Laser radar device

Abstract

A laser radar device (100) comprises: a polarization direction rotation unit (7) that rotates a polarization direction by a predetermined angle with respect to an input laser beam; a polarizing beamsplitter (8) that branches the laser beam, the polarization direction of which has been rotated by the polarization direction rotation unit (7), into a first direction and a second direction different from the first direction; a rotation control unit (15) that realizes circular scanning by the laser beam branched in the first direction and conical scanning by the laser beam branched in the second direction by rotating the polarization direction rotation unit (7) and the polarizing beamsplitter (8) at mutually different rotational angular velocities; and a signal processing unit (14) that calculates a wind velocity field using reflected light reflected by an object irradiated by the laser beams in each scanning.

Description

Laser radar device

[0001] The present disclosure relates to a laser radar device.

[0002] Related to the present disclosure, a technique for measuring wind (wind speed) using a laser radar device is known. For example, a laser radar device irradiates the atmosphere with laser pulse light (hereinafter simply referred to as "laser light"), receives scattered light from aerosols, and measures the wind speed in the direction of irradiation of the laser light by heterodyne detection of the scattered light and continuous light of a single frequency, which is local light of the irradiated laser light, to determine the Doppler shift caused by the movement of aerosols. Note that the Doppler shift is calculated from a spectrum obtained by Fourier transforming the signal after heterodyne detection (see, for example, Non-Patent Document 1).

[0003] The wind speed measured by the laser radar device is the wind speed in a direction parallel to the direction of irradiation of the laser light, and this wind speed is usually called the “line-of-sight wind speed.” On the other hand, when determining three-dimensional wind direction and wind speed (hereinafter, this wind direction and wind speed will also be referred to as the “wind speed field” or “wind speed vector”), multiple line-of-sight observations or scanning observations are performed to switch the irradiation direction of the laser light, and the three-dimensional wind speed field is calculated using a conventional calculation method such as vector calculations and processing based on the VAD (Velocity Azimuth Display) method.

[0004] Known examples of laser radar devices capable of calculating such wind velocity fields include vertical laser radar devices that perform multiple line-of-sight observations by constructing multiple optical systems so that laser light is irradiated in different directions in the atmosphere, and scanning laser radar devices that refract laser light by scanning multiple movable mirrors so that the laser light is irradiated in the direction of the atmosphere. In the following description, the laser light irradiated into the atmosphere may be referred to as transmitted light, laser pulse light, transmitted beam, transmitted laser beam, etc., but all of these are synonymous.

[0005] Radar Remote Sensing of Weather and Atmosphere, ISBN 4-87698-653-3

[0006] Laser radar devices that measure wind (hereinafter referred to as "wind measurement lidars" or simply "lidars") have traditionally been used in various fields, such as airports, wind power generation, and meteorological observation. However, the laser radar device disclosed herein is intended for application to airborne platforms, including flying cars. To utilize laser radar devices on airborne platforms, it is extremely important to understand the wind field along the airborne platform's flight path, and navigation support such as gust alerts and optimal route suggestions based on the results of this understanding is necessary. Therefore, the laser radar device must measure the wind field in the terrestrial hemisphere, and this measurement must be performed in real time.

[0007] For example, conventional vertical lidars that observe only the zenith direction can measure wind speed fields in a short time, but the measurement results are distance-resolved only in the altitude direction, and only information on the wind speed field at a single location where the lidar is installed is obtained. In contrast, scanning lidars can measure wind speed fields in three dimensions by scanning laser light in the azimuth (AZ) and elevation (EL) directions, making it possible to measure wind speed fields over an entire hemispherical space at multiple locations and multiple altitudes. However, this lidar requires time to scan the hemispherical space in all directions, and therefore lacks real-time capabilities.

[0008] For example, with scanning lidar, there is a time lag between the observation data from the north and the observation data from the south. In other words, with scanning lidar, the same time of the wind field is not guaranteed among the observation data scanned in all directions in a hemispherical space. At the same time, it is difficult to perform this measurement in a short time.

[0009] The reason why the above measurement requires time will be explained using as an example a pulsed wind measurement lidar, i.e., a wind measurement lidar using a method of resolving distance using time of fire (TOF). In the case of a pulsed wind measurement lidar, the laser light transmitted into the atmosphere by the wind measurement lidar is pulsed light with a predetermined repetition frequency, but integration is required to obtain a sufficient signal-to-noise ratio (SNR). If the repetition frequency is PRF and the number of integrations is N, the time required to complete the integration is PRF×N. Therefore, within the time required for this integration, the wind measurement lidar needs to stop scanning in a predetermined direction or scan at a low speed to approximately point in the same direction. Therefore, it takes time for the wind measurement lidar to scan the entire hemispherical space above the ground. As such, it is difficult for conventional wind measurement lidars to measure the wind velocity field in the hemispherical space above the ground in a short period of time, and there are issues with applying them to airborne platforms.

[0010] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a laser radar device that can measure the wind velocity field in the terrestrial hemisphere in a shorter time than conventional methods.

[0011] The laser radar device according to the present disclosure includes a polarization direction rotation unit that rotates the polarization direction of input laser light by a predetermined angle; a polarizing beam splitter that splits the laser light, whose polarization direction has been rotated by the polarization direction rotation unit, into a first direction and a second direction different from the first direction; a rotation control unit that rotates the polarization direction rotation unit and the polarizing beam splitter at different rotational angular velocities to realize a circular scan with the laser light split in the first direction and a conical scan with the laser light split in the second direction; and a signal processing unit that calculates a wind velocity field using light reflected by an object irradiated with the laser light during each scan.

[0012] According to the present disclosure, it is possible to measure the wind velocity field in the terrestrial hemisphere in a shorter time than conventionally possible.

[0013] FIG. 1 is a diagram illustrating a configuration example of a laser radar device according to embodiment 1. FIG. 2 is a diagram illustrating a change in the polarization direction of transmitted light input to a λ / 2 wavelength plate according to embodiment 1. FIG. 3 is a diagram illustrating a state in which the propagation direction of transmitted light into the atmosphere changes according to embodiment 1. FIG. 4 is a diagram illustrating a wind field in a certain region of a scan-side region according to embodiment 1. FIG. 5 is a diagram illustrating wind fields on the vertical side and scan side calculated by a signal processing unit according to embodiment 1. FIG. 6 is a diagram illustrating wind fields at multiple altitudes and multiple points calculated by a signal processing unit according to embodiment 1. FIG. 7 is a diagram illustrating a configuration example of a scan unit in a laser radar device according to embodiment 2.

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0015] Fig. 1 is a diagram showing an example of the configuration of a laser radar device 100 according to embodiment 1. As shown in Fig. 1, the laser radar device 100 includes, for example, a light source 1, a branching unit 2, a modulation unit 3, an amplification unit 4, a transmission-side optical system 5, a transmission-reception separation unit 6, a polarization direction rotation unit 7, a reception-side optical system 11, a reception-side polarizing beam splitter 12, an optical IQ detector 13, a signal processing unit 14, rotation control units 15 (15a, 15b), and a scanning unit 17 (a polarizing beam splitter 8, a polarizing optical element 9, a window 10, and a window 16).

[0016] The light source 1 outputs laser light, which is continuous light of a substantially single frequency. This laser light has a wavelength band that can be reflected by an object to be irradiated, such as aerosols in the atmosphere, and has linear polarization characteristics. The light source 1 is composed of, for example, a semiconductor laser and a solid-state laser, and is connected to the branching unit 2.

