Wind velocity detection device, wind velocity detection method, and flying body control device

Abstract

A wind velocity detection device 1 is provided with a control unit 15 that controls a state of measurement light Lm output from a measurement optical system 7 on the basis of a detection distance by the measurement light Lm, wherein the control unit 15 controls the measurement optical system 7 so that the measurement light Lm output into the atmosphere M is focused if the detection distance belongs to a short-distance range R1 at or below a first threshold T1, and controls the measurement optical system 7 so that the measurement light Lm output into the atmosphere M is made into parallel light if the detection distance belongs to a long-distance range R2 exceeding the first threshold T1.

Description

Wind speed detection device, wind speed detection method, and aircraft control device

[0001] The present disclosure relates to a wind speed detection device, a wind speed detection method, and an aircraft control device.

[0002] Light detection and ranging (LIDAR) is known as one of the sensing technologies using light. While LIDAR has recently been increasingly applied in the field of autonomous driving, it is originally a technology widely used in fields such as meteorology. As a LIDAR used in the field of meteorology, so-called wind LIDAR, which detects wind speed, is known. Wind LIDAR is used, for example, for wind condition surveys to select installation locations for wind power generators. In addition, in recent years, wind LIDAR is expected to be applied to the safe operation management of unmanned aerial vehicles such as drones, and manned aerial vehicles such as advanced air mobility (AAM) and urban air mobility (UAM).

[0003] Coherent detection is used to detect wind speed in LIDAR. In this method, laser light output from a light source is split into measurement light and reference light, and the measurement light is modulated and amplified before being emitted into the atmosphere. The signal source in WindLIDAR is scattered light generated when the measurement light is scattered by countless aerosols in the atmosphere. When the wind blows, the aerosols move with the wind, causing a change in the frequency of the scattered light (Doppler shift). Therefore, wind speed in the atmosphere can be detected by interfering the scattered light from the atmosphere as signal light with the reference light and determining the amount of peak frequency shift in the beat spectrum of the interference light (see, for example, Patent Document 1).

[0004] US Patent Application Publication No. 2021 / 0109218

[0005] S. Kameyama et al., “Compact all-fiber pulsed coherent Doppler lidar system for wind sensing” Applied Optics, Vol. 46, NO. 11, 10 April 2007, p.1953-1962

[0006] One LIDAR method uses pulsed light as the measurement light (see, for example, Non-Patent Document 1). In existing methods that use collimated pulsed light, the distance resolution is independent of the detection distance but depends on the pulse width, and achieving measurement at close distances of several tens of meters or less presents technical challenges. Another LIDAR method uses continuous wave (CW) light as the measurement light. In existing methods that use focused CW light, measurement is performed while changing the focal position of the measurement light, resulting in a technical challenge in that the distance resolution depends on the focal depth of the measurement light and is therefore dependent on the detection distance.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wind speed detection device, a wind speed detection method, and an aircraft control device that can perform optimal wind speed detection according to the detection distance.

[0008] The gist of the present disclosure is as follows.

[0009] [1] A wind speed detection device comprising: an output unit that outputs laser light; a branching unit that branches the laser light into measurement light and reference light; a conversion unit that converts the measurement light into pulsed light; a measurement optical system that outputs the measurement light into the atmosphere and receives scattered light of the measurement light in the atmosphere as signal light; a detection unit that outputs a detection signal based on the interference result between the reference light and the signal light; and a control unit that controls the state of the measurement light output from the measurement optical system based on the detection distance by the measurement light, wherein the control unit controls the measurement optical system so that the measurement light output into the atmosphere is focused when the detection distance falls within a short distance range equal to or less than a first threshold, and controls the measurement optical system so that the measurement light output into the atmosphere is collimated when the detection distance falls within a long distance range exceeding the first threshold.

[0010] In this wind speed detection device, when the detection distance falls within the short distance range, the measurement light, which is pulsed light, is focused and output into the atmosphere. When focusing pulsed light, the CNR (Carrier-to-Noise Ratio) of the signal light can be improved compared to when focusing CW light, when compared under the same energy and same focusing conditions. Therefore, wind speed can be detected quickly and accurately in the short distance range. Furthermore, in this wind speed detection device, when the detection distance falls within the long distance range, the measurement light, which is pulsed light, is collimated and output into the atmosphere. Unlike when focusing CW light, when the pulsed light is collimated, the distance resolution depends on the pulse width, but a constant distance resolution can be maintained regardless of the detection distance. In this way, this wind speed detection device controls the state of the measurement light based on the detection distance, allowing for optimal wind speed detection according to the detection distance.

[0011] [2] The wind speed detection device according to [1], wherein the control unit controls the output unit to output frequency-modulated light as the laser light when the detection distance falls within the ultra-short distance range, which is equal to or less than a second threshold set for the short distance range. When the detection distance falls within the ultra-short distance range, stray light components generated by the measurement optical system, etc., become larger than the signal component and overlap with each other in time, making it difficult to analyze wind speed based on the interference results between the reference light and the signal light. In contrast, using frequency-modulated light as the laser light makes it possible to separate the signal component and the stray light component on the frequency axis. This allows for accurate wind speed detection even when the detection distance falls within the ultra-short distance range.

[0012] [3] The wind speed detection device according to [1] or [2], wherein the control unit controls the conversion unit to change the pulse width of the measurement light in accordance with the detection distance when the detection distance falls within a short-to-medium distance range that exceeds a second threshold set for the short distance range. Generally, the larger the pulse width of the measurement light, the higher the CNR of the signal light. Therefore, by changing the pulse width of the measurement light in accordance with the detection distance, wind speed detection can be performed quickly and accurately in the short-to-medium distance range.

[0013] [4] The wind speed detection device according to any one of [1] to [3], wherein the output unit outputs CW light as the laser light, and the detection unit outputs a detection signal based on the interference result between the reference light, which is CW light, and the signal light. In this wind speed detection device, a wide range of detection distances can be set, from short distances to long distances. By using CW light as the reference light, an interference signal between the signal light and the reference light can be obtained regardless of the detection distance setting, even if the signal light is pulsed light or a temporal superposition of multiple pulsed light.

[0014] [5] The wind speed detection device according to any one of [1] to [4], wherein the measurement optical system has a deflection unit that deflects the output direction of the measurement light toward the atmosphere. In this case, the output direction of the measurement light is variable, making it possible to measure a three-dimensional wind speed vector including information on wind direction and wind speed.

[0015] [6] The wind speed detection device according to [5], wherein the control unit controls the deflection unit so that the scanning speed in the output direction of the measurement light is slower when the detection distance falls within the long distance range than when the detection distance falls within the short distance range. In the long distance range, where the pulsed measurement light is collimated, the CNR of the signal light is likely to be lower than in the short distance range, where the pulsed measurement light is focused. By slowing down the scanning speed in the output direction of the measurement light by the deflection unit, it is possible to increase the number of times the signal is averaged, thereby ensuring sufficient accuracy in wind speed detection in the long distance range.

[0016] [7] The wind speed detection device according to any one of [1] to [6], wherein at least the output section, the branching section, and the detection section are configured by optical integrated circuits. By configuring at least the output section, the branching section, and the detection section by optical integrated circuits, it is possible to achieve miniaturization of the device.

[0017] [8] The wind speed detection device according to any one of [1] to [7], further comprising an analysis unit that analyzes the wind speed in the atmosphere based on the detection signal. In this case, a series of processes from outputting the laser light to analyzing the wind speed can be performed within a single device.

[0018] [9] A wind speed detection method comprising: an output step of outputting laser light; a branching step of branching the laser light into measurement light and reference light; a conversion step of converting the measurement light into pulsed light; a measurement step of outputting the measurement light into the atmosphere and receiving scattered light of the measurement light in the atmosphere as signal light; and a detection step of outputting a detection signal based on an interference result between the reference light and the signal light, wherein in the measurement step, if the detection distance by the measurement light falls within a short distance range equal to or less than a first threshold, the measurement light output into the atmosphere is focused, and if the detection distance by the measurement light falls within a long distance range exceeding the first threshold, the measurement light output into the atmosphere is collimated.

[0019] In this wind speed detection method, when the detection distance falls within the short distance range, the measurement light, which is pulsed light, is focused and output into the atmosphere. When focusing pulsed light, the CNR (Carrier-to-Noise Ratio) of the signal light can be improved compared to when focusing CW light, when compared under the same energy and same focusing conditions. Therefore, wind speed detection can be performed quickly and accurately in the short distance range. Furthermore, in this wind speed detection method, when the detection distance falls within the long distance range, the measurement light, which is pulsed light, is collimated and output into the atmosphere. Unlike when focusing CW light, when collimating pulsed light, the distance resolution depends on the pulse width, but a constant distance resolution can be maintained regardless of the detection distance. In this way, this wind speed detection method controls the state of the measurement light based on the detection distance, thereby enabling optimal wind speed detection according to the detection distance.

