Laser radar device

Abstract

A laser radar device has a light source section (60; 60A; 60B) that periodically intensity-modulates laser light by intensity-modulation signals different in frequency from each other, outputs a plurality of intensity-modulated pulses; a telescope (9) that transmits the plurality of intensity-modulated pulses to a target, receives reflected light of the target as received light; a light-receiving section (11) that photoelectrically converts the received light, generates a received electric signal; and a signal processing section (12) that calculates a distance and a physical property parameter of the target from the received electric signal.

Description

Technical Field

[0001] This invention relates to lidar devices. Background Technology

[0002] As a distance measurement method based on lidar devices, there is a method called intensity-modulated pulse ToF (Time of Flight). Intensity-modulated pulse ToF refers to a method that calculates the distance to a target based on the pulse flight time from the start of emission to the point of reception. This method involves periodically modulating the intensity of the light pulse to improve the signal-to-noise ratio (SNR) of the reflected signal (HT signal) from a hard target (HT) present in a volume target (VT) with strong scattering, thereby extracting the HT signal and calculating the position of the hard target (HT). Non-Patent Document 1 relates to the intensity-modulated pulse ToF method and describes a device that uses a pulse generated by pulse combining and splitting, and then modulated with a single intensity modulation frequency, to identify a hard target (HT) within a volume target (VT).

[0003] Existing technical documents

[0004] Non-patent literature

[0005] Non-patent document 1: LJMullen, AJCVieira, PRHerezfeld and VMContarino, "Application of RADAR technology to aerial LIDAR systems for enhancement ofshallow underwater target detection," in IEEE Transactions on Microwave Theoryand Techniques, vol.43, no.9, pp.2370-2377, Sept.1995, doi: 10.1109 / 22.414591. Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] According to the technology described in Non-Patent Document 1, although the position of the target can be calculated, there is a problem that the physical properties of the target, such as the extinction coefficient, cannot be calculated.

[0008] This invention was made to solve this problem, and its purpose is to provide an intensity-modulated pulse ToF lidar device capable of calculating physical properties such as the extinction coefficient of a target.

[0009] Methods for solving problems

[0010] The lidar device according to an embodiment of the present invention includes: a light source unit that periodically modulates the intensity of a laser using intensity modulation signals with different frequencies and outputs multiple intensity modulation pulses; a telescope that sends the multiple intensity modulation pulses to a target and receives the reflected light from the target as received light; a light receiving unit that performs photoelectric conversion on the received light to generate a received electrical signal; and a signal processing unit that calculates the distance to the target and the extinction coefficient based on the received electrical signal.

[0011] Invention Effects

[0012] The lidar device according to the embodiments of the present invention can calculate the physical properties of a target, such as the extinction coefficient. Attached Figure Description

[0013] [ Figure 1 [ ] is a block diagram showing a structural example of the lidar device according to Embodiment 1.

[0014] [ Figure 2 [1] is a block diagram showing a structural example of the signal processing unit in Embodiment 1.

[0015] [ Figure 3A [Illustration 1] is a diagram showing an example of the hardware structure of the signal processing unit.

[0016] [ Figure 3B [Illustration 1] is a diagram showing an example of the hardware structure of the signal processing unit.

[0017] [ Figure 4 [ ] is a flowchart illustrating the operation of the lidar device according to Embodiment 1.

[0018] [ Figure 5 [Illustration of pulse train]

[0019] [ Figure 6A [Illustration 1] is a schematic diagram showing the waveform of the received signal.

[0020] [ Figure 6B [Illustration 1] is a schematic diagram of the received signal waveform and frequency analysis.

[0021] [ Figure 7 [Illustration] is a schematic diagram showing the relationship between distance and the SNR of the received signal.

[0022] [ Figure 8 [ ] is a schematic diagram of the signal processing method of the transfer function calculation unit.

[0023] [ Figure 9 ] Figure 9 A and Figure 9 B are schematic diagrams of the evaluated transfer functions.

[0024] [ Figure 10 [ ] is a schematic diagram showing the distance characteristics of the physical property parameters.

[0025] [ Figure 11 [ ] is a block diagram showing a structural example of the lidar device according to Embodiment 2.

[0026] [ Figure 12 [ ] is a block diagram showing a structural example of the intensity modulation signal generation unit in Embodiment 2.

[0027] [ Figure 13 [ ] is a flowchart illustrating the operation of the lidar device according to Embodiment 2.

[0028] [ Figure 14 ] Figure 14 A is a schematic diagram of a pulse train. Figure 14 B is a schematic diagram of the evaluated transfer function of the hard target HT. Figure 14 C is a schematic diagram of the transfer function of the evaluated volumetric target VT.

[0029] [ Figure 15 ] Figure 15 A is a schematic diagram of a pulse train. Figure 15 B is a schematic diagram of the evaluated transfer function of the hard target HT. Figure 15 C is a schematic diagram of the transfer function of the evaluated volumetric target VT.

[0030] [ Figure 16 [ ] is a block diagram showing a structural example of the lidar device according to Embodiment 3.

[0031] [ Figure 17 [ ] is a flowchart illustrating the operation of the lidar device according to Embodiment 3.

[0032] [ Figure 18 [ ] is a block diagram showing a structural example of the lidar device according to Embodiment 4.

[0033] [ Figure 19 [ ] is a block diagram showing a structural example of the signal processing unit in Embodiment 4.

[0034] [ Figure 20 [ ] is a flowchart illustrating the operation of the lidar device according to Embodiment 4. Detailed Implementation

[0035] Below, refer to Figures 1 to 17Various embodiments of the present invention will be described in detail. Furthermore, structural elements labeled with the same or similar reference numerals in the drawings have the same or similar structures or functions, and repeated descriptions related to such structural elements are omitted.

[0036] Implementation Method 1

[0037] First, refer to Figures 1-10 The lidar device of Embodiment 1 will be described.

[0038] <Structure>

[0039] Reference Figures 1 to 3B An example of the structure of the lidar device according to Embodiment 1 of the present invention will be described. For example... Figure 1 As shown, as an example, the lidar device of Embodiment 1 includes a light source 1, an intensity modulator 2, a trigger generation circuit 3, an intensity modulation signal generation unit 4, a pulse signal generation unit 5, a pulse modulation unit 6, a transmitting-side optical system 7, a transceiver splitter 8, a telescope 9, a receiving-side optical system 10, a light receiving unit 11, a signal processing unit 12, and a scanner 13. The light source 1, intensity modulator 2, intensity modulation signal generation unit 4, pulse signal generation unit 5, and pulse modulation unit 6 constitute the light source unit 60. The transmitting-side optical system 7 and the receiving-side optical system 10 are selective structural units. Figure 1 In the diagram, thick black arrows represent the flow of transmitted light, thick white arrows represent the flow of received light, and thin arrows represent the flow of electrical signals. The optical paths between light source 1 and intensity modulator 2, intensity modulator 2 and pulse modulator 6, pulse modulator 6 and transmitting optical system 7, transmitting optical system 7 and transceiver splitter 8, transceiver splitter 8 and telescope 9, transceiver splitter 8 and receiving optical system 10, and receiving optical system 10 and light receiver 11 can be implemented, for example, via optical fibers. The space between telescope 9 and scanner 13 is free space. The electrical paths for the flow of electrical signals are implemented via electrical wiring.

