WO2022206031A1 - Procédé de détermination de niveau de bruit, lidar et procédé de télémétrie - Google Patents

Procédé de détermination de niveau de bruit, lidar et procédé de télémétrie Download PDF

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Publication number
WO2022206031A1
WO2022206031A1 PCT/CN2021/138328 CN2021138328W WO2022206031A1 WO 2022206031 A1 WO2022206031 A1 WO 2022206031A1 CN 2021138328 W CN2021138328 W CN 2021138328W WO 2022206031 A1 WO2022206031 A1 WO 2022206031A1
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Prior art keywords
time
intensity
information
noise
time information
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PCT/CN2021/138328
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English (en)
Chinese (zh)
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章洪燕
许帅骑
杨晋
向少卿
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上海禾赛科技有限公司
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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
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • 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
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
    • 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
    • G01S7/491—Details of non-pulse systems
    • G01S7/493—Extracting wanted echo signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C3/00—Measuring distances in line of sight; Optical rangefinders
    • G01C3/02—Details
    • G01C3/06—Use of electric means to obtain final indication
    • G01C3/08—Use of electric radiation detectors

Definitions

  • the present disclosure relates to the technical field of photoelectric detection, and in particular, to a method for determining a noise level, a laser radar, and a method for ranging using the laser radar.
  • Lidar is a radar system that emits a laser beam to detect the position, speed and other characteristics of the target. It is an advanced detection method that combines laser technology with photoelectric detection technology. Because of its high resolution, good concealment, strong anti-active interference ability, good low-altitude detection performance, small size and light weight, lidar is widely used in autonomous driving, transportation and communication, unmanned aerial vehicles, intelligent robots, resource exploration and other fields.
  • the environment in which the lidar is located is usually full of various noises or background light, such as sunlight, the lights of other vehicles, the lights of buildings, and the laser light emitted by the lidar on other vehicles.
  • the lidar In order to accurately calculate the distance of the target, the lidar needs to obtain the noise level in the surrounding environment as accurately as possible, and distinguish the echo generated by the laser beam emitted by itself from the surrounding noise.
  • TDC time-to-digital converter
  • a single photon avalanche diode can be used as a detector in the lidar, and the SPAD can be triggered by a single photon to avalanche.
  • the output terminals of multiple SPADs are connected to the same TDC, as a macro pixel (pixel), the TDC provides the trigger moment and the number of SPADs that are simultaneously triggered in the macro pixel.
  • noise acquisition methods one is to fix the noise information, that is, the detection of all cycles in several cycles or even a period of time adopts the same fixed noise threshold, so that real-time noise information cannot be obtained; Data other than the arrival time of the signal is used to calculate the noise, but in this way, the noise and the signal will affect each other, and it is difficult to obtain accurate noise information.
  • the present invention provides a method for determining a noise level, including:
  • S102 Clamp the intensity information-time information curve with an estimated noise threshold
  • the intensity information-time information curve is a photon number histogram.
  • the step S101 includes: scanning a field of view multiple times, and superimposing the intensity information versus time information curves of the multiple scans as the intensity information-time information curve.
  • the method further includes: acquiring the total intensity of the optical signal, calculating an estimated noise intensity using the total intensity, comparing the estimated noise intensity with a preset noise intensity, and obtaining a smaller value, Take the smaller value as the estimated noise threshold.
  • the step of calculating the estimated noise intensity includes: multiplying the total number of photons S by a preset ratio K to obtain the estimated noise photon number, as the estimated noise intensity, the preset ratio K is between 0-1.
  • the step S101 further includes: receiving an optical signal through a detection unit, where the detection unit includes a plurality of single-photon avalanche diodes, and the preset noise intensity is based on the single-photon avalanche diodes in the detection unit. One or more of the number, the dead time of the single photon avalanche diode is determined.
  • the step S103 includes: obtaining the total intensity of the clamped intensity information-time information curve, relative to the average value of the time span, as the noise level.
  • step S102 for the intensity information corresponding to any time information, the smaller value of the intensity information and the estimated noise threshold is taken as the clamped intensity information.
  • the present invention also provides a method for ranging by means of laser radar, comprising:
  • S203 Calculate the distance of the target object based on the intensity information-time information curve after noise filtering.
  • the step S202 includes: judging whether the peak value of the intensity information-time information curve is higher than the noise level; when the peak value is higher than the noise level, based on the noise level, Perform noise filtering processing on the intensity information-time information curve.
  • the step S203 includes: calculating the center of gravity of the intensity information relative to the time information according to the intensity information-time information curve after noise filtering, and the time information corresponding to the center of gravity is taken as the flight time.
  • the step S203 includes: calculating the leading edge time of the echo pulse according to the filtered intensity information-time information curve, and using the leading edge time as the flight time, wherein the leading edge time is the time information corresponding to the intensity information on the leading edge of the echo pulse equal to the preset threshold.
