CN117192565A - Laser radar detection method - Google Patents
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Abstract
The application provides a laser radar detection method which is characterized by comprising a driving signal generation part, wherein the driving signal generation part acts on a laser source through a laser modulation driving circuit, and the laser source receives the driving signal and drives and emits a pulse type detection laser sequence; the array type return light receiving module receives a return light signal reflected by a detected object in a view field and generates a return signal, and the processing module generates a modulation signal according to a driving signal generated by the driving signal generating part and obtains a distance-related signal with the return signal according to a preset rule operation, wherein the distance-related signal at least comprises two different sequences, and the processing module outputs the distance information of the final detected object according to the distance-related signal. By the design, the signal to noise ratio of the detection signal can be improved on the basis of guaranteeing the target detection range.
Description
Technical Field
The application relates to the technical field of detection, in particular to a laser radar detection method.
Background
The principle of the active detection system, which is realized by especially using a laser source, is that the light source actively emits detected emitted light, for example, near infrared type detected light, the wavelength of which can be selected to be in the range of 800-1200nm, but the active detection system is not limited thereto, and the near infrared type detected wave can also ensure the safety when an artificial object exists in the field of view, so that the near infrared type active detection system is more and more commonly applied to various scenes, such as subsequent automatic driving, intelligent door locks, security camera shooting, mobile phone three-dimensional camera shooting, and the like.
Time of flight ("TOF") light detection and ranging ("LIDAR") is a technique for remote distance measurement. The TOF LIDAR sensor determines the distance between an instrument including the sensor and the object by measuring the time required for a laser pulse to propagate between the instrument and the object.
Currently widely used detection methods include indirect time of flight (ITOF) measurement schemes and direct time of flight (DTOF) measurement schemes. Most of the indirect flight time measurement schemes adopt a method for measuring phase offset, namely, the phase difference between a transmitted wave and a received wave, the abscissa of the transmitted wave and the received wave is time t, the ordinate is light intensity, and the flight time t can be obtained according to the phase difference of the transmitted wave and the received wave, so that the distance of a detected object can be obtained according to d=ct/2. The direct flight time measurement scheme generally directly obtains the time difference between the triggering of the transmitting end and the triggering of the corresponding receiving end through a picosecond-level resolution measurement system (SPAD+TDC is adopted), namely the flight time t, so that the distance of a detected object is calculated. There is a type called coherent detection, in which a coherent laser signal and a local laser oscillation signal are incident together on a photosensitive surface of a detector under the condition of meeting wavefront matching (i.e. the same phase relationship is maintained on the photosensitive surface of the whole laser detector), so as to generate beat frequency or coherent superposition, and the magnitude of an output electric signal of the detector is proportional to the square of the sum of a laser signal wave to be detected and a local laser oscillation wave, and the detection mode has advantages of itself, but has great disadvantages in terms of pixel level, rapid processing and efficient utilization of emission energy.
In recent years, some laser radar principles of direct time-of-flight detection (incoherent) have also been developed, and the principle is gradually changed into a detection technology known to more people, and the first prior art is: patent application number CN202010604232.3 discloses a novel laser ranging method and laser radar system, which provides a novel detection mechanism, does not adopt a coherent light principle on an optical path, performs correlation operation in an electric signal stage, and further obtains the distance or other information of a final detected object through the correlation operation of the electric signal, however, in practice, the method has the following limiting characteristics (1) known from the incoherent chirp signal amplitude modulation continuous wave laser three-dimensional imaging principle, and a difference frequency signal is generated by multiplying a delayed chirp signal with a local oscillation signal. From the viewpoint of energy utilization, the gain of the detector needs to be modulated at a high speed, so that the detection efficiency of the prior art is low, and the range is small; (2) The prior art adopts devices such as a broadband amplifier, a mixer, an A/D (analog/digital) and the like, and the dynamic range of the devices limits the dynamic range of a received laser signal, thereby limiting the dynamic receiving range of the prior art; (3) The performance of the laser three-dimensional imaging system realized by the prior art is greatly influenced by the chirp signal frequency modulation linearity and the frequency modulation flatness.
And the second prior art is as follows: the patent application number 202111112299.6 is a laser radar detection system, and compared with the prior art, a counting sequence generating module is added, which converts a photon counting sequence or an accumulated photon counting sequence into an adaptive photon counting sequence or an adaptive accumulated photon counting sequence respectively, and generates an accumulated counting sequence after being processed by a digital multiplier and a preset rule operation module, and similarly, the target information can be solved by analyzing the spectrum characteristics of the accumulated counting sequence.
The third prior art is: the patent application number 202210132268.5 is a laser radar detection system and a detection method, and compared with the prior art, the laser radar detection system and the detection method have the advantages that a counting sequence splicing module is added, a copy splicing signal is obtained according to the return signal, and by means of the design, smaller laser emission energy can be utilized, and smaller ranging deviation is achieved.
The prior art is four: the patent application number 2022103720865 is a laser radar detection system and detection device, which is characterized in that a modulation sequence correction module is added relative to the prior art, and the modulation sequence correction module receives the driving signal to drive and generate a corrected modulation sequence. So as to achieve flexible configuration of parameters under different applications.
