Method and system for establishing national elevation datum by using optical clock-optical fiber time frequency transfer network

Abstract

The invention discloses a method and a system for establishing a national elevation datum by using an optical clock-optical fiber time frequency transfer network. According to the method, large-distance and high-precision gravitational potential difference measurement and height difference transmission are realized through a high-precision optical clock by adopting optical fiber to carry out time-frequency signal transmission and accurate comparison, and the defects of accumulation of traditional elevation measurement errors, low precision, high measurement cost and difficulty in real-time updating of elevation data can be obviously improved; and the national elevation datum is established at centimeter-level precision. According to the method, a new thought is provided for unification of the global elevation datum, and a technical support foundation is laid for future gravitational potential measurement and integration of the elevation datum.

Description

Technical Field

[0001] The present invention belongs to the fields of geodesy, geophysics, and time-frequency science, and particularly relates to a method and system for establishing a national elevation datum using high-precision optical fiber time-frequency transfer. Background Art

[0002] Currently, the establishment and maintenance of a national elevation datum are of great significance to fields such as geographic information systems, engineering construction, resource management, and disaster monitoring. Traditional elevation measurement methods mostly rely on leveling, GNSS (Global Navigation Satellite System), and gravity measurement, etc. Although they meet the accuracy requirements to a certain extent, there are still the following deficiencies in the establishment of a large-scale and high-precision datum: Accuracy limitation: The measurement accuracy of existing technologies is affected by various factors such as atmospheric delay and equipment errors, resulting in insufficient reliability of elevation data.

[0003] Time synchronization problem: The synchronization of time between different observation stations is the key to achieving unified elevation calibration, and traditional time-frequency transfer methods often cannot provide sufficient accuracy and stability.

[0004] Difficulty in dynamic update: Once the existing datum is established, it is difficult to update it in real time to cope with changes brought about by natural phenomena such as crustal movement, thus affecting the timeliness of elevation data.

[0005] Unifying the global elevation datum through time-frequency transfer is an actual application of the principle of general relativity. This process mainly measures the geopotential by comparing the time-frequency signals emitted by a local high-precision optical clock and a remote optical clock, and combines the conversion model between the geopotential and the altitude to finally determine the altitude. For a long time, due to being restricted by the accuracy of atomic clocks, the application of this time-frequency transfer technology in the determination of geopotential and altitude has been limited and difficult to be widely used. Summary of the Invention

[0006] To overcome the deficiencies of the above-mentioned existing technologies, the present invention provides a method and system for establishing a national elevation datum using an optical clock-fiber time-frequency transfer network. Through a high-precision optical clock, the time-frequency signals are transmitted and accurately compared by using optical fibers in a countertransmission manner, realizing long-distance and high-precision geopotential difference measurement and height difference transfer, which can significantly improve the defects of cumulative errors, low accuracy, high measurement costs, and difficulty in real-time updating of elevation data in traditional elevation measurement, and achieve the establishment of a national elevation datum with centimeter-level accuracy.

[0007] According to one aspect of the specification of the present invention, a method for establishing a national elevation datum using an optical clock-fiber time-frequency transfer network is provided, including: Selecting a plurality of observation stations and configuring an optical clock for each station; Constructing an optical clock-fiber time-frequency transfer network to connect the optical clock optical fibers of each observation station; According to the constructed optical clock - optical fiber time - frequency transfer network, signal pairs are transmitted between remote observation sites. Using the frequency signal generated by the optical clock, remote optical fiber frequency comparison is carried out to extract the gravity frequency shift caused by the difference in gravity potential at different observation sites. According to the extracted gravity frequency shift, the gravity potential difference and elevation difference between each observation site are obtained. According to the elevation data of each observation site, a unified national elevation datum is formed.

[0008] As a further technical solution, the method further includes: An optical fiber time - frequency comparison model for bidirectional frequency transmission is established. Using the reference frequency provided by the connected optical clock, the femtosecond optical frequency comb is used to frequency - convert the optical clock signal. Frequency comparison is carried out on the frequency signal transmitted to the far - end at one end to measure the frequency difference between each site, so as to extract the gravity frequency shift.

