Patent Publication Number: US-2010109913-A1

Title: Foreign object detection system and method

Description:
FIELD OF THE INVENTION 
     The present invention relates to aircraft safety generally and more particularly to detection and warning of the presence of foreign objects on airport travel surfaces. 
     BACKGROUND OF THE INVENTION 
     There exist in the patent literature various proposals for detection and warning of the presence of foreign objects on airport travel surfaces. The following patent documents are believed to represent the current state of the art: 
     United States Published Patent Applications US 2002/0080046A1; 2002/0109625 A1, and 2002/0093433 A1. 
     Additionally, U.S. Pat. No. 6,064,429 deals with the detection of foreign objects in a general sense. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a highly efficient and cost-effective system and methodology for detection and warning of the presence of foreign objects on airport travel surfaces. 
     There is thus provided in accordance with a preferred embodiment of the present invention a system for detection of foreign objects on airport travel surfaces including a plurality of foreign object detector modules mounted on a corresponding plurality of existing aircraft travel surface lighting supports, the plurality of foreign object detector modules providing a corresponding plurality of detection outputs and a high speed detection output analyzer operative to receive at least one of the plurality of detection outputs and to provide a high speed output indication of foreign object presence. 
     There is also provided in accordance with another preferred embodiment of the present invention a system for detection of foreign objects on airport travel surfaces including a plurality of foreign object detector modules located along aircraft travel surfaces and providing a corresponding plurality of detection outputs and a high speed detection output analyzer operative to receive the plurality of detection outputs and to provide a high speed output indication of foreign object presence within less than 1 minute. 
     There is further provided in accordance with yet another preferred embodiment of the present invention a method for detection of foreign objects on airport travel surfaces including mounting a plurality of foreign object detector modules on a corresponding plurality of existing aircraft travel surface lighting supports, operating the plurality of foreign object detector modules providing a corresponding plurality of detection outputs and analyzing the detection outputs at high speed to provide a high speed output indication of foreign object presence. 
     There is also provided in accordance with still another preferred embodiment of the present invention a method for detection of foreign objects on airport travel surfaces including locating a plurality of foreign object detector modules along airport travel surfaces, operating the plurality of foreign object detector modules providing a corresponding plurality of detection outputs and analyzing the detection outputs at high speed to provide a high speed output indication of foreign object presence within less than 1 minute. 
     Preferably, the airport travel surfaces include at least one taxiway and at least one runway and the system employs at least some existing electrical power infrastructure associated with existing runway and taxiway lighting fixtures. 
     Additionally, the plurality of foreign object detector modules communicate with a computer system which includes an operator console operative to provide a foreign object presence alarm and an image of the foreign object to an operator. Preferably, the high speed detection output analyzer is located in the vicinity of the operator console. Preferably, the system also includes a laser pointer associated with at least one of the plurality of foreign object detector modules to assist in on-site inspections. 
     In accordance with another preferred embodiment of the present invention each of the plurality of foreign object detector modules incorporates at least one foreign object sensor module and a local processing module which receives an output from the at least one foreign object sensor module and provides the detection output including at least an initial determination of whether a foreign object is present. Preferably, the local processing module includes multiple sensor correlation software providing correlation between the output from multiple ones of the at least one foreign object sensor module in the detector module. 
     Alternatively, each of the plurality of foreign object detector modules incorporates at least one foreign object sensor module which provides the detection output to the high speed detection output analyzer which is remotely located with respect thereto. Preferably, the high speed detection output analyzer includes multiple sensor correlation software providing correlation between the detection output from multiple ones of the at least one foreign object sensor module in individual ones of the plurality of detector modules. Additionally, the high speed detection output analyzer includes multiple detector correlation software providing correlation between the detection output from multiple ones of the at least one foreign object sensor module in multiple ones of the plurality of detector modules. 
     In accordance with yet another preferred embodiment, each of the plurality of foreign object detector modules includes at least one camera and at least one illuminator. Preferably, the at least one illuminator includes a fixed field illuminator. Additionally or alternatively, the at least one illuminator includes a scanning illuminator. In accordance with another preferred embodiment, the at least one camera includes a fixed held camera. Alternatively or additionally, the at least one camera includes a scanning camera. Preferably, the at least one camera includes a zoom functionality. 
     Additionally, each of the plurality of foreign object detector modules also has associated therewith at least one of a light level sensor, a vibration sensor and a temperature sensor. 
