CN106483531B - Atmosphere Raman-Rayleigh scattering thermometric laser radar and inversion method - Google Patents

Abstract

The invention discloses an atmospheric Raman-Rayleigh scattering temperature measurement laser radar and an inversion method. The laser radar is composed of a laser emitting unit (1), a receiving telescope (2), a receiving optical fiber (3), and a signal detection unit (4) ) and a signal processing unit (5); using the high-resolution spectral detection method, the Rayleigh scattering spectrum signal generated by the laser above 30km on the atmospheric molecules and the Raman scattering spectral signal generated by the laser below 30km on the atmospheric molecules are measured. Using the characteristic that the Raman scattering spectrum is proportional to the echo intensity of the Rayleigh scattering spectrum, the inversion obtains the atmospheric temperature above and below 30 km, which expands the temperature measurement space range of the Rayleigh scattering temperature measurement lidar. It has the advantages of wide range of temperature measurement height and small temperature measurement error.

Description

Atmospheric Raman-Rayleigh scattering temperature measurement lidar and its inversion method

technical field

The invention relates to an atmospheric detection laser radar, in particular to an atmospheric Raman-Rayleigh scattering temperature measurement laser radar.

Background technique

Atmospheric temperature is one of the important parameters of the atmosphere. In the altitude range from above 30km to 80km in the atmosphere, the composition of the atmosphere is mainly neutral nitrogen and oxygen molecules, which is a blind area for radio wave detection. The temperature of this layer is mainly detected by laser radar technology. The mechanism of lidar detection of this layer is: use laser light to irradiate atmospheric molecules to generate Rayleigh scattering, obtain the atmospheric density by detecting the echo intensity of Rayleigh scattering, and then use the ideal gas state equation per unit volume P=NRT to calculate the temperature, Among them, P is the atmospheric pressure, which can be obtained by the atmospheric pressure model; N is the gas molecular density (mole number per unit volume); R is the gas constant; T is the temperature, then T=P/(NR) can be obtained, and because: Laser radar Rayleigh scattering echo intensity I _Rayleigh = σ _Rayleigh N, then T = Pσ _Rayleigh / (I _Rayleigh R), where σ _Rayleigh is the Rayleigh scattering cross section of atmospheric molecules, as long as the laser radar echo intensity I _Rayleigh is measured Atmospheric temperature can be measured.

But for below 30km, the measurement method deviates gradually from the actual temperature, and the further down, the greater the deviation, making the method no longer valid. This is because the atmosphere below 30km is no longer clean molecules, but contains more atmospheric aerosols (particles, water vapor, etc.), and the lower the altitude, the greater the content of atmospheric aerosols (of course, but in case of In high-altitude thin clouds, volcanoes, and large-scale sandstorms, high-altitude atmospheric aerosols may also have a high content), the volume of atmospheric aerosols is much larger than that of molecules, so the scattering cross section of aerosols is much larger than that of atmospheric molecules, resulting in The aerosol scattering (Mie scattering) component is added to the wave signal, and the mixed result of Rayleigh-Mie scattering is obtained, which makes the above detection temperature inversion no longer accurate.

However, the content of atmospheric aerosols changes with changes in atmospheric humidity (water vapor content), pollution (particulate matter pollution), volcanic ash, and dust, and these changes are difficult to accurately predict and cannot be accurately deducted from the echo optical signal. As a result, the existing atmospheric Rayleigh scattering temperature measurement lidar loses its ability to detect atmospheric temperatures below 30 km.

