Laser radar echo signal non-coherent accumulation method

Abstract

The invention relates to the technical field of laser radars, in particular to a laser radar echo signal non-coherent accumulation method, and the method comprises the steps: obtaining a plurality of echo signals, comparing the wave width of a timing voltage signal with a first preset threshold value, and judging whether the corresponding echo signals need to be accumulated or not according to a comparison result; auxiliary voltage signal wave widths of the echo signals needing to be accumulated under the at least two auxiliary threshold voltages are obtained; calculating characteristic parameters representing waveform characteristics of the echo signal according to the wave width of the auxiliary voltage signal; similarity comparison is carried out on the characteristic parameters of the echo signals needing to be accumulated and the characteristic parameters of the at least one candidate echo signal, and whether the echo signals needing to be accumulated and the candidate echo signals can be accumulated or not is judged according to a comparison result; performing time alignment processing on the plurality of echo signals which can be accumulated; and superposing the plurality of echo signals after time alignment to complete non-coherent accumulation, thereby solving the problem of how to improve the detection distance and ensure the measurement precision at the same time.

Description

Technical Field

[0001] This application relates to the field of lidar technology, and in particular to a method for noncoherent accumulation of lidar echo signals. Background Technology

[0002] LiDAR technology, with its high precision and rapid response, demonstrates significant advantages in industrial measurement applications such as material inventory, where the target surface is relatively fixed and exhibits minimal variations. In these applications, effective detection of weak echo signals from distant or low-reflectivity targets (such as wet coal powder) is often required. However, due to hardware design limitations, simply increasing the laser emission power or receiver aperture to extend the detection range is costly and faces bottlenecks. Therefore, enhancing the detection capability of weak signals through signal processing while maintaining the existing optical path and hardware configuration has become a crucial technical requirement.

[0003] For weak signal detection, a common approach is to noncoherently accumulate multiple echo signals. Existing solutions mainly focus on detecting targets with small reflective surfaces. The technical approach involves performing multiple measurements on the same target and accumulating the echo signals acquired from these multiple measurements in order to improve the signal-to-noise ratio.

[0004] However, the above-mentioned approach has significant shortcomings when applied to scenarios such as material inventory. This method lacks an effective mechanism for judging the necessity and feasibility of signal accumulation. Blindly accumulating echo signals from targets with different reflection characteristics and significantly different envelope shapes not only fails to effectively improve the signal-to-noise ratio but also leads to distortion of the accumulated signal waveform. This distortion significantly increases the angle measurement error during subsequent walk error compensation based on signal width, thus failing to guarantee the final measurement accuracy. Summary of the Invention

[0005] This application provides a noncoherent accumulation method for lidar echo signals to address the problem of ensuring measurement accuracy while increasing detection range.

[0006] This application provides a method for noncoherent accumulation of lidar echo signals, the method comprising: Multiple echo signals obtained by the lidar scanning and detecting the target area are acquired, and the echo signals include the timing voltage signal pulse width measured at the timing threshold voltage; The timing voltage signal width is compared with a first preset threshold, and the corresponding echo signal is determined to be accumulated based on the comparison result. For echo signals determined to need to be accumulated, the amplitude of the auxiliary voltage signal measured at at least two auxiliary threshold voltages is obtained, wherein the voltage value of the auxiliary threshold voltage is less than the voltage value of the timing threshold voltage. The characteristic parameters characterizing the waveform features of the echo signal are calculated based on the amplitude of the auxiliary voltage signal. The feature parameters of the echo signal to be accumulated are compared with the feature parameters of at least one candidate echo signal, and the comparison results are used to determine whether the echo signal to be accumulated and the candidate echo signal can be accumulated. Time alignment processing is performed on multiple echo signals that are determined to be able to accumulate; Multiple time-aligned echo signals are superimposed to complete non-coherent accumulation.

[0007] The above method determines whether the echo signal needs to be accumulated by comparing the pulse width of the timing voltage signal with a preset threshold. For signals that need to be accumulated, the pulse widths at at least two auxiliary threshold voltages are obtained and characteristic parameters are calculated. The similarity of the characteristic parameters is used to determine whether the signals can be accumulated. Then, the signals that can be accumulated are time-aligned and superimposed, thereby improving the measurement accuracy while increasing the detection range of the lidar.

[0008] Optionally, the step of calculating the characteristic parameters characterizing the waveform features of the echo signal based on the amplitude of the auxiliary voltage signal includes: A first auxiliary threshold voltage and a second auxiliary threshold voltage are selected, wherein the voltage value of the first auxiliary threshold voltage is greater than the voltage value of the second auxiliary threshold voltage; Acquire the pulse width of the first auxiliary voltage signal under the first auxiliary threshold voltage, and the pulse width of the second auxiliary voltage signal under the second auxiliary threshold voltage; Calculate the sum of the pulse width of the first auxiliary voltage signal and the pulse width of the second auxiliary voltage signal to obtain the pulse width and parameters; Calculate the ratio of the first auxiliary voltage signal pulse width to the second auxiliary voltage signal pulse width to obtain the pulse width ratio parameter; The characteristic parameter is composed of the wavelength and the wavelength ratio parameter.

