A satellite synchronization method and apparatus based on a wheel-type formation satellite constellation

Abstract

This application provides a satellite synchronization method and apparatus based on a wheel-type formation satellite constellation. After acquiring the observation data and satellite status information obtained by the main satellite and each auxiliary satellite from the target GNSS navigation satellite, the method, during a preset first synchronization period, uses a preset time synchronization algorithm to process the observation data obtained by the main satellite and any auxiliary satellite to obtain the relative clock difference between the main satellite and that auxiliary satellite, thus achieving time synchronization. A preset spatial synchronization algorithm is then used to periodically process the satellite status information to obtain the attitude information of each satellite, achieving spatial synchronization. During a preset second synchronization period, the main satellite and each auxiliary satellite are controlled to send phase synchronization signals to each other before and after the radar echo reception window, obtaining the phase synchronization error between the main satellite and each auxiliary satellite, thus achieving phase synchronization. This method improves upon the problems of long imaging periods, low imaging accuracy, and narrow imaging range in satellite imaging processes.

Description

Technical Field

[0001] This application relates to the field of satellite technology, and more specifically, to a satellite synchronization method and apparatus based on a wheel-type formation satellite constellation. Background Technology

[0002] Currently, the limited interferometric baselines in single-satellite or dual-satellite systems lead to problems such as long imaging cycles, low imaging accuracy, and narrow imaging range during satellite imaging. Furthermore, current synchronization technologies for single-satellite or dual-satellite systems only offer synchronization based on a single attribute, namely time synchronization, spatial synchronization, or phase synchronization, which limits the accuracy of inter-satellite synchronization. Summary of the Invention

[0003] The purpose of this application is to provide a satellite synchronization method and apparatus based on a wheel-type formation satellite constellation. By using three synchronization technologies—time synchronization, spatial synchronization, and phase synchronization—the accuracy of synchronization between satellites is improved, thereby addressing the problems of long imaging cycles, low imaging accuracy, and narrow imaging range during satellite imaging.

[0004] Firstly, a satellite synchronization method based on a wheel-like satellite constellation is provided, wherein the wheel-like satellite constellation includes one primary satellite and three secondary satellites. The method may include:

[0005] The system acquires the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as the satellite status information of each satellite.

[0006] During the first preset synchronization period, for any auxiliary satellite, a preset time synchronization algorithm is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively, so as to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite.

[0007] A preset spatial synchronization algorithm is used to periodically process the satellite state information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite;

[0008] During the preset second synchronization period, the main satellite and each auxiliary satellite are controlled to send phase synchronization signals to each other before and after the radar echo receiving window, so as to obtain the phase synchronization error between the main satellite and each auxiliary satellite, thereby achieving phase synchronization between the main satellite and each auxiliary satellite. The echo receiving window is the time period during which the main satellite and the corresponding auxiliary satellite receive the radar echo after the main satellite transmits the radar signal.

[0009] In an optional implementation, the radar reference frequency source on the primary satellite and each of the auxiliary satellites is a GNSS disciplined crystal oscillator.

[0010] In an optional implementation, the first synchronization period is the time period before the radars on the primary satellite and each of the auxiliary satellites perform echo acquisition;

[0011] The second synchronization period is the time period during which the radars on the main satellite and each of the auxiliary satellites are performing echo acquisition.

[0012] In an optional implementation, the preset time synchronization algorithm is represented as:

[0013]

[0014] Where, Δδt r,AB Let ΔR be the signal reception time difference between GNSS receiving earth station A and earth station B, c be the speed of light, and ΔR be the signal reception time difference between earth station A and earth station B. AB Let Δρ be the spherical distance between the receivers at Earth Station A and Earth Station B of the satellite and the GNSS receiver. AB Let ΔI be the geometric distance from the receivers of Earth Station A and Earth Station B to the GNSS. AB Let ΔP be the difference in atmospheric delay error between Earth Station A and Earth Station B. AB The residual error ΔO is the hardware delay calibration error of the satellite receiver. AB Let Δε be the single difference in GNSS satellite orbit errors detected by Earth Station A and Earth Station B. AB The error is the single difference between the GNSS receiver noise and multipath effect detected by Earth Station A and Earth Station B.

