CN102830107B - Laser radar detection method and system for measuring contents of solid water and liquid water in cloud - Google Patents

Abstract

The invention designs a laser radar detection method and system for measuring the solid and liquid water content in the cloud. The present invention utilizes the difference between the solid and liquid Raman scattering frequency shifts of water, uses the Surelite II-20 laser as the laser emission source to generate laser radiation with a wavelength of 355nm, and passes through the four detection channels of the optical receiving part: among them, two water detection channels , using narrow-band filters to detect the characteristic Raman echo signals of solid and liquid phases of water, the elastic scattering channel is used to detect the optical properties of aerosols or clouds, and the nitrogen Raman channel is used to detect the Raman of nitrogen Scattered light is used to normalize the Raman scattering signal of water to detect the phase state of water in clouds. Finally, the solid and liquid content of water in the cloud is inverted by the solid and liquid Raman scattering principle of water.

Description

Lidar detection method and system for measuring solid and liquid water content in clouds

Technical field:

The invention designs a laser radar detection method and system for measuring the solid and liquid water content in the cloud. The present invention utilizes the difference in Raman scattering frequency shift between solid and liquid water, and obtains the contents of solid and liquid water in clouds through narrow-band optical filters and different phase state inversion techniques of water. The present invention uses a Surelite II-20 laser as a laser emission source to generate laser radiation with a wavelength of 355nm, which passes through four detection channels of the optical receiving part: among them, two water detection channels use narrow-band filters to detect two phases of solid and liquid respectively The characteristic Raman echo signal of state water, the elastic scattering channel is used to detect the optical characteristics of aerosol or cloud, the nitrogen Raman channel is used to detect the Raman scattered light of nitrogen, and is used to normalize the Raman scattering signal of water ; To detect the phase state of water in the cloud. Finally, the solid and liquid content of water in the cloud is inverted by the solid and liquid Raman scattering principle of water.

Background technique:

The formation and evolution of clouds is a concrete manifestation of the movement process in the atmosphere and an important sign that indicates future weather changes. With the help of cloud observation, it is of great significance to correctly judge the movement of the atmosphere, especially for short-term nowcasting. In terms of artificial weather modification, only by fully grasping the parameter information of clouds can artificial weather modification activities be carried out more effectively. In terms of climate research, clouds have a radiative forcing effect, which affects the balance of payments of the Earth system, thereby affecting climate change. Studies have shown that global temperature changes caused by cloud radiation are more than three times greater than the effect of carbon dioxide. In terms of model research, the physical characteristics and processes of clouds are also an important topic, and the correct parameterization of cloud information is very important for global models and regional weather forecast models. Cloud parameters can be observed from the ground or space-based. Therefore, cloud parameter information, such as cloud height, cloud thickness, and cloud microphysical characteristics, is an important basis for testing numerical weather prediction and weather models.

For the detection of clouds, in addition to the detection of macroscopic physical characteristics such as cloud height, cloud thickness, and cloud shape, what needs to be solved urgently is the detection of microphysical structure information inside clouds, such as the phase state of water in clouds, water content, and water content. particle size distribution etc. The phase information of water in clouds is an important description parameter of clouds. Ice crystals or water droplets in clouds are the main substances in clouds, and the influence of clouds on atmospheric radiative transfer is mainly caused by the scattering and absorption of ice crystals or water droplets. According to the particle scattering theory, ice crystals or water droplets with different sizes and contents have different scattering characteristics, and the radiation effects caused by them are also different, and the size and content of ice crystals and water droplets in clouds vary with the atmospheric environment and cloud types, so , the content and particle size of water in clouds are very important to study the radiation effect of clouds. If the water content in the cloud is known, assuming that the particle size distribution of the water in the cloud satisfies a certain relationship, then the particle size spectrum distribution of the water in the cloud and the water content can be obtained by a simple mathematical relationship. Therefore, the study of water in the cloud The issue of content becomes critical.

