GB2097625A

GB2097625A - Airborne observation device

Info

Publication number: GB2097625A
Application number: GB8112402A
Authority: GB
Original assignee: Ferranti PLC
Current assignee: Ferranti International PLC
Priority date: 1981-04-23
Filing date: 1981-04-23
Publication date: 1982-11-03
Also published as: GB2097625B

Abstract

An aerial launched observation device comprises a remote station adapted to be launched from an artillery projectile or the like to make a retarded descent to earth. The remote station is caused to rotate about, or have a part rotate about, the descent trajectory including electronic imagine means 19, such as part of a c.c.d. camera 23 with a field of view inclined to the trajectory so that it rotates about the trajectory and scans portions of ground throughout the descent. The camera is arranged to be exposed by shutter means 28 to take 'still' images, the shutter means including a tiltable mirror 30 in the field of view 20 of the camera which at the time of exposure is progressively inclined oppositely to the relative motion between the station and the ground to form the stationary image of the ground on the camera imaging device. Subsequently to the exposure, the mirror is returned and the image converted by image processing means 22 into serial electronic signals for transmission to transmitter 38 to a command station (Figure 3) where their format is suitably modified for display on a television monitor (42). <IMAGE>

Description

SPECIFICATION Aerial observation device This invention relates to providing a visual overview of a ground region and in particularto an aerial observation device for providing this.

Military engagements are often fought between opposing forces which cannot see each other and projectiles fired in the general direction of the enemy stand only a remote chance of landing sufficiently near a target to damage it, particularly if it is armoured.

In order to provide an overview of an enemy position from which subsequent projectiles can be directed, remotely piloted vehicles (R.P.V.'s) have been used containing photographic or television equipment from which images are returned to the fire control station by radio or by return of the vehicle. It will be appreciated that the complexity required of R.P.V.'s to fly in a trajectory suitable for observation as well as stabilised for operation requires vehicles which are expensive and sufficiently large and slow moving to make them easy targets forthe enemy.

It has been proposed to eliminate the need for such observation devices by developing projectiles which perform a target seeking function for use in such situations.

One type proposed is launched to rise above the enemy by a shell or like projectile and then ejected to descend retarded by parachute. Thermal sensors on board detect the presence of a target in a region surrounding the landing zone and a sub-projectile ejected therefrom in the sensed direction to attack the target.

Another type proposed and described in British Patent Specification No. 1,467,552 relates to a guided missile wherein the missile contains a television camera from which a visual image of the target area of the missile are transmitted to a controller by radio or optical conductor. If a potential target is seen by the controller from the visual image the missile can be guided (with a laser target marker) to hit the target. The equipment required to be carried by the missile is of course destroyed although expensive and a feature of such a missile is that it is simpler, and therefore somewhat cheaper than one having self-contained homing characteristics based on such an image.

Both types of projectiles are limited in that the first type provides no information on other targets, it merely 'attacks" the first one it detects, while the second type provides information on potential targets which appear in a fairly narrowly defined field of view based on the trajectory of the missile but its complexity and cost justify its use only for armoured targets such as tanks.

There are still considered to be advantages to having a more general overview ofthe enemy position given by an observation device whereby a longer term observation of the disposition of potential targets enables their motion to be predicted, enabling cheaper unguided projectiles, such as artillery shells, to be aimed towards targets, unsighted to the gun, with a reasonable degree of accuracy.

It is an object of the present invention to provide an observation device, and a method, for providing an overview of a ground region which is of simpler and cheaper construction than previous such observation devices.

According to one aspect of the present invention an aerial observatiion device comprises a remote station, adapted to fall along a predetermined trajectory to earth, containing an electronic imaging device located to have a field of view directed at an acute angle to the trajectory of the station to intersect a ground region laterally of the trajectory, means operable to cause the field of view of the electronic imaging device to rotate about the trajectory axis during descent, shutter means operable to expose the electronic imaging device periodically to form at each exposure a stationary image of the ground thereon, image processing means responsive to the shutter means to electrically energise the device to store an image and to generate (serially) electrical signals from the electronic imaging device representing the image formed during each exposure, bearing means responsive to the bearing of the field of view at the time of exposure to produce bearing signals indicative of the bearing and a transmission means operable to transmit the image and bearing signals and a command station operable to receive signals transmitted by the remote state and to form a display image corresponding to each exposure of the electronic imagine device and the bearing of the image with respect to the trajectory of the remote station.

