CN115639572A - Satellite-borne laser radar for synchronously observing wind, temperature and aerosol - Google Patents

Abstract

A satellite-borne laser radar for synchronously observing wind, temperature and aerosol is characterized in that a laser emission unit emits single-frequency pulse laser to the atmosphere; the receiving telescope unit collects laser back scattering echoes and sends the laser back scattering echoes to the notch filter unit, aerosol signals are filtered out, atmospheric molecule Rayleigh scattering signals are reserved, echo filtering optical signals are formed, and the echo filtering optical signals are sent to the interferometer unit; the interferometer unit sequentially performs interference modulation on the sampled single-frequency pulse laser signals and the echo filtering optical signals to generate four paths of interference signals with the phase differences of 0 degrees, 90 degrees, 180 degrees and 270 degrees in sequence, the four paths of interference signals are respectively sent to the four signal detection units, the sampled laser optical signals and the echo filtering optical signals are sequentially detected, and the four paths of interference signals are sent to the processing inversion unit after photoelectric conversion and digitization are performed; the processing inversion unit utilizes the digital signals transmitted by the four signal detection units to invert the wind speed, the temperature and the aerosol extinction coefficient. The invention has the functions of measuring wind speed, temperature and aerosol through one satellite-borne laser radar device, and has high integration level and high cost-effectiveness ratio.

Description

A Spaceborne LiDAR for Synchronous Observation of Wind, Temperature and Aerosol

technical field

The invention belongs to the technical field of atmospheric optical remote sensing, and relates to a device for detecting atmospheric wind speed, temperature and aerosol laser radar by using a notch filter combined with a four-way interferometer.

Background technique

The detection of the wind speed, temperature, and aerosol profile of the Earth's atmosphere is of great value in research and application fields such as meteorology, climate, and environment. In order to measure the above profile, a variety of lidar detection technologies have been developed at home and abroad. The most commonly used technologies are coherent wind lidar, direct wind lidar, rotating Raman lidar, Raman lidar, micropulse meter scattering lidar, hyperspectral resolution lidar, etc.

Coherent detection lidar can only be used for atmospheric wind speed detection with high aerosol content, and the measurement height in the earth's atmosphere generally does not exceed 3km. Its receiving aperture is limited by coherence conditions and should not be enlarged. Therefore, in long-distance or spaceborne applications, it is mainly to increase the laser single pulse energy to improve the detection capability. Direct detection lidar generally measures wind speed through the transmission energy change of hyperspectral resolution optical elements. If FP etalon and Fizeau interferometer are used, there will be problems such as low energy utilization rate and poor field of view adaptability, which is not conducive to the improvement of comprehensive performance. If With the iodine molecular filter, the accuracy is lower and only for 532nm. In addition, traditional coherent detection technology and direct detection technology do not have the ability to simultaneously detect temperature and aerosol.

Rotating Raman lidar and Raman lidar are generally used for ground-based temperature profiling and aerosol detection. Due to the extremely small scattering signal, it is difficult to be used for spaceborne detection, and they do not have the ability to measure wind. Micropulse meter-scattering lidar is generally used for aerosol detection, and its extinction coefficient accuracy is lower than rotational Raman and Raman lidar. Hyperspectral resolution lidar generally improves the accuracy of aerosol detection by separating molecular Rayleigh scattering signals and aerosol meter scattering signals. Simultaneously measure wind speed and temperature.

Contents of the invention

The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a spaceborne laser radar detection device that combines a notch filter with a four-way interferometer, which can be realized by measuring the frequency shift of the laser radar echo light. Wind speed detection can also realize temperature measurement by measuring the broadening of Rayleigh scattering echo, and can also realize high-precision measurement of aerosol extinction coefficient by separating molecular scattering signals and aerosol signals by contrast.