[0015] In an optional implementation, obtaining the relative clock difference between the primary satellite and the secondary satellite to achieve time synchronization between the primary satellite and the secondary satellite includes:

[0016] After the radar timers on the primary satellite and the secondary satellite receive the current PPS pulse signal, they delay the PPS pulse signal according to the relative clock difference to trigger the generation of a timing signal PRF, so as to achieve time synchronization between the primary satellite and the secondary satellite.

[0017] In an optional implementation, the satellite status information includes the eccentricity, true anomaly, and latitudinal argument of the orbits corresponding to the primary satellite and the secondary satellite, the satellite's velocity, orbital inclination, and latitudinal argument.

[0018] For near-circular orbit satellites, the preset space synchronization algorithm is expressed as:

[0019]

[0020] in, N = v s / R s / ωe e, f, and u represent the eccentricity, true anomaly, and latitudinal argument of the corresponding satellite orbits, respectively. s R represents the velocity of the corresponding satellite. s ω represents the distance from the satellite to the Earth's center. e denoted as ω = ω_i, where i is the orbital inclination of the corresponding satellite, u is the latitudinal argument of the corresponding satellite, ψ is the yaw angle, and θ is the pitch angle.

[0021] In an optional implementation, phase synchronization between the main satellite and each auxiliary satellite is achieved by controlling the main satellite to send phase synchronization signals to each other before and after the radar echo reception window, thereby obtaining the phase synchronization error between the main satellite and each auxiliary satellite. This includes:

[0022] During the first half of the synchronization pulse interaction cycle, the master satellite is controlled to transmit radar signals, and the master satellite is also controlled to send a first phase synchronization signal to the target auxiliary satellite in front of the radar echo receiving window, so that the target auxiliary satellite receives the first phase synchronization signal; the target auxiliary satellite is any one of the three auxiliary satellites.

[0023] During the second half of the synchronization pulse interaction cycle, the main satellite is controlled to transmit radar signals, and the target auxiliary satellite is controlled to send a second phase synchronization signal to the main satellite in front of the radar echo receiving window, so that the main satellite receives the second phase synchronization signal.

[0024] Acquire synchronization pulse data after the main satellite and each auxiliary satellite have demodulated the phase synchronization signals they received;

[0025] Based on the synchronization pulse data of the main satellite and each auxiliary satellite, the phase synchronization error between the main satellite and each auxiliary satellite is determined.

[0026] Secondly, a satellite synchronization device based on a wheel-type satellite constellation is provided, wherein the wheel-type satellite constellation includes one main satellite and three auxiliary satellites, and the device may include:

[0027] The acquisition unit is used to acquire the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as the satellite status information of each satellite;

[0028] The processing unit is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively during a preset first synchronization period, using a preset time synchronization algorithm, to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite.

[0029] Furthermore, a preset spatial synchronization algorithm is used to periodically process the satellite state information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite;

[0030] The acquisition unit is further configured to, during a preset second synchronization period, control the main satellite to send phase synchronization signals to each auxiliary satellite before and after the radar echo receiving window, and acquire the phase synchronization error between the main satellite and each auxiliary satellite, so as to achieve phase synchronization between the main satellite and each auxiliary satellite. The echo receiving window is the time period during which the main satellite and the corresponding auxiliary satellite receive the radar echo after the main satellite transmits the radar signal.

[0031] Thirdly, an electronic device is provided, which includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus;

[0032] Memory, used to store computer programs;

[0033] When a processor executes a program stored in memory, it implements any of the steps described in the first aspect above.

[0034] Fourthly, a computer-readable storage medium is provided, wherein a computer program is stored therein, and when executed by a processor, the computer program implements the steps of any of the methods described in the first aspect above.

