Airborne video tracking system

[0002] This application is a continuation-in-part of U.S. patent application Ser. No. 08/641,131, filed Apr. 22, 1996 now U.S. Pat. No. 5,726,747.

[0003] 1. Field of the Invention

[0004] The present invention relates generally to tracking systems. More specifically, the present invention relates to an optical tracking system which is computer controlled and which is adapted for use on board an airborne platform such as aircraft, helicopter or the like.

[0005] 2. Description of the Prior Art

[0006] In the past optical tracking systems have been extensively used for acquiring, locating, and tracking objects of interest from an airborne platform. For example, in tracking the movement of illegal drugs via a land based vehicle from the air, an optical tracking system on board a helicopter can be extremely useful in that it continually provides updated information as to the movement, direction and location of the vehicle. By accurately identifying the movement, direction and location of the vehicle to law enforcement personnel on the ground an arrest can be made without undue endangerment to the individuals making the arrest.

[0007] An airborne optical tracking system can also be extremely useful in tracking illegal aliens entering the United States across its many boarders which cover several hundred miles of rugged terrain and which are not easily accessible by land. Other uses for airborne optical tracking system include search and rescue missions at sea and on land where the terrain is very rugged.

[0008] Generally, an optical tracking system for an airborne platform utilizing video cameras is referred to as an Airborne Video Tracking System (AVTS). These Airborne Video Tracking Systems are often manually controlled by either the pilot of the aircraft or a crew member. However, optical tracking systems which are manually controlled often lack the ability to quickly acquire a target. In addition, the manually controlled airborne optical tracking systems are generally unable to steer the optics to point to a specific latitude and longitude for the target in a rapid response time or to slave the optics of the optical tracking system with another tracking system and thereby follow the other tracking system. Such a tracking system may be an acquisition sight tracking system or an infrared or radar tracking system.

[0009] It is therefore an object of the present invention to provide an airborne tracking system which allows for the immediate acquisition of a target of interest by the user of the system.

[0010] It is another object of the present invention to provide instantaneous location including longitude and latitude coordinates for the target of interest.

[0011] It is still another object of the present invention to provide an airborne optical tracking system which may slaved with another tracking system so as to follow the other tracking system.

[0012] Various other advantages and objectives of the present invention will become apparent to those skilled in the art by the detailed description of the invention and its preferred embodiments.

[0013] The present invention overcomes some of the disadvantages mentioned above in that it comprises a highly accurate and reliable airborne video tracking system located on board an aircraft such as a helicopter or airplane for use in tracking a target of interest and then providing instantaneous location information including the longitude, latitude and altitude for the target.

[0014] The airborne video tracking system comprises an acquisition sight for use by a pilot of an aircraft to acquire and begin tracking the target. Once the pilot acquires the target an operator at an operator's console in the aircraft can use a track handle to manually take control of tracking the target from the pilot. The operator monitors the target utilizing a narrow field of view monitor and a wide field of view monitor located at the operator console. When the target is visible within the narrow field of monitor the operator can switch tracking of the target from the track handle to an automatic video tracking system. The automatic video tracking system tracks the target based upon the contrast between the target and its surroundings.

[0015] An airborne video tracking system computer receives azimuth and elevation positional signals from the tracking device being used to track the target. The tracking device may be the acquisition sight, the track handle, the automatic video tracking system or a tracking radar which is coupled to an infrared display system. The airborne video tracking system computer then processes the azimuth and elevation data from the tracking device and provides azimuth and elevation angle signals in an analog format to a gimballed mirror to steer the gimballed mirror to the target.

[0016] The gimballed mirror receives image forming light from the target and then directs the image forming light via a first turning mirror to a wide field of view camera and a zoom telescope. The wide field of view camera is connected to the wide field of view monitor via the airborne video tracking system computer at the operator console allowing a wide field of view image to be displayed to the operator at the operator's console.

[0017] The zoom telescope, which also receives image forming light from the gimballed mirror via a second turning mirror, provides a narrow field of view image ranging from about 0.1 degree to about one degree. The zoom telescope directs a narrow field of view image to a narrow field of view camera. The narrow field of view camera is connected to the narrow field of view monitor via the airborne video tracking system computer at the operator console allowing the narrow field of view image of the target to be displayed to the operator at the operator's console.

[0018] The computer includes a video time inserter/video data inserter which overlays time and positional information of the target on the narrow field of view display. The video time inserter/video data inserter also overlays time and positional information of the aircraft as well as positional indicators of the gimballed mirror on the wide field of view display.

[0019] The airborne video tracking system also provides for automatic calibration of analog signals (azimuth and elevation angles) received by the computer from the gimballed mirror which indicate the direction the gimballed mirror is pointing. The automatic calibration of analog signals supplied to the gimballed mirror by the computer to steer the gimballed mirror is provided for by the computer of the airborne video tracking system. In addition, automatic calibration of the acquisition sight and the infrared display system is also provided for by the computer of the airborne video tracking system.

[0020] The airborne video tracking system includes a cue point buffer in the computer which automatically saves a target's positional information including latitude, longitude and altitude whenever target location is determined by marking or triangulation. By depressing the F5 key on the computer's keyboard the operator can steer the gimballed mirror to the latest marked or triangulated target location. Prior marked or triangulated target locations are saved in a CUEPOINT.DAT file in the computer software. The operator may restore a prior target location in the CUEPOINT.DAT file by using the <ALT> and F5 keys on the computer's keyboard.

[0021] The airborne video tracking system also provides positional data in the National Marine Electronics Association protocol via its computer to a moving map display located on board the aircraft. The positional data which includes latitude and longitude information is provided for target locations, the aircraft or platform location and first, second, third, fourth and fifth waypoints.

[0022] To improve the accuracy of marking target locations an averaging function is included in the computer software program for the airborne video tracking systems computer. The resulting average of the calculated latitude and longitude for the target is within 600 feet of the actual target location.

[0023] To improve the accuracy of triangulating target locations, each line of sight vector used in triangulating target locations is weighted equally. When triangulation is used to locate a target, the accuracy of the altitude calculation for the target is ±300 feet, while the calculated latitude and longitude for the target is within 600 feet of the actual target location.

[0024] FIG. 1 is a simplified block diagram of the airborne tracking system constituting the present invention;

[0025] FIG. 2 is a detailed schematic diagram of the airborne tracking system of the present invention;

[0026] FIG. 3 illustrates an example of the position information provided on the wide field of view monitor of FIG. 2 for a target of interest;

[0027] FIG. 4 is a flow chart for the main program module avtsc.c;

[0028] FIG. 5 is a flow chart for the initialization program module init.c;

[0029] FIGS. 6aand 6bare a flow chart for the inertial navigation system program module ins.c;

[0030] FIG. 7 is a flow chart for the acquisition sight program module acqsight.c;

[0031] FIGS. 8aand 8bare a flow chart for the infrared display system program module irds.c;

[0032] FIG. 9 is a first flow chart for the gimbal program module gimbal.c;

[0033] FIG. 10 is a flow chart for the waypoint tracking module pointing.c;

[0034] FIG. 11 is a second flow chart for the gimbal program module gimbal.c;

[0035] FIGS. 12a,12band 12care a flow chart for the computer keyboard program module keyboard.c;

[0036] FIG. 13 is a flow chart for the tracking system displays program module displays.c; and

[0037] FIG. 14 is a flow chart for the estimate location function and the triangulation function of the program module pointing.c.

[0038] Referring to FIG. 1 there is shown a simplified block diagram of the airborne video tracking system 20 which is adapted for use on board an aircraft or helicopter or the like. Airborne video tracking system 20 includes an observer station 26 and an operator console 24. The operator console 24 is connected to observer station 26 which has the optical tracking elements of airborne video tracking system 20. The operator console 24 is also connected to an acquisition sight 22 which is generally located in the aircraft's cockpit and which is used by the aircraft's pilot for the initial acquisition of the target when airborne video tracking system 20 is being used to track a target such as the helicopter 37 illustrated in FIG. 2.

