Method for reducing step of real-time ionized layer delay grid product

Abstract

The invention discloses a method for reducing product steps of a real-time ionospheric delay grid, and relates to the field of satellite positioning. The method specifically comprises the following steps: selecting reference stations in a set area and satellites corresponding to the reference stations; carrying out PPP ambiguity fixation on reference stations one by one, and extracting ionospheric delay one by one by satellites; according to the extraction result of the ionospheric delay, selecting a forecast ionospheric delay or a check ionospheric delay; ionosphere delay benchmarks of different reference stations under the same reference satellite are unified, and a modeling reference station set {Site} is constructed; carrier phase double differences are constructed for the short baseline reference station for checking, and gross error satellites are removed; updating a modeling reference station set {Site}, and incorporating satellites with more than five reference stations in common view into a modeling satellite set {Sat}; checking the station satellite pairs of which the current epoch participates in modeling by adopting the station satellite pairs of which the historical epoch participates in modeling, and eliminating gross error station satellite pairs; and performing polynomial fitting on satellites one by one, generating a grid residual error, and completing modeling. According to the invention, a high-precision ionized layer delay grid product can be stably generated.

Description

Technical Field

[0001] The invention relates to the field of satellite positioning, and in particular to a method for reducing the step of real-time ionospheric delay grid products. Background Art

[0002] Accurate atmospheric correction information is the key to achieving fast ambiguity fixation for PPP-RTK (Precise Point Positioning-Real-Time Kinematic). Whether users can stably provide high-precision ionospheric delay grid products is one of the key factors for PPP-RTK users to obtain real-time centimeter-level positioning.

[0003] Affected by natural factors such as extreme weather, solar activity, geomagnetic activity, and non-natural factors such as equipment failure, power supply failure, and network failure, the ionospheric delay extracted by the regional reference station through ambiguity fixation inevitably has jumps and discontinuities, which affects the accuracy of ionospheric delay grid modeling. In addition, due to the number and distribution of reference stations, it is difficult for the reference stations within the region to be evenly distributed. If the reference stations around the reference station with ionospheric delay extraction errors are sparse, due to the lack of constraints from other reference stations, the regional fitting surface determined by the polynomial will be abnormally distorted, resulting in steps in the generated ionospheric delay grid product. To address the problem of ionospheric delay product steps, the existing technical solutions are mainly to increase the number of regional reference stations and timely eliminate abnormal reference stations by real-time monitoring of the quality of reference station observations. This solution can reduce the steps of ionospheric delay products and improve product availability, but it also has the following shortcomings: First, this solution requires the construction of additional reference stations, which increases the cost of station construction and maintenance; second, this solution requires accurate identification and elimination of reference stations with abnormal observation quality, which increases development and operation costs. Summary of the invention

[0004] In view of this, the present invention provides a method for reducing the step of real-time ionospheric delay grid products, which can stably generate high-precision ionospheric delay grid products without adding monitoring reference stations, thereby reducing station construction and operation costs.

[0005] The invention provides a method for reducing the step of a real-time ionospheric delay grid product, comprising the following steps: selecting a reference station in a set area and a satellite corresponding to the reference station; fixing PPP ambiguity for each reference station, and extracting ionospheric delay for each satellite; selecting a predicted ionospheric delay or a verified ionospheric delay according to the extraction result of the ionospheric delay; unifying the ionospheric delay benchmarks of different reference stations under the same reference satellite, and constructing a modeling reference station set {Site}; constructing a carrier phase double difference for a short baseline reference station for verification, and removing gross error satellites; updating the modeling reference station set {Site}, and including satellites that are co-visible with more than 5 reference stations into a modeling satellite collection {Sat}; using a station-satellite pair participating in modeling in a historical epoch to verify a station-satellite pair participating in modeling in a current epoch, and removing gross error station-satellite pairs; performing polynomial fitting and grid residual generation for each satellite to complete modeling.

[0006] Furthermore, the time difference between the historical epoch and the current epoch is less than a set value. ; The method of selecting to predict the ionospheric delay or to check the ionospheric delay according to the extraction result of the ionospheric delay comprises: if the ionospheric delay extraction fails, using the ionospheric delay extracted from the historical epoch to predict; if the ionospheric delay extraction is successful, using the ionospheric delay extracted from the PPP floating point solution to check the ionospheric delay extracted from the PPP ambiguity, and eliminating gross error satellites.