In the prior art, the photon counting sequence and the modulation sequence are multiplied to obtain the modulation counting sequence, and the modulation counting sequence in the integration time is accumulated and summed to further obtain the accumulated counting sequence. In an ideal case (when no background light or dark count exists), the photon counting sequence generates a counting result (hereinafter referred to as signal counting) in a corresponding counting unit only when the laser pulse sequence reflected by the target is received, and when the background light is strong or the dark counting rate is high, a large amount of counting results (hereinafter referred to as noise counting) caused by the background light or the dark counting exist in the photon counting sequence. Thus, the photon counting sequence is actually composed of a signal count and a noise count, wherein the noise count is multiplied by the modulation sequence, so that a great amount of noise is generated in the modulation counting sequence, and the signal-to-noise ratio of the accumulated counting sequence is reduced.
Obviously, the signal counting probability in single detection can be improved by improving the power of the transmitted pulse signal, or the signal counting result can be improved by increasing the detection times, so that the signal to noise ratio of the accumulated counting sequence is improved. However, this tends to increase the laser emission power or the total energy.
Disclosure of Invention
The application aims at overcoming the defects in the prior art, and the technical scheme adopted by the embodiment of the application is as follows:
the embodiment of the application provides a laser radar detection method, which is characterized by comprising a driving signal generation part, wherein the driving signal generation part acts on a laser source through a laser modulation driving circuit, and the laser source receives the driving signal and drives and emits a pulse type detection laser sequence; the array type return light receiving module receives a return light signal reflected by a detected object in a view field and generates a return signal, and the processing module generates a modulation signal according to a driving signal generated by the driving signal generating part and obtains a distance-related signal with the return signal according to a preset rule operation, wherein the distance-related signal at least comprises two different sequences, and the processing module outputs the distance information of the final detected object according to the distance-related signal.
Optionally, the at least two different sequences are obtained by integrating over at least two identical integration times.
Optionally, the device further comprises an accumulated count sequence analysis module, and the accumulated count sequence analysis module selects the at least two different sequences according to a preset rule.
Optionally, the accumulated count sequence analysis module uses an accumulated count sequence with the largest sum of absolute values of elements of the at least two different sequences as the distance-related signal.
Optionally, the accumulated count sequence analysis module compares absolute values of elements corresponding to the at least two different sequences, and selects an accumulated count sequence corresponding to a largest element as the distance-related signal.
Optionally, the at least two different sequences of elements are accumulated from the same number of sequence elements.
Optionally, the system further comprises a counting sequence copying and splicing module, wherein the counting sequence copying and splicing module obtains a copying and splicing sequence according to the return signal.
Optionally, the system further comprises a counting sequence generating module, wherein the counting sequence generating module generates an adaptive counting sequence according to the return signal.
Optionally, the system further comprises a modulation sequence correction module, and the modulation sequence correction module receives the driving signal to drive and generate a corrected modulation sequence.
Optionally, the device further comprises an accumulated count sequence correction module, and the distance-related signal is obtained after the at least two different sequences are corrected.
The beneficial effects of the application are as follows: the application provides a laser radar detection method which is characterized by comprising a driving signal generation part, wherein the driving signal generation part acts on a laser source through a laser modulation driving circuit, and the laser source receives the driving signal and drives and emits a pulse type detection laser sequence; the array type return light receiving module receives a return light signal reflected by a detected object in a view field and generates a return signal, and the processing module generates a modulation signal according to a driving signal generated by the driving signal generating part and obtains a distance-related signal with the return signal according to a preset rule operation, wherein the distance-related signal at least comprises two different sequences, and the processing module outputs the distance information of the final detected object according to the distance-related signal. By the design, the signal to noise ratio of the detection signal can be improved on the basis of guaranteeing the target detection range.
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In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a modularized working principle of a detection system according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a pulsed detection scheme according to an embodiment of the present application;
FIG. 3 is a schematic diagram of obtaining a distance-related signal according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a three-dimensional imaging system according to an embodiment of the present application;
FIG. 5 is a schematic diagram of a detection system according to an embodiment of the present application;
FIG. 6 is a schematic diagram of yet another detection system according to an embodiment of the present application;
FIG. 7 is a schematic diagram of a counting sequence waveform according to an embodiment of the present application;
FIG. 8 is a schematic diagram of waveforms according to an embodiment of the present disclosure;
FIG. 9 is a schematic diagram of a detection scheme according to an embodiment of the present application;
FIG. 10 is a schematic diagram of another detection scheme according to an embodiment of the present application;
FIG. 11a is a schematic diagram of a spectrum of a distance-related signal obtained by a prior art method according to an embodiment of the present application;
fig. 11b is a schematic diagram of a distance-related signal spectrum obtained by dividing an integration time into two segments according to an embodiment of the present application.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. The components of the embodiments of the present application generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the application, as presented in the figures, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
The detection systems currently employed basically comprise: the light source module 110, the processing module 120, and the light receiving module 130, where the light source module 110 includes, but is not limited to, a semiconductor laser, a solid state laser, or other types of lasers, when the semiconductor laser is used as the light source, a Vertical-cavity surface emitting laser VCSEL (Vertical-cavity surface-emitting laser) or an edge-emitting semiconductor laser EEL (edge-emitting laser) is used, and the light source module 110 emits a sine wave or a square wave or a triangular wave, or a pulse wave, or the like, and in the ranging application, most of the lasers having a certain wavelength, for example, infrared lasers (most preferably near infrared lasers with a wavelength of 950nm, etc.), the emitted light is projected into the field of view, the detected object 140 existing in the field of view may reflect the projected lasers to form return light, and the return light enters the detection system to be captured by the light receiving module 130, and the light receiving module 130 may include a photoelectric conversion part, where the four-phase delay receiving scheme in the ITOF ranging can be most commonly used to obtain a four-phase delay signal, and the four-phase delay receiving scheme is used to calculate the four-phase delay signal, and the four-delay signal is 90 ° and the four-phase-delay signal is calculated (the four-phase-delay signal is 90 ° and the four-phase-delay signal is 90) and the four-phase-delay signal is calculated by the four-phase, and the four-phase-delay signal is 90) and the four-phase angle is 90, and the four-phase delay time is the four phase, and the phase delay time and the receiving point, the receiving system is 0, and the receiving phase, and the receiving phase and the receiving system, and the receiving device:
The ratio of the difference of A1 and A3 to the difference of A2 and A4 is equal to the tangent of the phase angle. ArcTan is effectively a bivariate arctangent function, which can be mapped to the appropriate quadrant, defined as 0 ° or 180 ° when a2=a4 and a1> A3 or a3> A1, respectively.