Raman scattering lidar is an effective means to detect low-altitude atmospheric temperature, document 1 (Atmospheric temperature profiling in the presence of clouds with a pure rotational Ramanlidar by use of an interference-filter-based polychromator, APPLIED OPTICS Vol.39, No.9, 2000) introduced a method and system for detecting low-altitude atmospheric temperature using rotational Raman scattering. By detecting two detection channels, respectively detecting two molecular Raman scattering bands that are sensitive to temperature changes, the temperature is obtained by inversion. Since Raman scattering is produced by atmospheric molecules and is not affected by atmospheric aerosol content, but the Raman scattering intensity is much smaller than Rayleigh scattering, so Raman scattering is limited to low-altitude detection, and most Raman temperature measurement lidar detection heights Only a few kilometers to a dozen kilometers, and only a few can detect a height of 30-40km.

Document 2 (A new method for inversion of atmospheric temperature and aerosol backscattering coefficient by pure rotational Raman spectrum, Acta Geophysics, Vol.55, No.11: 3527-3533, 2012), adopts the principle method similar to Document 1, The difference is that the two selected rotational Raman channels are two single spectral lines of nitrogen molecules J=4 and J=14.

To sum up, at present, the detection of atmospheric temperature above and below 30km is realized by using two types of lidar, and the detection of Raman scattering uses two detection channels, and the system structure is relatively complicated.

Contents of the invention

The purpose of the present invention is to provide an atmospheric Raman-Rayleigh scattering temperature measurement lidar. The radar uses a high-resolution spectral detection method to detect the Rayleigh scattering spectral signal generated by the laser above 30km on the atmospheric molecules, and retrieves the atmospheric temperature above 30km; and uses a channel to detect the Raman generated by the laser below 30km on the atmospheric molecules Scattering spectrum signal, this channel corresponds to a section of the spectral signal in the Raman scattering spectrum that is not sensitive to temperature, using the characteristic that the Raman scattering spectrum generated by the laser on atmospheric molecules is proportional to the echo intensity of the Rayleigh scattering spectrum, using Rayleigh The similar method of Rayleigh scattering temperature measurement and inversion can obtain the atmospheric temperature below 30km, which expands the temperature measurement space range of Rayleigh scattering temperature measurement lidar. It has the advantages of simple system, wide range of temperature measurement height and small temperature measurement error.

In order to achieve the above object, the present invention adopts the following technical solutions:

Atmospheric Raman-Rayleigh scattering temperature measurement lidar is composed of a transmitting laser unit, a receiving telescope, a receiving optical fiber, a signal detection unit and a signal processing unit.

Wherein, the composition of the signal detection unit is: a collimating mirror, a first optical filter, a first focusing mirror and a first photodetector are coaxially installed sequentially in the output optical path of the receiving optical fiber; In the optical path between the first optical filters, and at an angle of 45 degrees to the optical axis, the second optical filter, the second focusing mirror and the second photodetector are coaxially installed in sequence in the reflection optical path of the beam splitter; the first photoelectric The detector and the second photodetector respectively output a Mie-Rayleigh signal I _Mie+Rayleigh and a Raman signal I _Raman .

The receiving optical axis of the receiving telescope is parallel to the laser beam emitted by the emitting laser unit. One end of the receiving optical fiber is installed at the focal point of the receiving telescope, and the other end is connected to the input end of the signal detection unit. The Mi-Rayleigh signal I output by the signal detection unit is _Mie+Rayleigh and Raman signal I _Raman are respectively connected to the input end of the signal processing unit, and the trigger signal output by the laser emitting unit is connected to the trigger signal input end of the signal processing unit.

Atmospheric Raman-Rayleigh scattering temperature measurement lidar retrieval method is as follows:

The temperature inversion in the altitude range above 30km is calculated according to the following formula:

T＝Pσ _Rayleigh /(I _Mie+Rayleigh R)

Among them, P is the atmospheric pressure, σ _Rayleigh is the Rayleigh scattering cross section of the atmospheric molecular constant, I _Mie+Rayleigh is the Mie-Rayleigh scattering intensity, and R is the ideal gas constant.

