GNSS-based offshore single-epoch ionosphere VTEC inversion method

Abstract

The invention relates to the field of ionosphere VTEC inversion, and discloses a GNSS-based offshore single-epoch ionosphere VTEC inversion method, which comprises the following steps: decoding a data stream of Beidou PPP-B2b or Galileo HAS, obtaining a state space correction number, and extracting a differential code deviation correction number; extracting total delay of the ionized layer by using a carrier phase smoothing pseudo-range method or a non-difference and non-combination PPP (Point-to-Point Protocol); the total delay of the ionosphere is corrected by using the satellite differential code deviation correction number; constructing a single-epoch ionosphere VTEC model by using a quadric surface model, the coordinates of the puncture point under the daily fixed geomagnetism, a projection function and the corrected total delay of the ionosphere; estimating parameters in the model in real time by using a least square algorithm; and according to the observation station position coordinates and the calculated parameters, the ionized layer VTEC of the observation station position is calculated in real time. According to the method disclosed by the invention, the resolving efficiency of the ionized layer VTEC can be improved, and single-station single-epoch ionized layer VTEC real-time inversion is realized.

Description

Technical Field

[0001] The present invention relates to the field of ionospheric VTEC inversion, and in particular to a GNSS-based marine single-epoch ionospheric VTEC inversion method. Background Art

[0002] The inversion of the vertical total electron content (VTEC) of the marine ionosphere is one of the most important space environment parameters in the study of radio wave propagation. It has important research significance and application value in many important fields such as marine radio wave communications, space-based radar imaging, satellite-borne radar systems, and spacecraft communication, navigation, and positioning.

[0003] At present, ground-based ionospheric VTEC inversion mainly focuses on the construction of global and regional ionospheric models. Numerical extrapolation is used to fill in blank areas where stations cannot be built at sea, resulting in the accuracy of ionospheric VTEC in blank areas of ocean stations being much lower than that in land areas. In terms of real-time performance, numerical forecasting and other methods are often used. On the sea surface, especially in the deep sea, there are problems such as high communication costs and limited power supply. It is impossible to deploy GNSS receivers and high-power computers over a large area, which seriously limits the computational efficiency and model selection of real-time ionospheric VTEC inversion. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a GNSS-based marine single-epoch ionospheric VTEC inversion method to improve the solution efficiency of ionospheric VTEC and achieve the purpose of single-station single-epoch ionospheric VTEC real-time inversion.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A GNSS-based marine single-epoch ionospheric VTEC inversion method comprises the following steps: Step 1, using a GNSS receiver to receive observation data, navigation ephemeris data and a data stream of Beidou PPP-B2b or Galileo HAS in real time; the observation data includes GNSS pseudorange and carrier phase observation values; Step 2, decode the data stream of Beidou PPP-B2b or Galileo HAS, obtain the state space correction number, extract the differential code deviation correction number of each satellite in the state space correction number, and calculate the GNSS satellite position coordinates according to the navigation ephemeris data; Step 3, respectively, the GNSS pseudorange and carrier phase observation values ​​in the observation data are combined without geometric distance, and the total ionospheric delay is extracted by using the carrier phase smoothed pseudorange method, or the total ionospheric delay is extracted by using the non-difference non-combined PPP; then the total ionospheric delay is corrected by using the satellite differential code bias correction number; Step 4, calculate the satellite altitude angle and azimuth according to the GNSS satellite position coordinates and the station position, then calculate the geographic coordinates and projection function of the ionospheric puncture point, and then calculate the day-solid geomagnetic coordinates of the puncture point according to the longitude and latitude of the geomagnetic north and south poles and the corresponding world coordinated time in the observation data; Step 5, construct a single-epoch ionospheric VTEC model using the quadratic surface model, the coordinates of the puncture point under the sun-solid geomagnetic field, the projection function, and the corrected total ionospheric delay; and estimate the parameters in the single-epoch ionospheric VTEC model in real time using the least squares algorithm; Step 6, based on the station location coordinates and the calculated parameters in the VTEC model, the ionospheric VTEC at the station location is calculated in real time.

[0006] In the above scheme, in step 2, the method for extracting the differential code bias correction number of each satellite in the state space correction number is as follows: ; In the formula, s is the GNSS system number, q is the satellite number, and They are the pseudorange OSB corrections for frequency 1 and frequency 2 published by Beidou PPP-B2b or Galileo HAS respectively. The pseudorange OSB corrections are part of the state space corrections.

