Method for Identifying Sunny and Rainy Moments by Utilizing Multiple Characteristic Quantities of High-frequency Satellite-ground Links

Abstract

A method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links is provided. The method may include the following steps of: extracting multiple characteristic quantities including standard deviation, trend, maximum value, minimum value, average value, skewness, kurtosis and information entropy; selecting an optimal time window through adjustment; and finally realizing the identification of the sunny and rainy moments by utilizing a classification algorithm. According to the method for identifying the sunny and rainy moments, sunny and rainy periods can be accurately distinguished by utilizing the signals of the high-frequency satellite-ground links, and real-time monitoring of large-range sunny and rainy distribution conditions is achieved.

Claims

1. A method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links, comprising the following steps: step 1: establishing high-frequency satellite-ground links; step 2: carrying out time domain sampling on the high-frequency satellite-ground links at intervals of ΔT to obtain an original received signal SN; step 3: filtering the original received signal SN with a wavelet analysis method and eliminating changes caused by tropospheric scintillation to obtain a signal S(n); step 4: extracting characteristic quantities of the signal S(n), for the signal S(n) at each moment; step 5: adjusting a calculation window area W.sub.i of each of the characteristic quantities, and selecting an optimal time window W; step 6: representing eigenvectors composed of the characteristic quantities obtained by the step 4 of two signals at different moments with x.sub.1 and x.sub.2, selecting a Gaussian kernel function K(x.sub.1, x.sub.2) and a penalty factor C: $K\left(x_1,x_2\right)=\exp \left(-\frac{.Math.x_1-x_2.Math.}{2{\sigma }^2}\right)$ where σ represents a bandwidth and is used for controlling an action range of the Gaussian kernel function; and constructing an optimization problem: $\underset{\alpha }{\min }\frac{1}{2}\underset{i=1}{\overset{n}{.Math.}}\underset{j=1}{\overset{n}{.Math.}}{\alpha }_i{\alpha }_j{y}_i{y}_{j}K\left(x_i,x_j\right)-\underset{i=1}{\overset{n}{.Math.}}{\alpha }_i$ $s.t.\underset{i=1}{\overset{n}{.Math.}}{\alpha }_i{y}_i=0$ $0\le {\alpha }_i\le C$ where y represents classification results, and a represents a Lagrange multiplier; step 7: solving an optimal α based on a quadratic programming problem, and constructing a decision function G(x) to distinguish between sunny and rainy moments: $G\left(x_i\right)=\mathrm{sign}\left(\underset{i}{.Math.}{\alpha }_i{y}_{i}K\left(x_i,x_j\right)+b\right)$ $b=y_j-\underset{i^{″}\in \mathrm{SV}}{.Math.}{\alpha }_{i^{″}}{y}_{i^{″}}K\left(x_j,x_{i^{″}}\right)$ where SV represents a support vector.

2. The method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links according to claim 1, wherein the method of filtering the original received signal SN with a wavelet analysis method in the step 3 comprises: determining a wavelet decomposition level to be 3 firstly, then starting wavelet decomposition calculation, quantifying a threshold of high frequency coefficients of wavelet decomposition, and finally performing one-dimensional wavelet reconstruction according to low-frequency coefficients of a bottom-most layer and high-frequency coefficients of respective layers to obtain the signal S(n).

3. The method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links according to claim 1, wherein the method of extracting characteristic quantities of the signal S(n) in the step 4 comprises: selecting a given ideal time window W, and extracting the following characteristic quantities of the signal S(n) at a n-th moment, the characteristic quantities comprising: (1) standard deviation (Std) $\mathrm{Std}\left(S\left(n\right)\right)=\left[\frac{1}{N+1}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^2\right],N=W\text{/}\Delta t$ (2) trend (Trd) $\mathrm{Trd}\left(S\left(n\right)\right)=\frac{1}{N}\underset{i=-N\text{/}2}{\overset{N\text{/}2}{.Math.}}{\alpha }_{i}S\left(n+i\right),{\alpha }_i=\left(-1,-1,\mathrm{.Math.}-1,0,1\mathrm{.Math.}1\right)$ (3) maximum value (Max)
Max(S(n))=max(S(n−N+i)),i=1,2, . . . ,N (4) minimum value (Min)
Min(S(n))=min(S(n−N+i)),i=1,2, . . . ,N (5) average value (Ave) $\mathrm{Ave}\left(S\left(n\right)\right)=\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}S\left(n+i-N\right),i=1,2,3,\mathrm{.Math.},N$ (6) kurtosis (Kur) $\mathrm{Kur}\left(S\left(n\right)\right)=\frac{N\left(N+1\right)}{\left(N-1\right)\left(N-2\right)\left(N-3\right)}\underset{i=1}{\overset{N}{.Math.}}{\left(\frac{S\left(n-N+i\right)-\stackrel{\_}{S}}{\mathrm{Std}\left(S\left(n\right)\right)}\right)}^4-\frac{3{\left(N-1\right)}^2}{\left(N-2\right)\left(N-3\right)},i=1,2,3,\mathrm{.Math.},N$ (7) skewness (Ske) $\mathrm{Ske}\left(S\left(n\right)\right)=\left(\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^3\right)/{\left(\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^2\right)}^{\frac{3}{2}},i=1,2,3,\mathrm{.Math.},N$ (8) information entropy (En) $\mathrm{En}\left(S\left(n\right)\right)=\underset{i=1}{\overset{N}{.Math.}}-p_i\log \left(p_i\right),i=1,2,3,\mathrm{.Math.},N$ where Δt represents a signal sampling time interval, S represents an average value of signal intensity within a given time window, and p.sub.i represents probability that a signal electric level value is S(n−N+i) at a (n−N+i)-th moment.

