Space-borne wind, temperature and aerosol synchronous observation lidar

Abstract

A kind of space-borne wind, temperature, aerosol synchronous observation laser radar, laser emission unit emits single-frequency pulsed laser into atmosphere;Receiving telescope unit collects laser backscattering echo and sends to wave filter unit, filters out aerosol signal and retains atmospheric molecular Rayleigh scattering signal, forms echo filter light signal into interferometer unit;Interferometer unit successively carries out interference modulation to sampling single-frequency pulsed laser and echo filter light signal, generates four-way interference signals with phase difference being 0°, 90°, 180° and 270° in turn, is sent into four signal detection units, successively detects sampling laser optical signal and echo filter light signal, and after photoelectric conversion and digitization, it is sent into processing inversion unit;Processing inversion unit uses the digital signal transmitted from four signal detection units, and inverts wind speed, temperature and aerosol extinction coefficient.The present application has the functions of measuring wind speed, temperature and aerosol by one space-borne laser radar device, and has high integration and high cost performance.

Description

Technical Field

[0001] This invention belongs to the field of atmospheric optical remote sensing technology, and relates to a device for detecting atmospheric wind speed, temperature, and aerosol lidar using a notch filter combined with a four-way interferometer. Background Technology

[0002] The detection of wind speed, temperature, and aerosol profiles in the Earth's atmosphere is of great value in meteorological, climatological, and environmental research and applications. To measure these profiles, various lidar detection technologies have been developed both domestically and internationally. Among the most commonly used technologies are coherent wind lidar, direct wind lidar, rotating Raman lidar, Raman lidar, micropulse Mie scattering lidar, and hyperspectral resolution lidar.

[0003] Coherent detection lidar can only be used for wind speed detection in the atmosphere where aerosol content is high, and its measurement altitude within the Earth's atmosphere generally does not exceed 3 km. Its receiving aperture is limited by coherence conditions and cannot be made large; therefore, in long-distance or spaceborne applications, the detection capability is mainly improved by increasing the energy of the laser single pulse. Direct detection lidar generally measures wind speed by measuring the transmission energy change of high-spectral-resolution optical elements. If FP etalons or Fizeau interferometers are used, there are problems such as low energy utilization and poor field-of-view adaptability, which are not conducive to improving overall performance. If iodine molecular filters are used, the accuracy is low and it is only applicable to 532 nm. Furthermore, traditional coherent detection and direct detection technologies do not have the ability to simultaneously detect temperature and aerosols.

[0004] Rotating Raman lidar and Raman lidar are generally used for ground-based temperature profiles and aerosol detection. Due to their extremely small scattered signals, they are difficult to use for spaceborne detection and lack wind measurement capabilities. Micropulse Mie scattering lidar is generally used for aerosol detection, but its extinction coefficient accuracy is lower than that of rotating Raman and Raman lidar. High-spectral-resolution lidar generally improves aerosol detection accuracy by separating molecular Rayleigh scattering signals and aerosol Mie scattering signals. Its accuracy is comparable to that of rotating Raman and Raman lidar, but its stronger signal strength makes it suitable for spaceborne applications. However, it cannot simultaneously measure wind speed and temperature. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a spaceborne lidar detection device that uses a notch filter combined with a four-way interferometer. This device can detect wind speed by measuring the frequency shift of the lidar echo light, measure temperature by measuring the broadening of the Rayleigh scattering echo, and achieve high-precision measurement of the aerosol extinction coefficient by contrast-separating molecular scattering signals and aerosol signals.

[0006] The technical solution of this invention is: a spaceborne simultaneous observation lidar for wind, temperature, and aerosols, comprising a laser emitting unit, a receiving telescope unit, a notch filter unit, an interferometer unit, four signal detection units, a processing and inversion unit, and a laser sampling unit, wherein:

[0007] Laser emitting unit: used to emit single-frequency pulsed laser light into the atmosphere;

[0008] Receiving telescope unit: used to collect laser backscattered echoes and send them to the notch filter unit;

[0009] Notch filter unit: used to filter out aerosol signals in laser backscattered echoes and retain Rayleigh scattering signals of atmospheric molecules, forming an echo filtered signal that is sent to the interferometer unit;

[0010] Laser sampling unit: used to sample the single-frequency pulsed laser emitted by the laser emitting unit and send it as a reference laser into the interferometer unit;

[0011] Interferometer unit: Processes the reference laser input by the laser sampling unit and the backscattered echo light input by the notch filter unit in sequence. First, the reference laser is subjected to interference modulation to generate four interference signals with optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4, respectively, which are then sent to four signal detection units. Then, the backscattered echo light is subjected to interference modulation to generate four interference signals with optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4, respectively, which are then sent to four signal detection units.

