Signal processing device, laser radar device, and signal processing method

Abstract

This signal processing device comprises: a frequency noise detecting unit (12-4) that detects transmission / reception optical path noise, which is frequency noise generated in a transmission / reception optical path different from a path of reference light within a laser radar device; and a frequency noise correcting unit (12-5) that performs correction for removing the detected transmission / reception optical path noise from a received signal relating to scattered light from a target.

Description

Signal processing device, laser radar device, and signal processing method

[0001] The present disclosure relates to a signal processing technique for a laser radar device.

[0002] Non-Patent Document 1 describes the general configuration of a coherent laser radar device. Specifically, Non-Patent Document 1 discloses a laser radar device that irradiates laser pulse light into the atmosphere, receives scattered light from aerosols, and measures the wind speed in the laser irradiation direction (line of sight) by heterodyne detection of the scattered light with a single-frequency continuous light, which is the local light of the transmitted light, to determine the Doppler shift caused by the movement of a target (a general term for a three-dimensional volume target such as aerosols or a two-dimensional hard target such as a wall). The laser pulse light irradiated into the atmosphere is frequency-modulated with respect to the local light, which is a nearly single-frequency continuous light. Therefore, in heterodyne detection, an intermediate frequency (beat frequency) signal is generated by the interference between the scattered light and the local light. If the target moves, a Doppler shift is added to the intermediate frequency. The Doppler shift is calculated from the frequency spectrum obtained by Fourier transforming the signal after heterodyne detection. The wind measurement direction is changed by switching the laser emission direction. The distance to the target is also calculated from the pulse flight time from the start of emission to reception. It is also possible to observe these simultaneously, for example, to measure the moving speed and distance to a target simultaneously. Also, Non-Patent Document 1 describes an equation for the signal to noise ratio (SNR) of a received signal in a coherent laser radar device.

[0003] S. Kameyama, et. al., “Compact all-fiber pulsed coherent Doppler lidar system for wind sensing,” Appl. Opt. 46(11), 1953-1962 (2007).

[0004] As can be seen from the SNR formula disclosed in Non-Patent Document 1, the SNR can be improved by reducing the reception bandwidth B. Here, the reception bandwidth B is given by, for example, the following formula:

[0005] As shown in this formula, the reception bandwidth B is a function B of the pulse width Δt determined by the light source unit. １ (Δt), a function B of the light source linewidth Δλ ２ (Δλ), and a function B of the wind speed width Δv determined by the measurement target or the surrounding environment of the measurement target ３ (Δv). Furthermore, the reception bandwidth B is determined by a noise function O(f) generated in the optical system inside the laser radar device, particularly in the optical path through which the reference light does not pass but only the transmitted and received pulsed light passes, i.e., in the transmission and reception optical path different from the path of the reference light. Causes of this noise include incomplete frequency modulation in the pulse modulator, ASE or parasitic oscillation in the amplifier, or fluctuations in the optical system installation environment such as vibration or temperature fluctuation. Noise generated by these causes can be classified as colored noise because its intensity is not uniform depending on the frequency (hereinafter referred to as "transmission and reception optical path noise"). In conventional technology, the SNR is calculated using a received signal containing transmission and reception optical path noise, so there is room for improvement in the SNR.

[0006] The present disclosure was made in response to the recognition of such problems, and one aspect of the present disclosure aims to provide a signal processing technology that can contribute to improving the SNR of a signal received by a laser radar device.

[0007] One aspect of a signal processing device according to an embodiment of the present disclosure includes a frequency noise detection unit that detects transmission and reception optical path noise, which is frequency noise generated in a transmission and reception optical path different from the path of a reference light within a laser radar device, and a frequency noise correction unit that performs correction to remove the detected transmission and reception optical path noise from a received signal related to scattered light from a target.

[0008] According to the signal processing device of the embodiment of the present disclosure, the transmission and reception optical path noise, which is frequency noise generated in a transmission and reception optical path different from the path of the reference light in the laser radar device, is detected, and the detected transmission and reception optical path noise is corrected to be removed from the reception signal related to the scattered light from the target, thereby improving the quality of the reception signal. Therefore, the signal processing device of the embodiment of the present disclosure can contribute to improving the SNR of the reception signal.

