Unmanned aerial vehicle-mounted water depth measurement continuous frequency conversion blue-green laser radar

Abstract

The invention discloses an unmanned aerial vehicle-mounted water depth measurement continuous frequency conversion blue-green laser radar according to the characteristic that continuous frequency conversion blue-green laser generates frequency change when encountering a water surface and a water bottom, convolution and fast Fourier transform and a time-frequency corresponding relation. The system is composed of a blue-green light frequency conversion laser, a laser power supply driver, a coding motor, a reflective optical wedge, a reflector, a large lens, a small lens, a balance light detection module, a high-speed laser acquisition processor, an IMU module, an RTK module, a 4G module, a controller, a 4G antenna, a server, a mobile phone terminal and the like. The laser radar is small in size, light in weight and suitable for the unmanned aerial vehicle to measure the water depth rapidly and precisely, the precision can reach the millimeter level, and 0-10 m water depth measurement can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of laser detection technology, and in particular to a continuous frequency variable blue-green laser radar for water depth measurement carried by an unmanned aerial vehicle. Background Art

[0002] At present, water depth measurement lidars mostly use dual-frequency (1064nm and 532nm) or single-frequency (532nm) lidars to detect water depth. Among them, a dual-frequency water depth measurement lidar of a satellite-borne laser near-coast terrain detection lidar and detection method (application number CN202011378792.8) uses time-of-flight ranging, and the emitted laser has severe jitter, large errors, large size, heavy weight, and high price. It must be carried on a helicopter through professional route planning to measure water depth, and the cost is high. Due to the large error, the obtained lidar water depth data needs to be processed with the existing control point errors before it can be used.

[0003] In addition, the patent for the Rayleigh scattering ocean lidar system (application number CN2015103663523) also uses the time-of-flight ranging principle, and the laser jitter is unknown. The structure of the transmitting lens group and the imaging large lens has not been announced. The ICCD sensitivity is low, and high-precision water depth measurement cannot be achieved.

[0004] The single-frequency water-measuring lidar (patent number ZL20211138986.X) uses a high-energy, high-repetition-rate, narrow-pulse-width laser. The ranging principle is time-of-flight ranging. The echo signal processing is difficult, and the error is generally within 0.25m. The accuracy is too low to meet the requirements of high-precision underwater terrain mapping.

[0005] In order to solve the problem of low measurement accuracy caused by the time-of-flight ranging of the above-mentioned laser radar, the present invention discloses a continuous frequency conversion blue-green laser radar for water depth measurement carried by an unmanned aerial vehicle. The laser radar emits a continuous frequency conversion blue-green laser beam to form a time-frequency diagram, and converts the frequency information into time information by convolution of the local oscillator laser signal and the laser echo signal and Fourier transformation. Combined with the propagation speed of light in water, it is carried on a drone at an altitude of 30-120m to measure the water depth of 0-10m. Summary of the invention

[0006] The invention discloses a drone-mounted water depth measurement continuous frequency conversion blue-green laser radar, which has a total weight of less than 10kg and is suitable for quickly detecting a water depth of 0-10m with an accuracy of millimeter level.

[0007] The technical solution principle adopted by the present invention is:

[0008] (1) The blue-green frequency conversion laser emits two beams of continuously frequency-converted blue-green lasers, namely the A laser emission signal and the C laser local oscillator signal; at the same time, the frequency domain and the time domain are matched to form a time-frequency diagram;

[0009] (2) A laser beam is emitted to the water surface, and the reflected laser causes the laser echo signal to shift in frequency. The laser transmits through the water, reaches the bottom of the water, and then reflects the laser, causing the laser echo signal to shift in frequency, forming a B laser echo signal, which is collected by a high-speed laser acquisition processor;

[0010] (3) Another C local oscillator laser signal is directly output to the high-speed laser acquisition processor, which performs a convolution operation on the C local oscillator laser signal and the B laser echo signal to obtain a convolution laser echo signal in the spatial domain;

[0011] (4) Using fast Fourier transform, the convolution laser echo signal in the spatial domain is transformed into the convolution laser echo signal in the frequency domain to form an amplitude-frequency diagram, identify the frequency peaks of the water surface and the bottom, and calculate the frequency difference △f;

[0012] (5) Based on the time-frequency diagram of (1), combined with the amplitude-frequency diagram, a time-frequency difference diagram is formed. The time difference △t corresponding to the frequency difference △f is converted. According to the transmission speed of the laser in water, the distance the laser travels in the water is calculated to obtain the measured water distance (i.e., water depth slant distance).

