Liquid water content inversion method based on airborne Ka-band precipitation cloud radar

Abstract

The present invention relates to a liquid water content inversion method based on an airborne Ka-band precipitation cloud radar. The full-size distribution measured in situ by an aircraft and the reflectivity of the airborne precipitation cloud radar are mainly used to clearly separate the reflectivity Z contributed by different hydrometeors from the total reflectivity measured by the airborne Ka-band precipitation cloud radar, and then the relationship between the mass concentration M and the reflectivity Z of each hydrometeor is obtained from the in situ measurement. The Z-M relationship of liquid water is applied to the separated liquid water echo to obtain the liquid water content of the entire vertical profile in the cloud. The method can significantly reduce the discreteness between the liquid water content and the reflectivity, thereby more accurately determining the liquid water content in the cloud.

Description

Technical Field

[0001] The invention belongs to the field of meteorology, and in particular relates to a liquid water content inversion method based on an airborne Ka-band precipitation cloud radar. Background Art

[0002] Liquid water content is an important cloud microphysical parameter. It is an important factor in determining the amount of precipitable water in clouds, and has a significant impact on aircraft safety, climate change, and artificial weather modification. Detecting the liquid water content in clouds is of great significance for monitoring and early warning of disastrous weather, commanding artificial weather modification operations, and finding the best operating area for human shadow catalysis.

[0003] Regarding the inversion method of liquid water content, there are currently three main different radar inversion methods: using the summarized Z-LWC empirical formula, using the joint inversion of cloud radar and microwave radiometer, and using the relationship between the reflectivity factor Z and the cloud droplet number concentration and particle diameter.

[0004] Previous studies used the empirically determined Z-LWC relationship to deduce cloud liquid water content from the measured total reflectivity, but this relationship is mainly determined by the particle size distribution, and Z is mainly weighted on larger particles, which leads to a large discreteness in the empirical relationship, so that there is a large uncertainty in extracting LWC from radar reflectivity. Liquid water content is inverted by cloud radar and microwave radiometer. This method is mainly applicable to non-precipitating clouds or weak precipitation clouds. When the precipitation intensity is too large, the data quality of the microwave radiometer is very poor and accurate liquid water content cannot be obtained. In addition, the joint inversion algorithm will produce large errors in mixed-phase clouds, and this method also fails to take into account the influence of particles in different phases on liquid water content. According to the relationship between the reflectivity factor and the cloud droplet number concentration and particle diameter, this method is not applicable to all clouds, and does not take into account the influence of particles in different phases on liquid water content. Summary of the invention

[0005] In view of the above-mentioned deficiencies of the prior art, the present invention proposes a liquid water content inversion method based on an airborne Ka-band precipitation cloud radar, comprising the following steps:

[0006] Based on three in-situ probes, namely, the airborne Ka-band precipitation cloud radar and fast cloud droplet probe, the two-dimensional stereo optical array imaging probe and the high-capacity spectral particle probe, the joint inversion of the liquid water content in the cloud includes:

[0007] Step 1: Calculate the reflectivity of non-precipitation particles using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe. Then, the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of the Ka-band precipitation cloud radar is obtained by fitting as follows:

[0008] log(FZ,np )=-0.087dBZ total -3.55

[0009] Among them, F Z,np The reflectivity ratio contributed by non-precipitation water, dBZ total is the total reflectivity Z measured by Ka-band precipitation cloud radar total Take the logarithm 10lgZ total The value after

[0010] Step 2: According to the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of Ka-band precipitation cloud radar, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo. np and precipitation particle echo Z p ;

[0011] Step 3: Determine the relationship between the cloud top temperature and the freezing temperature, and obtain the liquid water content in the cloud based on the determination result;

[0012] Step 4: For a given particle size distribution, the total mass concentration of the particles is obtained by summing the particle concentration of each probe at each level and the corresponding particle diameter;

[0013] From the particle size distribution observed in situ, it can be obtained that the total mass concentration is related to the echo intensity of separated liquid water, ice and precipitation particles, and the relationship between them is obtained, namely:

[0014] log(M lwc )=0.073dBZ lw +1.22

[0015] log(M ice )=0.094dBZ ice +2.55

[0016] log(M pre )=0.082dBZ pre -0.2

[0017] Among them, M lwc ,M ice ,M pre is the mass concentration of particles in different phases, dBZ lw ,dBZ ice ,dBZ pre Z lw , Z ice , Z pre Take the logarithm of the value.

[0018] Furthermore, step 1 calculates the reflectivity of non-precipitation particles based on the Mie scattering model using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe:

[0019]

[0020] Where λ represents the radar wavelength, |K| 2 is the dielectric constant (for 35 GHz cloud radar, water is 0.8797 and ice is 0.176), N(D) is the particle number concentration, σ Mie (D) is the backscatter cross-sectional area of ​​the radar, and D is the particle diameter.

