CN108593576A - A kind of relevant detection meter of atmospheric greenhouse gas - Google Patents

Abstract

The invention discloses an atmospheric greenhouse gas coherent detector, which comprises a light tube, a sun tracker, a collimating optical telescope, a chopper, a local oscillator laser, an optical fiber multiplexer, a high-speed photoelectric detector, a square law detector, a radio frequency Amplifiers, video amplifiers, lock-in amplifiers, microprocessors. Atmospheric greenhouse gas coherent detection meter draws on the idea of radio heterodyne receiver and coherent detection. Only when the solar radiation component with the same wavelength as the laser output by the local oscillator laser is coherently detected can the signal we use be output, which improves the solar photometer. spectral resolution. The invention has the advantage of alleviating the contradiction between the sunlight detection sensitivity and spectral resolution of the original photometer, and is suitable for column concentration measurement of atmospheric greenhouse gas components such as water vapor, carbon dioxide and methane.

Description

An Atmospheric Greenhouse Gas Coherent Detector

technical field

The invention relates to a coherent detection meter, in particular to a semiconductor laser with low power and narrow linewidth as a local oscillator light source, which is used for frequency mixing and coherent detection with sunlight received by a collimating telescope, and the wavelength of the local oscillator light can be tuned. An atmospheric greenhouse gas coherent detector that obtains the characteristic absorption spectrum distribution of a certain section of sunlight.

Background technique

The fully automatic sun photometer is used to measure the radiation of the sun and the sky in different bands, directions, and times of visible light and near-infrared to calculate the characteristics of atmospheric aerosols, water vapor, ozone and other components. The instrument is portable, reliable, High degree of automation, solar power supply, long-term unattended automatic observation in the field, measurable sky diffuse radiation distribution, polarized radiation distribution, high measurement accuracy, etc., can be used for atmospheric environment monitoring, satellite correction, etc.

The fully automatic sun photometer consists of an optical head, a control box and a two-axis stepper motor system, the optical head has two sighting tubes: one for measuring direct solar radiation without a condenser lens, and the other for the sky Radiometric with condenser lens. A four-quadrant detector is installed on the optical head for fine-tuning when the sun is automatically tracked. There are two microprocessors in the control box, which are used for data acquisition and control of the stepping motor system respectively. In the fully automatic measurement state, when the attached humidity sensor detects rain, the electronic control box will put the photometer in the shutdown state to protect the optical system of the instrument. The stepping motor system has two degrees of freedom of azimuth and measurement of altitude angle, the initial tracking of the sun is controlled by the time equation, and the four-quadrant detector system is used for precise tracking, with multiple automatic measurement programs.

But the disadvantage of the current sun photometer is: the spectral resolution is low, and the spectral resolution depends on the half-wave bandwidth of the filter used, generally 10nm, so it has a serious shortage in detecting the fine spectrum of atmospheric components. Of course, there is a contradiction between the spectral resolution and the detection sensitivity of the sun photometer. When the bandwidth of the filter is narrow, the spectral resolution is high, and the brightness of the solar radiation passing through the filter to the detector decreases, and the detection signal-to-noise ratio decreases.

Contents of the invention

The object of the present invention is to provide a coherent detector capable of measuring the concentration profile of greenhouse gases, which can overcome the contradiction between the spectral resolution and detection sensitivity of the current heliophotometer, and expand the use of heliophotometers in Capabilities for detection of atmospheric composition.

In order to achieve the above purpose, the present invention draws lessons from the ideas of radio heterodyne receiver and coherent detection, and transplants these two technologies into the sun photometer. The present invention includes a light tube 1, a sun tracker 2, an aiming optical telescope, 3, a chopper 4, an optical fiber multiplexer 5, a local oscillator laser 6 and its driver 7, a high-speed photodetector 9, and a radio frequency/DC splitter 10. Multi-stage radio frequency amplifier 11, square law detector 12, video amplifier 13, lock-in amplifier 14, A/D converter 15, microprocessor 16, switch signal pulse generator 17 and copper core cable 18.

The sun tracker 2 is aimed at the sun, and the sunlight is absorbed and scattered by the components in the atmosphere through the light tube 1 and reaches the collimating optical telescope 3 to be collected; the local oscillator laser 6 is driven by the temperature control of the driver and the current or voltage , emitting a single-frequency narrow-linewidth laser light, which becomes local oscillator light; the collected sunlight and local oscillator light are mixed together by the optical fiber multiplexer 5 and coherently detected by the high-speed photodetector 9 to output an electrical signal, and the output electrical signal The signal includes a radio frequency signal obtained by heterodyne interference and a directly detected direct current signal. The radio frequency signal obtained by heterodyne interference and the directly detected direct current signal are separated by the radio frequency/direct current separator 10, and the radio frequency signal continues to flow to the multistage radio frequency amplifier 11. When the radio frequency signal is sent to a sufficient level, the envelope signal is detected by the square law detector 12. This envelope signal corresponds to the amplitude of the radio frequency. The envelope signal is amplified by the video amplifier 13 and then combined with the periodic pulse of the chopper The signal is correlated in the lock-in amplifier 14, and the result of the calculation is converted into a digital signal by the A/D converter 15 and processed by the microprocessor 16; the sawtooth wave signal 8 generated by the microprocessor 16 is used to tune the driver of the local oscillator laser 7 Make the local oscillator laser 6 output laser with tunable wavelength to scan the absorption peaks of atmospheric greenhouse gases, so that the greenhouse gas coherent detector can output a section of characteristic absorption spectrum curve; The column concentration of a certain greenhouse gas, and the greenhouse gas concentration profile is obtained according to the prior curve.

The local oscillator laser 6 is a DFB distributed feedback semiconductor laser, a DBR distributed Bragg reflective semiconductor laser, or an L-band DFB distributed feedback fiber laser.