[0013] (6) Based on the motor encoder angle, the three attitude angles of POS and RTK positioning information, combined with the rotation matrix, the water depth slant range is converted into the actual water depth at the measurement position.

[0014] The specific technical solution adopted by the present invention is:

[0015] The UAV-mounted water depth measurement continuous frequency conversion blue-green lidar is mainly composed of blue-green light frequency conversion laser, laser power driver, encoding motor, reflective optical wedge, reflector, large lens, small lens, balanced light detection module, high-speed laser acquisition processor, IMU module, RTK module, 4G module, controller, 4G antenna, server and mobile phone terminal.

[0016] Blue-green frequency conversion laser. After receiving the signal from the controller, the laser emits a 380-600nm blue-green frequency conversion laser with a peak power of 400Mw, a pulse width of 1μs, a divergence angle of less than 0.2mrad, and a Gaussian distribution from the center to the surroundings. A small amount of light is separated by a beam splitter inside and transmitted to the photomultiplier tube to output the local oscillator laser signal. At the same time, the working status signal is transmitted to the controller at a frequency of 200Hz.

[0017] Laser power driver. After receiving the signal from the controller, the driver configures the power module according to the laser parameters to provide a stable DC power supply for the laser, with a voltage of 24V and a current of 150-320mA. At the same time, it transmits a working status signal to the controller at a frequency of 200Hz.

[0018] Encoder motor. After receiving the controller initialization command, the motor is immediately reset to zero and the motor angle is calculated from a fixed position. It is characterized by a 1000-line photoelectric encoder and a Hall sensor, a voltage of 24V, a speed of 3000R, a power of 64W, a constant force of 0.2NM, and an accuracy of 0.1NM. It transmits the working status signal to the controller at a frequency of 200Hz.

[0019] Reflector. The reflector is at an angle of 45° to the laser. The substrate is silicon, with a diameter of 3mm, a thickness of 3mm, gold-plated, and a reflectivity of >99.99%. It is characterized by a triangular disk fixed in the middle at the center of the large lens to reflect the laser beam to the reflective wedge.

[0020] Reflective optical wedge. This optical wedge has a self-balancing function, and its center is 30° and 75° to the irradiated laser beam. When it is installed on the motor and rotates, the angle between the reflected laser beam and the upper part changes continuously between 30° and 75°, forming a circular track with a scanning angle of 45°.

[0021] Large lens. This lens is actually a double single lens with positive focal power, a clear aperture of 60mm, a focal length of 128mm, and a distance of 106.7mm from the small lens. It includes a double cemented lens and a single lens; the double cemented lens includes a convex lens and a concave lens; the single lens is a convex lens and uses ZK7 glass with small dispersion.

[0022] Small lens. This lens is actually a doublet lens with negative optical power, a clear aperture of 10mm and a focal length of -35.6mm. The doublet lens consists of a flint glass convex lens in front and a Burman glass concave lens in the back.

[0023] Balanced optical detection module. The module has a spectral range of 380-1700nm, a bandwidth of 3dB, a response time of <0.2ns, a common mode rejection ratio of >30dB, and a voltage of 24V. At the same time, it sends data to the high-speed laser acquisition processor at a frequency of 200Hz, and sends working status signals to the controller at a frequency of 200Hz.

[0024] High-speed laser acquisition processor. This processor is mainly used to collect the local oscillator laser signal transmitted by the blue-green light frequency conversion laser and the laser echo signal detected by the balanced light detection module, and perform convolution operation and fast Fourier transform on the two signals to obtain the frequency difference between the surface and bottom echoes, convert it into the corresponding time difference, and combine the propagation speed of the laser in the water to obtain the water depth slant range, and substitute it into the rotation matrix together with the motor encoder angle, the three attitude angles of the IMU and the RTK positioning information, convert it into the actual water depth of the measured position, and transmit it to the controller. At the same time, the working status signal is transmitted to the controller at a frequency of 200Hz.