     In accordance with a preferred embodiment of the present invention, the system also includes controlling software which includes a communication module which handles communications with the plurality of detector modules via a communications network, and management software which interfaces with the communications module. Preferably, the management software interfaces with existing airport control systems, and with a database, a graphical user interface having image manipulation capability and an alarm indicator. Additionally or alternatively, the management software also interfaces with multiple detector correlation software, which provides information based on outputs from multiple ones of the plurality of detector modules. 
     Preferably, the high speed detection output analyzer provides at least first and second modes of operation, the first mode of operation being employed under conditions of normal visibility and the second mode of operation being employed under conditions of impaired visibility. Additionally, the high speed detection output analyzer provides differing levels of signal/noise filtering for operation in the first and second modes of operation. 
     Additionally or alternatively, the high speed detection output analyzer software employs at least one of frame segmentation, gray level histogram comparison and edge detection. Preferably, the frame segmentation and gray level histogram comparison are employed to generate gray scale difference maps highlighting suspected foreign objects. Additionally, the edge detection is employed to generate edge extraction difference maps highlighting suspected foreign objects. 
     Preferably, the high speed detection output analyzer is operative to provide the high speed output indication of foreign object presence within less than minute. 
     Preferably, the system also includes a storage unit, for storing the detection outputs in a time sequence. Additionally, the high speed detection output analyzer is operative to compare the detection outputs to the stored detection outputs. 
     Preferably, the plurality of foreign object detector modules have at least partially overlapping fields of view. Additionally or alternatively, the plurality of foreign object detector modules include a plurality of cameras, and the cameras have at least partially overlapping fields of view. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1  is a simplified pictorial illustration of a system for detection of foreign objects on airport travel surfaces constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIG. 2A  is a simplified block diagram illustration of the system of  FIG. 1  in accordance with one preferred embodiment of the present invention; 
         FIG. 2B  is a simplified block diagram illustration of the system of  FIG. 1  in accordance with another preferred embodiment of the present invention; 
         FIG. 3  is a simplified block diagram illustration of a combined system of the type shown in  FIG. 1 , which incorporates elements of at least one of the types shown in  FIGS. 2A and 2B ; 
         FIG. 4A  is a simplified block diagram illustration of a detector module forming part of the system of  FIG. 2A ; 
         FIG. 4B  is a simplified block diagram illustration of a central processor module forming part of the system of  FIG. 2B ; 
         FIG. 5  is a simplified block diagram illustration of a controlling software module, forming part of the computer system in accordance with the embodiment of  FIG. 2A ; 
         FIGS. 6A ,  6 B and  6 C are simplified pictorial illustrations of three alternative sensor or sensor/processor modules mounted on existing lighting supports useful in the invention of  FIGS. 1-5 ; 
         FIGS. 7A ,  7 B and  7 C are simplified illustrations of the azimuthal extent of protected areas provided by an array of sensors of the types shown respectively in  FIGS. 6A ,  6 B and  6 C; 
         FIGS. 8A ,  8 B and  8 C are simplified illustrations of the elevational extent of protected areas provided by an array of sensors of the types shown respectively in  FIGS. 6A ,  6 B and  6 C; and 
         FIGS. 9A-9L  are, together, a simplified flowchart illustrating the operation of a high speed detection output analyzer forming a portion of a system for detection of foreign objects on airport travel surfaces in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to  FIG. 1 , which is a simplified pictorial illustration of a system for detection of foreign objects on airport travel surfaces constructed and operative in accordance with a preferred embodiment of the present invention. 
     As seen in  FIG. 1 , the system is preferably incorporated into existing infrastructure of an airport having various airport travel surfaces, such as a taxiway  100  and a runway  102 . The present invention may be applicable as well to other aircraft travel surfaces such as aprons (not shown). 
     Preferably, the system employs some or all of existing runway and taxiway lighting fixtures  104  and may employ electrical power supplies and conduits (not shown) associated therewith for both power and data communication. The system is also useful with individually solar powered lighting fixtures. 
     In the illustrated preferred embodiment of the present invention, some, but not all, of the existing lighting fixtures are equipped with foreign object detector modules  106  which enable detection of foreign objects on a runway or taxiway. Detector modules  106  preferably communicate, through a controlling software module described hereinbelow with reference to  FIG. 5 , with an operator console  107 , which preferably forms part of a computer system  108 , which may be any conventional networked or standalone computer system. Operator console  107  preferably provides a foreign object presence alarm and an image of a detected foreign object  109  to an operator. The operator is thus enabled to make an abort decision as appropriate and is provided information relating to the location of the detected foreign object  109  in order to enable an on-site inspection to be carried out quickly and efficiently. 