[0009] 5A to 5D are schematic diagrams showing an overview of a series of processes performed by the signal processing device of the laser radar device according to embodiment 1. FIG. 5A is a diagram showing a received signal in the time domain. FIG. 5B is a diagram showing the frequency spectrum of the received signal. FIG. 5B(a) is a diagram showing the frequency spectrum of the received signal for range bin n=0. FIG. 5B(b) is a diagram showing the frequency spectrum of the received signal for range bin n=3. FIG. 5B(c) is a diagram showing a normalized frequency spectrum obtained by normalizing the frequency spectrum of the received signal for range bin n=0 by the absolute value of the power of the received signal for range bin n=3. FIG. 5C is a diagram showing a corrected frequency spectrum obtained by removing transmission and reception path noise from the frequency spectrum of the received signal for range bin n=3. 5A and 5B are diagrams showing frequency spectra after integration of corrected frequency spectra obtained from a plurality of received signals of range bin n=3. FIG. 5D is a diagram showing a frequency spectrum after integration processing of corrected frequency spectra obtained from a plurality of received signals of range bin n=3. FIG. 5C is a diagram showing a schematic diagram of an A-Scope. FIG. 5D is a diagram showing a modified example of the configuration of the laser radar device according to embodiment 1. FIG. 5E is a flowchart showing the operation of the laser radar device according to embodiment 2.

[0010] Various embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Components with the same or similar reference numerals in the drawings have the same or similar configurations or functions, and redundant descriptions of such components will be omitted. Furthermore, in this disclosure, the term "or" is used to mean an inclusive logical OR unless otherwise specified.

[0011] 1 to 3, a signal processing device according to a first embodiment of the present disclosure and a laser radar device including the signal processing device will be described. Fig. 1 is a configuration diagram showing the laser radar device according to the first embodiment of the present invention. As shown in Fig. 1, the laser radar device according to the first embodiment includes, as an example, a light source 1, a light splitting unit 2, a trigger generation circuit unit 3, a pulse modulation unit 4, a transmission-side optical system 5, a transmission-reception separation unit 6, a telescope 7, a reception-side optical system 8, an optical multiplexing unit 9, a light receiving unit 10, an AD conversion unit 11, and a signal processing device 12.

[0012] (Light Source) The light source 1 oscillates and emits continuous wave laser light of a substantially single frequency (hereinafter simply referred to as "single frequency") with a linewidth of several MHz or less. The light source 1 is realized by a semiconductor laser, a fiber laser, or a solid-state laser. The laser light emitted from the light source 1 is sent to the light splitting unit 2.

[0013] (Light Splitting Unit) The light splitting unit 2 splits the laser light emitted from the light source 1 into two systems. The light splitting unit 2 can be configured, for example, by a 1:2 fiber coupler. In the case of spatial propagation, the light splitting unit 2 can be configured by a partially transmitting mirror. The light splitting unit 2 sends one of the split laser lights to the optical multiplexer 9 as reference light for heterodyne detection, and sends the other to the pulse modulator 4 as seed light.

[0014] (Trigger Generation Circuit Unit) The trigger generation circuit unit 3 generates a pulse signal for pulsing a signal and an IF signal (intermediate frequency signal) for imparting a frequency shift to the signal as a trigger signal, and sends the generated trigger signal to the pulse modulation unit 4.

[0015] The trigger generating circuit unit 3 also sends the generated pulse signal to the AD converting unit 11 to use it as a trigger for the AD converting unit 11 .

[0016] The trigger generation circuit unit 3 also sends the generated pulse signal to the signal processing device 12 so that the signal processing device 12 can use the pulse signal when dividing the received signal into received signals for each range bin. The trigger generation circuit unit 3 also sends the generated IF signal to the signal processing device 12 so that the signal processing device 12 can calculate the moving speed of the target.

[0017] Targets include hard targets (HT) and soft targets (ST). A hard target (HT) is a target of a certain size with a clear boundary surface as a reflective or scattering surface, such as an automobile or an aircraft. A soft target (ST) is a target consisting of a large number of minute particulate scatterers distributed in space, such as aerosols, raindrops, fog, and cloud particles present in the atmosphere.

