Manned and airborne dual-frequency phase multi-feature water measurement laser radar

Abstract

The invention discloses a manned and airborne dual-frequency phase multi-feature water measurement laser radar, emitted near-infrared laser measures a micron-level water surface distance by adopting continuous period laser echo phase distance measurement, and green laser measures distance by adopting a plurality of Gaussian echo feature signals. The water measurement laser radar is mainly composed of a stabilized platform, a scanning system, a bottom plate, a laser reflector, a 1064nm laser ranging module, a 532nm laser, an optical receiving system, a comprehensive control system, a detection system, a laser measurement and acquisition system, a high-precision POS system, a POS antenna and the like, and can realize water surface micron-level and water bottom centimeter-level high-precision detection.

Description

Technical Field

[0001] The invention relates to the technical field of laser detection, and in particular to a dual-frequency water-measuring laser radar. Background Art

[0002] At present, water depth measurement laser radars mostly use the TOF (Time-of-Flight) ranging principle to realize dual-frequency (1064nm and 532nm) laser radars to detect water depth. For example, the dual-frequency water depth measurement laser radar (patent number CN202011378792.8) adopts the TOF (Time-of-Flight) ranging principle to realize a satellite-borne laser near-coast terrain detection laser radar and detection method for near-coast water and land terrain detection. A method for measuring water depth and a laser radar system (patent number 201710286077.3) also use the TOF (Time-of-Flight) ranging principle to measure water depth. In 2016, Fu Chengqun published a paper entitled "Design of Airborne Dual-frequency Laser Radar Prototype and Water-Land Joint Testing" in the Journal of PLA University of Science and Technology (Natural Science Edition), which also uses the TOF (Time-of-Flight) ranging principle to measure water depth. In 2018, Hu Shanjiang published a paper titled "Design and Development of Airborne Dual-Frequency LiDAR System" in "Infrared and Laser Engineering", which also adopted the TOF (Time-of-Flight) ranging principle to measure water depth.

[0003] The above-mentioned dual-frequency water depth measurement laser radar system adopts the TOF (Time-of-Flight) ranging principle, which has the problems of unclear Gaussian echo signal characteristics, large error in extracting water depth data, and error easily increasing with depth. The present invention discloses a manned aircraft-borne dual-frequency phase multi-feature water measurement laser radar. The near-infrared laser emitted by the laser radar adopts continuous periodic laser echo phase for ranging, and the green laser adopts multiple sinusoidal wave signals for ranging. Both are emitted by a scanning mirror, and have the characteristics of obvious echo characteristics and small error in measuring water surface and bottom. Summary of the invention

[0004] The invention discloses a manned aircraft-borne dual-frequency phase multi-feature water-measuring laser radar, which has a total weight of less than 70 kg and is suitable for rapid and accurate detection of water surfaces and bottoms.

[0005] The present invention is implemented by the following technical solutions:

[0006] The principle of water surface measurement is that the continuous infrared laser emitted by the 1064nm laser ranging module is divided into two beams, one of which is collected by the system and the other is reflected by the water surface and collected by the system. The wave number of the laser collected by the system when the reflected laser is received is calculated, multiplied by the laser wavelength, and the phase is added to achieve micron-level water surface ranging. The specific calculation is shown in formula (1).

[0007] (1)

[0008] Where D s is the distance from the laser port of the 1064nm laser ranging module to the water surface, λ is the wavelength, which is 1064nm, N is the wave number obtained by dividing the distance from the laser port of the 1064nm laser ranging module to the water surface by the wavelength of 1064nm, and △φ is the phase of the transmitted wave and the received wave relative to a complete wave movement.

[0009] The principle of underwater measurement is that a 532nm laser emits a laser beam with a multi-Gaussian distribution in time, which passes through the water surface, reaches the bottom of the water, passes through the scanning system after reflection, and is received by the optical receiving system. Among them, the laser beam emitted by the 532nm laser and the received laser beam both have the characteristics of multi-Gaussian distribution in time. See formula (2) for details.

[0010] (2)

[0011] Where D ws is the distance of 532nm laser from the water surface to the bottom of the water, v is the transmission speed of laser in water, generally 0.11m / ns, △t is the time it takes for laser to travel from the water surface to the bottom of the water, t wsup is the rising edge time of the water surface laser echo, t wfup is the rising edge time of the underwater laser echo. Among them, the 532nm laser emits a laser beam with multi-Gaussian characteristics for a long time, and it will reflect a laser echo with multi-Gaussian characteristics when it encounters the water surface and the bottom. In this way, the waveform similarity and linear operation matching waveform can be used to calculate high-precision △t. The specific calculation is as follows:

[0012] Compare the emitted multi-Gaussian characteristic laser wave and the collected multi-Gaussian characteristic laser echoes on the water surface and bottom, and normalize them to the wave with the longest wavelength in the time domain. The details are as follows:

[0013] First, determine the length of the longest wavelength.

