Method for determining altitude height in combination with GNSS frequency signal of Chinese space station

Abstract

The present application relates to the field of geodetic surveying, and particularly relates to a method for determining altitude based on GNSS frequency signals of Chinese space station. Through obtaining data such as GNSS satellite precise orbit, clock error and earth rotation parameters from IGS analysis center, RINEX format data is obtained by using synchronous observation of space station and ground station receiver, and the gravity potential of space station observation moment is determined in combination with EIGEN-6C4 gravity field model. The frequency observation value is derived from the carrier phase observation value, the observation equation is established in the dual-frequency ionosphere elimination processing mode, the gravity potential difference between space station and ground station is solved, and finally the gravity potential and altitude of ground station are obtained. The present application can replace the traditional leveling and gravity measurement, significantly reduce the cost, overcome the environmental restriction, and support the cross-sea and cross-ocean height transfer and the global height datum unification.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of geodesy, and particularly relates to a method for determining an altitude height by combining a GNSS frequency signal of a Chinese space station. BACKGROUND

[0002] Determination of gravity potential and altitude height plays an important role in the field of geodesy, and is an important basic physical quantity for disciplines such as seismology, geodynamics, aerospace, meteorology, oceanography, natural disaster research, and global change. It is also a key information source for national defense construction and national economic development. Determination of altitude height is closely related to the unification of global height datum, and is essential vertical spatial information in national economic construction. Since the end of the last century, the International Geodetic Association has established the strategic goal of determining the global geoid with a precision better than 1 cm and realizing the unification of global height datum.

[0003] Traditional methods for determining altitude height rely on joint measurement of gravity and leveling, but have limitations such as low efficiency and high cost. High-precision gravity field models have a resolution of only 5'x5', and can only provide regional mean results, which cannot meet the point accuracy requirements. Satellite gravity detection technology can recover high-precision global gravity potential field, but has low resolution (about 1°x1°). Therefore, these methods cannot meet the requirements of high resolution and high accuracy, and restrict the realization of global height datum unification.

[0004] To solve these problems, gravity potential measurement methods based on general relativity have gradually attracted attention and research. This method uses the correspondence between gravity potential difference and the rate difference of precise clocks, and determines the gravity potential difference between two places through time and frequency transfer technology. On this basis, relevant scholars have proposed the theoretical idea of determining gravity potential difference and altitude height by comparing clock time variation or observing electromagnetic wave frequency variation. However, there is still a lack of specific models and methods, and it has not been applied in GNSS.

[0005] In recent years, the compatibility and interoperability of GNSS systems have significantly improved, and the accuracy of the optical clock carried by the Chinese space station has reached 10 -18 orders of magnitude, providing technical conditions for realizing gravity potential measurement using GNSS frequency signals of the Chinese space station. This provides new possibilities for solving the limitations of existing methods and realizing global height datum unification. SUMMARY

[0006] The present application aims to solve the technical problems of large workload, high resource consumption, and terrain restrictions that prevent cross-sea operations in traditional leveling and gravity measurement processes.

[0007] The method for determining altitude height by combining GNSS frequency signals of the Chinese space station comprises the following steps:

[0008] Step 1: the space station and the ground station receiver synchronously observe GNSS, and obtain the observation values of GNSS pseudo-range and carrier phase observed by the space station and the ground GNSS receiver synchronously;

[0009] Step 2: download the data file of GNSS satellite from the IGS analysis center;

[0010] Step 3: based on the observation values and data files obtained in step 1 and step 2, the precise point positioning algorithm is used to calculate the three-dimensional coordinates, velocity and receiver clock bias of the space station;

[0011] Step 4: combined with the three-dimensional coordinates and velocity of the space station obtained in step 3, the EIGEN-6C4 gravity field model is used to determine the gravitational potential of the space station at the observation time, and the centrifugal potential model is used to calculate the centrifugal potential of the space station at the observation time, and the gravitational potential of the space station at the observation time is obtained by integrating the gravitational potential and the centrifugal potential;

[0012] Step 5: the precise three-dimensional position and velocity of the space station obtained in step 3, and the static observation coordinates and velocity information of the ground station, and the gravitational potential of the space station in step 4 are introduced into the relative observation to determine the ground station gravity potential model, and the gravitational potential difference between the space station and the ground station is taken as the unknown parameter to be solved, and the gravitational potential of the ground station is obtained;

[0013] Step 6: based on the gravitational potential of the ground station solved in step 5, the elevation of the ground station is obtained by Bruns formula based on the gravitational potential on the geoid.