     A laser pointer  110  may be incorporated in the detector module  106  to assist in on-site inspections. 
     Reference is now made to  FIG. 2A , which is a simplified block diagram illustration of the system of  FIG. 1  in accordance with one preferred embodiment of the present invention. In the embodiment of  FIG. 2A , each detector module  106  ( FIG. 1 ) comprises a foreign object sensor module  120 , comprising one or more sensors, such as cameras, and related devices as described hereinbelow with reference to  FIGS. 6A-6C , and a local processing module  122  which receives at least one output from the sensor module  120  and provides at least an initial determination of whether a foreign object is present. Local processing module  122  preferably comprises a high speed detection output analyzer as described hereinbelow with reference to  FIGS. 9A-9H  and  9 K- 9 L, and also preferably includes a multiple sensor correlation algorithm as described hereinbelow with reference to  FIG. 9I . Each detector module  106  communicates, in a wired or wireless manner as most appropriate, via a communications network  124 , such as a LAN, with the computer system  108  ( FIG. 1 ). 
     Reference is now made to  FIG. 2B , which is a simplified block diagram illustration of the system of  FIG. 1  in accordance with another preferred embodiment of the present invention. In the embodiment of  FIG. 2B , each detector module  106  ( FIG. 1 ) comprises a foreign object sensor module  130 , comprising one or more sensors, such as cameras, and related devices as described hereinbelow with reference to  FIGS. 6A-6C . Each detector module  106  communicates, in a wired or wireless manner as most appropriate, via a communications network  132 , such as a LAN, with the computer system  108  ( FIG. 1 ), which includes a central processing module  134 , which provides at least an initial determination of whether a foreign object is present. Central processing module  134  preferably comprises a high speed detection output analyzer as described hereinbelow with reference to  FIGS. 9A-9H  and  FIGS. 9K-9L , which preferably also includes a multiple sensor correlation algorithm as described hereinbelow with reference to  FIG. 9I  and a multiple detector correlation algorithm as described hereinbelow with reference to  FIG. 9J . 
     Reference is now made to  FIG. 3 , which is a simplified block diagram illustration of a combined system of the type shown in  FIG. 1 , which incorporates elements of at least one of the types shown in  FIGS. 2A and 2B . As seen in  FIG. 3 , multiple groups of detector modules  106  ( FIG. 1 ) may communicate via multiple computer networks, through management software described hereinbelow with reference to  FIG. 5 , with a computer system  140 , such as computer system  108  of  FIG. 1 . For example, first and second groups  142  and  144  of detector modules  106  ( FIG. 1 ), of the type shown in  FIG. 2A , may communicate via respective LANs  146  and  148 , while third and fourth groups  150  and  152  of detector modules  106  ( FIG. 1 ), of the type shown in  FIG. 2B , may communicate via respective LANs  154  and  158 , with computer system  140 . 
     Reference is now made to  FIG. 4A , which is a simplified block diagram illustration of a detector module forming part of the system of  FIG. 2A . As seen in  FIG. 4A , an output signal from camera  214  is preferably received by a frame grabber  230  which outputs to digital signal processing circuitry  232 , which performs image analysis on the output of camera  214 . Digital signal processing circuitry  232  preferably comprises a high speed detection output analyzer as described hereinbelow with reference to  FIGS. 9A-9H  and  9 K- 9 L, which also preferably includes a multiple sensor correlation algorithm as described hereinbelow with reference to  FIG. 9I . 
     A controller computer  234  receives an output from digital signal processing circuitry  232  and may also receive an output from one or more environmental sensors such as sensors  318 ,  319  and  320  ( FIG. 6A ). Controller computer  234  also provides control outputs to illuminators  212 , cameras  214 , laser pointers  216  and other elements described hereinabove with reference to  FIG. 4A . 
     A communications module  236  interfaces with controller computer  234  and provides data communications via communications network  124  ( FIG. 2A ), such as a LAN, with computer system  108  ( FIG. 1 ). It is appreciated that the communications may be wired and/or wireless and may employ the existing wiring connection  304  to lamp  308  ( FIG. 6A ). 
