Frequency discrimination curve calibration system, method and device

Abstract

The invention discloses a frequency discrimination curve calibration system, method and device. A frequency locking technology is adopted, the output laser frequency of the seed laser is stably locked on an absorption peak of the atom / molecule absorption cell, and the problem of frequency drift of the seed laser is effectively solved. Meanwhile, two acousto-optic modulators are used for implementing accurate out-of-cavity passive frequency modulation on the seed laser, and the laser frequency is moved to a preset zero-speed frequency point of an optical frequency discriminator and a linear working area edge frequency point from an atom / molecule absorption peak position. In the calibration process, the telescope vertically points to the zenith, and atmospheric echoes with zero Doppler frequency shift are provided as reference. At the moment, the optical frequency discriminator measures and records the transmittance of a preset zero-speed frequency point in the center of the linear working area and the transmittance of an edge frequency point, and a new frequency discrimination curve can be derived based on the linear hypothesis of the frequency discrimination curve.

Description

Technical Field

[0001] The present application relates to the field of laser remote sensing technology, and in particular to a system, method and device for calibrating a frequency discrimination curve. Background Art

[0002] In the field of laser remote sensing of wind farms, direct detection technology based on edge detection mainly relies on optical discriminators to extract Doppler frequency shift information and then invert the line-of-sight wind speed. The optical discriminator is an optical device with a steep monotonic transmittance characteristic. The calibration of its monotonic transmittance characteristic curve (discriminator curve) is an important part of the lidar system.

[0003] In the traditional method, tunable laser and high-precision spectrum analyzer are used to perform offline non-real-time calibration of the discrimination curve, but this method is time-consuming and labor-intensive, and the calibration results are unstable, which easily causes measurement system errors. Therefore, how to improve the accuracy and stability of the discrimination curve calibration has become an urgent problem to be solved. Summary of the invention

[0004] Based on the above problems, the present application provides a system, method and device for frequency discrimination curve calibration to improve the accuracy and stability of frequency discrimination curve calibration.

[0005] The present application discloses a system for frequency discrimination curve calibration, comprising: a first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a first photodetector, a second photodetector, a third photodetector and a frequency locking module;

[0006] The first optical path is emitted from the seed laser, reflected by the first beam splitter to the first reflector, and then sequentially passes through the electro-optic modulator, the atomic / molecular absorption cell, and is incident on the first photodetector;

[0007] The first photodetector is used to receive the first laser signal obtained by the atomic / molecular absorption cell through the first optical path, and obtain a first photoelectric signal based on the first laser signal;

[0008] The frequency locking module is used to receive the first photoelectric signal and generate a control signal so that the frequency of the laser output by the seed laser is locked on the absorption peak of the atomic / molecular absorption cell;

[0009] The second optical path is emitted from the seed laser, transmitted through the first beam splitter to the electrically controlled optical switch, and then sequentially passes through the first acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is reflected through the second beam splitter to the second photodetector;

[0010] The third optical path is emitted from the seed laser, transmitted through the first beam splitter to the electrically controlled optical switch, and then sequentially passes through the second acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is reflected through the second beam splitter to the second photodetector;

[0011] The second photoelectric detector is used to receive the first atmosphere echo signal obtained by the second optical path and the second atmosphere echo signal obtained by the third optical path, and obtain a second photoelectric signal based on the first atmosphere echo signal and obtain a third photoelectric signal based on the second atmosphere echo signal;

[0012] The fourth optical path is emitted from the seed laser, transmitted to the electrically controlled optical switch through the first beam splitter, and then sequentially passes through the first acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is transmitted to the optical discriminator through the second beam splitter, and is input into the third photodetector through the optical discriminator;

[0013] The fifth optical path is emitted from the seed laser, transmitted to the electrically controlled optical switch through the first beam splitter, and then sequentially passes through the second acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is transmitted to the optical discriminator through the second beam splitter, and is input into the third photodetector through the optical discriminator;

[0014] The third photoelectric detector is used to receive the third atmosphere echo signal obtained by the fourth optical path and the fourth atmosphere echo signal obtained by the fifth optical path, and obtain a fourth photoelectric signal based on the third atmosphere echo signal and obtain a fifth photoelectric signal based on the fourth atmosphere echo signal.

