GB2305573A

GB2305573A - High-speed optronic panoramic surveillance system

Info

Publication number: GB2305573A
Application number: GB9619770A
Authority: GB
Inventors: Jacques Rioland; Joel Rollin; Eric Sauty; Paul Thibout
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1995-09-22
Filing date: 1996-09-23
Publication date: 1997-04-09
Anticipated expiration: 2016-09-23
Also published as: FR2739192B1; FR2739192A1; GB9619770D0; GB2305573B

Abstract

The problem arising with panoramic surveillance systems is the incompatibility between the limitation of the frame refresh frequency and the need for a long integration time to allow detection of modern threats of attack. The invention proposes a specific optical combination which allows the successive projection, on to a single detector array, of images of elevation spaced bands, said combination comprising high speed nutation means which on each charge integration cancels out the apparent scrolling speed of the scene. A surveillance system according to the invention comprises an analysis head 1 rotated by a turntable 24 so that the head 1 scans a field of view along a line of sight LV, at least one optical module MO 1 , MO 2 forming an image by projection of the luminous flux F i on a detector array 4. Each module defines an optical channel comprising elements 51, M1, M'1; 52, M2, M'2, focusing elements L1 to L3, and a nutation device 20 rotating about the axis ZZ'.

Description

HIGH-SPEED OPTRONIC PANORAMIC SURVEILLANCE SYSTEM.

This invention relates to optronic panoramic surveillance in the infrared spectral transmission bands of the atmosphere. It applies to ground/ground and ground/air surveillance for detecting potential threats to land or air targets, particularly short-range ground to air missiles or medium-range ground to air missiles.

Passive surveillance systems are intended for surveying strategic zones requiring protection.

They enable potential threats, generally airborne, to be detected by the emissivity thereof in an infrared detection band.

Conventional panoramic surveillance systems associate an optical lens for focusing the flux incident on a detector consisting of elementary sensors of semi conductive material which integrate a number of charges proportional to the flux intensity received in their spectral sensitivity band, and a circuit for reading and processing said charges to form a display signal. Conventionally, the detector is in the form of a strip comprising a number of rows of elementary sensors in alignment, e.g. 4 x 256 sensors, the strip associated with an oscillatory mirror to scan the field of view in elevation.

All these detection elements are disposed in an analysis head disposed on a pivoting table driven at a uniform speed about a vertical axis. The pivoting movement of the table provides panoramic scanning of the scene under surveillance from an elementary field of view defined by the lens and the associated oscillatory mirror. Integration of the collected charges and their measurement are triggered, during the pivoting, in accordance with a regular pitch by means of a sampling clock. The data stream thus acquired is transmitted by the reading circuit to an electronic processing unit which controls a display of images per frame in accordance with a refresh speed linked to the sampling speed, and detection and automatic pursuit of the movable elements in said image.

The problem which conventionally arises with such panoramic surveillance systems is the incompatibility between the limitation of the frame refresh frequency and the need for a long integration time to allow the detection of modern high-speed threats having a high degree of manoeuvrability. To give an idea of order of magnitude, the frequency of rotation is typically 1 to 2 Hz and the elevation range covered is of the order of 0.1 rad. Higher frequencies, e.g. from 5 to 20 Hz, are imperative if multiple high-speed manoeuvrable threats are to be taken into account over a sufficiently large elevation angle, e.g. from -5 to +400.

The use of a detector array instead of a strip would enable the detection speed to be increased, because it uses simultaneously 30 to 100 times more elementary sensors, e.g. 128 x 128 or 256 x 256 sensors. The condition is that the movement of the line of sight during the charge integration time, typically from 10 to 100 ps, should remain small in comparison with the elementary field of each sensor.

At least 15 elementary fields are then scanned during the elementary integration time for a 5 Hz scanning frequency. The resulting image blur could be processed electronically, but is it expensive and does not prevent loss of information. With regard to conventional solutions using a reflectingmultifacet drum, these are difficult to use in very open optical systems.

