JP2014032068A - Gas concentration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration measuring device which causes no problem in measuring a gas concentration even in the case that vibration of each of a plurality of mirrors creates a slight change in an installation angle when a predetermined gas concentration is measured while a laser beam is reflected by the plurality of mirrors.SOLUTION: A plurality of mirrors installed to surround a region to be measured include: a plurality of mirrors sequentially reflecting a laser beam emitted by laser emitting means; a retroreflection body such as a retroreflector which causes the laser beam reflected by the n-th mirror which reflects the laser beam at n-th time to reflect at an emitting point of the laser beam in the n-th mirror; light quantity measuring means for measuring a light quantity of the laser beam which is reflected by the plurality of mirrors and the retroreflection body to be again reflected and returned to the plurality of mirrors; and computing means for computing a predetermined gas concentration in the region to be measured on the basis of the light quantity measured by the light quantity measuring means.

Description

  The present invention relates to a gas concentration measuring apparatus.

  Conventionally, when measuring a trace gas such as methane gas using a laser, the laser module irradiates the measurement area with laser light, and the laser light is reflected by the target in the measurement area and reflected by the photodetector. The measured laser light is measured by phase sensitive detection. And the apparatus which measures the density | concentration of the methane gas which exists in a to-be-measured area | region based on the light quantity of the said received laser beam is known (for example, refer prior art documents 1 and 2).

  As one of the applications of this device, a laser gas sensor irradiates a non-paved surface with laser light of a specific wavelength, receives reflected light from the non-paved surface, and detects gas when the received light intensity is below a predetermined value. There is known an in-vehicle leaked gas detection system that performs this determination (see, for example, Patent Document 1).

Anritsu Technical No. 82 Mar. 2006, pages 66-71 "Laser type remote gas detector" Takaya Iseki, Applied Physics, Vol. 69, No. 6, 663-696, 2000, "Trace detection technology using semiconductor laser"

JP 2009-42965 A

  Necessary for improving accuracy when using a laser-type remote gas detector to measure a wide range of greenhouse gas concentrations in the field of environmental measurement or to measure greenhouse gas generation (flux). An optical path length of several tens of meters or more and a reflector that returns laser light to the light receiving section stably with high efficiency are required. However, it is difficult to satisfy the above-mentioned conditions when measuring the movement in the field or when measuring with a high spatial resolution necessary for a certain kind of flux measurement.

  For example, in the invention described in Patent Document 1, a laser beam having a specific wavelength is irradiated on a non-paved surface (road shoulder) and reflected light from the non-paved surface is received. Although it is possible to detect leaked methane gas, it is impossible to measure the methane concentration with the accuracy required for environmental measurement. The reason is that if the optical path of several tens of meters required for high-precision methane gas measurement is secured only by making one round trip through the measurement area, the laser beam with the required intensity cannot be obtained by reflection from the non-paved surface. It is. Also, when considering a gas concentration measuring device that reflects laser light with a flat mirror instead of reflecting laser light on a non-paved surface, the gas concentration measuring device is several tens of meters long and the device is large. There is a problem.

  In order to reduce the overall shape of the gas concentration measurement device, a plurality of mirrors are arranged so as to surround the gas concentration measurement region, and the laser light generated by the laser light source is reflected by the plurality of mirrors. A device for sending to the light receiving element is conceivable. In this apparatus, the overall shape of the gas concentration measuring apparatus can be reduced in size while ensuring a long optical path length from the laser light source through the plurality of mirrors to the light receiving element.

  However, in this conceivable apparatus, when each of the mirrors constituting the plurality of mirrors changes its installation angle due to vibration or a change in the optical path for some reason, the laser light generated by the laser light source is applied to the light receiving element. There is a problem of not reaching.

  This problem also occurs when measuring the concentration of gases other than methane gas, such as carbon dioxide.

  In the present invention, when measuring the concentration of a predetermined gas while reflecting the laser beam by a plurality of mirrors, even if each of the plurality of mirrors has its installation angle slightly changed due to vibration or a change in the optical path, An object of the present invention is to provide a gas concentration measuring device that does not cause a problem in concentration measurement.