[0025] IMU module. This module is mainly used to obtain the pitch, roll and yaw angles of the platform with a resolution of 0.01°. At the same time, it sends data and working status signals to the controller at a frequency of 200Hz.

[0026] RTK module. This module is mainly used to obtain longitude and latitude information, with a horizontal accuracy better than 0.01m. At the same time, it sends data and working status signals to the controller at a frequency of 200Hz.

[0027] 4G module. This module supports dual communication functions of 4G DTU and radio communication (up to 50km). When there is no 4G signal, it automatically switches to radio communication, sends instructions forwarded by the server, and transmits data and working status signals to the server.

[0028] Controller. This controller is used to initialize and control the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, and obtain the working status of these modules.

[0029] 4G antenna. This antenna is used to enhance 4G signals and radio signals, making the signal stronger by more than 3dB.

[0030] Server. The server has a fixed IP address. The 4G module and the mobile phone are connected to the server through the IP address. The server then stores and forwards the data sent by the 4G module and the mobile phone, realizes the communication between the 4G module and the mobile phone, and realizes the remote control of the drone-borne water depth measurement continuous frequency conversion blue-green laser radar by the mobile phone, and transmits the water depth data measured by the drone-borne water depth measurement continuous frequency conversion blue-green laser radar to the mobile phone in real time.

[0031] Mobile phone. The mobile phone supports 4G and external wireless communication modules (paired with the 4G module radio communication of the laser radar). It is mainly responsible for connecting to the server, sending instructions to the drone-borne water depth measurement continuous frequency blue-green laser radar through the server in real time, and the returned water depth data of the target position is displayed on the mobile phone and stored.

[0032] Mounted on a drone, the working process of the drone-borne water depth measurement continuous frequency conversion blue-green laser radar is:

[0033] (1) The user starts the drone-mounted water depth measurement continuous frequency blue-green laser radar on the mobile phone, starts the signal server and 4G module to send to the controller, and the controller starts each component of the laser radar, and obtains the working status signal of each component, and sends it back to the mobile phone for display. Among them, the controller issues a start-up command to the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc. At the same time, the working status of the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, and 4G module is obtained and sent back to the mobile phone for display.

[0034] (2) The blue-green frequency conversion laser supplies power to the blue-green frequency conversion laser, transmits a local oscillator laser signal to the high-speed laser acquisition processor, and also transmits a laser beam to the water surface. At the same time, the status is sent to the controller.

[0035] (3) The encoder motor rotates according to the set parameters and starts scanning to obtain as much water area data as possible. At the same time, the rotation angle and working status are sent to the high-speed laser acquisition processor and controller respectively.

[0036] (4) The balanced light detection module detects the received laser echo signal and transmits it to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0037] (5) The IMU module collects the pitch angle, roll angle and yaw angle of the platform and sends them to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0038] (6) The RTK module obtains the longitude and latitude information and sends it to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0039] (7) The 4G module is connected to the mobile phone through the 4G signal and the server, which is then connected to the mobile phone through the radio signal. The server forwards the command to the drone-mounted water depth measurement continuous frequency conversion blue-green laser radar, which transmits data and working status signals back to the mobile phone.

[0040] (8) The high-speed laser acquisition processor collects the laser local oscillator signal and the laser echo signal, performs convolution, fast Fourier transform, frequency difference, and time difference operations, calculates the slant range and water depth, reads the motor angle, three attitude angle data, and positioning data, substitutes them into the rotation matrix, obtains the actual water depth of the target position, sends it to the controller, passes through the 4G module (and server), and is sent back to the mobile phone for display, and the data is stored in the mobile phone.

[0041] (9) Repeat steps (2) to (8) until all water depth echo signals in the target area are detected.

[0042] (10) The user turns off the drone-mounted water depth measurement continuous frequency blue-green laser radar on the mobile phone. The shutdown signal is sent to the controller through the 4G module, and the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc. are turned off in turn.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] (1) The blue-green frequency-converting laser changes frequency when encountering the water surface and bottom, and convolves with the local oscillator signal, performs Fourier transform, and converts the time difference to calculate the water depth.