[0035] This application provides a satellite synchronization method based on a wheel-type formation satellite constellation. After acquiring the observation data and satellite status information of the target GNSS navigation satellite obtained by the main satellite and each auxiliary satellite, during a preset first synchronization period, a preset time synchronization algorithm is used to process the observation data obtained by the main satellite and auxiliary satellite for any auxiliary satellite to obtain the relative clock difference between the main satellite and auxiliary satellite, thereby achieving time synchronization between the main satellite and auxiliary satellite. A preset spatial synchronization algorithm is used to periodically process the satellite status information to obtain the attitude information of the main satellite and auxiliary satellite, thereby achieving spatial synchronization between the main satellite and auxiliary satellite. During a preset second synchronization period, the main satellite is controlled to send phase synchronization signals to each auxiliary satellite before and after the radar echo reception window to obtain the phase synchronization error between the main satellite and each auxiliary satellite, thereby achieving phase synchronization between the main satellite and each auxiliary satellite. The echo reception window is the time period after the main satellite transmits the radar signal and the main satellite and the corresponding auxiliary satellite receive the radar echo. This method improves the synchronization accuracy between satellites in a wheel-type formation satellite constellation by using a triple synchronization technique of time synchronization, spatial synchronization, and phase synchronization, thereby addressing the problems of long imaging cycles, low imaging accuracy, and narrow imaging range during satellite imaging. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A schematic diagram of a wheel-type satellite formation constellation provided in this application embodiment;

[0038] Figure 2 A schematic flowchart illustrating a satellite synchronization method based on a wheel-type formation satellite constellation provided in this application embodiment;

[0039] Figure 3 A schematic diagram of the spatial synchronous Doppler gain relationship of the maximum coherence method provided in this application embodiment;

[0040] Figure 4 A schematic diagram illustrating the relationship between relative angular velocity and the Earth-fixed system SXoYoZo, provided in an embodiment of this application;

[0041] Figure 5 A schematic diagram of phase synchronization timing provided for an embodiment of this application;

[0042] Figure 6 A schematic diagram of a satellite synchronization device based on a wheel-type formation satellite constellation provided in this application embodiment;

[0043] Figure 7 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0044] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0045] The wheel-shaped satellite constellation of this application is a novel satellite formation system comprising four satellites located on the same plane: a primary satellite (or "main star"), b secondary satellites (or "auxiliary stars"), c secondary satellites, and d secondary satellites. The four satellites are arranged in a wheel shape (as shown in the diagram below), with the angle θ = 120° between the lines connecting adjacent secondary satellites and primary satellite a. Figure 1 As shown.

[0046] Compared to the single baseline of existing dual-satellite and single-satellite SAR (Synthetic Aperture Radar) constellation systems, the wheel-formation SAR constellation system proposed in this method has satellites with multiple different relative positions, thereby generating multiple interferometric baselines. This enhances interferometric measurement capabilities and allows for the acquisition of more accurate surface elevation information and 3D structure. Simultaneously, the multi-satellite configuration can cover a larger surface area, reducing data acquisition cycles and thus decreasing the time and resource costs of monitoring missions.

[0047] In addition, multi-satellite configurations can achieve more precise attitude control through reasonable satellite formation control, reduce post-processing image processing and geometric radiometric correction work, and provide higher quality radar images and interferometric data.

[0048] Furthermore, in the dual-transmit, dual-receive SAR operating mode of the primary satellite a and its six baselines with auxiliary satellites b, c, and d in a wheel-like formation, the four satellites need to work together to acquire effective interferometric data. This coordination is mainly manifested in the three-synchronization technology of time, space, and phase. Under this technical system, the signals received by separately placed radars have good coherence, but the transmitting and receiving radars must coordinate with each other to function properly. This requires all participating radar antennas to be pointed at the same ground target, all radars to know the radar signal transmission time, and all radars to accurately grasp the phase of each echo throughout the synthetic aperture time—that is, time, space, and phase synchronization. If these three are not synchronized, the constellation will be unable to perform accurate interferometric imaging, thus severely reducing the system's operational capabilities.

[0049] This application provides a time, space, and phase synchronization technology based on a wheel-type formation satellite constellation. This technology can achieve synchronization of time, space, and satellite orbit phase on the satellite while meeting the requirements for precise orbit control data interaction and combining the geometric characteristics of the constellation's wheel-type formation.

[0050] The radar reference frequency source on each satellite uses a GNSS disciplined crystal oscillator.

[0051] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application. Furthermore, the embodiments and features in the embodiments of this application can be combined with each other without conflict.

[0052] Figure 2 This is a flowchart illustrating a satellite synchronization method based on a wheel-type formation satellite constellation, provided as an embodiment of this application. Figure 2 As shown, the method may include:

[0053] Step S210: Obtain the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as their respective satellite status information.

[0054] The observation data may include the signal reception time of the GNSS receivers of each satellite, the spherical and geometric distances between the GNSS receivers of each satellite, atmospheric delay error, GNSS receiver noise and multipath effect error, etc.

