System for and method of synchronous acquisition of pulsed source light in performance of monitoring aircraft flight operation

Abstract

A system for and a method of synchronous acquisition of pulsed source light performs monitoring of aircraft flight operation. Diode sources of illumination (18, 108, 208) are pulsed (16, 106, 206) at one-half the video frame rate of an imaging camera (36, 136, 236). Alternate frames view the world-scene with lights of interest pulsed on, and then off, respectively. Video differencing (34, 134, 234) eliminates the background scene, as well as all lights not of interest. Suitable threshholding over a resulting array of camera pixel-differences acquires the desired lights and represents them as point symbology on a display (40, 140, 240). In an enhanced vision landing system embodiment, the desired lights (symbols) overlay or are fused on a thermal image of the scene; alternatively, the symbols overlay a visible scene (TV) image.

Description

. atmospheric extinction would entail provision of a compound-diode emitter assembly on the target aircraft.

Synchronous timing of airborne source beacons 208 and gated imaging cameras 236 is derived from GPS signals. Since typical imaging camera integration times are on the order of milliseconds or greater, the finite speed of light does not create significant issues with respect to relative source-camera synchronization over 5—mile ranges. At extreme ranges beyond 5 miles, knowledge of relative positions may be used to correct for small time-of-flight differences between PWM timing and readout electronics timing.

The equipment specifications described above emphasize optimum implementation for automatic air-to-air sensing of an arbitrary aircraft, e.g., from a UAV. However, there exists the option of implementing the above scheme at visible wavelengths using LEDs as source illuminators and suitable television cameras. Although it provides automated acquisition beyond the ability of the human eye, particularly in the presence of background, the gated LED-camera combination alternative also provides direct pilot visibility of the target aircraft beacons on a display 240 of information delivered by EVS 238.

The applications and implementations presented above apply equally, irrespective of whether the diode emitter is an LED or a laser diode. LEDs are typically used in applications requiring one or both of maximum beacon and camera economy and direct eye visibility. SWIR and laser diodes are typically used for highest operational performance.

It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.

Claims

1. A method of using an aircraft-borne system to accomplish early acquisition of landing zone illumination obscured from pilot view because of visible light extinguishing atmospheric conditions, comprising:

modulating the landing zone illumination being modulated at a modulation rate;, comprising:

using an imaging camera to acquire a sequence of image frames of a scene in which the modulated landing zone illumination is contained, the sequence of image frames being acquired at a rate that is synchronized with and is a known multiple of the modulation rate;

setting applying the known multiple to which a value is set that causes the sequence of image frames to include first and second sets of images representing, respectively, background scene information including the modulated landing zone illumination and background scene information not including the modulated landing zone illumination; and

processing the first and second sets of images to remove the background scene information from temporally corresponding images of the first and second sets and thereby provide processed image information from which acquisition of the modulated landing zone illumination can be performed.

2. The method of claim 1, in which the image frames are acquired at a rate that is twice the modulation rate.

3. The method of claim 1, in which the modulating of the landing zone illumination is accomplished by pulse width modulation.

4. The method of claim 1, in which the processing of corresponding images includes subtracting temporally corresponding images of the first and second sets to provide the modified scene.

5. The method of claim 1, in which the landing zone illumination is of an LED type that emits wavelengths of visible light and the imaging camera is sensitive to visible light.

6. The method of claim 1, in which the landing zone illumination is of a type that emits short-wave infrared (SWIR) light and the imaging camera is sensitive to SWIR light.

7. The method of claim 1, further comprising:

pulsing the in which the modulated landing zone illumination is pulsed at a pulsing rate, and further comprising:

operating the imaging camera at an acquisition rate to acquire the sequence of image frames of a scene, the pulsing and the acquisition rates exceeding the frame rate of a conventional television camera;

performing the processing of the first and second sets of images by forming N number of pairs of temporally corresponding images of the first and second sets; and

integrating the N number of pairs at an integration rate that exceeds the frame rate of a conventional television camera to establish a signal-to-noise ratio that increases with an increasing integration rate.

8. The method of claim 1, in which the landing zone illumination includes a field of airport lights.

9. The method of claim 1, in which the modulated landing zone illumination includes a pulsed light beacon.

10. The method of claim 9, in which the pulsed light beacon is of a portable type.

11. The method of claim 1, in which a landing zone receives the modulated landing zone illumination, and further comprising submodulating the modulated landing zone illumination at a submodulation rate providing identification information about the landing zone.