The temperature inversion in the altitude range below 30km is calculated according to the following formula:

T＝Pσ _Raman /(I _Raman R)

Among them, P is the atmospheric pressure, σ _Raman is the Raman scattering cross section of the atmospheric molecular constant, I _Raman is the Raman scattering intensity, and R is the ideal gas constant.

The above-mentioned spectroscope is a short-pass filter, which reflects Stokes Raman scattering spectrum longer than the laser wavelength and transmits Mi-Rayleigh scattering spectrum.

The above-mentioned first optical filter is a band-pass optical filter, the center wavelength of its transmission is the wavelength of the laser light emitted by the laser emitting unit, and the transmission bandwidth is 20cm ^-1 .

The above-mentioned second optical filter is a bandpass optical filter, its central transmission wavelength is 90.5 cm ^-1 longer than the laser wavelength, and its transmission bandwidth is 5 cm ^-1 .

principle

In the atmospheric scattering echo spectrum excited by laser, it includes _Mie scattering spectrum, Rayleigh scattering spectrum and Raman scattering spectrum. It is proportional to the density of atmospheric aerosol particles; the line width of the Rayleigh scattering spectrum is much larger than that of the laser spectrum, and the echo intensity I _Rayleigh of the Rayleigh scattering spectrum is proportional to the density N of atmospheric molecules; the meter scattering spectrum and the Rayleigh scattering spectrum are superimposed together, and what is received is the mixed intensity I _Mie+Rayleigh of the Mie-Rayleigh scattering spectrum. The ratio of the two varies with the ratio of atmospheric aerosol particles and atmospheric molecules in the atmosphere, roughly As the height increases, the proportion of the meter scattering spectrum gradually decreases (of course, the proportion of the meter scattering spectrum and Rayleigh scattering spectrum has uncertain variability with the degree of pollution). However, there is no effective spectral separation method to accurately separate the echo intensity I _Mie of the Mie scattering spectrum from the echo intensity I _Rayleigh of the Rayleigh scattering spectrum.

The Raman scattering spectrum is generated on both sides of the Rayleigh scattering spectrum. The Raman scattering spectrum is generated by laser irradiation on molecules such as nitrogen and oxygen in the atmosphere. The side longer than the laser wavelength is the Stokes Raman scattering spectrum, which is shorter than the laser wavelength. One side of the spectrum is the Anti-Stokes Raman scattering spectrum. Because molecules have many rotational energy levels, the Raman scattering spectrum also has many spectral lines. However, the intensity of the Raman spectral line at a position away from the laser wavelength of 90.5cm ^-1 hardly changes with temperature, and the intensity of the Raman spectral line is only proportional to the density N of atmospheric molecules. According to the above analysis, the intensity I _Raman and the intensity I _Rayleigh of the Raman spectral line at the position deviating from the laser wavelength of 90.5cm ^-1 are both proportional to the density N of atmospheric molecules, namely:

I _Raman = σ _Raman NLt

I _Rayleigh = σ _Rayleigh NLt

where σ _Raman and σ _Rayleigh are the known constant Raman scattering cross sections and Rayleigh scattering cross sections of atmospheric molecules respectively, L is the spatial resolution, and t is the time resolution, thus:

It can be seen from the formula that as long as I _Raman is measured, I _Rayleigh can be obtained.

Among them, the temperature inversion algorithm in the altitude range above 30 is:

Intercept the detection data above 30km in I _Mie +Rayleigh, there is no aerosol in the atmosphere in this section, and there is no meter scattering signal in the signal I _Mie+Rayleigh , that is, I _Mie+Rayleigh = I _Rayleigh in this height range, use the temperature inversion formula T =Pσ _Rayleigh /(I _Rayleigh R) gives:

T＝Pσ _Rayleigh /(I _Mie+Rayleigh R)

The temperature retrieval algorithm in the altitude range below 30km is:

Intercept the detection data below 30km in I _Raman , and use the signal intensity relationship between Rayleigh scattering and Raman scattering And the temperature inversion formula T = Pσ _Rayleigh / (I _Rayleigh R) to get:

T＝Pσ _Raman /(I _Raman R)

In addition, in the range above 30, it is not appropriate to replace the Rayleigh scattering signal with the Raman scattering signal according to the relationship between Rayleigh scattering and Raman scattering, because the Raman scattering cross section σ _Raman is smaller than the Rayleigh scattering cross section σ _Rayleigh , making the The signal-to-noise ratio of the Mann scattering signal is low, which will cause a large error in the inversion temperature and the problem that the detection height is not high enough. However, the signal-to-noise ratio of the Raman signal below 30km can be calculated by using the relationship between Rayleigh scattering and Raman scattering. The signal is substituted for the Rayleigh scattering signal to retrieve the temperature.

The advantages of the present invention are: by combining the Raman scattering and Mi-Rayleigh scattering channel signals, the Raman scattering signals of pure molecules are extracted from the low-altitude Mi-Rayleigh mixed signals, eliminating the influence of aerosols, not only realizing The existing Rayleigh temperature measurement lidar detects the temperature above 30km, and also realizes the temperature detection below 30km, which greatly expands the temperature measurement space range of the Rayleigh scattering temperature measurement lidar. It has the advantages of wide range of temperature measurement height and small temperature measurement error.

Description of drawings

Figure 1 is a schematic diagram of the structure of the atmospheric Raman-Rayleigh scattering temperature measurement lidar

Among them, 1 emitting laser unit, 2 receiving telescope, 3 receiving optical fiber, 4 signal detection unit, 5 signal processing unit.

FIG. 2 is a schematic structural diagram of a signal detection unit.

Among them, 3 receiving optical fiber, 41 collimating mirror, 42 beam splitter, 43 first optical filter, 44 first focusing mirror, 45 first detector, 46 second optical filter, 47 second focusing mirror, 48 second Detector, 5 signal processing units.

Figure 3 shows the laser spectrum, the scattered echo signal spectrum and the transmission spectrum of the optical element.

Among them, 42P spectroscope transmission spectrum, 43P first filter transmission spectrum, 46P second filter transmission spectrum.

Detailed ways

Below in conjunction with accompanying drawing, the present invention will be further described.

It can be seen from Figure 1 that the atmospheric Raman-Rayleigh scattering temperature measurement lidar is composed of a transmitting laser unit 1, a receiving telescope 2, a receiving optical fiber 3, a signal detection unit 4 and a signal processing unit 5.

As can be seen from Fig. 2, the composition of the signal detection unit 4 is: a collimating mirror 41, a first optical filter 43, a first focusing mirror 44 and a first photodetector 45 are coaxially installed sequentially in the output optical path of the receiving optical fiber 3; The beam splitter 42 is installed in the optical path between the collimating mirror 41 and the first optical filter 43, and is at an angle of 45 degrees with the optical axis, and the second optical filter 46, the second optical filter 46, and the second optical filter 46, The second focusing mirror 47 and the second photodetector 48; the first photodetector 45 and the second photodetector 48 respectively output a Mie-Rayleigh signal I _Mie+Rayleigh and a Raman signal I _Raman .

The receiving optical axis of the receiving telescope 2 is parallel to the laser beam emitted by the emitting laser unit 1, and one end of the receiving optical fiber 3 is installed at the focal point of the receiving telescope 2, and the other end is connected to the input end of the signal detection unit 4, and the signal detection unit 4 outputs The Mie+Rayleigh signal I _Mie+Rayleigh and the Raman signal I _Raman are respectively connected to the input end of the signal processing unit 5 , and the trigger signal output by the laser emitting unit 1 is connected to the trigger signal input end of the signal processing unit 5 .