[0007] In the above scheme, in step 3, the total ionospheric delay extracted by the carrier phase smoothing pseudorange method is corrected by the satellite differential code bias correction number as follows: ; The total ionospheric delay extracted by non-difference non-combined PPP is corrected by the satellite differential code bias correction as follows: ; In the formula, is the corrected total ionospheric delay, r is the receiver identification, c is the speed of light, is the total electron content of the ionospheric slant path, is the differential code deviation correction number at the receiver end, and are the frequencies of satellite observations L1 and L2 respectively and , is the ionospheric proportionality factor.

[0008] In the above scheme, in step 4, the ionospheric puncture point is the intersection of the line connecting the satellite and the measuring station and the thin layer of the ionosphere, and the daily geomagnetic coordinates of the puncture point are calculated using spherical trigonometry formulas.

[0009] In the above scheme, in step 5, the quadratic surface model is used to construct the single-epoch ionospheric VTEC model: ; In the formula, , , is the fitting coefficient of the VTEC model, is the solar geomagnetic latitude of the puncture point, is the solar-solid geomagnetic longitude of the puncture point; For a single GNSS system with a single satellite, the quadratic surface model, puncture point coordinates, and projection function are used. , construct a single-epoch ionospheric VTEC model, in which the projection function adopts a single-layer projection function; The ionospheric VTEC model constructed using the carrier phase smoothing pseudorange method is: ; The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: .

[0010] In the above scheme, in step 5, for multiple GNSS systems with multiple satellites, if the receiver observes m GNSS systems, each with a satellite count of , then the ionospheric VTEC model constructed using the carrier smoothing pseudorange method is: ; In the formula, For the m The GNSS system number is k m The total ionospheric delay corresponding to the satellite after being corrected by the satellite differential code bias correction number, where , where , and Respectively m The GNSS system number is k m The mapping function value corresponding to the satellite, the daily geomagnetic latitude and longitude of the puncture point, , , is the fitting coefficient of the VTEC model to be estimated, To be estimated m The receiver-side differential code deviation corresponding to each GNSS system; The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: ; In the formula, For the m The GNSS system number is k m The mapping function value corresponding to the satellite, ,in, and Respectively m The GNSS system number is k m The satellite corresponding to and Frequency value; Select one of the ionospheric VTEC models constructed using the carrier smoothing pseudorange method or the ionospheric VTEC model constructed using the non-difference non-combined PPP method, and use the least squares algorithm to calculate its least squares solution: .

[0011] In the above scheme, in step 6, the ionospheric VTEC fitting coefficients in the least squares solution are extracted , , , the latitude and longitude of the receiver position are obtained according to the precise single point positioning calculation, and then the sun-solid geomagnetic coordinates of the receiver position are calculated using the spherical trigonometry formula. The ionospheric VTEC value at the receiver position is calculated using the calculated VTEC fitting coefficient: ; In the formula, and are the solar-solid geomagnetic latitude and longitude at the receiver location, respectively.

[0012] Through the above technical solution, the GNSS-based marine single-epoch ionospheric VTEC inversion method provided by the present invention has the following beneficial effects: 1. The present invention receives observation data and navigation ephemeris data in real time through a GNSS receiver and combines the Beidou PPP-B2b or Galileo HAS data stream, and uses the non-difference non-combined PPP method or the carrier phase smoothed pseudorange method to extract the total ionospheric delay, providing high-precision basic data support for subsequent processing.

[0013] 2. The present invention uses satellite differential code deviation correction numbers to correct the total ionospheric delay, and at the same time uses spherical trigonometry formulas to calculate the solar-solid geomagnetic coordinates of the puncture point based on the satellite orbit coordinates and the station position, providing a spatial reference for constructing the ionospheric VTEC mathematical model.

[0014] 3. The present invention adopts a quadratic surface model to construct a single-epoch ionospheric VTEC mathematical model, combines the puncture point coordinates and projection function to construct a single-epoch ionospheric VTEC solution model, and adopts a least squares algorithm to solve the ionospheric VTEC fitting coefficient, providing a reliable numerical solution for subsequent VTEC.

[0015] 4. The present invention obtains the latitude and longitude at the receiver location based on precise single-point positioning calculations, then uses spherical trigonometry formulas to calculate the solar-solid geomagnetic coordinates at the receiver location, and uses the calculated VTEC fitting coefficient to calculate the ionospheric VTEC value at the receiver location, thereby significantly improving the availability and practicality of ionospheric inversion for end users.