[0020]

[10] The wind speed detection method according to [9], wherein the output step outputs frequency-modulated light as the laser light when the detection distance falls within the ultra-short distance range, which is equal to or less than a second threshold set for the short distance range. When the detection distance falls within the ultra-short distance range, stray light components generated by the measurement optical system, etc., become larger than the signal component and overlap in time, making it difficult to analyze wind speed based on the interference results between the reference light and the signal light. In contrast, using frequency-modulated light as the laser light makes it possible to separate the signal component and the stray light component on the frequency axis. This allows for accurate wind speed detection even when the detection distance falls within the ultra-short distance range.

[0021]

[11] The wind speed detection method according to [9] or

[10] , wherein, in the conversion step, if the detection distance falls within a short-to-medium distance range exceeding a second threshold set for the short distance range, the pulse width of the measurement light is changed according to the detection distance. Generally, the larger the pulse width of the measurement light, the higher the CNR of the signal light tends to be. Therefore, by changing the pulse width of the measurement light according to the detection distance, wind speed detection can be performed quickly and accurately in the short-to-medium distance range.

[0022]

[12] The wind speed detection method according to any one of [9] to

[11] , wherein the output step outputs CW light as the laser light, and the detection step outputs a detection signal based on the interference result between the reference light, which is CW light, and the signal light. In this wind speed detection method, a wide range of detection distances is set, from short distances to long distances. By using CW light as the reference light, an interference signal between the signal light and the reference light can be obtained regardless of the detection distance setting, even if the signal light is pulsed light or a temporal superposition of multiple pulsed light.

[0023]

[13] The wind speed detection method according to any one of [9] to

[12] , wherein the measurement step includes a deflection step of deflecting the output direction of the measurement light toward the atmosphere. In this case, the output direction of the measurement light is variable, and it is possible to measure a three-dimensional wind speed vector including information on wind direction and wind speed.

[0024]

[14] The wind speed detection method according to

[13] , wherein, in the deflection step, when the detection distance falls within the long distance range, the scanning speed in the output direction of the measurement light is reduced compared to when the detection distance falls within the short distance range. In the long distance range, where the pulsed measurement light is collimated, the CNR of the signal light is likely to be lower than in the short distance range, where the pulsed measurement light is focused. By reducing the scanning speed in the output direction of the measurement light during deflection, it is possible to increase the number of times the signal is averaged, thereby ensuring sufficient accuracy in wind speed detection in the long distance range.

[0025]

[15] The wind speed detection method according to any one of [9] to

[14] , further comprising an analysis step of analyzing the wind speed in the atmosphere based on the detection signal. In this case, a series of processes from outputting laser light to analyzing the wind speed can be performed.

[0026]

[16] An aircraft control device comprising the wind speed detection device according to any one of [1] to [8] and a control device that generates control signals related to takeoff and landing of an aircraft based on the detection signal output from the wind speed detection device. In this aircraft control device, the wind speed detection device performs optimal wind speed detection according to the detection distance, thereby realizing safe operation management of aircraft such as drones, AAMs, and UAMs.

[0027] According to the present disclosure, it is possible to perform optimal wind speed detection according to the detection distance.

[0028] 1A and 1B are schematic diagrams of an aircraft control device according to an embodiment of the present disclosure. A diagram illustrating the relationship between LIDAR type and distance resolution. A diagram illustrating the CNR comparison results between the pulsed light focusing method and the CW light focusing method. A diagram illustrating the relationship between stray light components and signal components in a short-distance range in a conventional pulsed light focusing method. A schematic diagram of a wind speed detection device according to an embodiment of the present disclosure. (a) is a schematic diagram of a beat spectrum between signal light and reference light when a frequency shifter is not used, and (b) is a schematic diagram of a beat spectrum between signal light and reference light when a frequency shifter is used. (a) is a schematic diagram illustrating the time waveform of the intensity of measurement light, and (b) is a schematic diagram illustrating the frequency modulation of measurement light. A diagram illustrating the state of measurement light for each detection distance. (a) and (b) are diagrams illustrating the relationship between stray light components and signal components in a short-distance range in this embodiment. (a) to (c) are diagrams illustrating the relationship between the peak intensity of the signal component and the spectral intensity at a frequency slightly shifted from the base of the stray light component when the chirp rate is used as a variable. A diagram illustrating an example of a window function. 1A to 1C are diagrams illustrating the separation of signal components and stray light components with respect to the position of a window function. A diagram illustrating the relationship between stray light components and signal components in the short to medium distance range in this embodiment. A diagram illustrating the relationship between pulse width and CNR. A flowchart illustrating an example of a wind speed detection method according to an embodiment of the present disclosure. A diagram illustrating wind speed detection at a detection distance of 10 m. A diagram illustrating wind speed detection results at a detection distance of 10 m. A diagram illustrating wind speed detection at a detection distance of 30 m. A diagram illustrating wind speed detection results at a detection distance of 30 m. A diagram illustrating wind speed detection at a detection distance of 60 m to 900 m. A diagram illustrating wind speed detection at a detection distance of 60 m to 900 m. A diagram illustrating wind speed detection results at a detection distance of 60 m to 900 m. A diagram illustrating wind speed detection results at a detection distance of 60 m to 900 m. A diagram illustrating wind speed detection results at a detection distance of 60 m to 900 m. A diagram illustrating wind speed detection results at a detection distance of 60 m to 900 m. A schematic diagram of a wind speed detection device according to a modified example.

[0029] Hereinafter, preferred embodiments of a wind speed detection device, a wind speed detection method, and an aircraft control device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0030] 1(a) and 1(b) are diagrams schematically illustrating an aircraft control device according to an embodiment of the present disclosure. As shown in Fig. 1(a) and 1(b), the aircraft control device 101 is configured to include a wind speed detection device 1 and a control device 102 that controls the operation of the aircraft H based on a detection signal D (see Fig. 5) output from the wind speed detection device 1. Examples of the aircraft H include unmanned aircraft such as drones, and manned aircraft such as advanced air mobility (AAM) or urban air mobility (UAM).

[0031] The aircraft control device 101 is installed, for example, near the ground surface. The installation height of the aircraft control device 101 is assumed to be, for example, an atmospheric layer called the ground layer. The ground layer refers to an atmospheric layer at a height of 100 m or less from the ground surface where the vertical gradient of wind speed and temperature is particularly large. The aircraft control device 101 may be installed on the ground surface, for example, as shown in FIG. 1( a). The aircraft control device 101 may be installed on the rooftop or roof of a building or other structure, as shown in FIG. 1( b). The aircraft control device 101 may be incorporated as a device in a control tower that operates the aircraft H.

[0032] The wind speed detection device 1 is a device that detects wind speed in the atmosphere. In the aircraft control device 101, the wind speed detection device 1 detects complex turbulence caused by many structures, particularly near the ground, and outputs a detection signal D to the control device 102. The control device 102 is a device that generates a control signal Q related to takeoff and landing of the aircraft H. The control device 102 is physically a computer system that includes memories such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a storage unit such as a hard disk, and a display unit such as a display. Based on the detection signal D from the wind speed detection device 1, the control device 102 outputs a control signal Q to the aircraft H, for example, related to the speed, route, or permission / prohibition of takeoff and landing of the aircraft H during takeoff and landing.

[0033] The wind speed detection device 1 may transmit the detection signal D to a server owned by a weather information provider. In this case, for example, the weather information provider may make a weather forecast based on the detection signal D and weather data transmitted to the server, and transmit the generated weather forecast information from a terminal device or the like to the aircraft control device 101 in the control tower. The aircraft control device 101 in the control tower may generate a control signal Q based on the weather forecast information. The wind speed detection device 1 may transmit the detection signal D directly to the aircraft control device 101 in the control tower.

[0034] Next, a description will be given of the above-mentioned wind speed detection device 1. The wind speed detection device 1 is a device that uses LIDAR (Light Detection and Ranging) to detect wind speed in the atmosphere M. The wind speed detection device 1 detects wind speed in the atmosphere M by using measurement light Lm, which is pulsed laser light, and performing coherent detection using signal light Ls and reference light Lr.

[0035] Conventional LIDAR methods include a pulse collimation method, in which collimated pulsed light is output into the atmosphere as measurement light, and a CW focusing method, in which CW light is focused in the atmosphere as measurement light, as shown in Figure 2. The pulse collimation method is characterized in that the distance resolution depends on the pulse width and does not depend on the detection distance. The CW focusing method is characterized in that the distance resolution depends on the focal depth of the measurement light and therefore depends on the detection distance, because measurement is performed while changing the focal position of the measurement light.

