Method for measuring data representative of the concentration of at least one tracer gas or of a set of gases comprising the tracer gas, and associated method and assembly

Abstract

The method comprises injecting a laser beam into the measurement cell carried by a drone at measurement instants, the beam having a measurement wavelength characteristic of the tracer gas to be detected. The spectral signature of the tracer gas or of the set of gases is broader than a tuning range of the measurement laser source. The method comprises injecting a reference laser beam into the measurement cell at reference instants, the beam having a reference wavelength located outside the spectral signature. The method comprises transmitting, to a computing system, data representative of the tracer gas concentration, obtained from the measurement signal, and data representative of the reference, obtained from the reference signal, in order to calculate a gas concentration from the data representative of the tracer gas concentration and the data representative of the reference.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for measuring representative data of the content of at least one tracer gas or of a set of gases including the tracer gas, associated method and assembly

[0003] The present invention relates to a method for measuring data representative of the levels of at least one tracer gas or of a set of gases including the tracer gas, the method comprising the following steps:

[0004] flight of a drone in the atmosphere away from the ground, the drone comprising at least one optical measurement cell and at least one laser measurement source, intended for the detection of the tracer gas;

[0005] injection, at a plurality of measurement times, into the measurement cell carried by the drone of a laser beam generated by the measurement laser source, at a measurement wavelength characteristic of the tracer gas to be detected, the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified;

[0006] detection, by a measurement detector, of a measurement signal originating from the measurement cell and resulting from the injection of the measurement laser beam into the measurement cell.

[0007] This method is particularly suited to determining the concentrations of a range of gases present in the atmosphere, gases with a broad spectral signature, generally exceeding the tunable bandwidth of a laser. It is especially applicable to the determination and quantification of volatile organic compound emissions through one-off or periodic measurement campaigns.

[0008] Volatile organic compounds include, for example, hydrocarbons such as ethane, butane, and propane, and aromatics such as benzene. More generally, a volatile organic compound is an organic compound with a vapor pressure of 0.01 kPa or more at a temperature of 293.15 K, for example, as defined in European Council Directive 1999 / 13 / EC of 11 March 1999.

[0009] The European Standard EN 17628:2022 defines methodologies applicable for the spot monitoring of emission values ​​from measurements of volatile organic compounds in ambient air. Examples of standardized technologies are Lidar Dial, SOF (Solar Occultation Flux measurement), tracer release followed by a moving infrared measurement (Fourier Transform Infrared or FTIR) and Reverse Dispersion Modeling which can be used with any type of measurement (e.g., flame ionization detector, ultraviolet or infrared measurements).

[0010] For the measurement of a single gas such as methane, WO2021191360 describes methods using a drone-mounted sensor that allow high-frequency acquisition of three-dimensional data, which only remote optical techniques could achieve until now (e.g., Lidar, solar occultation flux measurements).

[0011] Sensors for measuring a wide range of volatile organic compounds (VOCs) are difficult to integrate onto a drone. In particular, sensors such as photoionization detectors (PIDs) are effective at measuring a broad spectrum of VOCs. However, they are generally too imprecise and do not detect light alkanes (e.g., those with 2 to 4 carbon atoms), and they are not very sensitive to alkanes with 5 to 6 carbon atoms. They are also not fast enough (1 to 2 Hz) to keep up with concentration changes during rapid movement on a drone.

[0012] One aim of the invention is therefore to have a method for collecting significant representative data to quantify the emissions of a gas or a set of gases with a broad spectral signature, in particular the emissions of volatile organic compounds, the method being simple to implement, while giving accurate results.

[0013] Indeed, the invention relates to a method of the aforementioned type, characterized in that the spectral signature of the tracer gas or the set of gases to be measured is wider than a tunability width of the laser measurement source, the method comprising the following steps:

[0014] - injection, at at least one reference instant, into a measurement cell carried by the drone of a reference laser beam emitted by a reference laser source at a reference wavelength located away from the spectral signature of the tracer gas or the set of gases;

[0015] - detection by a reference detector of a reference signal from the injection of the reference laser beam into the measurement cell carried by the drone;

[0016] - transmission of representative tracer gas content data obtained from the measurement signal and representative reference data obtained from the reference signal to a calculation system configured to calculate a tracer gas content and / or the entire gas set from the representative tracer gas content data and the representative reference data.

[0017] The method according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination:

[0018] The reference laser beam injection step is performed at a plurality of reference times, each reference time corresponding to a measurement time.

[0019] the reference laser beam is injected into the same measuring cell as the measuring laser beam.

[0020] The method includes an alternation of injection of the measurement laser beam at each measurement instant, and of the reference laser beam at each reference instant, respectively without injection of the reference laser beam when the measurement laser beam is injected and without injection of the measurement laser beam when the reference laser beam is injected.

[0021] at least one measurement cell comprises two mirrors located opposite and apart from each other and delimiting between them a measurement cavity, the measurement laser beam being injected between the two mirrors and reflecting successively on the two mirrors before being extracted towards the measurement detector out of the measurement cavity.

[0022] The spectral signature is the spectral signature of a set of volatile organic compounds.

[0023] the injection frequency of the laser measurement beam into the measurement cell is greater than 10 Hz and is specifically between 20 Hz and 100 Hz.

[0024] The method includes measuring correction data obtained in the spectral signature using an additional sensor operating at a measurement frequency lower than the injection frequency of the measurement laser beam, the additional sensor being configured to detect correction data over a spectral width greater than the tunable width of the measurement laser source, the method including transmitting the correction data obtained by the additional sensor to the computing system, the computing system being configured to calculate the tracer gas content or the gas set using the correction data.

[0025] The invention also relates to a method for determining the content of at least one tracer gas or a set of gases including the tracer gas, comprising the following steps: implementation of a method for measuring representative data as defined above;

[0026] calculation, by a system for calculating the tracer gas content or the gas mixture at a plurality of measurement times using representative tracer gas data and representative reference data. The method according to the invention may comprise one or more of the following features, taken individually or in any technically feasible combination:

[0027] - the calculation includes, for each representative content data obtained at a measurement time, the determination of an intensity of the measurement signal constituting the representative content data, and the determination of an intensity of the reference signal constituting the representative reference data, the calculation of the tracer gas content or of the set of gases including a calculation of a difference between the intensity of the measurement signal and the intensity of the reference signal.