[0016] In summary, the GNSS-based marine single-epoch ionospheric VTEC inversion method provided by the present invention can realize the ionospheric VTEC inversion without network dependence, forming an autonomous ionospheric inversion system that does not require external enhancement services, providing a reliable technical solution for areas without ground-based enhancement coverage such as oceans and polar regions, and the equipment installation and maintenance costs are low, which can provide support for the research on marine ionospheric VTEC inversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0018] Figure 1 A schematic flow chart of a method for inverting marine single-epoch ionospheric VTEC based on GNSS disclosed in an embodiment of the present invention; Figure 2 A comparison diagram of VTEC obtained by the non-difference non-combined model and the carrier phase smoothed pseudorange model disclosed in the embodiment of the present invention and VTEC interpolated from the final ionospheric global grid model (GIM) of the IGS ionospheric analysis center CODE; Figure 3 This is a deviation comparison diagram of VTEC obtained by interpolation of the final ionospheric global grid model (GIM) using the non-difference non-combined PPP method and the carrier phase smoothed pseudorange method disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0020] The present invention provides a GNSS-based marine single-epoch ionospheric VTEC inversion method, such as Figure 1 As shown, the following steps are included: Step 1, using a GNSS receiver to receive observation data, navigation ephemeris data and a data stream of Beidou PPP-B2b or Galileo HAS in real time; the observation data includes GNSS pseudorange and carrier phase observation values; Step 2, decode the data stream of Beidou PPP-B2b or Galileo HAS, obtain the state space correction number, extract the differential code deviation correction number of each satellite in the state space correction number, and calculate the GNSS satellite position coordinates according to the navigation ephemeris data; The method for extracting the differential code bias correction number of each satellite in the state space correction number is as follows: ; In the formula, s is the GNSS system number, q is the satellite number, and They are the pseudorange OSB corrections for frequency 1 and frequency 2 published by Beidou PPP-B2b or Galileo HAS respectively. The pseudorange OSB corrections are part of the state space corrections.

[0021] Step 3, respectively, the GNSS pseudorange and carrier phase observation values ​​in the observation data are combined without geometric distance, and the total ionospheric delay is extracted by using the carrier phase smoothed pseudorange method, or the total ionospheric delay is extracted by using the non-difference non-combined PPP; then the total ionospheric delay is corrected by using the satellite differential code bias correction number; The total ionospheric delay extracted by the carrier phase smoothed pseudorange method is corrected by the satellite differential code bias correction as follows: ; The total ionospheric delay extracted by non-difference non-combined PPP is corrected by the satellite differential code bias correction as follows: ; In the formula, is the corrected total ionospheric delay, r is the receiver identification, c is the speed of light, is the total electron content of the ionospheric slant path, is the differential code deviation correction number at the receiver end, and are the frequencies of satellite observations L1 and L2 respectively and , is the ionospheric proportionality factor.

[0022] Step 4, calculate the satellite altitude angle and azimuth according to the GNSS satellite position coordinates and the station position, then calculate the geographic coordinates and projection function of the ionospheric puncture point, and then calculate the day-solid geomagnetic coordinates of the puncture point according to the longitude and latitude of the geomagnetic north and south poles and the corresponding world coordinated time in the observation data; The ionospheric piercing point is the intersection of the line connecting the satellite and the measuring station with the thin layer of the ionosphere. The daily geomagnetic coordinates of the piercing point are calculated using spherical trigonometry formulas.

[0023] Step 5, construct a single-epoch ionospheric VTEC model using the quadratic surface model, the coordinates of the puncture point under the sun-solid geomagnetic field, the projection function, and the corrected total ionospheric delay; and estimate the parameters in the single-epoch ionospheric VTEC model in real time using the least squares algorithm; The quadratic surface model is used to construct the single-epoch ionospheric VTEC model: ; In the formula, , , is the fitting coefficient of the VTEC model, is the solar geomagnetic latitude of the puncture point, is the solar-solid geomagnetic longitude of the puncture point; For a single GNSS system with a single satellite, the quadratic surface model, puncture point coordinates, and projection function are used. , construct a single-epoch ionospheric VTEC model, in which the projection function adopts a single-layer projection function; The ionospheric VTEC model constructed using the carrier phase smoothing pseudorange method is: ; The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: .

[0024] For multiple GNSS systems with multiple satellites, if the receiver observes m GNSS systems, each with a satellite count of , then the ionospheric VTEC model constructed using the carrier smoothing pseudorange method is: ; In the formula, For the m The GNSS system number is k m The total ionospheric delay corresponding to the satellite after being corrected by the satellite differential code bias correction number, where , where , and Respectively m The GNSS system number is k m The mapping function value corresponding to the satellite, the daily geomagnetic latitude and longitude of the puncture point, , , is the fitting coefficient of the VTEC model to be estimated, To be estimated m The receiver-side differential code deviation corresponding to each GNSS system; The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: ; In the formula, For the m The GNSS system number is k m The mapping function value corresponding to the satellite, ,in, and Respectively m The GNSS system number is k m The satellite corresponding to and Frequency value; Select one of the ionospheric VTEC models constructed using the carrier smoothing pseudorange method or the ionospheric VTEC model constructed using the non-difference non-combined PPP method, and use the least squares algorithm to calculate its least squares solution: .

