A method for determining geomagnetic disturbance period

Abstract

The present invention discloses a method for determining a geomagnetic disturbance period, comprising: obtaining N geomagnetic station data, where N is greater than or equal to 2; intercepting a sliding time window of the geomagnetic station data for each geomagnetic station data; obtaining the second-order derivative of the geomagnetic station data within each sliding time window, and calculating the correlation coefficient between corresponding geomagnetic stations based on the second-order derivative results; determining whether the correlation coefficient of the N geomagnetic station data within the same sliding time window is greater than a first preset threshold; if so, determining that magnetic disturbance occurs within the sliding time window; and determining whether the correlation coefficient of the N geomagnetic station data within K consecutive sliding time windows is greater than the first preset threshold; if so, determining the time period of the K consecutive sliding time windows as the magnetic disturbance occurrence period. The present invention has higher time resolution and more accurate determination of the magnetic disturbance occurrence period.

Description

Technical Field

[0001] The present invention relates to the field of geomagnetism in earth science, and in particular to a method for determining a geomagnetic disturbance period. Background Art

[0002] Correction of diurnal geomagnetic variations is a crucial step in magnetic survey data processing, and whether the influence of diurnal geomagnetic variations is eliminated directly affects the accuracy of magnetic survey data. Diurnal geomagnetic variations are divided into quiet variations and disturbed variations. To effectively eliminate the influence of diurnal geomagnetic variations, different diurnal correction methods are required for different diurnal variations. Usually, it is necessary to separate the geomagnetic data during the period of magnetic disturbance to obtain quiet diurnal variations and geomagnetic disturbances, and then correct them separately. Therefore, whether it is possible to reasonably distinguish quiet diurnal variations from geomagnetic disturbances and determine the time period of magnetic disturbances is particularly important for geomagnetic diurnal variation correction, which directly affects the effectiveness of geomagnetic diurnal variation correction and, in turn, the accuracy of magnetic survey data.

[0003] At present, the methods used at home and abroad to distinguish between geomagnetic calm and disturbance periods are based on multiple parameters. Using the geomagnetic index to judge the geomagnetic disturbance is a relatively common method. Among them, the K index is one of the most widely used geomagnetic indices. It was designed by Bartels et al. in 1939. It describes the disturbance intensity of a single geomagnetic station and uses 0 to 9 to describe the degree of disturbance caused by irregular changes in the geomagnetic field. Usually, magnetic disturbance is considered to have occurred when K>3. Later, in order to represent the global geomagnetic activity, the Kp index was calculated from the K index of 13 geomagnetic stations in the global geomagnetic network. The value range is 0 to 9 and is divided into 28 levels. Generally, magnetic disturbance is considered to have occurred when Kp>3. At the same time, when Kp=5,6, it is called a central geomagnetic storm, and when Kp=7,8,9, it is called a large geomagnetic storm; when the Kp index is converted into the form of equivalent amplitude, the Ap index appears, which ranges from 0 to 400. The larger the value, the greater the amplitude of the geomagnetic disturbance; there is also the Dst index, which mainly measures the intensity change of the horizontal component of the geomagnetic field and is calculated by 4 low-latitude geomagnetic stations. It is generally believed that magnetic disturbance occurs when Dst<-30, and the smaller the Dst value, the greater the degree of magnetic disturbance. In addition to the above commonly used geomagnetic indices, there are also aa, am, F107, AU, AL, AE and other indices. When used, multiple parameters are often used in combination to determine the time period when the magnetic disturbance occurs. In addition, some researchers use the diurnal amplitude as a criterion. In marine magnetic measurements, a diurnal amplitude greater than 100 nT is typically considered a magnetic disturbance. Bian Guanglang et al. proposed using six quantitative indicators—diurnal amplitude, diurnal amplitude difference, diurnal standard deviation, disturbance amplitude, disturbance amplitude difference, and disturbance standard deviation—to jointly identify disturbances. For example, disturbances are considered to occur when the diurnal amplitude is greater than 50, the amplitude difference is greater than 10, the standard deviation is greater than 10, the disturbance amplitude is greater than 20, the disturbance amplitude difference is greater than 1, and the disturbance standard deviation is greater than 2. While the geomagnetic index method is currently a common method used both domestically and internationally, each index value is calculated from geomagnetic data over a period of time. For example, the Kp index has a three-hour value, the Dst index has a one-hour value, and the F107 index has a daily value. This limited temporal resolution, particularly for disturbances lasting less than an hour, can be lost due to the large calculation window, rendering them indistinguishable. While using the daily amplitude quantification metric to determine the magnitude of geomagnetic disturbances can adjust the calculation window based on actual conditions, resulting in higher temporal resolution, the ability to distinguish magnetic disturbances based on their daily amplitude is inaccurate, resulting in some disturbances going unidentified due to their small amplitude. Given these issues with both the timing and amplitude of geomagnetic disturbances, the industry urgently needs to develop appropriate methods to determine the time period of geomagnetic disturbances. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a method for determining the geomagnetic disturbance period which can accurately determine the period when the magnetic disturbance occurs.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for determining a geomagnetic disturbance period comprises: obtaining N geomagnetic station data; N≥2; intercepting a sliding time window of the geomagnetic station data for each geomagnetic station data; obtaining the second-order derivative of the geomagnetic station data in each sliding time window, and calculating the correlation coefficient between corresponding geomagnetic stations based on the second-order derivative result; judging whether the correlation coefficient of the N geomagnetic station data in the same sliding time window is greater than a first preset threshold; if so, judging that magnetic disturbance occurs in the sliding time window; and judging whether the correlation coefficient of the N geomagnetic station data in K consecutive sliding time windows is greater than the first preset threshold; K≥2; if so, judging the time period of the K consecutive sliding time windows as the magnetic disturbance occurrence period.