The object of the invention is to solve the problem by proposing a panoramic surveillance system covering an elevation surveillance area which can be widely extended, with a high range of detection and refresh rate, particularly to allow detection of high-speed or distant targets. To this end, the invention makes use of a specific optical combination allowing successive projection, on one and the same detection matrix, of images of space bands cutting the field of view in elevation over a wide angular range, said combination also comprising means for scanning by nutation each band adapted to increase the charge integration time in the strip by stopping on the image.

More specifically, the invention relates to a highspeed optronic panoramic surveillance system comprising an analysis head rotated by a turntable so that the head scans along a line of sight a panoramic field of view composed of scenes successively observed by an optical part, said optical observation part forming an image by projection of the luminous flux originating from the scene on to a detector which integrates charges in proportion to the illumination received and which is associated with a charge reading circuit and an electronic processing unit to deliver a display signal, said surveillance system being characterised in that the optical observation part comprises at least one optical module cutting the field of view into analysis bands, each module defining an optical channel about an axis and comprising optical elements for transporting the image to the detector of the array type, including a focusing lens of optical axis centred on the detector, and an optical nutation device, rotated about the optical axis of the focusing lens to form successively on the detector the focused scene images at an apparent scrolling speed, and in order to impart to the line of sight a higher-speed nutation which on each charge integration cancels out the apparent scrolling speed of the observed scene.

According to a first embodiment, the surveillance system comprises a single observation module covering a single analysis band, e.g. 12O elevation, coupled to a nutation device which deflects the luminous flux about the optical axis of the observation module. The nutation device, for example, consists of a prism or a rotating mirror inclined to its axis of rotation.

According to another embodiment, the system according to the invention comprises a plurality of observation modules analysing preferably juxtaposed bands which then cover a wide angular elevation range, e.g. four modules covering from -4 to 40 elevation. The observation modules constitute optical channels over which the images of the observed scenes are transported for projection on to the detector array after deflection from an appropriately oriented mirror. The optical channels are multiplexed, e.g. by means of an appropriate alignment device, so as successively to integrate the images on the detector. According to one exemplified embodiment, the nutation device is common to all the observation modules and effects in combined manner nutation and multiplexing during its rotation.One example of a nutation device of this type comprises a periscope rotating about the bearing axis and comprising two mirrors together forming an angle which deflects the flux through the required nutation angle. According to another example the nutation device is an optical deflector bar of a specific shape, which also combines multiplexing and nutation.

Other advantages and features will be apparent from the following description and accompanying drawings wherein: Fig. 1 is a diagrammatic perspective of one example of a panoramic surveillance system according to a first embodiment of the invention.

Fig. 2 is a diagram showing the superposition of the scrolling and nutation movements.

Figs. 3a and 3b show the variation of the instantaneous rotational speed of a point image formed on the detector, in the form of a cycloid, and the variation of the angular abscissa o of this point image.

Figs. 4 to 10 are examples of an optical module and their effects in the context of a first embodiment of the invention employing a single analysis band and Fig. 11 is an example of use of the second embodiment of the invention comprising complementary analysis bands using a periscope type optical multiplexing and nutation device.

Fig. 1 is a perspective view of one exemplified embodiment of the optronic panoramic surveillance device according to a first embodiment of the invention. The surveillance device is termed "optronic inasmuch as the spectral detection band is an ultraviolet, visible or infrared transmission band of the atmosphere as opposed to the range of detection of the electromagnetic or hyperfrequency waves of radar warning systems.

In this first example illustrating the embodiment employing a single scanning band, the system of the invention incorporates a single optical observation module formed by a combination of optical elements defining a single optical channel. During a panoramic scan of the observation module this optical channel analyses a part of the surrounding space, the angle of elevation thereof being limited to a specific angle and being termed the analysis band.

Conventionally, the construction of the surveillance device shown in Fig. 1 consists mainly of an analysis head 1, a turntable 2 to rotate the analysis head, and a stationary processing unit 3.

The analysis head, turntable and processing unit are shown as transparent in the drawing in order to show some of the elements that they contain.

