CN110031847B - Dynamic short-term quantitative rainfall estimation method combining wavelet transformation and support vector machine with radar reflectivity - Google Patents

Dynamic short-term quantitative rainfall estimation method combining wavelet transformation and support vector machine with radar reflectivity Download PDF

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CN110031847B
CN110031847B CN201811200753.1A CN201811200753A CN110031847B CN 110031847 B CN110031847 B CN 110031847B CN 201811200753 A CN201811200753 A CN 201811200753A CN 110031847 B CN110031847 B CN 110031847B
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wavelet
rainfall
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CN110031847A (en
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张长江
王慧媛
曾静
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Zhejiang Normal University CJNU
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    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract

The invention discloses a dynamic quantitative precipitation estimation method combining wavelet transformation and a support vector machine with radar reflectivity, and belongs to the field of atmospheric science. Firstly, a matching library of radar echo and rainfall of an automatic station is established, a historical one-hour sample is obtained according to estimation time, wavelet transformation is carried out, a support vector machine model is established and trained in a wavelet domain, a dynamic rainfall estimation model in the wavelet domain is obtained, prediction is carried out in the wavelet domain after radar measures reflectivity factors of the rainfall echo, wavelet coefficients of the rainfall to be estimated can be obtained, and the estimated rainfall is 6 minutes after wavelet inverse transformation is carried out on the wavelet coefficients. The method combines the data description of wavelet transformation and the advantages of a support vector machine in small sample learning to carry out short-time dynamic quantitative precipitation estimation, and ensures the accuracy and the effectiveness of an estimation result. Experiments show that the estimation result of the method is superior to the effect of the rainfall estimation by using the Z-I relation no matter the root mean square error is calculated or the TS score is carried out.