[0045] (2) A blue-green frequency conversion laser is used to emit a laser beam that changes frequency from blue light to green light.

[0046] (3) Reflective optical wedge, with self-balancing function, the center is 30° and 75° to the irradiated laser beam, and cooperates with the motor to form a circular trajectory with a scanning angle of 45°.

[0047] (4) The large lens is a double single lens with positive focal length. The small lens is a double cemented lens with negative focal length. The combination of the two can eliminate spherical aberration, coma, astigmatism, field curvature and distortion, etc., so that the laser can be focused to a point, increasing the laser energy and measuring depth.

[0048] (5) The spectral range of the balanced optical detection module is 380-1700nm, the bandwidth is 3dB, the response time is <0.2ns, and the common mode rejection ratio is >30dB.

[0049] (6) The high-speed laser acquisition processor is mainly used to collect the local oscillator laser signal transmitted by the blue-green frequency conversion laser and the laser echo signal detected by the balanced light detection module, and perform convolution operation and fast Fourier transform on the two signals to obtain the frequency difference between the water surface and the bottom echo, which is converted into the corresponding time difference. The water depth slant range is obtained by combining the propagation speed of the laser in the water, and is substituted into the rotation matrix together with the motor encoder angle, the three attitude angles of the IMU and the RTK positioning information to convert it into the actual water depth at the measured position.

[0050] (7) The 4G module supports dual automatic switching communication functions of 4G DTU and radio communication (up to 50km). BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The water depth measurement principle of the present invention is

[0052] Figure 2 The invention discloses a continuous frequency-converting blue-green laser radar for measuring water depth carried by an unmanned aerial vehicle. DETAILED DESCRIPTION

[0053] 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.

[0054] Example:

[0055] Combination Figure 1 , explaining the water depth measurement principle of the UAV-borne water depth measurement continuous frequency blue-green laser radar.

[0056] (1) The blue-green frequency conversion laser emits two beams of continuously frequency-converted blue-green lasers, namely the A laser emission signal and the C laser local oscillator signal; at the same time, the frequency domain and the time domain are matched to form a time-frequency diagram;

[0057] (2) A laser beam is emitted to the water surface, and the reflected laser causes the laser echo signal to shift in frequency. The laser transmits through the water, reaches the bottom of the water, and then reflects the laser, causing the laser echo signal to shift in frequency, forming a B laser echo signal, which is collected by a high-speed laser acquisition processor;

[0058] (3) Another C local oscillator laser signal is directly output to the high-speed laser acquisition processor, which performs a convolution operation on the C local oscillator laser signal and the B laser echo signal to obtain a convolution laser echo signal in the spatial domain;

[0059] (4) Using fast Fourier transform, the convolution laser echo signal in the spatial domain is transformed into the convolution laser echo signal in the frequency domain to form an amplitude-frequency diagram, identify the frequency peaks of the water surface and the bottom, and calculate the frequency difference △f;

[0060] (5) Based on the time-frequency diagram of (1), combined with the amplitude-frequency diagram, a time-frequency difference diagram is formed. The time difference △t corresponding to the frequency difference △f is converted. According to the transmission speed of the laser in water, the distance the laser travels in the water is calculated to obtain the measured water distance (i.e., water depth slant distance).

[0061] (6) Based on the motor encoder angle, the three attitude angles of POS and RTK positioning information, combined with the rotation matrix, the water depth slant range is converted into the actual water depth at the measurement position.

[0062] Combination Figure 2 The components of the UAV-mounted continuous frequency conversion blue-green laser radar for water depth measurement are described, including blue-green light frequency conversion laser, laser power driver, encoding motor, reflective optical wedge, reflector, large lens, small lens, balanced light detection module, high-speed laser acquisition processor, IMU module, RTK module, 4G module, controller, 4G antenna, server and mobile phone terminal.