[0009] As a further technical solution, for the two observation sites where signal pairs are transmitted, the method further includes: The optical clock of one of the observation sites emits a frequency reference. The frequency reference is up - converted by the femtosecond optical frequency comb and then transmitted to the optical fiber by the fiber laser. After being transmitted through the optical fiber to the other observation site, the optical clock of the other observation site generates a local frequency reference, and a beat frequency is generated through the femtosecond optical frequency comb and the fiber laser. The beat frequency is beat - frequency with the frequency transmitted through the optical fiber to obtain the frequency difference between the two observation sites.

[0010] As a further technical solution, according to the extracted gravity frequency shift, obtaining the gravity potential difference and elevation difference between each observation site includes: By comparing the time - frequency signals generated by different observation sites, the gravity potential difference of each observation point is measured. Using the relationship between the gravity potential and the altitude, a conversion model between the gravity potential and the altitude is established to realize the conversion between the gravity potential difference and the elevation difference.

[0011] As a further technical solution, the method further includes: Detect the state of the optical clock - optical fiber time - frequency transfer network and the operating state of the optical clock, and perform real - time calculation on the optical clock - optical fiber frequency comparison data.

[0012] As a further technical solution, the method further includes: Set a national leveling reference point as one of the observation sites and set an optical clock. The optical clocks of different observation sites are connected through the optical clock - optical fiber time - frequency transfer network. Carry out joint measurements on different observation sites and the national leveling reference point to obtain the gravity potential difference and elevation difference between the leveling reference point and each observation site, and realize the construction of the elevation datum across the country.

[0013] As a further technical solution, the method further includes: Selecting an optical clock with a precision better than 10 -18 orders of magnitude as the time reference.

[0014] As a further technical solution, the method further includes: Based on the gravity potential difference data between different sites measured by the optical clock - optical fiber ratio measurement, and combining the conversion relationship between the gravity potential and the altitude, calibrating the elevation of each observation site; Using the gravity potential and elevation measured by the traditional elevation measurement method to evaluate the accuracy of the gravity potential and elevation measured by the optical clock - optical fiber time - frequency transfer network.

[0015] According to one aspect of the specification of the present invention, a system for establishing a national elevation datum using an optical clock - optical fiber time - frequency transfer network is provided, including: An optical clock, configured as a time reference at each observation site; An optical clock - optical fiber time - frequency transfer network, used to connect the optical clock fibers of each observation site; A data processing unit, used to, according to the constructed optical clock - optical fiber time - frequency transfer network, when performing signal pair - transmission between remote observation sites, use the frequency signal generated by the optical clock to perform remote optical fiber frequency comparison, extract the gravity frequency shift caused by the gravity potential difference at different observation sites, obtain the gravity potential difference and elevation difference between each observation site according to the extracted gravity frequency shift, and form a unified national elevation datum according to the elevation data of each observation site.

[0016] As a further technical solution, the system further includes: A real - time monitoring module, used to detect the state of the optical clock - optical fiber time - frequency transfer network and the operating state of the optical clock, and perform real - time calculation on the optical clock - optical fiber frequency comparison data.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a method for establishing a national elevation datum using an optical clock - optical fiber time - frequency transfer network, which can realize the determination of the gravity potential difference between two places. By applying the conversion model of the high - order gravity potential and the altitude, the elevation transfer can be effectively realized. This method has the characteristics of high efficiency and high precision in the process of large - range and long - distance elevation transfer, providing a new measurement means for the construction of the national elevation datum.

[0018] 2. The present invention has the advantages of high precision, high stability, high efficiency and long - distance, and can overcome the problems of low efficiency, high cost and insufficient precision in the traditional determination of gravity potential and altitude. Cooperating with a high - precision optical clock (precision better than 10 -18A method of optical clock - fiber frequency transfer with high precision and high accuracy is used to compare the frequencies of clocks at two locations, which can meet the accuracy requirements for determining the elevation datum with centimeter - level accuracy nationwide, significantly improve the low - accuracy problem in remote areas of the current national elevation datum, and provide new ideas for the application of high - precision quantum precision measurement in geodesy. Brief Description of the Drawings

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a schematic flowchart of the method for establishing a national elevation datum using an optical clock - fiber time - frequency transfer network provided by the embodiments of the present invention.