     Reference is now made to  FIG. 4B , which is a simplified block diagram illustration of a central processing module forming part of the system of  FIG. 2B . As seen in  FIG. 4B , the central processing module preferably comprises a server  240  which receives via communications network  132  ( FIG. 2B ), such as a LAN, output signals from a plurality of foreign object detector modules  106  ( FIG. 2B ) which include sensor modules  130  ( FIG. 2B ) and preferably provides them to a central processing module  242 , which preferably comprises parallel processors with the capacity to process all of the output signals in real time. Central processing module  242  preferably comprises a high speed detection output analyzer as described hereinbelow with reference to  FIGS. 9A-9H  and  9 K- 9 L, which preferably also includes a multiple sensor correlation algorithm as described hereinbelow with reference to  FIG. 9I  and a multiple detector correlation algorithm as described hereinbelow with reference to  FIG. 9J . Central processing module  242  preferably communicates, through management software described hereinbelow with reference to  FIG. 5 , with operator console  107  ( FIG. 1 ) to provide an indication of whether a foreign object is present. 
     Reference is now made to  FIG. 5 , which is a simplified block diagram illustration of a controlling software module forming part of the computer system in accordance with the embodiment of  FIG. 2A . The controlling software module is preferably installed in computer system  108  ( FIG. 1 ) and comprises a communication module  250  which handles the communications with the plurality of detector modules  106  ( FIG. 2A ) via communications network  124  ( FIG. 2A ). Communication module  250  interfaces with management software  252  which, in turn, interfaces with a database  254 , with a graphical user interface  256  having image manipulation capability provided by software, such as ADOBE® PHOTOSHOP®, and with an alarm indicator  258 . Additionally, communication module  250  or management software  252  may interface with existing airport control systems. The management software  252  may also interface with a multiple detector correlation algorithm  260 , a preferred embodiment of which is described in reference to  FIG. 9J  hereinbelow, which correlates outputs received from multiple detector modules  106  ( FIG. 2A ). 
     It is appreciated that a controlling software module similar to the controlling software module of  FIG. 5  may form part of the embodiment described in reference to  FIGS. 2B and 4B . In such a case, the management software  252  communicates via the communication module  250  with the central processing module  242  of  FIG. 4B  and does not interface with multiple detector correlation algorithm  260 , since this functionality is incorporated into central processing module  242 . 
     Reference is now made to  FIGS. 6A ,  6 B and  6 C, which are simplified pictorial illustrations of three alternative sensor or sensor/processor modules mounted on existing lighting supports useful in the invention of  FIGS. 1-5 . 
     Specific reference is now made to  FIG. 6A , which is a simplified pictorial illustration of a preferred embodiment of a detector module forming part of the system of  FIG. 2A . As seen in  FIG. 6A , an existing airport lighting assembly  300 , including a base  302  having an underground electrical wiring connection  304 , a support shaft  306  and a lamp  308  may provide a platform for the detector module  309 . Preferably a support surface  310  is mounted onto shaft  306  below lamp  308 . Mounted onto support surface  310  there are preferably provided a plurality of static imaging assemblies  311 , each preferably comprising an illuminator  312  and a camera  314 . Camera  314  is preferably equipped with optics  315  including, inter alia, a near IR filter which is employed during daylight operation when illuminator  312  is not employed. 
     One or more of the static imaging assemblies  311  may also comprise a selectably directable laser pointer  316  for indicating the location of a suspected foreign object. Alternatively, one or more scanning imaging assemblies may be employed instead of static imaging assemblies. 
     One or more environmental sensors, such as a light level sensor  318 , a vibration sensor  319  and a temperature sensor  320 , may also be mounted on support surface  310 . 
     Preferably illuminators  312 , cameras  314  and environmental sensors, such as sensors  318 ,  319  and  320 , are electrically connected to a local processor and communication module  322  which provides electrical power for operation and preferably also provides two-way data communication for controlling the operation of the illuminators  312 , cameras  314 , optics  315  and laser pointers  316  as well as processing image data from cameras  314 , including performing initial image analysis thereon and providing foreign object detection output signals and environmental sensor signals via communications network  124  ( FIG. 2A ), such as a LAN, to computer system  108  ( FIG. 1 ). 
     Preferably, electrical power supplied to lamp  308  via wiring  304  is employed to power the detector module and the various elements described hereinabove. Preferably a rechargeable battery  323  is provided to store electrical power during times that lamp  308  is illuminated and to enable such stored electrical power to be used during all other times for powering the detector module and the various elements described hereinabove. 
     Preferably, the static imaging assemblies  311  are enclosed within a suitable environmental enclosure  324  which includes portions that are transparent to light as required by the illuminators  312 , cameras  314  and laser pointers  316 . 
     It is appreciated that the detector module of  FIG. 6A  may also be useful in the embodiment of  FIG. 2B . In such a case, the local processor and communication module  322  does not provide local image processing. 