[0012] Signal detection unit: used to detect the optical signals contained in the interference signal, and after photoelectric conversion and digitization, send them to the processing and inversion unit;

[0013] Processing and inversion unit: Using the digital signals from the four signal detection units, wind speed, temperature and aerosol extinction coefficient are inverted.

[0014] Preferably, the wind speed v is inverted by the processing inversion unit as follows:

[0015]

[0016] In the formula, c is the speed of light and v is the wind speed. The phase difference in the interference of laser backscattered echo light. The interference phase difference of the reference laser is σ0, the emitted laser wavenumber is Δ0, and the reference optical path difference is Δ0.

[0017] Preferably, the temperature T retrieved by the processing inversion unit is specifically as follows:

[0018]

[0019] In the formula, Δ0 is the reference optical path difference, Q is the inversion constant, and V(r) is the value at distance r obtained by the following formula.

[0020]

[0021]

[0022] Wherein, I1, I2, I3, and I4 are the detection signals output by the signal detection unit, and the corresponding optical path differences are Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4, respectively, where λ is the wavelength of the single-frequency pulse laser.

[0023] Preferably, the process inversion unit inverts the aerosol extinction coefficient, specifically as follows:

[0024]

[0025] In the formula I m (r) = I0(r), where I0(r) is the incident light intensity at a distance r, and β m I0(r) is the atmospheric molecule backscattering coefficient at a distance r, which is calculated using the following formula.

[0026]

[0027] Wherein, I1, I2, I3, and I4 are the detection signals output by the signal detection unit, and the corresponding optical path differences are Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4, respectively, where λ is the wavelength of the single-frequency pulse laser.

[0028] Preferably, the single-frequency pulsed laser meets the following conditions: a single wavelength selection range of 0.3–2.2 μm and a relative linewidth ≤ 2 × 10⁻⁶. -7 λ, wavelength relative stability ≤ 1×10 -6 Pulse width ≤ 5μs, repetition frequency ≤ 40kHz, single pulse energy ≥ 1μJ.

[0029] Preferably, the receiving telescope unit uses a transmission lens or a reflection lens, with a transmittance of ≥0.5 for the laser wavelength emitted by the laser emitting unit, an effective aperture of ≥50mm, and a receiving field of view of ≥50μrad.

[0030] Preferably, the notch filter unit is an optical element or a combination of such elements that has the ability to suppress the laser emission wavelength but allows the transmission of adjacent wavelengths, including but not limited to FP etalons, molecular absorption cells, and Michelson interferometers.

[0031] Preferably, the notch filter unit has a suppression capability of more than 10 times for the laser wavelength signal emitted by the laser emitting unit, with a suppression bandwidth of 0.4 to 3 × 10⁻⁶. -6 λ.

[0032] Preferably, the interferometer unit is a Michelson interferometer or a Mach-Zehnder interferometer.

[0033] Preferably, the four signal detection units employ analog or photonic detection devices with time resolution and photoelectric conversion capabilities, including but not limited to PMT, APD, G-APD, or PIN.

[0034] The advantages of this invention compared to the prior art are:

[0035] (1) The present invention has the function of measuring wind speed, temperature and aerosols simultaneously through a single spaceborne lidar device, which has high integration and high cost-effectiveness.

[0036] (2) This invention measures temperature by elastic scattering echo signal, and the signal strength is 2 to 3 orders of magnitude higher than that of rotating Raman detection, which can effectively reduce the size of spaceborne payload.

[0037] (3) This invention is not limited by coherence conditions. It can improve the detection capability by increasing the aperture, which is beneficial to reduce the energy requirements of the laser and increase the system reliability. Attached Figure Description

[0038] Figure 1 This is a block diagram illustrating the composition and principle of the lidar of the present invention. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings.