[0040] (light source)

[0041] Light source 1 is a light source that emits a continuous wave laser of a single frequency. Light source 1 is connected to intensity modulator 2, supplying the continuous wave laser to intensity modulator 2.

[0042] (Trigger generation circuit section)

[0043] The trigger generation circuit 3 is connected to the intensity modulation signal generation unit 4, the pulse signal generation unit 5, and the signal processing unit 12, and generates a trigger signal (pulse irradiation trigger) for driving these structural units, and outputs the trigger signal to the intensity modulation signal generation unit 4, the pulse signal generation unit 5, and the signal processing unit 12. As the trigger generation circuit 3, for example, a pulse generator, a function generator, or an FPGA (field-programmable gate array) can be used.

[0044] (Intensity Modulation Signal Generation Unit 4)

[0045] The intensity modulation signal generation unit 4 generates an intensity modulation signal with frequency fk over time based on the trigger signal. k = 1 to M (M is an integer greater than or equal to 2). The intensity modulation signal generation unit 4 is connected to the intensity modulator 2 and the signal processing unit 12, and outputs the generated intensity modulation signal with frequency fk to the intensity modulator 2 and the signal processing unit 12. The frequencies f1 to fM are set to be different from each other to generate signals after intensity modulation at different frequencies. As a method for generating different frequencies fk, there are, for example, two methods: the first method is to generate a signal by giving the frequency signal f1 an offset frequency of δfk using a frequency mixer; the second method is to use the frequency of the signal generated by the reference signal generator as the reference frequency, and multiply the reference frequency using a multiplier or divide the frequency using a frequency divider. The reference signals for generating intensity modulation frequency signals do not need to be the same, and reference signals can be prepared separately for each intensity modulation frequency.

[0046] (Pulse signal generation unit)

[0047] The pulse signal generation unit 5 generates a pulse signal based on the trigger signal. The pulse signal generation unit 5 is connected to the pulse modulation unit 6 and outputs the generated pulse signal to the pulse modulation unit 6.

[0048] (Intensity modulator)

[0049] The intensity modulator 2 periodically modulates the intensity of the continuous-wave laser from the light source 1 based on the intensity modulation signal output from the intensity modulation signal generation unit 4. For example, an interferometer-type intensity modulator can be used as the intensity modulator 2, which incorporates an optical attenuator, a semiconductor optical amplifier, an acousto-optic element, and a phase modulator. The intensity modulator 2 is connected to the pulse modulation unit 6, and outputs the intensity-modulated continuous-wave laser to the pulse modulation unit 6.

[0050] (Pulse Modulation Section)

[0051] The pulse modulation unit 6 has a pulse modulator that modulates the intensity-modulated continuous-wave laser pulse from the intensity modulator 2 into a pulse with a repetition period Trep and a pulse width δT, based on the pulse signal output from the pulse signal generation unit 5. For example, an acousto-optic element or a phase modulator can be used as the pulse modulation unit 6. To obtain a high SNR (signal-to-noise ratio), the pulse modulation unit 6 may also have an optical amplifier to amplify the optical power of the pulse-modulated laser. The pulse modulation unit 6 is connected to the transmitting-side optical system 7 and outputs the amplified laser to the transmitting-side optical system 7. As described above, the light source unit 60 periodically modulates the intensity of the continuous-wave laser using intensity modulation signals with different frequencies, outputting multiple intensity-modulated pulses with different modulation frequencies. Furthermore, "periodically performing intensity modulation" means modulation in a manner where the optical power changes periodically. An example of a periodically intensity-modulated pulse is... Figure 5 The pulses are P1 and P2. Pulse P1 illustrates the situation where the optical power is periodically varied at a modulation frequency f1 while keeping the maximum optical power constant. Pulse P2 illustrates the situation where the optical power is periodically varied at a modulation frequency f2 while keeping the maximum optical power constant.

[0052] (Transmitter-side optical system)

[0053] The transmitting-side optical system 7 shapes the pulse-modulated or amplified laser light from the pulse modulation unit 6 into the desired beam diameter and spread angle. The transmitting-side optical system 7 consists of a lens group composed of concave and convex surfaces. The transmitting-side optical system 7 can also be a reflective optical system utilizing mirrors. The laser shaping performed by the transmitting-side optical system 7 is for achieving a high SNR; therefore, if a sufficient SNR can be obtained even without the transmitting-side optical system 7, it may not be necessary. The transmitting-side optical system 7 is connected to the transceiver splitter 8, outputting the shaped laser light to the transceiver splitter 8.

[0054] (Transceiver splitter)

[0055] The transceiver splitter 8 is a splitter that separates the transmitted light and the received light to designated ports. When laser propagation between the transceiver splitter 8 and other structures is carried out via spatial propagation, a polarizing beam splitter (PBS) can be used as the transceiver splitter 8. In the case of laser propagation via spatial propagation, the transceiver splitter 8 is positioned between the transmitting-side optical system 7 and the telescope 9, and is positioned on the optical axis of the transmitted light. When the transceiver splitter 8 is connected to other structures via optical fiber, a circulator can be used as the transceiver splitter 8. The transceiver splitter 8 outputs the transmitted light to the telescope 9 and the received light to the receiving-side optical system 10.

[0056] (Telescope; Scanner)

[0057] Telescope 9 transmits light in the desired direction via scanner 13 and receives reflected light, i.e., received light, from the target via scanner 13. Telescope 9 consists of a lens group composed of concave and convex surfaces. Telescope 9 can also be a reflecting telescope using mirrors. Scanner 13 is rotated via a control unit (not shown) to face the specified direction. Telescope 9 outputs the received light to transceiver splitter 8.

[0058] (Receiver-side optical system)

[0059] The receiver-side optical system 10 shapes the received light from the transceiver splitter 8 into a desired beam diameter and spread angle. The receiver-side optical system 10 is composed of a lens group consisting of concave and convex surfaces. The receiver-side optical system 10 can also be a reflective optical system utilizing mirrors. The shaping performed by the receiver-side optical system 10 is for obtaining a high SNR; therefore, if a sufficient SNR can be obtained even without the receiver-side optical system 10, it may not be necessary. The receiver-side optical system 10 is connected to the light-receiving unit 11 and outputs the received light to the light-receiving unit 11.

[0060] (Light-receiving area)

[0061] The light-receiving unit 11 performs photoelectric conversion on the received light to generate a received electrical signal. The light-receiving unit 11 is connected to the signal processing unit 12 and outputs the received electrical signal to the signal processing unit 12.

[0062] (Signal Processing Department)

[0063] The signal processing unit 12 processes the received electrical signal and calculates the physical distance characteristics. (See below for...) Figure 2 The structure of the signal processing unit 12 will be described. For example... Figure 2 As shown, the signal processing unit 12 includes a filtering processing unit 12-1, an A / D conversion unit 12-2, a distance bin segmentation unit 12-3, a frequency analysis unit 12-4, a cumulative processing unit 12-5, an SNR calculation unit 12-6, a distance characteristic calculation unit 12-7, a transfer function calculation unit 12-8, a physical property calculation unit 12-9, and a physical property-distance characteristic calculation unit 12-10.

