Method and system for measuring geopotential and altitude by using dual-frequency combined frequency transfer in open space

Abstract

The present invention discloses a method and system for measuring the geopotential and altitude by using an air-ground dual-frequency combined frequency transfer. The method includes: obtaining the ground observation values and space observation values of the air-ground microwave signals transmitted by using the air-ground dual-frequency combined microwave frequency transfer model; extracting the gravity frequency shift signal based on the ground observation values and space observation values; calculating the geopotential difference between the air and the ground based on the extracted gravity frequency shift signal, and at the same time, calculating the geopotential of the space vehicle in combination with the gravity field model; determining the geopotential and altitude of any ground station based on the geopotential of the space vehicle and the geopotential difference between the air and the ground. The present invention accurately extracts the gravity frequency shift signal by using the air-ground dual-frequency combined microwave frequency transfer and measures the geopotential and altitude.

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 extracting gravity frequency shift by transmitting and receiving dual-frequency combined microwave frequency signals between air and ground, and accurately determining gravity potential and altitude, and more particularly to a method and system for determining gravity potential and altitude by transmitting and receiving dual-frequency combined frequencies between air and ground. Background Art

[0002] The determination of gravity potential plays a very important role in the field of geodesy, and it is a basic physical field quantity required by disciplines and research fields such as seismology, geodynamics, aerospace, meteorology, oceanography, natural disasters and global change. It is also an important information source indispensable for national defense construction and national economic development. The determination of altitude is closely related to the unification of the global elevation datum and gravity potential, and it is the vertical spatial information necessary for national economic construction. Since the end of the last century, it has become the strategic goal of the International Association of Geodesy to determine the global geoid with an accuracy better than 1 cm and unify the global elevation datum. The traditional method for determining gravity potential needs to be realized by the method of gravity combined leveling, which has defects such as low efficiency and high cost; the high-precision gravity field model only has a resolution of 5′×5′, and provides an average result rather than the specific value of a point; although satellite gravity exploration technology can recover the global gravity potential field with higher precision, the resolution is generally low (about 1°×1°). Therefore, how to quickly and accurately determine the gravity potential and altitude of any site has become the primary problem that geodesists need to solve.

[0003] To solve these problems, a new method for measuring gravity potential using the principle of general relativity has received attention and research. This method mainly relies on the correspondence between the gravity potential difference and the rate difference of the operation of precise clocks, and determines the gravity potential difference between two places by means of time and frequency transfer. In recent years, with the maturity of clock manufacturing technology, clocks with an accuracy of up to 10 -19 orders of magnitude have been successfully developed internationally, and the accuracy of space (satellite)-borne clocks has also reached 10 -18This magnitude provides hardware guarantee for the implementation of measuring the gravity potential using time-frequency signals. However, to perform time-frequency comparison at the precision of an optical clock, corresponding precision time-frequency transfer technology must be adopted to link remote clocks. Therefore, how to perform high-precision remote time-frequency comparison has become an urgent problem to be solved. Using optical fibers or cables to connect atomic clocks at two locations for time-frequency comparison to determine the gravity potential difference is not affected by the external environment and does not generate errors during signal propagation, which can meet the requirements of high-precision time-frequency comparison. However, limited by geographical environment factors and the cost of laying optical fibers or cables, this method is difficult to apply in cases such as long baselines and cross-sea areas. Comparing airborne (spaceborne) optical clocks through microwave links to achieve time and frequency comparison of clocks at two locations has become a research hotspot. Compared with the fiber and cable comparison technology, airborne (spaceborne) atomic clocks have advantages such as all-weather, low cost, and being unrestricted by baseline length, providing a platform for implementing airborne dual-frequency combined microwave frequency signal transfer to measure the gravity potential and altitude globally.