The distance to the target is determined by the following formula:
to this end, it is also necessary to determine the frequency of the emitted laser light, where c is the speed of light,is the phase angle (measured in radians) and f is the modulation frequency. The above scheme can realize the effect of detecting the distance of the detected object in the field of view, the scheme is called a four-phase delay scheme to obtain detection results, of course, the receiving module generates different information by photoelectric conversion, in some cases, the information acquisition of the detected object is also realized by using a 0-degree and 180-degree two-phase scheme, and the target information is obtained by three phases of 0 degree, 120 degrees and 240 degrees, even the five-phase delay scheme is also disclosed in the literature, and the invention is not particularly limited.
In DTOF ranging, since the pixel unit of the array sensor is a SPAD (single photon avalanche photodiode) device, the array sensor works in a geiger mode, in the geiger mode, the avalanche photodiode absorbs photons to generate electron-hole pairs, the electron-hole pairs are accelerated under the action of a strong electric field generated by high reverse bias voltage, so that enough energy is obtained, then the electron-hole pairs collide with a crystal lattice to form a linkage effect, and a large number of electron-hole pairs are formed to cause avalanche phenomenon, and the current grows exponentially. The gain of the SPAD is theoretically infinite, a single photon can saturate the photocurrent of the SPAD, so that the SPAD becomes the first choice of a high-performance single photon detection system, the ranging principle is very simple, a light source emits pulse laser with a certain pulse width, for example, a few nanoseconds level, the pulse laser is reflected by a detection target and returns to an array type receiving module containing the SPAD in an avalanche state, a detection unit in the avalanche state can receive a returned signal, the distance between the detection system and the detection target can be output through the processing of the processing module, the detection is finished, a laser pulse can be emitted for tens of thousands times for obtaining a high-reliability result, the detection unit obtains a statistical result, thus a more accurate distance can be obtained through the processing of the statistical result, the following table 1 shows that the two more-application type ITOF ranging methods and the DTOF ranging method have certain limitations through the comparison of the table 1, and a novel detection method needs to be developed to obtain a more accurate and more interference-resistant result.
TABLE 1 ITOF vs. DTOF ranging methods
Fig. 2 is a schematic diagram of a pulsed detection scheme according to an embodiment of the present application, where, as shown in fig. 2, a system uses a pulsed laser, so that an active detection laser is a pulse laser sequence segment composed of a pulse sequence, a driving signal generating part generates a driving signal in the system, where the driving signal may be a chirp signal similar to the previous example, or another type of driving signal may be used, where the driving signal is essentially characterized in that the device emits laser light to obtain an emitted light signal with identifiable characteristics, the driving signal acts on the pulsed laser through a laser modulation driving circuit, the laser may use at least part of characteristics of the driving signal, for example, a total period of the driving signal as a period of the pulse sequence segment, a single pulse in the pulse segment may be selected to have the same or similar peak value, the method is not limited to the specific implementation scheme of the pulse laser segments emitted by the pulse laser source, the emitted pulse laser sequences are reflected by the detected object in the field of view to generate a return optical signal, the return optical signal is received by the photoelectric detector to form a photon counting sequence, a preset rule operation module contained in the processing module generates a discontinuous modulation sequence Y by using the driving signal on one hand, on the other hand, the photon counting sequence and the modulation sequence Y can be operated according to a preset rule to obtain a distance related signal, the distance related signal is further passed through a time-frequency domain conversion module to obtain a frequency spectrum signal converted by the distance related signal, and then the characteristics of the frequency spectrum signal, such as peak characteristics (including highest peak information, next highest peak information or peak information in a concerned region, etc.), are utilized to output information including the detected object distance, speed information, etc., which are not particularly limited herein, similarly, for a pulse type discontinuous detection scheme, a time-frequency domain conversion module includes a unit capable of performing time-frequency domain conversion processing, which may perform, for example, wavelet operation, segment FFT, FFT, chirp-Z operation, DFT, etc., and of course, detailed description for specific algorithm implementation is omitted herein, which is also merely exemplified herein, and of course, the time-frequency domain conversion module may also include a threshold detection unit and/or an information resolving unit, which are not limited herein.
