Method and system for extracting ionospheric VTEC based on DORIS carrier phase data

Abstract

The present invention provides a method and system for extracting ionospheric VTEC based on DORIS carrier phase data, using DOIRS dual-frequency carrier phase data to form a geometrically independent equation, correcting the geometric errors of antenna phase centers at beacon ends and satellite ends, and obtaining relative ionospheric STEC containing ambiguity parameters; introducing IGS global ionospheric model GIM ionospheric data, projecting the vertical ionospheric VTEC at the puncture point to the inclined ionospheric STEC, and correcting the low-orbit satellite orbit height error factor, and performing absolute value correction on DORIS relative ionospheric STEC. The data processing method of the present invention is simple, and only uses carrier phase data, which overcomes the problem of low accuracy of DORIS pseudorange observation values, and can accurately extract DORIS relative ionospheric TEC; introducing a high-precision global ionospheric model GIM as external ionospheric data, and can accurately correct DORIS relative ionospheric TEC to absolute ionospheric TEC.

Description

Technical Field

[0001] The present invention relates to an ionospheric VTEC extraction method, and in particular to a method and system for extracting ionospheric VTEC based on DORIS carrier phase data. Background Art

[0002] The ionosphere is an important part of the solar-terrestrial space environment. It is located in the entire space from 60 km above the earth's surface to the top of the magnetosphere. Due to its complex and changeable physical properties, it has an important impact on the satellite navigation and positioning system engineering based on radio technology. On the one hand, the ionospheric delay error is one of the most difficult errors in the processing of GNSS satellite observation data; on the other hand, the ionospheric VTEC can be inverted based on the GNSS dual-frequency pseudorange and carrier observation data. Using different ionospheric observation techniques to invert the Earth's ionospheric TEC has always been a research hotspot in space geodesy.

[0003] The inversion of ionospheric TEC using GNSS observation technology has been developed for more than 20 years. Its basic principle is to combine GNSS dual-frequency observation data into ionospheric observation equations, eliminate parameters unrelated to ionospheric parameters, including geometric position, troposphere, clock error and other information, and then use carrier phase observations and pseudorange observations to form carrier phase smoothed pseudorange observations, and finally eliminate the influence of differential code bias at the satellite and receiver ends to extract ionospheric VTEC. Since ionospheric TEC is difficult to distinguish from differential code bias, ionospheric TEC is usually modeled, and the satellite differential code bias is constrained, and finally ionospheric TEC is separated.

[0004] Since GNSS observation stations are mainly distributed in continental areas, especially in North America and Europe, and are less distributed in the ocean and the southern hemisphere, the ionospheric TEC extracted using ground-based GNSS technology is often unevenly distributed, that is, the ionospheric TEC distribution is more in the land coverage area, while it is less or even absent in the ocean area. Therefore, the global ionospheric model established only using ground-based GNSS technology has low model accuracy in the ocean area, which is significantly lower than that in the land coverage area. In order to further improve the accuracy of the global ionospheric model, it is necessary to consider supplementing the effective ionospheric TEC observation data in the ocean area.

[0005] Due to the development of various ionospheric observation technologies in recent years, the Doppler Radio Orbit Determination and Positioning System (DORIS) observation technology can also effectively extract ionospheric TEC information. At present, there are about 60 DORIS reference stations evenly distributed around the world, and about 7 low-orbit satellites are equipped with the third-generation DORIS receiver, which can provide carrier phase and pseudorange observation data for almost the entire land and offshore areas, further increasing the effective sampling space of the ionosphere.

[0006] The DORIS system transmits observation signals at two frequencies, 2036.25MHz and 401.25MHz. Its data processing strategy is basically similar to that of GNSS data processing, but there are also significant differences. Since the accuracy of the pseudorange observation value of the DORIS system is about 1km, it is not feasible to extract ionospheric TEC information using pseudorange or carrier smoothed pseudorange. However, using only carrier phase data has the problem of difficulty in ambiguity processing. Therefore, how to use DORIS data to extract ionospheric TEC is the first and most important step to fully utilize DORIS ionospheric data.