[0007] Preferably, the first preset threshold is 0.9.

[0008] Preferably, N=2.

[0009] Preferably, the geographical location between the N geomagnetic stations is smaller than a first preset range.

[0010] Preferably, the latitude difference between the N geomagnetic stations does not exceed 5°, and the longitude difference does not exceed 50°.

[0011] Preferably, if it is determined that the correlation coefficient of the N geomagnetic station data within the same sliding time window is not greater than a first preset threshold, it is determined that the sliding time window is magnetically calm.

[0012] Preferably, the geomagnetic station data is the geomagnetic F value.

[0013] The present invention has the following advantages over the prior art:

[0014] The present invention refers to the differences in the characteristics of quiet day changes and disturbance changes. Through sliding window control, the second-order derivative of the geomagnetic station data is obtained in each sliding window, and the correlation of the change trends of the data of the two geomagnetic stations is compared point by point. Through correlation analysis, it is determined whether geomagnetic disturbance occurs, which provides a new method and idea for determining the time period of magnetic disturbance. Compared with existing traditional methods, this method has higher time resolution and more accurate determination of the time period of magnetic disturbance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0016] Figure 1 Schematic diagram of the flow of the method for determining the geomagnetic disturbance period of this embodiment.

[0017] Figure 2 This is a comparison chart of the geomagnetic daily variation data of this embodiment.

[0018] Figure 3 This is a comparison chart of the second-order derivatives of two stations during the period of this embodiment.

[0019] Figure 4 This is a comparison chart of the second-order derivatives of the two stations in time period 2 of this embodiment.

[0020] Figure 5 This is a graph showing the window correlation coefficient results when the sliding window length is 15 minutes in this embodiment.

[0021] Figure 6 This is a graph showing the window correlation coefficient results when the sliding window length is 30 minutes in this embodiment.

[0022] Figure 7 This is a graph showing the window correlation coefficient results when the sliding window length is 60 minutes in this embodiment.

[0023] Figure 8 2 is a comparison chart of correlation coefficients of different sliding window lengths in this embodiment. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and examples.

[0025] Quiet day changes depend on local time, and their changes are relatively gentle and periodic. Geomagnetic disturbances are independent of local time, and depend on the non-periodic changes of universal time. The changes are complex. Data from two geomagnetic stations, DLT and GUA, in the International Geomagnetic Network Center, are selected for comparison. The geographical location of the DLT station is 11.945°N, 108.482°E, and the geographical location of the GUA station is 13.588°N, 144.867°E. The two stations have similar latitudes and a geographical location difference of about 4000km. The geomagnetic field F values ​​of the two geomagnetic stations from May 22 to June 2, 2018, and the geomagnetic index Kp values ​​at the corresponding time are taken and mapped at the same time, as shown below. Figure 2 shown.