According to another aspect of the present invention a method of aerial observation comprises launching a remote station containing electronic imaging means to descend in a substantially vertical trajectory with the field of view of the imaging means inclined to, and rotating about, the trajectory to intersect different regions of ground, exposing the imaging means to a succession of stationary images of the ground during the descent and transmitting signals representative of each image formed to a command station for conversion to observable images.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1(a), (b) and fc are sectional elevations through remote stations of observation devices according to the present invention demonstrating the disposition of the field of view of the imaging means and different arrangements for rotating the field, Figure 2 is a block schematic of the functional components of the remote station, and Figure 3 is a block schematic of the functional components of the command station.

Referring to Figure 1 (a) aerial observation device includes a remote station 10 which is adapted to be launched by a projectile, such as an artillery shell or rocket, fired over an area to be observed. The remote station is adapted to be carried in the projectile and ejected therefrom at predetermined height or projectile trajectory position in a known manner to fall to earth, retarded by a parachute 11, or the like, in a substantially vertical trajectory 12. The body of the remote station is in two parts, a first part 13 attached to the parachute is intended to descent without rotation about the trajectory 12 and a second part 14 coupled to the first by rotatable coupling 15 so as to rotate relative thereto about the trajectory axis 12 during the descent.When the remote station is launched by an artillery shell, the shell imports rotational movement to the remote station, the first part of the body being slowed to rest by the parachute and the second part being controlled by a set of arms 16 pivotally mounted for folding against the body during launch, which are arranged to extend from the second part body to limit the angular velocity of the part to within a desirable range of values. Where the remote station is launched without inherent rotation the arms 16 are skewed to impart limited rotation.

The lower nose portion 17 of the body is provided with a window 18 and is angled to the trajectory so as to provide for electronic imaging means (shown schematically at 19) in the second part of the body a field of view centred on the line 20 which is inclined at an acute angle to the trajectory axis 12to intersect the ground laterally of the trajectory and to sweep around the trajectory axis due to rotation of the second part of the body. it will be seen that the area of ground within the field of view varies as a function of the altitude of the remote station and the observed area spirals inwards towards the trajectory axis during descent.

The remote station 10 carries all apparatus necessary to observe the ground and transmit the observations to a command station. The remote station contains standard elements such as power supplies which are not shown but the elements active to observation are shown schematically at 21 and in greater schematic detail in Figure 2.

The electronic imaging means 19 comprises a charge coupled device (c.c.d.) having a two dimensional array of photo-electronic elements, such as, commercially available as RCA Corp. part number SID 52501. The c.c.d. is coupled to a driving circuit 22 comprising image processing means which the array elements respond to an image formed on the array by retaining a corresponding pattern of charges thereon and the charges are shifted out serially as video signals to form a known arrangement of a c.c.d. camera 23. The camera 23 has a camera exposure control input 24 producing a sync.

signal on line 25 and a video output on line 26, to video amplifier 26', and on line 27.

Whereas such c.c.d. cameras can be operated rapidly to present signals corresponding to real-time moving images to effect television operation the vibrational conditions met in the remote station of the present invention are such that it is preferred to form a series of 'still' images for transmission. The production of image signals is under the control of shutter means 28. The shutter means comprises a shutter control means 29 which issues exposure control signals on line 24to the c.c.d. camera 23 and receives the camera sync. signals from line 25. The shutter control means operates to "expose" the array of the imagine device to a new image in response to the sync. signal indicating that the video signals relating to the previous image have been read out on line 26.The shutter control means also receives the video output signal from line 26 by way of line 27 to control the exposure time as a function of the video signal level developed. The shutter means also comprises a movable light deflector 30, a plane mirror, tiltable about a pivot 31 by means of push rod 32 actuated by an electromagnetic coil 33 energised by the shutter control means 29.

The mirror 30 is located in the field of view (centred on line 20) of the imaging means such that tilting of the mirror by the push rod causes the image to be moved across the array. The axis of the pivoit 31 is such that as the field of view moves over a portion of ground (during rotation of the body) and the image thereof (consequently) moves across the imaging device, upon exposure dictated by the shutter control means 29 progressive tilting of the mirror at the correct rate counteracts such image movement and causes the image to remain stationary on the imaging device for the duration of the exposure. The mirror is thereafter restored to its initial position for future exposures.

In order to determine the rate at which the deflector mirror must be tilted it is required to know the rotational rate of the remote station part. This may be calculated theoretically and stored as a constant value or may be calculated from measurement made during the descent. One method makes use of information obtained in respect of the bearing made by the field of view at the times of the exposure in order to relate the areas covered by the images to maps at the command station.

