Method and system for transmitting unified global elevation reference by using no-load time-frequency signal

Abstract

The invention discloses a method and a system for transmitting a unified global elevation reference by using a no-load time-frequency signal. The method comprises the following steps: acquiring a time-frequency observation value transmitted based on the no-load time-frequency signal; calculating the gravity potential difference of the two ground stations based on the transmitted time-frequency observation values; according to the gravitational potential difference and the altitude conversion model, the altitude of the ground station to be measured on the regional geoid is obtained; according to the elevation conversion relation between the regional geoid and the globally unified elevation datum plane, the altitude on the regional geoid is converted to the globally unified elevation datum plane. According to the method, the defects of high cost, low efficiency and poor precision of traditional altitude measurement can be overcome, cross-sea elevation measurement is realized, global elevation datum unification is realized at centimeter-level precision, an elevation datum unification principle is combined with a time-frequency transmission technology, and a brand-new research method is provided for realizing global elevation datum unification.

Description

Technical Field

[0001] The present invention belongs to the fields of geodesy, geophysics and time-frequency science, and particularly relates to a method for transmitting a unified global elevation benchmark using high-precision time-frequency signals, specifically a method and system for transmitting a unified global elevation benchmark using unloaded time-frequency signals. Background Art

[0002] The elevation of ground points is the vertical spatial position information necessary for all geographic information products and engineering construction. Its datum is the geoid. The determination of elevation and the unification of global elevation datum are closely related to the gravity field, that is, the elevation of ground points can be determined by measuring the gravity potential difference between a ground point and a datum point on the mean sea level. The International Association of Geodesy regards the realization of high-precision determination of the global geoid and the unification of the global elevation datum as the strategic goal of the geodetic field in this century. To this end, many scholars at home and abroad have been committed to combining multiple technologies to achieve the unification of global elevation datums and improve the accuracy of geoid measurement. At present, the traditional method of measuring gravity potential and elevation is time-consuming and labor-intensive. With the increase of survey lines, the cumulative error increases. It is difficult to measure in areas with large gravity changes such as mountainous areas, and it is difficult to achieve the unification of global elevation datums. The reason is that the mean sea level is not a gravity potential equipotential surface (geoid). There is a gravity potential difference between countries or regions across the sea, and it is difficult to conduct cross-sea joint measurement through traditional methods. The high-precision gravity field model only has a resolution of 5′×5′, providing an average result rather than the specific value of the point; although satellite gravity detection technology can restore a relatively high-precision global gravity potential field, the resolution is generally low (about 1°×1°). Therefore, in order to solve the above problems, the method of using high-precision airborne time-frequency signals to transmit a unified global elevation benchmark has been widely studied, providing geodesists with a new research idea.

[0003] The unified global altitude benchmark using time-frequency transfer is a practical application of the principle of general relativity. It mainly achieves gravity potential measurement by comparing the time-frequency signals emitted by a local high-precision optical clock with those emitted by a remote optical clock. Then, the altitude is finally measured using a conversion model of gravity potential and altitude. For a long time, the technology of measuring gravity potential and altitude using time-frequency transfer has been limited by the accuracy of atomic clocks and has been difficult to apply in practice. In recent years, with the maturity of clock manufacturing technology, the world has successfully developed a 10-meter high-precision clock. -19 The precision of the portable optical clock has reached 10 -18This provides hardware support for the use of time-frequency comparison to unify the global elevation benchmark. When using time-frequency signal transmission to implement the unification of the global elevation benchmark, it is first necessary to use high-precision time-frequency transmission technology to measure the gravity potential of ground stations, then study the relationship between gravity potential and altitude, and realize the conversion of gravity potential and altitude in the entire region. Finally, study the relationship between the regional geoid and the globally unified geoid, and realize the conversion between different level surfaces and the unification of the global elevation benchmark. Therefore, how to perform high-precision conversion of gravity potential and altitude, realize the mutual conversion of different elevation systems and the unification of the global elevation benchmark has become an urgent problem to be solved. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a method and system for transmitting a unified global elevation benchmark using an unloaded time-frequency signal, which has an accuracy better than 10 -18 The optical clock of the same magnitude is used as a measuring device. It connects the optical clocks on the ground and in the space carrier (satellite or space station) through the space time-frequency link to perform high-precision time-frequency comparison, accurately extract the gravity potential frequency shift signal, and determine the gravity potential difference between ground stations. Then, the conversion model of gravity potential difference and altitude is used to realize the conversion between gravity potential difference and altitude. Further, through the conversion relationship between different elevation benchmarks, the conversion between elevation benchmarks is realized, and finally the research goal of unifying the elevation benchmark is achieved.