[0026] from Figure 2 As can be seen, referring to the kp index and Dst index at the same time, it can be judged Figure 2 When a magnetic disturbance occurs during the period Figure 2The diurnal geomagnetic curves for the two stations during period two show the same variation during period one. While the amplitudes of the disturbances differ, their occurrence and duration are consistent. In particular, the peaks of each disturbance appear to coincide. While the two diurnal curves for period two exhibit similar morphologies, their peaks occur at different times, consistent with the aforementioned differences in the characteristics of quiet diurnal variations and geomagnetic disturbances.

[0027] According to the characteristics of geomagnetic disturbance, the disturbance occurs at the global time, that is, no matter where the geomagnetic observatory is located, the geomagnetic observatories in each place respond at the same time when the disturbance occurs, and the same form of fluctuation is shown on the diurnal curve. Figure 2 As can be seen from the figure, the inflection time of the fluctuation curve is the same, and the Figure 1 The second-order derivatives of the data of the two stations in the two periods are obtained, and the results are shown in Figure 3 and Figure 4 As shown. Figure 3 The comparison of the second-order derivative of the F value of one or two stations in the middle period shows that the two groups of results have a high correlation, corresponding to Figure 4 Comparing the results of the second-order derivatives of the F values ​​of the two stations in the middle period, it can be seen that the two sets of results have a poor correlation. Therefore, the period of magnetic disturbance occurrence can be determined by analyzing the correlation between the second-order derivatives of the daily variation data of the two geomagnetic stations.

[0028] Based on the above theoretical analysis, the applicant proposed a method for determining the geomagnetic disturbance period. Figure 1 A method for determining a geomagnetic disturbance period includes:

[0029] S1. Acquire data from N geomagnetic stations; N = 2; the geographical locations between two geomagnetic stations are less than a first preset range, i.e., the latitude difference between the two geomagnetic stations does not exceed 5°, and the longitude difference between the two geomagnetic stations does not exceed 50°. The geomagnetic station data is the geomagnetic F value.

[0030] S2, for each geomagnetic station data, intercept the sliding time window of the geomagnetic station data; in each sliding time window, the second-order derivative of the geomagnetic station data is obtained, and the correlation coefficient between the corresponding geomagnetic stations is calculated based on the second-order derivative results;

[0031] S3, determine whether the correlation coefficient of the N geomagnetic station data in the same sliding time window is greater than a first preset threshold; if so, execute step S4; if not, execute step S7; wherein the first preset threshold is 0.9.

[0032] S4, it is determined that magnetic disturbance occurs in the window during the sliding;

[0033] S5, determining whether the correlation coefficient of the N geomagnetic station data within K consecutive sliding time windows is greater than a first preset threshold; K ≥ 2; if so, executing step S6;

[0034] S6, determining the time period of K consecutive sliding windows as the magnetic disturbance occurrence period;

[0035] S7, determining that the magnetic field in the window is still during the sliding operation.

[0036] This application considers using the method of comparing the trend of the daily curves of the two stations for judgment. The change of the second-order derivative can reflect the trend of the curve. When the second-order derivative is positive, the curve shows an upward trend. When it is negative, the curve shows a downward trend. The second-order derivative corresponding to the inflection point of the curve is zero. Select data from two geomagnetic stations with similar geographical locations (the latitude difference does not exceed 5°, and the longitude difference does not exceed 50°), take a sliding time window, and in each time window, respectively calculate the second-order derivatives of the data of the two stations, and perform a correlation analysis on the two groups of second-order derivative results. If the two groups of data have a good correlation (correlation coefficient>0.9), it is considered that magnetic disturbance occurs in the time window. When the correlation coefficients in the corresponding continuous sliding time windows are all>0.9, this period of time can be determined as the period of magnetic disturbance.

[0037] This application uses the statistical correlation analysis method based on the different characteristics of quiet day changes and disturbance changes. The correlation of the second-order derivative of the geomagnetic field F value at different geomagnetic stations (i.e., the consistency of the curve change trend) is used to determine whether a geomagnetic disturbance has occurred. The method is efficient and effective. This application uses a sliding time window for control during calculation. The time resolution is higher than that of the traditional geomagnetic index judgment method. The method is efficient and effective, and the judgment of the time of occurrence of geomagnetic disturbances is more accurate.

