JP2009162678A - Laser radar system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a laser radar apparatus for utilizing predictive information on a receive spectrum and a wind speed obtained from a measurement result in a high receive S/N ratio region, and accurately detecting the wind speed in a low receive S/N ratio region. <P>SOLUTION: In the laser radar apparatus for transmitting a single frequency laser light to the air, receiving it, processing a received signal obtained by a heterodyne detection and detecting the wind speed, a signal processing section 10 is provided with: a means for causing a gate to divide the received signal in accordance with a distance from the laser radar apparatus, and acquiring a distance dependency of the receive S/N ratio from the receive spectrum obtained by a FFT applied to the divided received signals; a means for dividing a to-be-detected region into the high S/N ratio region and the low S/N ratio region and discriminating them based on the distance dependency of the receive S/N ratio; and a means for processing the reception spectrum in the low S/N ratio region by acquiring the predictive information based on the information obtained from the reception spectrum in the high S/N ratio region, and detecting the wind speed in the low S/N ratio region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser radar device that measures a wind speed in the atmosphere by transmitting a transmission signal composed of laser light into the atmosphere, receiving a scattered signal from the atmosphere, and detecting a Doppler frequency shift of the scattered signal.

  As conventional laser radar devices of this type, those described in Patent Document 1 and Non-Patent Document 1, for example, are known. In this laser radar device, pulsed laser light is transmitted to the atmosphere, and scattered light from aerosol in the atmosphere is converted into an electric signal region by heterodyne detection to obtain a received signal. After the received signal is gated and divided into signals from each distance, each divided signal is subjected to FFT (Fast Fourier Transform) to obtain a received spectrum. When the reception S / N ratio is high, the peak frequency of this signal corresponds to the Doppler frequency shift, so that the wind speed can be measured by detecting the peak frequency.

JP 2007-85758 A S. Kameyama et al., Applied Optics, Vol. 46, No. 11, pp. 1953-1962, 2007

  In the signal processing of such a laser radar device, the wind speed is measured by detecting the peak frequency of the reception spectrum. The detection of the peak frequency is not problematic when the reception S / N ratio is high, but it is generally known that erroneous detection occurs when the reception S / N ratio is low. FIG. 9 is a schematic diagram of the reception spectrum when the reception S / N ratio is high ((a) in FIG. 9) and low ((b) in FIG. 9). In the case of (a) in FIG. 9, the signal component can be correctly detected by detecting peaks in the entire frequency region shown in the figure, whereas in the case of (b) in FIG. 9, the intensity of the signal component. Therefore, there is a problem that if a peak is simply detected, a noise component is detected, that is, erroneously detected.

  The present invention has been made in view of the above-described problems, and unlike conventional techniques, in signal processing after obtaining a reception spectrum, foresight information regarding the reception spectrum and wind speed is obtained from measurement results in a region where the reception S / N ratio is high. Accordingly, an object of the present invention is to provide a laser radar device that can reduce the erroneous detection in a region where the reception S / N ratio is low by using this foresight information.

  The present invention relates to a laser radar device that detects a wind speed by transmitting / receiving a laser beam having a single frequency to the atmosphere and processing the received signal obtained by heterodyne detection to detect the wind speed. A signal processing unit that performs a gate division so as to divide the received signal according to the distance from the laser radar device, and receives the received S / S from the received spectrum obtained by performing FFT on each of the divided received signals. Means for determining the distance dependence of the N ratio, means for distinguishing the detection target area into a high S / N ratio area and a low S / N ratio area based on the distance dependence of the reception S / N ratio, Obtaining foresight information based on information obtained from the received spectrum in the N ratio region, using the foresight information to perform processing on the received spectrum in the low S / N ratio region, and in the low S / N ratio region s wind In the laser radar apparatus characterized by comprising: means for detecting a.