     It is appreciated that any suitable number of cameras  314 , illuminators  312  and laser pointers  316  may be included in a detector module. It is also appreciated that the base  302  having underground electrical wiring connection  304 , may be replaced by an above-ground support and wiring connection. 
     Specific reference is now made to  FIG. 6B , which is a simplified pictorial illustration of a preferred embodiment of a detector module forming part of the system of  FIG. 2A . As seen in  FIG. 6B , an existing airport lighting assembly  350 , including a base  352  having an underground electrical wiring connection  354 , a support shaft  356  and a lamp  358  may provide a platform for the detector module. Preferably a support bracket  360  is mounted onto shaft  356  below lamp  358 . Mounted onto support bracket  360  there is preferably provided an enclosure  361 , which may be similar to enclosure  324  of  FIG. 6A , and preferably encloses a plurality of static imaging assemblies  362 , each preferably comprising at least one illuminator  363  and a pair of cameras  364  and  365 , preferably arranged in stacked relationship. This stacked relationship provides different elevations for cameras  364  and  365 , providing complementary fields of view as shown in  FIGS. 7B and 8B  and described hereinbelow in reference thereto. Alternatively, cameras  364  and  365  may be arranged side by side, having different elevational tilts to provide these complementary fields of view. Cameras  364  and  365  are preferably equipped with optics (not shown) including, inter alia, a near IR filter which is employed during daylight operation when illuminator  363  is not employed. 
     Disposed within enclosure  361  there is preferably provided a selectably directable laser pointer  366  for indicating the location of a suspect foreign object. Alternatively, one or more scanning imaging assemblies may be employed instead of static imaging assemblies. 
     One or more environmental sensors, such as a light level sensor  368 , a vibration sensor  369  and a temperature sensor  370 , may also be mounted on support bracket  360 . 
     Preferably illuminators  363 , cameras  364  &amp;  365  and environmental sensors, such as sensors  368 ,  369  and  370 , are electrically connected to a local processor and communication module  372  which provides electrical power for operation and preferably also provides two-way data communication for controlling the operation of the illuminators  363 , cameras  364  &amp;  365  and laser pointers  366  as well as processing image data from cameras  364  &amp;  365 , including performing initial image analysis thereon and providing foreign object detection output signals and environmental sensor signals via communications network  124  ( FIG. 2A ), such as a LAN, to computer system  108  ( FIG. 1 ). 
     Preferably, electrical power supplied to lamp  358  via wiring  354  is employed to power the detector module and the various elements described hereinabove. Preferably, a rechargeable battery  373  is provided to store electrical power during times that lamp  358  is illuminated and to enable such stored electrical power to be used during all other times for powering the detector module and the various elements described hereinabove. 
     It is appreciated that the detector module of  FIG. 6B  may also be useful in the embodiment of  FIG. 2B . In such a case, the local processor and communication module  372  does not provide local image processing. 
     It is appreciated that any suitable number of cameras  364  &amp;  365 , illuminators  362  and laser pointers  366  may be included in a detector module. It is also appreciated that the base  352  having underground electrical wiring connection  354 , may be replaced by an above-ground support and wiring connection. 
     Specific reference is now made to  FIG. 6C , which is a simplified pictorial illustration of a preferred embodiment of a detector module forming part of the system of  FIG. 2A . As seen in  FIG. 6C , an existing airport lighting assembly  400 , including a base  402  having an underground electrical wiring connection  404 , a support shaft  406  and a lamp  408  may provide a platform for the detector module. Preferably a support surface  410  is mounted onto shaft  406  below lamp  408 . Mounted onto support surface  410  there are preferably provided one or more scanning imaging assemblies  411 , each preferably comprising an illuminator  412  and a scanning camera  414 . Camera  414  is preferably equipped with optics  415  including, inter alia, a near IR filter which is employed during daylight operation when illuminator  412  is not employed. 
     Mounted onto support surface  410  there is preferably provided one or more selectably directable laser pointers  416  for indicating the location of a suspect foreign object. Alternatively, the laser pointer  416  may be included in one or more of the scanning imaging assemblies  411 . 
     One or more environmental sensors, such as a light level sensor  418 , a vibration sensor  419  and a temperature sensor  420 , may also be mounted on support surface  410 . 
     In accordance with a preferred embodiment of the present invention, a scanning illuminator  422  is mounted adjacent the base  402  to direct illumination parallel to and just above an aircraft travel surface, typically up to 2-3 cm above the surface. This illumination is designed to illuminate foreign objects on the aircraft travel surface without generally illuminating the travel surface itself, thus greatly increasing contrast. 