[0005] According to one aspect of the present invention, a method for transmitting a unified global elevation reference using an unloaded time-frequency signal is provided, comprising:

[0006] Obtaining time-frequency observation values ​​based on no-load time-frequency signal transmission;

[0007] Based on the transferred time-frequency observations, the gravity potential difference between the two ground stations is calculated;

[0008] According to the conversion model of gravity potential difference and altitude, the altitude of the ground station to be measured on the regional geoid is obtained;

[0009] According to the elevation conversion relationship between the regional geoid and the global unified elevation datum, the altitude on the regional geoid is converted to the global unified elevation datum.

[0010] As a further technical solution, the method further includes:

[0011] High-precision optical clocks are deployed in the space station and ground station to provide time and frequency references;

[0012] The space time and frequency transfer link is used to connect the time and frequency comparison of the optical clocks of the space station and the ground station.

[0013] As a further technical solution, the gravity potential difference between the two ground stations is calculated based on the transmitted time-frequency observation values, including: using the observation values ​​of the high-precision optical clocks of the space station and the ground station to perform a space-to-ground optical clock time-frequency comparison to obtain the gravity potential of any ground station; and obtaining the gravity potential difference between the known ground station and the ground station to be measured based on the gravity potential of the two.

[0014] As a further technical solution, the gravity potential difference between the two ground stations is calculated based on the transmitted time-frequency observation values, including: using the observation values ​​of high-precision optical clocks of the space station and the ground station to perform ground-space-ground optical clock time-frequency comparison to obtain the gravity potential difference between the known ground station and the ground station to be measured.

[0015] As a further technical solution, the conversion model of gravity potential difference and altitude is:

[0016]

[0017] Where, ΔW PQ represents the gravity potential difference between the two places, H P It means that the altitude of the known ground station P is high. represents the average gravity value of the ground station Q to be measured, represents the average gravity of a known ground station P, and R represents the radius of the earth.

[0018] As a further technical solution, when it is known that the ground station P is located on the geoid, the altitude of any point i to be measured is:

[0019]

[0020] Among them, C i is the number of digits of the Earth at point i, is the average gravity at point i.

[0021] As a further technical solution, the elevation conversion relationship between the regional geoid and the global unified elevation datum is:

[0022]

[0023] in, represents the gravity potential of the regional geoid, W0 represents the gravity potential of the global unified elevation datum, It represents the average gravity from the regional geoid to the global geoid at point P. Indicates the altitude of the ground station P to be measured on the regional geoid, H P It indicates that the altitude of the ground station P to be tested is high on the global unified elevation reference surface.

[0024] According to one aspect of the present invention, there is provided a system for transmitting a unified global elevation reference using an unloaded time-frequency signal, comprising:

[0025] The first main module is used to obtain time-frequency observation values ​​based on the transmission of the no-load time-frequency signal;

[0026] The second main module is used to calculate the gravity potential difference between the two ground stations based on the transmitted time-frequency observations;

[0027] The third main module is used to obtain the altitude of the ground station to be tested on the regional geoid according to the conversion model of gravity potential difference and altitude;

[0028] The fourth main module is used to convert the altitude on the regional geoid to the global unified elevation datum based on the elevation conversion relationship between the regional geoid and the global unified elevation datum.