[0021] Furthermore, in step 2, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo according to the relationship between the non-precipitation particle reflectivity ratio and the Ka-band precipitation cloud radar measured reflectivity. np and precipitation particle echo Z p , specifically:

[0022] Z np =Z total ×F Z,np

[0023] Z p =Z total ×(1-F Z,np ).

[0024] Furthermore, in step 3, when the cloud top temperature is lower than the freezing temperature and a mixed phase cloud composed of ice phase particles and liquid droplets develops and precipitation occurs, the echo information of non-precipitation clouds is extracted according to steps 1 and 2, and then the interference of ice phase particle information in the echo intensity is eliminated by using the relationship between ice phase particles and temperature, and the echo intensity information of liquid water clouds is obtained, thereby estimating the liquid water content in the cloud.

[0025] Furthermore, step 3 is specifically as follows:

[0026] Step 3.1: For the separated non-precipitation particles, if the temperature is greater than 0°C, it is considered that the cloud is all cloud water, and if the temperature is below -20°C, it is considered that the cloud is all ice particles;

[0027] Step 3.2: When the temperature T is between 0 and -20℃, the cloud is considered to be a mixture of ice and water. Assume that the proportion of liquid water in the cloud is linearly related to the ambient temperature. The liquid-water reflectivity ratio F Z,lw for:

[0028]

[0029] The liquid water reflectivity Z lw and the reflectivity Z of ice phase particles ice :

[0030] Z lw =Z np ×F Z,lw

[0031] Z ice =Z np ×(1-F Z,lw ).

[0032] Furthermore, in step 4, for a given particle size distribution, the total mass concentration of the particles can be obtained by summing the particle concentration of each probe at each level and the corresponding particle diameter, that is:

[0033]

[0034] Among them, ρ w is the density of water or ice particles in g·m -3 , n i is the concentration of particles in each level, r i is the diameter of each particle.

[0035] Furthermore, after step 4, the following steps are also included:

[0036] Step 5: Apply the ZM relation of liquid water to the separated liquid water echoes to obtain the liquid water content of the entire vertical profile in the cloud. The measured liquid water path is used to evaluate the inverted liquid water content.

[0037] Furthermore, based on the characteristics of the airborne Ka-band precipitation·cloud radar and in-situ measurements, the contributions of hydrometeors of different size ranges are clearly distinguished from the measured total reflectivity, and then the relationship between the mass concentration and reflectivity of each hydrometeor is obtained from the in-situ measurements. This method can significantly reduce the uncertainty between the liquid water content and Z, thereby more accurately determining the liquid water content.

[0038] Furthermore, this method is applicable to both non-precipitating clouds and precipitating clouds. Using this inversion algorithm, for any given cloud type, the liquid water content of the entire vertical profile in the cloud can be obtained.

[0039] Furthermore, the obtained liquid water content was evaluated and verified using an airborne microwave radiometer.

[0040] The present invention solves the following technical problems:

[0041] 1. The present invention utilizes airborne Ka-band precipitation cloud radar and in-situ observation equipment (FCDP, 2D-S,

[0042] The liquid water content of the entire vertical section of the cloud can be obtained by joint inversion of HVPS. For a given cloud type, the liquid water content of the entire vertical section of the cloud can be obtained. This is of great significance for the command of weather modification operations and for finding the best operation area for human shadow catalysis. The cloud particle data were screened based on temperature, which improved the generalization ability of cloud particle data screening.

[0043] 2. The inversion method obtained by the present invention is to clearly distinguish the contribution of hydrometeors of different size ranges from the measured total reflectivity, and then obtain the relationship between the mass concentration and reflectivity of each hydrometeor from the in-situ measurement. This method can significantly reduce the uncertainty between the liquid water content and the reflectivity, so that the liquid water content can be determined more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of the liquid water content inversion method based on airborne Ka-band precipitation cloud radar; DETAILED DESCRIPTION

[0045] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. The method flow chart is as follows: Figure 1 As shown, the following steps are included:

[0046] A method for inverting liquid water content based on airborne Ka-band precipitation cloud radar comprises the following steps:

[0047] Based on three in-situ probes, namely, the airborne Ka-band precipitation cloud radar and fast cloud droplet probe, the two-dimensional stereo optical array imaging probe and the high-capacity spectral particle probe, the joint inversion of the liquid water content in the cloud includes:

[0048] Step 1: Calculate the reflectivity of non-precipitation particles using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe. Then, the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of the Ka-band precipitation cloud radar is obtained by fitting as follows:

[0049] log(F Z,np )=-0.087dBZ total -3.55

[0050] Among them, F Z,np The reflectivity ratio contributed by non-precipitation water, dBZ total is the total reflectivity Z measured by Ka-band precipitation cloud radar total Take the logarithm 10lgZ total The value after

[0051] Step 2: According to the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of Ka-band precipitation cloud radar, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo. np and precipitation particle echo Z p ;

[0052] Step 3: Determine the relationship between the cloud top temperature and the freezing temperature, and obtain the liquid water content in the cloud based on the determination result;

[0053] Step 4: For a given particle size distribution, the total mass concentration of the particles is obtained by summing the particle concentration of each probe at each level and the corresponding particle diameter;

[0054] From the particle size distribution observed in situ, it can be obtained that the total mass concentration is related to the echo intensity of separated liquid water, ice and precipitation particles, and the relationship between them is obtained, namely:

[0055] log(M lwc )=0.073dBZ lw +1.22

[0056] log(M ice )=0.094dBZ ice +2.55

[0057] log(M pre )=0.082dBZ pre -0.2

[0058] Among them, M lwc ,M ice ,M pre is the mass concentration of particles in different phases, dBZ lw ,dBZ ice ,dBZ pre Z lw , Z ice , Z pre Take the logarithm of the value.

[0059] Furthermore, step 1 calculates the reflectivity of non-precipitation particles based on the Mie scattering model using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe:

[0060]

[0061] Where λ represents the radar wavelength, |K| 2 is the dielectric constant (for 35 GHz cloud radar, water is 0.8797 and ice is 0.176), N(D) is the particle number concentration, σ Mie (D) is the backscatter cross-sectional area of ​​the radar, and D is the particle diameter.

[0062] Furthermore, in step 2, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo according to the relationship between the non-precipitation particle reflectivity ratio and the Ka-band precipitation cloud radar measured reflectivity. np and precipitation particle echo Z p , specifically:

[0063] Z np =Z total ×F Z,np

[0064] Z p =Z total ×(1-F Z,np ).

[0065] Furthermore, in step 3, when the cloud top temperature is lower than the freezing temperature and a mixed phase cloud composed of ice phase particles and liquid droplets develops and precipitation occurs, the echo information of non-precipitation clouds is extracted according to steps 1 and 2, and then the interference of ice phase particle information in the echo intensity is eliminated by using the relationship between ice phase particles and temperature, and the echo intensity information of liquid water clouds is obtained, thereby estimating the liquid water content in the cloud.

[0066] Furthermore, step 3 is specifically as follows:

[0067] Step 3.1: For the separated non-precipitation particles, if the temperature is greater than 0°C, it is considered that the cloud is all cloud water, and if the temperature is below -20°C, it is considered that the cloud is all ice particles;

[0068] Step 3.2: When the temperature T is between 0 and -20℃, the cloud is considered to be a mixture of ice and water. Assume that the proportion of liquid water in the cloud is linearly related to the ambient temperature. The liquid-water reflectivity ratio F Z,lw for:

[0069]

[0070] The liquid water reflectivity Z lw and the reflectivity Z of ice phase particles ice :

[0071] Z lw =Z np ×F Z,lw

[0072] Z ice =Z np ×(1-F Z,lw ).

[0073] Furthermore, in step 4, for a given particle size distribution, the total mass concentration of the particles can be obtained by summing the particle concentration of each probe at each level and the corresponding particle diameter, that is:

[0074]

[0075] Among them, ρ w is the density of water or ice particles in g·m -3 , n i is the concentration of particles in each level, r i is the diameter of each particle.

[0076] Furthermore, after step 4, the following steps are also included:

[0077] Step 5: Apply the ZM relation of liquid water to the separated liquid water echoes to obtain the liquid water content of the entire vertical profile in the cloud. The measured liquid water path is used to evaluate the inverted liquid water content.

[0078] Furthermore, based on the characteristics of the airborne Ka-band precipitation·cloud radar and in-situ measurements, the contributions of hydrometeors of different size ranges are clearly distinguished from the measured total reflectivity, and then the relationship between the mass concentration and reflectivity of each hydrometeor is obtained from the in-situ measurements. This method can significantly reduce the uncertainty between the liquid water content and Z, thereby more accurately determining the liquid water content.

[0079] Furthermore, this method is applicable to both non-precipitating clouds and precipitating clouds. Using this inversion algorithm, for any given cloud type, the liquid water content of the entire vertical profile in the cloud can be obtained.

[0080] Furthermore, the obtained liquid water content was evaluated and verified using an airborne microwave radiometer.

