Thermal sensing system having a fast response calibration device

Details Thermal sensing system having a fast response calibration device Thermal sensing system having a fast response calibration device

1998-01-09

2000-10-03

Hannaher, Constantine

Radiant energy

Calibration or standardization methods

G01D 1800

Patent

active

061276790

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a thermal sensing system and more particularly to both imaging and non-imaging sensing systems incorporating an array of photon-detecting elements.
2. Discussion of Prior Art
Thermal imaging systems are known in the prior art. Such imaging systems can involve either series or parallel processing. In the former case a scene is scanned and each component of the scene is focused sequentially onto a detector. These systems are not easy to design however if compactness is important: the scanning mechanism renders the adaptation to lightweight imagers extremely difficult. An alternative arrangement for area imaging is to employ many detectors to sample simultaneously distinct sections of the scene. A major disadvantage of this system is that the transfer function from incident infrared flux to output signal (detector signal) is particularly sensitive to variation between detecting elements. This results in an image degraded by fixed pattern noise arising from sources both within and independent of the detecting elements. Imperfections in the optical system (e.g. vignetting) and variations in the associated electronic circuits are examples of the latter case. Photodetector sources can be static variations in characteristics (e.g. area, quantum efficiency or cut-off wavelength) or dynamic instabilities (temperature, offset voltage and slope resistance all drift over a period of time) which give rise to the need for regular array recalibration. Additionally l/f noise introduces an error which increases with the period between calibrations. Compensation for inter-detector variations is particularly important in "staring" applications which measure the absolute radiation intensity within a scene. Scanning imagers measure only changes in intensity across a scene. The output from a staring array is thus of poor contrast in comparison.
Non-imaging thermal detectors are also known in the prior art. They have applications in areas such as robotics and missile guidance systems for which human interpretation of detector output is not required. The actual detecting elements are similar to those described above in relation to imaging systems. In non-imaging systems however an object (robot or missile) is arranged to respond to a particular signal appearing on the detectors. This recognition feature may vary in its complexity. For example, pattern recognition can be linked to a number of response options or a less complex reflex can result in steering towards the achievement of a characteristic detector response. Staring arrays are particularly suitable in satisfying the lightweight requirements of missile systems. However in such missiles the detector system is subject to rapid temperature change as the missile cone heats up during flight. Frequent recalibration is necessary in order to maintain an acceptable accuracy.
An imaging system incorporating a detector array is disclosed by P. N. J. Dennis et al. in Proc. SPIE 572 22 (1985). The authors describe a two dimensional close packed array of cadmium mercury telluride detectors interfaced to a silicon charge coupled device (CCD). Infrared light incident on a detector elicits a response signal which is injected into the CCD and integrated over a period of time (the stare time). The subsequent signal processing system addresses the fundamental problems of poor contrast from the infrared scene and nonuniformity of detector element responses. The nonuniformity correction is made by exposing the array to two uniform scenes of different temperature with an arrangement of mirrors used to introduce them into the optical path. From measurements of stimulus infrared flux and detector response a correction factor is derived for each individual detector by forcing a uniform scene to give rise to a uniform image. The signal response is fitted linearly to incident radiation intensity and an offset and gradient derived to describe the transfer function for each detector in the array. All values of signal respo

REFERENCES:
patent: 4789788 (1988-12-01), Cox
patent: 4948964 (1990-08-01), Gohlke
patent: 5023459 (1991-06-01), Osborn et al.
patent: 5302824 (1994-04-01), Prager
patent: 5343040 (1994-08-01), Wiese et al.
patent: 5354987 (1994-10-01), MacPherson
patent: 5420421 (1995-05-01), Lindgren et al.
patent: 5820261 (1998-10-01), Yam
Bolgov et al., "IR Sources with Barrier-Free Injection Mechanism", Optoelectronics, Instrumentation and Data Processing, No. 4, 1989, pp. 92-95.
Dmitriev et al., "Dynamic Infrared Scene Simulators", Journal of Optical Technology, vol. 61, No. 10, Oct. 1994, pp. 711-719.

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