[0039] Referring to FIGS. 1 and 2, the acquisition sight 22 used in the present invention is a newton ring type acquisition sight wherein the aircraft's pilot looks through a glass lens which includes a circle or newton ring 23 projected to infinity. The pilot then aligns circle 23 of acquisition sight 22 with the target 37 such that the target 37 appears within circle 23 of acquisition sight 22 thereby providing for the initial acquisition of the target 37 by airborne video tracking system 20. Acquisition sights 22 then provides an analog signal (indicating azimuth and elevation of the target) to a system computer 42 (FIG. 2) located at the operator console 24. The system computer 42 processes the analog signal and then provides control signals to position the optics at the observer station 26 to the target 37.

[0040] Operator console 24 is also coupled to the aircraft's inertial navigation system 30 allowing system computer 42 to monitor the location of the aircraft having airborne video tracking system mounted therein. Positional information provided by the aircraft's inertial navigation system 30 includes the aircraft's latitude and longitude coordinates and the aircraft's elevation as well as the roll, pitch and heading of the aircraft. The inertial navigation system 30 is, in turn, connected to a global positioning system 28 located on board the aircraft. The global positioning system 28 provides position information updates for the aircraft to the aircraft's inertial navigation system 30 to correct for drifting which occurs in the inertial navigation system 30 after takeoff of the aircraft.

[0041] The operator console is connected to the aircraft's infrared display system 34 to receive synchro/sinusoidal signals from system 34 which indicate the direction infrared display system 34 is pointing. Infrared display system 34 is coupled to a tracking radar 32 which can be used to guide infrared display system 34. Interfacing with the aircraft's infrared display system 34 allows an operator the ability to monitor the aircraft's tracking radar from operator console 24.

[0042] Operator console 24 includes computer 42 which may be, for example, any IBM compatible PC computer. Connected to computer 42 is a keyboard 41 and a monitor 47. There is also a track handle 38 at operator's console 24 which is connected to computer 42 through an automatic video tracker 40 and a control unit 36. Track handle 38 allows an operator at console 24 to manually track the target 37 by depressing trigger switch 39 on track handle 38 once the aircraft's pilot acquires the target 37 using acquisition sight 22. The operator monitors the target 37 at the wide field of view monitor 46 which is located at operator's console 24.

[0043] By engaging a trigger switch 39 at the operator console 24, the operator takes control of tracking target 37 from the pilot using automatic video tracker 40 or track handle 38. When target 37 is within the narrow field of view as displayed on monitor 48, the operator at operator console 24 can switch to automatic video tracker 40 as the means for tracking target 37. The automatic video tracker 40 tracks the target 37 by contrasting the target 37 with its background. For the helicopter illustrated in FIG. 2, the helicopter is contrasted with the blue sky background. If the helicopter were camouflaged to match the trees of a forest and sufficient contrast were not available then automatic video tracker 40 would not be utilized as the tracking means for airborne video tracking system 20.

[0044] It should be noted that acquisition sight 22 and track handle 38 are connected in series allowing an operator at console 24 to acquire control of the tracking of a target 37 from acquisition sight 22 by depressing trigger switch 39 on track handle 38. Automatic video tracker 40 is also connected in series with track handle 38 allowing the operator to use automatic video tracker 40 to track target 37.

[0045] By using track handle 38 the operator at console 24 can position the target 37 within a wide field of view monitor 46 and within a narrow field of view monitor 48 which is located at the operator console 24. Displayed on the wide field of view monitor 46 and the narrow field of view monitor 48 is the video from the optics at observer's station 26. As shown in FIG. 3 positional information graphics are overlaid on the wide field of view display provided by monitor 46. In a like manner positional information graphics are displayed on the narrow field of view monitor 48.

[0046] There is also located at operator's console 24 a pair of video tape recorders 50 and 52 which receive and then record the video from the optics at the observer's station 26. Recorder 52 records the video from the narrow field of view camera 80 generated by the optics at observer station 26, with overlaid graphics generated by computer 42, while recorder 50 records the video from the wide field of view camera 74 generated by the optics at observer station 26, with overlaid graphics generated by computer 42. The operator can either turn on or turn off video tape recorders 50 and 52 by using the F4 function key on keyboard 41.

[0047] A gimballed mirror 56 located at observer station 26 receives image forming light from target 37 when mirror 56 is directed along optical path 67 to target 37 (which is also the line of sight to the target 37 as depicted in FIG. 2). Gimballed mirror 56 then reflects or directs the image forming light from target 37 along an optical path 62 to a pair of turning mirrors 64 and 68 which are positioned downstream from gimballed mirror 56 along optical path 62.

[0048] A portion of the image forming light from helicopter 37 is reflected by gimballed mirror 56 to turning mirror 64 and then redirected by turning mirror 64 along an optical path 65 to the lens of a wide field of camera 74. The remainder of the image forming light from helicopter 37 is reflected by gimballed mirror 56 to turning mirror 68 and then redirected along an optical path 66 by turning mirror 68 to the lens 73 of a telescope 70. Image forming light from helicopter 37 which passes through and then exits telescope 70 via a lens 79 is directed along optical path 78 to a flip mirror 76. As shown in FIG. 2, flip mirror 76 is positioned to direct the image forming light exiting telescope 70 along an optical path 77 to a narrow field of view camera 80. By rotating flip mirror 76 90 degrees from the position depicted in FIG. 2, flip mirror 76 can direct image forming light exiting telescope 70 to a narrow field of view camera 82. In the preferred embodiment of the present invention, narrow field of view camera 80 may be a black and white camera, while narrow field of view camera 82 may be a color camera or a low light level camera adapted for night missions.

[0049] That portion of the image forming light reflected by gimballed mirror 56 to turning mirror 64 which is a one inch turning mirror and then redirected by turning mirror 64 along an optical path 65 to the lens of a wide field of camera 74 comprises a one inch bundle of light. Turning mirror 64 is a one inch turning mirror. The view provided by camera 74 is an overall perspective of the scene including target 37 which the operator at operator console 24 observes on wide field of view monitor 46. The wide field of view appearing on monitor 46 is about four degrees.

[0050] Turning mirror 68 is a four inch turning mirror reflecting a four inch bundle of light from gimballed mirror 56 through telescope 70 to narrow field of view camera 80 or narrow field of view camera 82. Narrow field of view cameras 80 and 82 are coupled through a switch 84 to a video time inserter/video data inserter 44 which is comprised of two video overlay circuit boards in computer 42 and which is connected to narrow field of view monitor 48. The view provided by narrow field of view monitor 48 is very narrow and may be in the order of 0.1 degrees. Telescope 70 is a zoom telescope which can zoom from 20 inches to about 120 inches. At 20 inches zoom telescope 70 provides a one degree field of view, while at 120 inches the field of view is about a 0.1 degree field of view. Telescope 70 is connected to control unit 36 which provides control signals to telescope 70 to control the zoom function of telescope 70.

[0051] Gimballed mirror 56 is gyro stabilized to eliminate the roll of the aircraft and heading changes by the aircraft when tracking the target 37. The gimballed mirror 56 includes a support stand 57 and a gimbal interface 58 which is electrically connected to control unit 36. Control unit 36 which, for example, is responsive to an operator using track handle 38 provides analog control signals to the gimbal interface 58, which, in turn, orientates or steers gimballed mirror 56 to track target 37. There is also connected in series with track handle 38 an automatic video tracker 40 which when turned on by the operator locks on to video contrast to track target 37.

[0052] Gimballed mirror 56, and turning mirror 68 should be flat, for example, in the order of lambda over ten. Turning mirror 64 is also very flat, in the order of lambda over four. Gimballed mirror 56 which is a four inch mirror, is also light weight being fabricated from beryllium.

[0053] The light incident upon lens 73 of telescope 70 has a one inch hole or void in its center resulting from that portion of the image forming light which is reflected by turning mirror 64 to wide field of view camera 74. In addition, lens 73 has a one inch centrally located dark spot 72 which is non-transparent and which is optically aligned with mirror 64.

[0054] When power is first turned on to airborne video tracking system 20, monitor 47 provides the main screen menu which sets forth the function for each of the function keys on keyboard 41.

[0055] When the operator depresses the function F1 on keyboard 41, a Help Screen appears on monitor 47 at the operator console 24. The Help screen illustrated below provides a detailed explanation for each of the function keys on keyboard 41.