[0036] The pulsed focusing method, which focuses pulsed light as measurement light in the atmosphere, has a distance resolution that depends on the detection distance, similar to the CW focusing method. However, when compared under the same energy and focusing conditions, the CNR (Carrier-to-Noise Ratio) of the signal light tends to be higher. Figure 3 shows the CNR comparison results between the pulsed focusing method and the CW focusing method. Figure 3 plots the CNR of the signal light over a detection distance range of 60 m to 180 m when the optical energy of both the pulsed light and the CW light is 8 μJ and the pulse width of the pulsed light is 100 ns.

[0037] The results shown in Figure 3 show that the CNR of the pulsed focusing method is greater than that of the CW focusing method, regardless of the detection distance. It also shows that the ratio of the CNR of the pulsed focusing method to that of the CW focusing method becomes higher as the detection distance becomes shorter (especially when the detection distance is 100 m or less). The higher the CNR, the faster and more accurately wind speed can be detected. This shows that the pulsed focusing method is suitable for detecting complex turbulence at close range.

[0038] On the other hand, it has been said that the pulse method has difficulty in detecting wind speed in a short distance range, for example, at a detection distance of 40 m or less. This is thought to be partly because, when the detection distance is equal to or less than the distance corresponding to the pulse width of the measurement light, stray light components Ir generated in the measurement optical system (e.g., reflection components generated at the end face of an optical fiber or the surface of an optical element) become larger than the signal component Is and overlap with it in time, as shown in Figure 4, causing the signal component Is to be buried in the stray light component Ir.

[0039] The wind speed detection device 1 according to this embodiment enables wind speed detection using a pulse focusing method in the short-distance range through frequency modulation and pulse width modulation, which will be described later. The wind speed detection device 1 also switches between the pulse focusing method and the pulse collimation method for the short-distance range and the long-distance range, thereby achieving optimal wind speed detection according to the detection distance. Each component of the wind speed detection device 1 will be described in detail below.

[0040] 5 is a schematic diagram of a wind speed detection device according to an embodiment of the present disclosure. The device includes an output unit 2, a branching unit 3, a frequency shifter 4, a first amplifier (conversion unit) 5, a second amplifier 6, a measurement optical system 7, a multiplexing unit 8, a detection unit 9, a digitizer 10, an analysis unit 11, and a control unit 15. In this embodiment, the output unit 2 and the branching unit 3, the branching unit 3 and the frequency shifter 4, the frequency shifter 4 and the first amplifier 5, the first amplifier 5 and the second amplifier 6, the second amplifier 6 and the measurement optical system 7, the measurement optical system 7 and the multiplexing unit 8, the branching unit 3 and the multiplexing unit 8, and the multiplexing unit 8 and the detection unit 9 are all optically connected by optical fiber F.

[0041] In the wind speed detection device 1, at least the output unit 2, branch unit 3, and detection unit 9 are configured using a photonic integrated circuit (PIC) 12. In this embodiment, the output unit 2, branch unit 3, frequency shifter 4, first amplification unit 5, second amplification unit 6, multiplexer 8, detection unit 9, and the optical fiber F connecting these are configured using the photonic integrated circuit 12.

[0042] The output unit 2 is a part that outputs the laser light L. Examples of laser devices that make up the output unit 2 include a distributed feedback (DFB) laser device, a distributed Bragg reflector (DBR) laser device, and an external cavity laser device. In this example, the laser light L output from the output unit 2 is CW light. The laser light L is not light such as diffused light, but is beam-like light with a certain directivity.

[0043] A current control unit and a temperature control unit (not shown) are connected to the output unit 2. The current control unit is a controller that supplies a drive current to the laser device that constitutes the output unit 2. The current control unit modulates the drive current to modulate the frequency of the laser light L output from the output unit 2. The temperature control unit is a controller that maintains a constant temperature of the laser device that constitutes the output unit 2. The temperature control unit is configured to include, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the laser device based on the temperature measurement value of the thermistor attached to the laser device.

[0044] A signal generating unit 13 is connected to the output unit 2. The signal generating unit 13 generates a modulation signal G for the laser light L. The signal generating unit 13 is configured by, for example, a waveform generator, a function generator, etc. The signal generating unit 13 generates a voltage signal for modulating the current waveform output from the current control unit connected to the output unit 2 into an arbitrary shape. The modulation signal G generated by the signal generating unit 13 is also output to the digitizer 10 in order to synchronize the operation of the output unit 2 with the operation of the analysis unit 11.

[0045] The branching unit 3 is a unit that branches the laser light L from the output unit 2 into measurement light Lm and reference light Lr. The branching unit 3 is configured, for example, by an optical fiber coupler. The measurement light Lm is output from one output port of the branching unit 3 to the frequency shifter 4, and the reference light Lr is output from another output port of the branching unit 3 to the multiplexing unit 8. The reference light Lr is input to the multiplexing unit 8 as CW light.

[0046] In this embodiment, a delay fiber 16 is connected between the branching unit 3 and the multiplexing unit 8. The delay fiber 16 is configured, for example, by a polarization-maintaining fiber, a fiber coil, or the like. The delay fiber 16 can adjust the optical path length difference between the signal light Ls and the reference light Lr input to the multiplexing unit 8. By reducing the optical path length difference between the signal light Ls and the reference light Lr, PIIN (Phase Induced Intensity Noise) can be reduced.

[0047] The frequency shifter 4 is a part that shifts the frequency of the measurement light Lm. The frequency shifter 4 is configured, for example, by an acousto-optic element, an electro-optic element, an IQ modulator, a phase modulator, an intensity modulator, or the like. The frequency shifter 4 may have a signal generating unit (not shown) that generates a voltage signal for driving the frequency shifter 4. The signal generating unit may be configured, for example, by a waveform generator, a function generator, or the like.

[0048] Shifting the frequency of the measurement light Lm using the frequency shifter 4 makes it possible to determine the wind direction in the optical axis direction of the measurement light Lm. When the frequency of the measurement light Lm is not shifted, the beat spectrum of the interference light Ld (described later) shifts to a higher frequency relative to a reference beat spectrum (a beat spectrum without wind speed) depending on the wind speed, regardless of the wind direction, as shown in FIG. 6A, for example. When the frequency of the measurement light Lm is shifted, the beat spectrum of the interference light Ld (described later) shifts to a lower frequency relative to the reference beat spectrum if the wind is blowing in a positive direction (tailwind) relative to the optical axis of the measurement light Lm, and shifts to a higher frequency relative to the reference beat spectrum if the wind is blowing in a negative direction (headwind) relative to the optical axis of the measurement light Lm, for example. Therefore, by shifting the frequency of the measurement light Lm using the frequency shifter 4, both the wind speed and wind direction in the optical axis direction of the measurement light Lm can be suitably detected.

[0049] The first amplifier 5 converts the measurement light Lm from the branching unit 3 into pulsed light. The first amplifier 5 is composed of, for example, a semiconductor optical amplifier or an optical fiber amplifier. The first amplifier 5 converts the measurement light Lm, which is CW light, into pulsed light by amplifying a specific component of the measurement light Lm. A current control unit and a temperature control unit (not shown) are connected to the first amplifier 5. The current control unit is a controller that supplies a drive current to the amplifier device that constitutes the first amplifier 5. The current control unit controls the amplification factor of the measurement light Lm in the first amplifier 5 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplifier device that constitutes the first amplifier 5. The temperature control unit is composed of, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the amplifier device based on the temperature measurement value of the thermistor attached to the amplifier device. The measurement light Lm, which is CW light, can also be converted into pulsed light by frequency-shifting a specific component of the measurement light Lm using the frequency shifter 4 described above.

[0050] 7(a) is a schematic diagram showing the time waveform of the intensity of the measurement light Lm. As shown in FIG. 7(a), the measurement light Lm is generated by converting the CW laser light L output from the output unit 2 into pulsed light using the frequency shifter 4, the first amplifier 5, or both. The measurement light Lm is light whose intensity rises intermittently on the time axis with a pulse width Δt. When the output unit 2 outputs frequency-modulated light as the laser light L, light whose frequency is modulated linearly and periodically can be used as the measurement light Lm, as shown in FIG. 7(b). In the example of FIG. 7(b), the measurement light Lm is frequency-modulated to form a ramp waveform, with an UP ramp in which the frequency gradually increases linearly and a DOWN ramp in which the frequency gradually decreases linearly alternating with each pulse.

[0051] The second amplifier 6 amplifies the intensity of the measurement light Lm converted into pulsed light. The second amplifier 6 is composed of, for example, a semiconductor optical amplifier, an optical fiber amplifier, or the like. A current control unit and a temperature control unit (not shown) are connected to the second amplifier 6. The current control unit is a controller that supplies a drive current to the amplifier device that constitutes the second amplifier 6. The current control unit controls the amplification factor of the measurement light Lm in the second amplifier 6 by modulating the drive current. The temperature control unit is a controller that maintains a constant temperature of the amplifier device that constitutes the second amplifier 6. The temperature control unit is composed of, for example, a thermistor and a Peltier element, and drives the Peltier element to maintain a constant temperature of the amplifier device based on the temperature measurement value of the thermistor attached to the amplifier device.