[0021] Figure 2 It is a schematic diagram of the principle for measuring the geopotential and altitude using optical clock - fiber time - frequency transfer provided by the embodiments of the present invention.

[0022] Figure 3 It is a distribution diagram of the optical clock - fiber time - frequency transfer network of some stations for establishing a national elevation datum provided by the embodiments of the present invention. Detailed Embodiments

[0023] It should be noted that in the specification of the present invention, altitude and elevation refer to the same thing, and altitude difference and elevation difference refer to the same thing.

[0024] In recent years, with the continuous progress of clock manufacturing technology, optical clocks with an accuracy reaching the order of 10 -19 have been successfully developed internationally, and the accuracy of movable optical clocks has also been improved to the order of 10 -18 These technological advancements provide solid hardware support for unifying the global elevation datum using time - frequency comparison. Compared with traditional atomic clocks, optical clocks have extremely high frequency stability, and their time standard can reach picosecond - level accuracy, which can provide a more accurate time reference for the establishment of the elevation datum. In addition, the optical clock - fiber time - frequency transfer network has the characteristics of low loss and low delay, which can effectively solve the time and frequency comparison between different observation stations.

[0025] In recent years, with the development of optical clock technology and optical fiber communication technology, combining the two for high-precision time-frequency transfer can not only improve the accuracy of elevation measurement, but also achieve real-time update of elevation data, meeting the requirements of modern society for the accuracy and timeliness of geographical information. Therefore, using an optical clock-fiber optic time-frequency transfer network to establish a national elevation datum not only has important theoretical value, but also has broad application prospects, providing innovative technical support for national infrastructure construction and management.

[0026] The terms "including" and "having" and any variations thereof in the description and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. In addition, the technical features in each embodiment or individual embodiment provided by the present invention can be combined with each other arbitrarily to form a new technical solution. Such combination is not restricted by the order of steps and / or the structure composition mode, but must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] The embodiments of the present invention provide a method for establishing a national elevation datum using an optical clock-fiber optic time-frequency transfer network, as Figure 1 shown. First, select multiple observation stations and configure an optical clock for each station; then, construct an optical clock-fiber optic time-frequency transfer network to connect the optical clock fibers of each observation station; subsequently, according to the constructed optical clock-fiber optic time-frequency transfer network, perform signal pair transmission between remote observation stations, use the frequency signal generated by the optical clock to perform remote optical fiber frequency comparison, and extract the gravity frequency shift caused by the gravity potential difference at different observation stations; then, according to the extracted gravity frequency shift, obtain the gravity potential difference and elevation difference between each observation station, and form a unified national elevation datum based on the elevation data of each observation station.

[0029] The method for establishing a national elevation datum using an optical clock-fiber time-frequency transfer network according to the embodiments of the present invention aims to establish a national elevation datum using an optical clock-fiber time-frequency transfer network, and the main contents include the following aspects: 1. Construction and selection of optical clock: Select a high-precision optical clock (with an optical clock accuracy better than 10 -18 order of magnitude) as the time reference to ensure its frequency stability and measurement accuracy reach.

[0030] The configuration location of the optical clock is usually selected as an observation site with good environmental conditions. Among them, the observation site can establish a height difference correction connection with the national elevation datum point or be directly built on the elevation datum point.

[0031] 2. Design of optical clock-fiber time-frequency transfer network: Construct a low-loss and low-delay optical fiber network to connect the optical clocks of multiple observation sites to achieve effective transmission of time-frequency signals. By establishing a model for measuring the gravity potential and altitude using fiber optic time-frequency transfer, eliminate various error influences during the propagation of the optical frequency signal in the optical fiber network, and ensure reliable signal transmission and time-frequency comparison by designing the network topology.