[0017] The branching unit 2 divides the laser light input from the light source 1 into a transmission optical signal and a local optical signal, and outputs the transmission optical signal to the modulation unit 3 and the local optical signal to the optical IQ detector 13, respectively. The branching unit 2 is composed of, for example, a 1:2 optical coupler and a half mirror. Here, the branching unit 2 is described as being of a fiber type, but the branching unit 2 is not limited to this and may be of a space type. The output end of the branching unit 2 for the transmission optical signal is connected to the modulation unit 3, and the output end of the local optical signal is connected to the optical IQ detector 13.

[0018] The modulation unit 3 performs pulse modulation on the transmission optical signal input from the branch unit 2 and generates pulsed light by applying a desired frequency shift. The modulation unit 3 is composed of, for example, an LN (LiNbO3) modulator, an AOM (Acousto-Optics modulator), and an SOA (Semiconductor Optical Amplifier), and is connected to the amplification unit 4.

[0019] The amplifier 4 has a function of generating transmission light by amplifying the peak power of the pulsed light input from the modulator 3. The amplifier 4 is configured by, for example, an optical fiber amplifier, and is connected to a transmission optical system 5.

[0020] The transmitting optical system 5 has a function of shaping the transmitted light input from the amplifier 4 to a desired beam diameter and divergence angle. The transmitting optical system 5 is composed of, for example, a convex lens, a concave lens, an aspherical lens, or a combination thereof. However, the transmitting optical system 5 is not limited to these, and may be composed of, for example, a mirror.

[0021] The transmitting optical system 5 is optically connected to the transmission / reception separator 6. Here, "optically connected" does not mean an electrical or physical connection, but means a connection as a path for light propagation.

[0022] In the first embodiment, an example will be described in which the path from the light source 1 to the transmitting optical system 5 is configured using optical fiber. Specifically, in the first embodiment, the polarization direction of the transmitted light is maintained in the polarization direction determined by the light source 1 from the time when the light source 1 outputs laser light until the transmitted light exits the transmitting optical system 5. Therefore, in the first embodiment, the above path is configured using polarization-maintaining optical fiber. However, the above path does not necessarily have to be configured using optical fiber, and may be configured using a spatial optical system, for example. In the first embodiment, the polarization direction of the transmitted light at the position where it exits from the transmitting optical system 5 is defined as the reference optical axis.

[0023] The transmission / reception separator 6 is optically connected to the transmitting optical system 5, the polarization direction rotation unit 7, and the receiving optical system 11. The transmission / reception separator 6 is configured, for example, by a polarization-independent beam splitter. The transmission / reception separator 6 has a function of outputting the transmitted light input in the forward direction from the transmitting optical system 5 to the polarization direction rotation unit 7. At this time, the transmission / reception separator 6 does not output the transmitted light to the receiving optical system 11. The transmission / reception separator 6 also has a function of outputting the received light input in the reverse direction from the polarization direction rotation unit 7 to the receiving optical system 11. At this time, the transmission / reception separator 6 does not output the received light to the transmitting optical system 5.

[0024] The polarization direction rotation unit 7 is optically connected to the transmission / reception separation unit 6 and the polarized beam splitter 8. The polarization direction rotation unit 7 has the function of rotating the polarization direction of the transmission light having a specific polarization direction input from the transmission / reception separation unit 6 by a predetermined angle, and outputting the rotated transmission light to the polarized beam splitter 8. The polarization direction rotation unit 7 is formed of, for example, a λ / 2 wave plate. The polarization direction rotation unit 7 is also connected to the rotation control unit 15, and rotates under the control of the rotation control unit 15.

[0025] The polarizing beam splitter 8 is optically connected to the polarizing optical element 9 and the window 16. The polarizing beam splitter 8 has a function of guiding the S-polarized component to a first direction and the P-polarized component to a second direction, depending on the polarization direction of the rotated transmitted light input from the polarization direction rotation unit 7. Here, the first direction is, for example, the horizontal direction (scanning direction), and the second direction is the vertical direction.

[0026] In the following description, the first direction is the horizontal direction (scanning direction) and the second direction is the vertical direction. In the following description, the horizontal direction (scanning direction) side is also simply referred to as the "scanning side," and the vertical direction side is also simply referred to as the "vertical side."

[0027] The polarizing optical element 9 is optically connected to the polarizing beam splitter 8 and the window 10. The polarizing optical element 9 has the function of giving a predetermined angle of deflection to the transmitted light (P-polarized component) guided to the vertical side and outputting it to the window 10.

[0028] The window 10 is optically connected to the polarizing optical element 9. The window 10 has a function of transmitting the transmitted light output from the polarizing optical element 9 and guiding (irradiating) the light into the atmosphere.

[0029] The window 16 is optically connected to the polarizing beam splitter 8. The window 16 has a function of transmitting the transmitted light (S-polarized component) guided from the polarizing beam splitter 8 to the scan side and guiding it into the atmosphere.

[0030] In the first embodiment, the polarizing beam splitter 8, the polarizing optical element 9, the window 10, and the window 16 form a scanning unit 17. The scanning unit 17 is connected to a rotation control unit 15 and rotates under the control of the rotation control unit 15.

[0031] The receiving optical system 11 is optically connected to the transmission / reception separator 6. The receiving optical system 11 has a function of receiving, as received light, reflected light that is scattered when the transmitted light irradiated to the vertical side and the scanning side strikes an irradiated object. The optical axis of the receiving optical system 11 is tilted 45 degrees with respect to the optical axis of the transmitting optical system 5 so that the P-polarized component and the S-polarized component of the received received light are distinguished and received along the fast axis and the slow axis. This allows the receiving optical system 11 to always receive each polarization component along the same optical axis.

[0032] The receiving-side polarized beam splitter 12 is connected to the receiving-side optical system 11 and the optical IQ detector 13. The receiving-side polarized beam splitter 12 has the function of separating the received light received by the receiving-side optical system 11 into a P-polarized component and an S-polarized component, and outputting each of the separated components to the optical IQ detector 13.

[0033] The optical IQ detector 13 is connected to the branching unit 2, the receiving-side polarized beam splitter 12, and the signal processing unit 14. The function of the optical IQ detector 13 is known as a conventional technique, so a detailed description of its internal configuration and function will be omitted, and only an outline will be provided here.

[0034] Based on the above-described configuration and functions, the P-polarized and S-polarized components of the transmitted light are assigned to the vertical and scanning sides, while the P-polarized and S-polarized components of the received light received from the atmosphere are fixedly assigned to the optical axes of the fast and slow axes of the receiving optical system 11. When the optical IQ detector 13 receives the local light signal output from the splitter 2, it splits the received signal into two and applies a phase shift of π / 2 to one of the signals. Each of the split signals is then multiplexed with the P-polarized and S-polarized components split by the receiving polarized beam splitter 12. The light obtained by this multiplexing is split using a function equivalent to, for example, a 2:2 coupler and a half mirror, and the split light (interference light) is input to a balanced receiver or a differential amplifier detector, whereby beat signals (P-side RF signal and S-side RF signal) determined by the frequency shift applied by the modulator 3 are generated from the P-polarized and S-polarized components of the received light. The optical IQ detector 13 outputs the generated beat signal to the signal processing unit 14. The internal configuration of the optical IQ detector 13 may be constructed using a fiber system.

