Ionospheric modeling method, device and medium based on ground-based and satellite-based augmentation fusion

Abstract

The application discloses an ionosphere modeling method and device based on ground-based enhancement and satellite-based enhancement fusion and a medium, and the method comprises the following steps: acquiring reference station coordinates, real-time observation data of the reference station, satellite precise ephemeris, precise clock error, DCB and UPD products; extracting ionosphere delay of a satellite observed by a single station; subtracting ionosphere delay of all satellites of the same station from ionosphere delay of a reference star, performing reference star conversion, and simultaneously performing reference star conversion on all baseline solutions in an NRTK modeling area; and constructing an ionosphere model based on ground-based enhancement and satellite-based enhancement fusion by using a polynomial error compensation algorithm.The application extracts high-precision ionosphere delay information for ionosphere modeling of NRTK by combining the advantage that PPP single-station operation is not limited by the distance of the reference station, thereby improving the precision of ionosphere modeling of NRTK, expanding the service range of NRTK, enabling high-precision positioning services to be acquired in a sparse reference station area, and further reducing the construction cost of wide-range NRTK.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite navigation technology, in particular to an ionospheric modeling method, device and medium based on ground and satellite-based augmentation fusion. BACKGROUND

[0002] Network RTK (NRTK) technology estimates the error model of an area through a network of multiple reference stations, and provides the user with correction data of a certain reference grid close to his position using the data of a virtual reference station. Using network data transmission, the distance limitation is broken, and the user terminal within the region can obtain real-time high-precision positioning results.

[0003] The Virtual Reference Station (VRS) technology is the most mature and widely used NRTK technology at present. The solving process of the VRS technology is as follows: the calculation center calculates the reference station network ambiguity fixing, baseline error calculation according to the known coordinates of each reference station, satellite ephemeris, real-time observation data, etc.; at the same time, the approximate coordinates of the user station are received, and a virtual reference station is generated at the coordinates, the tropospheric delay and ionospheric delay at the virtual reference station position are modeled using the precise known coordinates of the reference station and the real-time observation data of the reference station, thereby constructing the virtual observation values of the virtual reference station, and finally the virtual observation values or corrections are encoded into RTCM differential messages and sent to the user for RTK positioning.

[0004] The core technology of NRTK is to construct a triangular network through continuous operation of the reference station, and to independently operate each triangular network, that is, to solve three baseline double difference ambiguities, thereby obtaining the double difference ionospheric and tropospheric delay information of the baseline, and then constructing the atmospheric error model. When the user logs in, the corresponding triangular network is selected according to the approximate position, and then the ionospheric and tropospheric atmospheric corrections at that position are interpolated using the linear interpolation parameters of the atmospheric error of the triangular network, thereby constructing the virtual observation values, and then providing RTK service. The main defects are:

[0005] First, the distance between NRTK reference stations is often more than 50 km, and in some wide areas, the distance between base stations is even more than 200 km. In the ambiguity fixing, due to the long baseline, the ionospheric and tropospheric delay errors are not completely eliminated by the double difference operation, and the residual errors greatly interfere with the fixing of the double difference ambiguity, which needs a long time to fix, and even cannot be fixed, which will seriously affect the error correction accuracy of the virtual reference station and further affect the service accuracy of NRTK.

[0006] Secondly, when the sketchy location provided by the user is not in the triangulation network, the ionospheric atmosphere error correction number interpolated by the linear interpolation model will be biased, thereby reducing the accuracy of the virtual observation value and affecting the positioning accuracy of the user.

[0007] Thirdly, in the case of wide area, the ground-based enhancement system is constructed, and the conventional station construction scheme is used, which requires a large number of reference stations to be constructed, thereby greatly increasing the construction cost and maintenance cost.

[0008] Therefore, it is necessary to improve the existing ionospheric modeling method to improve the positioning accuracy and reduce the construction cost and maintenance cost. SUMMARY

[0009] In view of the above defects, the technical problem to be solved by the present application is to provide an ionospheric modeling method, device and medium based on the fusion of ground-based and satellite-based enhancement, to solve the problems of low positioning accuracy and high construction cost and maintenance cost in the prior art.