Description

Dynamic short-term and temporary quantitative rainfall estimation method combining wavelet transformation and support vector machine with radar reflectivity
Technical Field
The invention belongs to the field of atmospheric science, and particularly relates to a dynamic radar reflectivity quantitative precipitation estimation method based on wavelet transformation and a support vector machine.
Background
The radar quantitative precipitation estimation is an important reference for short-time approaching early warning, and currently, radar precipitation estimation methods are mainly divided into two types, wherein one type is to determine precipitation intensity by using a Z-I relation and measure precipitation distribution, and the other type is to estimate precipitation intensity by combining the measurement of a rain gauge on points and a radar.
The basic principle of determining the precipitation intensity by using the Z-I relation is to convert the echo power into a radar reflectivity Z value based on the positive correlation relation between the reflectivity factor and the precipitation rate, establish an empirical relation between the reflectivity factor and the precipitation amount, estimate the precipitation amount according to a corresponding empirical formula after the radar measures the reflectivity factor of the precipitation echo, and accumulate the precipitation amount in a period of time. The radar rainfall measuring method has the advantages that when radar measurement errors and rainfall data have errors, the radar measurement errors and the rainfall data cannot be ordered in time, and the radar measurement errors and the rainfall data are influenced by various factors such as radar, rainfall types, radar detection heights, super refractive indexes, differences of ground rainfall, wind and the like, so that differences exist between radar estimated values and ground rainfall meter measured values, and uncertainty and randomness between radar reflectivity factors and rainfall are enhanced.
The rainfall meter and radar combined rainfall estimation utilizes rainfall meter station data and combines radar reflectivity factors to measure rainfall so as to improve the precision of radar rainfall measurement. The relatives have proposed many technical research results, such as variational method, kalman filtering method, probabilistic pairing method, terrain-based weighted random forest method, etc. However, the effect of these methods is not obvious in the application of actual weather service, and most commonly, the Z-I relationship is classified, the estimation result of the Z-I relationship is easily affected by other factors, and the estimation error is usually large.
Disclosure of Invention
In order to solve the technical problems, the invention provides a dynamic short-term quantitative rainfall estimation method combining wavelet transformation and a correlation vector machine with radar reflectivity, and aims to solve the problems of large rainfall prediction error, limited application range and the like in the conventional radar quantitative rainfall estimation problem.
The invention aims to provide a dynamic short-term quantitative precipitation estimation method combined with radar reflectivity, which comprises the following steps:
and S1, acquiring 6-minute radar echo data of a certain area and a 5-minute automatic station rainfall database.
And S2, averaging the rainfall data of the automatic station for 5 minutes to obtain precipitation data per minute, and accumulating the precipitation data in the corresponding time period according to the time of radar echo data to obtain precipitation data of 6 minutes.
And S3, matching the radar echo data and the rainfall data of the automatic station according to time and longitude and latitude to obtain a sample library in which the radar echo and the reflectivity correspond to each other one by one.
S4, selecting data corresponding to historical radar echo and rainfall of the automatic station for one hour, respectively performing stationary wavelet transformation to respectively obtain wavelet coefficients of radar echo and rainfall under high frequency and low frequency and in multiple scales, wherein the scale is related to the sample size within one hour, and the sample size obtained within one hour is set as n, 2 n1 ≤n<2 n1+1 The scale of the wavelet transform is n 1.
And S5, taking the wavelet coefficient obtained in S3 as a training sample, respectively training a corresponding model based on the support vector machine in each scale of wavelet transformation under high frequency and low frequency, and finally obtaining n1 support vector machine models under high frequency and n1 support vector machine models under low frequency.
S6: and obtaining radar precipitation echo data of 6 minutes at the current moment, and performing stationary wavelet transformation to obtain multi-scale radar echo wavelet coefficients under high frequency and low frequency.
S7: and taking the radar echo wavelet coefficient to be estimated obtained in the S6 as input, and inputting the coefficients of the same high-frequency/low-frequency channel and the same wavelet transformation scale into corresponding support vector machine models to obtain the wavelet coefficients of the rainfall to be estimated for 6 minutes at different scales under high frequency and low frequency.
S8: and performing wavelet inverse transformation on the wavelet coefficient of the rainfall to be estimated obtained by training in the S7 to obtain the value of the rainfall estimated in the method for 6 minutes.
Compared with the prior art, the invention has the following advantages:
(1) according to the dynamic short-term quantitative rainfall estimation method combining wavelet transformation and a support vector machine with radar reflectivity, the short-term dynamic quantitative rainfall estimation is carried out by combining the data description and the denoising capability of the wavelet transformation and the advantages of the support vector machine in small sample learning through the steps, and the accuracy and the effectiveness of an estimation result are guaranteed. Experiments show that the estimation result of the method has a much better effect compared with the quantitative precipitation estimation by a Z-I relational expression no matter the root mean square error is calculated or the TS scoring is carried out.
(2) In addition, the training sample of the estimation method only adopts wavelet transformation data of the past hour, the sample size is small, the transplantation is convenient, the algorithm complexity of the support vector machine for modeling is low, the training time is short, the time of once estimation is not more than 20 seconds, and the estimation method is more suitable for the application of actual weather service.
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FIG. 1 is a flow chart of the dynamic short-term quantitative precipitation estimation method of the present invention using wavelet transform and support vector machine in combination with radar reflectivity.
Detailed Description
The present invention will be further described in the following with reference to the drawings and example 1.
Example 1
The verification set of the invention is that 0.5-degree elevation radar echo data in Doppler weather radar 9 layer body scanning in Shanghai city Yangpu region and all precipitation automatic station data in Shanghai city during 2017 years and 6 months to 8 months, and 00-hour data at 6 months, 10 days and 12 days in 2017 years are selected as specific verification data for quantitative precipitation estimation of the dynamic radar based on wavelet transformation and a support vector machine, wherein the verification process comprises the following steps:
s1, acquiring 6-minute radar echo with 0.5-degree elevation angle in Doppler weather radar 9 layer body scanning in Shanghai city Yangpu district and automatic station rainfall data with 5-minute interval in Shanghai city as a database.
And S2, averaging the rainfall data of the automatic station for 5 minutes to obtain precipitation data per minute, and accumulating the precipitation data in the corresponding time period according to the time of the radar echo data to obtain precipitation data for 6 minutes.
And S3, matching the radar echo data and the rainfall data of the automatic station according to the time and the longitude and latitude to obtain a sample library in which the radar echo and the reflectivity correspond to each other one by one.
S4, selecting data corresponding to radar echo and automatic station rainfall between 11 hours and 00 hours in 6 months and 10 days in 2017 and between 12 hours and 00 hours in 10 months and 12 days in 6 months and 10 days in 2017 (the data do not include the data 00 hours in 12 hours in 6 months and 10 days in 2017), wherein the data are 2 in magnitude 8 And performing the stationary wavelet transform with the scale of 8 to respectively obtain the wavelet coefficients of radar echo and rainfall under high frequency and low frequency and 8 scales.
And S5, taking the wavelet coefficient obtained in S3 as a training sample, respectively training corresponding models based on the support vector machine in 8 scales of wavelet transformation under high frequency and low frequency, and finally obtaining 8 support vector machine models under high frequency and 8 support vector machine models under low frequency, wherein the total number of the support vector machine models is 16.
And S6, obtaining radar precipitation echo data of 6 minutes of 12 hours in 6 months, 10 days and 12 days in 2017, and similarly performing 8-layer stationary wavelet transform to obtain radar echo wavelet coefficients under high frequency and low frequency and 8 scales.
S7: and taking the radar echo wavelet coefficient to be estimated obtained in the S6 as input, and inputting the coefficients of the same high-frequency/low-frequency channel and the same wavelet transformation scale into corresponding support vector machine models to obtain the wavelet coefficients of the rainfall to be estimated for 6 minutes under 8 scales under high frequency and low frequency.
S8: and performing wavelet inverse transformation on the wavelet coefficient of the rainfall to be estimated, which is obtained by training in the S7, to obtain a value of the rainfall of 6 minutes between 00 minutes at 12 days 6 and 10 in 2017 and 06 minutes at 12 days 6 and 10 in 2017.