[0029] According to one aspect of the invention specification, there is provided a ground station device, comprising a high-precision clock, a memory and a processor, wherein the high-precision clock is used to provide a frequency reference and a time reference for the ground station, and the memory is used to store a computer program. When the processor runs the computer program stored in the memory, the processor executes the method of transmitting a unified global elevation reference using an unloaded time-frequency signal.

[0030] According to one aspect of the present specification, a non-transitory computer-readable storage medium is provided, wherein the non-transitory computer-readable storage medium stores computer instructions, wherein the computer instructions enable the computer to execute the method of transmitting a unified global elevation reference using an unloaded time-frequency signal.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention proposes a method for transmitting a unified global elevation benchmark using high-precision airborne time and frequency signals. By using high-precision satellite (space) optical clocks and adopting high-precision time and frequency signal comparison, cross-sea elevation measurement and measurement of gravity potential difference between two places can be achieved.

[0033] (2) The high-order model for conversion between gravity potential difference and altitude proposed in the present invention can significantly improve the conversion accuracy between gravity potential and altitude in high-altitude areas with significant altitude differences.

[0034] (3) The present invention can realize the conversion between different elevation datums by establishing a conversion model between the regional geoid and the global unified geoid, and finally achieve the research goal of global elevation datum unification. It provides a new idea for realizing global elevation datum unification with centimeter-level accuracy, and can provide technical support and innovative solutions for future gravity potential measurement and elevation datum unification. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings used in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A schematic flow chart of a method for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in an embodiment of the present invention.

[0037] Figure 2 A schematic diagram of the principle of measuring gravity potential and altitude using time-frequency comparison of an unloaded optical clock provided in an embodiment of the present invention.

[0038] Figure 3 A schematic diagram of the principle of realizing the measurement of gravity potential and altitude between ground cross-sea sites and the unification of global elevation benchmarks through satellites provided in an embodiment of the present invention.

[0039] Figure 4 A schematic diagram of the structure of a system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The unified global altitude benchmark using time-frequency transfer is a practical application of the principle of general relativity. It mainly achieves gravity potential measurement by comparing the time-frequency signals emitted by a local high-precision optical clock with those emitted by a remote optical clock. Then, the altitude is finally measured using a conversion model of gravity potential and altitude. For a long time, the technology of measuring gravity potential and altitude using time-frequency transfer has been limited by the accuracy of atomic clocks and has been difficult to apply in practice. In recent years, with the maturity of clock manufacturing technology, the world has successfully developed a 10-meter high-precision clock. -19 The precision of the portable optical clock has reached 10 -18 This provides hardware support for the use of time-frequency comparison to unify the global elevation benchmark. When using time-frequency signal transmission to implement the unification of the global elevation benchmark, it is first necessary to use high-precision time-frequency transmission technology to measure the gravity potential of ground stations, then study the relationship between gravity potential and altitude, and realize the conversion of gravity potential and altitude in the entire region. Finally, study the relationship between the regional geoid and the globally unified geoid, and realize the conversion between different level surfaces and the unification of the global elevation benchmark. Therefore, how to perform high-precision conversion of gravity potential and altitude, realize the mutual conversion of different elevation systems and the unification of the global elevation benchmark has become an urgent problem to be solved.

[0041] Using an airborne carrier equipped with a high-precision optical clock as a medium, the transmission of the gravity potential and altitude between two points on the ground through time and frequency comparison has become a hot topic for domestic and foreign scholars. Using a satellite-borne clock for time and frequency comparison requires the use of microwave or laser links to link the clocks at two locations. This method can directly measure the gravity potential difference between the two locations, avoiding the error accumulation in the measurement process of traditional methods; this method requires the atomic clock in the air and the atomic clock at the ground station to have an accuracy of 10 -18 The transmission accuracy of the time-frequency link reaches the measurement accuracy of the atomic clock. At the same time, to achieve the global elevation benchmark unification at the centimeter level, it is necessary to build a gravity potential and altitude conversion model applicable to all terrains. Therefore, how to accurately measure the gravity potential and realize the conversion between gravity potential and altitude has become the key to the unification of the global elevation benchmark.