4. The method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links according to claim 1, wherein a method of selecting the optimal time window W in the step 5 comprises: maximizing an average Euclidean distance between the characteristic quantities at sunny and rainy moments: $\max \frac{1}{N^{\prime }{M}^{\prime }}\underset{i^{\prime }=1}{\overset{N^{\prime }}{.Math.}}\underset{j^{\prime }=1}{\overset{M^{\prime }}{.Math.}}\sqrt{\underset{k=1}{\overset{8}{.Math.}}{\left(R_{i^{\prime }k}-S_{j^{\prime }k}\right)}^2}$ where N′ is a number of rainy moments, M′ is a number of rainless moments, R.sub.i′k is a k-th characteristic quantity at a i′-th rainy moment, and S.sub.j′k is a k-th characteristic quantity at a j′-th rainless moment.

5. The method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links according to claim 1, wherein a support vector machine SVM method is used to determine a sunny or rainy state at each moment in the step 7.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is an implementation flow chart of utilizing multiple characteristic quantities of high-frequency satellite-ground links; and

[0035] FIGS. 2A-2B are diagrams showing the effect of utilizing multiple characteristic quantities of high-frequency satellite-ground links to judge sunny and rainy moments.

DETAILED DESCRIPTION OF EMBODIMENTS

[0036] The invention will be further illustrated with reference to the accompanying drawings and specific embodiments hereinafter. It should be understood that these embodiments are only used to illustrate the invention, and not to limit the scope of the invention. Various modifications of equivalents forms made by those skilled in the art shall fall within the scope of the invention as defined by the appended claims.

[0037] A method for identifying sunny and rainy moments by utilizing multiple characteristic quantities of high-frequency satellite-ground links is provided, which extracts signal characteristics at each moment by signals of the high-frequency satellite-ground links, and uses a classification algorithm to realize the identification of sunny and rainy moments. Taking wavelet analysis for filtering and a support vector machine for classification as an example, as shown in FIG. 1, the method includes the following steps:

[0038] step 1: establishing high-frequency satellite-ground links;

[0039] step 2: carrying out time domain sampling on the high-frequency satellite-ground links at intervals of ΔT to obtain an original received signal SN;

[0040] step 3: filtering the original received signal SN with a wavelet analysis method, and eliminating rapid changes caused by tropospheric scintillation to obtain a signal S(n);

[0041] specifically, in the step 3, a wavelet decomposition level is determined to be 3 by selecting Gaus wavelets firstly, then wavelet decomposition calculation is started, and a threshold of high frequency coefficients of wavelet decomposition is quantified, and finally one-dimensional wavelet reconstruction is performed according to according to low-frequency coefficients of a bottommost layer and high-frequency coefficients of each layer for filtering SN to obtain the signal S(n).

[0042] step 4: extracting eight characteristic quantities of the signal S(n) for the signal S(n) at each moment;

[0043] specifically, in the step 4, a given ideal time window W is selected and the following characteristic quantities of the signal S(n) at the n-th moment are extracted, the characteristic quantities including:

[0044] (1) Standard deviation (Std)

[00011]$\mathrm{Std}\left(S\left(n\right)\right)=\left[\frac{1}{N+1}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^2\right],N=W\text{/}\Delta t$

[0045] (2) Trend (Trd)

[00012]$\mathrm{Trd}\left(S\left(n\right)\right)=\frac{1}{N}\underset{i=-N\text{/}2}{\overset{N\text{/}2}{.Math.}}{\alpha }_{i}S\left(n+i\right),{\alpha }_i=\left(-1,-1,\mathrm{.Math.}-1,0,1\mathrm{.Math.}1\right)$

[0046] (3) Maximum value (Max)

Max(S(n))=max(S(n−N+i)),i=1,2, . . . ,N

[0047] (4) Minimum value (Min)

Min(S(n))=min(S(n−N+i)),i=1,2, . . . ,N

[0048] (5) Average value (Ave)

[00013]$\mathrm{Ave}\left(S\left(n\right)\right)=\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}S\left(n+i-N\right),i=1,2,3,\mathrm{.Math.},N$