[0028] - The calculation of the tracer gas content or the gas set includes the calculation of a content in a gas set using representative content data measured at the measurement wavelength within the spectral signature of the gas set, representative reference data measured away from the spectral signature and a calibration model configured to determine a concentration in all gases in the gas set using representative content data and representative reference data, advantageously using a speciation of the gas set present in the gas set.

[0029] - The calculation of the tracer gas content or the gas set includes the calculation of a corrected tracer gas content from the representative content data and the reference data, the calibration model linking the corrected tracer gas content to a concentration in all gases of the gas set.

[0030] The invention also relates to a system for determining the levels of at least one tracer gas or of a set of gases including the tracer gas, the system for determining the levels comprising:

[0031] - a drone configured to fly in the atmosphere away from the ground, the drone comprising at least one optical measurement cell and a laser measurement source, intended for the detection of the tracer gas, a control system configured to activate the laser measurement source for the injection, at a plurality of measurement times, into the measurement cell carried by the drone, of a laser beam generated by the laser measurement source, at a measurement wavelength characteristic of the tracer gas to be detected, the drone further comprising a detector for measuring a measurement signal originating from the measurement cell and resulting from the injection of the laser measurement beam into the measurement cell, the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified,characterized in that the spectral signature of the tracer gas or the set of gases to be measured is wider than a tunability width of the measurement laser source, the drone comprising:

[0032] - a reference laser source, the control system being configured to activate the reference laser source at at least one reference instant, to inject into a measurement cell carried by the drone a reference laser beam emitted by the reference laser source at a reference wavelength located away from the spectral signature of the tracer gas or the set of gases;

[0033] - a reference detector of a reference signal from the injection of the reference laser beam into the measurement cell carried by the drone;

[0034] - a system for transmitting representative tracer gas content data obtained from the measurement signal and representative reference data obtained from the reference signal to a computing system,

[0035] the determination set comprising a calculation system configured to calculate a tracer gas content and / or the gas set from representative tracer gas content data and representative reference data.

[0036] The assembly according to the invention may comprise one or more of the following features, taken individually or in any technically possible combination:

[0037] the reference laser beam is injected into the same measuring cell as the measuring laser beam;

[0038] The drone includes an additional sensor operating at a measurement frequency lower than the injection frequency of the measurement laser beam. The additional sensor is configured to measure correction data obtained in the spectral signature over a spectral width greater than the tunable width of the measurement laser source. The transmission system is configured to transmit the correction data obtained by the additional sensor to the computing system. The computing system is configured to calculate the tracer gas content or the gas mixture using the correction data. The invention also relates to a method for measuring data representative of the content of at least one tracer gas or a gas mixture including the tracer gas. The method comprises the following steps:

[0039] flight of a drone in the atmosphere away from the ground, the drone comprising at least one optical measurement cell and at least one laser measurement source, intended for the detection of the tracer gas;

[0040] injection, at a plurality of measurement times, into the measurement cell carried by the drone, of a laser beam generated by the laser measurement source, at a measurement wavelength characteristic of the tracer gas to be detected, the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified; detection, by a measurement detector, of a measurement signal originating from the measurement cell and resulting from the injection of the laser measurement beam into the measurement cell,

[0041] characterized in that the spectral signature of the tracer gas or the set of gases to be measured is wider than a tunable width of the measurement laser source, the method comprising measuring correction data obtained in the spectral signature using an additional sensor operating at a measurement frequency lower than the injection frequency of the measurement laser beam, the additional sensor being configured to detect correction data over a spectral width greater than the tunable width of the measurement laser source,

[0042] the process comprising transmitting representative tracer gas content data obtained from the measurement signal and correction data obtained from the additional sensor to a computing system configured to calculate a tracer gas content and / or the gas set from the representative tracer gas content data and correction data.

[0043] The invention also relates to a method for determining the content of at least one tracer gas or a set of gases including the tracer gas, comprising the following steps:

[0044] implementation of a representative data measurement process as defined above;

[0045] calculation, by a calculation system of the tracer gas content or of the gas set at a plurality of measurement times using representative tracer gas data and correction data. The process and method defined above do not necessarily include the injection, at at least one reference time, into a measurement cell carried by the drone of a reference laser beam emitted by a reference laser source at a reference wavelength located away from the spectral signature of the tracer gas or the gas set, nor the detection by a reference detector of a reference signal from the injection of the reference laser beam into the measurement cell carried by the drone.

[0046] The invention also relates to a system for determining the levels of at least one tracer gas or of a set of gases including the tracer gas, the system for determining the levels comprising:

[0047] - a drone configured to fly in the atmosphere away from the ground, the drone comprising at least one optical measurement cell and a laser measurement source, intended for the detection of the tracer gas, a control system configured to activate the laser measurement source for the injection, at a plurality of measurement times, into the measurement cell carried by the drone, of a laser beam generated by the laser measurement source, at a measurement wavelength characteristic of the tracer gas to be detected

[0048] the drone further comprising a detector for measuring a measurement signal from the measurement cell and resulting from the injection of the measurement laser beam into the measurement cell, the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified, characterized in that the spectral signature of the tracer gas or the set of gases to be measured is wider than a tunability width of the measurement laser source, the drone comprising;

[0049] - at least one additional sensor operating at a measurement frequency lower than the injection frequency of the measurement laser beam, the additional sensor being configured to measure correction data obtained in the spectral signature over a spectral width greater than the tunability width of the measurement laser source;

[0050] - a system for transmitting representative tracer gas content data obtained from the measurement signal and representative reference data obtained from the reference signal to a computing system

[0051] the determination set comprising a calculation system configured to calculate a tracer gas content and / or the gas set from representative tracer gas content data.

[0052] the transmission system being configured to transmit the correction data obtained by the additional sensor to the calculation system, the calculation system being configured to calculate the tracer gas content or the gas set using the correction data.