[0064] (Filtering Processing Department)

[0065] The filtering unit 12-1 performs frequency filtering on the received electrical signal from the light-receiving unit 11 based on the intensity modulation signal at frequency fk from the intensity modulation signal generation unit 4. The filtering unit 12-1 is implemented, for example, using a bandpass filter with a center frequency fk (k = 1, 2, 3, ..., M), allowing the received electrical signal from the light-receiving unit 11 to pass through within the passband. The filtering unit 12-1 is connected to the A / D conversion unit 12-2 and outputs the filtered electrical signal to the A / D conversion unit 12-2. Alternatively, the filtering unit 12-1 may be located between the A / D conversion unit 12-2 and the accumulation processing unit 12-5.

[0066] (A / D conversion unit)

[0067] The A / D conversion unit 12-2 performs AD conversion on the filtered electrical signal from the filtering unit 12-1 based on the trigger signal (pulse irradiation trigger) from the trigger generation circuit unit 3. The A / D conversion unit 12-2 is connected to the distance compartment division unit 12-3 and outputs the digital signal after AD conversion to the distance compartment division unit 12-3.

[0068] (Distance from warehouse partition)

[0069] The distance cell segmentation unit 12-3 segments the digital signal after AD conversion in the time direction with a width equivalent to the pulse width according to the trigger signal (pulse illumination trigger). The distance cell segmentation unit 12-3 is connected to the frequency analysis unit 12-4 and outputs the segmented signal to the frequency analysis unit 12-4.

[0070] (Frequency Analysis Department)

[0071] The frequency analysis unit 12-4 performs a high-speed Fourier transform (FFT) on the signal of each segmented range cell based on the intensity modulation signal of frequency fk from the intensity modulation signal generation unit 4, thereby converting the signal of each range cell into a spectrum. The frequency analysis unit 12-4 is connected to the accumulation processing unit 12-5 and outputs the spectrum to the accumulation processing unit 12-5.

[0072] (Cumulative Processing Department)

[0073] The cumulative processing unit 12-5 accumulates multiple spectra obtained from multiple transmissions at the same frequency fk in the spectral space. The cumulative processing unit 12-5 is connected to the SNR calculation unit 12-6 and outputs the accumulated spectrum to the SNR calculation unit 12-6.

[0074] (SNR Calculation Department)

[0075] The SNR calculation unit 12-6 calculates the SNR of the received signal at a certain moment and a certain intensity modulation frequency. The SNR calculation unit 12-6 is connected to the range characteristic calculation unit 12-7 and outputs the calculated SNR to the range characteristic calculation unit 12-7.

[0076] (Distance Characteristics Calculation Department)

[0077] The distance characteristic calculation unit 12-7 calculates the relationship between distance and SNR at a certain intensity modulation frequency (distance characteristic: A-scope). The distance characteristic calculation unit 12-7 calculates A-scope for all intensity modulation frequencies f1 to fM. The distance characteristic calculation unit 12-7 is connected to the transfer function calculation unit 12-8 and outputs the calculated multiple distance characteristics (A-scope) to the transfer function calculation unit 12-8.

[0078] (Transfer Function Calculation Department)

[0079] The transfer function calculation unit 12-8 calculates the transfer function of a target within a range chamber based on multiple range characteristics (A-scope) at multiple intensity modulation frequencies (f1 to fM) related to a certain range chamber. Thus, the transfer function calculation unit 12-8 analyzes the transfer function characteristics of targets at the same range based on the frequency dependence of SNR. The transfer function calculation unit 12-8 is connected to the physical property calculation unit 12-9, and outputs the calculated transfer function to the physical property calculation unit 12-9.

[0080] (Physical Property Calculation Department)

[0081] The property characteristic calculation unit 12-9 compares the transfer function characteristics determined by the transfer function in each distance chamber n obtained by the transfer function calculation unit 12-8 with the transfer function expression based on equation (4) or equation (6) described later, or a transfer function expression based on an expression similar to these equations, thereby calculating the property characteristics of the target existing in the distance chamber n. Furthermore, the property characteristic calculation unit 12-9 can also compare the SNR in each distance chamber n obtained by the distance characteristic calculation unit 12-7 with the assumed SNR, thereby calculating the property characteristics of the target existing in the distance chamber n. The property characteristic calculation unit 12-9 is connected to the property distance characteristic calculation unit 12-10 and outputs the calculated property characteristics to the property distance characteristic calculation unit 12-10.

[0082] (Physical Property Distance Characteristic Calculation Department)

[0083] The distance characteristic calculation unit 12-10 calculates the physical property parameter data calculated by the physical property calculation unit 12-9 in the same way as the distance characteristic calculation unit 12-7. Figure 10As shown, based on the distance chamber information, AD conversion rate and distance chamber width, Δt = AD rate × distance chamber width × (n-1) is calculated. Δt is then converted into distance using L = v × Δt / 2 (v is the speed of light), and the physical property parameter curves for each distance are output.

[0084] Next, refer to Figure 3A and Figure 3B The hardware structure of the signal processing unit 12 will be described as an example. For example, Figure 3A As shown, the signal processing unit 12 is implemented by the processing circuit 100a. The processing circuit 100a can be, for example, a single circuit, a composite circuit, a programmable processor, a parallel programmable processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The functions of the structural units in the signal processing unit 12 can be implemented using independent processing circuits, or the functions of multiple structural units can be implemented using a single processing circuit.

[0085] As another example, such as Figure 3B As shown, the signal processing unit 12 is implemented by a processor 100b and a memory 100c. The program stored in the memory 100c is read and executed by the processor 100b, thereby realizing the functions of the structural units of the signal processing unit 12. The program is implemented as software, firmware, or a combination of software and firmware. In the example of the memory 100c, it includes non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory), as well as disks, floppy disks, optical disks, high-density disks, mini disks, and DVDs.

[0086] <Action>

[0087] Next, refer to Figures 4 to 10 The operation of the lidar device in Embodiment 1 will be explained.

[0088] In step ST1, the intensity modulation signal generation unit 4 generates an intensity modulation signal with frequency f1 according to the trigger signal, and outputs the generated intensity modulation signal with frequency f1 to the intensity modulator 2 and the signal processing unit 12. Then, the intensity modulator 2 uses the intensity modulation signal with frequency f1 to periodically modulate the intensity of the single-frequency continuous wave laser from the light source 1, and outputs the intensity-modulated continuous wave laser to the pulse modulation unit 6.

[0089] In step ST2, the pulse modulation unit 6 modulates the intensity-modulated continuous wave laser pulse into a pulse light P1 with a predetermined repetition period Trep and pulse width δT based on the pulse signal from the pulse signal generation unit 5 (refer to...). Figure 5 The pulse P1 is transmitted to the transmitting optical system 7. Hereinafter, the k-th transmitted pulse signal will be denoted as "Pk". Furthermore, the intensity modulation frequency corresponding to the transmitted pulse Pk and the received signal pulse from the target will be denoted as fk and Rk, respectively.

