WO2023103310A1 - 激光雷达及其测量目标反射率的方法和系统 - Google Patents

激光雷达及其测量目标反射率的方法和系统 Download PDF

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Publication number
WO2023103310A1
WO2023103310A1 PCT/CN2022/097731 CN2022097731W WO2023103310A1 WO 2023103310 A1 WO2023103310 A1 WO 2023103310A1 CN 2022097731 W CN2022097731 W CN 2022097731W WO 2023103310 A1 WO2023103310 A1 WO 2023103310A1
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Prior art keywords
echo
target
signal
detector
energy
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PCT/CN2022/097731
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English (en)
French (fr)
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胡天健
邝杰
李力
李艳芳
向少卿
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上海禾赛科技有限公司
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Publication of WO2023103310A1 publication Critical patent/WO2023103310A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
    • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/495—Counter-measures or counter-counter-measures using electronic or electro-optical means

Definitions

  • Embodiments of the present invention relate to the technical field of laser radar reflectivity measurement, and in particular to laser radar and its method and system for measuring target reflectivity.
  • Lidar has been widely used in the field of intelligent driving such as autonomous driving and the field of robotics. Its working principle is to transmit the detection beam and receive the echo reflected by the target through the detector, and obtain the detection information of the target by measuring the time difference between the detection beam and the echo signal.
  • the measurement of the target reflectivity in the intelligent driving application not only hopes to obtain the target reflectivity information of the target in the ranging range, but not only the reflectivity information of the long-distance target; In this case, the reflectivity information of multiple targets is respectively obtained, so as to perform target recognition through the reflectivity information.
  • embodiments of the present invention provide a laser radar and its method and system for measuring target reflectivity, which can realize the reflectivity measurement of multi-echo targets within a ranging range.
  • an embodiment of the present invention provides a method for measuring the reflectivity of a target by laser radar, where the laser radar includes a detector, and the method includes:
  • the determining the proportion of the energy of the reflected echo of the at least one target in the echo energy signal according to the at least one echo pulse signal to obtain the reflectivity of at least one target includes:
  • the detector When it is determined that the echo received by the detector is a single target reflected echo, according to the energy signal characteristics, determine the reflectivity of the single target;
  • the reflectivity of each target is respectively obtained according to the proportion of the energy of the reflected echoes of each target in the echo energy signal.
  • the determining whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo according to the characteristics of the pulse signal includes:
  • the detector determines whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo.
  • the method before determining whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo according to the number of the pulse groups, the method further includes:
  • the echo pulses contained in the at least one echo pulse signal whose amplitude exceeds a preset amplitude threshold are selected.
  • the reflectivity including:
  • the echo signal characteristics and the sum thereof of the reflected echo corresponding to each target are obtained;
  • the proportion of the echo signal characteristics of each target in the sum is taken as the proportion of the energy of the reflected echo of each target in the echo energy signal.
  • the echo signal characteristics of the reflected echo signals corresponding to the targets include at least one of the following:
  • Pulse peak value Pulse peak value, pulse leading edge slope, pulse trailing edge slope, pulse threshold pulse width, pulse coverage area.
  • obtaining the echo energy signal output by the detector after receiving the echo reflected by the probe beam from at least one target includes:
  • the difference between the energy signal received by the detector within the detection window and the ambient light energy signal is used as the echo energy signal.
  • the echo energy signal is determined according to the time-integrated amplitude of the echo electric signal.
  • the echo electrical signal is at least one of photocurrent, photovoltage, and number of detected photons.
  • the embodiment of the present invention also provides a laser radar measuring device for measuring target reflectivity, the laser radar includes a detector, and the measuring device includes:
  • the first signal acquisition unit is adapted to acquire at least one echo pulse signal output by the detector after receiving the echo reflected by the detection beam from at least one target;
  • the second signal acquisition unit is adapted to acquire the echo energy signal output by the detector after receiving the echo reflected by the detection beam from at least one target; the echo energy signal is adapted to indicate that the detector receives within the detection window All echo energy received;
  • the processing unit is adapted to determine the proportion of the energy of the reflected echo of the at least one target in the echo energy signal according to the at least one echo pulse signal, so as to obtain the reflectivity of the at least one target.
  • the embodiment of the present invention also provides a laser radar, including:
  • a detector adapted to receive and output at least one echo pulse signal and an echo energy signal in response to an echo of detection light reflected by at least one target; the echo energy signal being adapted to indicate that the detector is within a detection window All echo energy received;
  • a processor coupled to the detector, is adapted to determine the proportion of the energy of the reflected echo of the at least one target in the echo energy signal according to the at least one echo pulse signal, and obtain the energy of the at least one target Reflectivity.
  • the lidar also includes:
  • the second signal collector is adapted to collect signal features corresponding to the echo energy signal to obtain corresponding energy signal features
  • the processor is adapted to determine whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo according to the characteristics of the pulse signal, and when it is determined that the echo received by the detector is When a single target reflects an echo, determine the reflectivity of the single target according to the energy signal characteristics; when it is determined that the echo received by the detector is a multi-target reflected echo, according to the The proportion of energy in the echo energy signal is used to obtain the reflectivity of each target respectively.
  • the processor is adapted to determine the number of pulse groups in the at least one echo pulse signal conforming to the encoding of the transmitted pulse group; according to the number of pulse groups, determine the echo received by the detector
  • the type is single target reflection echo or multiple target reflection echo.
  • the processor is adapted to select the at least An echo pulse signal contains echo pulses whose amplitude exceeds a preset amplitude threshold.
  • the processor is adapted to obtain the echo signal characteristics and the sum of the reflected echoes corresponding to each target according to the pulse signal characteristics when the received echo type is determined to be multi-target reflected echoes , taking the proportion of the echo signal features of each target in the sum as the proportion of the energy of the reflected echo of each target in the echo energy signal.
  • the first signal collector includes at least one of the following:
  • the first analog-to-digital converter is adapted to sample the at least one echo pulse signal to obtain the pulse signal characteristics
  • a time-to-digital converter is adapted to sample the echo pulse signal to obtain the pulse signal characteristics
  • the second signal collector includes:
  • the second analog-to-digital converter is adapted to sample the echo energy signal to obtain the energy signal feature.
  • the detector includes a plurality of single-photon avalanche diodes connected in parallel, and the second analog-to-digital converter is adapted to determine the echo according to the integral of the amplitude of the echo electrical signal output by the detector over time.
  • An energy signal, the amplitude of the echo electrical signal is positively correlated with the number of triggered single photon avalanche diodes in the detector.
  • the detector includes: a silicon photomultiplier tube, and the silicon photomultiplier tube includes two output ports, wherein:
  • a first output port for outputting the at least one echo pulse signal
  • the second output port outputs the echo energy signal through the branch circuit.
  • the first output port includes: a coupling capacitor; the second output port includes: an integrating circuit.
  • the detector of the laser radar can receive the echo signal of the detection beam reflected by the target, and adopt the scheme of the laser radar in the embodiment of the present invention to measure the reflectivity of the target, and respectively obtain the detection beam received by the detector and reflected by at least one target output at least one echo pulse signal and echo energy signal after echoing, and then determine the proportion of the energy of the at least one target reflected echo in the echo energy signal according to the at least one echo pulse signal,
  • the reflectivity of at least one target can be obtained, wherein, on the one hand, since the echo energy signal is suitable for representing all the echo energy received by the detector within the detection window, on the other hand, it can be obtained according to the at least one
  • the echo pulse signal determines the proportion of the energy reflected by the at least one target in the echo energy signal, so the reflectivity of all targets in the detection window can be obtained, and multiple echoes within the ranging range can be obtained.
  • the reflectivity measurement of the target improves the accuracy and completeness of the target reflectivity measurement.
  • the pulse signal characteristics obtained based on the echo pulse signal output by the detector after receiving the target reflection can reflect the echo light intensity, and because the echo pulse signal has the characteristics of narrow pulse width , so it is easy to distinguish echoes from different targets according to the characteristics of the pulse signal, so firstly, it can be determined according to the characteristics of the pulse signal whether the type of the echo received by the detector is a single target reflection echo or a multi-target reflection echo , and then, when it is determined that the echo received by the detector is a single target reflected echo, the reflectivity of the single target can be determined according to the energy signal characteristics; when the echo received by the detector is determined In the case of multi-target reflected echoes, the reflectivity of each target can be obtained respectively according to the proportion of the energy of the reflected echoes of each target in the echo energy signal, so that different targets in the entire range can be accurately measured True reflectivity.
  • the dynamic range of the echo pulse signal is very narrow, if only the echo pulse signal feature is used, the reflectivity of the target cannot be accurately measured, but the reflectivity measurement with a high dynamic range can be achieved by using the echo energy signal feature, and, based on The characteristics of the pulse signal are used to distinguish and distribute the energy of the echo signal, so that the reflectivity of different targets in the entire range can be accurately measured, and the dynamic range and measurement accuracy can be improved.
  • the number of pulse groups in the at least one echo pulse signal conforming to the code of the transmitted pulse group is a single target echo
  • the wave is still a multi-target reflection echo, that is, only when the code of the pulse group matches the code of the transmitted pulse group, the target corresponding to the pulse group is recognized as the real target. Therefore, according to the number of pulse groups that match the code of the transmitted pulse group , the number of real targets can be determined, which can further improve the accuracy of lidar multi-target detection.
  • the interference of the noise pulse caused by various optical noise and electrical noise can be filtered out, and the echo of the real target can be extracted.
  • Wave pulse which can further improve the accuracy of the measurement.
  • the echo signal characteristics and the sum of the reflected echoes corresponding to each target are obtained, and then the proportion of the echo signal characteristics of each target in the sum is used as the reflected echo of each target.
  • the proportion of wave energy in the echo energy signal can truly reflect the real reflectivity information of each target in the detection window, thereby improving the accuracy of multi-target detection.
  • the environment can be avoided.
  • the influence of light on the detection results further improves the accuracy of lidar detection results.