[0010] Therefore, the ionospheric modeling method based on the fusion of ground-based enhancement and satellite-based enhancement provided by the present application comprises the following steps:

[0011] Obtaining data, including reference station coordinates, reference station real-time observation data, satellite precise ephemeris, precise clock error, DCB product and UPD product;

[0012] Using the above data, the ionospheric delay of the single station observing satellite is obtained;

[0013] The ionospheric delay of all satellites at the same station is subtracted from the ionospheric delay of the reference star, and the reference star conversion is performed, and the reference star conversion is also performed on all baseline solutions in the NRTK modeling area;

[0014] Using the polynomial error compensation, the ionospheric model based on the fusion of ground-based enhancement and satellite-based enhancement is constructed as follows:

[0015] ,

[0016] In the formula: is the ionospheric delay of the observed satellite s of the station i on the inclined path, is the coefficient of the polynomial model, is the geographic latitude and longitude of the satellite s at the piercing point; φ0, λ0 is the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area; ΔSTEC s is the grid point ionospheric residual error compensation term.

[0017] In the above method, preferably, the specific steps of obtaining the ionospheric delay of the single station observing satellite are as follows:

[0018] According to the base station coordinates, the ambiguity float solution is calculated using the ionosphere-free PPP algorithm;

[0019] Using the UPD product, the ambiguity is fixed using the inter-satellite single-difference algorithm to obtain the inter-satellite single-difference ambiguity fixed solution ΔN1, ΔN2;

[0020] The ionosphere-free phase combination formula is converted into an inter-satellite single-difference form;

[0021] In the formula: f1 and f2 are carrier waves, is the inter-satellite single-difference ΔDCB s is the inter-satellite single-difference DCB s , DCB s is the satellite s-end hardware delay, λ1 and λ2 are the wavelengths of the corresponding frequency points f1 and f2, ΔN1 and ΔN2 are the inter-satellite single-difference ambiguity fixed solutions of the corresponding frequency points f1 and f2, and ε L1 , ε L2 is the observation noise of the phase observations of the corresponding frequency points f1 and f2.

[0022] The slant ionospheric delay of the corresponding satellite is calculated and obtained through the following formula:

[0023] In the formula: DCB s The correction is made through the DCB product, is the ionospheric delay float solution of the reference star.

[0024] In the above method, preferably, the ionospheric delay is extracted using the following ionosphere-free phase combination

[0025]

[0026] In the formula: L1 and L2 are the phase observations of the carrier waves f1 and f2, respectively,

[0027] is the ionospheric delay of the corresponding frequency point, DCB r is the receiver-end hardware delay, DCB s is the satellite s-end hardware delay, λ1 and λ2 are the wavelengths of the corresponding frequency points f1 and f2, N1 and N2 are the ambiguities of the corresponding frequency points f1 and f2, and ε L1 , ε L2 is the observation noise of the phase observations of the corresponding frequency points f1 and f2.

[0028] In the above method, preferably, the specific steps of converting the reference star are as follows:

[0029] The cut-off height angle is set to 40 degrees, a first group of common satellites used for baseline fixed solutions of the NRTK modeling area is selected, and a second group of common satellites used for extracting ionospheric delay of all reference stations is selected;

[0030] The intersection of the first group of common satellites and the second group of common satellites is obtained to obtain a third group of common satellites;

[0031] The satellite with the highest elevation angle is selected from the third group of common satellites as a reference star;

[0032] The ionospheric delay of all satellites of the same station is subtracted from the ionospheric delay of the reference star to complete the reference star conversion; meanwhile, the reference star conversion is performed on all baseline solutions in the NRTK modeling area.