The technical solution of the present invention is: a space-borne wind, temperature, and aerosol synchronous observation lidar, including a laser emitting unit, a receiving telescope unit, a notch filter unit, an interferometer unit, four signal detection units, and a processing feedback unit. performance unit and laser sampling unit, of which:

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

Receiving telescope unit: used to collect the laser backscatter echo and send it to the notch filter unit;

Notch filter unit: used to filter out the aerosol signal in the laser backscatter echo and retain the Rayleigh scattering signal of atmospheric molecules to form an echo filter signal and send it to the interferometer unit;

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

Interferometer unit: respectively process the reference laser light sent by the laser sampling unit and the laser backscatter echo light sent by the notch filter unit in sequence; first, perform interference modulation on the reference laser light to generate an optical path difference The four-way interference signals of Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ/4 are respectively sent to four signal detection units; then, the laser light is backscattered back to Wavelight is subjected to interference modulation to generate four-way interference signals with optical path differences of Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ/4, which are respectively sent to four signal detection units;

Signal detection unit: used to detect the optical signal contained in the interference signal, and send it to the processing and inversion unit after photoelectric conversion and digitization;

Processing and inversion unit: use the digital signals from the four signal detection units to invert the wind speed, temperature and aerosol extinction coefficient.

Preferably, the processing and inversion unit inverts the wind speed v, specifically:

为激光后向散射回波光干涉相位差，

为参考激光的干涉相位差，σ₀为发射激光波数，Δ₀为基准光程差。where c is the speed of light, v is the wind speed,

is the laser backscatter echo light interference phase difference,

is the interference phase difference of the reference laser, σ ₀ is the wavenumber of the emitted laser, and Δ ₀ is the reference optical path difference.

Preferably, the processing and inversion unit inverts the temperature T, specifically:

In the formula, _Δ0 is the reference optical path difference, Q is the inversion constant, and V(r) is the value at the distance r obtained by the following formula,

Among them, I ₁ , I ₂ , I ₃ , and I ₄ are the detection signals output by the signal detection unit respectively, and the corresponding optical path differences are Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ/4, where λ is the wavelength of the single-frequency pulsed laser.

Preferably, the processing inversion unit inverts the aerosol extinction coefficient, specifically:

In the formula, I _m (r)=I ₀ (r), I ₀ (r) is the incident light intensity obtained at distance r, β _m (r) is the backscattering coefficient of atmospheric molecules at distance r, I ₀ (r ) is calculated by the following formula,

Among them, I ₁ , I ₂ , I ₃ , and I ₄ are the detection signals output by the signal detection unit respectively, and the corresponding optical path differences are Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ/4, where λ is the wavelength of the single-frequency pulsed laser.

Preferably, the single-frequency pulsed laser satisfies the following conditions: single wavelength selection range 0.3-2.2 μm, relative line width ≤ 2×10 ^-7 λ, relative wavelength stability ≤ 1×10 ^-6 , pulse width ≤ 5 μs, repetition Frequency ≤40kHz, single pulse energy ≥1μJ.

Preferably, the receiving telescope unit adopts a transmissive lens or a reflective lens, the transmittance to the laser wavelength emitted by the laser emitting unit is ≥0.5, the effective aperture is ≥50 mm, and the receiving field of view is ≥50 μrad.

Preferably, the notch filter unit is an optical element capable of suppressing laser emission wavelength but passing through adjacent wavelengths or a combination of these elements, including but not limited to FP etalon, molecular absorption cell, and Michelson interferometer.

Preferably, the suppression capability of the notch filter unit to the laser wavelength signal emitted by the laser emitting unit exceeds 10 times, and the suppression bandwidth is 0.4˜3×10 ⁻⁶ λ.

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

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

The advantage of the present invention compared with prior art is:

(1) The present invention has the functions of measuring wind speed, temperature and aerosol through a spaceborne laser radar device, which has high integration and high cost-efficiency ratio;

(2) The present invention measures temperature through elastic scattering echo signals, and the signal strength is 2 to 3 orders of magnitude higher than that of rotational Raman detection, which can effectively compress the scale of spaceborne loads;

(3) The present invention is not limited by the coherence condition, and can increase the detection capability by increasing the aperture, which is beneficial to reduce the energy requirement of the laser and increase the system reliability.

