A laser radar rapid field of view self-correction transceiver system and its control and use method

Abstract

The present invention discloses a laser radar rapid field of view self-correction transceiver system and a control and use method thereof in the field of laser radar atmospheric detection technology, wherein the system is composed of a laser transmitter, a half-wave plate, a beam expander, a first-stage reflector, a second-stage reflector, and a Cassegrain telescope. The present invention uses a gradient descent method to achieve optimal online planning of a self-correction adjustment path based on the inherent optical characteristics of a conventional laser radar transceiver structure, and can control the laser emission axis online to maintain an optimal position matching the telescope receiving axis during the observation process, which not only greatly shortens the field of view angle adjustment time when the laser radar is first turned on, but also ensures the signal quality of the detection data during the long-term observation of the laser radar, wherein the angle adjustment speed of the two-dimensional piezoelectric adjustment frame is fast and the operation is simple, further ensuring the time efficiency of the adjustment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser radar atmosphere detection, and in particular relates to a laser radar rapid field of view self-correction transceiver system and a control and use method thereof. Background Art

[0002] LiDAR technology is an active optical remote sensing detection method with the advantages of wide detection range, high temporal and spatial resolution, high precision and good accuracy. It has been widely used in the field of environmental monitoring and plays an important role in environmental monitoring. The most common laser radar light-receiving and light-receiving path is off-axis, that is, the laser emission axis and the telescope receiving axis do not coincide. Due to the small field of view of the telescope, the atmospheric echo signal in the off-axis light-receiving and light-receiving path needs to reach a certain height before entering the field of view of the telescope. This also leads to a large field of view blind area in the off-axis laser radar. The farther the distance between the laser emission axis and the telescope receiving axis, the larger the field of view blind area will be, which will reduce the effective detection distance of the laser radar.

[0003] At the same time, as a precision optical instrument, the mechanical structure of the laser radar system's light receiving and light transmission path is easily affected by changes in the temperature, humidity and air pressure of the working environment in actual applications. The slight deformation of the mechanical structure of the light receiving and light transmission path will cause the laser emission axis to deviate, and eventually the laser emission axis will move out of the telescope's optimal receiving field of view, causing the quality of the atmospheric echo signal received by the laser radar system to deteriorate, which is specifically manifested in a lower detection limit distance of the laser radar system.

[0004] At present, the self-calibration technology of the laser radar receiving and transmitting field of view is still at the level of moving the laser emission axis along a fixed route to scan and judge the signal strength. The specific scanning strategies include spiral path scanning method and cross-path scanning method. The self-calibration process of the above strategies is time-consuming and inefficient. At the same time, due to the large scanning range of the above methods, it can only be implemented before each laser radar system is turned on for observation. During the scanning process, the signal quality will change dramatically. During the long-term and continuous observation of the laser radar system outdoors, the impact of changes in working environment conditions on the detection performance changes slowly. Therefore, implementing a field of view calibration after starting the machine cannot guarantee the quality of the atmospheric echo signal during the entire detection process. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a laser radar rapid field of view self-correction transceiver system and a control and use method thereof, so as to solve the problems raised in the above background technology.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A laser radar fast field of view self-correction transceiver system, the system is composed of a laser transmitter, a half-wave plate, a beam expander, a first-stage reflector, a second-stage reflector, and a Cassegrain telescope;

[0008] The initial emission axis of the laser transmitter is parallel to the receiving axis of the telescope. After the laser is emitted, the polarization state of the laser signal is first further purified by a half-wave plate, and then the divergence angle of the laser beam is compressed by a beam expander. After the expanded laser signal passes through the first-stage reflector, the laser emission axis and the telescope receiving axis are orthogonal at 90°. Finally, the laser emission axis is rotated 90° again by a second-stage reflector installed on the secondary mirror mounting frame of the Cassegrain telescope. At this time, the laser emission axis will coincide with the receiving axis of the telescope and be emitted into the atmosphere. The atmospheric back echo signal received by the Cassegrain telescope will continue to enter the optical processing module of the next stage for further optical processing and photoelectric conversion.