So far, there are many ways to observe clouds. Satellite remote sensing has its own advantages. It can observe the global cloud distribution from satellite orbits. However, in terms of cloud phase detection, it can only classify clouds into water phase, ice phase, or mixed phase from a macroscopic point of view. Microscopically determine the phase state of cloud hydrometeor particles, and there are many problems in cloud classification, cloud overlap processing, low cloud observation, etc., large areas of snow/ice on the surface, the appearance of inversion layers, etc. Passive observations have a big impact. The airborne cloud droplet measuring instrument is a commonly used instrument in weather modification. It can measure various parameters of clouds on the flight path of the aircraft, mainly cloud droplet particle size spectrum, water content, etc. The advantage of the airborne cloud droplet particle detector is that it can directly measure the cloud droplet particles, and the result is relatively accurate. In addition, the aircraft can fly through the clouds to obtain cloud particle parameters in a large range. The disadvantage is that the detection cost of the aircraft is too high, and the Limited by air traffic control, there are not many opportunities to fly. As far as cloud ground observation is concerned, the most common method in meteorological operations is manual observation. Observers judge cloud height and cloud amount by judging cloud shape and comparing it with the target object. However, the temporal and spatial resolution of artificial observation is low, and the judgment of cloud height is not as accurate as that of instrumental measurement, and the judgment of cloud amount is subject to the subjective influence of observation and the limitation of the position of the observer. Grohe and All Sky Imager replaced. The ceilometer and the all-sky imager measure the macroscopic physical characteristics of the cloud, and do not involve the microphysical structure information inside the cloud. The radiosonde is to bring the cloud observation instrument into the cloud by the lift force of the balloon, and the cloud parameter sensor will transmit the measured relevant parameters back to the ground. The sounding method of cloud measurement can accurately obtain information such as cloud height, water content, and cloud particle size distribution, but the disadvantage is that the temporal and spatial resolution is low. Microwave radiometer is a commonly used passive observation instrument, which can be used to retrieve cloud water content. However, as a passive remote sensing device, microwave radiometer still needs to be improved in terms of detection capability and spatial resolution. Ordinary weather radar has limited ability to detect clouds due to its wavelength limitation. With the development of millimeter wave technology, millimeter wave radar has become a powerful tool for cloud observation. Compared with ordinary weather radar, millimeter wave radar has a shorter wavelength and better performance. Interacting with the water droplets and ice crystals in the cloud, coupled with scanning equipment, the millimeter-wave radar can detect the relevant parameters of the cloud within tens of kilometers centered on the radar. In order to facilitate on-the-spot observation, millimeter-wave radars are mostly made in the form of square cabins, which are convenient for hauling. NASA launched Cloudsat satellites with millimeter-wave radars as satellite payloads, which can measure global cloud distribution.

As far as the continuous observation of the microphysical characteristics of clouds is concerned, millimeter-wave radar is recognized as an effective detection device at present. Lidar has more advantages than millimeter-wave cloud radar: in terms of spatial resolution, the laser pulse width is calculated according to 10ns, and its distance resolution limit is 1.5m, which is higher than the spatial resolution of millimeter-wave radar; in terms of wavelength, millimeter-wave radar's The electromagnetic wavelength is 3mm or 8mm (domestic), which is generally much larger than the size of the particles in the cloud. The strength of the interaction between the two is bound to be limited, which restricts the detection ability of the millimeter-wave radar for small particles and thin clouds, while the laser radar generally uses The laser with a wavelength of less than 1 micron can better interact with the particles in the cloud, and can be used to monitor small particles and thin clouds in the early stage of cloud formation that cannot be observed by millimeter-wave radar; in terms of the mode of action, due to the high peak power of the laser, In addition to the traditional elastic effect (elastic scattering), nonlinear effects (Raman effect) may also be excited, which enriches the detection wavelength and can obtain more information about water in clouds; in terms of technology maturity, the key technology of millimeter-wave radar, especially It is the problem of magnetron life and cost, which is the main factor restricting the application of domestic millimeter-wave radar. Due to the high cost and maintenance cost, only a few domestic units currently have cloud-measuring millimeter-wave radar. Compared with millimeter-wave radar, The various technologies of lidar are relatively mature, the system is simple, and the operation and maintenance costs are low, so it has certain advantages in application and promotion.

Micropulse lidar for cloud and aerosol detection started earlier abroad, and the technology of non-spherical particle depolarization is relatively mature abroad. Most of the relevant sites in several observation programs in the United States and Europe have polarization lidar. Raman lidar with polarization channel can qualitatively describe the phase state of water in clouds, but to accurately obtain the water content in water vapor requires the knowledge of water spectroscopy (absorption spectrum or Raman scattering spectrum). Compared with water vapor differential absorption lidar, water vapor Raman lidar has advantages in system complexity and cost. Therefore, there are many researches on water vapor Raman lidar at home and abroad. The water vapor Raman lidar mainly measures the water vapor content in the atmosphere, and inside the cloud, the phases of water are mainly liquid water and solid water. Object lidar system. The present invention detects the Raman scattering spectrum of solid and liquid water in clouds, and establishes a laser radar system that can be used to quantitatively detect the contents of solid water and liquid water in clouds. Carry out calibration and develop an inversion algorithm for the water content in separated phases in clouds. The invention uses Raman technology to quantitatively obtain the solid and liquid water content in clouds, which is of great significance to the study of cloud microphysics and fills the gap in the detection of water phase state in clouds in my country.