[0004] To determine the gravity potential and altitude at the centimeter-level precision, the precision of the airborne (spaceborne)-ground time-frequency transfer link needs to reach 10 -18 magnitude. In practical applications, it is very difficult to eliminate various errors during signal propagation only through a single microwave link. Therefore, how to eliminate the errors during signal propagation and accurately extract the gravity frequency shift signal has become the key to time-frequency transfer for measuring the gravity potential and altitude. Summary of the Invention

[0005] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a method and system for measuring the gravity potential and altitude by using airborne-ground dual-frequency combined frequency transfer, which accurately extracts the gravity frequency shift signal and measures the gravity potential and altitude by using airborne-ground dual-frequency combined microwave frequency transfer.

[0006] According to one aspect of the specification of the present invention, there is provided a method for measuring the gravity potential and altitude by using airborne-ground dual-frequency combined frequency transfer, including:

[0007] Obtaining the ground observation values and space observation values of the airborne-ground microwave signals transmitted by using the airborne-ground dual-frequency combined microwave frequency transfer model;

[0008] Based on the ground observation values and space observation values, extracting the gravity frequency shift signal;

[0009] Based on the extracted gravity frequency shift signal, calculating the gravity potential difference between the air and the ground, and at the same time, combining the gravity field model, calculating the gravity potential of the space carrier;

[0010] Based on the gravity potential of the space carrier and combining the gravity potential difference between the air and the ground, determining the gravity potential and altitude of any ground station.

[0011] As a further technical solution, before transmitting the space-ground microwave signals by using the space-ground dual-frequency combined microwave frequency transfer model, the method further includes:

[0012] Setting the transmission times of the ground and space microwave signals, and simultaneously determining that the frequencies of the microwave signals transmitted by the uplink and downlink microwave links are the same and the polarization directions are opposite, wherein both the ground station and the space station are equipped with high-precision clocks;

[0013] Simultaneously receiving the microwave signals transmitted by the ground and space.

[0014] As a further technical solution, the method further includes:

[0015] Receiving the observed values collected by the space station equipment by using the broadcast telegrams transmitted by the space vehicle, and simultaneously downloading the observed values collected by the ground station equipment.

[0016] As a further technical solution, the method further includes:

[0017] Constructing a tidal model for eliminating the frequency shift of the microwave signals caused by the tidal effect.

[0018] As a further technical solution, the method further includes:

[0019] Constructing a second-order Doppler frequency shift model for eliminating the frequency shift of the microwave signals caused by the second-order Doppler frequency shift.

[0020] As a further technical solution, after calculating the geopotential of the space vehicle, it further includes:

[0021] Based on the geopotential of the space vehicle and the geopotential difference between the space and the ground, obtaining the geopotential of any ground station;

[0022] Combining the coordinates of the ground station, reducing the geopotential at the ground station to the global geoid, and determining the altitude of the ground station.

[0023] According to one aspect of the specification of the present invention, there is provided a system for measuring the geopotential and altitude by using the space-ground dual-frequency combined frequency transfer, including:

[0024] A first main module for obtaining the ground observed values and space observed values of the space-ground microwave signals transmitted by using the space-ground dual-frequency combined microwave frequency transfer model;

[0025] A second main module for extracting the gravity frequency shift signals based on the ground observed values and space observed values;

[0026] A third main module for calculating the geopotential difference between the space and the ground based on the extracted gravity frequency shift signals, and simultaneously calculating the geopotential of the space vehicle by combining the gravity field model;

[0027] The fourth main module is used to determine the gravity potential and altitude of any ground station based on the gravity potential of the space carrier and in combination with the gravity potential difference between the air and the ground.

[0028] As a further technical solution, the first main module is further used to execute the following instructions:

[0029] Set the transmission times of the ground and space microwave signals, and at the same time determine that the microwave signals transmitted by the uplink and downlink microwave links have the same frequency and opposite polarization directions, where both the ground station and the space station are equipped with high-precision clocks;

[0030] Receive the microwave signals transmitted by the ground and space simultaneously.

[0031] According to one aspect of the specification of the present invention, there is provided a ground station device, including a high-precision clock, a memory, and a processor. The high-precision clock is used to provide a frequency reference and a time reference for the ground station. 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 determining the gravity potential and altitude by air-ground dual-frequency combined frequency transfer.