[0009] Preferably, the second-stage reflector is composed of a piezoelectric adjustment frame and a dielectric film reflector, the dielectric film reflector assembly is mounted on the secondary mirror support frame of the Cassegrain telescope at an inclination angle of 45°, the receiving axis of the Cassegrain telescope passes through the center of the second-stage reflector, and the laser emission axis is made to coincide with the receiving axis of the Cassegrain telescope by adjusting the inclination angle of the piezoelectric adjustment frame;

[0010] The piezoelectric adjustment frame is composed of a two-dimensional mirror frame and a piezoelectric rotary motor. The piezoelectric adjustment frame is remotely controlled by a host computer through a serial port, and the current absolute rotation angle of the adjustment axis is returned to the host computer through the serial port. The step resolution of the piezoelectric rotary motor is 0.7 μrad, and the adjustment range of the piezoelectric adjustment frame is ±7°.

[0011] A method for controlling and using a laser radar rapid field of view self-correction transceiver system, the method comprising the following steps:

[0012] Step 1: After the LiDAR is turned on, perform detection and record the initial angles of the two piezoelectric rotary motors of the two-dimensional piezoelectric adjustment frame.

[0013] Step 2: Control two piezoelectric rotary motors to increase degrees, and calculate the adjustment axis angle The atmospheric echo signal quality characteristic value z under

[0014] Step 3: Ask Model and by judging Is it less than the set value? To determine whether the optimal position is reached;

[0015] Step 4: If the optimal position is not reached, update the angle of the piezoelectric rotary motor for the next step Repeat steps 2 to 3 until Less than the set value.

[0016] Preferably, the calculation formula of the signal quality characteristic value z is:

[0017]

[0018] Where P a , P b are the squared distance-corrected signal strength values ​​of point a and point b, respectively, and H a , H b are the heights corresponding to point a and point b respectively, and H a <H b ; The distances corresponding to the selected points a and b are above the distance where the field of view overlap factor is greater than 1, and the atmospheric echo signal will completely enter the telescope receiving field of view. The signal strength above the heights of points a and b is only affected by the matching state of the transmitting and receiving axes.

[0019] Preferably, the gradient at the current time t is By finding f at point The lower partial derivative is:

[0020]

[0021] In the formula, the numerical solution formulas for the partial derivatives in the x and y directions are as follows:

[0022]

[0023]

[0024]

[0025]

[0026] The angle of the piezoelectric rotary motor at the next moment t+1 The formula is as follows:

[0027]

[0028]

[0029] Where η is the learning rate, which is used to control the angle control rate of the piezoelectric rotary motor.

[0030] Preferably, the Model The calculation formula is as follows:

[0031]

[0032] Beneficial effects of the present invention:

[0033] The present invention uses the gradient descent method to achieve optimal online planning of the self-correction adjustment path based on the inherent optical characteristics of the conventional laser radar transceiver structure, and can control the laser emission axis online to maintain the optimal position matching the telescope receiving axis during the observation process. This not only greatly shortens the field of view angle adjustment time when the laser radar is first turned on, but also ensures the signal quality of the detection data during the long-term observation of the laser radar. The two-dimensional piezoelectric adjustment frame has a fast angle adjustment speed and simple operation, which further ensures the time efficiency of the adjustment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 It is a schematic diagram of the structure of the laser radar rapid field of view self-correction transceiver system of the present invention;

[0036] Figure 2 is a flow chart of the control and use method of the present invention;

[0037] Figure 3 It is a schematic diagram of the slope of the laser radar echo profile fitting of the present invention;

[0038] Figure 4 It is a schematic diagram of the parameter space of the laser radar signal quality index of the present invention;

[0039] Figure 5 It is a schematic diagram of the rapid field of view self-correction adjustment process of the laser radar of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] See also Figure 1 As shown, the present invention proposes a laser radar rapid field of view self-correction transceiver system, which is composed of a laser transmitter 1, a half-wave plate 2, a beam expander 3, a first-stage reflector 4, a second-stage reflector 5, and a Cassegrain telescope 6.

[0042] The fast field of view self-correction light receiving and receiving circuit is mainly used to guide the laser signal to be emitted from the telescope receiving axis into the atmosphere, wherein the initial emission axis of the laser transmitter 1 is parallel to the telescope receiving axis. After the laser is emitted, the polarization state of the laser signal is further purified by the half-wave plate 2, and then the laser beam divergence angle is compressed by the beam expander 3 to achieve the effect of concentrating the laser energy. After the beam expansion, the laser signal passes through the first-stage reflector 4, and the laser emission axis and the telescope receiving axis are orthogonal to each other by 90°. Finally, the laser emission axis is rotated 90° again by the second-stage reflector 5 installed on the secondary mirror mounting frame of the Cassegrain telescope 6. At this time, the laser emission axis will coincide with the telescope receiving axis and emit into the atmosphere. The atmospheric back echo signal received by the Cassegrain telescope 6 will continue to enter the optical processing module of the next stage for further optical processing and photoelectric conversion.