[0014] (3)

[0015] Where, L max is the length of the longest wavelength, L i (i is 1, 2, 3) are respectively the lengths of the emitted multi-Gaussian characteristic laser wave and the collected surface and bottom multi-Gaussian characteristic laser echoes, t down is the x-axis coordinate of the falling edge of the laser wave (including the echo), t up is the x-axis coordinate of the rising edge of the laser wave (including echo).

[0016] Second, laser waves (including echoes) whose length is shorter than the longest laser echo are resampled to laser waves (including echoes) whose length is equal to the longest laser echo.

[0017] The length of the waveform to be resampled is proportionally transformed into a waveform of the same length as the longest laser echo. Assume that the rising edge coordinates of the laser wave (including the echo) of the same length as the longest laser echo are the original coordinates, and the falling edge coordinates are L max , are all assigned 0, and other positions are resampled using formula (4).

[0018] (4)

[0019] Where, L i is the amplitude value of the resampled x-axis i coordinate, L i+1 is the amplitude value of the x-axis i+1 coordinate of the waveform to be resampled proportionally transformed, L i-1 is the amplitude value of the x-axis i-1 coordinate of the waveform to be resampled in equal proportion. Finally, the resampled waveform L is obtained.

[0020] Third, use formula (5) to calculate the similarity between the emitted multi-Gaussian characteristic laser wave and the collected water surface and bottom multi-Gaussian characteristic laser echoes to obtain the precise time when the laser reaches the water surface and the bottom.

[0021] (5)

[0022] In the formula, cosθ is the similarity index (the closer to 1, the more similar, generally greater than 0.6826 means similar), and Represent any two of the emitted multi-Gaussian characteristic laser waves and the collected surface and bottom multi-Gaussian characteristic laser echoes. If the cosθ value is greater than or equal to 0.6826, the rising edge time of the emitted laser, the surface laser echo, and the bottom laser echo is obtained.

[0023] The water measuring laser radar is mainly composed of a stable platform, a scanning system, a base plate, a laser reflector, a 1064nm laser ranging module, a 532nm laser, an optical receiving system, an integrated control system, a detection system, a laser measurement and acquisition system, a high-precision POS system, and a POS antenna.

[0024] Stable platform. This platform is made according to the principle of hydraulic balance. It can withstand a weight of 120kg and balance the pressure load. Its main function is to ensure that the laser radar mounted on it is relatively stable and can operate normally. It is square in shape with a circular hole in the middle, and a circular scanning system can be installed. The platform actively sends data to the integrated control system. In the case of unbalanced pressure, the integrated control system uses a load balancing algorithm to calculate the system load and send automatic load data to the stable platform to adjust the platform balance, thereby ensuring that the emitted laser trajectory is a perfect circle.

[0025] Scanning system. The scanning system consists of a hollow motor and two Fresnel mirrors. By rotating the hollow motor, the two Fresnel mirrors are driven to move relative to each other to achieve laser circular scanning. The hollow motor has an encoder that can automatically send the motor rotation angle data to the high-speed laser acquisition system. After receiving the signal from the integrated control system, the scanning system controls the hollow motor to rotate at the system set speed and sends the system status and rotation angle data to the integrated control system in real time.

[0026] The entire LiDAR is fixed on the bottom plate, which is a rectangular black plate made of magnesium-aluminum alloy wave-absorbing material. The hollow structure can reduce weight to the greatest extent. It is used to fix the 532nm laser, scanning system and other components of the LiDAR.

[0027] Laser reflector: The laser reflector is a laser-specific reflector made of silver-plated material with a reflectivity of 98% for 400nm-1200nm light. The mirror surface is 45° to the laser emission angle, which can ensure that the laser divergence angle remains unchanged and the laser echo does not move.

[0028] 1064nm laser ranging module. After receiving the signal from the integrated control system, the module emits a continuous period of 1064nm laser, which is divided into two beams by the laser beam splitter. One beam is measured by the ranging module, and the other beam is emitted to the reflector, passes through the scanning system, reaches the water surface, reflects back, and is received by the module. Finally, the ranging module measures the number of 1064nm laser waves transmitted by the laser in the air, multiplies it by the wavelength, obtains the distance between the laser radar and the water surface, and sends it to the integrated control system. Since the laser wavelength is 1064nm, the module can measure the distance with micron accuracy.