[0032] 3. Time-frequency comparison method: Establish a fiber optic time-frequency comparison model for bidirectional frequency transmission to eliminate the frequency shift caused by environmental factors during signal propagation; use the connected optical clock to provide the basic frequency, down-convert the optical clock signal using a femtosecond optical frequency comb, and then perform high-precision frequency comparison on the frequency signal transmitted remotely to measure the frequency difference between each site. Implement real-time monitoring and measurement to ensure the normal state of the optical clock and the optical fiber network, so as to maintain a high-precision time and frequency reference.

[0033] 4. Gravity potential measurement: By comparing the time-frequency signals generated at different sites, measure the gravity potential difference at each observation point. Use the relationship between the gravity potential and the altitude to establish a conversion model between the gravity potential and the altitude to achieve the conversion between the gravity potential difference and the altitude difference (i.e., elevation difference).

[0034] 5. Calibration and calculation of altitude: Based on the gravity potential difference data between different sites measured by fiber optic comparison, combined with other factors such as temperature and humidity, calibrate the altitude of each observation site. Use the gravity potential and altitude measured by traditional elevation measurement methods to evaluate the accuracy of the gravity potential and altitude measured by the optical clock-fiber time-frequency transfer network. Use advanced data processing algorithms to ensure the accuracy and consistency of elevation data and achieve the unification of the elevation datum across the country.

[0035] 6. System integration and application: Integrate the above technologies to form a complete system, including an optical clock, an optical fiber network, a data processing unit, and a monitoring module, providing a visual interface and a data storage solution for easy user operation and data analysis.

[0036] 7. Real-time update mechanism: Establish a dynamic update mechanism to ensure that the elevation datum can reflect in real time the changes caused by natural phenomena such as crustal movement, improving the timeliness and reliability of the datum.

[0037] The present invention proposes a method for establishing a national elevation datum using an optical clock-fiber optic time-frequency transfer network. The specific method and implementation steps are as follows: 1) Set up fiber optic time-frequency comparison observation stations at benchmark stations such as national elevation datum points and the benchmark point of Qingdao tide gauge station, and simultaneously equip high-precision optical clocks with a long-term stability better than 10 -18 order of magnitude to provide high-precision and high-stability frequency reference and time reference for the measuring stations. The leveling points and national elevation datum points where the elevation needs to be measured are connected by optical fibers, and fiber optic time-frequency transfer and comparison can be implemented for remote optical clocks (as Figure 2 shown).

[0038] Figure 2 Schematic diagram for measuring the gravity potential and altitude by optical clock-fiber optic time-frequency transfer. In the figure, the optical clock at point P emits a high-precision frequency reference, which is frequency-converted by a femtosecond optical frequency comb, and then a frequency signal is transmitted to the optical fiber by an optical fiber laser. For long-distance optical fiber frequency signal transmission, signal amplifiers and stabilizers are required. After the signal arrives at point Q, the optical clock at point Q generates a local frequency reference, and a beat frequency is generated through a femtosecond optical frequency comb and an optical fiber laser, and is beat with the frequency transmitted from point P to achieve frequency measurement. Through measurement, the frequency shift observation values of P and Q can be obtained and ; then, the gravity potential difference between the two places is obtained by using the relationship between the frequency shift, the gravity potential, and the relationship between the gravity potential and the altitude, realizing elevation transfer.

[0039] In practical applications, the method of transmitting frequency signals in opposite directions between the local clock and the remote clock is used for measurement. Assume that the frequency shift observation value measured at point P is , and the frequency shift observation value measured at point Q is , then the gravity frequency shift equations of point P and point Q can be determined:

[0040] In the formula, and Random errors during the optical fiber frequency transmission at points P and Q respectively. These errors can be reduced by averaging multiple measurements. The optical fiber frequency transfer method is affected by many error sources, such as: optical clock error, frequency transmission error in the optical fiber, etc. Assume that point P emits a signal with a frequency of through the optical fiber to point Q, and the received frequency at point Q is of the signal. It includes three parts: gravitational frequency shift, optical clock error, and frequency transmission error in the optical fiber:

[0041] Among them, is the gravitational frequency shift, is the sum of all clock errors, is the sum of all frequency transfer process errors.