Bearing means carried by the rotating part 14 of the body comprises a plurality of magnetic sensors 34, such as Hall effect sensors, arranged radially of the axis of rotation of the body. The outputs of the signals are fed to bearing processing means 35 which from the signals received as the sensors rotate through the earth's magnetic field forms a signal relating to the instanteous bearing value on line 36 and from the frequency of signal variation, a signal related to the rate of rotation of the body on line 37.

The line 37 supplies the rotation rate to the shutter control means 29 whereby the light deflecting means can be operated at the correct rate. The line 37 supplies the bearing data to transmission means 39 for modulation/transmission by radio to the command station along with the video signal from amplifier 27. If desired the command station, shown schematically in Figure 3, will normally be located on the ground at or near a fire control post for directing artillery fire to the area of observation. The command station comprises a receiver/demodulator 40 coupled to feed the serially transmitted image signals to a signal processing means 41 which operates as a scan converterto store the received signals of each imageandaltertheirrelativetimings to suit display in raster form on a c.r.t. display monitor 42. It will be appreciated that the remote station is capable of forming and transmitting successive 'still' images at a rate far in excess of that at which a human observer can observe them meaningfully at the command station and a recorder 43 of the picture signals (either in the form received from the remote station or in the form for display) is provided to enable said images to be viewed and interpreted at will or combined into composite displays.

It will be appreciated that many modifications of detail may be made to the system described above.

For instance within the remote unit different means for measuring the bearing and deflecting the field of view of the imaging means will present themselves.

The shutter control means and bearing processing means shown within the broken line 44 may in practice comprise a microprocessor suitably programmed with stored instructions to perform said bearing measurement and shutter control functions.

The remote station may also include altitude measuring means (not shown) producing signals representing the length of the remaining trajectory signals for transmission to the command station whereby the lateral displacement of the field of view from the trajectory can be determined. Alternatively the altitude may be calculated at the command station by analysis of image sizes in order to provide such information or the viewed region may be manually interpreted from maps of the area by recognition of terrain features.

Within the variations of detail which can be made to the remote station the essential feature is that the field of view of the imaging means is inclined to the trajectory axis 12 and rotates about it during descent. The system described with reference to Figure 1 (a) in which the whole imaging device rotates with part of the body of the remote station while another part does not rotate is useful where the remote unit requires a non-rotating portion, such as to carry other sensing devices, for instance, an array of microphone transducers as described in our application No. (G.W.83). In a non-rotating portion is nor required the whole body of the remote station may be arranged to fall inclined to the trajectory axis 12 as shown in Figure 1 (b) and rotate about it during descent in known manner.The field of view of the imaging device can then extend along the longitudinal axis of the body to make said acute angle to the trajectory.

An alternative arrangement in Figure 1 (c) is for the imaging device and other components to be contained in a non-rotating body, with the field of view of the imaging device on the axis of the trajectory coincidentally with the trajectory axis. An optical element rotatable contained within an end portion of the body deviates the field of view from the trajectory and by rotation of the end portion, or the optical element within the end portion, produces rotational scanning of the field of view. Bearing sensors as described are then mounted on the rotatable portion.

In all of the above described embodiments the trajectory of descent has been considered as sub stantiallyvertical. It will be appreciated that such a trajectory provides maximum ground coverage and ease of interpretation but that such a trajectory is not essential to the invention and there will be situations where an angled descent trajectory will be employed.

It will be appreciated also that the electronic imaging means is not limited to produce images from "iight" in the visible part of the spectrum. For instance the imagine means may be constructed to be infra-red or ultra-violet sensitive or be operated behind suitable filters in the optical path.

Claims

1. An aerial observation device comprising a remote station, adapted to fall along a predetermined trajectory to earth, containing an electronic imaging device located to have a field of view directed at an acute angle to the trajectory of the station to intersect a ground region laterally of the trajectory, means operable to cause the field of view of the electronic imaging device to rotate about the trajectory axis during descent, shutter means operable to expose the electronic imaging device periodically to form at each exposure a stationary image of the ground thereon, image processing means responsive to the shutter means to electrically energise the device to store an image and to generate (serially) electrical signals from the electronic imaging device representing the image formed during each exposure, bearing means responsive to the bearing of the field of view at the time of exposure to produce bearing signals indicative of the bearing and a transmission means operable to transmit the image and bearing signals and a command station operable to receive signals transmitted by the remote state and to form a display image corresponding to each exposure of the electronic imagine device and the bearing of the image with respect to the trajectory of the remote station.