  • the present invention also provides a laser radar, comprising:
  • a light emission module configured to emit a detection laser beam for detecting a target
  • a light detection module configured to receive echoes of the detection laser beam reflected on the target and convert them into electrical signals
  • the control module is coupled to the light emitting unit and the light detection module, and is configured to execute the method as described above to calculate the distance of the target.
  • the light detection module includes a plurality of detection units, each detection unit includes a plurality of single-photon avalanche diodes to receive the echoes.
  • FIG. 1 shows a method for determining a noise level according to an embodiment of the present invention
  • Figure 2 shows an intensity information-time information curve according to an embodiment of the present invention
  • Figure 3 shows the intensity information-time information curve after clamping
  • Figure 4 shows a schematic diagram of the number of echo photons obtained by multiple scans in one measurement
  • FIG. 5 shows a schematic diagram of a histogram obtained by accumulating the number of echo photons of multiple scans
  • Figure 6 shows a detection unit according to an embodiment of the present invention
  • Fig. 7 shows the curve waveform obtained after the intensity information-time information noise filtering processing
  • FIG. 8 shows a method for ranging by a lidar according to a preferred embodiment of the present invention
  • Figure 9 shows a data storage method according to the prior art
  • Figure 12 shows a block diagram of a lidar according to one embodiment of the present invention.
  • connection should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection Connection, or integral connection: it can be a mechanical connection, an electrical connection or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal communication of two elements or the interaction of two elements relation.
  • connection should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection Connection, or integral connection: it can be a mechanical connection, an electrical connection or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal communication of two elements or the interaction of two elements relation.
  • a first feature "on” or “under” a second feature may include direct contact between the first and second features, or may include the first and second features Not directly but through additional features between them.
  • the first feature being “above”, “over” and “above” the second feature includes that the first feature is directly above and diagonally above the second feature, or simply means that the first feature is level higher than the second feature.
  • the first feature “below”, “below” and “beneath” the second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature has a lower level than the second feature.
  • FIG. 1 shows a method 100 for determining a noise level according to an embodiment of the present invention, which can be used to determine a noise level or threshold in a lidar, which will be described in detail below with reference to FIG. 1 .
  • step S101 obtaining the intensity information-time information curve of the optical signal.
  • FIG. 2 shows an intensity information-time information curve according to an embodiment of the present invention, wherein the abscissa is the time information, and the ordinate is the parameter value representing the optical signal intensity information.
  • the abscissa in FIG. 2 is not an absolute time coordinate, and the abscissa is the time difference between the time when the laser radar transmits the light pulse and the time when the light signal is received.
  • the intensity information-time information curve shown in Fig. 2 can be the intensity information-time information curve obtained in one scan of the lidar for a certain field of view, or it can be obtained in multiple scans of a certain field of view Curves formed by superimposing the intensity information of the optical signal with respect to the time information are all within the protection scope of the present invention.
  • the ordinate in FIG. 2 can use the number of photons to represent the intensity of the optical signal.
  • step S102 the intensity information-time information curve is clamped by using an estimated noise threshold.
  • Estimated noise thresholds are shown in FIG. 2 (shown by the line of “Noise Thresholds” in FIG. 2 ).
  • the clamping refers to comparing the intensity information corresponding to any time scale with the estimated noise threshold, and taking the smaller value as the intensity information after clamping. That is, for the part of the intensity information-time information curve where the intensity information is higher than the estimated noise threshold, take the estimated noise threshold; for the intensity information-time information curve, the intensity information is lower than the estimated noise For the part of the threshold, take the actual intensity information.
  • the intensity information corresponding to each time scale is compared in turn to obtain a clamped intensity information-time information curve.
  • the estimated noise threshold set in FIG. 2 is used for clamping, and the clamped intensity information-time information curve shown in FIG. 3 is obtained.
  • step S103 the noise level is determined using the clamped intensity information-time information curve.
  • an average value of the clamped intensity information relative to the time information can be obtained as the noise level.
  • the area of the area covered by the clamped intensity information-time information curve can be obtained, and then divided by the total time span, that is, the time span of the clamped intensity information-time information curve on the horizontal axis, and the clamped intensity information-time information curve can be obtained.
  • the intensity information relative to the time span is averaged as the noise level.
  • the clamped intensity information shown in FIG. 3 is characterized by the number of photons, and the total number of photons in the total time span is calculated and divided by the total time span to obtain the noise level characterized by the number of photons.
  • the noise value can be calculated directly by using the intensity information-time information curve obtained by lidar detection, and it is not necessary to reserve a special detection time for noise measurement; and after obtaining an intensity information-time information curve, it can be
  • the noise level corresponding to the detection data can be obtained by calculating the detection data, that is, the real-time noise can be acquired while measuring the distance, and the accuracy of the noise level can be improved. Taking the noise level calculated in real time as the corresponding ranging noise threshold can improve the ranging accuracy.
