Ionized layer occultation inversion method and device based on aspheric symmetry hypothesis

Abstract

The invention provides an ionosphere occultation inversion method and device based on aspheric symmetry hypothesis. The method comprises the following steps: calculating occultation observation collision parameters and absolute total electron content through a data processing module; and constructing an aspheric symmetric hypothesis inversion function model through the model establishment module. The ionosphere occultation inversion method has the advantages that the problem that the inversion precision is difficult to improve due to the fact that a mainstream ionosphere occultation inversion algorithm is limited by the spherical symmetry hypothesis is solved, the ionosphere occultation inversion method based on the aspheric symmetry hypothesis is provided, and therefore the ionosphere occultation inversion precision is improved; the product can be applied to the fields of ionosphere weather monitoring and forecasting, navigation positioning enhancement and the like.

Description

Technical Field

[0001] The invention belongs to the field of ionospheric occultation inversion, and in particular relates to an ionospheric occultation inversion method and device based on a non-spherically symmetric assumption. Background Art

[0002] The ionosphere is an important near-Earth space environment, and its research has important scientific significance and application value. High-precision and reliable ionospheric observation data is a key element in ionospheric research. Among the many ionospheric observation technologies, ionospheric occultation technology stands out because of its advantages such as all-weather global coverage, low cost, long-term stability, high vertical resolution and high electron density inversion accuracy. The mainstream ionospheric occultation inversion algorithms include the Abel integral inverse transform inversion algorithm and the onion peeling inversion algorithm. They are all based on the spherical symmetry assumption. However, this assumption creates the most important model error and becomes a shackle to improve the accuracy of occultation inversion. In order to further improve the accuracy of ionospheric occultation inversion, external data or prior information should be used to develop high-precision inversion algorithms based on non-spherical symmetry assumptions. Summary of the invention

[0003] In view of this, the present invention aims to propose an ionospheric occultation inversion method and device with non-spherically symmetric assumption, so as to solve the problem that the mainstream ionospheric occultation inversion algorithm is limited by the spherically symmetric assumption, making it difficult to improve the inversion accuracy.

[0004] To achieve the above object, the technical solution of the present invention is achieved as follows: In a first aspect, a method for inverting ionospheric occultation based on a non-spherically symmetric assumption comprises the following steps: S1. Calculate the collision parameters and absolute total electron content of occultation observations through the data processing module; S2, constructing a non-spherically symmetric assumption inversion function model through a model building module; In step S1, the collision parameters and absolute total electron content of the occultation observation are solved by the data processing module, including: S11, generating an ionospheric occultation additional phase file after processing the original data of the ionospheric occultation observation, and using the ionospheric occultation additional phase file as an input file for ionospheric occultation inversion; S12. Under the assumption of straight-line propagation of radio waves, the coordinates of the occultation tangent point P and the collision parameter p are solved according to the vertical relationship and collinear relationship; S13, after cycle slip detection and repair of the dual-frequency additional phase observations of the ionospheric occultation additional phase file, high-frequency noise is suppressed by sliding window smoothing filtering, and then the dual-frequency phase is combined to obtain the relative total electron content; S14, using the observation data of the non-occultation period to correct the observation data of the occultation period, the relative TEC on both sides of the maximum collision parameter is highly reordered, the relative TEC of the non-occultation period is interpolated to the collision height equal to that of the occultation period by cubic spline, and the absolute total electron content is obtained by difference; In step S2, a non-spherically symmetric assumption inversion function model is constructed by a model building module, including: S21, deriving the electron density inversion formula, estimating the top electron density, and constructing the recursive relationship using the three-dimensional ionosphere empirical model; S22. Generate ionospheric electron density profile.

[0005] Furthermore, in step S21, an electron density inversion formula is derived, top electron density is estimated, and a recursive relationship is constructed using a three-dimensional ionosphere empirical model, including: The absolute total electron content is the integral of the electron density on the signal path, expressed as formula (5); Under the assumption of linear propagation of radio waves, the absolute total electron content of the BC segment is expressed as formula (6); There are several observations during the occultation period. If the collision parameters of continuous observations are used to make concentric circles, the BC segment path is decomposed into the sum of line segments between several spherical layers. Assuming that the electron density between spherical layers changes linearly, the integral can be solved and the absolute total electron content can be linearized into a linear combination of the electron density at the intersection of the path and each spherical layer. The expression is formula (7); Thus, the electron density inversion formula (9) is obtained; The estimated expression of the electron density at the top occultation point is formula (10); Under the assumption of non-spherical symmetry, given additional information, the electron density at the higher spherical occultation tangent point is recursively deduced to the electron density at the intersection point corresponding to the observation path. Using the three-dimensional ionosphere empirical model, the recursive relationship is constructed by assuming that the ratio of the electron density values ​​at the corresponding points in the actual ionosphere is consistent with the empirical model, and the expression is formula (11).

[0006] Further, in step S22, generating an ionospheric electron density profile includes: Substitute the recursive relationship into the electron density inversion formula. After estimating the electron density at the top occultation tangent point, the electron density at all occultation tangent points is derived step by step from high to low using the electron density inversion formula to realize ionospheric occultation inversion under the assumption of non-spherical symmetry, and finally generate the ionospheric electron density profile.

[0007] Furthermore, in step S12, under the assumption of straight-line propagation of radio waves, the coordinates of the occultation tangent point P and the collision parameter p are calculated according to the vertical relationship and the collinear relationship, and the expressions are as follows: (1) (2) In the formula, The space vector representing the occultation tangent point P; The space vector representing the center of the earth O; A spatial vector representing the navigation satellite coordinate A; Represents the space vector of the low-orbit satellite coordinate C; the denominator in the fraction represents the second-order norm; the numerator of the fraction represents the dot product; Represents the collision parameters.

[0008] Furthermore, in step S13, the relative total electron content is expressed as formula (3): (3) In the formula, Indicates the relative total electron content on the signal path; Represents the additional phase value on the carrier signal 1; Represents the additional phase value on the carrier signal 2; Represents the square of the frequency of carrier signal 1; Represents the square of the frequency of carrier signal 2.

[0009] Further, in step S14, the absolute total electron content expression is formula (4): (4) In the formula, It represents the absolute total electron content of the BC segment on the occultation observation signal path; It represents the relative total electron content of the AC segment on the occultation observation signal path; Represents the relative total electron content of segment AB on the non-occultation observation signal path.

[0010] Furthermore, formula (5), formula (6) and formula (7) are respectively: (5) In the formula, represents the absolute total electron content on the path; Indicates the path; represents the electron density; The infinitesimal element representing the path; (6) In the formula, represents the absolute total electron content of the BC segment; Represents collision parameters; Indicates the distance from the center of the Earth at a low-orbit satellite; represents the distance from the center of the earth at the microelement; represents the electron density at the microelement; Represents the electron density at the microelement symmetric to the occultation point; The infinitesimal element representing the path; (7) In the formula, Represents the index of the observation after the observation sequence is sorted from small to large by collision parameter; Represents collision parameters; represents the absolute total electron content; and Represents the electron density at the two intersections of the path and each sphere; represents a dimensionless coefficient; The expression of is formula (8); (8).

[0011] Furthermore, formula (9), formula (10) and formula (11) are respectively: (9) (10) In the formula, Represents the top ball layer collision parameters; Represents the collision parameters of a certain sphere layer near the top; represents the estimated electron density of the top spherical layer; Represents the absolute total electron content of a spherical layer near the top.

[0012] (11) In the formula, express The electron density at time M; express The electron density at point P at time; represents the actual inversion; Represents a model.

[0013] Furthermore, the ionospheric occultation additional phase file contains the position and velocity information of the navigation satellite and the low-orbit satellite as well as the dual-frequency additional phase observation value information.

[0014] In the second aspect, based on the same concept, the present invention also provides an ionospheric occultation inversion device based on a non-spherical symmetry assumption, comprising a data processing module and a model building module; the data processing module is used to solve the occultation observation collision parameters and the absolute total electron content; the model building module is used to construct an inversion function model based on a non-spherical symmetry assumption.

[0015] Compared with the prior art, the ionospheric occultation inversion method and device based on non-spherically symmetric assumption described in the present invention has the following beneficial effects: The present invention solves the problem that the mainstream ionospheric occultation inversion algorithm is limited by the spherical symmetry assumption, which makes it difficult to improve the inversion accuracy; the present invention provides an ionospheric occultation inversion method without spherical symmetry assumption, thereby improving the accuracy of ionospheric occultation inversion, and the product can be applied to the fields of ionospheric weather monitoring and forecasting, navigation and positioning enhancement, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 A technical roadmap for the embodiments of the present invention; Figure 2 Schematic diagram of the geometrical observation of occultation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0018] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0019] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0020] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0021] like Figure 1 to Figure 2 As shown, a non-spherically symmetric ionospheric occultation inversion method comprises the following steps: S1. Calculate the collision parameters and absolute total electron content of occultation observations through the data processing module; S2, constructing a non-spherically symmetric assumption inversion function model through a model building module; The mainstream ionospheric occultation inversion algorithm is limited by the spherical symmetry assumption, and the inversion accuracy is difficult to improve. The present invention improves the inversion accuracy by proposing an ionospheric occultation inversion algorithm with a non-spherical symmetry assumption. The specific steps are as follows: 1. Calculate the collision parameters and absolute total electron content of occultation observations The raw data of ionospheric occultation observation is decoded and verified, low-orbit satellite orbit is determined, and data preprocessing is performed to generate an ionospheric occultation additional phase file, which contains information such as the position and speed of navigation satellites and low-orbit satellites, and dual-frequency additional phase observation values. The present invention uses the ionospheric occultation additional phase file as the input file for ionospheric occultation inversion.

[0022] Since the bending angle caused by the ionosphere refracting the L-band navigation satellite signal will not exceed 0.03 degrees during the period of intense ionosphere changes, it can be assumed that the radio wave propagates in a straight line. Under the assumption of straight-line propagation of radio waves, the occultation tangent point P is the foot of the perpendicular from the center of the earth O to the radio wave path AC. The coordinates of the occultation tangent point P and the collision parameter p can be solved based on the vertical relationship and collinearity relationship: (1) (2) In the formula, The space vector representing the occultation tangent point P; The space vector representing the center of the earth O; A spatial vector representing the navigation satellite coordinate A; Represents the space vector of the low-orbit satellite coordinate C; the denominator in the fraction represents the second-order norm; the numerator of the fraction represents the dot product; Represents the collision parameters.

[0023] After cycle slip detection and repair of the dual-frequency additional phase observations of the ionospheric occultation additional phase file, the sliding window smoothing filter is used to suppress high-frequency noise, and then the dual-frequency phase is combined to obtain the relative total electron content (TEC): (3) In the formula, Indicates the relative total electron content on the signal path; Represents the additional phase value on the carrier signal 1; Represents the additional phase value on the carrier signal 2; Represents the square of the frequency of carrier signal 1; Represents the square of the frequency of carrier signal 2.

[0024] Since the duration of ionospheric occultation is short, the ionospheric changes and the azimuth changes of the occultation plane are usually small. Therefore, it can be assumed that the observations of the low-orbit satellite during the non-occultation period (such as at point B) and the occultation period (such as at point C) are in the same ionospheric background and the same occultation plane. Therefore, the observation data during the non-occultation period can be used to correct the observation data during the occultation period to obtain the absolute total electron content: (4) In the formula, It represents the absolute total electron content of the BC segment on the occultation observation signal path; It represents the relative total electron content of the AC segment on the occultation observation signal path; Represents the relative total electron content of segment AB on the non-occultation observation signal path.

[0025] Taking into account the observation interval of the receiver, in order to perform more rigorous correction, it is necessary to interpolate the relative total electron content observed during the non-occultation period to the same collision height of the relative total electron content observed during the occultation period, and thus obtain the absolute total electron content by difference.

[0026] 2. Constructing the inversion function model based on non-spherical symmetry assumption By definition, the absolute total electron content is the integral of the electron density over the signal path: (5) In the formula, represents the absolute total electron content on the path; Indicates the path; represents the electron density; A microelement representing a path.

[0027] Under the assumption of linear propagation of radio waves, the absolute total electron content of segment BC can be expressed as: (6) In the formula, represents the absolute total electron content of the BC segment; Represents collision parameters; Indicates the distance from the center of the Earth at a low-orbit satellite; represents the distance from the center of the earth at the microelement; represents the electron density at the microelement; Represents the electron density at the microelement symmetric to the occultation point; A microelement representing a path.

[0028] There are several observations during the occultation period. If the collision parameters of these consecutive observations are used to make concentric circles, the BC segment path is decomposed into the sum of line segments between several spherical layers. Assuming that the electron density between spherical layers changes linearly, the integral can be solved to linearize the absolute total electron content into a linear combination of the electron density at the intersection of the path and each spherical layer: (7) In the formula, Represents the index of the observation after the observation sequence is sorted from small to large by collision parameter; Represents collision parameters; represents the absolute total electron content; and Represents the electron density at the two intersections of the path and each sphere; represents the dimensionless coefficient, which is calculated by the following formula: (8) So we can get the electron density inversion formula: (9) Obviously, when the absolute total electron content and collision parameters obtained by observation are known, the electron density at a certain spherical layer occultation point is determined by the electron density at the intersection of all higher spherical layers and the path. Under the assumption of spherical symmetry, the electron density at the intersection corresponding to this observation path can be naturally replaced by the electron density at the occultation point of the higher spherical layer, thereby gradually deriving the electron density at all occultation points from high to low. The electron density at the top occultation point is estimated as follows: (9) In the formula, Represents the top ball layer collision parameters; Represents the collision parameters of a certain sphere layer near the top; represents the estimated electron density of the top spherical layer; Represents the absolute total electron content of a spherical layer near the top.

[0029] However, under the assumption of non-spherical symmetry, additional information should be given to achieve the recursion of the electron density at the higher spherical occultation tangent point to the electron density at the intersection point corresponding to this observation path. The present invention uses a three-dimensional ionosphere empirical model, such as the International Reference Ionosphere (IRI) model, the NeQuick model, etc., and assumes that the ratio of the electron density values ​​at the corresponding points in the actual ionosphere is consistent with the empirical model, thereby constructing a recursive relationship: (11) In the formula, express The electron density at time M; express The electron density at point P at time; represents the actual inversion; Represents a model.

[0030] Substituting the recursive relationship into the electron density inversion formula, after estimating the electron density at the top occultation tangent point, the electron density at all occultation tangent points can be derived step by step from high to low using the electron density inversion formula, thus realizing ionospheric occultation inversion under the assumption of non-spherical symmetry.

[0031] The present invention also provides an ionospheric occultation inversion device based on a non-spherically symmetric assumption, comprising a data processing module and a model building module; the data processing module is used to solve the occultation observation collision parameters and the absolute total electron content; the model building module is used to construct an inversion function model based on a non-spherically symmetric assumption.

[0032] Advantages of the present invention: The present invention solves the problem that the mainstream ionospheric occultation inversion algorithm is limited by the spherical symmetry assumption, which makes it difficult to improve the inversion accuracy; the present invention provides an ionospheric occultation inversion method without spherical symmetry assumption, thereby improving the accuracy of ionospheric occultation inversion, and the product can be applied to the fields of ionospheric weather monitoring and forecasting, navigation and positioning enhancement, etc.

[0033] Example 1 (1) Collect additional phase files of ionospheric occultation of six COSMIC-2 satellites in January 2025; collect NeQuick-2 model data (CCIR empirical coefficient files and MODIP geomagnetic latitude files); (2) Processing the navigation satellite and low-orbit satellite orbit data of the ionospheric occultation additional phase file and calculating the collision parameters through geometric relationships; (3) Process the dual-frequency additional phase data of the ionospheric occultation additional phase file, obtain smoothed additional phase data through cycle slip detection and repair, and sliding window smoothing, perform dual-frequency combination calculation on it, and obtain the ionospheric relative TEC on different paths. Then, highly reorder the relative TEC on both sides of the maximum collision parameter, and finally interpolate the relative TEC in the non-occultation period to the collision height equal to that in the occultation period through cubic spline interpolation, and obtain the absolute TEC by difference. (4) Based on the NeQuick-2 model, the electron density model values ​​at the intersection of the radio wave path and each spherical layer are calculated. After estimating the electron density at the top occultation tangent point, the electron density at all occultation tangent points is gradually derived from high to low using the ionospheric occultation inversion method based on the non-spherical symmetry assumption, and finally the ionospheric electron density profile product is generated.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An ionospheric occultation inversion method based on non-spherical symmetry assumption, characterized in that: The following steps are involved: S1. Calculate the collision parameters and absolute total electron content of occultation observations through the data processing module; S2, constructing a non-spherically symmetric assumption inversion function model through a model building module; In step S1, the collision parameters and absolute total electron content of the occultation observation are solved by the data processing module, including: S11, generating an ionospheric occultation additional phase file after processing the original data of the ionospheric occultation observation, and using the ionospheric occultation additional phase file as an input file for ionospheric occultation inversion; S12. Under the assumption of straight-line propagation of radio waves, the coordinates of the occultation tangent point P and the collision parameter p are solved according to the vertical relationship and collinear relationship; S13, after cycle slip detection and repair of the dual-frequency additional phase observations of the ionospheric occultation additional phase file, high-frequency noise is suppressed by sliding window smoothing filtering, and then the dual-frequency phase is combined to obtain the relative total electron content; S14, using the observation data of the non-occultation period to correct the observation data of the occultation period, the relative TEC on both sides of the maximum collision parameter is highly reordered, the relative TEC of the non-occultation period is interpolated to the collision height equal to that of the occultation period by cubic spline, and the absolute total electron content is obtained by difference; In step S2, a non-spherically symmetric assumption inversion function model is constructed by a model building module, including: S21, deriving the electron density inversion formula, estimating the top electron density, and constructing the recursive relationship using the three-dimensional ionosphere empirical model; S22. Generate ionospheric electron density profile.

2. The ionospheric occultation inversion method based on non-spherically symmetric assumption according to claim 1, characterized in that: In step S21, the electron density inversion formula is derived, the top electron density is estimated, and a recursive relationship is constructed using a three-dimensional ionosphere empirical model, including: The absolute total electron content is the integral of the electron density on the signal path, expressed as formula (5); Under the assumption of linear propagation of radio waves, the absolute total electron content of the BC segment is expressed as formula (6); There are several observations during the occultation period. If the collision parameters of continuous observations are used to make concentric circles, the BC segment path is decomposed into the sum of line segments between several spherical layers. Assuming that the electron density between spherical layers changes linearly, the integral can be solved and the absolute total electron content can be linearized into a linear combination of the electron density at the intersection of the path and each spherical layer. The expression is formula (7); Thus, the electron density inversion formula (9) is obtained; The estimated expression of the electron density at the top occultation point is formula (10); Under the assumption of non-spherical symmetry, given additional information, the electron density at the higher spherical occultation tangent point is recursively deduced to the electron density at the intersection point corresponding to the observation path. Using the three-dimensional ionosphere empirical model, the recursive relationship is constructed by assuming that the ratio of the electron density values ​​at the corresponding points in the actual ionosphere is consistent with the empirical model, and the expression is formula (11).

3. The ionospheric occultation inversion method based on non-spherically symmetric assumption according to claim 1, characterized in that: In step S22, generating an ionospheric electron density profile includes: Substitute the recursive relationship into the electron density inversion formula. After estimating the electron density at the top occultation tangent point, the electron density at all occultation tangent points is derived step by step from high to low using the electron density inversion formula to realize ionospheric occultation inversion under the assumption of non-spherical symmetry, and finally generate the ionospheric electron density profile.

4. The ionospheric occultation inversion method based on non-spherically symmetric assumption according to claim 1, characterized in that: In step S12, under the assumption of straight-line propagation of radio waves, the coordinates of the occultation tangent point P and the collision parameter p are calculated according to the vertical relationship and the collinear relationship. The expressions are as follows: (1) (2) In the formula, The space vector representing the occultation tangent point P; The space vector representing the center of the earth O; A spatial vector representing the navigation satellite coordinate A; Represents the space vector of the low-orbit satellite coordinate C; the denominator in the fraction represents the second-order norm; the numerator of the fraction represents the dot product; Represents the collision parameters.

5. The ionospheric occultation inversion method based on non-spherically symmetric assumption according to claim 1, characterized in that: In step S13, the relative total electron content expression is formula (3): (3) In the formula, Indicates the relative total electron content on the signal path; Represents the additional phase value on the carrier signal 1; Represents the additional phase value on the carrier signal 2; Represents the square of the frequency of carrier signal 1; Represents the square of the frequency of carrier signal 2.

6. The ionospheric occultation inversion method based on non-spherical symmetry assumption according to claim 1, characterized in that: In step S14, the absolute total electron content expression is formula (4): (4) In the formula, It represents the absolute total electron content of the BC segment on the occultation observation signal path; It represents the relative total electron content of the AC segment on the occultation observation signal path; Represents the relative total electron content of segment AB on the non-occultation observation signal path.

7. The ionospheric occultation inversion method based on non-spherical symmetry assumption according to claim 2, characterized in that: Formula (5), formula (6) and formula (7) are respectively: (5) In the formula, represents the absolute total electron content on the path; Indicates the path; represents the electron density; The infinitesimal element representing the path; (6) In the formula, represents the absolute total electron content of the BC segment; Represents collision parameters; Indicates the distance from the center of the Earth at a low-orbit satellite; represents the distance from the center of the earth at the microelement; represents the electron density at the microelement; Represents the electron density at the microelement symmetric to the occultation point; The infinitesimal element representing the path; (7) In the formula, Represents the index of the observation after the observation sequence is sorted from small to large by collision parameter; Represents collision parameters; represents the absolute total electron content; and Represents the electron density at the two intersections of the path and each sphere; represents a dimensionless coefficient; The expression of is formula (8); (8)。 8. The ionospheric occultation inversion method based on non-spherical symmetry assumption according to claim 2, characterized in that: Formula (9), formula (10) and formula (11) are respectively: (9) (10) In the formula, Represents the top ball layer collision parameters; Represents the collision parameters of a certain sphere layer near the top; represents the estimated electron density of the top spherical layer; It represents the absolute total electron content of a spherical layer near the top; (11) In the formula, express The electron density at time M; express The electron density at point P at time; represents the actual inversion; Represents a model.

9. The ionospheric occultation inversion method based on non-spherical symmetry assumption according to claim 1, characterized in that: The ionospheric occultation additional phase file contains the position, velocity information of navigation satellites and low-orbit satellites, as well as dual-frequency additional phase observation information.

10. An ionospheric occultation inversion device based on non-spherical symmetry assumption, using the ionospheric occultation inversion method based on non-spherical symmetry assumption as claimed in claims 1 to 9, characterized in that: It comprises a data processing module and a model building module; the data processing module is used to solve the collision parameters and absolute total electron content of occultation observations; the model building module is used to construct a non-spherically symmetric assumption inversion function model.

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