A method for eliminating the long-term trend of ionospheric total electron content based on GNSS observations

Abstract

The present invention discloses a method for eliminating the long-term trend of the ionospheric total electron content (TEC) based on GNSS observations. The method comprises: extracting oblique ionospheric total electron content (TEC) observation data from GNSS satellites before and after an ionospheric disturbance occurs, converting the TEC observation data into vertical TEC observation data; performing time series preprocessing on the vertical TEC observation data to obtain target TEC time series data; calculating the disturbance occurrence time range based on the target TEC time series data; performing TEC background observation preprocessing based on the disturbance occurrence time range to obtain original TEC background observations during the disturbance occurrence period; calculating the long-term trend of the ionospheric total electron content during the disturbance occurrence period based on the original TEC background observations during the disturbance occurrence period; and eliminating the long-term trend of the ionospheric total electron content during the ionospheric disturbance period. The present invention can quickly and accurately eliminate the long-term trend of the total electron content during the ionospheric disturbance period, thereby improving the accuracy and reliability of ionospheric disturbance monitoring.

Description

Technical Field

[0001] The present invention belongs to the field of space physics technology, and in particular relates to a method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations. Background Art

[0002] The ionosphere, located between the fully ionized magnetosphere and the completely neutral lower atmosphere, serves as a crucial transition zone for the exchange of matter, energy, and momentum between these spheres. In addition to conventional background variations such as annual, seasonal, and diurnal variations, the ionosphere is susceptible to various extreme weather events, space activities, and human activities, which can lead to anomalous structures such as ionospheric disturbances. Observations of the ionospheric total electron content (TEC) derived from the Global Navigation Satellite System (GNSS) offer advantages such as wide coverage, real-time observations, fine temporal and spatial resolution, high measurement accuracy, and weather resistance, making them the primary means of ionospheric exploration. Long-term trends in ionospheric TEC data are often caused by complex factors such as solar activity, geomagnetic activity, and neutral atmospheric composition, which interfere with short-term TEC variations. By eliminating these long-term trends, TEC data can more accurately reflect short-term disturbances and anomalous variations in the ionosphere, providing a clearer and more accurate data foundation for ionospheric scientific research.

[0003] Methods for eliminating long-term trends in the ionospheric total electron content (TEC) can generally be categorized as background correction or direct correction. Background correction involves describing the long-term trend of ionospheric TEC using a reference background value. GNSS observations before and after the disturbance are used, and methods such as quadratic difference calculations are used to eliminate the diurnal and daily variations in the background ionospheric electron content at the time of the disturbance, thereby estimating the TEC background trend before and after the disturbance. Direct correction methods use field-measured TEC data to monitor the time range of the disturbance, replacing the TEC observations at the time of the disturbance with lines connecting the disturbance boundary points to eliminate the influence of long-term trends and other non-disturbance factors. Both methods have limitations. Background correction methods can more accurately reflect long-term ionospheric trends, but the temporal and spatial range of the disturbance is dependent on the GNSS ground-based and satellite positions, requiring sufficient reference data to ensure the accuracy of the disturbance extraction range. Direct correction methods process observational data directly without relying on external models or reference data, but they cannot accurately reflect the background TEC variations during the disturbance.

[0004] Therefore, there is an urgent need for a method to eliminate the long-term trend of TEC based on GNSS observations, which combines the advantages of direct correction methods and background correction methods, to address the current limitations of eliminating the long-term trend of the total electron content in the ionosphere. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a method for eliminating the long-term trend of the total electron content in the ionosphere based on GNSS observations. A direct correction method is used to monitor the time range of the disturbance, and then the GNSS data reference background value method is used to eliminate the long-term trend of the total electron content during the ionosphere disturbance, so as to achieve the purpose of extracting the ionosphere disturbance.

[0006] To achieve the above object, the present invention provides a method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations, comprising:

[0007] Extracting oblique ionospheric total electron content (TEC) observation data from GNSS satellites before and after the ionospheric disturbance occurs, and converting the oblique ionospheric total electron content (TEC) observation data into vertical TEC observation data;

[0008] performing time series preprocessing on the vertical TEC observation data to obtain target TEC time series data;

[0009] Calculating a disturbance occurrence time range based on the target TEC time series data;

[0010] Based on the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period;

[0011] Based on the original TEC background observations during the period when the disturbance occurred, the long-term trend of the total electron content in the ionosphere during the period when the disturbance occurred was calculated;

[0012] Based on the original TEC background observations during the disturbance period and the long-term trend of the total electron content in the ionosphere during the disturbance period, the long-term trend of the total electron content in the ionosphere during the disturbance period is eliminated.