Invention content:

The purpose of the present invention is to provide a laser radar detection method and system for measuring the solid and liquid water content in clouds. The detection channel detects the characteristic Raman echo signals of solid and liquid phase water respectively. The invention inverts the solid and liquid content of water in the cloud according to the Raman scattering signal intensity of the solid and liquid water detection channel.

Technical solution of the present invention is as follows:

A lidar detection system for measuring solid and liquid water content in clouds, the detection system comprising:

1) The main control system is used to set the working mode of the system, including the detection mode of the laser transceiver system and the working mode of the laser, and send commands to the lower computer; the main control system includes a data analysis module, which analyzes the collected data in real time, and according to Inversion principle of solid and liquid water in clouds, real-time calculation and display of solid and liquid water content in clouds;

2) The laser emission system adjusts the working mode and laser energy of the laser according to the settings of the main control system;

3) The laser receiving system is used to collect atmospheric echo intensity signals at different distances and Raman scattering signals of water in clouds, and send them to the detection channel through the subsequent optical path;

4) The photoelectric detection system receives the optical signals of each detection channel, converts them into electrical signals and sends them to the data acquisition and analysis system;

5) The data acquisition system uses a photon counting card and a high-speed AD acquisition card to collect the signals detected by the photoelectric detection system and sends them to the data analysis system.

Wherein, the receiving system adopts the Meade LX200 telescope with high light reflection efficiency and the subsequent optical path of the narrow-band filter.

Wherein, the photoelectric detection system is divided into four detection channels, respectively receiving elastic scattering of atmospheric molecules, aerosols and clouds; Raman scattering of liquid water; Raman scattering of solid water and Raman scattering of nitrogen molecules.

Wherein, each of the four detection channels includes a lens, a filter and a photomultiplier tube. The transmission center wavelengths of the filters of the four detection channels are different. The first to fourth channels are 355nm, 401nm, 404nm, 386.7nm, 355nm corresponds to the elastic scattering wavelength, 401nm corresponds to the solid water Raman scattering wavelength, and 404nm corresponds to the liquid state Water Raman scattering wavelength, 386.7nm corresponds to the nitrogen Raman scattering wavelength in the atmosphere.

The present invention measures the lidar detection method of solid and liquid water content in cloud, and this method comprises the following steps:

1) Use the main control program to select the working mode of the laser, the acquisition mode of the receiving system and the initial value setting of the inversion water-solid and liquid content, and send instructions to the laser emitting system and the laser receiving system;

2) Use the laser emission system to control (SureliteⅡ-20) laser to emit pulsed laser with a wavelength of 355nm at a repetition rate of 20Hz;

3) Use the transceiver coaxial (Meade LX200) telescope in the laser receiving system to receive echoes at different distances;

4) Use the spectroscope and filter to send the echo signal into four detection channels respectively: channel 1 receives the elastic scattering of atmospheric molecules, aerosols and clouds, which is called the elastic scattering channel; channel 2 receives the Raman scattering of liquid water, which is called It is a liquid water detection channel; channel 3 receives Raman scattering of solid water and is called a solid water detection channel; channel 4 receives Raman scattering of nitrogen molecules, which is used to normalize the signal intensity of solid and liquid water detection channels;

5) The echo signal received by each channel passes through the photoelectric detection system, converts the optical signal into an electrical signal, and sends it to the data acquisition system;

6) The data acquisition system uses the data acquisition card (NI with a sampling rate of 10M) to collect the elastic scattering signal of channel 1, and uses two (P7882) photon counting cards to count the signals of the other three Raman channels;

7) The main control system analyzes the collected data in real time, and according to the inversion principle of solid and liquid water in the cloud, combined with the calibration results of the Raman lidar system, calculates and displays the content of solid and liquid water in the cloud in real time, and Save the results in real time.

Among them, according to the ratio R of the output of channel 3 and channel 2, the ratio of solid and liquid water is calculated, and the output of the two channels is corrected for spectral overlap, and the results are directly substituted into the single-phase solid and liquid water inversion algorithm for inversion. Determine the solid and liquid water content of clouds.

