Continuous wave wind measurement radar with layered measurement function

Abstract

The invention discloses a continuous wave laser radar device for multilayer resolution wind measurement and a method thereof. Wind field information of different distances or height layers is distinguished through a variable-focus optical system driven by a micromotor. The device comprises a laser emitting unit, an optical zoom system, a receiving and detecting unit and a signal processing and control unit. The laser emission unit generates continuous wave laser; the variable-focus system is composed of a fixed lens and a movable lens, and a micromotor drives the lenses to move to change the focusing position. The receiving unit adopts a coaxial light path and converts echo signals into electric signals; the signal processing unit analyzes Doppler frequency shift to obtain wind speed and wind direction; the control unit automatically switches the layering distance according to the'lens position-detection distance 'mapping. During measurement, the device completes laser focusing and signal acquisition layer by layer, and can realize multidirectional detection in cooperation with a scanning mechanism. The device is compact in structure, low in cost, high in layering precision, high in automation, suitable for wind power site selection and capable of meeting the efficient detection requirement of a multilayer wind field.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and more specifically to an apparatus and method for dynamically focusing a laser beam by a micro-motor-driven variable-focus mechanism to achieve hierarchical measurement of the atmospheric wind field for different distance layers in the same continuous-wave lidar wind measurement system. Background Art

[0002] A lidar wind radar uses the scattering effect of a laser beam with tiny particles (aerosols or molecules) in the atmosphere and combines the Doppler frequency shift principle to measure atmospheric parameters such as wind speed, wind direction, and turbulence. According to different working modes, it can be divided into: pulsed lidar wind radar and continuous-wave lidar wind radar.

[0003] The pulsed lidar wind radar measures through the flight time of pulsed light and the Doppler frequency shift. Its advantage is high range resolution, but pulsed lasers usually have high cost and large volume; the continuous-wave lidar wind radar uses a stable continuous-wave laser for measurement, with a relatively simple structure and lower cost, but echo signals from different distances are prone to aliasing, and additional stratification or range resolution means are required.

[0004] In the fields of wind energy assessment, meteorological monitoring, aviation safety, urban environment, and scientific research, it is often necessary to obtain wind speed and wind direction information at multiple heights and multiple distance segments. If a continuous-wave lidar cannot distinguish echo signals from different distances, it is difficult to form accurate stratified wind field data. Therefore, to achieve multi-layer wind field measurement, existing technologies usually adopt: multi-channel multi-laser schemes, modulation or beat frequency identification schemes, and variable-focus optical schemes.

[0005] The multi-channel multi-laser scheme configures multiple laser emission units and transceiver subsystems for independent measurement at different heights or distance segments, but the equipment volume, cost, and maintenance cost are all relatively high; the modulation or beat frequency identification scheme performs complex modulation on the laser and uses frequency or phase differences at the signal processing end to distinguish different distance intervals. This method requires high hardware and algorithm requirements for the system; the variable-focus optical scheme adjusts the optimal focus of the laser at different distance layers mechanically, enhancing and highlighting the echo signal of that distance layer. This method has a simple mechanism and good scalability, and is very suitable for the stratified measurement requirements of small and medium-sized continuous-wave lidars.

[0006] Existing variable-focus continuous-wave lidar wind radars often have problems such as large volume, insufficient focal length adjustment accuracy, unstable repeat positioning, and low automation. To meet the refined wind measurement requirements in multiple fields, a micro-motor-driven zoom mechanism with high precision, small size, and high automation is needed to achieve fast and reliable stratified detection in continuous-wave radars. Summary of the Invention

[0007] The main objective of the present invention is to provide a continuous wave laser wind lidar device and working method for hierarchical detection by a variable-focus optical system driven by a micro-motor. On the premise of keeping the overall volume of the device compact and the cost controllable, the focusing accuracy and the accuracy of hierarchical measurement are improved, and automatic hierarchical switching and signal processing are supported.

[0008] The present invention achieves the above object through the following structure and method:

[0009] Laser emission unit: A continuous wave laser with a wavelength in the range of 1 μm to 1.6 μm (such as a 1.55 μm fiber laser, a 1.064 μm semiconductor laser, etc.) is used to output a stable narrow linewidth laser. Combining collimation optical design, a laser beam with high quality and moderate divergence angle is obtained.

[0010] Micro-motor driven variable-focus optical system: The core lies in one or more movable lens groups, and the position of the lens in the optical axis direction or the spacing within the group is changed by driving the transmission mechanism (ball screw / gear set / linear module) with a micro-motor.