[0053] The invention will be better understood upon reading the following description, made with reference to the attached drawings, in which:

[0054] - [Fig. 1] Figure 1 is a view of a first measurement set according to the invention, comprising a drone shown in perspective and an associated computing system, shown schematically, intended to receive data collected by the drone;

[0055] - [Fig. 2] Figure 2 is viewed in perspective of a measurement sensor carried by the drone, the measurement sensor comprising a reference laser source and a measurement laser source injecting respective laser beams into a measurement cavity, with the measurement sensor control system;

[0056] - [Fig. 3] Figure 3 is a view of a spectral signature of a gas set consisting of volatile organic compounds, on which are shown the reference wavelength of the reference laser source and the measurement wavelength of the measurement laser source mounted in the measurement cell of Figure 2;

[0057] - [Fig. 4] Figure 4 schematically illustrates the successive introduction of the reference laser beam from the reference laser source and the measurement laser beam from the measurement laser source into the measurement cavity;

[0058] - [Fig. 5] Figure 5 illustrates an example of the drone's movement trajectory for implementing the measurement method according to the invention;

[0059] - [Fig. 6] Figure 6 illustrates a flowchart for implementing a method for determining the contents of the gas set.

[0060] An example of a set 6 for measuring atmospheric concentrations of at least one tracer gas, or preferably a set of gases including the tracer gas, is shown in Figure 1.

[0061] Measurement set 6 is intended in particular to measure, in a plurality of positions in the atmosphere, the levels of a set of gases, in particular a set of volatile organic compounds (or "VOCs"), in order to determine an emission footprint of these gases.

[0062] Using the determined concentrations, measuring set 6 is specifically intended to determine an emission flux of the gas set, in particular an emission flux of volatile organic compounds.

[0063] Volatile organic compounds include, for example, hydrocarbons such as ethane, butane, and propane, and aromatics such as benzene. More generally, a volatile organic compound is an organic compound with a vapor pressure of 0.01 kPa or more at a temperature of 293.15 K, for example, as defined in European Council Directive 1999 / 13 / EC of 11 March 1999.

[0064] Referring to Figure 4, the set of gases whose concentrations are to be determined, for example, exhibits a broad spectral signature S, defined particularly in the infrared (especially for wavelengths between 700 nm and 2 pm) or in the ultraviolet (especially for wavelengths between 10 nm and 380 nm). A "broad spectral signature" is understood to be a spectral signature S extending over a spectral width generally greater than the tunable width A of a laser. As a non-limiting example, for alkanes the spectral signature lies in the CH strain vibration range at less than 3000 cm⁻¹ -1 , and in the range of bending of CH2 groups between 1300 cm -1 and 1500 cm -1 .

[0065] The tunability width of a laser refers to the range of wavelengths at which the laser can emit, i.e., the range of frequencies over which the laser can be tuned.

[0066] As shown in Figure 1, the determination system 6 includes a drone 10, designed to measure representative tracer gas concentration data and representative reference data. It further includes a computing system 8, configured to calculate the tracer gas concentration and / or the gas mixture concentration, and optionally, a tracer gas flux and / or a gas mixture flux, using the representative data measured with the drone 10.

[0067] Representative data are for example measured in relation to an industrial installation 11 (see figure 5), such as an oil installation, in particular an installation for the exploitation, transport, refining, processing or storage of hydrocarbons.

[0068] The drone 10 is intended to move in the atmosphere above and around the facility 11 to perform at various points in the atmosphere above and around the facility 11, representative reference data measurements at a wavelength L1 spaced from the spectral signature S of the gas set and representative data measurements of the tracer gas content at a wavelength L2 within the spectral signature S of the tracer gas or the gas set.

[0069] As will be seen below, the measurements of the representative reference data are used by the calculation system 8 to determine a measurement reference which corresponds to an LB baseline for the measurement of tracer gas content.

[0070] Representative tracer gas content data, corrected using representative reference data, are used to determine the tracer gas content, and then advantageously, to calculate the content of a set of gases from the tracer gas content.

[0071] In this example, the representative reference data are advantageously obtained at a wavelength L1 corresponding to a gas whose content is negligible compared to the tracer gas content, or whose content can be subtracted from the set of gases, such as methane.

[0072] As illustrated in Figure 2, the drone 10 includes a box 12, a propulsion assembly 14, configured to allow the box 12 to take off away from the ground, and to move by flying in the atmosphere above the ground.

[0073] The drone 10 also includes a measuring assembly 16 which is, for example, positioned under the housing 12.

[0074] With reference to Figure 1, the propulsion assembly 14 comprises a plurality of propulsion organs 18, which here are propellers driven in rotation by a motor.

[0075] The propulsion assembly 14 further includes a power source 20 formed here by a battery and a system 22 for localizing and controlling the movement of the drone 10 in the atmosphere.

[0076] In this example, drone 10 is a multi-rotor rotary-wing drone. It has no wings, its lift being provided by the propulsion system 14.

[0077] Drone 10, for example, is a rotary-wing quadcopter drone, specifically a DJI M300 drone marketed by the company DJI.

[0078] The propulsion elements 18 here are propellers rotating around substantially vertical axes. By "substantially vertical," it is generally meant that the axes of rotation of the propellers are inclined at less than 20° from the vertical.

[0079] When the propeller motors are electrically powered by the battery, the propellers are driven to rotate around their axis, resulting in a downward airflow, which is configured to partially sweep the housing 12.

[0080] The control and location system 22 includes a position sensor, such as a GPS and / or an inertial measurement unit. It also includes a control unit, configured to guide the drone 10 along a trajectory pre-recorded before flight and loaded into the control and location system 22, or remotely and manually via a remote control. The control unit includes at least one processor and memory containing software modules configured to be executed by the processor to guide the drone 10 along the trajectory. The drone 10 is thus configured to automatically follow a predefined trajectory, or alternatively, to be piloted manually by an operator.

[0081] With reference to Figure 1, the measuring assembly 16 comprises a support 24 carrying a sensor 26 for measuring representative reference data and representative tracer gas data, mounted on the support 24, advantageously via dampers 27. It further comprises sensors 28, 29 for measuring temperature and pressure and advantageously, an altitude sensor 30.

[0082] The measuring assembly 16 further includes, carried by the support 24, a control system 31.

[0083] The support 24 here comprises an openwork frame, formed of members 32. In the example shown in Figure 2, the frame is rectangular in shape. It has members 32 along the sides of a rectangle, and members 32 along the diagonals of the rectangle.

[0084] The members 32 are for example made of polymer, to lighten the measuring assembly 16. The polymer is for example chosen from polyetheretherketone, poly(acrylonitrile butadiene styrene), poly(polylactic acid), poly(acrylonitrile styrene acrylate).

