical block 111, which is represented by arrow 123 in Figure 13, the diameter 122 is scanned by the image 119 of the detector in the direction of the arrow 137, whilst the successive diameters rotate in accordance with the arrow 124, the diameters 125 and 126 corresponding to the respective reflecting surfaces 127 and 128. In order to improve detection, the detector may comprise a plurality n of elements disposed in accordance with a line perpendicularto the axis XX', the images of the n detectors scanning each diameter as shown in Figure 16, the detection being effected in a serial mode, and the output signals of the detector being summed via delay lines.The detector may also comprise a plurality nx N of elements arranged in accordance with N rows and n columns, the columns and rows being respectively perpendicular and parallel to XX', the detector covering then a diametral band comprising N lines as shown in Figure 17. Then the detection is effected in a series-parallel mode.

Figure 18 shows a first variant of said third embodiment in a sectional view through its plane of symmetry which is perpendicular to the edge of the rotary dihedral. Said Figure again shows the lens 10, the mirror 13 and the dihedral mirrors 11 and 12 of Figure 1, which mirrors are incorporated in the optical block 112. The rotary drum is pyramidal. The surfaces 151 and 152 are disposed exteriorto said optical block. The circular image field 115 of the objective appears as a line section. The stationary system constituted by the converging lens 153 and the mirror 154, the lens 155 and the mirror 156, in conjunction with the rotary drum, forms, via a radiation path outside the axis of rotation XX', an image of the detector 14 in the field of the objective and of the dihedral.When the beam is reflected on the surface 151 the image of the detector scans the diameter 122, which is now perpendicular to the plane of the drawing.

Figure 19, in a sectional view in accordance with its plane of symmetry which is perpendicular to the edge of the rotating dihedral, represents a second variant of the third embodiment. The pyramidal drum has reflecting surfaces 159 and 160 facing the axis X X' on which the detector 114 is arranged. The image of the detector 114 is transferred to the circular image field 115 of the objective and of the dihedral by means of stationary lens elements 161, 165 and stationary mirrors 163, 162, 164 in conjunction with the reflecting surfaces 159, 160 of the drum.

When the beam 121 is reflected on the surface 159, the image of the detector, as in the preceding example, follows the diameter 122 of the circular image field which diameter is perpendicular to the plane of the Figure.

The pyramid form is adopted for a reflecting rotary drum. It may be based on a prismatic form.

In the same way as the other embodiments the arrangement in accordance with said third embodiment, when used on a missile, employs the spin axis of the gyroscope as the axis XX', the detector 114 being disposed on the intersection of the axes 21 and 22 in Figure 2, which axes are the axes of the gymbals by which the gyroscope is mounted on the missile. As in the preceding example, the axis X X' need not necessarily coincide with the axis of the missile, but may be movable around the centre 114 of the gymbals. This third embodiment has the advantage of providing two-dimensional scanning means of a single rotary movement, of analysing the entire field by means of a small number of detectors, all the points of the field being analysed with the same speed, of providing a very high information redundancy in the centre of the field, and of providing a very good sensitivity when seriesparallel detection is employed.

Claims

CLAIMS:

1. An arrangement for analysing a spatial field and determining the angular location of a radiating object in said field, comprising an optical fieldscanning system and a system for detecting the image of the said optical system, the optical fieldscanning system comprising a convergent objective and an optical element comprising a portion which rotates about an axis of rotation parallel to the optical axis of the objective, said optical element being constructed and arranged in such a way that the focal plane of the entire optical system is perpendicular to said axis of rotation causes the image of the field to rotate in the focal plane, and the system for detecting the image of the optical system comprising a system of stationary detectors in the plane of the field image or means for scanning said field image with a moving image of a stationary detector.

2. An arrangement as claimed in Claim 1, wherein the optical axis of the objective and said axis of rotation coincide and in which said rotary portion is designed such that the image of the field rotates through an angle which is twice that of the rotation of said rotary portion.

3. An arrangement as claimed in Claim 2, wherein the optical element with the rotary portion is arranged behind the objective and is constituted by a stationary reversing mirror, which is arranged perpendicularly to the axis of rotation or by a catadioptric reflecting element, the rotary portion being constituted by an assembly of plane reflecting mirrors forming a rectangular dihedral whose edge is perpendicular to the axis of rotation, the mirrors having the same inclinations relative to said axis of rotation.

4. An arrangement as claimed in Claim 2, wherein the optical element with the rotary portion is anassembly of three mirrors which rotate about said axis of rotation, one of said mirrors being parallel to the axis of rotation, the two other mirrors having equal and opposite inclinations relative to the first mirror and relative to the axis of rotation.