[0015] Optionally, the seed laser is a tunable single-frequency continuous wave laser, and the frequency of the laser output by the seed laser is tuned by the control signal.

[0016] Optionally, the atomic / molecular absorption cell is filled with a low-concentration high-purity gas, and the atomic / molecular energy level structure of the gas provides an absorption peak in the operating wavelength range of the laser radar system.

[0017] Optionally, the electrically controlled optical switch is a gate switch having one input terminal and two output terminals.

[0018] Optional,

[0019] The first acousto-optic modulator is used to bias the laser frequency of the incident seed laser in the second optical path and the fourth optical path by a first frequency shift amount, and chop it into pulse output;

[0020] The second acousto-optic modulator is used to bias the laser frequency of the incident seed laser in the third optical path and the fifth optical path by a second frequency shift amount, and chop it into pulse output.

[0021] Optionally, the pointing direction of the telescope is electrically controlled.

[0022] Optionally, the optical discriminator has a monotonic linear discriminator curve characteristic within the operating frequency range of the laser radar system.

[0023] Optional,

[0024] The first frequency shift is the frequency shift between the initial zero-speed frequency point at the center of the linear frequency discrimination curve of the optical discriminator and the absorption peak of the atomic / molecular absorption cell;

[0025] The second frequency shift is the frequency shift between the frequency point at the edge of the linear frequency discrimination curve of the optical discriminator and the absorption peak of the atomic / molecular absorption cell.

[0026] Based on the above-mentioned system for calibrating a discrimination curve, the present application also discloses a method for calibrating a discrimination curve, which is applied to the above-mentioned system. The method includes:

[0027] Control the telescope to point vertically to the zenith;

[0028] Obtaining a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path;

[0029] Acquire a first ratio of the fourth photoelectric signal to the second photoelectric signal, and acquire a second ratio of the fifth photoelectric signal to the third photoelectric signal;

[0030] Based on the first ratio and the second ratio, a frequency discrimination curve is calculated to complete calibration.

[0031] Based on the above-mentioned system for frequency discrimination curve calibration, the present application also discloses a device for frequency discrimination curve calibration, including: a control unit, an acquisition unit, a calculation unit and a calibration unit;

[0032] The control unit is used to control the telescope to point vertically to the zenith;

[0033] The acquisition unit is used to obtain a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path;

[0034] The calculation unit is used to obtain a first ratio of the fourth photoelectric signal to the second photoelectric signal, and to obtain a second ratio of the fifth photoelectric signal to the third photoelectric signal;

[0035] The calibration unit is used to calculate a frequency discrimination curve based on the first ratio and the second ratio to complete calibration.

[0036] The present application discloses a system, method and device for frequency discrimination curve calibration. The frequency locking technology is adopted to stably lock the output laser frequency of the seed laser to the absorption peak of the atomic / molecular absorption pool, which effectively solves the problem of frequency drift of the seed laser. At the same time, two acousto-optic modulators are used to perform precise extra-cavity passive frequency modulation on the seed laser, and the laser frequency is moved from the atomic / molecular absorption peak position to the preset zero-speed frequency point of the optical discriminator and the edge frequency point of the linear working area. During the calibration process, the telescope is pointed vertically to the zenith, providing an atmospheric echo with zero Doppler shift as a reference. At this time, the optical discriminator measures and records the preset zero-speed frequency point at the center of the linear working area, as well as the transmittance at the edge frequency points. Based on the linear assumption of the discrimination curve, a new discrimination curve can be derived. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0038] Figure 1a A schematic diagram of the structure of a system for calibrating a frequency discrimination curve disclosed in an embodiment of the present application;

[0039] Figure 1b A position relationship diagram of the frequency shift points used for frequency discrimination curve calibration disclosed in the embodiment of the present application;

[0040] Figure 2 A schematic diagram of a method for calibrating a frequency discrimination curve disclosed in an embodiment of the present application;

[0041] Figure 3 A schematic diagram of the measurement error caused by the variation of the linear frequency discrimination curve disclosed in the embodiment of the present application. DETAILED DESCRIPTION

[0042] In order to accurately understand the system, method and device for frequency discrimination curve calibration described in this application, a brief overview of the basic knowledge in this field is first given here.

