Calibration Method and Device for LiDAR System

Abstract

The present invention belongs to the technical field of lidar ranging, and particularly relates to a calibration method and device for a lidar system. It overcomes the technical problems of low accuracy, high cost, low efficiency existing in the existing calibration methods, and the inability to be applicable to the lidar with a coaxial optical system. The calibration system includes a calibration platform, a standard reflector, a pulsed laser emission light source and a lidar to be calibrated which are placed in parallel on the calibration platform. By using an external pulsed laser emission light source, a laser pulse is emitted, which hits the standard reflector, and the lidar to be calibrated receives the echo light energy reflected back. Through control, after each laser pulse is emitted, whether it is a coaxial or non-coaxial optical system, as many echo electrical signals with different intensities as possible can be quickly obtained. During the calibration process, the echo pulse width is used as a characteristic point to classify the echo electrical signals, and different time compensation values are calculated for the time values of different categories of echo electrical signals, so as to achieve higher calibration accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of lidar ranging, and particularly relates to a lidar calibration method and device. Background Art

[0002] A lidar detects the position, displacement and other characteristics of a target by emitting laser light to the target and processing the reflected light signal of the target. The lidar can quickly and accurately obtain the spatial information of surrounding objects. Since the intensities of the reflected light signals (hereinafter referred to as "echo signals") generated by objects at different distances and with different reflectivities are different, when the processor processes the echo signals, there is an uncertain difference between the distances calculated from the echo signals of different intensities and the true distances. In order to obtain accurate ranging values under various conditions, it is necessary to calibrate the lidar. Accurate calibration is beneficial to improving the ranging accuracy of the lidar and ensuring the reliability of the lidar operation.

[0003] Existing lidar calibration methods usually require multiple standard reflectors or a special reflector with multiple reflectivity regions for calibration to obtain sufficient reflected light information of different intensities. Using the above types of reflectors for calibration requires changing the reflectors and the relative positions between the reflectors and the lidar many times, and the amount of data obtained is limited, resulting in low calibration accuracy, low calibration efficiency and high cost.

[0004] Patent CN109001713A proposes a calibration system that uses a baffle to block the laser beam emitted by the lidar to adjust the energy of the emitted laser, so that the lidar receiving system can obtain echo energies of various different intensities. This method does not require changing the reflector or the relative position between the reflector and the lidar many times, achieving the effect of simplifying the calibration process. However, this method is applicable to an off-axis lidar with independent transmitting and receiving windows, and has defects for a coaxial lidar with a shared transmitting and receiving window: when the baffle blocks part of the transmitting window, it is equivalent to blocking both the transmitting and receiving windows at the same time, and the laser energy blocked at the baffle will be directly received by the receiving optical path and then converted into an echo signal, affecting the judgment of the true echo signal of the object to be measured and resulting in low calibration accuracy.

[0005] Therefore, it is necessary to provide a lidar calibration system and method with high accuracy, low cost, high efficiency, and applicable to both coaxial and off-axis optical systems. Summary of the Invention

[0006] The object of the present invention is to provide a calibration method and device applicable to lidar systems of coaxial and off-axis optical systems, so as to overcome the technical problems of low accuracy, high cost, low efficiency and inapplicability to coaxial optical system lidars existing in the existing calibration methods.

[0007] The technical solution of the present invention is to provide a calibration method for a lidar system, which is characterized in that it includes the following steps:

[0008] Step 1: Determine the lidar ranging formula;

[0009]

[0010] Among them, formula (1) is for unsaturated echo signals, formula (2) is for saturated echo signals with a pulse width less than the demarcation value, and formula (3) is for saturated echo signals with a pulse width greater than or equal to the demarcation value;

[0011] Among them, y is the distance between the lidar and the object, a is the actual laser propagation speed, b is the circuit delay, Δ t is equal to (t2 - t1) / 2, t1 is the moment when the pulsed laser emission light source emits a laser pulse, t2 is the peak moment point of the echo signal calculated by the lidar system processor; C1 is (t3 - t2) / 2, t3 is the true echo peak moment point of the saturated echo signal; Δ t ' is (t4 - t1) / 2, t4 is the rising edge moment point of the saturated echo signal calculated by the lidar system processor, and c2 is (t3 - t4) / 2;

[0012] Step 2: Calibrate C1 and C2;

[0013] Step 2.1: System setup;