[0011] Receiving and detecting unit: A coaxial or quasi-coaxial light emitting and receiving optical path is adopted, and the backscattered light is extracted from the main optical path through a beam splitter (or polarization beam splitter) and focused on a photodetector (APD, photomultiplier tube or coherent detector).

[0012] Signal processing and control system: Digital signal processing (DSP / FPGA / high-speed ADC) extracts the Doppler frequency component to obtain the wind speed (and wind direction); the controller (MCU / embedded system) manages the operation of the micro-motor and switches between multiple layers according to the pre-calibrated "focal length - distance" relationship. At the same time, it has functions of data storage, communication interface, fault diagnosis and safety protection.

[0013] Automatic hierarchical measurement: By precisely positioning the lens group through closed-loop control of the micro-motor, fast and stable multi-layer switching is realized.

[0014] Compact structure and easy integration: Only one continuous wave laser is required, combined with a variable-focus lens group, without multiple optical heads or high-power pulsed lasers.

[0015] High precision and high repeatability: Under strict mechanical and optical design, each focusing can maintain a small error, which is beneficial to long-term monitoring and data comparison.

[0016] Strong scalability: With the help of a scanning pan-tilt or a galvanometer mirror, hierarchical measurement over a larger azimuth range is realized to form a three-dimensional distribution of the wind field. Description of the Drawings

[0017] Figure 1 : Schematic diagram of the overall structure of the device of the present invention.

[0018] Figure 2 : Schematic diagram of the structure of a zoom optical system and the drive of a micro-motor.

[0019] Figure 3 : System control flowchart of the present invention.

[0020] Figure 4 : Schematic diagram of the "focal length - distance" calibration relationship and the division of hierarchical intervals.

[0021] Figure 5 : Schematic diagram of an optional scanning and rotating mechanism (dual-axis pan-tilt head). Specific embodiments

[0022] The following further elaborates on the preferred embodiments of the present invention in conjunction with the accompanying drawings, including aspects such as the hardware structure, optical design, mechanical structure, electrical control, software process, calibration, and experimental testing.

[0023] Embodiment 1: Overall hardware architecture.

[0024] Laser emission unit: In this embodiment, an erbium-doped fiber laser with a wavelength of 1550 nm is used, and the output power is set to about 200 mW; the linewidth is less than 100 kHz; in order to improve the system reliability and eye safety, the laser in the 1.55 μm band has a moderate atmospheric transmission loss and relatively lower harm to the human eye.

[0025] Power supply and temperature control: A precision regulated power supply is equipped, and the voltage fluctuation is controlled within ±1%; the temperature control module (TEC cooler and temperature sensor) stabilizes the working temperature of the laser within the range of ±0.1 °C to ensure the long-term stability of the wavelength and power output.

[0026] Beam collimation: A collimating mirror is connected to the exit fiber end to obtain an approximately parallel output beam; the beam diameter is about 5 - 10 mm, and the divergence angle is less than 1 mrad (can be finely adjusted according to the specific design).

[0027] Optical zoom system: In this embodiment, two groups of lenses are selected: the first group (201) is a fixed lens group, which is used for preliminary collimation, correction of chromatic aberration or spherical aberration; the second group (202) is a movable lens group, and the core is to finely adjust the focal length so as to achieve the optimal energy focusing at different distances. The material of each lens can be selected from fused silica or optical glass (such as BK7), which has a high transmittance and good performance in the 1550 nm region.

[0028] Micro-motor drive structure: A stepper motor (with micro-stepping) is used in conjunction with a ball screw assembly. The screw pitch is approximately 0.5 - 1 mm per revolution; the stepper motor has a step angle of 1.8°. If 16x micro-stepping drive is configured, the minimum step angle can reach 0.1125°, and the corresponding axial movement of the screw can be less than 1 micron per step. A linear guide and an anti-vibration structure are provided on the lens group slide rail to ensure smooth movement.

[0029] Position detection and closed-loop control: An optoelectronic encoder is coupled to the rear end of the motor, with a resolution of up to 10,000 - 20,000 pulses per revolution; the controller reads the encoder pulse count in real time, compares the target position with the actual position, and automatically adjusts the stepper motor pulse output; when the focal length reaches the target position and stabilizes, a "ready" signal is issued.

[0030] Focal length - distance mapping: During device production or maintenance, calibration is required (see "Calibration and Testing" later), to map each lens group position to the distance range of optimal focus; typically, segmented focusing from 100 meters to 3 - 5 kilometers can be achieved, and it can also cover a farther or nearer range according to the lens aperture and system design.