[0043] In the field of laser remote sensing, the horizontal axis of the discrimination curve of an optical discriminator represents the frequency or wavelength of the laser, while the vertical axis is determined by the ratio of the signal amplitudes measured by the photodetectors located at the input and output ports of the discriminator. Usually, drawing a discrimination curve requires the construction of a special calibration optical path, using a tunable laser and a high-precision spectrum analyzer to gradually adjust the output frequency of the laser, while recording the current laser frequency or wavelength (as the horizontal axis data of the discrimination curve), and collecting and storing the signal amplitudes detected by the two photodetectors (the ratio of which is the vertical axis data of the discrimination curve). This calibration process involves the adjustment of the optical path and the use of additional equipment, and is an offline and non-real-time calibration method.

[0044] Then, during the system detection phase, the lidar will calculate the Doppler frequency shift based on the transmittance of the atmospheric echo signal light through the optical discriminator and the previously saved discriminator curve data, thereby inverting the atmospheric wind field information.

[0045] The above method is time-consuming and laborious. People expect that the effective detection time of the lidar system between two calibrations can be as long as possible, that is, the validity period of a single calibration is long enough. However, in reality, there are many factors that may cause calibration failure, thereby introducing measurement system errors. For example, the laser frequency drifts during the non-calibration period, causing the transmittance of the laser through the optical discriminator to no longer be equal to the zero-speed value during calibration. This is equivalent to a horizontal displacement of the zero-speed operating point on the discriminator curve. This type of error is called a sum error. The sum error can be corrected by monitoring the frequency change of the laser emitted by the laser and subtracting the laser frequency shift from the uncorrected Doppler frequency shift.

[0046] However, there is another type of error, such as changes in the detection performance of the photodetectors at both ends of the optical discriminator (such as device aging, unstable gain control voltage, etc.) and changes in the performance of the optical splitter before the input port of the discriminator (such as mechanical stress release, changes in the splitting ratio caused by ambient temperature changes, etc.). These factors will cause the proportional factor of the optical discriminator's transmittance to the incident light intensity to change for incident light of the same frequency, that is, the slope of the discriminator curve changes. This type of error is called multiplicative error, and there is a lack of effective direct monitoring methods. Changes in the optical cavity temperature of the optical discriminator may introduce both summative and multiplicative errors at the same time, and are more difficult to monitor and correct directly.

[0047] Based on the above problems, this application aims to solve the problems of frequent offline calibration of the existing discrimination curve of direct detection wind laser radar, which is time-consuming and labor-intensive, with high maintenance costs, and the inability to effectively monitor and correct the discrimination performance of the system during the interval between two calibrations. Based on the linear assumption of the discrimination curve, this application proposes a low-cost, convenient, and accurate and stable real-time discrimination curve online calibration method.

[0048] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] Embodiment 1: This application discloses a system for frequency discrimination curve calibration.

[0050] For details, please refer to Figure 1a A system for calibrating a frequency discrimination curve disclosed in this embodiment includes: a first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a first photodetector 601, a second photodetector 602, a third photodetector 603 and a frequency locking module 7.

[0051] In the system described in this embodiment, the first optical path is emitted from the seed laser 1, and a part of the laser is reflected to the first reflector 301 through the first beam splitter 201. The reflected light beam then passes through the electro-optic modulator 4 and the atomic / molecular absorption cell 5 in sequence, and finally enters the first photodetector 601.

[0052] As an optional method, the seed laser 1 is a tunable single-frequency continuous wave laser, the frequency of its output laser is tuned by a control signal. The electro-optic modulator 4 is a Pockels cell, which is driven by an external sinusoidal signal to phase modulate the electric field of the incident laser beam.