[0033] In the above method, preferably, the specific steps of constructing the regional ionospheric model by using the polynomial error compensation are as follows:

[0034] The polynomial coefficients of the regional ionospheric model are estimated by using the ionospheric delay data of the single-station satellite through the least square parameter adjustment method;

[0035] The ionospheric delay of each satellite of each reference station is calculated according to the polynomial coefficients;

[0036] The ionospheric delay of each satellite of each reference station is subtracted from the ionospheric delay of the single-station observation satellite to obtain the ionospheric residual error of each satellite of each reference station;

[0037] The grid point coordinates of all VRSs in the NRTK modeling area are obtained, and the reference stations within a radius of 200 km are searched with each grid point as the center;

[0038] The ionospheric residual error compensation parameters of each grid point are obtained by using the ionospheric residual error and the corresponding reference station of each grid point through the inverse distance weighted algorithm;

[0039] The RMS values of the ionospheric residual errors of all grid points of each satellite are counted as the ionospheric modeling accuracy quality factors of each satellite in the modeling area;

[0040] The VRSs of each grid point are generated by using the polynomial coefficients of each satellite, the ionospheric delay of each satellite, the ionospheric residual error compensation parameters of each satellite of each grid point, and the ionospheric modeling accuracy quality factors of each satellite through the DCB product.

[0041] The application also provides an ionospheric modeling device based on the fusion of ground-based enhancement and satellite-based enhancement, characterized by comprising:

[0042] A data acquisition module is configured to acquire data, including reference station coordinates, reference station real-time observation data, satellite precise ephemeris, precise clock error, DCB product and UPD product.

[0043] a first calculation module configured to obtain ionospheric delay of the satellite observed by the single station by using the data;

[0044] a reference star conversion module configured to subtract the ionospheric delay of the reference star from the ionospheric delay of all the satellites of the same station, to complete the reference star conversion, and to perform the reference star conversion on all baseline solutions in the modeling area of the NRTK;

[0045] a modeling module configured to construct the ionospheric model based on the integration of ground-based enhancement and satellite-based enhancement by using a polynomial error compensation, as follows:

[0046] wherein: is the ionospheric delay of the satellite s observed by the station i on the slant path, is a coefficient of the polynomial model,

[0047] is the geographic latitude and longitude of the satellite s at the piercing point; φ0 and λ0 are the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area; ΔSTEC s is the grid point ionospheric residual error compensation term.

[0048] In the above device, preferably, the first calculation module comprises:

[0049] a ambiguity fixing unit configured to calculate ambiguity float solutions by using ionosphere-free PPP algorithm according to the coordinates of the reference station, and to obtain ambiguity fixed solutions ΔN1 and ΔN2 by using inter-satellite single-difference algorithm and UPD products.

[0050] an ionospheric delay extraction unit configured to extract ionospheric delay by using ionosphere-free phase combination

[0051]

[0052] a slant ionospheric delay calculation unit configured to convert the ionosphere-free phase combination formula into inter-satellite single-difference form.

[0053] wherein: f1 and f2 are carriers, is inter-satellite single-difference ΔDCB s is DCB s inter-satellite single-difference DCB s , DCB s is End hardware delay, λ1, λ2 are the wavelengths corresponding to the frequency points f1 and f2, ΔN1, ΔN2 are the inter-satellite single-difference ambiguity fixed solutions corresponding to the frequency points f1 and f2, ε L1 , ω L2 The observation noise of the phase observations corresponding to the frequency points f1 and f2 is calculated by the following formula: In the formula, the correction is made by the DCB product, The ionospheric delay floating solution of the reference satellite is calculated by the following formula:

[0054] In the above device, the reference satellite conversion module comprises:

[0055] The reference satellite acquisition unit is configured to set the cut-off elevation angle to 40 degrees, select a first group of common satellites used for baseline fixed solutions in the NRTK modeling area, and simultaneously select a second group of common satellites used for extracting ionospheric delays of all reference stations; the first and second groups of common satellites are intersected to obtain a third group of common satellites; the satellite with the highest elevation angle is selected from the third group of common satellites as the reference satellite;

[0056] The conversion unit is configured to subtract the ionospheric delay of all satellites at the same station from the ionospheric delay of the reference satellite to complete the reference satellite conversion; and perform reference satellite conversion on all baseline solutions in the NRTK modeling area.