[0007] Related terms meaning:

[0008] VTEC is the vertical total electron content

[0009] TEC is the total electron content

[0010] DORIS is a Doppler radio orbit determination system.

[0011] GNSS is the Global Navigation Satellite System

[0012] IGS is the international GNSS service

[0013] STEC is the tilted total electron content

[0014] GIM-VTEC is the Global Ionospheric Model - Vertical Total Electron Content

[0015] GIM-STEC is the Global Ionospheric Model-Slanted Total Electron Content

[0016] DORIS-STEC is a Doppler radio orbit determination system - tilt total electron content Summary of the invention

[0017] The present invention is mainly proposed for the DORIS ionosphere extraction method, and provides a technical solution for calculating ionospheric VTEC using DORIS carrier phase data.

[0018] The invention provides a method for extracting ionospheric VTEC based on DOIRS carrier phase data. The method adopts DOIRS dual-frequency carrier phase data to form a geometrically independent equation, corrects the geometric errors of antenna phase centers at a beacon end and a satellite end, and obtains a relative ionospheric STEC including ambiguity parameters. The IGS global ionospheric model GIM ionospheric data is introduced, the vertical ionospheric VTEC at the puncture point is projected to the inclined ionospheric STEC, and the low-orbit satellite orbit height error factor is corrected, so as to perform an absolute value correction on the DORIS relative ionospheric STEC.

[0019] Moreover, the implementation process includes the following steps,

[0020] Step 1: Combining ionospheric observation values ​​based on DORIS dual-frequency carrier phase data, correcting the antenna phase center geometric error, and marking the observation values ​​according to the ambiguity parameter characteristics;

[0021] Step 2: Obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the puncture point information according to the DORIS data, including longitude and latitude, satellite azimuth and satellite altitude;

[0022] Step 3, calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point according to the DORIS puncture point information, and project the VTEC to the inclined ionospheric STEC;

[0023] Step 4, according to the difference between the orbital altitude of DORIS low-orbit satellite and the orbital altitude of GPS satellite, the orbital altitude error factor is calculated, and the GIM-STEC is corrected to the GIM-STEC of the orbital altitude of DORIS low-orbit satellite;

[0024] Step 5, aligning and correcting DORIS-STEC and GIM-STEC, wherein the correction method is to select the error at the maximum satellite altitude angle to perform absolute value correction of the observation arc;

[0025] Step 6, project the corrected DORIS-STEC onto the vertical VTEC to obtain the ionospheric VTEC calculated based on the DORIS carrier phase data.

[0026] Furthermore, in step 1, the antenna phase center geometric deviation is calculated using the phase center deviation and the satellite elevation angle.

[0027] Moreover, in step 3, the external ionospheric data IGS global ionospheric model is introduced as a benchmark to perform an absolute value correction on the DORIS relative ionospheric information.

[0028] Furthermore, in step 4, based on the difference between the GPS navigation satellite orbit and the DORIS low-orbit satellite orbit altitude, the orbit altitude error factor is calculated, and the GIM ionosphere information is corrected to the ionosphere information of the DORIS low-orbit satellite orbit altitude.

[0029] The present invention also provides a system for extracting ionospheric VTEC based on DORIS carrier phase data, which is used to implement the method for extracting ionospheric VTEC based on DORIS carrier phase data as described above.

[0030] Furthermore, the following modules are included,

[0031] The first module is used to form an ionospheric observation value combination based on the DORIS dual-frequency carrier phase data, correct the antenna phase center geometric error, and mark the observation value according to the ambiguity parameter characteristics.