[0053] As an optional method, the atomic / molecular absorption cell 5 is filled with a certain high-purity low-pressure gas, the atomic / molecular energy level structure of which can provide a stable absorption peak for frequency locking in the laser operating wavelength range. For example, the iodine vapor absorption cell provides a frequency locking absorption peak for the doubled frequency 532nm green light of the common Nd:YAG solid-state laser. Specifically, Figure 1b As shown, the transmittance depression caused by gas molecule absorption can be seen from the transmittance curve of the atomic / molecular absorption cell 5.

[0054] In the system described in this embodiment, the first photodetector 601 is used to receive the first laser signal obtained by the atomic / molecular absorption cell 5 through the first optical path, and obtain a first photoelectric signal based on the first laser signal. The frequency locking module 7 is used to receive the first photoelectric signal and generate a control signal. The control signal acts on the seed laser 1 to lock the frequency of its output laser to a certain absorption peak of the atomic / molecular absorption cell 5. (Specifically, Figure 1b ν0 frequency point in the

[0055] In the system described in this embodiment, the second optical path is emitted from the seed laser 1, transmits a portion of the laser light through the first beam splitter 201 to the electrically controlled optical switch 8, and then enters the first acousto-optic modulator 901. The frequency-shifted low-energy pulse light output from the first acousto-optic modulator 901 enters the coupler 10, and then enters the laser amplifier 11 for amplification, and is then emitted into the atmosphere by the telescope 12 for atmospheric remote sensing detection, and a first atmospheric echo signal is obtained. The light continues to be transmitted, passes through the second reflector 302 to the second beam splitter 202, and reflects a portion of the light through the second beam splitter 202 to the second photodetector 602.

[0056] As an optional method, the electrically controlled optical switch 8 is a gating switch, which is a micromechanical optical fiber device with one input end and two output ends, and an external electrical signal can quickly control the gating switch state of the device.

[0057] In the system described in this embodiment, the third optical path is emitted from the seed laser 1, transmits a part of the laser light through the first beam splitter 201 to the electrically controlled optical switch 8, and then enters the second acousto-optic modulator 902. The second acousto-optic modulator 902 outputs a frequency-shifted low-energy pulse light through the coupler 10 and the laser amplifier 11 to reach the telescope 12. It is then emitted into the atmosphere by the telescope 12 for atmospheric remote sensing detection to obtain a second atmospheric echo signal. It continues to transmit, passes through the second reflector 302 to the second beam splitter 202, and reflects a part of the laser light through the second beam splitter 202 to the second photodetector 602.

[0058] In the system described in this embodiment, the second photoelectric detector 602 is used to receive the first atmospheric echo signal obtained by the second optical path and the second atmospheric echo signal obtained by the third optical path, and obtain the second photoelectric signal based on the first atmospheric echo signal, and obtain the third photoelectric signal based on the second atmospheric echo signal. The first atmospheric echo signal corresponds to the second photoelectric signal, and the second atmospheric echo signal corresponds to the third photoelectric signal.

[0059] In the system described in this embodiment, the fourth optical path is emitted from the seed laser 1, transmits a part of the laser light to the electrically controlled optical switch 8 through the first beam splitter 201, and then passes through the first acousto-optic modulator 901, the coupler 10, the laser amplifier 11, and the telescope 12 in sequence to perform atmospheric remote sensing detection. The third atmospheric echo signal collected by the telescope 12 continues to be transmitted through the second reflector 302 to reach the second beam splitter 202, and transmits a part of the laser light to the optical discriminator 13 through the second beam splitter 202, and is input into the third photodetector 603 through the optical discriminator 13.

[0060] In the system described in this embodiment, the fifth optical path is emitted from the seed laser 1, transmitted to the electrically controlled optical switch 8 through the first beam splitter 201, and then sequentially passes through the second acousto-optic modulator 902, the coupler 10, the laser amplifier 11, and the telescope 12 to perform atmospheric remote sensing detection. The fourth atmospheric echo signal collected by the telescope 12 continues to be transmitted through the second reflector 302 to reach the second beam splitter 202, and transmits a part of the laser to the optical discriminator 13 through the second beam splitter 202, and is input into the third photodetector 603 through the optical discriminator 13.