  The gas concentration measuring apparatus of the present invention includes a laser beam irradiation means for irradiating a gas in a measurement region with a laser beam, and a plurality of mirrors installed so as to sandwich the measurement region, the laser beam irradiation A plurality of mirrors that sequentially reflect the laser light emitted by the means, and a laser beam reflected by an n-th mirror that reflects the laser light n times among the plurality of mirrors; The amount of the laser beam reflected by the retroreflector reflected by the laser beam emission point, the plurality of mirrors and the retroreflector, and reflected again by the plurality of mirrors is returned. A light quantity measuring means for measuring, and a computing means for computing the concentration of a predetermined gas in the measurement area based on the light quantity measured by the light quantity measuring means.

  According to the present invention, when measuring the concentration of a predetermined gas while reflecting a laser beam with a plurality of mirrors, a retroreflector is used as a reflection means for turning back the laser beam reflected by the plurality of mirrors. Therefore, even if each of the plurality of mirrors vibrates or the like and the installation angle changes somewhat, there is an effect that no problem occurs in the gas concentration measurement.

It is a conceptual diagram which shows the gas concentration measuring apparatus 100 which is Example 1 of this invention. It is a conceptual diagram which shows the gas concentration measuring apparatus 200 which is Example 2 of this invention. It is a conceptual diagram which shows the gas concentration measuring apparatus 300 which is Example 3 of this invention. It is a conceptual diagram which shows the gas concentration measuring apparatus 400 which is Example 4 of this invention. It is a conceptual diagram which shows the gas concentration measuring apparatus 500 which is Example 5 of this invention.

  The modes for carrying out the invention are the following examples.

  FIG. 1 is a conceptual diagram showing a gas concentration measuring apparatus 100 that is Embodiment 1 of the present invention.

  The gas concentration measuring apparatus 100 includes a laser light source 10, plane mirrors M1, M2,..., M13, a retroreflector RR1, a perforated plane mirror 30, an imaging lens 31, and the like. The light receiving element 40 and the calculating means 50 are included.

  The laser light source 10 is a semiconductor laser that generates laser light having a wavelength of 1.6537 μm, which is one of the wavelengths most easily absorbed by methane gas.

  The measurement area 20 is an area for measuring the concentration of methane gas.

  In the gas concentration measuring apparatus 100, the number of plane mirrors installed is 13, but a plurality of n plane mirrors may be used. In this sense, the plane mirrors M1, M2,. Note that n is an integer of 2 or more.

  The plane mirrors M1, M2,..., Mn are installed on a substantially rectangular frame and, for example, are fixed inside the frame while maintaining a predetermined angle. Instead of a frame, a circular or polygonal cylinder may be used, or several stages may be used. The installation angle of each mirror is set so that the laser light emitted from the laser light source 10 is reflected by the mirrors M1, M2,..., Mn-1, Mn, and then reflected by the retroreflector RR1. Yes.

  The retro-reflector RR1, which is also expressed as a corner cube, combines three plane mirrors at right angles, and is a device that reflects light in the same path as the incident light regardless of the direction of the incident light. It is an example. As the retroreflector, there are a retroreflector coated with beads, prisms, and a fine retroreflector in addition to the retroreflector.

  That is, the retro-reflector RR1 is an example of a retroreflector that reflects the laser beam reflected by the n-th mirror that reflects the laser beam n times among the plurality of mirrors to the n-th mirror. is there. That is, the retro-reflector RR1 is used as a reflection point reflecting means for reflecting the laser beam reflected by the n-th mirror that reflects the laser beam n times to the laser beam exit point of the n-th mirror. ing.

  In addition, you may make it use a plane mirror instead of retroreflector RR1. However, when a plane mirror is used, the angle setting is complicated and unstable when the angle of the plane mirror is set so as to reflect the laser beam emission point of the n-th mirror. If the reflector RR1 is used, the angle setting is very easy and stable.

  The perforated plane mirror 30 is provided with a through hole at the center thereof, and is a normal plane mirror except for the center. Then, the laser light emitted from the laser light source 10 passes through the through hole of the plane mirror 30 and faces the mirror M1, while the laser light re-reflected in the order of the mirrors M2 and M1 in the return path becomes the hole. The light is reflected by the plane mirror of the perforated plane mirror 30 and forms an image on the imaging plane of the light receiving element 40 via the imaging lens 31.

  The light receiving element 40 is an element that measures the amount of laser light that is repeatedly reflected in the measurement target region 20. That is, the light receiving element 40 is a light amount measuring unit that measures the light amount of the laser light reflected by the plurality of mirrors and the retroreflector RR1, and the reflected light reflected again by the plurality of mirrors.