[0035] The signal processing unit 14 is connected to the optical IQ detector 13 and the rotation control unit 15. The signal processing unit 14 is equipped with components necessary for signal processing conventionally known in wind measurement lidars, such as an AD converter and a Fourier transformer, and performs processing to calculate wind speed from the spectrum after Fourier transformation. The signal processing unit 14 also controls the rotation control unit 15.

[0036] For example, the signal processing unit 14 performs AD conversion on the two beat signals generated by the P-polarized component and the S-polarized component using AD converters configured for each beat signal, and performs a fast Fourier transform (FFT) on each digitized signal to generate a frequency spectrum. The signal processing unit 14 then calculates wind velocity fields for each distance in the vertical and scanning directions based on the generated frequency spectra. The signal processing unit 14 is configured, for example, with an FPGA (Field-Programmable Gate Array) to calculate the wind velocity fields after the fast Fourier transform.

[0037] Rotation control unit 15 is connected to polarization direction rotation unit 7, signal processing unit 14, and scanning unit 17, and rotates polarization direction rotation unit 7 and scanning unit 17 independently under the control of signal processing unit 14. Specifically, rotation control unit 15 is made up of rotation control units 15a and 15b, and rotation control unit 15a has the function of rotating polarization direction rotation unit 7, and rotation control unit 15b has the function of rotating scanning unit 17, each at a predetermined rotational angular velocity.

[0038] The rotation control unit 15b rotates the scan unit 17 to change the irradiation direction of the transmission light guided from the polarizing beam splitter 8 to the scan side within a range of 0 to 360 degrees relative to the azimuth angle direction. Furthermore, the rotation control unit 15b rotates the scan unit 17 to change the irradiation direction of the vertical-side transmission light that is guided from the polarizing beam splitter 8 to the vertical side and to which a deflection angle has been added by the polarizing optical element 9.

[0039] The rotation control unit 15a has a function of rotating the polarization direction rotation unit 7, which includes the following two functions: one is to provide an offset angle to the rotation angle of the polarization direction rotation unit 7 with respect to the optical axis of the polarizing beam splitter 8, and the other is to rotate the polarization direction rotation unit 7 at a rotation angular velocity different from the rotation angular velocity of the scan unit 17.

[0040] As an example, if the offset angle given to the rotation angle of the polarization direction rotation unit 7 is α, the rotation angular velocity of the polarization direction rotation unit 7 is ω2, and the rotation angular velocity of the scan unit 17 is ωs, the relationship between ω2 and ωs is expressed by the following equation (1): ωs=2×ω2 (1)

[0041] Furthermore, the rotation angle θ of the polarization direction rotation unit 7 at time t ２ (t) is the rotation angle θ of the scanning unit 17 at time t according to the following equation (2). Ｓ (t) can be calculated using the following equation (3): θ ２ (t)=(ωs / 2)×t+α (2) θ Ｓ (t)=ωs×t (3)

[0042] Incidentally, providing an offset angle α to the rotation angle of the polarization direction rotation unit 7 with respect to the optical axis of the polarization beam splitter 8 is equivalent to making the vector corresponding to the optical axis of the λ / 2 wave plate (7) constituting the polarization direction rotation unit 7 and the vector obtained by projecting the normal vector of the reflecting surface of the polarization beam splitter (8) onto the λ / 2 wave plate (7) non-parallel.

[0043] By being provided with the above-described configuration and functions, in the laser radar device 100 according to the first embodiment, not only is the transmitted light output from the transmitting-side optical system 5 separated into two directions, the scanning side and the vertical side, but the P-polarized component of the transmitted light is always guided to the vertical side, and the S-polarized component of the transmitted light is always guided to the scanning side. Furthermore, by being provided with the above-described configuration and functions, the laser radar device 100 realizes a circular scan by the S-polarized component of the transmitted light guided to the scanning side, and a conical scan by the P-polarized component of the transmitted light guided to the vertical side.

[0044] Furthermore, in the laser radar device 100, light scattered by irradiation targets (aerosols, etc.) in the atmosphere located in both the vertical and scanning directions, i.e., reflected light, is incident again on the polarizing beam splitter 8 as received light and passes through the polarization direction rotation unit 7. At this time, the polarization direction of the received light from each direction is at an angle different from the polarization direction of the transmitted light, but the polarization direction of the combined component of the received light is always fixed in the same direction.

[0045] Next, a description will be given of an example of the operation of the laser radar device 100 according to the embodiment 1. In the following description, an example will be given in which the polarization direction rotator 7 is configured with a λ / 2 wave plate.

[0046] First, the light source 1 outputs laser light, which is continuous light consisting of a substantially single frequency. The branching unit 2 splits the laser light input from the light source 1 into a transmission optical signal and a local light signal, and outputs the transmission optical signal to the modulation unit 3 and the local light signal to the optical IQ detector 13. The modulation unit 3 pulse-modulates the transmission optical signal input from the branching unit 2 and imparts a desired frequency shift to generate pulsed light.

[0047] The amplifier 4 generates transmission light by amplifying the peak power of the pulsed light input from the modulator 3. The transmitting optical system 5 shapes the transmission light input from the amplifier 4 to a desired beam diameter and divergence angle. The transmission light output from the transmitting optical system 5 is input to a transmission / reception separator 6, which is a polarization-independent beam splitter, and is further input from the transmission / reception separator 6 to a λ / 2 wave plate that constitutes a polarization direction rotator 7.

[0048] The change in the polarization direction of the transmitted light input to the λ / 2 wave plate will be described in detail using Figure 2. In Figure 2, the left diagram illustrates the change in the polarization direction at time t = 0 seconds, and the right diagram illustrates the change in the polarization direction at time t = 1 second. For the sake of concreteness, the rotation angular velocity ωs of the scanning unit 17 is set to 90 degrees / second, and the offset angle α given to the rotation angle of the polarization direction rotation unit 7 is set to 22.5 degrees. Therefore, the rotation angular velocity ω2 of the λ / 2 wave plate, which is the polarization direction rotation unit 7, is 45 degrees / second.

[0049] Furthermore, from the above equations (2) and (3), at time t=0, the rotation angle θ of the λ / 2 wave plate ２ (t) is 22.5 degrees, and the rotation angle θ of the scanning unit 17 Ｓ (t) is 0 degrees. The rotation angle θ of the λ / 2 wave plate ２ (t) corresponds to the optical axis of the λ / 2 wave plate. Ｓ (t) is defined as the direction of the S-polarized component reflected by the polarizing beam splitter 8. The rotation angle θ of the scanning unit 17 is Ｓ(t) coincides with the reference optical axis mentioned above.

[0050] At time t=0, the rotation angle θ of the λ / 2 wave plate ２ Since (t) is 22.5 degrees, the polarization direction of the transmitted light that passes through the λ / 2 wave plate is rotated by 45 degrees with respect to the reference optical axis. Note that the transmitted light that passes through the λ / 2 wave plate propagates in a direction perpendicular to the paper surface, i.e., from the back side to the front side of the paper.