[0061] In the system described in this embodiment, the third photoelectric detector 603 is used to receive the third atmosphere echo signal obtained by the fourth optical path and the fourth atmosphere echo signal obtained by the fifth optical path. The fourth photoelectric signal is obtained based on the third atmosphere echo signal, and the fifth photoelectric signal is obtained based on the fourth atmosphere echo signal. The third atmosphere echo signal corresponds to the fourth photoelectric signal, and the fourth atmosphere echo signal corresponds to the fifth photoelectric signal.

[0062] As an optional method, the optical discriminator 13 has a monotonic linear discriminator curve characteristic within the operating frequency range of the laser radar system. Specifically, Figure 1b The linear working range is shown in the figure. The frequency discrimination curve involved in the edge technology of measuring wind by direct means is monotonic, which increases or decreases monotonically with the increase of the incident laser frequency. In this way, the change of the incident light frequency can be calculated from the measured transmittance change, and then the Doppler frequency shift can be obtained. Figure 1b Only the monotonically increasing situation is depicted. In actual work, the monotonically decreasing situation is similar, and this embodiment does not limit it here. The discrimination curve may appear nonlinear in a wider frequency range. However, in actual operation, the selected working frequency range is usually within its linear segment, and the discrimination curve can be approximated as an inclined straight line. The implementation of the method described in this embodiment is based on the linear assumption of the discrimination curve, so it is not applicable to the nonlinear region of the discrimination curve.

[0063] As an optional method, the first acousto-optic modulator 901 biases the frequency of the incident continuous wave seed laser by a first frequency shift amount, and chops it into a pulse output. The second acousto-optic modulator 902 biases the frequency of the incident continuous wave laser by a second frequency shift amount, and chops it into a pulse output. The first frequency shift amount is the frequency shift amount between the initial zero-speed frequency point at the center of the linear discrimination curve of the optical discriminator 13 and the absorption peak of the atomic / molecular absorption cell 5. The second frequency shift amount is the frequency shift amount between the frequency point at the edge of the linear discrimination curve of the optical discriminator 13 and the absorption peak of the atomic / molecular absorption cell 5. Specifically, the relative positional relationship between the first frequency shift amount Δν1 and the second frequency shift amount Δν2 is as follows: Figure 1b shown.

[0064] The system described in this embodiment is intended to solve the shortcomings of the current offline calibration method of the discrimination curve of the direct detection wind laser radar. This method needs to be repeated regularly, is time-consuming and labor-intensive, and has high maintenance costs, and lacks real-time monitoring and adjustment of the system's discrimination performance between two calibrations. To this end, the system described in this embodiment implements a low-cost, efficient and convenient real-time online calibration method based on the linear assumption of the discrimination curve. This method uses frequency locking technology to stably lock the laser output on the atomic or molecular absorption spectrum of the absorption cell, solving the problem of frequency drift. At the same time, two acousto-optic modulators are used to accurately perform passive frequency modulation outside the cavity, so that the laser frequency can be accurately moved from the absorption peak to the preset zero-speed frequency point and the linear working area boundary of the system optical discriminator. During the calibration process, the system telescope is vertically aligned with the zenith to obtain the atmospheric echo with zero Doppler shift as a reference. The optical discriminator measures and records the transmittance at these two frequency points, thereby calculating a new discrimination curve.

[0065] Based on the above-mentioned system for calibrating a discrimination curve, this embodiment discloses a method for calibrating a discrimination curve, which is applied to the above-mentioned system. Figure 2 , the method for calibrating a frequency discrimination curve comprises:

[0066] S1: Control the telescope to point vertically to the zenith.

[0067] In the method described in this embodiment, when the telescope is vertically pointed to the zenith, since the component of the wind field in the direction vertical to the zenith is almost zero, the laser beam is emitted vertically upward, and its atmospheric echo signal light has zero Doppler shift. Such echo signal light can be used to calibrate the optical discriminator's discriminator characteristic curve. Among them, the pointing direction of the telescope is electrically controlled. A single telescope is used here to describe the method described in this embodiment only for ease of understanding. In actual work, there are many different implementation methods, such as using three fixed-pointing telescopes, one of which is vertically pointed to the zenith for calibration, and the other two are tilted at a certain zenith angle and orthogonally pointed for horizontal wind field measurement, and the laser beam is emitted in rotation in three directions, etc. This embodiment does not specifically limit the number and type of telescopes, and it is sufficient to be able to complete the method described in this embodiment.