[0014] Preferably, the step 5 comprises the following steps:

[0015] Step 5.1: convert the phase observation value into frequency observation value by difference;

[0016] Step 5.2: eliminate the gross error in the observation value, and recalculate the frequency observation value for this epoch once the cycle slip occurs;

[0017] Step 5.3: use the frequency observation value to eliminate the influence of first-order ionospheric delay by using dual-frequency ionosphere combination to obtain the frequency observation equation;

[0018] Step 5.4: accurately correct the relevant error to obtain the frequency observation equation;

[0019] Step 5.5: the initial clock speed of the ground clock is calibrated by placing the ground clock at a known leveling point;

[0020] Step 5.6: single difference between the space station and the ground station is carried out to obtain the single difference frequency observation equation;

[0021] Step 5.7, parameter estimation of the parameters to be estimated in the single-difference frequency error equation;

[0022] Step 5.8, calculation of the gravity potential of the ground station.

[0023] Preferably, in step 5.1, the calculation formula is:

[0024]

[0025] where D represents the frequency observation value, S represents the GNSS satellite system, i represents the satellite number, r represents the ground mobile station, j represents the frequency, φ represents the carrier phase observation value, k represents the current epoch, k-1 represents the previous epoch, k+1 represents the next epoch, Δ t represents the sampling interval.

[0026] Preferably, in step 5.3, the combined frequency observation equation is:

[0027]

[0028] where λ represents the wavelength, IF represents the ionosphere-free combination, represents the variation of the geometric distance between the satellite and the ground, c represents the speed of light in vacuum, represents the variation of the mobile ground station clock error, represents the variation of the satellite clock error, represents the variation of the tropospheric delay, and ξ represents the un-modeled error.

[0029] The ground mobile station clock rate containing the gravity potential is:

[0030]

[0031] where υ r represents the initial clock rate of the station r, ΔW 0r represents the gravity potential difference between the station r and the geoid, and ζ represents the clock noise.

[0032] Further, the frequency observation equation is:

[0033]

[0034] where M w and M dry are the tropospheric wet delay and dry delay projection functions, and are the variations of the zenith tropospheric wet delay and dry delay, respectively.

[0035] Preferably, in step 5.4, the second-order ionospheric delay is corrected using the model combined with the global ionospheric delay grid product, the tropospheric dry delay is corrected using the Saastamoinen model, the Sagnac effect is corrected using the Earth-fixed coordinates of the station and the satellite, the antenna phase entanglement is corrected using the model, and the antenna phase center deviation is corrected using the IGS20.atx file combined with the model.

[0036] Preferably, in step 5.5, the gravitational potential of the known leveling point is calculated using the Bruns formula, and the clock difference of the clock at the known leveling point is fitted using least squares to obtain the clock speed. Subtracting the gravitational potential of the known leveling point from the calculated clock speed and dividing by the speed of light yields the initial clock speed υ of the ground clock. r The clock rate of the space station satellites calculated in step 3 is then fitted using the least squares method. Subtract the gravitational potential calculated in step 4 from the fitted clock speed and divide by the speed of light to obtain the initial clock speed υ of the clock on the space station. b .

[0037] Preferably, in step 5.6, the single-difference frequency observation equation is:

[0038]

[0039] Where Δ is the inter-station single difference operator.

[0040] Preferably, in step 5.7, the space station and the ground station simultaneously observe n satellites. Since the three-dimensional coordinates and velocities of both the space station and the ground station are known, the single-difference frequency error equation is:

[0041]

[0042] The parameter to be estimated is the gravitational potential difference ΔW between the stations rb. rb The wet tropospheric delay variability of stations r and b is estimated using the least squares method or the extended Kalman filter method.

[0043] Preferably, in step 5.8, based on the determined space station gravity potential W... b The gravitational potential W of the ground station r The formula for calculating W is r =W b +ΔW rb .

