A method for a single-channel millimeter-wave radar to identify the bright band at the zero-degree layer

Abstract

The present invention relates to the field of radar identification technology, and specifically to a method for a single-channel millimeter-wave radar to identify the bright band at the zero-degree level. From the height of the zero-degree level, the reflectivity factor, radial velocity, and spectral width profile are filtered, and the height that simultaneously satisfies the conditions of the reflectivity factor and radial velocity is searched as the top height of the bright band at the zero-degree level. The height that satisfies the conditions of the radial velocity and velocity spectral width is searched from bottom to top as the bottom height of the bright band at the zero-degree level. For the bright band height in the time dimension, outliers, isolated values, and mutation points are removed, and interpolation and filtering are performed. Compared with the prior art, the present invention utilizes the fact that the reflectivity factor and radial velocity detected by the millimeter-wave radar increase rapidly in the bright band interval at the zero-degree level, the radial velocity is sensitive to the phase state transition of particles at the bottom of the bright band at the zero-degree level, and the velocity spectral width increases and reaches a high value when the precipitation particles are converted from the ice phase to the mixed phase. Through two-way multi-condition search, it is realized that a single-channel millimeter-wave radar can also identify the bright band at the zero-degree level.

Description

Technical Field

[0001] The present invention relates to the technical field of radar identification, and in particular to a method for a single-channel millimeter-wave radar to identify the zero-degree layer bright band. Background Art

[0002] The zero-degree layer bright band refers to the high reflectivity factor echo band that appears below the 0°C atmospheric temperature height when the radar detects continuous precipitation in stratiform clouds, reflecting the obvious ice-water conversion zone in the precipitation cloud. The formation reason of the zero-degree layer bright band is as follows: when solid particles fall below the zero-degree layer, the surface melts and collides and aggregates, resulting in a sudden increase in the radar reflectivity. When the solid precipitation particles are completely melted into spherical water droplets, the speed increases, the scattering cross-section decreases, and the number of precipitations per unit volume decreases, resulting in a decrease in reflectivity.

[0003] The working wavelength of the millimeter-wave radar is mainly in the millimeter wave band, that is, the electromagnetic wave with a wavelength between 1 and 10 mm (frequency range of 30 to 300 GHz). The millimeter-wave radar can penetrate clouds and continuously detect the vertical profile of clouds, obtain particle information by using the scattering characteristics of cloud droplets to electromagnetic waves, and provide high-resolution radar data. The millimeter-wave radar has a short wavelength, high resolution, high sensitivity, and a detection mode of THI (time-vertical height scan), which is very suitable for identifying the zero-degree layer bright band. The detection quantities of the single-channel millimeter-wave radar are the reflectivity factor Z, the radial velocity V, and the velocity spectrum width W. Pulse compression technology, multi-pulse width detection mode and other technologies are adopted to improve the detection ability for different meteorological targets, and a more complete precipitation cloud echo profile than that of weather radar is obtained.

[0004] The traditional weather radar identification bright band technology identifies the interval where the maximum reflectivity decreases monotonically upward and downward to a certain threshold as the zero-degree layer bright band. For dual-polarization weather radars that can transmit and receive horizontal and vertical polarization waves, introducing polarization parameters sensitive to melting particles can improve the identification accuracy.

[0005] However, for millimeter-wave radars, the characteristics of the zero-degree layer bright band echo are different from those of weather radars. In the reflectivity factor profile, the characteristic of the rapid decrease at the bottom of the bright band is often missing, and the Mie scattering effect causes disturbances in the reflectivity at the bottom of the melting layer and the precipitation layer, making it difficult to judge whether it conforms to the zero-degree layer bright band characteristics by monotonic change.

[0006] It is difficult to identify the zero-degree layer bright band only relying on reflectivity for millimeter-wave radars. Dual-channel millimeter-wave radars can use the depolarization factor L dr as the polarization quantity to identify the zero-degree layer bright band, which is a problem that needs to be solved for single-channel millimeter-wave radars. In addition, due to the obvious error of the depolarization factor in the rain area being easily restricted by noise and dynamic range, when this situation occurs, a single-channel identification method is required for bright band determination.

[0007] Therefore, it is necessary to design a method for a single-channel millimeter-wave radar to identify the bright band at the zero-degree layer to solve the above problems. By the changes of the reflectivity factor, radial velocity, and velocity spectrum width profile in the vertical direction, the top and bottom of the bright band at the zero-degree layer can be identified. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for a single-channel millimeter-wave radar to identify the bright band at the zero-degree layer. By the changes of the reflectivity factor, radial velocity, and velocity spectrum width profile in the vertical direction, the top and bottom of the bright band at the zero-degree layer can be identified.

