Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
1999-08-19
2001-05-01
Mai, Huy (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C250S200000, C250S201800
Reexamination Certificate
active
06226125
ABSTRACT:
BACKGROUND
The present invention relates generally to electro-optical systems, and more particularly, to an electro-optical system having a ball turret and an exterior thermal reference source.
Typically, one or more thermal reference source(s) are an integral part of a sensor assembly used in an electro-optical system, such as those manufactured by the assignee of the present invention. Each thermal reference source(s) is placed within the field-of-view of a detector by repositioning a mirror and extending the travel of a scanner. This requires unnecessary modification of various components of the system. It would be desirable to eliminate such additional complications.
Three field of view electro-optical systems typically use reflective optics for all three (wide, medium and narrow) fields of view to ensure that the optical transmission characteristics are substantially equal in all fields of view. Calibrating the detector by viewing a thermal reference source using medium field of view optics is of little use if the transmission characteristics of wide and narrow fields of view optics are substantially different than those of the medium field of view optics. It would be desirable to have a system that improves upon the ability to calibrate the system.
Thermal reference sources are typically used with staring detector arrays, such as those used on INPP and V22 systems, for example, developed by the assignee of the present invention. However, moving mirrors have not been used to place those thermal reference sources within the field of view of the detector.
Other electro-optical systems use a shutter as a uniform temperature thermal reference source. The temperature of the shutter is typically not controlled and is not preferred for use in advanced electro-optical systems.
Accordingly, it is an objective of the present invention to provide for an improved multiple field of view electro-optical system employing a ball turret and an exterior thermal reference source.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, the present invention provides for an electro-optical system comprising a turret and a thermal reference source that is located exterior to the turret. The turret houses a detector array and optical elements that provide different fields of view for the detector array. The optical elements and detector array are moveable or rotatable so that the detector may view the exterior thermal reference source for calibration purposes and an image scene during normal operation.
The turret has a window through which the detector views the image scene and exterior thermal reference source. The turret is rotatable to move the field of view of the detector and selected optical elements so that the detector views either the exterior thermal reference source or the image scene.
The sensitivity of each detector element of the detector array is calibrated by flooding the detector array with a uniform source of illumination derived by pointing the detector array at the exterior thermal reference source. The calibration data, comprising gain and offset corrections associated with each detector element necessary to yield a uniform image, are electronically recorded. The gain and offset corrections are subsequently applied to the output of the detector array when viewing external scenes to obtain a better quality image.
REFERENCES:
patent: H1066 (1992-06-01), Petropoulos et al.
patent: 4123134 (1978-10-01), Meyers
patent: 5796474 (1998-08-01), Squire et al.
patent: 5936771 (1999-08-01), Cooper
Levy Israel D.
Molina, Jr. Armando A.
Alkov Leonard A.
Lenzen, Jr. Glenn H.
Mai Huy
Raufer Colin M.
Raytheon Company
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