Wherein, the inversion algorithm is as follows: the lidar equation of solid-state water Raman scattering is written as:

(1)

Among them, R is the detection height, P _ice is the Raman scattered optical power of solid water received by the Raman cloud measuring system, P ₀ is the emission power of the laser, C _ice is the system constant of the Raman lidar, and σ _ice is the power of solid water Differential scattering cross section, IWC is the water content of solid water, α(υ ₀ , r), α(υ _ice , r) are the extinction coefficients of atmospheric molecules and aerosols for emitted laser light and Raman scattered light;

For the nitrogen Raman channel, the received Raman scattered light power is:

(2)

Each parameter in formula (2) corresponds to each parameter in formula (1), where N _N2 is the density of nitrogen. After sorting and deforming formula (1) and formula (2), the expression of solid water content density is obtained:

(3)

where P _ice (R)/P _N2 (R) is obtained from radar measurements, C _N2 N _N2 (R)σ _N2 (υ ₀ ,υ _N2 ,T)/C _ice σ _ice (υ ₀ ,υ _ice , T) is abbreviated as K, where K is the system parameter, and β(R) is the backscattering coefficient of the molecule, then formula (3) becomes:

(4)

From formula (4), to obtain the content of solid water in the cloud, the process of obtaining the system parameter K of the Raman cloud lidar is the calibration of the lidar system. Lidar system calibration mainly uses millimeter-wave radar and sounding balloons.

Compared with the prior art, the present invention has the advantages that:

1. Use narrow-band filters to realize the separation and detection of Raman signals in 4 channels, to achieve effective detection of the solid and liquid content of water in clouds, and to fill the gap in the detection of water phase states in clouds in China;

2. By using sounding balloons to carry detection instruments for low clouds to detect water in clouds, and for high clouds to use millimeter wave cloud radar to detect, so as to achieve accurate calibration of Raman lidar system parameters.

3. It can realize the detection of the water phase state in the cloud with high spatial resolution and high time resolution.

4. The present invention can implement round-the-clock unattended monitoring.

Description of drawings:

Fig. 1 is a system block diagram of the present invention.

Fig. 2 is a main control flow chart of the present invention.

In Figure 1: L is the lens; BS is the filter group; F is the filter group plate; M is the total mirror; channel 1 is the elastic scattering channel; channel 2 is the liquid water detection channel; channel 3 is the solid water detection channel; channel 4 is a nitrogen Raman channel; PMT is a photomultiplier tube.

Detailed ways:

The present invention utilizes the difference between the solid and liquid Raman scattering frequency shifts of water, uses the Surelite II-20 laser as the laser emission source to generate laser radiation with a wavelength of 355nm, sets the laser working mode and system initial value setting through the main control system, and uses the telescope The backscattering signal of the cloud is received, and the backscattering signal becomes parallel light through the lens. The optical receiving part has 4 detection channels in total, and two of the water detection channels use narrow-band filters to detect the solid and liquid phases of water respectively. The characteristic Raman echo signal of , the elastic scattering channel is used to detect the optical characteristics of aerosol or cloud, the nitrogen Raman channel is used to detect the Raman scattered light of nitrogen, and is used to normalize the Raman scattered signal of water. The three Raman channels of the lidar system use two photon counting cards for photon counting, and the elastic scattering channel uses a high-speed AD acquisition card for acquisition. And the solid and liquid content of water in the cloud is inverted by the solid and liquid Raman scattering principle of water.

The system consists of a main control system, a SureliteⅡ-20 laser, a laser emitting system, a laser receiving system, a photoelectric detection system, a data acquisition system, and a data analysis system. Among them, each system is an independent unit, and the whole is controlled by the main control system computer to ensure the stability of the system. Wherein, the emission wavelength of the laser is 355nm. Among them, the receiving system adopts the Meade LX200 telescope with high light reflection efficiency and the subsequent optical path such as narrow-band filter. Wherein, the data analysis display is completed by the data analysis system integrated in the main control system on the main control computer.

