WO2010072996A1

WO2010072996A1 - Aircraft landing monitoring system

Info

Publication number: WO2010072996A1
Application number: PCT/GB2009/002903
Authority: WO
Inventors: Frederick John Scorer
Original assignee: Qinetiq Limited
Priority date: 2008-12-22
Filing date: 2009-12-17
Publication date: 2010-07-01
Also published as: GB0823330D0

Abstract

A system for monitoring the path of an aircraft approaching to land on an aircraft carrier (1) or similar moving platform, particularly in the case of failure or non-availability of other landing aids, utilises a camera (3) which is stabilised against motion of the platform and from which live video of the approach can be viewed by an officer who is in radio contact with the pilot and can talk him down as required. Stabilisation against heave and other vertical excursions of the platform is achieved by locating the camera at a position laterally offset from the runway and adjusting the roll angle of the acquired images so that the azimuth plane (P) effectively moves up and down with respect to the platform where it intersects an intended stabilised glideslope (G), in opposition to the vertical movement of the camera.

Description

Aircraft Landing Monitoring System

The present invention relates to a camera-based system for monitoring the paths of aircraft approaching to land on moving platforms, notably vessels at sea such as aircraft carriers or other ships which can accommodate aircraft landings of the type more particularly described herein.

The invention has been conceived particularly, though not exclusively, for use in conjunction with the execution of shipboard rolling vertical landings. The so-called rolling vertical landing (RVL) is a type of landing executed by vectored-thrust vertical/short takeoff and landing (V/STOL) and short takeoff and vertical landing (STOVL) aircraft as an alternative to a normal vertical landing, in which the aircraft approaches at an angle to the landing site and at relatively slow speed (in comparison to conventional fixed-wing landings) under a combination of jet-borne and wing-borne lift. Aircraft of this class include the well known V/STOL Harrier and Sea Harrier "jump jet" variants, and the STOVL F-35B variant of the Lightning Il yet to enter service. The RVL was developed originally as a manoeuvre for landing on unprepared areas in land-based operations so that debris disturbed by the jet efflux would tend to be blown behind the aircraft and not into the engine intakes. It is also considered to be a useful technique for shipboard operations, however, due to the ability to land with a higher aircraft weight than would be possible in the same meteorological conditions if a vertical landing was to be used, or to land at the same weight but with a reduced power setting as compared to the vertical landing thereby potentially increasing engine life. Other benefits can include a reduction in the erosion of deck coverings by engine exhaust as compared to vertical landings. While conceived with shipboard RVLs by V/STOL and STOVL aircraft in mind, however, the present invention may also find application in conjunction with conventional (wire-arrested) fixed wing carrier-borne landings which are typically conducted with shallower approach angles and at substantially higher speeds than RVLs, and also for helicopter landings if not performed vertically.

Note: all references in this specification to landing directions, approach angles, glideslopes etc. in the context of landings on vessels which may be underway are to those directions, angles, glideslopes etc. relative to the overall moving platform and not to the actual movement of the aircraft through the air. Various visual landing aids (VLAs) are in use or have been proposed to assist the pilots of aircraft approaching to land on an aircraft carrier, of which one currently in service with some navies for conventional fixed wing carrier-borne landings is the so-called Improved Fresnel Lens Optical Landing System (IFLOLS). Another, conceived particularly as an aid for use in executing shipboard RVLs, is proposed in our copending International patent application no. PCT/GB2009/001946. The present invention, on the other hand, is a system which can be used for monitoring approaches from the vessel itself e.g. as an adjunct to a primary VLA or in circumstances where the VLA is unserviceable.

The invention is predicated upon the use of a camera set up on the moving platform to observe approaching aircraft, and an-associated display by which the substantially live scene captured by the camera can be viewed and judgements made as to the accuracy or otherwise of the approach. For example the display may be disposed at a convenient location on the platform for viewing by a Landing Signals Officer (LSO) or the like who is in radio contact with the approaching pilot and can pass on information as appropriate. Alternatively or additionally a display could be provided in the aircraft cockpit for direct interpretation by the pilot, or there could even be a large screen on the platform visible from the aircraft. In any case, however, it will be appreciated that little useful information can be derived on the quality of the approach from such a system, and in particular whether the aircraft is correctly established on and following a desired gildeslope, unless the images acquired from the camera are stabilised to eliminate or at least substantially reduce apparent excursions of the aircraft in the display caused by movements of the platform on which the camera is mounted. In this respect compensation for rotations of the platform in pitch, roll and yaw can generally be achieved by sensing those rotations and applying image corrections in opposite senses. Compensation for excursions of the platform in the vertical sense, however- whether due to heave, pitch, roll or any combination of such motions - is not so straightforward. For example if the camera were located on the approach centreline it would not be possible to use simple pitch angle adjustment of the camera for such compensation unless the instantaneous range of the aircraft was also known.