  • lidar In the detection process of lidar, take the detector composed of single-photon avalanche diode SPAD(s) as an example, because SPAD can be triggered by a single photon to avalanche effect, so it is easily affected by environmental noise;
  • the photon detection efficiency (PDE) of the commonly used detection light band of lidar is low, and the signal intensity obtained by a single detection is very weak. It is in Geiger mode within the time window, that is, the state where the avalanche effect can be triggered by photons. This time window is called the "detection time window". Only a few triggers occur within the time window, and it is impossible to distinguish whether it is triggered by the echo signal reflected by the target or Triggered by ambient noise.
  • the same field of view range can be repeatedly scanned multiple times.
  • the light source at the transmitting end emits a light pulse for detection, and the controller of the lidar records the emission time t1 when the light pulse is emitted.
  • the light pulse encounters an external obstacle, is reflected by the obstacle, and returns to the The lidar is received by the photodetector at the receiving end.
  • the photodetector is an array of SPAD(s)
  • ambient light may also cause the SPAD to be triggered avalanche.
  • an avalanche electrical signal is generated, which is transmitted to the time-to-digital converter TDC.
  • the TDC outputs the time signal of the SPAD trigger and the signal of the number of SPADs that are triggered at the same time, and the subsequent memory stores the SPAD trigger time minus the launch time t1.
  • the timestamp timestamp that is, the time information represented by the horizontal axis in Figures 2 and 3) and the trigger number of the timestamp (hereinafter referred to as cnt) signal.
  • the trigger number cnt obtained by each measurement is stored in the corresponding memory location according to the timestamp timestamp.
  • a new trigger number cnt arrives at the corresponding position of a timestamp timestamp
  • the original stored value is compared with the new trigger number cnt. Accumulate and then update to this position.
  • a histogram is saved in the memory. As shown in Figure 5, the histogram reflects the sum of the number of triggers cnt corresponding to different timestamps on the time axis. In this way, the histogram is used to calculate
  • the time of flight corresponding to the echo pulse is obtained by operations such as the center of gravity, and then the ranging result is obtained.
  • the lidar in one time-of-flight measurement of the lidar for a field of view, the lidar actually performs multiple scans (multiple transmit-receive cycles), and the number of scans can range from dozens to several times. Hundreds of times, scan a field of view (or approximately one target point) within a period of time, and superimpose the curve of the intensity information received by the detector relative to the time information in the multiple scans as the intensity information - Time information curve.
  • nth scans For example, as shown in Figure 4, in the 1st, 2nd, ..., nth scans, only a very limited number of echoes or photons are received in each scan, but after the detection results of n scans are superimposed, Obtain the photon number histogram of one time-of-flight measurement in this field of view, as shown in Figure 5, where the scale of the abscissa is time information, and the scale width on the time axis is usually equal to the resolution of the time-to-digital converter in the lidar, That is, the resolution of the detection time of the lidar.
  • the total number of photons S can be obtained by accumulating the number of photons corresponding to each scale on the photon number histogram, which is used to represent the total intensity information.
  • a “measurement” corresponds to the time-of-flight measurement of a certain field of view within a detection period of the lidar (that is, within the period of generating a frame of point cloud) to generate a point cloud in a frame. Or multiple (one or more columns or one block) "points", a complete frame of point cloud is obtained after the measurement of all fields of view is completed; and “scanning” refers to the laser in a detection channel during a measurement process The process of completing a transmission and the detector completing the corresponding reception.
  • a “measurement” may include a single “scan” or multiple “scans” of the same target point, eg hundreds of times.
  • the method 100 further includes: acquiring the total intensity of the optical signal, calculating an estimated noise intensity (for example, represented by the number of photons) according to the total intensity, and setting parameters according to the receiving end of the lidar. Set the preset noise level.
  • the total intensity of the optical signal can be characterized by the total number of photons S received in the total time span.
  • the total time span corresponds to the total time during which the intensity information is recorded on the curve shown in FIG. 2 , that is, the difference between the maximum value and the minimum value of the time information.
  • the time range corresponding to the maximum detection distance and the minimum detection distance of the lidar can be used as the total time span. Or alternatively, as shown in FIG. 2 , only the intensity information corresponding to part of the time information is recorded.
  • the time period during which the reflected echo of the target can be expected to be obtained is used as the total time span of the intensity information-time information curve.
  • the total intensity of the optical signal can be characterized by the area covered by the intensity information-time information curve in FIG. 2 . According to a preferred embodiment of the present invention, the total intensity can be characterized by the total number of photons S received in the total time span.
  • the total number of photons S in the total time span can be multiplied by a preset ratio K to obtain the estimated noise photon number, which is used as the estimated noise intensity, and the preset ratio K is between 0- between 1.
  • the preset ratio K ⁇ (0,1), the empirical value of the ratio of the noise number to the total photon number can be obtained as K through simulation or actual measurement.