[0018] The trigger generating circuit unit 3 can be realized by a pulse generator, a function generator, or an FPGA (Field-programmable gate array).

[0019] (Pulse Modulation Unit) The pulse modulation unit 4 receives the laser light (seed light) from the light splitting unit 2 as incident light, and modulates the incident light at a predetermined repetition period t in response to a pulse signal supplied from the trigger generation circuit unit 3. ｒｅｐ and pulsed light having a pulse width Δt, and the converted pulsed light is frequency shifted by f in accordance with the IF signal. ＩＦ The pulse modulation unit 4 further applies a pulsed light to the optical system 5 to generate a pulsed transmission signal T as transmission light. The pulse modulation unit 4 can be configured, for example, by an acousto-optical element or a phase modulator and an optical amplifier. The pulse modulation unit 4 sends the generated pulsed transmission signal T as transmission light to the transmission-side optical system 5.

[0020] (Transmitting-Side Optical System) The transmitting-side optical system 5 shapes the transmitted light from the pulse modulation unit 4 so that it has a desired beam diameter and divergence angle. The transmitting-side optical system 5 is composed of a lens group consisting of, for example, concave and convex lenses. The transmitting-side optical system 5 may also be a reflective optical system equipped with a mirror. The shaped transmitted light is sent from the transmitting-side optical system 5 to the transmission / reception separation unit 6.

[0021] (Transmission / Reception Separator) The transmission / reception separator 6 sends shaped transmission light from the transmission-side optical system 5 to the telescope 7, and sends received light from the telescope 7 to the reception-side optical system 8. The transmission / reception separator 6 can be realized by a circulator if the optical system is configured with optical fiber. Alternatively, the transmission / reception separator 6 can be realized by a polarizing beam splitter (PBS) if the optical system is configured for air propagation. A quarter-wave plate may be inserted between the transmission / reception separator 6 and the telescope 7 to adjust polarization. The transmission / reception separator 6 is located between the transmission-side optical system 5 and the telescope 7, and on the optical axis of the transmitted light.

[0022] (Telescope) The telescope 7 expands the transmitted light from the transmission / reception separator 6 to a designed beam diameter, sends the expanded transmitted light toward the target space where the target is located, and receives scattered light from the target as received light and sends it to the transmission / reception separator 6. The telescope 7 is realized by a lens group consisting of concave and convex lenses, similar to the transmission-side optical system 5. The telescope 7 may also be a reflective type equipped with a mirror.

[0023] (Receiving-side optical system) The receiving-side optical system 8 shapes the received light from the transmission-reception separator 6 so that it has a designed beam diameter and divergence angle, and sends the shaped received light to the optical multiplexer 9. The receiving-side optical system 8 is realized by a lens group consisting of concave and convex lenses, similar to the transmitting-side optical system 5. The receiving-side optical system 8 may also be a reflective optical system equipped with a mirror. The receiving-side optical system 8 is positioned so that the optical axis of the received light from the transmission-reception separator 6 and the optical multiplexer 9 coincide.

[0024] (Optical Combining Unit) The optical combining unit 9 combines the reference light from the optical splitting unit 2 with the received light sent via the receiving optical system 8 to generate combined light. At this time, the combined light (combined signal) of the received light Ri and the reference light from the optical splitting unit 2 is a beat signal corresponding to the frequency shift imparted by the pulse modulation unit 4. When a Doppler shift frequency corresponding to the movement of a target, for example, wind speed, occurs in the received light, the frequency fn of the beat signal is set to the center frequency f ＩＦ + Doppler shift frequency f Ｄ The optical multiplexing unit 9 can be a combiner if the optical system is configured with optical fibers, or a polarizing beam splitter if the optical system is air-propagating. The optical multiplexing unit 9 may also be realized by an optical fiber coupler. The multiplexed light obtained by multiplexing in the optical multiplexing unit 9 is sent to the light receiving unit 10.

[0025] (Light-receiving unit) The light-receiving unit 10 converts the combined light, which is an optical signal, into an electrical signal. For example, a photodiode or an O / E converter can be used as the light-receiving unit 10. The light-receiving unit 10 is connected to the AD conversion unit 11, and supplies the converted electrical signal to the AD conversion unit 11.