[0055] The satellite status information includes the eccentricity, true anomaly, and latitudinal argument of the orbits corresponding to the primary satellite and the secondary satellite, the satellite's velocity, orbital inclination, and latitudinal argument.

[0056] Step S220: During the preset first synchronization period, for any auxiliary satellite, a preset time synchronization algorithm is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively, so as to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite.

[0057] The first synchronization period is the time before the radars on the main satellite and each auxiliary satellite begin echo reception, that is, the time after the radar is turned on but before it begins echo reception.

[0058] Ordinary single-satellite timing systems typically employ methods such as improving crystal oscillator accuracy or enhancing synchronization locking technology to ensure clock stability and precision. However, high-precision crystal oscillators are expensive, while enhanced synchronization locking technology places high demands on the performance of a single link.

[0059] This application utilizes a wheel-formation satellite constellation configuration, where the GNSS receivers of each satellite maintain time synchronization with the satellite links of the other three satellites through directional calibration. This significantly reduces time delay errors caused by the ionosphere and troposphere and the dependence on the performance of a single link, and the time synchronization accuracy is better than 5ns.

[0060] In practice, different GNSS receivers on the main satellite and auxiliary satellites synchronously observe the same target GNSS navigation satellite to determine the relative clock deviation between satellites, thereby achieving high-precision time comparison.

[0061] The PPS pulse signal output by the GNSS receiver is sent to the radar once per second. Before each SAR imaging operation, the radar timers on the primary and secondary satellites receive the current PPS pulse signal, and based on the relative clock difference, they delay the PPS pulse signal to trigger the generation of a timing signal PRF, thereby achieving time synchronization between the primary and secondary satellites.

[0062] In one embodiment, for any given satellite:

[0063] R A=ρ A +cδt r,A -cδt s +I A +P A +O A +ε A

[0064] R B =ρ B +cδt r,B -cδt s +I B +B B +O B +ε B

[0065] Taking the difference between the two observations above, we have:

[0066] ΔR AB =Δρ AB +cΔδt r,AB +ΔI AB +ΔP AB +ΔO AB +Δε AB

[0067] The symbols in the above formula have the following meanings:

[0068] Δδt r,AB Let ΔR be the signal reception time difference between GNSS receiving earth station A and earth station B, c be the speed of light, and ΔR be the signal reception time difference between earth station A and earth station B. AB Let Δρ be the spherical distance between the receivers of Earth Station A and Earth Station B and the GNSS receiver. AB Let ΔI be the geometric distance from the receivers of Earth Station A and Earth Station B to the GNSS. AB Let ΔP be the difference in atmospheric delay error between Earth Station A and Earth Station B. AB The residual error ΔO is the hardware delay calibration error of the satellite receiver. AB Let Δε be the single difference in GNSS satellite orbit errors detected by Earth Station A and Earth Station B. AB The error is the single difference between the GNSS receiver noise and multipath effect detected by Earth Station A and Earth Station B.

[0069] Therefore, the preset time synchronization algorithm can be expressed as:

[0070]

[0071] In other words, given the coordinates of the two earth stations, the relative clock difference between the user clocks of the two earth stations monitored by any satellite is:

[0072]

[0073] The relative clock difference between satellites corresponds to Δδt of the primary satellite. r,AB Δδt corresponding to any auxiliary satellite r,AB The difference Δδt.

[0074] Furthermore, after aligning the onboard time among the satellites in the constellation, each satellite uses the PPS pulse output by the GNSS receiver to trigger the generation of radar timing PRF (pulse repetition frequency) signals, thereby achieving alignment of the radar PRF signals of each satellite.

[0075] It should be noted that after the formation constellation performs time synchronization each time the SAR payload is powered on, it maintains time synchronization during subsequent imaging periods using a GNSS-tamed, highly stable crystal oscillator.

[0076] Since the radar reference frequency source on each satellite uses a GNSS disciplined crystal oscillator, the frequency difference between the crystal oscillator signals of the active and passive radars will be small enough after discipline. The radar timing clock signal is generated based on the disciplined crystal oscillator signal, thereby maintaining the synchronization of the timing signals of the active and passive radars during the radar's power-on time.