     Preferably illuminators  412  &amp;  422 , cameras  414  and environmental sensors, such as sensors  418 ,  419  and  420 , are electrically connected to a local processor and communication module  423  which provides electrical power for operation and preferably also provides two-way data communication for controlling the operation of the illuminators  412  &amp;  422 , cameras  414  and laser pointers  416  as well as processing image data from cameras  414 , including performing initial image analysis thereon and providing foreign object detection output signals and environmental sensor signals via communications network  124  ( FIG. 2A ), such as a LAN, to computer system  108  ( FIG. 1 ). 
     Preferably, electrical power supplied to lamp  408  via wiring  404  is employed to power the detector module and the various elements described hereinabove. Preferably, a rechargeable battery  424  is provided to store electrical power during times that lamp  408  is illuminated and to enable such stored electrical power to be used during all other times for powering the detector module and the various elements described hereinabove. 
     Preferably, the scanning imaging assemblies  411  are enclosed within a suitable environmental enclosure  425  and the scanning illuminator  422  is enclosed within a suitable environmental enclosure  426 . Enclosures  425  and  426  include portions that are transparent to light as required by the illuminators  412  &amp;  422 , cameras  414  and laser pointers  416 . 
     Preferably at least one scanning imaging assembly  411  is provided with zoom capabilities for enhancing resolution. 
     It is appreciated that the detector module of  FIG. 6C  may also be useful in the embodiment of  FIG. 2B . In such a case, the local processor and communication module  423  does not provide local image processing. 
     It is appreciated that any suitable number of cameras  414 , illuminators  412  &amp;  422  and laser pointers  416  may be included in a detector module. It is also appreciated that the base  402  having underground electrical wiring connection  404 , may be replaced by an above-ground support and wiring connection. 
     Reference is now made to  FIGS. 7A ,  7 B and  7 C, which are simplified illustrations of the azimuthal extent of protected areas provided by an array of sensors of the types shown respectively in  FIGS. 6A ,  6 B and  6 C.  FIGS. 7A-7C  illustrate an example of use of the invention on a runway having a width of 60 meters, where detector modules are deployed on both sides of the runway every 100 meters in  FIGS. 7A and 7C , and every 200 meters in  FIG. 7B . It is assumed that the runway surface is inclined downwardly towards its side edges for drainage purposes. 
     Turning to  FIG. 7A , it is seen that each detector module  309  of  FIG. 6A , designated here by reference numeral  450  and having three static imaging assemblies  311  ( FIG. 6A ) typically at an elevation of 50 cm above the runway, provides slightly less than 180 degree overall coverage of one side of the runway, each imaging assembly  311  providing 60 degree coverage which slightly overlaps with that provided by an adjacent imaging assembly  311 . In the illustrated example, each of detectors  1 ,  2  and  3  comprise three cameras, where the fields of view of the three cameras of detector  1  are designated as camera # 1 - 1 , camera # 1 - 2  and camera # 1 - 3 . Similar designations are used for the cameras of detectors  2  and  3 , as well as the field of view of one of the cameras of detector  4  (not shown), which is designated camera # 4 - 1 . 
     Turning to  FIG. 7B , it is seen that each detector module of  FIG. 6B , designated here by reference numeral  452  and having two static imaging assemblies  362  ( FIG. 6B ), each including first and second mutually stacked cameras  364  &amp;  365 , typically at elevations of approximately 80 cm above the runway, provides slightly less than 180 degree overall coverage of one side of the runway, each imaging assembly  362  providing 90 degree coverage which slightly overlaps with that provided by an adjacent imaging assembly  362 . Here, it is seen that lower cameras  365  have fields of view which are located relatively close to the edge of the runway, while higher cameras  364  have fields of view which slightly overlap the fields of view of cameras  365  and extend beyond the center of the runway. It is appreciated that even though the illustrated embodiment shows cameras  364  and  365  stacked one on top of the other, that they may also be situated side by side, with different elevation angles. 
     In the illustrated example, each of detectors  1 ,  2 ,  3  and  4  comprise two pairs of two cameras, where the fields of view of the four cameras of detector  1  are designated as camera # 1 - 1 , camera # 1 - 2 , camera # 1 - 3  and camera # 1 - 4 . Similar designations are used for the cameras of detectors  2 ,  3  and  4 . 
