Abstract:
A method for reducing handoff inaccuracies in a DIRCM countermeasures system comprising the step of adding a second on-axis camera to the DIRCM countermeasures system.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims rights under 35 USC§119(e) from U.S. patent application Ser. No. 60/920,712 filed Mar. 29, 2007, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to countermeasures systems and particularly to Directed Infra Red Countermeasures (DIRCM) systems. 
     2. Brief Description of Prior Developments 
     Handoff inaccuracies have been a challenge in some DIRCM systems since directed/focused energy became a requirement to deter Infra Red (IR) detecting-guided missiles. 
     Handoff inaccuracies are driven by platform specifics and environmental issues (variables). Such platform specifics and environmental issues include aircraft flexure; missile warner, specifics such as inherent tolerances, mounting inaccuracies, resolution, and processing latencies; and system processing latencies such as update rate, environmental changes, and DIRCM pointing errors. 
     The foregoing is further illustrated in  FIG. 1 . From  FIG. 1 , it will be understood that 1) sensor location and installation have mounting tolerances contributing to handoff inaccuracies as well as aircraft flexures  2 ) the missile acquisition warner electronics determines (processes) validity of threat this causes positional data to be late (latency)  3 ) once a declaration has been handed over (handoff) to the DIRCM controller it must then process the data and command the gimbal to slew to the latency riddled position before track and energy-on-target can occur. 
     SUMMARY OF INVENTION 
     According to the present invention, hand off inaccuracies may be reduced by adding a second on-axis camera to the DIRCM countermeasures system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described with reference to the accompanying drawings wherein: 
         FIG. 1  is a schematic drawing illustrating handoff inaccuracies. 
         FIG. 2  is an illustration of how a second wide field of view camera can improve the accumulative affects of hand-off inaccuracies 
         FIGS. 3 ,  4  and  5  are respectively top, side, and end views of cameras mounted on gimbals in a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the present invention a camera should be selected with a wide field-of-view (i.e. 10° FoV, with zoom) which allows acquisition of threat if not seen by fine-track-sensor (FTS). Such a camera does not impact existing optical prescription since the focal plane array does not need to increase in size to compensate for lower resolution; and mirror sizes do not require changes. FoV is selected to absorb hand-off errors. An IR imaging camera (long-wavelength) is selected to provide a two-color fine-track-sensor (FTS). A long-wavelength camera allows multi-role use for forward-looking IR (FUR) applications. In  FIG. 2  TOA refers to a Tracker Optics Assembly and TDA refers to a Tracker Detector Assembly. 
     A suitable camera would be a BAE Systems MIM500™ which is shown implemented in FIGS.  3 , 4  and  5 . This camera would preferable have the characteristics shown in Table 1: 
     
       
         
               
               
             
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Spectral response:  
                 7.5-14 microns 
               
               
                 Resolution:  
                 320 × 240 
               
               
                 Pixel Pitch:  
                 28 μm 
               
               
                 Frame Rate:  
                 60 Hz 
               
               
                 Digital Video:  
                 LVDS serial or 8 or 16-bit parallel (optional) 
               
               
                 Analog Video: 
                 RS_170 
               
               
                 Electronic Zoom:  
                 2x, 3x, 4x 
               
               
                 Interface and Control:  
                 RS-422 
               
               
                 Voltage:  
                 4.5-12.5 VDC 
               
               
                 Environment:  
                 −46° C. to +85° C. (operational) 
               
             
          
           
               
                 In production as thermal weapon sight for US Army (15,000) units 
               
               
                   
               
             
          
         
       
     
     The assessed requirements fpr resolution would be that two camera boresight must be on axis and coarsely boresighted to within ±1° or ±17.45mRad. The suggested camera would be 320×240 at 10° equates to 727/Rad/pixel with no extrapolation 48× better than assessed resolution. At full zoom resolution would be 2.2mRad, approximately 17× better than assessed requirement with no extrapolation. Frame rate must be adequate to capture image while aircraft pitches, rolls or yaws and be within FoV. The frame rate 60 Hz, at 100°/sec roll equates to 1.66°/frame well within the second camera&#39;s FoV of but marginal for a one camera system. 
     Referring to  FIGS. 3-5 , the camera is mounted on the gimbal in which it is attached to elevation arm, and rotates with both azimuth and elevation movement. A long-wave camera does not obstruct or use fine track sensor&#39;s optical path. Still referring to  FIGS. 3-5 , the pointer/tracker includes laser and image turning mirrors  10 , laser beam and mirror  12 , and track image and mirror  14 . There is also a gimbal base  16 , an elevation drive mechanism  18 , and an elevation axis  20 . There is a gimbal  22  with an embedded azimuth drive mechanism  24  as well as a base assembly  26  and a dual CCA which includes camera control, resolver excitation and rate sensor power. Also includes is the azimuth axis  30 , the dome  32 , and a second camera  34  mounted to the elevation axis. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.