2. An observation device as claimed in claim 1 in which the remote station comprises a body having a longitudinal axis along which the field of view is centred and fixed with respect to the body, said body being arranged to rotate during descent about an axis through the body making an acute angle to the longitudinal axis.

3. An observation device as claimed in claim 1 in which the remote station comprises a body having a first part arranged to descend along the trajectory without rotation thereabout and a second part arranged to rotate relative to the first part about an axis along said trajectory, said field of view of the electronic imaging device being by way of said second part to effect rotation of the field of view.

4. An observation device as claimed in claim 3 in which the electronic imaging device is carried by the second part and has its field of view inclined to said axis of rotation.

5. An aerial observation device as claimed in claim 3 in which the electronic imaging device is carried by the first part and has its field of view on said axis of rotation of the second part, and optical deflector means carried by the second part arranged to deflect the field of view of said axis and to rotate with the second part.

6. An aerial observation device as claimed in any of claims 2 to 5 in which the bearing means comprises a plurality of magnetic sensors extending radially of the trajectory across the rotatable part of the remote station body and bearing processing means responsive to the magnitude of the magnetic field through which the sensors move to determine the relationship between the rotatable part and the earth's magnetic field to provide signals indicative of the instantaneous bearing of the field of view and the rate of rotation of the field of view.

7. An aerial observation device as claimed in claim 6 in which the magnetic sensors are Hall effect sensors.

8. An aerial observation device as claimed in any one of the preceding claims in which the bearing processing means comprises a microprocessor responsive to a stored programme of instructions.

9. An aerial observation device as claimed in any one of the preceding claims in which the shutter means comprises a movable light deflector in the field of view of the electronic imaging device by way of which the ground image is received, light deflector moving means operable to tilt the deflector and shutter control means operable to energise the electronic imaging device to form an image thereon of the ground portion in the field of view and responsive to signals from the bearing means indicative of the rate of rotation of the field of view about the trajectory axis to move the light deflector progressively during exposure so that a stationary image of the ground is formed at the electronic imaging device.

10. An aerial observation device as claimed in claim 9 in which the movable light deflector comprises a plane mirrortiltable about one end thereof.

11. An aerial observation device as claimed in claim 9 or claim 10 in which the light deflector moving means is an electromagnetically actuated push-rod.

12. An aerial observation device as claimed in any one of claims 9 to 11 in which the shutter means is arranged to operate each time that signals representing the exposed image have been read from the electronic imaging device.

13. An aerial observation device as claimed in any one of the preceding claims in which the electronic imaging device comprises a twodimensional c.c.d. array of photo electronic elements.

15. An aerial observation device as claimed in claim 14 in which the image processing means comprises waveform generation means responsive to the shutter means to address the elements of the imaging device in sequence to derive a serial signal representative of the image.

16. An aerial observation device as claimed in any one of the preceding claims in which the transmission means is a radio frequency transmitter operable to transmit a signal modulated by the image signal and bearing signal to the command station.

17. An aerial observation device as claimed in any one of the preceding claims including altitude measuring means operable to measure length of the remainder of the trajectory and provide signals for transmission to the command station.

18. An aerial observation device as claimed in any one of the preceding claims in which the remote station includes means to retard the descent.

19. An aerial observation device as claimed in any one of the preceding claims in which the remote station includes means to control the rate of rotation of the field of view of the electronic imagine device.

20. An aerial observation device as claimed in any one of the preceding claims in which the remote station is adapted to be launched by ejection from a projectile fired over the observation area.

21. An aerial observation device as claimed in any one of the preceding claims in which the command station includes signal processing means responsive to the image signals from the remote station to produce a corresponding image on display imaging means.

22. An aerial observation device as claimed in claim 21 in which the display imaging means is a raster scanned c.r.t. monitor.

23. An aerial observation device comprising a remote station and command station substantially as herein described with reference to, and as shown in, the accompanying drawings.

24. A method of aerial observation comprising launching a remote station containing electronic imaging means to descend in a substantially vertical trajectory with the field of view of the imaging means inclined to, and rotating about, the trajectory to intersect different regions of ground, exposing the imaging means to a succession of stationary images of the ground during the descent and transmitting signals representative of each image formed to a command station for conversion to observable images.

25. A method as claimed in claim 24 in which the electronic imaging means is related about the trajectory to produce said rotating field of view.

26. A method of aerial observation substantially as herein described with reference to, and as shown by, the accompanying drawings.