[0051] The transmitted light, whose polarization direction has been rotated by 45 degrees, is aligned with the reference optical axis θ Ｓ When the light beam enters the polarized beam splitter 8 of the scanning unit 17 with which the time (t) coincides, it is split by the polarized beam splitter 8, and the S-polarized component reflected by the polarized beam splitter 8 is extracted. The extracted S-polarized component is folded into the X-Y plane shown in FIG. 2 and converted into transmitted light that propagates horizontally relative to the paper surface. Therefore, for example, if the X-axis direction shown in FIG. 2 is defined as north, the extracted S-polarized component becomes transmitted light that scans north. At this time, the scanning direction of the S-polarized component is determined by the rotation angle θ of the scanning unit 17. Ｓ This coincides with (t), but this is because an offset angle α is given to the λ / 2 wave plate.

[0052] On the other hand, the transmitted light, whose polarization direction is rotated by 45 degrees, is aligned with the reference optical axis θ Ｓ When the light enters the polarizing beam splitter 8 of the scanning unit 17 with which the time (t) coincides, it is split by the polarizing beam splitter 8, and the P-polarized component that passes through the polarizing beam splitter 8 is extracted. The extracted P-polarized component becomes transmitted light that is not bent within the X-Y plane shown in Figure 2, but propagates forward in a direction perpendicular to the paper surface. Therefore, for example, if the positive direction of the Z-axis shown in Figure 2 is defined as the zenith direction, the extracted P-polarized component becomes transmitted light that propagates toward the zenith (vertical side).

[0053] The polarization optical element 9 deflects the transmitted light propagating vertically by a predetermined angle and outputs it to the window 10. The window 10 irradiates the deflected transmitted light on the vertical side into the atmosphere. The window 16 also irradiates the transmitted light propagating toward the scanning side into the atmosphere. After that, each transmitted light is scattered by an irradiation object (aerosol, etc.) in the atmosphere, becomes reflected light, and reaches the respective windows 10 and 16 again. At this time, the polarization direction of each reflected light is maintained.

[0054] The reflected light on the vertical side that reaches the window 10 passes through the polarization optical element 9 again as received light. The polarization optical element 9 again applies a deflection angle to the received light on the vertical side so that the optical axis of the received light coincides with the optical axis of the transmitted light before the deflection angle was applied during transmission. The received light on the vertical side then returns to the λ / 2 wave plate, which is the polarization direction rotator 7, along the same path as during transmission. Similarly, the reflected light on the scanning side that reaches the window 16 returns to the λ / 2 wave plate, which is the polarization direction rotator 7, along the same path as during transmission as received light. As each received light that returns to the λ / 2 wave plate passes through the λ / 2 wave plate again, the polarization direction of each received light is rotated with respect to the optical axis of the λ / 2 wave plate.

[0055] At this time, for example, the polarization direction of the received light (S-polarized component) on the scanning side is rotated 45 degrees counterclockwise on the XY plane relative to the transmitted light (S-polarized component) on the scanning side. Furthermore, the polarization direction of the received light (P-polarized component) on the vertical side is rotated 135 degrees clockwise on the XY plane relative to the transmitted light (P-polarized component) on the vertical side (see FIG. 2). The combined component of the received light (S-polarized component) on the scanning side and the received light (P-polarized component) on the vertical side coincides with the polarization direction of the transmitted light when it exits the transmitting optical system 5 during transmission.

[0056] Next, the situation at time t=1 will be described. From the above equations (2) and (3), at time t=1, the rotation angle θ of the λ / 2 wave plate ２ (t) is 67.5 degrees, and the rotation angle θ of the scanning unit 17 Ｓ (t) is 90 degrees.

[0057] At time t=1, the rotation angle θ of the λ / 2 wave plate ２Since (t) is 67.5 degrees, the polarization direction of the transmitted light that has passed through the λ / 2 wave plate is rotated by 135 degrees with respect to the reference optical axis. Ｓ When (t) enters the polarized beam splitter 8 of the scanning unit 17 rotated by 90 degrees, it is split by the polarized beam splitter 8 and the S-polarized component reflected by the polarized beam splitter 8 is extracted. The extracted S-polarized component is folded into the XY plane shown in FIG. 2 and converted into transmitted light that propagates horizontally relative to the paper surface.

[0058] Therefore, when t=1, the extracted S-polarized component becomes a transmitted light that scans in the west direction, for example, when the X-axis direction is defined as north. This also applies when the scanning direction of the S-polarized component is determined by the rotation angle θ of the scanning unit 17. Ｓ This means that the wavelengths (t) and (t) coincide with each other. This is because, as described above, the offset angle α is given to the λ / 2 wave plate so that the wavelengths (t) and (t) coincide with each other.

[0059] Also, just as when t=0, the P-polarized component that passes through the polarizing beam splitter 8 is not bent into the XY plane, but becomes transmitted light that propagates toward the front in a direction perpendicular to the paper surface. Therefore, for example, if the positive direction of the Z-axis is defined as the zenith direction, the P-polarized component becomes transmitted light that propagates toward the zenith (vertical side).

[0060] Thereafter, as in the case of t=0, the polarization optical element 9 deflects the transmitted light propagating vertically by a predetermined angle and outputs it to the window 10. The window 10 irradiates the deflected transmitted light on the vertical side into the atmosphere. The window 16 also irradiates the transmitted light propagating toward the scanning side into the atmosphere. After that, each transmitted light is scattered by an irradiation target (aerosol, etc.) in the atmosphere, becomes reflected light, and reaches the respective windows 10 and 16 again. At this time, the polarization direction of each reflected light is maintained.

[0061] The reflected light on the vertical side that reaches the window 10 passes through the polarization optical element 9 again as received light. The polarization optical element 9 again applies a deflection angle to the received light on the vertical side so that the optical axis of the received light coincides with the optical axis of the transmitted light before the deflection angle was applied during transmission. The received light on the vertical side then returns to the λ / 2 wave plate, which is the polarization direction rotator 7, along the same path as during transmission. Similarly, the reflected light on the scanning side that reaches the window 16 returns to the λ / 2 wave plate, which is the polarization direction rotator 7, along the same path as during transmission as received light. As each received light that returns to the λ / 2 wave plate passes through the λ / 2 wave plate again, the polarization direction of each received light is rotated with respect to the optical axis of the λ / 2 wave plate.

[0062] At this time, for example, the polarization direction of the received light (S-polarized component) on the scanning side is rotated 45 degrees clockwise on the XY plane relative to the transmitted light (S-polarized component) on the scanning side. Furthermore, the polarization direction of the received light (P-polarized component) on the vertical side is rotated 225 degrees clockwise on the XY plane relative to the transmitted light (P-polarized component) on the vertical side (see Figure 2). The combined component of the received light (S-polarized component) on the scanning side and the received light (P-polarized component) on the vertical side coincides with the polarization direction of the transmitted light when it exits the transmitting optical system 5 during transmission. Furthermore, at t=0 and t=1, the polarization direction of the received light (S-polarized component) on the scanning side coincides with the polarization direction of the received light (P-polarized component) on the vertical side after passing through the λ / 2 wave plate.

[0063] In the above explanation, the cases of t = 0 and t = 1 were used as examples, but the above content is valid for any time. In other words, after passing through the λ / 2 wave plate, the polarization directions of the received light on the vertical side (P-polarized component) and the received light on the scanning side (S-polarized component) are always fixed, with the former tilted at +45 degrees from the reference optical axis and the latter tilted at -45 degrees.

[0064] That is, in the first embodiment, by adding an offset angle α to the rotation angle of the λ / 2 wave plate and controlling the rotation angular velocity of the λ / 2 wave plate to be half the rotation angular velocity of the polarized beam splitter 8, it is possible to keep the polarization directions of the received light (P-polarized component) on the vertical side and the received light (S-polarized component) on the scanning side always fixed with respect to the reference optical axis.