[0032] The second module is used to obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the puncture point information according to the DORIS data, including longitude and latitude, satellite azimuth and satellite altitude;

[0033] The third module is used to calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point based on the DORIS puncture point information, and project the VTEC to the inclined ionospheric STEC;

[0034] The fourth module is used to calculate the orbit height error factor according to the difference between the orbit height of the DORIS low-orbit satellite and the orbit height of the GPS satellite, and correct the GIM-STEC to the GIM-STEC of the orbit height of the DORIS low-orbit satellite;

[0035] The fifth module is used to align DORIS-STEC with GIM-STEC, where the correction method is to select the error at the maximum satellite altitude angle to perform absolute value correction of the observation arc;

[0036] The sixth module is used to project the corrected DORIS-STEC onto the VTEC in the vertical direction, thus obtaining the ionospheric VTEC calculated based on the DORIS carrier phase data.

[0037] Alternatively, it includes a processor and a memory, the memory is used to store program instructions, and the processor is used to call the stored instructions in the memory to execute the method for extracting ionospheric VTEC based on DORIS carrier phase data as described above.

[0038] Alternatively, it comprises a readable storage medium having a computer program stored thereon, and when the computer program is executed, the method for extracting ionospheric VTEC based on DORIS carrier phase data as described above is implemented.

[0039] In the above method of calculating ionospheric VTEC using DORIS carrier phase data, the ionospheric combined observation value is mainly calculated based on the dual-frequency carrier phase data in DORISRINEX3.0 format, and then the antenna phase center geometric deviation, projection function error and orbit height factor error are corrected in sequence to correct the DORIS relative ionospheric TEC to the absolute ionospheric VTEC in the vertical direction. The external ionospheric data introduced is the IGS global ionosphere GIM model.

[0040] Therefore, the present invention has the following advantages: 1. The data processing method is simple. The DORIS data preprocessing adopts a method similar to the GNSS data preprocessing to combine the ionospheric observation equation, and the data preprocessing processes such as coarse elimination and cycle slip detection are basically the same; 2. Only the carrier phase data is used, which overcomes the problem of low accuracy of DORIS pseudorange observation values, and can accurately extract DORIS relative ionospheric TEC; 3. The high-precision global ionospheric model GIM is introduced as the external ionospheric data, and the DORIS relative ionospheric TEC can be accurately corrected to the absolute ionospheric TEC. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a data processing flow chart of an embodiment of the present invention.

[0042] Figure 2 It is a flow chart of calculating ionospheric VTEC using GIM according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0044] Embodiment 1:

[0045] The embodiment provides a method for extracting ionospheric VTEC based on DORIS carrier phase data, which uses DOIRS dual-frequency carrier phase data to form a geometrically independent equation, corrects the geometric errors of the antenna phase centers at the beacon end and the satellite end, and obtains the relative ionospheric STEC containing ambiguity parameters. The IGS global ionospheric model GIM ionospheric data is introduced, the vertical ionospheric VTEC at the puncture point is projected to the inclined ionospheric STEC, and the low-orbit satellite orbit height error factor is corrected to perform an absolute value correction on the DORIS relative ionospheric STEC.

[0046] In specific implementation, the dual-frequency carrier phase data in RINEX DORIS 3.0 format can be used to extract ionospheric STEC, and then the IGS GIM external ionospheric data can be introduced to perform absolute value correction on the above ionospheric STEC. In the correction process, it is necessary to take into account the geometric correction of the antenna phase center, the projection function and the orbit height factor correction.

[0047] The data processing flow provided by the embodiment of the present invention is as follows Figure 1 As shown, the following steps are included:

[0048] Step 1: compose an ionospheric observation combination based on the DORIS dual-frequency carrier phase data, labeled as DORIS-STEC, and mark the observations according to the characteristics of the ambiguity parameters.

