Measuring equipment

Abstract

Provided is a measurement device which is capable of stably and quickly executing a change in the wavelength received by a light-receiving system, regardless of the atmospheric state. This measurement device is equipped with: a transmission system 101 for selectively emitting a first laser beam having a first wavelength and a second laser beam having a second wavelength which differs from the first wavelength into the atmosphere; a light-receiving system 102 equipped with a filter for which the first wavelength and the second wavelength are passbands; and a control unit 106 for adjusting the filter by directly light-guiding the first laser beam and / or the second laser beam from the transmission system to the filter.

Description

[Technical Field]

[0001] The present invention relates to a measurement device. [Background technology]

[0002] One of the measuring devices used to measure meteorological conditions is a differential absorption lidar (DIAL) device. A differential absorption lidar device emits laser light of two closely spaced wavelengths into the atmosphere, and detects the concentration of gas molecules or aerosols in the atmosphere based on the ratio of the amount of light received at the two wavelengths obtained by measuring the reflected or scattered light in the atmosphere. Patent Document 1 discloses an optical filter used in a differential absorption lidar. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 11,243,295 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, in LIDAR systems, it was necessary to remove the optical fiber installed after the telescope, an optical device that emits laser light into the atmosphere and receives reflected or scattered light, and adjust the light-receiving system (including the interference filter, etalon holder, and etalon) separately. The light-receiving system needed to be readjusted every time the wavelength of light received by the light-receiving system was changed, resulting in the need to repeatedly attach and detach the light-receiving system every time the wavelength was changed. Furthermore, when adjusting the etalon using a signal corresponding to atmospheric conditions, the scattered light signal may change significantly depending on the atmospheric conditions. During the day, background light from sunlight also fluctuates significantly, making it difficult to adjust the light-receiving system and change the wavelength of light received at any time required for measurement.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a measuring device that allows stable and rapid change of the wavelength of light received by the light receiving system, regardless of atmospheric conditions. [Means for solving the problem]

[0006] A measurement device according to one aspect of the present invention includes a transmitting system that selectively emits into the atmosphere a first laser light having a first wavelength and a second laser light having a second wavelength different from the first wavelength, a receiving system that includes a filter that has a passband for the first wavelength and the second wavelength, and a control unit that directly guides the first laser light and / or the second laser light from the transmitting system to the filter and adjusts the filter.

[0007] According to this aspect, since the first laser beam or the second laser beam is directly guided to the filter, the filter can be adjusted regardless of atmospheric conditions. Since the filter can be adjusted to be suitable for measurement using the first laser beam or the second laser beam regardless of atmospheric conditions, the wavelength received by the light receiving system can be stably and quickly changed when the wavelength of the first laser beam or the second laser beam is changed.

[0008] In the above aspect, in the measurement device, the light receiving system has a light receiving unit that receives scattered light that is emitted from the transmitting system, and a filter unit that is connected to the light receiving unit and has a filter, and the measurement device further has a first connection optical path that connects the light receiving unit and the filter unit, an optical switch provided in the first connection optical path, and a second connection optical path that connects the transmitting system and the optical switch, and the control unit may adjust the filter by controlling the optical switch so that the first laser light and / or the second laser light from the transmitting system is supplied to the filter unit.

[0009] According to this aspect, by controlling the optical switch, the first laser light and / or the second laser light can be supplied to the filter section, and the first laser light and / or the second laser light can be directly guided from the transmitting system to the filter, thereby making it possible to stably and quickly change the wavelength of light received by the light receiving system regardless of atmospheric conditions.

[0010] In the above aspect, in the measurement device, the light-receiving system may include a light-receiving unit that receives scattered light obtained by scattering light emitted from the transmitting system, and a filter unit connected to the light-receiving unit and having a filter, and the transmitting system may further include a window unit through which the first laser light and / or the second laser light passes when the first laser light and / or the second laser light is emitted into the atmosphere, and a shutter unit having a shutter member that is movable to block the window unit by switching between a first state in which the first laser light and / or the second laser light can pass through the window and a second state in which the first laser light and / or the second laser light cannot pass through the window. The control unit may adjust the filter by controlling the shutter unit to set the shutter unit to the second state.