[0007] Furthermore, the ionospheric delay extracted by the PPP floating point solution is checked to remove the gross error satellite, which includes: checking the difference between the ionospheric delay extracted by the PPP floating point solution and the ionospheric delay extracted by the PPP ambiguity, and removing the gross error satellite if the difference between the two exceeds a set threshold. Satellites with .sigma-delta errors are considered as gross error satellites and are removed.

[0008] Furthermore, the ionospheric delay benchmarks of different reference stations under the same reference satellite and constructing a modeling reference station set {Site} include: eliminating reference stations that fail to extract ionospheric delays or reference stations that cannot obtain historical epoch ionospheric delays; and unifying the ionospheric delays of different reference stations under the same reference satellite according to a set benchmark to form a modeling reference station set {Site}.

[0009] Furthermore, the short baseline reference station refers to a reference station whose distance is less than a set distance threshold. Two reference stations.

[0010] Furthermore, when the carrier phase double difference is constructed for the short baseline reference station for verification, the expression of the carrier phase double difference is as follows: (1) (1) In the formula, is the double difference operator, and the subscripts represent different frequencies; L represents the carrier phase observation value, ρ Represents the distance between the guard and the ground. T represents the tropospheric delay, I represents the ionospheric delay, N represents the carrier phase ambiguity, M represents the multipath error, ε represents the observation noise.

[0011] Furthermore, according to formula (1), formula (2) can be obtained, which is as follows: (2) According to formula (2), the double difference ambiguity can be obtained and double difference ambiguity ,Will , The difference exceeds the set threshold Satellites with .sigma-delta errors are considered as gross error satellites and are removed.

[0012] Furthermore, the station-satellite pair modeled using the historical epochs is checked against the station-satellite pair modeled in the current epoch, and the gross error station-satellite pair is eliminated, which includes: if the historical epoch has used the station-satellite pair for modeling, the ionospheric delay of the station-satellite pair in the current epoch is directly compared with the historical epoch, and if it is greater than the set threshold , then the station-satellite pair is directly eliminated; if the historical epoch has not used the station-satellite pair for modeling, it is directly used for modeling the ionospheric delay of the current epoch.

[0013] Furthermore, the expression of the polynomial fitting is: (3) (3) In the formula, I is the ionospheric delay, lat, lat 0 are the latitude and longitude of the modeling reference station, lon, lon 0 is the longitude and latitude of the center point of the region, C 00 、C 01 、C 10 、C 11 is the model coefficient.

[0014] Furthermore, the grid residual generation includes: according to the position of the reference station and the grid point, using the inverse distance weighted method to calculate to each grid point, to obtain the ionospheric residual value.

[0015] Compared with the existing technology, the present invention has the following beneficial technical effects: The present invention provides a method for reducing the step of real-time ionospheric delay grid products. The method makes full use of the characteristic that the ionospheric delay has a constant change trend in a short period of time. The ionospheric delay extracted from the previous epoch and the ionospheric delay change are used to predict the ionospheric delay of the current epoch, which can be used to verify the accuracy of the ionospheric delay extracted from the current epoch, suppress the interference of gross error values, and replace the missing ionospheric delay to ensure the continuity of ionospheric delay grid modeling. The method makes full use of the advantage of known coordinates of regional reference stations, introduces carrier phase double difference observation to verify gross error satellites, eliminates gross error station-satellite pairs, and avoids the step of ionospheric delay grid products. The method makes full use of the reference station-satellite pair information that has historically participated in ionospheric delay grid modeling, verifies the reference station-satellite pair of ionospheric delay grid modeling of the current epoch, and avoids the decrease in the availability of ionospheric delay grid products. The method is simple to implement, does not need to increase monitoring reference stations, has low station construction and operation and maintenance costs, and is suitable for commercial operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a method for reducing the step of real-time ionospheric delay grid products provided by the present invention. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0018] In the description of the present invention, it should be noted that the orientation or positional relationship indicated in the description is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred parts or elements must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0019] In order to provide better positioning services, a new generation of high-precision satellite positioning method PPP-RTK is proposed. PPP-RTK combines the advantages of Precise Point Positioning (PPP) and Network Real-time Kinematic (NRTK). Its idea is to use the ground regional reference station grid to obtain enhanced correction information such as satellite phase deviation, ionospheric delay, and tropospheric delay information. Users obtain enhanced correction information to achieve fast ambiguity fixation, thereby achieving instantaneous high-precision positioning. Among them, since ionospheric delay is easily affected by extreme weather such as typhoons and tsunamis, solar activity, and geomagnetic activity, and the ionosphere activity in different latitudes is different, how to obtain high-precision and high-stability ionospheric delay products in real time is the key to stably achieving high-precision real-time positioning of users.