Description of drawings

Fig. 1 is a block diagram of the composition principle of the laser radar of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the laser radar of the present invention is mainly composed 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 inversion unit 9 and a laser The sampling unit 10 is composed. Wherein the laser emitting unit 1 is used to emit a single-frequency pulsed laser into the atmosphere, the laser sampling unit 10 is used to take out part of the emitted laser as a reference laser, the receiving telescope unit 2 is responsible for collecting the backscattered echoes of the laser, and the relay optical unit (notch The filter unit 3 and the interferometer unit 4) are responsible for optically separating the echoes, wherein the notch filter unit 3 is mainly used to filter the aerosol signals in the echoes and retain the Rayleigh scattering signals of atmospheric molecules, and the four-way interferometer (Interferometer unit 4) Interferentially modulate the reference laser and the echo successively to generate four-way interference signals with optical path differences Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ/4 (wherein _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.

The single-frequency pulse laser emitted by the laser emitting unit 1 emits a single wavelength selection range of 0.3-2.2 μm, relative line width ≤ 2×10 ^-7 , relative wavelength stability ≤ 1×10 ^-6 , pulse width ≤ 5 μs, repetition frequency ≤ 40 kHz , Single pulse energy ≥ 1μJ.

The receiving telescope unit 2 can be either a transmissive lens or a reflective lens, the transmittance of the laser wavelength emitted by the laser emitting unit 1 is ≥0.5, the effective aperture is ≥50mm, and the receiving field of view is ≥50μrad.

The notch filter unit 3 is mainly used to filter the laser wavelength signal emitted by the laser emitting unit 1, so that the signal of this wavelength cannot enter the interferometer unit 4, and suppress the laser wavelength signal emitted by the laser emitting unit 1 after passing through the notch filter capacity more than 10 times. Formally, the notch filter unit 3 can be an optical element capable of suppressing the laser emission wavelength, such as an FP etalon, a molecular absorption cell, or a Michelson interferometer, or a combination of these elements.

The interferometer unit 4 modulates the reference laser light and the echo light sequentially in time to form four signals. The former is used to calculate the wavelength of emission, and the latter is used to calculate the echo wavelength λ and modulation contrast V. The interferometer unit 4 has four interference channels with interference optical path differences Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, and Δ ₀ +3λ/4. The interferometer unit 4 may be in the form of an interferometer such as a Michelson interferometer or a Mach-Zehnder interferometer. Wherein Δ ₀ is the reference optical path difference related to the wavelength λ and the range of the atmospheric temperature T to be measured, and the specific value range is 0.5Δ _opt to 1.5Δ _opt . Among them, the calculation formula of _Δopt is, and the unit is m:

a ₁ =-1.007710316073537×10 ⁹

b ₁ =2.387652330524953×10 ⁷

c ₁ =4.669103274194003×10 ⁴

a ₂ =-9.943932650209543

b ₂ =0.051216711849456

c ₂ =-7.167196097489528×10 ^-5

The four signal detection units 5-8 respectively correspond to the 4-way interference light signals output by the interferometer unit 4, respectively detect the 4-way interference output light of the reference laser and the echo laser in chronological order, and respectively detect the 4-way interference output light of the reference laser and the echo laser in chronological order. The 4 channels of interference output light of the laser and the echo laser are subjected to photoelectric conversion and analog-to-digital conversion to generate digital signals, which are then sent to the processing and inversion unit 9 . The four signal detection units 5-8 can be analog detection or photon detection devices such as PMT, APD, G-APD, PIN, etc. that have time resolution and photoelectric conversion capabilities.

The specific measurement process is:

(1) The laser emitting unit 1 emits laser light into the atmosphere, and the backscattered laser light scattered by the atmosphere enters the notch filter unit 3 after being collected by the receiving telescope unit 2;

(2) the backscattered laser light through the notch filter unit 3 enters the interferometer unit 4 after filtering out the meter scattering signal;

(3) The backscattered laser light passing through the interferometer unit 4 is divided into four interfering light signals (the four interfering optical path differences are Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2, Δ ₀ +3λ /4, λ is the working wavelength of the emitting laser), 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;

(4) The laser sampling unit 10 takes out a small part of the emitted laser light and guides it to the interferometer unit 4 as a reference laser light. The reference laser light passing through the interferometer unit 4 is divided into 4 interfering optical signals (the 4 interfering optical path differences increase according to λ/4), and enter the first signal detection unit 5, the second signal detection unit 6, and the third signal detection unit respectively. 7 and the fourth signal detection unit 8 .