A luminous flux Fi originating from the observed scene is propagated over the observation channel defined by the integrated optical module MO, as far as its focusing on a detector 4. In this Figure and the following Figures, the flux is limited to the end rays denoted in dotted lines. Depending on different possibilities for the architecture of the optical module as detailed hereinafter the observation channel is situated in the analysis head or extends from the latter to the processing unit, the detector then being respectively in the analysis head or in the processing unit.

The optical module in the exemplified embodiment of a surveillance device according to the invention as illustrated diagrammatically in Fig. 1 defines an observation channel situated in the analysis head 1.

It comprises: - a head lens 5 of centre 0 and optical axis XX', fixed on the spherical panoramic analysis head 1, and defining a central instantaneous line of sight LV for the observation channel; this lens projects the flux Fi from the observed scene on to the array detector 4 to form an image thereon; the detector is coupled to an electronic integrated charge reader and sampler 6 to form a display signal; and - a prism 7 mounted on the optical axis X'OX in a parallel beam in front of the lens 5; said prism, which is cut circularly from a triangular-section preform, rotates about the optical axis of the lens by known means to give a high-speed nutation Qn of the line of sight LV about said optical axis X'OX; the amplitude and the frequency of the nutation are adjusted to satisfy the conditions described hereinafter.

The turntable 2 on which the assembly of the above elements rests is driven at uniform speed by a servo motor (not shown) to impart to the optical axis X'OX a panoramic scanning movement in respect of the bearing about the vertical axis Z'Z.

The fixed processing unit 3 comprises an electronic module 8 for processing the signals from the detector 4 read by the electronic unit 6, transmitted by a connection, e.g. of the rotary joint type, to provide a display signal for the observed scene, and a target extraction module 9 coupled to the electronic unit 8. This extraction unit allows identification, tracking and transmission of the co-ordinates of detected potential threats to a control system 10, e.g. a fire-control or countermeasure system.

By nutation of the line of sight LV combined with the panoramic scan, the surveillance system of the invention enables the frequency of observation of the analysed scenes to be increased without affecting the detection in respect of the range. The amplitude and frequency of nutation are so adjusted as periodically to stop the apparent scan of the scene at the precise moment of integration of the charges received by the detector.

To obtain this "stop on image" the nutation frequency of the line of sight is locked on the image acquisition frequency.

In order to improve acquisition, it is advantageous, with reference to Fig. 2, to decouple the two rotations in order to split up their effects. When the panoramic scan is stopped, any point of the observed scene situated at infinity on the line of sight forms a point image I of the image of the scene in the focal plane of the detector. This image is animated, by the action of the nutation device, by a rotary movement of speed nn, and each point I follows a circular path C about the centre A of the detector marked by an angular abscissa 0.

The panoramic scan of angular speed Qb gives the point I a continuous scrolling movement, which in the Figure is manifest by a translatory movement, in a relative reference linked to the detector, over an apparently rectilinear trajectory T.

The combination of the two translation and nutation movements forms a cycloid, the period of which is fixed by that of the nutation. A cycloid r of this kind is shown in Fig. 3a by variation of the instantaneous speed of rotation flg against the angular abscissa e of the point image I. In Fig.

3b, the variation of the angular abscissa e against the time t shows plateaux pi of duration 6t, during which the point I is motionless. This immobility corresponds to an apparent stoppage of the scrolling of the line of sight.

Such stoppage in respect of bearing enables a fixed image to be obtained for the duration 6t of this stoppage, on each nutation cycle. This fixity can result in the production of a particularly distinct display because the charges which can be integrated in the detector for the entire duration 6t correspond precisely to this fixed image.

To obtain an effect of this kind, the position of the stoppage 10 of the point I (Fig. 2) is at the point of contact between the trajectories C and T.

To satisfy this condition, it is only necessary to link the amplitude a and the speed of rotation Qn of the nutation at the scanning speed Db by the following equation, which arises from the conventional relationship between angular and linear velocities: = = a a.Q To utilise this effect in order to improve the image clarity, the time at which integration of the charges starts is triggered when the apparent scrolling speed is cancelled out; this time coincides with the time at which the point I is in the stoppage position 10, on each nutation cycle, corresponding successively to the retrogression points ri of the cycloid r. The sampling clock is therefore programmed to control the triggering and duration of the integration of the charges at these times of coincidence and at the stoppage time 6t.