[0020] Since the ionospheric delay changes rapidly in time and space, in order to save broadcast resources and facilitate user use, and considering the strong spatial and temporal correlation of ionospheric delay within a certain area, the ionospheric delay is grid-modeled according to regional division. In order to obtain regional ionospheric grid products, it is first necessary to fix the PPP ambiguity for each reference station and extract the ionospheric delay error. On this basis, the overall surface fitting is performed using a polynomial related to the longitude and latitude and the center point of the region. The user end can obtain the polynomial fitting value and the grid residual value based on the approximate position of the reference station, and then obtain the ionospheric delay correction product and use it as a priori constraint to achieve fast ambiguity fixation on the user end.

[0021] As the basis of regional ionospheric grid products, regional reference stations stably provide high-quality and high-precision GNSS observations, which is the key to maintaining the stable generation of high-precision ionospheric delay grid products. However, regional reference stations are not only susceptible to natural factors such as extreme weather, solar activity and geomagnetic activity, but also to non-natural factors such as receiver equipment failure, power supply failure, and network failure. Affected by this, the ionospheric delay extracted after the PPP ambiguity of some reference stations is fixed will jump and be discontinuous, causing great interference to the subsequent ionospheric delay grid modeling. Especially in areas where reference stations are sparsely distributed, if the ionospheric delay of a reference station is extracted incorrectly, due to the lack of constraints from other reference stations in the surrounding area, the fitting surface determined by the polynomial will be abnormally distorted and deformed. At the user level, the ionospheric delay product will have a step change and reduced availability.

[0022] See also Figure 1 In view of the above shortcomings, the present invention proposes a method for reducing the step of real-time ionospheric delay grid products, which can reduce the step of ionospheric delay products and improve product availability.

[0023] The present invention proposes a method for reducing the step of real-time ionospheric delay grid products, which specifically includes the following steps: S10, selecting a reference station in a preset area and a satellite corresponding to the reference station; Select a certain area where multiple reference stations are located. Each reference station corresponds to one or more satellites. Input the real-time data stream of the reference stations in the area, which is observed by the Beidou system or other systems.

[0024] S11, PPP ambiguity fixation is performed for each reference station, and ionospheric delay is extracted for each satellite; Taking a certain epoch (time) in a certain area as an example, precise orbit clock error, DCB (Differential Code Bias, GNSS differential code bias), UPD (Uncalibrated Phase Delay) products, etc. are used to fix the PPP ambiguity of each reference station, and extract the ionospheric delay for each satellite corresponding to each reference station.

[0025] S12, selecting to predict the ionospheric delay or to check the ionospheric delay according to the extraction result of the ionospheric delay; If the PPP ambiguity fixation of a reference station fails and the ionospheric delay cannot be extracted, or the observation data of the current epoch of the reference station is missing and the ionospheric delay cannot be extracted, the ionospheric delay extracted from the historical epoch and the ionospheric delay change are used for forecasting, and the time difference between the historical epoch and the current epoch is less than the set value . Since the ionospheric delay has the characteristic of unchanged changing trend in a short period of time, the ionospheric delay of the current epoch can be predicted through the ionospheric delay extracted from the previous epoch and the change in ionospheric delay. On the one hand, it can be used to verify the accuracy of the ionospheric delay extracted from the current epoch and suppress the interference of gross error values; on the other hand, when the reference station cannot extract the ionospheric delay due to factors such as failure to fix the PPP ambiguity and missing observations, the predicted value can be used as a substitute to ensure the continuity of the ionospheric delay grid modeling. In order to distinguish the actual extracted ionospheric delay from the predicted ionospheric delay, the two are recorded as I real , I predict . For the actual extracted ionospheric delay I real , that is, the ionospheric delay is successfully extracted I real , using the ionospheric delay extracted from the PPP float solution of the regional reference station I real_ppp The actual extracted ionospheric delay I real Check if the difference between the two exceeds the set threshold Satellites with errors are considered as gross error satellites and are removed to avoid step changes in grid products.

[0026] S13, unify the ionospheric delay benchmarks of different reference stations under the same reference satellite and construct a modeling reference station set {Site}; The reference stations that failed to extract ionospheric delay or could not obtain historical epoch ionospheric delay were eliminated, and then the ionospheric delays of different reference stations belonging to the same reference satellite among the remaining reference stations were unified according to the set benchmark to form the modeling reference station set {Site}.