[0032] According to one aspect of the specification of the present invention, there is provided a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions cause the computer to execute the method for determining the gravity potential and altitude by air-ground dual-frequency combined frequency transfer.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The method for determining the gravity potential and altitude proposed by the present invention is based on a high-precision optical clock, uses a microwave signal link as a bridge to connect the optical clocks between the air (spacecraft) and the ground, performs high-precision microwave frequency transfer, effectively eliminates the frequency shift caused by various errors in the microwave signal propagation process through the air-ground dual-frequency combined microwave frequency transfer model, accurately extracts the gravity frequency shift signal, and then uses the gravity frequency shift equation to obtain the gravity potential difference at the location of the remote clock, and determines the gravity potential and altitude of any ground station. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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 following drawings 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.

[0036] Figure 1 It is a schematic flowchart of the method for determining the gravity potential and altitude by air-ground dual-frequency combined frequency transfer provided by the embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the principle for measuring the geopotential and altitude by airborne and ground dual - frequency combined frequency transfer provided by the embodiments of the present invention.

[0038] Figure 3 This is an application schematic diagram of the airborne and ground dual - frequency combined frequency transfer for measuring the geopotential and altitude provided by the embodiments of the present invention.

[0039] Figure 4 This is a system schematic diagram of the airborne and ground dual - frequency combined frequency transfer for measuring the geopotential and altitude provided by the embodiments of the present invention. Detailed implementation manners

[0040] The present invention utilizes airborne (space - borne) high - performance optical clocks, conducts airborne (space - borne) and ground frequency comparison through microwave links with the same frequency but different polarization directions, implements high - precision microwave frequency transfer, effectively extracts the gravity frequency shift signal, and measures the airborne (space - borne) and ground geopotential difference. The present invention proposes to use microwave links with the same frequency but different polarization directions for the up - link and down - link for frequency transfer. During the propagation of the up - link and down - link microwave links, the first - order Doppler frequency shift, the first - order ionospheric frequency shift, the tropospheric frequency shift, etc. are equal in magnitude and the same in sign. By taking the difference between the up - link and down - link same - frequency links, the influence of related errors can be eliminated. In addition, the present invention also considers the influence of higher - order ionospheric frequency shift, tidal effect, and Shapiro effect. Through error modeling, various errors are effectively eliminated, and the gravity frequency shift signal is extracted at the centimeter - level accuracy to achieve long - distance frequency comparison. According to the principle of general relativity, the geopotential difference between the airborne (space - borne) and the ground is calculated using the gravity frequency shift equation, and then through the gravity field model EGM2008, the geopotential and altitude of the airborne (space - borne) atomic clock are calculated. Combining with the geopotential difference measured by the method of transmitting the dual - frequency combined microwave frequency signal of the airborne platform, the geopotential of any ground station is obtained, and the geopotential at the measurement station is reduced to the global (regional) geoid to determine the altitude of the measurement station.

[0041] 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 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.

[0042] The block diagrams shown in the drawings are only functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices. The flowcharts shown in the drawings are only illustrative and do not necessarily include all contents and operations / steps, nor are they necessarily executed in the described order. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to the actual situation.

[0043] 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 with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. In addition, the technical features in each embodiment or a single 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 mode of structural composition, but must be based on what can be realized by those of ordinary skill in the art. When the combination of technical solutions results in contradictions or cannot be realized, it should be considered that such combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0044] An embodiment of the present invention provides a method for measuring gravity potential and altitude by air-ground dual-frequency combined frequency transfer, as Figure 1 shown, including: obtaining ground observation values and space observation values of air-ground microwave signals transmitted by an air-ground dual-frequency combined microwave frequency transfer model; extracting gravity frequency shift signals based on the ground observation values and space observation values; calculating the gravity potential difference between air and ground based on the extracted gravity frequency shift signals, and at the same time, combining with a gravity field model to calculate the gravity potential of a space carrier; determining the gravity potential and altitude of any ground station based on the gravity potential of the space carrier and the gravity potential difference between air and ground.