[0049] (6) Kurtosis (Kur)

[00014]$\mathrm{Kur}\left(S\left(n\right)\right)=\frac{N\left(N+1\right)}{\left(N-1\right)\left(N-2\right)\left(N-3\right)}\underset{i=1}{\overset{N}{.Math.}}{\left(\frac{S\left(n-N+i\right)-\stackrel{\_}{S}}{\mathrm{Std}\left(S\left(n\right)\right)}\right)}^4-\frac{3{\left(N-1\right)}^2}{\left(N-2\right)\left(N-3\right)},i=1,2,3,\mathrm{.Math.},N$

[0050] (7) Skewness (Ske)

[00015]$\mathrm{Ske}\left(S\left(n\right)\right)=\left(\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^3\right)\text{/}{\left(\frac{1}{N}\underset{i=1}{\overset{N}{.Math.}}{\left(S\left(n-N+i\right)-\stackrel{\_}{S}\right)}^2\right)}^{\frac{3}{2}},i=1,2,3,\mathrm{.Math.},N$

[0051] (8) Information entropy (En)

[00016]$\mathrm{En}\left(S\left(n\right)\right)=\underset{i=1}{\overset{N}{.Math.}}-p_i\log \left(p_i\right),i=1,2,3,\mathrm{.Math.},N$

[0052] where Δt represents a signal sampling time interval, S represents an average value of signal intensity within a given time window, and p.sub.i represents probability that a signal electric level value is S(n−N+i) at a (n−N+i)-th moment.

[0053] step 5: adjusting a calculation window area W.sub.i of each characteristic quantity, and selecting an optimal time window W to maximize an average Euclidean distance between the characteristic quantities at sunny and rainy moments;

[00017]$\max \frac{1}{N^{\prime }{M}^{\prime }}\underset{i^{\prime }=1}{\overset{N^{\prime }}{.Math.}}\underset{j^{\prime }=1}{\overset{M^{\prime }}{.Math.}}\sqrt{\underset{k=1}{\overset{8}{.Math.}}{\left(R_{i^{\prime }k}-S_{j^{\prime }k}\right)}^2}$

[0054] where N′ is a number of rainy moments, M′ is a number of rainless moments, R.sub.i′k is a k-th characteristic quantity at a i′-th rainy moment, and S.sub.j′k is a k-th characteristic quantity at a j′-th rainless moment.

[0055] step 6: representing eigenvectors composed of the eight characteristic quantities obtained by the step 4 of two signals at different moments with x.sub.1 and x.sub.2, selecting a Gaussian kernel function K(x.sub.1, x.sub.2) and a penalty factor C:

[00018]$K\left(x_1,x_2\right)=\exp \left(-\frac{.Math.x_1-x_2.Math.}{2{\sigma }^2}\right)$

[0056] where σ represents a bandwidth and is used for controlling an action range of the Gaussian kernel function;

[0057] and constructing an optimization problem:

[00019]$\underset{\alpha }{\min }\frac{1}{2}\underset{i=1}{\overset{n}{.Math.}}\underset{j=1}{\overset{n}{.Math.}}{\alpha }_i{\alpha }_j{y}_i{y}_{j}K\left(x_i,x_j\right)-\underset{i=1}{\overset{n}{.Math.}}{\alpha }_i$$s.t.\underset{i=1}{\overset{n}{.Math.}}{\alpha }_i{y}_i=0$$0\le {\alpha }_i\le C$

[0058] where y represents classification results, and a represents a Lagrange multiplier;

[0059] step 7: solving an optimal α based on a quadratic programming problem, and constructing a decision function G(x) to distinguish between sunny and rainy moments:

[00020]$G\left(x_i\right)=\mathrm{sign}\left(\underset{i}{.Math.}{\alpha }_i{y}_{i}K\left(x_i,x_j\right)+b\right)$$b=y_j-\underset{i^{″}\in \mathrm{SV}}{.Math.}{\alpha }_{i^{″}}{y}_{i^{″}}K\left(x_j,x_{i^{″}}\right)$

[0060] where SV represents a support vector.

[0061] A support vector machine SVM method is utilized to judge the state of sunny and rainy moments. The timing results of the identification of the sunny and rainy moments are shown in FIG. 2A-2B. The method for identifying sunny and rainy moments of the invention can accurately distinguish the sunny and rainy periods by utilizing the signals of the high-frequency satellite-ground links. Real-time monitoring of a large-range sunny and rainy distribution condition is of great significance for further improving the accuracy of detecting rainfalls by the satellite-ground links, and prompt the urban water logging monitoring and flood early warning.

[0062] Although the above embodiments are based on wavelet filtering and support vector machines as examples, where it involves identifying sunny and rainy moments based on multiple characteristic quantities of high-frequency satellite-ground links, it should be pointed out that for those skilled in the art, several changes and modifications can be made without departing from the principle of the invention, and these changes and modifications should also be regarded as the protection scope of the invention.