The following Figures illustrate different variants of embodiment of the optical module diagrammatically illustrated in Fig. 1 with, in particular, different examples of nutation systems. Like elements are denoted by like references. It should be noted that the detector array can, depending on whether the optical module is or is not bent, be disposed in the rotary analysis head or in the fixed processing unit, and that the nutation system rotates about the optical axis of the lens focusing on the detector.

Referring to Fig. 4, the nutation type is of the biprism type, in which a first nutation prism 11 of the type previously described but of a size adapted by the skilled man, is coupled to another fixed prism 12. This coupling provides compensation for the chromatic dispersion for the position corresponding to the charge integration. The biprism is located between an afocal system consisting of the lens 5 and a group of lens elements 13, and a second lens 14 which focuses the transported flux Fi on the detector 4. A nutation biprism of this type, adapted in respect of size, can also be located in front of the entry lens 5.

Fig. 5 shows a similar optical architecture (afocal head unit and second focusing lens) bent by a nutation system consisting of a mirror 15. The mirror is rotated by a motor 16 to rotate about an axis a'a forming a small angle with the normal N'N to the mirror. The value of the angle E is adapted to the value of the amplitude of nutation required corresponding to twice that value. Because of the reflection properties, the nutation in this case is not of circular section but of elliptical section, the major axis of the ellipse being twice as large as its minor axis.The observation module as a whole thus defined can be oriented to give a panoramic scan of the line of sight both horizontal (corresponding to the illustration in the drawing) and vertical (corresponding to a representation deduced from the foregoing by a rotation through 9or ) Fig. 6 shows a simplified nutation device directly using the head lens 5 for focusing the flux Fi on the detector 4, the lens 5 being off-centre and rotated by any known means. Two positions are shown. The lens not off-centre in solid lines and the lens offcentre in dotted lines. The eccentricity is obtained by angularly shifting the lens 5 so that its optical axis X'OX retains an angle 9 with the axis of rotation x'O'x while rotating about the latter.The effect of an off-centre rotation is shown in Fig. 7, which is a section perpendicularly to the plane of the previous Figure through 0, of an eccentric position of the intersected flux Fi centred on the optical axis 0 and the circular rotation Z centred at O'.

Fig. 8 shows an embodiment based on the principle described with reference to Figs. 4 and 5, but wherein the off-centre nutation element is an optical group 17 (non-eccentric position shown in solid lines) forming with the entry lens 5 an afocal system 18 which is combined with the focusing lens 14 which focuses the flux on the detector 4. The group 17 is off-centre (dotted lines) so that its optical axis Y'Y rotates about an axis of rotation x'x coinciding with the axis O"A of the focusing lens 14 centred at O" of the detector 4 centred at A.

The nutation system shown in Fig. 9 has the same basic architecture but uses a nutation device in the form of an optical flat 19 having an axis 1'1 inclined to the optical axis x'x. The optical flat is disposed in a convergent beam in the afocal system illustrated in Fig. 4 and comprising the head lens 5 and the optical group 13. The optical flat 19 is rotated under drive conditions adapted by the skilled man.

Fig. 10 shows a nutation system using a periscope 20 comprising two mirrors 21 and 22 together forming a small angle to give a nutation of the required amplitude corresponding to twice said value. The periscope is inserted in the parallel beam between the rear optical group 13 of the previous afocal system and the lens 14 for focusing on the detector 4 of centre A, said focusing lens 14 of centre 0" being disposed outside the afocal axis.

The mirrors of the periscope 21 and 22 are respectively inclined to the optical axis X'OX of the afocal system and to the parallel optical axis O"A of the focusing lens, so that the incident flux Fi can be deflected and focused on the detector 4 when the periscope is in the position shown in the drawing. Disposed in a parallel beam it shifts the luminous flux without affecting the focusing of the optical module. The periscope 20 rotates about the axis O"A of the focusing lens 13 by the action of a drive motor 23, its drive speed being, for example, ten times that of the bearing scanning speed. The nutation of the flux Fi results from the nonparallelism of the periscope mirrors, over a very small angle, e.g. 28 mrad.