[0040] like Figure 1As shown, the lidar of the present invention mainly consists of a laser emitting unit 1, a receiving telescope unit 2, a notch filter unit 3, an interferometer unit 4, four signal detection units 5-8, a processing and inversion unit 9, and a laser sampling unit 10. The laser emitting unit 1 emits a single-frequency pulsed laser into the atmosphere, the laser sampling unit 10 extracts a portion of the emitted laser as a reference laser, the receiving telescope unit 2 collects the backscattered laser echo, the relay optical unit (notch filter unit 3, interferometer unit 4) performs optical separation on the echo, the notch filter unit 3 mainly filters out aerosol signals in the echo and retains Rayleigh scattering signals from atmospheric molecules, the four-way interferometer (interferometer unit 4) successively modulates the reference laser and the echo to generate four interference signals with optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4 respectively (where Δ0 is the reference optical path difference), the four signal detection units 5-8 are responsible for detecting the optical signals separated by the interferometer unit 4 and generating digital data, and the processing and inversion unit 9 is responsible for calibrating the data and inverting the required information such as wind speed, temperature, and aerosol extinction coefficient.

[0041] The single-frequency pulsed laser emitted by laser emitting unit 1 has a single wavelength range of 0.3–2.2 μm and a relative linewidth ≤ 2 × 10⁻⁶. -7 Wavelength relative stability ≤1×10 -6 Pulse width ≤ 5μs, repetition frequency ≤ 40kHz, single pulse energy ≥ 1μJ.

[0042] The receiving telescope unit 2 can be either a transmission lens or a reflection lens. It has a transmittance of ≥0.5 for the laser wavelength emitted by the laser emitting unit 1, an effective aperture of ≥50mm, and a receiving field of view of ≥50μrad.

[0043] The notch filter unit 3 is mainly used to filter the laser wavelength signal emitted by the laser emitting unit 1, preventing the signal of that wavelength from entering the interferometer unit 4. The suppression capability of the laser wavelength signal emitted by the laser emitting unit 1 after passing through the notch filter is more than 10 times. The notch filter unit 3 can be in the form of an FP etalon, a molecular absorption cell, a Michelson interferometer, or other optical elements with laser emission wavelength suppression capabilities, or a combination of these elements.

[0044] Interferometer unit 4 modulates the reference laser and echo light sequentially to form four signals. The former is used to calculate the wavelength at the time of emission, and the latter is used to calculate the wavelength λ and modulation contrast V of the echo. Interferometer unit 4 has four interference channels with interference optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4. Interferometer unit 4 can be in the form of a Michelson interferometer, a Mach-Zehnder interferometer, etc. Here, Δ0 is the reference optical path difference related to the wavelength λ and the range of the atmospheric temperature T to be measured, specifically within the range of 0.5Δ. opt ~1.5Δ opt Among them, Δ opt The calculation formula is as follows, with the unit being m:

[0045]

[0046] a1 = -1.007710316073537 × 10 9

[0047] b1 = 2.387652330524953 × 10 7

[0048] c1 = 4.669103274194003 × 10 4

[0049] a2 = -9.943932650209543

[0050] b2 = 0.051216711849456

[0051] c2 = -7.167196097489528 × 10 -5

[0052] Four signal detection units 5-8 correspond to the four interference light signals output from interferometer unit 4, respectively. They detect the four interference output lights of the reference laser and the echo laser in chronological order, and then perform photoelectric conversion and analog-to-digital conversion on the four interference output lights of the reference laser and the echo laser in chronological order to generate digital signals, which are then sent to processing and inversion unit 9. The four signal detection units 5-8 can be analog detection or photon detection devices with time resolution and photoelectric conversion capabilities, such as PMT, APD, G-APD, and PIN.

[0053] The specific measurement process is as follows:

[0054] (1) The laser emitting unit 1 emits laser into the atmosphere. The backscattered laser scattered by the atmosphere is collected by the receiving telescope unit 2 and then enters the notch filter unit 3.

[0055] (2) After the backscattered laser light passes through the notch filter unit 3 and the Mie scattering signal is filtered out, it enters the interferometer unit 4.