[0063] Blue-green frequency conversion laser. After receiving the signal from the controller, the laser emits a 380-600nm blue-green frequency conversion laser with a peak power of 400Mw, a pulse width of 1μs, a divergence angle of less than 0.2mrad, and a Gaussian distribution from the center to the surroundings. A small amount of light is separated by a beam splitter inside and transmitted to the photomultiplier tube to output the local oscillator laser signal. At the same time, the working status signal is transmitted to the controller at a frequency of 200Hz.

[0064] Laser power driver. After receiving the signal from the controller, the driver configures the power module according to the laser parameters to provide a stable DC power supply for the laser, with a voltage of 24V and a current of 150-320mA. At the same time, it transmits a working status signal to the controller at a frequency of 200Hz.

[0065] Encoder motor. After receiving the controller initialization command, the motor is immediately reset to zero and the motor angle is calculated from a fixed position. It is characterized by a 1000-line photoelectric encoder and a Hall sensor, a voltage of 24V, a speed of 3000R, a power of 64W, a constant force of 0.2NM, and an accuracy of 0.1NM. It transmits the working status signal to the controller at a frequency of 200Hz.

[0066] Reflector. The reflector is at an angle of 45° to the laser. The substrate is silicon, with a diameter of 3mm, a thickness of 3mm, gold-plated, and a reflectivity of >99.99%. It is characterized by a triangular disk fixed in the middle at the center of the large lens to reflect the laser beam to the reflective wedge.

[0067] Reflective optical wedge. This optical wedge has a self-balancing function, and its center is 30° and 75° to the irradiated laser beam. When it is installed on the motor and rotates, the angle between the reflected laser beam and the upper part changes continuously between 30° and 75°, forming a circular track with a scanning angle of 45°.

[0068] Large lens. This lens is actually a double single lens with positive focal power, a clear aperture of 60mm, a focal length of 128mm, and a distance of 106.7mm from the small lens. It includes a double cemented lens and a single lens; the double cemented lens includes a convex lens and a concave lens; the single lens is a convex lens and uses ZK7 glass with small dispersion.

[0069] Small lens. This lens is actually a doublet lens with negative optical power, a clear aperture of 10mm and a focal length of -35.6mm. The doublet lens consists of a flint glass convex lens in front and a Burman glass concave lens in the back.

[0070] Balanced optical detection module. The module has a spectral range of 380-1700nm, a bandwidth of 3dB, a response time of <0.2ns, a common mode rejection ratio of >30dB, and a voltage of 24V. At the same time, it sends data to the high-speed laser acquisition processor at a frequency of 200Hz, and sends working status signals to the controller at a frequency of 200Hz.

[0071] High-speed laser acquisition processor. This processor is mainly used to collect the local oscillator laser signal transmitted by the blue-green frequency conversion laser and the laser echo signal detected by the balanced light detection module, and perform convolution operation and fast Fourier transform on the two signals to obtain the frequency difference between the surface and bottom echoes, convert it into the corresponding time difference, and combine the propagation speed of the laser in the water to obtain the water depth slant range, and substitute it into the rotation matrix together with the motor encoder angle, the three attitude angles of the IMU and the RTK positioning information, convert it into the actual water depth of the measured position, and transmit it to the controller. At the same time, the working status signal is transmitted to the controller at a frequency of 30Hz.

[0072] IMU module. This module is mainly used to obtain the pitch, roll and yaw angles of the platform with a resolution of 0.01°. At the same time, it sends data and working status signals to the controller at a frequency of 200Hz.

[0073] RTK module. This module is mainly used to obtain longitude and latitude information, with a horizontal accuracy better than 0.01m. At the same time, it sends data and working status signals to the controller at a frequency of 200Hz.

[0074] 4G module. This module supports dual communication functions of 4G DTU and radio communication (up to 50km). When there is no 4G signal, it automatically switches to radio communication, sends instructions forwarded by the server, and transmits data and working status signals to the server.

[0075] Controller. This controller is used to initialize and control the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, and obtain the working status of these modules.

[0076] 4G antenna. This antenna is used to enhance 4G signals and radio signals, making the signal stronger by more than 3dB.