[0056] When the function key F2 is depressed by the operator, the operator can perform a system calibration or boresight and set waypoints. When the function keys ALT and F2 are depressed by the operator, the operator can preform an alternate system calibration or boresight and set waypoints.

[0057] The function key F3 allows the operator to change the overlay color on wide field of view monitor 46 and narrow field of view monitor 48. The function key F4 activates recorders 50 and 52, while <Ctrl> F4 de-activates recorders 50 and 52.

[0058] The latest target location is automatically saved in a Cue Point buffer within computer 42 whenever the target location is determined by marking the target or triangulating the target. Depressing the <Ctrl> key and the F5 key simultaneously allows the operator to enter a written description of the target location into the software of computer 42. The operator then saves the description of the target to a CUEPOINT.DAT file by depressing the <enter> key. CUEPOINT.DAT is a module set forth in the computer software program. Depressing the <Alt> key and the F5 key simultaneously allows the operator to restore the location, that is the cue point from the CUEPOINT.DAT file.

[0059] Whenever a target location is saved in the Cue Point buffer, the operator of system 20 may, for example, steer the gimballed mirror 56 to point to a waypoint, such as waypoint one. The operator may than return to the target location in the Cue Point buffer by depressing the F5 key on keyboard 41.

[0060] In the CUEPOINT.DAT file the latest or last entry is defined as Laguna Peak with the latitude being expressed as “N 34 06.50” in degrees, the longitude being expressed as W “119 03.88” in degrees and the altitude being expressed as “1476” in feet. The julian date “196” (Jul. 15, 1997) is set forth next followed by the time of entry which is 11:14:39.

[0061] When the operator of airborne video tracking system 20 desires to point the gimballed mirror 56 of system 26 to a previously marked or triangulated target stored in the CUEPOINT.DAT file, the operator depresses the <Alt> key and the F5 key on keyboard 41 simultaneously to access the CUEPOINT.DAT file and then scrolls to the desired target, prior to depressing the <enter> key on keyboard 41. The operator may scroll the target locations or cue points saved in the CUE.POINT.DAT file by using the up and down arrows on keyboard 41. Depressing the <enter> key on keyboard 41 moves the selected target into the Cue Point buffer and also points the gimballed mirror 56 of system 26 to the selected target.

[0062] For example, if the operator desires to point gimballed mirror 56 to the water tower of the CUEPOINT.DAT file, the operator can scroll to the water tower and press the <enter> key on keyboard 41. This will result in the gimballed mirror 56 of system 20 being pointed to the location of the water tower.

[0063] It should be noted that the software will enter the current date and time for a target whenever the operator fails to provide a written description of the target in the description field of the CUEPOINT.DAT file of the software of. For example, in the CUEPOINT.DAT file the written description for the fourth entry is “196:11:14:09” which is the date and time substitution for “Laguna Peak”. The operator then entered the description “Laguna Peak” with the fifth entry in the CUEPOINT.DAT file.

[0064] When Cue Point is active monitor 47 and a written description of the last target location is to be provided monitor 47 appears as follows:

[0065] The function key F6 selects acquisition sight 22 as the means to track target 37.

[0066] The function key F7 selects infrared display system 34 as the active pointing or tracking device. Qualifying the function key F7 with the <Alt> key sends the currently designated location or waypoint to IRDS 34. A command is also sent to IRDS 34 to direct IRDS 34 to point to the designated location or waypoint. The designated location may be a triangulated target or a marked target.

[0067] The function key F8 allows the operator to select one of five waypoints as the active pointing device. Selecting a waypoint results in gimballed mirror 56 pointing to the latitude, longitude and altitude of the selected waypoint. The function key F9 allows the operator to triangulate the location of the target 37 being tracked by airborne video tracking system 20. The function key F10 allows airborne video tracking system 20 to calculate the present latitude and longitude of target 37 using an estimated altitude previously supplied to airborne video tracking system 20 by the operator. The estimated altitude entered by the operator at operator console 24 is displayed in the marked target box in the lower portion of console display 47. The triangulation function can be used to accurately determine the altitude of target 37 after the operator enters an estimated altitude for target 37.

[0068] When the operator depresses the function key ALT and the key 1 on keyboard 41, the operator selects waypoint one as the active pointing device. In a like manner, the operator can select waypoint 2, waypoint 3, waypoint 4 or waypoint 5 as the active pointing device by simultaneously depressing the ALT key and the key 2, 3, 4, or 5 depending upon which waypoint the operator desires to use as the active pointing device.

[0069] It should be noted that the operator can not select a particular waypoint as the active waypoint whenever the operator's at the Help screen or at a screen entitled Alternate Gimbal Drive Calibrate.

[0070] An operator at operator console 24 can first estimate the altitude by knowing the altitude of the aircraft and then making an educated guess as to the difference between the aircraft altitude and the target altitude.

[0071] The Setup Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Setup Screen by depressing the F2 key on keyboard 41 while the main menu is being displayed on monitor 47. This allows the operator at operator console 24 to perform a system calibration/boresight of the airborne video tracking system 20 (illustrated in FIG. 2) and to set the waypoints.

[0072] Setup Menu ACTIVE ACQ SIGHT

[0073] 1 Calibrate INS.

[0074] 2 Calibrate Gimbal Drive.

[0075] 3 Calibrate Gimbal Input.

[0076] 4 Calibrate Acquisition Sight.

[0077] 5 Calibrate IRDS.

[0078] 6 Adjust Tracking Box.

[0079] 7 Set Gimbal Limit Points.

[0080] 8 Edit Waypoints.

[0081] Enter password: ********

[0082] Press <Esc> to return to main screen.

[0083] From the setup screen, the operator can calibrate inertial navigation system 30 by depressing the one key on keyboard 41. The operator can also calibrate gimbal interface 58 from the setup screen by depressing the two key on keyboard 41. By selecting the three key on keyboard 41, the operator can calibrate input signals supplied from gimbal interface 58 through control unit 36 to computer 42. By selecting the three key on keyboard 41, the operator can calibrate acquisition sight 22.

[0084] Referring to FIGS. 1, 2 and 3, from the setup screen, the operator can calibrate infrared display system 34 by depressing the five key on keyboard 41. Depressing the six key on keyboard 41 allows the operator to change the size of tracking box 90 (FIG. 3) which is displayed on wide field of view monitor 46. The size (including width, height and position on monitor 46) of the tracking box 90 is changed whenever there iis a change in the zoom function on telescope 70. It should be noted that the telescope zoom function is not changed during the flight of the aircraft. Tracking box 90 represents the narrow field of view within wide field of view monitor 46.

[0085] Depressing the seven key on keyboard 41 allows the operator to set gimbal limit points for gimballed mirror 56 to prevent damage to gimballed mirror 56. Depressing the eight key on keyboard 41 allows the operator to edit waypoints which are fixed locations at a fixed altitude above sea level.

[0086] It should be noted that the Setup Screen as well as other screens display the active pointing device in the upper right hand corner. The active pointing devices are the acquisition sight, the infrared display system, cue point and selected waypoints. The setup screen also requires a password which the operator must provide to allow the operate to calibrate any of the devices identified in the setup screen.

[0087] The Calibrate Inertial Navigation Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Calibrate Inertial Navigation Screen by depressing the 1 key on keyboard 41 while in the Setup Screen.

[0088] Calibrate INS ACTIVE ACQ SIGHT

[0089] Turn aircraft to a known heading.

[0090] Modify corrected heading (in degrees):

[0091] +or UP Increment heading

[0092] −or DOWN Decrement heading

[0093] Displayed INS heading (in degree): 60.00

[0094] Corrected INS heading (in degree): 60.00

[0095] Press <Esc> to return to main screen . . .

[0096] The + key or the up arrow key on keyboard 41 is used to increment the inertial navigation system heading, while the − key or the down arrow key are used to decrement the inertial navigation system heading. The aircraft is first placed in a known heading or position and then the inertial navigation system heading is adjusted to compensate for any error which may occur in its heading.

[0097] The Calibrate Gimbal Drive Screen which appears on monitor 47 at the operator console 24 is set forth below., The operator accesses the Calibrate Gimbal Drive Screen by depressing the 2 key on keyboard 41 while in the Setup Screen.