[0049] First, read the observation file in DORIS RINEX 3.0 format, and form the ionospheric observation equation based on the dual-frequency carrier phase observation data, as shown in the following formula:

[0050]

[0051] In the formula,

[0052] for DORIS-STEC;

[0053] ξ -1 is the unit conversion factor;

[0054] is the combined ionospheric observation value based on the carrier phase;

[0055] f1 and f2 are the frequencies corresponding to the dual-frequency carrier phases;

[0056] λ f1 and λ f2 are the wavelengths corresponding to the dual-frequency carrier phases respectively;

[0057] and are the ambiguities corresponding to the dual-frequency carrier phases;

[0058] i is the station number, k is the satellite number;

[0059] ΔD is the geometric deviation of the antenna phase center between the beacon station and the DORIS receiver.

[0060] Since the ionospheric observations contain ambiguity parameters, it is necessary to detect the cycle slips of the observations and mark each continuous observation arc. Before detecting the cycle slips of the ambiguity, it is also necessary to remove the gross errors of the observations. For a complete observation arc, it is necessary to delete the observations with too short an arc (for example, an observation arc of not less than 20 minutes) and too small a satellite elevation angle (for example, not less than 10 degrees) to avoid inaccurate ambiguity estimation due to too short an arc or too small an elevation angle.

[0061] Step 2: Obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the longitude and latitude of the puncture point, satellite azimuth, satellite altitude and other information based on the DORIS data.

[0062] The orbit of the DORIS low-orbit satellite is calculated using the SP3 format precise orbit file, and the coordinates of the beacon station are known values. It is assumed that the free electrons in the ionosphere are concentrated in an infinitely thin single layer, and the height of the thin layer is assumed to be 450 km. The geographic longitude and latitude of the puncture point between the satellite signal and the thin layer are calculated, and the azimuth and altitude information of the satellite signal are calculated.

[0063] Step 3, calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point based on the DORIS puncture point information, marked as GIM-VTEC, and project VTEC to the inclined ionospheric STEC, marked as GIM-STEC.

[0064] Read the high-precision global ionosphere model, calculate the vertical ionospheric VTEC at the puncture point of the DORIS observation calculated in step 2, and then project the vertical ionospheric VTEC to STEC in the inclined direction. The projection function can be expressed as

[0065]

[0066] In the formula,

[0067] z′ is the angle between the center of the earth and the ionospheric piercing point and the satellite and the receiver;

[0068] α is the scaling factor;

[0069] z is the zenith distance of the satellite at the station;

[0070] R earth is the radius of the Earth;

[0071] H map is the height of the ionosphere thin layer.

[0072] In the embodiment, preferably H map =506.7km,α=0.9782,R e =6371km.

[0073] Step 4: Calculate the orbit height error factor based on the difference between the DORIS low-orbit satellite orbit height and the GPS satellite orbit height, and correct the initial GIM-STEC to the GIM-STEC of the DORIS low-orbit satellite orbit height.

[0074] Since GIM is calculated based on GNSS observation data, it includes ionospheric information from 60km to 20200km above the ground, while the ionosphere calculated by the DORIS low-orbit satellite only includes ionospheric information below the low-orbit satellite altitude. Therefore, when performing DORIS relative ionosphere correction, GIM-STEC needs to be corrected to the same altitude.

[0075] Step 5, aligning and correcting the initial DORIS-STEC obtained in step 1 and the corrected GIM-STEC obtained in step 4, wherein the correction method is to select the error at the maximum satellite elevation angle to perform absolute value correction of the observation arc.

[0076] Based on step 4, there is a significant deviation between DORIS relative ionosphere STEC and GIM ionosphere STEC, and the main part of the deviation is the ambiguity parameter. Considering that the projection function has the least impact on the ionosphere when the satellite altitude angle is the maximum, the present invention selects to calculate the ambiguity deviation between the two when the satellite altitude angle is the maximum, and applies the deviation to all epoch observations of the arc segment, thereby realizing the correction of DORIS absolute ionosphere.

[0077] Step 6: Project the DORIS-STEC corrected in step 5 onto the VTEC in the vertical direction to obtain the ionospheric VTEC calculated based on the DORIS carrier phase data.