(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 complete the photoelectric conversion and digitization of the optical signal, and transmit the digital signal to the processing and inversion unit 9 ;

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

The detection signals output by the signal detection units 5-8 are respectively expressed as: I ₁ , I ₂ , I ₃ , I ₄ , and the corresponding optical path differences are Δ ₀ , Δ ₀ +λ/4, Δ ₀ +λ/2 , Δ ₀ +3λ/4. Here, the sampled reference laser and the echo laser enter the interferometer at different times and then are detected, and there will be no coherence relationship. Through the four output channels, the light intensity, phase and modulation degree of the two lasers are successively calculated, and the wind speed is obtained by subtracting the phase of the reference laser from the measured echo laser phase.

如下：Then calculate the incident light intensity I ₀ , modulation degree V and interference phase difference

as follows:

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

之后，从距离r处散射返回的回波激光到达探测单元5～8，根据公式(1-1)，回波激光干涉相位差表示为

则r距离处，激光回波相对于发射激光的频移为：When the laser radar is working, the reference laser and the echo laser enter the interferometer unit 4 sequentially in time. Therefore, the detection units 5-8 first receive the reference laser signal, and according to the formula (1-1), the interference phase difference calculated for the reference laser is expressed as

After that, the echo laser scattered back from the distance r reaches the detection units 5-8. According to the formula (1-1), the echo laser interference phase difference is expressed as

Then at the r distance, the frequency shift of the laser echo relative to the emitted laser is:

In the formula, Δf is the relative frequency shift, σ ₀ is the emitted laser wavenumber (1/λ), and Δ ₀ is the reference optical path difference.

Then the wind speed at the time of atmospheric detection is calculated from the frequency shift.

The formula for calculating wind speed is:

where c is the speed of light and v is the speed of wind.

Atmospheric temperature calculated from modulation contrast.

The formula for calculating temperature is:

In the formula, Q is the inversion constant, which can be obtained according to the calibration. V(r) is the result of V at distance r from equation (1-1).

The above formula can be found in Wang Li, Zhao Baochang, Xiang Libin, etc., Principles of Selection of Reference Optical Path Difference in Wind Field Detection Interferometer [J], Acta Photonica Sinica, 2006, 35(8), 1254-1258.

According to formula (1-1), the incident light intensity I ₀ (r) obtained at a distance r is the Rayleigh backscattering signal of atmospheric molecules, which can be expressed as:

I _m (r) = I ₀ (r) (1-5)

In the lidar echo signal, the atmospheric molecular echo signal is expressed as:

In the formula, c _A is the laser radar system constant, which is related to the emission energy, optical efficiency, electronic efficiency, etc., and is generally obtained through system calibration. β _m (r) is the atmospheric molecule backscattering coefficient at distance r.

Then the extinction coefficient can be obtained from the molecular Rayleigh backscattering signal by the formula:

where dr is the differential of r.

For the above formula, please refer to Liu Bingyi, Zhuang Quanfeng, Qin Shengguang, etc., Research on Aerosol Classification Method Based on High Spectral Resolution Lidar [J], Infrared and Laser Engineering, 2017,46(4):0411001-1-13.

The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (10)

1. The utility model provides a satellite-borne wind, temperature, synchronous observation laser radar of aerosol which characterized in that includes: laser emission unit (1), receive telescope unit (2), notch filter unit (3), interferometer unit (4), four signal detection units (5 ~ 8), processing inversion unit (9) and laser sampling unit (10), wherein:

laser emitting unit (1): the single-frequency pulse laser is used for emitting single-frequency pulse laser to the atmosphere;

receiving telescope unit (2): the device is used for collecting laser backscattering echoes and sending the laser backscattering echoes to a notch filter unit (3);

notch filter unit (3): the aerosol signal filtering unit is used for filtering aerosol signals in laser backward scattering echoes and reserving atmospheric molecule Rayleigh scattering signals to form echo filtering signals and send the echo filtering signals to the interferometer unit (4);

laser sampling unit (10): the single-frequency pulse laser device is used for sampling single-frequency pulse laser emitted by the laser emission unit (1) and sending the single-frequency pulse laser as reference laser to the interferometer unit (4);