[0098] Gimbal Drive Calibration ACTIVE ACQ SIGHT

[0099] Azimuth scale factor: 1.71

[0100] Azimuth offset (volts): 2.72

[0101] Elevation Scale factor: 0.87

[0102] Elevation offset (volts): 0.13

[0103] Press <Tab> or <Up> or <Down> to use new value.

[0104] Press <Enter> to save changes.

[0105] Press <Esc> to return to main screen

[0106] The Azimuth scale factor, Azimuth offset (volts), Elevation Scale factor and Elevation offset (volts) for the gimbal drive calibration values are edited and then accepted using the Tab or Up arrow or Down arrow keys on keyboard 41. These gimbal drive calibration values are adjusted to allow for accurate and concise steering of gimballed mirror 56 by computer 42 via control unit 36.

[0107] The Calibrate Gimbal Input Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Calibrate Gimbal Input Screen by depressing the 3 key on keyboard 41 while in the Setup Screen.

[0108] Gimbal Input Calibration ACTIVE ACQ SIGHT

[0109] Azimuth scale factor: 1.04

[0110] Azimuth offset (volts): −0.54

[0111] Elevation scale factor: 1.27

[0112] Elevation offset (volts): 0.23

[0113] Press <Tab> or <Up> or <Down> to use new value.

[0114] Press <Enter> to save changes.

[0115] Press <Esc> to return to main screen . . .

[0116] The Azimuth scale factor, Azimuth offset (volts), Elevation Scale factor and Elevation offset (volts) for the gimbal input calibration values are edited and then accepted using the Tab or Up arrow or Down arrow keys on keyboard 41. These calibration values provide accurate calibration for the gimbal position indicators 95, 96, 97 and 98 on the wide field of view screen 46 shown in FIG. 3. When computer 42 is used to control gimballed mirror 56, the gimbal position indicators 95 and 96 align respectively with the acquisition pointing angle indicators 93 and 92. When computer 42 is providing an active waypoint and an operator is using the track handle 38 to steer the gimballed mirror 56 the gimbal position indicators 97 and 98 may differ significantly from the acquisition pointing angle indicators 93 and 92 as shown in FIG. 3.

[0117] The Calibrate Acquisition Sight Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Calibrate Acquisition Sight Screen by depressing the 4 key on keyboard 41 while in the Setup Screen.

[0118] Acquisition Sight Calibration ACTIVE ACQ SIGHT

[0119] Azimuth scale factor: 1:15

[0120] Azimuth offset (volts): 1:36

[0121] Elevation scale factor: 1:10

[0122] Elevation offset (volts): 0.11

[0123] Press <Tab> or <Up> or <Down> to use new value.

[0124] Press <Enter> to save changes.

[0125] Press <Esc> to return to main screen

[0126] The Azimuth scale factor, Azimuth offset (volts), Elevation Scale factor and Elevation offset (volts) for the acquisition sight calibration values are edited and then accepted using the Tab or Up arrow or Down arrow keys on keyboard 41.

[0127] The Calibrate Infrared Display System Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Infrared Display System Screen by depressing the 5 key on keyboard 41 while in the Setup Screen.

[0128] IRDS Calibration ACTIVE IRDS

[0129] Azimuth scale factor: 1.00

[0130] Azimuth offset (volts): 2.56

[0131] Elevation Scale factor: 1.00

[0132] Elevation offset (volts): 0.50

[0133] Press <Tab> or <Up> or <Down> to use new value.

[0134] Press <Enter> to save changes.

[0135] Press <Esc> to return to main screen

[0136] The Azimuth scale factor, Azimuth offset (volts), Elevation Scale factor and Elevation offset (volts) for the infrared display system calibration values are edited and then accepted using the Tab or Up arrow or Down arrow keys on keyboard 41.

[0137] The Adjust Tracking Box Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Adjust Tracking Box by depressing the 6 key on keyboard 41 while in the Setup Screen.

[0138] Adjust Tracking Box ACTIVE IRDS

[0139] Use cursor keys to move tracking box.

[0140] Use following keys to size tracking box:

[0141] T Taller

[0142] S Shorter

[0143] W Wider

[0144] N Narrower

[0145] Press <Enter> to save changes . . .

[0146] Press <Esc> to return to main screen . . .

[0147] The cursor keys on keyboard 41 are utilized to move tracking box 90 left, right, up or down on wide field of view monitor 46. Tracking box 90 is sized using the keys T, S, W and N on keyboard 41. Tracking box 90 illustrates the boundary of the narrow field of view overlaid on wide field of view monitor 46.

[0148] The Set Gimbal Limit Points Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Set Gimbal Limit Points Screen by depressing the 7 key on keyboard 41 while in the Setup Screen.

[0149] Gimbal Limits (degrees) ACTIVE IRDS

[0150] Forward warning point: 35

[0151] Aft warning point: −5

[0152] Up warning point: 35

[0153] Down warning point: −35

[0154] Forward stop point: 45

[0155] Aft stop point: −15

[0156] Up stop point: −45

[0157] Down stop point: −45

[0158] Press <Tab> or <Up> or <Down> to use new value.

[0159] Press <Enter> to save changes.

[0160] Press <Esc> to return to main screen . . .

[0161] The gimbal limits are set to prevent damage to gimballed mirror 56. Warning indicators, such as warning indicator 94 shown in FIG. 3 are also set via the set gimbal limits point screen. Warning indicators are provided at each end of the azimuth and elevation axis depicted in FIG. 3. When a position indicator such as position indictor 97 passes the warning indictor, the warning indicator 94 is displayed as shown in FIG. 3. This indicator tells the operator at operator console 24 that gimballed mirror 56 is approaching its azimuth and elevation limits for safe operation of gimballed mirror 56. The forward stop point, aft stop point, the up stop point and the down stop point for gimballed mirror 56 are edited from the set gimbal limits point screen and limit the drive signals supplied by control unit 36 to gimbal interface 58 to prevent damage to mirror 56.

[0162] The Edit Waypoints Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Edit Waypoints Screen by depressing the 8 key on keyboard 41 while in the Setup Screen.

[0163] Press <Tab> or <Up> or <Down> to use new value.

[0164] Press <Enter> to save changes.

[0165] Press <Esc> to return to main screen . . .

[0166] By accessing the Edit Waypoints Screen, the operator can edit the waypoint latitude, longitude, altitude and description fields for each waypoint shown on the screen.

[0167] In the alternative, the operator at operator console 24 can perform a system calibration/boresight of airborne video tracking system 20 by depressing the ALT key and F2 key on keyboard 41. This results in the following menu appearing on monitor 47 at operator console 24.

[0168] Setup Menu ACTIVE ACQ SIGHT

[0169] 1 Calibrate INS.

[0170] 2 Calibrate Gimbal Drive.

[0171] 3 Calibrate Gimbal Input.

[0172] 4 Calibrate Acquisition Sight.

[0173] 5 Calibrate IRDS.

[0174] 6 Adjust Tracking Box.

[0175] 7 Set Gimbal Limit Points.

[0176] 8 Edit Waypoints.

[0177] Enter password: ********

[0178] Press <Esc> to return to main screen.

[0179] When performing alternate calibration on the various components of airborne video tracking system 20, the operator must first process a gimbal input calibration by depressing the 3 key on keyboard 41 while the setup menu is being displayed on monitor 47. The following menu then appears on monitor 47.

[0180] Gimbal Input Calibration ACTIVE ACQ SIGHT

[0181] 1) Select a waypoint using the ALT key.

[0182] 2) Steer the gimbal to the waypoint.

[0183] 3) Accept 1st line-of-sight with F10 key.

[0184] 4) Establish a new line-of-sight by one of the following:

[0185] a) Move platform to a new location.

[0186] b) Select a new waypoint using the ALT key.

[0187] 5) Steer the gimbal to the waypoint.

[0188] 6) Accept 2nd line-of-sight with F10 key.

[0189] NOTE: The greater the change in azimuth and elevation the better the accuracy of the calibration.

[0190] Select a waypoint with the ALT key.

[0191] Press <Enter> to save changes . . .

[0192] Press <Esc> to return to main screen . . .