[0042] In order to achieve the measurement of gravitational potential and altitude with centimeter-level accuracy, the term should be considered in the gravitational frequency shift formula. The one-way frequency transfer equation in free space is determined as:

[0043] Among them, and represent the gravitational potentials at points P and Q, and are the third-order and fourth-order term frequency shifts respectively. The specific expressions can refer to the article published by Linet and Teyssandier in 2002. Combining equations (1) and (2), the gravitational potential difference between the two places can be obtained.

[0044] 2) According to the definition of gravitational potential, when the gravitational potential at the geoid is W0, the gravitational potential at any point P on the ground can be expressed as:

[0045] In the formula, H P is the orthometric height at point P (unit: m), is the gravity at point P on the geoid (unit: ( ))), (R is the radius of the earth), represents the term greater than or equal to . When the ground station is in a flat area, the first-order term is taken. When the ground station is in a mountainous area with rapid terrain changes, the second-order term is taken.

[0046] Assume that points P and Q are ground measurement stations. Given the gravitational potential at point P, when point Q is in a mountainous area with obvious changes in terrain height difference, the second-order term in equation (2) needs to be considered. The altitude at point Q can be expressed as:

[0047] Among them, is the gravity potential difference between two places. Through this model, when the altitude of point P is known, the altitude of any point Q can be measured by the optical clock-fiber time-frequency transfer technology, so as to realize altitude transfer.

[0048] Figure 2 It is a schematic diagram of establishing a national altitude datum by optical clock-fiber time-frequency transfer. In the figure, altitude control points are arranged at the national level benchmark point, Qingdao tide gauge station, and some important cities, and high-precision optical clocks are placed at the stations. The optical clocks at different stations are connected through a time-frequency optical fiber network. When different stations are jointly measured with the national level benchmark point, the gravity potential difference and altitude difference between the level origin and the arranged urban stations can be obtained. Through the joint measurement of many important level points and the level origin across the country, the direct gravity potential difference and altitude difference between the level origin and any level point can be measured, high-precision altitude transfer can be carried out, and finally the construction of the national altitude datum across the country can be realized.

[0049] The method of establishing a national altitude datum by using an optical clock-fiber time-frequency transfer network according to the present invention can realize the determination of the gravity potential difference between two places. By applying a conversion model of high-order gravity potential and altitude, altitude transfer can be effectively realized. This method has the characteristics of high efficiency and high precision in the process of large-range and long-distance altitude transfer, and provides a new measurement means for the construction of the national altitude datum. This technology has the advantages of high precision, high stability, high efficiency and long distance, and can overcome the problems of low efficiency, high cost and insufficient precision in traditional gravity potential and altitude measurement. Cooperating with a high-precision optical clock (precision better than 10 -18 order of magnitude) and a high-precision optical fiber frequency transfer method to compare the frequencies of the two clocks can meet the precision requirements for determining the altitude datum with centimeter-level precision across the country, significantly improve the low precision problem in remote areas of the current national altitude datum, and provide new ideas for the application of high-precision quantum precision measurement in geodesy.

[0050] As an implementation method, the altitude transfer between any level point and the level origin is realized by using the optical clock-fiber time-frequency comparison method of the present invention. The distribution diagram of the optical clock-fiber time-frequency transfer network of some stations is as Figure 3 shown.

[0051] In this implementation method, high-precision optical clocks are set at any altitude control point and the level origin, and the optical clocks between the two places are connected by optical fibers to carry out high-precision time-frequency transfer to collect data for measuring the gravity potential, and collect the time-frequency comparison data of the optical clocks at the two places.

[0052] To achieve the application goal, a method of using high-precision fiber optic time-frequency comparison to measure the gravity potential difference and altitude difference is adopted to carry out time-frequency transfer between two places, and the observed values are calculated to obtain the gravity potential difference of any ground site relative to the national elevation reference point, calculate the altitude difference between the two places, and realize the elevation transfer of the elevation of the leveling origin and any site.