[0014] Place the pulsed laser emission light source and the lidar to be calibrated in parallel on the calibration platform; place a standard reflector at a fixed known distance from the calibration platform;

[0015] Step 2.2: Obtain echo signals of different intensities;

[0016] The pulsed laser emission light source emits a laser pulse, which hits the standard reflector and the reflected light energy is received by the lidar to be calibrated;

[0017] Adjust the laser pulse or control the rotation of the internal rotating components of the lidar to be calibrated, so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, and thus obtains echo signals of different intensities;

[0018] Step 2.3: Classify and process the echo signals of different intensities to obtain a relationship list of C1 and C2 corresponding one-to-one to the pulse width of the saturated echo signal;

[0019] Step 3: Calibrate a and b;

[0020] Calibrate a and b in the lidar ranging formula to complete the calibration.

[0021] Furthermore, step 2.3 specifically includes the following steps:

[0022] Step 2.31: Determine the true peak time point of the unsaturated echo signal;

[0023] Take the echo peak time point calculated by the lidar system processor as the true peak time point of the unsaturated echo signal;

[0024] Step 2.32: Determine the true peak time point of the saturated echo signal;

[0025] Step 2.321: Take the true peak time point of the unsaturated echo signal determined in step 2.31 as the reference time point;

[0026] Step 2.322: For saturated echo signals with different pulse widths, calculate the difference between the echo signal time point calculated by the processor and the reference time point as the time compensation value; where the echo signal time point is the peak time point or rising edge time point of the echo signal;

[0027] Step 2.323: Store the pulse widths of different saturated echo signals and the corresponding time compensation values in the lidar internal memory as a calibration parameter table; that is, obtain a relationship list of C1 and C2 corresponding one-to-one with the saturated echo signal pulse width; realize the calibration of C1 and C2.

[0028] Furthermore, in step 2.1, the reflectivity of the standard reflector is greater than 95%.

[0029] Furthermore, to improve accuracy, in step 2.31, select the echo peak time points of multiple unsaturated echo signals, calculate their average time point, and take this average time point as the true peak time point of the unsaturated echo signal.

[0030] Furthermore, in step 2.2, adjust the laser pulse so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, and thus obtains echo signals of different intensities. Specifically:

[0031] Adjust the pulsed laser emission light source to emit laser pulses at different emission angles, so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, and thus obtains echo signals of different intensities;

[0032] Or,

[0033] By setting baffles in the emission optical path to block part of the laser pulses or the receiving window area, so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, and thus obtains echo signals of different intensities.

[0034] Further, step 3 is specifically as follows:

[0035] By measuring the peak time points of the standard reflector at different known distances from the radar, several sets of corresponding Δ t 、Δ t +c1 and the distance y are obtained, and the relationship curves of Δ t 、Δ t +c1 and y are fitted, and then a and b in y = aΔ t +b and y = a(Δ t +c1)+b can be determined;

[0036] By measuring the rising edge time points of the standard reflector at different known distances from the radar, several sets of corresponding Δ t '+c2 and the distance y are obtained, and the relationship curves of Δ t '+c2 and y are fitted, and then a and b in y = a(Δ t '+c2)+b can be determined.

[0037] The present invention also provides a calibration device for a lidar system, which is characterized in that it includes a calibration platform, a pulsed laser emission light source and a lidar to be calibrated placed in parallel on the calibration platform, and a standard reflector placed at a fixed known distance from the calibration platform.

[0038] Further, in order to obtain an echo signal with as large a saturation degree as possible, the reflectivity of the standard reflector is greater than 95%.

[0039] Further, the calibration device further includes a slide rail, the calibration platform is placed on the slide rail and can move along the slide rail; the standard reflector is in i groups, where i is a positive integer greater than or equal to 2; the i groups of standard reflectors are parallel to the slide rail and are arranged at different distances from the slide rail in sequence along the length direction of the slide rail; so that when the lidar to be calibrated moves along the slide rail, the emitted laser can hit the standard reflectors at different distances.

[0040] Further, the calibration device may further include a slide rail, the calibration platform is placed on the slide rail and can move along the slide rail; the standard reflector is in 1 group, perpendicular to the slide rail, and is placed in the emission optical path of the emitted laser, so that when the lidar to be calibrated moves along the slide rail, the emitted laser can hit the standard reflector.