[0090] In step ST3, the telescope 9 illuminates the target with pulsed light P1, which has been converted by the transmitting-side optical system 7 to a predetermined beam diameter and beam spread angle, via the scanner 13. The transmitted light P1, which is illuminating the atmosphere, is then reflected by the target, generating received light R1 when scattered by the target.

[0091] In step ST4, the telescope 9 receives the received light R1 through its aperture and outputs the received light R1 to the transceiver splitter 8. The received light R1 is then sent to the receiving-side optical system 10 via the transceiver splitter 8. After being converted by the receiving-side optical system 10 into a predetermined beam diameter and beam spread angle, the received light R1 is sent to the light receiving unit 11. The light receiving unit 11 converts the received light R1 into a received electrical signal, which is then sent to the signal processing unit 12.

[0092] The lidar device repeatedly performs the transmission and reception processing steps ST2 to ST4 a times or more. 'a' is an integer greater than or equal to 1 and is a design value. Hereinafter, 'a' will be referred to as the pulse accumulation count. That is, 'a' is the cumulative number of times a modulated pulse of the same intensity is applied.

[0093] like Figure 5 Thus, after pulse P1 irradiates the target a times and the repetition period Trep has elapsed, in step ST5, the intensity modulation signal generation unit 4 generates an intensity modulation signal with frequency f2 based on the trigger signal, and outputs the generated intensity modulation signal with frequency f2 to the intensity modulator 2 and the signal processing unit 12. Next, the intensity modulator 2 uses the intensity modulation signal with frequency f2 to periodically modulate the intensity of the single-frequency continuous-wave laser from the light source 1, and outputs the intensity-modulated continuous-wave laser to the pulse modulation unit 6.

[0094] In step ST6, the pulse modulation unit 6 pulse modulates the intensity-modulated continuous wave laser according to the pulse signal from the pulse signal generation unit 5, generating a pulse light P2 that is different from the pulse light P1 (refer to...). Figure 5 The generated pulse P2 is output to the transmitting side optical system 7.

[0095] In step ST7, the telescope 9 illuminates the target with pulsed light P2, which has been converted by the transmitting-side optical system 7 to a predetermined beam diameter and beam spread angle, via the scanner 13. The transmitted light P2, which is illuminating the atmosphere, is then reflected by the target, generating received light R2 when scattered by the target.

[0096] In step ST8, the telescope 9 receives the received light R2 through its aperture and outputs the received light R2 to the transceiver splitter 8. The received light R2 is then sent to the receiving-side optical system 10 via the transceiver splitter 8. After being converted by the receiving-side optical system 10 into a predetermined beam diameter and beam spread angle, the received light R2 is sent to the light receiving unit 11. The light receiving unit 11 converts the received light R2 into a received electrical signal, which is then sent to the signal processing unit 12.

[0097] The lidar device performs step ST5 until k = M is reached. For each value of k, steps ST6 to ST8 are repeated a times. Through the above actions, the receiving light R1 to RM are received a times each.

[0098] Next, the signal processing for steps ST9 to ST14 will be explained. Signal processing can be performed following step ST4 each time each received light is received, or it can be performed following step ST8 after all received light R1 to RM has been received. The following explanation will focus on the case where signal processing for steps ST9 to ST14 is performed after all received light R1 to RM has been received.

[0099] In step ST9, the filtering processing unit 12-1 performs frequency filtering processing on the received signals of all received light (R1 and Rk) based on the intensity modulation signal of frequency fk from the intensity modulation signal generation unit 4, and obtains an electrical signal corresponding to each modulation frequency.

[0100] In step ST10, the A / D conversion unit 12-2 performs AD conversion on the received signal of the received light Rk. The A / D conversion unit 12-2 sets the trigger signal from the trigger generation circuit unit 3 as the start trigger for AD conversion. Therefore, the start time of AD conversion is approximately consistent with the timing of the transmission pulse being transmitted, and AD conversion continues for a specified period or until the next transmission pulse is generated. The signal converted ΔT after the start of AD conversion corresponds to the received signal from a target located in space at a separation distance L = v × ΔT / 2 (v is the speed of light). The digitized received signal corresponds to one pulse.

[0101] In step ST11, the range cell segmentation unit 12-3 divides the digitized received signal into signals for each range cell. The range cell width is divided to a value equivalent to the pulse width, which is determined by design. Figure 6A This shows the time variation of the received signal obtained by receiving the received light Rk from the target, which was illuminated by a pulsed transmitted light Pk that has been pulsed once. n represents the tag of the segmented range cell, and tags with smaller n values ​​indicate reflected signals from closer locations.

[0102] In step ST12, the frequency analysis unit 12-4 performs an FFT on the received signal segmented according to each range cell, converting it into a spectral signal, and outputs the resulting spectral signal to the accumulation processing unit 12-5. The spectrum obtained by performing an FFT on the received signal of the received light Rk corresponding to the transmitted pulse Pk (modulation frequency fk) is affected by frequency shifts from the target and the environment, but it is approximately consistent with the modulation frequency within the receiving bandwidth B. Hereinafter, the received spectrum corresponding to the modulation frequency fk is denoted as fm. The receiving bandwidth B is a hypothetical frequency shift width determined by the target's moving speed and the surrounding environment.

[0103] In step ST13, as Figure 6B As shown, the cumulative processing unit 12-5 performs a-time accumulation on the spectral signal obtained by performing FFT on the signal of each distance cell.

[0104] In step ST14, the SNR calculation unit 12-6 calculates the ratio of peak intensity to out-of-band noise, thereby calculating the SNR of the spectrum fm of the received signal. The SNR calculation unit 12-6 outputs the accumulated spectrum fm and the SNR information in each range cell to the range characteristic calculation unit 12-7.

[0105] In step ST15, the distance characteristic calculation unit 12-7 calculates the curve representing the SNR for each distance, i.e., A-scope. For example... Figure 7As shown, for spectra f1 to fM, SNR information is collected in any range bin n. The range characteristic calculation unit 12-7 calculates Δt = AD rate × range bin width × (n-1) based on the range bin information, AD conversion rate, and range bin width. Δt is then converted to range using L = v × Δt / 2 (where v is the speed of light), and the A-scope is calculated. Hereinafter, the SNR in spectra fm and range bin n is denoted as SNRmn. Furthermore, as... Figure 8 As shown, the transfer function calculation unit 12-8 processes the SNR of the spectrum f1 to fM in each range cell n (n = 1, 2, 3, ...) based on the SNRmn information, and calculates the transfer function (curve of spectral frequency f on the vertical axis and horizontal axis) for each range cell. Furthermore, in Figure 8 In the example, for a distance chamber with n=3, a specific example is shown where the transfer function is obtained by arranging the spectrum f1 to fM along the frequency axis using the SNR.

[0106] In step ST16, the property calculation unit 12-9 calculates the property characteristics of the target existing in the distance chamber n. Specifically, the property calculation unit 12-9 compares the transfer function characteristics determined by the transfer function in each distance chamber n obtained by the transfer function calculation unit 12-8 with the transfer function expression based on the following equation (4) or equation (6) or a transfer function expression based on an expression similar to these equations, thereby calculating the property characteristics of the target existing in the distance chamber n. In addition, the property calculation unit 12-9 may also compare the SNR in each distance chamber n obtained by the distance characteristic calculation unit 12-7 with the assumed SNR, thereby calculating the property characteristics of the target existing in the distance chamber n. Here, the transfer function characteristics are... Figure 9 A or Figure 9 The curve shown in B has an overall shape, a slope, or a cutoff frequency fc when the curve is considered to have the same transfer function as the low-pass filter.