[0025] Step 6, based on the station location coordinates and the calculated parameters in the VTEC model, the ionospheric VTEC at the station location is calculated in real time.

[0026] Extracting ionospheric VTEC fitting coefficients from the least squares solution , , , the latitude and longitude of the receiver position are obtained according to the precise single point positioning calculation, and then the sun-solid geomagnetic coordinates of the receiver position are calculated using the spherical trigonometry formula. The ionospheric VTEC value at the receiver position is calculated using the calculated VTEC fitting coefficient: ; In the formula, and are the solar-solid geomagnetic latitude and longitude at the receiver location, respectively.

[0027] An experimental system was built at a near-shore offshore test station, and a 12-day VTEC real-time detection test was carried out using two models, namely the undifferenced uncombined precision point positioning (UUPPP) method and the carrier phase smoothing pseudorange (CPSP) method, to verify the effectiveness of this method.

[0028] The data sampling frequency is 5HZ, and the cut-off satellite elevation angle is 15°. The ionospheric VTEC real-time inversion equipment includes GNSS antenna, Novatel OEM729 core board and Advantech MIO-2263 embedded industrial computer. In order to reduce the impact of the electromagnetic environment on the GNSS signal, the GNSS antenna uses a customized anti-interference measurement GNSS antenna with a choke, and the data processing module uses the Beidou short message system installed on the experimental station. The experimental station is close to the port, and the signals of the radar and communication equipment of the passing ships affect the reception of GNSS signals to a certain extent. The experimental environment is close to the real marine observation platform environment.

[0029] The final ionospheric global grid model (GIM) of the IGS Ionospheric Analysis Center CODE was selected as the benchmark and compared with the VTEC inverted by this method. The results are as follows: Figure 2 , Figure 3 As shown in the figure, the horizontal axis is the annual accumulation of days, that is, January 1st of each year is the first day of the year, and the right side is accumulated to 365; the unit of the vertical axis TECU (Total Electron Content Unit) is a unit used to measure the total electron content in the atmosphere, used to describe the change of electron density in the ionosphere, 1 TECU=10 16 Number of electrons / m 2 .

[0030] Figure 2 GIM VTEC, UUPPP VTEC, and CPSP VTEC represent the VTEC obtained by interpolation of the ionospheric global grid model, the VTEC obtained by the non-difference non-combined PPP method, and the VTEC obtained by the carrier phase smoothed pseudorange method, respectively. Figure 2 It can be seen that the VTEC and GIM obtained by the non-difference non-combined PPP method and the carrier phase smoothed pseudorange method have good consistency, and the correlations of the two methods are calculated to be 0.74 and 0.61 respectively. The experimental results show that a method for real-time ionospheric VTEC inversion of a single-station single-epoch marine GNSS is effective.

[0031] Figure 3The accuracy of the non-difference non-combined PPP method and the carrier phase smoothed pseudorange method is further compared and analyzed, where GIM-UUPPP and GIM-CPSP represent the difference between the ionospheric global grid model and the non-difference non-combined PPP method and the carrier phase smoothed pseudorange method VTEC, respectively. The experimental results show that both methods in the inversion method of the present invention are effective, and the non-difference non-combined PPP method is slightly better than the carrier phase smoothed pseudorange method.

[0032] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A GNSS-based single-epoch ionospheric VTEC inversion method at sea, comprising the following steps: Step 1: Use a GNSS receiver to receive observation data, navigation ephemeris data, and Beidou PPP-B2b or Galileo HAS data streams in real time; The observation data includes GNSS pseudorange and carrier phase observation values; Step 2, decode the data stream of Beidou PPP-B2b or Galileo HAS, obtain the state space correction number, extract the differential code deviation correction number of each satellite in the state space correction number, and calculate the GNSS satellite position coordinates according to the navigation ephemeris data; Step 3, respectively, combine the GNSS pseudorange and carrier phase observation values ​​in the observation data without geometry distance, and extract the total ionospheric delay using the carrier phase smoothed pseudorange method, or use the non-difference non-combined PPP to extract the total ionospheric delay; Then the total ionospheric delay is corrected using the satellite differential code bias correction; Step 4, calculate the satellite altitude angle and azimuth according to the GNSS satellite position coordinates and the station position, then calculate the geographic coordinates and projection function of the ionospheric puncture point, and then calculate the day-solid geomagnetic coordinates of the puncture point according to the longitude and latitude of the geomagnetic north and south poles and the corresponding world coordinated time in the observation data; Step 5, construct a single-epoch ionospheric VTEC model using the quadratic surface model, the coordinates of the puncture point under the sun-solid geomagnetic field, the projection function, and the corrected total ionospheric delay; and estimate the parameters in the single-epoch ionospheric VTEC model in real time using the least squares algorithm; Step 6, based on the station location coordinates and the calculated parameters in the VTEC model, the ionospheric VTEC at the station location is calculated in real time.

