Method for multi-frequency multi-mode GNSS transoceanic height transfer and global height datum unification

Abstract

This invention belongs to the field of geodesy and geophysical exploration technology, and discloses a method for transoceanic elevation transfer and global elevation datum unification using multi-frequency, multi-mode GNSS. The method includes: Step 1, deploying multi-frequency, multi-mode GNSS receivers at multiple local leveling / gravity measurement points and simultaneously conducting GNSS static observations; Step 2, acquiring satellite precision clock track products; Step 3, calculating the gravitational potential at the satellite's location; Step 4, using a model for determining gravitational potential and altitude based on single-station non-differential multi-frequency, multi-mode GNSS signals to calculate the altitude of ground measurement points; Step 5, iteratively executing steps 1-4 to obtain the altitude of each transoceanic observation point; Step 6, obtaining the elevation difference between two different transoceanic measurement points through difference calculation; Step 7, determining the elevation datum difference between the two different transoceanic locations based on the least squares method, thus achieving the unification of transoceanic elevation datums. This invention overcomes the long-standing problem of transoceanic and transsea elevation transfer and achieves the unification of global elevation datums.

Description

Technical Field

[0001] This invention belongs to the field of geodesy and geophysical exploration technology, specifically involving a method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification. Background Technology

[0002] The Global Elevation Datum is a reference system based on the Earth's gravity field, uniformly defining elevations around the world. It is of great significance in fields such as geographic information mapping, environmental monitoring, disaster early warning, and resource development. It also serves as a core support for Earth science research, infrastructure construction, and national defense. Achieving global uniformity in elevation datums not only eliminates discrepancies in elevation data across different regions but also provides a unified standard for global elevation measurement and data sharing, which is of great value to national economic development and scientific research.

[0003] However, traditional methods for establishing elevation datums have many limitations. Leveling, as the primary method, requires point-by-point measurement, which is time-consuming, labor-intensive, inefficient, and unable to cover large areas. Furthermore, the construction and maintenance of leveling and gravity networks are costly, especially in complex terrain or remote areas where data acquisition is even more difficult. In addition, different countries and regions have long used their own elevation datums, leading to data inconsistencies and hindering international cooperation. While high-precision Earth gravity field models have achieved some success, their resolution is low and they can only provide regional averages, failing to meet the requirements for point-level accuracy. Satellite gravity detection technology, although capable of reconstructing high-precision global gravity potential fields, has even lower resolution and similarly fails to meet high-precision requirements. These factors collectively limit the achievement of a unified global elevation datum.

[0004] To overcome these challenges, the International Union of Geodesy (IUGS) proposed a strategic goal of unifying elevation datums with an accuracy better than one centimeter. This goal requires breaking through the bottlenecks of traditional technologies, constructing a high-precision, high-resolution model of the Earth's gravity field, and establishing a globally unified time and frequency reference system. However, existing technologies often require multiple observation stations for a series of processing steps to achieve accurate measurements of high elevations at multiple points, which is highly complex, time-consuming, and difficult to transfer elevations across oceans. Summary of the Invention

[0005] The purpose of this invention is to provide a method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification, in order to solve the technical problems of high complexity, long time consumption, and difficulties in transoceanic elevation transfer when performing accurate measurements of multiple high elevations in existing technologies.