[0068] S2: Obtain a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path.

[0069] S3: Obtain a first ratio of the fourth photoelectric signal to the second photoelectric signal, and obtain a second ratio of the fifth photoelectric signal to the third photoelectric signal.

[0070] In the method described in this embodiment, the ratio of the amplitudes of the photoelectric signals detected by the two photoelectric detectors is the vertical axis data of the frequency discrimination curve.

[0071] S4: Based on the first ratio and the second ratio, a frequency discrimination curve is calculated to complete calibration.

[0072] In the method described in this embodiment, the electrically controlled telescope changes its direction, for example, tilts to the due north or due south at a non-zero zenith angle. The second photoelectric signal and the fourth photoelectric signal are obtained again according to the second optical path and the fourth optical path. The ratio of the fourth photoelectric signal to the second photoelectric signal is calculated, and the current Doppler frequency shift is obtained based on the ratio and the discrimination curve obtained in step S4, and the line-of-sight wind speed in the tilted pointing direction is obtained according to the Doppler velocity measurement principle.

[0073] Accordingly, the electrically controlled telescope changes its direction, for example, tilting to the west or the east at a non-zero zenith angle. The second photoelectric signal and the fourth photoelectric signal are obtained again according to the second optical path and the fourth optical path. Similarly, the ratio of the fourth photoelectric signal to the second photoelectric signal is calculated again, and the current Doppler frequency shift is obtained based on the ratio and the discrimination curve obtained in step S4, and the line-of-sight wind speed in the tilted pointing direction is obtained according to the Doppler velocity measurement principle.

[0074] Then, the horizontal wind speed can be obtained based on the wind speed in the north (or south) and the wind speed in the west (or east). The above steps are repeated continuously to complete the real-time online calibration of the frequency discrimination curve and the wind field measurement.

[0075] As an optional method, Figure 3 This is a schematic diagram of the measurement error caused by the change of the linear frequency discrimination curve disclosed in the embodiment of the present application. Figure 3 It more clearly explains the error caused by not calibrating the frequency discrimination curve to the system measurement, as well as the linear frequency discrimination curve calibration principle involved in this application. Figure 3 Only the case where the discrimination curve increases monotonically with the increase of the incident laser frequency is described. In actual work, the case where the discrimination curve decreases monotonically is similar, and this embodiment does not limit this. Figure 3 As shown, the straight line Represents the discrimination frequency curve in the linear working area during the last calibration. Point A is the initial zero-speed working point, located in the center of the linear working area of ​​the discrimination frequency curve, and point B is located at the edge of the linear working area.

[0076] In order to determine the horizontal coordinate frequency of point A and point B, the entire lidar system needs to use the traditional offline calibration method of the discrimination curve to record the image measurement in a wider range of the discrimination curve, and then determine the linear working range, the zero-speed frequency point ν1 and the edge frequency point ν2, so as to obtain the first frequency shift Δν1=ν1-ν0, and the second frequency shift Δν2=ν2-ν0. The frequency shift of the acousto-optic modulator is set by an external RF drive source and will not change. The absorption peak frequency point ν0 is determined by the energy level structure of the atomic or molecular frequency standard used, and there is no drift problem when the laser frequency is locked on it. The vertical component of the atmospheric wind field is very small. If the stratospheric atmospheric echo is selected for calibration, the vertical component of the wind speed can be regarded as zero. At this time, the echo signal has no Doppler frequency shift, and the echo light frequency is equal to the transmitting laser frequency.

