Data processing: measuring – calibrating – or testing – Calibration or correction system – Error due to component compatibility
Patent
1997-08-11
2000-08-22
Assouad, Patrick
Data processing: measuring, calibrating, or testing
Calibration or correction system
Error due to component compatibility
702104, 702191, 2503381, 382275, G01J 506
Patent
active
061086118
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to apparatus for, and a method of, processing a signal received from an array of elements of a detector, and is particularly applicable to intra-red linear and two dimensional staring arrays and, especially, uncooled staring array sensors.
BACKGROUND OF THE INVENTION
Modem infrared sensors utilise a large number of detector elements to detect radiation and produce an electronic signal from which a thermal image or other information can be obtained. A major problem associated with such multi-element systems is that every element in the detector array has a unique response and offset associated with it, and these must be normalised to some common level for further processing or image display to be performed. Frequently, the response can vary by over 50%, and the offset by several thousand equivalent degrees centigrade, from element to element. In addition, some higher order, non-linear variations between elements are frequently present. The non-uniformity correction processing circuit must be able to cope with these large ranges of transfer without introducing additional noise or distortion into the signal.
Several approaches to correcting detector non-uniformity have been developed over the years. The most obvious approach, frequently used with cooled detector technology such as CMT and InSb materials, has been to digitise the detector output directly to a high resolution, typically 12 to 14 bits. The digital data corresponding to each element is then added to a corresponding offset coefficient and multiplied by a corresponding response coefficient to produce the normalised signal for each element in the array. This can then be further processed for overall offset and gain to produce the thermal image or other signal processing.
One technique developed for uncooled detectors utilises the fact that many such detectors respond only to changes in scene temperature, and therefore the radiation incident on the detector must be interrupted, "chopped", to induce a signal from the detector. Even those detectors which do not require modulation to produce a signal can benefit from employing interruption means, chopper, which provides regular stable referencing for the system. In such systems the signal from each detector can be derived by subtracting the output of each element when viewing the chopper, or reference, from the output produced when viewing the scene. This "image difference processing" (IDP) results in the direct cancellation of individual offset variations between elements, requiring only the correction of response variations from element to element to give a normalised result. Using this IDP process, the period of time when the detector views the chopper or reference is generally known as the "closed" field, while the period of time when the detector views the scene is known as the "open" field. Under normal circumstances, open and closed fields operate sequentially, however in some systems it may only be necessary to view the chopper or scene occasionally, permitting several open fields to occur between successive closed fields or vice versa. The unchopped system is merely the extreme case where many open fields exist and relatively few--perhaps only one during the life of the system--closed fields occur.
Unfortunately, most applications for uncooled detector systems involve man portable operation, where mass and power consumption are at a premium. In addition, uncooled detectors are generally lower cost than their cooled counterparts, and thus the cost of the support electronics represents a higher proportion of the system costs. For these reasons, the direct quantisation of the output from uncooled detectors is generally avoided, since analogue to digital converters with sufficient resolution and bandwidth to do this are both power hungry and expensive. High power consumption also results in increased system mass, due to the increased battery power required, and a consequential increase in operating costs.
Several novel processing architecture
REFERENCES:
patent: 4628352 (1986-12-01), Boue
patent: 4821108 (1989-04-01), Barbagelata et al.
patent: 5528035 (1996-06-01), Masarik et al.
patent: 5591973 (1997-01-01), Masarik et al.
patent: 5631466 (1997-05-01), Botti et al.
patent: 5682035 (1997-10-01), Gallagher et al.
patent: 5693940 (1997-12-01), Botti et al.
patent: 5729016 (1998-03-01), Klapper et al.
patent: 5763882 (1998-06-01), Klapper et al.
Assouad Patrick
Frank Robert J.
Gec Maconi Limited
Kinberg Robert
LandOfFree
Signal processing of an array of sensor elements in a detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal processing of an array of sensor elements in a detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal processing of an array of sensor elements in a detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-592731