[0057] In the above device, the modeling module comprises:

[0058] The ionospheric delay and residual calculation unit is configured to estimate the polynomial coefficients of the regional ionospheric model by using the ionospheric delay data of the single-satellite and by using the least squares parameter adjustment method; the ionospheric delay of each satellite at each reference station is calculated according to the polynomial coefficients; the ionospheric delay residual of each satellite at each reference station is obtained by subtracting the ionospheric delay of each satellite at each reference station from the ionospheric delay of the single-observed satellite;

[0059] The reference station searching unit is configured to acquire the grid point coordinates of all VRSs in the NRTK modeling area, and search for the reference stations within a radius of 200 km with each grid point as the center;

[0060] The compensation calculation unit is configured to use the ionospheric delay residual and the corresponding reference station of each grid point to obtain the ionospheric delay residual compensation parameters of each grid point by using the inverse distance weighted algorithm; the RMS value of the ionospheric delay residual of each satellite at all grid points is calculated as the ionospheric modeling accuracy quality factor of each satellite in the modeling area;

[0061] The VRS generation unit is configured to generate the VRS of each grid point by using the polynomial coefficients of each satellite, the ionospheric delay residual compensation parameters of each satellite at each grid point, and the ionospheric modeling accuracy quality factor of each satellite.

[0062] The application further provides a computer readable medium, which stores a computer program, and the computer program implements the ionospheric modeling method based on fusion of ground-based enhancement and satellite-based enhancement when executed by a processor.

[0063] According to the technical solution, the ionospheric modeling method, device and medium based on fusion of ground-based enhancement and satellite-based enhancement solve the problems of low ionospheric modeling precision, high construction cost and high maintenance cost of the prior art NRTK when outside the network or the baseline distance is long. The ionospheric error correction precision of the VRS is improved, high-quality differential data is provided for users, and the problem of poor terminal positioning effect caused by low-quality VRS differential data in a wide range is solved. Compared with the prior art, the application has the following beneficial effects:

[0064] First, the existing extraction of the ionospheric delay information of the CORS base station is to obtain a fixed ambiguity solution through baseline solution, and then calculate the double-difference ionospheric and tropospheric delay information of the baseline. The ionospheric delay information of a single base station is estimated by the ionosphere-free combined PPP and phase geometry-free combined technology, without forming a baseline and without being restricted by the distance of the base station.

[0065] Second, the existing ionospheric model uses the double-difference ionospheric delay parameters of the baseline in the triangular network to interpolate the ionospheric correction parameters at the VRS through a linear interpolation model. The model has limitations, and the interpolation precision is low when outside the triangular network. The single-station ionospheric delay parameters are used to construct a regional ionospheric model through a polynomial error compensation model, the ionospheric delay information at the virtual observation station is interpolated according to the position information of the virtual observation station, and then the double-difference ionospheric delay correction number is formed with the ionospheric delay information of the main reference station. When the virtual reference station is within a certain range outside the network, the ionospheric delay correction number with high precision can still be provided for the VRS. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the following will briefly introduce and describe the drawings needed in the description of the embodiments of the application or the prior art. Obviously, the drawings in the following description are only some embodiments of the application, and those skilled in the art can obtain other drawings according to these drawings without creating any creative labor.

[0067] Figure 1 A flowchart of the ionospheric modeling method based on fusion of ground-based enhancement and satellite-based enhancement is provided. DETAILED DESCRIPTION

[0068] The technical solutions and implementation manners of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the following described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0069] In order to make the technical solutions and implementation manners of the present application clearer and more understandable, several preferred specific embodiments for implementing the technical solutions of the present application are introduced below.

[0070] It should be noted that the orientation words such as "inner", "outer", "front", "rear", "left" and "right" in the present application are described based on the product use state as the reference object, and obviously, the use of the corresponding orientation words does not constitute a limitation on the protection scope of the present application.

[0071] Please refer to Figure 1 , Figure 1 A flow chart of an ionospheric modeling method based on the fusion of ground-based enhancement and satellite-based enhancement is provided in the present application.

[0072] As shown in Figure 1 , the ionospheric modeling method based on the fusion of ground-based enhancement and satellite-based enhancement provided in the present application comprises the following steps:

[0073] Step 110: acquiring fixed reference station coordinates, reference station real-time observation data, satellite precise ephemeris, precise clock error, DCB (Differential Code Bias) product and UPD (Uncalibrated Phase Delays) product.

