GB2315560A

GB2315560A - Imaging of moving objects

Info

Publication number: GB2315560A
Application number: GB9615222A
Authority: GB
Inventors: Martin R Maltby
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1996-07-19
Filing date: 1996-07-19
Publication date: 1998-02-04
Anticipated expiration: 2016-07-19
Also published as: GB9615222D0; GB2315560B

Abstract

An aircraft imaging arrangement for imaging objects (16) in the atmosphere moving relative to the aircraft, and a method for imaging such objects are provided. The imaging arrangement includes a camera assembly (10) mountable on a support (15) on the aircraft. The camera is focusable on a focal plane (14) externally of the aircraft through which focal plane objects (16) to be imaged (e.g. particles in the atmosphere) pass in flight. The camera also includes control means (17) to control at least one of the functions object illumination, exposure time and instantaneous camera velocity in order to produce a clear image in the camera (10) of objects (16) moving relative thereto in aircraft flight.

Description

IMAGING OF MOVING OBJECTS This invention relates to imaging apparatus and in particular to such an arrangement to yield quasi three dimensional images of objects, for example small particles, moving at high speed relative to imaging apparatus, and in particular images of cloud precipitate moving relative to an aircraft in flight.

Cloud precipitate can take on many different forms depending on the weather conditions that prevail at the time.

This precipitate can comprise liquid droplets such as rain, solid objects such as hail or flakes of ice crystals such as snow. Any combination of these precipitates may also be found in various weather conditions. For the context of this document the word "particles" is used to refer to objects that form precipitate, i.e. liquid droplets, solid objects or ice crystals, in any combination.

It is known that the precipitate found during thunderstorms in particular has markedly different characteristics to those found in other weather conditions.

The properties of particles that comprise the precipitate, for example particle type, size, shape and state, need to be researched. The research of icing conditions is particularly important as it has been found that aircraft engines can suffer severe power loss when such conditions are encountered.

Additionally, pure meteorological research is needed to ascertain the precipitation types generated in clouds as an aid to determining the physical processes and energy transfers that take place within clouds at altitude.

A permanent image of the particles must be obtained in order to study both the particles and their spatial distribution. Such an image is essential for this study due to the continual relative motion of the particle field. The image would yield information on the properties of the particles which would lead to an understanding of their effect if ingested into propulsion units. The data gathering exercise is by no means straightforward, however, as the particles must be analysed from an aircraft due to the altitude that such particles exist at. The relative speed between the aircraft and the particles is likely to be very high, leading to problems in obtaining a clear image.

It is known to obtain images of particles travelling at speed relative to imaging equipment by using a probe in the form of a hollow tube with limited cross sectional area which is open at one end to receive precipitate. The probe ingests particles and directs them to a laser array, the array yielding a two dimensional silhouette of the particles.

A disadvantage of such an arrangement for attempting detailed analysis of particles is that it yields only a two dimensional silhouette as the image. Such an image is of only limited use in the analysis of the features of the particle field being examined as, for example, a single particle may yield entirely different images depending on its relative orientation to the imaging apparatus. Furthermore, the spatial information of the particle field as relayed by this equipment will bear little relation to that which actually exists, as the equipment gathers an image of particles that have been disturbed as they passed into and through the probe. Further inaccuracies may exist in the image due to the very small sample that is being taken in relation to the whole particle field.

Such an arrangement is also not able to provide information pertaining to the surface properties of the particles, which will be of interest to both aircraft flight analysts and meteorological researchers. An additional reason for this lack of detail is that the objects are moving quickly in relation to the laser array which will ultimately lead to a lower quality image. The equipment described costs in the region of tens of thousands of pounds and so its use will be limited to only those research programmes that can afford such a sum.

It is an object of the invention to provide apparatus that will yield images which give a quasi three dimensional representation of a particle field moving relatively to the apparatus without disturbing the particle field and which overcomes the disadvantages of the prior art.

The image recording means, which may comprise a camera, may be located either inside or outside of the aircraft, with both locations involving their own specific considerations. An internal location would involve a window between the imaging apparatus and the particles, which must be kept clear for the image quality to be maintained. An outside location would require the apparatus to be suitably shielded to protect it from moisture, wind and debris damage.

According to one aspect of the invention there is provided an aircraft imaging arrangement for imaging objects in the atmosphere moving relative to the aircraft in flight, the arrangement including a camera mountable on a support on the aircraft, a said support on the aircraft for receiving the camera, the camera when mounted being focusable on a focal plane externally of the aircraft through which plane objects to be imaged will pass in flight, wherein the camera includes control means to control at least one of the functions, object illumination, exposure time and instantaneous camera velocity whereby to produce a clear image in the camera of objects moving relative thereto in aircraft flight.