[0042] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions, for example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to the steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0043] In order to make the purpose, 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, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention are arbitrarily combined with each other to form a new technical solution. This combination is not restricted by the sequence of steps and / or the structural composition mode, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that this combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] The embodiment of the present invention provides a method for transmitting a unified global elevation reference using an unloaded time-frequency signal, such as Figure 1 As shown, it includes: obtaining time-frequency observation values ​​based on the transmission of unloaded time-frequency signals; calculating the gravity potential difference between two ground stations based on the transmitted time-frequency observation values; obtaining the altitude of the ground station to be measured on the regional geoid according to the conversion model of gravity potential difference and altitude; converting the altitude on the regional geoid to the global unified altitude datum according to the altitude conversion relationship between the regional geoid and the global unified altitude datum.

[0045] In the embodiment of the present invention, two ground stations are set up across the sea or across continents, and the altitude of each station relative to the local reference geoid is a known value. The two points are connected by a time-frequency satellite or a space station, and the data collection work of high-precision time-frequency transmission and measurement of gravity potential is carried out to collect time-frequency comparison data.

[0046] like Figure 2 As shown in the figure, A represents a space station or satellite, B represents an arbitrary ground point, C represents a point on the quasi-geoid, D represents a point on the geoid, and E represents a point on the reference ellipsoid. The gravity potential of any measuring station is measured by a satellite or a space station, and then the altitude of any station relative to the reference surface is obtained by comparing the clocks on any reference surface. Through the conversion relationship between different reference surfaces or elevation systems, the elevation conversion between different elevation systems and between reference surfaces is realized, and finally the elevation benchmark is unified.

[0047] In order to achieve the application goal, the embodiment of the present invention uses a high-precision time-frequency transfer method to determine the gravity potential and altitude to carry out earth-satellite (air)-earth time-frequency transfer, and calculates the observation values ​​to obtain the altitude of the ground station relative to the local elevation reference, and then uses the conversion relationship between the regional geoid and the global unified geoid proposed in the embodiment of the present invention to convert the altitude of the regional geoid to the altitude on the global unified geoid, thereby realizing the unification of the global elevation reference.

[0048] like Figure 3 As shown in the figure, S represents the Chinese space station or satellite, P and Q represent two ground stations across the sea, and the two stations are connected through a satellite or a space station. When the two ground stations can observe the same time-frequency satellite at the same time, the gravity potential difference between points P and Q is obtained by differentiating the time-frequency signals of the two measuring stations, and then the conversion model mentioned in the embodiment of the present invention is used to convert the gravity potential and the altitude. The relationship between the local reference geoid of P and Q and the globally unified geoid is used to convert the reference surface, and finally the unification of the elevation benchmark of the two places across the sea is realized.

[0049] In the embodiment of the present invention, the data collection process includes the following steps:

[0050] a. Atomic clock settings: The atomic clocks on the ground and in space are high-precision optical clocks with a long-term stability of 10 -18 Magnitude.

[0051] b. Data collection: Setting up cross-sea or cross-continental ground stations can simultaneously observe the same time-frequency satellite or space station, and continuously collect and record the satellite (space)-ground time-frequency comparison data.

[0052] c. Data download: Receive data collected by space equipment using broadcast messages sent by space carriers, and download data collected by ground equipment at the same time.

[0053] d. Data processing: Utilize the method of high-precision airborne time-frequency signal transmission to unify the global elevation benchmark, calculate the gravity potential and altitude of any two ground stations, and convert the elevation benchmark to a unified level. The method of the present invention can be used to unify the elevation benchmark in a small area, and then compare it with the elevation measured by the traditional method to analyze the accuracy of the method of the present invention.

[0054] By using high-precision airborne time-frequency signals to transmit a unified global elevation benchmark, the following results can be achieved:

[0055] (1) Realize high-precision conversion between gravity potential and altitude: It is able to convert the gravity potential and altitude of any ground station with centimeter-level accuracy.