[0074] Step 120: using the fixed reference station coordinates, reference station real-time observation data, satellite precise ephemeris, precise clock error, UPD product and UPD product to extract ionosphere observed by a single station. Specifically, the following steps are included:

[0075] Step 121: calculating ambiguity float solution using ionosphere-free PPP algorithm according to the reference station coordinates;

[0076] Step 122: using inter-satellite single-difference algorithm to fix ambiguity according to the UPD product to obtain inter-satellite single-difference ambiguity fixed solution ΔN1, ΔN2;

[0077] Step 123: using ionosphere-free phase combination to extract ionosphere delay The ionosphere-free phase combination formula is as follows:

[0078] In the formula, the following applies: Phase observations of carrier f1 and f2 respectively,

[0079] Ionospheric delay of corresponding frequency point, DCB r Hardware delay of receiver end, DCB s Hardware delay of satellite s, λ1 and λ2 are the wavelengths of corresponding frequency points f1 and f2, N1 and N2 are the ambiguities of corresponding frequency points, and ε L1 , ε L2 Observation noise of phase observations of corresponding frequency points f1 and f2.

[0080] GF (Geometry Free), r represents the reference station; s is the satellite observed by the reference station r; 1 and 2 are frequency points f1 and f2 of satellite s respectively.

[0081] Step 124, since the ambiguity is fixed based on the inter-satellite single difference, the reference star with fixed ambiguity is taken as the reference to convert the geometry-free phase combination formula into the following inter-satellite single difference form:

[0082] ΔL GF = (γ2-1) ΔI1+ ΔDCB s + λ1 ΔN1 Δ- λ2 ΔN2 + Δε L1 - Δε L2 ;

[0083] In the formula, f1 and f2 are carriers, Inter-satellite single difference ΔDCB s Inter-satellite single difference DCB s , DCB s Hardware delay of satellite s, λ1 and λ2 are the wavelengths of corresponding frequency points f1 and f2, ΔN1 and ΔN2 are the inter-satellite single difference ambiguity fixed solutions of corresponding frequency points f1 and f2, and ε L1 , ε L2 Observation noise of phase observations of corresponding frequency points f1 and f2.

[0084] Step 125, take the ionospheric float solution of the reference star as the reference to calculate the slant ionospheric delay of the corresponding satellite by the following formula:

[0085] In the formula: DCB s Corrected by the DCB product.

[0086] Step 130, convert the reference star. Since the reference star when extracting the ionospheric delay is inconsistent with the reference star of the NRTK baseline solution, it is necessary to convert the reference star. The specific steps are as follows:

[0087] Step 131, set the cut-off elevation angle to 40 degrees, select the first group of common satellites for baseline fixed solution in NRTK modeling area, and select the second group of common satellites for extracting ionospheric delay of all reference stations;

[0088] Step 132, take the intersection of the first and second groups of common satellites to obtain the third group of common satellites;

[0089] Step 133, select the satellite with the highest elevation angle from the third group of common satellites as the reference star;

[0090] Step 134, subtract the ionospheric delay of all satellites at the same station from the ionospheric delay of the reference star to complete the reference star conversion; at the same time, perform reference star conversion on all baseline solutions in the NRTK modeling area.

[0091] Step 140, construct the ionospheric model based on ground-based enhancement and satellite-based enhancement fusion using polynomial error compensation as follows.

[0092]

[0093] In the formula, is the ionospheric delay of the observed satellite s in the inclined path of station i, with unit TECU; is the coefficient of the polynomial; is the true latitude and longitude of satellite s at the piercing point, φ0 and λ0 are the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area; ΔSTEC s is the grid point ionospheric residual error compensation term. The specific steps are as follows:

[0094] Step 141, first assume that the model ionospheric residual compensation ΔSTEC s is 0, and use the ionospheric delay data of the satellite obtained in step 120 to estimate the polynomial coefficients in the ionospheric model based on ground-based enhancement and satellite-based enhancement fusion by least squares parameter adjustment method.