[0085] As illustrated in Figure 2, the frame members 32 define a first region 34 for supporting the control system 31, and a second region 36 for supporting the or each measuring sensor 26, offset from the first region 34.

[0086] With reference to Figures 1 and 2, the representative data measurement sensor 26 comprises at least one measurement cell 50 open to the atmosphere, at least one reference laser source 52, intended for the detection of representative reference data away from the spectral signature S of the tracer gas and the gas set, and a measurement laser source 54, intended for the detection of a tracer gas intended to be quantified, preferably to quantify the content in the gas set.

[0087] The measuring sensor 26 includes, for each laser source 52, 54, a respective detector 56A, 56B, or alternatively, a common detector, intended to receive the signals enabling the detection respectively of the representative reference data and the representative data of the tracer gas, the signals being respectively from the reference laser source 52 and the measuring laser source 54.

[0088] The sensor 26 further advantageously includes heat exchange plates 58 mounted respectively on each source 52, 54 and on each detector 56A, 56B. The measuring cell 50 is here a single cell for measuring in the same volume the representative reference data and the representative data of the tracer gas contents.

[0089] With reference to Figures 2 and 3, the measuring cell 50 comprises two facing supports 60A, 60B, and connecting bars 62 linking the supports 60A, 60B. The measuring cell 50 further comprises facing mirrors 64A, 64B, carried respectively by the supports 60A, 60B, the mirrors 64A, 64B delimiting between them a measuring cavity 66.

[0090] In this example, the supports 60A, 60B are mounted parallel to each other, perpendicular to a longitudinal axis A-A' of the measuring cavity 66. The axis A-A' is preferably horizontal when the measuring assembly 16 rests on a horizontal flat support.

[0091] The 60A, 60B supports here have a prismatic shape and a polygonal outer contour, preferably square.

[0092] The connecting bars 62 fix the distance between the supports 60A, 60B. In this example, the connecting bars 62 extend between the vertices of the polygon defining the outline of the supports 60A, 60B. They extend parallel to each other, delimiting intermediate passage spaces.

[0093] The measuring cavity 66 is open in at least one direction, preferably in at least two directions, between the opposing supports 60A, 60B and between the connecting bars 62.

[0094] The length of the measuring cavity 66, taken between supports 60A, 60B is for example less than 50 cm and is in particular between 5 cm and 20 cm.

[0095] The length of the measuring cavity 66 is adjusted according to the expected concentration range of the tracer gas being measured. For example, the length of the measuring cavity 66 is greater if the tracer gas is present in trace amounts and / or if its response to the measured wavelength is weak. Conversely, the length of the measuring cavity 66 is shorter if the tracer gas is present in a relatively high concentration or if its response to the measured wavelength is strong.

[0096] Mirrors 64A and 64B are each mounted on a support 60A and 60B respectively, so that they are positioned opposite each other. Mirrors 64A and 64B are concave, with their concave surfaces facing each other.

[0097] A first support 60A and a first mirror 64A include at least one hole 68, 70, here two holes 68, 70 to allow respectively the injection of a first beam from the reference laser source 52 and a second beam from the measurement laser source 54. The second mirror 64B opposite the first mirror 64A, and the second support 64B include at least one hole 70, 71, here two holes 70, 71 for signal extraction, to allow each detector 56A, 56B to receive a signal from the measurement cavity 66.

[0098] The reference laser source 52 and the measurement laser source 54 are mounted on one face of the first support 60A, outside the measurement cavity 66, on either side of the longitudinal axis A-A' of the cavity.

[0099] Each source 52, 54 includes a laser component 74 and advantageously, a temperature control element 76, for example a Peltier element.

[0100] With reference to Figure 4, the laser component 74 of the reference laser source 52 is, for example, configured to emit a reference laser beam centered on a reference wavelength L1 located away from the spectral signature S. The laser component 74 of the measurement laser source 54 is configured to emit a measurement laser beam centered on a measurement wavelength L2, distinct from the wavelength L1, and located in the spectral signature S.

[0101] The wavelengths L1, L2 are preferably advantageously separated by at least 5 nm, in particular by at least 100 nm.

[0102] As mentioned above, the reference wavelength L1 is chosen from a range of wavelengths located away from the spectral signature S of the tracer gas.

[0103] The reference laser source 52 also emits with a spectral width smaller than the spectral width of the tracer gas's spectral signature S. By way of non-limiting example, the emission spectral width of the reference laser source 52, and more generally, the tunable width of the reference laser source 52, is notably less than 10 cm -1 for example by adjusting the current and temperature of a laser diode. This width can be between 1.5 cm -1 and 2.0 cm -1 , in particular by tuning by simply varying the current.

[0104] The reference wavelength L1 is, for example, chosen to be a characteristic wavelength of a gas other than the tracer gas or the set of gases whose content is to be determined using tracer gas content quantification. This gas is, for example, carbon dioxide or methane.

[0105] For example, for methane the reference laser source 52 is configured to emit the reference laser beam centered on the wavelength L1 between 3230 nm and 3250 nm, in particular between 3238 nm and 3242 nm. For the detection of the tracer gas, the measurement wavelength L2 is for example chosen in the spectral signature S of the tracer gas, for example by being characteristic of a molecular group of the tracer gas.

[0106] The measurement laser source 54 also emits with a spectral width smaller than the spectral width of the tracer gas's spectral signature S. By way of non-limiting example, the emission spectral width of the measurement laser source 54, and more generally, the tunable width of the measurement laser source 54, is notably less than 10 cm -1 for example by adjusting the current and temperature of a laser diode. This width can be between 1.5 cm -1 and 2.0 cm -1, in particular by tuning by simply varying the current.

[0107] In the non-limiting example shown in Figure 4, the wavelength L2 is within the CH strain vibration range of butane. The measuring laser source 54 is configured to emit the measuring laser beam centered on the wavelength L2 between 2925 cm -1 and 3000 cm -1 , particularly between 2965 cm -1 and 2967 cm -1 .

[0108] The spectral signature S of the tracer gas is at least 10% wider than the tunability width of the measurement laser source 54, thus preventing the determination, by the measurement laser source 54 alone, of representative reference data usable as a baseline for representative tracer gas content data.

[0109] More generally, the wavelength associated with a target molecule is chosen based on the spectral signature of each target molecule and any interfering molecules. Wavelength selection depends on the measurement environment (pressure, temperature, concentration of target and interfering molecules, etc.).