[0026] (AD Conversion Unit) The AD conversion unit 11 converts the analog electrical signal supplied from the light receiving unit 10 into a digital signal. The pulse modulation unit 4 uses the pulse signal from the trigger generation circuit unit 3 as an output start trigger, and the AD conversion unit 11 uses the pulse signal from the trigger generation circuit unit 3 as an AD conversion start trigger. Therefore, the start time of AD conversion approximately coincides with the timing when the transmission pulse is transmitted, and AD conversion continues for a predetermined period or until the next transmission pulse is generated. The signal being AD converted ΔT after the start of AD conversion corresponds to the atmosphere located in space at a distance L = cΔT / 2, or the received signal from the hard target HT, where c is the propagation speed of the pulse transmission signal. The digitized received signal corresponds to one pulse. The AD conversion unit 11 is connected to the signal processing device 12 and supplies the converted digital signal to the signal processing device 12.

[0027] (Signal Processing Device) Next, the configuration of the signal processing device 12 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing an example configuration of the signal processing device 12. As shown in Fig. 2, the signal processing device 12 includes a range bin division unit 12-1, a frequency analysis unit 12-2, a peak frequency detection unit 12-3, a frequency noise detection unit 12-4, a frequency noise correction unit 12-5, an integration processing unit 12-6, an SNR calculation unit 12-7, a distance characteristic calculation unit 12-8, and a movement speed calculation unit 12-9.

[0028] The range bin division unit 12-1 is connected to the AD conversion unit 11 and the frequency analysis unit 12-2. The peak frequency detection unit 12-3 is connected to the frequency analysis unit 12-2. The frequency noise detection unit 12-4 is connected to the peak frequency detection unit 12-3. The frequency noise correction unit 12-5 is connected to the frequency noise detection unit 12-4. The integration processing unit 12-6 is connected to the frequency noise correction unit 12-5. The SNR calculation unit 12-7 is connected to the integration processing unit 12-6. The distance characteristic calculation unit 12-8 is connected to the SNR calculation unit 12-7. The movement speed calculation unit 12-9 is connected to the distance characteristic calculation unit 12-8.

[0029] (Range Bin Division Unit) The range bin division unit 12-1 divides the AD converted digital signal in the time direction by a width equivalent to the pulse width based on the pulse signal from the trigger generation circuit unit 3. This divides the combined light expressed in digital format into signals corresponding to multiple spatial regions. The range bin division unit 12-1 outputs the divided signals to the frequency analysis unit 12-2.

[0030] (Frequency Analysis Unit) The frequency analysis unit 12-2 converts the signal for each bin into a frequency spectrum (hereinafter, sometimes referred to as a "spectrum" or a "spectral signal") by performing a fast Fourier transform (FFT) process on the signal for each bin. The frequency analysis unit 12-2 outputs the spectrum to the peak frequency detection unit 12-3.

[0031] (Peak Frequency Detector) The peak frequency detector 12-3 detects peak frequencies from the spectrum of each range bin of n=1 or more. The peak frequency detector 12-3 outputs the detected peak frequencies to the frequency noise detector 12-4.

[0032] (Frequency Noise Detector) The frequency noise detector 12-4 calculates transmission and reception optical path noise, which is frequency noise generated in a transmission and reception optical path that is different from the path of the reference light within the laser radar device. The frequency noise (transmission and reception optical path noise) is calculated from the spectrum of one or more range bins. As an example, the frequency noise detector 12-4 calculates the transmission and reception optical path noise by analyzing the received signal due to scattering from the telescope 7. The frequency noise detector 12-4 outputs the calculated frequency noise to the frequency noise corrector 12-5.

[0033] (Frequency noise correction unit) The frequency noise correction unit 12-5 performs correction to remove calculated transmission and reception optical path noise from the received signal related to scattered light from the target. Specifically, the frequency noise correction unit 12-5 removes the frequency noise calculated by the frequency noise detection unit 12-4 as unnecessary frequency noise from the spectrum of each range bin of n=1 or more. Removing frequency noise includes removing all or part of the frequency noise.

[0034] (Integration Processing Unit) The integration processing unit 12-6 integrates, in spectral space, a plurality of spectra obtained from data of a plurality of shots after frequency noise has been removed, and outputs the integrated spectrum to the SNR calculation unit 12-7.

