WO2023037269A1

WO2023037269A1 - Spectrometer and method for detecting volatile organic compounds

Info

Publication number: WO2023037269A1
Application number: PCT/IB2022/058430
Authority: WO
Inventors: Bernard P. Masterson; Andrew D. Sappey
Original assignee: Onpoint Technologies, Llc
Priority date: 2021-09-08
Filing date: 2022-09-07
Publication date: 2023-03-16

Abstract

A spectrometer is described that is configured to gather an air mass, such as one proximate to a vehicle, a broadband light source configured to emit a probe beam through the air mass, a photodetector, and beam-steering optics that at least in part define a monitored optical path and direct the probe beam along the monitored optical path to the uncooled photodetector. Processing circuitry may determine a presence of or a relative concentration of volatile organic compounds (VOCs) in the air mass based on an output of the photodetector.

Description

SPECTROMETER AND METHOD FOR DETECTING VOLATILE ORGANIC COMPOUNDS CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No.63/241,552, filed September 8, 2021, entitled “SPECTROMETER AND METHOD FOR DETECTING VOLATILE ORGANIC COMPOUNDS,” the contents of which being incorporated by reference in their entirety herein. BACKGROUND [0002] Pipelines are primary means of transport for crude oil, refined petroleum, and natural gas liquids. As each of these commodities includes volatile organic compounds (VOCs), safe and non-polluting operation of the pipelines requires continuous and accurate monitoring of pipelines for leaks. Pipeline leaks are generally “detected” by comparing output volume to a known input volume between two monitored locations along the pipeline. While this method is simple, it has low sensitivity and does not indicate the position of the leak in between the monitored points. BRIEF SUMMARY [0003] Embodiments disclosed herein include a spectrometer and a spectrometry method for monitoring VOC leaks from pipelines and other assets using a simple, light- weight, and low power spectrometer sensitive to hydrocarbons that absorb mid-infrared (MIR) light from 2800 – 3300 cm^-1 (3.57 microns – 3.03 microns). The spectrometer may be mounted onto a land-based or airborne vehicle that traverses predetermined routes over or adjacent to pipelines or other assets to detect and locate VOC leaks, and estimate the size of the leak, by “sniffing” the air for hydrocarbon vapor. [0004] Instead of detecting certain individual species of hydrocarbon molecules, embodiments disclosed herein detect them as a class of compounds by focusing on broadband mid-infrared (MIR) absorption at wavelengths equal to or approximately 3.3 microns, which is characteristic of various hydrocarbons, such as methane among others. [0005] In a first aspect, a spectrometer includes broadband light source that emits a probe beam, an uncooled photodetector, and beam-steering optics. The beam-steering optics at least in part define a monitored optical path and direct the probe beam along the monitored optical path and to the uncooled photodetector. [0006] In a second aspect, a method for detecting volatile organic compounds includes directing a probe beam along a monitored optical path to yield a transmitted beam, and detecting the transmitted beam, or a beam derived therefrom, with an uncooled photodetector. BRIEF DESCRIPTION OF THE DRAWINGS [0007] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. [0008] FIG. 1 is a schematic diagram of a vehicle-mounted spectrometer detecting volatile organic compounds emitted by a pipeline according to various embodiments of the present disclosure. [0009] FIG.2 is a schematic diagram of a spectrometer for detecting volatile organic compounds emitted by a pipeline according to various embodiments of the present disclosure. [0010] FIG. 3 is a flowchart illustrating a method for detecting volatile organic compounds according to various embodiments of the present disclosure. [0011] FIG. 4 is another schematic diagram of a spectrometer for detecting volatile organic compounds emitted by a pipeline according to various embodiments of the present disclosure. DETAILED DESCRIPTION [0012] The present disclosure relates to a spectrometer and method for detecting volatile organic compounds (VOCs) or other hydrocarbons. As noted above, safe and non- polluting operation of the pipelines requires continuous and accurate monitoring of pipelines for leaks. Generally, it is not feasible to have personnel continuously travel along a pipeline or other collection site and perform various tests to determine a presence of a leak. As such, it can be ideal to have unmanned aerial vehicles, land vehicles, and the like autonomously detect the presence of VOC leaks. [0013] According to various embodiments described herein, a vehicle and a spectrometer thereof are disclosed for monitoring VOC leaks from pipelines and other areas using a simple, light-weight, and low power spectrometer sensitive to hydrocarbons that absorb mid-infrared (MIR) light having a wavelength from 2800 – 3300 cm^-1 (3.57 microns – 3.03 microns). The spectrometer may be mounted onto a land-based or airborne vehicle that traverses predetermined routes over or adjacent to pipelines or other assets to detect and locate VOC leaks, and estimate the size of the leak, by “sniffing” the