According to another embodiment of the invention, an architecture using a number of optical modules of the type described above enables the optical channels to be multiplied so that a plurality of substantially juxtaposed analysis bands can be scanned with a very small overlap to provide continuity of display. Under these conditions, the overall elevation coverage can extend over a very wide range. For example, if each band covers an angular range of 12" elevation, coverage of four complementary bands spreads out in respect of elevation over a range which can extend from -4" to +44 .

The optical channels are multiplexed by a suitable optical system, e.g. an alternate-alignment rotating optical deflector, so that the flux focused on these channels can be processed by a single detector array. Integration of the collected charges and their measurement is triggered during the pivoting movement in accordance with a suitable pitch by means of the sampling clock. Also, depending on the type of nutation system used, the optical architecture is such that the units utilising the optical channels each make use of one nutation system or alternatively use a single common nutation system. In the latter case, the nutation system can be so adapted as to cumulate the nutation and optical multiplexing functions.

Fig. 11 is an example of a surveillance system comprising four optical channels disposed in quadrature using four optical modules. The surveillance system conventionally comprises the spherical analysis head 1, of a diameter of 300 mm, rotated by the turntable 2 around a central vertical axis Z'Z passing through the centre S of the spherical head, and the fixed processing unit 3.

Since the drawing is a central section only two channels are visible. In this example, the nutation system, of the periscope type 20 as described above, is common to the optical modules and provides the double function of nutation and multiplexing of the optical channels.

Each optical module MOI and MO2 comprises its own part situated in the rotary analysis head 1 and a common part disposed in the fixed processing unit 3.

The first of these parts comprises an entry lens 51 or 52 combined with an optical group by means of an optical deflecting mirror 61 or 62 parallel to the axis of rotation of the analysis head coinciding with the optical axis of the common optical part.

The entry lens and its combined group consisting of two menisci M1, M'1 or M2, M'2, form an entry afocal optical system of magnification 5. The axes A1 or A2 of these afocal systems are successively aligned with the entry axis of the periscopic nutation system 20.

The common part is made up of the periscopic mutation system 20 and an optical image transport and focusing group G of optical axis co-linear with the panoramic scanning axis. The optical group G consists of three lens elements, the first two, L1 and L2, forming an afocal group, and the third, L3, being the focusing lens, at the focus of which the detector array is disposed. The image thus transported is focused on the infrared detector array 4 which in this case comprises 256 x 256 elementary sensors disposed in a cryostat K. The cooling system for this cryostat (not shown) and the conditions of use are known to the skilled man.

Here again the detector is coupled with an electronic signal processing unit and a target extraction unit (these units are not shown).

The incident fluxes, e.g. F1 and F2, picked up by the entry afocal optical units aimed along the lines of sight LV1 and LV2 are transmitted in parallel beams at the outlet of the analysis head so that the periscopic system also operates with a parallel beam, thus enabling the previous focusing adjustments to be retained. In the processing units, the fluxes repositioned by the periscopic system on the optical axis of the group G are transported and focused successively (by means of said optical group G) on the detector 4 on rotation of the nutation periscope. The periscope is driven by its motor (not shown) at a suitable rotary frequency, equal in this case to 200 Hz, so as to rotate about the optical axis of the transport and focusing group G. In the exemplified embodiment, this motor is a constant frequency supplied hysteresis synchronous motor.

These successive focusing operations thus provide optical multiplexing between the channels. The analysis head 1 itself is driven by an annular motor 24 integrated in the turntable 2 at the rotational frequency of 5 Hz. Position sensors, such as sensors C1 and C2, are conventionally inserted between the rotor 25 and the stator 26 of this annular motor to allow checks of the speed of drive and of the bearings, e.g. bearings R1 and R2, in order to stabilise the turntable.

The value of the scan frequency of the analysis head, e.g. 5 Hz, corresponds to the frequency of rotation, e.g. 180 Hz, of the nutation and multiplexing periscope. Synchronisation between the speed of rotation of the periscopic nutation system, the duration (conventionally 100 ps) and the charge integration times (effected by the sampling clock of the detector) then enable a plurality of optical channels to be multiplexed, four channels in the present case, and the apparent scrolling of the image formed by each optical channel to be stopped on each charge integration. Kinematic study of the nutation shows that the image movement during an integration time of 100 ps is negligible in respect of the bearing and very small in respect of elevation, typically less than 65 prad.