[0045] The embodiment of the present invention measures the gravity potential and altitude of any ground point by using a high-precision airborne optical clock. Taking the high-precision optical clock as the basis and using a microwave signal link as a bridge to connect the optical clocks between air (space) and ground for high-precision microwave frequency transfer. The various errors caused by frequency shift during the propagation of microwave signals are effectively eliminated through the air-ground dual-frequency combined microwave frequency transfer model, and the gravity frequency shift signal is accurately extracted. Then, the gravity potential difference at the location of the remote clock is obtained by using the gravity frequency shift equation to determine the gravity potential and altitude of any ground station.

[0046] The principle of measuring the geopotential and altitude using the air-ground dual-frequency combined frequency transfer is as follows Figure 2 As shown in the figure, E represents the position of the ground station, S represents the space station or satellite, the blue line and the red line respectively represent the uplink and downlink microwave links, which are respectively connected to high-precision atomic clocks for high-precision microwave frequency measurement; the frequencies of the microwave signals are f1 and f2 respectively. When applying the present invention, f1 = f2 is set, and the polarization directions are opposite, so that various errors can be eliminated by this method, and the gravity frequency shift signal can be accurately extracted.

[0047] As a preferred embodiment, the embodiment of the present invention sets up ground stations at arbitrary points, takes the geopotential and altitude at the position of this point as the measurement objects for data collection, and gives the three-dimensional coordinates and geopotential of the ground stations.

[0048] In order to achieve the application goal, the embodiment of the present invention uses the method of measuring the geopotential and altitude by using the air-borne dual-frequency combined microwave frequency signal transfer to carry out air-ground microwave frequency transfer, calculates the observed values, and obtains the geopotential and altitude of the ground stations.

[0049] Figure 3 It is the schematic diagram of the example application given by the present invention. In the figure, the space station can perform frequency comparison with ground clocks at any position. Through microwave frequency comparison, the geopotential of any site can be obtained. Combining the geopotential differences of different points to the geoid, the altitude of any ground point can be determined.

[0050] The data collection process includes the following steps:

[0051] a. Atomic clock setting: The atomic clocks on the ground and in space are high-precision optical clocks, and the long-term stability reaches 10 -18 magnitude.

[0052] b. Data collection: Set the emission times of the space and ground microwave signals, and at the same time determine that the frequencies of the emitted microwave signals are the same and the polarization directions are opposite. At the same time, receive the microwave signals emitted by the space and the ground, and collect and record various data.

[0053] c. Data download: Use the broadcast telegrams broadcast by the space vehicle to receive the data collected by the space equipment, and at the same time download the data collected by the ground equipment.

[0054] d. Data processing: Use the method of measuring the geopotential and altitude by using the air-borne dual-frequency combined microwave frequency signal transfer to measure the geopotential, calculate the geopotential of any ground station, and compare it with the measurement results of the traditional method to analyze the accuracy of the method of the present invention.

[0055] Through the method of measuring the geopotential and altitude by using the air-borne dual-frequency combined microwave frequency signal transfer, the following results can be obtained:

[0056] Measuring the geopotential: It is possible to measure the geopotential of any ground station at the centimeter-level accuracy.

[0057] Measuring the altitude: Without leveling measurement, the altitude measurement of any point can be achieved, and the cross-sea height transfer can be realized.

[0058] In the embodiment of the present invention, the microwave frequency signals transmitted simultaneously in the up and down directions by the space (satellite)-borne equipment (the frequencies of the microwave signals are equal, and the polarization directions are opposite) are used. By setting the working frequency point, the up and down microwave frequencies are differentiated, and various errors in the signal propagation process can be effectively eliminated, and the accuracy of extracting the gravity frequency shift signal can be improved. Further, through the ground station equipped with a high-performance optical clock for the space (satellite)-ground microwave frequency comparison, since the measurement accuracy of the optical clock is relatively high, it is necessary to eliminate the influence of the troposphere and ionosphere in the signal propagation process at a higher accuracy level. By setting the microwave link with the same frequency but different polarization directions, the influence of the higher-order ionospheric frequency shift can be effectively eliminated, and the time-frequency transfer accuracy can be improved.