[0078] Based on step 5, the oblique path ionospheric STEC is obtained. In order to describe the vertical distribution of ionospheric TEC, it is also necessary to project this STEC to the vertical direction. The projection function is the same as the projection function in step 3. Through the above steps, the ionospheric VTEC can be calculated using DORIS carrier phase data.

[0079] Embodiment 2:

[0080] Based on Example 1, in step 1, the phase center deviation and the satellite elevation angle are used to calculate the antenna phase center geometric deviation.

[0081] The antenna phase center deviation includes the antenna phase center deviation of the beacon station and the DORIS receiver. Since this error is also related to the satellite elevation angle, it is also necessary to project this geometric deviation to the direction of the observed signal according to the satellite elevation angle. The formula for calculating the antenna phase center geometric deviation is expressed as:

[0082] ΔD=D1-D2=-(d s +d b )sine

[0083] In the formula,

[0084] ΔD is the geometric deviation of the antenna phase center;

[0085] D1 is the geometric deviation of the antenna phase center at the receiver;

[0086] D2 is the geometric deviation of the antenna phase center of the beacon station;

[0087] d s is the antenna phase center deviation at the receiver;

[0088] d b is the antenna phase center deviation of the beacon station;

[0089] e represents the altitude angle of the low-orbit satellite.

[0090] In the embodiment, the d of the low-orbit satellites Jason-2, HY-2A, SARAL and CryoSat-2 s They are 0.1640, 0.1620, 0.1580 and 0.1538 m respectively. Currently, the DORIS beacon station uses Starec antenna, and the geometric correction parameter d b It is 0.487m.

[0091] Embodiment 3:

[0092] On the basis of Example 1, in step 3, the external ionospheric data IGS global ionospheric model is introduced as a benchmark to perform absolute value correction on the DORIS relative ionospheric information. The data processing flow chart is as follows: Figure 2 As shown, the epoch and longitude and latitude of the puncture point are input, the grid VTEC is calculated by binary interpolation, the grid VTEC is calculated by temporal interpolation, and then the vertical ionospheric VTEC is projected to the inclined ionospheric STEC.

[0093] The ionospheric VTEC at the puncture point is calculated based on GIM. The calculation method is binary interpolation method, and the calculation formula is expressed as:

[0094]

[0095] In the formula,

[0096] E() is the vertical ionospheric VTEC at the puncture point;

[0097] λ0 is the longitude of the grid point, β0 is the latitude of the grid point;

[0098] p is the longitude scale factor, q is the latitude scale factor;

[0099] E 0,0 , E 1,0 , E 0,1 , E 1,1 They are the vertical ionospheric VTEC at the four grid points respectively;

[0100] Δλ, Δβ represent the longitude and latitude differences.

[0101] Considering the relationship between the ionospheric grid model and the earth's rotation, the interpolation method in the time domain is expressed as

[0102]

[0103] in,

[0104] t is the input time;

[0105] T i and T i+1 are the moments of epoch i and i+1 respectively;

[0106] λ is the longitude of the puncture point, i ' is the longitude at epoch i, λ i ' +1 is the longitude at epoch i+1;

[0107] β is the latitude of the puncture point;

[0108] E(β,λ,t) is the vertical ionospheric VTEC at epoch t;

[0109] E i (β,λ i ') is the vertical ionospheric VTEC at epoch i;

[0110] E i+1 (β,λ i ' +1 ) is the vertical ionospheric VTEC at epoch i+1.

[0111] Embodiment 4:

[0112] On the basis of Example 1, in step 4, the difference between the GPS navigation satellite orbit and the DORIS low-orbit satellite orbit altitude is fully considered, the orbit altitude error factor is calculated, and the GIM ionosphere information is corrected to the ionosphere information of the DORIS low-orbit satellite orbit altitude.

[0113] Since the altitude of low-orbit satellites is much lower than that of GPS satellites, it is also necessary to correct the VTEC of GPS satellite altitude to the VTEC of DORIS satellite altitude. The correction coefficients for Jason-2 (1350km), HY-2A (970km), SARAL (800km) and CryoSat-2 (720km) are 0.925, 0.880, 0.856 and 0.744 respectively.