[0056] (2) Achieve a unified global elevation benchmark: The altitude of any point can be measured without leveling, and the defect of traditional elevation measurement that it is difficult to achieve cross-sea measurement can be solved. Cross-sea and intercontinental elevation transmission can be achieved, and a unified global elevation benchmark can be achieved at the centimeter-level accuracy level.

[0057] In an embodiment of the present invention, the method for transmitting a unified global elevation reference using a high-precision airborne time-frequency signal further includes the following steps:

[0058] 1) The target station shall establish a ground observation station and be equipped with a long-term stability better than 10 -18 High-precision optical clocks of the order of magnitude provide high-precision and high-stability frequency references and time references for ground stations. Space carriers (satellites or space stations) equipped with optical clocks of equal precision can implement space-ground optical clock time-frequency comparisons, as well as ground-space (satellite)-ground optical clock time-frequency comparisons (such as Figure 2 Assume that the microwave frequency emitted by point A is f A , the microwave frequency received at point B is f B , considering that the relative frequency deviations of the atomic clocks at points A and B are y A and A , then the one-way microwave frequency transmission model in free space is:

[0059]

[0060] In the model is the Doppler frequency shift caused by the mutual motion between the space station and the ground station, is the frequency shift caused by the gravitational potential, and The terms represent the impact of the ionosphere, troposphere and other hardware equipment on the microwave frequency.

[0061] It should be noted that when directly performing air-to-ground comparison, the gravity potential of any ground point can be obtained, and then the gravity potential difference between two ground stations can be calculated based on the gravity potential. When using ground-to-air (satellite)-to-ground optical clock time-frequency comparison, the gravity potential difference between two ground points can be obtained.

[0062] 2) According to the definition of gravity potential, when the gravity potential at the geoid is W0, any point P on the ground (such as Figure 3 ) can be expressed as:

[0063]

[0064] In the formula, H P is the orthometric height at point P (unit: m), is the gravity of point P on the geoid (unit: (m / s 2 )), (R is the radius of the earth), Indicates greater than or equal to When the ground station is located in a flat area, the first-order term is obtained, and when the ground station is located in a mountainous area with a rapid terrain change, the second-order term is obtained.

[0065] Assume that points P and Q are ground stations (such as Figure 2 As shown in the figure, the gravity potential of point P is known. When point Q is located in a mountainous area with a significant elevation difference, the second-order term in equation (2) needs to be considered. The altitude at point Q can be expressed as:

[0066]

[0067] Where, ΔW PQ is the gravity potential difference between the two places. When point P is located on the geoid, H in equation (3) P =H0,W P =W0, then the altitude at any point i is:

[0068]

[0069] Among them, C i is the number of digits of the Earth at point i.

[0070] 3) Use time-frequency transfer technology to accurately obtain the gravity potential of the ground station, and then calculate the station based on the regional geoid The altitude of the area as the reference (H L ). The difference between the regional elevation datum and the global elevation datum at any point P is:

[0071]

[0072] in, is the average gravity of the regional geoid to the global geoid at point P. Then the regional altitude to the global benchmark altitude is converted to:

[0073]

[0074] By using equations (5) and (6), the regional altitude can be converted to the global unified geoid datum, thus achieving the unification of the global elevation datum.

[0075] The method of using high-precision airborne time-frequency signals to transmit a unified global elevation benchmark can effectively connect two ground points across the sea or across continents, and realize the measurement of gravity potential difference between the two places (or between the air (star) and the ground). Through the conversion model of high-order gravity potential and altitude, it can realize the conversion of centimeter-level accuracy in mountainous areas with obvious elevation changes. Through the conversion model between the regional and global unified geoid, it can eventually realize the unification of global elevation benchmarks. It has the advantages of high precision, high stability, and cross-sea operation, and can overcome the disadvantages of low efficiency, high cost, and poor accuracy of traditional gravity potential and altitude measurement. When the stability of the high-precision atomic clock used for measurement reaches 10 -18 At this level, it can meet the centimeter-level accuracy to unify the global elevation benchmark, greatly improving the efficiency of high-altitude measurements and providing a guarantee for geodesy to enter the time-frequency quantum era.

