Calibrating focal plane arrays using multiple variable radiometric sources

• US 5,354,987 A
• Filed: 12/07/1992
• Issued: 10/11/1994
• Est. Priority Date: 12/07/1992
• Status: Expired due to Fees

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Texas Instruments, Inc.
• Inventors: MacPherson, Craig A.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US07/987,039
• Time in Patent Office: 673 Days
• Field of Search: 250/252.1 A, 250/330
• US Class Current: 250/252.1
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: G01J 5/0808 Convex mirrors
• CPC Class Codes: G01J 5/0814 Particular reflectors, e.g. faceted or dichroic mirrors
• CPC Class Codes: G01J 5/0816 using attenuators
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A method and system for calibrating focal plane arrays wherein a reference source is periodically disposed between the scene and the detectors so that response measurements can be made at three or more different controlled flux levels. In a first embodiment, a passive infrared reference is used with multiple discrete reflectivity levels. By varying the reflectivity of passive sources during construction, the detectors see some portion of the self-emission of the source and some portion of the detector cryostat temperature. This information is used to obtain accurate calibration. A second embodiment uses continuously varying passive infrared references. Third and fourth embodiments replace the passive discrete and passive continuous infrared sources with active sources. Signal processing is provided to interpolate between the reference measurements.

Claims

1. A system for calibrating the detector elements of a focal plane array comprising:

(a) at least one detector element for observing a scene emitting indicia of temperatures in a known temperature range; and

(b) a reference source having a pair of end portions and a continuous portion with different magnitudes of infrared emission at different locations thereof and continuously less infrared emissive from one of said end portions to the other of said end portions, said reference source successively providing plural magnitudes of reference energy, said magnitudes of reference energy including a magnitude of energy at substantially each of the upper and lower boundaries of said known range and at least one magnitude intermediate said upper and lower boundaries of said known range; and

(c) means to periodically cause said magnitudes of energy from said reference source to impinge upon said at least one detector element in place of said scene.

2. The system of claim 1 wherein said reference source is a passive source.

3. The system of claim 2 further including computing means responsive to the output of said at least one detector element when said reference source causes said reference energy to impinge upon said at least one detector element to adjust the output of each of said at least one detector element when said at least one detector element is observing a scene.

4. The system of claim 1 further including computing means responsive to the output of said at least one detector element when said reference source causes said reference energy to impinge upon said at least one detector element to adjust the output of each of said at least one detector element when said at least one detector element is observing a scene.