[0065] Therefore, in the first embodiment, the optical axes (fast axis and slow axis) of the receiving optical system 11 are fixed at an angle (rotated) 45 degrees relative to the reference optical axis so that they coincide with the polarization direction of the received light (P-polarized component) on the vertical side (+45 degrees from the reference optical axis) and the polarization direction of the received light (S-polarized component) on the scanning side (-45 degrees from the reference optical axis), thereby making it possible to always couple the P-polarized component to the fast axis of the receiving optical system 11 and the S-polarized component to the slow axis. Therefore, in the first embodiment, it is possible to fix the optical axis of the receiving optical system 11 so that the received light received from the vertical side always propagates along the fast axis of the receiving optical system 11, and the received light received from the scanning side always propagates along the slow axis of the receiving optical system 11.

[0066] Thereafter, the receiving-side polarizing beam splitter 12 separates the P-polarized component and the S-polarized component of the received light received by the receiving-side optical system 11, and outputs each of the separated components to the optical IQ detector 13.

[0067] The optical IQ detector 13 uses the local light signal received from the splitter 2 to perform the above-mentioned multiplexing of the P-polarized component and the S-polarized component split by the receiver-side polarized beam splitter 12, thereby generating the above-mentioned beat signals (P-side RF signal and S-side RF signal). The optical IQ detector 13 outputs the generated beat signals to the signal processor 14. The signal processor 14 performs the above-mentioned processing using the two beat signals, thereby calculating the wind velocity field for each distance in the vertical direction and the scanning direction.

[0068] Next, referring to Figure 3, we will explain how the propagation direction of the transmitted light into the atmosphere changes as the transmitted light irradiated from the laser radar device 100 is scanned on the vertical side and the scanning side using the above-mentioned operation example.

[0069] <Vertical Side> On the vertical side, as described above, the polarizing optical element 9 generates a predetermined deflection angle in the transmitted light, resulting in a scan tilted by that deflection angle from the zenith direction, i.e., a conical scan. On the vertical side, when the scanning unit 17 rotates once from 0 degrees to 360 degrees, the wind velocity field in a predetermined circular area is calculated. Therefore, on the vertical side, the angular difference in the irradiation direction of the transmitted light is maximized between transmitted light deflected in opposite directions, such as south and north, or west and east.

[0070] In this way, the laser radar device 100 can calculate the three-dimensional wind field in the shaded area in Figure 3 from data (hereinafter simply referred to as "wind speed value data") indicating wind speed values ​​(absolute values ​​of the wind speed field) in the line of sight direction for one rotation scanned on the vertical side. This calculation process is performed using an existing method. For example, vector calculation and the VAD (Velocity Azimuth Display) method can be used.

[0071] Note that in Figure 3, the three-dimensional wind field calculated for only one altitude is shown with diagonal lines, but it is possible to obtain a wind field for each altitude. For example, in the first embodiment, the transmitted light is pulsed, which is a TOF method and allows distance resolution. On the other hand, distance resolution is also possible even if the transmitted light is continuous wave (CW) light. In this case, the beam divergence angle formed by the transmitting optical system 5 is changed and the focusing position is scanned, thereby measuring wind at the focusing position. In this case, pulsing in the modulation unit 3 is not necessary in the laser radar device 100, and the focusing position can be made variable.

[0072] <Scanning side> On the scanning side, the transmitted light is bent in a direction perpendicular to the zenith (vertical) direction, and is irradiated horizontally onto the ground surface. Scanning on the scanning side completes one revolution when the scanning unit 17 rotates from 0 degrees to 360 degrees. In other words, this is a PPI (Plan-position indicator) scan.

[0073] On the scanning side, measurements are taken at a single altitude of approximately 0 m, but measurements can be taken at multiple locations at different horizontal distances from the laser radar device 100, making it possible to determine wind fields at multiple locations even at a single altitude. For example, as shown in Figure 4, the wind field in a certain area can be calculated by using wind speed values ​​in different line-of-sight directions from wind speed value data in line-of-sight directions from 0 degrees to 360 degrees calculated by PPI scanning. This can be done using any existing method, such as vector calculation or the VAD method.

[0074] Next, the state of the wind velocity field on the vertical side and the scan side calculated by the vector calculation and the VAD method will be described with reference to FIG.

[0075] The wind field is indicated by the thick arrows in Figure 5. Also, Figure 5 shows how wind fields at multiple heights can be obtained at one point on the vertical side, and at multiple points at one height on the scanning side.

[0076] Here, these wind velocity fields are defined as variables. For example, the horizontal wind velocity field acquired on the vertical side is defined as U Ｖ (U ＶＸ ,U ＶＹ ; x = 0, y = 0, z ｉ ) where z ｉ represents the altitude, and the subscript i is used to distinguish the altitude. Ｖ is the horizontal wind speed vector, and its x- and y-components are U ＶＸ , U ＶＹ It is defined as:

[0077] On the vertical side, if the position where the laser radar device 100 is installed is defined as x=0, y=0, data indicating the wind velocity field (hereinafter also simply referred to as "wind velocity field data") is not available at other x, y positions, but wind velocity field data for multiple altitudes is available in the altitude direction. Therefore, the wind velocity field data in the altitude direction at x=0, y=0 on the vertical side is z ｉ is a function of

[0078] On the other hand, the horizontal wind velocity field acquired on the scanning side is called U Ｓ (U ＳＸ ,U ＳＹ;x,y,z ０ On the scanning side, the altitude of the location where the laser radar device 100 is installed is defined as z ０ If we define it as such, there is no wind field data at other altitudes, but at altitude z ０ has wind field data from multiple points. Therefore, the height z ０ The wind field data at multiple points in the figure is a function of x and y.

[0079] Next, the signal processing unit 14 of the laser radar device 100 calculates the wind velocity field U Ｖ and U Ｓ An example of calculating the wind velocity field at multiple points and multiple heights approximately using the above formula will be described below. Ｖ is also called "wind field at multiple heights at one point", and the above wind field U Ｓ is also called "wind field at one altitude at multiple locations."

[0080] The signal processing unit 14 calculates wind speed fields at multiple locations and multiple altitudes from the wind speed field data at one location and multiple altitudes acquired on the vertical side and the wind speed field data at multiple locations and one altitude acquired on the scanning side, for example, by the following steps (1) to (3).

[0081] (1) The signal processing unit 14 detects the altitude z ０ For example, the signal processing unit 14 defines a circle with a radius R centered at x = 0, y = 0 from the wind field data obtained on the scanning side, and averages the wind field data in this range. Then, the signal processing unit 14 calculates the averaged data at an altitude z ０ The above process is expressed by the following equation (4), for example.

[0082] (2) Next, the signal processing unit 14 calculates the altitude z from the vertical wind field data. ０ The wind speed field ratio R based on the wind speed field data ｉ The above process is expressed by the following equation (5), for example.

[0083] (3) Next, the signal processing unit 14 calculates the ratio R ｉ Using the following equation (6), the wind speed field U Ｃ Calculate.