[0031] The transceiver optical path adopts a coaxial design: At the output end, a part of the main beam - for example, using a beam splitter (50:50 or 90:10) to split the echo - is used to ensure a compact optical path of the system; or a polarization beam splitter (PBS) is used to separate the transmitted light and the echo light in terms of polarization (to be used in combination with coherent detection).

[0032] Detector: An InGaAs avalanche photodiode (APD) module is used, which has high sensitivity in the 1550 nm band; the APD gain can be adjusted by software and should match the expected echo intensity; if the echo power is very low, a preamplifier with low noise can be used.

[0033] Filtering and protection: A band-pass filter (center wavelength 1550 nm, bandwidth 1 - 2 nm) is installed in the detection optical path to suppress ambient stray light; mechanically, dust and splash-proof structures are added to adapt to outdoor environments.

[0034] Coherent or direct detection: If a coherent detection scheme is used, a local oscillator light needs to be separated separately, and the echo and the local oscillator are beat-interfered in front of the detector to improve the signal-to-noise ratio and measurement accuracy; if direct detection is adopted, the Doppler signal can also be obtained through modulation - demodulation algorithms, but higher requirements are placed on power and noise suppression.

[0035] Signal processing unit: The analog front end includes a low-noise transimpedance amplifier, a band-pass filter, etc., to filter out DC or extremely low-frequency drift and high-frequency noise; the amplification factor can be adjusted by software or hardware and is adaptively adjusted according to the echo intensity.

[0036] Analog-to-Digital Conversion and Digital Signal Processing: A high-speed ADC is adopted, and the sampling rate is determined according to the maximum expected Doppler frequency shift, generally reaching several hundred kHz to several MHz; DSP or FPGA is used to implement real-time FFT operations or phase-locked amplification algorithms to extract the peak position, amplitude, and width of the spectrum; the offset of the spectrum center is proportional to the wind speed, and the spectrum peak width can be used to characterize the turbulence intensity.

[0037] Data Fusion and Result Output: Multi-layer measurement data is stored indexed by distance and can be interpolated or fitted; information such as wind speed (V), wind direction, signal-to-noise ratio (SNR), and aerosol concentration is output to the host computer. Communication methods can be selected from RS232 / 485, Ethernet, Wi-Fi, etc.

[0038] Control Unit: The hardware consists of a main control MCU or an embedded processor, such as the ARM Cortex-A series or the FPGA+Microblaze architecture. It includes a motor drive module, a laser power supply module, a communication interface, and a storage unit, etc.

[0039] Software Workflow: Power-on self-check → Read configuration and calibration data → Enter the measurement loop; in the measurement loop, for each target distance layer: 1. Set the corresponding lens position → Motor movement → Position stabilization; 2. Laser emission and power stabilization; 3. Collect echo signals → DSP operation → Extract Doppler frequency shift and signal-to-noise ratio; 4. Store or transmit the results; if a scanning pan-tilt is enabled, repeat the above hierarchical measurement process at different azimuth angles.

[0040] Safety Protection and Fault Diagnosis: Protect and stop in case of abnormalities such as overcurrent, stall, and overtravel of the micro-motor; immediately turn off the laser and issue a warning in case of overheating and overcurrent of the laser; set a watchdog timer to prevent the program from crashing.

[0041] Optional Scanning and Rotating Mechanisms: Stepper motors or servo motors are used to control the horizontal (Yaw) and pitch (Pitch) angles respectively; the rotation range can reach 360° horizontally and -10° to +90° vertically, depending on the specific installation method. If faster scanning is required, a high-speed galvanometer can also be used to deflect within a small angle range; generally only used for local monitoring or relatively short-distance ranges.

[0042] Example 2: Calibration and Testing Methods.

[0043] Calibration Environment: In an outdoor open area, several reflective targets (such as high-reflectivity plates or special retroreflectors) can be set at known distances: such as 100 m, 200 m, 300 m, 500 m, 800 m, 1000 m, etc.; it is recommended to choose a time period with no obvious atmospheric turbulence and good visibility for testing to reduce the impact of atmospheric disturbances on the measurement.

[0044] Calibration steps: The control unit moves the lens group one by one, and the motor position that maximizes the echo signal intensity is recorded as the "optimal focusing position"; record the encoder reading at this position and establish a one-to-one mapping with the target distance; through interpolation or polynomial fitting, generate a continuous "motor step value - distance" curve.

[0045] Data recording: Conduct multiple measurements at the same distance point to evaluate the repeatability error; under normal atmospheric conditions, the repeat error should be less than 1 - 2% of the distance value, and if there is a systematic deviation, the optical alignment needs to be fine-tuned again.

