X-band rain-measuring radar attenuation and deviation synchronous correction method and system

Abstract

The invention discloses an X-band rain-measuring radar attenuation and deviation synchronous correction method and system, and the method comprises the steps: carrying out the attenuation and deviation synchronous correction of a reflectivity factor observed by an X-band rain-measuring radar through employing a constructed synchronous correction function; meanwhile, an optimal attenuation correction coefficient and an optimal deviation correction coefficient are obtained by searching an optimal solution of a target function between the constructed corrected reflectivity factor and a standard reference reflectivity factor, so that the correction coefficient of a synchronous correction function is synchronously updated, the reflectivity factor observed by the X-waveband rain measuring radar is received in real time, and the X-waveband rain measuring radar is obtained. And inputting the updated synchronous correction function to obtain the reflectivity factor after attenuation and deviation synchronous correction. According to the method, the correction function of the synchronous constraint attenuation and the deviation coefficient is constructed, so that the problem that the attenuation correction error is too large when the observation deviation exists is effectively solved, and the data quality and the rainfall monitoring capability of the X-band rain measurement radar are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weather radar, in particular to a method and system for simultaneously correcting attenuation and bias of an X-band rain radar. BACKGROUND

[0002] Attenuation correction is an essential quality control step in the data processing of X-band rain radar. However, the existing attenuation correction methods do not consider the observation bias. In fact, bias and attenuation often exist simultaneously in X-band radar, especially after long-term continuous observation, as the hardware parameters drift, such as the decrease of transmission power, the bias will gradually appear and increase. Since bias correction and attenuation correction will interfere with each other, i.e. bias correction will be excessive when there is attenuation, and attenuation correction will be insufficient or excessive when there is bias. Therefore, step-by-step attenuation correction followed by bias correction, or bias correction followed by attenuation correction, cannot obtain accurate results.

[0003] Therefore, a method for simultaneously correcting attenuation and bias is needed, which can constrain attenuation and bias, solve the problem of excessive attenuation correction error when there is observation bias, and further improve the data quality and rainfall monitoring capability of X-band rain radar. SUMMARY

[0004] The purpose of the present application is to provide a method and system for simultaneously correcting attenuation and bias of an X-band rain radar, which can reduce the influence of attenuation and bias, and improve the data quality and rainfall monitoring capability of X-band rain radar by simultaneously correcting the original observation data of the X-band rain radar.

[0005] To achieve the above purpose, the present application provides a method for simultaneously correcting attenuation and bias of an X-band rain radar, which uses a constructed simultaneous correction function to simultaneously correct the reflectivity factor observed by the X-band rain radar, and the simultaneous correction function is:

[0006] ,

[0007] wherein, is the corrected reflectivity factor, and the correction coefficient includes: attenuation correction coefficient and , bias correction coefficient , is the distance from the radar to the rainfall area;

[0008] By finding the optimal solution of the objective function between the corrected reflectivity factor and the standard reference reflectivity factor , the optimal attenuation correction coefficient and , and the bias correction coefficient , the correction coefficient of the synchronization correction function is updated synchronously, and the target function is:

[0009] ,

[0010] In the formula, is the farthest detection distance of the radar.

[0011] Preferably, the correction coefficient update condition includes rainfall in the observation area of the X-band radar and the existence of standard reference radar data at the same period as the rainfall.

[0012] Preferably, in each round of synchronous update of the correction coefficient, the initial value of the correction coefficient is the optimal attenuation correction coefficient obtained in the last round of update and , the bias correction coefficient .

[0013] Preferably, the standard reference radar data acquisition method includes an S-band meteorological business radar or a satellite-borne rain measuring radar.

[0014] Preferably, the method for finding the optimal solution of the target function is: obtaining the historical observation reflectivity factor in the rainfall period and the standard reference reflectivity factor at the same period, constructing a paired data set, and finding the optimal solution of the target function through iterative optimization algorithm.

[0015] Preferably, the paired data set construction method is: calculating the proportion of rainfall echo area at each time in the paired data set, and extracting N groups of paired data with the rainfall echo area proportion greater than a threshold T A .

[0016] Preferably, the method for finding the optimal solution of the target function is: substituting the paired data into the target function , using the bounded multi-element scalar function minimization method, taking the attenuation correction coefficient , and the bias correction coefficient value obtained in the last round of update as the initial value, setting the parameter boundary, calculating the gradient of the target function, and constantly updating and adjusting , and three parameter values until the target function converges to the minimum value, at which time and , values are the optimal parameter values of this round.