Claims (5)

1. The dynamic short-term quantitative rainfall estimation method combining wavelet transformation and a support vector machine with radar reflectivity is characterized in that: the method comprises the following steps:
s1, acquiring 6 minutes of radar echo data of a certain area and a 5 minutes of automatic station rainfall database;
s2, averaging the rainfall data of the automatic station for 5 minutes to obtain precipitation data per minute, and accumulating the precipitation data in a corresponding time period according to the time of radar echo data to obtain precipitation data of 6 minutes;
s3, matching the radar echo data and the rainfall data of the automatic station according to time and longitude and latitude to obtain a sample library in which the radar echo and the reflectivity correspond to each other one by one;
s4, selecting data corresponding to historical radar echo and rainfall of the automatic station for one hour, respectively performing stationary wavelet transformation to respectively obtain wavelet coefficients of radar echo and rainfall under high frequency and low frequency and in multiple scales, wherein the scale is related to the sample size within one hour, and the sample size obtained within one hour is set as n, 2 n1 ≤n<2 n1+1 Then the scale of the wavelet transform is n 1;
s5, taking the wavelet coefficient obtained in S4 as a training sample, respectively training a corresponding model based on a support vector machine in each scale of wavelet transformation under high frequency and low frequency, and finally obtaining n1 support vector machine models under high frequency and n1 support vector machine models under low frequency;
s6: obtaining radar precipitation echo data of 6 minutes at the current moment, and performing stationary wavelet transformation to obtain multi-scale radar echo wavelet coefficients under high frequency and low frequency;
s7: taking the radar echo wavelet coefficient to be estimated obtained in the S6 as input, and inputting the coefficients of the same high-frequency/low-frequency channel and the same wavelet transformation scale into corresponding support vector machine models to obtain the wavelet coefficients of the rainfall to be estimated for 6 minutes at different scales under high frequency and low frequency;
s8: and performing wavelet inverse transformation on the wavelet coefficient of the rainfall to be estimated obtained by training in the S7 to obtain the value of the rainfall estimated in the method for 6 minutes.
2. The method for dynamic short-lived quantitative precipitation estimation of radar reflectivity using wavelet transform and support vector machines as claimed in claim 1, wherein: in step S4, one hour of history data is selected, and the data is subjected to stationary wavelet transform.
3. The method for dynamic short-lived quantitative precipitation estimation of radar reflectivity using wavelet transform and support vector machines as claimed in claim 2, wherein: in step S4, the scale of the stationary wavelet transform is related to the amount of samples in one hour.
4. The method for dynamic short-lived quantitative precipitation estimation of radar reflectivity using wavelet transform and support vector machines as claimed in claim 1, wherein: in step S5, a support vector machine model is constructed and trained in different frequency channels and different wavelet scales in the wavelet domain, and is estimated.
5. The method for dynamic short-lived quantitative precipitation estimation of radar reflectivity using wavelet transform and support vector machines as claimed in claim 1, wherein: in step S6, the time for each precipitation estimation is 6 minutes.
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