[0046] Stratification interval setting: According to user needs, divide the detection distance range into several segments (such as 20 segments), and calculate the motor positions corresponding to the center distances of each segment; different intervals (ranging from dozens of meters to hundreds of meters) can be selected according to different requirements such as wind energy, meteorology, or industrial applications.

[0047] Doppler wind measurement performance test: Turntable method, aim the radar at a rotating target (such as a calibration turntable, rotating reflector), and the rotational speed corresponds to the Doppler frequency shift of the known linear velocity to verify the measurement accuracy; compare the actual linear velocity \(V_{\text{real}}\) of the turntable with the radar measurement result \(V_{\text{meas}}\), and if the error is within ±0.2 m / s, it is considered qualified (or the specific allowable range depends on the application).

[0048] Field comparison test, compare with a meteorological wind measurement tower or known wind speed instruments (such as cup anemometers, ultrasonic anemometers, etc.) with relatively high recognized accuracy; record the wind speed at the same height and in the same time period, and statistically analyze the error distribution (deviation, mean square error) to verify the reliability of the radar data.

[0049] Environmental adaptation test: Conduct a temperature cycle test (-20°C to +50°C) to examine the performance changes of the micromotor, lens, detector, etc. under extreme temperatures; if it is applied in a marine environment, salt spray and humidity tests need to be carried out to ensure the anti-corrosion of the lens and mechanical components.

[0050] Continuous operation reliability: Let the system run continuously for several days to several weeks in an unattended state, and observe the cumulative motor positioning error, laser power fluctuation, and detector dark current drift, etc.; if significant performance degradation occurs, timely maintenance or adjustment of the maintenance strategy is required.

[0051] Example 3: Application scenarios and measurement processes.

[0052] Fixed-point multi-layer measurement: Around a wind farm or a meteorological observation station, used for long-term monitoring of the wind field profile in a single azimuth.

[0053] Operation process: 1. Power on the system, initialize and load the focal length - distance table; 2. The user sets the measurement layer list, such as 100 m, 200 m, 300 m, 400 m, 500 m; 3. The control unit switches the focal length of the lens group in sequence and collects the echo Doppler spectrum; 4. The signal processing unit outputs the wind speed and wind direction parameters of each layer; 5. Periodically repeat the measurement, and the results can be stored or remotely transmitted.

[0054] Omnidirectional scanning multi - layer measurement (with pan - tilt head): Monitoring around airport runways, evaluating airflows around urban high - rise buildings, and researching the three - dimensional wind field of the boundary layer in scientific research, etc.

[0055] Operation process: 1. After initialization, the pan - tilt head returns to the zero point; 2. According to the horizontal angle range (such as 0° - 360°), pitch angle range (such as - 5° - +45°), and the layered distance list input by the user; 3. On each azimuth angle, the layered measurement process is executed in sequence; 4. Record and fuse the wind field data of all azimuths and all distance layers; 5. A three - dimensional vector wind field display can be generated through software interpolation or imaging algorithms.

[0056] Example 4: Specific function implementation and extension.

[0057] Fast layer switching: If a faster refresh rate is required in wind energy assessment, the acceleration - deceleration curve of the micro - motor and the data acquisition algorithm can be optimized; The actual measurement shows that: with a reasonable lead screw pitch and stepping motor speed, it only takes 0.5 - 1 second to switch the focal length of one layer, and about 1 second for measurement sampling, and the data acquisition of one layer can be completed within a few seconds.

[0058] Doppler frequency shift algorithm selection: FFT spectrum analysis: Suitable for Doppler peak detection in general cases; Coherent demodulation: Suitable for situations where the signal is weak and the noise is high, and higher sensitivity can be obtained; Adaptive filter: Can effectively suppress low - frequency noise and target drift.

[0059] Software interface and data management: Provide a visual interface to display the real - time Doppler spectrum, wind speed data curve, and layered wind direction indication; Support data export in formats such as CSV, MAT, HDF5, etc., which is convenient for scientific researchers to further analyze; Remotely update the firmware and parameters, and support remote monitoring and maintenance within the Internet or local area network.

[0060] Fault tolerance and self - repair: If the micro - motor loses steps, the controller will reset the lead screw to the zero - point limit and return to zero; When the laser power is too low or the detector gain is abnormal, the system can automatically switch to the backup gain scheme or reduce the number of measurement layers to ensure the basic measurement function.