[0114] The ionospheric STEC at the corresponding orbital altitude is obtained by multiplying the STEC calculated using GIM by the above coefficient.

[0115] In specific implementation, the method proposed in the technical solution of the present invention can be implemented by technical personnel in this field using computer software technology to realize automatic operation process. System devices for implementing the method, such as computer-readable storage media storing the corresponding computer program of the technical solution of the present invention and computer equipment running the corresponding computer program, should also be within the scope of protection of the present invention.

[0116] In some possible embodiments, a system for extracting ionospheric VTEC based on DORIS carrier phase data is provided, comprising the following modules:

[0117] The first module is used to form an ionospheric observation value combination based on the DORIS dual-frequency carrier phase data, correct the antenna phase center geometric error, and mark the observation value according to the ambiguity parameter characteristics.

[0118] The second module is used to obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the puncture point information according to the DORIS data, including longitude and latitude, satellite azimuth and satellite altitude;

[0119] The third module is used to calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point based on the DORIS puncture point information, and project the VTEC to the inclined ionospheric STEC;

[0120] The fourth module is used to calculate the orbit height error factor according to the difference between the orbit height of the DORIS low-orbit satellite and the orbit height of the GPS satellite, and correct the GIM-STEC to the GIM-STEC of the orbit height of the DORIS low-orbit satellite;

[0121] The fifth module is used to align DORIS-STEC with GIM-STEC, where the correction method is to select the error at the maximum satellite altitude angle to perform absolute value correction of the observation arc;

[0122] The sixth module is used to project the corrected DORIS-STEC onto the VTEC in the vertical direction, thus obtaining the ionospheric VTEC calculated based on the DORIS carrier phase data.

[0123] In some possible embodiments, a system for extracting ionospheric VTEC based on DORIS carrier phase data is provided, including a processor and a memory, the memory being used to store program instructions, and the processor being used to call the stored instructions in the memory to execute a method for extracting ionospheric VTEC based on DORIS carrier phase data as described above.

[0124] In some possible embodiments, a system for extracting ionospheric VTEC based on DORIS carrier phase data is provided, comprising a readable storage medium having a computer program stored thereon, and when the computer program is executed, a method for extracting ionospheric VTEC based on DORIS carrier phase data as described above is implemented.

[0125] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for extracting ionospheric VTEC based on DORIS carrier phase data, characterized in that: The DOIRS dual-frequency carrier phase data is used to form a geometrically independent equation to correct the geometric errors of the antenna phase centers at the beacon and satellite ends, and the relative ionospheric STEC containing ambiguity parameters is obtained. The IGS Global Ionospheric Model (GIM) ionospheric data is introduced to project the vertical ionospheric VTEC at the puncture point to the inclined ionospheric STEC, and the low-orbit satellite orbit height error factor is corrected to make an absolute value correction of the DORIS relative ionospheric STEC. The geometric error of the antenna phase center is related to the satellite elevation angle. According to the projection of the satellite elevation angle to the direction of the observation signal, the formula for calculating the geometric deviation of the antenna phase center is expressed as: ΔD=D1-D2=-(d s +d b )sine In the formula, ΔD is the geometric deviation of the antenna phase center; D1 is the geometric deviation of the antenna phase center at the receiver; D2 is the geometric deviation of the antenna phase center of the beacon station; d s is the antenna phase center deviation at the receiver; d b is the antenna phase center deviation of the beacon station; e represents the altitude angle of the low-orbit satellite; When correcting the error factor of the low-orbit satellite orbital altitude, the ionospheric STEC of the corresponding orbital altitude is obtained by multiplying the STEC calculated by GIM by the correction factor to obtain the corrected GIM-STEC. After correcting the geometric error of the antenna phase center, the observation value is marked with arc segments according to the characteristics of the ambiguity parameters; when the initial DORIS-STEC is aligned with the corrected GIM-STEC, the correction method is to select the error at the maximum satellite elevation angle to perform absolute value correction on the observation arc segment.