  In the present invention, the foresight information regarding the reception spectrum and the wind speed is obtained from the measurement result in the region where the reception S / N ratio is high, and the wind speed in the region where the reception S / N ratio is low is obtained using this foresight information. It is possible to provide a laser radar device that can reduce erroneous detection in a region where the S / N ratio is low.

Embodiment 1 FIG.
A laser radar apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a diagram schematically showing a configuration of a laser radar apparatus according to the present invention.

  In FIG. 1, a light source 1 is connected to an optical distributor 2, and the optical distributor 2 is connected to a pulse modulator 3 and a frequency shifter 6. The pulse modulator 3 is connected to the optical circulator 4. The optical circulator 4 is connected to a transmission / reception optical system 5 and an optical coupler 7. The optical coupler 7 is connected to the frequency shifter 6 and the optical receiver 8. The optical receiver 8 is connected to the A / D converter 9. The A / D converter 9 is connected to the signal processing unit 10. The control unit 11 is connected to the A / D converter 9, the signal processing unit 10, and the pulse modulator 3.

  In FIG. 1, between the light source 1 and the optical distributor 2, between the optical distributor 2 and the pulse modulator 3, between the pulse modulator 3 and the optical circulator 4, and between the optical circulator 4 and the transmission / reception optical system 5. Between the optical circulator 4 and the optical coupler 7, between the optical distributor 2 and the frequency shifter 6, between the frequency shifter 6 and the optical coupler 7, and between the optical coupler 7 and the optical receiver 8. Are all connected by optical circuits (indicated by thick lines), for example, by optical fibers. Also, between the optical receiver 8 and the A / D converter 9, between the A / D converter 9 and the signal processing unit 10, between the control unit 11 and the A / D converter 9, and between the control unit 11 and The signal processing unit 10 and the control unit 11 and the pulse modulator 3 are all connected by an electric circuit (indicated by a thin line).

  The control unit 11 transmits a modulation signal to the pulse modulator 3 and a trigger signal to the A / D converter 9 and the signal processing unit 10. The light source 1 transmits CW light having a single frequency. The light distributor 2 divides the light from the light source into two and sends one to the pulse modulator 3 and the other to the frequency shifter 6. The pulse modulator 3 applies pulse modulation to the input optical signal based on the modulation signal from the control unit 11. The frequency shifter 6 gives a predetermined frequency shift to the input optical signal.

  The optical circulator 4 sends the optical signal from the pulse modulator 3 to the transmission / reception optical system 5 and sends the optical signal from the transmission / reception optical system 5 to the optical coupler 7. The transmission / reception optical system 5 transmits an optical signal from the optical circulator 4 to the atmosphere, receives scattered light from the atmosphere as reception light, and transmits the received light to the optical circulator 4. The optical coupler 7 combines the optical signals from the frequency shifter 6 and the optical circulator 4 and sends them to the optical receiver 8. The optical receiver 8 converts the optical signal from the optical coupler 7 into an electrical signal by heterodyne detection, and sends it to the A / D converter 9 as a received signal.

  The A / D converter 9 performs A / D conversion on the received signal simultaneously with the input of the trigger signal from the control unit 11, and sends it to the signal processing unit 10. The signal processing unit 10 processes the reception signal from the A / D converter 9 in synchronization with the trigger signal from the control unit 11, and measures the distance dependency of the wind speed in the laser beam transmission / reception direction.

  In FIG. 1, the frequency shift by the frequency shifter 6 is arranged for the purpose of identifying the positive or negative of the Doppler frequency shift by placing the IF frequency on the electric signal obtained by heterodyne detection. 1 can be removed from the position shown in FIG. 1, and the frequency shifter 6 can be made to function as the pulse modulator 3 by using the frequency shifter 6 to the pulse modulator 3 and sending a modulation signal thereto. In the said nonpatent literature 1, this structure is taken.