air for hydrocarbon vapor. [0014] Instead of detecting certain individual species of hydrocarbon molecules, embodiments disclosed herein detect them as a class of compounds by focusing on broadband MIR absorption at wavelengths equal or close to 3.3 microns, which is characteristic of various hydrocarbons, such as methane among others. In various aspects, a spectrometer may include a broadband light source that emits a probe beam, an uncooled photodetector, and beam-steering optics. The beam-steering optics at least in part define a monitored optical path and direct the probe beam along the monitored optical path and to the uncooled photodetector. In further aspects, a method for detecting volatile organic compounds includes directing a probe beam along a monitored optical path to yield a transmitted beam, and detecting the transmitted beam, or a beam derived therefrom, with an uncooled photodetector. [0015] Turning now to the drawings, FIG.1 is a schematic of a vehicle 100 according to various embodiments. The vehicle 100 may include an unmanned aerial vehicle (UAV), a manned aerial vehicle, an unmanned ground vehicle, a manned ground vehicle, and so forth. Examples of aerial vehicles include copters, airplane-style drones, dirigibles, and so forth. Examples of ground vehicles include vehicles having wheels and tires, vehicles having tank treads, biological robots (e.g., dog-like robots, humanoid robots, and the like having legs), etc. Additionally, water-based robots, such as watercrafts, swimming robots emulating movement of fish, snakes, and the like may be employed. According to various embodiments, the vehicle 100 may include a spectrometer 105 for detecting volatile organic compounds 110 emitted by a pipeline 115 or other area, where the pipeline 115 may carry hydrocarbons 120 for example. [0016] According to various embodiments, the vehicle 100 may navigate into an area relative to a pipeline 115 (or other area to be sampled). The spectrometer 105 may be positioned on a front of the vehicle 100 to collect a mass of air, such as a mass of air positioned close or otherwise relative to the pipeline 115. The spectrometer 105 includes an elongated tubular-shaped housing in some embodiments having one or more apertures that are communicated to an interior cavity of the housing. When the vehicle 100 moves in a frontward direction, the mass of air or other atmosphere positioned relative to the vehicle will travel through the apertures as an input into an interior of the spectrometer 105 for analysis. Such analysis may be performed to identify a presence of hydrocarbons 120 and, in some specific implementations, methane. Upon the detection of methane or other hydrocarbon 120, the vehicle 100 may enter into a geolocation travel routine to further identify a source of the hydrocarbon 120 and/or an area in which a highest relative concentration of the hydrocarbon 120 is detected. [0017] In various embodiments, the spectrometer 105 and/or the housing thereof extends laterally beyond a front edge of the vehicle 100. By doing so, air generated by propellers or other mechanisms of the vehicle does not disturb or impair a flow of the mass of air to be collected by the spectrometer 105. [0018] Turning now to FIG.2, a schematic diagram of the spectrometer 105 is shown according to various embodiments. Generally, the spectrometer 105 may include a broadband light source 125, beam-steering optics 130, and a photodetector 135 among other components, as will be described. The photodetector 135 may include an uncooled photodetector in some embodiments. The broadband light source 125 may emit a probe beam 140 that propagates along a total optical path 145a...145c between the broadband light source 125 and the photodetector 135. Specifically, the total optical path 145 includes a source-side optical path 145a, a detector-side optical path 145c, and a monitored optical path 145b positioned therebetween. [0019] The monitored optical path 145b may be at least in part defined by the beam- steering optics 130. For instance, the beam-steering optics 130 may direct the probe beam 140 to the photodetector 135 via optical paths 145b and 145c. In various embodiments, a length of the optical path 140b is between 0.4 meters and two meters, although other dimensions may be employed. The source-side optical path 140a may be positioned between the broadband light source 125 and the beam-steering optics 130. The detector- side optical path 145c may be positioned between the beam-steering optics 130 and the photodetector 135. [0020] As the probe beam 140 propagates along the optical paths 145a, 145b, and 145c, absorptive species, such as hydrocarbon VOCs, that are present in a mass of air collected by the spectrometer 105 absorb parts of probe beam 140, thereby altering spectral content of the probe beam 140 and yielding a transmitted beam 148. The photodetector 135, such as an uncooled photodetector, may thus detect the transmitted beam 148. Based on measurements of the transmitted beam 148 a presence, a lack of, and/or a relative concentration of hydrocarbons 120 may be identified. [0021] It is understood that ideal optics would require a spectrometer 100 one meter or more in length. This may make it difficult to mount the spectrometer 100 on a mobile vehicle 100, and