[0107] In intensity-modulated pulse ToF mode, the received signal power Pr from a target (extinction coefficient c, absorption coefficient α, backscattering coefficient β) located at a distance L (=vt / 2) is represented by the following equation (1). In equation (1), v is the propagation velocity within the volume target VT, t is time, A is the system coefficient, and Y is the normalization constant. When equation (1) is Fourier transformed under the assumption of equation (2), it becomes equation (3).

[0108]

[0109] P(t)~Ye-cut(2)

[0110]

[0111] Therefore, when an intensity-modulated pulse with an intensity modulation angular frequency of ω = 2πf is sent to the target, the modulation frequency ω of the received signal is... m The components are represented by equation (4). Under the assumption of equation (2), the transfer function T(ω) of the target is represented by equation (4), which is equivalent to the case of a first-order low-pass filter (LPF).

[0112]

[0113] Under the assumption of equation (2), the cutoff frequency fc of the transfer function is expressed by the extinction coefficient c, which is represented by equation (5).

[0114]

[0115] For example, c = 1m -1 The cutoff frequency of the transfer function of a scattering medium (VT) with a refractive index n = 1.3 is equivalent to fc = 37 MHz.

[0116] In addition, strictly speaking, in equation (1), L(t) = vt / 2, therefore, the more accurate transfer function of the target is expressed by the following equation (6).

[0117]

[0118] The transfer function characteristics of the target calculated based on the measurement results ( Figure 8 The transfer function of equation (4) or (6) or similar to equation (4) or (6) can be compared with the right lower figure to estimate physical property parameters (e.g., extinction coefficient c). Figure 9 A shows the fitting of the transfer function based on equation (4). Figure 9 B shows the fitting of the transfer function based on equation (6). For example, if it is to estimate the extinction coefficient c, the cutoff frequency fc is obtained by comparing the transfer function characteristics based on the measurement results with transfer functions such as equation (4), and the extinction coefficient c is calculated according to equation (5).

[0119] Furthermore, the physical property parameter data calculated by the physical property calculation unit 12-9 is the same as that of the distance property calculation unit 12-7, such as... Figure 10 As shown, the distance property calculation unit 12-10 calculates Δt = AD rate × distance chamber width × (n-1) based on the distance chamber information, AD conversion rate and distance chamber width. It converts Δt into distance using L = v × Δt / 2 (v is the speed of light) and outputs the property parameter curve for each distance.

[0120] As shown in equation (7), the extinction coefficient c in equation (1) is expressed using the absorption coefficient α and the scattering coefficient b (or the backscattering coefficient β). Additionally, Ω is the solid angle of the transmitting and receiving optical system.

[0121] c=α+b=α+∫βdΩ (7)

[0122] As shown in equation (7), the extinction coefficient c is related to more than two physical property parameters. Therefore, in the prior art, a certain relationship is assumed between these parameters. For example, in the design of laser sensors, it is assumed that the backscattering coefficient β and the extinction coefficient c have a linear relationship, and their ratio is set as the lidar ratio S1, assuming the relationship of equation (8).

[0123] c = S1β (8)

[0124] The lidar ratio S1 is determined by the particle size, laser wavelength λ, particle shape, etc. The target is determined, and the backscattering coefficient is calculated using the lidar ratio S1, which has been determined through simulation or other measurements, as well as equations (1) and (8).

[0125] According to this existing method, there are the following problems: when the physical property information of the target is unknown, or when the measurement is carried out in special environments such as the air or the sea, the assumption of Equation (8) cannot be used, or the accuracy of the physical property value calculated when using Equation (8) is reduced.

[0126] In contrast, the method according to the present invention can estimate physical properties without specifically assuming the correlation between physical property parameters required in the prior art.

[0127] <Effect>

[0128] The transfer function of the data output from the transfer function calculation unit 12-8 contains information about the extinction coefficient, and the SNR output from the SNR calculation unit 12-6 contains information about the extinction coefficient and the scattering coefficient. Therefore, as described above, regarding the pulse received signal from a target located at a distance L, in addition to the SNR, the transfer function characteristics of the intensity modulation frequency fk are also calculated, thereby enabling the independent detection of the target's extinction coefficient and scattering coefficient.

[0129] Existing lidar devices suffer from the inability to independently calculate extinction and scattering coefficients. Typically, they rely on known target information or approximate the relationship between extinction and scattering coefficients based on known target information before formulating a formula. This leads to problems such as low accuracy of measurements or miscalculation of physical properties when the target differs from the initial assumption. The method of this invention eliminates the need to formulate the relationship between extinction and scattering coefficients, thus solving the problems of existing lidar devices.

[0130] <Variation Example>

[0131] The following describes a variation of Embodiment 1. As a method for generating pulsed lasers, not only can a method for pulsed continuous-wave lasers be used, but also any one or a combination of general methods such as directly generating Q-switched lasers, mode-locked lasers, or other pulsed-wave lasers. As a method for generating intensity-modulated pulses, methods can also include generating intensity-modulated pulses using an intensity modulator made with an electrolytic absorption modulator, an electro-optic crystal or optical block, or similar structures, or using such modulators; generating simulated intensity-modulated pulses by directly exciting a light source using an electrical signal pulse train; generating simulated intensity-modulated pulses by dividing a pulsed laser using a beam splitter, delaying one pulse, and then combining them again; and generating simulated intensity-modulated pulses by placing a wavelength conversion crystal in a resonator whose reflectivity is reduced only on one side of the mirror, etc.

[0132] While a direct detection method is assumed in the optical detection unit, the technology of this invention can be applied to coherent lidar, differential absorption lidar, and dual-polarization lidar by using intensity-modulated pulses as the transmitted light. When applied to coherent lidar, in addition to the target's physical properties, the target's moving velocity can be calculated, thus enabling higher precision and a greater number of parameter measurements. When applied to differential absorption lidar, the light source unit outputs an intensity-modulated pulse of a first wavelength and an intensity-modulated pulse of a second wavelength different from the first wavelength. The signal processing unit can further calculate the target's absorption wavelength and concentration as the target's physical properties based on the ratio of the received signal intensity of the first wavelength received light to the received signal intensity of the second wavelength received light. When applied to dual-polarization lidar, the light source unit outputs intensity-modulated pulses with two orthogonal polarization states. The signal processing unit can further calculate the target's particle shape as the target's physical properties based on the ratio of the received signal intensity of the two polarizations. Furthermore, while a transceiver optical system is assumed in the optical system, a structure with different transceiver axes is also possible. In the case of misalignment between the transmitter and receiver, a telescope (not shown) different from telescope 9 is connected to the receiving-side optical system 10, while the transmitter-receiver separation unit 8 and the receiving-side optical system 10 are not connected. This misalignment structure is a general structure and will not cause any impact during the operation of Embodiment 1.

[0133] Implementation Method 2

[0134] Below, refer to Figures 11-13 The lidar device of Embodiment 2 will be described.