[0077] Step S230: Using a preset space synchronization algorithm, the satellite status information is processed periodically to obtain the attitude information of the main satellite and the auxiliary satellite, so as to achieve space synchronization between the main satellite and the auxiliary satellite.

[0078] The satellite's attitude information includes yaw angle and pitch angle.

[0079] When a wheel-like constellation is in operation, the primary satellite transmits radar signals, and the primary satellite and three auxiliary satellites simultaneously receive the radar echoes. To achieve interferometric altimetry or wide-swath imaging, the transmitting and receiving antenna beams of each satellite must simultaneously cover the same area, requiring spatial synchronization of the antenna beams. During spatial synchronization, the ground-based telemetry and control system transmits the imaging area location information to the primary and auxiliary satellite platforms in real time. Based on its own position and attitude information, the platform uses a spatial synchronization algorithm to calculate the beam pointing of its receiving antenna. Through the attitude controller and beam control unit, it controls the pointing of the auxiliary satellite's receiving antenna to achieve beam synchronization with the primary satellite's transmitting platform.

[0080] The wheel-like formation in this application uses the "maximum coherence method" to achieve spatial synchronization. Both the main satellite and each auxiliary satellite employ Doppler guidance, meaning that the Doppler center frequency is compensated during imaging to reduce the impact of the Doppler effect on satellite imaging quality. This ensures that the Doppler center positions of both the main and auxiliary satellites are at their respective relative maximum gain positions, guaranteeing high Doppler decoherence. However, because the auxiliary satellites' receiving beams are not aimed at the main satellite's beam illumination area, the maximum gain of the receiving antenna is not utilized, resulting in a slight loss of gain.

[0081] Since both the primary and secondary stars undergo zero-Doppler attitude guidance, the common area illuminated by the secondary and primary stars is equivalent to a frontal side view, meaning the Doppler center frequency within the scene is 0. Simulation analysis shows that the gain loss from the maximum coherence method is between -0.15dB and -0.25dB (e.g., ...). Figure 3 As shown in the figure, considering factors such as attitude control error and antenna beam error, the overall error is approximately 0.03°, resulting in an additional gain loss of approximately 0.06dB. All of the above errors are within the acceptable range of the system.

[0082] In some embodiments, for near-circular orbit satellites, the preset space synchronization adjustment algorithm is expressed as:

[0083]

[0084] in, N = v s / R s / ω e e, f, and u represent the eccentricity, true anomaly, and latitudinal argument of the corresponding satellite orbits, respectively. s R represents the velocity of the corresponding satellite. s ω represents the distance from the satellite to the Earth's center. e denoted as ω = ω_i, where i is the orbital inclination of the corresponding satellite, u is the latitudinal argument of the corresponding satellite, ψ is the yaw angle, and θ is the pitch angle.

[0085] Specifically, in practical applications of SAR satellite imagery, the satellite's ground target images must have precise pixel locations. However, according to the SAR satellite's imaging algorithm, the filtering parameters (Doppler center frequency and Doppler modulation slope) used to estimate azimuth greatly affect the azimuth estimation.

[0086] The variation in Doppler center frequency caused by the Earth's rotation results in range migration, posing challenges to imaging processing. Studies show that for L / C band SAR, the Doppler center frequency varies globally by approximately ±11 kHz, necessitating on-board attitude compensation to reduce this variation. D This range allows for compensation of distance migration.

[0087] Doppler center frequency f D Defined as:

[0088] In the formula: λ SAR This is the operating wavelength for SAR. R is the velocity vector of the satellite relative to the target point; R is the position vector of the satellite relative to the target point; R is the distance of the satellite relative to the target point.

[0089] Where R = R s -Rt (2)

[0090] In the formula: R s R is the satellite's position vector relative to the Earth's center; t The vector of the target point relative to the geocenter;

[0091] From f D The formula shows that f D Because of the direction of satellite observation of ground target points The relative velocity between the satellite and the ground target point There's no verticality issue. The direction the satellite observes ground targets is determined by the direction of the satellite's SAR antenna beam. Since the SAR antenna is mounted on the satellite, the antenna beam direction is directly related to the satellite's attitude. (Relative velocity vector) This relates to the satellite's velocity and the velocity of the ground target point. In a fixed Earth coordinate system, with the ground target point stationary, the relative velocity vector... This refers to the satellite's velocity in this coordinate system. The satellite's velocity in the Earth-fixed coordinate system is the satellite's velocity minus the gravitational velocity caused by the Earth's rotation; it is entirely determined by the satellite's orbit and is independent of the satellite's attitude. From and Considering their respective causes, the two are independent of each other. Therefore, it is possible to adjust the attitude so that the center beam of the satellite's SAR antenna is perpendicular to the relative velocity.