[0029] 532nm laser. After receiving the signal from the integrated control system, the laser emits a beam with multi-Gaussian distribution in time, peak power of 1000Kw, pulse width of 3±2ns, divergence angle less than 2mrad, M 2 Less than 1.2 small jitter (<500ps), 532nm laser with repetition rate of 5-300Khz. At the same time, the working status signal is transmitted to the integrated control system. It is characterized by adopting external triggering and multi-stage amplification technology to emit high repetition rate, picosecond jitter, divergence angle less than 2mrad, 532nm collimated green laser to realize underwater terrain detection.

[0030] Optical receiving system. The optical system uses a Cassegrain receiving structure consisting of a central opening primary mirror and a secondary mirror, a field-of-view mirror, and two convex lenses to form two shallow water and deep water channels, corresponding to two four-quadrant PMT detectors respectively.

[0031] Comprehensive control system. The comprehensive control system controls the work of the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc. At the same time, the comprehensive control system obtains the working status signals of the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc., and displays them on the screen in real time to ensure the normal and stable operation of the system. It is characterized by the use of ZYNQ to realize nanosecond delay sampling and sampling time length setting of the high-speed laser acquisition system.

[0032] Detection system. The detection system includes a medium water four-quadrant PMT detection module and a deep water four-quadrant PMT detection module. Since a single laser echo signal cannot accurately and effectively identify the multi-Gaussian characteristic laser echo, the optical receiving system is focused on two four-quadrant PMT detection modules, and four echo signals can be obtained in both medium water and deep water. The four signals are superimposed to extract the multi-Gaussian characteristic laser echo signal, see formula (8).

[0033] (6)

[0034] In the formula, WS is the echo signal, n is the number of laser echo signals acquired simultaneously (take 4), S j is the jth laser echo signal (j∈[1,4]).

[0035] Laser acquisition system. The laser acquisition system uses FPGA to achieve 532nm laser acquisition with a pulse width of 3±2ns, a frequency of 5-300Khz, an acquisition speed of 3GSPS, and a storage of 2T. It can automatically attenuate strong echo signals and amplify weak signals to within 5-10V, ensuring that effective signals are clear and recognizable. At the same time, it can send the surface and bottom distances and system status to the integrated control system in real time.

[0036] POS system. The POS system uses RTK positioning technology to obtain high-precision (millimeter-level) GPS position data; uses IMU to obtain high-precision attitude position data (the heading angle is [-90,90], the roll angle is [0,360] and the yaw angle is [-180,180] with an angle resolution of 0.01°) and transmits it to the integrated control unit. At the same time, the POS system can send POS data and system status data to the integrated control system in real time. Before use, the POS system must fly horizontally for 30 minutes in an 8-shaped manner to correct the accumulated errors of the three attitude angles of the IMU.

[0037] POS antenna. This antenna is a dual antenna, requiring a minimum installation distance of 2m to achieve millimeter-level GPS positioning. The antenna is connected to the POS system via a coaxial cable, and the initial position data is differentiated and then substituted into the RTK algorithm to obtain the current position fixed solution and obtain millimeter-level GPS positioning data.

[0038] The working process of the manned aircraft-borne dual-frequency phase multi-signature water measurement lidar is as follows:

[0039] (1) The user starts the manned dual-frequency phase multi-signature water-measuring laser radar mounted on the manned platform on the screen. The start signal is sent to each component of the laser radar through the integrated control system, and the start time data and the working status signal of each component are obtained. The laser radar self-test is completed and the self-test results of each component are displayed on the screen. Among them, the integrated control unit issues a start command to the stabilization platform, 532nm laser, scanning system, 1064nm laser ranging module, detection system, laser acquisition system, and POS system, and the working status of each component is displayed on the screen.

[0040] (2) The integrated control system reads the data sent by the stable platform, uses a load balancing algorithm to calculate the system load, sends automatic load data to the stable platform, and adjusts the platform balance.

[0041] (3) The integrated control system reads the position data, attitude data, and UTC time data sent by the POS system and transmits them to the high-speed laser sampling system (the high-speed laser sampling system stores the position data, attitude data, UTC time, and echo signal together) to obtain the high-precision working status of the POS system.

[0042] (3) The integrated control system sends a signal to the 1064nm laser ranging module, which emits a 1064nm continuous periodic infrared laser to measure the distance from the water surface to the module.

[0043] (4) The integrated control system sends an external trigger signal to the 532nm laser, which emits a 532nm multi-Gaussian echo characteristic laser, which is reflected to the scanning system through the reflector below the optical receiving system. At the same time, the laser sends the laser main wave signal to the high-speed laser acquisition system and sends the working status signal to the integrated control system.

[0044] (5) The integrated control system transmits control parameters to the optical scanning system to control the rotation of the hollow motor, thereby driving the two Fresnel mirrors in the middle to rotate, so that the laser trajectory is a perfect circle.