[0084] In the above calculation, the signal processing unit 14 calculates the change in the wind velocity field in the height direction at one point of x=0, y=0 by calculating the change in the wind velocity field in the height direction at the height z ０ The ratio of the wind speed field data at each altitude to the wind speed field data at ｉ Calculate the ratio R ｉ is maintained at different points (any x, y), this ratio R ｉ By multiplying the wind field data at each height by ｉ The wind field U Ｃ The situation is shown in Figure 6.

[0085] In the above example, the signal processing unit 14 can perform calculations on the absolute value of the wind velocity field, i.e., the wind velocity value, but it can also perform calculations on the wind direction. That is, the signal processing unit 14 calculates the wind direction change in the altitude direction at a point x = 0, y = 0 by calculating the wind direction change in the altitude z ０ Then, when calculating the wind speed field at height i, the wind speed field U is calculated by the amount of the wind speed field change. Ｓ (U ＳＸ ,U ＳＹ ;x,y,z ０ ) can be rotated.

[0086] Therefore, the signal processing unit 14 calculates the wind speed and wind direction at an altitude z ０ It is assumed that the change in the altitude direction with respect to the value at x = 0, y = 0 also holds true for values ​​other than x = 0, y = 0. Then, based on this assumption, the signal processing unit 14 calculates the altitude z ０This corresponds to determining wind speed and direction at multiple altitudes and multiple locations by applying the above-mentioned change tendency to the scanning data, which only holds data at x = 0, y = 0, but has data other than x = 0, y = 0. Note that "change tendency" here refers to a ratio or change angle, and "applying" refers to multiplication or addition.

[0087] Next, the effects of the laser radar device 100 according to the first embodiment will be described. The laser radar device 100 according to the first embodiment has the above-described configuration, and thus can calculate the wind velocity field in the hemispherical space above ground in the time required for the transmitted light to complete one scan in both the vertical direction and the scanning direction. This is equivalent to measuring the wind velocity field in the hemispherical space above ground in a shorter time than conventional methods. This also improves the real-time nature of the calculation of the wind velocity field in the hemispherical space above ground. Furthermore, the laser radar device 100 according to the first embodiment can achieve the above-described effects as a single device, rather than using multiple lidar devices.

[0088] Furthermore, the laser radar device 100 according to the first embodiment can be changed to function as only a vertical lidar or only a scanning lidar, for example, by appropriately adjusting the offset angle α applied to the λ / 2 wave plate that constitutes the polarization direction rotation unit 7.

[0089] For example, in the above example, the offset angle α applied to the λ / 2 wave plate is set to 22.5 degrees. This is intended to distribute the transmitted light (transmitted power) equally to both the vertical side and the scanning side. In other words, in the laser radar device 100 according to the first embodiment, by appropriately adjusting the value of the offset angle α, it is possible to constantly direct the transmitted light (transmitted power) only to the vertical side, or to constantly direct the transmitted light (transmitted power) only to the scanning side.

[0090] Therefore, by appropriately adjusting the offset angle α according to the user and operation method of the laser radar device 100, it is possible to select a mode for measuring the wind velocity field over the entire terrestrial hemisphere, which is the objective of the present disclosure, or a mode for observing only the vertical direction or a mode for observing only the scan direction. Furthermore, for example, when a mode for observing only the vertical direction is selected, all of the transmitted light (transmitted power) is guided vertically, which increases the SNR and extends the observable distance, making it possible to maintain the performance of conventional vertical-type lidars.

[0091] In other words, as a single lidar device, the laser radar device 100 according to embodiment 1 can exhibit the performance obtained with a conventional vertical-type lidar, and can also exhibit the performance obtained with a scanning-type lidar, and can also measure the wind velocity field over the entire terrestrial hemisphere in a shorter time than conventional methods, which is the objective of this disclosure.

[0092] Another effect of the laser radar device 100 according to embodiment 1 is that the real-time performance of the calculation of the wind velocity field in the terrestrial hemisphere can be improved, allowing the functions of the laser radar device 100 to be utilized for navigation assistance and optimal route setting for airborne mobile platforms such as aircraft and drones.

[0093] For example, when setting an optimal route for an airborne mobile platform, multiple routes may be candidates for the route from the start point to the end point. In this case, by taking into account the wind field obtained by the laser radar device 100, a route that minimizes the required power and required time is extracted and presented, thereby enabling effective route selection support. In addition, route selection support requires real-time performance, but this problem is also solved by the laser radar device 100 according to the first embodiment.

[0094] As described above, according to the first embodiment, the laser radar device 100 includes the polarization direction rotation unit 7 that rotates the polarization direction of the input laser beam by a predetermined angle, the polarizing beam splitter 8 that splits the laser beam, whose polarization direction has been rotated by the polarization direction rotation unit 7, into a first direction and a second direction different from the first direction, the rotation control unit 15 that rotates the polarization direction rotation unit 7 and the polarizing beam splitter 8 at different rotational angular velocities to realize a circular scan with the laser beam split in the first direction and a conical scan with the laser beam split in the second direction, and the signal processing unit 14 that calculates a wind field using light reflected by an object irradiated with the laser beam during each scan. As a result, the laser radar device 100 according to the first embodiment can measure a wind field in a hemispherical space above the ground in a shorter time than conventional methods.

[0095] The first direction is the horizontal direction, and the second direction is the vertical direction. This enables the laser radar device 100 according to the first embodiment to measure the wind velocity field in the hemispherical space above the ground in a shorter time than conventional methods.

[0096] Furthermore, a polarizing optical element 9 is provided after the polarizing beam splitter 8 in the vertical direction, and the polarizing optical element 9 deflects the laser light split in the vertical direction by the polarizing beam splitter 8 by a predetermined angle, thereby achieving conical scanning with the laser light split in the vertical direction. In this way, the laser radar device 100 according to the first embodiment can achieve conical scanning with the laser light split in the vertical direction.

[0097] The polarization direction rotation unit 7 is configured with a λ / 2 wave plate, and the rotation control unit 15 rotates the λ / 2 wave plate and the polarizing beam splitter 8 at different rotational angular velocities while maintaining a state in which the vector corresponding to the optical axis of the λ / 2 wave plate and the vector obtained by projecting the normal vector of the reflecting surface of the polarizing beam splitter 8 onto the λ / 2 wave plate are not parallel to each other. As a result, the laser radar device 100 according to the first embodiment rotates the first direction by a rotation angle θ of the scanning unit including the polarizing beam splitter 8. Ｓ (t).

[0098] The polarization direction rotation unit 7 is configured with a λ / 2 wave plate, and the rotation control unit 15 rotates the λ / 2 wave plate and the polarizing beam splitter 8 at different rotational angular velocities with an offset angle with respect to the optical axis of the polarizing beam splitter 8 being given to the rotation angle of the λ / 2 wave plate. As a result, the laser radar device 100 according to the first embodiment rotates the first direction at a rotation angle θ of the scanning unit including the polarizing beam splitter 8. Ｓ (t).

[0099] The magnitude of the offset angle can be set arbitrarily, which makes it possible for the laser radar device 100 according to the first embodiment to always guide the transmitted light only in the first direction, or to always guide the transmitted light only in the second direction.