Using the coherent detection method of atmospheric greenhouse gases, only the solar radiation component with the same wavelength as the laser output by the local oscillator laser is coherently detected, and the signal we use can be output, which improves the spectral resolution of the sun photometer.

Description of drawings

Fig. 1 is the structural diagram of a specific embodiment of atmospheric greenhouse gas coherent detection meter of the present invention, wherein: 1-light tube, 2-sun tracker, 3-collimating optical telescope, 4-chopper, 5-optical fiber Combiner, 6-local oscillator laser, 7-driver, 8-sawtooth wave voltage, 9-high-speed photodetector, 10-RF/DC splitter, 11-multistage RF amplifier, 12-square law detector, 13 -Video amplifier, 14-lock-in amplifier, 15-A/D converter, 16-microprocessor, 17-switch signal pulse generator, 18-coaxial cable.

Fig. 2 is a characteristic absorption spectrum diagram of a section of gas output by the present invention under sawtooth wave modulation.

Detailed ways

The atmospheric greenhouse gas coherent detector shown in Figure 1 includes a light tube 1, a sun tracker 2, a collimating optical telescope 3, a chopper 4, an optical fiber multiplexer 5, a local oscillator laser 6 and its driver 7, and a high-speed detector 9. RF/DC splitter 10, multistage RF amplifier 11, square law detector 12, video amplifier 13, lock-in amplifier 14, A/D converter 15, microprocessor 16, switch signal pulse generator 17 and the same core cable18.

The sun tracker 2 is aimed at the sun, and the sunlight is absorbed and scattered by the components in the atmosphere through the light tube 1 and reaches the collimating optical telescope 3 to be collected; the local oscillator laser 6 is driven by the temperature control of the driver and the current or voltage , emitting a single-frequency narrow-linewidth laser light, which becomes local oscillator light; the collected sunlight and local oscillator light are mixed together by the optical fiber multiplexer 5 and coherently detected by the high-speed photodetector 9 to output an electrical signal, and the output electrical signal The signal includes a radio frequency signal obtained by heterodyne interference and a directly detected direct current signal. The radio frequency signal obtained by heterodyne interference and the directly detected direct current signal are separated by the radio frequency/direct current separator 10, and the radio frequency signal continues to flow to the multistage radio frequency amplifier 11. When the radio frequency signal is sent to a sufficient magnitude, the envelope signal is detected by the square law detector 12. This envelope signal corresponds to the amplitude of the radio frequency. The envelope signal is amplified by the video amplifier and then combined with the periodic pulse signal of the chopper 4 Correlation calculations are carried out in the lock-in amplifier 14, and the calculation results are converted into digital signals by the A/D converter 15 and processed by the microprocessor 16; the sawtooth wave signal 8 generated by the microprocessor 16 tunes the driver 7 of the local oscillator laser Make the local oscillator laser 6 output laser with tunable wavelength to scan the absorption peak of atmospheric greenhouse gas, so that the greenhouse gas coherent detector can output a section of characteristic absorption spectrum curve; the basic absorption spectrum curve uses an inversion algorithm to deduce a certain According to the column concentration of the greenhouse gas, the greenhouse gas concentration profile is obtained according to the prior curve.

Claims (2)

1. A coherent detection meter for atmospheric greenhouse gases, comprising a light tube (1), a sun tracker (2), a collimating optical telescope (3), a chopper (4), an optical fiber multiplexer (5), a local oscillator Laser (6) and its driver (7), high-speed detector (9), RF/DC splitter (10), multi-stage RF amplifier (11), square law detector (12), video amplifier (13), locking Amplifier (14), A/D converter (15), microprocessor (16), switch signal pulse generator (17) and coaxial cable (18); It is characterized in that: The sun tracker (2) is aimed at the sun, and sunlight is absorbed and scattered by various components in the atmosphere through the light tube (1) and then reaches the collimating optical telescope (3) and is collected by it; the local oscillator laser (6) Under the temperature control of the driver and driven by current or voltage, a laser with a narrow linewidth of a single frequency is emitted and becomes local oscillator light; the collected sunlight and local oscillator light are mixed together by a fiber combiner (5) and processed by high-speed photoelectric The detector (9) coherently detects the output electrical signal, and the output electrical signal includes the radio frequency signal obtained by heterodyne interference and the direct current signal equivalent to direct detection, and the radio frequency signal obtained by heterodyne interference and the directly detected direct current signal are detected by radio frequency Separated from the DC splitter (10), the radio frequency signal continues to flow to the multistage radio frequency amplifier (11), and when the radio frequency signal is sent to a sufficient magnitude, the envelope signal is detected by the square law detector (12), and the envelope signal corresponds to The amplitude and envelope signal of the radio frequency are amplified by the video amplifier and then correlated with the periodic pulse signal of the chopper (4) in the lock-in amplifier (14), and the result of the operation is converted into a digital signal by the A/D converter (15) , processed by the microprocessor (16); the sawtooth wave signal (8) generated by the microprocessor (16) tunes the driver (7) of the local oscillator laser so that the local oscillator laser (6) outputs laser light with tunable wavelength, to Scan the absorption peaks of atmospheric greenhouse gases, so that the greenhouse gas coherent detector can output a characteristic absorption spectrum curve; the basic absorption spectrum curve uses an inversion algorithm to deduce the column concentration of a certain greenhouse gas in the entire atmosphere, and obtains the greenhouse gas according to the prior curve. Gas concentration profile. 2. A kind of atmospheric greenhouse gas coherent detection meter according to claim 1, is characterized in that: described local oscillator laser (6) is DFB distribution feedback semiconductor laser, DBR distribution Bragg reflection semiconductor laser or L-band DFB distribution Feedback fiber laser.