  The computing unit 50 is a computing unit that computes the concentration of methane gas in the measurement target region 20 based on the amount of light measured by the light receiving element 40.

  Next, the operation of the above embodiment will be described.

  First, the laser light source 10 emits a laser beam having a wavelength (for example, 1.6537 μm) that is easily absorbed by methane gas, passes through the through hole of the perforated flat mirror 30, crosses the region to be measured 20, and is reflected by the mirror M 1. After that, the light is reflected in the order of mirrors M2, M3,..., Mn, and reaches the retroreflector RR1. The laser beam reflected by the retroreflector RR1 is re-reflected by the mirrors Mn,..., M3, M2, M1 in the reverse order to the above, reflected by the perforated plane mirror 30, and passes through the imaging lens 31. It reaches the light receiving element 40.

  In the light receiving element 40, the received laser light is phase-sensitively detected, and the amount (concentration) of methane gas in the measurement target region 20 is measured.

  By the way, if the area to be measured 20 sandwiched between the mirrors M1, M2,..., Mn and the retroreflector RR1 is a square and one side is 1 m, the laser light passes through the area to be measured 20. The optical path length is 1 m × 2n. When n = 31, the optical path length is 62 m, and even when the concentration is 2 ppm close to the methane concentration in the background atmosphere, the concentration × optical path length = 128 ppm · m, and high-precision measurement is possible.

  When selecting one of the retro-reflector and the other retroreflector as RR1, it is selected according to the intensity of the laser beam returning to the light receiving element 40. When the optical path length is long and the intensity of the laser beam returning to the light receiving element 40 becomes weak, a retro reflector is selected as RR1. When the optical path length is small, RR1 is selected from retroreflectors other than the retroreflector. When a retroreflector other than a retroreflector is selected as RR1, the reflected light beam diffuses. Therefore, a laser beam absorbing material or a light trap is disposed around the mirror Mn, and unnecessary laser light is disposed. Suppresses reflection.

  The size of the mirrors M1 to Mn is selected as follows. That is, the length of one side of the mirror M1 is set to about 4 to 8 cm according to the size of the imaging lens 31. In the case of a rectangle, align the long sides. When the retro reflector RR1 is used, the size of the mirror Mn is matched with the length of one side to the size of the effective diameter. When a retroreflector other than the retroreflector RR1 is used, the shape and size are the same (usually square). It is theoretically best to change the size of the mirror between the mirrors M1 and Mn in proportion to the distance. However, if there is room in the space, the size is the same as that of the mirror M1 in consideration of the cost. There may be a portion to be the same as the mirror Mn. All mirrors may be the same size. Since the laser beam has a spread, a material or a light trap that absorbs the laser beam is arranged around the mirror according to the spread angle to suppress unnecessary reflection of the laser beam.

  The reflectivity, surface accuracy, and retroreflector selection of the mirrors M1 to Mn (whether to select a retroreflector or a retroreflector other than the retroreflector) are determined by the light receiving element 40 in consideration of the optical path length. Select so that a laser beam of moderate intensity returns. If the received light intensity is too low, the methane concentration measurement accuracy will be low. If the received light intensity is too high, the response of the light receiving element is saturated, and a systematic error may occur in the methane concentration measurement. If the received light intensity is too high, the laser methane meter is usually made to issue a warning, so try to avoid such excessive received light intensity. By designing such an optical system, it is possible to produce a device of an appropriate size according to the purpose. Therefore, when measuring the concentration of methane gas, it is relatively easy to move the gas concentration measuring device. Since the concentration measuring apparatus is small, there is little restriction on the measurement area.

  In addition, even if each of the plurality of mirrors M1 to Mn is slightly changed in installation angle due to vibration or the like, the retroreflector RR1 is a laser in the original mirror Mn as long as it can be reflected by all the plane mirrors M1 to Mn. Since the laser beam is returned to the light emission point or the vicinity thereof, the laser beam reaches the light receiving element 40 by using the same or almost the same path as the forward path. Therefore, since the laser beam emitted from the laser light source 10 is surely directed to the light receiving element 40, the concentration can be reliably measured.

  The gas concentration measuring apparatus 100 uses n pieces of M1 to Mn as plane mirrors, but even if the area to be measured 20 is the same, a large number of these plane mirrors are provided (n The larger the value, the longer the optical path length of the laser light. Further, in the gas concentration measuring apparatus 100, the plane mirror is provided inside one rectangular frame. If this frame is provided in two stages and a plane mirror is provided in each frame, the optical path length is 2. Double. Furthermore, if the above-mentioned frame is made up of three or more stages, the optical path length becomes m times. In these cases, only one retro reflector RR1 is necessary.

