阅读说明：本技术 一种基于北斗系统的矢量电离层延迟改正方法 (Vector ionosphere delay correction method based on Beidou system ) 是由 李奇 马冠一 耿长江 万庆涛 于 2019-09-24 设计创作，主要内容包括：本发明公开了一种基于北斗系统的矢量电离层延迟改正方法,该方法包括：利用多个组网的地面监测站分别测量电离层薄壳矢量的电离层延迟；多个组网的地面监测站将穿刺点的五元组矢量电离层延迟观测值汇总到中心处理站；中心处理站将多个穿刺点的五元组矢量电离层延迟观测值转化为格网点矢量电离层延迟,形成矢量电离层产品数据；中心处理站将矢量电离层产品数据通过上传站上传至GEO卫星；由GEO卫星在D2导航电文进行播发；利用矢量电离层产品数据进行矢量电离层改正。本发明的方法能够大幅提高大TEC梯度场景下的电离层延迟校正精度。(The invention discloses a vector ionosphere delay correction method based on a Beidou system, which comprises the following steps: respectively measuring the ionospheric delay of ionospheric thin-shell vectors by using a plurality of networked ground monitoring stations; collecting quintuple vector ionosphere delay observation values of puncture points to a central processing station by a plurality of networked ground monitoring stations; the central processing station converts the five-tuple vector ionosphere delay observation values of the plurality of puncture points into grid point vector ionosphere delay to form vector ionosphere product data; the central processing station uploads the vector ionosphere product data to the GEO satellite through the uploading station; broadcasting the navigation message at D2 by the GEO satellite; and carrying out vector ionosphere correction by using the vector ionosphere product data. The method can greatly improve the ionospheric delay correction accuracy in the large TEC gradient scene.)

1. A vector ionosphere delay correction method based on a Beidou system comprises the following steps:

respectively measuring the ionospheric delay of ionospheric thin-shell vectors by using a plurality of networked ground monitoring stations;

collecting quintuple vector ionosphere delay observation values of puncture points to a central processing station by a plurality of networked ground monitoring stations;

the central processing station converts the five-tuple vector ionosphere delay observation values of the plurality of puncture points into grid point vector ionosphere delay to form vector ionosphere product data;

the central processing station uploads the vector ionosphere product data to the GEO satellite through the uploading station; broadcasting the navigation message at D2 by the GEO satellite;

and carrying out vector ionosphere correction by using the vector ionosphere product data.

2. The Beidou system-based vector ionospheric delay correction method of claim 1, wherein said ground monitoring stations using a plurality of networking measure ionospheric thin-shell vectors individually; the method specifically comprises the following steps:

each ground monitoring station utilizes Beidou double-frequency observation, and the basic equation for calculating the total electron content is as follows:

VTEC＝STEC*cosχ (1)

STEC＝n₀(ρ₂-ρ₁)+B_r+B_s(2)

ρ₁and ρ₂Representing pseudo-range observations of corresponding dual-frequency carriers; n is₀＝8.991*10¹⁶m^-3Is a constant; STEC and VTEC represent the total content of ionospheric electron concentration in vertical and oblique directions, respectively; parameter B_rAnd B_sThe hardware deviation of the ground monitoring station and the Beidou navigation satellite; χ is the zenith angle of the puncture point.

3. The Beidou system-based vector ionospheric delay correction method of claim 2, wherein the quintuple vector ionospheric delay observed value of the puncture point is: [ lon, lat, VTEC, x, y ], wherein lon and lat are respectively the longitude and latitude of the puncture point; [ x y ] represents the projection vector of the electromagnetic wave propagation path of the puncture point on the ionospheric pellicle, wherein x represents the east component and the east is positive, y represents the south component and the south is positive.