     Turning to  FIG. 7C , it is seen that each detector module of  FIG. 6C , designated here by reference numeral  454  and having at least one scanning imaging assembly  411  ( FIG. 6C ) typically at an elevation of 50 cm above the runway, provides 180 degree overall coverage of one side of the runway. 
     Reference is now made to  FIGS. 8A ,  8 B and  8 C, which are simplified illustrations of the elevational extent of protected areas provided by an array of sensors of the types shown respectively in  FIGS. 6A ,  6 B and  6 C. It is appreciated that  FIGS. 8A-8C  are not drawn to scale in order to emphasize the effect of the incline of the runway from its center to its sides, which is practice is about 2%. 
       FIG. 8A  illustrates that in the illustrated example, the field of view of imaging assembly  311  ( FIG. 6A ) extends generally to the center of the runway.  FIG. 8B  illustrates that in the illustrated example, the field of view of imaging assembly  362  ( FIG. 6B ) partly extends beyond the center of the runway.  FIG. 8B  also shows that lower cameras  365  ( FIG. 6B ) have fields of view which are located relatively close to the edge of the runway, while higher cameras  364  ( FIG. 6B ) have fields of view which slightly overlap the fields of view of cameras  365  ( FIG. 6B ) and extend beyond the center of the runway.  FIG. 5C  illustrates that in the illustrated example, the field of view of imaging assembly  411  ( FIG. 6C ) extends generally to the center of the runway.  FIG. 8C  also shows the effect of a zoom in function providing a narrower, higher resolution, field of view  460  than the zoom out function, which scans fields of view  460  and  462 . 
     Reference is now made to  FIGS. 9A-9L , which, together, are a simplified flowchart illustrating the operation of a high speed detection output analyzer forming a portion of a system for detection of foreign objects on airport travel surfaces in accordance with a preferred embodiment of the present invention. 
     Turning to  FIG. 9A , it is seen that operation of the high speed detection output analyzer forming a portion of the system for detection of foreign objects on airport travel surfaces in accordance with a preferred embodiment of the present invention may begin with receipt of a light level indication, such as from light level sensor  318  in the embodiment of  FIG. 6A , light level sensor  368  in the embodiment of  FIG. 6B  or light level sensor  418  in the embodiment of  FIG. 6C . Based on the light level, day (normal visibility) or night (impaired visibility) operation is indicated. 
     During daytime, assuming that weather conditions do not impair visibility, each detector module, such as detector modules  106  ( FIGS. 1 ,  2 A &amp;  2 B) and the detector modules described hereinabove in connection with  FIGS. 6A-6C , captures at least one frame in its field of view. A typical frame, being part of a runway, is designated by reference numeral  502 . If the frame capture is an initial day or night frame capture for a detector module, the analyzer processes frame  502  according to the single frame detection algorithm described hereinbelow in reference to  FIGS. 9B-9F . If the frame capture is not an initial day or night frame capture for a detector module, the analyzer processes frame  502  according to the change detection algorithm described hereinbelow in reference to  FIGS. 9G-9H . 
     Turning to  FIG. 9B , extraction of an airport travel surface, preferably by frame segmentation, takes place, yielding an image showing only the aircraft travel surface, here designated by reference numeral  504  in  FIG. 9B . 
     A histogram or other suitable representation of the distribution of grey-level pixels on the aircraft travel surface is then preferably generated in order to determine a typical airport travel surface pixel grey level. An example of such a histogram is here designated by reference numeral  506 . 
     Suspect areas on the aircraft travel surface are then located by finding non-typical airport travel surface pixels. This is preferably accomplished, as shown in  FIG. 9C , by generating local histograms by employing a running window as illustrated at reference numeral  508 . Each local histogram is compared with an expected value and a map of suspect areas is generated based on differences between local histogram values and expected histogram values. An example of such a map is designated by reference numeral  510 . 
     Preferably, while the steps illustrated in  FIGS. 9B and 9C  take place, a parallel analysis also occurs, as shown in  FIG. 9D . Turning to  FIG. 9D , it is seen that edge detection is carried out on frame  502  ( FIG. 9A ) in order to find unexpected edges which may indicate the presence of foreign objects. Examples of detected edges are indicated by reference numerals  512  and  514 . The detected edges are compared with corresponding expected edge configurations, here designated by reference numerals  513  and  515 , stored in a database which may or may not be local to the detector module. Additionally, the system analyzes detected edges for relationships between edges or edge enclosed areas, such as edge enclosed areas  516 , which together match expected edge configuration  517 . It is noted that the edge  518 , which corresponds to a foreign object, does nod have a matching configuration in the database. 