  FIG. 2 is a conceptual diagram showing a gas concentration measuring apparatus 200 that is Embodiment 2 of the present invention.

  The gas concentration measuring apparatus 200 is an embodiment in which the GPS 70, the storage means 80, and the display means DP1 are provided in the gas concentration measuring apparatus 100.

  The GPS 70 is a global positioning system and measures data of a position where the GPS 70 exists.

  The storage unit 80 is a unit that stores the position data measured by the GPS 70 and the methane gas concentration calculated by the calculation unit 50 in association with each other.

  The display means DP1 is a means for displaying the position data measured by the GPS 70 and the methane gas concentration calculated by the calculation means 50 in association with each other. For example, a map including the position where the concentration measurement is performed is displayed, the concentration measurement position on the map is displayed with a marker, and the measured concentration value is displayed together with the displayed marker. . If the measured density value is equal to or greater than a predetermined threshold, the measured density value is displayed in a conspicuous color or the like. Furthermore, the measured density value may be divided into several ranks, a color corresponding to the rank may be determined in advance, and a color corresponding to the measured density value may be displayed on the map.

  In the gas concentration measuring apparatus 200, a two-dimensional ultrasonic anemometer may be provided.

  FIG. 3 is a conceptual diagram showing a gas concentration measuring apparatus 300 that is Embodiment 3 of the present invention.

  The gas concentration measuring device 300 is an embodiment in which the gas concentration measuring device 100 is placed on the roof of the automobile 90.

  FIG. 3A is a right side view of the gas concentration measuring apparatus 300. FIG. 3 (2) is a plan view of the gas concentration measuring apparatus 300.

  In the gas concentration measuring apparatus 300, when measuring the gas concentration, the automobile 90 is driven at a constant speed as much as possible, and the concentration of the methane gas MG flowing from the surrounding methane generation source is measured. Methane gas is not exhausted from the automobile 90 so much and the possibility that the exhaust gas reaches the gas concentration measuring device 100 is small. Therefore, an automobile using gasoline, diesel, or the like as fuel may be used as the automobile 90. An electric vehicle may be used.

  When the gas concentration measuring apparatus 100 is installed in the automobile 90, a ski carrier may be provided on the roof of the automobile 90, and the gas concentration measuring apparatus 100 may be fixed to the ski carrier. You may make it fix 100 directly.

  As shown in FIG. 3, since all of the plane mirrors M1 to Mn have their reflecting surfaces installed perpendicular to the ground surface, there is an advantage that dirt hardly adheres to the reflecting surfaces of the plane mirrors M1 to Mn.

  FIG. 4 is a conceptual diagram showing a gas concentration measuring apparatus 400 that is Embodiment 4 of the present invention. 4A is a right side view of the gas concentration measuring device 400, and FIG. 4B is a front view of the gas concentration measuring device 400. FIG.

  The gas concentration measuring device 400 is an embodiment in which the gas concentration measuring device 100 is placed on the roof of the automobile 90 to reduce the influence of turbulent flow during traveling.

  That is, the gas concentration measuring apparatus 400 is an embodiment in which the center including the centers of the plurality of mirrors M1 to Mn and the retroreflector RR1 is maintained perpendicular to the ground.

  The gas concentration measuring apparatus 400 measures the concentration of methane gas while the automobile 90 is stopped or traveling at a certain speed. Since the surface including the center of the plurality of mirrors M1 to Mn and the retroreflector RR1 is perpendicular to the ground and also perpendicular to the traveling direction, it is affected by other objects including the automobile 90. The concentration can be measured in a difficult state. That is, even if the plane mirrors M1 to Mn and the like move together with the automobile 90, the turbulent flow caused by the automobile 90 and the plane mirrors M1 to Mn and the like is small in the measured region 20, and thus the measurement value of the methane gas MG is affected. Few.

  In the gas concentration measuring apparatuses 300 and 400, the gas concentration measuring apparatus 100 may be mounted on other transportation means such as a ship, a helicopter, and an airplane instead of the automobile 90.