[0059] Specifically as follows:

[0060] 1) A ground observation station is set up at the target measurement station, and a high-precision optical clock is set at the same time to provide a high-precision and high-stability frequency reference and time reference for the ground measurement station. When the optical clock reaches a certain accuracy, how to eliminate various errors in the signal propagation process and accurately extract the gravity frequency shift signal becomes the key point. Assume that the microwave frequency transmitted at point A is f A , and the microwave frequency received at point B is f B . Considering that the relative frequency deviations of the atomic clocks at point A and point B are y A and y B respectively, then the one-way microwave frequency transfer model in free space is:

[0061]

[0062] In the model is the Doppler frequency shift caused by the relative motion between the space station and the ground station, is the frequency shift caused by the geopotential, and terms respectively represent the influence of the ionosphere, troposphere and other hardware devices on the microwave frequency.

[0063] The main errors in the

[0064]

[0065] formula come from the first-order and second-order Doppler frequency shifts: and represent the correction models of the first-order and second-order Doppler frequency shifts, f represents the frequency of the microwave, v I and vJ denote the velocities at points I and J, N IJ denote the unit vector from I to J. According to the above model, when the uplink and downlink have the same frequency, the first-order Doppler frequency shift can be eliminated by uplink and downlink differencing.

[0066] 2) Analyze the influence of the ionosphere and troposphere during the microwave transmission process. When a microwave signal propagates in the atmosphere, the frequency shift caused by the atmospheric influence is divided into ionospheric frequency shift and tropospheric frequency shift. Among them, the ionospheric frequency shift is:

[0067]

[0068] It can be seen from the formula that the magnitudes of the first-order and second-order ionospheric frequency shifts are only related to the frequency of the microwave signal. In addition to being related to the signal frequency, the second-order ionospheric frequency shift is also related to the polarization direction of the microwave signal and the angle between the geomagnetic field and the signal propagation direction. When the uplink and downlink microwave links have the same frequency but different polarization directions, the magnitudes of the first-order, second-order, and third-order ionospheric frequency shifts are equal and have the same sign, and can be eliminated by uplink and downlink differencing.

[0069] The influence of the tropospheric frequency shift is:

[0070]

[0071] In the formula, ΔL d and ΔL w are the dry and wet delay components of the troposphere respectively. It can be seen from formula (5) that the tropospheric frequency shift is independent of the frequency of the microwave signal, and the uplink and downlink differencing at any frequency can eliminate it.

[0072] Optionally, the embodiment of the present invention also eliminates errors based on tidal model correction. By using the high-performance tidal model shown in formula (6), the tidal effects on the space vehicle and the ground station are calculated in real time, and the influence of the tidal effect on the microwave frequency is modeled and analyzed. Through model correction, the frequency shift of the microwave signal caused by the tidal effect is effectively eliminated.

[0073] The tidal potential ΔV(r, φ, λ) at any site can be obtained by spherical harmonic expansion to order N:

[0074]

[0075] where n is the order, m represents the degree, and (r, φ, λ) are the geocentric radius, latitude, and longitude at any point; GM is the gravitational constant of the earth, R e represents the radius of the earth's equator, represents the fully normalized associated Legendre polynomial, represents the spherical harmonic coefficient.

[0076] Optionally, the embodiments of the present invention also eliminate the second-order Doppler frequency shift of the microwave signal based on the model shown in formula (3) to improve the extraction accuracy of the gravity frequency shift signal.

[0077] 3) Set the microwave transmitting devices of the ground station and the space station (satellite). Set the frequencies of the uplink and downlink microwave links to be equal and the polarization directions to be the same. Use the no-load dual-frequency combined microwave frequency signal transmission model to transmit the space (satellite)-ground microwave signal. Use the method of measuring the gravity potential by dual-frequency combined frequency transmission to measure the gravity potential difference between the ground station and the space station. The basic method is as follows:

[0078] Dividing the difference between the uplink and downlink of the same frequency by 2 can effectively eliminate various frequency shifts such as the first-order Doppler frequency shift, ionospheric frequency shift, and tropospheric frequency shift, and extract the gravity frequency shift. The model of the dual-frequency dual-link (dual-frequency combination) combination is:

[0079]

[0080] Among them, f r represents the frequency of the received microwave signal, f Dop2 represents the second-order Doppler frequency shift. The subscripts AB and BA respectively represent the transmission from A to B and the transmission from B to A. Δf other represents the sum of other various errors. Through the microwave links with the same frequency but different polarization directions for the uplink and downlink, the ionospheric frequency shift, tropospheric frequency shift, first-order Doppler frequency shift, etc. can be effectively eliminated.