     A map, here designated by reference numeral  519 , is generated to indicate the location of the non-matched, suspect detected edge and the extent to which the suspect detected edge differs from the matching configuration in the database. 
     Turning to  FIG. 9E , it is seen that the results of the parallel processes described above in  FIGS. 9B-9C  and  9 D respectively are correlated in order to determine whether a foreign object is deemed to have been located. This is preferably carried out by comparing a histogram map here designated by reference numeral  520  with an edge map, here designated by reference numeral  522 . 
     If a foreign object is deemed to have been located, a message is sent to a human operator through any suitable medium or media and a “marked up” version of frame  502  ( FIG. 9A ), here designated by reference numeral  524 , emphasizing the location of the foreign object and providing location information, is displayed for the operator. 
     As indicated in  FIG. 9F , upon receipt of an acknowledgment from the human operator of his receipt of the message, a foreign object designator, such as a laser pointer  110  ( FIG. 1 ) may be directed at the foreign object, as illustrated at reference numeral  526 . 
     If a foreign object is not found by correlation or should the operator determine that a foreign object is not present, the frame  502  ( FIG. 9A ) and the data generated relative thereto as described hereinabove, together with a global histogram of frame  502  ( FIG. 9A ), here indicated by reference numeral  528 , are stored in a database, which may or may not be local to a given detector module. The stored information may be used as a base image for later comparison. It may be used together with multiple stored based images, which are preferably historically deweighted. 
     Turning to  FIGS. 9G and 9H , if the frame capture is not an initial frame capture for a detector module, a global histogram is generated for the current frame, as designated by reference numeral  530  and this global histogram is compared with one or more stored global histograms of preceding frames, preferably employing histogram equalization, as illustrated at reference numeral  532 . 
     In addition, the current frame and the base frame images are brought into registration and compared, as illustrated at reference numeral  534 , to indicate changes therebetween and a difference map, designated by reference numeral  536 , is produced. The difference map is thresholded, to render a thresholded difference map, as indicated by reference numeral  538 . If peaks remain in the thresholded difference map a multi-sensor analysis is conducted, as indicated in  FIG. 9I . 
     In the illustrated embodiment, the multi-sensor analysis is carried out in two stages, initially employing outputs of sensors, such as cameras, on a single detector module and thereafter on outputs of sensors, such as cameras, on multiple detector modules. Alternatively, any other suitable multi-sensor analysis regime may be employed. 
     As seen in  FIGS. 9I and 9J , suspected foreign object information is received from multiple sensors, such as cameras  314 , in detector module  309 , in the embodiment of  FIG. 6A . This information preferably includes size, shape and associated gray levels of the suspected foreign object detected, and location information within the field of view of the sensor. Additionally, the global histogram map  530  of  FIG. 9G  and the difference map  536  of  FIG. 9H  may also be included in the information received. This information from multiple sensors is considered together and compared with stored information which helps to distinguish detected patterns extending over the fields of view  540  of multiple sensors, such as skid marks  542 , which do not constitute foreign objects, from an actual foreign object  544 . 
     If a foreign object is still believed to be present, suspected foreign object information is received from multiple sensors, such as cameras, in multiple detector modules. This information preferably includes size, shape and associated gray levels of the suspected foreign object detected, and location information within the field of view of the detector. Additionally, the global histogram map  530  of  FIG. 9G  and the difference map  536  of  FIG. 9H  may also be included in the information received. This information from multiple detectors is considered together and compared with stored information which helps to distinguish detected patterns extending over the fields of view  550  of multiple sensors, such as cameras, on multiple detector modules  552 , such as slush  554  or a moving vehicle, which do not constitute foreign objects, from an actual foreign object  556 . 
     Reference is now made to  FIG. 9K , which illustrates operation in an impaired visibility environment. If fixed illumination is employed, multiple images are captured at multiple times and combined, for example by averaging, to provide a combined noise reduced frame  560  for analysis. 
     As seen in  FIG. 9L , if scanning illumination is employed, the operation of the scanner and of the camera is synchronized to provide a suitable frame  562  for analysis. 
     The frames  560  or  562  may then be processed for further signal to noise enhancement and are then processed as described hereinabove for frames, such as frame  502 , captured during the day. It is appreciated that frames captured under impaired visibility conditions may be analyzed entirely or partially separately from frames captured under full visibility conditions. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications which would occur to persons skilled in the art upon reading the specification and which are not in the prior art.