  • FIG. 1A shows a schematic diagram of a circuit structure of a SiPM
  • Figure 1B shows a schematic diagram of the circuit structure of another SiPM
  • FIGS. 2A to 2C show schematic diagrams of several typical multi-echo scenarios in lidar detection
  • Fig. 3 shows a flow chart of a method for measuring target reflectivity by laser radar in an embodiment of the present invention
  • Fig. 4A and Fig. 4B respectively show the waveform diagrams of the echo pulse signal and the echo energy signal
  • Fig. 6 shows a schematic diagram of signals output by the integrating circuit shown in Fig. 5 in an embodiment of the present invention
  • FIG. 7 shows a flow chart of a specific method for obtaining target reflectivity in an embodiment of the present invention
  • Fig. 8 shows a schematic diagram of the principle of collecting pulse signal characteristics in an embodiment of the present invention
  • Fig. 9 shows a specific implementation flowchart of a method for measuring target reflectivity by laser radar in an embodiment of the present invention
  • Fig. 10 shows a schematic diagram of a reflectance mapping curve in a reflectance calibration table in an embodiment of the present invention
  • Fig. 11 shows a schematic structural diagram of a laser radar measuring device for measuring target reflectivity in an embodiment of the present invention
  • Fig. 12 shows a schematic structural diagram of a lidar in an embodiment of the present invention.
  • SiPMs used for lidar have two output ports, the first output port Output1 and the second output port Output2, and the signals output from the first output port Output1 or from the second output port Output2 can be used Measure the reflectivity of the target.
  • SiPM 0A includes a plurality of micro-units ⁇ -cells connected in parallel, and each micro-unit ⁇ -cell includes a SPAD and a quenching resistor connected in series R Q , the cathode port Cathode is used to apply the bias voltage Vbias; the anode port Anode is used as the second output port Output2 to output the echo energy signal; the first output port Output1 is used to output the at least one echo pulse signal.
  • FIG. 1B Also shown in Figure 1B is a schematic diagram of the circuit structure of a dual-port SiPM.
  • a branch circuit b01 is set at the cathode port Cathode of SiPM 0B as an output branch to form the first output port Output1
  • a branch circuit b02 is set at the anode port Anode to form the second output port Output2.
  • the first branch circuit b01 outputs the echo pulse signal through the coupling capacitor C S0
  • the second branch circuit b02 outputs the echo energy signal through the integration circuit (such as the integration circuit shown in FIG. 5 ).
  • SiPM lidar to measure target reflectivity is generally based on the pulse signal characteristics of the echo pulse signal. For example, based on the peak value of the echo pulse signal to measure the reflectivity of the target, this solution requires the lidar to be equipped with a high-speed analog-to-digital converter (Analog- to-Digital, ADC), which will greatly increase the power consumption and cost of the lidar, and because the heat dissipation design will increase the volume of the lidar and increase the complexity of the radar structure, it is not suitable for the small size, low cost, and low cost of the lidar Power consumption trends.
  • ADC analog-to-digital converter
  • TDC Time-to-Digital Converter
  • the random jitter of the leading edge slope and pulse width of the echo pulse signal is large, and it is difficult to obtain high-precision reflectivity measurement values; moreover, the dynamic range of the echo pulse signal is very narrow, and it is easy to saturate (when the target distance is relatively close, Even for targets with low reflectivity, the intensity of the echo pulse signal is enough to saturate the SiPM), and the reflectivity of the target can hardly be detected, resulting in the failure of the reflectivity measurement.
  • the reflectivity can be measured based on the echo energy signal output from the second output port.
  • This method has a large dynamic range and measurement accuracy.
  • the laser radar emits a detection optical signal, and the detector receives the echo optical signal and converts it into an electrical signal. After the flight time corresponding to the farthest target detection distance of the laser radar, the detector no longer receives the echo optical signal reflected by the detection optical signal.
  • the total time for the detector to receive the echo optical signal corresponding to the detection optical signal may be referred to as a detection window.
  • the detection light signal may be reflected by only one object, and the detector receives the echo light signal reflected by the object, that is, a single target echo or a single event; the detection light may also be reflected by multiple different objects, Make the detector receive the echo optical signals respectively reflected by multiple objects, that is, multi-target reflected echo, or called multi-echo or multi-event.
  • the echo energy signal output by the second output port covers a long time, the echo signals of multiple targets overlap and cannot be distinguished, so the reflectivity of each target corresponding to the multiple echoes cannot be measured.
  • the measured reflectance value in the case of multiple echoes is uncertain, and it is easy to cause the drift of the reflectance measurement value due to the energy accumulation of multiple echoes, and there are also some limitations.
  • FIG. 2A the schematic diagram of several typical multi-echo scenarios in the lidar detection process shown in Figure 2.
  • a detection beam emitted by a light emitting unit of the lidar such as a laser
  • the detection beam s1 emitted by the laser radar A is respectively irradiated on the target objects T1 and T2 at different distances from the laser radar A, and the echoes r1 and r2 reflected by the two target objects T1 and T2 will be received .
  • the detection beam emitted by the lidar may encounter a translucent object, so that part of the detection beam will be reflected back by the translucent object, and the other part will pass through the translucent object.
  • An object shines on another object and is reflected back by the light-transmitting object. As shown in FIG.
  • the target object T3 will reflect an echo r3 to the laser radar A, and at the same time, the A part of the detection beam s2 passes through the target object T3 and irradiates the target object T4 , and the echo r4 reflected by the target object T4 is transmitted to the laser radar A through the target object T3 .
  • the embodiment of the present invention respectively obtains at least one echo pulse signal and echo energy signal output by the detector after receiving the echo reflected by the detection beam from at least one target, and then according to the at least one echo pulse signal
  • the reflectivity of the at least one target can be obtained by determining the proportion of the energy of the echo reflected by the at least one target in the echo energy signal.
  • the echo energy signal is suitable for representing all the echo energy received by the detector within the detection window
  • the at least one echo pulse signal Determine the proportion of the energy of the at least one target reflected echo in the echo energy signal, so the reflectivity of all targets in the detection window can be obtained, and the reflectivity of multiple echo targets within the ranging range can be realized measurement to improve the accuracy and completeness of target reflectance measurements.
  • the detector used may be a SiPM, or a photodetector device such as a photodiode (Photodiode, PD), PIN PD, SPAD, etc., and the embodiment of the present invention does not limit the specific device of the detector type, as long as the detection device can detect the echo reflected by the detection beam by at least one target, and based on the echo, the echo pulse signal and the echo energy signal of the at least one target can be output.
  • a photodetector device such as a photodiode (Photodiode, PD), PIN PD, SPAD, etc.
  • the following method may be used specifically to measure the target reflectance.
  • the at least one echo pulse signal may be obtained through a first output port of the detector, and the echo energy signal may be obtained through a second output port of the detector.
  • the coupling capacitor CF corresponding to each micro-cell ⁇ -cell can be respectively set in the SiPM, and the original photocurrent output by the SPAD passes through the coupling capacitor CF for a small time Constant (for example, several nanoseconds) AC coupling generates a voltage signal as the at least one echo pulse signal, as shown in FIG. 4A , whose pulse width W A may only be several nanoseconds.
  • a small time Constant for example, several nanoseconds
  • the echo energy signal is adapted to represent all echo energy received by the detector within the detection window.
  • the echo energy signal may be determined according to the integral of the amplitude of the echo electrical signal over time.
  • a series of long-time pulse signals can be output through the second output port of the detector, as shown in Fig. 4B, the pulse width W B may reach more than 100 nanoseconds, and the second output
  • the long-duration pulse signal output from the port has rich DC components, which can well reflect the echo energy and has a large dynamic range.
  • an integrating circuit may be provided at the second output port of the detector, for example, the second output port Output2 of the SiPM shown in FIG. 1 , to output the echo energy signal.
  • the echo electrical signal may specifically be at least one of photocurrent, photovoltage, number of detected photons, and the like.
  • the SPAD works in the Geiger mode under the reverse bias +Vs, after the SPAD is triggered by a photon, the cathode output current pulse passes through the first resistor R1 and the capacitor C
  • the composed RC circuit is integrated, converted into a voltage signal V by the operational amplifier OA, and then supplied to the second ADC (for example, a low-speed ADC can be selected) for sampling, and the integrated signal obtained can be used as the echo energy signal.
  • the switch K can be closed once to clear the integrated charge on the capacitor C.
  • the measurement error caused by single-pulse jitter can be significantly reduced, and the measurement accuracy of the target reflectivity can be improved.
  • the integration circuit will integrate all the echo pulses within the preset time. For example, if the laser of the lidar emits m pulses each time the ToF is measured, the echo pulse signal will also be reflected by an object. Including m pulses, after receiving the m pulse signals, the SiPM can output the total current integration of the m pulses through the integrating circuit shown in FIG. 5 as the echo energy signal. If the detection light is respectively reflected by n objects, the SiPM will receive m*n pulses in the detection window. If the preset time is set as the total time of the entire detection window, this can be output by the integration circuit shown in Figure 5. Total current integration of m*n pulses.
  • m 4 in this embodiment. If the echo pulse signal output by the first output port of the detector is PL0, the corresponding second output port is integrated by the integration circuit to obtain the integrated photocurrent signal IL0.
  • the ambient light may also have a large difference.
  • S02. Determine, according to the at least one echo pulse signal, the proportion of energy reflected by the at least one target in the echo energy signal, to obtain a reflectivity of the at least one target.
  • one or more targets corresponding to the target reflected echo can be identified, and the target reflected echo corresponding to each target can be determined.
  • the ratio of the echo energy signal to obtain the reflectivity of each target so it can realize the reflectivity measurement of multiple echo targets within the ranging range.
  • S021. Collect signal features corresponding to the at least one echo pulse signal and the echo energy signal respectively, to obtain corresponding pulse signal features and energy signal features.
  • a signal collector can be used to separately collect signal characteristics of the echo pulse signal and the echo energy signal, so as to obtain the signal characteristic corresponding to the at least one echo pulse signal and the echo corresponding to the echo energy signal.
  • Signal features for the convenience of description, are hereinafter referred to as pulse signal features and energy signal features respectively.
  • a first signal collector is used to sample the at least one echo pulse signal to obtain pulse signal characteristics; a second signal collector is used to sample the echo energy signal to obtain the energy signal characteristics.
  • the first signal collector may specifically be an ADC (hereinafter referred to as the first ADC) or a TDC; the second signal collector may also use an ADC, which may be called the second ADC for distinction .
  • the second ADC may use exactly the same device as the first ADC, or may use a device different in structure, parameters, etc., as long as the required sampling requirements can be met.
  • the pulse signal feature may specifically be one or more of the peak value, pulse leading edge slope, pulse trailing edge slope, pulse threshold pulse width, and pulse coverage area of the at least one echo pulse signal.
  • one or more of the above parameters may be used as the pulse signal characteristic of the at least one echo pulse signal.
  • the peak value of the echo pulse may be obtained by sampling by using the first ADC as the characteristic of the pulse signal.
  • a high-speed, medium-speed or low-speed ADC may be configured in the signal readout circuit of the detector as the first ADC.