[0011] According to this aspect, when the shutter unit is in the second state, the shutter member blocks light passing through the transmission system. The scattered light scattered by the shutter member is supplied to the filter unit through the light receiving unit. The control unit adjusts the filter in accordance with the supplied scattered light. This makes it possible to stably and quickly change the wavelength of light received by the light receiving system regardless of atmospheric conditions.

[0012] In the above aspect, in the measurement device, the light receiving unit may further include a light detecting unit connected to the filter unit and detecting the intensity of detection light that is light that has passed through the filter unit, and the control unit may adjust the filter based on a detection signal generated by the light detecting unit detecting the first laser light and / or the second laser light. The control unit may also adjust the filter so that the intensity of the detection signal generated by detecting the first laser light is maximized.

[0013] According to this aspect, for example, the filter can be adjusted so that the detection signal corresponding to the light that has passed through the filter becomes large, and the filter can be adjusted to be suitable for measuring the actual atmosphere using the measurement device.

[0014] In the above aspect, the control unit may adjust the filter so that the intensity of the detection signal when the first laser beam is detected is maximized and the intensity of the detection signal when the second laser beam is detected is maximized.

[0015] By adjusting the filters so that the intensity of the detection signals for each of the first laser light and the second laser light is maximized, it becomes possible to adjust the filters to be more suitable for measuring the actual atmosphere using the measurement device.

[0016] In the above aspect, the filter section may have an incident angle control unit that controls the incident angle of light incident on the filter, and the control section may control the incident angle control unit based on the detection signal. Also, in the above aspect, the filter section may have a temperature control unit that controls the temperature of the filter, and the control section may control the temperature control unit based on the detection signal.

[0017] By adopting a control method for adjusting a filter depending on the type of filter, it becomes possible to appropriately adjust the filter. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a measurement device that can stably and quickly change the wavelength of light received by the light receiving system regardless of atmospheric conditions. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a LIDAR device according to a first embodiment. [Figure 2] FIG. 1 is a diagram showing an example of the relationship between the absorption spectrum of water vapor and wavelength. [Figure 3] FIG. 10 is a diagram showing the water vapor mixing ratio at different altitudes depending on the magnitude of absorption. [Figure 4] FIG. 10 is a diagram showing the water vapor mixing ratio at different altitudes depending on the magnitude of absorption. [Figure 5] FIG. 4 is a diagram illustrating an example of processing by a control unit according to the first embodiment. [Figure 6]10A and 10B are diagrams illustrating another example of processing by the control unit according to the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating signal stability. [Figure 8] FIG. 10 is a diagram illustrating an example of the configuration of a LIDAR device according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of processing by a control unit according to the second embodiment. [Figure 10] FIG. 1 is a diagram illustrating a configuration of a LIDAR device as a reference example. DETAILED DESCRIPTION OF THE INVENTION

[0020] [First embodiment] A first embodiment will now be described. Fig. 1 shows the configuration of a differential absorption LIDAR device 10 according to the first embodiment. The differential absorption LIDAR device 10 has a transmission system 101, a light-receiving system 102, an optical switch 103, a coupler 104, a wavemeter 105, and a control unit 106. The differential absorption LIDAR device 10 also has a power supply unit that supplies power necessary for operation and a communication unit (not shown) that can communicate with an external information processing device.

[0021] The differential absorption LIDAR device 10 measures the concentrations of gas molecules and aerosols in the atmosphere by emitting laser beams of two different wavelengths generated by a transmission system 101 from the differential absorption LIDAR device 10 into the atmosphere. In this specification, the differential absorption LIDAR device 10 is described as measuring the concentration of water vapor in the atmosphere. Specifically, the differential absorption LIDAR device 10 alternately emits laser beams of wavelengths (referred to as "on wavelengths") at which the optical absorption of molecules, etc. to be measured is relatively high and laser beams of wavelengths (referred to as "off wavelengths") at which the optical absorption of molecules, etc. to be measured is relatively low into the atmosphere. When the laser beams of each wavelength are emitted into the atmosphere, they are absorbed, reflected, or scattered by various components in the atmosphere. The differential absorption LIDAR device 10 receives reflected light and scattered light of the laser beam reflected and scattered by the atmosphere using a light receiving system 102, and measures the intensity of the reflected light and scattered light. The differential absorption LIDAR device 10 calculates the concentration of molecules, etc. to be measured based on the ratio between the intensity of reflected light and scattered light based on the on-wavelength laser light and the intensity of reflected light and scattered light based on the off-wavelength laser light.