[0035] (SNR Calculation Unit) The SNR calculation unit 12-7 calculates the SNR of the received signal and outputs the calculated SNR to the distance characteristic calculation unit 12-8.

[0036] (Distance Characteristics Calculation Unit) The distance characteristics calculation unit 12-8 calculates the relationship between distance and SNR (distance characteristics: A-scope) and outputs the calculated distance characteristics (A-scope) to the movement speed calculation unit 12-9.

[0037] (Movement Speed ​​Calculation Unit) The movement speed calculation unit 12-9 calculates the movement speed of the target in the line of sight direction from the peak frequency information of the signal spectrum.

[0038] Next, an example of the hardware configuration of the signal processing device 12 will be described with reference to Figures 3A and 3B. As an example, as shown in Figure 3A, the signal processing device 12 is realized by a processing circuit 100a. The processing circuit 100a is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. The functions of the components included in the signal processing device 12 may be realized by separate processing circuits, or the functions of multiple components may be realized together by a single processing circuit.

[0039] As another example, as shown in FIG. 3B , the signal processing device 12 is realized by a processor 100b and a memory 100c. A program stored in the memory 100c is read by the processor 100b and executed, thereby realizing the functions of the components of the signal processing device 12. The program is realized as software, firmware, or a combination of software and firmware. Examples of the memory 100c include 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-EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs.

[0040] <Operation> Next, the operation of the signal processing device 12 and the laser radar device according to the first embodiment will be described with reference to FIG.

[0041] In step ST1, light source 1 emits oscillated laser light, and light splitting unit 2 splits the laser light emitted from light source 1 into two systems. Light splitting unit 2 sends one of the split laser lights to optical multiplexer 9 as reference light for heterodyne detection, and sends the other to pulse modulator 4 as seed light for transmission light.

[0042] In step ST2, the pulse modulation unit 4 converts the incident light received from the light splitting unit 2 into pulsed light in accordance with the pulse signal supplied from the trigger generation circuit unit 3, and generates the converted pulsed light into a pulsed transmission signal T in accordance with the IF signal. The generated pulsed transmission signal T is sent to the transmission-side optical system 5 as transmission light.

[0043] In step ST3, the transmitting optical system 5 shapes the transmitted light from the pulse modulation unit 4, the transmission / reception separator 6 sends the shaped transmitted light to the telescope 7, and the telescope 7 expands the transmitted light from the transmission / reception separator 6 to a predetermined beam diameter and sends the expanded transmitted light toward the target into the atmosphere. The transmitted light sent into the atmosphere is irradiated onto the target, and the scattered light scattered by the target has a Doppler shift frequency f corresponding to the moving speed of the target. Ｄ is superimposed.

[0044] In step ST5, the telescope 7 sends the light received from the target to the transmission / reception separator 6, which sends the light received from the telescope 7 to the receiving optical system 8, which shapes the light received from the transmission / reception separator 6 and sends it to the optical multiplexer 9, which multiplexes the reference light from the light splitter 2 and the light received from the receiving optical system 8. The multiplexed light obtained by multiplexing in the optical multiplexer 9 is sent to the light receiving unit 10. The light receiving unit 10 converts the multiplexed light into an electrical signal and supplies the converted electrical signal to the AD converter 11.

[0045] In step ST6, the AD conversion unit 11 performs AD conversion on the electrical signal supplied from the light receiving unit 10.

[0046] In step ST7, the range bin division unit 12-1 divides the digitized received signal for one pulse into signals for each range bin. The range bins are divided so that the range bin width corresponds to the pulse width of the transmitted pulse, and the pulse width is determined by design. By dividing the signal by time by the range bin division unit 12-1, the received signal for one pulse is divided into received signals of scattered light from different distances (ranges).

[0047] 5A is a diagram showing a received signal in the time domain. More specifically, FIG. 5A shows the time variation of the received signal obtained by receiving scattered light from a target irradiated with one pulse of transmitted light. n represents the label of the divided range bin, and a label with a smaller value of n indicates a reflected signal from a closer location.

[0048] The range bin division unit 12-1 transmits the AD converted received signal of each range bin to the frequency analysis unit 12-2.