[0045] (6) The laser reflected from the water surface and the bottom of the water passes through the scanning system and is received by the receiving optical system. The laser echo signal is sent to the detection system (shallow water PMT detection module and deep water PMT detection module) through the shallow water channel and the deep water channel. At the same time, the working status signal is sent to the integrated control system.

[0046] (7) The detection system, integrated control system, 1064nm laser ranging module and 532nm laser send and receive shallow and deep water channel signals, motor data and POS data, surface distance data, and laser main wave signals to the high-speed laser acquisition system for storage. At the same time, the laser acquisition system sends working status signals to the integrated control system.

[0047] (8) Repeat steps (2) to (7) until all water depth echo signals in the target area are detected.

[0048] (9) When the user turns off the LiDAR on the screen, the integrated control system sends a shutdown signal to each component of the LiDAR, and simultaneously obtains the shutdown time data and the working status of each component, and transmits them to the screen for display.

[0049] (10) When the manned platform returns to the ground, the user connects the computer to the lidar, reads the data collected by the laser acquisition system, processes it with echo signal processing software, and outputs three-dimensional point cloud water depth data.

[0050] Compared with the prior art, the present invention has the following advantages:

[0051] (1) The continuous infrared laser emitted by the 1064nm laser ranging module is divided into two beams, one of which is collected by the system and the other is reflected by the water surface and collected by the system. The wave number of the laser collected by the system when the reflected laser is received is calculated, multiplied by the laser wavelength, and the phase is added to achieve micron-level ranging on the water surface.

[0052] (2) A 532nm laser emits a laser beam with a multi-Gaussian distribution in time, which passes through the water surface, reaches the bottom of the water, passes through the scanning system after reflection, and is received by the optical receiving system. The laser wave (including the echo) whose length is shorter than the longest laser echo is resampled to a laser wave (including the echo) of the same length as the longest laser echo, so as to align the laser echoes and use the vector similarity calculation method to obtain the precise distance of the laser water depth.

[0053] (3) The scanning system consists of a hollow motor and two Fresnel mirrors. One Fresnel mirror is installed outside the hollow motor and the other is installed inside. When the motor rotates, the Fresnel mirrors will also rotate to form a double wedge, ensuring that the angle between the laser emitted from the middle and the vertical line is 10°, and the trajectory on the water surface is a perfect circle. The motor has an encoder that can send angle data to the high-speed laser acquisition system in real time.

[0054] (4) The detection system includes a medium water four-quadrant PMT detection module and a deep water four-quadrant PMT detection module. Since a single laser echo signal cannot accurately and effectively identify the multi-Gaussian characteristic laser echo, the optical receiving system is focused on two four-quadrant PMT detection modules, and four echo signals can be obtained in both medium water and deep water. The four signals are superimposed to extract the multi-Gaussian characteristic laser echo signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The system structure of the present invention DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, preferred embodiments are given below and the specific implementation of the present invention is further described in detail in conjunction with the accompanying drawings.

[0057] Example:

[0058] Combination Figure 1 , explaining the manned dual-frequency phase multi-feature water-measuring laser radar. The water surface and water depth measurement principle is shown in formulas (1)-(5). It is mainly composed of fixed platform, scanning system, bottom plate, laser reflector, 1064nm laser ranging module, 532nm laser, optical receiving system, integrated control system, detection system, laser measurement and acquisition system, high-precision POS system and POS antenna.

[0059] Stable platform. This platform is made according to the principle of hydraulic balance. It can withstand a weight of 120kg and balance the pressure load. Its main function is to ensure that the laser radar mounted on it is relatively stable and can operate normally. It is square in shape with a circular hole in the middle, and a circular scanning system can be installed. The platform actively sends data to the integrated control system. In the case of unbalanced pressure, the integrated control system uses a load balancing algorithm to calculate the system load and send automatic load data to the stable platform to adjust the platform balance, thereby ensuring that the emitted laser trajectory is a perfect circle.

[0060] Scanning system. The scanning system consists of a hollow motor and two Fresnel mirrors. By rotating the hollow motor, the two Fresnel mirrors are driven to move relative to each other to achieve laser circular scanning. The hollow motor has an encoder that can automatically send the motor rotation angle data to the high-speed laser acquisition system. After receiving the signal from the integrated control system, the scanning system controls the hollow motor to rotate at the system set speed and sends the system status and rotation angle data to the integrated control system in real time.

[0061] The entire LiDAR is fixed on the bottom plate, which is a rectangular black plate made of magnesium-aluminum alloy wave-absorbing material. The hollow structure can reduce weight to the greatest extent. It is used to fix the 532nm laser, scanning system and other components of the LiDAR.

[0062] Laser reflector: The laser reflector is a laser-specific reflector made of silver-plated material with a reflectivity of 98% for 400nm-1200nm light. The mirror surface is 45° to the laser emission angle, which can ensure that the laser divergence angle remains unchanged and the laser echo does not move.