[0056] (3) The backscattered laser after passing through the interferometer unit 4 is divided into 4 interference optical signals (the path differences of the 4 interference optical signals are Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4, respectively, where λ is the working wavelength of the emitted laser), and enter the first signal detection unit 5, the second signal detection unit 6, the third signal detection unit 7, and the fourth signal detection unit 8 respectively.

[0057] (4) The laser sampling unit 10 extracts a small portion of the emitted laser as a reference laser and introduces it into the interferometer unit 4. The reference laser after passing through the interferometer unit 4 is divided into 4 interference light signals (the path difference of the 4 interference light signals increases in increments of λ / 4), and enters the first signal detection unit 5, the second signal detection unit 6, the third signal detection unit 7 and the fourth signal detection unit 8 respectively.

[0058] (5) The first signal detection unit 5, the second signal detection unit 6, the third signal detection unit 7 and the fourth signal detection unit 8 respectively perform photoelectric conversion and digitization of the optical signal and transmit the digital signal to the processing and inversion unit 9;

[0059] (6) The processing and inversion unit 9 calibrates and inverts the digital signals input from signal detection units 5-8 to obtain wind speed, temperature, and aerosol extinction coefficient data. The specific processing method is as follows:

[0060] The detection signals output by signal detection units 5-8 are represented as I1, I2, I3, and I4, respectively, with corresponding optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2, and Δ0+3λ / 4. Here, the sampled reference laser and echo laser enter the interferometer and are detected at different times, thus avoiding coherence. The intensity, phase, and modulation of each laser are calculated sequentially through the four output channels. The wind speed is then calculated by subtracting the phase of the reference laser from the measured echo laser phase.

[0061] Then calculate the incident light intensity I0, modulation degree V, and interference phase difference. as follows:

[0062]

[0063] The frequency shift is then calculated from the phase difference between the echo laser and the reference laser.

[0064] When the lidar is operating, the reference laser and the echo laser enter the interferometer unit 4 sequentially. Therefore, the reference laser signal is received first by the detection units 5-8. According to formula (1-1), the interference phase difference calculated from the reference laser is expressed as: Subsequently, the echo laser light scattered and returned from a distance r reaches detector units 5-8. According to formula (1-1), the phase difference of the echo laser interference is expressed as... Then, at a distance r, the frequency shift of the laser echo relative to the emitted laser is:

[0065]

[0066] In the formula, Δf is the relative frequency shift, σ0 is the emitted laser wavenumber (1 / λ), and Δ0 is the reference optical path difference.

[0067] Then, the wind speed during atmospheric sounding is calculated using frequency shift.

[0068] The formula for calculating wind speed is:

[0069]

[0070] In the formula, c is the speed of light and v is the wind speed.

[0071] Atmospheric temperature is calculated from modulation contrast.

[0072] The formula for calculating temperature is:

[0073]

[0074] In the formula, Q is the inversion constant, which can be obtained from calibration. V(r) is the result of V at a distance r in formula (1-1).

[0075] The above formula can be found in Wang Li, Zhao Baochang, Xiang Libin et al., Selection principle of reference optical path difference in wind field detection interferometer [J], Acta Photonica Sinica, 2006, 35(8), 1254-1258.

[0076] According to formula (1-1), the incident light intensity I0(r) at a distance r is the Rayleigh backscattering signal of atmospheric molecules, which can be expressed as:

[0077] I m (r)=I0(r) (1-5)

[0078] In lidar echo signals, atmospheric molecular echo signals are represented as:

[0079]

[0080] In the formula, c A β is a system constant for lidar systems, related to emission energy, optical efficiency, and electronic efficiency, and is generally obtained through system calibration. m (r) is the backscattering coefficient of atmospheric molecules at a distance r.

[0081] The extinction coefficient can then be obtained from the molecular Rayleigh backscattering signal using the formula:

[0082]

[0083] In the formula, dr is the derivative of r.

[0084] For details of the above formula, please refer to Liu Bingyi, Zhuang Quanfeng, Qin Shengguang, et al., Research on Aerosol Classification Method Based on Hyperspectral Resolution LiDAR [J], Infrared and Laser Engineering, 2017, 46(4):0411001-1-13.