[0077] In the method described in this embodiment, the electrically controlled optical switch first selects the first acousto-optic modulator to lock the vertically emitted laser frequency at the zero-speed frequency point ν1, and the optical frequency of the atmospheric echo signal is also ν1. Assume that the amplitude of the second photoelectric signal at this time is S A1 , the fourth photoelectric signal amplitude is S A2 , then the vertical coordinate of point A on the discrimination curve is T A =S A2 / S A1 Then the electrically controlled optical switch selects the second acousto-optic modulator, locking the vertically emitted laser frequency at the edge frequency ν2, and the atmospheric echo signal optical frequency is also ν2. Suppose the amplitude of the third photoelectric signal at this time is S B1 , the fifth photoelectric signal amplitude is S B2 , then the vertical coordinate of point B on the discrimination curve is T B =S B2 / S B1 According to the vertical and horizontal coordinates of points A and B, the equation of the frequency discrimination curve is:

[0078]

[0079] At this point, a round of frequency discrimination curve calibration is completed. Subsequently, the lidar system enters the detection state, calculates the transmittance based on the signal amplitude of the two photodetectors, and then calculates the echo signal frequency according to formula (1), thereby obtaining the Doppler frequency and inverting the line-of-sight wind speed.

[0080] In the method described in this embodiment, the performance of the optical discriminator, the two photodetectors, the second beam splitter and other devices will change over time. When the discriminator curve is not updated, the calculated Doppler frequency shift will produce errors. Figure 3 As shown, Represents the current real frequency discrimination curve after the system has been running for a period of time. The zero speed point changes from the original point A to point A', and the corresponding transmittance should be changed from T A Change to TA '. However, if the demodulation curve is not updated and the old demodulation curve is still used to calculate the frequency shift, the transmittance T A ' will be mistakenly identified as the corresponding A" working point, and the corresponding atmospheric echo frequency will be wrongly calculated as ν1', which will produce an error of ν1'-ν1.

[0081] The method described in this embodiment first uses the traditional offline calibration method to determine the linear working frequency range and the frequency shift amount of the two acousto-optic modulators, and then realizes the flexible rotation of the system calibration state and the detection state through the electrically controlled optical switch, thereby realizing the real-time online calibration of the linear discrimination curve. In the method described in this embodiment, the laser frequency emitted by the laser is locked to the absorption peak of the gas molecules, which effectively solves the problem of long-term drift of the laser frequency. By switching the telescope pointing and the state of the electrically controlled optical switch, the system can seamlessly switch between detection and calibration modes and update the discrimination curve in real time. Using this real-time discrimination curve for wind field inversion can significantly reduce the measurement error caused by the instability of the optical discriminator, thereby improving the measurement accuracy.

[0082] Based on the system for calibrating a discrimination curve disclosed in the above embodiment, this embodiment correspondingly discloses a device for calibrating a discrimination curve, including: a control unit, an acquisition unit, a calculation unit and a calibration unit;

[0083] The control unit is used to control the telescope to point vertically to the zenith;

[0084] The acquisition unit is used to obtain a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path;

[0085] The calculation unit is used to obtain a first ratio of the fourth photoelectric signal to the second photoelectric signal, and to obtain a second ratio of the fifth photoelectric signal to the third photoelectric signal;

[0086] The calibration unit is used to calculate a frequency discrimination curve based on the first ratio and the second ratio to complete calibration.

[0087] The embodiments in this specification are described in a progressive manner. As for the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the methods.

[0088] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0089] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, a software module executed by a processor, or a combination of the two. The software module may be placed in a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

[0090] The features described in the embodiments of this specification can be replaced or combined with each other, so that professional and technical personnel in this field can implement or use the present application.