In one aspect the present invention seeks to address this problem and accordingly in this aspect resides in a system for monitoring the path of an aircraft approaching to land on a runway on a moving platform comprising a camera mounted on the platform with a field of view to observe at least a substantial part of the approach of such an aircraft, and an associated display at a chosen location by which the substantially live scene captured by the camera can be viewed; said camera being located at a position laterally offset from said runway; means for sensing excursions of the platform in the vertical sense; and means for adjusting the roll angle of images acquired from said camera in response to such sensing means whereby to aid stabilisation of such images against the effects on said camera of such excursions.

In use of a system according to the invention the distance by which the camera is laterally offset from the runway can act as a "lever arm" by which the azimuth plane of its field of view can be raised or lowered with respect to the runway by altering the effective camera roll angle and thereby effect corrections for vertical excursions of the platform. In this respect it would be possible to physically roll the camera if equipped with a suitable gimbal mounting or the like, but for mechanical simplicity and reliability and to reduce maintenance costs it is preferred to use a camera which is fixed in position on the platform and to perform all effective roll angle adjustments and any other image corrections to stabilise for other movements of the platform in an electronic image processor controlled by suitable software algorithms.

'As an aid to interpretation of the approach by the LSO or other person viewing the display it is preferred that the scene displayed is overlaid with a line or other suitable marking indicating the path which the approaching aircraft - or more particularly a specified sighting point on the aircraft - should follow in the display if the aircraft approaches correctly along a specified glideslope relative to the platform. Further markings may also be used to indicate an acceptable range of vertical deviation from the specified glideslope, and to indicate the position along the glideslope at which the aircraft should cross the stern of the vessel in the case of a landing on an aircraft carrier or the like.

While the location of the camera in accordance with the invention provides a ready means for the LSO or other person viewing the display to perceive variations in height of an approaching aircraft from a specified glideslope relative to the platform, its offset position is less conducive to the perception of lateral deviations from the extended runway centreline. For this reason a second camera, mounted flush with the runway centreline and with a field of view to observe at least a substantial part of the approach, may also be incorporated in the system. These and other features of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic plan view of the aft region of an aircraft carrier incorporating a system according to the invention;

Figure 2 is a simplified block diagram of the system;

Figure 3 is a schematic rear view of the aircraft carrier of Figure 1 , illustrating the principle of stabilisation for vertical excursions; and

Figures 4 to 7 are representations of screen shots of an aircraft approaching to land on an aircraft carrier as displayed from the processed output of a camera in a system according to the invention.

Referring to Figure 1 , there is shown the aft region of an aircraft carrier 1 incorporating a system according to the invention. A runway for landing aircraft approaching from astern of the ship is indicated at 2, with the usual "tramline" centreline markings at 2A. A camera 3 is mounted facing aft at a fixed, elevated position on an "island" superstructure 4 of the ship, set back from the stern deck-edge 5 and laterally offset from the runway 2. The lateral field of view F of the camera is indicated by the broken lines in the Figure and is typically around 30°, centred on an axis A extending aftwards to port in the illustrated arrangement where the superstructure 4 is to starboard of the runway. The vertical field of view is typically 17-24° and the elevation angle may typically be 0-5° depending on the camera format aspect ratio. In any event the field of view and camera orientation is so chosen in relation to the position of the camera mounting to be sufficient to keep an approaching aircraft fully in view throughout the final approach to the runway 2 from some kilometres directly astern the ship until after the aircraft has crossed the stern deck-edge 5.

The camera 3 may typically be a standard 576-line resolution TV (video) camera, or a 1080-line high definition system camera if desired. The scene which it captures is viewed substantially live (subject to normal and inconsequential latency and processing delays) on a display 7 (Figure 2) at an LSO's console at any convenient location in the ship, after certain manipulations are effected in a software-controlled image processor 8. The LSO will be in radio contact with the pilots of approaching aircraft and can talk them down, or if necessary wave them off, in accordance with his view of the approach. The display 7 also includes markings to assist the task of the LSO as will be more particularly described hereinafter.

It will be appreciated that the camera 3, being fixed to the superstructure 4, will be subject to the motion of the ship 1 as it pitches, rolls, yaws and heaves. The purpose of the image processor 8 is therefore to stabilise the successive image frames acquired from the camera to eliminate apparent excursions of the approaching aircraft in the display 7 due to such motion, it being understood in this respect that the intention is for the aircraft itself to follow a desired glideslope stabilised in space relative to the overall ship and not to attempt to follow flight-deck excursions. For this purpose also information on the instantaneous motion of the deck is derived from a suite of conventional sensors 9 - such as inertial (accelerometers and gyros) and/or satellite positioning sensors - and is fed to the processor 8 which computes and applies the consequent rotational and translational adjustments to the image frames to achieve the desired stabilisation for the effect of that motion at the camera mounting position.