[0027] S14, construct carrier phase double difference for short baseline reference station to check and remove gross error satellites; A short baseline reference station is a reference station whose distance to other reference stations is less than the set distance threshold. The reference station with a distance less than the set distance threshold is selected The carrier phase double difference is constructed from two reference stations. The expression of the carrier phase double difference is as follows: (1) (1) In the formula, is the double difference operator, and the subscripts represent different frequencies; L represents the carrier phase observation value, ρ Represents the distance between the guard and the ground. T represents the tropospheric delay, I represents the ionospheric delay, N represents the carrier phase ambiguity, M represents the multipath error, ε represents the observation noise.

[0028] Double-difference observation can eliminate the errors between the satellite and receiver ends and most of the atmospheric delay errors. The remaining main errors are satellite-to-earth distance, residual atmospheric error, multipath, and observation noise. Since the satellite-to-earth distance can be obtained using the known precise orbit and regional reference station coordinates, the tropospheric delay can be substituted into the estimate after the PPP ambiguity is fixed. Since the multipath and observation noise of the carrier phase observation value are small and negligible, the double-difference ionospheric delay of the short baseline reference station approaches zero. At this time, the carrier phase double difference only has double-difference ambiguity, which can be used to check the integer ambiguity of the reference station after the PPP ambiguity is fixed, eliminate the gross error satellite, and avoid the step in the grid product. Therefore, equation (1) can be expressed as equation (2): (2) According to formula (2), the double difference ambiguity can be obtained At the same time, the fixed inter-satellite single-difference ambiguities of the two reference stations are replaced by the inter-station single-difference ambiguities to obtain another set of double-difference ambiguities: ,Will , If the difference exceeds the set threshold Satellites with errors are considered as gross error satellites and are removed to avoid step changes in grid products.

[0029] S15, update the modeling reference station set {Site}, and include satellites that are co-visible with more than 5 reference stations into the modeling satellite collection {Sat}; After completing the verification of the carrier phase double difference constructed for the short baseline reference station, update the modeling reference station set {Site}, then add the satellites that are co-viewed (simultaneously observed) by more than 5 reference stations to the modeling satellite collection {Sat}, and record the corresponding reference station list.

[0030] S16, using the station-star pairs involved in modeling in historical epochs to check the station-star pairs involved in modeling in the current epoch, and eliminating the gross error station-star pairs; Each satellite in the region is included in the modeling satellite collection {Sat}. The reference station list of each satellite is traversed. If the historical epoch has used the station-satellite pair for modeling, the ionospheric delay of the station-satellite pair in the current epoch is directly compared with it. If it is greater than the set threshold, , then the station-satellite pair is directly removed; if the historical epoch has not used the station-satellite pair for modeling, it is directly used for ionospheric delay modeling in the current epoch, which can avoid the decrease in the availability of ionospheric delay grid products.

[0031] S17, perform polynomial fitting and grid residual generation for each satellite to complete the modeling.

[0032] For each satellite in the satellite collection {Sat}, the overall surface fitting is performed using a polynomial related to the reference station, longitude and latitude, and the regional center point. The ionospheric residual is calculated to each grid point using the inverse distance weighted method based on the position of the reference station and the grid point to complete the generation of the ionospheric delay grid product. The expression of the polynomial fitting is: (3) (3) In the formula, I is the ionospheric delay, lat, lat 0 are the latitude and longitude of the modeling reference station, lon, lon 0 is the longitude and latitude of the center point of the region, C 00 、C 01 、C 10 、C 11 is the model coefficient, and the modeling is completed according to the model coefficient. The user end can obtain the polynomial fitting value and the grid residual value according to the approximate position of the reference station, and then obtain the ionospheric delay correction product and use it as a priori constraint to achieve fast ambiguity fixation at the user end.

[0033] S18, outputs stable high-precision ionospheric delay grid products.

[0034] From the above description, it can be known that the method for reducing the step of the real-time ionospheric delay grid product provided by the present invention makes full use of the characteristic that the ionospheric delay has a constant change trend in a short period of time, and predicts the ionospheric delay of the current epoch through the ionospheric delay extracted from the previous epoch and the change in ionospheric delay, which can be used to verify the accuracy of the ionospheric delay extracted from the current epoch, suppress the interference of the gross error value, and replace the missing ionospheric delay to ensure the continuity of the ionospheric delay grid modeling; make full use of the advantage of the known coordinates of the regional reference station, introduce the carrier phase double difference observation to verify the gross error satellite, eliminate the gross error station-satellite pair, and avoid the step of the ionospheric delay grid product; make full use of the reference station-satellite pair information that has historically participated in the ionospheric delay grid modeling, verify the reference station-satellite pair of the current epoch ionospheric delay grid modeling, and avoid the decrease in the availability of the ionospheric delay grid product; the method is simple to implement, does not need to increase the monitoring reference station, has low station construction and operation and maintenance costs, and is suitable for commercial operation.