[0081] 4) Obtain the gravity potential difference between any two positions based on the observation values of the no-load dual-frequency combined microwave frequency signal transmission. Since the main error of the no-load dual-frequency combined microwave frequency signal transmission comes from the clock error of the space (satellite)-borne atomic clock, the accuracy of the atomic clock directly determines the measurement accuracy of the gravity potential and altitude. According to this model, when the accuracy of the atomic clock reaches the order of 10 -18 the gravity potential and altitude can be measured with centimeter-level accuracy.

[0082] The implementation basis of each embodiment of the present invention is achieved through programmed processing by 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 actual situation, on the basis of the above embodiments, the embodiments of the present invention provide a system for measuring the gravity potential and altitude by space-ground dual-frequency combined frequency transmission, which is used to execute the method for measuring the gravity potential and altitude by space-ground dual-frequency combined frequency transmission in the above method embodiments.

[0083] See Figure 4, the device includes: a first main module for obtaining ground and space observation values of the air-ground microwave signal transmitted using the air-ground dual-frequency combined microwave frequency transfer model; a second main module for extracting the gravity frequency shift signal based on the ground and space observation values; a third main module for calculating the gravity potential difference between the air and the ground based on the extracted gravity frequency shift signal, and simultaneously calculating the gravity potential of the space vehicle in combination with the gravity field model; a fourth main module for determining the gravity potential and altitude of any ground station based on the gravity potential of the space vehicle and the gravity potential difference between the air and the ground

[0084] The system for measuring the gravity potential and altitude by transmitting the no-load dual-frequency combined microwave frequency signal provided by the embodiment of the present invention adopts Figure 4 several modules therein, which can effectively eliminate the frequency shifts caused by the ionosphere, troposphere, and Doppler effect, and has the advantages of high precision, high stability, and real-time performance. It can overcome the disadvantages of low efficiency, high cost, and poor accuracy in traditional gravity potential and altitude measurement. When the stability of the high-precision atomic clock used for measurement reaches 10 -18 magnitude, it can meet the application requirements for measuring the gravity potential with centimeter-level accuracy, greatly improving the efficiency of gravity potential measurement and reducing the measurement cost of the gravity potential.

[0085] It should be noted that the system embodiment provided by the present invention, in addition to being used to implement the method in the above method embodiment, is also used to implement the methods in other method embodiments provided by the present invention. The difference is only in setting the corresponding functional modules, and its principle is basically the same as that of the above system embodiment provided by the present invention. As long as those skilled in the art, based on the above system embodiment, refer to the specific technical solutions in other method embodiments, obtain the corresponding technical means by combining technical features, and the technical solutions composed of these technical means, and on the premise of ensuring the practicability of the technical solutions, improve the modules in the above system embodiment to obtain the corresponding system-like embodiments for implementing the methods in other method-like embodiments. For example:

[0086] Based on the content of the above system embodiment, as a preferred embodiment, in the system for measuring the gravity potential and altitude by transmitting the air-ground dual-frequency combined frequency provided by the embodiment of the present invention, the first main module is further used to execute the following instructions:

[0087] Set the emission time of the ground and space microwave signals, and simultaneously determine that the frequencies of the microwave signals transmitted by the uplink and downlink microwave links are the same and the polarization directions are opposite, where both the ground station and the space station are equipped with high-precision clocks;

[0088] Receive the microwave signals transmitted by the ground and space simultaneously.

[0089] An embodiment of the present invention further provides an electronic device, including a memory and a processor. A computer program is stored in the memory. When the processor runs the computer program stored in the memory, the processor executes the above various possible methods.