[0052] The measurement optical system 7 outputs the measurement light Lm into the atmosphere M and receives scattered light Lf of the measurement light Lm in the atmosphere M as signal light Ls. As shown in FIG. 5 , the measurement optical system 7 includes a spatial optical system circulator 21, a movable stage 22, a lens (optical element) 23, and a rotating stage (deflection unit) 25 on which a beam deflector 24 is mounted. The circulator 21 includes a polarizing beam splitter 26 and a λ / 4 wave plate 27. A lens 28 is disposed upstream of the polarizing beam splitter 26, and a lens 29 mounted on the movable stage 22 is disposed downstream of the λ / 4 wave plate 27. In addition, a lens 30 is disposed upstream of the optical fiber F connected to the detection unit 9, and is used to optically couple the signal light Ls to the optical fiber F.

[0053] To stabilize the performance of the circulator 21, a temperature control unit (not shown) may be used to control the temperature of the entire circulator 21 to be constant. The temperature control unit includes, for example, a thermistor and a Peltier element, and drives the Peltier element based on the temperature measurement value of the thermistor attached to the circulator 21 so that the temperature of the entire circulator 21 is maintained constant.

[0054] The movable stage 22 is a stage having a movable axis at least in the optical axis direction of the measurement light Lm. A driving element such as a stepping motor or a piezoelectric element is used to drive the movable stage 22. A stage controller (not shown) is connected to the movable stage 22. The stage controller outputs a control signal to the driving element to control the position of the movable stage 22.

[0055] The lens 23 is an optical element that collimates the measurement light Lm and outputs it into the atmosphere M. The lens 23 may be, for example, a convex lens, an achromatic lens, an aspherical lens, or a combination lens formed by combining multiple lenses. The lenses 23 and 29 form a pair of lenses that constitute a telescope. The distance between the lens 23 and the lens 29 is adjusted by displacing the movable stage 22 in the optical axis direction of the measurement light Lm. This allows the focal position of the measurement light Lm emitted into the atmosphere M via the lens 23 to be displaced in the optical axis direction of the measurement light Lm.

[0056] The beam deflector 24 is a component that deflects the output direction of the measurement light Lm toward the atmosphere M in any direction. For example, a wedge substrate or the like can be used as the beam deflector 24. The rotation stage 25 is a stage that rotates the beam deflector 24 around the optical axis of the measurement light Lm. Driving elements such as a stepping motor and a piezoelectric element are used to drive the rotation stage 25. A stage controller (not shown) is connected to the movable stage 22. The stage controller outputs a control signal J to the driving element to control the position of the rotation stage. The control signal J is output to the signal generating unit 13 to synchronize the operations of the output unit 2 and the analyzing unit 11.

[0057] In the measurement optical system 7, the measurement light Lm emitted from the optical fiber F on the output side of the second amplifier 6 passes through a lens 23 and is emitted into the atmosphere M as a beam of light with a certain directivity. The output direction of the measurement light Lm changes based on the rotation angle of the beam deflector 24 caused by the rotary stage 25. The signal source in the wind speed detection device 1 is scattered light Lf generated when the measurement light Lm is scattered by countless aerosols P in the atmosphere M. A portion of the scattered light Lf returns to the measurement optical system 7 as signal light Ls via the lens 23. The signal light Ls is separated from the measurement light Lm by the circulator 21 and output to the multiplexer 8.

[0058] The multiplexing unit 8 multiplexes the reference light Lr from the branching unit 3 with the signal light Ls that has returned from the atmosphere M. The multiplexing unit 8 is configured, for example, by an optical fiber coupler. The multiplexing unit 8 generates interference light Ld between the reference light Lr and the signal light Ls. The interference light Ld is output from an output port of the multiplexing unit 8 to the detection unit 9.

[0059] The detector 9 outputs a detection signal D based on the interference result between the reference light Lr and the signal light Ls. In this embodiment, since the measurement light Lm is pulsed light, the scattered light Lf (signal light Ls) generated by scattering of the measurement light Lm at a specific distance is also pulsed light. On the other hand, the reference light Lr is CW light, being a portion of the laser light L from the output unit 2 branched by the branching unit 3. Therefore, in the light-collecting method, the detector 9 outputs a detection signal D based on the interference result between the reference light Lr, which is CW light, and the signal light Ls, which is pulsed light. In addition, in the collimating method, the detector 9 outputs a detection signal D based on the interference result between the reference light Lr, which is CW light, and the signal light Ls, which is a temporal superposition of multiple pulsed light beams.

[0060] The detection unit 9 is composed of, for example, a photodetector, an avalanche photodiode, a balanced detector, etc. The detection unit 9 outputs an analog electrical signal based on the intensity of the interference light Ld input from the multiplexer 8 as a detection signal D to the digitizer 10. The digitizer 10 is a device that converts an analog electrical signal into a digital signal. The digitizer 10 is composed of, for example, an A / D converter, etc. The digitizer 10 converts the detection signal D, which is an analog electrical signal, into a digital signal and outputs the converted digital signal to the analysis unit 11.

[0061] The analysis unit 11 is a part that analyzes the wind speed in the atmosphere M based on the detection signal D. Physically, the analysis unit 11 is a computer system that includes memories such as RAM and ROM, processors such as CPU and GPU, a communication interface, and a storage unit such as a hard disk. Examples of such computer systems include personal computers, cloud servers, smart devices (smartphones, tablet terminals, etc.), microcomputers, and FPGAs (field-programmable gate arrays). The computer system functions as the analysis unit 11 by executing a program stored in the memory with the CPU or GPU.

[0062] As described above, the signal source in the wind speed detection device 1 is scattered light Lf generated when the measurement light Lm is scattered by countless aerosols P in the atmosphere M. When wind blows in the atmosphere M, the aerosols P move with the wind, causing a change in frequency (Doppler shift) of the scattered light Lf. When the analysis unit 11 receives the detection signal D output from the digitizer 10, it refers to the peak frequency of the beat spectrum of the interference light Ld based on the detection signal D. The analysis unit 11 detects the wind speed in the atmosphere M by calculating the amount of shift in the peak frequency of the beat spectrum of the interference light Ld.

[0063] The control unit 15 controls the state of the measurement light Lm output from the measurement optical system 7 based on the detection distance of the measurement light Lm. Like the analysis unit 11, the control unit 15 is physically a computer system including memory such as RAM and ROM, a processor such as a CPU and GPU, a communication interface, and a storage unit such as a hard disk. Examples of such computer systems include personal computers, cloud servers, smart devices (smartphones, tablet terminals, etc.), microcomputers, and FPGAs (field-programmable gate arrays). The computer system functions as the analysis unit 11 by executing a program stored in the memory using the CPU or GPU. The analysis unit 11 and the control unit 15 may be configured as the same computer system.

[0064] The control unit 15 receives an input of a detection distance setting for the measurement light Lm. As shown in FIG. 8 , the control unit 15 controls the state of the measurement light Lm output from the measurement optical system 7 based on the input detection distance setting. In this embodiment, a first threshold T1 is set for the detection distance. When the detection distance falls within a short distance range R1 that is equal to or less than the first threshold T1, the control unit 15 controls the measurement optical system 7 so that the measurement light Lm output into the atmosphere M is condensed. When the detection distance falls within a long distance range R2 that exceeds the first threshold T1, the control unit 15 controls the measurement optical system 7 so that the measurement light Lm output into the atmosphere M is collimated.

[0065] In this embodiment, a second threshold T2 is set for the short distance range R1. When the detection distance falls within an ultra-short distance range R1a, which is equal to or less than the second threshold T2 set for the short distance range R1, the control unit 15 controls the output unit 2 to output frequency-modulated light as the laser light L. When the detection distance falls within an intermediate-short distance range R1b, which exceeds the second threshold T2 set for the short distance range R1, the control unit 15 controls the first amplifier (converter) 5 to change the pulse width Δt of the measurement light Lm according to the detection distance. Furthermore, in this embodiment, when the detection distance falls within the long distance range R2, the control unit 15 controls the rotating stage (deflection unit) 25, on which the beam deflector 24 is mounted, to reduce the scanning speed in the output direction of the measurement light Lm compared to when the detection distance falls within the short distance range R1.

[0066] The first threshold T1 is determined based on a distance at which the distance resolution of the focusing method, which depends on the detection distance, is equal to the distance resolution of the collimation method, which depends on the pulse width. In one example, the first threshold T1 is set in the range of 100 m to 300 m. The second threshold T2 is determined based on a distance corresponding to the pulse width Δt of the measurement light Lm. In one example, the second threshold T2 is set in the range of 20 m to 60 m.