4. The Beidou system-based vector ionosphere delay correction method according to claim 3, wherein the central processing station converts quintuple vector ionosphere delay observation values of a plurality of puncture points into grid point vector ionosphere delays to form vector ionosphere product data; the method specifically comprises the following steps:

step S1), collecting quintuple vector ionosphere delay observation values [ lon, lat, VTEC, x, y ] of puncture points fed back by all the monitoring stations on the ground;

step S2) dividing the thin spherical shell area in the designated range into a plurality of lattice points according to longitude and latitude intervals;

step S3), for the jth grid point, the VTEC of all the neighbor puncture points of the jth grid point is a linear function of longitude and latitude, and the conditions are as follows:

VTEC_i＝c₀+c₁*lat_i+c₂*lon_i(11)

wherein, lat_iAnd lon_iLongitude and latitude of the ith neighbor puncture point; VTEC_iThe VTEC value of the ith neighbor puncture point;

obtaining coefficient c by least squares linear fitting₀、c₁And c₂；

Step S4) calculating the difference Δ VTEC between the true value and the fitting value_i：

ΔVTEC_i＝VTEC_i-(c₀+c₁*lat_i+c₂*lon_i) (12)

Delta VTEC of all neighbor puncture points_iIs a linear function of a longitude and latitude projection vector, and satisfies the following conditions:

ΔVTEC_i＝a₀+a₁*y_i+b₁*x_i(13)

obtaining coefficient a by least squares linear fitting₀、a₁And b₁；[x_i,y_i]The projection vector of the electromagnetic wave propagation path of the ith neighbor puncture point on the ionosphere thin shell;

step S5) calculating VTEC of j grid point_j0：

VTEC_i0＝VTEC_i+a₀(14)

Wherein VTEC_i0Is VTEC_iThe correction value of (1); d_ijThe distance between the jth lattice point and the ith neighbor puncture point is R, and R is the radius of a neighbor area defined by the jth lattice point;

step S5) calculating an ionospheric delay parameter for the j-th grid point: d τ_j0、dτ_ja1And d τ_jb1：

Ionospheric vertical delay d τ of jth grid point_j0Comprises the following steps:

wherein f is₁Is the frequency of carrier 1；

Ionospheric east correction parameter d tau for jth grid point_ja1Ionospheric correction parameter d τ in the southbound direction_jb1Respectively as follows:

dτ_ja1＝a₁，dτ_jb1＝b₁(17)

step S6) the ionospheric delay parameters of all grid points are collected to form vector ionospheric product data.

5. The vector ionospheric delay correction method based on the beidou system of claim 4, wherein the step S2) is specifically:

the thin spherical shell area with east longitude of 70-145 degrees and north latitude of 7.5-55 degrees is divided into 320 lattice points according to longitude and latitude of 5 multiplied by 2.5 degrees.

6. The Beidou system-based vector ionospheric delay correction method of claim 4 or 5, wherein the content broadcast by the GEO satellite in the D2 navigation message comprises: ionospheric vertical delay of ionospheric grid points, ionospheric east correction parameters, ionospheric south correction parameters, and ionospheric vertical delay error indices; the ionospheric vertical delay occupies 9 bits, the ionospheric east correction parameters and the ionospheric south correction parameters respectively occupy 8 bits, and the ionospheric vertical delay error index occupies 4 bits.

7. The Beidou system-based vector ionosphere delay correction method according to claim 6, wherein the vector ionosphere correction is performed by using vector ionosphere product data, specifically:

for a puncture point, the positions of 4 grid points around the puncture point are p₁,p₂,p₃,p₄Expressing the vertical ionospheric delay parameter of lattice point spread by d τ₁,dτ₂,dτ₃,dτ₄Represents; the distance weights of the puncture point and the four grid points are respectively used

wherein, d τ_k＝(dτ_k0,dτ_ka1,dτ_kb1),k＝1,2,3,4；

The final pseudo-range ionospheric correction IC for the puncture point_pComprises the following steps:

wherein, χ_pThe zenith angle of the puncture point, [ x ]_p,y_p]Is the projection vector of the observation path of the puncture point on the ionosphere shell.

Technical Field

The invention relates to the field of satellite navigation, in particular to a vector ionosphere delay correction method based on a Beidou system.

Background

In fig. 1, a network element related to a beidou navigation ionosphere product is shown, and in the existing vector ionosphere delay correction method, an important problem is that the electron density information of an ionosphere thin shell is assumed to be isotropic, as shown in fig. 2, for two observations passing through the same puncture point, if one of the observed satellites is north, the receiver is south, the other observed receiver is south, and the satellite is north, but as long as the altitude angles of the satellites are the same, the ionosphere correction values obtained by the two observations according to the prior art are the same.

However, in an objective sense, due to the large amount of free electrons contributed by the plasma layer, the electron density distribution of the ionosphere is often not isotropic, i.e., the two actual observed TEC delays in fig. 2 may be very different, and especially when sunrise, sunset, winter, spring, night, or ionospheric disturbances occur, the anisotropy is especially severe. This in turn leads to increased error in scalar ionospheric corrections and, consequently, worse results.

Disclosure of Invention

The invention aims to overcome the technical defects and provides a novel vector ionosphere delay correction method based on the Beidou system.

In order to achieve the purpose, the invention provides a vector ionosphere delay correction method based on a Beidou system, which comprises the following steps:

respectively measuring the ionospheric delay of ionospheric thin-shell vectors by using a plurality of networked ground monitoring stations;

collecting quintuple vector ionosphere delay observation values of puncture points to a central processing station by a plurality of networked ground monitoring stations;

the central processing station converts the five-tuple vector ionosphere delay observation values of the plurality of puncture points into grid point vector ionosphere delay to form vector ionosphere product data;

the central processing station uploads the vector ionosphere product data to the GEO satellite through the uploading station; broadcasting the navigation message at D2 by the GEO satellite;

and carrying out vector ionosphere correction by using the vector ionosphere product data.

As an improvement of the above method, the ground monitoring stations using a plurality of networks respectively measure the ionospheric delay of the ionospheric thin-shell vector; the method specifically comprises the following steps:

each ground monitoring station utilizes Beidou double-frequency observation, and the basic equation for calculating the total electron content is as follows:

VTEC＝STEC*cosχ (1)

STEC＝n₀(ρ₂-ρ₁)+B_r+B_s(2)

ρ₁and ρ₂Representing pseudo-range observations of corresponding dual-frequency carriers; n is₀＝8.991*10¹⁶m^-3Is a constant; STEC and VTEC represent the total content of ionospheric electron concentration in vertical and oblique directions, respectively; parameter B_rAnd B_sThe hardware deviation of the ground monitoring station and the Beidou navigation satellite; χ is the zenith angle of the puncture point.

As an improvement of the above method, the observed value of the five-tuple vector ionospheric delay of the puncture point is: [ lon, lat, VTEC, x, y ], wherein lon and lat are respectively the longitude and latitude of the puncture point; [ x y ] represents the projection vector of the electromagnetic wave propagation path of the puncture point on the ionospheric pellicle, wherein x represents the east component and the east is positive, y represents the south component and the south is positive.

As an improvement of the above method, the central processing station converts the five-tuple vector ionosphere delay observed values of a plurality of puncture points into grid point vector ionosphere delays to form vector ionosphere product data; the method specifically comprises the following steps:

step S1), collecting quintuple vector ionosphere delay observation values [ lon, lat, VTEC, x, y ] of puncture points fed back by all the monitoring stations on the ground;

step S2) dividing the thin spherical shell area in the designated range into a plurality of lattice points according to longitude and latitude intervals;

step S3), for the jth grid point, the VTEC of all the neighbor puncture points of the jth grid point is a linear function of longitude and latitude, and the conditions are as follows:

VTEC_i＝c₀+c₁*lat_i+c₂*lon_i(11)

wherein, lat_iAnd lon_iLongitude and latitude of the ith neighbor puncture point; VTEC_iThe VTEC value of the ith neighbor puncture point;

obtaining coefficient c by least squares linear fitting₀、c₁And c₂；

Step S4) calculating the difference Δ VTEC between the true value and the fitting value_i：

ΔVTEC_i＝VTEC_i-(c₀+c₁*lat_i+c₂*lon_i) (12)

Delta VTEC of all neighbor puncture points_iIs a linear function of a longitude and latitude projection vector, and satisfies the following conditions:

ΔVTEC_i＝a₀+a₁*y_i+b₁*x_i(13)

obtaining coefficient a by least squares linear fitting₀、a₁And b₁；[x_i,y_i]The projection vector of the electromagnetic wave propagation path of the ith neighbor puncture point on the ionosphere thin shell;

step S5) calculating VTEC of j grid point_j0：

VTEC_i0＝VTEC_i+a₀(14)

Wherein VTEC_i0Is VTEC_iThe correction value of (1); d_ijThe distance between the jth lattice point and the ith neighbor puncture point is R, and R is the radius of a neighbor area defined by the jth lattice point;

step S5)Calculating the ionospheric delay parameter of the jth grid point: d τ_j0、dτ_ja1And d τ_jb1：

Ionospheric vertical delay d τ of jth grid point_j0Comprises the following steps:

wherein f is₁Is the frequency of carrier 1;

ionospheric east correction parameter d tau for jth grid point_ja1Ionospheric correction parameter d τ in the southbound direction_jb1Respectively as follows:

dτ_ja1＝a₁，dτ_jb1＝b₁(17)

step S6) the ionospheric delay parameters of all grid points are collected to form vector ionospheric product data.

As a modification of the above method, the step S2) is specifically:

the thin spherical shell area with east longitude of 70-145 degrees and north latitude of 7.5-55 degrees is divided into 320 lattice points according to longitude and latitude of 5 multiplied by 2.5 degrees.

As an improvement of the above method, the content broadcast by the GEO satellite in the D2 navigation message includes: ionospheric vertical delay of ionospheric grid points, ionospheric east correction parameters, ionospheric south correction parameters, and ionospheric vertical delay error indices; the ionospheric vertical delay occupies 9 bits, the ionospheric east correction parameters and the ionospheric south correction parameters respectively occupy 8 bits, and the ionospheric vertical delay error index occupies 4 bits.

As an improvement of the above method, the performing vector ionospheric correction using vector ionospheric product data specifically includes:

for a puncture point, the positions of 4 grid points around the puncture point are p₁,p₂,p₃,p₄Expressing the vertical ionospheric delay parameter of lattice point spread by d τ₁,dτ₂,dτ₃,dτ₄Represents; the distance weights of the puncture point and the four grid points are respectively used

Represents; then the vector ionospheric corrections for the puncture point are:

wherein, d τ_k＝(dτ_k0,dτ_ka1,dτ_kb1),k＝1,2,3,4；

The final pseudo-range ionospheric correction IC for the puncture point_pComprises the following steps:

wherein, χ_pThe zenith angle of the puncture point, [ x ]_p,y_p]Is the projection vector of the observation path of the puncture point on the ionosphere shell.

The invention has the advantages that:

1. the method can greatly improve the ionospheric delay correction precision in the large TEC gradient scene;

2. the method of the invention can be applied in the following scenarios:

improving the ionospheric delay correction accuracy of all types of satellite navigation positioning, including GPS Galileo GlonassBeidou and the like;

the method is applied to ionospheric delay correction of services such as remote sensing, tracking, monitoring and the like of targets such as satellites, missiles, space debris and the like;

ionospheric delay correction applied to incoherent scatter radar;

the ionospheric delay correction method is applied to ionospheric delay correction of the radio astronomical observation array.

Drawings

FIG. 1 is a schematic diagram of a networking relationship of network elements related to a Beidou navigation ionosphere product;

FIG. 2 is a schematic view of an isotropic ionosphere thin shell;

FIG. 3 is a schematic view of a puncture point and zenith angle;

FIG. 4 is a schematic view of a projection vector of an observation path on an ionosphere thin shell;

FIG. 5 is a schematic diagram of a user's puncture points and grid points;

FIG. 6 is a diagram of ionospheric correction errors 200 round simulation results.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

The invention discloses a vector ionosphere delay correction method based on a Beidou system, which comprises the following steps:

step 1) measuring the vector ionospheric delay of an ionospheric thin shell by using a ground monitoring station network;

the basic equation for calculating the Total Electron Content (TEC) by using Beidou double-frequency observation is as follows:

VTEC＝STEC*cosχ (1)

STEC＝n₀(ρ₂-ρ₁)+B_r+B_s(2)

ρ 1 and ρ 2 represent pseudo range observations of the corresponding carriers.Is a constant that represents a pseudorange difference of 1 meter for the TEC of 8.991 TECUs. STEC and VTEC represent vertical and oblique TEC (total content of ionospheric electron concentration), respectively. Parameter B_rAnd B_sThe unit of the hardware deviation is the same as that of TEC, and the unit of the hardware deviation is the TECU. It is assumed that the hardware deviations of all the ground monitoring stations and the Beidou navigation satellite are known quantities which are accurately calibrated in advance.

Assuming that the ionosphere shell is 375km with fixed height, assuming that the coordinates of the ground monitoring station and the Beidou navigation satellite are accurately measured, x is the zenith angle of the puncture point, and is completely determined by the geometric relationship between the satellite and the monitoring station as shown in FIG. 3.

Step 2) the ground monitoring station network collects the vector ionosphere delay observation values of the puncture points to a central processing station;

all ground monitoring stations gather scalar ionosphere delay observation values to a central processing station according to a quintuple format, wherein the quintuple comprises [ lon, lat, VTEC, x and y ], and the lon and the lat are longitude and latitude of the puncture point respectively; [ x y ] has the meaning shown in FIG. 4, and represents the projection vector of the electromagnetic wave propagation path on the ionosphere thin shell, wherein x represents the east component and is positive, y represents the south component and is positive.

Step 3) the central processing station converts the ionosphere thin-shell vector ionosphere delay of the ground monitoring station network into grid point vector ionosphere delay;

the thin spherical shell area covering the east longitude of the China range of 70-145 degrees and the north latitude of 7.5-55 degrees is divided into 320 grid points according to the longitude and latitude of 5 multiplied by 2.5 degrees, and the numbering rule of the grid points is shown in table 1.

TABLE 1 Compass table for the number of points in the grid of the ionization layer of the Beidou system

In order to solve the above problems, a vector ionosphere correction technical scheme is introduced, and the core content of the vector ionosphere correction technical scheme is that an ionosphere correction parameter d τ in the prior art is upgraded from a single scalar to an array vector, and the ionosphere correction parameter vector of the first order comprises 3 elements:

wherein d τ₀For ionospheric correction parameters of order 0, equivalent to the prior art d τ scalar, for downward compatibility with existing systems, d τ_a1For ionospheric east correction parameters, d τ_b1Parameters are corrected for ionospheric southbound:

if the ionospheric shell is considered anisotropic, it is possible to obtain different values, recorded as

The simplest linear function is used to represent f (x, y), i.e.:

f(x,y)＝a₀+a₁y+b₁x (9)

equation (7) then becomes:

step 3.1: fitting and removing the longitude and latitude trend of the VTEC of the puncture point:

for any grid point, the VTEC of all the neighbor puncture points is assumed to be a linear function of longitude and latitude, and the following conditions are satisfied:

VTEC_i＝c₀+c₁*lat_i+c₂*lon_i(11)

wherein, lat_iAnd lon_iLongitude and latitude of the ith neighbor puncture point; VTEC_iThe VTEC value of the ith neighbor puncture point;

the coefficient [ c ] can be obtained by least squares linear fitting₀c₁c₂]. Further obtaining:

VTEC_i'＝VTEC_i-(c₀+c₁*lat_i+c₂*lon_i) (12)

step 3.2: and fitting the longitude and latitude projection vector trend of the VTEC:

for any grid point, the VTEC' of all the neighbor puncture points is assumed to be a linear function of a longitude and latitude projection vector, and the following conditions are satisfied:

VTEC_i'＝a₀+a₁*x_i+b₁*y_i(13)

[x_i,y_i]the propagation path of the electromagnetic wave of the ith neighbor puncture point is in the ionosphereA projection vector on the shell;

the coefficient [ a ] can be obtained by least squares linear fitting₀a₁b₂]And:

VTEC_i0＝VTEC_i+a₀(14)

step 3.3: calculating VTEC of all grid points by utilizing puncture point quintuple fed back by all monitoring stations₀

And VTEC₀And ionospheric delay d τ₀There is a conversion between:

and:

dτ_a1＝a₁，dτ_b1＝b₁(17)

after the summation, obtaining the grid point ionosphere vector parameter [ d tau₀,dτ_a1,dτ_b1]。

Step 4), uploading the vector ionosphere product data to a GEO satellite through an uploading station by a central processing station and broadcasting the vector ionosphere product data in a D2 navigation message by the GEO satellite;

the broadcast content is vertical delay (d tau) of grid point of ionized layer₀) Ionospheric grid point vector parameter (d τ)_a1,dτ_b1) And ionosphere grid point vertical retardation error index (GIVEI). d τ takes 9 bits, (d τ)_a1,dτ_b1) Takes 16 bits and GIVEI 4 bits.

dτ_a1And d τ_b1Each of 8 bits, corresponding to a binary representation of 1-256, and the scaling relationship is 0.01 times the integer represented by the 8 bits. Namely a₁And b₁Is a number which is an integer multiple of 0.01 between 0.01 and 2.56.

The ionosphere grid point vector delay information occupies (9+16+4) × 320 ═ 9280 bits.

And 5) carrying out ionospheric correction by using the vector ionospheric product data.

Fig. 5 shows a schematic diagram of the user puncture point and the grid point. The positions of 4 lattice points around the puncture point are respectively p_i(i 1-4) vertical ionospheric delay of lattice point propagation is represented by d τ_i(i is 1 to 4). The distance weights of the puncture point and the four grid points are respectively omega_i(i is 1 to 4). Then the vector ionospheric correction of the puncture point can be obtained by:

wherein, d τ_k＝(dτ_k0,dτ_ka1,dτ_kb1),k＝1,2,3,4；

The final pseudo-range ionospheric correction IC for the puncture point_pComprises the following steps:

wherein x_pThe zenith angle of the puncture point, [ x ] as shown in FIG. 2_p,y_p]The projection vector of the observation path on the ionosphere shell as shown in fig. 4. The unit of the pseudo-range ionospheric correction amount IC is m.

In addition, a set of data is designed to simulate and verify the existing scalar ionosphere correction technical scheme and the vector ionosphere correction scheme designed by the invention. The simulation area is assumed to be four grid points around Beijing:

grid point 257, p1 ═ 37.5115; grid point No. 267 p2 ═ 37.5120; grid point No. 97 p3 ═ 40115; grid point No. 107 p4 ═ 40120;

assuming that there are many ground monitoring stations and Beidou navigation satellites distributed in various places, the STEC observation data in the area is generated based on the IRI model and by adding random errors appropriately. Some data are randomly taken as user observation data, namely a verification set, and the rest data are taken as observation data of the ground monitoring station. 100 sets of data are generated in each round, and 200 rounds of simulation are carried out for 20000 scenes. To evaluate the quality of the correction, define Δ ═ IC — the actual ionospheric delay | as the ionospheric correction error. The average corrected error for each round of simulation is shown in fig. 6. The average correction error for scalar ionospheric correction is 0.105m overall, the average correction error for vector ionospheric correction is 0.085m overall, the average correction error is reduced by 0.02m overall, and the overall optimization margin is about 20%.

The difference between scalar ionospheric correction and vector ionospheric correction is small when the ionospheric TEC gradient is small and the contribution of the plasma layer is small. The advantage of vector ionospheric correction is more pronounced when the ionospheric TEC gradient is larger and the contribution of the plasma layer is larger. In the simulated 20000-time scenes, 359 scenes with the optimized amplitude of the vector ionospheric correction larger than 0.1m exist, the correction error of the worst scalar ionospheric correction reaches 1.3m, the correction error of the corresponding vector ionospheric correction is 0.8m, and the optimized amplitude can reach 0.5 m. As shown in fig. 6.

More ground monitoring stations are added to realize the fitting of vector parameters, and the surrounding of each grid point needs to be surrounded by the ground stations from all directions and the puncture points of the satellites to the greatest extent so that the observation data can reflect vector direction information as much as possible. And moreover, the longitude and latitude trends of the puncture points VTEC need to be removed, and at least 16 neighbor puncture points distributed in different directions are needed around each grid point through preliminary estimation. Assuming that there are 6 Beidou satellites in view at the same time, the minimum number of observation stations requires at least three ground monitoring stations around each grid point, with about one observation station per 30,000 square kilometers. The more observation stations, the better the fitting effect and the higher the ionosphere correction precision. And upgrading the ionospheric correction data formats of all network elements to a new vector format from end to end. The ionosphere correction can also be realized by adopting a simple implementation scheme through publishing and using the vector ionosphere product information by the Internet and a terminal application program APP so as to avoid huge engineering cost brought by network element upgrading, navigation protocol upgrading and message format upgrading.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.