  • the pulse signal characteristics specifically include the echo pulse leading edge slope and threshold pulse width (including at least one of the high threshold pulse width and the low threshold pulse), and TDC can be used to analyze the at least one echo signal Sampling is performed to obtain the echo pulse leading edge slope and pulse width as the pulse signal characteristics.
  • the at least one echo pulse signal can be obtained through its first output port Output1, and the first output port Output1 can output the response of each photosensitive element SPAD to the optical signal.
  • the characteristics of the pulse signal can be obtained by sampling a first ADC or TDC at the first output port Output1.
  • step S022. Determine whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo according to the characteristics of the pulse signal. When it is determined that the echo received by the detector is a single-target reflected echo , execute step S023; when it is determined that the echoes received by the detector are multi-target reflected echoes, execute step S024.
  • the transmitting end device for example, a laser
  • the transmitting end device will send out a set of laser pulses, which can be called a set of transmitting pulses for the convenience of description.
  • encoding is performed with the time interval between two adjacent pulses to obtain the encoding of the transmitted pulse group.
  • the encoding of the echo pulse signal received by the detector of the channel (for example, the time interval between adjacent pulses in the plurality of echo pulses) conforms to the encoding of the transmitting pulse group of the channel, the The target detected by the echo signal is identified as a real target, and then the reflectivity of the corresponding target can be measured according to the echo signal data.
  • the amplitude contained in the at least one echo pulse signal can be selected to exceed the preset amplitude
  • the echo pulse of the threshold value is used as the echo pulse corresponding to the real target for subsequent target reflectivity measurement. In this case, only when the amplitude of the echo pulse signal output by the detector exceeds the preset amplitude threshold value, can it be confirmed as the echo pulse of the real target, so that the measurement accuracy can be further improved.
  • the amplitude of the at least one echo pulse signal exceeds the preset amplitude threshold and conforms to the encoding of the transmitted pulse group, it is considered to be the echo reflected by the real target.
  • the echo pulse signal corresponding to the wave.
  • the echo pulse signal conforming to the encoding of the transmitting pulse group may be selected first from the at least one echo pulse signal, and then the amplitude may be selected from the encoding echo pulse signal conforming to the transmitting pulse group For echo pulses that exceed the preset amplitude threshold, determine the number of pulse groups that conform to the encoding of the transmitted pulse group, and determine that the type of echo received by the detector is a single-target reflected echo according to the number of pulse groups Or multiple target reflection echoes.
  • the reflected echo signal characteristics corresponding to each target and their sum can be obtained, and the proportion of the echo signal characteristics of each target in the sum can be used as the reflected echo signal of each target.
  • the ratio of the energy of the echo in the echo energy signal, and further the reflectance of each target can be respectively obtained according to the ratio of the energy of the echo reflected by each target in the echo energy signal.
  • the embodiment of the present invention does not limit the specific form of the echo signal characteristics of the reflected echo signals corresponding to each target, as long as the characteristics of the reflected echo corresponding to each target can be reflected.
  • the echo signal characteristics of the reflected echo signals corresponding to each target may be the pulse peak value, pulse leading slope, pulse trailing slope, pulse threshold pulse width, and pulse peak value of the echo pulse corresponding to each target.
  • the above-mentioned parameters can be specifically obtained by sampling through a signal collector such as ADC or TDC in the specific sampling steps in the above-mentioned steps, and details can be found in the introduction of the above-mentioned embodiments.
  • the pulse signal characteristics obtained based on the echo pulse signal output by the detector after receiving the target reflection can reflect the echo light intensity, and because the echo pulse signal has the characteristics of narrow pulse width, it is easy to distinguish different targets according to the pulse signal characteristics. Therefore, it can first be determined according to the characteristics of the pulse signal whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo, and then, when it is determined that the echo received by the detector When the wave is a single-target reflected echo, the reflectivity of the single target can be determined according to the energy signal characteristics; when the echo received by the detector is determined to be a multi-target reflected echo, the The proportion of echo energy in the echo energy signal is used to obtain the reflectivity of each target, so that the real reflectivity of different targets within the entire ranging range can be accurately measured. If applied to intelligent driving, it can provide a reliable basis for intelligent decision-making such as intelligent driving, and ensure driving safety.
  • all echo pulses output by the detector of the detection channel within a detection window can be obtained.
  • the echo energy signal is adapted to represent all echo energy received by the detector within the detection window.
  • the echo energy signal may be determined according to the time-integrated amplitude of the echo electric signal.
  • the echo electrical signal may be one or more of photocurrent, photovoltage or number of detected photons.
  • the ambient light energy signal output by the detector receiving ambient light can be obtained, and the energy signal received by the detector within the detection window can be compared with the ambient light energy signal The difference is used as the echo energy signal.
  • the pulse signal feature may specifically include a pulse amplitude, that is, a pulse peak value; the energy signal feature may include an integral of the echo electrical signal amplitude over time.
  • the photocurrent integral of the echo is used as the energy signal characteristic of the echo energy signal
  • the photocurrent integral of all echoes obtained by the detector within the detection window is the first photocurrent integral V Z
  • the The photocurrent integral of the detector receiving the ambient light output in the detection window is the second photocurrent integral (also called passive photocurrent integral) V B
  • the photocurrent integral of the echo energy signal also called active photocurrent integration
  • V d V Z -V B
  • the second photocurrent integral V B is measured when the laser of the lidar does not emit light and the detector of the same channel does not measure distance.
  • step S13 Determine whether the type of the echo received by the detector is a single-target reflected echo or a multi-target reflected echo according to the pulse signal characteristics of the echo pulse signal, and if it is determined to be a single-target reflected echo, then perform the step S14: If it is determined to be reflected echoes from multiple targets, execute step S15.
  • the echo pulse that meets the preset condition can be selected from all the echo pulses, and according to the echo pulse group that meets the preset condition The number determines the type of echo. Wherein, if there is only one set of echo pulse groups that meet the preset conditions, it is determined that this measurement event is a single event, and what the detector receives is a single target reflected echo; if the echo pulse group that meets the preset conditions If there are two or more groups, it is determined that the current measurement is multiple events, and the detector receives reflected echoes from multiple targets.
  • the preset condition is specifically: the pulse amplitude (that is, the peak value of the pulse) of the echo pulse exceeds a preset amplitude threshold, and the time code of the echo pulse (such as the number of pulses and the interval between adjacent pulses The time interval) conforms to the time code of the transmitted pulse group, then it is identified as a group of echo pulses, as a real echo of a target.
  • the reflectivity of the single target may be calculated by using a linear interpolation method according to the echo energy signal obtained through sampling.
  • R R 1 +(V d0 -V d (d,R 1 ))*(R 2 -R 1 )/(V d (d,R 2 )-V d (d,R 1 )) (1)
  • R represents the reflectivity of the single target
  • R 1 is the reflectivity value of the first standard reflector plate
  • R 2 is the reflectivity value of the second standard reflectivity plate
  • V d0 is the temperature compensation and equivalent photon detection Efficiency (Photon Detection Efficiency, PDE) compensation (i.e. ambient light compensation) of the photocurrent integral value of the echo electrical signal (also called the active photocurrent integral value)
  • V d (d, R 1 ) and V d ( d, R 2 ) is the active photocurrent integral value when the lidar illuminates the first standard reflectivity plate and the second standard reflector plate at a distance d.
  • R 1 , R 2 , V d (d, R 1 ) and V d (d, R 2 ) can all be obtained by querying the reflectance calibration table stored in the lidar, and the specific
  • the first standard reflector and the second standard reflector are two standard reflectors with different reflectances used in the calibration process.
  • the photocurrent integral V d of the echo electrical signal, the photocurrent integral of ambient light (also called the passive photocurrent integral) V B , the target distance d, and the detector (such as SiPM) can be obtained through the direct detection of the laser radar. temperature T.
  • A02 perform temperature compensation on the measured echo photocurrent integral V d of the detector, and convert to obtain the photocurrent integral value V d, T0 at the calibration temperature T 0 :
  • V d, T0 V d /(k*T+b) (2)
  • k and b are calibration parameters
  • V d is the photocurrent integral value at the calibration temperature T 0
  • V d is the measured echo photocurrent integral of the detector.
  • the photocurrent integral value (also called the active photocurrent integral value) V d0 of the echo electric signal after ambient light compensation is obtained .
  • V B ⁇ V B0 that is, the current ambient light is weak ambient light, which may be indoors, in a tunnel or in a rainy day
  • the value of V B0 is 200mV. It can be understood that V B0 can also be other values.
  • the embodiment of the present invention does not limit its specific value, as long as the accuracy of target reflectivity measurement can be improved. .
  • the echo signal characteristics and the sum of the reflected echoes corresponding to each target can be obtained, and the echo signal characteristics of each target in the sum can be obtained.
  • the proportion is used as the proportion of the energy reflected by each target in the echo energy signal, and the reflectance of each target is respectively obtained.
  • the energy signal characteristics corresponding to the echo energy signal measured this time include: active photocurrent integration V d , since the integration time of the integration circuit at the second output port of the detector is not less than the total time of one detection, thus in one detection Among them, the first photocurrent integral V Z of all echoes can cover the echo pulse group information of all events, and the active photocurrent integral V d after deducting the echo photocurrent integral V B of the ambient photocurrent integral V is The sum of the energies of the echo pulse groups of all events, so according to the proportion of the energy of each event echo in the active photocurrent integral, the photocurrent integral corresponding to each event can be obtained, that is, the echo of each target Energy, and then the reflectivity of each target can be calculated.
  • the echo pulse signal assigned to the event i can be calculated using the formula Wave energy:
  • V di S i *V d /sum(S i ) (3)
  • the reflectivity R i of the target corresponding to the i-th event can be calculated.
  • the echo signal characteristic of the echo pulse signal corresponding to the i-th event is that S i may include the pulse peak value, the pulse leading edge slope, and the pulse trailing edge slope of the echo pulse signal corresponding to the i-th event , threshold pulse width and pulse coverage area, etc., but not limited thereto.
  • the area covered by the pulse can be calculated according to the echo pulse signal, as S i , which can more accurately reflect the energy difference between the strong echo and the weak echo.
  • the area covered by the pulse can be calculated from the slope of the leading edge of the pulse, the slope of the trailing edge of the pulse and the pulse width obtained by the TDC.
  • the laser radar can calibrate the echo energy signal when it leaves the factory.