[0077] Server. The server has a fixed IP address. The 4G module and the mobile phone are connected to the server through the IP address. The server then stores and forwards the data sent by the 4G module and the mobile phone, realizes the communication between the 4G module and the mobile phone, and realizes the remote control of the drone-borne water depth measurement continuous frequency conversion blue-green laser radar by the mobile phone, and transmits the water depth data measured by the drone-borne water depth measurement continuous frequency conversion blue-green laser radar to the mobile phone in real time.

[0078] Mobile phone. The mobile phone supports 4G and external wireless communication modules (paired with the 4G module radio communication of the laser radar). It is mainly responsible for connecting to the server, sending instructions to the drone-borne water depth measurement continuous frequency blue-green laser radar through the server in real time, and the returned water depth data of the target position is displayed on the mobile phone and stored.

[0079] Mounted on a drone, the working process of the drone-borne water depth measurement continuous frequency conversion blue-green laser radar is:

[0080] (1) The user starts the drone-mounted water depth measurement continuous frequency blue-green laser radar on the mobile phone, starts the signal server and 4G module to send to the controller, and the controller starts each component of the laser radar, and obtains the working status signal of each component, and sends it back to the mobile phone for display. Among them, the controller issues a start-up command to the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc. At the same time, the working status of the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, and 4G module is obtained and sent back to the mobile phone for display.

[0081] (2) The blue-green frequency conversion laser supplies power to the blue-green frequency conversion laser, transmits a local oscillator laser signal to the high-speed laser acquisition processor, and also transmits a laser beam to the water surface. At the same time, the status is sent to the controller.

[0082] (3) The encoder motor rotates according to the set parameters and starts scanning to obtain as much water area data as possible. At the same time, the rotation angle and working status are sent to the high-speed laser acquisition processor and controller respectively.

[0083] (4) The balanced light detection module detects the received laser echo signal and transmits it to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0084] (5) The IMU module collects the pitch angle, roll angle and yaw angle of the platform and sends them to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0085] (6) The RTK module obtains the longitude and latitude information and sends it to the high-speed laser acquisition processor. At the same time, it sends the working status to the controller.

[0086] (7) The 4G module is connected to the mobile phone through the 4G signal and the server, which is then connected to the mobile phone through the radio signal. The server forwards the command to the drone-mounted water depth measurement continuous frequency conversion blue-green laser radar, which transmits data and working status signals back to the mobile phone.

[0087] (8) The high-speed laser acquisition processor collects the laser local oscillator signal and the laser echo signal, performs convolution, Fourier transform, frequency difference, and time difference operations, calculates the slant range and water depth, reads the motor angle, three attitude angle data, and positioning data, substitutes them into the rotation matrix, obtains the actual water depth of the target position, sends it to the controller, passes through the 4G module (and server), and is transmitted back to the mobile phone for display, and the data is stored in the mobile phone.

[0088] (9) Repeat steps (2) to (8) until all water depth echo signals in the target area are detected.

[0089] (10) The user turns off the drone-mounted water depth measurement continuous frequency blue-green laser radar on the mobile phone. The shutdown signal is sent to the controller through the 4G module, and the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc. are turned off in turn.

[0090] 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.

[0091] The technical contents not described in detail in the present invention are all known technologies.

Claims

1. UAV-mounted water depth measurement continuous frequency blue-green laser radar, characterized by Principle of the technical solution adopted: (1) The blue-green frequency conversion laser emits two beams of continuously frequency-converted blue-green lasers, namely the A laser emission signal and the C laser local oscillator signal; at the same time, the frequency domain and the time domain are matched to form a time-frequency diagram; (2) A laser beam is emitted to the water surface, and the reflected laser causes the laser echo signal to shift in frequency. The laser transmits through the water, reaches the bottom of the water, and then reflects the laser, causing the laser echo signal to shift in frequency, forming a B laser echo signal, which is collected by a high-speed laser acquisition processor; (3) Another C local oscillator laser signal is directly output to the high-speed laser acquisition processor, which performs a convolution operation on the C local oscillator laser signal and the B laser echo signal to obtain a convolution laser echo signal in the spatial domain; (4) Using fast Fourier transform, the convolution laser echo signal in the spatial domain is transformed into the convolution laser echo signal in the frequency domain to form an amplitude-frequency diagram, identify the frequency peaks of the water surface and the bottom, and calculate the frequency difference △f; (5) Based on the time-frequency diagram of (1), combined with the amplitude-frequency diagram, a time-frequency difference diagram is formed, and the time difference △t corresponding to the frequency difference △f is converted. According to the transmission speed of the laser in water, the distance the laser travels in the water is calculated to obtain the measured water distance (i.e., water depth slant distance); (6) Based on the motor encoder angle, the three attitude angles of POS and RTK positioning information, combined with the rotation matrix, the water depth slant range is converted into the actual water depth at the measurement position.