[0092] Define a geostationary coordinate system SXoYoZo, with the three axes instantaneously coinciding with the orbital system. The Zo axis points from the satellite to the Earth's center, the Yo axis is the normal to the satellite's orbital plane, and the Xo axis follows the right-hand rule with Zo and Yo. Figure 4 As shown. M is the ascending node of the satellite, and P is the intersection of the meridian circle where the satellite is located and the equatorial plane.

[0093] As analyzed in the previous section, the relative velocity vector... This can be expressed as the satellite's velocity minus the traction velocity caused by the Earth's rotation:

[0094] In the formula: v s v represents the satellite's velocity. e The traction velocity is caused by the Earth's rotational angular velocity.

[0095] In the Earth-fixed coordinate system SXoYoZo, v e It can be represented as:

[0096] v e =[v e sinα v e cosα 0] T (4)

[0097] In the formula: v e =ω e R s cosβ.

[0098] In the spherical right triangle ΔMPS, the following relationship holds:

[0099]

[0100] In the formula: β is the central angle corresponding to SP; α is the angle between MS and SP; i is the satellite orbital inclination; u is the satellite's latitude argument.

[0101] From equations (4) and (5), we can obtain the traction velocity v caused by the Earth's rotation. e for:

[0102] v e =R s ω e [cos i sin i cos u 0] T (6)

[0103] If the track angle is Θ, then the satellite's velocity v s In the coordinate system SXoYoZo, this can be represented as:

[0104] v s =[v s cosΘ,0,-v s sinΘ] T (7)

[0105] In the formula: e and f are the eccentricity and true anomaly of the satellite orbit, respectively.

[0106] Using equations (6) and (7), the relative velocities between the satellite and the ground target in the coordinate system SXoYoZo can be obtained. for:

[0107]

[0108] To achieve a Doppler center frequency of zero, it is only necessary to find a direction perpendicular to the direction of each center beam of the SAR antenna and parallel to the relative velocity mentioned above.

[0109] The only difference between the various SAR positions lies in the different downward angles of the SSAR antenna's center beam. The downward angle can be understood as the angle around the satellite body (X). b The rotation angle of the axis, then the satellite body X b The axis is always perpendicular to the direction of each center beam of the SAR. Therefore, as long as the attitude is adjusted so that X... b The axis is parallel to the direction of relative velocity. This can eliminate the Doppler center frequency.

[0110] At this moment, the Earth-fixed coordinate system SXoYoZo coincides with the orbital system, and the satellite body X... b The orientation of the axis is the same in the orbital frame and in the Earth-fixed frame (SXoYoZo). Make X b Since the axial direction is parallel to the relative velocity vector, the satellite's yaw and pitch angles need to be adjusted. Assuming the yaw and pitch angle adjustments are ψ and θ, respectively, then X... b The axes pointing in the Earth-fixed coordinate system SXoYoZo can be represented as:

[0111] X b =[cosθcosψ cosθsinψ -sinθ] T (9)

[0112] Using equations (8) and (9) and the relation The two-dimensional attitude compensation law can be obtained:

[0113]

[0114] In the formula: N = v s / R s / ω e .

[0115] For near-circular orbit satellites, the satellite's two-dimensional guidance angle can be approximated as:

[0116]

[0117] in, N = v s / R s / ω e e, f, and u represent the eccentricity, true anomaly, and latitudinal argument of the satellite orbit, respectively.

[0118] During the operation of the wheel formation constellation, this application outputs the corresponding yaw angle and pitch angle as the actual guidance attitude angle of the satellite at the latitude argument at time t, thereby realizing the all-zero Doppler trajectory of the radar beam running according to the target yaw angle and pitch angle.

[0119] Step S240: During the preset second synchronization period, the main satellite and each auxiliary satellite are controlled to send phase synchronization signals to each other before and after the radar echo receiving window, so as to obtain the phase synchronization error between the main satellite and each auxiliary satellite and achieve phase synchronization between the main satellite and each auxiliary satellite.

