Single-Beidou multi-stage base station combined GNSS monitoring method and system

Abstract

The invention provides a high-precision single-Beidou multi-stage base station combined GNSS monitoring method and system suitable for a sheltered environment, a multi-stage base station is built on site, a communication technology is utilized, a lower-stage base station continuously receives information of an upper-stage base station, the lower-stage base station continuously updates the position of the lower-stage base station and broadcasts the information to a server / observation station, the observation station solves the relative position of the lower-stage base station, and the communication technology is utilized. And the absolute coordinate position is calculated and reported to the server for further processing. Therefore, the system can continuously and dynamically respond when the position of any lower-level base station or even the positions of multiple lower-level base stations change, the displacement amount of the observation station is corrected in real time, and it is ensured that the displacement monitoring result of the observation station is always accurate and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite positioning, and in particular to a single Beidou multi-level base station combined GNSS monitoring method and system. Background Art

[0002] For current GNSS surface displacement monitoring, due to its simple setup, low cost, stable performance, and 24-hour automatic operation, currently the method of one point with one base station is generally adopted. At each monitoring project point, a single base station is used to drive multiple measurement stations, and a measurement baseline is constructed for each measurement station. This method is simple and flexible to set up and has high efficiency. However, for the situation where the base station moves together with the measurement stations, it cannot be effectively processed.

[0003] In many cases, it is difficult to find a rock foundation for the base station foundation, and only the method of pouring cement piles can be used for simple reinforcement. Such simple cement piles may slide together with the soft foundation.

[0004] For measurement stations, in most cases, the on-site observation environment cannot fully meet the monitoring standards, such as the requirement for the minimum satellite observation elevation angle. There are also situations of base station occlusion on-site, such as the presence of mature trees or forests around, or slope occlusion.

[0005] The existing measurement method of constructing a measurement baseline for each measurement station also has difficulty in supporting the setup of multiple temporary on-site base stations and the temporary change of the base station site location. Because this will change the original measurement baseline, if a control network is introduced, it will introduce additional workload and bring a large amount of workload to subsequent data processing, making it difficult to compare and reference the data before and after and assist in decision-making. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a single Beidou multi-level base station combined GNSS monitoring method and system with high precision applicable to occlusion environments.

[0007] To achieve the above purpose, the present invention provides a single Beidou multi-level base station combined GNSS monitoring method, including the following steps: S1. Set up multiple base stations B1, B2 and on-site measurement stations R1, connect the on-site base stations B1, B2 to the Cors station C1, and the base stations form a cascaded combination relationship; S2. The R1 receives the RTCM information of B1, B2, calculates its own absolute coordinates cord11, and calculates its relative coordinates enu11, enu12 relative to B1, B2; B1, B2 receive the RTCM information of C1, and B1, B2 calculate their own precise positions in real time and correct the coordinates cord01, cord02 of B1, B2 themselves as base stations. S3. Base stations B1 and B2 broadcast RTCM information using coordinates cord01 and cord02. S4. R1 reports the absolute coordinate cord11, relative coordinates enu11 and enu12 to the server, and B1 and B2 report cord01 and cord02 to the server. S5. R1 reports the original observations to the server, and B1 and B2 report the original observations to the server. S6. The server processes the measurement results. In S1, the relationship between each level of on-site base stations is a parallel networking relationship, and the relationship between the upper-level and lower-level base stations is a master-slave networking relationship, forming multi-level base stations; the roles of the base stations and the measurement stations can be interchanged without affecting the observation results; in S6, multiple on-site base stations, measurement stations, and CORS stations report their respective single Beidou information to the server; the server performs simple screening and merging based on the signal-to-noise ratio of the base station information. For the observation information such as RTCM1124 broadcast by the upper-level base stations, the server selects the missing satellite frequency information of the on-site base stations and merges it into the above message to obtain a complete local single Beidou message; then it broadcasts the message to each measurement station for edge calculation. It is characterized in that: the server synthesizes the information of multiple on-site base stations, virtualizes a base station, and pushes the virtual base station to the measurement station. The virtualization steps are as follows: Report the original observations of each constellation of the on-site base stations to the server. The server simultaneously receives the original observations broadcast by the upper-level base stations. For the on-site base stations, the server performs screening and merging according to the signal-to-noise ratio information. For the original observations broadcast by the upper-level base stations, the server selects the missing satellite frequency information of the on-site base stations and merges it into the above message. Unify the coordinate system to a certain virtual reference station on-site. The server performs calculations, or broadcasts this message to the measurement station receiver for edge calculation.

[0008] Further, the base station supports soft foundation slopes and sliding surfaces, allowing the base station to slide during the entire measurement life cycle.