[0053] The data acquisition process includes the following steps: a. Atomic clock setting: The atomic clocks at the leveling origin and any site are high-precision optical clocks, with a long-term stability better than 10 -18 magnitude, and femtosecond optical frequency combs are equipped at different sites to perform up-conversion and down-conversion of frequencies.

[0054] b. Data acquisition: Set any site and the elevation reference point to be connected by a fiber optic network, and configure data recording parameters such as sampling frequency and data format on the data acquisition device. Start the data acquisition program, and the system will record the time-frequency comparison data from the remote optical clock and the local optical clock in real time.

[0055] c. Data download: Use the local storage device to record the collected data, preprocess the original data, and screen out the unqualified data.

[0056] d. Data processing: Use the relevant models of optical clock-fiber optic time-frequency comparison to measure the gravity potential and altitude, calculate the gravity potential and altitude of any two ground sites, and establish the national elevation system. The elevation transfer can be realized in a small area using this method, and then compared with the elevation measured by the traditional method to analyze the accuracy of the method of the present invention.

[0057] By using the method of optical clock-fiber optic time-frequency comparison to measure the gravity potential and altitude, the following effects can be achieved: 1. Realize the measurement of high-precision gravity potential difference and altitude difference: It is possible to measure the gravity potential difference and altitude difference between any ground site and the national elevation reference point at the centimeter-level accuracy. This method has no transfer link and has high accuracy.

[0058] 2. Provide a new method for the construction of the national elevation benchmark: Realize the measurement of the altitude of any point without leveling measurement, and solve the defect that it is difficult to achieve cross-sea measurement in traditional elevation measurement, realize large-range and long-distance elevation transfer, and provide a new method for establishing the national elevation benchmark at the centimeter-level accuracy.

[0059] In summary, the present invention discloses a method for establishing a national elevation benchmark using an optical clock-fiber optic time-frequency transfer network. This method is mainly based on the principle of general relativity. By constructing a high-precision fiber optic time-frequency signal comparison link, using high-precision optical clocks (with an accuracy better than 10 -18(in the order of magnitude), achieve high-precision time-frequency comparison between different geographical locations, measure the gravity potential difference and height difference between two locations, and achieve remote high-precision elevation transfer. Specifically, it includes: First, using an optical clock as the main measurement tool, connect the optical clocks at elevation control points through a stable optical fiber network. Then, use a femtosecond optical frequency comb to perform down-conversion and up-conversion on the optical clock frequency signal to achieve conversion between different frequency signals. Utilize the high-precision frequency signal generated by the optical clock to perform remote optical fiber frequency comparison, determine the gravitational frequency shift caused by the difference in gravity potential at different observation stations, and combine the relevant theories of general relativity to measure the gravity potential difference and elevation difference between remote measurement stations, and apply the optical fiber frequency transfer technology to the measurement of gravity potential and altitude. When the remote optical clock frequency signal propagates in the optical fiber, due to the long distance, a signal amplification device needs to be set according to the signal attenuation degree, and the frequency shift caused by multi-source errors such as temperature, humidity, and pressure needs to be considered. A two-way differential signal needs to be established to eliminate the environmental impact, accurately extract the gravitational frequency shift signal, and obtain the gravity potential difference between the remote sites. Combine the theory of physical geodesy to establish a conversion model between gravity potential and altitude and achieve the conversion, determine the height difference between different measurement stations and reference points, and achieve elevation transfer. Finally, combine geodetic technology and data processing algorithms to achieve the unification and real-time update of the national elevation benchmark. The present invention combines optical clock frequency measurement technology, femtosecond optical frequency comb frequency conversion technology, optical fiber frequency transfer technology, and the measurement of gravity potential and altitude, and has the characteristics of high precision, high reliability, and real-time performance. It can overcome the defects of low efficiency, error accumulation, and poor accuracy in traditional altitude measurement, achieve the unification of the national elevation benchmark at the centimeter-level accuracy, and can be widely applied to fields such as geographic information systems, aerospace, marine surveys, and national infrastructure construction, providing a new technical solution and system support for the establishment and maintenance of the national elevation benchmark.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network, characterized in that, Including: Select multiple observation stations and configure an optical clock for each station; Construct an optical clock - optical fiber time - frequency transfer network to connect the optical clock fibers of each observation station; According to the constructed optical clock - optical fiber time - frequency transfer network, perform signal pair - transmission between remote observation stations, use the frequency signal generated by the optical clock to perform remote optical fiber frequency comparison, and extract the gravitational frequency shift caused by the difference in gravitational potential at different observation stations; According to the extracted gravitational frequency shift, obtain the gravitational potential difference and elevation difference between each observation station; According to the elevation data of each observation station, form a unified national elevation datum.

2. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 1, wherein The method further includes: Establish a fiber - optic time - frequency comparison model for two - way frequency transmission, use the connected optical clock to provide a reference frequency, frequency - convert the optical clock signal using a femtosecond optical frequency comb, perform frequency comparison on the frequency signal transmitted to the far - end at one end, measure the frequency difference between each station, and extract the gravitational frequency shift.

3. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 2, characterized in that, For two observation stations with signal pair - transmission, the method further includes: The optical clock of one of the observation stations emits a frequency reference, the frequency reference is up - converted by a femtosecond optical frequency comb and then transmitted to the optical fiber using an optical fiber laser, and after transmission through the optical fiber, it reaches the other observation station. The optical clock of the other observation station generates a local frequency reference, and a beat frequency is generated through the femtosecond optical frequency comb and the optical fiber laser. The beat frequency is beat - frequency with the frequency transmitted through the optical fiber to obtain the frequency difference between the two observation stations.

4. The method for establishing a national elevation datum using an optical clock-fiber time-frequency transfer network according to claim 1, characterized in that, According to the extracted gravitational frequency shift, obtaining the gravitational potential difference and elevation difference between each observation station includes: By comparing the time - frequency signals generated by different observation stations, measure the gravitational potential difference of each observation point; Use the relationship between gravitational potential and altitude to establish a conversion model between gravitational potential and altitude to realize the conversion between gravitational potential difference and elevation difference.

5. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 1, characterized in that The method further includes: Detect the state of the optical clock - optical fiber time - frequency transfer network and the operating state of the optical clock, and perform real - time calculation on the optical clock - optical fiber frequency comparison data.

6. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 1, characterized in that The method further includes: Set the national level benchmark point as one of the observation stations and set an optical clock. The optical clocks of different observation stations are connected through the optical clock - optical fiber time - frequency transfer network; Perform joint measurement on different observation stations and the national level benchmark point to obtain the gravitational potential difference and elevation difference between the level benchmark point and each observation station, and realize the construction of the elevation datum across the country.

7. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 1, wherein The method further includes: Select an optical clock with a precision better than 10 -18 orders of magnitude as the time reference.

8. The method for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 1, wherein The method further includes: Based on the gravitational potential difference data between different stations measured by the optical clock - optical fiber comparison, combined with the conversion relationship between gravitational potential and altitude, calibrate the elevation of each observation station; Use the gravitational potential and elevation measured by traditional elevation measurement methods to evaluate the accuracy of the gravitational potential and elevation measured by the optical clock - optical fiber time - frequency transfer network.

9. A system for establishing a national elevation datum using an optical clock-fiber time-frequency transfer network, characterized in that, Including: Optical clocks, configured as time references at each observation station; An optical clock - optical fiber time - frequency transfer network, used to connect the optical clock fibers of each observation station; A data processing unit, which, according to the constructed optical clock-fiber time-frequency transfer network, when signals are transmitted in pairs between remote observation sites, uses the frequency signal generated by the optical clock to perform remote fiber frequency comparison, extracts the gravity frequency shift caused by the difference in gravity potential at different observation sites, obtains the gravity potential difference and elevation difference between each observation site according to the extracted gravity frequency shift, and forms a unified national elevation datum according to the elevation data of each observation site.

10. The system for establishing a national elevation datum by using an optical clock-fiber time-frequency transfer network according to claim 9, wherein The system further includes: A real-time monitoring module, which is used to detect the state of the optical clock-fiber time-frequency transfer network and the operating state of the optical clock, and perform real-time calculation on the optical clock-fiber frequency comparison data.

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