[0006] The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification includes the following steps: Step 1: Deploy multi-frequency, multi-mode GNSS receivers at multiple local leveling / gravity measurement points, establish connections between them and local high-precision clocks, and conduct synchronous GNSS static observations. Step 2: Obtain satellite precision clock track products from the International GNSS Service Analysis Center; Step 3: Determine the satellite's real-time position based on the satellite's precise orbit data in the satellite precision clock track product, and calculate the gravitational potential at the satellite's location; Step 4: Based on the model of determining gravity potential and altitude using single-station non-differential multi-frequency multi-mode GNSS signals, the satellite gravitational potential is accurately transmitted to the ground, and the altitude of the ground measuring point under the global geoid is calculated. Step 5: Move the multi-frequency multi-mode GNSS receiver and local high-precision clock to multiple remote leveling / gravity measurement points across the ocean, and repeat steps 1 to 4 to obtain the elevation of each transoceanic observation point under the global geoid. Step 6: Integrate the local measurement point elevation obtained in Step 4 with the transoceanic measurement point elevation obtained in Step 5, and calculate the elevation difference between the two transoceanic measurement points through difference calculation. Step 7: Based on the calculated elevation difference between the two different locations across the ocean and the elevation difference of the known benchmarks at the two different locations across the ocean, determine the elevation benchmark difference between the two different locations across the ocean using the least squares method, thereby achieving the unification of the elevation benchmarks for the two different locations across the ocean.

[0007] Preferably, step 4 specifically includes the following sub-steps: Step 4.1: Perform center differential calculation on the multi-frequency multi-mode GNSS carrier phase observations to obtain the phase frequency observations; Step 4.2: Construct the non-differential multi-frequency multi-mode GNSS observation equations, expand and simplify them according to the weak field approximation; Step 4.3: The station performs static observations at known leveling / gravity points, constructs a multi-frequency, multi-mode GNSS model with ionospheric desiccation and linearization, and then simplifies it to achieve accurate calculation of the station's altitude based on extended Kalman filtering.

[0008] Preferably, in step 4.2, the non-differential multi-frequency multi-mode GNSS observation equation is constructed, which can be simplified as follows:

[0009] in, l Indicates wavelength. D Represents the phase frequency observation value. The rate of change representing the geometric distance between the satellite and the ground. c This represents the speed of light in a vacuum. S Indicates a satellite system. i Indicates the satellite number, j The first multi-frequency multi-mode GNSS signal represents the...j One frequency; r Indicates a ground mobile station. and This indicates the variability of clock bias between the station and the satellite. and These represent the rates of variability in tropospheric and tropospheric delay, respectively. Mw For tropospheric delayed projection function, This indicates other errors and noise.

[0010] Preferred, the rate of change of clock bias The weak-field approximation is expressed as follows:

[0011] in, W Take the gravity potential at the ground (corresponding station) and the gravitational potential at the satellite. U , v For the satellite's speed, the clock bias variability includes the clock bias variability of both the station and the satellite.

[0012] Preferably, the conversion relationship between gravitational potential and altitude is expressed as follows:

[0013] in, The gravitational potential of the station is W 0 represents the constant gravitational potential at the geoid. The average gravitational acceleration, The station is at a high altitude.

[0014] Preferably, the simplified expression of the observation equation obtained by combining the gravity potential-altitude conversion relationship, the calculation formula for the rate of change of clock error, and the non-differential multi-frequency multi-mode GNSS observation equation is as follows:

[0015] Among them, the gravitational potential at the satellite U It is precisely obtained from the satellite's orbital position and the Earth's gravity field model.

[0016] Preferably, in step 4.3, for multi-mode, multi-frequency observations, the observations with ionospheric delay eliminated are:

[0017] In the formula, G and C This refers to the Galileo and BDS satellite navigation systems, corresponding to multi-mode signal satellite navigation systems. and or jThese are the de-ionization combination coefficients for the j-th frequency band in the five-frequency signals of Galileo and BDS, respectively. j =1,2,3,4,5.

[0018] Preferably, in step 4.3, the station performs static observations at a known leveling / gravity point, in which case the velocity of the ground station is zero; i The speed of a satellite v s,i Accurately determined by precision satellite products; at this point, the model after linearization and combining multi-frequency, multi-mode GNSS ionospheric components is expressed as:

[0019] In the formula, d To derive the Doppler observations minus the calculated values, u The direction cosine, x For three-dimensional coordinate increments, IF This represents the combination of ionospheric delays; if the sampling interval is greater than 1 Hz, the rate of change of tropospheric delay can be approximately ignored, and the linearized model above can be further simplified to:

[0020] The simplified model, based on extended Kalman filtering, can accurately calculate the altitude of the station and output the altitude of the station.