[0067] 8 is a diagram showing the state of the measurement light for each detection distance. As shown in FIG. 8, in this embodiment, measurement light Lm in different states is output into the atmosphere M in the ultra-short distance range R1a, the intermediate-short distance range R1b, and the long distance range R2. In the ultra-short distance range R1a, the measurement light Lm, which is pulsed light, is output into the atmosphere M in a condensed state. Therefore, in the ultra-short distance range R1a, the wind speed can be detected with a higher distance resolution as the detection distance becomes shorter.

[0068] In the ultra-short distance range R1a, the distance resolution does not depend on the pulse width Δt. Generally, the CNR of the signal light Ls tends to increase as the pulse width Δt of the measurement light Lm increases. Therefore, it is preferable to set the pulse width Δt of the measurement light Lm in the ultra-short distance range R1a larger than the pulse width Δt of the measurement light Lm in the medium-short distance range R1b and the long distance range R2.

[0069] In the ultra-short distance range R1a, as shown in FIG. 7B, pulsed light whose frequency is modulated linearly and periodically is used as the measurement light Lm. When pulsed light whose frequency is modulated linearly and periodically is used as the measurement light Lm, as shown in FIG. 9A, the stray light component Ir and the signal component Is generated in the measurement optical system, etc., overlap in time but have different frequencies, as shown in FIG. 9B. Therefore, by performing a Fourier transform on the detection signal D, the signal component Is and the stray light component Ir can be separated on the frequency axis, as shown in FIG. 9B. Therefore, wind speed can be detected in the ultra-short distance range R1a without reducing the pulse width Δt of the measurement light Lm.

[0070] In the example of FIG. 8 , the chirp rate γ is set to decrease with the detection distance. Setting the chirp rate γ in this manner enables separation of the stray light component Ir and the signal component Is while maintaining a high signal level. FIGS. 10( a ) to 10 ( c ) show the relationship between the peak intensity of the signal component and the spectral intensity at a frequency slightly shifted from the base of the stray light component when the chirp rate γ is a variable. The peak intensity of the signal component is the peak intensity of the beat spectrum of the interference light Ld in the detection signal D, and the spectral intensity at a frequency slightly shifted from the base of the stray light component is the intensity of the beat spectrum of the interference light Ld at the base frequency of the stray light component Ir (76 MHz in this example). Here, the diameter of the lens 23 is set to 50 mm, the pulse width Δt is set to 800 ns, the pulse waveform is a rectangular pulse, and the frequency shift by the frequency shifter 4 is set to 80 MHz. The detection distance (light collection position) was set to 10 m, 20 m, and 30 m, and the threshold value used to separate the signal component Is and the stray light component Ir was set to 0.05.

[0071] As shown in Figure 10(a), when the detection distance was 10 m, the chirp rate at which the spectral intensity at 76 MHz, the frequency at which the stray light component Ir reaches the base frequency, was 94 THz / s. As shown in Figure 10(b), when the detection distance was 20 m, the chirp rate at which the spectral intensity at 76 MHz, the frequency at which the stray light component Ir reaches the base frequency, was 50 THz / s. As shown in Figure 10(c), when the detection distance was 30 m, the chirp rate at which the spectral intensity at 76 MHz, the frequency at which the stray light component Ir reaches the base frequency, was 36 THz / s. Furthermore, at both detection distances, the peak intensity of the signal component decreased as the chirp rate increased. These results demonstrate that the chirp rate capable of separating the signal component Is and the stray light component Ir is dependent on the detection distance, and that by setting the chirp rate γ to a small value depending on the detection distance, the signal component Is and the stray light component Ir can be separated while maintaining a high signal level.

[0072] When using a rectangular pulse with a steep falling edge or a pulse with an unintended chirp at the pulse end, it is preferable to use a window function Iw to separate the signal component Is and the stray light component Ir, as shown in Fig. 11. Examples of the window function Iw include the Hanning function, Hamming function, Blackman function, and Blackman-Nuttall function. When applying the window function Iw, it is preferable to align the start and end points of the window function Iw with the start and end points of the stray light component Ir, rather than the start and end points of the signal component Is, as shown in Fig. 11.

[0073] 12(a) to 12(c) are diagrams showing the separation of the signal component and the stray light component with respect to the position of the window function. Here, the diameter of the lens 23 was 50 mm, the pulse width Δt was 800 ns, the pulse waveform was a rectangular pulse, the chirp rate was 50 THz / s, and the frequency shift by the frequency shifter 4 was 80 MHz. The detection distance (focusing position) was 30 m, and a Blackman function was used as the window function. As shown in FIG. 12(a), when the start and end points of the window function Iw were aligned with the start and end points of the stray light component Ir, the spectrum of the signal component Is and the spectrum of the stray light component Ir were almost completely separated.

[0074] In contrast, when the start and end points of the window function Iw are aligned with the start and end points of the signal component Is as shown in Fig. 12(b), and when the start and end points of the window function Iw are aligned with the start and end points of the stray light component and the end points of the signal component Is as shown in Fig. 12(c), the spectral tails of the signal component Is and the stray light component Ir overlap. From this result, from the viewpoint of separating the signal component Is and the stray light component Ir, it is preferable to align the start and end points of the window function Iw with the start and end points of the stray light component Ir.

[0075] In the very short distance range R1a, the scanning speed S1 in the output direction of the measurement light Lm is set relatively higher than the scanning speed S2 in the long distance range R2. In the example of FIG. 8, in the very short distance range R1a, the scanning speed S1 in the output direction of the measurement light Lm is constant regardless of the detection distance. In the very short distance range R1a, the measurement light Lm has a sufficient pulse width Δt, and measurement is performed in a focused state, so it is thought that the CNR of the signal light Ls can be sufficiently ensured. Therefore, by sufficiently increasing the scanning speed S1, high-speed wind speed detection is possible.

[0076] In the medium-short distance range R1b, similar to the very short distance range R1a, the measurement light Lm, which is a pulsed light, is output into the atmosphere M in a focused state. In the medium-short distance range R1b, the shorter the detection distance, the higher the distance resolution for detecting wind speed. In the medium-short distance range R1b, the frequency of the laser light L is not modulated. Instead, the pulse width Δt of the measurement light Lm is varied according to the detection distance. In the example of FIG. 8, the pulse width Δt of the measurement light Lm increases linearly in proportion to the detection distance. The pulse width Δt of the measurement light Lm is set within a range in which the distance corresponding to the pulse width Δt is shorter than the detection distance. This allows the stray light component Ir and the signal component Is to be separated on the time axis, as shown in FIG. 13. In the medium-short distance range R1b, the distance resolution is determined by the focusing state, not the pulse width Δt, so there is no need to reduce the pulse width Δt to improve the distance resolution. Therefore, wind speed detection in the medium-short distance range R1b can be performed without reducing the pulse width Δt of the measurement light Lm.

[0077] Even in the short distance range R1, which includes both the ultra-short distance range R1a and the intermediate-short distance range R1b, the CNR of the signal light Ls tends to increase as the pulse width Δt of the measurement light Lm increases, as shown in Figure 14. Figure 14 plots the CNR of the signal light obtained with measurement light of different pulse widths over a detection distance range of 0 m to 70 m. In Figure 14, the optical energy of the pulsed light is 1.1 μJ, the diameter of the lens 23 is 50 mm, and the intensity spectrum is averaged 1,000 times. The median and minimum CNR values ​​of 400 measurements are plotted.

[0078] As shown in Figure 14, at a detection distance of 10 m, only the CNR for a pulse width of 50 ns is shown. However, at a detection distance of 20 m, the CNR for a pulse width of 100 ns is higher than the CNR for a pulse width of 50 ns. At a detection distance of 30 m, the CNR for a pulse width of 200 ns is higher than the CNRs for pulse widths of 50 ns and 100 ns. At a detection distance of 60 m, the CNR for a pulse width of 400 ns is higher than the CNRs for pulse widths of 50 ns, 100 ns, and 200 ns. These results show that the CNR of the signal light Ls increases as the pulse width Δt of the measurement light Lm increases, and that wind speed detection can be performed quickly and accurately by changing the pulse width Δt of the measurement light Lm according to the detection distance.

[0079] Note that if the pulse width Δt is made excessively small, the beat spectrum of the interference light Ld may become too broad, resulting in a decrease in wind speed resolution. Furthermore, generally, the narrower the pulse width, the higher the cost of optical amplification. In this embodiment, in the medium-to-short distance range R1b of the short distance range R1, which exceeds the second threshold T2, the pulse width Δt of the measurement light Lm is changed according to the detection distance. In the very short distance range R1a, which is equal to or less than the second threshold T2, the frequency of the laser light L is modulated to set the pulse width Δt of the measurement light Lm larger than that in the medium-to-short distance range R1b. This avoids the problems of a decrease in wind speed resolution and an increase in optical amplification costs due to an excessively small pulse width Δt.