[0091] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for calibrating a frequency discrimination curve, characterized in that: include: A first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a first photodetector, a second photodetector, a third photodetector and a frequency locking module; The first light path is emitted from the seed laser, reflected by the first beam splitter to the first reflector, and then sequentially passes through the electro-optic modulator and the atomic / molecular absorption cell to be incident on the first photodetector; The first photodetector is used to receive the first laser signal obtained by the atomic / molecular absorption cell through the first optical path, and obtain a first photoelectric signal based on the first laser signal; The frequency locking module is used to receive the first photoelectric signal and generate a control signal so that the frequency of the laser output by the seed laser is locked on the absorption peak of the atomic / molecular absorption cell; The second optical path is emitted from the seed laser, transmitted through the first beam splitter to the electrically controlled optical switch, and then sequentially passes through the first acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is reflected through the second beam splitter to the second photodetector; The third optical path is emitted from the seed laser, transmitted through the first beam splitter to the electrically controlled optical switch, and then sequentially passes through the second acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is reflected through the second beam splitter to the second photodetector; The second photoelectric detector is used to receive the first atmosphere echo signal obtained by the second optical path and the second atmosphere echo signal obtained by the third optical path, and obtain a second photoelectric signal based on the first atmosphere echo signal and obtain a third photoelectric signal based on the second atmosphere echo signal; The fourth optical path is emitted from the seed laser, transmitted to the electrically controlled optical switch through the first beam splitter, and then sequentially passes through the first acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is transmitted to the optical discriminator through the second beam splitter, and is input into the third photodetector through the optical discriminator; The fifth optical path is emitted from the seed laser, transmitted to the electrically controlled optical switch through the first beam splitter, and then sequentially passes through the second acousto-optic modulator, the coupler, the laser amplifier, the telescope and the second reflector to reach the second beam splitter, and is transmitted to the optical discriminator through the second beam splitter, and is input into the third photodetector through the optical discriminator; The third photoelectric detector is used to receive the third atmosphere echo signal obtained by the fourth optical path and the fourth atmosphere echo signal obtained by the fifth optical path, and obtain a fourth photoelectric signal based on the third atmosphere echo signal and obtain a fifth photoelectric signal based on the fourth atmosphere echo signal.

2. The system according to claim 1, characterized in that The seed laser is a tunable single-frequency continuous wave laser, and the frequency of the laser output by the seed laser is tuned by the control signal.

3. The system according to claim 1, characterized in that The atomic / molecular absorption cell is filled with a low-concentration high-purity gas, and the atomic / molecular energy level structure of the gas provides an absorption peak in the operating wavelength range of the laser radar system.

4. The system according to claim 1, characterized in that The electrically controlled optical switch is a gate switch having one input terminal and two output terminals.

5. The system according to claim 1, characterized in that The first acousto-optic modulator is used to bias the laser frequency of the incident seed laser in the second optical path and the fourth optical path by a first frequency shift amount, and chop it into pulse output; The second acousto-optic modulator is used to bias the laser frequency of the incident seed laser in the third optical path and the fifth optical path by a second frequency shift amount, and chop it into pulse output.

6. The system according to claim 1, characterized in that The pointing direction of the telescope is adjusted by electrical control.

7. The system according to claim 1, characterized in that The optical frequency discriminator has a monotonic linear frequency discriminator curve characteristic within the operating frequency range of the laser radar system.

8. The system according to claim 5, characterized in that The first frequency shift is the frequency shift between the initial zero-speed frequency point at the center of the linear frequency discrimination curve of the optical discriminator and the absorption peak of the atomic / molecular absorption cell; The second frequency shift is the frequency shift between the frequency point at the edge of the linear frequency discrimination curve of the optical discriminator and the absorption peak of the atomic / molecular absorption cell.

9. A method for calibrating a frequency discrimination curve, characterized in that: Applied to the system according to any one of claims 1 to 8, the method comprises: Control the telescope to point vertically to the zenith; Obtaining a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path; Acquire a first ratio of the fourth photoelectric signal to the second photoelectric signal, and acquire a second ratio of the fifth photoelectric signal to the third photoelectric signal; Based on the first ratio and the second ratio, a frequency discrimination curve is calculated to complete calibration.

10. A device for calibrating a frequency discrimination curve, characterized in that: include: Control unit, acquisition unit, calculation unit and calibration unit; The control unit is used to control the telescope to point vertically to the zenith; The acquisition unit is used to obtain a first photoelectric signal, a second photoelectric signal, a third photoelectric signal, a fourth photoelectric signal and a fifth photoelectric signal according to the first optical path, the second optical path, the third optical path, the fourth optical path and the fifth optical path; The calculation unit is used to obtain a first ratio of the fourth photoelectric signal to the second photoelectric signal, and to obtain a second ratio of the fifth photoelectric signal to the third photoelectric signal; The calibration unit is used to calculate a frequency discrimination curve based on the first ratio and the second ratio to complete calibration.

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