[0022] The transmission system 101 includes laser devices 1011 and 1012, couplers 10131 and 10132, an optical switch 1014, an isolator 10152, a λ / 2 wave plate 10153, an amplifier 1016, a collimating lens 10171, a cylindrical lens 10172, and mirrors 10173, 10174, and 10175. The transmission system 101 may also include a window 1018 provided between the inside and outside of the housing of the differential absorption LIDAR device 10.

[0023] The laser device 1011 is a device that generates a first laser beam. The laser device 1012 is a device that generates a second laser beam. The laser devices 1011 and 1012 can change the wavelength of the laser beam they generate under the control of the control unit 106. Examples of lasers that can be used include semiconductor lasers, solid-state lasers, and gas lasers, and a single-mode laser is preferable. Furthermore, a single-frequency laser with an oscillation wavelength spectral width of about 1 kHz to 1 MHz is preferable.

[0024] Coupler 10131 is optically connected to laser device 1011, optical switch 1014, and optical switch 1019. The connection can be made using, for example, optical fiber. In this specification, optical connection may be simply referred to as "connection." Coupler 10131 distributes and outputs the laser light input from laser device 1011 to optical switch 1014 and optical switch 1019.

[0025] Coupler 10132 is connected to laser device 1012, optical switch 1014, and optical switch 1019. Coupler 10132 distributes the laser light input from laser device 1012 to optical switch 1014 and optical switch 1019 and outputs the distributed light.

[0026] Optical switch 1014 selectively outputs to isolator 10152 either the laser light from laser device 1011 supplied via coupler 10131 or the laser light from laser device 1012 supplied via coupler 10132. In this case, optical switch 1014 has two input ports and one output port, and output switching by optical switch 1014 is controlled by control unit 106. Various types of optical switches can be used, such as mechanical switches, MEMS switches, and optical waveguide switches. Optical switch 1014, which switches the wavelength to be emitted into the atmosphere, needs to alternate between both wavelengths for each pulse, so an optical waveguide switch that achieves high switching speeds is more preferable. On the other hand, optical switch 1019, which switches the wavelength of light input to wavemeter 105, is preferably a mechanical switch or an MEMS switch because a measurement time of several seconds to several tens of seconds is set for the same wavelength.

[0027] The isolator 10152 is a device that transmits laser light only in the forward direction and blocks laser light in the backward direction. The light emitted from the optical switch 1014 into free space is collimated by the collimating lens 10151, and includes the isolator 10152, the λ / 2 wave plate 10153, and the condenser lens 10154.

[0028] The laser light supplied from the optical switch 1014 is collimated by a collimating lens 10151 and enters an isolator 10152. The isolator 10152 prevents light from the downstream amplifier 1016 from returning to the laser devices 1011 and 1012, which would cause fluctuations in the oscillation wavelength of the laser light. The polarization of the laser light emitted from the isolator 10152 is adjusted by a λ / 2 wave plate 10153 to a polarization suitable for optical amplification in the downstream amplifier 1016, and then focused by a focusing lens 10154 and enters the amplifier 1016.

[0029] The amplifier 1016 amplifies the laser light output from the isolator 10152. A general semiconductor optical amplifier can be used as the amplifier 1016. The degree of amplification by the amplifier 1016 can be controlled by the control unit 106.

[0030] The laser light amplified by the amplifier 1016 is collimated by a collimating lens 10171 and a cylindrical lens 10172, and is irradiated toward a window 1018 through mirrors 10173, 10174, and 10175. The laser light is finally emitted from the differential absorption LIDAR device 10 into the atmosphere through the window 1018.

[0031] The light receiving system 102 includes a telescope 1021, a filter unit 1022, and a photodetector 1023. The light receiving system 102 receives reflected light and scattered light based on the laser light irradiated into the atmosphere, and generates an intensity signal indicating the intensity of the light.

[0032] The telescope 1021 has a primary mirror 10211 and a secondary mirror 10212. Light received by the telescope 1021 is focused into an optical fiber P1 and output to a filter unit 1022. Although the telescope 1021 is illustrated as a Cassegrain type reflecting telescope, other types of telescopes such as a Newtonian type may also be used. Furthermore, a refracting telescope using a lens that has good transmission of the wavelength of the laser light used may also be used.