[0061] Specific implementation effect: Conduct five-layer stratified measurements at 100 m, 200 m, 300 m, 400 m, and 500 m. Each time the focal length is switched, it takes about 1 s, and it takes about 1 s to collect and process Doppler data. Therefore, the single-layer wind speed result can be obtained within 2 s. After comparison with the reference ultrasonic anemometer, the wind speed measurement deviation is within ±0.3 m / s, and the correlation coefficient can reach more than 0.95. It runs continuously for 24 hours without failure, and the motor positioning repeat error is less than 0.02 mm. Compared with the previous solutions that require multiple lasers or multi-channel systems, the present invention only uses one continuous-wave laser and one zoom mechanism, greatly reducing the hardware cost and maintenance difficulty.

Claims

1. A continuous-wave laser wind lidar device with layer-by-layer measurement, characterized in that, Including: a laser emission unit for generating a continuous-wave laser beam; An optical zoom system disposed between the laser emission unit and the atmosphere to be measured, comprising a fixed lens group and at least one movable lens group. The movable lens group is driven by a micro-motor driving mechanism to move in the optical axis direction, so as to change the focusing characteristics of the laser beam at different distances; A receiving and detecting unit for receiving the scattered return light in the atmosphere to be measured and converting it into an electrical signal; a signal processing unit for performing Doppler frequency shift analysis on the electrical signal to obtain meteorological parameters such as wind speed and wind direction; a control unit connected to the optical zoom system and the signal processing unit, configured to automatically switch the micro-motor driving position according to the pre-calibrated "lens position - detection distance" relationship, so as to measure the wind speed at different distance layers and output the results.

2. The device according to claim 1, characterized in that, The micro-motor driving mechanism includes a stepping motor and a ball screw structure. The stepping motor realizes closed-loop control through an encoder with a resolution of not less than 10,000 pulses per revolution, thereby controlling the positioning error of the movable lens group within the micron range.

3. The device according to claim 1, characterized in that, The receiving and detecting unit adopts a coaxial optical path design, and uses a beam splitter to separate the emitted light and the return light. The detector is an InGaAs avalanche photodiode (APD) or a photomultiplier tube, and a narrowband filter is provided in the optical path to suppress ambient light interference.

4. The device according to claim 1 or 2, characterized in that, The signal processing unit includes a high-speed analog-to-digital converter and a digital signal processor, and extracts the Doppler shift frequency peak by means of fast Fourier transform or coherent beat frequency detection, and then calculates the wind speed information.

5. The device according to claim 1 or 2, characterized in that, The control unit pre-stores multiple sets of calibration data corresponding to lens positions and detection distances, and can sequentially drive the micro-motor to the corresponding positions after receiving multi-layer measurement instructions, and complete echo signal acquisition and spectrum analysis at each position, so as to realize multi-layer measurement.

6. The device according to claim 1 or 2, characterized in that It further includes a scanning and rotating mechanism for changing the laser beam emission angle in the horizontal and pitch directions to obtain multi-layer wind field information in a larger range; when the scanning angle is changed, the control unit automatically repeats the multi-layer measurement process.

7. The device according to claim 1 or 2, characterized in that, The micro-motor driving mechanism is equipped with limit switches and optoelectronic or magnetic encoders, which can perform zero calibration during power-on self-check, and automatically stop the motor movement and alarm when detecting abnormalities such as stall and overtravel.

8. The device according to claim 1 or 2, characterized in that, The laser emission unit adopts a 1.55 μm erbium-doped fiber laser or a 1.064 μm semiconductor laser, and the output power is adjustable within the range of 10 - 500 mW, and is equipped with a temperature control module to ensure the stability of the wavelength and power.

9. The device according to claim 1 or 2, characterized in that The control unit is equipped with a network or serial communication interface for outputting the measurement results to an external data platform, and can receive remote configuration instructions to change the multi-layer settings, scanning strategy or laser power parameters.

10. A continuous wave stratified wind measurement method based on the device as described in claim 1, characterized in that, Including the following steps:

1. Initialize the device and perform micro-motor zero calibration, and read the "lens position - detection distance" calibration table; 2. Set the multi-layer distance list according to the measurement requirements, and load the corresponding relationship between the focal length position and the multi-layer distance into the control unit; 3. The control unit drives the micro-motor to move the movable lens group to the focal length position of the first target distance, and the emission unit outputs a continuous-wave laser; 4. The receiving and detecting unit acquires the echo signal, and the signal processing unit performs Doppler spectrum analysis on it to obtain data such as the wind speed and wind direction of this distance layer; 5. The control unit sequentially switches to the focal length positions of the remaining distance layers and repeats step 4) to complete the wind speed measurement of all layers; 6. If a scanning and rotating mechanism is equipped, repeat the above layer measurement steps at different azimuth angles to obtain three-dimensional wind field data; 7. Store the final measurement results or output them to an external system to achieve continuous monitoring of the multi-layer wind field in the target area.

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