[0081] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

Claims

1. The liquid water content inversion method based on airborne Ka-band precipitation cloud radar mainly includes the following steps: Based on three in-situ probes, namely, the airborne Ka-band precipitation cloud radar and fast cloud droplet probe, the two-dimensional stereo optical array imaging probe and the high-capacity spectral particle probe, the joint inversion of the liquid water content in the cloud includes: Step 1: Calculate the reflectivity of non-precipitation particles using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe. Then, the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of the Ka-band precipitation cloud radar is obtained by fitting as follows: log(F Z,np )=-0.087dBZ total -3.55 Among them, F Z,np The reflectivity ratio contributed by non-precipitation water, dBZ total is the total reflectivity Z measured by Ka-band precipitation cloud radar total Take the logarithm 10lgZ total The value after Step 2: According to the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of Ka-band precipitation cloud radar, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo. np and precipitation particle echo Z p ; Step 3: Determine the relationship between the cloud top temperature and the freezing temperature, and obtain the liquid water content in the cloud based on the determination result; Step 4: For a given particle size distribution, the total mass concentration of the particles is obtained by summing the particle concentration of each probe at each level and the corresponding particle diameter; From the particle size distribution observed in situ, it can be obtained that the total mass concentration is related to the echo intensity of separated liquid water, ice and precipitation particles, and the relationship between them is obtained, namely: log(M lwc )=0.073dBZ lw +1.22 log(M ice )=0.094dBZ ice +2.55 log(M pre )=0.082dBZ pre -0.2 Among them, M lwc ,M ice ,M pre is the mass concentration of particles in different phases, dBZ lw ,dBZ ice ,dBZ pre Z lw , Z ice , Z pre Take the logarithm of the value, where Z lw is the liquid water reflectivity, Z ice is the reflectivity of ice particles.

2. The liquid water content inversion method based on airborne Ka-band precipitation cloud radar according to claim 1, characterized in that : Step 1: Calculate the reflectivity of non-precipitation particles based on the Mie scattering model using the full range of the fast cloud droplet probe and the 50-100 μm particle size distribution of the two-dimensional stereo optical array imaging probe: Where λ represents the radar wavelength, |K| 2 is the dielectric constant, N(D) is the particle number concentration, σ Mie (D) is the backscatter cross-sectional area of ​​the radar, and D is the particle diameter.

3. The method for inverting liquid water content based on airborne Ka-band precipitation cloud radar according to claim 1, characterized in that: Step 2: According to the relationship between the reflectivity ratio of non-precipitation particles and the measured reflectivity of Ka-band precipitation cloud radar, the non-precipitation particle echo Z is segmented from the Ka-band precipitation cloud radar echo. np and precipitation particle echo Z p , specifically: WITH np =Z total ×F Z,np WITH p =Z total ×(1-F Z,np )。 4. The method for inverting liquid water content based on airborne Ka-band precipitation cloud radar according to claim 2, characterized in that: Step 3: When the cloud top temperature is lower than the freezing temperature and a mixed phase cloud composed of ice phase particles and liquid droplets develops and precipitation occurs, the echo information of non-precipitation clouds is extracted according to steps 1 and 2. Then, by using the relationship between ice phase particles and temperature, the interference of ice phase particle information in the echo intensity is eliminated to obtain the echo intensity information of liquid water clouds, thereby estimating the liquid water content in the clouds.

5. The method for inverting liquid water content based on airborne Ka-band precipitation cloud radar according to claim 4, characterized in that: Step 3 is as follows: Step 3.1: For the separated non-precipitation particles, if the temperature is greater than 0°C, it is considered that the cloud is all cloud water, and if the temperature is below -20°C, it is considered that the cloud is all ice particles; Step 3.2: When the temperature T is between 0 and -20℃, the cloud is considered to be a mixture of ice and water. Assume that the proportion of liquid water in the cloud is linearly related to the ambient temperature. The liquid-water reflectivity ratio F Z,lw for: The liquid water reflectivity Z lw and the reflectivity Z of ice phase particles ice : WITH lw =Z np ×F Z,lw WITH ice =Z np ×(1-F Z,lw )。 6. The method for inverting liquid water content based on airborne Ka-band precipitation cloud radar according to claim 1, characterized in that: Step 4 For a given particle size distribution, the total mass concentration of the particles can be obtained by integrating the particle concentration of each probe at each level and its corresponding particle diameter, that is: Among them, ρ w is the density of water or ice particles in g·m -3 , n i is the concentration of particles in each level, r i is the diameter of each particle.

7. The method for inverting liquid water content based on airborne Ka-band precipitation cloud radar according to claim 1, characterized in that: After step 4, also include: Step 5: Apply the ZM relation of liquid water to the separated liquid water echoes to obtain the liquid water content of the entire vertical profile in the cloud. The measured liquid water path is used to evaluate the inverted liquid water content.

8. The liquid water content inversion method based on airborne Ka-band precipitation cloud radar as claimed in claim 7, wherein the obtained liquid water content is evaluated and verified using an airborne microwave radiometer.

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