[0063] 532nm laser. After receiving the signal from the integrated control system, the laser emits a beam with multi-Gaussian distribution in time, peak power of 1000Kw, pulse width of 3±2ns, divergence angle less than 2mrad, M 2 Less than 1.2 small jitter (<500ps), 532nm laser with repetition rate of 5-300Khz. At the same time, the working status signal is transmitted to the integrated control system. It is characterized by adopting external triggering and multi-stage amplification technology to emit high repetition rate, picosecond jitter, divergence angle less than 2mrad, 532nm collimated green laser to realize underwater terrain detection.

[0064] 1064nm laser ranging module. After receiving the signal from the integrated control system, the module emits a continuous period of 1064nm laser, which is divided into two beams by the laser beam splitter. One beam is measured by the ranging module, and the other beam is emitted to the reflector, passes through the scanning system, reaches the water surface, reflects back, and is received by the module. Finally, the ranging module measures the number of 1064nm laser waves transmitted by the laser in the air, multiplies it by the wavelength, obtains the distance between the laser radar and the water surface, and sends it to the integrated control system. Since the laser wavelength is 1064nm, the module can measure the distance with micron accuracy.

[0065] Optical receiving system. The optical system uses a Cassegrain receiving structure consisting of a central opening primary mirror and a secondary mirror, a field-of-view mirror, and two convex lenses to form two shallow water and deep water channels, corresponding to two four-quadrant PMT detectors respectively.

[0066] Comprehensive control system. The comprehensive control system controls the work of the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc. At the same time, the comprehensive control system obtains the working status signals of the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc., and displays them on the screen in real time to ensure the normal and stable operation of the system. It is characterized by the use of ZYNQ to realize nanosecond delay sampling and sampling time length setting of the high-speed laser acquisition system.

[0067] Detection system. The detection system includes a medium water four-quadrant PMT detection module and a deep water four-quadrant PMT detection module. Since a single laser echo signal cannot accurately and effectively identify the multi-Gaussian characteristic laser echo, the optical receiving system is focused on two four-quadrant PMT detection modules, and four echo signals can be obtained in both medium water and deep water. The four signals are superimposed to extract the multi-Gaussian characteristic laser echo signal, see formula (6).

[0068] Laser acquisition system. The laser acquisition system uses FPGA to achieve 532nm laser acquisition with a pulse width of 3±2ns, a frequency of 5-300Khz, an acquisition speed of 3GSPS, and a storage of 2T. It can automatically attenuate strong echo signals and amplify weak signals to within 5-10V, ensuring that effective signals are clear and recognizable. At the same time, it can send the surface and bottom distances and system status to the integrated control system in real time.

[0069] POS system. The POS system uses RTK positioning technology to obtain high-precision (millimeter-level) GPS position data; uses IMU to obtain high-precision attitude position data (the heading angle is [-90,90], the roll angle is [0,360] and the yaw angle is [-180,180] with an angle resolution of 0.01°) and transmits it to the integrated control unit. At the same time, the POS system can send POS data and system status data to the integrated control system in real time. Before use, the POS system must fly horizontally for 30 minutes in an 8-shaped manner to correct the accumulated errors of the three attitude angles of the IMU.

[0070] POS antenna. This antenna is a dual antenna, requiring a minimum installation distance of 2m to achieve millimeter-level GPS positioning. The antenna is connected to the POS system via a coaxial cable, and the initial position data is differentiated and then substituted into the RTK algorithm to obtain the current position fixed solution and obtain millimeter-level GPS positioning data.

[0071] The working process of the manned aircraft-borne dual-frequency phase multi-signature water measurement lidar is as follows:

[0072] (1) The user starts the manned dual-frequency phase multi-signature water-measuring laser radar mounted on the manned platform on the screen. The start signal is sent to each component of the laser radar through the integrated control system, and the start time data and the working status signal of each component are obtained. The laser radar self-test is completed and the self-test results of each component are displayed on the screen. Among them, the integrated control unit issues a start command to the stabilization platform, 532nm laser, scanning system, 1064nm laser ranging module, detection system, laser acquisition system, and POS system, and the working status of each component is displayed on the screen.

[0073] (2) The integrated control system reads the data sent by the stable platform, uses a load balancing algorithm to calculate the system load, sends automatic load data to the stable platform, and adjusts the platform balance.

[0074] (3) The integrated control system reads the position data, attitude data, and UTC time data sent by the POS system and transmits them to the high-speed laser sampling system (the high-speed laser sampling system stores the position data, attitude data, UTC time, and echo signal together) to obtain the high-precision working status of the POS system.