make traversing air and terrain difficult. Accordingly, in various embodiments, the optics may be optimized to provide a smaller footprint of a spectrometer 100. In the example of FIG. 2, the beam-steering optics 130 may include five beam- steering optics units 155a...155d (collectively “beam-steering optics units 155”) arranged such that monitored optical path 145b is a W-shaped section and four passes through a volume traversed by the probe beam 140. The beam-steering optics 155 may create a spectrometer 100 having smaller dimensions and a reduced footprint. A distance between adjacent beam-steering optics 130, such as beam-steering optics 155a and 155b, may be between ten centimeters and twenty centimeters for adequate sampling of the target volume for leaking VOCs, although other dimensions may be employed. The beam- steering optics 130 may be configured to yield different geometries of the monitored optical path 145b, including more than or fewer than five beam-steering optics (and associated passes), and be nonlinear. Accordingly, while FIG.2 shows five beam-steering optics units 155, it is understood that other numbers of beam-steering optics units 155 may be employed. [0022] In order to optimize the beam-steering optics 130 and provide a spectrometer 150 with heightened sensitivity to detect a class of hydrocarbons or VOCs (or specific hydrocarbons or VOCs), the beam-steering optics 130 may be positioned in a cavity of the spectrometer 105 having a width of approximately 1.0 m to 1.5 m, which is impractical for use in vehicle applications. As such, in various embodiments, the cavity of the spectrometer 105 in which the beam-steering optics 130 resides may be 25 cm wide where the probe beam 140 is passed through multiple times (e.g., four times or other suitable number of times). [0023] The beam-steering optics 130 may include reflective optical elements such as mirrors, refractive optical elements, and diffractive optical elements, among others. Refractive optical elements may include prisms and the like, whereas diffractive optical elements may include diffraction gratings and so forth. In various embodiments, each beam-steering optic 130 may be achromatic (e.g., having a constant reflectivity and/or refractive index) across the emission spectrum of the broadband light source 125 to minimize wavelength-dependent properties of the beam-steering optics 130 on the spectral content of the probe beam 140. In various embodiments, at least one of the beam-steering optics 130 may be a metal mirror having a relatively high reflectivity at VOC absorption wavelengths, e.g., between 3.0 microns and 3.5 microns. Examples of such metal mirrors include silver mirrors, gold mirrors, aluminum mirrors, and dielectric-coated versions thereof. [0024] In various embodiments, the broadband light source 125 is one of a light- emitting diode (LED), a broadband lamp, a superluminescent diode, and an amplified spontaneous emission light source. It is understood that LED implementations may considerably reduce resource usage of the vehicle 100 increasing flight or ground travel time by utilizing less resources of a battery or other power source. In any event, light from the broadband light source 125 may have an emission spectrum 161 with peak intensity in wavelengths between 3.1 microns and 3.4 microns, for example, as this range includes absorption bands of hydrocarbon VOCs. The emission spectrum 161 may have a spectral width 164, where the spectral width 164 may be at least 540 nm (0.54 microns) wide, which is advantageous for simultaneous detection of a large number VOCs species. The spectral width 164 may be a full-width half-max width. [0025] Further, in some embodiments, the spectrometer 105 may include a beam collimator 167 that collimates the probe beam 140, for instance, before the probe beam 140 reaches the beam-steering optics 130. The beam collimator 167 may include at least one of a lens and a curved mirror in some embodiments. [0026] In various embodiments, the photodetector 135 may be preselected such that it is sensitive to MIR wavelengths absorbed by hydrocarbon VOCs, which are between 3.0 microns and 3.6 microns in wavelength. To this end, the photodetector 135 may include a one of an indium arsenide antimonide (InAsSb) photodiode, an indium arsenide (InAs) photodiode, and the like. An advantage of the photodetector 135 includes dramatically reducing power consumption and weight compared to cooled photodetectors, which may include a thermoelectric cooler and/or a dewar cooler assembly. This may increase energy efficiency and utilize less power resources (e.g., battery and fuel). As such, a flight time of an UAV or use time of a ground-based vehicle may be further increased. Thus, in various embodiments, the spectrometer 105 does not include at least one of a thermoelectric cooler and a dewar cooler assembly. [0027] Further, in some embodiments, the spectrometer 105 includes a bandpass filter 170 that intersects the total optical path 145, for example, along the detector-side optical path 145c, as shown in FIG. 2. In such embodiments, the transmitted beam 148 is the probe beam 140 after both propagation along monitored optical path 145b and through the bandpass filter 170. [0028] In various embodiments, the bandpass filter 170 may have a