[0009] By acquiring the waveform width of the echo signal at two different auxiliary threshold voltages and calculating their sum and ratio, a feature parameter that can simultaneously reflect the overall width and shape proportion characteristics of the signal is constructed, providing a quantitative basis for accurately judging the similarity between signals.

[0010] Optionally, the step of comparing the feature parameters of the echo signals to be accumulated with the feature parameters of at least one candidate echo signal includes: The characteristic parameters of the echo signal to be accumulated are defined as the first feature vector, which includes the first width sum parameter and the first width ratio parameter. The characteristic parameters of the candidate echo signal are defined as the second feature vector, which includes the second width sum parameter and the second width ratio parameter. Calculate the outer product of the first feature vector and the second feature vector, and obtain the absolute value of the outer product; The absolute value of the outer product is compared with a second preset threshold. If the absolute value of the outer product is less than the second preset threshold, it is determined that the echo signal to be accumulated and the candidate echo signal can be accumulated.

[0011] By calculating the absolute value of the cross product between the feature vectors of two echo signals and comparing it with a preset threshold, the similarity of signal waveforms is quantitatively judged based on the geometric relationship of the vector space, providing a mathematical basis for selecting signal pairs suitable for non-coherent accumulation.

[0012] Optionally, the formula for calculating the outer product is: the product of the first waveform width sum parameter and the second waveform width ratio parameter, minus the product of the second waveform width sum parameter and the first waveform width ratio parameter.

[0013] The difference between two feature vectors is quantified by a specific formula for calculating the outer product. This calculation method can sensitively reflect the comprehensive differences in the width and shape ratio of the signals, thus providing a clear mathematical measure for judging the similarity of signal waveforms.

[0014] Optionally, the step of time-aligning multiple echo signals determined to be capable of accumulation includes: The first and second echo signals that need to be aligned are converted into discrete digital sequences, respectively. The centroid position of the first echo signal digital sequence is calculated by summing the product of the index number of each sampling point in the digital sequence and the square of the amplitude of the sampling point signal, and then dividing by the sum of the squares of the amplitudes of all sampling points. Calculate the centroid position of the second echo signal digital sequence; Calculate the difference between the centroid position of the first echo signal and the centroid position of the second echo signal to obtain the time offset; The second echo signal digital sequence is shifted according to the time offset.

[0015] By calculating the centroid position of the digital sequence of echo signals and determining its time offset, and then performing a shift operation on the signals, time alignment between echo signals can be achieved, providing a timing reference for subsequent signal superposition.

[0016] Optionally, when the time offset is a non-integer number of sampling intervals, the shift operation uses linear interpolation to obtain the signal amplitude value of the sampled point after the shift.

[0017] When the time offset is a non-integer number of sampling intervals, linear interpolation is used to obtain the sampled values ​​at the same time point after alignment, thereby improving the accuracy of signal time alignment.

[0018] Optionally, the method further includes determining the number of signals to be accumulated, the step of determining the number of signals to be accumulated including: Add the first echo signal that needs to be accumulated to the set of signals to be accumulated, according to the detection order; The next candidate echo signal is added to the set of signals to be accumulated according to the detection order. Determine whether any two echo signals in the current set of signals to be accumulated are both determined to be able to accumulate each other; If the determination is yes, then continue to add the next candidate echo signal to the set of signals to be accumulated and perform the determination again; If the determination is negative, the last candidate echo signal added will be removed from the set of signals to be accumulated. Check whether the composite signal obtained after accumulating all echo signals in the set of signals to be accumulated meets the condition that no accumulation is required, and check whether the composite signal obtained after accumulating the remaining signals after removing any signal from the set of signals to be accumulated does not meet the condition that no accumulation is required. If all the check results are yes, then the number of signals in the current set of signals to be accumulated is determined to be the number of signals to be accumulated.

[0019] By iteratively adding candidate signals to the set of signals to be accumulated and checking the accumulability of all signal pairs in the set, a maximum set of signals that meets specific conditions is finally identified, thereby adaptively determining the number of signals to be accumulated to achieve an effective signal-to-noise ratio improvement.

[0020] Optionally, the method further includes: improving the angular resolution of the lidar to partially overlap adjacent detection spots formed by the lidar in the target area, thereby enhancing the waveform consistency of adjacent echo signals.

[0021] By increasing the angular resolution of the lidar to make adjacent detection spots overlap, the waveform consistency of adjacent echo signals can be enhanced, thus providing more favorable conditions for judging the accumulability of signals.

[0022] Optionally, the method is applied to a material inventory scenario; wherein the target area is a material stacking surface with a stable surface morphology, and the difference in the waveform width and waveform ratio parameters of the echo signal corresponding to the detection point of the lidar is less than a preset difference threshold.