Atmospheric Raman-Rayleigh scattering temperature measurement lidar retrieval method is as follows:

The temperature inversion in the altitude range above 30km is calculated according to the following formula:

T＝Pσ _Rayleigh /(I _Mie+Rayleigh R)

Among them, P is the atmospheric pressure, σ _Rayleigh is the Rayleigh scattering cross section of the atmospheric molecular constant, I _Mie+Rayleigh is the Mie-Rayleigh scattering intensity, and R is the ideal gas constant.

The temperature inversion in the altitude range below 30km is carried out according to the following formula:

T＝Pσ _Raman /(I _Raman R)

Among them, P is the atmospheric pressure, σ _Raman is the Raman scattering cross section of the atmospheric molecular constant, I _Raman is the Raman scattering intensity, and R is the ideal gas constant.

The spectroscope 42 is a short-pass filter, which reflects Stokes Raman scattering spectrum longer than the laser wavelength and transmits Mi-Rayleigh scattering spectrum.

The above-mentioned first optical filter 43 is a band-pass optical filter, the center wavelength of its transmission is the wavelength of the laser light emitted by the laser emitting unit 1 , and the transmission bandwidth is 20 cm ⁻¹ .

The above-mentioned second optical filter 46 is a band-pass optical filter, its central transmission wavelength is 90.5 cm ⁻¹ longer than the laser wavelength, and its transmission bandwidth is 5 cm ⁻¹ .

The working process of the present invention is:

The laser emitting unit 1 emits a beam of laser light into the air, and the laser irradiates the atmospheric aerosol particles and atmospheric molecules in the air to generate Mie scattering spectra, Rayleigh scattering spectra and Raman scattering spectra (including Stokes and Anti-Stokes Raman scattering spectra) Echoes are received by the receiving telescope 2 and converged to the receiving optical fiber 3, and transmitted into the signal detection unit 4. The Raman signal I _Raman and the Mi-Rayleigh signal I _Mie+Rayleigh output by the signal detection unit 4 are respectively connected to the signal processing unit 5, the trigger signal output by the laser emitting unit 1 is connected to the trigger signal input of the signal processing unit 5 for synchronous data acquisition.

After the echo light signal enters the signal detection unit 4 through the receiving optical fiber 3, it is first collimated into parallel light by the collimator 41, and then the spectrum is split by the beam splitter 42; 42P (Fig. 3), it can be seen that the Stokes Raman scattering spectrum longer than the laser wavelength in the atmospheric scattering echo light is reflected, and the Mi-Rayleigh scattering spectrum and the Anti-Stokes Raman scattering spectrum shorter than the laser wavelength are transmitted; the spectroscope 42 The reflected light enters the second optical filter 46, and the second optical filter 46 is a bandpass filter. From the transmission spectrum 46P (Fig. 3) of the second optical filter, it can be seen that the second optical filter 46 only allows Stokes Raman In the scattering spectrum, the spectral lines whose intensity does not change with temperature pass through, and the transmitted light is converged to the second detector 48 through the second focusing lens 47, and the second detector 48 converts the optical signal into an electrical signal to obtain I _Raman , which is sent to the signal processing Unit 4.

The transmitted light of spectroscopic mirror 42 irradiates the first optical filter 43, and the first optical filter 43 is a band-pass optical filter. From the first optical filter transmission spectrum 43P (Fig. 3), it can be seen that the Anti- The Stokes Raman scattering spectrum is suppressed, the first optical filter 43 only allows the Mi-Rayleigh scattering spectrum to pass through, and converges to the first detector 45 through the first focusing mirror 44, and the first detector 45 converts the optical signal into The electric signal is obtained by I _Mie+Rayleigh and sent to the signal processing unit 4 .

The signal processing unit 4 synchronously collects the I _Mie+Rayleigh and I _Raman signals detected and output by the first detector 45 and the second detector 48 according to the synchronization signal of the laser emitting unit 1 .