[0080] In the intermediate-short distance range R1b, the scanning speed S1 in the output direction of the measurement light Lm is set relatively higher than the scanning speed S2 in the long distance range R2. In the example of Fig. 8, the scanning speed S1 in the output direction of the measurement light Lm in the intermediate-short distance range R1b is the same as the scanning speed S1 in the output direction of the measurement light Lm in the very short distance range R1a, and is constant regardless of the detection distance. By setting the scanning speed S1 sufficiently high, high-speed wind speed detection is possible.

[0081] In the long distance range R2, the measurement light Lm, which is pulsed light, is output into the atmosphere M in a collimated state. In the long distance range R2, the frequency of the laser light L is not modulated, and the pulse width Δt of the measurement light Lm is constant regardless of the detection distance. The pulse width Δt in the long distance range R2 is set to a range that balances CNR and distance resolution. As an example, the pulse width Δt in the long distance range R2 is set to a range smaller than the pulse width Δt in the very short distance range R1a. Furthermore, the pulse width Δt in the long distance range R2 is set to a range larger than the minimum pulse width Δt used in the medium to short distance range R1b and smaller than the maximum pulse width Δt. In the long distance range R2, the distance resolution is determined by the pulse width Δt of the measurement light Lm, and a constant distance resolution is maintained regardless of the detection distance.

[0082] In the long-distance range R2, the scanning speed S2 in the output direction of the measurement light Lm is set relatively slower than the scanning speed S1 in the short-distance range R1 in the output direction of the measurement light Lm. In the example of Figure 8, the scanning speed S2 in the output direction of the measurement light Lm is constant in the long-distance range R2 regardless of the detection distance. In the long-distance range R2, where the pulsed measurement light Lm is collimated, the CNR of the signal light Ls is likely to be lower than in the short-distance range R1, where the pulsed measurement light Lm is focused. By reducing the scanning speed in the output direction of the measurement light Lm during deflection, it is possible to increase the number of times the signal is averaged, thereby ensuring sufficient accuracy in wind speed detection in the long-distance range R2.

[0083] 15 is a flowchart showing an example of a wind speed detection method according to an embodiment of the present disclosure. The wind speed detection method according to this embodiment is implemented using the above-described wind speed detection device 1. As shown in FIG. 15, this wind speed detection method includes a setting step S01, an output step S02, a branching step S03, a conversion step S04, a measurement step S05, a detection step S06, and an analysis step S07.

[0084] The setting step S01 is a step for setting various measurement conditions used for wind speed detection. In the setting step S01, parameters independent of the detection distance are first set. Examples of parameters independent of the detection distance include the diameter of the lens 23, the pulse waveform of the measurement light Lm, the frequency shift by the frequency shifter 4, and the pulse repetition frequency of the measurement light Lm. Next, in the setting step S01, the detection distance is set. Based on whether the set detection distance falls within the ultra-short distance range R1a, the intermediate-short distance range R1b, or the long distance range R2, the following parameters are set: whether to perform frequency modulation of the laser light L output from the output unit 2; the pulse width Δt of the pulsed light generated by the first amplifier unit 5; the position of the movable stage 22 in the measurement optical system 7; and the scanning speed of the measurement light Lm by the rotation stage 25 on which the beam deflector 24 is mounted.

[0085] The output step S02 is a step of outputting the laser light L. In the output step S02, the laser light L, which is CW light, is output from the output unit 2. When modulating the frequency of the laser light L, a modulation signal G generated by the signal generation unit 13 is input to the output unit 2. This generates laser light L whose frequency is linearly and periodically modulated, and outputs it from the output unit 2.

[0086] The branching step S03 is a step of branching the laser light L into measurement light Lm and reference light Lr. In the branching step S03, the laser light L output from the output unit 2 is branched by the branching unit 3, one of which is the measurement light Lm and the other is the reference light Lr. The measurement light Lm is input to the first amplifier 5 via the frequency shifter 4, and the reference light Lr is input to the multiplexer 8 after being delayed by the delay fiber 16.

[0087] The conversion step S04 is a step of converting the measurement light Lm into pulsed light. In the conversion step S04, the measurement light Lm, which is CW light, is converted into pulsed light by amplifying a specific component of the measurement light Lm in the first amplifier 5. The measurement light Lm converted into pulsed light is input to the measurement optical system 7 after its intensity is amplified by the second amplifier 6.

[0088] The measurement step S05 is a step of outputting the measurement light Lm into the atmosphere M and receiving scattered light Lf of the measurement light Lm in the atmosphere M as signal light Ls. In the measurement step S05, the measurement light Lm is output into the atmosphere M in a collimated state via the measurement optical system 7. The measurement light Lm is scattered by countless aerosols P in the atmosphere M and becomes scattered light Lf. A portion of the scattered light Lf returns to the measurement optical system 7 and is input to the multiplexing unit 8 as signal light Ls. In the multiplexing unit 8, the reference light Lr, which is a CW light, and the signal light Ls are multiplexed to generate interference light Ld.

[0089] In the measurement step S05, measurement light Lm, the state of which varies depending on the detection distance, is emitted into the atmosphere M. When the detection distance falls within the ultra-short distance range R1a, frequency-modulated pulsed light is focused into the atmosphere M as measurement light Lm. When the detection distance falls within the ultra-short distance range R1a, the beam deflector 24 scans the output direction of the measurement light Lm at a scanning speed S1 that is relatively higher than the scanning speed S2 in the long distance range R2. When the detection distance falls within the medium-short distance range R1b, pulsed light having a pulse width Δt corresponding to the detection distance is not frequency-modulated and is focused into the atmosphere M as measurement light Lm. When the detection distance falls within the medium-short distance range R1b, the beam deflector 24 scans the output direction of the measurement light Lm at a scanning speed S1 that is relatively higher than the scanning speed S2 in the long distance range R2.

[0090] When the detection distance falls within the long distance range R2, the frequency is not modulated, and pulsed light having a constant pulse width Δt regardless of the detection distance is used as the measurement light Lm, which is output in a collimated state into the atmosphere M. Furthermore, when the detection distance falls within the long distance range R2, the output direction of the measurement light Lm is scanned by the beam deflector 24 at a scanning speed S2 that is relatively slower than the scanning speed S1 in the very short distance range R1a and the intermediate short distance range R1b.

[0091] The detection step S06 is a step of outputting a detection signal based on the interference result between the reference light Lr and the signal light Ls. In the detection step S06, the interference light Ld generated by the multiplexer 8 is detected by the detector 9, and an analog electrical signal based on the interference light Ld is generated as the detection signal D. The generated detection signal D is analog-to-digital converted by the digitizer 10 and output to the analyzer 11.

[0092] The analysis step S07 is a step of analyzing the wind speed in the atmosphere M based on the detection signal D. In the analysis step S07, the peak frequency of the beat spectrum of the interference light Ld is referenced based on the detection signal D. Then, the wind speed in the atmosphere M is detected by determining the amount of shift in the peak frequency in the beat spectrum of the interference light Ld. If detection is to be performed at a different distance, the detection distance, etc. is reset in step S01, and steps S02 to S07 are executed again. After wind speed detection has been performed within the desired distance range, the process ends.

[0093] As described above, in the wind speed detection device 1, when the detection distance falls within the short-distance range R1, where the detection distance is equal to or less than the first threshold T1, the measurement light Lm, which is pulsed light, is focused and output into the atmosphere M. When focusing pulsed light, the CNR of the signal light Ls can be improved compared to when focusing CW light, when compared under the same energy and focusing conditions. Therefore, wind speed detection can be performed quickly and accurately in the short-distance range R1. Furthermore, when the detection distance falls within the long-distance range R2, where the detection distance exceeds the first threshold T1, the measurement light Lm, which is pulsed light, is collimated and output into the atmosphere. Unlike when focusing CW light, when the pulsed light is collimated, the distance resolution depends on the pulse width Δt, but a constant distance resolution can be maintained regardless of the detection distance. In this way, the wind speed detection device 1 can perform optimal wind speed detection according to the detection distance by controlling the state of the measurement light Lm based on the detection distance.

[0094] In this embodiment, when the detection distance falls within the ultra-short distance range R1a, which is equal to or less than the second threshold T2 set in the short distance range R1, the control unit 15 controls the output unit 2 to output frequency-modulated light as the laser light L. When the detection distance falls within the ultra-short distance range R1a, stray light components generated by the measurement optical system 7 and the like become larger than the signal components and overlap in time, making it difficult to analyze the wind speed based on the interference results between the reference light and the signal light. In contrast, using frequency-modulated light as the laser light makes it possible to separate the signal component Is and the stray light component Ir on the frequency axis. This allows for accurate wind speed detection even when the detection distance falls within the ultra-short distance range R1a.