Images are thus provided which contain information in three dimensions. This will greatly increase the detail shown in the recorded images and allow for a much greater understanding of the cloud precipitate than was previously available. The present invention will not interfere in any way with the particle field, leading to an image that shows the true representation of the spatial pattern of the particles. This aspect will also provide a clear image as the objects will be stationary in relation to the camera.

The apparatus may conveniently include means to illuminate the objects, the illumination means being arranged to illuminate substantially only those objects that pass through the focal plane of the camera, which may be achieved by positioning the illumination means substantially at the focal plane of the camera.

This aspect will enhance the clarity of the resultant images and allow images to be obtained in a wide variety of light conditions. By only illuminating the objects that lie substantially on the focal plane, the image will not show the objects that lie in a region between the camera and the focal plane. These objects will be out of focus and if illuminated would obstruct the objects that are of interest in the image.

The illumination means may comprise a light source that operates during the image recording operation for a time period substantially the same as the duration of the said operation.

This aspect will provide the objects to be recorded with sufficient light to record the image and also will aid its clarity by illuminating the objects for just long enough for them to be recorded, thereby effectively "freezing their progress through space as far as the camera is concerned.

The arrangement may include means to substantially match the instantaneous camera velocity with the velocity of the objects at the focal plane of the camera at least at a given instant during the camera exposure time.

This aspect will lead to the production of a clear image, as the objects will appear to be still in relation to the camera. The resultant images will hence be very clear and show a greater level of detail than would otherwise be available.

The arrangement may also conveniently include means to substantially match the instantaneous camera velocity with the velocity of the objects, by co-ordinating the rotational velocity of the camera with the instantaneous measured velocity of the aircraft, and may have means to rotate at least that part of the camera that records the image, the arrangement desirably includes a stationary casing in which that part of the camera that records an image is rotatable, the casing defining an aperture positioned therein through which the objects on the focal plane will be visible to that part of the camera that records an image when the said velocities match.

This will yield clear pictures by matching the velocities of the camera and the objects through the use of a rotating apparatus. This will further enable successive images to be recorded quickly, as the apparatus will not require a lengthy reset operation. The aperture will enable the use of photographic films with varying exposure time requirements as it will act to reduce the amount of light reaching the film. This is of particular importance if a high speed film is being used. This aspect will also allow the camera to be rotated at variable rates so that a stationary image can be obtained for differing aircraft and precipitate speeds.

According to another aspect of the invention there is provided an aircraft fuselage including an arrangement according to the first aspect mounted therein.

According to another aspect of the invention there is provided a method for imaging objects in the atmosphere moving relative to an aircraft in flight, the method including the steps of mounting a camera on a support on the aircraft, the camera when mounted being focusable on a focal plane externally of the aircraft through which plane objects to be imaged will pass in flight, and controlling at least one of the functions, object illumination, exposure time and instantaneous camera velccity whereby to produce a clear image in the camera of objects moving relative thereto in aircraft flight.

The method may conveniently include substantially matching the instantaneous camera velocity with the velocity of the objects at the focal plane of the camera at least at a given instant during the camera exposure time, which may be achieved by co-ordinating the rotational velocity of the camera with the instantaneous measured velocity of the aircraft.

This aspect allows clear images to be obtained of objects that are in motion relative to a camera and in particular by matching the rotation speed of the camera to that of the objects.

The invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a plan schematic view of the arrangement according to the invention; Figure 2 is a plan schematic view showing how the invention may be employed for use on an aircraft D a-ita y Figure 3 is an enlarged detail of the area III of Figure 2.

Referring to Fig 1 at least that part of the camera that records an image, in the form of an assembly 10, is mounted inside a protective casing 12 which includes an aperture 18. The assembly 10 is fixedly attached to a support 15. Particulate 16 to be analysed is that which passes, in a direction indicated by arrow 13, through a focal plane 14 of a camera lens 20. A controller 17 is provided to independently control illumination, exposure time and instantaneous camera velocity. An aircraft air speed indicator 19 and ground speed indicator 21 are linked to the velocity matching means 23 such that communication may occur.

The velocity matching means is similarly linked to the controller 17.

Referring to Fig 2 the assembly 10, support 15 and the casing 12 are fixed to an aircraft 22 inside a fuselage 24. The particulate 16 is viewed through a window 26 and the focal plane 14 of the assembly 10 set to be focused near to an intake of engine 28. A region containing the focal plane 14 is illuminated by a light source 30.