  Next, the operation of the laser radar device of FIG. 1 will be described. First, the control unit 11 transmits a modulation signal having a predetermined pulse width and repetition period to the pulse modulator 3 and synchronizes with the modulation signal to the A / D converter 9 and the signal processing unit 10. Send a trigger signal. In parallel with this, a CW optical signal having a single frequency is transmitted from the light source 1, and after this optical signal is distributed by the optical distributor 2, one is supplied to the pulse modulator 3 and the other is supplied to the frequency shifter 6. send.

  Next, in the pulse modulator 3, the CW optical signal input based on the modulation signal from the control unit 11 is pulsed. This pulsed optical signal is transmitted to the atmosphere via the optical circulator 4 and the transmission / reception optical system 5. The optical signal transmitted to the atmosphere is scattered by a scatterer such as aerosol floating in the atmosphere, and this scattered light is received by the transmission / reception optical system 5 as reception light. At this time, since a scatterer such as aerosol moves on the wind, a Doppler frequency shift corresponding to the wind speed occurs in the received light. The received light is sent to the optical coupler 7 via the transmission / reception optical system 5 and the optical circulator 4. In the optical coupler 7, the local light from the frequency shifter 6 and the received light are combined and sent to the optical receiver 8.

  In the optical receiver 8, the local light and the received light are subjected to heterodyne detection and converted into a received signal which is an electric signal region. At this time, the frequency of the received signal has the same value as the Doppler frequency shift corresponding to the wind speed. Next, the A / D converter 9 starts the A / D conversion of the received signal from the optical receiver 8 simultaneously with receiving the trigger signal, and sends this digital signal to the signal processing unit 10.

  The signal processing unit 10 starts signal processing in synchronization with receiving the trigger signal. This signal processing will be described below. FIG. 2 shows a schematic diagram of an operation for obtaining a Doppler spectrum for each distance in signal processing. In the signal processing, the received digital signal is first gated and divided (time sample (a)) with a time width corresponding to the distance resolution. When the distance resolution is ΔL and the gate number is n (= 1, 2,... N), each gate corresponds to a distance ΔL × n.

  Next, the divided digital signal of each gate is subjected to FFT to obtain a reception spectrum for each distance (reception spectrum of (b)). Next, the peak intensity is detected for each received spectrum, and the received S / N ratio is obtained from this intensity. Regarding the received S / N ratio, the standard deviation of the intensity on the frequency axis in the spectrum of only noise when there is no received light is obtained, and the ratio of the peak intensity to the standard deviation may be obtained.

  The reception S / N ratio derivation is performed for each distance (each gate), and the reception S / N ratio distance dependency is obtained with the horizontal axis representing the distance and the vertical axis representing the reception S / N ratio. This reception S / N ratio distance dependency is schematically shown in FIG. At this time, as shown in FIG. 3, generally, the reception S / N ratio is high in the short-distance region, and the reception S / N ratio tends to decrease as the region becomes a long-distance region.

  Next, a threshold value relating to a reception S / N ratio set in advance is compared with the reception S / N ratio distance dependency, and a region having a reception S / N ratio higher than the threshold value is a high S / N ratio region, A region having a reception S / N ratio lower than the threshold is distinguished as a low S / N ratio region.

  Next, wind speed detection is performed for the above-described high S / N ratio region. In the same manner as in the prior art, the peak speed is detected in the entire fixed wind speed detection range set in advance on the reception spectrum, and the center of gravity is calculated for the periphery of this peak. Since this wind speed detection process is performed only for the gate having a high reception S / N ratio, the detection range in the peak detection is wide as the entire fixed wind speed detection range set in advance on the reception spectrum. However, the signal peak can be accurately detected.

  Next, the distance dependence of the wind speed in this region is obtained from the wind speed detection result for the high S / N ratio region. FIG. 4 schematically shows the distance dependence of the wind speed. At this time, the fluctuation of the wind speed with respect to the distance is generally continuous, but takes an irregular value as shown in FIG. 4 according to the degree of disturbance of the entire wind speed field.