[0110] In the example just described, each laser component of the reference laser source 52 and the measurement laser source 54 is, for example, a laser diode. A laser diode is an optoelectronic component made from semiconductor materials. It emits coherent monochromatic light. It is, for example, formed of a semiconductor junction, which has three characteristic regions: an n-type confinement layer, an active region, and a p-type confinement layer. The diode is, for example, a distributed feedback diode.

[0111] As mentioned above, the measuring cell 50 operates by direct absorption of laser light in the measuring cavity 66, in contact with the gases whose concentration is to be measured. It is therefore a measuring cell 50 for performing direct laser absorption spectroscopy (DLAS). Referring to Figure 3, the measuring cavity 66 allows for multiple reflections 82 of the laser beams injected from the reference laser source 52 or from the measuring laser source 54 to increase the optical path length. The measuring cell is thus a multipass spectroscopic cell, or Herriott cell.

[0112] With reference to Figure 2, the temperature control element 76 is configured to stabilize the temperature of the laser sources 52, 54 and the detectors 56A, 56B. In the example shown in the figures, the heat exchange plates 58 are mounted on the back of the reference laser source 52, the measuring laser source 54, and the detectors 56A, 56B, in thermal contact with the temperature control elements 76.

[0113] The heat exchange plates 58 are made of metal, for example aluminium. They protrude from the sources 52, 54, to be swept by the airflow generated by the propulsion elements 18 during the rotation of the propellers.

[0114] Thus, the calories absorbed by the temperature control element 76 are dissipated using the heat exchange plates 58, without the need to mount an additional fan to control the temperature of the sources 52, 54 or the detectors 56A, 56B. This reduces the weight of the drone 10.

[0115] Each detector 56A, 56B is configured to detect the intensity of a signal extracted from the measuring cavity 66 at wavelengths including respectively the wavelength L1 of the emission beam of the reference laser source 52 and the wavelength L2 of the emission beam of the measuring laser source 54.

[0116] Thus, the measured intensity can be related to the incident intensity by Beer-Lambert's law as described below:

[0117] I = I0 exp(LNK)

[0118] where I is the measured intensity, lo is the incident intensity, L is the length of the optical path traveled in the measurement cell 50, N is the number of molecules of the gas studied in the path and K is the absorption coefficient of this gas.

[0119] With reference to Figure 2, the shock absorbers 27, when present, have spring wires 80 connecting the support 24 to each of the supports 60A, 60B of the measuring cell 50. These spring wires 80 are suitable for partially absorbing the vibrations of the propulsion assembly 14 and the movement in the air of the drone 10.

[0120] As shown in Figure 1, the temperature sensor 28 is positioned between the opposing supports 60A and 60B. The sensor 28 is, for example, a thermistor or a thermocouple, configured to measure the electrical resistance of a metallic element, which varies with temperature. The pressure sensor 29 comprises, for example, a pressure measuring tube opening into the measuring cavity 66.

[0121] The presence of a temperature measurement sensor 28 and a pressure measurement sensor 29 directly within the measurement cell 50, preferably in the measurement cavity 66, enhances the reliability of the data collected, particularly when the concentration of the gases to be measured in the measurement cavity 66 is low.

[0122] The altitude sensor 30, when present, includes an altimeter, equipped for example with a laser pointing towards the ground to measure the height at which the drone 10 is located.

[0123] The control system 31 includes a selective power supply unit 90 for each of the sources 52, 54, a data collection unit 92 for measurements taken by each detector 56A, 56B, and at least one heat exchanger 94, configured to dissipate the heat generated by units 90, 92 without requiring its own ventilation. These units are housed in a casing 96.

[0124] The power supply unit 90 is configured to selectively and successively supply, at each measurement instant, the reference laser source 52 and, where applicable, the measurement laser source 54 to obtain a first phase of illumination of the measurement cavity 66 exclusively by the reference laser source 52, without illumination by another laser source, in particular by the measurement laser source 54, then a second phase of illumination of the measurement cavity 66 exclusively by the measurement laser source 54, without illumination by another laser source, in particular by the reference laser source 52.

[0125] Thus, successive measurement phases of representative reference data, and of tracer gas content, can be carried out in the same measurement cavity 66 of the measurement cell 50 at successive measurement times.

[0126] The power supply unit 90 is for example connected to the power source 20 of the propulsion unit 18.

[0127] The data collection unit 92 includes at least one memory, configured to store representative data consisting of light intensity spectra as a function of wavelength recorded at different times by each detector 56A, 56B.

[0128] Representative data are stored, for example, at a frequency above 1 Hz, specifically between 10 Hz and 100 Hz. The stored spectra preferably include more than 256 points, for example, between 256 and 2696 points. Thus, very good resolution is obtained for determining the intensity of the peaks measured in the measuring cell 50 as a function of wavelength, which makes it possible to deduce concentrations, even if these concentrations are very low.

[0129] The data collection unit 92 is connected to the teletransmission system 31A to allow the export of data to a ground receiving station, during the flight of drone 10 or after the flight of drone 10, at a frequency which may be lower than the acquisition frequency, for example between 1 Hz and 5 Hz.

[0130] The heat exchanger 94 is in thermal contact with each of the power supply units 90 and data collection units 92. It is configured to remove the heat produced by these units 90, 92.

[0131] The heat exchanger 94 is configured to be swept by the airflow generated by the propulsion components 18, to remove the heat produced by the units 90, 92. Thus, no fan is needed in the housing 96 to cool the units 90, 92, which reduces the weight and power consumption of the drone 10.

[0132] The teletransmission system 31A includes a transmitter, configured to transmit data to the computing system 16, this data being, for example, the data collected by unit 92 or a fraction of this data.

[0133] For example, the computing system 8 is located on the ground, at a distance from drone 14.

[0134] Alternatively, the computing system 8 is mounted in the drone 10. In the case where the computing system 8 is located on the ground, it is connected to the drone 10 and in particular to the teletransmission system 31A to allow the reception of representative data collected by the drone 10 to the computing system 8.

[0135] Referring to Figure 1, the computing system 8 is located in a land-based computing infrastructure, for example in a computing cloud. It comprises at least one computer 100 and at least one human-machine interface 102 allowing a user to connect to the computer 100 to perform operations on the computer 100.

