Remote emissions sensing system and method incorporating spectral matching by data interpolation
First Claim
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1. A system for remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within a wavelength absorption band, the system comprising:
- a spectrometer that comprises a sensor made up of an array of sensor pixels, wherein the spectrometer receives electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within a wavelength absorption band of a gas present in an exhaust plume of a passing vehicle, the spectrometer spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on the sensor, and wherein each sensor pixel generates an output signal based on an intensity of a portion the electromagnetic radiation that is incident thereon;
a storage module that stores a scale that associates each sensor pixel with a wavelength range, wherein the wavelength range associated with each sensor pixel is a prediction of the wavelength range of the spectrum of electromagnetic radiation that will be incident on that particular sensor pixel; and
a scale module that (i) that determines an offset amount of wavelength drift in the spectrometer based on spectral data derived from the output signals generated by the sensor pixels while an exhaust plume of a passing vehicle is in the optical path, and (ii) adjusts for the determined wavelength drift by shifting the scale by the offset amount, wherein the offset amount includes a fractional pixel offset amount.
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Abstract
A system and method for correcting for “wavelength drift” in an RES system. One advantage provided by the invention includes the ability to correct for offset amounts of “wavelength drift” that are not divisible by an integer number of pixels (e.g., fraction pixel offset amounts) in an optical detector used in the RES system. Correction of fractional pixel offset amounts may enhance spectral matching, enable substantially continuous calibration of an RES system, and/or other benefits.
66 Citations
19 Claims
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1. A system for remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within a wavelength absorption band, the system comprising:
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a spectrometer that comprises a sensor made up of an array of sensor pixels, wherein the spectrometer receives electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within a wavelength absorption band of a gas present in an exhaust plume of a passing vehicle, the spectrometer spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on the sensor, and wherein each sensor pixel generates an output signal based on an intensity of a portion the electromagnetic radiation that is incident thereon; a storage module that stores a scale that associates each sensor pixel with a wavelength range, wherein the wavelength range associated with each sensor pixel is a prediction of the wavelength range of the spectrum of electromagnetic radiation that will be incident on that particular sensor pixel; and a scale module that (i) that determines an offset amount of wavelength drift in the spectrometer based on spectral data derived from the output signals generated by the sensor pixels while an exhaust plume of a passing vehicle is in the optical path, and (ii) adjusts for the determined wavelength drift by shifting the scale by the offset amount, wherein the offset amount includes a fractional pixel offset amount. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within a wavelength absorption band, the method comprising:
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receiving electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within a wavelength absorption band of a gas present in an exhaust plume of a passing vehicle; spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on an array of sensor pixels, wherein each sensor pixel generates an output signal based on an intensity of a portion of the electromagnetic radiation that is incident thereon; storing a scale that associates each sensor pixel with a wavelength range, wherein the wavelength range associated with each sensor pixel is a prediction of the wavelength range of the spectrum of electromagnetic radiation that will be incident on that particular sensor pixel; determining an offset amount of wavelength drift based on spectral data derived from the output signals generated by the sensor pixels while an exhaust plume of a passing vehicle is in the optical path; and adjusting for wavelength drift of the offset amount by shifting the scale by the offset amount, wherein the offset amount includes a fractional pixel offset amount. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A system for remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within a wavelength absorption band, the system comprising:
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a spectrometer that comprises a sensor made up of an array of sensor pixels, wherein the spectrometer receives electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within a wavelength absorption band of a gas present in an exhaust plume of a passing vehicle, the spectrometer spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on the sensor, and wherein each sensor pixel generates an output signal based on an intensity of a portion of the electromagnetic radiation that is incident thereon; a storage module that stores a plurality of scales and a plurality of sets of reference values that correspond to the scales, wherein each scale associates the sensor pixels with predetermined wavelength ranges, the wavelength range associated with each sensor pixel by a given scale being a prediction of the wavelength range of the spectrum of electromagnetic radiation that will be incident on that particular sensor pixel for the given scale, and wherein each set of reference values are related to expected values of the output signals generated by the sensor pixels while the exhaust plume of the passing vehicle is present in the optical path, based on the wavelength ranges associated with the sensor pixels by a scale that corresponds to that particular set of reference values; a shift module that compares the sets of reference values with a set of signal values of the output signals that are generated by the sensor pixels while the exhaust plume of the passing vehicle is present in the optical path in order to determine which set of reference values most closely correlates with the signal values that are generated while the exhaust plume of the passing vehicle is present in the optical path; and an adjustment module that adjusts a current scale to substantially match the scale that corresponds to the set of reference values that most closely correlates with the signal values that are generated while the exhaust plume of the passing vehicle is present in the optical path, wherein the current scale is presently implemented in determining the concentration of the gas based on the output signals. - View Dependent Claims (16)
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17. A system for remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within a wavelength absorption band, the system comprising:
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a spectrometer that comprises a sensor made up of an array of sensor pixels, wherein the spectrometer receives electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within a wavelength absorption band of a gas present in an exhaust plume of a passing vehicle, the spectrometer spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on the sensor, and wherein each sensor pixel generates an output signal based on an intensity of a portion the electromagnetic radiation that is incident thereon; and a processor that calibrates the system based on the output signals generated by the sensor pixels while the exhaust plume of the passing vehicle is present in the optical path, wherein the calibration of the system corrects for wavelength drift in the spectrometer.
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18. A system for remotely sensing a concentration of a gas in an exhaust plume emitted by a vehicle, wherein the gas absorbs electromagnetic radiation with a wavelength that falls within one or more wavelength absorption bands, the system comprising:
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a spectrometer that comprises a sensor made up of an array of sensor pixels, wherein the spectrometer receives electromagnetic radiation that has traveled along an optical path, the electromagnetic radiation including electromagnetic radiation with a wavelength that falls within one or more wavelength absorption bands of a gas present in an exhaust plume of a passing vehicle, the spectrometer spatially arranging the electromagnetic radiation by wavelength into a spectrum that is incident on the sensor, and wherein each sensor pixel generates an output signal based on an intensity of a portion the electromagnetic radiation that is incident thereon; and a processor that performs a peak-match between one or more output signals generated by sensor pixels that receive a portion of the spectrum created by the spectrometer while the exhaust plume of the passing vehicle is in the optical path and one or more sets of reference spectral data to determine a wavelength drift offset of the spectrometer, wherein the processor further determines the concentration of the gas in the exhaust plume of the passing vehicle based on the one or more output signals generated by the sensor pixels that receive a portion of the spectrum created by the spectrometer while the exhaust plume of the passing vehicle is in the optical path, and wherein the determination of the concentration of the gas made by the processor is corrected for the wavelength drift offset determined by the processor. - View Dependent Claims (19)
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Specification