2. The method for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 1, characterized in that: The implementation process includes the following steps: Step 1: Combining ionospheric observation values ​​based on DORIS dual-frequency carrier phase data, correcting the antenna phase center geometric error, and marking the observation values ​​according to the ambiguity parameter characteristics; Step 2: Obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the puncture point information according to the DORIS data, including longitude and latitude, satellite azimuth and satellite altitude; Step 3, calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point according to the DORIS puncture point information, and project the VTEC to the inclined ionospheric STEC; Step 4, according to the difference between the orbital altitude of DORIS low-orbit satellite and the orbital altitude of GPS satellite, the orbital altitude error factor is calculated, and the GIM-STEC is corrected to the GIM-STEC of the orbital altitude of DORIS low-orbit satellite; Step 5, aligning and correcting the initial DORIS-STEC obtained in step 1 and the GIM-STEC obtained in step 4, wherein the correction method is to select the error at the maximum satellite elevation angle to perform absolute value correction of the observation arc; Step 6, project the corrected DORIS-STEC onto the vertical VTEC to obtain the ionospheric VTEC calculated based on the DORIS carrier phase data.

3. The method for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 1, characterized in that: In step 1, the antenna phase center geometric deviation is calculated using the phase center deviation and the satellite elevation angle.

4. The method for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 1, characterized in that: In step 3, the external ionospheric data IGS global ionospheric model is introduced as a benchmark to perform absolute value correction on the DORIS relative ionospheric information.

5. The method for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 1, 2, 3 or 4, characterized in that: In step 4, based on the difference between the GPS navigation satellite orbit and the DORIS low-orbit satellite orbit altitude, the orbit altitude error factor is calculated, and the GIM ionosphere information is corrected to the ionosphere information of the DORIS low-orbit satellite orbit altitude.

6. A system for extracting ionospheric VTEC based on DORIS carrier phase data, characterized in that: Used to implement a method for extracting ionospheric VTEC based on DORIS carrier phase data as described in any one of claims 1-5.

7. The system for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 6, characterized in that: Includes the following modules, The first module is used to form an ionospheric observation value combination based on the DORIS dual-frequency carrier phase data, correct the antenna phase center geometric error, and mark the observation value according to the ambiguity parameter characteristics. The second module is used to obtain the location information of the beacon station and the orbit information of the low-orbit satellite, and calculate the puncture point information according to the DORIS data, including longitude and latitude, satellite azimuth and satellite altitude; The third module is used to calculate the vertical ionospheric VTEC of the IGS global ionospheric model GIM at the puncture point based on the DORIS puncture point information, and project the VTEC to the inclined ionospheric STEC; The fourth module is used to calculate the orbit height error factor according to the difference between the orbit height of the DORIS low-orbit satellite and the orbit height of the GPS satellite, and correct the GIM-STEC to the GIM-STEC of the orbit height of the DORIS low-orbit satellite; The fifth module is used to align DORIS-STEC with GIM-STEC, where the correction method is to select the error at the maximum satellite altitude angle to perform absolute value correction of the observation arc; The sixth module is used to project the corrected DORIS-STEC onto the VTEC in the vertical direction, thus obtaining the ionospheric VTEC calculated based on the DORIS carrier phase data.

8. The system for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 6, characterized in that: It comprises a processor and a memory, the memory is used to store program instructions, and the processor is used to call the stored instructions in the memory to execute a method for extracting ionospheric VTEC based on DORIS carrier phase data as described in any one of claims 1 to 5.

9. The system for extracting ionospheric VTEC based on DORIS carrier phase data according to claim 6, characterized in that: It comprises a readable storage medium, on which a computer program is stored. When the computer program is executed, a method for extracting ionospheric VTEC based on DORIS carrier phase data as described in any one of claims 1 to 5 is implemented.

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