[0090] Among them, the memory is connected to the processor. The memory can be a flash memory, a read-only memory, or other memories. The processor can be a central processing unit or a single-chip microcomputer.

[0091] In addition, an embodiment of the present disclosure further provides a computer-readable storage medium. A computer program is stored on the computer-readable storage medium. The computer program is executed by the processor to perform the above various possible methods.

[0092] The computer-readable storage medium includes a volatile or non-volatile, removable or non-removable medium implemented in any method or technology for storing information such as computer-readable instructions, data structures, computer program modules, or other data. The computer-readable storage medium includes, but is not limited to, RAM (Random Access Memory), ROM (Read-Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash memory, or other memory technologies, CD-ROM (Compact Disc Read-Only Memory), digital versatile disc (DVD, Digital Video Disc), or other optical disc storage, magnetic cassette, tape, 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.

[0093] In summary of the above embodiments, the method for measuring the gravity potential and altitude by using the no-load dual-frequency combined microwave frequency signal transmission proposed in the present invention has the following advantages:

[0094] (1) Through the high-precision frequency reference of the space (satellite)-borne optical clock and the ground optical clock, the present invention can effectively measure the gravitational frequency shift of the microwave signal caused by the change of the gravity potential. Specifically, using a high-precision optical clock as a tool for measuring frequency can provide a high-precision time and frequency reference, significantly improving the measurement accuracy of the microwave link; and in the process of measuring the gravity potential by using the microwave time-frequency signal transmission, a high-precision time and frequency reference is crucial for accurately measuring the gravity potential.

[0095] (2) The present invention adopts the same-frequency combination of the uplink and downlink for frequency transfer, which can effectively eliminate the first-order Doppler frequency shift. The reason is as follows: In the process of unidirectional microwave frequency transfer, the microwave signal is affected by the Doppler effect and generates Doppler frequency shift. Among them, the influence of the first-order Doppler frequency shift reaches 10 -5 ~10 -6 orders of magnitude. With the current positioning and velocity measurement accuracy, it is very difficult to eliminate this frequency shift through the model.

[0096] (3) When the present invention adopts microwave links with the same frequency but different polarization directions for the uplink and downlink, it can effectively eliminate the tropospheric frequency shift, the first-order ionospheric frequency shift, and the second-order ionospheric frequency shift. The reason is as follows: In the process of microwave signal propagation in the atmosphere, it is affected by the ionosphere and the troposphere. Through research, the frequency shift caused by the troposphere is independent of the frequency of the microwave signal, the frequency shift caused by the ionosphere is related to the frequency of the microwave signal, and the second-order ionospheric frequency shift is also related to the polarization direction of the microwave signal.

[0097] (4) The present invention eliminates the frequency shift caused by the second-order Doppler frequency shift and the tidal effect by adding a second-order Doppler frequency shift model and a tidal correction model, and improves the extraction accuracy of the gravity frequency shift signal.

[0098] (5) The present invention uses the high-precision gravity frequency shift signal to determine the air (satellite)-ground gravity potential difference. Using the existing gravity field model, the gravity potential of the space atomic clock can be accurately determined. Combining the gravity potential lookup data, the gravity potential of the ground point can be obtained. Furthermore, using the conversion relationship between the gravity potential and the altitude, a conversion model for the entire region can be established to determine the altitude of any point.

[0099] In summary, the method for measuring the gravity potential and altitude by using the no-load dual-frequency combined microwave frequency signal transfer proposed by the present invention realizes the high-precision measurement of the microwave signal frequency by using a high-precision optical clock. The proposed dual-frequency combined frequency transfer method can effectively eliminate the errors in the signal propagation process, correct the frequency shift caused by the second-order Doppler frequency shift and the tidal effect, improve the extraction accuracy of the gravity frequency shift signal, and provide a new idea for the high-precision measurement of the gravity potential and altitude. This method can provide important technical support and innovative solutions for the measurement of the gravity potential and altitude.