[0076] The method of unifying the global elevation datum by using time-frequency transmission proposed in the present invention has the following advantages:

[0077] The measuring tool of the present invention is selected with a long-term stability better than 10 -18 The optical clocks of the order of magnitude provide a high-precision time and frequency reference for the determination of gravity potential and altitude. The time and frequency comparison of the optical clocks in the two places is connected through a space time and frequency transmission link, and the gravity potential difference between the two places is measured through the ground-space (satellite)-ground time and frequency link. In actual measurements, since the clocks between the two places are connected through a space time and frequency link, cross-sea altitude transmission can be achieved.

[0078] The present invention expands the conversion formula of gravity potential difference and height difference to quadratic terms. Compared with the traditional conversion model, it can effectively improve the altitude measurement accuracy in mountainous areas where the height difference changes rapidly. It solves the problem of how to achieve high-precision conversion of gravity potential difference and height difference between two places after obtaining high-precision gravity potential difference measurement results using time-frequency transfer technology.

[0079] The present invention can directly measure the gravity potential difference between two places through time-frequency comparison, and then construct a conversion model between the regional elevation benchmark and the global unified elevation benchmark according to the relationship between different regional elevation benchmarks, so as to realize the conversion between different elevation benchmarks and realize the unification of elevation benchmarks across seas and continents.

[0080] The implementation basis of each embodiment of the present invention is to implement programmed processing through a device with a processor function. Therefore, in engineering practice, the technical solutions and functions of each embodiment of the present invention are encapsulated into various modules. Based on this reality, on the basis of the above embodiments, an embodiment of the present invention provides a system for transmitting a unified global elevation reference using an unloaded time-frequency signal, and the system is used to execute the method for transmitting a unified global elevation reference using an unloaded time-frequency signal in the above method embodiment.

[0081] See also Figure 4 The system includes: a first main module, used to obtain time-frequency observation values ​​based on the transmission of unloaded time-frequency signals; a second main module, used to calculate the gravity potential difference between two ground stations based on the transmitted time-frequency observation values; a third main module, used to obtain the altitude of the ground station to be measured on the regional geoid according to the conversion model of gravity potential difference and altitude; a fourth main module, used to convert the altitude on the regional geoid to the global unified elevation reference surface according to the elevation conversion relationship between the regional geoid and the global unified elevation reference surface.

[0082] It should be noted that the system embodiment provided by the present invention is used to implement the methods in the above method embodiment as well as the methods in other method embodiments provided by the present invention. The only difference is that the corresponding functional modules are set. The principle is basically the same as the principle of the above system embodiment provided by the present invention. As long as the technical personnel in this field refer to the specific technical solutions in other method embodiments on the basis of the above system embodiment, obtain the corresponding technical means and the technical solutions composed of these technical means by combining the technical features, and on the premise of ensuring the practicality of the technical solutions, improve the modules in the above system embodiment to obtain the corresponding system class embodiments, which are used to implement the methods in other method class embodiments. For example:

[0083] Based on the content of the above system embodiment, as a preferred embodiment, in the system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in the embodiment of the present invention, the second main module is further used to execute the following instructions:

[0084] Using the observation values ​​of high-precision optical clocks in the space station and the ground station, a time-frequency comparison of the space-ground optical clocks is performed to obtain the gravity potential of any ground station; based on the gravity potential of the known ground station and the ground station to be measured, the gravity potential difference between the two is obtained.

[0085] Based on the content of the above system embodiment, as a preferred embodiment, in the system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in the embodiment of the present invention, the second main module is further used to execute the following instructions:

[0086] Using the observation values ​​of high-precision optical clocks in the space station and the ground station, a time-frequency comparison of the ground-space-ground optical clocks is performed to obtain the gravity potential difference between the known ground station and the ground station to be measured.