[0075] (3) The integrated control system sends a signal to the 1064nm laser ranging module, which emits a 1064nm continuous periodic infrared laser to measure the distance from the water surface to the module.

[0076] (4) The integrated control system sends an external trigger signal to the 532nm laser, which emits a 532nm multi-Gaussian echo characteristic laser, which is reflected to the scanning system through the reflector below the optical receiving system. At the same time, the laser sends the laser main wave signal to the high-speed laser acquisition system and sends the working status signal to the integrated control system.

[0077] (5) The integrated control system transmits control parameters to the optical scanning system to control the rotation of the hollow motor, thereby driving the two Fresnel mirrors in the middle to rotate, so that the laser trajectory is a perfect circle.

[0078] (6) The laser reflected from the water surface and the bottom of the water passes through the scanning system and is received by the receiving optical system. The laser echo signal is sent to the detection system (shallow water PMT detection module and deep water PMT detection module) through the shallow water channel and the deep water channel. At the same time, the working status signal is sent to the integrated control system.

[0079] (7) The detection system, integrated control system, 1064nm laser ranging module and 532nm laser send and receive shallow and deep water channel signals, motor data and POS data, surface distance data, and laser main wave signals to the high-speed laser acquisition system for storage. At the same time, the laser acquisition system sends working status signals to the integrated control system.

[0080] (8) Repeat steps (2) to (7) until all water depth echo signals in the target area are detected.

[0081] (9) When the user turns off the LiDAR on the screen, the integrated control system sends a shutdown signal to each component of the LiDAR, and simultaneously obtains the shutdown time data and the working status of each component, and transmits them to the screen for display.

[0082] (10) When the manned platform returns to the ground, the user connects the computer to the lidar, reads the data collected by the laser acquisition system, processes it with echo signal processing software, and outputs three-dimensional point cloud water depth data.

[0083] The above embodiments are only used to illustrate the present invention, but not to limit the present invention. A person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the patent protection scope of the present invention shall be defined by the claims.

[0084] The technical contents not described in detail in the present invention are all known technologies.

Claims

1. Manned airborne dual-frequency phase multi-feature water measurement laser radar, characterized in that: The principle of water surface measurement is that the continuous infrared laser emitted by the 1064nm laser ranging module is divided into two beams, one of which is collected by the system and the other is reflected by the water surface and collected by the system. When the reflected laser is received, the wave number of the laser collected by the system is calculated, multiplied by the laser wavelength, and the phase is added to achieve micron-level ranging on the water surface. The specific calculation is shown in formula (1); (1) Where D s is the distance from the laser port of the 1064nm laser ranging module to the water surface, λ is the wavelength, which is 1064nm, N is the wave number obtained by dividing the distance from the laser port of the 1064nm laser ranging module to the water surface by the wavelength of 1064nm, △φ is the phase of the transmitted wave and the received wave relative to a complete wave movement; The principle of underwater measurement is that a 532nm laser emits a laser beam with a multi-Gaussian distribution in time, which passes through the water surface, reaches the bottom of the water, passes through the scanning system after reflection, and is received by the optical receiving system. Among them, the laser beam emitted by the 532nm laser and the received laser beam both have the characteristics of multi-Gaussian distribution in time; see formula (2) for details; (2) Where D ws is the distance of 532nm laser from the water surface to the bottom of the water, v is the transmission speed of laser in water, generally 0.11m / ns, △t is the time it takes for laser to travel from the water surface to the bottom of the water, t wsup is the rising edge time of the water surface laser echo, t wfup is the rising edge moment of the underwater laser echo; the 532nm laser emits a laser beam with multi-Gaussian characteristics for a long time, and will reflect a laser echo with multi-Gaussian characteristics when it encounters the water surface and the bottom of the water; in this way, the waveform similarity and linear operation matching waveform can be used to calculate high-precision △t, and the specific calculation is as follows: Compare the emitted multi-Gaussian characteristic laser wave and the collected water surface and bottom multi-Gaussian characteristic laser echoes, and normalize them to the wave with the longest wavelength in the time domain, as follows: First, determine the length of the longest wavelength; (3) Where, L max is the length of the longest wavelength, L i (i is 1, 2, 3) are respectively the lengths of the emitted multi-Gaussian characteristic laser wave and the collected surface and bottom multi-Gaussian characteristic laser echoes, t down is the x-axis coordinate of the falling edge of the laser wave (including the echo), t up is the x-axis coordinate of the rising edge of the laser wave (including echo); Second, laser waves (including echoes) whose length is shorter than the longest laser echo are resampled to laser waves (including echoes) of the same length as the longest laser echo; The length of the waveform to be resampled is proportionally transformed into a waveform of the same length as the longest laser echo; the rising edge coordinates of the laser wave (including the echo) of the same length as the longest laser echo are set as the original coordinates, and the falling edge coordinates are set as L max , are all assigned 0, and other positions are resampled using formula (4); (4) Where, L i is the amplitude value of the resampled x-axis i coordinate, L i+1 is the amplitude value of the x-axis i+1 coordinate of the waveform to be resampled proportionally transformed, L i-1 is the amplitude value of the x-axis i-1 coordinate of the waveform to be resampled in equal proportion; finally, the resampled waveform L is obtained; Third, use formula (5) to calculate the similarity between the emitted multi-Gaussian characteristic laser wave and the collected water surface and bottom multi-Gaussian characteristic laser echoes to obtain the precise time when the laser reaches the water surface and the bottom; (5) In the formula, cosθ is the similarity index (the closer to 1, the more similar, generally greater than 0.6826 means similar), and They represent any two of the emitted multi-Gaussian characteristic laser waves and the collected surface and bottom multi-Gaussian characteristic laser echoes respectively; if the cosθ value is greater than or equal to 0.6826, the rising edge moments of the emitted laser, the surface laser echo, and the bottom laser echo are obtained.