[0009] Further, when there are obstructions in the measurement field, any number of base stations can be set up in different directions of the obstruction to improve accuracy.

[0010] Further, all levels of the multi-level base stations adopt single Beidou configurations, and RTCM1124 format messages are used for communication between base stations at all levels, covering multi-band information transmitted by Beidou satellites operating in MEO, GEO, IGSO, and LEO orbits. When the number of satellites or frequency bands exceeds the message capacity limit, multiple RTCM1124 messages are used for information transmission.

[0011] Further, in S6, multiple base stations, survey stations, and CORS stations at the measurement site report their respective single Beidou information to the server. The server performs simple screening and merging based on the signal-to-noise ratio of the base station information. For the original observables such as RTCM1124 broadcast by the upper-level base stations and CORS stations, the server selects the missing satellite frequency information of the on-site base stations and merges it into the above message to obtain a complete local single Beidou message, and then broadcasts it to each survey station for edge calculation.

[0012] The beneficial effects of the present invention are as follows: Multiple levels of base stations are built on-site using communication technology. The lower-level base stations continuously receive the information of the upper-level Cors base stations, so that the lower-level base stations can continuously update their own positions and continuously broadcast their own positions to the survey stations. The survey stations calculate their relative positions and calculate their absolute coordinate positions, and report them to the server for further processing. In this way, when the position of any one base station changes, or even the positions of multiple base stations change, the system can continuously and dynamically respond, and the displacement of the survey stations can be corrected in real time to ensure that the monitoring results of the survey station displacements are always accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For ease of explanation, the present invention is described in detail by the following preferred embodiments and accompanying drawings.

[0014] Figure 1 is a flowchart of a single Beidou multi-level base station combined GNSS monitoring method and system according to the present invention; Figure 2 is a c measurement flowchart of a single Beidou multi-level base station combined GNSS monitoring method and system according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The following further describes a single Beidou multi-level base station combined GNSS monitoring method and system according to the present invention with reference to the accompanying drawings: Embodiment 1 Figure 1 For the system construction process: Build base stations B1 and B2 at the measurement site; Build a survey station R1 at the measurement site; Assume that the upper-level base station C1 already exists and is a Cors site, then connect B1 and B2 to C1 to receive the differential correction information broadcast by C1; Continuously measure Figure 2 As shown, the measurement process is as follows: Base stations B1 and B2 receive the differential correction information of C1, such as the RTCM1124 format message, which contains the following information: Pseudorange P(s,r), where s and r represent the satellite and base station receiver numbers respectively; Phase L(s,r); Signal-to-noise ratio SNR(s,r); Its undifferenced observation equation can be expressed as

[0016] where: ρ represents the geometric distance between the base station and the satellite; I(r) represents the ionospheric delay of the satellite; T(r) represents the tropospheric delay; dt(r) and dt(s) represent the clock biases of the satellite and the base station receiver respectively; λ represents the carrier wavelength; N(s,r) represents the carrier phase integer ambiguity parameter; d(s), d(r), b(s), and b(r) represent the pseudorange and carrier phase hardware delays of the satellite and the receiving end respectively; dm(s,r) is the multipath error of the pseudorange; δm(s,r) is the multipath error of the carrier phase; e(s,r) and ε(s,r) are the observation noises of the pseudorange and the carrier phase; c is the speed of light.

[0017] Based on the above information, base stations B1 and B2 calculate their own real-time accurate positions, including latitude, longitude, and altitude; When there is a nearby base station broadcasting its ECEF coordinates (x0, y0, z0) and the pseudoranges (P01, P02, P03, P04) and carrier phase values (L01, L02, L03, L04) of the 4 received satellites, use this data to correct the coordinates of the base station receiver. The following are the steps to correct the coordinates of the base station receiver: Calculate the geometric range between each satellite and the base station: R01 = c * (P01 - d01) (where c is the speed of light and d01 is the clock bias from the base station to satellite 1); R02 = c * (P02 - d02); R03 = c * (P03 - d03); R04 = c * (P04 - d04); Convert the geometric range to the pseudorange observation: P01' = R01 + d01; P02' = R02 + d02; P03' = R03 + d03; P04' = R04 + d04; Calculate the difference between the carrier phase observations: ΔL01 = L01 - λ1 * N01 (where λ1 is the L1 wavelength and N01 is the integer ambiguity); ΔL02 = L02 - λ2 * N02; ΔL03 = L03 - λ3 * N03; ΔL04 = L04 - λ4 * N04; Calculate the ECEF coordinates (X, Y, Z) of the corrected receiver: Construct matrix A and vector b: A = [2 * (X1 - x0), 2 * (Y1 - y0), 2 * (Z1 - z0)] [2 * (X2 - x0), 2 * (Y2 - y0), 2 * (Z2 - z0)] [2 * (X3 - x0), 2 * (Y3 - y0), 2 * (Z3 - z0)] [2 * (X4 - x0), 2 * (Y4 - y0), 2 * (Z4 - z0)] b = [c * (P01' - P01) - ΔL01] [c * (P02' - P02) - ΔL02] [c * (P03' - P03) - ΔL03] [c * (P04' - P04) - ΔL04]. Solve the linear equation system Ax = b, where x = [X, Y, Z] are the ECEF coordinates of the corrected receiver; convert the ECEF coordinates to latitude, longitude and altitude coordinates [lat, lon, alt].