2. The method for inversion of single-epoch ionospheric VTEC at sea based on GNSS according to claim 1, characterized in that: In step 2, the method for extracting the differential code bias correction number of each satellite in the state space correction number is as follows: ； In the formula, s is the GNSS system number, q is the satellite number, and They are the pseudorange OSB corrections for frequency 1 and frequency 2 published by Beidou PPP-B2b or Galileo HAS respectively. The pseudorange OSB corrections are part of the state space corrections.

3. The method for inversion of single-epoch ionospheric VTEC at sea based on GNSS according to claim 1, characterized in that: In step 3, the total ionospheric delay extracted by the carrier phase smoothing pseudorange method is corrected by the satellite differential code bias correction number as follows: ； The total ionospheric delay extracted by non-difference non-combined PPP is corrected by the satellite differential code bias correction as follows: ； In the formula, is the corrected total ionospheric delay, r is the receiver identification, c is the speed of light, is the total electron content of the ionospheric slant path, is the differential code deviation correction number at the receiver end, and are the frequencies of satellite observations L1 and L2 respectively and , is the ionospheric proportionality factor.

4. The method for inversion of single-epoch ionospheric VTEC at sea based on GNSS according to claim 1, characterized in that: In step 4, the ionospheric puncture point is the intersection of the line connecting the satellite and the measuring station and the thin layer of the ionosphere, and the daily geomagnetic coordinates of the puncture point are calculated using spherical trigonometry formulas.

5. The method for inversion of single-epoch ionospheric VTEC at sea based on GNSS according to claim 3, characterized in that: In step 5, the quadratic surface model is used to construct the single-epoch ionospheric VTEC model: ； In the formula, , , is the fitting coefficient of the VTEC model, is the solar geomagnetic latitude of the puncture point, is the solar-solid geomagnetic longitude of the puncture point; For a single GNSS system with a single satellite, the quadratic surface model, puncture point coordinates, and projection function are used. , construct a single-epoch ionospheric VTEC model, in which the projection function adopts a single-layer projection function; The ionospheric VTEC model constructed using the carrier phase smoothing pseudorange method is: ； The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: 。 6. The method for inversion of single-epoch ionospheric VTEC at sea based on GNSS according to claim 5, characterized in that: In step 5, for multiple GNSS systems with multiple satellites, if the receiver observes m GNSS systems, each with a satellite count of , then the ionospheric VTEC model constructed using the carrier smoothing pseudorange method is: ； In the formula, For the m The GNSS system number is k m The total ionospheric delay corresponding to the satellite after being corrected by the satellite differential code bias correction number, where , where , and Respectively m The GNSS system number is k m The mapping function value corresponding to the satellite, the daily geomagnetic latitude and longitude of the puncture point, , , is the fitting coefficient of the VTEC model to be estimated, To be estimated m The receiver-side differential code deviation corresponding to each GNSS system; The ionospheric VTEC model constructed using the non-difference non-combination PPP method is: ； In the formula, For the m The GNSS system number is k m The mapping function value corresponding to the satellite, ,in, and Respectively m The GNSS system number is k m The satellite corresponding to and Frequency value; Select one of the ionospheric VTEC models constructed using the carrier smoothing pseudorange method or the ionospheric VTEC model constructed using the non-difference non-combined PPP method, and use the least squares algorithm to calculate its least squares solution: 。 7. The method for inversion of marine single-epoch ionospheric VTEC based on GNSS according to claim 1, characterized in that: In step 6, extract the ionospheric VTEC fitting coefficients from the least squares solution , , , the latitude and longitude of the receiver position are obtained according to the precise single point positioning calculation, and then the sun-solid geomagnetic coordinates of the receiver position are calculated using the spherical trigonometry formula. The ionospheric VTEC value at the receiver position is calculated using the calculated VTEC fitting coefficient: ； In the formula, and are the solar-solid geomagnetic latitude and longitude at the receiver location, respectively.

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