[0095] In this embodiment, when the detection distance falls within the medium-to-short distance range R1b, which exceeds the second threshold T2 set for the short distance range R1, the control unit 15 controls the first amplifier (converter) 5 to change the pulse width Δt of the measurement light Lm according to the detection distance. As described above, the CNR of the signal light Ls tends to increase as the pulse width Δt of the measurement light Lm increases. Therefore, by changing the pulse width Δt of the measurement light Lm according to the detection distance, wind speed can be detected quickly and accurately in the medium-to-short distance range R1b.

[0096] In this embodiment, the output unit 2 outputs CW light as the laser light L, and the detection unit 9 outputs a detection signal D based on the interference result between the reference light Lr, which is CW light, and the signal light Ls. In the wind speed detection device 1, a wide range of detection distances is set, from a short distance range R1 to a long distance range R2. By using CW light as the reference light Lr, an interference signal between the signal light Ls and the reference light Lr can be obtained regardless of the detection distance setting, even if the signal light Ls is pulsed light or a temporal superposition of multiple pulsed light beams.

[0097] In this embodiment, the measurement optical system 7 has a rotation stage 25 on which a beam deflector 24 is mounted as a deflection unit that deflects the output direction of the measurement light Lm toward the atmosphere M. By using such a deflection unit, the output direction of the measurement light Lm can be changed, and it becomes possible to measure a three-dimensional wind speed vector including information on the wind direction and wind speed.

[0098] In this embodiment, when the detection distance falls within the long-distance range R2, the control unit 15 controls the deflection unit so that the scanning speed in the output direction of the measurement light Lm is slower than when the detection distance falls within the short-distance range R1. In the long-distance range R2, where the pulsed measurement light Lm is collimated, the CNR of the signal light Ls is likely to be lower than in the short-distance range R1, where the pulsed measurement light Lm is focused. By slowing down the scanning speed in the output direction of the measurement light Lm by the deflection unit, it is possible to increase the number of times the signal is averaged, thereby ensuring sufficient accuracy in wind speed detection in the long-distance range R2.

[0099] In this embodiment, of the components of the wind speed detection device 1, at least the output unit 2, branching unit 3, and detection unit 9 are configured using an optical integrated circuit 12. By configuring at least the output unit 2, branching unit 3, and detection unit 9 using an optical integrated circuit 12, it is possible to reduce the size of the device. In addition, this embodiment further includes an analysis unit 11 that analyzes the wind speed in the atmosphere M based on the detection signal D. This allows a series of processes from outputting the laser light L to analyzing the wind speed to be performed within a single device.

[0100] Examples of the present disclosure will be described below. In these examples, examples of wind speed analysis will be introduced in accordance with the above embodiment, with detection distances of 10 m (ultra-short distance range), 30 m (medium-short distance range), and 60 m to 900 m (long distance range).

[0101] For wind speed analysis at a detection distance of 10 m, the focusing position of the measurement light Lm was first adjusted to 10 m using the movable stage 22. The pulse width Δt of the measurement light Lm was set to 800 ns, the chirp rate γ to 94 THz / s, and the scanning speed of the deflector to 10 rounds / s. The diameter of the lens 23 was set to 50 mm, a parameter independent of the detection distance. As shown in FIG. 16( a), the pulse waveform of the measurement light Lm was set to rectangular, the frequency shift by the frequency shifter 4 to 80 MHz, and the pulse repetition frequency of the measurement light Lm to 100 kHz (= pulse interval Δr = 10 μs). The frequency of the measurement light Lm was linearly and periodically modulated so that the UP lamp and the DOWN lamp alternated with each pulse.

[0102] Simultaneously with the output of the measurement light Lm into the atmosphere M, scanning of the measurement light Lm by the deflection unit was started, and the signal light Ls from the atmosphere M was detected by coherent detection. As shown in Figure 16(b), the detection signal D output from the digitizer 10 is a pulse signal with a time interval corresponding to the pulse repetition frequency of the measurement light Lm. Each pulse component of this signal contains information about the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 10 m.

[0103] In the wind speed analysis, the obtained detection signal D is first divided into time slots with a pulse interval (=10 μs). Next, each time slot is multiplied by a window function ranging from 0 ns to 800 ns, and then a Fourier transform is performed to calculate each intensity spectrum. By averaging the intensity spectra for 500 time slots for each of the UP lamp and the DOWN lamp, the average intensity spectrum S of the UP lamp at a detection distance of 10 m is obtained, as shown in Figure 16(c). ＵＰ and the average intensity spectrum S of the DOWN lamp ＤＯＷＮ The obtained average intensity spectrum of the UP lamp S ＵＰ and the average intensity spectrum S of the DOWN lamp ＤＯＷＮ Based on this, each centroid frequency f ＵＰ and f ＤＯＷＮ Get.

[0104] Center of gravity frequency f ＵＰ , f ＤＯＷＮ The line-of-sight wind speed V based on ＬＯＳ The calculation formulas for are as follows: ＬＯＳ is the wind speed in the output direction of the measurement light Lm emitted into the atmosphere M. In the following equations (1) and (2), λ is the wavelength of the measurement light Lm, f ｓｈｉｆｔ is the frequency shift by the frequency shifter 4, f ｄоｐｐｌｅｒ is the Doppler shift. Note that the centroid frequency f ＵＰ , f ＤＯＷＮ If only one of the above is obtained, f is calculated by the following formula (3) or formula (4). ｄоｐｐｌｅｒ In the following formulas (3) and (4), γ is the chirp rate, Z is the detection distance, and c is the speed of light.ＬＯＳ = λ × (f ｄоｐｐｌｅｒ / 2) ... (1) f ｄоｐｐｌｅｒ = ((f ＵＰ +f ＤＯＷＮ ) / 2)-f ｓｈｉｆｔ …(2) f ｄоｐｐｌｅｒ = f ＵＰ +((2×γ×Z) / c)-f ｓｈｉｆｔ …(3) f ｄоｐｐｌｅｒ = f ＤＯＷＮ -((2×γ×Z) / c)-f ｓｈｉｆｔ …(4)

[0105] By repeating the above procedure every 10 ms, it is possible to detect the radial wind speed every 10 ms at a detection distance of 10 m, as shown in Figure 17(a). Based on the results of detecting the radial wind speed for one scanning revolution of the deflection unit (= 100 ms), it is possible to calculate a three-dimensional wind speed vector every 100 ms at a detection distance of 10 m, as shown in Figure 17(b). By calculating the wind speed vector over a certain period of time, it is possible to calculate the average wind speed, maximum wind speed, average wind direction, turbulence intensity (= wind speed standard deviation / average wind speed), etc. at a detection distance of 10 m.

[0106] For wind speed analysis at a detection distance of 30 m, the focusing position of the measurement light Lm was first adjusted to 30 m using the movable stage 22. The pulse width Δt of the measurement light Lm was set to 200 ns, the chirp rate γ to 0 THz / s, and the scanning speed of the deflector to 10 rounds / s. The diameter of the lens 23 was set to 50 mm, a parameter independent of the detection distance. As shown in FIG. 18( a), the pulse waveform of the measurement light Lm was set to rectangular, the frequency shift by the frequency shifter 4 to 80 MHz, and the pulse repetition frequency of the measurement light Lm to 100 kHz (= pulse interval Δr = 10 μs).

[0107] Simultaneously with the output of the measurement light Lm into the atmosphere M, scanning of the measurement light Lm by the deflection unit was started, and the signal light Ls from the atmosphere M was detected by coherent detection. As shown in Figure 18(b), the detection signal D output from the digitizer 10 is a pulse signal with a time interval corresponding to the pulse repetition frequency of the measurement light Lm. Each pulse component of this signal contains information about the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 30 m.

[0108] In wind speed analysis, the obtained detection signal D is first divided into time slots with a pulse interval (=10 μs). Next, each time slot is multiplied by a window function in the range of 200 ns to 400 ns, and then a Fourier transform is performed to calculate each intensity spectrum. By averaging the intensity spectra for 1000 time slots, the average intensity spectrum S at a detection distance of 30 m is obtained as shown in Figure 18(c). ３０ The centroid frequency f Ｃ Obtain the centroid frequency f Ｃ The line-of-sight wind speed V based on ＬＯＳ The calculation formulas for V are as follows: ＬＯＳ = λ × (f ｄоｐｐｌｅｒ / 2) ... (5) f ｄоｐｐｌｅｒ = f Ｃ -f ｓｈｉｆｔ …(6)

[0109] By repeating the above procedure every 10 ms, it is possible to detect the radial wind speed every 10 ms at a detection distance of 30 m, as shown in Figure 19(a). Based on the results of detecting the radial wind speed for one scanning revolution of the deflection unit (= 100 ms), it is possible to calculate a three-dimensional wind speed vector every 100 ms at a detection distance of 30 m, as shown in Figure 19(b). By calculating the wind speed vector over a certain period of time, it is possible to calculate the average wind speed, maximum wind speed, average wind direction, turbulence intensity (= wind speed standard deviation / average wind speed), etc. at a detection distance of 30 m.