5. An arrangement as claimed in Claim 2, wherein said optical element with a rotary portion is a Péchan prism, which rotates about an axis which is perpendicular to the plane entrance and exit surface of said Péchan prism.

6. An arrangement as claimed in Claim 2, wherein said optical element with a rotary portion is a Wollaston prism arranged before the objective and rotating about an axis parallel to the reflecting surface of said prism.

7. An arrangement as claimed in any one of the Claims 1 to 6, wherein the detector system is a linear array comprising a plurality of detector elements, which array is stationary relative to the axis of rotation and perpendicular to said axis, the detector elements being arranged in at least one row, one of the ends of said array coinciding with the image focal point of the optical field scanning system.

8. An arrangement as claimed in any one of the Claims 1 to 6, wherein the detection system comprises a rotary drum provided with reflecting surfaces which drum is connected to the rotary portion of the optical field scanning system,which reflecting surfaces are regularly arranged around the axis of rotation of the drum, means for imaging a stationary detector in the image plane of said optical field scanning system using via one of the surfaces of the drum, the drum and the imaging means being arranged in such a way that during rotation of the drum the image of the detector describes a curve which passes through the centre of the field image and which is symmetrical relative to said centre for each surface of the drum, the curves described having the same shape for all the surfaces, but being shifted from one surface to another.

9. An arrangement as claimed in Claims 3 and 8, wherein the rectangular dihedral of the optical element with a rotary portion and the reflecting elements of the rotary drum are arranged on one block.

10. An arrangement as claimed in Claim 9, wherein the detector is exterior to the axis of rotation.

11. An arrangement as claimed in Claim 9, wherein the detector is situated on the axis of rotation.

12. An arrangement as claimed in any one of the Claims 8 to 11, wherein the detector comprises n elements arranged in a line perpendiculartothe axis of rotation.

13. An arrangement as claimed in any one ofthe Claims 8 to 11, wherein the detector comprises a matrix of n x N elements disposed in accordance with N rows and n columns, the columns and the rows being respectively perpendicular and parallel to the axis of rotation.

14. An arrangement as claimed in Claim 1, wherein the optical axis of the objective does not coincide with the axis of rotation and wherein the optical element with a rotary portion is the objective itself, whilst the system for detecting the image is a stationary array of detectors arranged in at least one row, the length of said array being equal to that of the diameter of the field image and its centre being situated on the axis of rotation.

15. An arrangement as claimed in Claim 7, wherein the objective is provided with mirrors one of which is rotatable about the axis of rotation and causes the focus of the objective plus mirror systemto describe a circle about the axis of rotation equal to the field image.

16. An automatic aiming system for a missile, comprising a gyroscope stabilizer, wherein said automatic aiming system comprises an analysing arrangement as claimed in Claim 7, whose axis of rotation coincides with the spin axis of the gyroscope, the image focal point of the optical field scanning system being situated at the point of intersection of the two axes of the gymbal suspension of the gyroscope on the missile, and the array of detectors being disposed on the axis of said gymbal suspension which is movable relative to the missile.

17. An automatic aiming system for a missile, comprising a gyroscope stabilizer, wherein said automatic aiming system comprises an analysing arrangement as claimed in any one of the Claims 8 to 13, whose axis of rotation coincides with the spin axis of the gyroscope, the detector being disposed on the point of intersection of the two axes of the gyroscope.

18. An automatic aiming system for a missile, comprising a gyroscope stabilizer, wherein said automatic aiming system comprises an analysing arrangement as claimed in Claim 14 or 15, whose axis of rotation coincides with the spin axis of the gyroscope, the array of detectors being disposed on that axis of the gymbal suspension of the gyroscope on the missile, which is movable relative to the missile.

19. An arrangement for analysing a spatial field substantially as described with reference to Figure 4 of the accompanying drawings.

20. An arrangement for analysing a spatial field substantially as described with reference to Figure 5 ofthe accompanying drawings.

21. An arrangement for analysing a spatial field substantially as described with reference to Figure 7 ofthe accompanying drawings.

22. An arrangement for analysing a spatial field substantially as described with reference to Figure 8 of the accompanying drawings.

23. An arrangement for analysing a spatial field substantially as described with reference to Figure 13 of the accompanying drawings.

24. An arrangement for analysing a spatial field substantially as described with reference to Figure 18 of the accompanying drawings.

25. An arrangement for analysing a spatial field substantially as described with reference to Figure 19 of the accompanying drawings.