The frame refresh frequency is then equal to the analysis head scan frequency: the detector array successively receives on each scan cycle four images with apparent rotations of 90C between them. The signal processing unit, by the use of means known per se, enables these images to be restored to the normal direction of observation.

The invention is not limited to the exemplified embodiments described and illustrated. The n optical modules of the multiple channel embodiment may, for example, be disposed similarly to cover the same angular elevation range. The advantage of this variant embodiment is that it allows a frame frequency n times greater than the analysis head scan frequency.

A system for switching multiple optical channels of the same elevation coverage to optical channels of complementary coverage allows changeover from a mode in which a single analysis band and a high frame frequency is used, to a mode in which a widened elevation angle coverage is used. The advantages of the two modes are thus exploited.

Also, it is possible to change the structure of the optical systems without departing from the scope of the invention, e.g. by using diopter elements instead of specular elements. Thus the periscopic nutation and multiplexing system can use, instead of the periscope mirrors, a quasi-parallelepipedal deflector bar, the entry and exit surfaces of which form a dihedral of an angle equal to half the nutation angle.

Claims

1. A high-speed optronic panoramic surveillance system comprising an analysis head rotated by a turntable so that the head scans along a line of sight a panoramic field of view composed of scenes successively observed by an optical part, said optical observation part forming an image by projection of the luminous flux originating from the scene on to a detector which integrates charges in proportion to the illumination received and which is associated with a charge reading circuit and an electronic processing unit to deliver a display signal, wherein the optical observation part comprises at least one optical module cutting the field of view into analysis bands, each module defining an optical channel about an axis and comprising optical elements for transporting the image to the detector of the matrix type, including a focusing lens of optical axis centred on the detector, and an optical nutation device, rotated about the optical axis of the focusing lens to form sucessively on the detector the focused scene images at an apparent scrolling speed, and in order to impart to the line of sight a higher-speed nutation which on each charge integration cancels out the apparent scrolling speed of the observed scene.

2. A surveillance system according to claim 1, wherein the nutation device is a prism disposed on the optical axis of the line of sight in a parallel beam before the lens; and, by rotation about the optical axis of the lens, the prism effects a nutation of the line of sight, the amplitude A and the speed Qn of the nutation being adjusted to satisfy the equation: Qb = a. Qn ( Qb being the scanning speed)

3.A surveillance system according to claim 1, wherein the nutation device is a biprism consisting of a first prism which by rotation about the optical axis of the lens effects a nutation of the line of sight coupled to another fixed prism, the biprism being disposed between an afocal assembly consisting of the lens and a group of lens elements, and a second lens which focuses the transported flux on the detector array.

4. A surveillance system according to claim 3, wherein the nutation biprism is disposed in front of the entry lens of the optical observation module.

5. A surveillance system according to claim 1, wherein the nutation device consists of a mirror rotated by a motor to turn about an axis, forming an angle with the normal to the mirror and in that said mirror is disposed between an afocal assembly consisting of the lens and a group of lens elements, and a second lens which focuses the transported flux on the detector array, the optical module being bent by the nutation mirror.

6. A surveillance system according to claim 1, wherein the nutation device consists of the head lens which directly focuses the flux on the detector, the lens being rotated about an axis and being rendered off-centre by a constant angular shift between its optical axis and the axis of rotation while rotating about the latter.

7. A surveillance system according to claim 1, wherein the nutation device is an optical group which with the entry lens forms an afocal system, said optical group is off-centre so that its optical axis rotates about an axis parallel to the optical axis of a lens focusing on the detector.

8. A surveillance system according to claim 1, wherein the nutation device is an optical flat with its axis inclined to the optical axis of the head lens, in that the flat is disposed in convergent beams in an afocal assembly consisting of the lens and a group of lens elements, a second focusing lens of optical axis centred on the detector array, and in that the flat is rotated about the optical axis coinciding with the optical axis of the lens of the detector.