[0023] The method is applied to material inventory scenarios. It utilizes the stable surface morphology of the material stack and the similar waveform characteristics of the echo signals from the detection points to provide a suitable application environment for non-coherent accumulation based on waveform similarity.

[0024] Optionally, the method of comparing the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal also includes: Calculate the Euclidean distance between the vector formed by the characteristic parameters of the echo signal to be accumulated and the candidate echo signal, and determine whether the signal can be accumulated by judging whether the Euclidean distance is less than a preset distance threshold; Alternatively, the cosine similarity between the vector formed by the feature parameters of the echo signal to be accumulated and the candidate echo signal can be calculated, and whether the signal can be accumulated can be determined by judging whether the cosine similarity is greater than a preset similarity threshold.

[0025] By calculating the Euclidean distance or cosine similarity between feature vectors and making judgments based on preset thresholds, an alternative mathematical metric is provided to evaluate the similarity of echo signal waveforms, in order to support the determination of signal accumulability.

[0026] As can be seen from the above technical solutions, this application provides a noncoherent accumulation method for lidar echo signals. This method acquires multiple echo signals obtained by lidar scanning and detecting a target area. The echo signals include the waveform width of a timing voltage signal measured at a timing threshold voltage. The waveform width of the timing voltage signal is compared with a first preset threshold, and the comparison result determines whether the corresponding echo signal needs to be accumulated. For echo signals determined to need accumulation, the waveform width of auxiliary voltage signals measured at at least two auxiliary threshold voltages is acquired, where the voltage value of the auxiliary threshold voltage is less than the voltage value of the timing threshold voltage. Feature parameters characterizing the waveform features of the echo signals are calculated based on the auxiliary voltage signal waveform widths. The feature parameters of the echo signals to be accumulated are compared with the feature parameters of at least one candidate echo signal, and the comparison result determines whether the echo signals to be accumulated and the candidate echo signals can be accumulated. The multiple echo signals determined to be able to be accumulated are time-aligned. The time-aligned multiple echo signals are superimposed to complete noncoherent accumulation, thus solving the problem of ensuring measurement accuracy while increasing detection distance. Attached Figure Description

[0027] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart of the noncoherent accumulation method for lidar echo signals provided in the embodiments of this application; Figure 2 This is a schematic diagram of the laser radar scanning point cloud in the noncoherent accumulation method of laser radar echo signal provided in the embodiments of this application; Figure 3 This is a schematic diagram of the echo signal in the non-coherent accumulation method for lidar echo signals provided in the embodiments of this application; Figure 4 A schematic diagram showing the comparison of three threshold voltages and their corresponding waveforms in the non-coherent accumulation method of lidar echo signals provided in the embodiments of this application; Figure 5 This is a schematic diagram of the overlapping light spot in the noncoherent accumulation method of lidar echo signal provided in the embodiments of this application; Figure 6 This is a schematic diagram of the calibration curve for the echo signal wander error. Detailed Implementation

[0029] The embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described below do not represent all embodiments consistent with this application. They are merely examples of systems and methods consistent with some aspects of this application.

[0030] LiDAR is a type of area scanning sensor that can scan and detect the shape and position of objects within an area. It has many advantages, such as high measurement accuracy and fast response speed.

[0031] During lidar detection, the amplitude and bandwidth of echo signals from targets at different distances and with different reflectivities vary significantly. Compensation for echo signal walk error typically employs a function of the form f(x) = xg(w), where the independent variable x is the distance calculated from the intersection of the echo signal's leading edge and the threshold voltage, and the dependent variable is the compensated target distance. w is the echo signal bandwidth (a representation of signal energy), and g(w) is the compensation value determined by the signal bandwidth. g(w) is calibrated before the product leaves the factory, and the calibration curve is shown below. Figure 6As shown, when the echo signal width is small, even small fluctuations in the width can cause significant changes in the compensation value, leading to increased measurement errors. For applications such as material inventory, where the surface morphology is stable and variations at different locations are minimal, the waveforms of echoes from adjacent measurement points are similar. Non-coherent accumulation of adjacent echoes with similar waveforms can effectively improve the signal-to-noise ratio of the echo signal. Without altering the optical path, hardware design, or ensuring measurement accuracy, this effectively increases the detection range of the lidar or its ability to detect low-reflectivity targets (such as wet coal powder), thus expanding the application scope of lidar.

[0032] If two or more echo signals with significantly different envelopes are accumulated, the accumulated signal will be "distorted," which will not effectively improve the signal-to-noise ratio and detection range of the echo signal, and the measurement accuracy cannot be guaranteed.

[0033] To address the challenge of ensuring measurement accuracy while increasing detection range, see [link to relevant documentation]. Figure 1 This application provides a method for noncoherent accumulation of lidar echo signals, the method comprising: S100: Acquire multiple echo signals obtained by the lidar scanning and detecting the target area.