  Next, the distance dependence of the wind speed in FIG. 4 is analyzed, and the standard deviation of the wind speed between adjacent gates (distances) is obtained. This standard deviation is a parameter corresponding to the degree of turbulence of the entire wind velocity field, and a gate corresponding to the farthest distance in the high S / N ratio region and a gate corresponding to the low S / N ratio region adjacent thereto. In the meantime, a value indicating how much the wind speed difference can be statistically generated in the current wind turbulence state. This value is used as look-ahead information in signal processing in the low S / N ratio region described later.

  Next, wind speed detection is performed for the above-described low S / N ratio region. In this detection, attention is first paid to the gate corresponding to the longest distance in the high S / N ratio region and the gate in the low S / N ratio region adjacent thereto. In the latter received spectrum, the peak detection range is limited to the range of the standard deviation with the former wind speed detection value as the center, and the peak detection is performed within this limited range. After the peak detection, the wind speed is detected by the same method as that in the high S / N ratio region such as the gravity center calculation.

  With respect to the gate in the low S / N ratio region corresponding to a far distance from the gate in the low S / N ratio region, based on the wind speed detection result and the standard deviation in the adjacent gate among the adjacent gates. Then, the wind speed may be detected sequentially on the long distance side.

  In the laser radar apparatus according to the first embodiment of the present invention described above, in the signal processing, unlike the conventional case, the reception S / N ratio is differentiated into a high S / N ratio region and a low S / N ratio region. Is used to detect the wind speed. In particular, in the signal processing in the low S / N ratio region, the detection range in the reception spectrum using the wind speed detection value with high accuracy in the high S / N ratio region and the degree of disturbance obtained from the distance dependence as the foresight information. By limiting to the above, it is possible to increase the probability of avoiding erroneous detection in the reception spectrum.

  FIG. 5 is a diagram showing an effect related to avoiding this false detection, schematically showing a reception spectrum in a high S / N ratio region and a reception spectrum in a low S / N ratio region adjacent thereto. Yes. A solid line indicates a reception spectrum with a high S / N ratio range, and a broken line indicates an adjacent reception spectrum with a low S / N ratio range. In this figure, in the received spectrum in the low S / N ratio region (indicated by a broken line), a noise peak higher than the signal peak occurs, and this noise is detected when peak detection is performed for the entire wind speed detection range on the received spectrum. A peak will be detected. However, if the signal processing shown in the first embodiment of the present invention is performed, peak detection is performed only for the limited range shown in FIG. 5, so that signal peaks can be detected correctly.

  In the laser radar apparatus according to the first embodiment of the present invention described above, the standard deviation of the wind speed between adjacent gates (distances) is obtained in the high S / N ratio region, and this is used as foresight information as a low-profile information. It was used for processing in the S / N ratio region. This foresight information may be obtained by a process different from the above. This will be described next.

  The distance dependence of the wind speed in the high S / N ratio region is analyzed in more detail, and a graph is created with the horizontal axis representing the distance difference between the gates and the vertical axis representing the standard deviation of the wind speed difference between the gates. Next, fitting is performed on this graph using a model formula. For example, the following equation (1) based on the Kolmogorov wind velocity field, which is a general equation related to turbulence in the atmosphere, may be used as the model equation.

σ ₁ = √ (9/20) · ε ^1/3 · D ^1/3 (1)

Here, ε is a vortex dissipation coefficient (m ² / s ³ ), and D is a distance difference between the gates. ε is a parameter indicating the degree of disturbance of the wind speed field. FIG. 6 shows a schematic diagram obtained by fitting Equation (1) to the above graph. From the fitting result of FIG. 6, the standard deviation of the wind speed difference between adjacent gates may be obtained by the following equation (2).

σ ₂ = √ (9/20) · ε ^1/3 · ΔL ^1/3 (2)

Embodiment 2. FIG.
Next, a laser radar apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS. In the first embodiment, the degree of turbulence in the wind speed field is obtained from the distance dependence of the wind speed in the high S / N ratio region. On the other hand, in the second embodiment, the degree of the disturbance is obtained from the shape of the reception spectrum in the high S / N ratio region.