2. The manned airborne dual-frequency phase multi-feature water measurement laser radar as claimed in claim 1, characterized in that The water measurement laser radar is mainly composed of a stable platform, a scanning system, a bottom plate, a laser reflector, a 1064nm laser ranging module, a 532nm laser, an optical receiving system, an integrated control system, a detection system, a laser measurement and acquisition system, a high-precision POS system, and a POS antenna. Stable platform: This platform is made according to the principle of hydraulic balance. It can withstand a weight of 120kg and balance the pressure load. Its main function is to ensure that the laser radar mounted on it is relatively stable and can operate normally. It is square in shape with a circular hole in the middle, and a circular scanning system can be installed. The platform actively sends data to the integrated control system. In the case of unbalanced pressure, the integrated control system uses a load balancing algorithm to calculate the system load and send automatic load data to the stable platform to adjust the platform balance, thereby ensuring that the emitted laser trajectory is a perfect circle. Scanning system: The scanning system consists of a hollow motor and two Fresnel mirrors. The hollow motor is rotated to drive the two Fresnel mirrors to move relative to each other to achieve laser circular scanning. The hollow motor has an encoder that can automatically send the motor rotation angle data to the high-speed laser acquisition system. After receiving the signal from the integrated control system, the scanning system controls the hollow motor to rotate at the system set speed and sends the system status and rotation angle data to the integrated control system in real time. Bottom plate: The entire laser radar is fixed on the bottom plate. The bottom plate is a rectangular block, black, and made of magnesium-aluminum alloy absorbing material. The hollow structure can reduce weight to the greatest extent. It is used to fix the 532nm laser, scanning system and other components of the laser radar. Laser reflector: The laser reflector is a laser-specific reflector made of silver-plated material with a light reflectivity of 98% in the range of 400nm-1200nm. The mirror surface is 45° to the laser emission angle, which can ensure that the laser divergence angle remains unchanged and the laser echo does not move. 1064nm laser ranging module: After receiving the signal from the integrated control system, the module emits a continuous period of 1064nm laser, which is divided into two beams by the laser beam splitter. One beam is measured by the ranging module, and the other beam is emitted to the reflector, passes through the scanning system, reaches the water surface, reflects back, and is received by the module. Finally, the ranging module measures the number of 1064nm laser waves transmitted by the laser in the air, multiplies it by the wavelength, obtains the distance between the laser radar and the water surface, and sends it to the integrated control system; since the laser wavelength is 1064nm, the module can measure the distance with an accuracy of microns; 532nm laser: After receiving the signal from the integrated control system, the laser emits a beam with multi-Gaussian distribution in time, peak power of 1000Kw, pulse width of 3±2ns, divergence angle less than 2mrad, M 2 Less than 1.2 small jitter (<500ps), 532nm laser with repetition rate of 5-300Khz; at the same time, transmit the working status signal to the integrated control system; it is characterized by adopting external triggering and multi-stage amplification technology, emitting high repetition rate, picosecond jitter, divergence angle less than 2mrad, 532nm collimated green laser, to achieve underwater terrain detection; Optical receiving system: The optical system adopts a Cassegrain receiving structure consisting of a central opening primary mirror and a secondary mirror, a field-of-view mirror and two convex lenses to form two shallow water and deep water channels, corresponding to two four-quadrant PMT detectors respectively; Integrated control system: The integrated control system controls the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc.; at the same time, the integrated control system obtains the working status signals of the stable platform, 532nm laser, 1064nm laser ranging module, scanning system, detection system, high-speed laser acquisition system, POS system, etc., and displays them on the screen in real time to ensure the normal and stable operation of the system; it is characterized by the use of ZYNQ to achieve nanosecond delay sampling and sampling time length setting of the high-speed laser acquisition system; Detection system: The detection system includes a medium water four-quadrant PMT detection module and a deep water four-quadrant PMT detection module. Since a single laser echo signal cannot accurately and effectively identify the multi-Gaussian characteristic laser echo, the optical receiving system is focused on two four-quadrant PMT detection modules, and four echo signals can be obtained for both medium water and deep water. The four signals are superimposed to extract the multi-Gaussian characteristic laser echo signal, see formula (8). (6) In the formula, WS is the echo signal, n is the number of laser echo signals acquired simultaneously (take 4), S j is the jth laser echo signal (j∈[1,4]); Laser acquisition system: The laser acquisition system uses FPGA to achieve 532nm laser acquisition with a pulse width of 3±2ns, a frequency of 5-300Khz, an acquisition speed of 3GSPS, and a storage of 2T. It can automatically attenuate strong echo signals and amplify weak signals to within 5-10V, ensuring that effective signals are clear and recognizable; at the same time, it can send the water surface and bottom distance and system status to the integrated control system in real time; POS system: The POS system uses RTK positioning technology to obtain high-precision (millimeter-level) GPS position data; uses IMU to obtain high-precision attitude position data (the heading angle is [-90,90], the roll angle is [0,360] and the yaw angle is [-180,180] with an angle resolution of 0.01°), and transmits it to the integrated control unit; at the same time, the POS system can send POS data and system status data to the integrated control system in real time; before use, the POS system must fly horizontally for 30 minutes in an 8-shaped manner to correct the accumulated errors of the three attitude angles of the IMU; POS antenna: This antenna is a dual antenna and requires an installation distance of at least 2m to achieve millimeter-level GPS positioning. The antenna is connected to the POS system via a coaxial cable, and the initial position data is differentiated and then substituted into the RTK algorithm to obtain the current position fixed solution and obtain millimeter-level GPS positioning data.