  • the general process is as follows:
  • FIG. 10 a schematic diagram of the reflectance mapping curve in the reflectance calibration table obtained by calibration, according to the distance d obtained by the actual detection of the lidar and the return photocurrent integral signal V d , by querying the distance d on the horizontal axis and the vertical axis
  • the target reflectivity R of the corresponding target can be found by the corresponding reported integrated photocurrent signal V d .
  • the laser radar 11A includes a detector 11B, and the measuring device 110 may include: a first signal acquisition unit 111, a second signal acquisition unit 112 and a processing unit 113, wherein:
  • the first signal acquisition unit 111 is adapted to acquire at least one echo pulse signal output by the detector after receiving the echo reflected by the probe beam from at least one target;
  • the second signal acquisition unit 112 is adapted to acquire an echo energy signal output by the detector after receiving the echo reflected by the detection beam from at least one target; the echo energy signal is adapted to indicate that the detector is detecting All echo energy received within the window;
  • the processing unit 113 is adapted to determine the proportion of the energy of the reflected echo of the at least one target in the echo energy signal according to the at least one echo pulse signal, so as to obtain the reflectivity of the at least one target.
  • the processing unit may be a central processing unit (Central Processing Unit, CPU), a system on a chip (System-on-a-Chip, SoC), a microcontroller unit (Microcontroller Unit, MCU), a special application integrated circuit (Application Specific Integrated Circuit, ASIC), Complex Programmable Logic Device (Complex Programmable Logic Device, CPLD), Field Programmable Gate Array (Field Programmable Gate Array, FPGA) or Digital Signal Processor (Digital Signal Processor, DSP), etc.
  • CPU Central Processing Unit
  • SoC System-on-a-Chip
  • MCU microcontroller Unit
  • ASIC Application Specific Integrated Circuit
  • ASIC Application Specific Integrated Circuit
  • Complex Programmable Logic Device Complex Programmable Logic Device
  • CPLD Complex Programmable Logic Device
  • FPGA Field Programmable Gate Array
  • DSP Digital Signal Processor
  • the measurement device 110 can be integrated inside the laser radar 11A, so that the laser radar 11A can output the detected reflectance of the target in real time during the detection process, so as to realize the detection of possible occurrences in the measurement range.
  • the measurement device 110 may share some modules or components with the lidar 11A, for example, the processing unit 113 may be implemented by a processor inherent in the lidar or an FPGA computing device.
  • the first signal acquisition unit 111 may specifically be an ADC or a TDC
  • the second signal acquisition unit 112 may specifically be an ADC
  • the first signal acquisition unit 111 may be disposed on the detector 11B.
  • the first output port, the second signal acquisition unit 112 may be set at the second output port of the detector 11B.
  • the embodiment of the present invention also provides a laser radar.
  • the laser radar 120 includes: a detector 121 and a processor 122, wherein:
  • the detector 121 is adapted to receive and respond to the echo of the detection light reflected by at least one target, and output at least one echo pulse signal and an echo energy signal; the echo energy signal is adapted to indicate that the detector is in the All echo energy received within the detection window;
  • the processor 122 coupled to the detector 121, is adapted to determine the proportion of the energy of the at least one target reflected echo in the echo energy signal according to the at least one echo pulse signal, to obtain The reflectivity of at least one target.
  • the lidar By using the above laser radar to measure the reflectivity of the target, the reflectivity measurement of at least one echo target in the whole ranging process can be realized. If the lidar is applied to intelligent driving, it can provide a reliable basis for intelligent decision-making such as intelligent driving, and ensure driving safety.
  • the detector 121 may specifically be a SiPM, or a photodiode (Photodiode, PD), PIN PD, Single Photon Avalanche Diode (Single Photon Avalanche Diode, SPAD) and other photodetection devices.
  • the specific device type of the detector is not limited, as long as the detection device can detect the echo reflected by the detection beam by at least one target, and can output the echo pulse signal of the at least one target based on the echo And echo energy signal.
  • a first output port for outputting the at least one echo pulse signal
  • the second output port outputs the echo energy signal through the branch circuit.
  • the first output port may include: a coupling capacitor; the second output port may include: an integrating circuit.
  • the three-port SiPM shown in Figure 1A can be used as the detector to detect the echo.
  • the corresponding coupling capacitor CF can be connected to the first output port Output1 and each micro-cell ⁇ -cell to output the echo.
  • the pulse signal is coupled to the integrating circuit through the second output port Output2 to output the echo energy signal.
  • a dual-port SiPM can also be used as a detector to measure the echo, as shown in the schematic structural diagram of the SiPM shown in Figure 1B, the branch circuit b01 can be set at the cathode port Cathode of the SiPM 0B as an output branch to form the first output port Output1; Branch circuit b02 is set at the anode port Anode to form the second output port Output2, wherein the first branch circuit b01 outputs the echo pulse signal through the coupling capacitor C S0 , and the second branch circuit b02 passes through the integration circuit (such as shown in Figure 5 Integrator circuit) outputs the echo energy signal.
  • the integration circuit such as shown in Figure 5 Integrator circuit
  • the lidar 120 may also include: a first signal collector 123 and a second signal collector 124, wherein:
  • the first signal collector 123 is adapted to collect the signal feature corresponding to the at least one echo pulse signal to obtain the corresponding pulse signal feature;
