A method for refining the global ionospheric model using occultation data

Abstract

The present invention discloses a method for refining a global ionosphere model using occultation data, the method comprising the following steps: S01, calculating the coordinates of the entry and exit points of the occultation event rays; S02, calculating the absolute electron content and projection function on the observation path of the global ionosphere model at the entry and exit points using the spherical harmonic coefficients of the global ionosphere model; S03, calculating the prior model value of the absolute electron content on the observation path corresponding to the occultation event; S04, calculating the prior error of the absolute electron content on the observation path corresponding to the occultation event; S05, updating the spherical harmonic coefficients of the global ionosphere model. The method solves the problem that the prior art either has limited effect due to the inability to build an IGS station in the ocean area, or has to collect observation data from GNSS observation stations around the world, resulting in a more complicated calculation.

Description

Technical Field

[0001] The present invention relates to the field of GNSS positioning technology, and in particular to a method for refining a global ionosphere model by using occultation data. Background Art

[0002] Ionospheric error is an important error source for GNSS single-frequency single-point positioning. Ionospheric model is an important way to improve GNSS single-frequency single-point positioning. The global ionospheric model calculated using GNSS data has the characteristics of high accuracy, global coverage, and ease of use. At present, there are many international GNSS analysis institutions that can provide global ionospheric products, such as CODE, Wuhan University, Chinese Academy of Sciences and other institutions. However, the ionospheric products provided by these institutions are based on the observation data of the global IGSGNSS continuously operating stations. Since the IGS continuously operating stations are limited in global scope and unevenly distributed, the accuracy of the obtained ionospheric products has regional differences. In ocean areas and land areas where IGS stations are sparsely distributed, the accuracy of ionospheric products is relatively low.

[0003] More than 70% of the Earth's surface is covered by ocean, which means that the accuracy of global ionosphere models is unreliable over most ocean regions.

[0004] In order to improve the accuracy of global ionospheric products in areas with sparse IGS stations, the literature [1] proposed to use the observation data of regional GNSS stations to obtain dual-frequency ionospheric delays, and then refine the global ionospheric model. This method can effectively improve the accuracy of the global ionospheric model near regional GNSS stations. However, since IGS stations cannot be built in vast ocean areas, the effect of this method is limited.

[0005] Reference [2] proposed a method for global ionosphere modeling using multi-source data. However, this method must collect observation data from GNSS observation stations around the world to extract and calculate the total electron content of the slant path. However, this method requires a lot of GNSS data, and the calculation process includes phase smoothing pseudorange, DCB separation, spherical harmonic function modeling and other steps, which makes the calculation more complicated.

[0006] [1]Yang Wang, Yibin Yao, Liang Zhang*and MingshanFang,ARefinementMethod of Real-Time Ionospheric Model for China,Remote Sensing,2020,12(20),3354,DOI:10.3390 / rs12203354

[0007] [2]Yao Yibin*,Liu Lei*,Kong Jian and ZhaiChangzhi,Global IonosphericModeling Based on Multi-GNSS,Satellite Altimetry and Formosat-3 / COSMIC Data,GPS Solutions,2018,22:104,DOI:10.1007 / s10291-018-0770-6 Summary of the invention

[0008] In order to solve the above shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for refining the global ionospheric model using occultation data.

[0009] The technical solution of the present invention is: a method for refining a global ionosphere model using occultation data, the method comprising the following steps:

[0010] S01. Calculate the coordinates of the entry and exit points of the occultation event rays;

[0011] S02. Calculate the absolute electron content and projection function on the observation path of the global ionosphere model at the entry point and the exit point using the spherical harmonic coefficients of the global ionosphere model;

[0012] S03, calculating the a priori model value of the absolute electron content on the observation path corresponding to the occultation event;

[0013] S04. Calculate the a priori error of the absolute electron content on the observation path corresponding to the occultation event;

[0014] S05. Update the spherical harmonic coefficients of the global ionospheric model.

[0015] Furthermore, the step S01 calculates the entry and exit points of the occultation event rays according to the low-orbit satellite coordinates and the GNSS satellite coordinates.

[0016] Furthermore, the calculation method of the a priori model value of the absolute electron content on the observation path corresponding to the occultation event in step S03 is as follows:

[0017]

[0018] in, is the a priori model value of the absolute electron content on the observation path, VTEC in VTEC is the total electron content in the vertical direction where the ray penetrates the thin layer of the ionosphere. out MF is the total electron content in the vertical direction where the ray passes through the thin layer of the ionosphere, in is the projection function of the penetration point, MFout is the projection function of the exit point.

[0019] Furthermore, the VTEC in and VTEC out The calculation method is as follows:

[0020]

[0021] VTEC(φ IPP ,λ s ) indicates that the latitude of the geocenter is φ IPP and longitude λ s The total electron content in the vertical direction at nm and S nm are the spherical harmonic coefficients of the global ionospheric model, is the Legendre function, N is the order of the spherical harmonic function, and m is the degree of the spherical harmonic function.

[0022] Furthermore, the calculation method of the a priori error of the absolute electron content on the observation path corresponding to the occultation event in step S04 is as follows:

[0023]

[0024] In the formula, represents the prior error, STEC i represents the absolute electron content on the observation path of the i-th occultation event, given by the occultation observation data; Represents the prior model value of the absolute total electron content on the observation path of the i-th occultation event.

[0025] Furthermore, the method for updating the spherical harmonic coefficients of the global ionospheric model in step S05 is as follows:

[0026]

[0027] In the formula, is the updated spherical harmonic coefficient, K k is the gain matrix, R is the observation error of STEC, is the prior covariance matrix, which can be obtained according to the accuracy of the global ionospheric spherical harmonics model and the law of error propagation. k The matrix is ​​the design matrix corresponding to the calculation formula of the a priori model value of the absolute electron content on the observation path of the corresponding occultation event,

[0028]

[0029] in, φ in represents the dimension of the penetration point, λ in represents the longitude of the penetration point, φout represents the dimension of the exit point, λ out Indicates the longitude of the exit point.

[0030] Furthermore, the MF in and MF out The calculation method is as follows:

[0031] MF=cosZ ipp ;

[0032] Where MF represents the projection function, Z ipp Indicates the zenith distance.

[0033] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention adopts occultation data, and according to the characteristics of the occultation data, proposes to use the spherical harmonic function of the global ionosphere model to calculate the prior model value of the corresponding occultation event, and uses the prior model value to calculate the prior error, and uses the prior error to update the spherical harmonic coefficient, so as to obtain more accurate spherical harmonic coefficients of the global ionosphere model after the occultation data is updated. Since the occultation events are uniformly distributed globally, a large number of occultation events occur in both the ocean and the land, so the accuracy of the global ionosphere model in sparse station areas can be improved. In addition, the present invention adopts the existing global ionosphere model product for refined modeling, and it is no longer necessary to collect global GNSS observation data, and it is no longer necessary to perform complex calculations of phase smoothing pseudorange, DCB separation, spherical harmonic function modeling and other steps based on GNSS observation data, so it is easier to collect data and the calculation steps are simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the present invention;

[0035] Figure 2 Another flow chart of the present invention. DETAILED DESCRIPTION

[0036] The invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0037] Implementation Example 1: Reference Figure 1 and Figure 2 , a method for refining a global ionospheric model using occultation data, the method comprising the following steps:

[0038] S01. Calculate the coordinates of the entry and exit points of the occultation event rays;

[0039] S02. Calculate the absolute electron content and projection function on the observation path of the global ionosphere model at the entry point and the exit point using the spherical harmonic coefficients of the global ionosphere model;

[0040] S03, calculating the a priori model value of the absolute electron content on the observation path corresponding to the occultation event;

[0041] S04. Calculate the a priori error of the absolute electron content on the observation path corresponding to the occultation event;

[0042] S05. Update the spherical harmonic coefficients of the global ionospheric model.

[0043] When used, the present invention adopts occultation data, and according to the characteristics of occultation data, proposes to use the global ionosphere model spherical harmonic function to calculate the prior model value of the corresponding occultation event, and uses the prior model value to calculate the prior error, and uses the prior error to update the spherical harmonic coefficient, so as to obtain the more accurate global ionosphere model spherical harmonic coefficient obtained after the occultation data is updated. Since the occultation event is uniformly distributed globally, a large number of occultation events occur in both the ocean and the land, so the accuracy of the global ionosphere model in the sparse station area can be improved. In addition, the present invention adopts the existing global ionosphere model product for refined modeling, and it is no longer necessary to collect global GNSS observation data, and it is no longer necessary to perform complex calculations of phase smoothing pseudorange, DCB separation, spherical harmonic function modeling and other steps based on GNSS observation data, so it is easier to collect data and the calculation steps are simpler.

[0044] Furthermore, the step S01 calculates the entry and exit points of the occultation event rays according to the low-orbit satellite coordinates and the GNSS satellite coordinates.

[0045] By calculating the entry and exit points of the occultation event rays through the low-orbit satellite coordinates and the GNSS satellite coordinates, the precise coordinates of the entry and exit points of the occultation event rays can be obtained, which are used to calculate the total electron content in the vertical direction of the corresponding points.

[0046] Furthermore, the calculation method of the a priori model value of the absolute electron content on the observation path corresponding to the occultation event in step S03 is as follows:

[0047] STEC=VTEC in / MF in +VTEC out / MF out ;

[0048] in, is the a priori model value of the absolute electron content on the observation path, VTEC in VTEC is the total electron content in the vertical direction where the ray penetrates the thin layer of the ionosphere. out MF is the total electron content in the vertical direction where the ray passes through the thin layer of the ionosphere, in is the projection function of the penetration point, MF out is the projection function of the exit point.

[0049] The absolute electron content on the observation path of the corresponding occultation event is calculated by the total electron content in the vertical direction at the entry and exit points of the occultation event and the projection function.

[0050] Furthermore, the VTEC in and VTEC out The calculation method is as follows:

[0051]

[0052] VTEC(φ IPP ,λ s ) indicates that the latitude of the geocenter is φ IPP and longitude λ s The total electron content in the vertical direction at nm and S nm are the spherical harmonic coefficients of the global ionospheric model, is the Legendre function, N is the order of the spherical harmonic function, and m is the degree of the spherical harmonic function.

[0053] The total electron content in the vertical direction of the occultation event entry and exit points is calculated based on the coordinates of the occultation event entry and exit points.

[0054] Furthermore, the calculation method of the a priori error of the absolute electron content on the observation path corresponding to the occultation event in step S04 is as follows:

[0055]

[0056] In the formula, represents the prior error, STEC i represents the absolute electron content on the observation path of the i-th occultation event, given by the occultation event product; Represents the prior model value of the absolute total electron content on the observation path of the i-th occultation event.

[0057] The a priori error is obtained by calculating the difference between the a priori model value and the model value of the total electron content in the vertical direction corresponding to multiple occultation events.

[0058] Here STEC1, STEC2, ..., STEC N The calculation method is:

[0059]

[0060] Here The calculation method is:

[0061]

[0062] The latitude of the geocenter is φ IPP and longitude λs The total electron content in the vertical direction at nm and S nm are the spherical harmonic coefficients of the global ionospheric model, is the Legendre function, N is the order of the spherical harmonics, and M is the degree of the spherical harmonics.

[0063] Furthermore, the method for updating the spherical harmonic coefficients of the global ionospheric model in step S05 is as follows:

[0064]

[0065] In the formula, is the updated spherical harmonic coefficient, K is the gain matrix, K k , R is the observation error of STEC, is the prior covariance matrix, which can be obtained according to the accuracy of the global ionospheric spherical harmonics model and the law of error propagation. k The matrix is ​​a design matrix corresponding to the calculation formula of the prior model value of the absolute electron content on the observation path of the corresponding occultation event.

[0066]

[0067] in, φ in represents the dimension of the penetration point, λ in represents the longitude of the penetration point, φ out represents the dimension of the exit point, λ out Indicates the longitude of the exit point.

[0068] Update the spherical harmonic coefficients of the global ionospheric model using a priori errors.

[0069] It should be noted that Figure 2 The essence of the algorithm is step S04 and step S05. Figure 2 The refined model in refers to the spherical harmonic functions of the global ionosphere model with updated spherical harmonic coefficients of the global ionosphere model.

[0070] Furthermore, the MF in and MF out The calculation method is as follows:

[0071] MF=cosZ ipp ;

[0072] Where MF represents the projection function, Z ipp Indicates the zenith distance.

[0073] The projection function of the entry and exit points of the occultation event is obtained through the zenith distance.

[0074] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for refining a global ionospheric model using occultation data, characterized in that: The method comprises the following steps: S01. Calculate the coordinates of the entry and exit points of the occultation event rays; S02. Calculate the absolute electron content and projection function on the observation path of the global ionosphere model at the entry point and the exit point using the spherical harmonic coefficients of the global ionosphere model; S03, calculating the a priori model value of the absolute electron content on the observation path corresponding to the occultation event; S04. Calculate the a priori error of the absolute electron content on the observation path corresponding to the occultation event; S05. Update the spherical harmonic coefficients of the global ionospheric model; The calculation formula of the a priori model value of the absolute electron content on the observation path corresponding to the occultation event in step S03 is as follows: in, is the a priori model value of the absolute electron content on the observation path, VTEC in VTEC is the total electron content in the vertical direction where the ray penetrates the thin layer of the ionosphere. out MF is the total electron content in the vertical direction where the ray passes through the thin layer of the ionosphere, in is the projection function of the penetration point, MF out is the projection function of the exit point; The VTEC in and VTEC out The calculation method is as follows: VTEC(φ IPP ,λ s ) indicates that the latitude of the geocenter is φ IPP and longitude λ s The total electron content in the vertical direction at nm and S nm are the spherical harmonic coefficients of the global ionospheric model, is the Legendre function, N is the order of the spherical harmonic function, and m is the degree of the spherical harmonic function; The method for updating the spherical harmonic coefficients of the global ionosphere model in step S05 is as follows: In the formula, is the updated spherical harmonic coefficient, K k is the gain matrix, R is the observation error of STEC, is the prior covariance matrix, H k The matrix is ​​the design matrix corresponding to the calculation formula of the a priori model value of the absolute electron content on the observation path of the corresponding occultation event; in, φ in represents the dimension of the penetration point, λ in represents the longitude of the penetration point, φ out represents the dimension of the exit point, λ out Indicates the longitude of the exit point.

2. The method for refining the global ionospheric model using occultation data according to claim 1, characterized in that: The step S01 calculates the entry and exit points of the occultation event rays according to the low-orbit satellite coordinates and the GNSS satellite coordinates.

3. The method for refining the global ionospheric model using occultation data according to claim 1, characterized in that: The method for calculating the a priori error of the absolute electron content on the observation path corresponding to the occultation event in step S04 is as follows: In the formula, represents the prior error, STEC i represents the absolute electron content on the observation path of the i-th occultation event, given by the occultation event product; Represents the prior model value of the absolute total electron content on the observation path of the i-th occultation event.

4. The method for refining the global ionospheric model using occultation data according to claim 1, characterized in that: The MF in and MF out The calculation method is as follows: MF=cosZ ipp Where MF represents the projection function, Z ipp Indicates the zenith distance.

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