The premise of using this system for detection is that when the laser is in good working condition, using the difference in the frequency shift of the solid and liquid Raman scattering of water, use a narrow-band filter to detect the characteristic Raman echoes of the solid and liquid phases of water. Signal, through the solid and liquid Raman scattering principle of water to invert the solid and liquid content of water in the cloud. The specific steps are:

Set the initial start information such as laser working mode, system working time, system initial value, and inversion initial value in the main control system program. The laser emission system controls the Surelite II-20 laser to produce laser radiation with a wavelength of 355nm. The echoes at different distances are received by the Meade LX200 telescope with a different axis of transmission and reception. The echo signal is turned into parallel light by the lens, and sent to 4 detection channels respectively. Two of the water detection channels use narrow-band filters to detect the characteristic Raman echo signals of solid and liquid phase water respectively. Elastic scattering The channel is used to detect the optical characteristics of aerosol or cloud, and the nitrogen Raman channel is used to detect the Raman scattered light of nitrogen, which is used to normalize the Raman scattered signal of water. The echo received by each channel passes through the photoelectric detection system to convert the optical signal into an electrical signal. In the data acquisition system, a NI data acquisition card with a sampling rate of 10M is used to collect elastic scattering signals, and two P7882 photon technology cards are used to count three Raman channels. The collected data is analyzed by the data analysis system, and the solid and liquid contents of water in the cloud are reversed through the solid and liquid Raman scattering principle of water, and displayed on the main control interface. At the same time, the original data and analysis results are controlled by the main control The system organizes and saves.

Embodiment one:

As shown in Figure 1, the lidar detection system of the present invention measures solid and liquid water content in the cloud, and this detection system comprises:

1) The main control system is used to set the working mode of the system, including the light output mode of the laser emission system and the detection mode of the photoelectric detection system. Before the system works, the main control system sends the setting command to the lower computer; the data analysis system is the main control system A software module, which analyzes the collected data in real time, and calculates and displays the content of solid and liquid water in the cloud in real time according to the inversion principle of solid and liquid water in the cloud; the main control system also completes the analysis of the collected data and analysis results are stored and processed in real time;

2) The laser emission system adopts SureliteⅡ-20 laser, and the emission wavelength is 355nm. The control system of the laser emission system can be used as a lower computer to receive setting commands from the upper computer to adjust the working mode and laser energy of the laser;

3) The laser receiving system adopts the Meade LX200 telescope with high reflective efficiency and the narrow-band filter and other subsequent optical paths. Considering the optical efficiency, each part is coated with a corresponding full-reflection film or anti-reflection film to collect atmospheric returns at different distances. The wave intensity signal is sent to each detection channel through the subsequent optical path;

4) The photoelectric detection system uses EMI9214 photomultiplier tubes to receive the optical signals of each detection channel and convert them into electrical signals and send them to the data acquisition and analysis system. It is divided into 4 detection channels to receive atmospheric molecules, aerosols, Elastic scattering of clouds, Raman scattering of liquid water, Raman scattering of solid water and Raman scattering of nitrogen gas molecules. ;

5) The data acquisition system uses a photon counting card (P7882) and a high-speed AD acquisition card (NI5105) to collect the signal detected by the photoelectric detection system, and sends the signal to the data analysis system.

Embodiment two:

As shown in Figure 2, the laser radar detection method of the present invention measures solid and liquid water content in the cloud, the method comprises the following steps:

1) Use the main control program to select the working mode of the laser, the acquisition mode of the receiving system, and the initial value setting of the inverted water-solid and liquid content, etc., and send instructions to the laser emitting system and the laser receiving system;

2) Use the laser emission system to control the SureliteⅡ-20 laser to emit pulsed laser light with a wavelength of 355nm at a repetition rate of 20Hz;

3) Use the coaxial Meade LX200 telescope in the laser receiving system to receive echoes at different distances;

4) Use the spectroscope and filter to send the echo signal into 4 detection channels: channel 1 receives the elastic scattering of atmospheric molecules, aerosols and clouds, which is called the elastic scattering channel, through which the extinction coefficient profile can be obtained, Used for attenuation correction of Raman scattering signals. Channel 2 receives the Raman scattering of liquid water and is called liquid water detection channel. The interference filter F2 in front of PMT2 has a center wavelength of λ _L and a passband bandwidth of 0.2nm. Channel 3 receives the Raman scattering of solid water and is called the solid water detection channel. The interference filter F3 in front of PMT3 has a central wavelength of λ _I and a passband bandwidth of 0.2nm. Channel 4 receives Raman scattering of nitrogen molecules and is used to normalize solid and liquid water detection channels. Corresponding narrow-band interference filters are also placed in front of channel 1 and channel 4 to filter out noise.