[0018] According to the observations over a period of time, base stations B1 and B2 correct their coordinates as base stations, cord01[lat01, lon01, alt01], cord02[lat02, lon02, alt02].

[0019] Set the observation duration to 100 epochs. During this process, B1 calculates 100 coordinate points cord01 - 00 to cord01 - 99 of itself cumulatively, and B2 calculates 100 coordinate points cord02 - 00 to cord02 - 99 of itself cumulatively; when the error distribution conforms to the Gaussian distribution, the standard deviation of a single measurement is 5 cm, which is also the standard service level provided by the current Cors station.

[0020] Measured 100 times as above, the errors conform to the normal distribution, Calculate the error of a single measurement: SE_single = σ = 5 cm; SE_avg100 = σ / sqrt(n) = 5 cm / sqrt(100) = 0.5 cm; Compared with single measurement, the error is reduced by: (5 cm - 0.5 cm) / 5 cm = 90%; Compared with single measurement, 100 measurements can reduce the error by 90%. In this way, the base station coordinates of base stations B1 and B2 can be corrected to 5 mm to meet the monitoring requirements.

[0021] If 10,000 epochs are used and combined with filtering methods such as IGG3, the coordinates of B1 and B2 can be corrected to a smaller error range, such as 0.5 mm.

[0022] In the subsequent differential information broadcast, base stations B1 and B2 adjust the broadcast content, such as RTCM1005, according to the corrected coordinates cord01 and cord02. The base station reports cord01 and cord02 to the server through the communication network. In Embodiment 2, the original base station observations can also be reported to the server. The measuring station R1 receives the differential correction information broadcast by base stations B1 and B2 as described above. The measuring station R1 calculates its own absolute position coordinates cord11 and cord12 according to the base station information. The measuring station R1 calculates its coordinates enu11 in the northeast celestial direction relative to B1 and enu12 in the northeast celestial direction relative to B2 according to the base station information. The original observations of the measuring station can be reported to the server. Usually, more than 4 stars will be observed. At this time, adjustment processing is performed at each step. In this embodiment, the least squares method is used to fit the best observed values. R1 reports the measurement results to the server, and the server performs coordinate fusion positioning by integrating the base station and measuring station information. The server further performs post-processing according to the satellite original observation information reported by the base station and the measuring station. The server can integrate the information of multiple on-site base stations, virtualize a base station, and push the virtual base station to the measuring station. The virtual method is as follows: Report the original observations of each constellation of the on-site base stations to the server. The server simultaneously receives the original observations broadcast by the superior base station CORS station. For the on-site base stations, the server performs simple screening and merging according to the signal-to-noise ratio. For the original observations broadcast by the superior base station CORS station, the server selects the star frequency information missing from the on-site base stations and merges it into the above message. Unify the coordinate system to a certain virtual reference point on site; The server performs calculations or broadcasts this message to the receiver at the measuring station for edge calculations.

[0023] Due to the introduction and real-time update of the absolute coordinates of the base station, making full use of the existing CORS stations, setting up two-level or even multi-level base stations, and introducing any number of parallel base stations within each level of base station can improve the accuracy and reliability of the measurement results; subtracting the absolute coordinates of the virtual base station from the absolute coordinates of the measuring station can conveniently obtain the relative displacement of the measuring station without caring about the changes in the real position and quantity of the base stations.

[0024] Example 3 Establishment of a virtual base station Based on Example 2, further optimized, the server can comprehensively process the original observations of multiple base stations (such as B1, B2, B3) and CORS stations on site as follows; Each base station reports the original observations (such as pseudorange, carrier phase, signal-to-noise ratio, etc.) to the server; The server receives the observation data of all base stations and CORS stations, screens and combines the observations according to parameters such as the signal-to-noise ratio, and completes the missing satellite frequency information of the on-site base stations; The server unifies the coordinate systems of each base station to a certain virtual reference point on site, fuses the observation messages of local base stations and CORS stations, and generates virtual base station messages; The server pushes the virtual base station observation message to each measuring station, and the measuring station combines its own observations for edge calculations to obtain high-precision coordinates and realize real-time monitoring of the displacement.