[0044] Preferably, in step 6, the formula for calculating altitude is:

[0045]

[0046] Among them, H rW0 is the gravity constant on the geoid at the altitude of the ground station, W0 is the gravity constant on the geoid at the altitude of the ground station,

[0047] The present application has the following advantages: the present application is a method for determining gravity potential and altitude based on GNSS frequency signals of the Chinese space station, which realizes the transmission of gravity potential from the space station to the ground station by taking the gravity potential of the space station as the reference and taking the GNSS satellite as the medium, and further obtains the altitude from the gravity potential of the ground station, and can realize global coverage, overcome the defects of traditional gravity / level measurement, and help realize the unification of global height datum.

[0048] The method can significantly reduce the investment of manpower, material resources and financial resources, and overcome the constraints of weather, terrain and environmental factors, and not only can replace traditional leveling and gravity measurement, but also provides technical support for cross-sea, cross-ocean height transmission and the unification of global height datum. BRIEF DESCRIPTION OF DRAWINGS

[0049] Fig. 1 is a method flowchart of the method for determining altitude according to the present application in combination with GNSS frequency signals of the Chinese space station.

[0050] Fig. 2 is a schematic diagram of the present application for determining gravity potential and altitude according to GNSS frequency signals. DETAILED DESCRIPTION

[0051] The specific embodiments of the present application will be further described in detail below with reference to the drawings, and by describing the embodiments, so as to help the skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical scheme of the present application.

[0052] As shown in Figs. 1-2 The present application provides a method for determining altitude in combination with GNSS frequency signals of the Chinese space station, which comprises the following steps:

[0053] Step 1: The receivers of the space station and the ground station are synchronized to perform GNSS observation, and the observation values of GNSS pseudo-range and carrier phase observed by the space station and the ground GNSS receiver are obtained.

[0054] The receiver on the space station is connected to the carried strontium atomic optical clock to provide a high-precision time reference for observation; the clock of the ground station is connected to a local high-precision hydrogen atomic clock, and static observation is performed at a known site. The clock outputs 1PPS (one pulse per second) and 10Hz signals to the GNSS receiver to ensure data synchronization. Save and generate RINEX format files containing pseudo-range and carrier phase observation values.

[0055] Step 2, download the data file of GNSS satellite from IGS analysis center. The data file includes precise orbit / clock error, earth rotation parameter, etc.

[0056] Step 3, based on the observation value and data file obtained in step 1 and step 2, the three-dimensional coordinates, velocity and clock error of each observation time are calculated, and the three-dimensional coordinates, velocity and receiver clock error of the space station are calculated by the precise point positioning algorithm.

[0057] Step 4, combined with the three-dimensional coordinates and velocity of the space station obtained in step 3, the gravitational potential of the space station at the observation time is determined by the EIGEN-6C4 gravity field model in the gravity potential calculation module, and the centrifugal potential of the space station at the observation time is calculated by the centrifugal potential model, and the gravitational potential of the space station at the observation time is obtained by combining the gravitational potential and the centrifugal potential.

[0058] Step 5, the precise three-dimensional position and velocity of the space station obtained in step 3, and the static observation coordinates and velocity information of the ground station, and the gravity potential of the space station in step 4 are introduced into the relative observation determination ground station gravity potential model, and the gravity potential difference between the space station and the ground station is taken as the unknown parameter to solve, and the gravity potential of the ground station is obtained.

[0059] Step 5 includes the following steps:

[0060] Step 5.1, convert the phase observation value into frequency observation value by difference:

[0061]

[0062] Wherein, D represents the Doppler frequency observation value, S represents the GNSS satellite system, i represents the satellite number, r represents the ground mobile station, φ represents the carrier phase observation value, k represents the current epoch, k-1 represents the previous epoch, k+1 represents the next epoch, Δ t Indicates the sampling interval.

[0063] Step 5.2, eliminate the gross error in the observation value, and recalculate the frequency observation value at this epoch once the cycle slip occurs.