2. The drone-borne water depth measurement continuous frequency conversion blue-green laser radar as claimed in claim 1, characterized in that The radar consists of blue-green frequency conversion laser, laser power driver, encoder motor, reflective optical wedge, reflector, large lens, small lens, balanced light detection module, high-speed laser acquisition processor, IMU module, RTK module, 4G module, controller, 4G antenna, server and mobile phone terminal. Blue-green frequency conversion laser; after receiving the signal from the controller, the laser emits a 380-600nm blue-green frequency conversion laser with a peak power of 400Mw, a pulse width of 10μs, a divergence angle of less than 0.2mrad, and a Gaussian distribution from the center to the surroundings. A small amount of light is split by the beam splitter inside and transmitted to the photomultiplier tube to output the local oscillator laser signal; at the same time, the working status signal is transmitted to the controller at a frequency of 50Hz; Laser power driver: After receiving the signal from the controller, the driver configures the power module according to the laser parameters to provide a stable DC power supply for the laser, with a voltage of 24V and a current of 150-320mA; at the same time, it transmits a working status signal to the controller at a frequency of 30Hz; Encoder motor; after receiving the controller initialization command, the motor is immediately reset to zero and the motor angle is calculated from a fixed position; it is characterized by a 1000-line photoelectric encoder and a Hall sensor, a voltage of 24V, a speed of 3000R, a power of 64W, a constant force of 0.2NM, and an accuracy of 0.1NM; it transmits a working status signal to the controller at a frequency of 30Hz; Reflector; the reflector is at an angle of 45° to the laser, the substrate is silicon, the diameter is 3mm, the thickness is 3mm, it is gold-plated, and the reflectivity is >99.99%; it is characterized by a triangular disk fixed in the middle at the center of the large lens to reflect the laser beam to the reflective wedge; Reflective optical wedge; the optical wedge has a self-balancing function, and the center is 30° and 75° to the irradiated laser beam. When it is installed on the motor and rotates, the angle between the reflected laser beam and the upper part changes continuously between 30° and 75°, forming a circular trajectory with a scanning angle of 45°; Large lens; This lens is actually a double single lens with positive focal power, a clear aperture of 60mm, a focal length of 128mm, and a distance of 106.7mm from the small lens; It includes a double glued lens and a single lens; The double glued lens includes a convex lens and a concave lens; The single lens is a convex lens, using ZK7 glass with small dispersion; Small lens; the lens is actually a double cemented lens with negative optical power, a clear aperture of 10mm, and a focal length of -35.6mm; the double cemented lens includes a flint glass convex lens in front and a Burmese glass concave lens in the back; Balanced light detection module; the module has a spectral range of 380-1700nm, a bandwidth of 3dB, a response time of <0.2ns, a common mode rejection ratio of >30dB, and a voltage of 24V; at the same time, it sends data to the high-speed laser acquisition processor at a frequency of 30Hz, and sends working status signals to the controller at a frequency of 30Hz; High-speed laser acquisition processor; this processor is mainly used to collect the local oscillator laser signal transmitted by the blue-green light frequency conversion laser and the laser echo signal detected by the balanced light detection module, and perform convolution operation and fast Fourier transform on the two signals to obtain the frequency difference between the water surface and the bottom echo, convert it into the corresponding time difference, and combine the propagation speed of the laser in the water to obtain the water depth slant range, and substitute it into the rotation matrix together with the motor encoder angle, the three attitude angles of the IMU and the RTK positioning information, convert it into the actual water depth of the measured position, and transmit it to the controller; at the same time, send the working status signal to the controller at a frequency of 30Hz; IMU module; This module is mainly used to obtain the pitch angle, roll angle and yaw angle of the platform with a resolution of 0.01°; at the same time, it sends data and working status signals to the controller at a frequency of 200Hz; RTK module; This module is mainly used to obtain longitude and latitude information, with a horizontal accuracy better than 0.01m; at the same time, it sends data and working status signals to the controller at a frequency of 200Hz; 4G module: This module supports dual communication functions of 4G DTU and radio communication (up to 50km). When there is no 4G signal, it automatically switches to radio communication, sends instructions forwarded by the server, and transmits data and working status signals back to the server. Controller; This controller is used to initialize and control the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, and obtain the working status of these modules; 4G antenna; This antenna is used to enhance 4G signals and radio signals to more than 3dB; Server; the server has a fixed IP address, and the 4G module and the mobile phone are connected to the server through the IP address. The server then stores and forwards the data sent by the 4G module and the mobile phone, realizes the communication between the 4G module and the mobile phone, and realizes the mobile phone to remotely control the drone-borne water depth measurement continuous frequency conversion blue-green laser radar, and transmits the water depth data measured by the drone-borne water depth measurement continuous frequency conversion blue-green laser radar to the mobile phone in real time; Mobile phone: This mobile phone supports 4G and external wireless communication modules (paired with the 4G module radio communication of the laser radar). It is mainly responsible for connecting to the server, sending instructions to the drone-borne water depth measurement continuous frequency blue-green laser radar through the server in real time. The water depth data of the target position sent back is displayed on the mobile phone and stored.