[0025] The present invention supports the dynamic access and large-scale fusion of multiple base stations, innovatively introduces a screening mechanism based on the signal-to-noise ratio, and realizes the intelligent completion of the satellite frequency information observed by the base stations, ensuring the integrity of the data and the high reliability of the virtual base station messages. Compared with the traditional virtual base station technology, the present invention breaks through the limitations of the number and layout method of base stations, not only improves the integrity of the virtual base station, but also realizes high-precision edge calculations at the measuring station end, significantly expanding the applicable scope and engineering application value of the system. Overall, this solution realizes higher-precision, higher-reliability and stronger adaptability GNSS monitoring, which is an important improvement and breakthrough for the existing virtual base station technology.

[0026] After summarizing in Examples 1, 2, and 3, the server fills multiple Beidou satellites (such as 22 satellites) in multiple frequency bands (such as B1I, B1C, B2a, B3I) into multiple RTCM1124 messages according to different frequency band combinations such as L1+L2, L1+L5, and the server distributes the RTCM1124 messages to each measuring station. Similarly, the Beidou base station can also directly send multiple RTCM1124 messages to the measuring station.

[0027] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A single Beidou multi-level base station combined GNSS monitoring method, characterized in that: It includes the following steps: S1. Set up multiple on-site base stations B1, B2 and on-site measurement stations R1, connect the on-site base stations B1, B2 to the Cors station C1, and form a cascaded combination relationship between the base stations; S2. The R1 receives the RTCM information of B1 and B2, calculates its own absolute coordinates cord11, and calculates the relative coordinates enu11 and enu12 of R1 relative to B1 and B2; B1 and B2 receive the RTCM information of C1, and B1 and B2 calculate their own precise positions in real time and correct the coordinates cord01 and cord02 of B1 and B2 themselves as base stations; S3. The base stations B1 and B2 broadcast RTCM information using the coordinates cord01 and cord02; S4. R1 reports the absolute coordinates cord11 and relative coordinates enu11, enu12 to the server; B1 and B2 report cord01 and cord02 to the server; S5. R1 reports the original observations to the server, and B1 and B2 report the original observations to the server; S6. The server processes the measurement results; In S1, there is a parallel networking relationship between each level of on-site base stations, where C1 is the upper-level base station, and B1 and B2 are the lower-level base stations. There is a master-slave networking relationship between the upper-level and lower-level base stations, forming a multi-level base station; The roles of the on-site base station and the measurement station can be interchanged without affecting the measurement results and without the need to correct historical data; in S6, multiple on-site base stations, measurement stations, and CORS stations measure and report their respective single Beidou information to the server; The server performs simple screening and merging according to the signal-to-noise ratio of the base station information. For the observation information such as RTCM1124 broadcast by the upper-level base station, the server selects the missing satellite frequency information of the on-site base station and merges it into the above message to obtain a complete local single Beidou message; Then it broadcasts it to each measurement station for edge calculation; the server synthesizes the information of multiple on-site base stations, virtualizes a base station, and pushes the virtual base station to the measurement station. The virtual steps are as follows: Report the original observations of each constellation of the on-site base station to the server; The server simultaneously receives the original observations broadcast by the upper-level base station; For the on-site base station, the server performs screening and merging according to the signal-to-noise ratio information; For the original observations broadcast by the upper-level base station, the server selects the missing satellite frequency information of the on-site base station and merges it into the above message; Unify the coordinate system to a certain virtual reference site on-site; The server calculates or broadcasts this message to the measurement station receiver for edge calculation.

2. The single Beidou multi-level base station combined GNSS monitoring method according to claim 1, wherein: The base station supports soft foundation slopes and sliding surfaces, and allows the base station to slide throughout the measurement life cycle.

3. A single Beidou multi-level base station combined GNSS monitoring method according to claim 1, characterized in that: When there are obstructions in the measurement site, set up multiple base stations in different directions of the obstruction and network them to improve accuracy, and this networking method does not affect the previous observation data and there is no need to adjust the observation data.

4. The single Beidou multi-level base station combined GNSS monitoring method according to claim 3, characterized in that: All levels of the multi-level base station adopt a single Beidou configuration, and the base stations at all levels communicate using RTCM1124 format messages, covering the multi-band information transmitted by Beidou satellites operating on MEO, GEO, IGSO, and LEO orbits. When the number of satellites or frequency bands exceeds the message capacity limit, multiple RTCM1124 messages are used for information transmission.

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