[0100] 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 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 recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. Method for measuring geopotential and altitude by using dual-frequency combined frequency transfer in open space, characterized in that, Comprising: Obtaining ground observations and space observations of the air-ground microwave signal transmitted using the air-ground dual-frequency combined microwave frequency transfer model; Extracting the gravity frequency shift signal based on the ground observations and space observations; Calculating the gravity potential difference between the air and the ground based on the extracted gravity frequency shift signal, and simultaneously calculating the gravity potential of the space vehicle in combination with the gravity field model; Determining the gravity potential and altitude of any ground station based on the gravity potential of the space vehicle and the gravity potential difference between the air and the ground; The method further comprises: Constructing a second-order Doppler frequency shift model for eliminating the frequency shift of the microwave signal caused by the second-order Doppler frequency shift; ， Represents the correction model for the second-order Doppler shift, Represents the frequency of the microwave, and Represents the velocities at points I and J, Represents the unit vector from I to J; Construct a tidal model to eliminate the frequency shift of microwave signals caused by tidal effects, and the tidal potential at any site is obtained by spherical harmonic expansion to the Nth order. ， where n is the order and m represents the degree, are the geocentric radius, latitude, and longitude at any site; GM is the gravitational constant of the Earth, represents the radius of the Earth's equator, represents the fully normalized associated Legendre polynomial, , represents the spherical harmonic coefficient.

2. The method for measuring the geopotential and altitude by using the airborne dual-frequency combined frequency transfer according to claim 1, wherein Before transmitting the air-ground microwave signal using the air-ground dual-frequency combined microwave frequency transfer model, the method further comprises: Setting the transmission times of the ground and space microwave signals, and simultaneously determining that the microwave signals transmitted by the uplink and downlink microwave links have the same frequency and opposite polarization directions, wherein both the ground station and the space station are equipped with high-precision clocks; Receiving the microwave signals transmitted by the ground and space simultaneously.

3. The method for measuring the geopotential and altitude by combining the dual-frequency transmissions in the airspace according to claim 2, characterized in that The method further comprises: Receiving the observations collected by the space station equipment by using the broadcast message transmitted by the space vehicle, and simultaneously downloading the observations collected by the ground station equipment.

4. The method for measuring the geopotential and altitude by using the dual-frequency combined frequency transfer in open space according to claim 1, characterized in that After calculating the gravity potential of the space vehicle, it further comprises: Obtaining the gravity potential of any ground station based on the gravity potential of the space vehicle and the gravity potential difference between the air and the ground; Combining the coordinates of the ground station, reducing the gravity potential at the ground station to the global geoid, and determining the altitude of the ground station.

5. A system for measuring gravity position and altitude by air-ground dual-frequency combined frequency transmission, used to implement the method described in any one of claims 1 to 4, characterized in that: Comprising: A first main module for obtaining ground observations and space observations of the air-ground microwave signal transmitted using the air-ground dual-frequency combined microwave frequency transfer model; A second main module for extracting the gravity frequency shift signal based on the ground observations and space observations; A third main module for calculating the gravity potential difference between the air and the ground based on the extracted gravity frequency shift signal, and simultaneously calculating the gravity potential of the space vehicle in combination with the gravity field model; A fourth main module for determining the gravity potential and altitude of any ground station based on the gravity potential of the space vehicle and the gravity potential difference between the air and the ground.

6. The system for measuring the gravity potential and altitude by combining dual-frequency transmissions in airspace according to claim 5, characterized in that, The first main module is further configured to execute the following instructions: Setting the transmission times of the ground and space microwave signals, and simultaneously determining that the microwave signals transmitted by the uplink and downlink microwave links have the same frequency and opposite polarization directions, wherein both the ground station and the space station are equipped with high-precision clocks; Receiving the microwave signals transmitted by the ground and space simultaneously.

7. A ground station device, characterized in that, 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, the memory is used to store a computer program, and when the processor runs the computer program stored in the memory, the processor executes the method for determining the gravity potential and altitude by air-ground dual-frequency combined frequency transfer according to any one of claims 1 to 4.

8. A non-transitory computer-readable storage medium, characterized in that, The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions cause the computer to execute the method for determining the gravity potential and altitude by air-ground dual-frequency combined frequency transfer according to any one of claims 1 to 4.

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