[0135] <Structure>

[0136] like Figure 11 As shown, the overall structure of the lidar device in Embodiment 2 is similar to... Figure 1 The structure of the lidar device in Embodiment 1 shown is the same. For example... Figure 11 As shown, in the lidar device of Embodiment 2, the light source unit 60A includes a light source 1, an intensity modulator 2, an intensity modulation signal generation unit 4A, a pulse signal generation unit 5, and a pulse modulation unit 6. In the lidar device of Embodiment 2, the structure of the intensity modulation signal generation unit 4A in the light source unit 60A differs from that of the intensity modulation signal generation unit 4 in Embodiment 1.

[0137] like Figure 12 As shown, the intensity modulation signal generation unit 4A has an intensity modulation signal (f) generation unit group 4-1 composed of M intensity modulation signal (f) generation units, and an intensity modulation signal mixing unit 4-2 connected to the intensity modulation signal (f) generation unit group 4-1.

[0138] The intensity modulation signal (f) generation unit 4-1 generates M intensity modulation signals of different frequencies. The intensity modulation signal (f) generation unit 4-1 consists of a function generator, an FPGA, a reference signal generator, and an RF frequency signal generator such as a multiplier or frequency divider.

[0139] The intensity modulation signal mixing unit 4-2 mixes the M intensity modulation signals from the intensity modulation signal (f) generation unit group 4-1. The intensity modulation signal mixing unit 4-2 is, for example, a mixer with an RF frequency.

[0140] <Action>

[0141] In Embodiment 1, a laser pulse is generated by intensity modulation using a certain intensity modulation frequency fk, and each of the M pulses is irradiated a times to accumulate them. In contrast, in Embodiment 2, M intensity modulation signals with different frequencies (f1 to fM) are simultaneously applied to the transmitted pulse, and the transmitted pulse is irradiated a times to accumulate them. In this respect, the operation of Embodiment 2 differs from that of Embodiment 1. In other aspects, the operation of Embodiment 2 is the same as that of Embodiment 1. For the differences, please refer to... Figure 13 Please provide an explanation.

[0142] In step ST21, the intensity modulation signal (f) generation unit group 4-1 generates intensity modulation signals with frequencies f1 to fM according to the trigger signal, and outputs the M intensity modulation signals with frequencies f1 to fM to the intensity modulation signal mixing unit 4-2 and the signal processing unit 12.

[0143] In step ST22, the intensity modulation signal mixing unit 4-2 mixes the M intensity modulation signals. The intensity modulation signal mixing unit 4-2 outputs the mixed signal to the intensity modulator 2. The intensity modulation signal mixing unit 4-2 may also output the mixed signal to the signal processing unit 12. Following the operation of the intensity modulation signal mixing unit 4-2, the intensity modulator 2 uses the mixed intensity modulation signal to intensity modulate the single-frequency continuous wave laser from the light source 1, and outputs the intensity-modulated continuous wave laser to the pulse modulation unit 6.

[0144] In step ST23, the pulse modulation unit 6 modulates the intensity-modulated continuous wave laser pulse into a pulse light P based on the pulse signal from the pulse signal generation unit 5, and outputs the pulse light P to the transmitting side optical system 7.

[0145] In step ST24, the telescope 9 illuminates the target with pulsed light P, which has been converted by the transmitting-side optical system 7 to a predetermined beam diameter and beam spread angle, via the scanner 13. The transmitted light P, which is illuminating the atmosphere, is then reflected by the target, generating received light R when scattered by the target.

[0146] In step ST25, the telescope 9 receives the received light R through its aperture and outputs the received light R to the transceiver splitter 8. The received light R is then sent to the receiving-side optical system 10 via the transceiver splitter 8. After being converted by the receiving-side optical system 10 into a predetermined beam diameter and beam spread angle, the received light R is sent to the light receiving unit 11. The received light R is converted into a received electrical signal by the light receiving unit 11, and the received electrical signal is sent to the signal processing unit 12.

[0147] The lidar device repeatedly performs the transmission and reception processing steps ST23 to ST25 more than a times.

[0148] The processing of steps ST26 to ST33 is the same as that of steps ST9 to ST16 in embodiment 1.

[0149] <Variation Example>

[0150] In the above explanation, M different intensity modulation signal generation units were prepared. However, in the case of M = XY, X different intensity modulation signal generation units were prepared, and X intensity modulations were applied to one pulse. While varying the intensity modulation frequency, Y pulses were applied. This allows the transfer function characteristics of the target for M different intensity modulations to be calculated using the Y pulses. The number of such signal generators and the number of pulse applications can be appropriately varied.

[0151] Implementation Method 3

[0152] Below, refer to Figures 14-17The lidar device of Embodiment 3 will be described. In the structures of Embodiments 1 and 2, due to the non-uniformity of pulse power or the degree of intensity modulation between the intensity-modulated pulses generated when intensity modulation is applied to each pulse Pk at frequency fk, the transfer function characteristics to be calculated sometimes produce errors. The explanation will be changed in a different paragraph.

[0153] like Figure 14 As in case A, when the difference in pulse parameters between modulation pulses of different intensities is small, such as Figure 14 B or Figure 14 As in C, the transfer function (dotted line) evaluated based on the SNR of the received signal from the target is roughly consistent with the true value (solid line). On the other hand, for example, Figure 15 As in case A, when the difference in pulse parameters between modulation pulses of different intensities is large, such as Figure 15 B or Figure 15 As in C, the discrepancy between the transfer function (dotted line) evaluated based on the SNR of the received signal from the target and the true value (solid line) becomes a cause of miscalculation. Here, pulse parameters represent the envelope shape of each intensity-modulated pulse, the peak component constituting each intensity-modulated pulse, the intensity modulation frequency assigned to the optical pulse, and similar parameters. Furthermore, the difference in pulse parameters represents the difference between the envelope shape of each intensity-modulated pulse, the peak component constituting each intensity-modulated pulse, the intensity modulation frequency assigned to the optical pulse, and similar parameters relative to the ideal value.

[0154] Therefore, the lidar device in Embodiment 3 is configured to monitor a portion of the intensity-modulated pulse signal and apply control to optimize the pulse parameters of each pulse (P1 to PM), thereby calculating a more accurate transfer function based on the detected SNR.

[0155] <Structure>

[0156] The lidar device of Embodiment 3 differs from the lidar device of Embodiment 1 in the following aspects. That is, as... Figure 16 As shown, the lidar device of Embodiment 3 further includes a light pulse branching section 14, a light pulse monitoring section 15, and a light pulse correction section 16. The light pulse branching section 14 is disposed between the pulse modulation section 6 and the transmitting-side optical system 7. The light pulse monitoring section 15 is disposed after the light pulse branching section 14. The light pulse correction section 16 is disposed after the light pulse monitoring section 15 and is connected to the intensity modulation signal generation section 4B and the pulse signal generation section 5B. In addition, the light source 1, the intensity modulator 2, the intensity modulation signal generation section 4B, the pulse signal generation section 5B, and the pulse modulation section 6 constitute the light source section 60B. Alternatively, the lidar device of Embodiment 2 can be modified by adding the light pulse branching section 14, the light pulse monitoring section 15, and the light pulse correction section 16 to the lidar device of Embodiment 2.