passband that spans wavelengths between wavelengths λ_min and λ_max, inclusive, a lower stop band at infrared wavelengths less than λ_min, and an upper stop band at infrared wavelengths exceeding λ_max. The center wavelength of the passband may be between λ_min and λ_max. In some embodiments, λ_min and λ_max, are such that the passband corresponds to the vibrational mode hydrocarbon C-H stretching motion. This vibrational mode occurs at substantially different wavelengths based on whether the leaking hydrocarbon is aromatic (e.g., benzene) or aliphatic (e.g., octane). The absorption for a hydrocarbon ranges from about 3.03 microns to 3.57 microns. The absorption for various blends of gasoline, for example, would fall within this range. [0029] Correspondingly, the bandpass filter 170 may have a passband that spans this range, which nearly transmits light throughout the entire C-H stretch region of all hydrocarbons and blocks light outside of this spectral region. Thus, any light transmitted through bandpass filter 170 is differentially absorbed by the leaking hydrocarbons. [0030] In various embodiments, λ_min may be between 3.0 microns and 3.3 microns inclusive, and λ_max may be between 3.5 microns and 3.7 microns inclusive. In certain embodiments, λ_min = 3.03 microns and λ_max = 3.57 microns inclusive, for instance, to determine a presence of hydrocarbons (e.g., hydrocarbons as a class without determine a specific type of hydrocarbon). In other embodiments, λ_min = 3.0 microns and λ_max = 3.65 microns. In some embodiments, the bandpass filter 170 is configured to detect methane on the Q-branch vibrational transitions, which is a specific type of hydrocarbon. In these embodiments, λ_min is greater than or equal to 3.311 microns and λ_max is less than or equal to 3.322 microns. In such embodiments, (λ_max- λ_min) is less than 11 nanometers, for example. [0031] The bandpass filter 170 may have a transmission spectrum that includes passbands that correspond to absorption peaks of a specific class of hydrocarbons, such as aromatic or aliphatic hydrocarbons. Such passbands are, in embodiments, the only passbands of the bandpass filter 170 within the emission spectrum 161. In some embodiments, the bandpass filter 170 includes at least one of the following aliphatic passbands: a passband centered at 3.39 microns, and a passband centered at 3.42 microns. [0032] The spectrometer 105 may also include a focusing element 173 that focuses the transmitted beam 148 onto a photosensitive area of the photodetector 135. The focusing element 173 may include a lens, such as a calcium fluoride lens for example or a condenser lens. The focusing element 173 may intersect the optical path 145c at a distance 176 from the photodetector 135 along optical path 145c. The distance 176 may differ from a focal length of the focusing element 173 by less than a half of the depth of focus of focusing element 173. In some embodiments, this focal length may be between ten millimeters and twenty-five millimeters. Positioning the focusing element 173 in the detector-side optical path 145c increases an upper length limit of monitored optical path 145b, which allows for higher absorption and hence more accurate spectroscopic measurements. [0033] In various embodiments, at least one of the spectrometer 105 and the vehicle 100 includes electronics 200. The electronics 200 may be employed to increase the sensitivity of the spectrometer 105 or otherwise control operation of the spectrometer 105. In various embodiments, the electronics 200 includes a function generator 203, driver circuitry 206, and a lock-in amplifier 209. The driver circuitry 206 may be electrically coupled to the broadband light source 125. In some embodiments, the driver circuitry 206 generates a signal that turns the broadband light source 125 on and off at a predetermined rate (e.g., 1 kHz to 10 kHz). The lock-in amplifier 209 may be electrically coupled, directly or indirectly, to an output port or other output of the photodetector 135. The function generator 203 may generate a waveform signal 212 and may be electrically coupled to both the driver circuitry 206 and the lock-in amplifier 209, which may receive the waveform signal 212. [0034] When the broadband light source 125 is turned on based on the driving signal generated by the driver circuitry 206, and there is no absorption, a first power level is expected as measured at the transmitted beam 148. Similarly, when the broadband light source 125 is turned off based on the driving signal generated by the driver circuitry 206, a second power level is expected as measured at the transmitted beam 148. In lock-in detection, when a VOC or other content in the cell 236 is absorbed, an upper level of the power signal will be attenuated relative to full light. The lower level, however, needs to be constantly sampled to determine the two power levels, namely, 100% light and 100% absorbing, relative to no light. As such, the LED may be driven by detecting a light level when the LED is on and subtracts a light level when the LED is off, which results in a relative signal that is much more sensitive than merely measuring an output of the photodetector 135 with the light always on. [0035] In various embodiments, the driver circuitry 206 may modulate an amplitude of the