3. The drone-borne water depth measurement continuous frequency conversion blue-green laser radar as claimed in claim 1, characterized in that Mounted on a drone, the working process is: (1) The user starts the drone-borne water depth measurement continuous frequency blue-green laser radar on the mobile phone, starts the signal server and 4G module to send to the controller, the controller starts each component of the laser radar, and obtains the working status signal of each component, and sends it back to the mobile phone for display; the controller issues a start command to the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc.; at the same time, the working status of the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module is obtained, and sent back to the mobile phone for display; (2) The blue-green frequency conversion laser supplies power to the blue-green frequency conversion laser, transmits a local oscillator laser signal to the high-speed laser acquisition processor, and also transmits a laser beam to the water surface; at the same time, it sends the status to the controller; (3) The encoder motor rotates according to the set parameters and starts scanning to obtain as much water area data as possible; at the same time, the rotation angle and working status are sent to the high-speed laser acquisition processor and controller respectively; (4) The balanced light detection module detects the received laser echo signal and transmits it to the high-speed laser acquisition processor; at the same time, it sends the working status to the controller; (5) The IMU module collects the pitch angle, roll angle and yaw angle of the platform and sends them to the high-speed laser acquisition processor; at the same time, it sends the working status to the controller; (6) The RTK module obtains longitude and latitude information and sends it to the high-speed laser acquisition processor; at the same time, it sends the working status to the controller; (7) The 4G module is connected to the mobile phone through the 4G signal and the server, and the latter is connected to the mobile phone through the radio signal; the server forwards the command to the drone-borne water depth measurement continuous frequency variable blue-green laser radar, which returns the data and working status signal to the mobile phone; (8) The high-speed laser acquisition processor collects the laser local oscillator signal and the laser echo signal, performs convolution, fast Fourier transform, frequency difference, and time difference operations, calculates the slant range and water depth, reads the motor angle, three attitude angle data, and positioning data, substitutes them into the rotation matrix, obtains the actual water depth of the target position, sends it to the controller, passes through the 4G module (and server), and transmits it back to the mobile phone for display, and stores the data in the mobile phone; (9) Repeat steps (2) to (8) until all water depth echo signals in the target area are detected; (10) The user turns off the drone-mounted water depth measurement continuous frequency blue-green laser radar on the mobile phone. The shutdown signal is sent to the controller through the 4G module, and the blue-green light frequency conversion laser, laser power driver, high-speed laser acquisition processor, encoder motor, balanced light detection module, IMU module, RTK module, 4G module, etc. are turned off in turn.

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