[0033] The telescope 1021 is connected to the filter unit 1022 through the optical switch 103. The optical switch 103 will be described later.

[0034] The filter unit 1022 has a collimating lens 10221, an interference filter 10222, an etalon filter 10223, a filter cover 10224, and a condenser lens 10225. The filter unit 1022 filters the light supplied through the optical switch 103.

[0035] The filter unit 1022 transmits light in a wavelength range including the on wavelength and off wavelength of the laser light, for example, by using an interference filter 10222. Next, an etalon filter 10223, which has a steeper transmittance characteristic than the interference filter, transmits only light in the vicinity of each of the on wavelength and off wavelength. The transmitted light is supplied to the photodetector 1023 through a condenser lens 10225. If necessary, multiple interference filters 10222 and / or etalon filters 10223 may be used in a stacked manner.

[0036] The etalon filter 10223 is housed in a filter cover 10224. Although not shown, the filter cover 10224 has, for example, an incident angle control unit having a drive element for changing the rotation angle of the etalon filter 10223 in response to a control signal from the control unit 106, and a temperature control unit having a temperature control element for changing or maintaining the temperature of the etalon filter 10223 in response to a control signal from the control unit 106. The filter cover 10224 can also be called an etalon holder.

[0037] The photodetector 1023 is, for example, an avalanche photodiode or a photomultiplier tube, converts light incident on the photodetector 1023 into an electrical signal, and outputs a detection signal corresponding to the incident light. The photodetector 1023 outputs the detection signal to, for example, the control unit 106.

[0038] The optical switch 103 is connected to the telescope 1021 through a connecting optical path P1. The optical switch 103 is also connected to a coupler 104 through a connecting optical path P2, and laser light from the laser devices 1011 and 1012 is supplied to the optical switch 103. The optical switch 103 switches the connection so that light from the telescope 1021 or light from the transmission system 101 is selectively supplied to the filter unit 1022. The switching of the optical switch 103 is controlled by a control unit 106.

[0039] Coupler 104 is an element that distributes light supplied from coupler 10131 or coupler 10132 so that the light is supplied to optical switch 103 and wavemeter 105. Coupler 104 makes it possible to supply light of the same wavelength to switch 103 and wavemeter 105.

[0040] Wavelength meter 105 is a device that measures the wavelength of the laser light generated by laser devices 1011 and 1012. Optical switch 1019 measures the wavelength input to wavelength meter 105 by switching between on wavelength and off wavelength, and control unit 106 stabilizes the oscillation wavelength of laser devices 1011 and 1012 so that it becomes the set wavelength.

[0041] The control unit 106 is a device that performs information processing in the differential absorption LIDAR device 10. The control unit 106 performs, for example, setting the wavelength of the laser light output by the laser devices 1011 and 1012, switching the output laser light by controlling the optical switch 1014, switching the light supplied to the filter unit 1022 by controlling the optical switch 103, and processing based on the detection signal detected by the photodetector 1023. The control unit 106 has a processor and memory, and a program required for the above information processing is stored in the memory, and the above information processing is performed by the processor executing the program.

[0042] The on wavelength and off wavelength in the differential absorption LIDAR device 10 will be described with reference to FIG. 2. FIG. 2 shows the spectrum of the absorption cross section of water vapor. The on wavelength light is set to a wavelength with a relatively large absorption cross section, and the off wavelength light is set to a wavelength with a smaller absorption cross section than the on wavelength. For example, wavelength λ11 is selected as the on wavelength and wavelength λ12 is selected as the off wavelength. Alternatively, on wavelength λ21 and off wavelength λ22 are selected such that the absorption cross section of the on wavelength is smaller than that for wavelength λ11.