[0157] The optical pulse branching section 14 branches a portion of the intensity-modulated pulse generated by the pulse modulation section 6 and outputs the branched portion of the pulse to the optical pulse monitoring section 15.

[0158] The optical pulse monitoring unit 15 converts the optical pulse signal into an electrical signal.

[0159] The optical pulse correction unit 16 compares the electrical signal from the optical pulse monitoring unit 15 with a pre-stored ideal intensity modulation pulse waveform, and outputs a feedback signal to the intensity modulation signal generation unit 4 and the pulse signal generation unit 5 to make the waveform of the pulse output from the pulse modulation unit ideal. For example, the optical pulse correction unit 16 outputs a feedback signal for controlling the pulse power and modulation intensity of the transmitted pulse.

[0160] <Action>

[0161] Next, refer to Figure 17 The operation of the lidar device according to Embodiment 3 will be explained. The operation of the lidar device in Embodiment 3 differs from that of the lidar device in Embodiment 1 in that steps ST41, ST42, ST43, and ST44 are added. Repeated explanations are omitted; therefore, only the differences from the operation of Embodiment 1 will be explained.

[0162] In step ST41, the optical pulse monitoring unit 15 receives the optical pulse signal that is branched from the optical pulse branching unit 14 as a monitoring signal, and converts the received optical pulse signal into an electrical signal.

[0163] In step ST42, the optical pulse correction unit 16 compares the waveform of the electrical signal from the optical pulse monitoring unit 15 with the ideal intensity modulation pulse waveform stored in advance, and outputs a feedback signal to the intensity modulation signal generation unit 4 and the pulse signal generation unit 5 to suppress the deviation of these waveforms, that is, to make the waveform of the pulse output from the pulse modulation unit become the ideal waveform.

[0164] In step ST1 after generating the feedback signal, the intensity modulation signal generation unit 4B generates an intensity modulation signal with frequency f1 based on the feedback signal, and outputs the generated intensity modulation signal with frequency f1 to the intensity modulator 2 and the signal processing unit 12. Next, the intensity modulator 2 uses the intensity modulation signal with frequency f1 generated based on the feedback signal to intensity modulate the single-frequency continuous wave laser from the light source 1, and outputs the intensity-modulated continuous wave laser to the pulse modulation unit 6.

[0165] In step ST2 after the feedback signal is generated, the pulse modulation unit 6 pulse modulates the intensity-modulated continuous wave laser according to the pulse signal generated based on the feedback signal from the pulse signal generation unit 5.

[0166] The same applies to the pulse Pk (k = 2 to M). In step ST43, a monitoring signal is received by the optical pulse monitoring unit 15, and in ST44, a feedback signal is generated. An intensity modulation signal based on the frequency fk of the feedback signal is generated (step ST5), and a pulse Pk based on the feedback signal is generated.

[0167] <Effect>

[0168] According to the lidar device of embodiment 3, the difference between the pulse power and intensity modulation of each intensity modulation pulse relative to the ideal value generated when intensity modulation is applied to each pulse Pk at frequency fk can be suppressed. Therefore, it is possible to prevent errors in the characteristics of the transfer function to be calculated.

[0169] Implementation Method 4

[0170] Below, refer to Figures 18-20 The lidar device of Embodiment 4 will be described. Similar to the lidar device of Embodiment 3, the purpose of the lidar device of Embodiment 4 is to correct errors in the transfer function characteristics calculated based on the non-uniformity of pulse power and intensity modulation between intensity modulation pulses generated when intensity modulation is applied to each pulse Pk at a frequency fk. The methods for achieving this purpose differ between the lidar device of Embodiment 4 and the lidar device of Embodiment 3. Clearly, the lidar device of Embodiment 4 is configured to monitor a portion of the intensity modulation pulse signal, observe the parameters of the actual intensity modulation pulse relative to the ideal intensity modulation pulse parameters, calculate uncertainties in the received signal, such as possible errors in the transfer function, based on this information, and use this information to correct the detected SNR, thereby calculating a more accurate transfer function. This will be explained in detail below.

[0171] <Structure>

[0172] The lidar device of Embodiment 4 differs from the lidar device of Embodiment 1 in the following aspects. That is, as... Figure 18 As shown, the lidar device of Embodiment 4 further includes a light pulse branching section 14 and a light pulse monitoring section 15A. The light pulse branching section 14 is disposed between the pulse modulation section 6 and the transmitting-side optical system 7. The light pulse monitoring section 15A is disposed after the light pulse branching section 14. The light pulse monitoring section 15A is electrically connected to the signal processing section 12A. The light pulse monitoring section 15A converts the light pulse signal into an electrical signal and supplies the converted electrical signal to the signal processing section 12A as a light pulse monitoring signal. Furthermore, as... Figure 19As shown, the signal processing unit 12A also includes a transfer function calculation and correction unit 12-11. As an example, the transfer function calculation and correction unit 12-11 is disposed in the signal processing unit 12 between the transfer function calculation unit 12-8 and the physical property calculation unit 12-9. Furthermore, similar to Embodiment 1, the light source 1, intensity modulator 2, intensity modulation signal generation unit 4, pulse signal generation unit 5, and pulse modulation unit 6 constitute the light source unit 60. Alternatively, the lidar device of Embodiment 2 can be modified by adding a light pulse branching unit 14, a light pulse monitoring unit 15A, and a transfer function calculation and correction unit 12-11 to the lidar device of Embodiment 2.

[0173] The optical pulse branching section 14 branches a portion of the intensity-modulated pulse generated by the pulse modulation section 6 and outputs the branched portion of the pulse to the optical pulse monitoring section 15A.

[0174] The optical pulse monitoring unit 15A converts the optical pulse signal into an electrical signal (optical pulse monitoring signal).

[0175] The transfer function calculation and correction unit 12-11 compares the electrical signal (optical pulse monitoring signal) from the optical pulse monitoring unit 15A with information related to the optimal driving conditions of the intensity modulation pulse, namely, that the spectral characteristics of the received signal from the target are consistent with respect to the intensity modulation pulse, and that the frequency response characteristics of the received signal are consistent with respect to the target. The transfer function calculation and correction unit 12-11 corrects the output from the transfer function calculation unit 12-8. This information includes the ideal intensity modulation pulse waveform.

[0176] <Action>

[0177] Next, refer to Figure 20 The operation of the lidar device according to Embodiment 4 will be explained. The difference between the operation of the lidar device in Embodiment 4 and that in Embodiment 3 is the addition of step ST55, and the processing performed after the step of receiving the monitoring signal (ST41A) is the processing of step ST55. Repeated explanations are omitted; therefore, only the differences from the operation in Embodiment 3 will be explained.

[0178] in addition, Figure 20 Steps ST51 to ST54 in the above are the same as those in Implementation Method 3. Figure 17 Steps ST1 to ST8 are essentially the same. "Essentially" is because the process of generating a feedback signal based on the monitoring signal (steps ST41 to ST44) is omitted. Figure 20 The processing shown is the same as Figure 17The processing shown is different. In addition, similar to Embodiment 3, the lidar device in Embodiment 4 can also perform the processing of generating a feedback signal based on the monitoring signal (steps ST41 to ST44).