The temperature retrieval algorithm in the altitude range above 30 is:

Intercept the detection data above 30km in I _Mie +Rayleigh, there is no aerosol in the atmosphere in this section, and there is no meter scattering signal in the signal I _Mie+Rayleigh , that is, I _Mie+Rayleigh = I _Rayleigh in this height range, use the temperature inversion formula T =Pσ _Rayleigh /(I _Rayleigh R) gives:

T＝Pσ _Rayleigh /(I _Mie+Rayleigh R)

The temperature retrieval algorithm in the altitude range below 30km is:

Intercept the detection data below 30km in I _Raman , and use the signal intensity relationship between Rayleigh scattering and Raman scattering And the temperature inversion formula T = Pσ _Rayleigh / (I _Rayleigh R) to get:

T＝Pσ _Raman /(I _Raman R)

Thus, the simultaneous acquisition of the atmospheric temperature above 30 km and below 30 km is realized.

Claims (4)

1. atmosphere Raman-Rayleigh scattering thermometric laser radar, which is characterized in that the laser radar by transmitting laser cell (1), connect Receive telescope (2), reception optical fiber (3), detecting signal unit (4) and signal processing unit (5) composition；

Wherein, the composition of detecting signal unit (4) is：Collimating mirror is sequentially coaxially installed in the output light path of reception optical fiber (3) (41), the first optical filter (43), the first focus lamp (44) and the first photodetector (45)；Spectroscope (42) is mounted on collimating mirror (41) in the optical path between the first optical filter (43), and with optical axis be in 45 degree of angles, in the reflected light path of spectroscope (42) according to It is secondary to be co-axially mounted the second optical filter (46), the second focus lamp (47) and the second photodetector (48)；First photodetector (45) and the second photodetector (48) exports rice-Rayleigh signal I respectively_Mie+RayleighWith Raman signal I_Raman；

The reception optical axis of receiving telescope (2) is parallel with the laser beam that transmitting laser cell (1) issues, and the one of reception optical fiber (3) End is installed on the focal point of receiving telescope (2), and the other end is connected to the input terminal of detecting signal unit (4), signal detection list Rice-Rayleigh signal the I of first (4) output_Mie+RayleighWith Raman signal I_RamanIt is connected respectively to the input of signal processing unit (5) The trigger signal at end, transmitting laser cell (1) output is connected to the trigger signal input terminal of signal processing unit (5).

2. atmosphere Raman according to claim 1-Rayleigh scattering thermometric laser radar, which is characterized in that the spectroscope It (42) is low pass filter, the Stokes Raman Scattering Spectra reflection longer than optical maser wavelength, rice-Rayleigh Scattering Spectra transmission.

3. atmosphere Raman according to claim 1-Rayleigh scattering thermometric laser radar, which is characterized in that described first Optical filter (43) is bandpass filter, and centre of homology wavelength is the optical maser wavelength for emitting laser cell (1) and issuing, transmission bandwidth For 20cm^-1；

Second optical filter (46) is bandpass filter, and centre of homology wavelength is 90.5cm longer than optical maser wavelength^-1, transmission bandwidth is 5cm^-1。

4. rice-Rayleigh the signal measured with atmosphere Raman described in claim 1-Rayleigh scattering thermometric laser radar I_Mie+RayleighWith Raman signal I_RamanThe method of inverting atmospheric temperature, which is characterized in that

Temperature retrieval in 30km or more altitude range is calculated as follows：

T=P σ_Rayleigh/(I_Mie+RayleighR)

Wherein, P is atmospheric pressure, σ_RayleighFor atmospheric molecule constant Rayleigh cross-section, I_Mie+RayleighFor rice-Rayleigh scattering Intensity, R are ideal gas constant；

Temperature retrieval in 30km or less altitude range is calculated as follows：

T=P σ_Raman/(I_RamanR)

Wherein, P is atmospheric pressure, σ_RamanFor atmospheric molecule constant raman scattering cross section, I_RamanIt is reason for Raman scattering intensities, R Think gas constant.