The assembly 10 is mounted on driven rotating apparatus (not shown) so that the assembly 10 is travelling in the same direction as the particulate 16 when the camera lens 20 passes the aperture 18 in the casing 12, i.e.

travelling in the opposite direction to aircraft flight when the lens 20 passes the aperture 18. The assembly 10 is set up so that it has a fixed focal plane 14. It is the particulate 16 that passes through this focal plane 14 that the assembly 10 will capture an image of as the lens 20 passes the aperture 18.

In order to obtain the best possible image the assembly 10 will rotate at such a speed that its effective tangential velocity at the focal plane 14 is equal to the cruise velocity of the aircraft 22. This will yield an image wherein the particulate 16 will appear to be stationary. The velocity matching means 23 selectively compares the speeds indicated by the air speed indicator 19 and the ground speed indicator 21 respectively with the instantaneous camera velocity. If any difference is encountered, the velocity matching means 23 communicates with the controller 17 so it may consequently increase or decrease the rotational speed of the assembly 10 to accommodate the change. The air speed indicator 19 is used in the system to allow for the influence of any other effects, such as wind, which will cause the particulate 16 to have its own movement. The focal plane 14 is assumed to be planar and in a direction parallel with the direction of flight of the aircraft 22. Since the particles 16 travel in a generally linear manner in relation to the aircraft 22, the focal plane 14 is arranged to lie within a region occupied by the particles 16 that are to be recorded.

For this reason the light source 30 is arranged to illuminate a region that includes the focal plane 14 and wherein the assembly 10 rotates such that its effective tangential velocity at the focal plane 14 is equal to the cruise velocity of the aircraft 22. The light source 30 should face in the direction of the oncoming particulate 16 so that the particles between the camera lens 20 and the focal plane 14 are not illuminated and should provide a short burst of high intensity light. This illumination is controlled by the controller 17.

If the camera 10 is a video camera then analysis of the images could be more easily carried out within the aircraft during flight.

Claims

1. An aircraft imaging arrangement for imaging objects in the atmosphere moving relative to the aircraft in flight, the arrangement including a camera mountable on a support on the aircraft, a said support on the aircraft for receiving the camera, the camera when mounted being focusable on a focal plane externally of the aircraft through which plane objects to be imaged will pass in flight, wherein the camera includes control means to control at least one of the functions, object illumination, exposure time and instantaneous camera velocity whereby to produce a clear image in the camera of objects moving relative thereto in aircraft flight.

2. An arrangement as in claim 1 including means to illuminate the objects.

3. An arrangement as in claim 2 wherein the illumination means is arranged to illuminate substantially only those objects that pass through the focal plane of the camera.

4. An arrangement as in claim 2 or 3 wherein the illumination means is positioned substantially at the focal plane of the camera.

5. An arrangement as in claim 2, 3 or 4 in which the illumination means comprises a light source that operates during the image recording operation for a time period substantially the same as the duration of the said operation.

6. An arrangement as in any one of claims 1 to 5 including means to substantially match the instantaneous camera velocity with the velocity of the objects at the focal plane of the camera at least at a given instant during the camera exposure time.

7. An arrangement as in claim 6 wherein the means to substantially match the instantaneous camera velocity with the velocity of the objects comprise means to rotate at least that part of the camera that records the image.

8. An arrangement as in claim 7 including a stationary casing in which that part of the camera that records an image is rotatable, the casing defining an aperture positioned therein through which the objects on the focal plane will be visible to that part of the camera that records an image when the said velocities match.

9. An arrangement as in claim 7 or 8 including means to co-ordinate the rotational velocity of the camera with the instantaneous measured velocity of the aircraft.

10. An aircraft fuselage including an arrangement according to any preceding claim mounted therein.

11. A method for imaging objects in the atmosphere moving relative to an aircraft in flight, the method including the steps of mounting a camera on a support on the aircraft, the camera when mounted being focusable on a focal plane externally of the aircraft through which plane objects to be imaged will pass in flight, and controlling at least one of the functions, object illumination, exposure time and instantaneous camera velocity whereby to produce a clear image in the camera of objects moving relative thereto in aircraft flight.

12. A method as in claim 11 including substantially matching the instantaneous camera velocity with the velocity of the objects at the focal plane of the camera at least at a given instant during the camera exposure time.

13. A method as in claim 11 or 12 including the step of coordinating the rotational velocity of the camera with the instantaneous measured velocity of the aircraft.

14. An aircraft imaging arrangement substantially as described herein with reference to the accompanying drawing.

15. An aircraft fuselage substantially as described herein with reference to the accompanying drawing.

16. A method for imaging objects in the atmosphere substantially as described herein.