  • the receiving end parameters of the lidar include the total number of detection units (pixels), the number of SPADs in each detection unit, and the dead time of the SPAD, according to which the SPAD (unit time) is calculated. ) of the average maximum noise trigger photon number S max , which is taken as the preset noise intensity. Regarding how to calculate S max , specific examples will be given below.
  • the estimated noise intensity calculated according to the intensity information-time information curve is compared with the preset noise intensity S max , a smaller value is obtained, and the smaller value is used as the estimated noise threshold.
  • step S102 for the intensity information corresponding to any time information, the smaller value of the intensity information and the estimated noise threshold is taken as the clamped intensity information.
  • the step S101 further includes: receiving the echo through a detection unit, where the detection unit includes a plurality of single-photon avalanche diodes.
  • the preset noise intensity is determined based on one or more of the number of single-photon avalanche diodes in each detection unit and the dead time of single-photon avalanche diodes.
  • FIG. 6 shows an embodiment of the detection unit.
  • the detection module includes a plurality of detection units, and the detection units P1, P2 and P3 are shown in the figure, and each detection unit includes nine single-photon avalanche diodes respectively.
  • the nine single-photon avalanche diodes are all connected to a time-to-digital converter TDC, so that the TDC can obtain the time signal of the SPAD triggered in the detection unit and the signal of the number of SPADs triggered at the same time, and store them in the memory.
  • a detection unit can trigger up to 9 times within the SPAD dead time.
  • the dead time of the SPAD in the detection unit shown in Figure 6 is set to be 20 ns, and the same SPAD can be triggered at most once within 20 ns.
  • the noise level can be calculated directly by using the intensity information-time information curve (such as a histogram) obtained by detection, and it is not necessary to reserve a detection time for noise measurement; and real-time noise can be obtained while ranging, which can be used as Ranging noise threshold.
  • the noise threshold can be used to judge whether the echo is valid, that is, the echo pulse signal reflected from the target object or the noise signal. If the measured echo strength is lower than the noise threshold, it is judged as noise and filtered.
  • the set noise threshold is higher than the actual noise level, the actual detected echo will be misjudged as noise, resulting in data loss; if the set noise threshold is lower than the actual noise level, some noise signals will be judged as targets Objects reflect echoes, creating noise in the point cloud.
  • the environmental noise around the lidar is also constantly changing, and the inability to obtain the noise in real time will also cause lost points or noise.
  • the above embodiments of the present invention can acquire the noise level in real time, improve the signal-to-noise ratio of the laser radar, and thus improve the ranging accuracy.
  • the present invention also provides a method 200 for ranging by using a laser radar, including:
  • S201 Calculate the noise level through the method 100 as described above.
  • S202 Perform noise filtering processing on the intensity information-time information curve based on the noise level.
  • a peak value is obtained on the intensity information-time information curve, that is, the maximum value of the intensity information on the total flight time span, and it is determined whether the peak value is higher than the noise level, and if it is higher than the noise level level, the intensity information-time information curve is subjected to noise filtering processing.
  • the noise filtering process for example, compares the intensity information corresponding to each time scale with the noise level, retains the intensity information data higher than the noise level, and subtracts the noise level from the intensity information data to obtain the intensity corresponding to the actual detection signal.
  • Information-time information curve For example, compares the intensity information corresponding to each time scale with the noise level, retains the intensity information data higher than the noise level, and subtracts the noise level from the intensity information data to obtain the intensity corresponding to the actual detection signal.
  • S203 Calculate the distance of the target object based on the intensity information-time information curve after noise filtering.
  • the step S203 includes: according to the time information corresponding to the center of gravity of the intensity information-time information curve after noise filtering processing on the time axis, as the flight time, calculating the time of the target object. distance.
  • the curve waveform obtained after the noise filtering process is shown.
  • the center of gravity position of the curve waveform is obtained, and the flight time Tof1 corresponding to the center of gravity position is taken as the time of flight in this measurement process.
  • Time of flight which is used to calculate the distance to the target and generate a data point in the point cloud.
  • the maximum value of the intensity information is obtained, and as the echo intensity, the detection light intensity emitted by the lidar is obtained, and the target object can be calculated based on the echo intensity and the detection light intensity. reflectivity.
  • Fig. 8 shows a method for ranging by a lidar according to a preferred embodiment of the present invention, wherein the detection methods shown in Figs. 4-7 are combined. This is described in detail below with reference to FIG. 8 .
  • the lidar performs multiple scans, taking 500 times as an example.
  • step S301 the i-th scan is performed, and i is initially 1.
  • the laser of the lidar emits the detected light pulse, and the controller of the lidar records the emission time t1 of the emitted light pulse.
  • the light pulse encounters an external obstacle, is reflected by the obstacle and returns to the lidar, and is detected by the photoelectric detection of the receiving end. received by the device.
  • the photodetector is an array of SPAD(s)
  • ambient light may also cause the SPAD to be triggered avalanche.
