In-action boresight

Details In-action boresight In-action boresight

2000-12-26

2003-07-01

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Angle measuring or angular axial alignment

Automatic following or aligning while indicating measurement

C244S003160, C244S003130, C250S203200, C356S141100

Reexamination Certificate

active

06587191

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to an in-action boresight for laser designation systems.
Modem weapon systems, which employ laser-guided bombs and missiles, require highly accurate alignment of their designation systems in order to achieve a high probability of target acquisition. Traditional methods of achieving this involve ground-based pre-flight calibration of detectors with their corresponding designator, commonly known as boresighting. Ground-based boresight systems are typically robust, heavy and bulky. After ground-based boresighting has been conducted, however, misalignments can develop between the detectors and designators due to environmental conditions, i.e. mechanical and thermal loads including vibrations, shocks and temperature variation. These misalignments can significantly degrade the performance of the designation systems.
To overcome the misalignment problem, in-flight boresight systems have been developed which can be operated a short time prior to weapon operation. Thus, the misalignments that could normally have occurred from boresighting to designator operation are significantly reduced. These systems, however, are typically made up of a large number of optical components which have the potential for introducing further thermo-optical errors and are prone to in-flight misalignment. Furthermore, current methods rely on local heating of specific types of targets, such as ceramics, using laser radiation in order to generate hot-spots, which are then detected by sensor systems. These methods have number of drawbacks, which are discussed below.
As an example, consider
FIG. 1
which shows a target
500
where a laser beam (not shown) is incident on the target surface
502
, thereby generating laser spot
504
. Heat is conducted by target
500
and this results in a temperature distribution on target surface
502
. Concentric closed loops
506
,
508
and
510
are isotherms (lines of constant temperature on target surface
502
) and indicate a typical temperature distribution caused by laser spot
504
. The temperature is highest at laser spot
504
and decreases with radial distance. It will be readily appreciated that isotherms
506
,
508
and
510
are in general non-circular and non-symmetric around laser spot
504
. This is due to asymmetric conduction within the material that makes up target
500
. Thus, a sensor (not shown) that is operative to detect the local heating which results from laser spot
504
, will incorrectly detect a center
512
for example, instead of the correct center
501
of laser spot
504
.
The above description illustrates a number of major drawbacks of current boresight systems. Firstly, a period of time, which is non-negligible when compared with the time required for boresighting, is required to heat target surface
502
at the center
501
of laser spot
504
to a temperature that allows sensor detection (typically 25 degrees Celsius above target surface temperature). Secondly, a specific target type is required, such as certain ceramics, which has the particular conductive properties required for generating thermally detectable laser spot. Thirdly, asymmetric conduction on the target surface, as depicted graphically in
FIG. 1
, can result in incorrect detection of the laser spot center, thereby degrading the accuracy of the system. Fourthly, in order to effect thermal detection, a large number of additional optical components must be added to the designation system. As mentioned above, these additional optical components increase the probability of in-flight misalignment and reduce accuracy.
There is therefore a need for an accurate and rapid in-action boresight which has a minimum of additional optical components. The system should not rely on laser heating of specific targets, but should rather detect an optical laser spot. This would both increase the system accuracy and eliminate the time required for heating a target, thereby reducing the overall boresighting time. Furthermore, the system should not be limited to a specific target type, but should allow boresighting on a variety of targets.
SUMMARY OF THE INVENTION
The present invention is a method for in-action boresighting of designation systems.
According to the teachings of the present invention there is provided, a method for boresighting of a designation system, including a tracker responsive to a detector with reference to an indicator, comprising the steps of (a) directing a beam of light at a target, using a light source, so that the beam of light is reflected from a spot on the target while the spot temperature remains substantially constant; (b) focusing at least part of the reflected light as an image on the detector; and (c) determining a misalignment of the indicator and image.
There is furthermore provided, in a boresighting system for aligning an indicator with an image of a spot on a target, a method of displaying the alignment, comprising the steps of providing a video monitor; and displaying a representation of the indicator together with a representation of the image on the video monitor.


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