Radiometry using an uncooled microbolometer detector
AssigneeOpgal Ltd.
InventorErnest Grimberg
Life of this patent
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Abstract
An infra-red imaging camera comprises focusing optics for gathering infra-red energy from an external scene, and an uncooled and unshielded detector arranged to detect infra red energy. Internal temperature sensing together with approximation of the temperature response of the camera provides a time varying calibration that allows the infra-red energy received at the detector to be used as a temperature measurement for objects in the camera's field of view.
Claims18
An infra-red imaging camera comprising:
- an uncooled and unshielded detector comprising an array of infra-red (IR) sensors arranged to detect infra red radiated energy, said array comprising a plurality of IR sensors,
- a non-uniformity corrector, associated with said detector, operable to perform non-uniformity correction on outputs of said array to provide uniform outputs having a uniform response to energy detected at said uncooled sensor,
- a calibrator to carry out periodic calibration operations by taking at least one calibration temperature measurement of a temperature of a shutter of said camera while said shutter is closed, using a first temperature sensor located on said shutter, and to derive a reference temperature from said at least one calibration temperature measurement, said reference temperature being a temperature indicative of radiated energy not from an external scene, and a reference level comprising an average video signal of said IR sensors at the time of said calibration temperature measurement, said average being taken over said plurality of IR sensors, and to calculate a temperature of objects in said camera's field of view for each of said plurality of IR sensors from a difference between a respective uniform output of said sensor and said reference level, said temperature being calculated using a same signal to temperature function for each of said sensors, wherein said reference temperature is an offset of said function, and
- focusing optics configured for gathering infra-red energy from an external scene, said focusing optics being entirely located to define an optical unit;
- wherein said shutter is positioned between said optical unit and said detector.
Temperature correction apparatus, for correcting a response of a radiometer in accordance with a local camera temperature, said radiometer comprising:
- an unshielded uncooled infra-red (IR) detector comprising an array of IR sensors, said array comprising a plurality of IR sensors, configured for providing an image response in order to form a temperature image in accordance with IR radiation impinging on said IR detector's field of view (FOV),
- focusing optics configured for gathering infra-red energy from an external scene, said focusing optics being entirely located to define an optical unit;
- a shutter, configured for controllably obscuring said FOV, an internal face of said shutter forming a measurement surface for an internal temperature reference unit, wherein said shutter is positioned between said optical unit and said detector;
- a non-uniformity corrector, associated with said detector, operable to perform non-uniformity correction on outputs of said array to provide uniform outputs having a uniform response to energy detected at said uncooled sensor,
- said temperature correction apparatus comprising:
- a temperature sensor configured for determining a local camera temperature while said shutter is closed using said measurement surface,
- a referencer, configured for deriving a reference temperature from said local camera temperature, said reference temperature being a temperature indicative of radiated energy not from an external scene, and for using a response of said IR sensor to said local camera temperature to approximate a temporal effect of temperature drift of said local temperature;
- and
- a signal corrector associated with said temperature sensor and said referencer, said signal corrector being configured to discount impinging IR radiation not from an external source by calculating a temperature of objects in said radiometer's field of view for each of said plurality of IR sensors from a difference between a respective uniform output of said sensor and a reference level comprising an average video signal of said IR sensors at the time of said local camera temperature measurement, said average being taken over said plurality of IR sensors, said temperature being calculated using a same signal to temperature function for each of said uniform outputs, wherein said reference temperature is an offset of said function.
A method for correcting a response of an uncooled and unshielded a radiometer in accordance with a calibration temperature measurement, said radiometer comprising focusing optics for gathering infra-red energy from an external scene, said focusing optics being entirely located to define an optical unit, an array of infra-red (IR) sensors, for providing an image response in order to form a temperature image in accordance with IR radiation impinging on said IR sensor's field of view (FOV), said array comprising a plurality of IR sensors, and a shutter, for controllably obscuring said FOV, wherein said shutter is positioned between said optical unit and said radiometer, said method comprising:
- performing, while said FOV is obscured by said shutter, a calibration temperature measurement to determine a temperature of said shutter;
- performing non-uniformity correction (NUC) on outputs of said array to provide uniform outputs having a uniform response to energy detected at said uncooled sensor;
- deriving from said temperature of said shutter a first reference temperature, said first reference temperature being a temperature reflecting impinging IR radiation not from an external source;
- determining a reference level comprising an average video signal, said average being taken over said plurality of IR sensors at the time of said calibration temperature measurement;
- and
- calculating a temperature of objects in said radiometer's field of view for each of said sensors from a difference between a respective uniform output of said sensor and said reference level, said temperature being calculated using a same signal to temperature function for each of said uniform outputs, wherein said first reference temperature is an offset of said function.
Dependencies are inferred from the claim text.