[0017] Preferably, the multi-element scalar function minimization method includes sequential least squares programming and truncated Newton method.

[0018] Preferably, the reflectivity factor of the X-band rain measurement radar observation is received in real time, the synchronous correction function is inputted after updating the correction coefficient, the reflectivity factor after the correction of the synchronous attenuation and deviation is calculated in sequence on each distance base from the radar center to the farthest detection distance of the radar .

[0019] The X-band rain measurement radar attenuation and deviation synchronous correction system comprises:

[0020] The attenuation and deviation synchronous correction module: the reflectivity factor of the X-band rain measurement radar observation is corrected by the synchronous correction function, and the synchronous correction function is:

[0021] ,

[0022] In the formula, is the corrected reflectivity factor, and the correction coefficient comprises: the attenuation correction coefficient and the deviation correction coefficient , is the distance from the radar to the rainfall area;

[0023] The correction coefficient synchronous updating module: the optimal attenuation correction coefficient and the deviation correction coefficient are obtained by searching for the optimal solution of the target function between the corrected reflectivity factor and the standard reference reflectivity factor , so that the correction coefficient of the synchronous correction function is updated synchronously, and the target function is:

[0024] ,

[0025] In the formula, is the farthest detection distance of the radar.

[0026] Advantages: compared with the existing attenuation correction method, the present application is not affected by the observation deviation, the problem of too large attenuation correction error when there is observation deviation is effectively solved by constructing the correction function of the synchronous constraint attenuation and deviation coefficient, and the data quality and rainfall monitoring ability of the X-band rain measurement radar are improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the method of the present application;

[0028] Figure 2 The correction coefficient updating flowchart;

[0029] ​Figure 3 Figure 4 is a position and coverage range diagram of four X-band radars in the embodiment;

[0030] Figure 4 Figure 5 is a comparison diagram of only attenuation correction effect for synchronous correction of attenuation and bias of observation data of four X-band radars, wherein figure (a) is a standard reference radar X-band reflectivity factor, figure (b) is an original observed X-band reflectivity factor, figure (c) is an X-band reflectivity factor after existing library-by-library attenuation correction, and figure (d) is an X-band reflectivity factor after correction by the method. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described in detail below with reference to the embodiments and the accompanying drawings.

[0032] The X-band rain measuring radar attenuation and bias synchronous correction method described in the present application is applied to an X-band rain measuring radar data processing terminal, and is suitable for single-polarization and dual-polarization X-band rain measuring radars, such as Figure 1 as shown in figure 1, and the specific method is as follows:

[0033] S1, construct a synchronous correction function:

[0034] (1),

[0035] wherein, is a corrected reflectivity factor, unit: mm 6 / m 3 ; is an observed reflectivity factor, unit: mm 6 / m 3 ; is a distance from the radar to the rain area, unit: km; and are attenuation correction coefficients, unit: km -1 , unit: none; is a bias correction coefficient, unit: mm 6 / m 3 .

[0036] S2, construct a target function between the corrected reflectivity factor and the standard reference reflectivity factor :

[0037] (2);

[0038] wherein, is the farthest detection distance of the radar.

[0039] S3, find the target function the minimum of the objective function, to obtain the optimal attenuation correction coefficient and the bias correction coefficient to update the synchronization correction function, as shown in the following equation: Figure 2 The update process is as follows:

[0040] S301, initialization stage, the attenuation correction coefficient and the bias correction coefficient obtained in the last round of update are taken as the initial values of this round of update, and the default values are used if there is no last round of coefficient values for the first time , and are respectively taken as 0.75 and 1.0.

[0041] S302, collect the historical observation reflectivity factor in the rainfall period of the previous 3 days and the standard reference reflectivity factor in the same period, and construct a paired data set; calculate the rainfall echo area proportion of each time point in the paired data set (the proportion of the echo area greater than 20 dBZ in the total area of radar observation), and extract N groups of effective paired data with the rainfall echo area proportion greater than threshold T A , T A is in the range of (0.3, 1.0), and the default value is 0.5; if N> 30, go to the next step, otherwise, expand the historical data acquisition range, and continue to search for 3 days of historical data from the current collection end time.