[0041] Further, the calibration device may further include an electric baffle disposed in front of the pulsed laser emission light source or in front of the lidar to be calibrated, and the received light energy is adjusted by blocking the emission light source or the area of the receiving window.

[0042] The beneficial effects of the present invention are:

[0043] The calibration system of the lidar system of the present invention uses an external pulsed laser emission light source to emit laser pulses, which hit a standard reflector, and the lidar to be calibrated receives the returned echo light energy; by adjusting the laser pulses or controlling the rotation of the internal rotating components of the lidar to be calibrated, so that after each laser pulse is emitted, whether it is a coaxial optical system or an off-axis optical system, as many echo electrical signals with different intensities as possible can be obtained conveniently and quickly, and during the calibration process, the echo electrical signals are classified with the echo pulse width as the characteristic point, and different time compensation values are calculated for the time values of different categories of echo electrical signals to achieve higher calibration accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is the signal processing process of lidar emission and reception;

[0045] Figure 2 is the emission pulse signal and the unsaturated echo pulse signal;

[0046] Figure 3 is the emission pulse signal and the saturated echo pulse signal;

[0047] Figure 4 is a schematic diagram of the calculation method of a and b;

[0048] Figure 5 is a schematic diagram of the calibration device Figure 1 ;

[0049] In the figure, the reference numerals are: 1 - pulsed laser emission light source, 2 - lidar to be calibrated, 3 - calibration platform;

[0050] Figure 6 is the first scheme of the lidar calibration system composition (calibrating a, b);

[0051] In the figure, the reference numerals are: 2 - lidar to be calibrated, 4 - slide rail, 51 - first standard reflector, 52 - second standard reflector, 53 - third standard reflector, 54 - fourth standard reflector, 55 - fifth standard reflector;

[0052] Figure 7 is the second scheme of the lidar calibration system composition (calibrating a, b);

[0053] In the figure, the reference numerals are: 2 - lidar to be calibrated, 4 - slide rail, 5 - standard reflector;

[0054] Figure 8 is the emission pulse signal and the echo pulse signal with a larger saturation degree;

[0055] Figure 9 is the optical path transceiver schematic diagram of Embodiment 3;

[0056] Figure 10 Schematic diagram of the calibration device Figure 2 ;

[0057] In the figure, the reference numerals are: 1 - pulsed laser emission light source, 2 - lidar to be calibrated, 3 - calibration platform, 6 - electrically controlled baffle plate. Specific implementation manners

[0058] To make the above objects, features and advantages of the present invention more obvious and understandable, the specific implementation manners of the present invention will be described in detail below with reference to the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0059] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0060] Embodiment 1

[0061] The calibration device used in this embodiment is as Figure 5 shown. A pulsed laser emission light source 1 and a lidar 2 to be calibrated are placed in parallel on the calibration platform 3. A standard reflector is placed at a fixed known distance from the calibration platform 3, and the reflectivity of the standard reflector is generally greater than 95%. The pulsed laser emission light source emits laser pulses at a set frequency, hits the standard reflector, and the backscattered light energy is received by the lidar to be calibrated. Since there are rotating components in the optical path of the lidar to be calibrated, different backscattered energies can be received.

[0062] The ranging principle of the lidar is the time-of-flight method, that is: after the laser pulse hits the object to be measured, the reflected optical signal is received by the photodetector and converted into an electrical signal that can be recognized by the processor through a circuit. The time from the emission of the laser pulse to the reception of the reflected optical signal is the round-trip time of the laser pulse once, divided by 2 is the one-way time for the laser pulse to reach the object to be measured, and then the distance from the lidar to the object to be measured is calculated according to "distance = time * speed". As Figure 1The following is a simple schematic of the laser radar transmitting and receiving signal processing process. The signal processor can be an FPGA, an SOC, or other integrated circuits with data operation capabilities. The signal processor controls an external laser emission light source (laser) through a laser drive circuit, enabling it to emit pulsed laser light according to a preset pulse width and frequency. The reflected light generated after the laser hits the object to be measured, i.e., the echo light, is received by a photodetector, generating a weak pulsed photocurrent signal. The pulsed photocurrent signal is converted into an easily recognizable pulsed voltage signal through a signal amplification circuit. The analog-to-digital converter samples the pulsed voltage signal, converts the sampled analog voltage data into a digital signal, and sends it to the signal processor. The signal processor processes and operates on the digital signal output by the analog-to-digital converter, can obtain the peak time point of the echo signal, and calculates the final distance value through calculation.