The method by which image stabilisation against vertical excursions of the ship is principally accomplished in accordance with the invention can be appreciated by reference to Figure 3. That is to say, by virtue of the lateral offset L of the camera 3 from the runway centreline, changing the effective roll angle of images from the camera (about the axis A of Figure 1 ) will effectively raise and lower the azimuth plane P of the camera's field of view with respect to the runway, as indicated by the broken lines P' in Figure 3. More particularly it is arranged that the effective camera roll angle is adjusted so as to change the height from the deck at which the azimuth plane intersects the intended stabilised glideslope G (or more particularly the intended path of a chosen sighting point on the aircraft) at the position X (Figures 1 and 3) abeam of the camera's location, in direct opposition to changes of height at the camera's location due to heave, pitch and/or roll. This form of stabilisation will only be correct for an aircraft which is on the approach centreline and lateral displacement of the aircraft from the centreline will introduce certain stabilisation errors. However the magnitude of these is reduced as the camera to centreline offset distance L increases so in any practical implementation it is desirable to mount the camera as far laterally offset from the runway as possible.

Stabilisation against the other components of ship motions is also achieved by the processor 8. Stabilisation against ship roll rotations also involves adjustment of the effective camera roll angle so the actual roll adjustment which is applied at any instant when the ship is both rolling and heaving and/or pitching will be the sum (or difference depending on the sense of motion) of the individual rotations required to compensate for each component. Stabilisation against ship pitch rotations involves translational image adjustments in the vertical sense while stabilisation against ship yaw rotations involves translational image adjustments in the horizontal sense. Due to various factors, however, including the fact that the effective roll axis of the camera 3 is skewed to the longitudinal direction of the ship (the axis A in the example of Figure 1 is approximately 13° to port of that direction) there is a certain cross-coupling between the corrections required to be made for the various ship motions. That is to say while the predominant corrections for each form of motion are as indicated above, for the highest level of stabilisation to be achieved with this camera geometry adjustments of the effective camera roll angle to compensate for vertical excursions and roll rotations also need to be accompanied by slight adjustments of the effective camera pitch angle (vertical image translation), adjustments of the effective camera pitch angle to compensate for ship pitch rotations also need to be accompanied by slight adjustments of the effective camera roll angle, and adjustments of the effective camera yaw angle (horizontal image translation) to compensate for ship yaw rotations also need to be accompanied by slight adjustments of the effective camera roll and pitch angles.

To illustrate the effects of the image stabilisation described above Figures 4 to 7 are representations of typical display content based on screen shots taken from video recorded from a camera mounted to an aircraft carrier and stabilised in accordance with the principles of the invention while an approach was made by a Harrier aircraft 6 for a simulated RVL. This trial was conducted to simulate the use of a camera system in accordance with the geometry depicted in Figure 1 to monitor approaches to an aircraft carrier longer and wider than the vessel upon which the camera was actually mounted and the positions of the stern deck-edge 5, runway 2 and centreline markings 2A have accordingly been adjusted in Figures 4 to 7 to more closely represent the scenes which would be viewed in the display 7 at the corresponding stages of the approach to the notional vessel. In this trial the camera 3 was laterally offset by 130ft (40m) from the centreline of the notional runway 2 and at a height of 10ft (3m) above the notional flight deck. The horizon, where visible in these Figures, is indicated at 10. The prevailing sea conditions during this trial were equivalent to sea state 6 ("very rough") for the responses of the notional vessel. Figures 4 to 7 give a view of the approaching aircraft 6 from a distance out of approximately 0.3 nautical miles (550m) (Figure 4) to the point of crossing the notional ship's stern (Figure 7) and it can be seen from these Figures how successive image frames (of which only a very few have been selected from those captured during the time period represented by these Figures) variously roll and translate within the overall display frame 7A to stabilise the view of the aircraft notwithstanding the motions of the ship upon which the camera is mounted. As between those Figures the visible changes in image roll angle are due predominantly to heave and/or roll of the ship while the visible changes in image height (i.e. vertical translational position) within the overall frame are due predominantly to pitching of the ship; (yaw of the ship did not require compensation on this occasion). Thus it is seen how the image roll angle decreases from Figure 4 to Figure 5 and then increases from Figure 5 to Figures 6 and 7 as the ship heaves down and up again and slightly rolls, while the image moves down from Figure 4 to Figure 5, up from Figure 5 to Figure 6 and down slightly from Figure 6 to Figure 7 as the ship pitches first stern down then stern up and then begins to pitch stern down again. While these rotational and translational image movements are apparent particularly from the positions of the edges 11 of the images relative to the overall display frame 7A in Figures 4 to 7 it may alternatively be preferred to use a display frame which is smaller than the field of view of the camera so that the edges (which may be distracting) are not actually visible in the final display, the fields of view of the display and camera of course being selected so that the whole of the required scene is still visible after allowing for the area "lost" during stabilisation.