[0085] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A space-borne wind, temperature, aerosol synchronous observation lidar, characterized in that It comprises a laser emission unit (1), a receiving telescope unit (2), a wave filter unit (3), an interferometer unit (4), four signal detection units (5-8), a processing inversion unit (9) and a laser sampling unit (10), wherein: The laser emission unit (1) is used for emitting single-frequency pulsed laser into the atmosphere. The receiving telescope unit (2) is used for collecting laser backscattering echo and sending it to the wave filter unit (3). The wave filter unit (3) is used for filtering out aerosol signals in the laser backscattering echo and retaining atmospheric molecular Rayleigh scattering signals to form echo filtered signals sent to the interferometer unit (4). The laser sampling unit (10) is used for sampling the single-frequency pulsed laser emitted by the laser emission unit (1) and sending it as reference laser to the interferometer unit (4). The interferometer unit (4) processes the reference laser sent by the laser sampling unit (10) and the laser backscattering echo light sent by the wave filter unit (3) in sequence; first, the reference laser is interfered to generate four-way interference signals with optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2 and Δ0+3λ / 4, which are sent to the four signal detection units (5-8) respectively; then, the laser backscattering echo light is interfered to generate four-way interference signals with optical path differences of Δ0, Δ0+λ / 4, Δ0+λ / 2 and Δ0+3λ / 4, which are sent to the four signal detection units (5-8) respectively. The signal detection units (5-8) are used for detecting the optical signals contained in the interference signals, and sending the photoelectric converted and digitized signals to the processing inversion unit (9). The processing inversion unit (9) inverses the wind speed, temperature and aerosol extinction coefficient from the digital signals transmitted by the four signal detection units (5-8). The processing inversion unit (9) inverses the temperature T, specifically:

2. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: The processing inversion unit (9) inverts the wind speed , in particular: where c is the speed of light, is the wind speed, The processing inversion unit (9) inverses the aerosol extinction coefficient, specifically: x (r) is the interference phase difference of the laser backscattered echo light, Wherein, I1, I2, I3, I4 are the detection signals output by the signal detection units (5-8), and the corresponding optical path differences are Δ0, Δ0+λ / 4, Δ0+λ / 2 and Δ0+3λ / 4 respectively, and λ is the wavelength of the single-frequency pulsed laser. 0 is the interference phase difference of the reference laser, σ0 is the emission laser wave number, is the reference optical path difference, r is the distance.

3. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: The receiving telescope unit (2) adopts a transmission lens or a reflection lens, and the transmittance of the laser wavelength emitted by the laser emission unit (1) is ≥0.5, the effective aperture is ≥50mm, and the receiving field of view is ≥50μrad. wherein is the reference optical path difference, Q is the inverse constant, is the value at distance r obtained by the equation Wherein, I1, I2, I3, I4 are detection signals output by the signal detection units (5-8), and corresponding optical path differences are Δ0, Δ0+λ / 4, Δ0+λ / 2, Δ0+3λ / 4 respectively, and λ is the wavelength of the single-frequency pulsed laser, is the modulation degree.

4. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: The wave filter unit (3) is an optical element or a combination of these elements with laser emission wavelength suppression capability but transmittance of adjacent wavelengths, including but not limited to FP etalon, molecular absorption cell and Michelson interferometer. wherein , is the intensity of the incident light at a distance r, is the backscattering coefficient of the atmospheric molecules at a distance r, is calculated by the formula The interferometer unit (4) is a Michelson interferometer or a Mach-Zehnder interferometer.

5. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: The single-frequency pulsed laser satisfies the conditions: single wavelength selected in the range of 0.3-2.2 mu m, relative line width ≤2×10 -7 -1, wavelength relative stability ≤1×10 -6 -4, pulse width ≤5 mu s, repetition frequency ≤40 kHz, single pulse energy ≥1 mu J.

6. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: The four signal detection units (5-8) adopt analog detection or photonic detection devices with time resolution and photoelectric conversion capability, including but not limited to PMT, APD, G-APD or PIN.

7. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: ​ 8. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 7, characterized in that: The trap filter unit (3) has a suppression ability of more than 10 times to the laser wavelength signal emitted by the laser emission unit (1), and the suppression bandwidth is 0.4~3×10 -6 λ.

9. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: ​ 10. The space-borne wind, temperature, and aerosol synchronous observation lidar according to claim 1, characterized in that: ​

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