12. The method of claim 11, in which the landing zone identification information identifies an airport.

13. A method of using an aircraft-borne system to accomplish early acquisition of landing zone illumination obscured from pilot view because of visible light extinguishing atmospheric conditions, comprising:

modulating the landing zone illumination at a modulation rate, the landing zone illumination emitting light in first and second wavelength ranges;

using first and second imaging cameras that are sensitive to light in the respective first and second wavelength ranges to acquire sequences of image frames of a scene in which the landing zone illumination is contained, the sequences of image frames being acquired at rates that are synchronized to the modulation rate, and each of the sequences of image frames including first and second sets of images representing, respectively, background scene information including the landing zone illumination and background scene information not including the landing zone illumination;

processing the first and second sets of images of each sequence to remove the background scene information from temporally corresponding images of the first and second sets and thereby provide processed image information; and

fusing the processed image information relating to each of the sequences and performing on the fused processed image information acquisition of the landing zone illumination.

14. The method of claim 13, in which the modulating of the landing zone illumination is accomplished by pulse width modulation.

15. The method of claim 13, in which the first and second wavelength ranges include wavelengths of, respectively, visible light and SWIR light.

16. A method of accomplishing early acquisition of light emitted by a target source located at a distance from an imaging camera to perform monitoring of aircraft flight operation, comprising:

modulating the target source light emission being modulated at a modulation rate;, comprising:

using the imaging camera to acquire a sequence of image frames of a scene in which the modulated target source light emission is contained, the sequence of image frames being acquired at a rate that is synchronized with and is a known multiple of the modulation rate;

setting applying the known multiple to which a value is set that causes the sequence of image frames to include first and second sets of images representing;, respectively, background scene information including the modulated target source light emission and background scene information not including the modulated target source light emission; and

processing the first and second sets of images to remove the background scene information from temporally corresponding images of the first and second sets and thereby provide processed image information from which acquisition of the modulated target source light emission can be performed to enable the monitoring of aircraft flight operation.

17. The method of claim 16, in which the modulated target source light emission propagates from a ground system, and in which the imaging camera is included and the first and second sets of images are processed in an aircraft-borne system, thereby enabling the monitoring of aircraft flight operation by the aircraft.

18. The method of claim 16, in which the modulated target source light emission propagates from an aircraft-borne system, and in which the imaging camera is included and the first and second sets of images are processed in a ground system, thereby enabling the ground system to monitor flight operation of the aircraft.

19. The method of claim 16, in which the modulated target source light emission propagates from a first aircraft-borne system, and in which the imaging camera is included and the first and second sets of images are processed in a second aircraft-borne system, thereby enabling monitoring flight operation of the first aircraft by the second aircraft.

20. The method of claim 19, in which one of the first and second aircraft-borne systems is on a piloted aircraft and the other one of the first and second aircraft-borne systems is on an unpiloted aircraft.

21. The method of claim 19, in which the first and second aircraft-borne systems are on different piloted aircraft.

22. The method of claim 16, further comprising submodulating the modulated target source light emission at a submodulation rate providing identification information about the target source of light emission.

23. The method of claim 16, in which the image frames are acquired at a rate that is twice the modulation rate.

24. The method of claim 16, in which the processing of corresponding images includes subtracting temporally corresponding images of the first and second sets to provide the modified scene.

25. The method of claim 16, in which the target source light emission propagates from an LED that emits wavelengths of visible light and the imaging camera is sensitive to visible light.

26. The method of claim 16, in which the target source light emission propagates from a target light source that emits short-wave infrared (SWIR) light and the imaging camera is sensitive to SWIR light.

27. The method of claim 16, in which the modulated target source light emission includes a pulsed light beacon of a portable type.

28. The method of claim 1, in which the loading zone illumination defines a suitable landing zone for rotary wing aircraft.

29. The method of claim 7, in which the imaging camera is sensitive to visible light.

30. The method of claim 29, in which the imaging camera is a CCD or CMOS sensor camera.

31. The method of claim 7, in which the imaging camera is sensitive to SWIR light.

32. The method of claim 31, in which the imaging camera is an InGaAs sensor camera.

33. The method of claim 11, in which the submodulating of the modulated landing zone illumination is performed by pulse code modulation.

34. The method of claim 16, in which the modulated target source of illumination defines a suitable landing zone for rotary wing aircraft.

35. The method of claim 16, further comprising a vision processor which is responsive to the sequence of image frames acquired by the imaging camera and which relates to a database to produce database imagery that, in combination with real-time imagery produced from the sequence of image frames acquired by the imaging camera, provides a combined verified vision system.

36. The method of claim 17, in which the ground system includes a GPS receiver and the aircraft-borne system includes a GPS receiver, and in which the GPS receivers receive GPS signals from which is derived the synchronization of the rate of acquisition of the sequence of image frames and the modulation rate.

37. The method of claim 18, in which the ground system includes a GPS receiver and the aircraft-borne system includes a GPS receiver, and in which the GPS receivers receive GPS signals from which is derived the synchronization of the rate of acquisition of the sequence of image frames and the modulation rate.

38. The method of claim 19, in which the first and second aircraft-borne systems include GPS receivers that receive GPS signals from which is derived the synchronization of the rate of acquisition of the sequence of image frames and the modulation rate.

39. The method of claim 22, in which the submodulating of the modulated target source light emission is performed by pulse code modulation.