[0043] FIG. 3 shows an example of measurements of water vapor mixing ratios at different altitudes when wavelength λ11 is used as the on wavelength and wavelength λ12 as the off wavelength. FIG. 4 shows an example of measurements of water vapor mixing ratios at different altitudes when wavelength λ21 is used as the on wavelength and wavelength λ22 as the off wavelength. Because wavelength λ21 has a smaller absorption cross section, as shown in FIG. 4, the water vapor mixing ratio is measured up to a higher altitude than in the case of FIG. 3. Thus, in the differential absorption LIDAR device 10, the measurement results obtained vary depending on the selection of the on wavelength and the off wavelength. The desired measurement results are determined based on atmospheric conditions, such as the amount of water vapor, and the desired altitude range, and appropriate on wavelengths and off wavelengths are selected to achieve such measurements. For example, in times of high water vapor content (e.g., summer), using a wavelength with a relatively small absorption cross section as the on wavelength increases the maximum measurable altitude.

[0044] When changing the on wavelength and off wavelength, it is preferable to also change the wavelength filtered by the filter unit 1022. In particular, in the case of a filter having a steep transmission characteristic with respect to wavelength, such as an etalon filter, it is necessary to precisely match the laser oscillation wavelength with the transmittance peak of the etalon filter to ensure a sufficient signal-to-noise (S / N) ratio. Figure 5 shows a flowchart of the adjustment process of the filter unit 1022 in the differential absorption LIDAR device 10, performed by the control unit 106.

[0045] In step S501, the control unit 106 changes the oscillation wavelength of the laser device 1011. In step S502, the control unit 106 changes the oscillation wavelength of the laser device 1012. Here, it is assumed that the laser device 1011 emits laser light of an ON wavelength, and the laser device 1012 emits laser light of an OFF wavelength.

[0046] In step S503, the control unit 106 switches the optical switch 103 so that the laser light from the laser device 1011 is incident on the filter unit 1022. Specifically, by switching by the control unit 106, the laser light of the ON wavelength is incident on the light receiving unit 102 through the connecting optical path P2.

[0047] In step S504, the control unit 106 controls at least one of the incident angle and temperature of the interference filter 10222 and / or the etalon filter 10223. This changes the transmittance spectrum of the filter unit 1022 for the on wavelength.

[0048] In step S505, the control unit 106 acquires from the detector 1023 a signal of the laser light having the ON wavelength.

[0049] In step S506, the control unit 106 determines whether the signal detected by the detector 1023 is a peak value. The fact that the detected signal is a peak value means that the peak wavelength of the transmittance spectrum of the filter unit 1022 can be matched with the on wavelength.

[0050] If a negative determination is made in step S506, the process is repeated from step S504.

[0051] If the determination in step S506 is affirmative, it is determined that the filter adjustment is complete, and the control unit 106 switches the optical switch 103 so that light from the telescope 1021 is supplied to the filter unit 1022. This enables atmospheric measurement by the differential absorption LIDAR device 10.

[0052] 5, the filter unit 1022 is adjusted based on only the laser light of the on wavelength, but the filter unit 1022 may be adjusted using laser light of the on wavelength and the off wavelength. Fig. 6 shows a flowchart of the adjustment process of the filter unit 1022 using laser light of the on wavelength and the off wavelength.

[0053] In step S601, the control unit 106 changes the oscillation wavelength of the laser device 1011. In step S602, the control unit 106 changes the oscillation wavelength of the laser device 1012.

[0054] In step S 603 , the control unit 106 switches the optical switch 103 so that the laser light from the laser device 1011 is incident on the filter unit 1022 .

[0055] In step S604, the control unit 106 controls at least one of the incident angle and temperature of the interference filter 10222 and / or the etalon filter 10223. As a result, the transmittance spectrum of the filter unit 1022 changes.

[0056] In step S605, the control unit 106 acquires a first detection signal of the laser light having the ON wavelength by switching the optical switch 1019.

[0057] In step S606, the control unit 106 acquires a second detection signal of the laser light whose wavelength becomes the off wavelength by switching the optical switch 1019.

[0058] In step S607, the control unit 106 determines whether the first detection signal and the second detection signal are at peak values.

[0059] If a negative determination is made in step S607, the process is repeated from step S604.

[0060] If the determination in step S607 is affirmative, filter adjustment is deemed complete, and the control unit 106 switches the optical switch 103 so that light from the telescope mirror 1021 is supplied to the filter unit 1022. This enables atmospheric measurement by the differential absorption LIDAR device 10. The above adjustment process is an example for two wavelengths, but adjustments can be made in the same way for three or more wavelengths. In the case of three wavelengths, adjustments can be made in the same way by using an optical switch 1019 with three input ports and one output port.