[0087] Based on the contents of the above system embodiment, as a preferred embodiment, the system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in the embodiment of the present invention, the conversion model between the gravity potential difference and the altitude is:

[0088]

[0089] Where, ΔW PQ represents the gravity potential difference between the two places, H P It means that the altitude of the known ground station P is high. represents the average gravity value of the ground station Q to be measured, represents the average gravity of a known ground station P, and R represents the radius of the earth.

[0090] Based on the contents of the above system embodiment, as a preferred embodiment, the system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in the embodiment of the present invention, when it is known that the ground station P is located on the geoid, the altitude of any measured point i is:

[0091]

[0092] Among them, C i is the number of digits of the Earth at point i, is the average gravity at point i.

[0093] Based on the content of the above system embodiment, as a preferred embodiment, the system for transmitting a unified global elevation reference using an unloaded time-frequency signal provided in the embodiment of the present invention, the elevation conversion relationship between the regional geoid and the global unified elevation reference is:

[0094]

[0095] in, represents the gravity potential of the regional geoid, W0 represents the gravity potential of the global unified elevation datum, It represents the average gravity from the regional geoid to the global geoid at point P. Indicates the altitude of the ground station P to be measured on the regional geoid, H P It indicates that the altitude of the ground station P to be tested is high on the global unified elevation reference surface.

[0096] An embodiment of the present invention also provides a ground station device, including a high-precision clock, a memory and a processor, wherein the high-precision clock is used to provide frequency reference and time reference for the ground station, and the memory is used to store computer programs. When the processor runs the computer program stored in the memory, the processor executes the method of transmitting a unified global elevation reference using an unloaded time-frequency signal.

[0097] The memory is connected to the processor, the memory may be a flash memory or a read-only memory or other memory, and the processor may be a central processing unit or a single-chip microcomputer.

[0098] In addition, an embodiment of the present disclosure further provides a computer-readable storage medium, on which a computer program is stored, and the computer program is executed by a processor to perform the above-mentioned various possible methods.

[0099] The computer-readable storage medium includes volatile or non-volatile, removable or non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, computer program modules or other data). Computer-readable storage media include, but are not limited to, RAM (Random Access Memory), ROM (Read-Only Memory), EEPROM (Electrically Erasable Programmable read only memory), flash memory or other memory technology, CD-ROM (Compact Disc Read-Only Memory), Digital Versatile Disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer.

[0100] In summary, the present invention relates to a method for unifying the global elevation benchmark by using high-precision airborne time-frequency signal transmission. The method uses an airborne (satellite) high-performance optical clock to measure the gravity potential of ground stations by means of time-frequency transmission, establishes a high-precision gravity potential and altitude conversion model, converts the gravity potential of any point to the global unified geoid, and realizes the unification of the global elevation benchmark.

[0101] The present invention uses a high-precision optical clock carried on a satellite or space station to achieve time and frequency comparison with an optical clock of a ground station through an air-to-ground link. Since the method does not require laying optical fibers (cables), it is not limited by terrain conditions and can achieve cross-sea elevation transmission.

[0102] There are three key technical nodes in the method of the present invention: First, to achieve time-frequency transmission at the centimeter-level accuracy, high-precision optical clocks need to be set up at different locations, and the accuracy of the optical clocks needs to reach 10 -18 Order of magnitude; secondly, it is necessary to build a conversion model of gravity potential and altitude for the entire region, and the model accuracy must meet the centimeter-level accuracy requirements; finally, it is necessary to build a unified global elevation datum model to realize the conversion of elevations on any elevation datum at different points to a globally unified elevation datum, thereby achieving global elevation datum unification.