broadband light source 125 based on the waveform signal 212, and the lock-in amplifier 209 may detect a detector signal 215 output by the photodetector 135, which is synchronously modulated with the probe beam 140. The detector signal 215 may include a current (e.g., measured in milliamps or microamps) in some embodiments. The lock-in amplifier 209 may generate an output that includes a lock-in output signal 218 via lock-in detection of the waveform signal 212 and the detector signal 215, or a signal derived therefrom. Non-limiting examples of lock-in detection include homodyne detection and heterodyne detection. In various embodiments, the fundamental frequency of the waveform signal 212 is between 8 kHz and 12 kHz. Modulating a mid-IR LED at this frequency range has a relatively small effect on a lifetime of the broadband light source 125 (e.g., an LED) compared to other frequencies. [0036] In various embodiments, the spectrometer 105 may include a transimpedance amplifier 221 electrically coupled to the output port of the photodetector 135 and to an input port of the lock-in amplifier 209. The transimpedance amplifier 221 electrically amplifies the detector signal 215 and outputs an amplified signal 224. In some embodiments, the transimpedance amplifier 221 receives the detector signal 215 as a current input that converts the current to a voltage that is electrically amplified and output as the amplified signal 224. In such embodiments, the lock-in amplifier 209 may detect the amplified signal 224, and may output a lock-in output signal 218 via lock-in detection of the amplified signal 224 and the waveform signal 212. [0037] At least one of the spectrometer 105 and the vehicle 100 may also include processing circuitry 230, which may include a data processor in some examples, where the data processor may include at least one hardware processor or an application-specific integrated circuit (ASIC), or the like. In any event, the processing circuitry 230 may receive at least one of the amplified signal 224 or the lock-in output signal 218. In various embodiments, the processing circuitry 230 may determine, from the lock-in output signal 218, a relative concentration of VOCs along monitored optical path 145b, as described in part of with respect to FIG.3. In various embodiments, the processing circuitry 230 may include at least one of data acquisition hardware, at least one hardware processor, and memory, where operation of the processing circuitry 230 may be controlled by program instructions stored in the memory and executable by the at least one hardware processor. [0038] FIG.3 is a flowchart illustrating a non-limiting example of a method 300 for detecting volatile organic compounds using a vehicle 100 and/or a spectrometer 105. The method 300 may be implemented by one or more aspects of the spectrometer 105 and, in some embodiments, the method 300 may be directed by the processing circuitry 230 of at least one of the vehicle 100 and the spectrometer 105. [0039] Beginning with box 305, box 305 includes collecting air mass at a collection site, such as a pipeline 115. To this end, in some embodiments, the processing circuitry 230 may autonomously, or at the direction of a pilot (remote or present), navigate to a pipeline 115 or other desired collection site. The spectrometer 105 in some implementations may be positioned on a front of the vehicle 100. As such, the processing circuitry 230 may direct the vehicle 100 to move in a predetermined direction (e.g., frontward in the example of FIG.1) to force air through apertures of the spectrometer 105, forcing an air mass into a body or a housing of the spectrometer 105. [0040] Next, box 310 includes driving a light source, such as a broadband light source 125, with a driving signal to generate a probe beam 140. As noted above, in some implementations, the probe beam 140 may be amplitude modulated. [0041] Box 320 includes directing a probe beam 140 along an optical path 145 including, but not limited to, monitored optical path 145b, to yield a transmitted beam 148. In an example of box 320, the beam-steering optics 130 may direct the probe beam 140 along the monitored optical path 145b to yield the transmitted beam 148. [0042] Box 330 includes spectrally filtering either the probe beam 140 or the transmitted beam 148 with a bandpass filter 170. In an example of box 330, the bandpass filter 170 spectrally filters one of the probe beam 140 and the transmitted beam 148 [0043] Box 340 includes detecting the transmitted beam 148, or a beam derived therefrom, with a photodetector 135 which may include an uncooled photodetector 135 in various embodiments. In an example of box 340, the photodetector 135 detects the transmitted beam 148. Generally, in mid-infrared sensing, traditional systems use cooled mid-infrared detectors. In cooled mid-infrared detectors, the detectors must be cooled substantially to reduce noise in a circuit and are generally preferred in all applications. It was discovered that a control circuit of a thermoelectric cooler used to cool the cooled detectors creates substantial interference and noise in the circuit impairing the ability to detect VOCs, and requires substantial power. An uncooled photodetector 135, on the other hand, is more appropriate for spectrometers 105 for us on