[0034] It should be understood that the echo signal includes the timing voltage signal pulse width measured at the timing threshold voltage. The lidar actively emits a laser beam and calculates the distance to the target point by measuring the time it takes for the laser beam to hit the target area of ​​the object and reflect back. This repeated process acquires tens of thousands of data points, which are used to construct the shape on the measured object's surface, called a point cloud. Figure 2 As shown in the diagram, the receiving unit of the lidar performs photoelectric conversion and signal amplification on the reflected light from the target to form a signal like... Figure 3 The echo signal is shown. Where V th The timing threshold voltage is typically 10% to 50% of the echo signal amplitude, and the specific value is determined based on the system signal-to-noise ratio and measurement accuracy requirements; t0 is the acquired laser flight time, and w = t1 - t0 is the signal width.

[0035] S200: Compare the timing voltage signal width with the first preset threshold, and determine whether the corresponding echo signal needs to be accumulated based on the comparison result.

[0036] Specifically, a reasonable first preset threshold is first set. This first preset threshold should be based on the requirements for echo signal strength and quality in the actual application scenario, as well as the performance parameters of the lidar, such as signal-to-noise ratio, sampling frequency, and pulse width. For example, the first preset threshold is set based on outdoor strong light environment (lidar is generally applicable both indoors and outdoors, and the threshold setting is based on adapting to the worst environment), and is generally set to 3 to 5 times the standard deviation of the total noise (system noise + environmental noise) (indoor low light environment - because the total noise amplitude is smaller, the signal-to-noise ratio is higher than outdoors). The initial value can be determined through system calibration or simulation experiments, and dynamically adjusted according to the measured echo quality. Then, the timing voltage signal pulse width is compared with the first preset threshold in real time. If the timing voltage signal pulse width is greater than or equal to the first preset threshold, it is determined that the signal-to-noise ratio of the echo signal meets the requirements, and the pulse width change caused by noise will not cause a large change in the error compensation value, and the echo signal does not need to be accumulated; if the timing voltage signal pulse width is less than the first preset threshold, it is considered that the echo signal needs to be accumulated with adjacent signals.

[0037] S300: For echo signals determined to need to be accumulated, acquire the amplitude of the auxiliary voltage signal measured at at least two auxiliary threshold voltages for the echo signals to be accumulated, where the voltage value of the auxiliary threshold voltage is less than the voltage value of the timing threshold voltage.

[0038] It should be understood that in practice, when determining that a certain echo signal needs to be accumulated, we do not solely rely on the timing threshold voltage V. th The echo signal quality and characteristics are determined by its corresponding waveform width w. To more accurately evaluate the quality and characteristics of the echo signal, we introduce two additional auxiliary threshold voltages V0. sim1 and V sim2 Both of these voltage values ​​are less than the timing threshold voltage V. th And satisfy V th >V sim1 >V sim2 The order of events is as follows. For each echo signal that needs to be accumulated, the corresponding auxiliary voltage signal pulse width, i.e., w, is measured at both auxiliary threshold voltages. sim1 and w sim2 ,like Figure 4 As shown. This multi-level judgment mechanism helps us to understand the performance of the echo signal at different voltage thresholds more comprehensively, thereby more accurately determining whether it is suitable for accumulation, and the possible impact of accumulation on the final measurement results.

[0039] S400: Characteristic parameters that characterize the waveform of the echo signal, calculated based on the amplitude of the auxiliary voltage signal.

[0040] In some embodiments, the step of calculating characteristic parameters representing the waveform characteristics of the echo signal based on the amplitude of the auxiliary voltage signal includes: A first auxiliary threshold voltage and a second auxiliary threshold voltage are selected, wherein the voltage value of the first auxiliary threshold voltage is greater than the voltage value of the second auxiliary threshold voltage.

[0041] The waveform width of the first auxiliary voltage signal under the first auxiliary threshold voltage and the waveform width of the second auxiliary voltage signal under the second auxiliary threshold voltage are obtained.

[0042] Calculate the sum of the pulse widths of the first auxiliary voltage signal and the second auxiliary voltage signal to obtain the pulse width and parameters.

[0043] Calculate the ratio of the first auxiliary voltage signal width to the second auxiliary voltage signal width to obtain the width ratio parameter.

[0044] The characteristic parameters are composed of the wavelength width and the wavelength width ratio parameter.

[0045] Specifically, for the echo signal that needs to be accumulated, the waveform width w of the first auxiliary voltage signal corresponding to the first auxiliary threshold voltage and the second auxiliary threshold voltage is obtained. sim1 Second auxiliary voltage signal waveform width w sim2 Then adjust the waveform width w of the first auxiliary voltage signal. sim1 Second auxiliary voltage signal waveform width w sim2 Perform "sum" and "scale" operations to obtain the beamwidth and parameter w. sum Wavewidth ratio parameter w ratio Among them, the wave width and parameter w sum The calculation formula and the beamwidth ratio parameter w ratio The calculation formula is as follows: w sum =w sim1 +w sim2 ; w ratio =w sim1 ×w sim2 .