[0035] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for reducing the step of real-time ionospheric delay grid products, characterized in that: The following steps are involved: Select a reference station in a set area and a satellite corresponding to the reference station; PPP ambiguity fixation is performed for each reference station, and ionospheric delay is extracted for each satellite; According to the extraction result of ionospheric delay, choose to predict ionospheric delay or check ionospheric delay; Unify the ionospheric delay benchmarks of different reference stations under the same reference satellite and construct a modeling reference station set {Site}; Construct carrier phase double difference for short baseline reference station to check and remove gross error satellites; The modeling reference station set {Site} is updated, and satellites that are co-visible with more than five reference stations are included in the modeling satellite collection {Sat}; The station-satellite pairs involved in modeling in historical epochs are used to check the station-satellite pairs involved in modeling in the current epochs, and the gross error station-satellite pairs are eliminated; Polynomial fitting and grid residual generation are performed for each satellite to complete the modeling.

2. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The time difference between the historical epoch and the current epoch is less than the set value ; The step of selecting, according to the extraction result of the ionospheric delay, to predict the ionospheric delay or to check the ionospheric delay comprises: If the ionospheric delay extraction fails, the ionospheric delay extracted from the historical epoch is used for forecasting; If the ionospheric delay is extracted successfully, the ionospheric delay extracted by the PPP floating point solution is used to check the ionospheric delay extracted by the PPP ambiguity to eliminate the gross error satellite.

3. The method for reducing the step of real-time ionospheric delay grid product according to claim 2, characterized in that: The ionospheric delay extracted by the PPP floating point solution is checked to remove the gross error satellites, including: The difference between the ionospheric delay extracted by the PPP floating point solution and the ionospheric delay extracted by the PPP ambiguity is checked, and the difference between the two exceeds the set threshold. Satellites with .sigma-delta errors are considered as gross error satellites and are removed.

4. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The ionospheric delay benchmarks of different reference stations under the same reference satellite, and the modeling reference station set {Site} are constructed to include: Eliminate the reference stations that fail to extract ionospheric delay or cannot obtain the historical epoch ionospheric delay; The ionospheric delays of different reference stations under the same reference satellite are unified according to the set benchmark to form a modeling reference station set {Site}.

5. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The short baseline reference station refers to a station whose distance is less than the set distance threshold. Two reference stations.

6. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: When constructing the carrier phase double difference for the short baseline reference station for verification, the expression of the carrier phase double difference is as follows: （1） (1) In the formula, is the double difference operator, and the subscripts represent different frequencies; L represents the carrier phase observation value, ρ Represents the distance between the guard and the ground. T represents the tropospheric delay, I represents the ionospheric delay, N represents the carrier phase ambiguity, M represents the multipath error, ε represents the observation noise.

7. The method for reducing the step of the real-time ionospheric delay grid product according to claim 6, characterized in that: According to formula (1), formula (2) can be obtained, which is as follows: （2） According to formula (2), the double difference ambiguity can be obtained and double difference ambiguity ,Will , The difference exceeds the set threshold Satellites with .sigma-delta errors are considered as gross error satellites and are removed.

8. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The use of the station-satellite pairs involved in modeling in historical epochs to check the station-satellite pairs involved in modeling in the current epoch and eliminating the gross error station-satellite pairs includes: If the historical epoch has been modeled using the station-satellite pair, the ionospheric delay of the station-satellite pair in the current epoch is directly compared with it. If it is greater than the set threshold , then the station star pair is directly eliminated; If the station-satellite pair is not used for modeling in the historical epoch, it is directly used for modeling the ionospheric delay in the current epoch.

9. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The expression of the polynomial fitting is: （3） (3) In the formula, I is the ionospheric delay, lat, lat 0 are the latitude and longitude of the modeling reference station, lon, lon 0 is the longitude and latitude of the center point of the region, C 00 、C 01 、C 10 、C 11 is the model coefficient.

10. The method for reducing the step of real-time ionospheric delay grid product according to claim 1, characterized in that: The grid residual generation includes: according to the position of the reference station and the grid point, using the inverse distance weighted method to calculate each grid point to obtain the ionospheric residual value.

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