[0049] In step ST8, the frequency analysis unit 12-2 determines whether the label number of the range bin is 0. If the label number of the range bin is 0, the process proceeds to step ST11. If the label number of the range bin is not 0, the process proceeds to step ST9.

[0050] In step ST11 or ST9, the frequency analysis unit 12-2 performs an FFT on the received signal divided into range bins for each range bin to convert it into a spectral signal, and sends the resulting spectral signal to the peak frequency detection unit 12-3. If the received signal is small, the FFT-processed spectral signal may be integrated. Figure 5B (a) shows an example of the spectrum of the received signal for range bin n=0, and Figure 5B (b) shows an example of the spectrum of the received signal for range bin n=3.

[0051] In step ST10, the peak frequency detection unit 12-3 detects the peak frequency and its intensity (peak intensity) of the spectrum for each range bin or the spectrum integrated for each range bin, and sends the detected peak frequency and its intensity to the frequency noise detection unit 12-4. The peak intensity may be detected by calculating the spectrum intensity at the position of the peak frequency, or by calculating the spectrum intensity at the centroid frequency position obtained by centroid calculation. Figure 5B (b) shows the peak frequency f detected from the received signal corresponding to the range bin n=3. ３ An example is shown.

[0052] In step ST12, the frequency noise detection unit 12-4 calculates the transmission / reception path noise O(f) based on the information of the spectrum obtained by the frequency analysis unit 12-2. As a calculation method, for example, the spectrum obtained by the frequency analysis unit 12-2 may be used as it is. That is, the received signal R at range bin n=0 is calculated as follows: ０ , i.e., the spectrum S obtained from the received signal due to scattering in the telescope. ０ (a) of FIG. 5B shows the spectrum S ０ FIG.

[0053] The frequency noise detection unit 12-4 may calculate normalized transmission / reception path noise O(f) by normalizing the transmission / reception path noise O(f) obtained by this method or another method according to the absolute value of the received signal power at each range bin n. Normalizing the transmission / reception path noise O(f) makes it possible to obtain a more accurate transmission / reception path noise O(f). (c) of FIG. 5B shows the frequency noise S corresponding to the range bin n=3, which is obtained by normalizing the spectrum of the received signal at range bin n=0 by the absolute value of the power of the received signal at range bin n=3. ３ FIG.

[0054] In step ST13, the frequency noise correction unit 12-5 calculates a noise-corrected spectrum Mn for the spectrum Sn obtained from the received signal Rn in each range bin n (n=1 to N) by using the transmission / reception path noise O(f) identified by the frequency noise detection unit 12-4. More specifically, the frequency noise correction unit 12-5 subtracts the transmission / reception path noise O(f) for n=0 or the normalized transmission / reception path noise O(f) from the spectrum Sn. As an example of the corrected spectrum, FIG. 5C shows a corrected spectrum Mn for a signal in a range bin n=3, in which noise has been corrected. ３ From the multiple received signals obtained from the multiple transmitted beams, multiple corrected spectra Mn are obtained for each range bin n (n = 1 to N). The frequency noise corrector 12-5 sends the multiple corrected spectra Mn for each range bin to the integration processor 12-6.

[0055] In step ST14, the integration processing unit 12-6 integrates a plurality of corrected spectra Mn for each range bin and sends the integrated spectrum to the SNR calculation unit 12-7. ３ The spectrum obtained by integrating the above is shown.

[0056] In step ST15, the SNR calculation unit 12-7 calculates the ratio between the peak intensity and the out-of-band noise to calculate the SNR, and sends the calculated SNR to the distance characteristic calculation unit 12-8.

[0057] In step ST16, the distance characteristics calculation unit 12-8 calculates Δt=AD rate×range bin width×(n−1) from the range bin information, AD conversion rate, and range bin width, converts Δt to distance using L=c×Δt / 2, and outputs an SNR graph for each distance, i.e., an a-scope, to the movement speed calculation unit 12-9. An example of the output a-scope is shown in FIG.

[0058] Furthermore, the moving speed calculation unit 12-9 calculates the amount of Doppler shift Δf from the peak frequency information of the signal spectrum, and calculates v=λΔf / 2 to calculate the moving speed of the target in each range bin in the line of sight direction.

