CN-117805762-B - Differential phase and attenuation joint estimation method for dual-polarized weather radar

CN117805762BCN 117805762 BCN117805762 BCN 117805762BCN-117805762-B

Abstract

The invention discloses a differential phase and attenuation joint estimation method for a dual-polarized weather radar, which improves the accuracy of phase and attenuation estimation by adaptively adjusting gamma H and gamma DP under high resolution and reduces the deviation caused by delta hv and noise. The differential phase and attenuation joint estimation method provided by the invention can be applied to dual-polarized weather radars of any wave band, especially wave bands with higher frequencies such as X, ku, ka wave bands and the like, and the improvement effect is more remarkable. The method improves the accuracy of differential phase estimation and attenuation correction, and is beneficial to improving the accuracy of quantitative precipitation estimation. In addition, the invention does not introduce new parameters, and only adaptively adjusts the relation coefficient between the attenuation and the differential phase shift rate, so that the invention can be applied to a radar DSP to realize real-time processing of data.

Inventors

DONG XICHAO
LIU SIYUE
TIAN WEIMING
HU CHENG

Assignees

北京理工大学
北京理工大学重庆创新中心

Dates

Publication Date: 20260512
Application Date: 20231229

Claims (5)

1. A method for jointly estimating differential phase and attenuation for a dual polarized weather radar, comprising: Step 1, linear fitting of a 3km sliding window is applied to a measured curve of ψ DP of a radar, and the fitted curve of ψ DP is recorded as ; Step 2, presetting a plurality of different (gamma H ,γ DP ) pairs according to the range of gamma H and gamma DP calculated by theoretical simulation, and under the condition of different (gamma H ,γ DP ) pairs, based on Performing first attenuation correction, and respectively recording the corrected reflectivity factor and differential reflectivity as And And utilize And And Performing first differential phase estimation, and recording the estimated differential phase shift rate as ; Step 3, continuing to base on the conditions of the different (gamma H ,γ DP ) pairs Directly estimating by using empirical relation between attenuation and phase and method II, respectively, performing second attenuation correction by using phase to constrain attenuation estimation, and searching (gamma H ,γ DP ) pair for minimum difference between attenuation rate A H and differential attenuation rate A DP estimated by two methods for each distance library, namely optimal (gamma H ,γ DP ) pair, and recording the estimated value of ZPHI method under the optimal (gamma H ,γ DP ) pair condition as And ; Step 4, under the condition that each distance library is in the optimal (gamma H ,γ DP ) pair, utilizing Performing third attenuation correction to obtain And I.e. the final estimated value of the attenuation corrected reflectivity factor and differential reflectivity, and using And And Performing second differential phase estimation to obtain The final estimated value of the differential phase shift rate is obtained; and 5, changing different radial directions, and repeating the steps 1 to 4 to finish all radial attenuation correction and differential phase estimation.
2. The method for jointly estimating differential phase and attenuation for dual polarized weather radar according to claim 1, wherein said step 1 comprises: Since rainfall is substantially constant over a distance, K DP (° km) over that distance can be considered a constant value, then phi DP (°) is a linear function of distance, since when the frequency is high, interference factors such as delta hv (°) are present in large numbers, linear fitting of sliding windows is applied to the measured curve of ψ DP (°) to eliminate the effects of large fluctuations in phase, we term the fitted curve of ψ DP as 。
3. The method for combined differential phase and attenuation estimation for dual polarized weather radar according to claim 2, wherein said step 2 comprises: step 21, first attenuation correction: Presetting a plurality of different (gamma H ,γ DP ) pairs according to the range of gamma H and gamma DP calculated by theoretical simulation The curve is approximated as phi DP , and under the condition of each group (gamma H ,γ DP ) pair, the first attenuation correction is performed by an empirical linear relation between A H (dB/km) and A DP (dB/km) and K DP , and the first attenuation correction estimated intrinsic reflectivity factor Z Hint (dB) and intrinsic differential reflectivity Z DRint (dB) are respectively (r k represents the position of the kth distance bin, wherein K represents any distance bin in the radial direction): (1); (2); Here we will refer to it as respectively And ; Step 22, first differential phase estimation: First, it should be noted that all Z Hint and Z DRint in the following calculations refer to the first attenuation correction estimate And And this step is continued separately under the