[0013] Optionally, using a projection function to convert oblique ionospheric total electron content (TEC) observation data into vertical TEC observation data includes:

[0014]

[0015] Among them, TEC S is the observed oblique TEC; TEC V is the vertical TEC; SF is the tilt factor; E i is the elevation angle at the puncture point; E0 is the elevation angle at the receiver position; r e is the average radius of the Earth; h m is the height of the ionospheric thin layer model.

[0016] Optionally, performing time series preprocessing on the vertical TEC observation data to obtain target TEC time series data includes:

[0017]

[0018] Where x is the time after class normalization; y is the TEC time series after class normalization; τ0 is the total duration of the TEC time series, and ζ0 is the TEC background value.

[0019] Optionally, calculating the disturbance occurrence time range based on the target TEC time series data includes:

[0020] A ball with a center at (x0, y0) and a radius of R0 is set above the target TEC time series data. When the ball rolls over the class-normalized TEC time series, there is a contact point between the ball and the class-normalized TEC time series. The ball rotates around the contact point and rolls in the direction of increasing time t until it lands on the next contact point. The contact point between the ball and the class-normalized TEC time series is calculated as (x0+Δx, y0+Δy):

[0021]

[0022]

[0023] Where α is the angle between the line connecting the two contact points and the radius of the sphere; β is the complementary angle of α; θ is the angle between the horizontal line when the y value of the first contact point is fixed and the line connecting the two contact points; δ is the leading edge angle of the sphere; Δx is the time step after class normalization; Δy is the step size of the TEC after class normalization; and R0 is the radius of the sphere.

[0024] Optionally, in combination with the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period, including:

[0025] Normalize the TEC time series to XY space by inverse class normalization:

[0026]

[0027] Among them, the corresponding points of (x1, y1) and (x2, y2) are (t1, TEC1) and (t2, TEC2), and the TEC value during the disturbance is TEC d ;τ0 is the total duration of TEC sequence; is the TEC background value;

[0028] The original TEC background observation during the disturbance is obtained based on the average value of the GNSS vertical TEC data reference background two days before and after the disturbance:

[0029]

[0030] TEC Previous TEC is the TEC value between the start and end time of the disturbance one day before the disturbance occurs; TEC afterTEC is the TEC value between the start and end time of the disturbance one day after the disturbance occurs; TEC m is the original TEC background observation during the disturbance period; TEC m1 ,TEC m2 TEC m The starting point value and the ending point value.

[0031] Optionally, calculating the long-term trend of the total electron content in the ionosphere during the period when the disturbance occurs based on the original TEC background observation during the period when the disturbance occurs includes:

[0032] The original TEC background observation during the disturbance period is linearly transformed so that the starting point value of the original TEC background observation during the disturbance period is TEC1 and the ending point value is TEC2, and the long-term trend of the total electron content in the ionosphere during the disturbance period is obtained. t :

[0033] TEC t =kTEC m +c

[0034]

[0035] Among them, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance; TEC m is the original TEC background observation during the disturbance; k is the slope of the linear transformation; c is the intercept of the linear transformation; TEC2 is the TEC time series and TEC m The end point value of the corresponding time range; TEC1 is the TEC timing and TEC m The starting point value of the corresponding time range; TEC m2 For TEC m The end point value of TEC m1 For TEC m The starting point value.

[0036] Optionally, the long-term trend of total electron content during the period of ionospheric disturbance removal includes:

[0037] DTEC=TEC d -TEC t

[0038] Where DTEC is the TEC value during the ionospheric disturbance that eliminates the long-term trend of the total electron content, and TEC d is the TEC value during the disturbance period, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance.

[0039] Technical effect of the invention: The present invention discloses a method for eliminating the long-term trend of the total electron content in the ionosphere based on GNSS observations, which can quickly and accurately eliminate the long-term trend of the total electron content during ionospheric disturbances, improve the accuracy and reliability of ionospheric disturbance monitoring, and have a profound impact on ionospheric scientific research and space weather monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0041] Figure 1 A schematic diagram of extracting the time range of ionospheric disturbance occurrence calculated according to an embodiment of the present invention;

[0042] Figure 2 This is a flow chart of a method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of a long-term trend calculation of the total electron content during ionospheric disturbances based on GNSS observation data according to an embodiment of the present invention;