[0021] Preferably, in step 7, the following was selected. m Experiments were conducted at several sites, and the calculated elevation difference between the two locations across the ocean was: The elevation difference between two known benchmarks in two different locations across the ocean is The elevation datum difference between the two different locations across the ocean is The error is The elevation datum difference can be obtained using the least squares principle. The optimal valuation is .

[0022] Preferably, the satellite precision clock track product includes precision orbit, satellite clock error, and differential code deviation. Based on the satellite precision orbit data, the real-time position of the satellite is determined, and combined with the EGM2008 gravity field model, the gravitational potential of the satellite's position is calculated.

[0023] The technical advantages of this invention are as follows: This invention uses multi-frequency multi-mode GNSS as a key bridge and adopts a single-station data processing mode, which enables multiple stations to process data in parallel. It also constructs a model of multi-frequency multi-mode GNSS after ionospheric de-combination and linearization, realizing the accurate measurement of gravity potential and altitude at any point. It effectively completes the conversion of elevation benchmarks between ocean and sea, overcomes the long-standing problem of elevation transfer across oceans and seas, and realizes the unification of global elevation benchmarks. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification method of the present invention.

[0025] Figure 2 This is a schematic diagram illustrating the principle of the multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification method of the present invention. Detailed Implementation

[0026] The following detailed description of the embodiments, with reference to the accompanying drawings, will further illustrate the specific implementation of the present invention, in order to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0027] like Figure 1-Figure 2 As shown, this invention provides a method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification, including the following steps.

[0028] Step 1: Deploy multi-frequency, multi-mode GNSS receivers at multiple local leveling / gravity measurement points, establish connections between them and local high-precision clocks, and conduct synchronous GNSS static observations.

[0029] A high-precision clock can output a 1PPS (pulses per second) signal and a 10Hz signal to the receiver, providing a nanosecond-level high-precision time reference, thereby enabling synchronous GNSS static observations.

[0030] Step 2: Obtain satellite precision clock track products from the International GNSS Service Analysis Center.

[0031] Satellite precision clock and orbit products include core data such as precision orbit, satellite clock bias, and differential code deviation, providing fundamental support for subsequent satellite parameter calculations and model operations.

[0032] Step 3: Determine the satellite's real-time position based on the satellite's precise orbit data in the satellite precision clock track product, and calculate the gravitational potential of the satellite's location.

[0033] This step combines the satellite's real-time position with the EGM2008 gravity field model to calculate the gravitational potential at the satellite's location.

[0034] Step 4: Based on the model of determining gravity potential and altitude using single-station non-differential multi-frequency multi-mode GNSS signals, the satellite gravitational potential is accurately transmitted to the ground, and the altitude of the ground measuring point under the global geoid is calculated.

[0035] This step specifically includes the following sub-steps.

[0036] Step 4.1: Perform center differential calculation on the multi-frequency multi-mode GNSS carrier phase observations to obtain the phase frequency observations.

[0037] Step 4.2: Construct the non-differential multi-frequency multi-mode GNSS observation equations, expand and simplify them according to the weak field approximation.

[0038] The non-differential multi-frequency multi-mode GNSS observation equation is constructed and simplified as follows:

[0039] in, l Indicates wavelength. D Represents the phase frequency observation value. The rate of change representing the geometric distance between the satellite and the ground. c This represents the speed of light in a vacuum. S Indicates a satellite system. i Indicates the satellite number, j The first multi-frequency multi-mode GNSS signal represents the... j One frequency band; r Indicates a ground mobile station. and This indicates the variability of clock bias between the station and the satellite. and These represent the rates of variability in tropospheric and tropospheric delay, respectively. Mw For tropospheric delayed projection function, This indicates other errors and noise.