[0120] The echo reception window is the time period during which the main satellite and its corresponding auxiliary satellites receive radar echoes after the main satellite transmits the radar signal. The second synchronization period is the time period during which the radars on the main satellite and each auxiliary satellite are collecting echoes.

[0121] In a wheel-type interferometric SAR satellite system, because the radars on different satellites use their own different frequency sources, there must be a fixed frequency difference and a time-varying frequency difference caused by phase noise between their radar carriers, introducing interferometric phase errors. Phase errors directly affect the accuracy of interferometric altimetry and the quality of SAR imaging. To reduce phase errors, the radar carriers of different satellites need to be synchronized, i.e., both their frequency and phase must be the same. Therefore, the purpose of phase synchronization is to establish a common relative phase reference between the primary and secondary satellite SARs, making the echo signals of the primary and secondary satellite SARs coherent and ensuring that the phase difference meets the requirements of interferometric altimetry.

[0122] In practice, during the first half of the synchronization pulse interaction cycle, the main satellite is controlled to transmit radar signals and send the first phase synchronization signal to the target auxiliary satellite in front of the radar echo receiving window, so that the target auxiliary satellite receives the first phase synchronization signal; the target auxiliary satellite is any one of the three auxiliary satellites.

[0123] During the second half of the synchronization pulse interaction cycle, the main satellite is controlled to transmit radar signals, and the target auxiliary satellite is controlled to send a second phase synchronization signal to the main satellite in front of the radar echo receiving window, so that the main satellite can receive the second phase synchronization signal.

[0124] Acquire synchronization pulse data after the main satellite and each auxiliary satellite have demodulated the phase synchronization signals they received;

[0125] Based on the synchronization pulse data of the main satellite and each auxiliary satellite, the phase synchronization error between the main satellite and each auxiliary satellite is determined.

[0126] Specifically, since the reference frequency source for the main satellite and each auxiliary satellite uses a GNSS disciplined crystal oscillator, the frequency accuracy of the atomic clocks used on the satellites is within 10... -12 The magnitude is above that of the radar carrier frequency difference between the master satellite and each auxiliary satellite after taming is small enough to stabilize the mechanism, so that the sampling during the phase error data acquisition process satisfies the Nyquist theorem.

[0127] In addition, a synchronous horn antenna is used to alternately transmit phase synchronization pulse signals between the primary satellite and any of the secondary satellites. This process is carried out periodically during bistatic SAR data acquisition, with the radar transmission signal switched from the primary SAR antenna to eight synchronous horn antennas. The synchronization pulse transmitted by the primary satellite is received and acquired by the synchronous horn antenna on the secondary satellite. After an appropriate delay, the secondary satellite then sends a synchronization pulse signal back to the primary satellite, completing one synchronization pulse exchange cycle. This cycle repeats until imaging is completed.

[0128] Meanwhile, the main satellite and each auxiliary satellite demodulate and acquire data from the phase synchronization pulses they receive. The obtained synchronization pulse data is transmitted to the ground via a data transmission system. The ground processing extracts the phase synchronization error, compensates for the auxiliary satellite echoes, and completes phase synchronization.

[0129] For a pulse repetition cycle, such as Figure 5 As shown, the master satellite first transmits a radar signal, and then, during the idle period T before and after the echo reception window, the master satellite transmits a phase synchronization signal to the auxiliary satellite. Subsequently, the auxiliary satellite receives the synchronization signal from the master satellite. In the next pulse repetition cycle, the auxiliary satellite uses the same idle period T to transmit a synchronization signal to the master satellite, thus achieving pulse transmission. Therefore, phase synchronization is performed during the idle period T before and after the echo reception window.

[0130] It should be noted that, to achieve phase synchronization, each satellite's payload system includes two four-channel synchronous transceiver modules and eight synchronization antennas. The two four-channel synchronous transceiver modules are located on the left and right wings of the satellite, respectively, enabling symmetrical reception and meeting the requirement for simultaneous imaging of both left-side and right-side SAR signals. Furthermore, since phase synchronization occurs during SAR imaging, different antennas are needed to perform radar signal transmission and reception, as well as synchronization signal transmission and reception. Therefore, each four-channel synchronous transceiver module contains four synchronization antennas. During phase synchronization, these four antennas sequentially transmit radar signals, alternately transmit phase synchronization pulse signals from their respective satellite platforms, and receive auxiliary satellite echo compensation feedback from ground processing.