[0046] By acquiring the waveform width of the echo signal at two different auxiliary threshold voltages and calculating their sum and ratio, a feature parameter that can simultaneously reflect the overall width and shape proportion characteristics of the signal is constructed, providing a quantitative basis for accurately judging the similarity between signals.

[0047] S500: Compare the similarity of the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal, and determine whether the echo signal to be accumulated and the candidate echo signal can be accumulated based on the comparison result.

[0048] In some embodiments, the step of comparing the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal includes: The characteristic parameters of the echo signal to be accumulated are defined as the first characteristic vector, which includes the first waveform width and parameter and the first waveform width ratio parameter.

[0049] The characteristic parameters of the candidate echo signal are defined as the second characteristic vector, which includes the second width sum parameter and the second width ratio parameter.

[0050] Calculate the cross product of the first eigenvector and the second eigenvector, and obtain the absolute value of the cross product.

[0051] The absolute value of the outer product is compared with a second preset threshold.

[0052] If the absolute value of the outer product is less than the second preset threshold, it is determined that the echo signal to be accumulated and the candidate echo signal can be accumulated.

[0053] Specifically, the characteristic parameters w of the echo signal that need to be accumulated sum-1 and w ratio-1 and the characteristic parameters w of the candidate echo signal sum-2 and w ratio-2 Represented in vector form (w) sum-1， w ratio-1 ) and (w sum-2， w ratio-2 If the outer product O P The absolute value is less than the second preset threshold O th If the required echo signal and candidate echo signal can be accumulated, then it is considered that they can be accumulated; otherwise, it is considered that they cannot be accumulated.

[0054] It should be understood that, in practical applications, the second preset threshold O th The settings are not fixed, but are determined after comprehensive consideration of various factors such as the specific characteristics of the lidar system, signal processing requirements, and environmental noise levels. Typically, O... th The value of is in the range of 0.1 to 0.5, and can be optimized and determined through univariate experimental methods or orthogonal experimental methods. For example, simulations are conducted under different signal-to-noise ratio conditions, and the value of O that provides the most significant improvement in signal-to-noise ratio after accumulation is selected. th The value is set as a target value.

[0055] By calculating the absolute value of the cross product between the feature vectors of two echo signals and comparing it with a preset threshold, the similarity of signal waveforms is quantitatively judged based on the geometric relationship of the vector space, providing a mathematical basis for selecting signal pairs suitable for non-coherent accumulation.

[0056] In some embodiments, the formula for calculating the outer product is: the product of the first wavelength width sum parameter and the second wavelength width ratio parameter, minus the product of the second wavelength width sum parameter and the first wavelength width ratio parameter.

[0057] Specifically, the outer product O P The calculation formula is: O P =w sum-1 ×w ratio-2 -w sum-2 ×w ratio-1 .

[0058] The difference between two feature vectors is quantified by a specific formula for calculating the outer product. This calculation method can sensitively reflect the comprehensive differences in the width and shape ratio of the signals, thus providing a clear mathematical measure for judging the similarity of signal waveforms.

[0059] S600: Performs time alignment processing on multiple echo signals that are determined to be able to accumulate.

[0060] In some embodiments, the step of time-aligning multiple echo signals determined to be capable of accumulation includes: The first and second echo signals that need to be aligned are converted into discrete digital sequences, respectively.

[0061] The centroid position of the digital sequence of the first echo signal is calculated by summing the product of the index number of each sampling point in the digital sequence and the square of the amplitude of the sampling point signal, and then dividing by the sum of the squares of the amplitudes of all sampling points signal.

[0062] Calculate the centroid position of the digital sequence of the second echo signal.

[0063] Calculate the difference between the centroid positions of the first echo signal and the second echo signal to obtain the time offset.

[0064] The digital sequence of the second echo signal is shifted according to the time offset.

[0065] It should be understood that for echo signals that accumulate sequentially over time, the centroid method can be used for envelope alignment. Assume the first echo signal... Second echo signal The digital sequence sampled by the analog-to-digital converter (ADC) is and ,in This is the index of the sampling point, and the centroid is calculated using the square of the amplitude (i.e., power). The formula for the centroid location of the first echo signal is as follows: .

[0066] The formula for the centroid position of the second echo signal is as follows: .

[0067] The formula for the difference between the centroid positions of the first and second echo signals is as follows: .

[0068] in, Indicates the second echo signal Compared to the first echo signal The time offset (in units of sampling point intervals). If This indicates the second echo signal. Relative to the first echo signal Lag; if This indicates the second echo signal. Relative to the first echo signal Advanced.

[0069] The second echo signal move This allows for communication with the first echo signal. Envelope alignment. When When the result is not an integer, linear interpolation can be used to obtain the sampled values ​​at the same time point after alignment.

[0070] By calculating the centroid position of the digital sequence of echo signals and determining its time offset, and then performing a shift operation on the signals, time alignment between echo signals can be achieved, providing a timing reference for subsequent signal superposition.