The chirp signal generator is taken as an example for illustration, on one hand, the chirp signal generator generates a chirp signal as a modulation sequence Y, the modulation sequence can be discretization of the continuous signal in the example, and finally converted into a digital type modulation sequence signal, the period of laser emission is selected as a chirp signal period T (that is, the total duration in the section of the emitted laser is selected as the period characteristic of the chirp signal), on the other hand, the chirp signal generator controls the laser modulation driving circuit to generate a pulse laser driving signal, the pulse laser driving signal controls the pulse laser to emit a laser pulse sequence, and the emission optical system projects the laser pulse sequence to the target area; the laser pulse energy in the laser pulse sequence is equal, and only an example is cited herein, the receiving system includes a receiving optical system, a photodetector, a digital correlator, a digital integrating accumulator, etc., where the receiving optical system focuses the laser pulse sequence reflected by the target to the photodetector, and the photodetector starts detecting when the laser pulse sequence is emitted, so as to obtain a photon counting result in the emission period of the laser pulse sequence, in order to ensure that the calculation amount of the subsequent calculation result is smaller, the scene in the field of view is first irradiated with the pulse sequence emitted for L times (where L is an integer greater than or equal to 1), more optimally, in order to obtain more accurate detection results, an order of several hundred thousand, etc. can be selected, and of course, in order to ensure the accuracy of the data or the effect of operation accuracy and rapidness, etc., it is not limited to statistically obtaining a statistical value for all detection results of the L times, and generating a statistical photon sequence X for all detection results obtained by using the excitation information of the return light for L times, for example, the statistical result X obtained by the statistical result obtained by the excitation information for the return light for example, such a scene as described below is generated by an example and a statistical sequence and composed of photons X According to the scheme, L (L is a positive integer and L is more than or equal to 1) times of accumulation detection are carried out on a laser pulse sequence reflected by a target, each time of accumulation detection comprises M (M is a positive integer and M is more than or equal to 1) detection pulses, and the photon counting result obtained by the ith (i is a positive integer and 1 is more than or equal to i is less than or equal to M) detection pulse in the (d) time of accumulation detection is more than or equal to 1 and less than or equal to L is x di The basic count sequence X consisting of M probe pulse count results is thus obtained as:
the L times of accumulation detection are firstly carried out to obtain a basic counting sequence X (X is L X) d And then multiplying X by Y to obtain Z (Z is L Z) d Is added up) and then Z is added up in segments to obtain S.
FIG. 3 can also be interpreted as a detailed description of another embodiment of the present invention, and is also an embodiment of the present invention, in which the laser source emits L pulse sequences for outputting, the reflected detection laser re-receiving end of the object to be detected in the field of view forms a photon counting result X of the returned light, which can be L returned results, the modulation sequence can obtain a modulated counting sequence Z according to each output modulation sequence and multiplication operation with each returned photon counting sequence, and finally the segmentation and accumulation result is performed to obtain a final counting sequence S d ，
x d ＝{x di |i＝1，2，...，N} (4)
A discontinuous modulation sequence Y is obtained analogously to the previous scheme and then let X d Multiplying by Y to obtain Z d ，
Z d ＝{Z di |Z di ＝x di ·y i ，i＝1，2，...，N} (5)
Then to Z d Performing sectional accumulation to obtain S d Similar to the piecewise accumulation scheme shown in equation 13, the illustration is, of course, only schematically illustrated hereinIn this case, the actual implementation is not limited to this manner. This solution may require a greater computational effort than before, and requires a more optimal solution to achieve probing with fast output requirements, which is not limiting here.
The photon counting sequence or the accumulated photon counting sequence in the embodiment can be generated not only by the laser pulse sequence received by the photoelectric detector array, but also by the ambient background light, including natural background light and unnatural background light, received by the photoelectric detector array. Photon counting results generated by ambient background light, reasons of the detector array and the like can reduce the signal to noise ratio of the detection system, so that the detection performance is deteriorated.
Since natural background light, such as sunlight, and the like, and counting results generated by the detector array itself generally obey a certain statistical rule, the statistical rule can be determined according to a photon counting sequence or an accumulated photon counting sequence; on the other hand, since the generation rule of the laser pulse sequence and the photon counting rule generated by the laser pulse sequence are known, the photon counting statistical rule generated by unnatural background light interference, such as interference light of other detection equipment, and the like, can be distinguished from the photon counting sequence or accumulated photon counting sequence; according to the ambient background light and photon counting statistics rules generated by the detector array, the photon counting sequence or accumulated photon counting sequence generated by the photoelectric detector array can be corrected, so that the signal-to-noise ratio and the detection performance of the detection system are improved.
To suppress the above problem, in some embodiments, a count sequence generating module is added to the receiving system, which is used to obtain the photon count sequence, or accumulate the statistical characteristics of the photon count sequence, and generate an adaptive count sequence or accumulate the adaptive count sequence according to a preset rule.