5) Pass the echo signal received by each channel through the photoelectric detection system to convert the optical signal into an electrical signal;

6) Use the NI data acquisition card (NI5105) with a sampling rate of 10M to collect elastic scattering signals, and use two P7882 photon technology cards to count the three Raman channels;

7) The data analysis module of the main control system will analyze the collected data in real time, and calculate and display the content of solid and liquid water in the cloud in real time according to the inversion principle of solid and liquid water in the cloud;

Among them, the laser emitting system SureliteⅡ-20 emits 355nm laser, and the telescope Meade LX200 is used to receive the backscattering signal of the cloud, and the backscattering signal becomes parallel light through the lens. The optical receiving part has 4 detection channels, two of which are water detection channels , using narrow-band filters to detect the characteristic Raman echo signals of solid and liquid phases of water, the elastic scattering channel is used to detect the optical properties of aerosols or clouds, and the nitrogen Raman channel is used to detect the Raman of nitrogen Scattered light is used to normalize the Raman scattering signal of water. The three Raman channels of the lidar system use two photon counting cards (P7882) for photon counting, and the elastic scattering channel uses a high-speed AD acquisition card (NI5105) for acquisition. The lidar system can be used to realize the simultaneous observation of the solid and liquid water content in the cloud.

Among them, the photodetection system uses a photodetector system with high quantum efficiency and wide response spectrum.

Among them, for liquid water detection and solid water detection channels, the extreme weather observation time windows (ice clouds with only solid water and water clouds with only liquid water) were selected respectively, combined with millimeter-wave cloud radar and balloon sounding, respectively Calibrate the liquid water detection channel and the solid water detection channel.

Among them, the photon counting card of the data acquisition system adopts a data acquisition device with a peak photon detection efficiency > 70% and a time resolution > 300ps. The collected data information is connected with the main control program. According to the inversion of solid and liquid water in the cloud Principle, calculate and display the content of solid and liquid water in the cloud in real time.

Among them, the initial value setting of the inversion water solid and liquid content in the main control system is determined according to the Raman scattering characteristics of solid and liquid water to identify the Raman scattering wavelength of a certain phase state, and the Raman scattering wavelength of solid and liquid water The selection can be carried out by calculating the ratio of the Raman scattering spectra of solid and liquid water. When the ratio of solid and liquid (I _i -I _l )/(I _l + I _i ) is the maximum R _max , the wavelength is selected as the wavelength of solid water. Raman characteristic wavelength λ _I , on the contrary, when the solid-liquid ratio is minimum R _min , this wavelength is selected as the Raman scattering wavelength λ _L of liquid water.

The inversion method of solid and liquid water in clouds is as follows. The lidar equation of solid water Raman scattering can be written as:

(1)

Among them, R is the detection height, that is, the height of the detection point from the ground, which can be measured by lidar; P _ice is the Raman scattered optical power of solid water received by the Raman cloud measuring system, which can be measured through the detection channel 3; P ₀ is the emission power of the laser, C _ice is the system constant of Raman lidar, σ _ice is the differential scattering cross section of solid water, IWC is the water content of solid water, α(υ ₀ , r), α(υ _ice , r) are The extinction coefficients of atmospheric molecules and aerosols for emitted laser light and Raman scattered light can be measured through detection channel 1.

For the nitrogen Raman channel, that is, the fourth detection channel, the received Raman scattered light power is: the parameters in each equation are clearly defined, the known ones need to be given, and the unknown ones are given the calculation method

(2)

Each parameter in formula (2) corresponds to each parameter in formula (1), where N _N2 is the density of nitrogen. By arranging and deforming formula (1) and formula (2), the expression of solid water content density can be obtained:

(3)

where P _ice (R)/P _N2 (R) can be obtained from radar measurements, C _N2 N _N2 (R)σ _N2 (υ ₀ ,υ _N2 ,T)/C _ice σ _ice (υ ₀ ,υ _ice ,T) can be abbreviated as K, where K is the system parameter, β(R) is the backscattering coefficient of the molecule, then formula (3) can be changed to:

(4)

From formula (4), in order to obtain the content of solid water in the cloud, it is necessary to know the system parameter K of the Raman cloud lidar. The process of obtaining K is called system calibration. The calibration of the lidar system mainly uses millimeter-wave radar and sounding balloons . The calibration process of the system parameter K is as follows: for low clouds, the sounding balloon can be used to carry the detection instrument to detect the water in the clouds; for high clouds, the millimeter-wave cloud radar can be used to measure the cloud by selecting specific cloud samples for observation. The water content in the system, combined with the measurement results of each channel of the laser radar, and through the above inversion formula, the system parameter K is calculated. The above algorithm is an inversion algorithm for solid water, and for a single liquid water, the algorithm is the same and will not be repeated here.