  • the SPAD receives the photon, it generates an avalanche electrical signal, which is transmitted to the time-to-digital converter TDC.
  • the TDC outputs the time signal of the SPAD trigger and the signal of the number of SPADs that are triggered at the same time, and stores the SPAD trigger time minus the time stamp of the launch time t1.
  • timestamp that is, time information
  • cnt the trigger number of the timestamp
  • step S302 the detection results of the i-th scan and the detection results of the previous i-1 times are accumulated.
  • a new trigger number cnt arrives at the position corresponding to a certain timestamp timestamp
  • the original stored value and the new trigger number cnt are accumulated and then updated to the position.
  • all cnt values are accumulated (time stamps are not distinguished) to obtain the total number of SPAD triggers, which are used to obtain the total intensity of the optical signal for one measurement.
  • step S303 it is determined whether i has reached a preset number of scans N, for example, 500. If it has not been reached yet, accumulate i, and go back to step S301 to continue scanning detection. If the preset number of scans N has been reached, proceed to step S304.
  • a preset number of scans N for example, 500.
  • step S304 a histogram is generated. Since N scans have been completed, the number of triggers cnt obtained in each scan is stored in the corresponding memory location according to the time stamp timestamp. After multiple measurements are superimposed, a histogram is stored in the memory, as shown in Figure 5. The histogram reflects the sum of the number of triggers cnt corresponding to different timestamps on the timeline. The data in memory can be read out as a histogram. At the same time, all the cnt values are accumulated to obtain the total intensity of the optical signal represented by the number of photons in one measurement.
  • step S305 the data of the histogram is filtered. After that, steps S306 and S307 are performed respectively.
  • step S306 the noise level is obtained, for example, the noise threshold around the lidar is obtained according to the method 100 described above.
  • step S307 the peak value of the signal is found according to the filtered histogram, that is, the point with the largest ordinate in the histogram is found.
  • step S308 according to the noise level obtained in step S306, it is determined whether the signal peak value found in step S307 is valid, that is, whether the signal peak value is greater than the noise level. When the signal peak value is greater than the noise level, the signal peak value is valid, and then step 309 is performed. When the signal peak value is lower than the noise level, the signal peak value is invalid and not processed.
  • step S309 ranging information is obtained.
  • the center of gravity of the intensity information in the total time span is calculated, and the time information corresponding to the center of gravity is used as the flight time to calculate the distance of the target object.
  • the distance to the target object is calculated using the echo pulse leading edge time. Specifically, the intensity information of the front edge of the echo pulse is compared with a preset threshold, and the time information corresponding to the intensity information whose intensity is equal to the preset threshold is used as the flight time.
  • the above-mentioned preset threshold is a noise threshold.
  • the above-mentioned preset threshold is an average value of the signal peak value and the noise threshold value.
  • step 309 the above-mentioned methods of S202-S203 may be used to perform noise filtering processing on the intensity information-time information curve based on the noise level, and then based on the intensity information-time information curve after the noise filtering processing, Calculate the distance and/or reflectivity of the target.
  • the detection results of N scans are superimposed and stored. After all scans are completed, the data in the memory can be read out as a histogram, and the histogram data is filtered. , look for signal peaks.
  • the noise calculation method of the present invention the real-time noise value of the histogram can be obtained as the current noise threshold. When it is judged that the peak value of the histogram signal is greater than the noise threshold, the peak value is an effective peak value, and then the echo arrival time is calculated. Therefore, the noise level and ranging information of the current measurement can be obtained almost simultaneously after one measurement is completed. Compared with the solution of setting a uniform noise threshold for the lidar, the solution of dynamically calculating the noise level of the embodiment of the present invention is more accurate.
  • the noise level is calculated by using the scheme of the embodiment of the present invention, and the distance and/or reflectivity of the target object are calculated after the intensity information is filtered out of the noise.
  • the filtered intensity information can reflect a more real echo pulse signal. Conducive to improving the measurement accuracy.
  • the second aspect of the present invention relates to a method for storing detection data of a lidar, which can be combined with the method 100 for determining a noise level applied to the first aspect of the present invention.
  • each time scale of its time resolution needs to have a corresponding storage location, and all the triggered SPAD number information cnt obtained by multiple measurements are stored in the same time as the time.
  • the time resolution of the time-to-digital converter TDC can reach the order of picoseconds ps, so a register with a very large space is required.
  • SPAD can be triggered by a single photon to avalanche effect, so it is easily affected by ambient light noise; on the other hand, SPAD has low photon detection efficiency (PDE) for the commonly used detection light band of lidar, and the signal obtained by a single detection
  • PDE photon detection efficiency
  • the intensity is very weak, as shown in Figure 4.
  • the lidar can perform multiple repeated measurements during one detection of the same field of view (one measurement is called a sweep). , the number of repetitions can reach 400-500 times, or more or less), the results of multiple measurements or scans are accumulated to obtain a histogram, and the distance is measured from this, and then a point cloud on the lidar is obtained. point.