[0038] Experimental data

[0039] The above-mentioned DLT and GUA geomagnetic station data were selected, and the sliding time window lengths were selected as 15 minutes, 30 minutes, and 60 minutes respectively. The correlation coefficient of the second-order derivative of the geomagnetic F value in each time window was calculated. The results are as follows Figure 5-Figure 7 shown.

[0040] from Figure 5-Figure 7 As can be seen from the figure, as the time window increases, the amplitude of the correlation coefficient decreases in turn. The other three groups of correlation coefficients have different resolutions on the time scale. As the time window increases, the time period resolution decreases. The three groups of correlation coefficient results are compared with the geomagnetic diurnal variation curves at the corresponding time. The results are shown in Figure 8 shown.

[0041] from Figure 8 It can be seen that on the synchronous corresponding daily variation curve, when the correlation coefficient is ≥0.9, magnetic disturbances have occurred, but some small disturbance periods have not been identified, such as Figure 8In the boxed data, a small magnetic disturbance occurred, but the three groups of correlation coefficients corresponding to this period were all less than 0.9. This is mainly because the small magnetic disturbance is not obvious in the correlation of the second-order derivative of the geomagnetic field F value. However, large disturbances can be identified by the correlation coefficient, for example Figure 8 The periods of magnetic disturbance identified by the second-order derivative correlation analysis method are: 16:58-21:18 on May 22, 12:58-16:38 on May 24, 13:46-22:30 on May 26, 18:53-20:42 on May 27, 11:20-15:50 on May 30, 13:10-19:32 on June 1, and 17:32-20:35 on June 2. However, the periods of magnetic disturbance identified by the geomagnetic index method are only 06:00-12:00 on May 23 and 15:00 on May 31 to 22:00 on June 1. From the identification results, it can be seen that the method of calculating the second-order derivative correlation coefficient of the geomagnetic field F value can better distinguish the time periods of magnetic disturbance occurrence, which is more accurate than the identification method of the geomagnetic index method, identifies more periods of magnetic disturbance occurrence and has more precise start and end times, and has better application effect.

[0042] The other three groups of correlation coefficients have different time resolutions. The 15-minute time window can divide the magnetic disturbance period more finely, that is, the division of the start and end time of the period is more accurate, but the amount of calculated data in the time window is small, which makes the error of the correlation coefficient calculation result larger. The 60-minute time window does not divide the magnetic disturbance period finely enough, but because of the large amount of calculated data, the correlation coefficient is more reliable. Therefore, when using this method to determine the magnetic disturbance period, the time window should be reasonably selected according to user needs, or as Figure 8 For example, multiple sets of time window results are used for joint comparison and judgment to obtain more reasonable results.

[0043] The above specific implementation manner is a preferred embodiment of the present invention and does not limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A method for determining a geomagnetic disturbance period, characterized in that: include: Obtain data from N geomagnetic stations; N≥2； For each geomagnetic station data, a sliding time window of the geomagnetic station data is intercepted; In each sliding time window, the second-order derivative of the geomagnetic station data is obtained, and the correlation coefficient between the corresponding geomagnetic stations is calculated based on the second-order derivative results; Determining whether the correlation coefficient of the N geomagnetic station data within the same sliding time window is greater than a first preset threshold; If yes, it is determined that magnetic disturbance occurs in the sliding time window; and whether the correlation coefficient of the N geomagnetic station data in K consecutive sliding time windows is greater than a first preset threshold; K ≥ 2; If yes, the time period of K consecutive sliding windows is determined as the magnetic disturbance occurrence period; The data of geomagnetic stations are geomagnetic F values.

2. The method for determining the geomagnetic disturbance period according to claim 1, wherein: The first preset threshold is 0.

9.

3. The method for determining the geomagnetic disturbance period according to claim 1, wherein: N＝2。 4. The method for determining the geomagnetic disturbance period according to claim 1, wherein: The geographical locations between the N geomagnetic stations are smaller than a first preset range.

5. The method for determining the geomagnetic disturbance period according to claim 1, wherein: The latitude difference between N geomagnetic stations does not exceed 5°, and the longitude difference does not exceed 50°.

6. The method for determining the geomagnetic disturbance period according to claim 1, wherein: If it is determined that the correlation coefficient of the N geomagnetic station data within the same sliding time window is not greater than the first preset threshold, it is determined that the sliding time window is magnetically quiet.

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