[0059] In the present embodiment, the laser radar device has been described assuming a case where the laser radar device is a Doppler lidar, but the laser radar device may also be a coherent differential absorption lidar (DIAL). When the laser radar device is a coherent DIAL, the ON wavelength optical path and the OFF wavelength optical path are different.

[0060] As described above, according to the signal processing device 12 of the first embodiment or a laser radar device including the signal processing device 12, the transmission / reception path noise O(f) generated in the optical system through which the transmitted light or the received light passes is detected, and the detected transmission / reception path noise O(f) is removed from the received light. Therefore, the reception bandwidth of the received light from the target is reduced, and the SNR of the received light from the target can be improved.

[0061] <Modification> Fig. 7 is a diagram showing a modification of the configuration of the laser radar device according to embodiment 1. As shown in Fig. 7, a scanner 13 may be placed immediately after the telescope 7, and the laser beam may be configured to perform spatial scanning over time.

[0062] Furthermore, scattered light from the telescope 7 may be so strong that it saturates the light-receiving unit 10. In such cases, it is advisable to place a variable optical attenuator before or after the receiving optical system 8. FIG. 7 shows an example configuration in which the variable optical attenuator 14 is placed after the receiving optical system 8. The variable optical attenuator 14 attenuates scattered light (i.e., scattered light for range bin n=0) based on information (pulse signal) from the trigger generation circuit 3 to prevent saturation of the light-receiving unit 10, while not attenuating the scattered light for other range bins n (=1 to N) to prevent a decrease in the received signal level. The variable optical attenuator 14 can be configured as a variable optical attenuator or optical modulator.

[0063] Second Embodiment Next, a laser radar device according to a second embodiment will be described. The configuration of the laser radar device according to the second embodiment is similar to that of the laser radar device according to the first embodiment, and therefore a description of the configuration will be omitted. The operation of the laser radar device according to the second embodiment differs from that of the laser radar device according to the first embodiment.

[0064] The operation of the laser radar device according to the second embodiment will be described with reference to Fig. 8. Steps ST21 to ST23 and ST25 to ST27 correspond to steps ST1 to ST3 and ST5 to ST7 in Fig. 4.

[0065] In step ST28, the frequency analysis unit 12-2 determines whether the label number of the range bin is one of n=1 to N, and the processes of steps ST29 to ST31 are performed for each of the range bins n=1 to N.

[0066] In step ST29, the frequency analysis unit 12-2 performs FFT on the received signal divided into each range bin to convert it into a spectrum signal for each range bin, and sends the obtained spectrum signal to the peak frequency detection unit 12-3. If the received signal is small, the FFT-processed spectrum signal may be integrated.

[0067] In step ST30, the peak frequency detection unit 12-3 detects the peak frequency corresponding to the peak of the spectrum for each range bin or the spectrum accumulated for each range bin, and the intensity of the peak frequency (peak intensity), and sends the detected peak frequency and its intensity to the frequency noise detection unit 12-4.

[0068] In step ST31, the frequency noise detection unit 12-4 calculates the frequency noise of the range bin to be processed.

[0069] In step ST33, the frequency noise detection unit 12-4 performs statistical processing or processing using AI (artificial intelligence) on the multiple spectra Sn obtained for the multiple range bins n (n = 1 to N) to identify noise components common to the multiple spectra Sn, thereby calculating the transmission / reception path noise O(f). This operation can be achieved, for example, by generating information in which the spectrum Sn obtained from the received signal Rn in each range bin n is corrected for the amount of signal attenuation according to the distance of each range bin n (n = 1 to N), and then determining the presence or absence of frequency noise common to each range bin n through statistical processing. Alternatively, this can be achieved by comparing past time-series information for each range bin and identifying a frequency noise spectrum that is independent of time fluctuations.

[0070] In step ST34, the frequency noise correction unit 12-5 determines whether the label number of the range bin is one of n=1 to N, and the process of step ST35 is performed for each of the range bins n=1 to N.

[0071] In step ST35, the frequency noise correction unit 12-5 calculates a noise-corrected spectrum Mn for the spectrum Sn obtained from the received signal Rn in each range bin n (n = 1 to N) by using the transmission / reception path noise O(f) identified by the frequency noise detection unit 12-4.