[0040] Variation of clock bias (Including the variability of clock biases at stations and satellites), expressed using the weak-field approximation, is as follows:

[0041] in, W Take the gravity potential at the ground (corresponding station) and the gravitational potential at the satellite. U , v The speed of the satellite.

[0042] This step also needs to take into account the conversion relationship between gravitational potential and altitude, and the corresponding expression is as follows:

[0043] in, The gravitational potential of the station is W 0 represents the constant gravitational potential at the geoid. The average gravitational acceleration, The station is at a high altitude.

[0044] The simplified form of the observation equation is obtained by applying the above expressions (the conversion relationship between gravity potential and altitude, the calculation formula for the rate of change of clock error, and the non-differential multi-frequency multi-mode GNSS observation equation):

[0045] Among them, constant gravitational potential W 0 can be taken as the value recommended by the International Union of Geodesy. W 0 = 62636856.0 m 2 / s 2 Mean gravitational acceleration Surface gravity or the commonly used average value of 9.80665 m / s can be used. 2 Or conventional gravity representation; gravitational potential at the satellite U It is precisely obtained from the satellite's orbital position and the Earth's gravity field model.

[0046] Step 4.3: The station performs static observations at known leveling / gravity points, constructs a multi-frequency, multi-mode GNSS model with ionospheric desiccation and linearization, and then simplifies it to achieve accurate calculation of the station's altitude based on extended Kalman filtering.

[0047] Taking the multi-frequency observations from Galileo and BDS as an example, the observations with ionospheric delay eliminated are as follows:

[0048] In the formula, G and C This refers to Galileo and BDS (corresponding to satellite navigation systems with multimode signals). and or j These are the corresponding five-frequency signals (multi-frequency signals) of Galileo and BDS, respectively. j Ionospheric desiccation combination coefficients for each frequency band j =1,2,3,4,5.

[0049] If the station is conducting static observations at a known leveling / gravity point, then the velocity of the ground station is zero. i The speed of a satellite v s,i Accurately determined by precision satellite products. At this point, the linearized model of the multi-frequency, multi-mode GNSS de-ionospheric combination is expressed as:

[0050] In the formula, d To derive the Doppler observations minus the calculated values, u The direction cosine, x For three-dimensional coordinate increments, IFThis represents the combination of ionospheric delays. If the sampling interval is greater than 1 Hz, the rate of change of tropospheric delay can be approximately ignored, and the linearized model described above is further simplified to:

[0051] The simplified model, based on extended Kalman filtering, can accurately calculate the altitude of the station and output the altitude of the station.

[0052] Step 5: Move the multi-frequency multi-mode GNSS receiver and local high-precision clock to multiple remote leveling / gravity measurement points across the ocean, and repeat steps 1 to 4 to obtain the elevation of each transoceanic observation point under the global geoid.

[0053] This step first uses the observation mode of step 1 to carry out data acquisition; the non-differential multi-frequency multi-mode GNSS observation equation does not need to be reconstructed. Then, based on the satellite gravitational potential calculation method of step 3 and the model of step 4, the elevation of the transoceanic observation point under the global geoid is obtained.

[0054] Step 6: Integrate the local measurement point elevation obtained in Step 4 with the transoceanic measurement point elevation obtained in Step 5, and calculate the elevation difference between the two transoceanic measurement points through difference calculation.

[0055] Step 7: Based on the calculated elevation difference between the two different locations across the ocean and the elevation difference of the known benchmarks at the two different locations across the ocean, determine the elevation benchmark difference between the two different locations across the ocean using the least squares method, thereby achieving the unification of the elevation benchmarks for the two different locations across the ocean.

[0056] In this step, if you select m Experiments were conducted at several sites, and the calculated elevation difference between the two locations across the ocean was: The elevation difference between two known benchmarks in two different locations across the ocean is The elevation datum difference between the two different locations across the ocean is The error is The elevation datum difference can be obtained using the least squares principle. The optimal valuation is .