[0193] It is desired that Gimbal Input Calibration be performed when the aircraft upon which airborne video tracking system 20 is mounted is airborne. The operator at operator console 24 first depresses the ALT key and either the 1, 2, 3, 4 or 5 key on keyboard 41 to select a particular waypoint as a first line of sight.

[0194] For example, when the operator at operator console 24 depresses the ALT key and the 2 key, the selected waypoint will be Lone Pine. The operator may then use track handle 38 to steer gimballed mirror 56 toward the selected waypoint (which is Lone Pine) until gimballed mirror 56 acquires a line of sight with the selected waypoint. When gimballed mirror 56 acquires a line of sight with the selected waypoint, the selected waypoint will appear in the center of narrow field of view of monitor 48. The operator next uses the F10 key on keyboard 41 to accept this line of sight which is the first line of sight vector. The acquisition sight 22 may also be used to steer gimballed mirror 56.

[0195] The operator at operator console 24 must next establish a second line of sight. The second line of sight may be establish by (1) moving the aircraft or platform to a new location, or (2) selecting a new waypoint by using the ALT key.

[0196] For example, when the operator depresses the ALT key and the 3 key, the second waypoint will be the Water Tower. The operator next uses track handle 38 to steer gimballed mirror 56 toward the water tower until gimballed mirror 56 acquires a line of sight with the water tower. When gimballed mirror 56 acquires a line of sight with the water tower, the water tower will appear in the center of narrow field of view of monitor 48. The operator next uses the F10 key on keyboard 41 to accept this line of sight which is the second line of sight vector. Computer 42 then calibrates the analog signals (azimuth and elevation) from gimbal interface unit 58 which indicate the azimuth and elevation of gimballed mirror 56.

[0197] It should be noted that the Gimbal Input Calibration menu appearing on monitor 47 includes a sentence which indicates to the operator which one of the six sequential steps the operator is required to execute to successfully complete the alternate gimbal input calibration. The Gimbal Input Calibration menu appearing on monitor 47 also includes a note which indicates to the operator that the accuracy of the calibration is dependent upon the change in azimuth and elevation between the first line sight of vector and the second line of sight vector.

[0198] When the alternate gimbal input calibration is complete the operator must next perform a gimbal drive calibration by first depressing the ALT key and F2 (accessing the setup screen) and then depressing the 2 key on keyboard 41. The following menu appears on monitor 47.

[0199] Gimbal Drive Calibration ACTIVE ACQ SIGHT

[0200] Press F10 to auto calibrate the Gimbal Drive

[0201] NOTE: The Gimbal Input must be calibrated first.

[0202] WARNING: The gimbal will automatically be panned over the full azimuth and elevation range within the warning indicators.

[0203] Press <Enter> to save changes . . .

[0204] Press <Esc> to return to main screen . . .

[0205] The Alternate Gimbal Drive Calibration menu is used to calibrate the analog signals (azimuth and elevation) provided by computer 42 to gimbal interface unit 58 to steer gimballed mirror 56. When the operator depresses the F10 key on keyboard 41 computer 42 calibrates the analog signals (azimuth and elevation) provided by computer 42 to gimbal interface unit 58 to steer gimballed mirror 56. The alternate gimbal drive calibration screen includes a warning message indicating that gimballed mirror 56 is panned over the full range of azimuth and elevation within its warning indicators 94 (illustrated in FIG. 3) during the calibration process. The alternate gimbal drive calibration screen also includes a message which indicates to the operator at operator console 24 that the alternate gimbal input calibration must be processed by computer 42 prior to the alternate gimbal drive calibration being processed by computer 42.

[0206] The alternate gimbal drive calibration and the alternate gimbal input calibration are each processed or calculated within the keyboard.c module.

[0207] When the operator depresses the ALT Key and F2 (accessing the setup screen) and then depresses the 2 key on keyboard 41, the following menu, which is the alternate acquisition sight calibration menu, appears on monitor 47.

[0208] Acq Sight Calibration ACTIVE WAYPOINT Lone Tree

[0209] 1) Select a waypoint using the ALT key.

[0210] 2) Point the Acquisition Sight to the waypoint.

[0211] 3) Accept 1st line-of-sight with F10 key.

[0212] 4) Establish a new line-of-sight by one of the following:

[0213] a) Move platform to a new location.

[0214] b) Select a new waypoint using the ALT key.

[0215] 5) Point the Acquisition Sight to the waypoint.

[0216] 6) Accept 2nd line-of-sight with F10 key.

[0217] NOTE: The greater the change in azimuth and elevation the better the accuracy of the calibration.

[0218] Designate 1st line-of-sight.

[0219] Press <Enter> to save changes . . .

[0220] Press <Esc> to return to main screen . . .

[0221] Acquisition sight 22 is calibrated by selecting a first waypoint to establish a first line of sight vector and then pointing acquisition sight 22 to the first waypoint prior to the operator at operator console 24 accepting the first line of sight vector by depressing the F10 key on keyboard 41. A second line of sight vector is next established by either pointing acquisition sight 22 at a second waypoint or moving the platform to a new location and then pointing acquisition sight 22 at the first waypoint. When the first and second line-of sight vectors have been accepted by the operator at operator console 24 then computer 42 automatically calibrates acquisition sight 22.

[0222] When the operator depresses the ALT Key and F2 (accessing the setup screen) and then depresses the 5 key on keyboard 41, the following menu, which is the alternate infrared display system calibration menu, appears on monitor 47.

[0223] IRDS Calibration ACTIVE WAYPOINT Lone Tree

[0224] 1) Select a waypoint using the ALT key.

[0225] 2) Point the IRDS to the waypoint.

[0226] 3) Accept 1st line-of-sight with F10 key.

[0227] 4) Establish a new line-of-sight by one of the following:

[0228] a) Move platform to a new location.

[0229] b) Select a new waypoint using the ALT key.

[0230] 5) Point the IRDS to the waypoint.

[0231] 6) Accept 2nd line-of-sight with F10 key.

[0232] NOTE: The greater the change in azimuth and elevation the better the accuracy of the calibration.

[0233] Designate 2nd line-of-sight.

[0234] Press <Enter> to save changes . . .

[0235] Press <Esc> to return to main screen . . .

[0236] Infrared display system 34 is calibrated by selecting a first waypoint to establish a first line of sight vector and then pointing infrared display system to the first waypoint prior to the operator at operator console 24 accepting the first line of sight vector by depressing the F10 key on keyboard 41. A second line of sight vector is next established by either pointing infrared display system 34 to a second waypoint or moving the platform to a new location and then pointing infrared display system 34 to the first waypoint. When the first and second line-of sight vectors have been accepted by the operator at operator console 24 then computer 42 automatically calibrates infrared display system 34.

[0237] The Select Waypoint Screen which appears on monitor 47 at the operator console 24 is set forth below. The operator accesses the Select Waypoints Screen from the main menu screen by depressing the F8 key on keyboard 41.

[0238] Choose the number of the desired waypoint.

[0239] Press <Esc> to return to main screen . . .

[0240] By accessing the Select Waypoint Screen the operator can select one of five waypoints as the active pointing waypoint for airborne video tracking system 20. For example if the operator at operator console 24 depresses key 4 on keyboard 41, the active pointing waypoint for tracking system 20 will be Laguna Peak.

[0241] The narrow field of view monitor 48 provides the following display for an operator to view.

[0242] Marked Target

[0243] 166:16:25:05

[0244] N 34 06.60

[0245] W 119 06.60

[0246] Altitude =0

[0247] 166:16:29:17

[0248] The program listing for the computer software used by computer 42 is written in the well known computer software language c. Upon power up of system 20, the software enters the main program which is in the AVTSC.C module. This module initializes and updates all airborne video tracking system computer functions. This module also includes an abort function which exits to dos (program steps 104 and 106). If, for example, an operator attempts to uses the software on an authorized computer the software will exit to dos.

[0249] Referring to FIGS. 1, 2 and 4, after system initialization (program step 102) and an indication not to abort, the software retrieves and then updates data from inertial navigation system 30 (program step 108). During program step 110 the software retrieves the acqsight angles from acquisition sight 22. During program step 112 the software retrieves the irds angles from infrared display system 34. During program step 114 the software retrieves the gimbal angles for gimballed mirror 56 from gimbal interface 58 through analog output signals from interface 58.