[0044] Figure 4 This is a schematic diagram of ionospheric disturbances after eliminating the long-term trend of total electron content, calculated based on GNSS observation data, according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0046] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0047] like Figure 2 As shown, this embodiment provides a method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations, including:

[0048] Extract the oblique ionospheric total electron content (TEC) observation data of the GNSS satellite before and after the ionospheric disturbance occurs, and convert the oblique ionospheric total electron content (TEC) observation data into vertical TEC observation data;

[0049] Perform time series preprocessing on vertical TEC observation data to obtain target TEC time series data;

[0050] Calculate the time range of disturbance occurrence based on target TEC time series data;

[0051] Combined with the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period;

[0052] Based on the original TEC background observations during the disturbance period, the long-term trend of the total electron content in the ionosphere during the disturbance period is calculated;

[0053] Based on the original TEC background observations during the disturbance period and the long-term trend of the total electron content in the ionosphere during the disturbance period, the long-term trend of the total electron content in the ionosphere during the disturbance period is eliminated.

[0054] Furthermore, the projection function is used to convert the oblique ionospheric total electron content TEC observation data into vertical TEC observation data, including:

[0055]

[0056] Among them, TEC S is the observed oblique TEC; TEC V is the vertical TEC; SF is the tilt factor; E i is the elevation angle at the puncture point; E0 is the elevation angle at the receiver position; r e is the average radius of the Earth; h m is the height of the ionospheric thin layer model.

[0057] Furthermore, the vertical TEC observation data is preprocessed to obtain the target TEC time series data. The process includes: unifying the ionospheric disturbance observations into disturbances with TEC decrease. If the ionospheric disturbance is a disturbance with TEC rapidly increase, the TEC value takes a negative sign. In addition, the TEC time series is normalized to the XY space using the total TEC time series duration and the TEC background value, so that the TEC time series data is limited to a certain range:

[0058]

[0059] Where x is the time after class normalization; y is the TEC time series after class normalization; τ0 is the total time length of the TEC time series, is the TEC background value.

[0060] Further, such as Figure 1 The disturbance occurrence time range calculated based on the target TEC time series data includes:

[0061] A ball with a center at (x0, y0) and a radius of R0 is set above the target TEC time series data. When the ball rolls over the class-normalized TEC time series, there is a contact point between the ball and the class-normalized TEC time series. The ball rotates around the contact point and rolls forward until it lands on the next contact point. The contact point between the ball and the class-normalized TEC time series is calculated as (x0+Δx, y0+Δy):

[0062]

[0063]

[0064] Where α is the angle between the line connecting the two contact points and the radius of the sphere; β is the complementary angle of α; θ is the angle between the horizontal line with the fixed y value of the first contact point and the line connecting the two contact points; δ is the leading edge angle of the sphere; Δx is the time step after class normalization; Δy is the step size of the class normalized TEC; and R0 is the radius of the sphere. During non-perturbation, the time series of each contact point and the TEC are identical. During perturbation, there is a longer time span between adjacent contact points. The starting point of the perturbation is denoted as (x1, y1) and the ending point is denoted as (x2, y2).

[0065] α, β, θ, and δ are angles, with Δx being positive. All angles are in radians, with α∈[0,π], θ∈[-π / 2,π / 2], and δ∈[-π,π]. Based on geometric relationships, the next contact point is the one with the smallest angular distance δ from the leading edge of the ball. If the next contact point is outside 2R0, the first data point outside 2R0 is designated as the next contact point. During non-perturbation periods, each contact point has the same TEC timing. During perturbations, the TEC decreases rapidly, resulting in a longer time span between adjacent contact points. The perturbation starts at (x1,y1) and ends at (x2,y2).

[0066] Furthermore, based on the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period, including:

[0067] Normalize the TEC time series to XY space by inverse class normalization:

[0068]

[0069] Among them, the corresponding points of (x1, y1) and (x2, y2) are (t1, TEC1) and (t2, TEC2), and the TEC value during the disturbance is TEC d ;τ0 is the total duration of TEC time series;ζ0 is the TEC background value;

[0070] The original TEC background observation during the disturbance is obtained based on the average value of the GNSS vertical TEC data reference background two days before and after the disturbance:

[0071]

[0072] TEC Previous TEC is the TEC value between the start and end time of the disturbance one day before the disturbance occurs; TEC after The TEC value between the start and end time of the disturbance one day after the disturbance occurs; the original TEC background observation during the disturbance period is recorded as TEC m ;TEC m1 ,TEC m2 TEC m The starting point value and the ending point value.