[0136] The human-machine interface 102 includes, for example, a keyboard, a screen, and / or a control device on the screen, such as a mouse or a touch screen.

[0137] The computer 100 preferably includes at least one processor 104 and a memory 106 configured to contain software modules to be executed by the processor 104 to perform functions. Alternatively, the computer 100 is at least partially in the form of one or more programmable circuits, for example of the FPGA (Field-Programmable Gate Array) type, or in the form of an electronic circuit dedicated to an application of the ASIC (Application-Specific Integrated Circuit) type.

[0138] In the example shown in Figure 1, the calculator 100 includes a module 110 for calculating tracer gas levels, using representative tracer gas data measured by the measuring sensor 26 and using representative reference data measured by the measuring sensor 26, to deduce a corrected tracer gas level.

[0139] Calculator 100 also includes a module 112 for calculating the concentration of a set of gases, using the tracer gas-corrected concentration obtained from representative data and a calibration model. It optionally includes a module 114 for calculating the flux of the set of gases.

[0140] The calculation module 110 is configured to correct each representative data of tracer gas content measured by detector 56B of measuring sensor 26, at each measurement instant, using the reference representative data, measured at the same measurement instant or at a close measurement instant by the first detector 56A of measuring sensor 26. This is done for example by subtraction between the values ​​of the representative data.

[0141] By "immediate measurement", we generally mean an instant of measurement separated by less than one second from the instant of measurement under consideration.

[0142] Thus, the value of the representative reference data serves as the baseline LB for determining the value of the representative data in tracer gas. The representative data are measured in the same measuring sensor 26, at the same measurement time or at close measurement times, with the same measurement disturbances, particularly in terms of vibrations or turbulence.

[0143] Calculation module 112 is configured to calculate the contents of a set of gases, using the corrected tracer gas content determined by calculation module 110, and using the calibration model.

[0144] The calibration model includes, for example, a speciation of the gases emitted by the installation 11 among the set of gases and possibly, a determination of the relative content of each gas in the set of gases individually emitted by the installation 11, as a function of the tracer gas content.

[0145] Thus, the calculation module 112 is configured to calculate a total content in the entire gas at each measurement point corresponding to a measurement instant of the tracer gas content. The flux calculation module 114 is configured, using content measurements made in a measurement plane along a trajectory, to deduce a flux through the measurement plane, by double surface integration in the measurement plane, as described for example in WO 2021204941 or in WO 2021234017.

[0146] A method for determining the content of at least one set of gases, in particular in a measurement plane 120 along a trajectory 122 visible in Figure 5, will now be described.

[0147] The method is implemented by placing the measurement plane 120 preferably opposite an industrial installation 11, with a view to detecting and quantifying a source 124 of gas within the installation 11.

[0148] The method includes a phase 150 of in-flight measurements of the drone 10 to determine representative reference data and representative tracer gas content data, followed by a phase 152 of calculation of the tracer gas content and / or a set of gases, using the representative reference data and the representative tracer gas content data.

[0149] The tracer gas and the entire gas mixture are present in a plume emitted from source 124 within installation 11.

[0150] Initially, at step 154, the drone 10 is launched into flight. The propulsion mechanisms 18 are activated by the localization and control system 22 to allow the drone 10 to take off and move towards the measurement plane 120 where the measurements are to be carried out.

[0151] The propulsion components 18 generate lift. The localization and control system 22 controls the movement of the drone 10, either by remote manual command or by following an automatic program loaded into the system 22.

[0152] During the flight of drone 10, at step 156, measurements are taken along a measurement trajectory 122, an example of which is given in Figure 5.

[0153] In the example in Figure 5, the measurement trajectory 122 follows, for example, a creeping ladder movement.

[0154] The drone 10 moves along a plurality of lines 160 parallel to a first direction D1, with a connecting segment 162 between each pair of adjacent parallel lines 160. The connecting segment 162 is along a second direction D2 transverse to the first direction D1.

[0155] Here, the first direction D1 is a horizontal direction and the second direction D2 is a vertical direction. In this example, all the parallel lines 160 swept by the drone 10 extend substantially in the same vertical measurement plane 120.

[0156] The extent E1 of the lines 160 following the first direction D1 is chosen according to the width of the plume emitted by the source 124, in order to sweep the entire plume. This extent E1 is generally greater than 20 m and is between 20 m and 500 m.

[0157] The distance between lines 160 is defined by a span E2 of the connecting segments 162 along the second direction. This span E2 is, for example, greater than 1 m and specifically between 1 m and 50 m.

[0158] The position, extent and orientation of the measurement trajectory 122 are determined, for example, from an assumed position of the source 124 and the wind direction, as described, for example, in the Applicant's French patent application No. 22 12559.

[0159] During the movement of the drone 10 along the measurement trajectory 122, the representative data measurement sensor 26, the temperature measurement sensor 28, the pressure measurement sensor 29 and possibly the altitude sensor 30 when present, are activated at successive measurement times.

[0160] The measurements by the different sensors 26, 28, 29, 30 are carried out during the movement of the drone 10, without having to immobilize the drone 10. The frequency of the measurements is advantageously greater than 1 Hz, in particular between 10 Hz and 100 Hz.

[0161] For this purpose, the power supply unit 90 selectively and successively powers the reference laser source 52, then the measurement laser source 54.

[0162] Advantageously, during each activation phase of the reference laser source 52, the laser component 74 of the measuring laser source 54 is deactivated. The laser component 74 of the reference laser source 52 emits a reference laser beam at wavelength L1, which is injected through the injection hole 68 into the measuring cavity 66.

[0163] The thickness of the reference laser beam is advantageously greater than 1 mm, and in particular between 3 mm and 6 mm. This eliminates measurement artifacts that can be created by particles suspended in the measurement cavity 66.

[0164] With reference to Figure 3, the reference laser beam is reflected successively on mirrors 64A, 64B, moving back and forth in the measuring cavity 66 to increase the optical path length L.

[0165] A first signal is collected through the sampling hole 71, resulting from the first beam emitted by the reference laser source 52.

[0166] This first signal is captured by detector 56A, and the representative reference data captured by detector 56A are sent to data acquisition unit 92 for storage. As mentioned above, this representative reference data allows the intensity of a baseline to be established. This representative reference data is taken independently of the spectral signature S of the tracer gas or a gas mixture including the tracer gas.