[0095] Step 142, calculate the ionospheric delay STEC0 of each satellite at each reference station according to the polynomial coefficients;

[0096] Step 143, subtract the ionospheric delay STEC0 of each satellite at each reference station from the extracted ionospheric delay to obtain the ionospheric residual of each satellite at each reference station;

[0097] Step 144, obtain the grid point coordinates of all VRSs in the NRTK modeling area, and search for reference stations within a radius of 200 km with each grid point as the center;

[0098] Step 145, using ionospheric residual and each grid point corresponding to the reference station, using the inverse distance weighted algorithm to interpolate the ionospheric residual compensation parameter of each grid point;

[0099] Step 146, statistics of all grid points of each satellite ionospheric residual RMS value as the modeling area of each satellite in the internal compliance accuracy quality factor;

[0100] Step 147, the polynomial coefficients of each satellite The ionospheric delay STEC0 of each satellite, the ionospheric residual compensation parameter of each grid point of each satellite, and the ionospheric modeling accuracy quality factor of each satellite are sent to the DCB product to generate the VRS of each grid point.

[0101] Based on the above method, the application also provides an ionospheric modeling device based on the fusion of ground-based enhancement and satellite-based enhancement, comprising:

[0102] The data acquisition module is used for acquiring data, including reference station coordinates, reference station real-time observation data, satellite precise ephemeris, precise clock error, DCB product and UPD product;

[0103] The first calculation module is used for obtaining the ionospheric delay of the satellite observed by the single station by using the above data;

[0104] The reference star conversion module is used for subtracting the ionospheric delay of all satellites of the same station from the ionospheric delay of the reference star to complete the reference star conversion, and simultaneously performing the reference star conversion on all baseline solutions in the NRTK modeling area;

[0105] The modeling module is used for constructing the ionospheric model based on the fusion of ground-based enhancement and satellite-based enhancement by using the polynomial error compensation as follows:

[0106] In the formula: The ionospheric delay of the observed satellite s of the station i on the inclined path is The coefficient of the polynomial is The geographic latitude and longitude of the satellite s at the piercing point are φ0 and λ0; the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area are φ0 and λ0; and the STEC0 is the ionospheric delay of the satellite s at the piercing point. s The grid point ionospheric residual error compensation term is.

[0107] The ionospheric modeling method based on the fusion of ground-based enhancement and satellite-based enhancement in the application can be realized as a computer software program. For example, the application also provides a computer readable medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned ionospheric modeling method based on the fusion of ground-based enhancement and satellite-based enhancement.

[0108] In summary of the above specific embodiments, the ionospheric modeling method, device and medium based on ground and satellite enhancement fusion provided by the present application have the following advantages compared with the prior art:

[0109] First, the present application uses PPP single base station operation, and high-precision ionospheric delay information can be obtained after ambiguity is fixed, which improves the ionospheric delay information extraction precision under the condition of medium-long baseline and is not limited by the distance of base stations.

[0110] Second, the ionospheric interpolation model constructed by the present application is an atmospheric model covering the entire CORS network range, which expands the NRTK service range and can maintain service accuracy when the virtual reference station is within a certain range outside the network.

[0111] Third, the present application can achieve the same service as the traditional NRTK using fewer base stations, thereby reducing the construction cost of NRTK in a wide range.

[0112] Finally, it should be noted that the terms "include", "contain" or any other variants used in this text are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "includes one" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0113] The present application is not limited to the above best mode, and anyone should know that structural changes made under the inspiration of the present application fall within the protection scope of the present application, and any technical solutions with the same or similar technical solutions as the present application fall within the protection scope of the present application.