[0072] Steps ST37 to ST39 are similar to steps ST14 to ST16 in FIG. 4, and therefore a description thereof will be omitted.

[0073] It is possible to combine the embodiments, and to modify or omit each embodiment as appropriate.

[0074] The signal processing device of the present disclosure can be used as a signal processing device for a laser radar device.

[0075] 1 Light source, 2 Light splitting unit, 3 Trigger generation circuit unit, 4 Pulse modulation unit, 5 Transmitting optical system, 6 Transmission / reception separation unit, 7 Telescope, 8 Receiving optical system, 9 Optical multiplexing unit, 10 Light receiving unit, 11 AD conversion unit, 12 Signal processing device, 12-1 Range bin division unit, 12-2 Frequency analysis unit, 12-3 Peak frequency detection unit, 12-4 Frequency noise detection unit, 12-5 Frequency noise correction unit, 12-6 Integration processing unit, 12-7 SNR calculation unit, 12-8 Distance characteristic calculation unit, 12-9 Moving speed calculation unit, 13 Scanner, 14 Variable optical attenuation unit, 100a Processing circuit, 100b Processor, 100c Memory.

Claims

1. A signal processing device comprising: a frequency noise detection unit that detects transmission and reception optical path noise, which is frequency noise generated in a transmission and reception optical path different from the path of a reference light within a laser radar device; and a frequency noise correction unit that performs correction to remove the detected transmission and reception optical path noise from a received signal related to scattered light from a target.

2. A laser radar device comprising: a signal processing device as claimed in claim 1; a light source which emits continuous wave laser light of a single frequency; a light splitting section which splits the laser light from said light source into said reference light and seed light; a trigger generation circuit section which generates a trigger signal; a pulse modulation section which generates pulsed laser light from said seed light based on the generated trigger signal as transmission light; and a telescope which emits the generated transmission light into a target space in which a target is present, wherein said frequency noise detection section detects said transmission and reception optical path noise by analyzing a reception signal due to scattering from said telescope.

3. A laser radar device as described in claim 2, further comprising an optical combining section that combines received light, which is scattered light from the target, with the reference light to generate combined light, wherein the signal processing device further comprises a range bin division section that divides the generated combined light into signals corresponding to a plurality of spatial regions, and wherein the frequency noise correction section removes the transmission and reception optical path noise from the frequency noise of each of the plurality of spatial regions.

4. A laser radar device as described in claim 3, further comprising: a transmission / reception separation section which sends the transmitted light from said pulse modulation section to a telescope and sends the received light from said telescope to a receiving optical system; and a variable optical attenuation section which is provided in the optical path between said transmission / reception separation section and said optical multiplexing section, and which is driven based on a trigger signal from said trigger generation circuit section, and which attenuates the received light from said telescope.

5. A laser radar device comprising: a signal processing device as claimed in claim 1; a light source which emits continuous wave laser light of a single frequency; a light splitting section which splits the laser light from said light source into said reference light and said seed light; a trigger generation circuit section which generates a trigger signal; a pulse modulation section which generates pulsed laser light from said seed light based on the generated trigger signal as transmission light; a telescope which emits the generated transmission light into a target space in which a target is present; and a combining section which combines received light, which is scattered light from said target, with the reference light to generate combined light, wherein said signal processing device further comprises a range bin division section which divides the generated combined light into signals corresponding to a plurality of spatial domains; and said frequency noise detection section detects said transmission and reception optical path noise by analyzing frequency noise in a plurality of spatial domains and identifying noise common to the frequency noise in said plurality of spatial domains.

6. A laser radar device according to any one of claims 2 to 5, wherein the signal processing device calculates the moving speed and distance of the target using the signal from which the transmission and reception optical path noise has been removed.

7. A signal processing method performed by a signal processing device having a frequency noise detection unit and a frequency noise correction unit, comprising: a step in which the frequency noise detection unit detects transmission and reception optical path noise, which is frequency noise generated in a transmission and reception optical path different from a path of a reference light within a laser radar device; and a step in which the frequency noise correction unit performs correction to remove the detected transmission and reception optical path noise from a received signal related to scattered light from a target.

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