  • the controller of the lidar gates some (a row or column or any shape of interest) macro pixels by supplying high voltage to the SPAD, and then sends a synchronization signal to notify the laser at the transmitter that it can emit light, and the laser at the transmitter
  • a light pulse for detection is sent out.
  • the light pulse encounters an external obstacle, is reflected by the obstacle and returns to the lidar, and can be received by the photodetector at the receiving end. .
  • the photodetector is a SPAD(s) array
  • an avalanche electrical signal is generated, which is transmitted to the time-to-digital converter, and the time-to-digital converter outputs the time signal t 1a triggered by the SPAD and the SPAD triggered at the same time.
  • the number signal cnt 1a (here 1a represents the first trigger of the a-th scan)
  • the timestamp 1a (hereinafter referred to as tp 1a ) of t 1a -t a is calculated by the subtraction procedure
  • tp 1a and the time The number of triggers for stamping the cnt 1a signal is transmitted and stored in memory.
  • a macro pixel includes multiple SPADs, and SPADs can be detected again after the dead time, so in one scan, SPAD triggering may occur at another time, and the memory stores tp 2a and cnt 2a of this trigger (2a is Represents the 2nd trigger of the a-th probe). Multiple triggers in one scan need to be stored as time information.
  • the controller of the lidar sends a signal again according to the preset program to control the transmitting end to send out the detection light pulse at time t b .
  • the SPAD receives the photon
  • the avalanche electrical signal is transmitted to the time-to-digital converter TDC, and the time-to-digital converter TDC outputs the time signal t 1b triggered by the SPAD and the signal cnt 1b of the number of SPADs triggered at the same time (the b-th detection 1 trigger)
  • the subsequent memory stores the timestamp timestamp 1b (hereinafter referred to as tp 1b ) of the SPAD trigger time t 1b -t b and the trigger number cnt 1b signal of the timestamp.
  • a macro pixel includes multiple SPADs, and the SPADs can be detected again after the dead time, so in one scan, the SPAD may be triggered again at another time, and the memory stores tp 2b and cnt 2b of this trigger
  • the trigger number cnt obtained by each measurement is stored in the corresponding memory location according to the timestamp.
  • the original stored value is compared with The new trigger number cnt is accumulated and then updated to this position.
  • a histogram is saved in the memory. As shown in Figure 5, the histogram reflects the sum of the trigger numbers cnt corresponding to different timestamps on the time axis. In this way, the histogram is used to calculate the center of gravity or the frontier time and other operations to obtain the time information corresponding to the echo, which is used as the flight time for distance calculation to generate a point on the point cloud.
  • a data storage method is shown in Figure 9.
  • the abscissa is time t
  • the scale interval of the abscissa is the resolution of TDC
  • each time scale corresponds to a storage location R (register).
  • R register
  • a SPAD trigger occurs at time scale 0.
  • the timestamp tp 1 (trigger time - the current transmission time)
  • the trigger number information cnt 1a are obtained by calculation, and cnt 1a is stored.
  • a represents the a-th detection
  • b is the b-th detection
  • the numbers represent the corresponding time scale and the corresponding storage location
  • the storage location R corresponds to the time scale one-to-one
  • the memory only stores the trigger number cnt
  • the data processing When the circuit reads the data, the time corresponding to the trigger number cnt can be known according to the storage location).
  • a histogram is obtained by accumulating the data of many detection scans (400-500 times), and the detection results of hundreds of scans are superimposed into a histogram to obtain a point in the point cloud.
  • the storage location corresponding to the time scale stores the accumulated sum of all the trigger quantities cnt triggered at this moment.
  • SPAD triggering does not occur at every time scale in a scan, as shown in Figure 9, a histogram data is superimposed by many detection results, and each time scale may be triggered at a certain scan A SPAD trigger occurs during the process, so that the memory receives the corresponding data.
  • each time scale needs to have a corresponding storage location, and all the trigger numbers cnt obtained from multiple measurements are stored in the storage location corresponding to the time.
  • the time interval of tp that is, the resolution of TDC
  • the rate is on the order of ps, requiring very large registers.
  • the inventor of the present application has conceived that it is not necessary to set a corresponding storage location for each time scale of the TDC time resolution.
  • the invention adopts the data storage method of weighted accumulation, compresses the original signal under the condition of keeping the ranging precision, and greatly reduces the storage space required for storing the histogram. Specifically, the weighted accumulation data storage method can reduce the total storage space to 1/10 of the original range.
  • the time precision of the stored intensity information in the present invention is the first time precision, and the first time precision may be n times the time resolution of the time-to-digital converter TDC.
  • the intensity information refers to the optical signal intensity information corresponding to the time information.
  • different parameters can be used to represent the optical signal intensity: for example, the detector is a SPAD array, and the SPAD that is triggered at the same time corresponding to the time information can be used.