[0071] In some embodiments, when the time offset is a non-integer number of sampling intervals, the shift operation uses linear interpolation to obtain the signal amplitude value of the sampled point after the shift.

[0072] When the time offset is a non-integer number of sampling intervals, linear interpolation is used to obtain the sampled values ​​at the same time point after alignment, thereby improving the accuracy of signal time alignment.

[0073] S700: Superimposes multiple time-aligned echo signals to complete non-coherent accumulation.

[0074] The above method determines whether the echo signal needs to be accumulated by comparing the pulse width of the timing voltage signal with a preset threshold. For signals that need to be accumulated, the pulse widths at at least two auxiliary threshold voltages are obtained and characteristic parameters are calculated. The similarity of the characteristic parameters is used to determine whether the signals can be accumulated. Then, the signals that can be accumulated are time-aligned and superimposed, thereby improving the measurement accuracy while increasing the detection range of the lidar.

[0075] In some embodiments, the method further includes determining the amount of signal to be accumulated, the step of determining the amount of signal to be accumulated including: The first echo signal that needs to be accumulated is added to the set of signals to be accumulated according to the detection order.

[0076] The next candidate echo signal is added to the set of signals to be accumulated according to the detection order.

[0077] Determine whether any two echo signals in the current set of signals to be accumulated are both determined to be able to accumulate each other.

[0078] If the determination is yes, then continue to add the next candidate echo signal to the set of signals to be accumulated and perform the determination again.

[0079] If the determination is negative, the last candidate echo signal added will be removed from the set of signals to be accumulated.

[0080] Check whether the composite signal obtained after accumulating all echo signals in the set of signals to be accumulated meets the condition that no accumulation is required, and check whether the composite signal obtained after accumulating the remaining signals after removing any signal from the set of signals to be accumulated does not meet the condition that no accumulation is required.

[0081] If all the check results are yes, then the number of signals in the current set of signals to be accumulated is determined to be the number of signals to be accumulated.

[0082] Specifically, if the signal obtained after accumulating n signals satisfies the timing threshold voltage V th The signal bandwidth w is greater than or equal to the first preset threshold w th If the condition that no accumulation is required is not met, and after removing any one of the signals, the remaining (n-1) signals after accumulation do not meet the condition that no accumulation is required, then the number of signals that need to be accumulated for the current signal is considered to be n.

[0083] By iteratively adding candidate signals to the set of signals to be accumulated and checking the accumulability of all signal pairs in the set, a maximum set of signals that meets specific conditions is finally identified, thereby adaptively determining the number of signals to be accumulated to achieve an effective signal-to-noise ratio improvement.

[0084] In some embodiments, the method further includes: improving the angular resolution of the lidar to partially overlap adjacent detection spots formed by the lidar on the target area, thereby enhancing the waveform consistency of adjacent echo signals, such as... Figure 5 As shown.

[0085] By increasing the angular resolution of the lidar to make adjacent detection spots overlap, the waveform consistency of adjacent echo signals can be enhanced, thus providing more favorable conditions for judging the accumulability of signals.

[0086] In some embodiments, where computational power allows, signals that can accumulate can be searched between non-adjacent probe points within a single scan cycle.

[0087] It should be understood that, provided the computing power is sufficiently robust to support the corresponding computational load, within a single scan cycle, the search should not be limited to adjacent detection points, but should extend to non-adjacent detection points to identify signals with accumulable characteristics. The advantage of this approach is that it allows for a more comprehensive and thorough uncovering of potential signals suitable for accumulation, thereby enhancing the signal accumulation effect. This provides a richer and more accurate data foundation for subsequent processing and analysis based on these accumulated signals, ultimately improving the performance and accuracy of the entire lidar echo signal processing system.

[0088] In some embodiments, the method is applied to a material inventory scenario; wherein the target area is a material stacking surface with a stable surface morphology, and the difference in the waveform width and waveform ratio parameters of the echo signal corresponding to the detection point of the lidar is less than a preset difference threshold.

[0089] It should be understood that in material inventory scenarios, the target area is set as a material stacking surface with a stable surface morphology, which is determined based on actual application requirements. A material stacking surface with a stable surface morphology means that its position and shape change little within a certain period of time, which is beneficial for stable detection and signal acquisition by lidar. The difference in waveform width and waveform ratio parameters of the echo signals corresponding to the lidar detection points is less than a preset difference threshold. The setting of the preset difference threshold needs to comprehensively consider the material characteristics, lidar performance, and accuracy requirements of the actual application scenario, and is not a fixed universal value. In practical applications, it is usually determined through extensive experimental data statistics and analysis. For example, for a specific bulk material (such as coal, ore, etc.), under its typical stacking state, a specific model of lidar is used to perform multiple scans, collecting echo signals from a large number of detection points. The waveform width and waveform ratio parameters of these signals are extracted and analyzed to calculate the normal fluctuation range of these parameters between adjacent signals under a stable surface morphology. The preset difference threshold can be set slightly higher than the upper limit of this normal fluctuation range to ensure that normal minor surface changes can be effectively distinguished from significant differences that may be caused by noise or abnormal interference. For example, experimental measurements show that when a certain material is stably stacked, the difference in waveform width between adjacent detection points is typically within 5%, and the difference in waveform proportion parameters is typically within 8%. Therefore, the preset difference threshold for waveform width can be set to 8%, and the preset difference threshold for waveform proportion parameters can be set to 10%. This ensures sensitivity to changes in the actual surface morphology while improving robustness to noise and other interference factors. Of course, users can also adjust and optimize the preset difference thresholds according to specific application requirements and the field environment to achieve optimal signal accumulation and subsequent processing results.