9. A surveillance system according to claim 1, wherein the nutation device is a periscope consisting of two mirrors and together forming an angular gap to give a nutation of amplitude equal to twice said angular gap, said periscope being inserted in parallel beams in the optical module between a rear optical group forming an afocal assembly with the entry lens, and a lens for focusing the flux on the detector, said lens being disposed outside the axis of the afocal assembly so that the mirrors of the periscope are respectively inclined to the optical axis of the afocal assembly and to the optical axis of the focusing lens, and in that the periscope rotates about said optical axis by the action of a drive motor.

10. A surveillance system according to claim 9, wherein the mirrors of the periscope are replaced by an optical bar having end surfaces coinciding with said mirrors.

11. A surveillance system according to claim 1, comprising a plurality of optical modules uniformly distributed about the axis of rotation of the analysis head and defining a plurality of optical channels to scan a plurality of analysis bands, wherein the optical channels comprise a common nutation device of the periscope type according to claim 9 or claim 10 and are multiplexed optically by said periscope device so that the fluxes originating from the scenes observed by the entry lenses and transmitted in parallel beams to the processing unit are repositioned by the periscope device on the axis of rotation of the periscope device, and then transported and focused successively by an optical group on the matrix detector.

12. A surveillance system according to claim 11, wherein the integration of the collected charges and their measurement are triggered during the panoramic scan of the analysis head in accordance with a pitch adapted by means of the sampling clock, the speed of rotation of the periscope nutation device, the duration and integration times of the charges are synchronised so that stoppage of the apparent scrolling of the image formed by each optical channel coincides with each charge integration.

13. A surveillance system according to claim 12, wherein each optical module comprises an individual part situated in the rotating analysis head having an axis of rotation and a common part disposed in the fixed processing unit having an optical axis co-linear with the axis of rotation of the analysis head, in that the individual part consists of the entry lens combined with an optical group by means of an optical deflecting mirror parallel to the axis of rotation of the analysis head, in that the entry lens and its combined group form an afocal entry optical assembly having parallel axes, in that the axes of these afocal assemblies are successively aligned with the entry axis of the periscopic nutation device, and in that the common part consists of the periscopic nutation device and an optical image transport and focusing group of optical axis co-linear with the panoramic scanning axis, at the focus of which the detector array is disposed.

14. A surveillance system according to any one of claims 11 to 13, wherein the detector array successively receives on each scanning cycle of the analysis head n images formed by the n optical channels with apparent rotation of 360/n between them, and the signal processing module restores the images to the normal observation sense.

15. A surveillance system according to any one of claims 12 to 14, wherein the n optical modules cover the same angular elevation range corresponding to n superposed analysis bands, thus giving a frame frequency n times greater than the scanning frequency of the analysis head.

16. A surveillance system according to any one of claims 12 to 14, wherein the n optical modules cover n complementary angular elevation ranges corresponding to n substantially juxtaposed elevation bands.

17. A surveillance system according to any one of claims 12 to 14, wherein a device for switching between multiple optical channels of the same elevation coverage and optical channels of complementary coverage provides a change from a mode using n superposed analysis bands and n times higher frame frequency to a mode using n substantially juxtaposed analysis bands and n times wider elevation coverage.

18. A system for multiplexing optical channels picking up fluxes originating from scenes for observation, comprising a common final lens having an optical axis and focusing said fluxes on a detector array and a periscope according to claim 9 or claim 10 rotating about the axis of the lens focusing on the detector.

19. A surveillance system substantially as hereinbefore described with reference to the accompanying drawings and as illustrated in Figure 1, or in Figure 11, of those drawings, or in Figure 1 of those drawings modified as shown in either of Figures 4, or 5, or 6 and 7, or B, or 9, or 10 of those drawings.

20. A surveillance system substantially as hereinbefore described with reference to the accompanying drawings and as illustrated in Figure 1, or in Figure 11, of those drawings, or in Figure 1 of those drawings modified as shown in either of Figures 4, or 5, or 6 and 7, or 8, or 9, or 10 of those drawings.