It will be noted that in all of Figures 4 to 7 the respective images have a positive roll angle all in the same sense despite variations in vertical excursion of the ship. There are two reasons for this. Firstly because it is preferred to present the scene with the sighting point marker 12 (referred to below) extending substantially horizontally. Secondly because the camera during this trial was mounted higher than ideal so an angular offset was required to position its azimuth plane correctly even for the ship's "equilibrium" condition - the ideal camera height being equal to the height of the intended sighting point path at the position X in Figures 1 and 3 in the ship's "equilibrium" condition.

With further reference to Figures 4 to 7 it is also seen that to aid the LSO a marker line 12 is computed and overlaid on the scene, which represents the path which a specified sighting point on the aircraft (in the present case the nominal pilot's eye position) should follow in the display if the aircraft approaches correctly along the specified glideslope. In the illustrated example this line represents a glideslope angle of 6° (which is typical for RVLs) to a nominal sightline/deck intersection point T (Figure 1 ) on the runway centreline (this particular point pertaining in the "equilibrium" condition of the ship although in practice the actual point of intersection of the sightline with the deck will shift along the runway from this position with vertical excursions of the ship as more particularly explained in PCT/GB2009/001946). Lines 13 and 14 are also added to indicate fixed acceptable margins of error in height from the specified glideslope, which in the illustrated example represent errors of 4.4ft (1.3m) above and below the line 12 respectively. A further line 15 represents the position along the glideslope corresponding to stern crossing, being in the illustrated example a line extending vertically from the stern crossing point Y in Figure 1 (and thus being subject to the same apparent angles as the roll angles of the images in Figures 4 to 7).

From a review of Figures 4 to 7 they show that initially (Figure 4) the aircraft was too low in its approach, being below even the line 14 in the display. It subsequently went slightly high compared to the specified glideslope and tracked slightly high as shown by the pilot's eye position being slightly above line 12 in Figures 5 and 6. At the point of stern crossing (Figure 7) the aircraft was very slightly low but well within the acceptable margin of error, the pilot's eyepoint being between the lines 12 and 14.

It will be appreciated that while the camera 3 provides a ready means for the LSO viewing the display 7 to perceive variations in height of an approaching aircraft from the specified glideslope, its offset position is less conducive to the perception of lateral deviations from the extended runway centreline. For this reason a second camera 15 (Figure 1 ) is mounted flush with the runway centreline pointing astern and with a field of view of observe at least the same phases of the approach as the camera 3, in order to enable the LSO to monitor for lateral deviations. A separate display fed by this camera with pitch and roll stabilisation may be provided for this purpose or it may be preferred to inset the view from this camera into the same display 7 as the camera 3.

Claims

1. A system for monitoring the path of an aircraft approaching to land on a runway on a moving platform comprising a camera mounted on the platform with a field of view to observe at least a substantial part of the approach of such an aircraft, and an associated display at a chosen location by which the substantially live scene captured by the camera can be viewed; said camera being located at a position laterally offset from said runway; means for sensing excursions of the platform in the vertical sense; and means for adjusting the roll angle of images acquired from said camera in response to such sensing means whereby to aid stabilisation of such images against the effects on said camera of such excursions.

2. A system according to claim 1 further comprising means for adjusting the pitch angle of images acquired from said camera in response to such sensing means whereby to further aid stabilisation of such images against the effects on said camera of such excursions.

3. A system according to claim 1 or claim 2 wherein the scene displayed is overlaid with a marking indicating the path which a specified sighting point on the aircraft should follow in the display if the aircraft approaches correctly along a specified glideslope relative to the platform.

4. A system according to any preceding claim wherein the scene displayed is overlaid with markings indicating an acceptable range of vertical deviation from the path which a specified sighting point on the aircraft should follow in the display if the aircraft approaches correctly along a specified glideslope relative to the platform.

5. A system according to any preceding claim wherein said platform is an aircraft carrier or the like and the scene displayed is overlaid with a marking indicating the position along a specified glideslope at which the aircraft should cross the stern of the vessel.

6. A system according to any preceding claim further comprising a camera mounted flush with the runway centreline and with a field of view to observe at least a substantial part of the approach of the aircraft.

7. An aircraft carrier equipped with a system according to any preceding claim.