For mixed-phase clouds, when lidar measures mixed-phase clouds, due to the overlap of Raman spectra of solid and liquid water, part of the Raman scattering of liquid water enters the solid water detection channel, and part of the Raman of solid water Raman scattering into the liquid water detection channel. To use the above inversion method for single-phase water, it is first necessary to correct the detected values of solid and liquid water. According to the research on the Raman spectrum of solid and liquid water, the ratio of ice cloud is R _max , the ratio of water cloud is R _min , the ratio R between solid and liquid water is greater than R _min and less than R _max , the ratio of R and the two It is related to the mixing ratio between them, and a mathematical model can be established to establish a one-to-one correspondence between the ratio of solid and liquid water and R. Therefore, when performing lidar observations on mixed-phase water, first use the established mathematical model to calculate the ratio of solid to liquid water based on the ratio R of the output of the solid and liquid channels. Spectral overlap correction, the corrected results can be directly brought into the single-phase solid and liquid water inversion algorithm for inversion.

The present invention utilizes the difference between the solid and liquid Raman scattering frequency shifts of water, uses the Surelite II-20 laser as the laser emission source to generate laser radiation with a wavelength of 355nm, and passes through the four detection channels of the optical receiving part: among them, two water detection channels , using narrow-band filters to detect the characteristic Raman echo signals of solid and liquid phases of water, the elastic scattering channel is used to detect the optical properties of aerosols or clouds, and the nitrogen Raman channel is used to detect the Raman of nitrogen Scattered light is used to normalize the Raman scattering signal of water to detect the phase state of water in clouds. And the solid and liquid content of water in the cloud is inverted by the solid and liquid Raman scattering principle of water.

Claims (6)

1. an Airborne Lidar examining system of measuring solid, liquid state liquid water content in cloud, this detection system comprises:

1) master control system, for system operating mode is set, comprises laser transmitting-receiving system detection mode, laser works mode, and order is sent to slave computer; Master control system comprises data analysis module, and the data of collection are carried out to real-time analysis, and according to the inversion principle of solid, liquid state water in cloud, calculates in real time and show the content of solid, liquid state water in cloud;

2) laser transmitting system, according to the setting of master control system, adjusts working method and the laser energy of laser instrument;

3) laser receiver system, effect is to collect the atmosphere echo signal intensity at different distance place, the Raman scattering signal of Yun Zhongshui, and is sent to detection channels by follow-up light path;

4) Photodetection system, receives the light signal of each detection channels, and converts electric signal to and be sent to data acquisition and analysis system; This Photodetection system is divided into four detection channels, receives respectively the elastic scattering of atmospheric molecule, gasoloid, cloud; The Raman scattering of aqueous water; The Raman scattering of solid water and the Raman scattering of nitrogen molecule;

5) data acquisition system (DAS), adopts photon counting card and high-speed AD acquisition card to gather the signal that Photodetection system is surveyed, and sends to data analysis system.

2. Airborne Lidar examining system according to claim 1, wherein, described receiving system adopts Meade LX200 telescope and the follow-up light path of narrow band pass filter of high reflector efficiency.

3. Airborne Lidar examining system according to claim 1, wherein, in described four detection channels, each detection channels includes a slice lens, a tablet filter and a photomultiplier.

4. a laser radar detection method of measuring solid, liquid state liquid water content in cloud, the method comprises the following steps:

1) utilize primary control program to select the initial value design of the working method of laser instrument, the acquisition mode of receiving system and inverting water solid, liquid state content, and send instruction to laser transmitting system and laser receiver system;

2) utilize laser transmitting system to control laser instrument and take the pulse laser that the repetition frequency emission wavelength of 20Hz is 355nm;

3) utilize the echo of receiving and dispatching coaxial telescope reception different distance place in laser receiver system;

4) utilize spectroscope and optical filter that echoed signal is sent into respectively to 4 detection channels: the elastic scattering that passage 1 receives atmospheric molecule, gasoloid, cloud is called elastic scattering passage; The Raman scattering that passage 2 receives aqueous water is called aqueous water detection channels; The Raman scattering that passage 3 receives solid water is called solid water detection channels; Passage 4 receives the Raman scattering of nitrogen molecule;

5) echoed signal that each passage receives, by Photodetection system, is converted into electric signal by light signal, and gives data acquisition system (DAS);

6) data acquisition system (DAS) is utilized the elastic scattering signal of data collecting card acquisition channel 1, utilizes two photon counting cards to count the signal of another three Raman passages;

7) master control system is carried out real-time analysis to the data that gather, and according to the inversion principle of solid, liquid state water in cloud, in conjunction with the calibration result of Raman laser radar system, calculate in real time and show the content of solid, liquid state water in cloud, and result is carried out preserving and processing in real time.