[0064] Step 5.3, using the frequency observation value, the ionosphere-free combination of double frequency is used to eliminate the influence of first-order ionosphere delay, and the combined frequency observation equation is

[0065]

[0066] Wherein, λ represents the wavelength, IF represents the ionosphere-free combination, Indicates the variation of the geometric distance between the satellite and the ground, c represents the speed of light in vacuum, Indicates the variation of the mobile ground station clock error, denotes the rate of change of the satellite clock error, denotes the rate of change of the tropospheric delay, and ξ denotes the un-modeled error.

[0067] The high-precision clock is generally less affected by the frequency drift, and the clock rate of the ground station containing the gravity potential can be expressed as:

[0068]

[0069] wherein υ r denotes the initial clock rate of the station r, ΔW 0r denotes the gravity potential difference between the station r and the geoid, and ζ denotes the clock noise.

[0070] The frequency observation equation is further obtained as:

[0071]

[0072] wherein M w and M dry are the projection functions of the tropospheric wet delay and dry delay, and are the rates of change of the zenith tropospheric wet delay and dry delay, respectively.

[0073] Step 5.4, accurate correction of the correlation error. The second-order ionospheric delay is corrected using the model combined with the global ionospheric delay grid product, the tropospheric dry delay is corrected using the Saastamoinen model, the Sagnac effect is corrected through the coordinates of the station and the satellite in the earth-fixed system, the antenna phase wrapping is corrected using the model, and the antenna phase center offset is corrected using the IGS 20.atx file combined with the model.

[0074] Step 5.5, the initial clock rate υ r of the ground clock is calibrated by placing the ground clock at a known leveling point. The gravity potential of the known leveling point is calculated by the Bruns formula, the clock error of the clock at the known leveling point is least square fitted, and the clock rate of the clock is obtained. The calculated clock rate is subtracted from the gravity potential of the known leveling point divided by the speed of light, and the initial clock rate υ r of the ground clock is obtained.

[0075] The space station satellite clock error calculated in step 3 is fitted by the least square method to obtain the clock rate The fitted clock rate is subtracted from the gravity potential calculated in step 4 divided by the speed of light, and the initial clock rate υ b of the clock on the space station is obtained.

[0076] Step 5.6, the inter-station single difference between the space station and the ground is performed to eliminate the satellite orbit, clock error and other satellite-related errors, and the single difference frequency observation equation is

[0077]

[0078] where Δ is the single difference operator between stations.

[0079] Step 5.7, the space station and the ground station observe n satellites simultaneously, and the three-dimensional coordinates and velocities of the space station and the ground station are known, the single difference frequency error equation is:

[0080]

[0081] where the estimated parameters are the gravity potential differences ΔW rb between stations rb, the zenith tropospheric wet delay rate of stations r and b, and the parameters are estimated by least squares method or extended Kalman filter method.

[0082] Step 5.8, based on the space station gravity potential W r determined in step 4 and the calculated gravity potential difference ΔW rb between the space station and the ground station, the gravity potential W b of the ground station can be obtained:

[0083] W r = W b + ΔW rb

[0084] Step 6, based on the gravity potential of the ground station solved in step 5, the elevation of the ground station is obtained from the Bruns formula with the gravity potential on the geoid as the reference. The calculation formula is:

[0085]

[0086] where H r is the elevation of the ground station, W0 is the gravity constant on the geoid, is the average value of the gravity of the ground station along the plumb line, which can be replaced by the gravity value of the ground station when the height is small. Or a more rigorous surface shallow method is used to calculate, that is, the average value of the gravity along the plumb line through the ground station is obtained.

[0087] The patent takes the gravity potential of the Chinese space station as the reference, uses GNSS satellites as the bridge, realizes the transfer from the gravity potential of the space station to the gravity potential of the ground station, and further calculates the elevation from the gravity potential of the ground station. This method effectively overcomes the limitations of traditional gravity measurement and leveling, and provides technical support for the unification of global height datum.

[0088] ​Taking Wuhan station as an example, the GNSS receiver of the station realizes synchronous observation with the space station receiver through an external high-precision clock, and GNSS satellite signal data are obtained together. The research adopts the GNSS satellite precise ephemeris and clock error products provided by the IGS station, combines the precise point positioning algorithm, and accurately solves the running speed and gravity potential value of the space station at the observation time. On this basis, joint processing is carried out with the gravity potential difference data of the space station-Wuhan station obtained in step 4. After long-term continuous observation, the observation data are optimized by adjustment method, and finally the gravity potential value of Wuhan station is determined. Based on the calculation method of step 6, the elevation of Wuhan station is further calculated.