[0073] Furthermore, based on the original TEC background observations during the disturbance, the long-term trend of the total electron content in the ionosphere during the disturbance is calculated, including:

[0074] TEC m Do a linear transformation so that TEC m The starting point value is TEC1, the ending point value is TEC2, and the long-term trend of the total electron content in the ionosphere during the disturbance is obtained. t :

[0075] TEC t =kTEC m +c

[0076]

[0077] Among them, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance; TEC m is the original TEC background observation during the disturbance; k is the slope of the linear transformation; c is the intercept of the linear transformation; TEC2 is the TEC time series and TEC m The end point value of the corresponding time range; TEC1 is the TEC timing and TEC m The starting point value of the corresponding time range; TEC m2 For TEC m The end point value of TEC m1 For TEC m The starting point value.

[0078] Furthermore, the long-term trend of total electron content during the period of eliminating ionospheric disturbances includes:

[0079] DTEC=TEC d -TEC t

[0080] Where DTEC is the TEC value during the ionospheric disturbance that eliminates the long-term trend of the total electron content, and TECd is the TEC value during the disturbance period, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance.

[0081] An application example of this embodiment is:

[0082] Taking the data measured by a GNSS observation station on December 7, 2014, as an example, the Long March 4B carrier rocket launched at 03:26:04 UT on that day injected exhaust gas into the ionosphere, causing a significant decrease in the total electron content (TEC) near the rocket's trajectory. To eliminate the long-term trend in TEC during that day's ionospheric disturbance and obtain the TEC change caused by the ionospheric disturbance, the following steps were performed, using the observation data from a GNSS station and satellite 10 at 03:20:00 UT as an example:

[0083] Extract the slant TEC observation data of the GNSS satellite and use the projection function to convert the slant TEC into vertical TEC: Take the two target times of 03:26:04 (the time of rocket launch, that is, the time when ionospheric disturbance has not yet occurred) and 03:31:01 (the time when TEC begins to drop rapidly) as examples. The slant TEC values ​​observed by GNSS at 03:26:04 and 03:31:01 are TEC respectively. S01 =39.252621138615800TECU and TEC S02 =39.672895715650380TECU, the elevation angles E0 at the receiver position are E 01 =0.9462 and E 02 = 0.9103. The average radius of the Earth r e Take 6378km, the height of the ionosphere thin layer model h m Take 350km and use the projection function to convert oblique TEC into vertical TEC:

[0084]

[0085] TEC timing preprocessing: Normalize the TEC timing class to XY space, with τ0 set to 2h and ζ0 set to 40TECU. Take the TEC values ​​of 03:26:04 and 03:31:01 UTC as an example:

[0086]

[0087] Calculate the contact point: take radius R0 = 0.5. The time before the disturbance occurs: 03:26:04 (x 01 ,y 01 ) and the moment when TEC begins to drop rapidly: 03:31:01 and (x 02 ,y 02) as an example:

[0088] (1) Calculate the time when the ionospheric disturbance has not yet occurred (x 01 ,y 01 )’s next touchpoint:

[0089] (x 01 ,y 01 ) and the first moment after (x 01_next1 ,y 01_next1 ) is: Δx 01_1 =1.388888888889106×10 -4 , Δy 01_1 =1.503571014093152×10 -4 .

[0090]

[0091] δ 01_1 =β 01_1 -θ 01_1 =-0.824821366604825,

[0092] (x 01 ,y 01 ) and the second moment after (x 01_next2 ,y 01_next2 ) is: Δx 01_2 =2.7777777777778212×10 -4 , Δy 01_2 =-8.561414517538335×10 -4 .

[0093]

[0094] δ 01_2 =β 01_2 -θ 01_2 =0.299263296368674,

[0095] (x 01 ,y 01 ) and the 3933rd moment (x 01_next3933 ,y 01_next3933 ) is:

[0096] Δx 01_3933 =0.546250000000000, Δy 01_3933 =-0.030083169546805.

[0097]

[0098] δ 01_3933 =β 01_3933 -θ 01_3933 =0.633885824937236

[0099] Calculate (x 01 ,y 01 ) and the leading edge angle v in the range of 2R0 thereafter, a total of 3933 moments 01_1 to δ 01_3933 , we get δ 01_1 is the minimum value, that is, (x 01 ,y 01 ) is the next contact point at the next moment (x 01_next1 ,y 01_next1 ).