  FIG. 7 is a schematic diagram of a reception spectrum in a high S / N ratio region. A solid line indicates a weak turbulent flow, a broken line indicates a turbulent flow, and a one-dot chain line indicates a strong turbulent flow. As can be seen from FIG. 7, the reception spectrum has a spread according to the degree of disturbance of the wind speed field, and the spread increases as the disturbance becomes stronger.

  Next, the operation of the laser radar device according to the second embodiment of the present invention will be described. The operation up to wind speed detection in the high S / N ratio region is the same as that according to the first embodiment of the present invention.

  Next, in the laser radar device of the second embodiment, attention is paid to one or more reception spectra in the high S / N ratio region, and a reference spectrum is generated from this reception spectrum or a spectrum obtained by integrating these.

  Next, signal processing in the low S / N ratio region will be described. For the received spectrum related to the low S / N ratio region, first, matching processing for performing a correlation operation with the reference spectrum is performed. By this matching process, the component having the most similar characteristic to the reference spectrum is raised from the received spectrum. Peak detection is performed on the result of this matching processing, and wind speed detection is performed using this peak.

  FIG. 8 schematically shows the effect of this matching process. 8A shows a reference spectrum generated from a spectrum in a high S / N ratio region, FIG. 8B shows a received spectrum in a low S / N ratio region, and FIG. 8C shows a spectrum after matching processing. In FIG. 8, since a noise peak larger than the signal peak is generated in the original reception spectrum, if the peak detection is performed as it is, a false detection occurs. However, in the spectrum after the matching process, the signal component is highlighted and the peak detection is performed. Thus, the signal can be correctly detected.

  In the above-described laser radar device according to the second embodiment of the present invention, the reference spectrum is obtained from the received spectrum in the high S / N ratio region. However, the width of this spectrum is measured and symmetrical with this width. A separate spectrum may be separately generated for reference.

It is a figure which shows typically an example of a structure of the laser radar apparatus by this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the signal processing operation | movement with the laser radar apparatus which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the erroneous detection in case the conventional receiving S / N ratio is low.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Light source, 2 Optical distributor, 3 Pulse modulator, 4 Optical circulator, 5 Transmission / reception optical system, 6 Frequency shifter, 7 Optical coupler, 8 Optical receiver, 9 A / D converter, 10 Signal processing part, 11 Control part .

Claims (3)

In a laser radar device that transmits and receives a laser beam having a single frequency to the atmosphere, performs signal processing on a reception signal obtained by heterodyne detection, and detects wind speed,
A signal processing unit that detects the wind speed by processing the received signal,
The received signal is divided by applying a gate so as to be divided according to the distance from the laser radar device, and the distance dependency of the received S / N ratio is obtained from the received spectrum obtained by performing FFT on each of the divided received signals. Means to seek,
Means for distinguishing a detection target region into a high S / N ratio region and a low S / N ratio region based on the distance dependency of the reception S / N ratio;
The foresight information is obtained based on the information obtained from the received spectrum in the high S / N ratio region, and the received spectrum in the low S / N ratio region is processed using the foresight information, and the low S / N Means for detecting wind speed in the N ratio region;
A laser radar device comprising:   The information obtained from the received spectrum in the high S / N ratio region is the wind speed distance dependence, and the foresight information is the standard deviation of the wind speed difference between adjacent gates obtained from the wind speed distance dependence. The laser radar apparatus according to claim 1, wherein wind speed detection is performed in a reception spectrum in a low S / N ratio region based on the standard deviation.   The information obtained from the received spectrum in the high S / N ratio region is a spread of the received spectrum, and the foresight information is a reference spectrum obtained from the spread of the received spectrum, and using the reference spectrum, 2. The laser radar apparatus according to claim 1, wherein matching processing is performed on a reception spectrum in a low S / N ratio region, and wind speed is detected in the spectrum after the matching processing.

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