FIG. 4 is the presentThe embodiment of the application provides a schematic diagram of a three-dimensional imaging system; fig. 4 is a block diagram of a count sequence generation module compared with fig. 3, and the functions of other blocks are the same as those shown in fig. 3, so that a detailed description is omitted. In fig. 4, the counting sequence generating module generates an adaptive counting sequence according to the photon counting sequence statistics and the preset rules. Counting photons in sequence X d And adaptive correction sequence X dm ＝{x dmi I=1, 2,..n } operates according to a prescribed preset rule, thereby changing the photon counting sequence X d The number of high-value elements in the sequence X is obtained da . For example, the operation may be performed according to a preset rule of formula (6):
obtaining X da The subsequent signal processing procedure of (a) is the same as that of the previous embodiment, and will not be described again.
Fig. 5 is a schematic diagram of a detection system according to an embodiment of the present application. The difference between the embodiment shown in fig. 5 and the embodiment shown in fig. 2 is that a counting sequence copy splicing module is added between the photoelectric detector and the digital multiplier in the detection system, and other modules are the same as those in the embodiment shown in fig. 2 and will not be described again. In the embodiment shown in FIG. 5, the count sequence copy splice module copies the photon count sequence X d Conversion to replication splice sequence X c ：
X c ＝{x ci |i＝1,2,...,N} (7)
The digital multiplier obtains a modulation count sequence Zd:
Z d ＝{z di |z di ＝x ci ·y i ,i＝1,2,...,N} (8)
the preset rule operation module is used for modulating the counting sequence Z d Performing sectional accumulation to obtain a sectional accumulation counting sequence S d ：
Wherein N is 0 Is the integer with the value closest to N/M, K is the integer and(R max is the maximum detectable distance).
The preset rule operation module accumulates L segmentation accumulated counting sequences obtained in the L laser pulse sequence transmitting process to obtain an accumulated counting sequence S:
Fig. 6 is a schematic diagram of another detection system according to an embodiment of the present application, where the detection system shown in fig. 6 includes a driving signal generating portion (on one hand, generating a modulation sequence Y and on the other hand, generating a laser driving parameter), a laser modulation driving circuit (for performing modulation driving on a pulse laser), a pulse laser (for generating a laser pulse sequence), and an emission optical system (for shaping and expanding the laser pulse sequence to irradiate a target area); on the one hand, the driving signal generating section generates a chirp signal as the modulation sequence Y:
Y＝{y i |y i ＝cos[2πf 0 (i-1)Δt+πk(i-1) 2 Δt 2 +φ Y ],i＝1,2,...,N} (11)
wherein f 0 For the initial frequency of the chirp signal, B is the chirp signal bandwidth, T is the chirp signal period, k is the frequency modulation slope and k=b/T, Δt is the system time stepping interval and has nΔt=t; on the other hand, the driving signal generating part generates laser driving parameters, the laser driving parameters control the laser modulation driving circuit to generate laser driving signals, the pulse laser is controlled to emit laser pulse sequences, and the emission optical system performs shaping, beam expansion and the like on the laser pulse sequences to irradiate the target area; the energy of each laser pulse in the laser pulse sequence is equal or different; laser pulse repetition frequency f s The method comprises the steps of carrying out a first treatment on the surface of the The emission period of the laser pulse sequences is equal to the chirp signal period T, and each laser pulse sequence From M 0 ≤M＝f s T (M is a positive integer) laser pulses.
The receiving system shown in fig. 6 includes a receiving optical system, a photodetector, a counting sequence generating module, a digital multiplier, a preset rule operation module, etc., wherein the receiving optical system focuses the laser pulse sequence reflected by the target onto the photodetector, the photodetector starts to detect when the laser pulse sequence is transmitted, and the photon counting sequence obtained when the photodetector detects the (d) (d is a positive integer and d is less than or equal to L) th laser pulse sequence is Xd, assuming that the laser pulse sequence is co-transmitted for L (L is an integer greater than or equal to 1):
X d ＝{x di |i＝1，2，K，N} (12)
the digital multiplier obtains a modulation counting sequence Z d ：
Z d ＝{z di |z di ＝x di y i ：i＝1，2，K，N} (13)
The preset rule operation module accumulates L segmentation accumulated counting sequences obtained in the L laser pulse sequence transmitting process to obtain an accumulated counting sequence S:
fig. 7 is a schematic diagram of a counting sequence waveform according to an embodiment of the present application. The photon counting sequence and the modulation sequence are multiplied to obtain a modulation counting sequence as shown in fig. 7, and the modulation counting sequence in the integration time is accumulated and summed to further obtain an accumulated counting sequence. In an ideal case (when no background light or dark count exists), the photon counting sequence generates a counting result (hereinafter referred to as signal counting) in a corresponding counting unit only when the laser pulse sequence reflected by the target is received, and when the background light is strong or the dark counting rate is high, a large amount of counting results (hereinafter referred to as noise counting) caused by the background light or the dark counting exist in the photon counting sequence. Thus, the photon counting sequence is actually composed of a signal count and a noise count, wherein the noise count is multiplied by the modulation sequence, so that a great amount of noise is generated in the modulation counting sequence, and the signal-to-noise ratio of the accumulated counting sequence is reduced.
Obviously, the signal counting probability in single detection can be improved by improving the power of the transmitted pulse signal, or the signal counting result can be improved by increasing the detection times, so that the signal to noise ratio of the accumulated counting sequence is improved. However, this tends to increase the laser emission power or the total energy.