5. laser radar detection method according to claim 4, wherein, according to the ratio R of passage 3, passage 2 outputs, calculate the ratio of solid, liquid state water, two passage outputs are carried out to spectra overlapping correction, the single phase solid, liquid of the direct substitution of result state water inversion algorithm carries out inverting, can determine solid, liquid state liquid water content in cloud.

6. laser radar detection method according to claim 5, wherein, described inversion algorithm is as follows: the laser radar equation of solid water Raman scattering is written as:

$P_{\mathrm{ice}}\left(R\right)=\frac{C_{\mathrm{ice}}{P}_0\mathrm{IWC}{\mathrm{\σ}}_{\mathrm{ice}}({\mathrm{\υ}}_0,{\mathrm{\υ}}_{\mathrm{ice}},T)}{R^2}\×\exp (-{\∫}_0^R(\mathrm{\α}({\mathrm{\υ}}_0,r)+\left(\mathrm{\α}({\mathrm{\υ}}_{\mathrm{ice}},r)\right)\mathrm{dr})---\left(1\right)$

Wherein R is for surveying height, P _icefor Raman is surveyed the Raman scattering luminous power of the solid water that cloud system receives, P ₀the emissive power of laser, C _icethe system constants of Raman lidar, σ _icefor the differential scattering of solid water, IWC is solid water water cut, α (υ ₀, r), α (υ _ice, r) be atmospheric molecule and the gasoloid extinction coefficient to Emission Lasers and Raman diffused light;

For nitrogen Raman passage, the Raman scattering luminous power that it receives is:

$P_{N_2}\left(R\right)=\frac{C_{N_2}{P}_0{N}_{N_2}\left(R\right){\mathrm{\σ}}_{N_2}({\mathrm{\υ}}_0,{\mathrm{\υ}}_{N_2},T)}{R^2}\×\exp (-{\∫}_0^R(\mathrm{\α}({\mathrm{\υ}}_0,r)+\left(\mathrm{\α}({\mathrm{\υ}}_{N_2},r)\right)\mathrm{dr})---\left(2\right)$

In formula (2), each parameter is corresponding respectively with each parameter in formula (1), wherein, and N _n2the density of nitrogen; By formula (1) and formula (2) through arranging, distortion, obtain solid water containing the expression formula of metric density:

$\mathrm{IWC}=\frac{P_{\mathrm{ice}}}{P_{N_2}}\frac{C_{N_2}{N}_{N_2}\left(R\right){\mathrm{\σ}}_{N_2}({\mathrm{\υ}}_0,{\mathrm{\υ}}_{N_2},T)}{C_{\mathrm{ice}}{\mathrm{\σ}}_{\mathrm{ice}}({\mathrm{\υ}}_0,{\mathrm{\υ}}_{\mathrm{ice}},T)}\×\exp (-{\∫}_0^R(\mathrm{\α}({\mathrm{\υ}}_{N_2},r)-\left(\mathrm{\α}({\mathrm{\υ}}_{\mathrm{ice}},r)\right)\mathrm{dr})---\left(3\right)$

In formula, P _ice(R)/P _n2(R) from radargrammetry, obtain C _n2n _n2(R) σ _n2(υ ₀, υ _n2, T)/C _iceσ _ice(υ ₀, υ _ice, T) be abbreviated as K, wherein K is systematic parameter, the backscattering coefficient that β (R) is molecule, formula (3) becomes:

$\mathrm{IWC}=\frac{P_{\mathrm{ice}}}{P_{N_2}}\mathrm{K\β}\left(R\right)\×\exp (-{\∫}_0^R(\mathrm{\α}({\mathrm{\υ}}_{N_2},r)-\left(\mathrm{\α}({\mathrm{\υ}}_{\mathrm{ice}},r)\right)\mathrm{dr})$

By formula (4), obtain the content of solid water in cloud, wherein obtain Raman and survey the demarcation that the process of the systematic parameter K of cloud laser radar is laser radar system.