[0100] The laser radar device 100 also includes a light source 1 that outputs laser light having a wavelength band that can be reflected by an irradiated target and that has linear polarization characteristics; a branching unit 2 that branches the laser light output from the light source 1; a modulator 3 that pulse-modulates one of the laser lights branched by the branching unit 2; an amplifier 4 that amplifies the power of the laser light pulse-modulated by the modulator 3; a transmitting optical system 5 that shapes the laser light amplified by the amplifier 4; a transmission / reception separator 6 that separates the laser light shaped by the transmitting optical system 5 from light reflected by the irradiated target; a receiving optical system 11 that receives the reflected light separated by the transmission / reception separator 6; and a detector 13 that obtains a predetermined interference signal by combining the reflected light received by the receiving optical system 11 with the other laser light branched by the branching unit 2. The polarization direction rotation unit 7 rotates the polarization direction of the laser light separated by the transmission / reception separator 6 by a predetermined angle, and a signal processing unit 14 calculates a wind field based on the interference signal obtained by the detector 13. As a result, the laser radar device 100 according to the first embodiment can measure the wind velocity field in the hemispherical space above the ground in a shorter time than conventional methods.

[0101] Furthermore, the optical axis of the receiving-side optical system 11 is arranged at an angle of 45 degrees with respect to the optical axis of the transmitting-side optical system 5. This makes it possible for the laser radar device 100 according to the first embodiment to fix the optical axis of the receiving-side optical system 11 so that the received light received from the second direction (vertical direction) always propagates along the fast axis of the receiving-side optical system 11, and the received light received from the first direction (horizontal direction) always propagates along the slow axis of the receiving-side optical system 11.

[0102] The first direction is the horizontal direction, and the second direction is the vertical direction, and the signal processing unit 14 generates data indicating the wind speed fields at multiple points at multiple altitudes based on data indicating the wind speed field at multiple points at one altitude obtained by calculating the wind speed field in the horizontal direction and data indicating the wind speed field at one point at multiple altitudes obtained by calculating the wind speed field in the vertical direction, and calculates the wind speed fields at the multiple points at multiple altitudes from the generated data. This makes it possible for the laser radar device 100 according to the first embodiment to measure the wind speed field in a hemispheric space above the ground in a shorter time than conventional methods.

[0103] The signal processing unit 14 also generates data representing the wind velocity field at a point at an altitude of 0 in the vertical direction, calculates a ratio of data representing the wind velocity field at one point at multiple altitudes based on the generated data, and multiplies the calculated ratio by the data representing the wind velocity field at multiple points at one altitude obtained by calculating the wind velocity field in the horizontal direction. This enables the laser radar device 100 according to the first embodiment to measure the wind velocity field in the terrestrial hemisphere in a shorter time than conventional methods.

[0104] Embodiment 2. In the first embodiment, a laser radar device 100 capable of measuring a wind velocity field in a hemispherical space above the ground in a shorter time than conventional devices was described. In the second embodiment, a laser radar device 100b is described which has fewer components than the first embodiment and is capable of varying the elevation angle (EL) when scanning the transmitted light on the scanning side.

[0105] Fig. 7 is a diagram showing an example of the configuration of a scanning unit 17b in a laser radar device 100b according to embodiment 2. The laser radar device 100b according to embodiment 2 differs from the laser radar device 100 according to embodiment 1 shown in Fig. 1 in that the scanning unit 17 is replaced with a scanning unit 17b. The other configuration of the laser radar device 100b according to embodiment 2 is the same as that of the laser radar device 100 according to embodiment 1 shown in Fig. 1, so the same reference numerals are used and their description will be omitted.

[0106] Scanning unit 17b is composed of polarized output polarizing beam splitter rotator 18, polarized output polarizing beam splitter 19, window 10, and window 16. That is, in scanning unit 17b, polarized beam splitter 8 that constitutes scanning unit 17 in embodiment 1 is replaced with polarized output polarizing beam splitter 19. This also makes scanning unit 17b unnecessary to have polarizing optical element 9 that constitutes scanning unit 17 in embodiment 1. Note that scanning unit 17b is rotated by rotation control unit 15b, similar to scanning unit 17 in embodiment 1.

[0107] The polarized output polarized beam splitter 19 is optically connected to the polarization direction rotation unit 7 and the windows 10 and 16. The polarized output polarized beam splitter 19 has an inclined surface on the side of the P-polarized component, i.e., the side of the transmitted light that is guided vertically. For example, a cube-type polarized beam splitter has a cubic shape and the opposing surfaces are horizontal, but the polarized output polarized beam splitter 19 has one of its opposing surfaces inclined at a predetermined angle rather than horizontal, taking into account the incident surface of the transmitted light from the polarization direction rotation unit 7.

[0108] With this configuration, a deflection angle occurs in the light emitted from the polarized output polarized beam splitter 19, i.e., the transmitted light guided to the vertical side, depending on the refractive index of the polarized output polarized beam splitter 19. This makes the polarizing optical element 9 used in the first embodiment unnecessary in the scanning unit 17b.

[0109] The polarized output polarized beam splitter 19 does not have an inclination on the surface on the side of the S-polarized component, i.e., the transmitted light guided to the scanning side, so the transmitted light guided to the scanning side is irradiated in the same manner as in the first embodiment.

[0110] The polarized output polarized beam splitter rotator 18 is composed of, for example, a rotation stage. The polarized output polarized beam splitter rotator 18 rotates and fixes the polarized output polarized beam splitter 19. The polarized output polarized beam splitter rotator 18 is electrically connected to the signal processing unit 14 and rotates under the control of the signal processing unit 14.

[0111] Next, we will explain an example of operation and effects of the laser radar device 100b according to embodiment 2. Note that the example of operation of the laser radar device 100b according to embodiment 2 differs from the example of operation of the laser radar device 100 according to embodiment 1 only in the example of operation of the scanning unit 17b, and therefore, the example of operation of the scanning unit 17b will be explained here.

[0112] For example, in the first embodiment, the polarized beam splitter 8 constituting the scanning unit 17 polarizes the P-polarized component, i.e., the transmitted light guided to the vertical side, in a direction approximately 90 degrees different from the scanning direction. Therefore, for example, if the transmitted light output from the polarization direction rotation unit 7 is directed toward the zenith (90 degrees relative to the ground), the transmitted light on the scanning side is irradiated horizontally to the ground, and the transmitted light on the vertical side is irradiated toward the zenith. Furthermore, in the first embodiment, a polarizing optical element 9 is provided after the polarized beam splitter 8 on the vertical side, so that the transmitted light on the vertical side is tilted from the zenith direction. In the first embodiment, scanning this transmitted light results in a conical scan, and as described above, a wind velocity field can be obtained by, for example, VAD processing.

[0113] On the other hand, in the second embodiment, as described above, a polarized output polarized beam splitter 19 having an inclined surface on the side of the P-polarized component, i.e., the transmitted light guided to the vertical side, is provided in place of the polarized beam splitter 8. As a result, in the second embodiment, as in the first embodiment, a deflection angle can be imparted to the light emitted from the polarized output polarized beam splitter 19, i.e., the transmitted light guided to the vertical side. Furthermore, in this case, the polarizing optical element 9 used in the first embodiment is not necessary, and the number of parts is reduced compared to the first embodiment.

[0114] Furthermore, in the second embodiment, for example, by controlling the polarized output polarized beam splitter rotation unit 18 via the signal processing unit 14 in response to an instruction from the user, the polarized output polarized beam splitter 19 is rotated and fixed at a predetermined position, whereby the elevation angle of the transmitted light on the scanning side can be changed to a predetermined elevation angle.

