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.

The invention claimed is: 
     
       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 the known multiple to a value 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 modulation 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 propagates from 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 propagates from a landing zone light source 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 thein 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 being modulated at a modulation rate, the landing zone illumination and emitting light in first and second wavelength ranges;, comprising: 
 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 modulated 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 modulated landing zone illumination and background scene information not including the modulated 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 modulated landing zone illumination. 
 
     
     
       14. The method of  claim 13 , in which the modulating modulation 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 the known multiple to a value 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.