[0042] S303, substitute the effective paired data into the objective function , and use a multivariate scalar function minimization method with boundary constraints, such as "sequential least squares programming" or "truncated Newton method", to take the values of , and obtained in the last round of update as initial values, set the parameter boundary , calculate the gradient of the objective function, and constantly update and adjust the values of , and three parameters until the objective function converges to the minimum value. At this time, the values of the attenuation correction coefficient and the bias correction coefficient are the optimal parameter values of this round, and the optimal three parameter values of this round are updated to the attenuation and bias synchronization correction coefficient table for subsequent real-time correction.

[0043] S4, real-time receive the reflectivity factor observed by the X-band rain measurement radar, input the synchronization correction function after updating the coefficient, and from the radar center to the farthest detection distance of the radar​ The reflectivity factor on each distance bin is calculated in turn after the attenuation and bias correction.

[0044] In this embodiment, the derivation process of the synchronization correction function is further provided:

[0045] The attenuation correction formula of X-band high-frequency radar is:

[0046] (1.1)

[0047] wherein, and are the reflectivity factors before and after correction, respectively, in units of mm 6 / m 3 , is the distance from the radar, in units of km, is the attenuation coefficient, in units of dB / km.

[0048] The relationship between the attenuation coefficient and the reflectivity factor is:

[0049] (1.2)

[0050] wherein, and are the attenuation correction coefficients, and for X-band radar the variation range is small, about 0.75, and depends on the operating frequency, regional climate characteristics and season.

[0051] Let:

[0052] (1.3)

[0053] Then formula 1.1 is transformed into:

[0054] (1.4)

[0055] The differential of formula 1.3 is:

[0056] (1.5)

[0057] Further:

[0058] (1.6)

[0059] The integral of formula 1.6 is:

[0060] (1.7)

[0061] (1.8)

[0062] Substitute equation 1.8 into equation 1.4, and rearrange to get:

[0063] (1.9)

[0064] Based on equation 1.9, define the radar observation bias coefficient as , which takes the value , when there is no bias, when there is negative bias, when there is positive bias.

[0065] The relationship between the biased and attenuated reflectivity factor and the unbiased and attenuated reflectivity factor is as follows:

[0066] (1.10)

[0067] Rewrite equation 1.9 as:

[0068] (1.11)

[0069] where is the biased and attenuated reflectivity factor in actual observation (unit: mm 6 / m 3 ), is the reflectivity factor after simultaneous correction of attenuation and bias (unit: mm 6 / m 3 ), and are attenuation coefficients, is the bias coefficient.

[0070] In the simultaneous correction function, the attenuation correction coefficients and , and the bias correction coefficient have the characteristics of slow change, and do not need to be updated in real time, but can be updated once a month. The prerequisite for updating the correction coefficients is that there is a large range of rainfall in the X-band observation area, and there is standard reference radar data at the same period. The standard reference radar can be selected as an S-band meteorological operational radar or a spaceborne rain measurement radar data. The X-band rain measurement radar observation period is 5-6 minutes, and the standard reference radar and the rain measurement radar observation time difference is within ±3 minutes, which is considered as the same period.

[0071] This invention takes the reflectivity factor observed by the X-band rain measurement radar in a certain area as an example to specifically explain the effect of simultaneous correction of attenuation and bias. The radar parameters are shown in Table 1, and the data time is July 29, 2021, 11:00 (UTC).

[0072] Table 1 Radar parameters of the test

[0073] .

[0074] The detection radius of radar X is 75km. The positions of the four radars and the coverage of the 75km radius are as follows: Figure 3 As shown. Using the satellite-borne rainfall radar data as the standard reference data, through S3 and Figure 2 The method solves three coefficients for four X-band radars respectively as shown in Table 2. In order to facilitate the solution, the coefficients Fixed to 0.75 (coefficient The coefficient As can be seen from the "Decibel Form (dB)" column, all four radars have negative deviations and the observations are weak, with XPR02 having the largest deviation of -5.1dB.

[0075] Table 2 Attenuation and bias synchronization correction coefficients for X-band radar

[0076] .