[0063] As Figure 2 shown, the signal processor emits a laser pulse P1 at time t1. At time t2, after the laser pulse hits the standard reflector, t2 is the peak time of the echo signal P2 generated by the reflected light, and t2 is calculated by the signal processor. The ranging formula of the lidar is:

[0064] y = aΔ t + b (1)

[0065] where a is the actual laser propagation speed, Δ t is (t2 - t1) / 2, and b is the circuit delay. Due to factors such as air density, temperature, humidity, etc., the value of a needs to be specifically determined through calibration. Δ t is directly calculated by the processor. The circuit delay b is affected by many factors such as circuit structure and also needs to be determined through calibration.

[0066] For targets with different test distances and different reflectivities, the measured echo light energy is inconsistent. Limited by the circuit, when the echo energy is high, the echo signal will reach the saturation state. As Figure 3 shown, a laser pulse P1 is emitted at time t1. At time t3 is the peak time of the real echo signal, and at time t2 is the peak time of the echo signal P2 calculated by the signal processor. If t2 is directly used as the peak time of the echo signal, a large ranging error will be introduced, and this error increases with the increase in the saturation degree of the echo signal. Therefore, the present invention provides a method to find the real echo peak time t3 according to t2 and the pulse width of the echo signal, that is, when the echo signal is saturated, different time compensation values c1 are obtained according to different echo signal pulse widths. Therefore, when using formula (1) to calculate the distance between the lidar and the object to be measured, it is necessary to compensate the flight time of the light, that is:

[0067] y = a(Δ t + c1)+ b (2)

[0068] In order to obtain more accurate compensation values for saturated echo signals with various pulse widths, it is necessary to collect a large number of echo signals with various saturation levels. The method adopted in this embodiment is as follows: At a fixed position on the distance calibration platform, a standard reflector is placed. In order to obtain an echo signal with as large a saturation level as possible, the reflectivity of the reflector is greater than 95%. The pulsed laser emission light source emits laser pulses continuously at a fixed frequency, and at the same time, the rotating components inside the lidar to be calibrated operate normally to obtain echo signals with different amplitudes, including unsaturated echo signals and saturated echo signals with various degrees. Among them, for the unsaturated echo signal, the echo peak time point t3 can be directly calculated by the signal processor, and t3 is the true echo peak time point. To improve accuracy, an average operation can be performed on t3 of the unsaturated echo signal. For the saturated echo signal, the pulse width and t2 of each echo signal can be obtained. Therefore, through calculation, the time compensation value c1 corresponding to the saturated echo signal with different pulse widths can be obtained, and c1 = (t3 - t2) / 2.

[0069] According to the minimum resolution of the processor for collecting echo signals, for the unsaturated echo pulse width, the corresponding c1 = 0. For each saturated echo pulse width, its time compensation value c1 is calculated, and finally a one-to-one correspondence list between the echo pulse width and the time compensation value is obtained. This parameter table is stored in the internal memory of the lidar, and the lidar reads the parameters in real time during distance calculation.

[0070] The method for calibrating a and b is as follows: Measure the echo time points of objects at different known distances from the radar to obtain several groups of corresponding Δ t + c1 and distances y, and fit the relationship curve between Δ t + c1 and y to determine a and b. By calibrating at least two distances, the values of a and b can be obtained. However, to improve the data accuracy, multiple distances can be calibrated to improve the fitting accuracy. Suppose a total of 5 standard reflectors are placed. After 5 measurements, 5 groups of Δ t + c1 and y are obtained, which are (Δ t 1, y1), (Δ t 2, y2), (Δ t 3, y3), (Δ t 4, y4), (Δ t 5, y5). As Figure 4 shown, by performing a linear fit on the 5 groups of data, the values of a and b can be obtained. There are various ways to adjust the distance between the radar and the object to be measured. Figure 6One of the ways is shown as follows: The lidar 2 to be calibrated is placed on the slide rail 4 for horizontal movement. At different positions perpendicular to its moving direction, a plurality of standard reflectors are placed, namely: the first standard reflector 51, the second standard reflector 52, the third standard reflector 53, the fourth standard reflector 54, and the fifth standard reflector 55; so that when the lidar moves horizontally, the emitted laser can hit the standard reflectors at different distances. Figure 7 Another way to adjust the distance between the lidar and the object to be measured is shown as follows. Only one standard reflector 5 is used, and by controlling the distance of the lidar 2 to be calibrated moving back and forth along the slide rail 4, the distance between the lidar 2 to be calibrated and the standard reflector 5 is adjusted. The deployment methods of the two devices are different, but the data processing methods are the same.