[0090] In some embodiments, the method of comparing the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal further includes: The Euclidean distance between the vector formed by the characteristic parameters of the echo signal to be accumulated and the candidate echo signal is calculated, and the signal can be accumulated by judging whether the Euclidean distance is less than a preset distance threshold.

[0091] It should be understood that the specific operation for calculating Euclidean distance involves first extracting the feature parameters of the echo signal to be accumulated and the feature parameters of at least one candidate echo signal, and then constructing a vector from these feature parameters. For example, assuming the echo signal's feature parameters include amplitude, frequency, and phase, these parameters can be arranged in a certain order to form a vector. Then, the Euclidean distance between these two vectors is calculated. Euclidean distance is a commonly used method to measure the distance between two vectors in space, and its formula is the square root of the sum of the squares of the differences between corresponding elements of the two vectors. When the calculated Euclidean distance is less than a pre-set distance threshold, it is determined that the two echo signals can be accumulated, because a small distance indicates that they are relatively close in terms of feature parameters and have a high similarity.

[0092] Alternatively, the cosine similarity between the vector formed by the feature parameters of the echo signal to be accumulated and the candidate echo signal can be calculated, and the signal can be determined to be able to be accumulated by judging whether the cosine similarity is greater than a preset similarity threshold.

[0093] It should be understood that the method for calculating cosine similarity also involves first extracting the feature parameters of the echo signal to be accumulated and the candidate echo signal, and constructing a vector. Cosine similarity is an index that measures the degree of similarity between two vectors by calculating the cosine value of the angle between them. Its value ranges from -1 to 1, with the closer the value is to 1, the more similar the two vectors are. By calculating the cosine similarity between the vectors formed by the feature parameters of the echo signal to be accumulated and the candidate echo signal, and comparing the calculation result with a pre-set similarity threshold, when the cosine similarity is greater than the preset similarity threshold, it is determined that the two echo signals can be accumulated, indicating that they are relatively consistent in the distribution and direction of their feature parameters and have a high degree of similarity.

[0094] As can be seen from the above technical solutions, the embodiments of this application provide a non-coherent accumulation method for lidar echo signals. This method acquires multiple echo signals obtained by lidar scanning and detecting a target area. The echo signals include the waveform width of a timing voltage signal measured at a timing threshold voltage. The waveform width of the timing voltage signal is compared with a first preset threshold, and the comparison result determines whether the corresponding echo signal needs to be accumulated. For echo signals determined to need accumulation, the waveform width of auxiliary voltage signals measured at at least two auxiliary threshold voltages is acquired, where the voltage value of the auxiliary threshold voltage is less than the voltage value of the timing threshold voltage. Feature parameters characterizing the waveform features of the echo signals are calculated based on the auxiliary voltage signal waveform width. The feature parameters of the echo signals to be accumulated are compared with the feature parameters of at least one candidate echo signal, and the comparison result determines whether the echo signals to be accumulated and the candidate echo signals can be accumulated. The multiple echo signals determined to be able to be accumulated are time-aligned. The time-aligned multiple echo signals are superimposed to complete non-coherent accumulation, solving the problem of ensuring measurement accuracy while increasing detection distance.

[0095] Similar parts between the embodiments provided in this application can be referred to mutually. The specific implementation methods provided above are only a few examples under the overall concept of this application and do not constitute a limitation on the scope of protection of this application. For those skilled in the art, any other implementation methods extended from the solution of this application without creative effort shall fall within the scope of protection of this application.

Claims

1. A method for noncoherent accumulation of lidar echo signals, characterized in that, The method includes: Multiple echo signals obtained by the lidar scanning and detecting the target area are acquired, and the echo signals include the timing voltage signal pulse width measured at the timing threshold voltage; The timing voltage signal width is compared with a first preset threshold, and the corresponding echo signal is determined to be accumulated based on the comparison result. For echo signals determined to need to be accumulated, the amplitude of the auxiliary voltage signal measured at at least two auxiliary threshold voltages is obtained, wherein the voltage value of the auxiliary threshold voltage is less than the voltage value of the timing threshold voltage. The characteristic parameters characterizing the waveform of the echo signal are calculated based on the amplitude of the auxiliary voltage signal. The feature parameters of the echo signal to be accumulated are compared with the feature parameters of at least one candidate echo signal, and the comparison results are used to determine whether the echo signal to be accumulated and the candidate echo signal can be accumulated. Time alignment processing is performed on multiple echo signals that are determined to be able to accumulate; Multiple time-aligned echo signals are superimposed to complete non-coherent accumulation.

2. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The steps for calculating the characteristic parameters representing the waveform characteristics of the echo signal based on the amplitude of the auxiliary voltage signal include: A first auxiliary threshold voltage and a second auxiliary threshold voltage are selected, wherein the voltage value of the first auxiliary threshold voltage is greater than the voltage value of the second auxiliary threshold voltage; Acquire the pulse width of the first auxiliary voltage signal under the first auxiliary threshold voltage, and the pulse width of the second auxiliary voltage signal under the second auxiliary threshold voltage; Calculate the sum of the pulse width of the first auxiliary voltage signal and the pulse width of the second auxiliary voltage signal to obtain the pulse width and parameters; Calculate the ratio of the first auxiliary voltage signal pulse width to the second auxiliary voltage signal pulse width to obtain the pulse width ratio parameter; The characteristic parameter is composed of the wavelength and the wavelength ratio parameter.

3. The noncoherent accumulation method for lidar echo signals according to claim 2, characterized in that, The steps of comparing the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal include: The characteristic parameters of the echo signal to be accumulated are defined as the first feature vector, which includes the first width sum parameter and the first width ratio parameter. The characteristic parameters of the candidate echo signal are defined as the second feature vector, which includes the second width sum parameter and the second width ratio parameter. Calculate the outer product of the first feature vector and the second feature vector, and obtain the absolute value of the outer product; The absolute value of the outer product is compared with a second preset threshold. If the absolute value of the outer product is less than the second preset threshold, it is determined that the echo signal to be accumulated and the candidate echo signal can be accumulated.

4. The noncoherent accumulation method for lidar echo signals according to claim 3, characterized in that, The formula for calculating the outer product is: the product of the first wavelength sum parameter and the second wavelength ratio parameter, minus the product of the second wavelength sum parameter and the first wavelength ratio parameter.

5. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The steps for time alignment of multiple echo signals determined to be capable of accumulation include: The first and second echo signals that need to be aligned are converted into discrete digital sequences, respectively. The centroid position of the first echo signal digital sequence is calculated by summing the product of the index number of each sampling point in the digital sequence and the square of the amplitude of the sampling point signal, and then dividing by the sum of the squares of the amplitudes of all sampling points. Calculate the centroid position of the second echo signal digital sequence; Calculate the difference between the centroid position of the first echo signal and the centroid position of the second echo signal to obtain the time offset; The second echo signal digital sequence is shifted according to the time offset.

6. The noncoherent accumulation method for lidar echo signals according to claim 5, characterized in that, When the time offset is a non-integer number of sampling intervals, the shift operation uses linear interpolation to obtain the signal amplitude value of the sampled point after the shift.

7. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The method further includes determining the required number of signals to be accumulated, the step of determining the required number of signals to be accumulated comprising: Add the first echo signal that needs to be accumulated to the set of signals to be accumulated, according to the detection order; The next candidate echo signal is added to the set of signals to be accumulated according to the detection order. Determine whether any two echo signals in the current set of signals to be accumulated are both determined to be able to accumulate each other; If the determination is yes, then continue to add the next candidate echo signal to the set of signals to be accumulated and perform the determination again; If the determination is negative, the last candidate echo signal added will be removed from the set of signals to be accumulated. Check whether the composite signal obtained after accumulating all echo signals in the set of signals to be accumulated meets the condition that no accumulation is required, and check whether the composite signal obtained after accumulating the remaining signals after removing any signal from the set of signals to be accumulated does not meet the condition that no accumulation is required. If all the check results are yes, then the number of signals in the current set of signals to be accumulated is determined to be the number of signals to be accumulated.

8. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The method further includes: By improving the angular resolution of the lidar, the adjacent detection spots formed by the lidar on the target area partially overlap.

9. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The method is applied to a material inventory scenario; wherein the target area is a material stacking surface with a stable surface morphology, and the difference in the waveform width and waveform ratio parameters of the echo signal corresponding to the detection point of the lidar is less than a preset difference threshold.

10. The noncoherent accumulation method for lidar echo signals according to claim 1, characterized in that, The method of comparing the feature parameters of the echo signal to be accumulated with the feature parameters of at least one candidate echo signal also includes: Calculate the Euclidean distance between the vector formed by the characteristic parameters of the echo signal to be accumulated and the candidate echo signal, and determine whether the signal can be accumulated by judging whether the Euclidean distance is less than a preset distance threshold; Alternatively, the cosine similarity between the vector formed by the feature parameters of the echo signal to be accumulated and the candidate echo signal can be calculated, and whether the signal can be accumulated can be determined by judging whether the cosine similarity is greater than a preset similarity threshold.

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