[0077] Based on the coefficients in Table 2, the reflectivity factor of the real-time X-band rainfall radar observation is corrected for attenuation and deviation using the synchronous correction equation described in S1, and compared with the standard reference radar data, as shown in Figure 4 As shown. The original observed X-band reflectivity factor ( Figure 4 b) Compared with the standard reference radar ( Figure 4 a) The gap is large, especially in the area indicated by the red ellipse. Figure 4 c) X-band reflectivity factor relative to the original observation ( Figure 4 b) The echo is enhanced (red arrow), but due to the negative bias of -5.1dB in XPR02, the original observed X-band reflectivity factor attenuation correction is seriously insufficient. The reflectivity factor after attenuation correction has not been significantly improved, and is comparable to the standard reference radar ( Figure 4 a) is still far behind. The reflectivity factor of this method ( Figure 4 d) relative to Figure 4 b and Figure 4 c is significantly improved compared to the standard reference radar ( ​ a) The echoes are nearly consistent, indicating that this method is effective. Compared with the method of only performing attenuation correction, the accuracy of X-band reflectivity factor observation is significantly improved.

Claims

1. A method for synchronously correcting attenuation and deviation of an X-band rainfall radar, characterized in that: The reflectivity factor of X-band rainfall radar observations is corrected by using the constructed synchronous correction function. Perform synchronous correction of attenuation and deviation, and the synchronous correction function is: ， Where, is the corrected reflectivity factor, the correction coefficients include: attenuation correction coefficient and , deviation correction coefficient , is the distance from the radar to the rainfall area; By finding the corrected reflectivity factor constructed Reflectance factor with standard reference The optimal solution of the objective function between the two is obtained to obtain the optimal attenuation correction coefficient and , deviation correction coefficient , to synchronously update the correction coefficient of the synchronous correction function, the objective function is: ， Where, The maximum detection distance of the radar.

2. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 1 is characterized in that: The correction coefficient updating conditions include the presence of rainfall in the X-band radar observation area and the existence of standard reference radar data in the same period as the rainfall.

3. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 1 is characterized in that: When the correction coefficient is updated synchronously in each round, the initial value of the correction coefficient is the optimal attenuation correction coefficient obtained in the previous round of update and , deviation correction coefficient .

4. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 1 is characterized in that: The standard reference radar data acquisition method includes: S-band meteorological service radar or space-borne precipitation radar.

5. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 1 is characterized in that: The method for finding the optimal solution of the objective function is: obtaining the historical observed reflectivity factor during the rainfall period and the standard reference reflectivity factor during the same period, constructing a paired data set, and finding the optimal solution of the objective function through cyclic iteration of the optimization algorithm.

6. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 5 is characterized in that: The paired data set construction method is as follows: calculate the rainfall echo area ratio at each moment in the paired data set, extract the rainfall echo area ratio greater than the threshold T A N groups of paired data.

7. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 5 is characterized in that: The method for finding the optimal solution of the objective function is: substituting the paired data into the objective function In the process, the attenuation correction coefficient obtained in the previous update is obtained by using the multivariate scalar function minimization method with boundary constraints. 、 and bias correction coefficient The value is used as the initial value, the parameter boundary is set, the gradient of the objective function is calculated, and the adjustment is continuously updated. 、 and Three parameter values, until the objective function converges to the minimum value, at this time and 、 The value is the optimal parameter value of this round.

8. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 7, characterized in that: The multivariate scalar function minimization method includes sequential least squares programming and truncated Newton method.

9. The X-band rainfall radar attenuation and deviation synchronous correction method according to claim 1, characterized in that: Receive the reflectivity factor of X-band rain radar observation in real time, input the synchronous correction function after the correction coefficient is updated, and Maximum detection distance to radar , calculate the reflectivity factor after synchronous correction of attenuation and deviation on each distance library in turn.

10. An X-band rain radar attenuation and deviation synchronous correction system, characterized by: include: Attenuation and deviation synchronous correction module: Using the constructed synchronous correction function, the reflectivity factor of the X-band rain radar observation is corrected. Perform synchronous correction of attenuation and deviation, and the synchronous correction function is: ， Where, is the corrected reflectivity factor, the correction coefficients include: attenuation correction coefficient and , deviation correction coefficient , is the distance from the radar to the rainfall area; Correction coefficient synchronization update module: by finding the corrected reflectivity factor constructed Reflectance factor with standard reference The optimal solution of the objective function between the two is obtained to obtain the optimal attenuation correction coefficient and , deviation correction coefficient , to synchronously update the correction coefficient of the synchronous correction function, the objective function is: ， Where, The maximum detection distance of the radar.

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