  Further, the gas concentration measuring devices 300 and 400 may be provided with a GPS 70 and a two-dimensional ultrasonic anemometer. Further, the gas concentration measuring devices 300 and 400 may be provided with a printing device that prints a map and prints the concentration of methane gas calculated by the calculation device 50 at a corresponding position on the map.

  As described above, if the gas concentration measuring device 100 and the GPS 70 are mounted on the transportation means and the printing device is connected, a methane map in which the measured concentration value of the methane gas MG is displayed on the map can be easily created. . Instead of printing with a printing device, it may be displayed on a personal computer screen, another electronic display device (IPad (registered trademark), etc.), a mobile phone screen, or the like.

  Even if the GPS is not installed, for example, an allowable upper limit concentration value of methane gas MG may be determined in advance, and if a concentration value exceeding the allowable upper limit concentration value is measured during concentration measurement, a warning may be given by a puzzer or the like.

  In each of the above embodiments, the concentration of methane gas MG is measured, but if the concentration of carbon dioxide gas is measured instead of measuring the concentration of methane gas MG, the degree of influence on the greenhouse effect can be measured. . Furthermore, you may make it measure the density | concentration of gas other than methane gas and a carbon dioxide gas. In this case, it is necessary to use a laser beam that is most easily absorbed by the gas whose concentration is to be measured.

  Further, in the gas concentration measurement apparatuses 300 and 400, instead of mounting the gas concentration measurement apparatus 100 on the roof of the automobile 90, the gas concentration measurement apparatus 100 is mounted in the vicinity of the front end (front bumper) of the automobile 90 or at the rear part of the automobile 90 (rear part of the rear glass). You may do it. If the gas concentration measuring device 100 is mounted in the vicinity of the front end of the automobile 90, when measuring the gas concentration while the automobile 90 is traveling, the influence of the air flow caused by the traveling of the automobile 90 is small, and the automobile 90 is discharged. There is little influence of the gas to do. If a ski carrier fixed to the rear part of the automobile 90 is used, the gas concentration measuring device 100 can be easily mounted on the rear part of the automobile 90.

  FIG. 5 is a conceptual diagram showing a gas concentration measuring apparatus 500 that is Embodiment 5 of the present invention. FIG. 5 (1) is a diagram showing the entire gas concentration measuring apparatus 500, and FIG. 5 (2) is a diagram showing the relationship between the three-dimensional ultrasonic anemometer 60 and the central portion 21 of the measurement region. .

  The gas concentration measuring device 500 includes a gas concentration measuring device 100a instead of the gas concentration measuring device 10 in the gas concentration measuring device 200, deletes the GPS 70 and the storage means 80, the three-dimensional ultrasonic anemometer 60, In this embodiment, the data processing means 65 is provided. In the gas concentration measuring apparatus 500, the GPS 70 and the storage unit 80 may be provided.

  In the gas concentration measuring apparatus 100a, the plane mirrors M1, M2,..., Mn, and the retroreflector RR1 are not arranged on the opposing frames of the quadrangle, but are arranged on the substantially circumference in the gas concentration measuring apparatus 100. This is an example.

  The plane mirrors M1, M2,..., Mn are installed substantially on the circumference, and are fixed, for example, to the inner circumference of a metal cylinder while maintaining a predetermined angle. Instead of a cylinder, a polygonal cylinder may be used, or a loop may be used.

  The three-dimensional ultrasonic anemometer 60 includes sensors S11, S12, and S13, sensors S21, S22, and S23, and a wind speed measuring unit 61. At a certain timing, the sensors S11, S12, and S13 constitute a transmitter, and the sensors S21, S22, and S23 constitute a receiver, that is, three sets of transmitters and receivers are provided, and one transmitter And the propagation time of the ultrasonic wave are measured between one and the corresponding receiving unit. In addition, at the next timing, the sensors S21, S22, and S23 constitute a transmitter, and the sensors S11, S12, and S13 constitute a receiver, and this is repeated.

  The wind speed is measured by measuring the ultrasonic propagation time. In other words, when the ultrasonic wave is emitted from the leeward to the leeward, the propagation time of the ultrasonic wave is shortened by the amount of the wind speed, and conversely, when the ultrasonic wave is emitted from the leeward to the windward, only the amount of the wind speed is obtained. Propagation time of ultrasonic waves becomes longer. The wind speed is measured based on the change in the propagation time. The three-dimensional ultrasonic anemometer 60 is provided with three sets of transmission / reception units at intervals of 120 degrees, and by calculating the difference in propagation time obtained from the three sets of transmission / reception units, not only in the horizontal direction but also in the vertical direction Wind speed, that is, three-dimensional wind speed can be measured.