  • the quantity is used as the intensity information; if the detector is SiPM, the output level/current intensity corresponding to the time information can be used to represent the optical signal intensity information.
  • the detection data of the radar includes time information and intensity information corresponding to the time information.
  • the time information is the time when one or more single-photon avalanche diode SPADs in the detection unit (P1, P2, P3...) are triggered, and the intensity information is the triggering time.
  • the number of single-photon avalanche diodes SPADs that are triggered by time, that is, the intensity of the optical signal is characterized by the number of single-photon avalanche diodes SPADs that are triggered.
  • the time information is the time stamp timestamp of the triggering of the single-photon avalanche diode SPAD, that is, the time difference t between the time t a emitted from the laser and the time t 1a when the single-photon avalanche diode SPAD is triggered 1a -t a .
  • the single-photon avalanche diode SPAD is used as an example for illustration.
  • Those skilled in the art can easily understand that the present invention is not limited to this, and other types of photodetectors can also be used, including but not limited to avalanche photodiode APD. , silicon photomultiplier tube SiPM, etc.
  • the data storage method of the present invention is specifically as follows: with a first time precision, according to the weight of the time information, the intensity information is stored; the first time precision is the time interval between any two adjacent first time scales , and is n times the time resolution of the radar detection data, where n>1; the weight is associated with the time information and the time interval of at least one first time scale.
  • Figures 10 and 11 show a specific schematic diagram of a storage method according to a preferred embodiment of the present invention, and the implementation of the data storage method of the present invention will be described in detail below with reference to Figures 10 and 11 .
  • the abscissa is the flight time
  • the interval of the time scale of the abscissa is, for example, the time resolution of the lidar, such as the time resolution of the time-to-digital converter TDC, which can reach the order of picoseconds ps.
  • the first time scale is set based on the time resolution of the lidar.
  • the interval between two adjacent first time scales spans 16 interval of the time resolution of the lidar.
  • the time scale corresponding to the time resolution of lidar can also be called “fine scale”. Also known as “coarse scale”.
  • the weight of the time x includes a first weight and a second weight
  • the first weight is associated with the time interval between the time x and one of the adjacent first time scales
  • the second weight Associated with the time interval between said instant x and another adjacent first time scale.
  • the first weight is associated with the time interval between the moment x and the first time scale A adjacent to the left thereof, and the first weight is, for example, (16-x)
  • the second weight is associated with the time interval between the moment x and the first time scale A+1 adjacent to the right side thereof, and the second weight is, for example, x. Therefore, the moment x is represented by its weight at two adjacent coarse scales (A, A+1), where the weight of x at coarse scale A is (16-x), and at coarse scale A+
  • the weight of 1 is x (x represents the distance from A at this moment), which is equivalent to the fine scale of x at this moment.
  • the data at the fine scale is stored at the addresses corresponding to two adjacent thick scales to represent the value of the scale x, rather than storing the scale x itself. This process is represented by the equation as follows:
  • the left side of the equal sign is the sum of the weights applied according to the coarse scale storage, the start value and the end value of the coarse scale, and the right side of the equal sign is the specific value of the timestamp. It can be seen that the storage method of coarse scale + weight can accurately represent the specific value of the timestamp.
  • the newly added intensity information on the coarse scale A is cnt*(16-x), and the coarse scale A+1
  • the newly added intensity information is cnt*x, which can be accumulated separately in multiple scans.
  • the fine scale represents the time-to-digital converter TDC time resolution. For a timestamp, the starting value of its coarse scale is A, and its fine scale is at the corresponding 0-15 fine scale x scale in its coarse scale.
  • a register is allocated for each coarse scale, the coarse scale interval of the abscissa is 16 times the TDC resolution, and each coarse scale corresponds to a register.
  • a coarse scale time fine scale 0 to 15
  • all trigger quantity information cnt is weighted, and stored in the registers corresponding to storage positions A and A+1 after summing with the original data.
  • the trigger quantity information cnt in the next coarse scale time is weighted and stored in the registers corresponding to the coarse scales A+1 and A+2. For example, when a SPAD trigger occurs at time 2', the time information tp 3 ' and cnt 3a ' are obtained.
  • the received signals tp 2 and cnt 2b are assigned weights cnt 2b *(16-x 2b ) and cnt 2b *x 2b on the coarse scale A and A+1 respectively, which are respectively the same as the original stored data.
  • After the summation is stored in the registers corresponding to the coarse scale A and A+1.
  • a histogram is obtained by accumulating the data of many scans. In several scans, all the trigger numbers cnt corresponding to the triggers at times 0 to 15 are stored in the registers corresponding to the coarse scales A and A+1.
  • the present invention adopts the weighted accumulation storage method, only needs to set registers corresponding to the coarse scales from 0 to n+1, and the required number of registers is reduced to the original one. 1/16, although the storage bit width of each register increases, the space occupied becomes larger, but because the storage location to be allocated is greatly reduced, the weighted accumulation data storage method can reduce the total storage space to the original 1/ 10 ranges.