[0103] The method of the invention can overcome the defects of traditional altitude measurement, such as high cost, low efficiency and poor accuracy, realize cross-sea elevation measurement, achieve global elevation benchmark unification with centimeter-level accuracy, and combine the elevation benchmark unification principle with time-frequency transfer technology, providing a new research method for achieving global elevation benchmark unification.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A method for transmitting a unified global elevation datum using an unloaded time-frequency signal, characterized in that: include: Obtaining time-frequency observation values ​​based on no-load time-frequency signal transmission; Based on the transferred time-frequency observations, the gravity potential difference between the two ground stations is calculated; According to the conversion model of gravity potential difference and altitude, the altitude of the ground station to be measured on the regional geoid is obtained; According to the elevation conversion relationship between the regional geoid and the global unified elevation datum, the altitude on the regional geoid is converted to the global unified elevation datum.

2. The method for transmitting a unified global elevation reference using an unloaded time-frequency signal according to claim 1, characterized in that: The method further comprises: High-precision optical clocks are deployed in the space station and ground station to provide time and frequency references; The space time and frequency transfer link is used to connect the time and frequency comparison of the optical clocks of the space station and the ground station.

3. The method for transmitting a unified global elevation reference using an unloaded time-frequency signal according to claim 2, characterized in that: Based on the transmitted time-frequency observation values, the gravity potential difference between the two ground stations is calculated, including: using the observation values ​​of the high-precision optical clocks of the space station and the ground station to perform space-ground optical clock time-frequency comparison to obtain the gravity potential of any ground station; based on the gravity potential of the known ground station and the ground station to be measured, the gravity potential difference between the two is obtained.

4. The method for transmitting a unified global elevation reference using an unloaded time-frequency signal according to claim 2, characterized in that: Based on the transmitted time-frequency observations, the gravity potential difference between the two ground stations is calculated, including: using the observations of high-precision optical clocks of the space station and the ground station to perform ground-space-ground optical clock time-frequency comparison to obtain the gravity potential difference between the known ground station and the ground station to be measured.

5. The method for transmitting a unified global elevation reference using an unloaded time-frequency signal according to claim 1, characterized in that: The conversion model of gravity potential difference and altitude is: Where, ΔW PQ represents the gravity potential difference between the two places, H P It means that the altitude of the known ground station P is high. represents the average gravity value of the ground station Q to be measured, represents the average gravity of a known ground station P, and R represents the radius of the earth.

6. The method for transmitting a unified global elevation datum using an unloaded time-frequency signal according to claim 5, characterized in that: When it is known that the ground station P is located on the geoid, the altitude of any measured point i is: Among them, C i is the number of digits of the Earth at point i, is the average gravity at point i.

7. The method for transmitting a unified global elevation datum using an unloaded time-frequency signal according to claim 1, characterized in that: The elevation conversion relationship between the regional geoid and the global unified elevation datum is: in, represents the gravity potential of the regional geoid, W0 represents the gravity potential of the global unified elevation datum, It represents the average gravity from the regional geoid to the global geoid at point P. Indicates the altitude of the ground station P to be measured on the regional geoid, H P It indicates that the altitude of the ground station P to be tested is high on the global unified elevation reference surface.

8. A system for transmitting a unified global elevation datum using an unloaded time-frequency signal, characterized in that: include: The first main module is used to obtain time-frequency observation values ​​based on the transmission of the no-load time-frequency signal; The second main module is used to calculate the gravity potential difference between the two ground stations based on the transmitted time-frequency observations; The third main module is used to obtain the altitude of the ground station to be tested on the regional geoid according to the conversion model of gravity potential difference and altitude; The fourth main module is used to convert the altitude on the regional geoid to the global unified elevation datum based on the elevation conversion relationship between the regional geoid and the global unified elevation datum.

9. A ground station device, characterized in that: It includes a high-precision clock, a memory and a processor, wherein the high-precision clock is used to provide a frequency reference and a time reference for a ground station, and the memory is used to store a computer program. When the processor runs the computer program stored in the memory, the processor executes the method for transmitting a unified global elevation reference using an unloaded time-frequency signal as described in any one of claims 1 to 7.

10. A non-transitory computer readable storage medium, characterized in that: The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions enable the computer to execute the method of transmitting a unified global elevation reference using an unloaded time-frequency signal as described in any one of claims 1 to 7.

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