3. The manned airborne dual-frequency phase multi-feature water-measuring laser radar as claimed in claim 1, further characterized by: The working process of the water measuring laser radar mounted on a manned platform: (1) The user starts the manned dual-frequency phase multi-signature water-measuring laser radar mounted on the manned platform on the screen. The start signal is sent to each component of the laser radar through the integrated control system, and the start time data and the working status signal of each component are obtained. The laser radar self-test is completed and the self-test results of each component are displayed on the screen. Among them, the integrated control unit issues a start command to the stabilization platform, 532nm laser, scanning system, 1064nm laser ranging module, detection system, laser acquisition system, and POS system, and the working status of each component is displayed on the screen. (2) The integrated control system reads the data sent by the stable platform, uses a load balancing algorithm to calculate the system load, sends automatic load data to the stable platform, and adjusts the platform balance; (3) The integrated control system reads the position data, attitude data, and UTC time data sent by the POS system and transmits them to the high-speed laser sampling system (the high-speed laser sampling system stores the position data, attitude data, UTC time, and echo signal together) to obtain the high-precision working status of the POS system; (3) The integrated control system sends a signal to the 1064nm laser ranging module, which emits a 1064nm continuous period infrared laser to measure the distance from the water surface to the module; (4) The integrated control system sends an external trigger signal to the 532nm laser, which emits a 532nm multi-Gaussian echo characteristic laser, which is reflected by the reflector below the optical receiving system to the scanning system. At the same time, the laser sends the laser main wave signal to the high-speed laser acquisition system and sends the working status signal to the integrated control system. (5) The integrated control system transmits control parameters to the optical scanning system to control the rotation of the hollow motor, thereby driving the two Fresnel mirrors in the middle to rotate, so that the laser trajectory is a perfect circle; (6) The laser reflected from the water surface and the bottom passes through the scanning system and is received by the receiving optical system. The laser echo signal is sent to the detection system (shallow water PMT detection module and deep water PMT detection module) through the shallow water channel and the deep water channel. At the same time, the working status signal is sent to the integrated control system. (7) The detection system, integrated control system, 1064nm laser ranging module and 532nm laser send and receive shallow and deep water channel signals, motor data and POS data, water surface distance data, and laser main wave signals to the high-speed laser acquisition system for storage; at the same time, the laser acquisition system sends a working status signal to the integrated control system; (8) Repeat steps (2) to (7) until all water depth echo signals in the target area are detected; (9) When the user turns off the LiDAR on the screen, the integrated control system sends a shutdown signal to each component of the LiDAR, and simultaneously obtains the shutdown time data and the working status of each component, and transmits it to the screen for display; (10) When the manned platform returns to the ground, the user connects the computer to the lidar, reads the data collected by the laser acquisition system, processes it with echo signal processing software, and outputs three-dimensional point cloud water depth data.

Images