a vehicle 100, such as a UAV. [0044] Box 350 includes determining an absorption coefficient of the monitored optical path 145b from respective intensities of the probe beam 140 and the transmitted beam 148. In an example of box 350, the processing circuitry 230 may determine an absorption coefficient of the monitored optical path 145b from respective intensities of the probe beam 140 and the transmitted beam 148. As noted above, in various embodiments, the processing circuitry 230 may include at least one hardware processor and memory that stores machine-readable instructions that, when executed by the at least one hardware processor, direct the processor to determine the absorption coefficient as well as perform other analyses of the data collected therein. In some embodiments, the processing circuitry 230 may employ the Beer-Lambert law to determine the absorption coefficient. [0045] Next, at box 360, box 360 includes determining an amplitude of the transmitted beam via lock-in detection of a detector signal output by the photodetector 135. In an example of box 360, the lock-in amplifier 209 may generate a lock-in output signal 218 via lock-in detection of the waveform signal 212 and either one of signal 215 and signal 224. As such, the processing circuitry 230 may determine an amplitude of the lock-in output signal 218. [0046] Thereafter, at box 370, box 370 includes adjusting a flight path based on measurements of the spectrometer 105. In one embodiment, the spectrometer 105 may identify a small presence of a VOC and may then perform a localization flight routine by sampling nearby areas to identify a higher presence of the VOC if present. In another embodiment, the spectrometer 105 may identify a high presence of a VOC and may then perform a localization flight routine to confirm that the area associated therewith is a highest relative concentration area by sampling nearby areas to identify a lower presence of the VOC if applicable. If no VOCs are detected by the spectrometer 105, a flight path or flight plan may remain unaltered in various embodiments. In areas in which VOCs are detected, geographical coordinates (e.g., latitude and longitude) may be recorded in memory of the vehicle 100 and/or the spectrometer 105 in association with measurements of the spectrometer 105, which may be communicated remotely to a monitoring station. [0047] Moving along to FIG.4, FIG.4 is another schematic diagram of a spectrometer 105 according to various embodiments. The spectrometer 105 includes a broadband light source 125, an input focusing element 233, a bandpass filter 170, a focusing element 173 (e.g., a lens), a photodetector 135, and a transimpedance amplifier 221. The input focusing element 233 may include an off-axis parabolic mirror, a condenser lens, or the like, and may be an example of a beam-steering optic 130, as may be appreciated. [0048] The spectrometer 105 further includes electronics 200 that includes processing circuitry 230. While being shown as part of the spectrometer 105, in other embodiments, the processing circuitry 230 may be part of the vehicle 100, such as a controller of the vehicle 100. The function generator 203 may generate a waveform signal 212. In some embodiments, the waveform signal 212 may have a one-hundred percent modulation depth at a one-kilohertz frequency. [0049] The broadband light source 125 may emit a probe beam 140 that propagates along an optical path 145. The optical path 145 includes optical paths 145a...145c. In the use scenario of FIG. 4, the input focusing element 233 may direct the probe beam 140 through a spectrometry cell 236 (and the monitored optical path 145b therein), to yield a transmitted beam 148. It is understood that, in some implementations, the vehicle 100 does not include a spectrometry cell 236, instead relying on a housing of the spectrometer 100. The transmitted beam 148 propagates along optical path 145c through bandpass filter 170 and the focusing element 173, which may include a lens, to the photodetector 135, which may include an uncooled photodetector in various embodiments. The length of the spectrometry cell 236 may be, for example, approximately ten centimeters, which may be positioned within a housing of the spectrometer 105, such that the length of the monitored optical path 145b is also approximately ten centimeters. In some embodiments, the focusing element 173 may be a lens formed of CaF₂ and may have a focal length of either 12.5 mm or 25 mm. [0050] The photodetector 135 may output a detector signal 215. The transimpedance amplifier 221 may output an amplified signal 224, which may include a voltage signal. The spectrometry cell 236 may contain volatile organic compounds 110 emitted from a collection area contained by a reservoir of the spectrometry cell 236. [0051] According to various embodiments, the broadband light source 125 may include a MIR 3.3-micron LED (Hamamatsu L15893). The input focusing element 233 may include an off-axis parabolic mirror having a 25-mm focal length, which may collimate and direct the probe beam 140 towards the photodetector 135, which may include a Hamamatsu model P13243-013CA InAsSb photovoltaic photodetector according to various embodiments. The bandpass filter 170 may have a passband centered at 3.05 microns, and thus transmits