[0167] Then, in each activation phase of the measuring laser source 54, the laser component 74 of the reference laser source 52 is deactivated. The laser component 74 of the measuring laser source 54 emits a measuring laser beam at a wavelength L2 distinct from the wavelength L1. This laser beam is introduced through the injection hole 70 into the measuring cavity 66.

[0168] As before, the thickness of the measurement laser beam is advantageously greater than 1 mm, and in particular between 3 mm and 6 mm.

[0169] The laser measurement beam is reflected successively on mirrors 64A, 64B, moving back and forth in the measurement cavity 66 to increase the optical path length L.

[0170] A second signal is collected through the sampling hole 72 resulting from the second beam emitted by the measuring laser source 54. This second signal is captured by the detector 56B, and the representative data captured by the detector 56B are sent to the data acquisition unit 92 for storage. The representative data are representative tracer gas content data, taken from the spectral signature S of this gas or a set of gases including this tracer gas.

[0171] The measurements being carried out successively at each measurement instant allow to determine light intensities at two wavelengths L1, L2, representative respectively of a baseline reference and of the content of a tracer gas.

[0172] At step 170, when drone 10 has finished its mission and returns to the ground, the representative data collected by detectors 56A, 56B at each measurement instant and stored in the memory of the data collection unit 92, are transmitted by the teletransmission system 31A to the computing system 8, for example via a ground station.

[0173] In the calculation system 8, for each measurement instant, representative data are stored in association with the geographical position data of the drone 10 measured by the localization and control system 22 at the measurement instant, with the temperature and pressure measured by the sensors 28, 29 at the measurement instant, possibly with the altitude measured by the altitude sensor 30 at the measurement instant and with a timestamp of the measurement instant. The calculator 100 is then activated at step 172 to calculate, at each measurement instant, the content of at least the tracer gas.

[0174] To this end, calculation module 110 determines the light intensity value at wavelength L2 and subtracts the light intensity value at wavelength L1, which serves as the baseline reference, from this light intensity. This yields a corrected value for the representative gas data to be measured.

[0175] Calculation module 110 then calculates the corrected tracer gas content at each measurement point along measurement path 122.

[0176] In step 174, the calculation module 112 calculates, at each measurement point corresponding to a measurement instant, the concentration of a set of gases exhibiting a broad spectral signature S, based on the tracer gas concentration determined by the calculation module 110 and the calibration model. Thus, the concentration of the gas set is determined at each measurement point along the trajectory 122.

[0177] At step 176, the flux calculation module 114 then performs a double integration of the gas ensemble content data, using wind speed data either at each measurement point or at each altitude to determine a flux in the gas ensemble.

[0178] Examples of flow calculation methods are given in WO 2021204941 or in WO 2021234017.

[0179] Thus, thanks to the method according to the invention, it is very simple to implement a method for measuring data representative of a tracer gas to quantify a set of gases, even if this tracer gas or set of gases has a wide spectral signature S, greater than the tunability width of a laser source 52, 54.

[0180] The method comprises the simultaneous or near-simultaneous measurement of a reference signal, offset from the spectral signature S, to allow the definition of a reliable baseline. The two measurements are carried out within the same measurement cell 50, successively at the same measurement time, or at close measurement times, under the same disturbances in terms of vibration, turbulence, or atmosphere, ensuring a reliable differential measurement.

[0181] Next, from the tracer gas content, a calibration model is used to obtain a reliable estimate of the content of a set of gases, and the associated flux from a source 124.

[0182] In one variant, the drone 10 is further equipped with at least one 180 sensor which has a lower performance than the measuring sensor 26. The or each 180 sensor advantageously has a wider detection width than the tunability width of the laser source 54 but a lower measurement frequency, for example less than 5 times the measurement frequency of the laser source 54.

[0183] Since the detection width scanned by sensor 180 is wider than that scanned by laser source 54, correction data are acquired by sensor 180 at a lower frequency than the representative data. This allows the detection of other representative bands of the spectral signature S, located outside the measurement wavelength L2. These correction data are, for example, representative of other gases in the gas set. The calculation module 112 advantageously uses the correction data, in addition to the tracer gas content determined by the calculation module 112, to recalibrate the total content of the gas set or to determine and / or recalibrate the individual contents of each gas in the gas set.

[0184] A first 180 sensor, for example, includes a photoionization detector (designated by the acronym "PID"), specifically a MiniPID 2 HS sensor marketed by IONSCIENCE. This first 180 sensor enhances sensitivity to volatile organic compounds, particularly aromatics.

[0185] A second 180 sensor is advantageously used in addition to the first 180 sensor. The second 180 sensor is configured to measure humidity in order to correct the contribution of the water spectrum to the measurement at wavelength L2.

[0186] Thus, if the 180 sensor is not suitable for making online measurements on a set of gases, at a frequency compatible with a flight of a drone 10, it nevertheless allows the measurement made using the laser source 54 on the tracer gas to be recalibrated at regular intervals, improving the subsequent accuracy on the total content of the set of gases and / or on the contents of each of the gases in the set of gases to be determined.

[0187] As described above, the calibration model uses speciation, which by definition includes the identification and quantification of the different chemical entities (or species) present within the mixture of gases. In the case of a mixture of gases, such speciation does not simply establish a total concentration of an element (e.g., carbon or sulfur), but distinguishes the species present in the mixture from one another (e.g., carbon dioxide, carbon monoxide, hydrogen sulfide, sulfur dioxide, etc.).

[0188] Speciation is carried out, for example, during the establishment of the calibration model by taking samples of emitted gas, then identifying and quantifying the emitted gases, for example by chromatography, particularly in gas phase, possibly coupled with mass spectrometry, by spectroscopic methods, particularly optical, and / or by electrochemical and / or semiconductor sensors.

[0189] Thus, the relative concentrations of each gas in the set of individually emitted gases with respect to the tracer gas content can be determined, which then allows an individual content of each gas to be obtained from the tracer gas content, and then possibly the content of the set of gases forming the mixture to be obtained from the sum of the individual contents.