  • the second signal collector 124 is adapted to collect signal features corresponding to the echo energy signal to obtain corresponding energy signal features
  • the processor 122 is adapted to determine whether the type of the echo received by the detector 121 is a single-target reflected echo or a multi-target reflected echo according to the characteristics of the pulse signal.
  • the reflectivity of the single target is determined according to the energy signal characteristics;
  • the echo received by the detector 121 is determined to be a multi-target reflected echo, the The proportion of the energy of the reflected echo in the echo energy signal is used to obtain the reflectivity of each target respectively.
  • the processor 122 is adapted to determine the number of pulse groups in the at least one echo pulse signal conforming to the encoding of the transmitted pulse group; according to the number of pulse groups, determine that the detector 121 receives Whether the type of the received echo is single-target reflected echo or multi-target reflected echo.
  • the processor 122 is adapted to determine whether the type of the echo received by the detector 121 is a single-target reflected echo or a multi-target reflected echo according to the number of the pulse groups , selecting an echo pulse whose amplitude exceeds a preset amplitude threshold contained in the at least one echo pulse signal.
  • the processor 122 is adapted to obtain the echo signal characteristics and For the sum, the proportion of the echo signal characteristics of each target in the sum is taken as the proportion of the energy of the reflected echo of each target in the echo energy signal.
  • the first signal collector 123 may include at least one of the following:
  • a first analog-to-digital converter (not shown), adapted to sample the at least one echo pulse signal to obtain the pulse signal characteristics
  • a time-to-digital converter (not shown), adapted to sample the echo energy signal to obtain the characteristics of the pulse signal
  • the second signal collector 124 may include: a second analog-to-digital converter 124 adapted to sample the echo energy signal to obtain the energy signal feature.
  • the detector 121 includes a plurality of single-photon avalanche diodes connected in parallel, and the second analog-to-digital converter is adapted to integrate the amplitude of the echo electrical signal output by the detector with time.
  • the echo energy signal is determined, and the amplitude of the echo electrical signal is positively correlated with the number of triggered single photon avalanche diodes in the detector.
  • the processor may specifically be any device capable of data processing, such as a CPU, SoC, MCU, ASIC, CPLD, FPGA, or DSP.

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Abstract

本说明书实施例提供了一种激光雷达及其测量目标反射率的方法和系统，所述激光雷达包括探测器，所述方法包括：分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。采用上述方案能够实现对测距范围内多回波目标的反射率测量。

Description

激光雷达及其测量目标反射率的方法和系统 技术领域
本发明实施例涉及激光雷达反射率测量技术领域，尤其涉及激光雷达及其测量目标反射率的方法和系统。
背景技术
激光雷达目前已被广泛应用于自动驾驶等智能驾驶领域以及机器人领域。其工作原理是通过发射探测光束，并通过探测器接收目标反射的回波，通过测量探测光束和回波信号之间的时间差以获得目标的探测信息。
激光雷达应用于智能驾驶时，容易遇到一些多回波场景。为了保障行车安全，智能驾驶应用中对目标反射率的测量，既希望能够获得目标在测距范围的目标反射率信息，而不仅仅获得远距离目标的反射率信息；同时也需要在多回波情形下，分别获得多个目标的反射率信息，以通过反射率信息进行目标识别。
发明内容
有鉴于此，本发明实施例提供一种激光雷达及其测量目标反射率的方法和系统，能够实现对测距范围内多回波目标的反射率测量。
首先，本发明实施例提供了一种激光雷达测量目标反射率的方法，所述激光雷达包括探测器，所述方法包括：
分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
可选地，所述根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率，包括：
分别采集所述至少一个回波脉冲信号和所述回波能量信号对应的信号特征， 得到对应的脉冲信号特征和能量信号特征；
根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波；
当确定所述探测器接收到的回波为单目标反射回波时，根据所述能量信号特征，确定所述单目标的反射率；
当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
可选地，所述根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，包括：
确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量；
根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
可选地，在根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波之前，还包括：
选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲。
可选地，所述当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率，包括：
根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和；
将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比。
可选地，所述各目标对应的反射回波信号的回波信号特征包括以下至少一种：
脉冲峰值、脉冲前沿斜率、脉冲后沿斜率、脉冲阈值脉宽、脉冲覆盖面积。
可选地，获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波能量信号包括：
获取所述探测器接收环境光输出的环境光能量信号；
将所述探测器在探测窗口内接收到的能量信号与环境光能量信号之差作为回波能量信号。
可选地，根据回波电信号幅度随时间的积分确定所述回波能量信号。
可选地，所述回波电信号为光电流、光电压、探测光子数中的至少一种。
本发明实施例还提供了一种激光雷达测量目标反射率的测量装置，所述激光雷达包括探测器，所述测量装置包括：
第一信号获取单元，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号；
第二信号获取单元，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
处理单元，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
本发明实施例还提供了一种激光雷达，包括：
探测器，适于接收并响应于探测光被至少一个目标反射的回波，输出至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
处理器，与所述探测器耦接，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
可选地，所述激光雷达还包括：
第一信号采集器，适于采集所述至少一个回波脉冲信号对应的信号特征，得到对应的脉冲信号特征；
第二信号采集器，适于采集所述回波能量信号对应的信号特征，得到对应的能量信号特征；
所述处理器，适于根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，当确定所述探测器接收到的回波为单目标反射回波时，根据所述能量信号特征，确定所述单目标的反射率；当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
可选地，所述处理器，适于确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量；根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
可选地，所述处理器，适于在根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波之前，选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲。
可选地，所述处理器，适于在确定接收到的回波类型为多目标反射回波时，根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和，将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比。
可选地，所述第一信号采集器，包括以下其中至少一种：
第一模数转换器，适于对所述至少一个回波脉冲信号进行采样，得到所述脉冲信号特征；
时间数字转换器，适于对所述回波脉冲信号进行采样，得到所述脉冲信号特征；
所述第二信号采集器，包括：
第二模数转换器，适于对所述回波能量信号进行采样，得到所述能量信号特征。
可选地，所述探测器包括多个并联的单光子雪崩二极管，所述第二模数转换器，适于根据所述探测器输出的回波电信号幅度随时间的积分确定所述回波能量信号，所述回波电信号幅度与所述探测器中被触发的单光子雪崩二极管的数量正相关。
可选地，所述探测器包括：硅光电倍增管，所述硅光电倍增管包括两个输出端口，其中：
第一输出端口，输出所述至少一个回波脉冲信号；
第二输出端口，通过分支电路输出所述回波能量信号。
可选地，所述第一输出端口包括：耦合电容；所述第二输出端口包括：积分电路。
通过激光雷达的探测器可以接收到探测光束被目标反射的回波信号，采用本发明实施例中的激光雷达测量目标反射率的方案，分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号，进而根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，可以得到至少一个目标的反射率，其中，一方面，由于所述回波能量信号适于表示所述探测器在探测窗口内接收到的所 有回波能量，另一方面，可以根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，因此可以得到所述探测窗口内所有目标的反射率，实现对测距范围内多回波目标的反射率测量，提高目标反射率测量的准确性和完整性。