[0100] (2) Calculate the time when TEC begins to drop rapidly (x 02 ,y 02 )’s next touchpoint:

[0101] (x 02 ,y 02 ) and the first moment after (x 02_next1 ,y 02_next1 ) is: Δx 02_1 =1.388888888889106×10 -4 , Δy 02_1 =-0.007534892018917.

[0102]

[0103] δ 02_1 =β 02_1 -γ 02_1 =1.559901892946139.

[0104] (x 02 ,y 02 ) and the second moment after (x 02_next2 ,y 02_next2 ) is: Δx 02_2 =2.7777777777778212×10 -4 , Δy 02_2 =-0.024166831198669.

[0105]

[0106] δ 02_2 =β 02_2 -θ 02_2 =1.583473439350501.

[0107] (x 02 ,y 02 ) and the 2654th moment after (x 02_next2654 ,y 02_next2654 ) is: Δx 02_2654 =0.368611111111111, Δy 02_2654 =-0.053589760385010.

[0108]

[0109] δ 02_2654 =β 02_2654 -θ 02_2654 =0.526058073413885.

[0110] (x 02 ,y 02 ) and the 3636th moment (x 02_next3636 ,y 02_next3636 ) is: Δx 02_3636 =0.505000000000000, Δy 02_3636 =-0.020173451757626.

[0111]

[0112] δ 02_3636 =β 02_3636 -θ 02_3636 =0.569774883335386

[0113] Calculate (x 02 ,y 02 ) and the leading edge angle δ in the range of 2R0 thereafter, a total of 3636 moments 02_1 to δ 02_3636 , we get δ 02_2654 is the minimum value, that is, (x 02 ,y 02 ) is the next contact point 2654 moments later (x 02_next2654 ,y 02_next2654 ).

[0114] The above calculations prove that during the non-disturbance period, the timing of each contact point is the same as that of the TEC; during the disturbance period, there is a long time span between adjacent contact points. The starting point of the disturbance is (x 02 ,y 02 ), the end point is (x 02_next2654 ,y 02_next2654 );

[0115] TEC background observation preprocessing: normalize the contact points obtained in the previous step by inverse class, and take the starting point of the disturbance as (x 02 ,y 02 ) and the end point (x 02_next2654 ,y 02_next2654 ) as an example:

[0116]

[0117] Get the starting point of the disturbance in the TEC time series: (t 02 ,TEC 02 ),lie in Figure 3 The beginning of the middle dashed line; the end point of the disturbance in the TEC time series: (t 02_next2654 ,TEC 02_next2654 ),lie in Figure 3 The end of the middle dashed line. The TEC value during the disturbance is TEC d ,for Figure 3 The background value of GNSS vertical TEC data two days before and after the disturbance is Figure 3 Medium-thin line, Figure 3 The thin line at the bottom is the vertical TEC data of the day before the disturbance. Previous , Figure 3 The thin line above is the vertical TEC data one day after the disturbance occurred. after The vertical TEC data before and after the disturbance are added together to obtain the average value. Denoted as TEC m TEC m The starting point is the TEC data background value at the beginning of the disturbance, denoted as TEC m1 =31.548326846658036TECU;TEC m The end of the disturbance is the TEC data background value at the end of the disturbance, denoted as TEC m2 =29.943995178658910TECU.

[0118] Calculate the long-term trend of the total electron content in the ionosphere during the disturbance: m Do a linear transformation so that TEC m1 =TEC 02 ,TEC m2 =TEC 02_next2654 ;

[0119]

[0120] Obtain the long-term trend of the total electron content in the ionosphere during the disturbance period t =kTEC m +c, for Figure 3 Middle dotted line.

[0121] Obtain the TEC change value DTEC=TEC after eliminating the long-term trend of the total electron content during the ionospheric disturbance d -TEC t ,for Figure 4 Middle solid line.

[0122] like Figure 3 As shown, the method of this embodiment is used to calculate the long-term trend of the ionospheric disturbance caused by rocket exhaust based on the actual measurement data of satellite No. 10 on December 7, 2014 at a certain GNSS observation station. Figure 3 The middle dashed line is the long-term trend of the total electron content during the ionospheric disturbance. Figure 4 This is the TEC value after removing the long-term trend of the total electron content during ionospheric disturbances. It can be seen that using GNSS observations to remove the long-term trend of the total electron content during ionospheric disturbances clearly shows the decrease in TEC during ionospheric disturbances, effectively extracting ionospheric disturbances.

[0123] The present invention discloses a method for eliminating the long-term trend of the total electron content in the ionosphere based on GNSS observations. The method can quickly and accurately eliminate the long-term trend of the total electron content during ionospheric disturbances, improve the accuracy and reliability of ionospheric disturbance monitoring, and have a profound impact on ionospheric scientific research and space weather monitoring.