On the other hand, as can be seen from fig. 7, when the background light or dark count rate is constant, the longer the integration time, the more noise is introduced. Since the integration time is proportional to the maximum detection range, the larger the required maximum detection range, the longer the integration time, the more noise is introduced and the lower the signal-to-noise ratio, which is clearly detrimental to the detection of long-range targets. While reducing the integration time may reduce the noise count in the photon counting sequence, thereby increasing the signal-to-noise ratio of the accumulated counting sequence, reducing the integration time also means reducing the target detection range, which is a common problem with the prior art. How to reconcile the contradiction is of great importance for improving the detection efficiency.
In addition, since the target distance is proportional to the frequency of the accumulated counting sequence, in order to satisfy the nyquist sampling law, the laser pulse emission frequency is required to be at least two times of the frequency of the accumulated counting sequence, so when the target distance is far, the required laser pulse emission frequency is also high, and in order to satisfy a certain ranging accuracy, a certain detection period T is required to be maintained, which increases the length of the accumulated counting sequence and increases the data transmission amount and the processing amount.
Fig. 8 is a schematic waveform diagram according to an embodiment of the present application. As shown in fig. 8, the signal-to-noise ratio of the accumulation count sequence is improved by dividing the integration time into a plurality of segments (fig. 8 shows a case of two segments, but is not limited to two segments). In contrast to fig. 7, on the one hand, the total integration time remains unchanged, i.e. tc=tc1+tc2, so the target detection range is not changed; on the other hand, the integration time is divided into two sections, and the accumulated count sequence 1 and the accumulated count sequence 2 are respectively obtained in the corresponding integration time, and in fig. 8, the echo signal falls into the first section of integration time, and because the integration time Tc1 is smaller than the integration time Tc, when the noise count level such as background light or dark count is constant, the noise introduced into the accumulated count sequence 1 is smaller, so that the signal-to-noise ratio is higher, and the target information is easier to extract in the frequency spectrum domain.
While this embodiment increases the signal-to-noise ratio of the accumulated count sequence by reducing the integration time compared to the prior art, the number of accumulated count sequences is increased, for example, if the integration time is divided into two segments, two accumulated count sequences are obtained, which increases the data transmission and processing pressures. For this purpose, it is possible to determine in which integration time the echo signal falls before the data transmission and processing, and then to transmit and process only the accumulated count sequence data corresponding to the integration time. For example, when the integration time T1 is equal to the integration time T2, since the level of noise count caused by background light or dark count is substantially the same in both integration times, when there is an echo signal, the sum of absolute values of the elements of the accumulation count sequence including the signal light will be larger, so that it can be determined which set of accumulation count sequence data is transmitted and processed accordingly.
The integration time-slicing approach introduces more accumulated count sequences, but on the other hand may also reduce the memory requirements for the modulation sequence. Because the accumulated counting sequences generated in different integration time are mutually independent, the modulation sequences used for generating the two groups of accumulated counting sequences can be completely identical, namely the same modulation sequences can be used in the integration time Tc1 and Tc2, and because the distance information obtained in different integration time has fixed deviation with the real target distance, the real target distance information can be obtained by only correcting the calculated distance information. At this time, from the viewpoint of signal processing, the detection range corresponding to the shortened integration time is smaller, so that the requirement on the minimum laser pulse emission frequency is reduced, and further, the requirements on data transmission and processing are also reduced.
In a further embodiment, as in the detection scheme shown in FIG. 2, the photodetector begins to detect when a sequence of laser pulses is emitted, assuming co-emission L (L is greater than or equal toInteger of 1) laser pulse sequence, the photon counting sequence obtained by the photoelectric detector when detecting the (d is a positive integer and d is less than or equal to L) th laser pulse sequence is X d
X d ＝{x di |i＝1，2，...，N} (15)
The digital multiplier obtains a modulation counting sequence Z d ：
Z d ＝{Z di |Z di ＝x di ·y i ，i＝1，2，...，N} (16)
The preset rule operation module is used for modulating the counting sequence Z d And carrying out sectional accumulation, and setting a plurality of accumulation parameters to obtain a plurality of sectional accumulation counting sequences. In one implementation, the method is implemented by introducing an accumulation parameter K 1 Two segment accumulation count sequences S can be obtained 1d And S is 2d 。
If two accumulation parameters are introduced, three segment accumulation count sequences can be obtained, and if x accumulation parameters are introduced, x+1 segment accumulation count sequences can be obtained. It should be noted that the present application does not limit the specific values of the accumulation parameters, and in one implementation, the accumulation parameters may be reasonably set so that each element in different segment accumulation count sequences is accumulated and generated by the same number of modulation count sequence elements.
The preset rule operation module then accumulates the segmented accumulated count sequences obtained in the L laser pulse sequence transmitting process to obtain accumulated count sequences S, and the accumulated count sequence analysis module obtains analysis accumulated count sequences S according to the accumulated count sequences n In one implementation, the accumulated count sequence with the largest sum of absolute values of the elements is selected as the analyzed accumulated count sequence S n 。
In another implementation, in order to reduce the operand and the data storage, the absolute values of the corresponding elements in the accumulated count sequence are selected for comparison, the accumulated count sequence corresponding to the largest element is selected as the analysis accumulated count sequence, and finally, the signal processing system performs the analysis of the accumulated count sequence S n Processing to obtain targetInformation.