[0179] exist Figure 20 In step ST41A, the optical pulse monitoring unit 15A receives the optical pulse signal branched from the optical pulse branching unit 14 as a monitoring signal, converts the received optical pulse signal into an electrical signal, and supplies the converted electrical signal as an optical pulse monitoring signal to the transfer function calculation and correction unit 12-11 of the signal processing unit 12A.

[0180] In step ST55, the transfer function calculation and correction unit 12-11 compares the waveform of the electrical signal (optical pulse monitoring signal) obtained from the optical pulse monitoring unit 15 in step ST41A with the ideal intensity modulation pulse waveform stored in advance, predicts or calculates the error in the transfer function calculation result that may be caused by the deviation of these waveforms, corrects the error, and thereby corrects the transfer function.

[0181] In this embodiment, the transfer function calculation and correction unit 12-11 performs correction after both the cumulative processing and the SNR calculation. However, this embodiment can also be modified so that the transfer function calculation and correction unit 12-11 performs correction before either the cumulative processing or the SNR calculation. When the correction is performed by the transfer function calculation and correction unit 12-11 before the cumulative processing, the transfer function calculation and correction unit 12-11 is located between the frequency analysis unit 12-4 and the cumulative processing unit 12-5, and the processing in step ST55 is performed immediately after step ST12. When the correction is performed by the transfer function calculation and correction unit 12-11 before the SNR calculation, the transfer function calculation and correction unit 12-11 is located between the cumulative processing unit 12-5 and the SNR calculation unit 12-6, and the processing in step ST55 is performed immediately after step ST13.

[0182] <Effect>

[0183] According to the lidar device of embodiment 4, the error in the transfer function characteristics calculated based on the non-uniformity of pulse power and intensity modulation between intensity modulation pulses generated when intensity modulation is applied to each pulse Pk at frequency fk is corrected, and more accurate physical property calculations can be performed.

[0184] Furthermore, the implementation methods can be combined, or the implementation methods can be modified or omitted as appropriate.

[0185] Industrial availability

[0186] The lidar device of the present invention can be used as a lidar device for calculating physical properties such as the extinction coefficient of a target.

[0187] Label Explanation

[0188] 1: Light source; 2: Intensity modulator; 3: Trigger generation circuit; 4: Intensity modulation signal generation unit; 4-1: Intensity modulation signal generation unit group; 4-2: Intensity modulation signal mixing unit; 4A: Intensity modulation signal generation unit; 4B: Intensity modulation signal generation unit; 5: Pulse signal generation unit; 5B: Pulse signal generation unit; 6: Pulse modulation unit; 7: Transmitter-side optical system; 8: Transceiver splitter; 9: Telescope; 10: Receiver-side optical system; 11: Light receiving unit; 12: Signal processing unit; 12A: Signal processing unit; 12-1: Filtering unit; 12-2: A / D conversion unit; 12-3: Distance... 12-4: Displacement Division Unit; 12-5: Accumulation Processing Unit; 12-6: SNR Calculation Unit; 12-7: Distance Characteristic Calculation Unit; 12-8: Transfer Function Calculation Unit; 12-9: Physical Property Calculation Unit; 12-10: Physical Property and Distance Characteristic Calculation Unit; 12-11: Transfer Function Calculation and Correction Unit; 13: Scanner; 14: Optical Pulse Branching Unit; 15: Optical Pulse Monitoring Unit; 15A: Optical Pulse Monitoring Unit; 16: Optical Pulse Correction Unit; 60: Light Source Unit; 60A: Light Source Unit; 60B: Light Source Unit; 100a: Processing Circuit; 100b: Processor; 100c: Memory.

Claims

1. A lidar device, the lidar device comprising: The light source unit periodically modulates the intensity of the laser by using intensity modulation signals with different frequencies, and outputs multiple intensity modulation pulses. A telescope that sends the plurality of intensity-modulated pulses to the target and receives the reflected light from the target as received light; The light-receiving unit performs photoelectric conversion on the received light to generate a received electrical signal; as well as The signal processing unit calculates the distance and extinction coefficient of the target based on the received electrical signal. The light source generates multiple intensity modulation signals with different frequencies over time, or simultaneously generates multiple intensity modulation signals with different frequencies and mixes them, thereby generating the multiple intensity modulation pulses. The light source unit outputs intensity-modulated signals with different frequencies to the signal processing unit. The signal processing unit uses information about the frequency used in generating any one of the plurality of intensity modulation pulses to perform frequency analysis on the received electrical signal to generate a spectral signal, and detects the frequency and signal-to-noise ratio of the spectral signal. The signal processing unit uses information about the frequencies used in generating two or more intensity modulation pulses among the plurality of intensity modulation pulses to perform frequency analysis on the received electrical signal, generates multiple spectra of the received light reflected from a target at the same distance, and analyzes the frequency dependence of the signal-to-noise ratio of the multiple spectra. The signal processing unit analyzes the transfer function characteristics of the targets at the same distance based on the frequency dependence of the signal-to-noise ratio. The lidar device evaluates the extinction coefficient of the target at the same distance based on the transfer function characteristics.

2. The lidar device according to claim 1, wherein, The light source outputs an intensity modulation pulse of a first wavelength and an intensity modulation pulse of a second wavelength different from the first wavelength. The signal processing unit calculates the absorption wavelength and concentration of the target based on the ratio of the received signal intensity of the first wavelength received light to that of the second wavelength received light.

3. The lidar device according to claim 1, wherein, The light source outputs intensity-modulated pulses with two orthogonal polarization states. The signal processing unit evaluates the particle shape of the target based on the ratio of the received signal strengths based on the two polarizations.

4. The lidar device according to claim 1, wherein, The lidar device also has: A light pulse monitoring unit performs photoelectric conversion on the intensity modulation pulse generated by the light source unit; and The optical pulse correction unit outputs a feedback signal for controlling the pulse power and modulation intensity of the transmitted pulse based on the electrical signal from the optical pulse monitoring unit.

5. The lidar device according to claim 4, wherein, The optical pulse correction unit maintains an ideal intensity modulation pulse waveform, compares the waveform of the electrical signal from the optical pulse monitoring unit with the ideal intensity modulation pulse waveform to calculate the deviation, and outputs a feedback signal to the light source unit to suppress the deviation.

6. The lidar device according to claim 1, wherein, The lidar device also includes an optical pulse monitoring unit, which performs photoelectric conversion on the intensity-modulated pulses generated by the light source unit. The signal processing unit also includes a transfer function calculation and correction unit, which is connected to the optical pulse monitoring unit and performs correction based on the electrical signal from the optical pulse monitoring unit.

7. The lidar device according to claim 6, wherein, The transfer function calculation and correction unit pre-stores information related to the optimal driving conditions of the intensity modulation pulse, namely, that the spectral characteristics of the received signal from the target are consistent with respect to the intensity modulation pulse, and that the frequency response characteristics of the received signal are consistent with respect to the target. The transfer function calculation and correction unit compares the electrical signal from the optical pulse monitoring unit with the information, thereby correcting the uncertainty of the received signal caused by the intensity modulation transmission pulse.

Images