Claims

1. A method for ionospheric modeling based on the fusion of ground-based augmentation and satellite-based augmentation, characterized in that, The method comprises the following steps: obtaining reference station coordinates, real-time observation data of the reference station, satellite precise ephemeris, precise clock error, DCB product and UPD product; extracting ionospheric delay of a satellite observed by a single station by using the reference station coordinates, real-time observation data of the reference station, satellite precise ephemeris, precise clock error, DCB product and UPD product; subtracting ionospheric delay of all satellites at the same station from ionospheric delay of a reference star to perform reference star conversion, and performing reference star conversion on all baseline solutions in the NRTK modeling area; constructing the ionospheric model based on the fusion of ground-based enhancement and satellite-based enhancement by using polynomial error compensation as follows: ， wherein: is the ionospheric delay of the observing satellite s on the slant path at the station i, is the coefficient of the polynomial, is the geographic latitude and longitude of the satellite s at the piercing point; φ0, λ0are the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area; ΔSTEC s is the grid point ionospheric residual error compensation term; The specific steps of the conversion reference star are as follows: setting the cut-off elevation angle to 40 degrees, selecting a first group of common satellites used for baseline fixed solutions in the NRTK modeling area, and simultaneously selecting a second group of common satellites of all reference stations when extracting ionospheric delay; taking the intersection of the first and second groups of common satellites to obtain a third group of common satellites; selecting the satellite with the highest elevation angle from the third group of common satellites as the reference star; subtracting ionospheric delay of all satellites at the same station from ionospheric delay of the reference star to complete the reference star conversion; and performing reference star conversion on all baseline solutions in the NRTK modeling area.

2. The method of claim 1, wherein, The specific steps of obtaining the ionospheric delay of a satellite observed by a single station are as follows: calculating ambiguity float solution by using ionosphere-free PPP algorithm according to the reference station coordinates; obtaining inter-satellite single-difference fixed ambiguity ΔN1 and ΔN2 by using inter-satellite single-difference algorithm with the UPD product; The geometry-free phase combination formula is converted into an inter-satellite single-difference form; In the formula, f1 and f2 are carrier frequencies, is an inter-satellite single-difference ΔDCB s is an inter-satellite single-difference DCB s , DCB s is a satellite s end hardware delay, λ1 and λ2 are wavelengths corresponding to the frequency points f1 and f2, ΔN1 and ΔN2 are inter-satellite single-difference ambiguity fixed solutions corresponding to the frequency points f1 and f2, and ε L1 , ε L2 is observation noise of phase observations corresponding to the frequency points f1 and f2; The slant ionospheric delay for the corresponding satellite is calculated by the following equation where: DCB s Corrected by DCB product, Float solution of ionospheric delay for reference stars.

3. The method of claim 1, wherein, Extracting ionospheric delay using the following geometry-free phase combination wherein: are phase observations of carrier f1 and f2 respectively, is ionospheric delay of frequency f1, DCB r is receiver end hardware delay, DCB s is satellite s end hardware delay, λ1, λ2 are wavelengths of corresponding frequencies f1 and f2, N1, N2 are ambiguities of corresponding frequencies f1 and f2, ε L1 , ε L2 are observation noises of phase observations of corresponding frequencies f1 and f2.

4. The method of claim 1, wherein, The specific steps of constructing the regional ionospheric model by using polynomial error compensation are as follows: estimating the polynomial coefficients of the regional ionospheric model by using least square parameter adjustment method with the ionospheric delay data of the single station satellite; calculating the ionospheric delay of each satellite at each reference station according to the polynomial coefficients; subtracting the ionospheric delay of each satellite at each reference station from the ionospheric delay of each satellite observed by a single station to obtain the ionospheric residual error of each satellite at each reference station; obtaining the grid point coordinates of all VRSs in the NRTK modeling area, and searching for the reference stations within a radius of 200 km with each grid point as the center; Using ionospheric residual and the corresponding reference station of each grid, the inverse distance weighted algorithm is used to interpolate the grid point ionospheric residual error compensation term ΔSTEC of each grid point s ; statistically obtaining the RMS value of all grid point ionospheric residual errors of each satellite as the ionospheric modeling accuracy quality factor of each satellite in the modeling area; generating the VRS of each grid point by using the polynomial coefficients of each satellite, the ionospheric residual error compensation parameters of each satellite at each grid point, and the ionospheric modeling accuracy quality factor of each satellite.