conditions of each different set of (gamma H ,γ DP ) pairs; for the distance library k, calculating the average value of Z DRint standard deviations in a plurality of sliding windows where the average value is located as the standard deviation of the distance library k Selecting all Δr (r m ;r n )(r m ≤r k ≤r n and r m ≠r n ) satisfying the following formula in one predetermined interval [ L min ;L max ]: (3); For each Δr (r m ;r n ), its corresponding Δψ DP (r m ;r n ) can be considered as ΔΦ DP (r m ;r n where Δδ hv (r m ;r n ) is negligible), and further, based on Δψ DP (r m ;r n ), each Δr (r m ;r n ) corresponding K DP (r k ) (formula (5)) is estimated from downscaled weights w (r k ) calculated from the self-consistent (SC) relation between K DP and Z Hint and Z DRint (formula (4)): (4); (5); Wherein, the And Average values of Z Hint and Z DRint of all distance libraries between r m and r n , respectively, Δr 0 being the length of a single distance library; On the distance library K, for different length Δr (r m ;r n ) in each of all different (γ H ,γ DP ) pairs, the standard deviation of all K DP (r k estimated based thereon is calculated And find the cause The minimum Δr (r m ;r n ), recording all paths corresponding to Δr (r m ;r n ) for that length, and calculating the average of all K DP (r k for that length as the final estimate of differential phase shift at distance bin K in the first differential phase estimate, we will note this as 。
4. The method for jointly estimating differential phase and attenuation for dual polarized weather radar as claimed in claim 3, wherein said step 3 comprises: step 31, second attenuation correction: First, it should be noted that all K DP in the following calculations refer to the first differential phase estimation And this step is continued separately under the conditions of each different set of (gamma H ,γ DP ) pairs; repeating the steps (1) - (2) (called method I), performing second attenuation correction, and recording the attenuation rate estimated at the distance bin k and the differential attenuation rate as respectively And ; On the distance library k, when the second attenuation correction is performed by another method (called method II), the attenuation rates of the H-polarization and V-polarization channels and the differential attenuation rates estimated by using the path of any minimum Δr (r m ;r n ) recorded in the previous step are respectively: (6); (7); (8); Wherein ζ Hatt (r k ) and ζ Vatt (r k ) are both decay reflectance factors in linear units (mm 6 m -3 ), γ V is a coefficient of linear relation between A V and K DP , and γ V =γ H -γ DP ; Averaging all A H (r k ) and all A DP (r k ) estimated by formulas (6) - (8) respectively to obtain final estimated values of the attenuation rate and the differential attenuation rate at the distance base k based on the method II in the second attenuation correction, and respectively recording the final estimated values as And ; Step 32, selection of the optimal (γ H ,γ DP ) pair: On the distance library k, (γ H ,γ DP ) that minimizes the difference between the results of the attenuation correction method I and the attenuation correction method II (formula (9)) is selected for all preset (γ H ,γ DP ) pairs as a (γ H ,γ DP ) pair corresponding to the distance library k, also referred to as an optimal (γ H ,γ DP ) pair (formula (10)): (9); (10); Searching the respective optimal (gamma H ,γ DP ) pairs of all the radial distance libraries by using (9) - (10), determining the corresponding pairs at the optimal (gamma H ,γ DP ) pairs And And the results of the attenuation correction at this time are respectively recorded as And 。
5. The method for jointly estimating differential phase and attenuation for dual polarized weather radar according to claim 4, wherein said step 4 comprises: step 41, third attenuation correction: Will be And Substituting into (3) - (5), searching again to enable The minimum Deltar (r m ;r n ) and the corresponding path are repeated from the formulas (6) to (8) under the condition that each distance library is in the optimal (gamma H ,γ DP ) pair, and the third attenuation correction is carried out, and the formulas (6) and (7) are slightly modified as the optimal (gamma H ,γ DP ) pair of each distance library is different: (11); (12); Note that K DP is still referred to herein We respectively record the intrinsic reflectivity factor and the estimated value of the intrinsic differential reflectivity at the distance bin k as And The final estimated value of the intrinsic reflectivity factor and the intrinsic differential reflectivity at the position of the distance library k in the invention; Step 42, second differential phase estimation: Will be And Substituting the new materials into the materials (3) - (5), and searching for new use again The minimum Deltar (r m ;r n ) and the average value of all K DP (r k under the length is calculated and is recorded as K DP2nd (r k ), namely the final estimated value of the differential phase shift rate at the distance K in the method.