[0061] The advantages of adjusting the filter section 1022 by directly guiding the laser light from the transmission system 101 to the filter section 1022 will be described with reference to FIGS.

[0062] Figure 7 shows a detection signal SG1 by the photodetector 1023 when laser light from the transmission system 101 is directly guided to the filter section 1022, and a detection signal SG2 by the photodetector 1023 when reflected light and scattered light of laser light irradiated from the differential absorption LIDAR device 10 are guided to the filter section 1022, as in the differential absorption LIDAR device 10X of the conventional reference example shown in Figure 10.

[0063] FIG. 7 shows a comparison of signal variability when the detection signal is measured every 0.5 seconds for 10 minutes. During these 10 minutes, the coefficient of variation (standard deviation / average value) when the laser beam is directly guided is 2%, while the coefficient of variation for the atmospheric signal is 18%, demonstrating stable signal detection. Thus, while the detection signal SG1 maintains a stable value over time, the detection signal SG2 fluctuates over time due to atmospheric influences and other factors. While adjusting the filter unit 1022 using such a fluctuating detection signal may result in inappropriate adjustment, the differential absorption LIDAR device 10 can adjust the filter unit 1022 based on a stable signal. Therefore, the differential absorption LIDAR device 10 can stably and quickly change the wavelength of light received by the light receiving system, regardless of atmospheric conditions.

[0064] [Second embodiment] A second embodiment will now be described. FIG. 8 shows the configuration of a differential absorption LIDAR device 10A according to the second embodiment. In the second embodiment, descriptions common to the first embodiment will be omitted as much as possible. In the differential absorption LIDAR device 10 according to the first embodiment, the switch 103 is used to guide the laser light from the transmission system 101 to the filter unit 1022, whereas in the differential absorption LIDAR device 10A, the laser light from the transmission system 101 is reflected and scattered by a shutter 8012 (described below) before being guided to the filter unit 1022. The differential absorption LIDAR device 10A differs from the first embodiment in that, when adjusting the filter unit 1022, light based on the laser light is supplied to the filter unit 1022 so as not to be emitted into the atmosphere, and the laser light is directly guided to the filter unit 1022.

[0065] Similar to the differential absorption LIDAR device 10, the differential absorption LIDAR device 10A has a transmitting system 101, a light receiving system 102, a coupler 104, a wavemeter 105, and a control unit 106. Unlike the differential absorption LIDAR device 10, the differential absorption LIDAR device 10A has a connecting optical path P3 that directly connects the telescope 1021 and the filter unit 1022 without going through an optical switch 103 or the like.

[0066] The differential absorption LIDAR device 10A further includes a shutter unit having a switch 8011 and a shutter 8012. The switch 8011 controls the position of the shutter 8012 under control of the control unit 106. The shutter 8012 is a member that can block the window 1018 by switching between a first state in which the laser light generated by the transmission system 101 can pass through the window 1018 and a second state in which the laser light cannot pass through the window 1018. When the laser light from the transmission system 101 is irradiated onto the shutter 8012, the light reflected and scattered by the shutter 8012 enters the telescope 1021. Note that, as shown in FIG. 8 , the differential absorption LIDAR device 10A significantly differs from the conventional differential absorption LIDAR device 10X, which is a reference example, in that it includes the switch 8011 and the shutter 8012. It is desirable that the shutter 8012 can completely cover the skylight 1018 in the second state to prevent light from entering from outside. Not only does it block the laser light emitted into the atmosphere, but it also blocks light from outside, allowing for stable adjustment.

[0067] Referring to FIG. 9, adjustment of the filter section 1022 in the differential absorption LIDAR device 10A will be described.

[0068] In step S901, the control unit 106 controls the switch 8011 so that the shutter 8012 transitions from the first state to the second state.

[0069] In step S902, the control unit 106 changes the oscillation wavelength of the laser device 1011. In step S903, the control unit 106 changes the oscillation wavelength of the laser device 1012.

[0070] In step S904, the control unit 106 controls the amplifier so that laser light of lower intensity than that during measurement is incident on the filter unit, thereby preventing excessive reflected light and scattered light from entering the detector 1023 and damaging the detector 1023.

