Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2000-08-09
2002-03-19
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C250S342000, C356S141300, C359S558000, C359S568000, C359S601000, C318S638000, C324S522000, C361S023000
Reexamination Certificate
active
06359681
ABSTRACT:
BACKGROUND
The present invention relates to a combined forward-looking infrared/laser sensor. More particularly, the present invention relates to a targeting and imaging system that combines a mid-wave forward-looking infrared (FLIR) subsystem and a laser subsystem, including a laser range receiver (LRR) and a laser spot tracker (LST).
FLIR systems employ an array of infrared (IR) detectors for generating an image based on the IR emissions from a particular area of interest (AOI). In military applications, for example, the AOI may contain targets such as tanks, trucks, and/or other military vehicles or military hardware. These targets emit heat; therefore, they are typically warmer than their surrounding environment. Consequently, they can be distinguished in an IR image generated by a FLIR system.
The use of lasers in conjunction with FLIR systems is generally well known in the art. For example, lasers can be used to designate specific targets which are visible in a FLIR image. In one prior FLIR/laser system, laser energy is swept across a target that is visible in the FLIR image and used for the purpose of generating a 3-D image of the target. The 3-D image can, in turn, be used for target recognition and/or target classification (U.S. Pat. No. 5,345,304). In another prior FLIR/laser system, a laser is used for determining the range of a target from the FLIR/laser system's host platform (U.S. Pat. No. 4,771,437). In yet another prior FLIR/laser system, a laser is used to determine the relative position and velocity of targets (U.S. Pat. No. 4,574,191). In addition, lasers have been used for the purpose of directing laser guided munitions to a desired target visible in a FLIR image.
In each of the aforementioned prior FLIR/laser systems, the ability of the FLIR/laser system to accurately recognize, detect, locate and/or track targets is dependent upon the ability of the system to maintain an accurate alignment between the FLIR and laser. Any fixed misalignment between the FLIR line-of-sight (LOS) and the laser LOS will result in laser overspill. As illustrated in
FIG. 1
, laser overspill is defined as the unintended amount of laser energy
110
that misses the target
105
and reflects off the background. Laser overspill is likely to result in range measurement error, as illustrated by R
err
in FIG.
2
. False range information, in turn, will result in less accurate target recognition, detection, location, and velocity information, as well as less accurate weapon guidance data.
Boresighting is a common term of art which refers to the process of aligning the LOS of a given system. Prior designs, such as the Low Altitude Night Terrain—following Infrared Navigation (LANTIRN) system, employ boresighting processes to minimize fixed alignment errors between the FLIR LOS and the laser LOS. Boresighting processes typically involve optical and/or mechanical realignment of, for example, the FLIR LOS and the laser LOS. Moreover, boresighting processes may be manual or they may be automatic. As stated, boresighting processes are generally well known in the art.
Unfortunately, the alignment error between, for example, a FLIR LOS and a laser LOS is not necessarily a fixed error. In military applications, FLIR/laser based systems are typically installed on moving platforms, such as tactical aircraft (e.g., an F-15 or an F-16). These platforms subject the FLIR/laser based system to large mechanical forces and vibrations. These forces and vibrations directly act upon the optical components which govern the FLIR LOS and the laser LOS. Moreover, FLIR LOS and laser LOS displacements about the pitch axis appear to have the most detrimental affect on system performance (i.e., the ability to accurately recognize, detect, locate and/or track targets).
As illustrated in
FIG. 3
, prior designs such as LANTIRN employ a separate FLIR optics pitch bearing
205
and laser optics pitch bearing
210
, as well as a separate FLIR aperture
215
and laser aperture
220
. Consequently, the aforementioned mechanical forces and vibrations acting upon the FLIR/laser based system will cause the FLIR LOS and the laser LOS to nutate about the pitch axis independent of each other, resulting in LOS jitter and a dynamic (i.e., continuously changing) FLIR LOS-to-laser LOS alignment error in addition to any exiting fixed alignment error. Although the boresighting processes mentioned previously can be used to correct fixed alignment errors, they are generally ineffective with respect to correcting dynamic alignment errors.
Yet another problem associated with prior systems such as LANTIRN, which may significantly contribute to LOS alignment errors, is the fact that FLIR images rotate about the roll axis as a function of gimbal pitch angle. To compensate for this anomaly, prior designs such as LANTIRN counter-rotate the entire FLIR detector assembly. However, FLIR detector assemblies are relatively large, and rotating a large mass to counter rapidly changing gimbal pitch angles has many disadvantages. First and foremost, it is very difficult to counter-rotate a large mass with sufficient response time to compensate for high speed pitch rotations. The inability to compensate for high speed pitch rotations can result in additional FLIR LOS-to-laser LOS alignment errors. Second, the wires which connect to the FLIR detector array elements must pass through a rotating interface. Rotating the interface and the wires passing through the interface significantly impacts system reliability.
SUMMARY
The present invention is a high resolution, gimbaled mid-wave FLIR/laser based system which comprises an electro-optic subsystem that is designed to minimize FLIR LOS-to-laser LOS alignment errors, including fixed alignment errors and dynamic alignment errors, so as to provide more accurate target recognition, detection, location and/or tracking information. If used in conjunction with a military weapon delivery system, these performance enhancements translate into greater survivability for the host platform which can now release its weapons at longer (i.e., safer) standoff ranges in hostile environments.
In addition, the present invention comprises a number of other subsystems and subsystem capabilities which support and further enhance the effectiveness of the electro-optics subsystem. For example, the present invention comprises a single processing subsystem which provides a number of important and novel image processing and image preprocessing functions including: a “dead” detector cell replacement function, a scene-based pattern removal function, a 2-D sharpen filter, a dynamic range control function, and a 2× image enhancement function which employs a unique subpixel dithering process.
The present invention also comprises a novel fault isolation subsystem. The fault isolation subsystem is capable of distinguishing fault conditions which arise in the amplifier portions of the various servo systems from fault conditions which arise in the servo motor portion of the servo systems. Thus maintenance personnel need only remove and replace the defective portion of a servo system without having to remove and replace the entire servo system.
Finally, the present invention comprises a novel electromagnetic interference (EMI) grid. This grid more thoroughly prevents undesired energy from entering the system and interfering with electrical signals. The grid also prevents undesired energy generated by the system to radiate, thereby interfering with the operation of other systems in close proximity.
It is an object of the present invention to provide a high resolution, FLIR/laser based targeting and imaging system.
It is another object of the present invention to provide a high resolution FLIR/laser based system that minimizes alignment errors between the FLIR LOS and the laser LOS.
It is yet another object of the present invention to minimize alignment errors, caused by FLIR LOS and laser LOS jitter by providing a single pitch bearing and a common aperture for both the FLIR optics and the laser optics.
It is still another object of
Bauer Helmuth
Booth John R.
Cole Jeffrey L.
Donahue John J.
Hill Timothy A.
Buczinski Stephen C.
Burns Doane , Swecker, Mathis LLP
Lockheed Martin Corporation
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