  The three-dimensional ultrasonic anemometer 60 is commercially available as a device that has a quick response and can measure the wind direction, the wind speed, and the air temperature in about 0.1 seconds, and measures the gas concentration to estimate the amount of gas generated. Giving you important information.

  The data processing means 65 is a means for storing the methane gas concentration in the measurement area 20 calculated by the calculating means 50 and the wind direction and wind speed data output from the three-dimensional ultrasonic anemometer 60 and executing necessary processing. is there.

  The installation angle of each mirror is set so that the laser light emitted from the laser light source 10 is reflected by the mirrors M1, M2,..., Mn and then reflected by the retro-reflector RR1. In this way, by arranging the mirrors M1, M2,..., Mn, and the retroreflector RR1 on the circumference, the methane concentration with a large weight is measured at the center of the circle (the center 21 of the region to be measured). It is possible. For example, in the case of measuring the amount of methane generated (flux) in combination with the three-dimensional ultrasonic anemometer 60, the small wind speed measuring unit of the three-dimensional ultrasonic anemometer 60 and the central part of the cylinder are made to coincide with each other. The deviation (about 15 cm) between the wind speed measurement position and the methane concentration measurement position found in the open path methane flux measurement apparatus can be eliminated.

  When measuring the methane flux by the vortex correlation method or the simple vortex accumulation method, it is optimal to set the diameter of the cylinder to about 30 cm, but n = 21 is possible by using a small plane mirror. Yes, the optical path length is about 13 m. In this case, it is possible to achieve the required accuracy by using two stages of mirrors, performing a temporal average operation, or both. The methane flux measurement can be performed as a measurement of the amount of methane generated when a methane generation source is specified by movement measurement or the like by the gas concentration measurement devices 300 and 400 shown in Examples 3 and 4.

100, 200, 300, 400, 500 ... gas concentration measuring device,
10 ... Laser light source,
20 ... measurement area,
21 ... the center of the area to be measured,
M1 to Mn: plane mirror,
RR1 ... Retro reflector,
30 ... perforated flat mirror,
40: light receiving element,
60 ... 3D ultrasonic anemometer,
70 ... GPS,
90 ... car.

Claims (10)

Laser light irradiation means for irradiating the gas in the measurement area with laser light;
A plurality of mirrors disposed so as to sandwich the region to be measured, the mirrors sequentially reflecting the laser light emitted by the laser light irradiation means;
Among the plurality of mirrors, the laser beam reflected by the n-th mirror (n is an integer of 2 or more) that reflects the laser beam n-th time is used as the laser beam emission point of the n-th mirror. A reflective retroreflector;
A light amount measuring means for measuring the amount of laser light reflected by the plurality of mirrors and the retroreflector, and the reflected light reflected again by the plurality of mirrors;
A computing means for computing the concentration of a predetermined gas in the measurement area based on the light quantity measured by the light quantity measuring means;
A gas concentration measuring device comprising: In claim 1,
GPS for measuring position data;
Storage means for storing the position data measured by the GPS and the gas concentration calculated by the calculation means in association with each other;
A gas concentration measuring device comprising: In claim 2,
The concentration measuring apparatus is mounted on a predetermined transportation means. In claim 3,
A gas concentration measuring apparatus comprising printing means for printing a map and printing the calculated gas concentration at a corresponding position on the map. In claim 3,
A gas concentration measuring device characterized in that a surface formed by the center of each mirror constituting the plurality of mirrors and the center of the retroreflector is disposed substantially perpendicular to the traveling direction of the transport means. . In claim 1,
A gas concentration measuring apparatus, wherein a line connecting the center of each mirror constituting the plurality of mirrors and the center of the retroreflector forms a substantially circular or square shape. In claim 1,
A gas concentration measuring apparatus comprising an ultrasonic anemometer for measuring a wind direction and a wind speed in the measurement area. In claim 7,
The gas concentration measuring apparatus, wherein the ultrasonic anemometer is installed at substantially the center of the measurement area. In any one of Claims 1-9,
The gas concentration measuring device, wherein the predetermined gas is methane gas or carbon dioxide gas. In claim 1,
The gas concentration measuring device, wherein the retroreflector is a retroreflector or a retroreflector coated with a bead, a prism, or a fine retroreflector.

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