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

Abstract

The application discloses an X-band rain measuring radar attenuation and deviation synchronous correction method and system, uses a constructed synchronous correction function to perform attenuation and deviation synchronous correction on reflectivity factors observed by an X-band rain measuring radar, simultaneously finds an optimal solution of a target function between the constructed corrected reflectivity factors and standard reference reflectivity factors, obtains optimal attenuation correction coefficients and deviation correction coefficients, synchronously updates correction coefficients of the synchronous correction function, receives reflectivity factors observed by the X-band rain measuring radar in real time, inputs the updated synchronous correction function, and obtains the reflectivity factors after attenuation and deviation synchronous correction. The application solves the problem of excessive attenuation correction error when there is observation deviation by constructing a correction function of synchronous constraint attenuation and deviation coefficients, and further improves the data quality and rain monitoring capability of the X-band rain measuring radar.

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 in 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 in 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 a 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 a 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 formula 1.8 into formula 1.4, and rearrange to get:

[0063] (1.9)

[0064] Based on formula 1.9, define the radar observation bias coefficient as , which takes the value of , when there is no bias, negative bias, 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 formula 1.9 as:

[0068] (1.11)

[0069] wherein, 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, and 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 observation time difference between the standard reference radar and the rain measurement radar is within ±3 minutes, which is considered as the same period.

[0071] The present application 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 experiment

[0073] .

[0074] The detection radius of X radar is 75 km, and the coverage of four radar positions and 75 km radius is shown in Fig. 1. The data of spaceborne rain radar is used as the standard reference data, and the three coefficients of four X-band radars are solved by the method of S3 and S4, as shown in Table 2. In order to facilitate the solution, the coefficient a is fixed at 0.75 (the coefficient a varies little). From the column of “coefficient a (dB) ”, it can be seen that the four radars are all negative deviation, and the observation is weak, among which XPR02 is the largest to-5.1 dB. Figure 3 Figure 2

[0075] Table 2 Attenuation and bias synchronous correction coefficients of X-band radars

[0076] .

[0077] Based on the coefficients in Table 2, the reflectivity factor of X-band rain radar observation obtained in real time is corrected by the synchronous correction equation of S1, and compared with the standard reference radar data, as shown in Fig. 2. The original observation of X-band reflectivity factor (b) is quite different from the standard reference radar (a), especially in the area shown by the red ellipse. After the conventional attenuation correction of each database (c), the echo is enhanced (red arrow) compared with the original observation of X-band reflectivity factor (b), but due to the-5.1 dB negative bias of XPR02, the attenuation correction of the original observation of X-band reflectivity factor is seriously insufficient, and the reflectivity factor after attenuation correction has not been significantly improved, and is still quite different from the standard reference radar (a). The reflectivity factor of this method (d) has obvious improvement compared with (b) and (c), and the echo is close to the standard reference radar (a), which shows that the correction of this method is effective, and compared with the method of only attenuation correction, the accuracy of X-band reflectivity factor observation is obviously improved. Figure 4 Figure 4 Figure 4 Figure 4 Figure 4 Figure 4 Figure 4 Figure 4 Figure 4 ​ ​​​​​​​​​​​​​​​

Claims

1. A method for synchronously correcting attenuation and bias of an X-band rain radar, characterized in that, Using the constructed synchronization correction function, the reflectivity factor observed by the X-band rain measuring radar is corrected The attenuation and bias are corrected synchronously, and the synchronization correction function is: ， wherein is the corrected reflectivity factor, the correction factors including: an attenuation correction factor and a bias correction factor is the distance from the radar to the rain region;​ The optimal attenuation correction factor is obtained by finding the optimal solution of the objective function between the constructed post-corrected reflectance factor and the standard reference reflectance factor The optimal bias correction factor and is obtained by finding the optimal solution of the objective function between the constructed post-corrected reflectance factor and the standard reference reflectance factor The correction factors of the synchronous correction function are updated synchronously, and the objective function is: ， In the formula, is the farthest detection distance of the radar.

2. The method according to claim 1, wherein, The correction coefficient updating condition comprises that there is rainfall in the observation area of the X-band radar and there is standard reference radar data in the same period as the rainfall.

3. The method according to claim 1, wherein the method is characterized by, The initial value of the correction coefficient in each round of correction coefficient synchronous update is the optimal attenuation correction coefficient obtained in the last round of update and , the bias correction coefficient .

4. The method of claim 2, wherein the method is characterized by, The standard reference radar data acquisition method comprises an S-band weather service radar or a satellite-borne rain measuring radar.

5. The method for X-band precipitation radar attenuation and bias correction method according to claim 1, characterized in that, The method for finding the optimal solution of the target function comprises: obtaining historical observation reflectivity factors in a rainfall period and standard reference reflectivity factors in the same period, constructing a paired data set, and finding the optimal solution of the target function through cyclic iteration of an optimization algorithm.

6. The method according to claim 5, wherein the attenuation and bias correction is synchronized with the X-band precipitation radar. The pairing data set construction method is: calculating the rainfall echo area proportion of each moment in the pairing data set, and extracting N groups of pairing data with the rainfall echo area proportion greater than a threshold T A .

7. The X-band precipitation radar attenuation and bias correction method of claim 5, wherein, The method for finding the optimal solution of the objective function is: substituting the paired data into the objective function In the method, the attenuation correction coefficient obtained in the last round of update is taken as the initial value of the attenuation correction coefficient 、 and the bias correction coefficient , the parameter boundary is set, the gradient of the objective function is calculated, and the values of the three parameters are continuously updated and adjusted 、 and until the objective function converges to the minimum value, at which time and 、 the values of the three parameters are the optimal parameter values of this round.

8. The X-band precipitation radar attenuation and bias correction method of claim 7, wherein, The multivariate scalar function minimization method comprises a sequential least squares programming or a truncated Newton method.

9. The X-band precipitation radar attenuation and bias correction method of claim 1, wherein, Real-time receiving X-band rain radar observation reflectivity factor, input synchronization correction function after updating the correction coefficient, from the radar center to the farthest detection distance of the radar , the attenuation and deviation of the reflectivity factor after the synchronization correction of each distance library is calculated in turn.

10. An X-band rain monitoring radar attenuation and bias synchronous correction system, characterized in that, The method comprises: The attenuation and bias synchronous correction module uses the constructed synchronous correction function to correct the reflectivity factor observed by the X-band rain measuring radar The attenuation and bias synchronous correction is performed, and the synchronous correction function is: ， wherein is the corrected reflectivity factor, the correction factors including: an attenuation correction factor and a bias correction factor , is the distance from the radar to the rain region; The revised coefficient synchronous updating module obtains the optimal attenuation correction coefficient and the bias correction coefficient by finding the optimal solution of the target function between the constructed post-revision reflectivity factor and the standard reference reflectivity factor. The target function is:​​​​ ， In the formula, is the farthest detection distance of the radar.

Images