Fig. 9 is a schematic diagram of a detection scheme according to an embodiment of the present application. In the detection scheme shown in FIG. 9, the photodetector starts to detect when the laser pulse sequence is emitted, and assuming that L (L is an integer greater than or equal to 1) laser pulse sequences are co-emitted, the adaptive sequence obtained when the photodetector detects the (d) (d is a positive integer and d is less than or equal to L) laser pulse sequences is X dai ：
X da ＝{x dai |i＝1,2,…,N} (17)
The digital multiplier obtains a modulation counting sequence Z d ：
Z d ＝{z di |z di ＝x dai ·y i ,i＝1,2,…,N} (18)
The preset rule operation module is used for modulating the counting sequence Z d And carrying out sectional accumulation, and setting a plurality of accumulation parameters to obtain a plurality of sectional accumulation counting sequences. In one implementation, the method is implemented by introducing an accumulation parameter K 1 Two segment accumulation count sequences S can be obtained 1d And S is 2d ：
Wherein N is 0 The integer with the value closest to N/M can be used, and the specific value is not limited; k is an integer and (R max The maximum detectable distance), the specific value is not limited. K (K) 1 Is a positive integer and K 1 K is less than or equal to K. Similarly, if two accumulation parameters are introduced, three segment accumulation count sequences can be obtained, and if x accumulation parameters are introduced, x+1 segment accumulation count sequences can be obtained. It should be noted that the present application does not limit the specific values of the accumulation parameters, and in one implementation, the accumulation parameters may be reasonably set so that each element in different segment accumulation count sequencesThe elements are accumulated from the same number of modulation count sequence elements.
The preset rule operation module then accumulates the segmented accumulated count sequence obtained in the process of transmitting the L laser pulse sequences to obtain an accumulated count sequence S, and the accumulated count sequence S can be obtained by a formula (17):
the accumulated count sequence analysis module obtains an analyzed accumulated count sequence S according to the accumulated count sequence n In one implementation, the accumulated count sequence with the largest sum of absolute values of the elements is selected as the analyzed accumulated count sequence S n From formula (18):
in another implementation manner, in order to reduce the operand and the data storage amount, the absolute values of the corresponding elements in the accumulated count sequence are selected for comparison, and the accumulated count sequence corresponding to the largest element is selected as the analysis accumulated count sequence, namely:
Finally, the signal processing system analyzes the accumulated count sequence S n And processing to obtain target information.
The rule that the accumulated count sequence analysis module obtains the analyzed accumulated count sequence according to the accumulated count sequence may be preset, and the above embodiment provides the rule of sum of absolute values and accumulation of maximum elements for illustration, but the application is not limited in particular.
Fig. 10 is a schematic diagram of another detection scheme according to an embodiment of the present application. In the detection scheme shown in fig. 10, a photodetector included in the receiving system starts detection when a laser pulse sequence is transmitted, and the photodetector obtains an accumulated photon count sequence X obtained during the transmission of the L laser pulse sequences, assuming that L (L is an integer greater than or equal to 1) laser pulse sequences are co-transmitted:
the digital multiplier obtains an accumulated modulation count sequence Z:
Z＝{z i |z i ＝x i ·y i ,i＝1,2,...,N} (24)
the preset rule operation module performs segmented accumulation on the accumulated modulation count sequence Z to obtain an accumulated count sequence S. In one implementation, the method is implemented by introducing an accumulation parameter K 1 Two accumulated count sequences S can be obtained 1 And S is 2 ：
Wherein N is 0 The integer with the value closest to N/M can be used, and the specific value is not limited; k is an integer and (R max The maximum detectable distance), the specific value is not limited. K (K) 1 Is a positive integer and K 1 K is less than or equal to K. Similarly, if two accumulation parameters are introduced, three segment accumulation count sequences can be obtained, and if x accumulation parameters are introduced, x+1 segment accumulation count sequences can be obtained. It should be noted that the present patent does not limit the specific value of the accumulation parameter, and in one implementation, the accumulation parameter may be reasonably set so that each element in different accumulation count sequences is accumulated and generated by the same number of accumulation modulation count sequence elements.
As with the detection scheme shown in FIG. 9, the accumulated count sequence analysis module obtains an analyzed accumulated count sequence S from the accumulated count sequence n The specific method can be as followsThe formulas (21) and (22) are given. And will not be described in detail herein.
The accumulated count sequence correction module corrects the accumulated count sequence to obtain a corrected accumulated count sequence, and finally, the signal processing system corrects the accumulated count sequence S m And processing to obtain target information.
In the above embodiments, the preset rule operation module generates the analysis accumulation count sequence by introducing an accumulation parameter and dividing the integration time into two segments. It should be noted that the number of the accumulation parameters, the segmented accumulation count sequence and the accumulation count sequence involved in the method is not limited, the integration time can be divided into any number according to the detection requirement, and the accumulation parameters, the segmented accumulation count sequence or the accumulation count sequence of any number are introduced, so that the optimal detection effect is realized.
Fig. 11a is a schematic diagram of a distance-related signal spectrum obtained by a prior art method according to an embodiment of the present application. Fig. 11b is a schematic diagram of a distance-related signal spectrum obtained by dividing an integration time into two segments according to an embodiment of the present application. It can be seen from fig. 11 a-11 b that a higher signal to noise ratio can be obtained using the above described embodiments.