[0250] When tracking is by waypoint, the software determines the required gimbal orientation angles for the waypoint and then provides them in the form of analog output signals which are supplied to gimbal interface 58. Gimbal interface 58 then orientates gimballed mirror 56 to the waypoint allowing airborne video tracking system 20 to begin tracking (program steps 118 and 120). When tracking is not by waypoint, the analog output signals for controlling the orientation of gimballed mirror 56 are determined by computer 42 from the acqsight and irds angular inputs and then supplied via control unit 36 to gimbal interface 58 (program step 120). During program step 122 the software again retrieves the gimbal angles for gimballed mirror 56 from gimbal interface 58 through analog output signals from interface 58.

[0251] The keyboard functions entered by the operator at operator console 24 are processed during program step 124. The console display appearing on monitor 47, the wide field of view display appearing on monitor 46 and the narrow field of view display appearing on monitor 48 are updated during program step 126.

[0252] During program step 128 the mode of operation is checked. If the mode is changed to exit by the operator at operators console 24 the software exits to dos (program step 106) and returns the displays of airborne video tracking system 20 to their default mode.

[0253] Referring to FIGS. 1, 2 and 5 the module INIT.C is the software module which initializes all Airborne Video Tracking System Computer interfaces, initializes waypoints, initializes Analog to Digital and Digital to Analog boards in system 20.

[0254] During program step 130 certain global variables within the INIT.C module are set. Tracking is set to use acquisition sight 22 as the means for acquiring target 37.When waypoint tracking is being used by airborne video tracking system 20 the waypoint is preset to waypoint one which for the waypoint screen illustrated above is the Dome at an altitude of 1413 feet. The estimated altitude is initially set to zero. A “designated_point.alt” is undefined. The “designated_point.alt” is used with the triangulation calculation for determining the location of a target. The serial number is set for the particular computer which is to be used to run the software of Appendix A.

[0255] When the serial number of the computer does not match the serial number in the software the program is aborted (program steps 132 and 146). When the serial number of the computer matches the serial number in the software the program loads data from the file setup.cal which is the calibration file for all devices connected to computer 42. During program step 136 the displays including monitor 47, wide field of view monitor 46 and narrow field of view monitor 48 are initialized. During program step 138 the video tape recorder ports are initialized allowing for communication with wide field of view recorder 50 and narrow field of view recorder 52. During program step 140 an analog input/output board is initialized allowing analog data from track handle 38, automatic video tracker 40 or acquisition sight 22 to be read by computer 42. The analog signal from gimbal interface 58 is also read through this input/output board.

[0256] During program step 142 the inertial navigation system board which couples inertial navigation system 30 to computer 42 is initialized. It should be noted that the the inertial navigation system board is an “ARINC 429” interface board within computer 42. The signals from inertial navigation system 30 are signals having a digital format.

[0257] During program step 144 the infrared display system board which couples infrared display system 34 to computer 42 is initialized. It should be noted that the the infrared display system board is a “Synchro” interface board within computer 42 which converts synchro data to digital data. As shown in FIG. 2 terminal 43 is the input terminal for synchro data from infrared display system 34, while terminal 45 is the input terminal for ARINC 429 data from inertial navigation system 30.

[0258] Referring to FIGS. 1, 2, 6aand 6b, the module INS.C in the software is utilized to input the aircraft location and orientation from inertial navigation system 30 including the aircraft latitude, longitude and altitude and the aircraft roll, pitch and heading. During program step 140 updated latitude data for the aircraft is obtained from inertial navigation system 30 and the latitude is then extracted from the latitude data. During program step 142 updated longitude data for the aircraft is obtained from inertial navigation system 30 and the longitude is then extracted from the longitude data. During program step 144 updated altitude data for the aircraft is obtained from inertial navigation system 30 and the altitude is then extracted from the altitude data. For the wide field of view illustrated in FIG. 3 the aircraft latitude is North 34 degrees 6.40 minutes, the aircraft longitude is West 119 degrees 6.50 minutes and the aircraft altitude is ten feet.

[0259] During program steps 146, 148, 150 and 152 aircraft roll, pitch, heading and ground speed data is obtained from the inertial navigation system 30. The monitor 47 at operator console 24 displays the aircraft roll, pitch and heading in degrees. The wide field of view monitor 46 displays the aircraft heading in degrees and the aircraft speed in miles per hour. For the wide field of view illustrated in FIG. 3 the aircraft heading is 280 degrees and the aircraft speed is 385 miles per hour.

[0260] During program steps 154 the latest time, data and day is obtained from computer 42. If communication between computer 42 and inertial navigation system 30 is established, then time is obtained from inertial navigation system 30 (program step 160). However, when communication between computer 42 and inertial navigation system 30 is not established, then time is obtained from computer 42. During program step 163 the computer clock is updated to the time provided by inertial navigation system 30.

[0261] During program step 166, 168, 170 and 172 the heading is corrected to provide for a positive angle between 0 degrees and 360 degrees. When the heading provided by inertial navigation system 30 is greater than 360 degrees then 360 degrees is subtracted from the heading to provide a corrected heading (program steps 166 and 168). When the heading provided by inertial navigation system 30 is less than 0 degrees, 360 degrees are added to the heading to provide a corrected heading (program steps 170 and 172).

[0262] Referring to FIGS. 1, 2 and 7, the module ACQSIGHT.C in the software is utilized to input the acquisition sight angles (azimuth and elevation) for acquisition sight 22 as well as track handle 38 and automatic video tracker 40. The tracking mode is examined during program step 174. If tracking is performed by waypoint or the infrared display system 34 then the software returns to the main program. When, however, acquisition sight 22 is being used to track target 37 position data is obtained from the analog voltages provided by acquisition sight 22 to computer 42.

[0263] During program step 176 there is a set up of conversion scale factors to convert volts to degrees for both azimuth and elevation. During program step 178 the conversion scale factors of program step 176 are modified or adjusted to convert azimuth volts to radians. During program step 180 the azimuth analog data is retrieved from an A/D board within computer 42 and then converted to a voltage value. This azimuth analog data is a count representative of the azimuth analog voltage signal from acquisition sight 22. During program step 182, the azimuth analog data with adjustments is converted to an angle in radians. During program step 184, the value acqsight.AZ is established as the azimuth angle in radians for use by gimballed mirror 56 and other functions of airborne video tracking system 20.

[0264] It should be noted that computer 42 reads an azimuth analog value from track handle 38, acquisition sight 22 or automatic video tracker 40 and then converts this azimuth analog value to an azimuth angle in radians which is supplied as a voltage to gimballed mirror 56 to point mirror 56 to target 37. It should also be noted that the identical procedure is used to provide the elevation angle in radians to gimballed mirror 56 (program steps 186-192).

[0265] Referring to FIGS. 1, 2, 8aand 8b, the module IRDS.C in the software inputs the Infrared Display System angles (azimuth and elevation) from system 34. Infrared display system 34 provides azimuth and elevation data in a synchro or sinusoidal format via a pair of channels through a synchro board in computer 42. Each channel can be in a tracking mode, a stabilizing mode or a non-tracking mode. During program step 202 the elevation channel is sampled to determine if the channel is tracking or stabilizing. If the elevation channel is not tracking or stabilizing then computer 42 can not read the elevation data and the software proceeds to program step 216 to sample the azimuth channel. If the elevation channel is tracking (program step 202) then the software of the IRDS.C module freezes the elevation channel data (program step 204). During program step 206 a test is made to determine if the data is stable. If the elevation channel data is not stable then the software of the IRDS.C module proceeds to program step 216.

[0266] When the elevation channel data is stabilized the tracking flag is set to no indicating that the data is stabilized. The elevation channel is retrieved and the elevation channel is next set to a tracking mode to obtain another sample of elevation data. During program step 210, the elevation data is then converted directly to an angle in radians. The elevation angle is kept in radians between +180 degrees and −180 degrees (program step 212). The calculated value for the elevation angle is set to irds.EL during program step 214 and is available to other functions within the software. The azimuth channel data from infrared display system 34 is processed in exactly the same manner as the elevation channel data during program steps 216-228.