[0071] In step S905, the control unit 106 controls at least one of the incident angle and the temperature of the interference filter 10222 and / or the etalon filter 10223. As a result, the transmittance spectrum of the filter unit 1022 changes.

[0072] In step S906, the control unit 106 acquires a first detection signal of the laser light having the ON wavelength by switching the optical switch 1019.

[0073] In step S907, the control unit 106 acquires a second detection signal of the laser light whose wavelength becomes the off wavelength by switching the optical switch 1019.

[0074] In step S908, the control unit 106 determines whether the first detection signal and the second detection signal are at peak values.

[0075] If a negative determination is made in step S908, the process is repeated from step S905.

[0076] If the determination in step S908 is affirmative, it is determined that filter adjustment is complete, and the control unit 106 switches the optical switch 103 so that light from the telescope 1021 is supplied to the filter unit 1022. This enables atmospheric measurement by the differential absorption LIDAR device 10. Note that although the processing described in FIG. 9 uses the first detection signal and the second detection signal, only the first detection signal may be used, as in the processing described in the first embodiment with reference to FIG. 5.

[0077] In the differential absorption LIDAR device 10A, too, the filter section 1022 can be adjusted based on a stable signal without being affected by the atmosphere. Therefore, the differential absorption LIDAR device 10A can stably and quickly change the wavelength of light received by the light receiving system, regardless of atmospheric conditions.

[0078] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, conditions, shape, size, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other. [Explanation of symbols]

[0079] 10, 10A, 10X...differential absorption lidar device, 101...transmission system, 102...light receiving system, 103...optical switch, 104...coupler, 105...wavelength meter, 106...control unit, 1011, 1012...laser device, 1022...filter unit, 1023...photodetector, 8011...switch, 8012...shutter

Claims

1. a transmission system that selectively emits into the atmosphere a first laser beam having a first wavelength and a second laser beam having a second wavelength different from the first wavelength; a light receiving system including a filter having a pass band for the first wavelength and the second wavelength; a control unit that directly guides the first laser light and / or the second laser light from the transmission system to the filter and adjusts the filter.

2. 2. The measuring device according to claim 1, The light receiving system includes: a light receiving unit that receives scattered light that is the light emitted from the transmission system; a filter unit connected to the light receiving unit and having the filter; The measuring device is a first connecting optical path connecting the light receiving unit and the filter unit; an optical switch provided in the first connection optical path; a second connection optical path connecting the transmission system and the optical switch, The control unit a measuring device that controls the optical switch to adjust the filter so that the first laser light and / or the second laser light from the transmission system is supplied to the filter section;

3. 2. The measuring device according to claim 1, The light receiving system includes: a light receiving unit that receives scattered light that is the light emitted from the transmission system; a filter unit connected to the light receiving unit and having the filter; The transmission system includes: a window portion through which the first laser beam and / or the second laser beam passes when the first laser beam and / or the second laser beam is emitted into the atmosphere; a shutter member that has a shutter member that is movable to switch between a first state in which the first laser beam and / or the second laser beam can pass through the window portion and a second state in which the first laser beam and / or the second laser beam cannot pass through the window portion, thereby blocking the window portion; The control unit controls the shutter unit to adjust the filter so that the shutter unit is in the second state.

4. The measuring device according to claim 2 or 3, the light receiving unit further includes a light detecting unit connected to the filter unit and configured to detect the intensity of detection light that has passed through the filter unit; The control unit The measurement device, wherein the light detection unit adjusts the filter based on a detection signal obtained by detecting the first laser light and / or the second laser light.

5. 5. The measuring device according to claim 4, The control unit The measurement device adjusts the filter so that the intensity of the detection signal detected by the first laser light is maximized.

6. 5. The measuring device according to claim 4, The control unit a measuring device that adjusts the filter so that the intensity of the detection signal when the first laser beam is detected is maximized and the intensity of the detection signal when the second laser beam is detected is maximized.

7. 5. The measuring device according to claim 4, the filter unit has an incident angle control unit that controls an incident angle of light incident on the filter, The control unit controls the incident angle control unit based on the detection signal.

8. 5. The measuring device according to claim 4, the filter unit has a temperature control unit that controls the temperature of the filter, The control unit controls the temperature control unit based on the detection signal.

Images