[0043] The second-stage reflector 5 is composed of a piezoelectric adjustment frame and a dielectric film reflector. The reflector assembly is placed and installed on the secondary mirror support frame of the telescope at an inclination angle of 45°. At this time, the receiving axis of the telescope will pass through the center of the second-stage reflector 5. By fine-tuning the inclination angle of the piezoelectric adjustment frame, the laser emission axis can be made to coincide with the telescope receiving axis.

[0044] The piezoelectric adjustment frame is composed of a two-dimensional mirror frame and a piezoelectric rotary motor, wherein the piezoelectric rotary motor is used to replace the mechanical rotating structure on the conventional two-dimensional mirror frame, and the piezoelectric effect can be used to achieve a rotation angle with a resolution of 0.7 μrad, and the inclination angle of the two-dimensional mirror frame can be adjusted more precisely. In the actual engineering application of the present invention, the adjustment range of the piezoelectric adjustment frame is ±7°.

[0045] See also Figure 2 As shown, based on the above-mentioned laser radar rapid field of view self-correction transceiver system, the following control method is proposed to achieve rapid field of view self-correction, and the control method is implemented through two sub-steps: the first step is the self-calibration of the field of view angle parameters implemented before the laser radar observes, and the second step is the self-correction of the transceiver field of view implemented during the observation process.

[0046] The specific process is as follows:

[0047] Step 1: Turn on the laser radar for detection and record the initial angles of the two piezoelectric rotary motors of the two-dimensional piezoelectric adjustment frame The deflection angle of the deflection reflector is achieved by changing the angle of the piezoelectric rotary motor, thereby changing the direction of the emitted laser;

[0048] Step 2: Control two piezoelectric rotary motors to increase degrees, and calculate the adjustment axis angle The atmospheric echo signal quality characteristic value z under

[0049] Step 3: Ask Model and by judging Is it less than the set value? To determine whether the optimal position is reached;

[0050] Step 4: If the optimal position is not reached, update the angle of the piezoelectric rotary motor for the next step Repeat steps 2 to 3 until Less than the set value.

[0051] Among them, there are more than one evaluation method for the signal quality characteristic value z, and the method used in this article is:

[0052] After correcting the atmospheric echo signal by the square of the distance, two points a and b are selected on the echo signal curve, and the calculation formula of the characteristic value z is:

[0053]

[0054] Where P a , P b are the squared distance-corrected signal strength values ​​of point a and point b, respectively, and H a , H b are the heights corresponding to point a and point b respectively, and H a <H b .

[0055] The selection requirements for points a and b are as follows: the distance corresponding to the selected points needs to be above the distance where the field of view overlap factor is greater than 1. Under ideal conditions, the atmospheric echo signal will completely enter the telescope's receiving field of view. At the same time, assuming that the atmospheric conditions change smoothly in a short period of time, the signal strength above this height is relatively only affected by the matching state of the transmitting and receiving axes.

[0056] In practical applications, the vector space of the signal quality z corresponding to the two piezoelectric adjustment axes at different angles is as follows: Figure 3 As shown, the vector space satisfies the definition of a strongly convex function: for any convex set Signal quality index z(θ x ,θ y ) is defined in D, and z x (θ x ,θ y ) and z y (θ x ,θ y ) exists at every point on D. Assume that for any two points (θx1,θy1) and (θx2,θy2) in D, we have:

[0057] z(θ x2 ,θ y2 )≥z(θ x1 ,θy1 )+z x (θ x1 ,θ y1 )(θ x1 -θ x2 )+z y (θ x1 ,θ y1 )(θ y1 -θ y2 ) (2)

[0058] Convex optimization problems in vector space can be solved using gradient descent, such as Figure 5 As shown, the rate of change of the index will reach the maximum along the gradient direction, and the moving step length is iteratively calculated along the gradient direction, which can converge to the extreme point of the vector space at a faster speed.