[0071] Embodiment 2

[0072] The calibration device used in this embodiment is exactly the same as that in Embodiment 1, but different processing methods are proposed for calibration data acquisition and processing. Refer to Figure 8 , when the echo signal is too saturated, limited by the circuit structure, the echo pulse width does not change significantly with the echo energy, and the trailing edge of the echo pulse jitters greatly. If the calibration is still performed on the peak moment point of the echo light, the accuracy of the calibration parameters will decrease. However, when the echo signal is too saturated, the rising edge of the echo signal is very stable, and it is more suitable to use the rising edge moment point for calibration. The rising edge moment point is obtained by the signal processor through threshold judgment. At this time, it is necessary to measure the rising edge flight time compensation parameter. At this time, the ranging formula is:

[0073] y = a(Δ t '+ c2) + b (3)

[0074] where Δ t ' is (t4 - t1) / 2, t4 is the rising edge moment point of the echo signal, and c2 is the rising edge flight time compensation value (t3 - t4) / 2.

[0075] In actual calibration applications, peak moment point compensation or rising edge moment point compensation can be adopted according to needs. When the echo pulse width is small, the peak moment point compensation method has higher accuracy; when the echo pulse width is large, the rising edge moment point compensation method has higher accuracy. Therefore, when calibrating, a reasonable echo pulse width demarcation value can be selected. When the actually measured pulse width is less than the demarcation value, the peak moment point compensation method is used, and when the pulse width is greater than the demarcation value, the rising edge moment point compensation method is used. To sum up, the lidar ranging calibration formula is obtained:

[0076]

[0077] Among them, formula (1) is for unsaturated echo signals, formula (2) is for saturated echo signals with a pulse width less than the demarcation value, and formula (3) is for saturated echo signals with a pulse width greater than or equal to the demarcation value.

[0078] Embodiment 3

[0079] The calibration device used in this embodiment is exactly the same as that in Embodiment 1. Among them, the pulsed laser emission light source changes from emitting light at a single angle to emitting light at multiple angles, and the rotating component inside the lidar to be calibrated is in a non-operating state. That is, by changing the emission light direction, the purpose of adjusting the received reflected light energy is achieved. Refer to Figure 9 , taking the emission light angle of the pulsed laser emission light source as -2° - 2° as an example, when the laser hits different positions on the reflector, is reflected by the reflector into the receiving optical path, and finally forms an image on the photodetector, due to different incident light angles, the imaging positions of the light spots at different positions on the photodetector are different. The reflected light formed by the 0° emission light can be completely imaged on the photodetector, and as the offset angle of the emission light increases, only part of the light spots can be imaged on the photodetector, that is, as the emission light angle increases, the received echo light energy by the photodetector gradually decreases. In this way, different echo light energies can be obtained. The calculation method is the same as that in Embodiment 1 and Embodiment 2.

[0080] Embodiment 4

[0081] Refer to Figure 10 . The calibration device used in this embodiment is: a pulsed laser emission light source 1 and a lidar 2 to be calibrated are placed in parallel on the calibration platform 3. An electric baffle 6 is placed in front of the pulsed laser emission light source 1 or in front of the lidar 2 to be calibrated, and the received light energy is adjusted by blocking the emission light source or the area of the receiving window. The rotating component inside the lidar to be calibrated does not need to work, and the center of the radar receiving field of view is parallel to the center of the emission field of view of the pulsed laser emission light source, so that different echo light energies can be received. The echo light energy is received by the receiving optical path of the lidar to be calibrated and converted into an electrical signal recognizable by the processor, and then the compensation value is calculated. The calculation steps can refer to Embodiment 1 and Embodiment 2.

[0082] After calculating the flight time compensation value, the compensation parameters are stored in the internal memory of the lidar. For the next calibration of a and b, an external emission light source can be continued to be used to calculate the values of a and b through multi-distance measurement, or the external laser emission light source can be turned off, and the self-emission light source of the lidar to be calibrated can be used to emit laser pulses and process the echo signals, and record multiple different known distances of Δ t , and calculate the values of a and b.