  • the time interval between adjacent first time scales is 16 times the time resolution (fine scale) of radar detection data, that is, data compression is performed with a weight of 16.
  • the weight here can be any large positive integer.
  • the time interval of the coarse scale is 2 m times that of the fine scale, where m is a positive integer, so as to facilitate implementation in an FPGA or an ASIC.
  • the first weight is (16-x), the second weight is x, the present invention is not limited to this, the first weight may be x, and the second weight is (16-x ), or the first weight may be 1-(x/n), and the second preset weight may be x/n, as long as the first weight is equal to the time x and one of the adjacent first time scales
  • the second weight may be associated with the time interval between the moment x and another adjacent first time scale.
  • the storage method of the second aspect of the present invention can be applied to the method 100 of determining the noise level of the first aspect of the present invention.
  • step S101 of the method 100 an intensity information-time information curve of an optical signal is obtained, and the intensity information-time information curve is, for example, a photon number histogram.
  • the curves of intensity information relative to time information of multiple scans are superimposed to obtain, and the data obtained from each scan can be weighted and stored according to the storage method of the second aspect of the present invention, and finally a photon number histogram is obtained.
  • the total intensity S of the optical signal when calculating the total intensity S of the optical signal, it can be performed according to different ways.
  • the total intensity S of the optical signal is the accumulated sum of the original trigger number cnt data before weighting, and the histogram is two parallel steps.
  • the total intensity S of the optical signal can be calculated from the histogram, all of which are within the scope of the present invention.
  • the photon number histogram obtained by the storage method of the second aspect of the present invention when the noise level is calculated, since the time precision of the histogram data storage is n times the time resolution of the radar detection data, that is, the number of scales on the abscissa of the histogram becomes The intensity information corresponding to each time scale is processed in steps S102, S103, and the required calculation amount is correspondingly greatly reduced, which improves the data processing and calculation efficiency while maintaining the calculation accuracy unchanged.
  • the present invention also relates to a laser radar 300, as shown in FIG. 12, including a light emission module 301, a light detection module 302 and a control module 303, wherein the light emission module 301 refers to the part of the laser radar for laser emission, which can be Contains circuits, devices, structures, etc., configured to emit a detection laser beam for detection of a target.
  • the light detection module 302 refers to the part of the laser radar used to detect the echo signal of the laser, which may include circuits, devices, structures, etc., and is configured to receive the echo reflected by the detection laser beam on the target and convert it into electric signal.
  • the control module 303 is coupled to the light emission module 301 and the light detection module 302, and is configured to execute the method 100, 200 or 300 as described above to calculate the distance of the target object.
  • the light detection module 302 includes a plurality of detection units as shown in FIG. 6 , and each detection unit includes a plurality of single-photon avalanche diodes for receiving echoes.
  • the light emitting module 301 includes a light emitting array 3011, which is implemented by, for example, a Vertical-Cavity Surface-Emitting Laser (VCSEL) array.
  • the light emitting array 3011 includes multiple rows and multiple columns. Wherein, each row and each column are respectively provided with a plurality of light emitting units 30111, and each light emitting unit 30111 includes at least one light emitter; the light emitting array 3011 is also correspondingly configured with an emitting array driving circuit, which is coupled to each light emitting unit 30111.
  • the transmitter is used to drive the light transmitter to work.
  • the photodetection module 302 includes a photodetection array 3021, and the photodetection array 3021 may use, for example, a detection unit as shown in FIG. 6 to receive the optical echo signal after the detection beam reaches the target OB.
  • the photodetection module 302 may further include a signal readout circuit 3022 for reading out and transmitting the signals generated by the photodetection array 3021 to the control module 303 .
  • a transmitting lens group 304 may be further provided, which is located on the outgoing optical path of the light transmitting array 3011; May be located on the focal plane of the receiving lens group 305 .
  • the control module 303 is coupled to the light emission array 3011 and the photoelectric detection array 3021; respectively controls the light emission arrays to emit detection beams according to a certain order and power, and the corresponding light detection arrays receive echo signals.

Abstract

La présente invention concerne un procédé de détermination d'un niveau de bruit comprenant les étapes suivantes : S101, obtenir une courbe d'informations de temps et d'informations d'intensité d'un signal optique ; S102, limiter la courbe d'informations de temps et d'informations d'intensité au moyen d'un seuil de bruit estimé ; et S103, déterminer un niveau de bruit au moyen de la courbe d'informations de temps et d'informations d'intensité limitée. La présente invention concerne en outre un procédé de télémétrie au moyen d'un lidar et un lidar.
PCT/CN2021/138328 2021-03-31 2021-12-15 Procédé de détermination de niveau de bruit, lidar et procédé de télémétrie WO2022206031A1 (fr)

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