[0124] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations, characterized in that: include: Extracting oblique ionospheric total electron content (TEC) observation data from GNSS satellites before and after the ionospheric disturbance occurs, and converting the oblique ionospheric total electron content (TEC) observation data into vertical TEC observation data; performing time series preprocessing on the vertical TEC observation data to obtain target TEC time series data; Calculating a disturbance occurrence time range based on the target TEC time series data includes: A ball with a center at (x0, y0) and a radius of R0 is set above the target TEC time series data. When the ball rolls over the class-normalized TEC time series, there is a contact point between the ball and the class-normalized TEC time series. The ball rotates around the contact point and rolls in the direction of increasing time t until it lands on the next contact point. The contact point between the ball and the class-normalized TEC time series is calculated as (x0+Δx,y0+Δy): Where α is the angle between the line connecting the two contact points and the radius of the ball; β is the complementary angle of α; θ is the angle between the horizontal line when the y value of the first contact point is fixed and the line connecting the two contact points; δ is the leading edge angle of the ball; Δx is the time step after class normalization; Δy is the step size of TEC after class normalization; R0 is the radius of the ball; Based on the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period; Based on the original TEC background observations during the period when the disturbance occurred, the long-term trend of the total electron content in the ionosphere during the period when the disturbance occurred was calculated; Based on the original TEC background observations during the disturbance period and the long-term trend of the total electron content in the ionosphere during the disturbance period, the long-term trend of the total electron content in the ionosphere during the disturbance period is eliminated.

2. The method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to claim 1, characterized in that: The projection function is used to convert the oblique ionospheric total electron content TEC observation data into vertical TEC observation data, including: Among them, TEC s is the observed oblique TEC; TEC V is the vertical TEC; SF is the tilt factor; E i is the elevation angle at the puncture point; E0 is the elevation angle at the receiver position; r e is the average radius of the Earth; h m is the height of the ionospheric thin layer model.

3. The method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to claim 1, characterized in that: Performing time series preprocessing on the vertical TEC observation data to obtain target TEC time series data includes: Where x is the time after class normalization; y is the TEC time series after class normalization; τ0 is the total time length of the TEC time series, is the TEC background value.

4. The method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to claim 1, characterized in that: Combined with the time range of the disturbance, TEC background observation preprocessing is performed to obtain the original TEC background observation during the disturbance period, including: Normalize the TEC time series to XY space by inverse class normalization: Among them, the corresponding points of (x1, y1) and (x2, y2) are (t1, TEC1) and (t2, TEC2), and the TEC value during the disturbance is TEC d ;τ0 is the total duration of TEC sequence; is the TEC background value; The original TEC background observation during the disturbance is obtained based on the average value of the GNSS vertical TEC data reference background two days before and after the disturbance: TEC Previous TEC is the TEC value between the start and end time of the disturbance one day before the disturbance occurs; TEC after TEC is the TEC value between the start and end time of the disturbance one day after the disturbance occurs; TEC m is the original TEC background observation during the disturbance period; TEC m1 ,TEC m2 TEC m The starting point value and the ending point value.

5. The method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to claim 1, characterized in that: Based on the original TEC background observations during the period of the disturbance, the long-term trend of the total electron content in the ionosphere during the period of the disturbance is calculated, including: The original TEC background observation during the disturbance period is linearly transformed so that the starting point value of the original TEC background observation during the disturbance period is TEC1 and the ending point value is TEC2, and the long-term trend of the total electron content in the ionosphere during the disturbance period is obtained. t : TEC t =k×TEC m +c Among them, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance; TEC m is the original TEC background observation during the disturbance; k is the slope of the linear transformation; c is the intercept of the linear transformation; TEC2 is the TEC time series and TEC m The end point value of the corresponding time range; TEC1 is the TEC timing and TEC m The starting point value of the corresponding time range; TEC m2 For TEC m The end point value of TEC m1 For TEC m The starting point value.

6. The method for eliminating the long-term trend of the total electron content of the ionosphere based on GNSS observations according to claim 1, characterized in that: Long-term trends in total electron content during the period of ionospheric disturbance removal include: DTEC=TEC d -TEC t Where DTEC is the TEC value during the ionospheric disturbance that eliminates the long-term trend of the total electron content, and TEC d is the TEC value during the disturbance period, TEC t is the long-term trend of the total electron content in the ionosphere during the disturbance.

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