In other embodiments, the counting sequence copying and splicing module, the counting sequence generating module, the accumulated counting sequence analyzing module, the accumulated counting sequence correcting module and the modulation sequence correcting module in the above embodiments may be arbitrarily combined, for example, in the embodiment shown in fig. 2, the accumulated parameters in the embodiments shown in fig. 9 and 10 may be introduced, and the integration time may be divided into multiple segments to generate the analyzed accumulated counting sequence, and of course, the accumulated counting sequence analyzing module may also be introduced. The present application is not particularly limited. The principle is similar to that of the above embodiment, and will not be described again here.
In addition to the above-mentioned incoherent chirp signal amplitude modulation continuous wave laser three-dimensional imaging technology (hereinafter referred to as technology 1), the present application mainly includes incoherent sinusoidal/pulse amplitude modulation laser three-dimensional imaging technology (itof, hereinafter referred to as technology 2) and pulse photon counting laser three-dimensional imaging technology (dtof, hereinafter referred to as technology 3), and compared with the above-mentioned technology, the present application has the following advantages:
(the prior art mainly comprises an incoherent sine/pulse amplitude modulation laser three-dimensional imaging technology (itof, hereinafter referred to as technology 1) and a pulse photon counting laser three-dimensional imaging technology (dtif, hereinafter referred to as technology 2) besides the incoherent chirp signal amplitude modulation continuous wave laser three-dimensional imaging technology and the technologies described in the first to fourth patents, and compared with the above technologies, the invention has the following advantages:
compared with the technology 1:
(1) The invention and the technology 2 are to accumulate signal energy and analyze the accumulated signal energy to obtain the target distance, from the energy utilization point of view, all the laser pulse energy reflected by the target is totally received, but the energy in the technology 2 is difficult to be totally utilized in one detection, so the invention has higher energy utilization rate;
(2) The invention utilizes narrow pulse to detect, has distance resolution, and can effectively avoid multipath effect;
(3) The invention has no serious problem of distance blurring;
(4) The method adopts the methods of correlation receiving, fourier analysis, spectrum detection and the like, and the ranging performance is less affected by the interference of the background light;
comparative technique 2
(1) In the second technique and the invention, the signal energy is accumulated through multiple detection to improve the signal-to-noise ratio, and in order to ensure a certain detection range, the signal receiving time length corresponding to the detection range needs to be set. Different from the second technology, the invention carries out correlation accumulation on the counting result in the integration time, so the signal-to-noise ratio can be improved by segmenting the integration time and reducing the signal receiving time length, and the detection range can be ensured by keeping the total integration time unchanged.
(2) The invention needs to transmit an accumulated counting sequence instead of a photon counting sequence, thereby greatly reducing the data storage and transmission quantity;
(3) According to the invention, the target distance information is extracted from the frequency spectrum, so that the influence of pulse shape distortion on the ranging performance is reduced;
(4) The method adopts the methods of correlation receiving, fourier analysis, spectrum detection and the like, and the ranging performance is less affected by the interference of the background light;
(5) The related receiving method adopted by the invention ensures that most of noise counts caused by background light and dark counts cannot be effectively accumulated, thus having a larger dynamic receiving range.
It should be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures. The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. The laser radar detection method is characterized by comprising a driving signal generation part, wherein the driving signal generation part acts on a laser source through a laser modulation driving circuit, and the laser source receives the driving signal and drives and emits a pulse type detection laser sequence; the array type return light receiving module receives a return light signal reflected by a detected object in a view field and generates a return signal, and the processing module generates a modulation signal according to a driving signal generated by the driving signal generating part and obtains a distance-related signal with the return signal according to a preset rule operation, wherein the distance-related signal at least comprises two different sequences, and the processing module outputs the distance information of the final detected object according to the distance-related signal.
2. The lidar detection method according to claim 1, wherein the at least two different sequences are obtained by integration over at least two identical integration times.
3. The lidar detection method of claim 1, further comprising an accumulated count sequence analysis module that selects the at least two different sequences according to a preset rule.
4. A lidar detection method according to claim 3, wherein the accumulated count sequence analysis module uses an accumulated count sequence for which the sum of absolute values of the elements of the at least two different sequences is the largest as the distance-dependent signal.
5. The lidar detection method of claim 3, wherein the cumulative count sequence analysis module compares absolute values of the at least two different sequence corresponding elements and selects a cumulative count sequence corresponding to a largest element of the at least two different sequence corresponding elements as the distance-related signal.
6. The lidar detection method of claim 1, wherein the at least two different sequences of elements are accumulated from the same number of sequence elements.
7. The lidar detection method of claim 1, further comprising a counting sequence replication splice module that obtains a replication splice sequence based on the return signal.
8. The lidar detection method of claim 1, further comprising a counting sequence generation module that generates an adaptive counting sequence from the return signal.
9. The lidar detection method of claim 1, further comprising a modulation sequence correction module that receives the drive signal to drive generation of a corrected modulation sequence.
10. The lidar detection method of claim 1, further comprising an accumulated count sequence correction module that obtains the range-dependent signal after correcting the at least two different sequences.
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