Claims

1. A calibration method for a lidar system, characterized in that, It includes the following steps: Step 1: Determine the ranging formula of the lidar. Among them, formula (1) is for unsaturated echo signals, formula (2) is for saturated echo signals with pulse widths less than the demarcation value, and formula (3) is for saturated echo signals with pulse widths greater than or equal to the demarcation value. Among them, y is the distance between the lidar and the object, a is the actual laser propagation speed, b is the circuit delay, Δ t equals (t2 - t1) / 2, t1 is the moment when the pulsed laser emission light source emits a laser pulse, t2 is the peak moment point of the echo signal calculated by the lidar system processor; C1 is (t3 - t2) / 2, representing the time compensation value corresponding to the saturated echo signal of different pulse widths, t3 is the true echo peak moment point of the saturated echo signal; Δ t ' is (t4 - t1) / 2, t4 is the rising edge moment point of the saturated echo signal calculated by the lidar system processor, c2 is (t3 - t4) / 2, representing the rising edge flight time compensation value; Step 2: Calibrate C1 and C2. Step 2.1: System setup. Place the pulsed laser emission light source and the lidar to be calibrated in parallel on the calibration platform; place a standard reflector at a fixed known distance from the calibration platform. Step 2.2: Obtain echo signals of different intensities. The pulsed laser emission light source emits laser pulses, which hit the standard reflector, and the lidar to be calibrated receives the reflected echo light energy. Adjust the laser pulses or control the rotation of the internal rotating components of the lidar to be calibrated so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, thereby obtaining echo signals of different intensities. Step 2.3: Classify and process the echo signals of different intensities to obtain a relationship list of C1 and C2 corresponding one-to-one with the pulse widths of the saturated echo signals. Step 3: Calibrate a and b. Calibrate a and b in the lidar ranging formula to complete the calibration.

2. The calibration method of the lidar system according to claim 1, characterized in that, Step 2.3 specifically includes the following steps: Step 2.31: Determine the true peak time point of the unsaturated echo signal. Take the echo peak time point calculated by the lidar system processor as the true peak time point of the unsaturated echo signal. Step 2.32: Determine the true peak time point of the saturated echo signal. Step 2.321: Take the true peak time point of the unsaturated echo signal determined in step 2.31 as the reference time point. Step 2.322: For saturated echo signals with different pulse widths, calculate the difference between the echo signal time point calculated by the processor and the reference time point as the time compensation value; where the echo signal time point is the peak time point or the rising edge time point of the echo signal. Step 2.323: Store the pulse widths of different saturated echo signals and the corresponding time compensation values in the internal memory of the lidar as a calibration parameter table.

3. The calibration method of the lidar system according to claim 2, characterized in that: The reflectivity of the standard reflector in step 2.1 is greater than 95%.

4. The calibration method of the lidar system according to claim 3, characterized in that: In step 2.31, select the echo peak time points of multiple unsaturated echo signals, calculate their average time point, and take this average time point as the true peak time point of the unsaturated echo signal.

5. The calibration method of the lidar system according to claim 4, characterized in that: In step 2.2, adjusting the laser pulses so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, thereby obtaining echo signals of different intensities, specifically: Adjust the pulsed laser emission light source to emit laser pulses at different emission angles so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, thereby obtaining echo signals of different intensities; Or, By setting a baffle in the emission optical path to block part of the laser pulses or the receiving window area, so that after each laser pulse is emitted, the lidar to be calibrated receives echo light energy of different intensities, thereby obtaining echo signals of different intensities.

6. The calibration method of the lidar system according to claim 5, characterized in that, Step 3 specifically is: By measuring the peak moment points of the standard reflector at different known distances from the radar, several corresponding groups of Δ t and Δ t + c1 and the distance y are obtained, and the relationship curves of Δ t and Δ t + c1 with y are fitted, and then the a and b in y = aΔ t + b and y = a(Δ t + c1)+ b can be determined; By measuring the rising edge time points of a standard reflector at different known distances from the radar, several corresponding sets of Δ are obtained. t '+c2 and the distance y, and fitting the relationship curve between Δ t '+c2 and y, the values of a and b in y = a(Δ t '+c2)+b can be determined.

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