[0267] Referring to FIGS. 1, 2 and 9, the module GIMBAL.C in the software is utilized to input the Line Of Sight of the gimballed mirror 56 (azimuth and elevation). During program step 230 there is a set up of conversion scale factors to convert volts to degrees for both azimuth and elevation gimbal angles. During program step 232 the conversion scale factors of program step 230 are modified or adjusted to convert azimuth volts to radians. During program step 234 the azimuth analog data is retrieved from the A/D board within computer 42 and then converted to a voltage value. This azimuth analog data is a count representative of the azimuth analog voltage signal from gimballed mirror 56. During program step 236, the azimuth analog data for gimballed mirror 56 with adjustments is converted to an angle in radians. The azimuth angle is set equal to the gimbal_input.Az variable which is available to other functions within the computer software of Appendix A. The gimballed mirror analog elevation data is processed in exactly the same manner as the gimballed mirror analog azimuth data (program steps 240-246). Once the azimuth and elevation angles for gimballed mirror 56 are converted to radians, the location of gimbal position indicator 95 and 96 are set on wide field of view monitor 46.

[0268] Referring to FIGS. 1, 2 and 10, when tracking is by waypoint or the fixed position of an object on the ground, the azimuth and elevation angles for pointing gimballed mirror 56 at the waypoint are determined in the pointing.c module of the software. During program step 248 the aircraft's geographic location (latitude, longitude and altitude) is converted into a geocentric XYZ coordinate location with the earth's center being the origin for the X, Y and Z axis. During program step 252 the object or waypoint's geographic location is converted into a geocentric XYZ coordinate location. The waypoints coordinates are rotated to account for longitudinal distance from the aircraft to the waypoint. The aircraft is now located at Y equal to zero.

[0269] The aircraft coordinates are set to 0,0,0 to establish a new coordinate system to describe the waypoint with respect to the aircraft (program step 254). The coordinate system is then rotated to align the aircraft with the surface of the earth (program step 256). During program step 258 the coordinate system is next rotated to account for the roll, pitch and heading of the aircraft. The azimuth and elevation angles for gimballed mirror 56 are calculated to point the gimballed mirror 56 to the target 37 during program step 260.

[0270] Referring to FIGS. 1, 2 and 11, the gimbal.c module is used to control the orientation of the gimballed mirror 56. A selection is made as to which input angles to output to the gimballed mirror 56 (program step 262). The infrared display system angles are irds.az and irds.el; the acquisition sight angles are acq_sight.az and acq_sight.el and the waypoint angles are pointing.az and pointing.el. During program step 264 there is a limit placed on gimbal travel to within the gimbal stops. During program step 266 conversion scale factors are set up for both azimuth and elevation to convert degrees to volts. During program step 268 adjustment parameters to convert azimuth angular data to volts are retrieved. During program step 270 the azimuth angle in radians with adjustments is converted to volts. During program step 272 adjustment parameters to convert elevation angular data to volts are retrieved. During program step 274 the elevation angle in radians with adjustments is converted to volts. During program step 276 the gimbal azimuth and gimbal elevation angles in an analog signal format are output to gimbal interface 58. Gimballed interface unit 58 then steers gimballed mirror 56 to the target 37.

[0271] Referring to FIGS. 1, 2, 12a, 12band 12C, the keyboard.c module is utilized to process keyboard input from the operator at operator console 24. During program step 280 a determination is made as to whether the mode for airborne video tracking system 20 is the startup mode. If the mode is the startup mode then monitor 47 is selected and the main screen menu is displayed during program step 282. However if the mode is not the startup mode then the software proceeds to program step 284 to sample the input from keyboard 41. If the operator has not used a key on the keyboard 41 to select a particular console display, then the program returns to the main program a function.

[0272] During program step 286 the key input is retrieved and the corresponding console screen is displayed. The various modes are entered by the operator via the function and numeral keys on keyboard 41. For example, if the operator at operator console 24 enters (1) the F2 function key or (2) the ALT key simultaneously with the F2 key (ALTERNATE CALIBRATION) the setup screen will be appear on monitor 47 (program step 300). When the operator at operator console 24 enters the F8 function key the select waypoint screen will be appear on monitor 47 (program step 338). When the operator at operator console 24 enters the “8” key from the setup screen the edit waypoint screen will appear on monitor 47 (program step 334). When the operator at operator console 24 enters the “6” key from the setup screen the adjust tracking box screen will appear on monitor 41 (program step 326).

[0273] When the operator utilizes the alternate calibration function of the keyboard.c module, computer 42 will perform the required processing functions to automatically calibrate the analog signals (azimuth and elevation angles) received by computer 42 from the interface unit 58 of gimballed mirror 56 (program step 343). Computer 42 will also perform the required processing functions to automatically calibrate the analog signals (azimuth and elevation angles) supplied to the interface unit 58 of gimballed mirror 56 (program step 345) to steer gimballed mirror 56. Further, computer 42 will perform the required processing functions to automatically calibrate acquisition sight 22 (program step 347) and to automatically calibrate infrared display system 34 (program step 349).

[0274] Referring to FIGS. 1, 2 and 13, the displays.c module in the software controls the displays in airborne video tracking system 20. If the mode is main screen the console display provided by monitor 47 is updated (program step 352). This update includes the aircraft latitude, longitude, altitude, speed, heading, roll and pitch.

[0275] The display for the wide field of view monitor 46 (FIG. 3) is updated during program step 353. The display for the narrow field of view monitor 48 is updated during program step 354. When computer 42 is processing the alternate gimbal drive calibration the display for the wide field of view monitor 46 (FIG. 3) is not updated, that is program step 353 is skipped. The overlay1 display in the software is the wide field of display, while the overlay2 display in the software is the narrow field of display.

[0276] The current time is read from computer 42 during program step 356. During program step 358 a display location flag is checked. If the flag is “yes”, a location is displayed on the monitors of airborne video tracking system 20. For example, in the marked target box appearing on monitor 47 the current latitude and longitude of target 37 is displayed. In addition, the current latitude and longitude of target 37 is displayed on narrow field of view monitor 48. The F10 key on the keyboard sets the location flag to “yes”.

[0277] The designation time is set equal to the current time. The designated time is the time that target was designated for display. In the marked target box and the narrow field of view display the designated time is 166:16:25:05. The real time shown in the narrow field of view display is 166:16:29:17. If the software is in the main screen mode then monitor 47 displays the target location in the marked target box during program step 364. Target 37 position information including latitude, longitude, altitude and designated target time is displayed on the narrow field of view monitor 52 during program step 366.

[0278] During program step 368 the display location flag is set equal to IS_DISPLAYED to indicate that target position information is being displayed. The time location displayed is set equal to the current time.

[0279] If the display location flag is set to IS_DISPLAYED, then the display time (designated target time) is tested. If the display time is greater than ten seconds the display location flag is set to IS NOT DISPLAYED (program step 372). The marked target display is then cleared from narrow field of view monitor 48 with only the current time being overlaid on the monitor.

[0280] Referring to FIGS. 1, 2 and 14, the estimate location function for the target is within the POINTING.C module. When the operator depresses the F10 function key on keyboard 41, computer 42 determines or calculates the latitude and longitude of target 37 from the pointing angles (azimuth and elevation angles) from gimballed mirror 56 and the estimated altitude of target 37 provided by the operator at operator console 24.

[0281] When the operator holds the F10 function key on keyboard 41 in a down position, that is the operator continually depresses the F10 function key on keyboard 41, the accuracy of the target location calculation by computer 42 significantly increases. Each second a new location for target 37 is calculated and then averaged with the previously calculated locations for target 37.The resulting average of the calculated latitude and longitude for target 37 is now within 600 feet of the actual target location.

[0282] During program step 382, the pointing angles are converted to angles for a platform with a roll, pitch and heading of zero. During program step 384 the geocentric coordinates of the aircraft are determined, that is the coordinate system for the aircraft is now an XYZ coordinate system.

[0283] During program step 386 the geocentric coordinates of the target 37 are determined, that is the coordinate system for the target is now an XYZ coordinate system. This determination is; a mathematical determination. Target 37 is assumed to reside on the surface of an ellipsoid. The surface of the ellipsoid resides at the estimated altitude above the surface of the earth. The intersection of the line of sight vector with the surface of the ellipsoid establishes the geocentric coordinates of the target 37 or the object. The geocentric coordinates of the object are next converted to a geographic location in program step 388 (latitude and longitude of target 37).