进一步地，在整个测量计算过程中，一方面，由于基于探测器接收目标反射后输出的回波脉冲信号得到的脉冲信号特征可以反映回波光强度，且由于回波脉冲信号具有脉宽窄的特点，因此根据所述脉冲信号特征容易区分来自不同目标的回波，故首先可以根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，进而，当确定所述探测器接收到的回波为单目标反射回波时，可以根据所述能量信号特征，确定所述单目标的反射率；当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率，从而可以准确地测量得到整个测距范围内不同目标真实的反射率。其中，由于回波脉冲信号的动态范围很窄，若只使用回波脉冲信号特征，无法准确地测量目标反射率，而采用回波能量信号特征能够实现高动态范围的反射率测量，并且，基于脉冲信号特征进行回波信号的区分和能量分配，从而可以准确地测量得到整个测距范围内不同目标的反射率，能够提高动态范围和测量精度。
进一步地，通过确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量，进而根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标回波还是多目标反射回波，也即仅当脉冲组的编码符合发射脉冲组的编码时，才将该脉冲组对应的目标认定为真实目标，因此根据符合发射脉冲组的编码的脉冲组的数量，可以确定真实目标的数量，从而可以进一步提高激光雷达多目标探测的准确性。
进一步地，通过选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲，可以滤除各种光噪声和电噪声引起的噪声脉冲的干扰，提取出真实目标的回波脉冲，从而能够进一步提高测量的准确性。
进一步地，根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和，进而将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比，采用上述方式，能够真实反映探测窗口内各目标的真实反射率信息，从而可以提高多目标探测的准确性。
进一步地，通过获取所述探测器接收环境光输出的环境光能量信号，并将 所述探测器在探测窗口内接收到的能量信号与环境光能量信号之差作为回波能量信号，可以避免环境光对探测结果的影响，进一步提高激光雷达探测结果的准确性。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据提供的附图获得其他的附图。
图1A示出了一种SiPM的电路结构示意图；
图1B示出了另一种SiPM的电路结构示意图；
图2A至图2C示出了激光雷达探测中几种典型的多回波场景示意图；
图3示出了本发明实施例中一种激光雷达测量目标反射率的方法的流程图；
图4A和图4B分别示出了回波脉冲信号和回波能量信号的波形示意图；
图5示出了本发明实施例中一种积分电路的具体结构示意图；
图6示出了本发明实施例中一种图5所示积分电路输出的信号示意图；
图7示出了本发明实施例中一种得到目标反射率的具体方法的流程图；
图8示出了本发明实施例中一种采集脉冲信号特征的原理示意图；
图9示出了本发明实施例中一种激光雷达测量目标反射率的方法的具体实施流程图；
图10示出了本发明实施例中一种反射率校准表中反射率映射曲线示意图；
图11示出了本发明实施例中一种激光雷达测量目标反射率的测量装置的结构示意图；
图12示出了本发明实施例中一种激光雷达的结构示意图。
具体实施方式
激光雷达发射的探测光束遇到目标后，一部分被目标反射回激光雷达。激光雷达包括探测器，通过探测器可以接收目标反射的回波信号，进而通过测量探测光束和回波信号之间的时间差可以获得目标的探测信息。硅光电倍增管(Silicon Photomultiplier，SiPM)，是一种由工作在盖革模式的雪崩二极管(或称为单光子雪崩二极管，Single Photon Avalanche Diode，SPAD)阵列组成的且 具有单光子响应特性的新型光电探测器件。由于SiPM通常是基于互补金属氧化物半导体(Complementary Metal Oxide Semiconductor，CMOS)工艺制造的器件，具有极高的光电增益(～10 6)，近年来开始被应用于激光雷达领域。
很多用于激光雷达的SiPM都具有第一输出端口Output1和第二输出端口Output2两个输出端口，从所述第一输出端口Output1或从所述第二输出端口Output2输出的信号均可以被用来测量目标的反射率。
如图1A所示的一种三端口SiPM的电路结构示意图，其中，SiPM 0A包括多个彼此并联的微单元μ-cell，每个微单元μ-cell包括一个SPAD以及与之串联的淬灭电阻R Q，阴极端口Cathode用于施加偏置电压Vbias；阳极端口Anode用于作为第二输出端口Output2，输出回波能量信号；第一输出端口Output1用于输出所述至少一个回波脉冲信号。
又如图1B所示的一种双端口SiPM的电路结构示意图，SiPM 0B与SiPM 0A的不同之处在于，在SiPM 0B的阴极端口Cathode设置分支电路b01作为输出支路，形成第一输出端口Output1，在阳极端口Anode设置分支电路b02，形成第二输出端口Output2。其中，第一分支电路b01通过耦合电容C S0输出回波脉冲信号，第二分支电路b02通过积分电路(例如图5所示的积分电路)输出回波能量信号。
传统上，应用SiPM的激光雷达测量目标反射率，一般是基于回波脉冲信号的脉冲信号特征进行。例如，基于回波脉冲信号的峰值测量目标反射率，此种方案需要激光雷达在探测器信号读出电路配置带宽超过200兆、位数超过10位(bit)的高速模数转换器(Analog-to-Digital，ADC)，这将大大增加激光雷达的功耗和成本，且由于散热设计将增大激光雷达的体积，增加雷达结构的复杂度，并不适应激光雷达小体积、低成本、低功耗的发展趋势。
又如，基于回波脉冲信号的前沿斜率和脉宽测量目标反射率，一般需要激光雷达配置时间数字转换器(Time-to-Digital Converter，TDC)对回波脉冲信号进行采样，是目前飞行时间(Time of Flight，ToF)测量功耗、成本相对较优的方案，十分适合激光雷达的小型化。然而，回波脉冲信号的前沿斜率和脉宽随机抖动很大，很难获得高精准度的反射率测量值；并且，回波脉冲信号的动态范围很窄，容易饱和(目标距离较近时，即使是低反射率的目标，回波脉冲信号的强度也足以使SiPM饱和)，几乎探测不到目标的反射率，造成反射率测量失效。
针对上述基于回波脉冲信号进行测量所存在的上述问题，可以基于第二输 出端口输出的回波能量信号测量反射率，该方法具有很大的动态范围及测量精准度。激光雷达发射探测光信号，探测器接收回波光信号并转换为电信号，在激光雷达的最远目标探测距离对应的飞行时间之后，探测器不再接收该探测光信号被反射的回波光信号。探测器对应该探测光信号接收回波光信号的总时间可以称为探测窗口。在探测窗口内，探测光信号可能仅被一个物体反射，探测器接收到该一个物体反射得到的回波光信号，即单目标回波或单一事件；探测光也可能被多个不同的物体反射，使探测器接收到多个物体分别反射得到的回波光信号，即多目标反射回波，或称为多回波或多事件。
经研究发现，由于第二输出端口输出的回波能量信号覆盖时间较长，多目标回波信号相互交叠而无法区分，所以无法测量多回波所对应的各个目标的反射率。此外，在多回波情形下测量到的反射率数值具有不确定性，容易因为多回波的能量累积引起反射率测量值的漂升，也存在一些局限性。
然而，激光雷达应用于智能驾驶中，容易遇到一些多回波的场景，参照图2所示的激光雷达探测过程中典型的几种多回波场景示意图。一种场景是，激光雷达的一个光发射单元，例如一个激光器所发射的探测光束可能同时照射到前后两个物体上。如图2A所示，激光雷达A发射的探测光束s1分别照射到与激光雷达A距离不同的目标物体T1和T2上，则会接收到这两个目标物体T1、T2反射的回波r1、r2。另一种场景是，激光雷达发射的探测光束可能遇到透光性物体，这样，所述探测光束的一部分会被所述透光性物体反射回来，另一部分则会透过所述透光性物体照射到另一个物体上后并经所述透光性物体反射回来。如图2B所示，激光雷达A发射的探测光束s2先照射到透明或半透明的目标物体T3(例如玻璃)后，所述目标物体T3会向激光雷达A反射回波r3，同时，所述探测光束s2的其中一部分会透过所述目标物体T3照射到目标物体T4，所述目标物体T4反射的回波r4透过所述目标物体T3传递至所述激光雷达A。还有一种场景是，在雨雪、尘埃等天气情形下，激光雷达发射的探测光束的一部分会被雨滴、雪、灰尘等散射回激光雷达，另一部分散射至目标物体，被目标物体反射回激光雷达。如图2C所示，激光雷达A发射的探测光束s3照射到雨滴D0上，发生散射，一部分会作为回波信号r5反射回激光雷达A，另一部分会散射至目标物体T5，目标物体T5反射的回波r6到达激光雷达。
综上可知，目前激光雷达所采用的目标反射率测量方法，难以实现对测距范围内多回波目标的反射率测量，而对于智能驾驶及机器人领域等激光雷达广 泛应用的领域，多回波场景是广泛存在的，因此如何实现对测距范围内多回波目标的识别及探测是亟待解决的问题。
为此，本发明实施例通过分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号，进而根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，可以得到至少一个目标的反射率。采用本发明实施例方案，一方面，由于所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量，另一方面，可以根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，因此可以得到所述探测窗口内所有目标的反射率，实现对测距范围内多回波目标的反射率测量，提高目标反射率测量的准确性和完整性。
在本发明实施例中，所采用的探测器可以是SiPM、也可以是光电二极管(Photodiode，PD)、PIN PD、SPAD等光电探测器件，本发明实施例并不限定所述探测器的具体器件类型，只要通过所述探测器件能够探测得到探测光束被至少一个目标反射的回波，并基于所述回波能够输出所述至少一个目标的回波脉冲信号及回波能量信号即可。
为使本领域技术人员更好地理解本发明实施例的发明构思、技术原理及优点，以及更好地实施本发明，以下结合附图，通过一些具体应用示例进行详细说明。
参照图3所示的激光雷达测量目标反射率的方法的流程图，在本发明实施例中，具体可以采用如下方法进行目标反射率的测量。
S01，分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号。
在具体实施中，可以通过探测器的第一输出端口获取所述至少一个回波脉冲信号，通过所述探测器的第二输出端口获取所述回波能量信号。
作为一具体示例，若探测器具体为SiPM，参照图1，可以在SiPM内分别设置与各微单元μ-cell对应的耦合电容CF，SPAD输出的原始光电流通过耦合电容CF经过一个小的时间常数(例如几纳秒)交流耦合生成电压信号作为所述至少一个回波脉冲信号，如图4A所示，其脉宽W A可能只有几纳秒。
其中，所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量。
在发明一些实施例中，可以根据回波电信号幅度随时间的积分确定所述回波能量信号。激光雷达在测量过程中，可以通过所述探测器的第二输出端口输出一系列长时脉冲信号，如图4B所示，其脉宽W B，可能达百纳秒以上，所述第二输出端口输出的长时脉冲信号具有丰富的直流成分，能够很好地反映回波能量的大小，动态范围大。
为了获得所述回波能量信号，可以在所述探测器的第二输出端口，例如图1所示SiPM的第二输出端口Output2设置一积分电路，以输出所述回波能量信号。在具体实施中，所述回波电信号具体可以为光电流、光电压、探测光子数等其中至少一种。
参照图5所示的一种积分电路的具体结构示意图，例如，SPAD在反向偏压+Vs下工作于盖革模式，SPAD被光子触发后，阴极输出电流脉冲经第一电阻R1和电容C组成的RC电路进行积分，经运算放大器OA转换为电压信号V后供第二ADC(例如可以选用低速ADC)采样，得到积分信号可以作为所述回波能量信号。在一个探测窗口的积分之后，可以将开关K闭合一次，将电容C上的积分电荷清零。
在上述示例中，由于采用的是累计积分的方式，因此可以显著减小单脉冲抖动带来的测量误差，提高目标反射率的测量精度。
在具体实施中，积分电路会把预设时间内的所有回波脉冲都积分进去，例如，若每次ToF测量时激光雷达的激光器发射m个脉冲，则被一个物体反射后回波脉冲信号也包括m个脉冲，SiPM接收到这m个脉冲信号后，可以通过图5所示的积分电路输出这m个脉冲的总电流积分，作为所述回波能量信号。若探测光被n个物体分别反射，则在探测窗口内SiPM将接收到m*n个脉冲，若将预设时间设为整个探测窗口的总时间，可以通过图5所示的积分电路输出这m*n个脉冲的总电流积分。
参照图6所述的积分电路的输出信号的示意图，本实施例中m＝4。若探测器的第一输出端口输出的回波脉冲信号为PL0，对应的第二输出端口经积分电路积分得到光电流积分信号IL0。
在具体实施中，考虑到环境光对探测结果的影响，可以获取所述探测器接收环境光输出的环境光能量信号，并将所述探测器在探测窗口内接收到的能量信号与环境光能量信号之差作为回波能量信号。
在具体应用过程中，由于具体天气条件或地理条件的差别，环境光也可能 有较大差异，为了能够更加真实地反映不同的环境光对目标反射率的影响，针对不同的环境光状态，可以设置与之对应的环境光能量参数。
S02，根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
在本发明实施例中，通过融合回波脉冲信号和回波能量信号的信息，能够识别出目标反射回波对应的一个或多个目标，并可以确定各目标对应的目标反射回波在所述回波能量信号中的占比，从而得到各目标的反射率，因此能够实现测距范围内多回波目标的反射率测量。
在具体实施中，可以根据具体需求，以及具体应用环境的差异，对上述实施例作进一步的扩展或优化。以下分别通过一些应用场景进行示例性说明。
对于步骤S02，以下示出一种可选示例，参照图7所示的得到目标反射率的具体方法的流程图，具体可以包括如下测量过程。
S021，分别采集所述至少一个回波脉冲信号和所述回波能量信号对应的信号特征，得到对应的脉冲信号特征和能量信号特征。
在具体实施中，可以采用信号采集器分别对回波脉冲信号和回波能量信号采集信号特征，得到所述至少一个回波脉冲信号对应的信号特征，以及所述回波能量信号对应的回波信号特征，为描述方便，以下分别称为脉冲信号特征和能量信号特征。