[0057] This patent uses multi-frequency, multi-mode GNSS as a key bridge and adopts a single-station data processing mode to achieve accurate measurement of elevation differences across oceans and seas. It effectively completes the conversion of elevation benchmarks between two locations across oceans and seas, overcomes the long-standing problem of elevation transfer across oceans and seas, and lays a solid foundation for the unification of global elevation benchmarks.

[0058] With the goal of achieving transoceanic elevation transfer and elevation datum unification between China and the United States, the specific implementation path is as follows: Step 1: Deploy multi-frequency, multi-mode GNSS receivers and local high-precision clocks at known domestic leveling points (such as the Qingdao leveling origin) and multiple surrounding leveling / gravity measurement points. After establishing the equipment connection, the high-precision clock outputs a 1PPS (pulse per second) and 10Hz signal to provide a nanosecond-level time reference, and simultaneously conduct GNSS static observations.

[0059] Step 2: Obtain multi-mode GNSS precision orbit, satellite clock bias, and other data from the IGS analysis center.

[0060] Step 3: Combine the acquired data with the EGM2008 gravity field model to calculate the satellite's gravitational potential.

[0061] Step 4: Using single-station non-differential multi-frequency multi-mode GNSS signals to determine the gravity potential and elevation model, the elevation of the Qingdao leveling datum and other domestic connection points under the global geoid is calculated. The equipment is then migrated to multiple benchmark leveling points in the United States (such as the US National Height Datum associated measurement points), and static observations are conducted using the same domestic observation techniques. Based on the same IGS precise data products, satellite gravitational potential calculation methods, and elevation calculation models, the elevation of the benchmark leveling points in the United States under the global geoid is calculated.

[0062] Step 5: Integrate the elevation data of domestic measuring points such as the Qingdao leveling datum with the US benchmark leveling point.

[0063] Step 6: Obtain the transoceanic elevation difference between the measuring points in China and the United States through difference calculation. Step 7: Combining the measured elevation difference between known benchmarks in China and the United States, the least squares method is used to calculate and determine the elevation datum difference between the two countries, thus completing the transoceanic elevation transfer between China and the United States and the unification of global elevation datums.

[0064] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification, characterized by: Includes the following steps: Step 1: Deploy multi-frequency, multi-mode GNSS receivers at multiple local leveling / gravity measurement points, establish connections between them and local high-precision clocks, and conduct synchronous GNSS static observations. Step 2: Obtain satellite precision clock track products from the International GNSS Service Analysis Center; Step 3: Determine the satellite's real-time position based on the satellite's precise orbit data in the satellite precision clock track product, and calculate the gravitational potential at the satellite's location; Step 4: Based on the model of determining gravity potential and altitude using single-station non-differential multi-frequency multi-mode GNSS signals, the satellite gravitational potential is accurately transmitted to the ground, and the altitude of the ground measuring point under the global geoid is calculated. Step 5: Move the multi-frequency multi-mode GNSS receiver and local high-precision clock to multiple remote leveling / gravity measurement points across the ocean, and repeat steps 1 to 4 to obtain the elevation of each transoceanic observation point under the global geoid. Step 6: Integrate the local measurement point elevation obtained in Step 4 with the transoceanic measurement point elevation obtained in Step 5, and calculate the elevation difference between the two transoceanic measurement points through difference calculation. Step 7: Based on the calculated elevation difference between the two different locations across the ocean and the elevation difference of the known benchmarks at the two different locations across the ocean, determine the elevation benchmark difference between the two different locations across the ocean using the least squares method, thereby achieving the unification of the elevation benchmarks for the two different locations across the ocean.

2. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification according to claim 1, characterized in that: Step 4 specifically includes the following sub-steps: Step 4.1: Perform center differential calculation on the multi-frequency multi-mode GNSS carrier phase observations to obtain the phase frequency observations; Step 4.2: Construct the non-differential multi-frequency multi-mode GNSS observation equations, expand and simplify them according to the weak field approximation; Step 4.3: The station performs static observations at known leveling / gravity points, constructs a multi-frequency, multi-mode GNSS model with ionospheric desiccation and linearization, and then simplifies it to achieve accurate calculation of the station's altitude based on extended Kalman filtering.

3. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification according to claim 2, characterized in that: In step 4.2, the non-differential multi-frequency multi-mode GNSS observation equations are constructed, which can be simplified as follows: in, λ Indicates wavelength. D Represents the phase frequency observation value. The rate of change representing the geometric distance between the satellite and the ground. c This represents the speed of light in a vacuum. S Indicates a satellite system. i Indicates the satellite number, j The first multi-frequency multi-mode GNSS signal represents the... j One frequency; r Indicates a ground mobile station. and This indicates the variability of clock bias between the station and the satellite. and These represent the rates of variability in tropospheric and tropospheric delay, respectively. Mw For tropospheric delayed projection function, This indicates other errors and noise.

4. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification according to claim 3, characterized in that: Variation of clock bias The weak-field approximation is expressed as follows: in, W Take the gravity potential at the ground (corresponding station) and the gravitational potential at the satellite. U , v For the satellite's speed, the clock bias variability includes the clock bias variability of both the station and the satellite.

5. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification according to claim 4, characterized in that: The conversion relationship between gravitational potential and altitude is expressed as follows: in, The gravitational potential of the station is W 0 represents the constant gravitational potential at the geoid. The average gravitational acceleration, The station is at a high altitude.

6. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification according to claim 5, characterized in that: The simplified form of the observation equation, obtained by combining the gravitational potential-altitude conversion relationship, the calculation formula for clock error variability, and the non-differential multi-frequency multi-mode GNSS observation equation, is as follows: Among them, the gravitational potential at the satellite U It is precisely obtained from the satellite's orbital position and the Earth's gravity field model.

7. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification according to claim 2, characterized in that: In step 4.3, for multi-mode, multi-frequency observations, the observations with ionospheric delay eliminated are: In the formula, G and C This refers to the Galileo and BDS satellite navigation systems, corresponding to multi-mode signal satellite navigation systems. and η j These are the de-ionization combination coefficients for the j-th frequency band in the five-frequency signals of Galileo and BDS, respectively. j =1,2,3,4,5.

8. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification according to claim 7, characterized in that: In step 4.3, the station performs static observations at a known leveling / gravity point, so the velocity of the ground station is zero; i The speed of a satellite v s,i Accurately determined by precision satellite products; at this point, the model after linearization and combining multi-frequency, multi-mode GNSS ionospheric components is expressed as: In the formula, d To derive the Doppler observations minus the calculated values, u The direction cosine, x For three-dimensional coordinate increments, IF This represents the combination of ionospheric delays; if the sampling interval is greater than 1 Hz, the rate of change of tropospheric delay can be approximately ignored, and the linearized model above can be further simplified to: The simplified model, based on extended Kalman filtering, can accurately calculate the altitude of the station and output the altitude of the station.

9. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation datum unification according to claim 1, characterized in that: In step 7, the following was selected. m Experiments were conducted at several sites, and the calculated elevation difference between the two locations across the ocean was: The elevation difference between two known benchmarks in two different locations across the ocean is The elevation datum difference between the two different locations across the ocean is The error is The elevation datum difference can be obtained using the least squares principle. The optimal valuation is .

10. The method for multi-frequency, multi-mode GNSS transoceanic elevation transfer and global elevation benchmark unification according to claim 1, characterized in that: Satellite precision clock and orbit products include precision orbits, satellite clock bias, and differential code deviation. Based on satellite precision orbit data, the real-time position of the satellite is determined, and combined with the EGM2008 gravity field model, the gravitational potential of the satellite's position is calculated.

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