light throughout the entire C-H stretch region of all hydrocarbons and blocks light outside of this spectral region. The bandpass of this embodiment may be approximately 500 nm full-width-at-half-maximum (FWHM). [0052] The probe beam 140 may be focused onto the photodetector 135 surface by the focusing element 173, which may include a lens. The transimpedance amplifier 221 may convert the detector signal 215 to a voltage signal (e.g., amplified signal 224), which may then be received by the lock-in amplifier 209. The lock-in amplifier 209 may output a lock-in output signal 218 via lock-in detection of waveform signal 212 and detector signal 215. The processing circuitry 230 may determine an amplitude of the lock-in output signal 218, which may correlate to a relative concentration of volatile organic compounds 110 in an air mass. [0053] In embodiments in which the broadband light source 125 is an LED, such as an infrared LED, light may be emitted having a center wavelength from 2 to 4 microns or, for example, 3 microns. As such, a bandpass filter 170 may be selected to filter at a center wavelength of approximately 3.1 microns to 3.4 microns, which may facilitate the detection of specific hydrocarbons or VOCs. For instance, for detection of methane, the bandpass filter 170 may filter spectral features, such as Q-branches of methane, by having a center wavelength of approximately 3.3 microns. It is understood that similar principals may apply for the identification of gasoline, benzene, pylene, xylene, acetylene, acetylene, and/or other hydrocarbons. [0054] In some embodiments, the processing circuitry of the vehicle 103 or the spectrometer 100 may store a time constant for exchange of air masses where the time constant is speed dependent. The time constant may reflect time for exchanges of air volume within the spectrometer 100. The time constant may be determined on openness (e.g., size and position of apertures of the spectrometer 100) of the spectrometer 100. To this end, if the vehicle 103 flies through a methane plume too quickly, the spectrometer 100 might miss detection of the plume simply because not enough gas molecules made it into the sensing region to be detected before exiting the plume. On the other hand, if the vehicle 103 is stationary in a plume, diffusion of VOCs into the cell to provide the sample is relied upon. Eddy Covariance may be employed to calculate a flux of a particular species into a measurement region by measuring and utilizing a vertical wind velocity as well as a concentration. In this case, a horizontal velocity of the vehicle 103 may be employed to calculate a flux. In sum, the processing circuitry of the vehicle 103 and/or spectrometer 100 may determine a presence of a VOC (or lack thereof) as a function of a measurement of a VOC (e.g., a relative concentration), a horizontal velocity of the vehicle 103, an openness of the housing of the spectrometer 100, as well as other factors. The horizontal velocity of the vehicle 103 may be measured by an accelerometer of the vehicle 103, global positioning system (GPS) measurements, and so forth. The features, structures, embodiments, and/or characteristics described above may be combined in one or more embodiments in any suitable manner, and the features discussed in the various embodiments are interchangeable, if possible. In the following description, numerous specific details are provided in order to fully understand the embodiments of the present disclosure. However, a person skilled in the art will appreciate that the technical solution of the present disclosure may be practiced without one or more of the specific details, or other methods, components, materials, and the like may be employed. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the present disclosure. [0055] Although the relative terms such as “on,” “below,” “upper,” and “lower” are used in the specification to describe the relative relationship of one component to another component, these terms are used in this specification for convenience only, for example, as a direction in an example shown in the drawings. It should be understood that if the device is turned upside down, the “upper” component described above will become a “lower” component. When a structure is “on” another structure, it is possible that the structure is integrally formed on another structure, or that the structure is “directly” disposed on another structure, or that the structure is “indirectly” disposed on the other structure through other structures. [0056] In this specification, the terms such as “a,” “an,” “the,” and “said” are used to indicate the presence of one or more elements and components. The terms “comprise,” “include,” “have,” “contain,” and their variants are used to be open ended, and are meant to include additional elements, components, etc., in addition to the listed elements, components, etc. unless otherwise specified in the appended claims. [0057] The terms “first,” “second,” etc. are used only as labels, rather than a limitation for a number of the objects. It is understood that if multiple components are shown, the components may be referred to as a “first” component, a “second” component, and so forth, to the extent applicable. [0058] The above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