例如，采用第一信号采集器对所述至少一个回波脉冲信号进行采样，得到脉冲信号特征；采用第二信号采集器对所述回波能量信号进行采样，得到所述能量信号特征。作为可选示例，所述第一信号采集器具体可以是ADC(以下称为第一ADC)或者是TDC；所述第二信号采集器也可以采用ADC，为进行区分，可以称为第二ADC。所述第二ADC可以与所述第一ADC采用完全相同的器件，也可以采用结构、参数等不同的器件，只要能够满足所需要的采样需求即可。
通过所述ADC或TDC，可以得到相应信号的数字采样特征。在具体实施中，所述脉冲信号特征具体可以是所述至少一个回波脉冲信号的峰值、脉冲前沿斜率、脉冲后沿斜率、脉冲阈值脉宽和脉冲覆盖面积等其中一种或多种。
参照图8所示的一种采集脉冲信号特征的原理示意图，为方便理解，这里仅以检测到一个脉冲为例，可以理解的是，在实际应用中，可能存在多个脉冲，则可以分别按照同样方式确定各个脉冲的脉冲信号特征。
继续参照图8，假设设置两个脉冲阈值，分别为低阈值L0，高阈值H0，且检测到脉冲m0的峰值为P0，脉冲m0在低阈值L0时的时刻分别为前沿时刻t1和后沿时刻t4，在高阈值H0的时刻分别为前沿时刻t2和后沿时刻t3，则可以获得回波脉冲m0的峰值为P0，前沿斜率k1则为高阈值对应的前沿时刻t2与低阈值对应的前沿时刻t1之差，即k1＝t2-t1；后沿斜率k2则为高阈值对应的后沿时刻t3与低阈值对应的后沿时刻t4之差，即k2＝t3-t4。低阈值脉宽W L＝t4-t1，高阈值脉宽W H＝t3-t2。
在具体实施中，可以取以上其中一个或多个参数作为所述至少一个回波脉冲信号的脉冲信号特征。作为一可选示例，采用第一ADC可以采样得到回波脉冲的峰值作为所述脉冲信号特征。在一具体应用中，可以在探测器的信号读出电路中配置一个高速、中速或低速ADC作为所述第一ADC。作为另一可选示例，所述脉冲信号特征具体包括回波脉冲前沿斜率和阈值脉宽(包括高阈值脉宽和低阈值脉冲其中至少一种)，可以采用TDC对所述至少一个回波信号进行采样，获得回波脉冲前沿斜率和脉宽作为所述脉冲信号特征。
例如，若采用图1所示的SiPM作为探测器，则可以通过其第一输出端口Output1获取所述至少一个回波脉冲信号，所述第一输出端口Output1可以输出各光敏元件SPAD对光信号的响应，作为所述至少一个回波脉冲信号，则可以通过在所述第一输出端口Output1设置第一ADC或TDC，采样得到所述脉冲信号特征。
S022，根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，当确定所述探测器接收到的回波为单目标反射回波时，执行步骤S023；当确定所述探测器接收到的回波为多目标反射回波时，执行步骤S024。
在具体实施中，为了避免通道间干扰，激光雷达的每个通道在做测量时，发射端器件(例如，激光器)，均会发出一组激光脉冲，为描述方便，可以称为发射脉冲组。在一些具体示例中，以相邻两个脉冲之间的时间间隔进行编码，得到该发射脉冲组的编码。相应地，该通道的探测器接收到的回波脉冲信号的编码(例如，多个回波脉冲中各相邻脉冲之间的时间间隔)符合该通道的发射脉冲组的编码时，才将该回波信号测到的目标识别为一个真实目标，进而可以根据该回波信号数据测量对应目标的反射率。
因此，在本发明一些实施例中，通过确定所述至少一个回波脉冲信号中符 合发射脉冲组的编码的脉冲组数量，可以确定所包含的真实目标的数量，故作为一可选示例，可以先确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量，进而可以根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
考虑到激光雷达探测器的工作环境，存在各种光噪声和电噪声，为了减少噪声脉冲的干扰，作为一可选示例，可以选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲作为真实目标对应的回波脉冲，用于后续目标反射率的测量。这种情况下，只有所述探测器输出的回波脉冲信号的幅度超过所述预设幅度阈值，才确认为是真实目标的回波脉冲，从而可以进一步提高测量的准确性。
在具体实施中，综合考虑到上述两个方面因素，只有当所述至少一个回波脉冲信号的幅度超过预设幅度阈值，且符合发射脉冲组的编码时，才被认为是真实目标反射的回波对应的回波脉冲信号。
在一些可选示例中，可以先从所述至少一个回波脉冲信号中选取幅度超过预设幅度阈值的回波脉冲，然后从所述超过预设幅度阈值的回波脉冲中确定符合发射脉冲组的编码的脉冲组数量，并根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
在另一些可选示例中，可以先从所述至少一个回波脉冲信号中选取出符合发射脉冲组的编码的回波脉冲信号，再从符合发射脉冲组的编码的回波脉冲信号中选取幅度超过预设幅度阈值的回波脉冲，确定其中符合发射脉冲组的编码的脉冲组数量，并根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
S023，根据所述能量信号特征，确定所述单目标的反射率。
S024，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
作为一些可选示例，可以根据所述脉冲信号特征，获取各目标对应的反射回波信号特征及其总和，并将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比，进而可以根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
在具体实施中，本发明实施例中并不限定各目标对应的反射回波信号的回波信号特征的具体形式，只要能够反映各目标对应的反射回波的特征即可。在 一些可选示例中，所述各目标对应的反射回波信号的回波信号特征可以为各目标对应的回波脉冲的脉冲峰值、脉冲前沿斜率、脉冲后沿斜率、脉冲阈值脉宽、脉冲覆盖面积等其中一种或多种。上述各参数具体可以通过前述步骤中的具体采样步骤，通过ADC或TDC等信号采集器进行采样得到，具体可以参见前述实施例介绍。
以下简述上述实施例的目标反射率探测原理：
由于基于探测器接收目标反射后输出的回波脉冲信号得到的脉冲信号特征可以反映回波光强度，且由于回波脉冲信号具有脉宽窄的特点，因此根据所述脉冲信号特征容易区分来自不同目标的回波，故首先可以根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，进而，当确定所述探测器接收到的回波为单目标反射回波时，可以根据所述能量信号特征，确定所述单目标的反射率；当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率，从而可以准确地测量得到整个测距范围内不同目标真实的反射率。若应用于智能驾驶，则可以为智能驾驶等智能决策提供可靠依据，保障行车安全。
为使本领域技术人员更好地理解和实施本发明实施例中的目标反射率测量方法，以下通过一个具体应用场景进行示例介绍，参照图9所示的激光雷达测量目标反射率的方法的流程图，具体可以包括如下步骤：
S11，获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波脉冲信号及回波能量信号。
对于任一探测通道，可以获取该探测通道的探测器在一个探测窗口内输出的所有回波脉冲。
如前实施例所述，所述回波能量信号适于表示所述探测器在所述探测窗口内接收到的所有回波能量。在具体实施中，可以根据回波电信号幅度随时间的积分确定所述回波能量信号。所述回波电信号可以为光电流、光电压或探测光子数中的一种或多种。
考虑到环境光的影响，在一可选示例中，可以获取所述探测器接收环境光输出的环境光能量信号，并将所述探测器在探测窗口内接收到的能量信号与环境光能量信号之差作为所述回波能量信号。
S12，分别采集所述回波脉冲信号和所述回波能量信号对应的信号特征， 得到对应的脉冲信号特征和能量信号特征。
在具体实施中，所述脉冲信号特征具体可以包括脉冲幅值，也即脉冲峰值；所述能量信号特征可以包括回波电信号幅度随时间的积分。
例如，若将回波的光电流积分作为所述回波能量信号的能量信号特征，假设所述探测器在探测窗口内得到的所有回波的光电流积分为第一光电流积分V Z，所述探测器在探测窗口内接收环境光输出的光电流积分为第二光电流积分(也可称为被动光电流积分)V B，则所述回波能量信号的光电流积分(也可称为主动光电流积分)V d＝V Z-V B。其中，所述第二光电流积分V B在激光雷达的激光器不发光，同一通道的探测器不测距情况下测量得到。
S13，根据所述回波脉冲信号的脉冲信号特征确定所述探测器接收到的回波的类型是单目标反射回波还是多目标反射回波，若确定为单目标反射回波，则执行步骤S14；若确定为多目标反射回波，则执行步骤S15。
在具体实施中，为了滤除干扰信号，找到真实目标对应的回波脉冲，可以选取所述所有回波脉冲中符合预设条件的回波脉冲，并根据符合预设条件的回波脉冲组的数量确定回波的类型。其中，若符合预设条件的回波脉冲组仅有一组，则确定本次测量事件是单一事件，所述探测器接收到的是单目标反射回波；若符合预设条件的回波脉冲组有两组或两组以上，则确定本次测量是多事件，所述探测器接收到的是多目标反射回波。
作为一可选示例，所述预设条件具体为：回波脉冲的脉冲幅度(即脉冲峰值)超过预设幅度阈值，且所述回波脉冲的时间编码(例如脉冲数量及相邻脉冲之间的时间间隔)符合发射脉冲组的时间编码，则识别为一组回波脉冲，作为一个目标的真实回波。
S14，根据所述回波能量信号，确定所述单目标的反射率。
在本发明一些实施例中，可以根据采样得到的回波能量信号，可以采用线性插值法计算得到所述单目标的反射率。
具体而言，例如回波光电流信号V d，查找所述激光雷达中存储的反射率校准表，根据公式(1)计算得到所述单目标的反射率。
R＝R 1+(V d0-V d(d,R 1))*(R 2-R 1)/(V d(d,R 2)-V d(d,R 1))  (1)
其中，R表征所述单目标的反射率，R 1是第一标准反射板的反射率值，R 2是第二标准反射率板的反射率值，V d0是经过温度补偿和等效光子探测效率(Photon Detection Efficiency，PDE)补偿(即环境光补偿)后的回波电信号的 光电流积分值(也可以称为主动光电流积分值)，V d(d,R 1)和V d(d,R 2)是距离d下，激光雷达照射第一标准反射率板和第二标准反射板时的主动光电流积分值。R 1、R 2、V d(d,R 1)和V d(d,R 2)均可通过查询所述激光雷达内存储的反射率校准表获得，从所述反射率校准表中得到具体数值，所述第一标准反射板和所述第二标准反射板为标定过程中所采用的两个反射率不同的标准反射板。
以下给出一种通过温度补偿和PDE补偿(即环境光补偿)获得回波电信号的光电流积分值(也可以称为主动光电流积分值)V d0的示例方式，具体可以包括如下步骤：
A01，通过激光雷达的直接探测可以获得回波电信号的光电流积分V d、环境光光电流积分(也可称为被动光电流积分)V B、目标距离d、探测器(如SiPM)的温度T。
A02，根据公式(2)对测量得到的探测器的回波光电流积分V d做温度补偿，换算得到标定温度T 0下的光电流积分值V d,T0：
V d,T0＝V d/(k*T+b)  (2)
其中，k、b均为标定参数，V d,T0为标定温度T 0下的光电流积分值，V d为测量得到的探测器的回波光电流积分。
A03，根据环境光光电流积分V B与预设环境光阈值V B0的关系，得到经环境光补偿后的回波电信号的光电流积分值(也可以称为主动光电流积分值)V d0。
在一可选示例中，若V B≤V B0，即当前环境光为弱环境光，可能是室内、隧道中或者阴雨天，则可以令V d0＝V d,T0；若V B>V B0，当前环境光为强环境光，则可以令V d0＝V d,T0*(A*V d,T0+B*V B+C)，其中，A、B、C均为标定参数。作为一具体示例，V B0取值为200mV，可以理解的是，V B0也可以为其他取值，本发明实施例并不限定其具体取值，只要能够提高目标反射率测量的准确性即可。
S15，融合所述回波脉冲信号和所述回波能量信号，测量得到所述多目标反射回波对应的各目标的反射率。
具体而言，首先可以根据所述回波脉冲信号的回波信号特征，获取各目标对应的反射回波的回波信号特征及其总和，将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
假设此次测量的回波能量信号对应的能量信号特征包括：主动光电流积分 V d，由于所述探测器第二输出端口的积分电路的积分时间不小于一次探测的总时间，从而在一次探测中，所述所有回波的第一光电流积分V Z能够覆盖所有事件的回波脉冲组信息，在扣除环境光电流积分V B后的回波光电流积分后的主动光电流积分V d即为所有事件的回波脉冲组的能量之和，因此根据各事件回波的能量在所述主动光电流积分中的占比，可以获得每个事件对应的光电流积分，即每个目标的回波能量，进而可以计算各目标的反射率。
具体地，假设第i个事件对应的回波脉冲信号的回波信号特征为S i，S i反适于反映第i个事件的回波能量强度，则可以采用公式计算事件i分到的回波能量：
V di＝S i*V d/sum(S i)    (3)
将计算得到的事件i的回波能量V di代入至公式(1)，可以计算第i个事件对应的目标的反射率R i。
在具体实施中，假设第i个事件对应的回波脉冲信号的回波信号特征为S i可以包括所述第i个事件对应的回波脉冲信号的脉冲峰值、脉冲前沿斜率、脉冲后沿斜率、阈值脉宽和脉冲覆盖面积等其中至少一种，而并不限于此。
作为一可选示例，可以根据回波脉冲信号计算脉冲覆盖的面积，作为S i，可以更准确地反映出强回波和弱回波的能量差异。在具体实施中，脉冲覆盖的面积可以通过TDC获得的脉冲前沿斜率、脉冲后沿斜率和脉宽计算得出。
为使本领域技术人员更好地理解和实施，以下对步骤S14中激光雷达所存储的反射率校准表的标定过程进行示例介绍。可以理解的是，以下标定过程并不用于限定本发明的保护范围。
为了使用所述回波能量信号测量目标反射率，激光雷达在出厂时可以对所述回波能量信号进行校准标定，其大致过程如下：
1)分别采用第一标准反射率板(反射率为R 1)和第二标准反射率板(反射率为R 2)对回波能量信号进行标定：
1.1)调整激光雷达与标准反射率板的相对位置，使所述激光雷达各通道激光光斑正入射至所述标准反射率板，得到回波光电流信号，或者所述回波光电流的积分信号V d；
1.2)调整所述第一标准反射率板到所述激光雷达的距离，获得所述激光雷达对不同距离下所述第一标准反射率板的探测器(例如SiPM)输出的回波光电 流的积分信号V d的数值。
2)根据标定过程中测量得到的V d与距离d、反射率R 1、R 2的数值关系，生成反射率校准表，存储至所述激光雷达的存储空间，完成校准标定。
如图10所示的一种标定得到的反射率校准表中反射率映射曲线示意图，根据激光雷达实际探测得到的距离d、回报光电流积分信号V d，通过查询横轴的距离d、纵轴对应的回报光电流积分信号V d，可以查到相应目标的目标反射率R。