[0110] For wind speed analysis at detection distances of 60 m to 900 m, the measurement light Lm was first adjusted to be a parallel beam using the movable stage 22. The pulse width Δt of the measurement light Lm was set to 400 ns, the chirp rate γ to 0 THz / s, and the scanning speed of the deflector to 1 round / s. The diameter of the lens 23 was set to 50 mm, a parameter independent of the detection distance. As shown in FIG. 20( a), the pulse waveform of the measurement light Lm was set to rectangular, the frequency shift by the frequency shifter 4 to 80 MHz, and the pulse repetition frequency of the measurement light Lm to 100 kHz (= pulse interval Δr = 10 μs).

[0111] Simultaneously with the output of the measurement light Lm into the atmosphere M, scanning of the measurement light Lm by the deflection unit was started, and the signal light Ls from the atmosphere M was detected by coherent detection. As shown in Figure 20(b), the detection signal D output from the digitizer 10 is a continuous signal with a time interval corresponding to the pulse repetition frequency of the measurement light Lm. This signal component contains information on the peak frequency of the beat spectrum of the interference light Ld at a detection distance of 60 m or more.

[0112] In wind speed analysis, the obtained detection signal D is first divided into time slots with a pulse interval (=10 μs). Each time slot is further divided into sub-slots #1 to #15 with a 400 ns interval. Each data of sub-slots #1 to #15 is multiplied by a 400 ns window function based on the pulse width Δt, and then a Fourier transform is performed to calculate each intensity spectrum. For each intensity spectrum, the intensity for 10,000 time slots is averaged to obtain an average intensity spectrum S for every 60 m detection distance, as shown in FIG. ６０ , S １２０ , ...S ９００ The obtained average intensity spectrum S ６０ , S １２０ , ...S ９００ Based on this, the centroid frequency f ６０ , f １２０ , ...f ９００ Obtain the centroid frequency f ６０ , f １２０ , ...f ９００ The line-of-sight wind speed V based on ＬＯＳ The above-described formulas (5) and (6) can be used to calculate the above.

[0113] By repeating the above procedure every 100 ms, it is possible to detect the radial wind speed every 100 ms at a distance that is an integer multiple of the detection distance of 60 m, as shown in Figure 22. Based on the results of detecting the radial wind speed for one scanning revolution of the deflection unit (= 1000 ms), it is possible to obtain a three-dimensional wind speed vector every 1000 ms at a distance that is an integer multiple of the detection distance of 60 m, as shown in Figure 23. By obtaining the wind speed vector over a certain period of time, it is possible to calculate the average wind speed, maximum wind speed, average wind direction, turbulence intensity (= wind speed standard deviation / average wind speed), etc. at a distance that is an integer multiple of the detection distance of 60 m.

[0114] The present disclosure is not limited to the above-described embodiments. For example, in the above-described embodiments, a configuration in which the spatial optical system circulator 21 is used in the measurement optical system 7 is exemplified. However, as shown in FIG. 24 , an optical fiber device circulator 31 may be used in the measurement optical system 7. In the example of FIG. 24 , an end Fa of an optical fiber F connected to an output port of the optical fiber device circulator 31 is mounted on a movable stage 32. By using the movable stage 32 to change the distance from the end Fa of the optical fiber F to the lens 23, the focal position of the measurement light Lm emitted into the atmosphere M via the lens 23 can be displaced in the optical axis direction of the measurement light Lm.

[0115] 5, the output direction of the measurement light Lm toward the atmosphere M is deflected in an arbitrary direction using the beam deflector 24, but the deflection of the output direction of the measurement light Lm may be achieved using other configurations. For example, a mirror may be disposed outside the lens 23, and the output direction of the measurement light Lm toward the atmosphere M may be deflected in an arbitrary direction by adjusting the angle of the mirror. In the example of FIG. 24, the output direction of the measurement light Lm toward the atmosphere M may be deflected in an arbitrary direction by moving the orientation of the end Fa of the optical fiber F up, down, left, or right.

[0116] 1...wind speed detection device, 2...output section, 3...branching section, 5...first amplifier section (conversion section), 7...measurement optical system, 9...detection section, 11...analysis section, 12...optical integrated circuit, 15...control section, 24...beam deflection plate (deflection section), 25...rotation stage (deflection section), M...atmosphere, L...laser light, Lm...measurement light, Lf...scattered light, Ls...signal light, Lr...reference light, D...detection signal, T1...first threshold, T2...second threshold, R1...short distance range, R1a...ultra-short distance range, R1b...medium-short distance range, R2...long distance range, 101...aircraft control device, 102...control device, H...aircraft, Q...control signal.

Claims

1. A wind speed detection device comprising: an output unit that outputs laser light; a branching unit that branches the laser light into measurement light and reference light; a conversion unit that converts the measurement light into pulsed light; a measurement optical system that outputs the measurement light into the atmosphere and receives light scattered by the measurement light in the atmosphere as signal light; a detection unit that outputs a detection signal based on the interference result between the reference light and the signal light; and a control unit that controls the state of the measurement light output from the measurement optical system based on the detection distance by the measurement light, wherein the control unit controls the measurement optical system so that the measurement light output into the atmosphere is focused when the detection distance falls within a short distance range not greater than a first threshold, and controls the measurement optical system so that the measurement light output into the atmosphere is collimated when the detection distance falls within a long distance range exceeding the first threshold.

2. A wind speed detection device as described in claim 1, wherein the control unit controls the output unit so that frequency-modulated light is output as the laser light when the detection distance falls within an ultra-short distance range that is equal to or less than a second threshold value set in the short distance range.

3. A wind speed detection device as described in claim 1 or 2, wherein the control unit controls the conversion unit so that the pulse width of the measurement light changes according to the detection distance when the detection distance falls within a medium-to-short distance range that exceeds a second threshold value set for the short distance range.

4. A wind speed detection device according to any one of claims 1 to 3, wherein the output unit outputs CW light as the laser light, and the detection unit outputs a detection signal based on the interference result between the reference light, which is CW light, and the signal light.

5. A wind speed detection device according to any one of claims 1 to 4, wherein the measurement optical system has a deflection unit that deflects the output direction of the measurement light toward the atmosphere.

6. A wind speed detection device as described in claim 5, wherein the control unit controls the deflection unit so that the scanning speed in the output direction of the measurement light is slower when the detection distance falls within the long distance range than when the detection distance falls within the short distance range.

7. A wind speed detection device according to any one of claims 1 to 6, wherein at least the output section, the branching section, and the detection section are configured by optical integrated circuits.

8. A wind speed detection device according to any one of claims 1 to 7, further comprising an analysis unit that analyzes the wind speed in the atmosphere based on the detection signal.

9. A wind speed detection method comprising: an output step of outputting laser light; a branching step of branching the laser light into measurement light and reference light; a conversion step of converting the measurement light into pulsed light; a measurement step of outputting the measurement light into the atmosphere and receiving light scattered by the measurement light in the atmosphere as signal light; and a detection step of outputting a detection signal based on the result of interference between the reference light and the signal light, wherein in the measurement step, the measurement light outputted into the atmosphere is focused when the detection distance by the measurement light falls within a short distance range not greater than a first threshold, and the measurement light outputted into the atmosphere is collimated when the detection distance by the measurement light falls within a long distance range exceeding the first threshold.

10. A wind speed detection method as described in claim 9, wherein in the output step, if the detection distance falls within an ultra-short distance range that is equal to or less than a second threshold value set in the short distance range, frequency-modulated light is output as the laser light.

11. A wind speed detection method as claimed in claim 9 or 10, wherein in the conversion step, if the detection distance falls within a medium-to-short distance range exceeding a second threshold value set for the short distance range, the pulse width of the measurement light is changed according to the detection distance.

12. A wind speed detection method according to any one of claims 9 to 11, wherein in the output step, CW light is output as the laser light, and in the detection step, a detection signal is output based on the interference result between the reference light, which is CW light, and the signal light.

13. A wind speed detection method according to any one of claims 9 to 12, wherein the measuring step includes a deflecting step of deflecting the output direction of the measurement light directed into the atmosphere.

14. A wind speed detection method as described in claim 13, wherein in the deflection step, when the detection distance falls within the long distance range, the scanning speed in the output direction of the measurement light is made slower than when the detection distance falls within the short distance range.

15. A wind speed detection method according to any one of claims 9 to 14, further comprising an analysis step of analyzing the wind speed in the atmosphere based on the detection signal.

16. An aircraft control device comprising: a wind speed detection device according to any one of claims 1 to 8; and a control device that generates control signals related to takeoff and landing of the aircraft based on the detection signal output from the wind speed detection device.

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