[0059] The gradient at the current time t By finding f at point The vector obtained by the partial derivative is:

[0060]

[0061] Among them, the numerical solution method for the partial derivatives in the x and y directions is:

[0062]

[0063]

[0064]

[0065]

[0066] The angle of the piezoelectric rotary motor at the next moment t+1 The update formula is:

[0067]

[0068]

[0069] Where η is the learning rate, which is used to control the angle control rate of the piezoelectric rotary motor;

[0070] Model The calculation formula is as follows:

[0071]

[0072] The pseudo code of the laser radar receiving and transmitting field of view fast self-correction algorithm based on the gradient descent method is as follows:

[0073] Input: Initial angles of the two piezoelectric rotary motors Learning rate η; optimal field of view angle determination condition

[0074] process:

[0075] 1: Randomly select the angle increment of the piezoelectric rotary motor at time t0

[0076] 2: Calculate the time t0 using formula (3)

[0077] 3: Update the angle of the piezoelectric rotary motor at time t using formulas (8) and (9)

[0078] 3: repeat

[0079] While

[0080] Calculate the time t by formula (3)

[0081] Update the piezoelectric rotary motor angle at time t+1 using formulas (8) and (9):

[0082] end for

[0083] until the stopping condition is reached

[0084] Output: The angle of the piezoelectric rotary motor corresponding to the optimal field of view

[0085] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0086] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A control and use method based on a laser radar rapid field of view self-correction transceiver system, characterized in that: The system is composed of a laser transmitter (1), a half-wave plate (2), a beam expander (3), a first-stage reflector (4), a second-stage reflector (5), and a Cassegrain telescope (6); The initial emission axis of the laser transmitter (1) is parallel to the receiving axis of the telescope. After the laser is emitted, the polarization state of the laser signal is first further purified by a half-wave plate (2), and then the divergence angle of the laser beam is compressed by a beam expander (3). After the laser signal after beam expansion passes through a first-stage reflector (4), the laser emission axis and the telescope receiving axis are in an orthogonal state of 90°. Finally, the laser emission axis is rotated 90° again by a second-stage reflector (5) installed on a secondary mirror mounting frame of a Cassegrain telescope (6). At this time, the laser emission axis will coincide with the receiving axis of the telescope and be emitted into the atmosphere. The atmospheric back echo signal received by the Cassegrain telescope (6) will continue to enter the optical processing module of the next stage for further optical processing and photoelectric conversion. The second-stage reflector (5) is composed of a piezoelectric adjustment frame and a dielectric film reflector, the dielectric film reflector assembly is mounted on a secondary mirror support frame of a Cassegrain telescope (6) at an inclination angle of 45°, the receiving axis of the Cassegrain telescope (6) passes through the center of the second-stage reflector (5), and the laser emission axis is made to coincide with the receiving axis of the Cassegrain telescope (6) by adjusting the inclination angle of the piezoelectric adjustment frame; The piezoelectric adjustment frame is composed of a two-dimensional mirror frame and a piezoelectric rotary motor. The piezoelectric adjustment frame is remotely controlled by a host computer through a serial port, and returns the current absolute rotation angle of the adjustment axis to the host computer through the serial port. The step resolution of the piezoelectric rotary motor is 0.7 μrad, and the adjustment range of the piezoelectric adjustment frame is ±7°. The control method comprises the following steps: Step 1: After the LiDAR is turned on, perform detection and record the initial angles of the two piezoelectric rotary motors of the two-dimensional piezoelectric adjustment frame. Step 2: Control two piezoelectric rotary motors to increase a certain angle And calculate the adjustment axis angle The atmospheric echo signal quality characteristic value z under Step 3: Ask Model and by judging Is it less than the set value? To determine whether the optimal position is reached; Step 4: If the optimal position is not reached, update the angle of the piezoelectric rotary motor for the next step Repeat steps 2 to 3 until Less than the set value; The calculation formula of the signal quality characteristic value z is: Where P a , P b are the squared distance-corrected signal strength values ​​of point a and point b, respectively, and H a , H b are the heights corresponding to point a and point b respectively, and H a <H b ; The distances corresponding to the selected points a and b are above the distance where the field of view overlap factor is greater than 1, and the atmospheric echo signal will completely enter the telescope receiving field of view. The signal strength above the heights of points a and b is only affected by the matching state of the transmitting and receiving axes.

2. According to claim 1, a control and use method based on a laser radar rapid field of view self-correction transceiver system is characterized in that: The gradient at the current time t By finding f at point The lower partial derivative is: In the formula, the numerical solution formulas for the partial derivatives in the x and y directions are as follows: The angle of the piezoelectric rotary motor at the next moment t+1 The formula is as follows: Where η is the learning rate, which is used to control the angle control rate of the piezoelectric rotary motor.

3. The control and use method of the laser radar rapid field of view self-correction transceiver system according to claim 1 is characterized in that: Said Model The calculation formula is as follows:

Images