[0115] For example, in the first embodiment, as described above, the transmitted light on the scanning side is horizontal to the ground, and therefore PPI scanning is performed on the scanning side with an elevation angle of 0 degrees. However, if it is desired to scan while avoiding obstacles such as structures, it may be better to change the elevation angle. In this regard, in the second embodiment, as described above, the elevation angle of the transmitted light on the scanning side can be changed to a predetermined elevation angle by rotating the polarized output polarized beam splitter 19 using the polarized output polarized beam splitter rotator 18. This function is convenient when it is desired to scan while avoiding obstacles such as the structures on the scanning side.

[0116] As described above, according to the second embodiment, the laser radar device 100b includes, instead of the polarizing beam splitter 8, a polarized output polarized beam splitter 19 that splits the laser light, whose polarization direction has been rotated by the polarization direction rotation unit 7, into a first direction and a second direction and that can impart a predetermined angle of deflection to the laser light split in the second direction, and the rotation control unit 15 rotates the polarization direction rotation unit 7 and the polarized output polarized beam splitter 19 at different rotational angular velocities. As a result, the laser radar device 100b according to the second embodiment has the same effects as the first embodiment and, in addition, has a smaller number of parts than the first embodiment.

[0117] The first direction is the horizontal direction, and the second direction is the vertical direction, and a rotation unit 18 is provided to rotatably fix the polarized output polarized beam splitter 19 so that the elevation angle when scanning in the horizontal direction can be changed. This allows the laser radar device 100b according to the second embodiment to change the elevation angle of the transmitted light in the horizontal direction to a predetermined elevation angle.

[0118] It should be noted that the present disclosure allows for free combination of the embodiments, modification of any of the components of the embodiments, or omission of any of the components of the embodiments.

[0119] The present disclosure makes it possible to measure the wind velocity field in the terrestrial hemisphere in a shorter time than conventional methods, and is suitable for use in laser radar devices.

[0120] REFERENCE SIGNS LIST 1 light source, 2 branching unit, 3 modulation unit, 4 amplification unit, 5 transmission side optical system, 6 transmission / reception separation unit, 7 polarization direction rotation unit, 8 polarized beam splitter, 9 polarization optical element, 10 window, 11 reception side optical system, 12 reception side polarized beam splitter, 13 optical IQ detector (detector), 14 signal processing unit, 15 rotation control unit, 15a rotation control unit, 15b rotation control unit, 16 window, 17 scanning unit, 17b scanning unit, 18 polarized output polarized beam splitter rotation unit (rotation unit), 19 polarized output polarized beam splitter, 100 laser radar device, 100b laser radar device, U Ｃ Wind speed field, U Ｓ Wind speed field, U Ｖ Wind speed field, θ ２ Rotation angle of the λ / 2 wave plate, θ Ｓ Rotation angle of the scanning unit.

Claims

1. A laser radar device comprising: a polarization direction rotation unit which rotates the polarization direction of input laser light by a predetermined angle; a polarizing beam splitter which splits the laser light whose polarization direction has been rotated by the polarization direction rotation unit into a first direction and a second direction different from the first direction; a rotation control unit which realizes a circular scan by the laser light branched in the first direction and a conical scan by the laser light branched in the second direction by rotating the polarization direction rotation unit and the polarizing beam splitter at different rotational angular velocities; and a signal processing unit which calculates a wind field using light reflected by an object to be irradiated with the laser light in each of the scans.

2. A laser radar device according to claim 1, wherein said first direction is a horizontal direction and said second direction is a vertical direction.

3. The laser radar device according to claim 2, further comprising a polarizing optical element disposed downstream of the polarizing beam splitter in the vertical direction, and wherein the polarizing optical element gives a predetermined angle of deflection to the laser light split in the vertical direction by the polarizing beam splitter, thereby realizing a conical scan by the laser light split in the vertical direction.

4. A laser radar device as claimed in any one of claims 1 to 3, characterized in that the polarization direction rotation unit is composed of a λ / 2 wavelength plate, and the rotation control unit rotates the λ / 2 wavelength plate and the polarizing beam splitter at different rotational angular velocities while maintaining a state in which a vector corresponding to the optical axis of the λ / 2 wavelength plate and a vector obtained by projecting the normal vector of the reflecting surface of the polarizing beam splitter onto the λ / 2 wavelength plate are not parallel to each other.

5. A laser radar device as claimed in any one of claims 1 to 3, characterized in that the polarization direction rotation unit is composed of a λ / 2 wavelength plate, and the rotation control unit rotates the λ / 2 wavelength plate and the polarizing beam splitter at different rotational angular velocities with an offset angle being imparted to the rotation angle of the λ / 2 wavelength plate with respect to the optical axis of the polarizing beam splitter.

6. A laser radar device according to claim 5, wherein the magnitude of said offset angle can be set arbitrarily.

7. A laser radar device as claimed in claim 1, comprising: a light source which outputs laser light having a wavelength band which can be reflected by an object to be irradiated with the laser light and which has linear polarization characteristics; a branching unit which branches the laser light output from said light source; a modulation unit which pulse-modulates one of the laser lights branched by the branching unit; an amplification unit which amplifies the power of the laser light pulse-modulated by the modulation unit; a transmitting optical system which shapes the laser light amplified by the amplification unit; a transmission / reception separation unit which separates the laser light shaped by the transmitting optical system from light reflected by the object to be irradiated with the laser light; a receiving optical system which receives the reflected light separated by the transmission / reception separation unit; and a detector which obtains a predetermined interference signal by combining the reflected light received by the receiving optical system with the other laser light branched by the branching unit, wherein the polarization direction rotation unit rotates the polarization direction of the laser light separated by the transmission / reception separation unit by a predetermined angle, and the signal processing unit calculates a wind field based on the interference signal obtained by the detector.

8. A laser radar device according to claim 7, wherein the optical axis of said receiving optical system is arranged at an angle of 45 degrees to the optical axis of said transmitting optical system.

9. The laser radar device of claim 1, wherein the first direction is a horizontal direction, the second direction is a vertical direction, and the signal processing unit generates data indicative of wind speed fields at multiple points at multiple altitudes based on data indicative of the wind speed field at multiple points at multiple altitudes obtained by calculating the wind speed field in the horizontal direction and data indicative of the wind speed field at one point at multiple altitudes obtained by calculating the wind speed field in the vertical direction, and calculates the wind speed fields at multiple points at multiple altitudes from the generated data.

10. The laser radar device according to claim 9, characterized in that the signal processing unit virtually generates data indicating the wind speed field at a point at an altitude of 0 in the vertical direction, calculates a ratio of the data indicating the wind speed field at one point at multiple altitudes based on the generated data, and generates data indicating the wind speed field at multiple points at multiple altitudes by multiplying the calculated ratio by the data indicating the wind speed field at multiple points at one altitude obtained by calculating the wind speed field in the horizontal direction.

11. A laser radar device as described in claim 1, further comprising, instead of the polarizing beam splitter, a polarized output polarizing beam splitter that can split the laser light, whose polarization direction has been rotated by the polarization direction rotation unit, into the first direction and the second direction and give a predetermined angle of deflection to the laser light split into the second direction, and wherein the rotation control unit rotates the polarization direction rotation unit and the polarized output polarizing beam splitter at rotational angular velocities different from each other.

12. A laser radar device as described in claim 11, characterized in that the first direction is a horizontal direction, the second direction is a vertical direction, and a rotating unit is provided for rotatably fixing the polarized output polarized beam splitter so that the elevation angle when scanning with respect to the horizontal direction can be changed.

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