本说明书中还提供了能够与上述激光雷达测量目标反射率的测量方法对应的测量装置，参照图11所示的激光雷达测量目标反射率的测量装置的结构示意图，在本发明实施例中，如图11所示，激光雷达11A包括探测器11B，测量装置110可以包括：第一信号获取单元111、第二信号获取单元112和处理单元113，其中：
所述第一信号获取单元111，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号；
所述第二信号获取单元112，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
所述处理单元113，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
在具体实施中，所述处理单元可以是中央处理器(Central Processing Unit，CPU)、片上系统(System-on-a-Chip，SoC)、微控制单元(Microcontroller Unit，MCU)、特殊应用集成电路(Application Specific Integrated Circuit，ASIC)、复杂可编程逻辑器件(Complex Programmable Logic Devic，CPLD)、现场可编程门阵列(Field Programmable Gate Array，FPGA)或者数字信号处理器(Digital Signal Processor，DSP)等任意可以进行数据处理的器件。
在具体实施中，所述测量装置110可以集成在所述激光雷达11A内部，这样，所述激光雷达11A在探测过程中，可以即时地输出探测得到的目标反射率，实现对测量范围内可能出现的任意目标的反射率的测量。所述测量装置110可以与所述激光雷达11A共用一些模块或组件，例如所述处理单元113可以采用所述激光雷达中固有的处理器或FPGA运算器件实施。
在具体实施中，所述第一信号获取单元111具体可以为ADC或TDC，所述第二信号获取单元112具体可以为ADC，所述第一信号获取单元111可以设置于所述探测器11B的第一输出端口，所述第二信号获取单元112可以设置于所述探测器11B的第二输出端口。
所述测量装置的具体实施方式及工作原理及优点等均可以参见前述测量方法的详细描述，此处不再赘述。
本发明实施例还提供了一种激光雷达，参照图12所示的激光雷达的结构示意图，激光雷达120包括：探测器121和处理器122，其中：
所述探测器121，适于接收并响应于探测光被至少一个目标反射的回波，输出至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
所述处理器122，与所述探测器121耦接，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
采用上述激光雷达，对目标的反射率进行测量，可以实现测距全程内至少一个回波目标的反射率测量。若将所述激光雷达应用于智能驾驶，则可以为智能驾驶等智能决策提供可靠依据，保障行车安全。
在具体实施中，所述探测器121具体可以是SiPM、也可以是光电二极管(Photodiode，PD)、PIN PD、单光子雪崩二极管(Single Photon Avalanche Diode，SPAD)等光电探测器件，本发明实施例并不限定所述探测器的具体器件类型，只要通过所述探测器件能够探测得到探测光束被至少一个目标反射的回波，并基于所述回波能够输出所述至少一个目标的回波脉冲信号及回波能量信号即可。
在具体实施中，所述探测器具体可以包括：SiPM，所述SiPM可以包括两个输出端口，其中：
第一输出端口，输出所述至少一个回波脉冲信号；
第二输出端口，通过分支电路输出所述回波能量信号。
在具体实施中，所述第一输出端口可以包括：耦合电容；所述第二输出端口可以包括：积分电路。
例如可以采用图1A所示的三端口SiPM作为探测器对回波进行探测，在具体实施中，可以在第一输出端口Output1与各个微单元μ-cell分别连接相应的耦合电容CF以输出回波脉冲信号，通过第二输出端口Output2耦合积分电路以 输出回波能量信号。
或者，也可以采用双端口SiPM作为探测器对回波进行测量，如图1B所示的SiPM的结构示意图，可以在SiPM 0B的阴极端口Cathode设置分支电路b01作为输出支路，形成第一输出端口Output1；在阳极端口Anode设置分支电路b02，形成第二输出端口Output2，其中第一分支电路b01通过耦合电容C S0输出回波脉冲信号，第二分支电路b02通过积分电路(例如图5所示的积分电路)输出回波能量信号。
在具体实施中，继续参照图12，所述激光雷达120还可以包括：第一信号采集器123和第二信号采集器124，其中：
所述第一信号采集器123，适于采集所述至少一个回波脉冲信号对应的信号特征，得到对应的脉冲信号特征；
所述第二信号采集器124，适于采集所述回波能量信号对应的信号特征，得到对应的能量信号特征；
所述处理器122，适于根据所述脉冲信号特征确定所述探测器121接收到的回波的类型为单目标反射回波还是多目标反射回波，当确定所述探测器121接收到的回波为单目标反射回波时，根据所述能量信号特征，确定所述单目标的反射率；当确定所述探测器121接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
作为一可选示例，所述处理器122，适于确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量；根据所述脉冲组的数量，确定所述探测器121接收到的回波的类型为单目标反射回波还是多目标反射回波。
作为另一可选示例，所述处理器122，适于在根据所述脉冲组的数量，确定所述探测器121接收到的回波的类型为单目标反射回波还是多目标反射回波之前，选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲。
在具体实施中，所述处理器122，适于在确定接收到的回波类型为多目标反射回波时，根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和，将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比。
在具体实施中，所述第一信号采集器123，可以包括以下其中至少一种：
第一模数转换器(未示出)，适于对所述至少一个回波脉冲信号进行采样，得到所述脉冲信号特征；
时间数字转换器(未示出)，适于对所述回波能量信号进行采样，得到所述脉冲信号特征；
所述第二信号采集器124，可以包括：第二模数转换器124，适于对所述回波能量信号进行采样，得到所述能量信号特征。
在本说明书一些实施例中，所述探测器121包括多个并联的单光子雪崩二极管，所述第二模数转换器，适于根据所述探测器输出的回波电信号幅度随时间的积分确定所述回波能量信号，所述回波电信号幅度与所述探测器中被触发的单光子雪崩二极管的数量正相关。
在具体实施中，所述处理器具体可以为CPU、SoC、MCU、ASIC、CPLD、FPGA或者DSP等任意可以进行数据处理的器件。
激光雷达的具体工作原理及可实现示例、优点等均可以参见前述方法的具体实施例，此处不再详细描述。
虽然本发明实施例披露如上，但本发明并非限定于此。任何本领域技术人员，在不脱离本发明的精神和范围内，均可作各种更动与修改，因此本发明的保护范围应当以权利要求所限定的范围为准。

Claims (19)

  1. 一种激光雷达测量目标反射率的方法，所述激光雷达包括探测器，其特征在于，所述方法包括：
    分别获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
    根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
  2. 根据权利要求1所述的方法，其特征在于，所述根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率，包括：
    分别采集所述至少一个回波脉冲信号和所述回波能量信号对应的信号特征，得到对应的脉冲信号特征和能量信号特征；
    根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波；
    当确定所述探测器接收到的回波为单目标反射回波时，根据所述能量信号特征，确定所述单目标的反射率；
    当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
  3. 根据权利要求2所述的方法，其特征在于，所述根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，包括：
    确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量；
    根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
  4. 根据权利要求3所述的方法，其特征在于，在根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波之前，还包括：
    选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲。
  5. 根据权利要求2所述的方法，其特征在于，所述当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率，包括：
    根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和；
    将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比。
  6. 根据权利要求5所述的方法，其特征在于，所述各目标对应的反射回波信号的回波信号特征包括以下至少一种：
    脉冲峰值、脉冲前沿斜率、脉冲后沿斜率、脉冲阈值脉宽、脉冲覆盖面积。
  7. 根据权利要求1所述的方法，其特征在于，获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波能量信号包括：
    获取所述探测器接收环境光输出的环境光能量信号；
    将所述探测器在探测窗口内接收到的能量信号与环境光能量信号之差作为回波能量信号。
  8. 根据权利要求1所述的方法，其特征在于，根据回波电信号幅度随时间的积分确定所述回波能量信号。
  9. 根据权利要求8所述的方法，其特征在于，所述回波电信号为光电流、光电压、探测光子数中的至少一种。
  10. 一种激光雷达测量目标反射率的测量装置，所述激光雷达包括探测器，其特征在于，所述测量装置包括：
    第一信号获取单元，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的至少一个回波脉冲信号；
    第二信号获取单元，适于获取所述探测器接收探测光束被至少一个目标反射的回波后输出的回波能量信号；所述回波能量信号适于表示所述探测器在探测窗口内接收到的所有回波能量；
    处理单元，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
  11. 一种激光雷达，其特征在于，包括：
    探测器，适于接收并响应于探测光被至少一个目标反射的回波，输出至少一个回波脉冲信号和回波能量信号；所述回波能量信号适于表示所述探测器在 探测窗口内接收到的所有回波能量；
    处理器，与所述探测器耦接，适于根据所述至少一个回波脉冲信号确定所述至少一个目标反射回波的能量在所述回波能量信号中的占比，得到至少一个目标的反射率。
  12. 根据权利要求11所述的激光雷达，其特征在于，还包括：
    第一信号采集器，适于采集所述至少一个回波脉冲信号对应的信号特征，得到对应的脉冲信号特征；
    第二信号采集器，适于采集所述回波能量信号对应的信号特征，得到对应的能量信号特征；
    所述处理器，适于根据所述脉冲信号特征确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波，当确定所述探测器接收到的回波为单目标反射回波时，根据所述能量信号特征，确定所述单目标的反射率；当确定所述探测器接收到的回波为多目标反射回波时，分别根据各目标反射回波的能量在所述回波能量信号中的占比，分别得到各目标的反射率。
  13. 根据权利要求12所述的激光雷达，其特征在于，所述处理器，适于确定所述至少一个回波脉冲信号中符合发射脉冲组的编码的脉冲组数量；根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波。
  14. 根据权利要求13所述的激光雷达，其特征在于，所述处理器，适于在根据所述脉冲组的数量，确定所述探测器接收到的回波的类型为单目标反射回波还是多目标反射回波之前，选择所述至少一个回波脉冲信号中包含的幅度超过预设幅度阈值的回波脉冲。
  15. 根据权利要求12所述的激光雷达，其特征在于，所述处理器，适于在确定接收到的回波类型为多目标反射回波时，根据所述脉冲信号特征，获取各目标对应的反射回波的回波信号特征及其总和，将所述各目标的回波信号特征在总和中的占比，作为各目标反射回波的能量在所述回波能量信号中的占比。
  16. 根据权利要求12所述的激光雷达，其特征在于，所述第一信号采集器，包括以下其中至少一种：
    第一模数转换器，适于对所述至少一个回波脉冲信号进行采样，得到所述脉冲信号特征；
    时间数字转换器，适于对所述回波脉冲信号进行采样，得到所述脉冲信号 特征；
    所述第二信号采集器，包括：
    第二模数转换器，适于对所述回波能量信号进行采样，得到所述能量信号特征。
  17. 根据权利要求16所述的激光雷达，其特征在于，所述探测器包括多个并联的单光子雪崩二极管，所述第二模数转换器，适于根据所述探测器输出的回波电信号幅度随时间的积分确定所述回波能量信号，所述回波电信号幅度与所述探测器中被触发的单光子雪崩二极管的数量正相关。
  18. 根据权利要求17所述的激光雷达，其特征在于，所述探测器包括：硅光电倍增管，所述硅光电倍增管包括两个输出端口，其中：
    第一输出端口，输出所述至少一个回波脉冲信号；
    第二输出端口，通过分支电路输出所述回波能量信号。
  19. 根据权利要求18所述的激光雷达，其特征在于，所述第一输出端口包括：耦合电容；所述第二输出端口包括：积分电路。
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