[0089] The application also provides an embodiment of a computer system for realizing multi-station collaborative calculation and geographic information comprehensive processing. The computer system comprises a processor and a memory, and the components interact with each other through a system bus. The memory adopts a hierarchical storage architecture and is configured to store non-transitory computer readable instructions (containing a plurality of computer program modules) and time series data generated in the calculation process; the processor constructs a distributed data processing pipeline by executing the instructions, realizes parallel processing of multi-station observation data, unification of space-time reference and error compensation analysis, and finally generates geographic spatial information products containing elevation, gravity potential difference and other elements.

[0090] In specific implementation, the processor can adopt a heterogeneous computing architecture, including but not limited to: a central processing unit (CPU), a multi-core processor adopting X86 or ARM architecture, responsible for task scheduling, logical operation and system control; a graphics processing unit (GPU), configured with CUDA or OpenCL acceleration core, used for large-scale matrix operation and algorithm acceleration; a digital signal processor (DSP), which can be selected for special chips for GNSS raw signal processing; a field programmable gate array (FPGA), supporting hardware-level data preprocessing acceleration; the processor cluster is interconnected through a PCIe high-speed bus, and can dynamically allocate processing tasks according to the computing load, realizing efficient processing of multi-source heterogeneous data.

[0091] The memory system adopts a hybrid storage scheme, including: a first-level storage, a cache pool composed of DDR4 / DDR5 memory, configured with ECC check function, used for temporarily storing real-time calculation data; a second-level storage: an NVMe protocol solid state disk array, storing historical observation data sets and intermediate calculation results; a third-level storage: a cold storage system equipped with a RAID5 disk array and a tape library, used for long-term data archiving. Each storage level realizes automatic data migration through intelligent prefetching algorithm, and the memory surface is provided with a temperature sensor and a wear leveling controller, to ensure the reliability of data storage.

[0092] At the software level, the computer program modules comprise: a data preprocessing module, realizing cycle slip detection, multipath error elimination and data format standardization; a precise point positioning module, integrating a PPP algorithm library; an adjustment calculation engine, supporting joint solution of least square method and Kalman filtering; an error modeling library, containing correction models for troposphere delay, ionosphere disturbance and the like; a visualization interface, providing a RESTful API and a WebGL three-dimensional display interface.

[0093] The above describes the present application in conjunction with the drawings, and it is obvious that the specific implementation of the present application is not limited by the above manner, and various non-essential improvements using the inventive concept and technical solution of the present application or directly applying the inventive concept and technical solution of the present application to other occasions without improvement are all within the protection scope of the present application.

Claims

1. A method for determining an altitude height by combining a Chinese space station GNSS frequency signal, characterized in that, It comprises the following steps: Step 1: the space station and the receiver of the ground station synchronously observe GNSS, and the observation values of the GNSS pseudoranges and carrier phases synchronously observed by the space station and the ground GNSS receiver are obtained; Step 2: the data file of the GNSS satellite is downloaded from the IGS analysis center; Step 3: the three-dimensional coordinates, velocity and receiver clock bias of the space station are calculated by the precise point positioning algorithm based on the observation values and the data file obtained in steps 1 and 2; Step 4: the three-dimensional coordinates and velocity of the space station obtained in step 3 are combined, the gravitational potential of the space station at the observation time is determined by the EIGEN-6C4 gravity field model, the centrifugal potential of the space station at the observation time is calculated, and the gravitational potential of the space station at the observation time is obtained by integrating the gravitational potential and the centrifugal potential; Step 5: the precise three-dimensional position and velocity of the space station obtained in step 3, the coordinate and velocity information of the ground station observed statically, and the gravitational potential of the space station in step 4 are introduced into the relative observation to determine the gravity potential model of the ground station, and the gravity potential difference between the space station and the ground station is taken as an unknown parameter to be solved, so that the gravity potential of the ground station is obtained; Step 6: based on the gravity potential of the ground station solved in step 5, the elevation of the ground station is obtained by taking the gravity potential on the geoid as the reference by the Bruns formula; The step 5 comprises the following steps: Step 5.1: the phase observation value is converted into a frequency observation value by difference; Step 5.2: the gross error in the observation value is eliminated, and once the cycle slip occurs, the frequency observation value is recalculated for this epoch; Step 5.3: the frequency observation equation is obtained by using the frequency observation value and the dual-frequency ionosphere combination to eliminate the influence of the first-order ionosphere delay; Step 5.4: the relevant error is accurately corrected to obtain the frequency observation equation; Step 5.5: the initial clock speed of the ground clock is calibrated by placing the ground clock at a known leveling point; Step 5.6: the inter-station single-difference between the space station and the ground station is obtained to obtain the single-difference frequency observation equation; Step 5.7: the parameters to be estimated in the single-difference frequency error equation are estimated; Step 5.8: the gravity potential of the ground station is calculated.