Claims

25 DEMANDS 1. A method for measuring representative data of the content of at least one tracer gas or a set of gases including the tracer gas, the method comprising the following steps: flight of a drone (10) in the atmosphere away from the ground, the drone (10) comprising at least one optical measurement cell (50) and at least one laser measurement source (54), intended for the detection of the tracer gas; injection, at a plurality of measurement times, into the measurement cell (50) carried by the drone (10) of a laser beam generated by the measurement laser source (54), at a measurement wavelength characteristic of the tracer gas to be detected, the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified; detection, by a measurement detector (56B) of a measurement signal originating from the measurement cell (50) and resulting from the injection of the measurement laser beam into the measurement cell (50), characterized in that the spectral signature of the tracer gas or the set of gases to be measured is wider than a tunability width of the laser measurement source, the method comprising the following steps: - injection, at at least one reference instant, into a measurement cell (50) carried by the drone (10) of a reference laser beam emitted by a reference laser source (52) at a reference wavelength located away from the spectral signature of the tracer gas or the set of gases; - detection by a reference detector (56A) of a reference signal from the injection of the reference laser beam into the measurement cell (50) carried by the drone (10); - transmission of representative tracer gas content data obtained from the measurement signal and representative reference data obtained from the reference signal to a computing system (8) configured to calculate a tracer gas content and / or the gas set from the representative tracer gas content data and the representative reference data.

2. Method according to claim 1, wherein the injection step of the reference laser beam is carried out at a plurality of reference times, each reference time corresponding to a measurement time.

3. A method according to any one of claims 1 or 2, wherein the reference laser beam is injected into the same measuring cell (50) as the measuring laser beam.

4. A method according to any one of claims 1 to 3, comprising an alternation of injection of the measurement laser beam at each measurement instant, and of the reference laser beam at each reference instant, respectively without injection of the reference laser beam when the measurement laser beam is injected and without injection of the measurement laser beam when the reference laser beam is injected.

5. A method according to any one of the preceding claims, wherein at least one measuring cell (50) comprises two mirrors (64A, 64B) situated opposite and apart from each other and delimiting between them a measuring cavity (66), the measuring laser beam being injected between the two mirrors (64A, 64B) and reflecting successively on the two mirrors (64A, 64B) before being extracted towards the measuring detector (56B) out of the measuring cavity (66).

6. A method according to any one of the preceding claims, wherein the spectral signature is the spectral signature of a set of volatile organic compounds.

7. A method according to any one of the preceding claims, wherein the injection frequency of the measuring laser beam into the measuring cell (50) is greater than 10 Hz and is in particular between 20 Hz and 100 Hz.

8. A method according to any one of the preceding claims, comprising measuring correction data obtained in the spectral signature using an additional sensor (180) operating at a measurement frequency lower than the injection frequency of the measurement laser beam, the additional sensor (180) being configured to detect correction data over a spectral width greater than the tunability width of the measurement laser source, the method comprising transmitting the correction data obtained by the additional sensor (180) to the computing system (8), the computing system (8) being configured to calculate the tracer gas content or the gas set using the correction data.

9. Method for determining the content of at least one tracer gas or of a set of gases including the tracer gas, comprising the following steps: implementation of a method for measuring representative data according to any one of claims 1 to 8; calculation, by a calculation system (8) of the tracer gas content or of the set of gases at a plurality of measurement times using representative tracer gas data and representative reference data.

10. Method according to claim 9, wherein the calculation comprises, for each representative content data obtained at a measurement time, the determination of an intensity of the measurement signal constituting the representative content data, and the determination of an intensity of the reference signal constituting the representative reference data, the calculation of the tracer gas content or of the set of gases comprising a calculation of a difference between the intensity of the measurement signal and the intensity of the reference signal.

11. A method according to any one of claims 9 to 10, wherein the calculation of the tracer gas content or of the gas set comprises calculating a content in a gas set using representative content data measured at the measurement wavelength within the spectral signature of the gas set, representative reference data measured away from the spectral signature, and a calibration model configured to determine a concentration in all gases of the gas set using representative content data and representative reference data, advantageously using a speciation of the gas set present in the gas set, the calibration model optionally including a determination of the relative content of each gas of the gas set individually emitted, as a function of the tracer gas content.

12. Method according to claim 11, wherein the calculation of the tracer gas content or the gas mixture comprises the calculation of a corrected tracer gas content from the representative content data and the reference data, the 28 calibration model relating the corrected tracer gas content to a concentration of all gases in the gas set.

13. A set for determining the concentrations of at least one tracer gas or a set of gases including the tracer gas, the set for determining comprising: a drone (10) configured to fly in the atmosphere away from the ground, the drone (10) comprising at least one optical measuring cell (50) and a measuring laser source (54) for the detection of the tracer gas, a control system (31) configured to activate the measuring laser source (54) for the injection, at a plurality of measurement times, into the measuring cell (50) carried by the drone (10), of a laser beam generated by the measuring laser source (54) at a measurement wavelength characteristic of the tracer gas to be detected the drone (10) further comprising a detector (56B) for measuring a measurement signal from the measurement cell (50) and resulting from the injection of the measurement laser beam into the measurement cell (50), the measurement wavelength being located within a spectral signature characteristic of the tracer gas or the set of gases to be quantified, characterized in that the spectral signature of the tracer gas or of the set of gases to be measured is wider than a tunability width of the measurement laser source (54), the drone (10) comprising; - a reference laser source (52), the control system (31) being configured to activate the reference laser source (52) at at least one reference instant, to inject into a measuring cell (50) carried by the drone (10) a reference laser beam emitted by the reference laser source (52) at a reference wavelength located away from the spectral signature of the tracer gas or the gas set; - a reference detector (56A) of a reference signal from the injection of the reference laser beam into the measurement cell (50) carried by the drone (10); - a system (31A) for transmitting representative tracer gas content data obtained from the measurement signal and representative reference data obtained from the reference signal to a computing system (8) the determination system comprising a calculation system (8) configured to calculate a tracer gas content and / or the gas set from representative tracer gas content data and representative reference data.29 14. Assembly according to claim 13, wherein the reference laser beam is injected into the same measuring cell (50) as the measuring laser beam.

15. Assembly according to any one of claims 13 or 14, wherein the drone (10) includes an additional sensor (180) operating at a measurement frequency lower than the injection frequency of the measurement laser beam, the additional sensor (180) being configured to measure correction data obtained in the spectral signature over a spectral width greater than the tunability width of the measurement laser source (54), the transmission system (31A) being configured to transmit the correction data obtained by the additional sensor (180) to the computing system (8), the computing system (8) being configured to calculate the tracer gas content or the gas set using the correction data.

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