[0009] To achieve the above purpose, the present invention provides a method for a single-channel millimeter-wave radar to identify the bright band at the zero-degree layer, including the following steps:

[0010] S1: Select a height region containing the zero-degree layer;

[0011] S2: Filter the reflectivity factor, radial velocity, and spectrum width profile;

[0012] S3: Search from top to bottom in the height region, and use the height that simultaneously satisfies the reflectivity factor and radial velocity conditions as the top height of the bright band at the zero-degree layer;

[0013] S4: Search from bottom to top at a certain height below the top of the bright band, and use the height that satisfies the radial velocity and velocity spectrum width conditions as the bottom height of the bright band at the zero-degree layer;

[0014] S5: Remove outliers, isolated values, and mutation points from the bright band height in the time dimension, and perform interpolation and filtering;

[0015] The methods for selecting the height region in S1 are as follows:

[0016] a) Estimate the height where the air temperature is 0°C through where T S is the monthly average or seasonal average sea-level air temperature, and γ is the air temperature lapse rate;

[0017] b) Use numerical model data and radiosonde data to determine the approximate height of 0°C;

[0018] The filtering is median filtering, mean filtering, or Gaussian filtering.

[0019] Compared with the prior art, the present invention utilizes the characteristics that the reflectivity factor and radial velocity detected by the millimeter-wave radar increase rapidly in the interval of the bright band at the zero-degree layer, the radial velocity is sensitive to the phase state transition of particles at the bottom of the bright band at the zero-degree layer, and the velocity spectrum width also increases and reaches a relatively high value during the process of precipitation particles converting from the ice phase to the mixed phase. Thus, the single-channel millimeter-wave radar can also identify the bright band at the zero-degree layer through two-way multi-condition search. Brief Description of the Drawings

[0020] Figure 1 This is the technical flow chart of the present invention;

[0021] Figure 2 This is the schematic diagram of the bright band at the zero degree layer of the vertical profile of the reflectivity of the present invention;

[0022] Figure 3 This is the schematic diagram of the original radar profile of the present invention;

[0023] Figure 4 This is the schematic diagram of the recognition result of the bright band at the zero degree layer of a single profile of the present invention;

[0024] Figure 5 This is the schematic diagram of the recognition result of the bright band at the zero degree layer at multiple times of the present invention;

[0025] Figure 6 This is the schematic diagram of removing outliers, isolated points, mutation points and interpolation of the present invention; Detailed implementation manners

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] As Figures 1 to 6 , the present invention provides a method for a single-channel millimeter-wave radar to recognize the bright band at the zero degree layer, including the following steps:

[0028] S1: Select a height region ΔN1 interval containing the zero degree layer;

[0029] S2: Filter the reflectivity factor, radial velocity, and spectral width profile;

[0030] S3: Search from top to bottom in the height region for the height that simultaneously satisfies the reflectivity factor and radial velocity conditions as the top height of the bright band at the zero degree layer;

[0031] S4: Search from bottom to top from a certain height below the top of the bright band for the height that satisfies the radial velocity and velocity spectral width conditions as the bottom height of the bright band at the zero degree layer;

[0032] S5: Remove outliers, isolated values and mutation points from the bright band height in the time dimension, and perform interpolation and filtering;

[0033] The methods for selecting the height region in S1 are as follows:

[0034] By to estimate the height where the air temperature is 0 °C, T S is the monthly average or quarterly average sea-level air temperature, and γ is the air temperature lapse rate;

[0035] Use numerical model data and radiosonde data to determine the approximate height of 0 °C;

[0036] The filtering is median filtering, mean filtering or Gaussian filtering.

[0037] Example:

[0038] 1. According to the monthly or seasonal average sea level temperature Ts, assuming that the temperature decrease rate is γ℃ / km, it can be obtained by To estimate the height of 0℃ temperature. Or use numerical model data and radiosonde data to determine the approximate height of 0℃. With this height as the center, select the height interval ΔN1 as the area where the zero-degree layer top is located.

[0039] 2. Perform median filtering on the reflectivity factor, radial velocity, and spectral width profile. You can also use mean filtering, Gaussian filtering, etc. as needed.

[0040] 3. Search a library N from top to bottom in interval ΔN1 i If the following conditions are met, then this library N i The height is the height of the bright band top H t :

[0041] (1)N i The total reflectivity increase in the interval of the following N1 consecutive libraries is higher than the reflectivity threshold ΔZ1 (ensuring a higher reflectivity increase), and the total reflectivity increase in the interval of the following N2 consecutive libraries is higher than the reflectivity threshold ΔZ2 (N1>N2, ΔZ1<ΔZ2, ensuring a higher reflectivity increase), N i The number of N3 reservoirs with increased reflectivity is greater than N c (to ensure that the reflectivity is increasing overall); the radial velocity conditions are similar (specific parameters are different), but it should be noted that since the radial velocity sometimes responds slightly slower than the reflectivity to particle melting, the radial velocity requirement is: from N i The following N d The library that meets the radial velocity condition can be found in the libraries.

[0042] (2)N i The reflectivity is higher than the reflectivity threshold Z t1 And the highest reflectivity in the N4 reservoir is higher than the reflectivity threshold Z t2 , N i The radial velocity is lower than the velocity threshold V t1 (Ensure that there are radar echo characteristics of solid precipitation above the top of the bright band and high reflectivity characteristics within the bright band).

