Transmission quantification of open path FTIR spectra with temperature compensation
First Claim
1. A method for determining, using a computing device, an actual concentration of a gas in a path, the method comprising the steps of:
- coupling an output from a spectrometer to the computing device;
storing on the computing device, reference transmittance data for at least one concentration of the gas and a sample input signal corresponding to an analytical spectrum (IA) of light that has propagated along the path, the analytical spectrum corresponding to light absorbed along the path;
dividing, using the computing device, the analytical spectrum by the reference transmittance data to determine a plurality of residual spectra, including a residual spectrum for each concentration in the reference transmittance data;
separating, using the computing device, each of the residual spectra into absorbing and non-absorbing residual portions; and
identifying, out of the plurality of residual spectra, a residual spectra with a minimum difference between absorbing and non-absorbing portions; and
determining, from the residual spectra with the minimum difference and without a background spectrum I0, the actual concentration of the gas in the path.
2 Assignments
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Accused Products
Abstract
A transmission quantification approach that is effective at quantifying the concentration of key atmospheric gases, including water vapor and methane, does not require a background spectrum and is immune to changes between background and absorbance spectra. By using local minima and maxima in transmission of a target gas, this approach creates two spectral arrays as long as a single beam input spectra. One of these spectral arrays represents the points in wave-number space that are less absorbing points, and the other represents the more absorbing points. A concentration for a given gas is calculated by determining what reference concentration creates a residual after division by a pure gas spectrum that forces these two arrays to converge.
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Citations
24 Claims
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1. A method for determining, using a computing device, an actual concentration of a gas in a path, the method comprising the steps of:
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coupling an output from a spectrometer to the computing device; storing on the computing device, reference transmittance data for at least one concentration of the gas and a sample input signal corresponding to an analytical spectrum (IA) of light that has propagated along the path, the analytical spectrum corresponding to light absorbed along the path; dividing, using the computing device, the analytical spectrum by the reference transmittance data to determine a plurality of residual spectra, including a residual spectrum for each concentration in the reference transmittance data; separating, using the computing device, each of the residual spectra into absorbing and non-absorbing residual portions; and identifying, out of the plurality of residual spectra, a residual spectra with a minimum difference between absorbing and non-absorbing portions; and determining, from the residual spectra with the minimum difference and without a background spectrum I0, the actual concentration of the gas in the path. - View Dependent Claims (2, 3)
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4. A method for determining an actual concentration of a gas in a path, the method comprising the steps of:
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providing, using a spectrometer, an optically derived analytical spectrum (IA) for the path, and transmittance reference data for the gas, wherein the transmittance data comprises a plurality of transmittance spectrum for each of a corresponding plurality of different concentrations of the gas, and wherein the analytical spectrum corresponds to light absorbed along the path; dividing the analytical spectrum by the transmittance spectrum for each of the plurality of different concentrations of the gas, to determine residual spectra for the different concentrations of the gas; using mask functions derived from the transmittance reference data, separating each of the residual spectra into absorbing and non-absorbing residual portions; smoothing the absorbing and non-absorbing residual portions to produce smoothed absorbing and non-absorbing residual portions; and determining an actual concentration of the gas in the path without a background spectrum I0 by identifying the concentration of the gas for which a difference between the smoothed absorbing and non-absorbing residual portions is a minimum compared to differences between the smoothed absorbing and non-absorbing residual portions for other concentrations of the gas. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A non-transitory computer readable medium encoded with a computer program containing instructions stored therein for causing a computer processor to perform a plurality of functions to determine an actual concentration of a gas in an path using an optically derived analytical spectrum (IA) for the path, and using transmittance reference data for the gas, wherein the transmittance data comprise a plurality of transmittance spectrum for each of a corresponding plurality of different concentrations of the gas, and wherein the analytical spectrum corresponds to light absorbed along the path, said plurality of functions including:
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coupling with an output from a spectrometer to the computing device; dividing the analytical spectrum by the transmittance spectrum for each of the plurality of different concentrations of the gas, to determine residual spectra for the different concentrations of the gas; using mask functions derived from the transmittance reference data, separating each of the residual spectra into absorbing and non-absorbing residual portions; smoothing the absorbing and non-absorbing residual portions to produce smoothed absorbing and non-absorbing residual portions; and determining an actual concentration of the gas in the path without a background spectrum I0 by identifying the concentration of the gas for which a difference between the smoothed absorbing and non-absorbing residual portions is a minimum compared to differences between the smoothed absorbing and non-absorbing residual portions for other concentrations of the gas.
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15. A system for determining an actual concentration of a gas in a path using an optically derived analytical spectrum (IA) for the path, and using transmittance reference data for the gas, wherein the transmittance data comprise a plurality of transmittance spectrum for each of a corresponding plurality of different concentrations of the gas, and wherein the analytical spectrum corresponds to light absorbed along the path, the system comprising:
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a memory in which are stored the transmittance data, and a plurality of machine executable instructions; an input port coupled to a spectrometer output to receive an input signal corresponding to the analytical spectrum; and a processor that is coupled to the memory and the input port, the processor executing the machine executable instructions to carry out a plurality of functions, including; dividing the analytical spectrum by the transmittance spectrum for each of the plurality of different concentrations of the gas, to determine residual spectra for the different concentrations of the gas; using mask functions derived from the transmittance reference data, separating each of the residual spectra into absorbing and non-absorbing residual portions; smoothing the absorbing and non-absorbing residual portions to produce smoothed absorbing and non-absorbing residual portions; and determining an actual concentration of the gas in the path without a background spectrum I0 by identifying the concentration of the gas for which a difference between the smoothed absorbing and non-absorbing residual portions is a minimum compared to differences between the smoothed absorbing and non-absorbing residual portions for other concentrations of the gas. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification