Space benchmark assessment method and space benchmark assessment system

Abstract

The present invention relates to a space reference assessment method and a space reference assessment system, comprising the following steps: obtaining broadcast ephemeris and precise ephemeris to calculate a first set of seven parameters; using broadcast ephemeris, PPP-B2b telegram data and precise ephemeris to calculate a second set of seven parameters; using PPP-B2b services to resolve ground station coordinates and IGS precise coordinates to calculate a third set of seven parameters; using ERP parameters in the broadcast ephemeris and IERS C04 parameters to calculate ERP forecast errors; comparing the first set of seven parameters, the second set of seven parameters and the third set of seven parameters with the ERP forecast errors, and analyzing the correlations. The present invention can assess the navigation accuracy of BDCS delivered to global and China and surrounding areas through the RNSS and PPP-B2b services of the Beidou navigation system using the three sets of seven parameters, and at the same time, using three rotation parameters of the seven parameters to perform correlation analysis with the Earth Rotation Parameter (ERP) forecast errors to further determine the error sources affecting the space reference accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of space benchmark assessment, and in particular to a space benchmark assessment method and a space benchmark assessment system. Background Art

[0002] The accuracy with which a satellite navigation system's coordinate framework is implemented and maintained determines its high-precision, stable service and interoperability. Currently, the four major international GNSS navigation systems (Beidou Navigation System (BDS), GPS, GLONASS, and Galileo) each implement the coordinate reference frames BDCS, WGS84, PZ90.11, and GTRF, respectively. These coordinate reference frames all employ satellite geodetic techniques to estimate monitoring station coordinates and achieve regular millimeter-level alignment to the International Terrestrial Reference Frame (ITRF), thereby ensuring high spatial reference accuracy and interoperability between systems. The stations used in implementing each navigation system's coordinate framework include its own monitoring stations, and information about these monitoring stations is not publicly available to navigation users. This makes it impossible for navigation users with real-time requirements to directly utilize these coordinate frames and evaluate their accuracy.

[0003] Currently, BDS-3 provides seven types of services globally and in China's surrounding areas. Satellite-broadcast navigation services include meter-level navigation positioning and timing services (RNSS) and decimeter- to centimeter-level precise point positioning services (PPP-B2b). BDCS provides millimeter-level spatial references for these services, and can be delivered to navigation users globally, in China, and in surrounding areas at varying degrees of accuracy via RNSS and PPP-B2b services.

[0004] Broadcast ephemeris is implemented and maintained based on the spatial reference of each system. The spatial reference of precise ephemeris is currently maintained mainly by IGS14, which is consistent with ITRF2014. Therefore, the accuracy of the spatial reference implementation of the navigation system can be evaluated by calculating seven parameters (3 translation parameters, 3 rotation parameters and 1 scale factor) between the broadcast ephemeris and precise ephemeris of each system.

[0005] Liu Yuchen and others from the Shanghai Astronomical Observatory of the Chinese Academy of Sciences used the January 2019 BDS broadcast ephemeris and the Shanghai Astronomical Observatory's post-processed precision ephemeris to calculate seven parameters between the satellite orbits in the two ephemeris. The BDS broadcast ephemeris is based on the BDCS, and the results show that the alignment accuracy of the BDCS and ITRF is at the centimeter level. Malys et al. from the National Geospatial Administration compared the broadcast ephemeris with precise orbit products for eight weeks from July to September 2019. They evaluated the spatial reference accuracy of various GNSS systems by calculating the translation and rotation parameters between the two orbit products. When evaluating the BDS broadcast ephemeris, the precise orbits were provided by Wuhan University, while those of other GNSS systems were evaluated using products provided by the German Research Centre for Geosciences (GFZ). The results show that the difference between the BDCS and IGS14 is approximately 6 cm, comparable to the accuracy of GPS. Guo Chen et al. from Wuhan University also compared the broadcast ephemeris of various systems with the precise ephemeris (GFZ), and found that the BDS broadcast ephemeris reference frame is consistent with the ITRF2014 up to 10 cm.

[0006] The spatial references of various systems contain errors due to various factors, including errors in the ground reference frame, satellite orbits, and Earth's rotation parameters. Existing research methods primarily use satellite geodetic techniques to estimate the coordinates of ground monitoring stations and align them to the ITRF, and evaluate the accuracy of achieving and maintaining the spatial reference using broadcast ephemeris, PPP-B2b messages, and precise ephemeris comparison methods. However, the sources of error that affect the accuracy of the spatial reference have not been clearly identified. Summary of the Invention

[0007] In view of the above technical problems, an object of the present invention is to provide a spatial reference evaluation method and a spatial reference evaluation system to clearly identify the error sources that affect the accuracy of the spatial reference.

[0008] The technical solution for achieving the purpose of the present invention is: a spatial reference evaluation method comprising the following steps:

[0009] Step S1: Obtain broadcast ephemeris and precise ephemeris, and calculate the first set of seven parameters;

[0010] Step S2, calculating the second set of seven parameters using the broadcast ephemeris, PPP-B2b message orbit corrections, and precise ephemeris;

[0011] Step S3: Calculate the third set of seven parameters by using the PPP-B2b service to solve the ground station coordinates and the IGS precise coordinates;

[0012] Step S4, calculating the ERP prediction error using the ERP parameters in the broadcast ephemeris and the IERS C04 parameters;

[0013] Step S5: Compare the first set of seven parameters, the second set of seven parameters, and the third set of seven parameters with the ERP prediction error, and analyze the correlation.

[0014] According to a technical solution of the present invention, in step S1, it specifically includes:

[0015] Step S11: Obtain the difference between the coordinate frame of the BeiDou satellite navigation system and the ITRF2014 / IGS14 frame through the Helmet conversion parameter. The formula is:

[0016] X GNSS =X trans +(1+X scale )*X rotate *X itrf

[0017] Among them, X trans are three translation parameters, X scale is the scale factor, X rotate are 3 rotation parameters, X GNSS is the satellite position in the navigation system coordinate frame, X itrf is the current epoch position of the station or satellite in the ITRF2014 / IGS14 coordinate frame;

[0018] Step S12: Before comparing the satellite centroid coordinates provided by the precise ephemeris with the position of the satellite antenna phase center provided by the broadcast ephemeris, a correction from the satellite antenna phase center to the centroid is required. The phase center correction model is:

[0019]

[0020] Among them, R ciscts is the rotation matrix between the inertial system and the earth-fixed system, x phs 、y phs 、z phs is the satellite antenna phase center deviation in the satellite-fixed coordinate system, and X, Y, and Z are the satellite antenna phase center correction values;

[0021] Step S13: Calculate the unit vector of the satellite-fixed system in the inertial system according to the BeiDou satellite attitude control mode;

[0022] Step S14: using the unit vector of the satellite-fixed system in the inertial system and the phase center correction model to complete the correction from the center of mass to the satellite antenna phase center to the center of mass;

[0023] Step S15: Based on the difference between the spatial reference of the BeiDou satellite navigation system and the ITRF2014 / IGS14 framework in step S11, the translation parameters, rotation parameters and scale factors are calculated to evaluate the accuracy of the BDCS.

[0024] According to a technical solution of the present invention, in step S13, the satellite types are different and the orientation of the satellite fixed coordinate system is different.

[0025] In the IGSO / MEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the Earth, the Y axis is the cross product of the Z axis and the direction from the satellite to the sun, and the X axis, Y axis, and Z axis form a right-handed system. The unit vector calculation formula of the fixed system in the inertial system is:

[0026]

[0027] in, is the satellite position vector in the inertial system, is the sun's position vector in the inertial system;

[0028] In the GEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the earth, the Y axis is the cross product of the Z axis and the satellite velocity direction, and the X axis, Y axis, and Z axis form a right-handed system. The calculation formula of the unit vector of the fixed system in the inertial system is:

[0029]

[0030] in, is the position vector of the satellite in the inertial system, is the velocity vector of the satellite in the inertial system.

[0031] According to a technical solution of the present invention, in step S2, the satellite position after the navigation system satellite orbit is corrected is further calculated, and the specific steps are as follows:

[0032] Step S201: Obtain satellite orbit correction data in PPP-B2b message data;

[0033] Step S202: Add the satellite orbit correction number to the satellite orbit position in the broadcast ephemeris to obtain the corrected satellite orbit position in the navigation system coordinate frame.

[0034] According to a technical solution of the present invention, after completing step S202, the second set of seven parameters is calculated using the calculation method of steps S11 to S15.

[0035] According to a technical solution of the present invention, in step S3, the following steps are specifically included:

[0036] Step S31: Select iGMAS and IGS stations in China and its surrounding areas, and calculate the station coordinates using the precise point positioning method using PPP-B2b signal observation data;

[0037] Step S32: Obtain the Tianjie IGS station coordinates provided by IGS and the precise station coordinates provided by iGMAS;

[0038] Step S33: Calculate the third set of seven parameters using the formula in step S21 to evaluate the BDCS accuracy.

[0039] According to a technical solution of the present invention, in step S4, it specifically includes:

[0040] Step S41, obtaining an IERS C04 sequence;

[0041] Step S42: Obtain ERP parameters of the Beidou satellite navigation system in the broadcast ephemeris;

[0042] Step S43: Subtract the ERP parameter from the IERS C04 to obtain the ERP prediction error used by the Beidou navigation system in the precise orbit determination process. According to a technical solution of the present invention, the ERP prediction error includes polar motion and day length change.

[0043] According to one aspect of the present invention, a spatial reference assessment system is proposed, which uses the spatial reference assessment method described in any one of the above technical solutions to identify error sources.

[0044] According to the present invention, a space reference assessment method and system are proposed. These methods compare and calculate seven parameters using the navigation system's broadcast ephemeris (under the BDCS framework) and precise ephemeris (under the IGS14 framework). Furthermore, they compare and calculate seven parameters using the navigation system's broadcast ephemeris plus orbit corrections from the PPP-B2b message (under the BDCS framework) and the precise ephemeris (under the IGS14 framework). Furthermore, ground station coordinates are estimated using the Precision Point Positioning (PPP) method using the PPP-B2b signal (under the BDCS framework) and compared with the precise coordinates provided by the International GNSS Service (IGS) (under the IGS14 framework). The seven parameters are then calculated between the two coordinate frames. The two sets of seven parameters can be used to assess the accuracy of the BDCS. Furthermore, three of the seven rotation parameters are compared with the predicted errors of the Earth Orientation Parameter (ERP) to further identify error sources affecting the accuracy of the space reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematically showing a flow chart of a spatial reference assessment method according to one embodiment of the present invention;

[0046] Figure 2 Schematically showing a flow chart of a spatial reference assessment method according to another embodiment of the present invention;

[0047] Figure 3Schematic diagram showing the EOP error, the time series of rotation parameters for seven parameters used in calculating broadcast and precise ephemeris, the rotation parameters calculated using BDS / GPS corrections broadcasted via PPP-B2b messages, and the rotation parameters calculated using precise point positioning solutions using PPP-B2b signals, used in processing precise orbit determination data for the Beidou navigation system according to one embodiment of the present invention;

[0048] Figure 4 Schematically showing the time series of the coordinate differences between the POL2 station coordinates and the IGS coordinates in the ENU direction calculated by PPP before and after the calculation of the rotation parameters according to one embodiment of the present invention. DETAILED DESCRIPTION

[0049] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below only illustrate some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0050] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0051] like Figure 1 and Figure 2 As shown, a spatial reference evaluation method of the present invention includes the following steps:

[0052] Step S1: Obtain broadcast ephemeris and precise ephemeris, and calculate the first set of seven parameters;

[0053] Step S2, calculating the second set of seven parameters using the broadcast ephemeris, PPP-B2b message orbit corrections, and precise ephemeris;

[0054] Step S3: Calculate the third set of seven parameters by using the PPP-B2b service to solve the ground station coordinates and the IGS precise coordinates;

[0055] Step S4, calculating the ERP prediction error using the ERP parameters in the broadcast ephemeris and the IERS C04 parameters;

[0056] Step S5: Compare the first set of seven parameters, the second set of seven parameters, and the third set of seven parameters with the ERP prediction error, and analyze the correlation.

[0057] In one embodiment of the present invention, preferably, the step S1 specifically includes:

[0058] Step S11: Obtain the difference between the coordinate frame of the BeiDou satellite navigation system and the ITRF2014 / IGS14 frame through the Helmet conversion parameter. The formula is:

[0059] X GNSS =X trans +(1+X scale )*X rotate *X itrf

[0060] Among them, X trans are three translation parameters, X scale is the scale factor, X rotate are three rotation parameters, X GNSS is the satellite position in the navigation system coordinate frame, X itrf is the current epoch position of the station or satellite in the ITRF2014 / IGS14 coordinate frame;

[0061] Step S12: Before comparing the satellite centroid coordinates provided by the precise ephemeris with the position of the satellite antenna phase center provided by the broadcast ephemeris, a correction from the satellite antenna phase center to the centroid is required. The phase center correction model is:

[0062]

[0063] Among them, R ciscts is the rotation matrix between the inertial system and the earth-fixed system, x phs 、y phs 、z phs is the satellite antenna phase center deviation in the satellite-fixed coordinate system, and X, Y, and Z are the satellite antenna phase center correction values;

[0064] Step S13: Calculate the unit vector of the satellite-fixed system in the inertial system according to the BeiDou satellite attitude control mode;

[0065] Step S14: using the unit vector of the satellite-fixed system in the inertial system and the phase center correction model to complete the correction from the center of mass to the satellite antenna phase center to the center of mass;

[0066] Step S15: Based on the difference between the spatial reference of the BeiDou satellite navigation system and the ITRF2014 / IGS14 framework in step S11, the translation parameters, rotation parameters and scale factors are calculated to evaluate the accuracy of the BDCS.

[0067] In one embodiment of the present invention, preferably, in step S13, different satellite types have different orientations of satellite fixed coordinate systems.

[0068] In the IGSO / MEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the Earth, the Y axis is the cross product of the Z axis and the direction from the satellite to the sun, and the X axis, Y axis, and Z axis form a right-handed system. The unit vector calculation formula of the fixed system in the inertial system is:

[0069]

[0070] in, is the satellite position vector in the inertial system, is the sun's position vector in the inertial system;

[0071] In the GEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the earth, the Y axis is the cross product of the Z axis and the satellite velocity direction, and the X axis, Y axis, and Z axis form a right-handed system. The calculation formula of the unit vector of the fixed system in the inertial system is:

[0072]

[0073] in, is the position vector of the satellite in the inertial system, is the velocity vector of the satellite in the inertial system.

[0074] In one embodiment of the present invention, preferably, in step S2, the process further includes calculating the corrected position of the navigation system satellite orbit, specifically the following steps:

[0075] Step S201: Obtain satellite orbit correction data in PPP-B2b message data;

[0076] Step S202: Add the satellite orbit correction number to the satellite orbit position in the broadcast ephemeris to obtain the corrected satellite orbit position in the navigation system coordinate frame.

[0077] In one embodiment of the present invention, preferably, after completing step S202, the second set of seven parameters is calculated using the calculation method of steps S11 to S15.

[0078] like Figure 2 As shown in FIG, for the basic navigation service provided by Beidou satellites, the first set of seven parameters is directly calculated using the satellite orbit position in the broadcast ephemeris and the position in the precise ephemeris; and for the PPP-B2b service provided by Beidou satellites, the satellite position after satellite orbit correction in the navigation system coordinate frame is first calculated, and then the calculation method and formula in step S1 are used to calculate the second set of seven parameters, thereby completing the accuracy assessment.

[0079] In one embodiment of the present invention, preferably, step S3 specifically includes:

[0080] Step S31: Select iGMAS and IGS stations in China and its surrounding areas, and calculate the station coordinates using the precise point positioning method using PPP-B2b signal observation data;

[0081] Step S32: Obtain the Tianjie IGS station coordinates provided by IGS and the station precise coordinates provided by iGMAS;

[0082] Step S33: Calculate the third set of seven parameters using the formula in step S21 to evaluate the BDCS accuracy.

[0083] In one embodiment of the present invention, preferably, step S4 specifically includes:

[0084] Step S41, obtaining an IERS C04 sequence;

[0085] Step S42: Obtain ERP parameters of the Beidou satellite navigation system in the broadcast ephemeris;

[0086] Step S43: Subtract the ERP parameter from the IERS C04 to obtain the ERP prediction error used by the Beidou navigation system in the precise orbit determination process.

[0087] In one embodiment of the present invention, preferably, the ERP prediction error includes the polar shift in the EOP and the change in the Earth's rotation rate.

[0088] According to one aspect of the present invention, a spatial reference assessment system is proposed, which uses the spatial reference assessment method described in any one of the above technical solutions to identify error sources.

[0089] Figure 3 These are the time series of the seven rotation parameters used in the precise orbit determination data processing of the Beidou navigation system: the EOP prediction error, the seven parameters calculated from broadcast and precise ephemeris, the seven parameters calculated from BDS / GPS corrections broadcast via PPP-B2b messages, and the seven parameters calculated from station coordinates derived from precise point positioning using PPP-B2b signals. They are denoted as dEOPC04, RotBRDC, RotB2bC, RotB2bG, and RotPPP, respectively. The Xp component of polar motion corresponds to the rotation parameter Ry, the Yp component corresponds to the rotation parameter Rx, and the UT1-UTC corresponds to the rotation parameter Rz.

[0090] from Figure 3As can be seen from the figure, the RotBRDC parameters Rx and Ry agree well with the Yp and Xp forecast errors, respectively. Rz does not agree well with the UT1-UTC difference. This is mainly because the BDS-3 broadcast ephemeris is generated using observation data from regional monitoring stations within China. In addition to the EOP forecast error, the regional distribution of stations, and the influence of plate motion on station coordinate accuracy, all other factors affect the rotation component Rz.

[0091] RotB2bC agrees well with all three rotation parameters of RotBRDC. The Rx and Ry parameters are consistent with the Yp and Xp forecast errors, respectively, and differ significantly from the UT1-UTC error. RotB2bG agrees well with the Rx and Ry parameters of RotBRDC. Unlike RotB2bC, the Rz parameter of RotB2bG differs significantly from that of ROTBRDC, and the difference from the UT1-UTC error is small. This is mainly because the calculation of GPS orbit corrections in the PPP-B2b message uses seven domestic stations and some IGS stations around the world. The IGS station coordinates were updated at the end of 2021 using the weekly solution precise coordinates provided by IGS, and the station coordinates changed little. However, the stations used to calculate the BDS orbit corrections in the PPP-B2b message are the same seven stations within China used in the broadcast ephemeris calculation, and the station coordinates were updated in 2020. The three rotation parameters of RotPPP show smaller time series variations than those calculated using other methods, but exhibit similar trends. RotPPP is closer to the Rz parameter of RotB2bGPS, due to RotPPP's use of observations from both the BDS and GPS systems. From the perspective of PPP-B2b positioning, precise positioning results are also subject to overall rotation due to EOP forecast errors.

[0092] Figure 4 This is the time series of the difference between the coordinates of the POL2 station and the IGS coordinates in the ENU direction calculated by PPP before and after the calculation of the rotation parameters. Figure 4 As shown in Figure 2, during the period of about 180 days when the EOP error is large, the estimated station coordinates have systematic errors. After the station coordinates are rotated by seven parameters, the accuracy of the north direction is significantly improved. Figure 3 By comparing the EOP forecast error time series with that of the previous two periods, it is found that the EOP forecast error also becomes larger within the same time segment, indicating that the EOP forecast error causes the overall rotation of the PPP positioning results.

[0093] This invention proposes a space reference assessment method and system. These methods use the navigation system's broadcast ephemeris plus orbit corrections from the PPP-B2b message (under the BDCS framework) to compare with precise ephemeris (under the IGS14 framework) and calculate seven parameters. They also use the Precise Point Positioning (PPP) method using the PPP-B2b signal to estimate ground station coordinates (under the BDCS framework). These are then compared with the precise coordinates provided by the International GNSS Service (IGS) (under the IGS14 framework) and the seven parameters calculated between the two coordinate frameworks. The seven parameters can be used to assess the accuracy of the BDCS. Furthermore, three rotational parameters within the seven parameters are compared with the predicted errors of the Earth Orientation Parameter (ERP) to further identify error sources affecting the accuracy of the space reference.

[0094] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes the element.

[0095] It should also be noted that the above is a preferred embodiment of the present invention. It should be noted that although the preferred embodiment of the present invention has been described, it is clear that those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles of the present invention. Such improvements and modifications should also be considered as within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiment and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A spatial benchmark assessment method, characterized in that: The following steps are involved: Step S1: Obtain broadcast ephemeris and precise ephemeris, and calculate the first set of seven parameters; Step S2, calculating the second set of seven parameters using the broadcast ephemeris, PPP-B2b message orbit corrections, and precise ephemeris; Step S3: Calculate the third set of seven parameters by using the PPP-B2b service to solve the ground station coordinates and the IGS precise coordinates; Step S4, calculating the ERP prediction error using the ERP parameters in the broadcast ephemeris and the IERS C04 parameters; Step S5: Compare the first set of seven parameters, the second set of seven parameters, and the third set of seven parameters with the ERP prediction error, and analyze the correlation.

2. The method according to claim 1, characterized in that In the step S1, it specifically includes: Step S11: Obtain the difference between the coordinate frame of the BeiDou satellite navigation system and the ITRF2014 / IGS14 frame through the Helmet conversion parameter. The formula is: X GNSS =X trans +(1+X scale )*X rotate *X itrf Among them, X trans are three translation parameters, X scale is the scale factor, X rotate are 3 rotation parameters, X GNSS is the station / satellite position in the navigation system coordinate frame, X itrf is the current epoch position of the station or satellite in the ITRF2014 / IGS14 coordinate frame; Step S12: Before comparing the satellite centroid coordinates provided by the precise ephemeris with the position of the satellite antenna phase center provided by the broadcast ephemeris, a correction from the satellite antenna phase center to the centroid is required. The phase center correction model is: Among them, R ciscts is the rotation matrix between the inertial system and the earth-fixed system, x phs 、y phs 、z phs is the satellite antenna phase center deviation in the satellite-fixed coordinate system, and X, Y, and Z are the satellite antenna phase center correction values; Step S13: Calculate the unit vector of the satellite-fixed system in the inertial system according to the BeiDou satellite attitude control mode; Step S14: using the unit vector of the satellite-fixed system in the inertial system and the phase center correction model to complete the correction from the center of mass to the satellite antenna phase center to the center of mass; Step S15: Based on the difference between the spatial reference of the BeiDou satellite navigation system and the ITRF2014 / IGS14 framework in step S11, the translation parameters, rotation parameters and scale factors are calculated to evaluate the accuracy of the BDCS.

3. The method according to claim 2, characterized in that In step S13, different satellite types have different directions of satellite fixed coordinate systems. In the IGSO / MEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the Earth, the Y axis is the cross product of the Z axis and the direction from the satellite to the sun, and the X axis, Y axis, and Z axis form a right-handed system. The unit vector calculation formula of the fixed system in the inertial system is: in, is the satellite position vector in the inertial system, is the sun's position vector in the inertial system; In the GEO satellite fixed coordinate system, the Z axis of the attitude control model points to the center of the earth, the Y axis is the cross product of the Z axis and the satellite velocity direction, and the X axis, Y axis, and Z axis form a right-handed system. The calculation formula of the unit vector of the fixed system in the inertial system is: in, is the position vector of the satellite in the inertial system, is the velocity vector of the satellite in the inertial system.

4. The method according to claim 2, characterized in that In the step S2, the satellite position after the navigation system satellite orbit correction is calculated, and the specific steps are: Step S201: Obtain satellite orbit correction data in PPP-B2b message data; Step S202: Add the satellite orbit correction number to the satellite orbit position in the broadcast ephemeris to obtain the satellite position after the satellite orbit is corrected in the navigation system coordinate frame.

5. The method according to claim 4, characterized in that After completing step S202 , the second set of seven parameters is calculated using the calculation method of steps S11 to S15 .

6. The method according to claim 2, characterized in that In the step S3, it specifically includes: Step S31: Select iGMAS and IGS stations in China and its surrounding areas, and calculate the station coordinates using the precise point positioning method using PPP-B2b signal observation data; Step S32: Obtain the Tianjie IGS station coordinates provided by IGS and the station precise coordinates provided by iGMAS; Step S33: Calculate the third set of seven parameters using the formula in step S1 to evaluate the accuracy of BDCS.

7. The method according to claim 1, characterized in that In the step S4, it specifically includes: Step S41, obtaining an IERS C04 sequence; Step S42: Obtain ERP parameters broadcast by the Beidou satellite navigation system in the broadcast ephemeris; Step S43: Subtract the ERP parameter from the IERS C04 to obtain the ERP prediction error used by the Beidou navigation system in the precise orbit determination process.

8. The method according to claim 7, characterized in that The ERP forecast error includes polar motion and day length change.

9. A spatial reference assessment system, characterized in that: The spatial reference evaluation method according to any one of claims 1 to 8 is used to identify the error sources.

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