2. The method of claim 1, wherein the method further comprises: In step 5.1, the calculation formula is: wherein, D represents a frequency observation value, S represents a GNSS satellite system, i represents a satellite number, r represents a ground mobile station, j represents a frequency, represents a carrier phase observation value, k represents a current epoch, k -1 represents a previous epoch, k +1 represents a next epoch, represents a sampling interval.

3. The method of claim 2, wherein the method further comprises: In step 5.3, the combined frequency observation equation is: wherein, λ denotes the wavelength, IF denotes the ionosphere-free combination, denotes the rate of change of the geometric range between satellite and ground, c denotes the speed of light in vacuum, denotes the rate of change of the mobile ground station clock bias, denotes the rate of change of the satellite clock bias, denotes the rate of change of the tropospheric delay, denotes unmodeled errors; The clock speed of the ground mobile station containing the gravity potential is: where denotes the initial clock rate of the station r , denotes the difference in gravity potential between the station r and the geoid, denotes the noise of the clock; The further obtained frequency observation equation is: where and are the tropospheric wet and dry delay projection functions, and are the zenith tropospheric wet and dry delay rate of change, respectively.

4. The method of claim 3, wherein the method further comprises: In step 5.4, the second-order ionosphere delay is corrected by using the model combined with the global ionosphere delay grid product, the tropospheric dry delay is corrected by using the Saastamoinen model, the Sagnac effect is corrected by using the coordinates of the ground station and the satellite, the antenna phase wrapping is corrected by using the model, and the antenna phase center deviation is corrected by using the IGS20.atx file combined with the model.

5. The method of claim 4, wherein the method further comprises: In step 5.5, the gravity potential of the known leveling point is calculated by Bruns formula, the clock error of the clock at the known leveling point is least square fitted, and then the clock speed of the clock is obtained; the initial clock speed of the ground clock is obtained by subtracting the gravity potential of the known leveling point from the calculated clock speed and dividing by the speed of light ; the satellite clock error of the space station is fitted by least square method according to the space station satellite clock error solved in step 3 ; The initial clock rate of the clock on the space station is obtained by subtracting the gravitational potential calculated in step 4 from the fitted clock rate divided by the speed of light .

6. The method of claim 5, wherein the method further comprises: In step 5.6, the single-difference frequency observation equation is wherein is the inter-station single-difference operator.

7. The method of claim 6, wherein the method further comprises: In step 5.7, the space station and the ground station observe simultaneously n The single-difference frequency error equation is: where the unknown parameters are the gravity potential differences between the stations rb , the zenith tropospheric wet delay variations of the stations r and b The unknown parameters are calculated by least square method or extended Kalman filter method.​ 8. The method of claim 7, wherein the method further comprises: In step 5.8, the gravity potential of the space station is determined based on the determined gravity potential of the ground station The gravity potential of the ground station is calculated as .​ 9. The method of claim 8, wherein the method further comprises: In step 6, the calculation formula of the elevation is: wherein H r h is the altitude of the ground station, W 0 is the gravitational constant on the geoid, is the average value of the gravity along the plumb line of the ground station; the average value of the gravity is replaced by the gravity value of the ground station when the height is small; or the average value of the gravity is calculated along the plumb line passing through the ground station.

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