Method and apparatus for reducing handoff inaccuracies in a countermeasures system

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.

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.

According to the present invention, hand off inaccuracies may be reduced by adding a second on-axis camera to the DIRCM countermeasures system.

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.

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:

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'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'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.