CLAIMS Therefore, the following is claimed: 1. A vehicle, comprising: a spectrometer, comprising: an input configured to gather an air mass relative to the vehicle; a broadband light source configured to emit a probe beam through the air mass; driver circuity configured to output a signal for driving the broadband light source; an uncooled photodetector; a plurality of beam-steering optics that at least in part define a monitored optical path and direct the probe beam along the monitored optical path to the uncooled photodetector, at least one of the beam-steering optics comprising a condenser lens; and a lock-in amplifier configured to receive a signal from the uncooled photodetector and generate a lock-in output signal using lock-in detection of a waveform signal and the signal received from the uncooled photodetector; and processing circuitry of at least one of the vehicle and the spectrometer configured to determine a relative concentration of volatile organic compounds (VOCs) in the air mass based on an output of the lock-in amplifier.

2. The vehicle of claim 1, wherein the broadband light source is one of a light- emitting diode (LED), a broadband lamp, a superluminescent diode, and an amplified spontaneous emission light source. 3. The vehicle of claim 1, wherein an emission spectrum of the broadband light source has a peak between 3.03 microns and 3.57 microns inclusive, and has a spectral width of at least 0.

3 microns and less than 0.8 microns.

4. The vehicle of claim 1, wherein: the uncooled photodetector is one of an indium arsenide antimonide photodiode and an indium arsenide photodiode; and the spectrometer further comprises a bandpass filter intersecting an optical path between the broadband light source and the uncooled photodetector, the monitored optical path comprising the optical path.

5. The vehicle of claim 1, wherein the lock-in detection comprises at least one of homodyne detection and heterodyne detection.

6. A spectrometer, comprising: an input configured to gather an air mass; a broadband light source configured to emit a probe beam through the air mass; an uncooled photodetector; and a plurality of beam-steering optics that at least in part define a monitored optical path and direct the probe beam along the monitored optical path to the uncooled photodetector; and processing circuitry configured to determine a presence of or a relative concentration of volatile organic compounds (VOCs) in the air mass based on an output of the uncooled photodetector.

7. The spectrometer of claim 6, wherein the broadband light source is one of a light-emitting diode (LED), a lamp, a superluminescent diode, and an amplified spontaneous emission light source. 8. The spectrometer of claim 6, wherein an emission spectrum of the broadband light source has a peak between 3.03 microns and 3.57 microns inclusive, and has a spectral width of at least 0.3 microns and less than 0.

8 microns.

9. The spectrometer of claim 6, wherein the uncooled photodetector is one of an indium arsenide antimonide photodiode and an indium arsenide photodiode.

10. The spectrometer of claim 6, wherein the spectrometer further comprises a bandpass filter intersecting an optical path between the broadband light source and the uncooled photodetector, the monitored optical path comprising the optical path.

11. The spectrometer of claim 10, wherein: a passband of the bandpass filter spans wavelengths between λ_min and λ_max, inclusive; the bandpass filter has a lower stop band at infrared wavelengths less than λ_min microns and an upper stop band at infrared wavelengths exceeding λ_max microns; and λ_min is between 3.0 microns and 3.3 microns, and λ_max is between 3.5 microns and 3.7 microns, wherein: wavelengths λ_min and λ_max are approximately equal to either 3.0 microns and 3.5 microns respectively, and the bandpass filter comprises a passband centered at 3.317 microns.

12. The spectrometer of claim 6, further comprising: driver circuitry electrically coupled to the broadband light source; a lock-in amplifier electrically coupled to an output port of the uncooled photodetector; and a function generator electrically coupled to both the driver circuitry and the lock-in amplifier.

13. The spectrometer of claim 12, further comprising a transimpedance amplifier electrically coupled to the output port of the photodetector and to an input port of the lock-in amplifier.

14. The spectrometer of claim 13, wherein the processing circuitry comprises: at least one hardware processor communicatively coupled to the lock-in amplifier that receives a lock-in output signal generated by the lock-in amplifier in response to one of a detector signal output by the photodetector and a signal derived therefrom; and machine-readable instructions that, when executed by the at least one hardware processor, determines the presence of or the relative concentration of the VOCs from the lock-in output signal.

15. The spectrometer of claim 13, wherein the VOCs comprise methane.

16. The spectrometer of claim 6, wherein the monitored optical path is at least part of an optical path between the broadband light source and the photodetector, and further comprises: a focusing element intersecting the optical path at a distance from the photodetector along the optical path, the distance differing from a focal length of the focusing element by less than half of a depth of focus of the focusing element.

17. A method for detecting volatile organic compounds, comprising: driving a light source with a driving signal to generate a probe beam, the probe beam being amplitude modulated; directing the probe beam along a monitored optical path to yield a transmitted beam; detecting the transmitted beam, or a beam derived therefrom, with an uncooled photodetector; and determining a presence or a relative concentration of a volatile organic compound (VOC) based at least in part on the transmitted beam or the beam derived therefrom.

18. The method of claim 17, further comprising determining an absorption coefficient of the monitored optical path from respective intensities of the transmitted beam, wherein the presence or the relative concentration of the VOC is determined based at least in part on the absorption coefficient.

19. The method of claim 16, further comprising determining an amplitude of the transmitted beam via lock-in detection of a detector signal output by the uncooled photodetector.

20. The method of claim 16, wherein an emission spectrum of the broadband light source has a peak between 3.03 microns and 3.57 microns inclusive, and has a spectral width of at least 0.3 microns and less than 0.8 microns.