Description

Differential phase and attenuation joint estimation method for dual-polarized weather radar Technical Field The invention relates to the technical field of weather radars, in particular to a differential phase and attenuation joint estimation method for a dual-polarized weather radar. Background Dual polarized weather radar is an important tool for quantitative precipitation estimation, and the measured reflectivity factor Z H, the differential reflectivity Z DR between orthogonal polarized radar echoes and the differential phase shift K DP are all important parameters for rainfall inversion. Thus, for accurate quantitative precipitation estimation, a guaranteed accuracy of Z H、ZDR and K DP is necessary. The differential phase shift rate K DP is obtained by deriving the differential propagation phase Φ DP distance, where Φ DP is the phase difference between the horizontally polarized and vertically polarized echoes caused by the forward propagation. However, the measured differential phase ψ DP contains not only Φ DP but also the backscatter differential phase δ hv caused by Mie scattering caused by large droplets or melted ice particles. Delta hv is particularly apparent when the frequency is high and varies considerably with distance, which poses a challenge for accurate estimation of K DP. Furthermore, ψ DP may have significant noise during light and medium rain, and may also affect the accuracy of the K DP estimation. Therefore, to get an accurate K DP, it is necessary to filter out noise and the δ hv component in ψ DP. Attenuation of radar signals is a major factor affecting the accuracy of the measurements Z H and Z DR. Radar signal beams, when traversing the atmosphere, lose some energy due to scattering and absorption caused by precipitation particles. Attenuation is primarily dependent on the radar pulse wavelength relative to the particle size. When the frequency is high and the wavelength is short, the attenuation of the radar signal is not negligible. Meanwhile, since precipitation particles are not isotropically distributed, the differences in attenuation experienced by the orthogonally polarized echoes are also significant. Therefore, in order to reduce the impact of attenuation on quantitative precipitation estimates, it is also necessary to perform accurate attenuation corrections for Z H and Z DR. Since K DP is not affected by power attenuation, it is widely used in attenuated stapling. However, the accuracy of the attenuation correction is affected by the accuracy of the estimated value of K DP, and particularly when the frequency is high, the difficulty in accurately estimating K DP is increased by the presence of a large number of interference factors such as delta hv. For the estimation of K DP, compared with the traditional fitting, the resolution and accuracy of the result can be greatly improved by using the Z H and Z DR subjected to attenuation correction to carry out differential phase estimation. Thus, it is clear that the accuracy of the attenuation correction in turn affects the accurate estimate of K DP, since the attenuation is not negligible when the frequency is high. In addition, empirical coefficients γ H and γ DP in the quasi-linear relation between the attenuation ratio a H and the differential attenuation ratio a DP and the differential phase shift ratio K DP, respectively, are also important factors affecting the attenuation correction and the differential phase estimation accuracy. since γ H and γ DP are sensitive to temperature, drop Spectral Distribution (DSD) and drop size variations, the range of variation is large, even in the same rain-drop zone. Thus, if a priori fixed values are set for γ H and γ DP, the accuracy of the results is reduced, and particularly when K DP is large, the inaccuracy of γ H and γ DP is further amplified. Therefore, it is necessary to adaptively adjust γ H and γ DP at a high resolution based on a range bin and to reduce the influence of disturbance factors such as δ hv to improve the accuracy of attenuation correction and differential phase estimation. Disclosure of Invention The invention provides a differential phase and attenuation joint estimation method for a dual-polarized weather radar, which mainly solves the technical problems of self-adaption and high-resolution adjustment of experience coefficients. In order to solve the technical problems, the invention provides a self-adaptive and high-resolution differential phase and attenuation joint estimation method, which comprises the following steps: Step 1, applying sliding window linear fitting to a measured curve of ψ DP of radar, and marking the fitted curve of ψ DP as Step 2, presetting a plurality of different (gamma H,γDP) pairs according to the range of gamma H and gamma DP calculated by theoretical simulation, and under the condition of different (gamma H,γDP) pairs, based onPerforming first attenuation correction, and respectively recording the corrected reflectiv