5. An ionospheric modeling device based on the fusion of ground-based augmentation and satellite-based augmentation, characterized in that, It comprises: a data acquisition module configured to obtain reference station coordinates, real-time observation data of the reference station, satellite precise ephemeris, precise clock error, DCB product and UPD product; a first calculation module configured to obtain ionospheric delay of a satellite observed by a single station by using the above data; a reference star conversion module configured to subtract ionospheric delay of all satellites at the same station from ionospheric delay of a reference star to complete the reference star conversion, and perform reference star conversion on all baseline solutions in the NRTK modeling area; a modeling module configured to construct the ionospheric model based on the fusion of ground-based enhancement and satellite-based enhancement by using polynomial error compensation as follows: wherein: is the ionospheric delay of the observation satellite s on the slant path at the observation station i, is the coefficient of the polynomial, is the geographic latitude and longitude of the satellite s at the piercing point; φ0, λ0are the geographic latitude and longitude of the center point of the NRTK ionospheric modeling area; ΔSTEC s is the grid point ionospheric residual error compensation term; The reference star conversion module comprises: a reference star acquisition unit configured to set a cut-off height angle to 40 degrees, select a first group of common satellites used for baseline fixed solutions of all NRTK modeling areas, and simultaneously select a second group of common satellites used for extracting ionospheric delay of all reference stations; obtain a third group of common satellites by taking the intersection of the first and second groups of common satellites; and select a satellite with the highest height angle from the third group of common satellites as a reference star; a conversion unit configured to subtract the ionospheric delay of all satellites of a same station from the ionospheric delay of the reference star to complete reference star conversion; and simultaneously perform reference star conversion on all baseline solutions in the NRTK modeling area.

6. The apparatus of claim 5, wherein, The first calculation module comprises: a fuzzy degree fixing unit configured to calculate fuzzy degree floating point solutions by using ionosphere-free PPP algorithm according to reference station coordinates; and fix fuzzy degrees by using inter-satellite single-difference algorithm to obtain inter-satellite single-difference fuzzy degree fixed solutions ΔN1 and ΔN2 by using UPD products. Ionospheric delay extraction unit, used to extract ionospheric delay using geometrically non-geometric phase combination. The tilted ionospheric delay calculation unit is used to convert the geometrically undefined phase combination formula into an inter-satellite single difference form based on a reference star with fixed ambiguity. In the formula: f1 and f2 are carrier waves. Inter-satellite single difference ΔDCB s Inter-satellite single difference DCB s DCB s For satellite S-end hardware delay, λ1 and λ2 are the wavelengths of corresponding frequency points f1 and f2, ΔN1 and ΔN2 are the fixed solutions of inter-satellite single-difference ambiguities for corresponding frequency points f1 and f2, and ε L1 ε L2 The observation noise corresponds to the phase observations at frequencies f1 and f2; the ionospheric delay floating-point solution of the reference star is used. Based on this, the tilted ionospheric delay of the corresponding satellite is calculated using the following formula; Where: DCB s Corrections were made using DCB products.

7. The apparatus of claim 6, wherein, The modeling module comprises: an ionospheric delay and residual calculation unit configured to estimate polynomial coefficients of a regional ionospheric model by using least square parameter adjustment method based on ionospheric delay data of single station satellites; calculate ionospheric delay of each satellite of each reference station based on the polynomial coefficients; and subtract the ionospheric delay of each satellite of each reference station from the ionospheric delay of the observed satellite of the single station to obtain ionospheric residual of each satellite of each reference station; a reference station searching unit configured to obtain grid point coordinates of all VRSs in the NRTK modeling area, and search for reference stations within a radius of 200 km with each grid point as a center; a compensation calculation unit configured to use inverse distance weighted algorithm to interpolate ionospheric residual compensation parameters of each grid point by using the ionospheric residual and the corresponding reference station of each grid point; and statistically calculate RMS values of ionospheric residuals of all grid points of each satellite as ionospheric modeling accuracy quality factors of each satellite in the modeling area; a VRS generation unit configured to generate VRSs of each grid point by using the polynomial coefficients of each satellite, the ionospheric residual compensation parameters of each satellite of each grid point, and the ionospheric modeling accuracy quality factors of each satellite.

8. A computer readable medium having stored thereon a computer program, characterized in that The computer program, when executed by a processor, implements the ionospheric modeling method based on fusion of ground-based enhancement and satellite-based enhancement according to any one of claims 1 to 4.

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