interferometer unit (4): respectively processing the reference laser sent by the laser sampling unit (10) and the laser back scattering echo light sent by the notch filter unit (3) according to the sequence; firstly, the reference laser is subjected to interference modulation to generate optical path difference in sequenceIs Δ ₀ 、Δ ₀ +λ/4、Δ ₀ +λ/2、Δ ₀ The four paths of interference signals of +3 lambda/4 are respectively sent to four signal detection units (5-8); then, the laser back scattering echo light is subjected to interference modulation to generate optical path differences of delta in sequence ₀ 、Δ ₀ +λ/4、Δ ₀ +λ/2、Δ ₀ The four paths of interference signals of +3 lambda/4 are respectively sent to four signal detection units (5-8);

signal detection units (5-8): the device is used for detecting optical signals contained in interference signals, carrying out photoelectric conversion and digitization and then sending the optical signals into a processing inversion unit (9);

processing the inversion unit (9): the wind speed, the temperature and the aerosol extinction coefficient are inverted by using digital signals transmitted by the four signal detection units (5-8).

2. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the processing inversion unit (9) inverts the wind speed v, and specifically comprises the following steps:

wherein c is the speed of light, v is the speed of wind,

for the laser back scattering echo light interference phase difference,

for reference to the interference phase difference, σ, of the laser light ₀ For emitting laser wave number, Δ ₀ The reference optical path difference is obtained.

3. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the processing inversion unit (9) inverts the temperature T, and specifically comprises the following steps:

in the formula,. DELTA. ₀ Q is an inversion constant, V (r) is a value at a distance r obtained by the following equation,

wherein, I ₁ 、I ₂ 、I ₃ 、I ₄ Respectively, the detection signals output by the signal detection units (5-8), the corresponding optical path differences are respectively delta ₀ 、Δ ₀ +λ/4、Δ ₀ +λ/2、Δ ₀ And +3 lambda/4, wherein lambda is the wavelength of the single-frequency pulse laser.

4. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the processing inversion unit (9) inverts the aerosol extinction coefficient, and specifically comprises the following steps:

in the formula I _m (r)＝I ₀ (r)，I ₀ (r) incident light intensity, beta, obtained at a distance r _m (r) is the backscattering coefficient of atmospheric molecules at a distance r, I ₀ (r) is calculated by the following formula,

wherein, I ₁ 、I ₂ 、I ₃ 、I ₄ Are respectively a signal ofThe detection signals output by the detection units (5-8) respectively have corresponding optical path differences of delta ₀ 、Δ ₀ +λ/4、Δ ₀ +λ/2、Δ ₀ +3 λ/4, λ is the wavelength of the single-frequency pulse laser.

5. The satellite-borne wind, temperature and aerosol synchronous observation laser radar according to claim 1, characterized in that: the single-frequency pulse laser satisfies the following conditions: the single wavelength selection range is 0.3-2.2 μm, and the relative line width is less than or equal to 2 x 10 ^-7 Lambda, relative stability of wavelength less than or equal to 1 x 10 ^-6 The pulse width is less than or equal to 5 microseconds, the repetition frequency is less than or equal to 40kHz, and the single pulse energy is more than or equal to 1 microseconds.

6. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the receiving telescope unit (2) adopts a transmission lens or a reflection lens, the transmittance of the laser wavelength emitted by the laser emitting unit (1) is more than or equal to 0.5, the effective caliber is more than or equal to 50mm, and the receiving field of view is more than or equal to 50 μ rad.

7. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the notch filter unit (3) is an optical element or a combination of elements with the capability of suppressing laser emission wavelength and transmitting adjacent wavelengths, including but not limited to FP etalon, molecular absorption cell, michelson interferometer.

8. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 7, wherein: the suppression capability of the notch filter unit (3) on laser wavelength signals emitted by the laser emission unit (1) exceeds 10 times, and the suppression bandwidth is 0.4-3 multiplied by 10 ^-6 λ。

9. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the interferometer unit (4) is a Michelson interferometer or a Mach-Zehnder interferometer.

10. The spaceborne wind, temperature and aerosol synchronous observation laser radar as claimed in claim 1, wherein: the four signal detection units (5-8) adopt analog detection or photon detection devices with time resolution and photoelectric conversion capacity, including but not limited to PMT, APD, G-APD or PIN.

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