[0043] 4. The library N where the bright band top is located obtained from above i Select the height interval ΔN2 downward, and search for a certain library N from bottom to top in ΔN2 j The radial velocity and velocity spectrum width meet the corresponding conditions, then this library N j The height of the bright band bottom height Hb :

[0044] (1) Consistent with the conditions in (1) of the above three steps, the direction is changed to upward, and the specific parameters are different;

[0045] (2) N j has a radial velocity higher than the velocity threshold V b1 (ensuring that the radial velocity characteristics of rainfall exist below the bright band), N j to N i the maximum value of the velocity spectrum width in the interval is higher than the spectrum width threshold W b (ensuring that the velocity spectrum width threshold for the mixed phase is satisfied within the bright band).

[0046] 5. Process the time dimension of a precipitation process (optional):

[0047] (1) Eliminate outliers based on the N s times standard deviation principle.

[0048] (2) Eliminate isolated values: Take a total of N t1 time steps before and after a certain time step as an interval. If the number of valid points in this interval is less than N v , then eliminate it.

[0049] (3) Eliminate extreme mutation points: Take a total of N t2 time steps before and after a certain time step as an interval. If the height H of the bright band top t (the height H of the bright band bottom b ) and the difference between the average value of this interval is greater than H mt (H mb ), then eliminate it. The K-nearest neighbor frequency method can be used to replace steps (2) and (3), and the threshold can be relaxed for a second round of eliminating isolated points and mutation points.

[0050] (4) Interpolate (such as linear interpolation) for the time steps with missing measurements (or failure to successfully identify the bright band) between valid points with a tolerance of N f .

[0051] (5) Perform median filtering (or other filtering) on the height H of the bright band top t and the height H of the bright band bottom b in the time dimension.

[0052] The above is only the preferred implementation mode of the present invention, which is only used to help understand the method and its core idea of the present application. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements should also be regarded as the protection scope of the present invention.

[0053] As a whole, the present invention solves the problem that in the prior art, due to the depolarization factor, obvious errors are prone to occur in the rain area due to noise and dynamic range limitations. When this situation occurs, a single-channel recognition method is required for bright band determination. However, it is difficult to identify the zero-degree layer bright band only relying on reflectivity for a single-channel millimeter-wave radar. By utilizing the changes of reflectivity factor, radial velocity, and velocity spectrum width profile in the vertical direction, the top and bottom of the zero-degree layer bright band can be identified, which has great application value.

Claims

1. A method for identifying the bright band of the zero-degree layer by a single-channel millimeter-wave radar, characterized in that, It includes the following steps: S1: Select a height region ΔN1 interval containing the zero-degree layer; S2: Filter the reflectivity factor, radial velocity, and spectral width profile; S3: Search downward from the top in the height region for the height that simultaneously satisfies the reflectivity factor and radial velocity conditions as the top height of the bright band of the zero-degree layer; The specific conditions for satisfying the reflectivity factor and radial velocity in S3 are: S3-1, N i The total increase in reflectivity within the following interval of N1 consecutive libraries is higher than the reflectivity threshold ΔZ1 to ensure a relatively high increase in reflectivity; the total increase in reflectivity within the interval of N2 consecutive libraries is higher than the reflectivity threshold ΔZ2, where N1 > N2 and ΔZ1 < ΔZ2, to ensure a relatively high growth rate of reflectivity; N i The number of libraries with an increase in reflectivity within the following N3 libraries is greater than N c , and the requirement for the radial velocity is: from N i The following N d libraries that meet the radial velocity conditions are found within; S3-2, N i The reflectance is higher than the reflectance threshold Z t1 and the highest reflectance in the downward N4 library is higher than the reflectance threshold Z t2 , N i The radial velocity is lower than the velocity threshold V t1； S4: Search upward from a certain height below the top of the bright band for the height that satisfies the radial velocity and velocity spectral width conditions as the bottom height of the bright band of the zero-degree layer; The specific conditions for satisfying the radial velocity and velocity spectral width in S4 are: S4-1, the requirement for the radial velocity is: find the libraries that meet the radial velocity condition from N libraries above Nj; d among N libraries; S4-2, N j has a radial velocity higher than the velocity threshold V b1 , to ensure that the radial velocity characteristics of rainfall exist below the bright band; N j from N i to the maximum value of the velocity spectrum width in the interval is higher than the spectrum width threshold W b , to ensure that the velocity spectrum width threshold for the mixed phase is satisfied within the bright band; S5: Remove outliers, isolated values, and mutation points from the bright band height in the time dimension, and perform interpolation and filtering.

2. The method for identifying the bright band of the zero-degree layer by a single-channel millimeter-wave radar according to claim 1, characterized in that, The methods for selecting the height region in S1 are: A. Estimate the height where the air temperature is 0°C by where T S is the monthly or seasonal average sea-level air temperature, and γ is the lapse rate of air temperature; B. Use numerical model data and radiosonde data to determine the approximate height of 0°C.

3. The method for identifying the bright band of the zero-degree layer by a single-channel millimeter-wave radar according to claim 1, characterized in that, The filtering is median filtering, mean filtering, or Gaussian filtering.

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