[0284] The pointing.c module also includes a triangulation function which is accessed by depressing the F9 function key on keyboard 41. To utilize the triangulation function the operator must designate one location point for the target meaning that the operator must provide an estimated altitude and then utilize the F10 key on keyboard 41 to mark the target location. Computer 42 then calculates an estimated latitude and longitude for target 37.This establishes a reference vector for target 37. During program step 394 a determination is made as to whether one location point for the target 37 has been designated. If one location point has been designated the software proceeds to program step 396 to perform the triangulation function.

[0285] At this time it should be noted that all function keys except F1 or F8 may be utilized from any screen appearing on monitor 47. Thus, for example, the operator may depress the function key F9 or the function key F10 on keyboard 41 while the setup screen is displayed on monitor 47. Once the operator at operator console 24 estimates the altitude of target 37 by entering the altitude via keyboard 41, the operator can then use the F9 or F10 key to provide an initial designation for the location of target 37, which is used to establish the reference vector for the target. Computer 42 also uses the aircraft location (latitude, longitude and altitude) and orientation (roll, pitch and heading), and the azimuth and elevation angles of gimballed mirror 56 to calculate the reference vector. The altitude entered by the operator may be positive which is above sea level or negative which is below sea level.

[0286] The operator then utilizes the F9 key to obtain a second line of sight vector for target 37 which is calculated from the aircraft's current location (latitude, longitude and altitude) and orientation (roll, pitch and heading), and the azimuth and elevation angles of gimballed mirror 56. The two line of sight vectors are then used to calculate the current latitude, longitude and altitude of target 37.By continuing to use the F9 key and thereby continuing to use the triangulation function of the pointing.c module, the operator can accurately determine the latitude, longitude and altitude of target 37.

[0287] For subsequent triangulations, computer 42 uses all previous line of sight vectors with equally weight now being given to each line of sight vector when determining target location.

[0288] After target 37 is pointed to and marked using the F10 key on keyboard 41, the operator may depress the F9 key on keyboard 41 to triangulate target 37.The operator may then continue to depress the F9 key on keyboard 41 to continually recalculate the location for target 37 by triangulation with each calculated location for target 37 being stored in computer 42. The platform or aircraft's location is also stored in computer 42for each calculation of the target's location. Each target location and its corresponding platform location form a line of sight vector. The pointing.c module of the computer program now weights equally each line of sight vector calculated by triangulation. This results in a significant improvement in determining the location of target 37, in particular with respect to the calculated altitude for target 37. The accuracy of the altitude calculation for target 37 is now ±300 feet, while the calculated latitude and longitude for target 37 is within 600 feet of the actual target location.

[0289] While FIG. 1 illustrates a helicopter as target 37, it should be understood that the present invention is easily adapted for use in tracking a fixed target which is located on, the earth's surface. For example, the airborne video tracking system 20 may be used to locate a storage facility for illegal countraband, such as a warehouse which is in a mountainous terrain or a dense rain forest. When the operator of system 20 uses the triangulation function to accurately determine the location of the ground target including the target's latitude, longitude and altitude, the pilot of the platform vehicle may than radio the location of the target to ground based personnel, allowing the ground based personnel to move against the target.

[0290] It should also be noted that whenever an operator attempts to triangulate without sufficient change in the line of sight to allow for triangulation a warning message is provided to the operator and computer 42 does not process the triangulation function.

[0291] The wide and narrow field of view overlays now include a compass (not illustrated) which appears in the lower left hand corner of wide field of view monitor 46 and narrow field of view monitor 48. The compass comprises a pointing arrow with a cross bar and the letters N (north), E (east), S (south) and W (west). The compass arrow is conformally mapped to a level surface at the estimated altitude of the target. For example, if the target is a road, the operator can point the gimballed mirror 56 to the road to determine the direction of travel of the road. The compass illustrates north, south, east and west orientation at a point which is in the center of the wide field of view screen 46 and the narrow field of view screen 48.

[0292] When a target, such as helicopter 37 (FIG. 2), is above airborne video tracking system 20, the compass arrow will allow for a determination of the target's approximate direction of travel. The operator of airborne video tracking system 20 provides an estimated altitude for helicopter 37 and then steers gimballed mirror 56 of airborne video tracking system 56 to point to helicopter 37.The operator manually tracks target 37 by depressing trigger switch 39 on track handle 38 and using track handle 37 to track target 37 even when target 37 is positioned above the platform for system 20.

[0293] Airborne video tracking system 20 also includes the National Marine Electronics Association (NMEA) protocol 0183 for providing positional information via communications port one of computer 42 to a moving map display which includes a computer located on the platform for system 20. In the default mode, this positional information indicates the location to which gimballed mirror 56 of system 20 is pointing.

[0294] By utilizing the <shift> key and the number keys one through five on keyboard 41, the operator of system 20 can toggle on and off the positional data for waypoints one, two three, four and five via communications port one of computer 42 to the moving map display. Positional data for the present aircraft location is toggled on and off with the <shift> key and the number key zero. Positional data for the cue point location or target location is toggled on and off with the <shift> key and the number key six.

[0295] The NMEA 0183 protocol is a series of ASCII strings that includes positional data. The nmea.c module in the software provides positional data by utilizing (1) the RMC (Recommended Minimum Specific GNSS Data); (2) RMB (Recommended Minimum Navigation Data); (3) GGA (Global Positioning System Fix Data) and (4) GSA (GNSS DOP and Active Satellites) strings.

[0296] The RMC string includes a header “$GPRMC” which identifies the string followed by Greenwich Mean Time (GMT) and then a status character. The status character provides an indication of when to process the positional data. When the status character is an “A”, the positional data is valid. When the status character is a “V” indicates that the positional data is marginal and not to be processed. A status character of “V” occurs whenever the GPS data from global positioning system 28 does not have time data include within the data.

[0297] The RMC string next includes latitude data, followed by longitude data and a pair of data fields which are set to zero. These fields represent ground speed in knots and course over ground in degrees. The next field in the RMC string is “GMD” which identifies the Greenwich Mean Day followed by an asterisk and then a checksum. A carriage return is included at the end of the RMC string.

[0298] The second string is the RMB string which includes navigation data from a present position to a destination waypoint. The RMB string starts with an identifier “$GPRMB” followed by a status indicator which is either the character “A” or the character “V”. The remainder of the RMB string is blank, that is navigation data is not included in the string. The RMC string concludes with a checksum followed by a carriage return.

[0299] The third string is the GGA string which is a simulated GPS fix data string. The GGA string includes an identifier “$GPGGA” followed by a field which provides Greenwich Mean Time and then fields which provide latitude and longitude information. The GGA string next includes a GPS Quality indicator which is set to one indicating a GPS fix followed by the number of satellites in use which is set at eight in the GGA string. Since airborne video tracking system 20 includes inertial navigation system 20, there is not a requirement for GPS data from satellites as is normally required when using navigational and radio communications equipment supported by the NMEA 0183 protocol. This allows the user of airborne video tracking system 20 to set the number of satellite to the desired number of satellites within a range of between 0-12 to comply with the NMEA 0183 standard. The GGA string next includes a 0.5 which is horizontal dilution of position, followed by the altitude above mean-sea-level which is in feet. and the Geoidal separation in feet. The altitude and Geoidal separation are set at zero in the GGA string for waypoints one through five and the cue point. For the platform location the altitude may vary in the GGA string, while the Geoidal separation is set at zero.

[0300] The fourth string is the GSA string which represents the simulated satellites acquired. The GSA string includes an identifier “$GPGSA” followed by a field which is the character “A” indicating automatic mode and a field which is the character “1” for the cue point position string and the character “2” for the waypoint position strings. A one indicates that the location is not established. A two indicates a two dimensional fix which is latitude and longitude but not altitude. In the platform GSA string the word “quality” follows the character “A” and is an indicator of the quality of the positional data.

[0301] From the foregoing, it may readily be seen that the present invention comprises a new, unique and exceedingly useful airborne video tracking system which constitutes a considerable improvement over the known prior art. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.