[0131] Corresponding to the above method, embodiments of this application also provide a satellite synchronization device based on a wheel-type formation satellite constellation, such as... Figure 6 As shown, the device includes:

[0132] The acquisition unit 610 is used to acquire the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as the satellite status information of each satellite;

[0133] The processing unit 620 is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively for any auxiliary satellite during a preset first synchronization period using a preset time synchronization algorithm, so as to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite.

[0134] Furthermore, a preset spatial synchronization algorithm is used to periodically process the satellite state information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite;

[0135] The acquisition unit 610 is also used to, during a preset second synchronization period, control the main satellite to send phase synchronization signals to each auxiliary satellite before and after the radar echo receiving window, and acquire the phase synchronization error between the main satellite and each auxiliary satellite, so as to achieve phase synchronization between the main satellite and each auxiliary satellite. The echo receiving window is the time period during which the main satellite and the corresponding auxiliary satellite receive the radar echo after the main satellite transmits the radar signal.

[0136] The functions of each functional unit of the satellite synchronization device based on the wheel-type formation satellite constellation provided in the above embodiments of this application can be implemented through the above methods and steps. Therefore, the specific working process and beneficial effects of each unit in the satellite synchronization device based on the wheel-type formation satellite constellation provided in the embodiments of this application will not be repeated here.

[0137] This application also provides an electronic device, such as... Figure 7 As shown, it includes a processor 710, a communication interface 720, a memory 730, and a communication bus 740, wherein the processor 710, the communication interface 720, and the memory 730 communicate with each other through the communication bus 740.

[0138] Memory 730 is used to store computer programs;

[0139] When the processor 710 executes the program stored in the memory 730, it performs the following steps:

[0140] The system acquires the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as the satellite status information of each satellite.

[0141] During the first preset synchronization period, for any auxiliary satellite, a preset time synchronization algorithm is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively, so as to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite.

[0142] A preset spatial synchronization algorithm is used to periodically process the satellite state information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite;

[0143] During the preset second synchronization period, the main satellite and each auxiliary satellite are controlled to send phase synchronization signals to each other before and after the radar echo receiving window, so as to obtain the phase synchronization error between the main satellite and each auxiliary satellite, thereby achieving phase synchronization between the main satellite and each auxiliary satellite. The echo receiving window is the time period during which the main satellite and the corresponding auxiliary satellite receive the radar echo after the main satellite transmits the radar signal.

[0144] The communication bus mentioned above can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not mean that there is only one bus or one type of bus.

[0145] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0146] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0147] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0148] The implementation methods and beneficial effects of the various components of the electronic device in the above embodiments for solving the problem can be found in [reference needed]. Figure 2 The steps in the illustrated embodiments are used to implement the electronic device. Therefore, the specific working process and beneficial effects of the electronic device provided in this application will not be repeated here.

[0149] In another embodiment provided in this application, a computer-readable storage medium is also provided, which stores instructions that, when executed on a computer, cause the computer to perform the satellite synchronization method based on a wheel-type formation satellite constellation as described in any of the above embodiments.

[0150] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute any of the satellite synchronization methods based on wheel-type formation satellite constellations described in the above embodiments.

[0151] Those skilled in the art will understand that the embodiments in this application can be provided as methods, systems, or computer program products. Therefore, the embodiments in this application can take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, the embodiments in this application can take the form of computer program products implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0152] This application describes embodiments of methods, apparatus (systems), and computer program products according to embodiments of this application with reference to flowchart illustrations and / or block diagrams. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0153] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0154] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0155] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0156] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims in this application and their equivalents, then this application also intends to include these modifications and variations.

Claims

1. A satellite synchronization method based on a wheel-type formation satellite constellation, characterized in that, A wheel-type satellite formation comprises one main satellite and three auxiliary satellites, and the method includes: The main satellite and each auxiliary satellite synchronously observe the target GNSS navigation satellite, and obtain their respective observation data and satellite status information. During the first preset synchronization period, for any auxiliary satellite, a preset time synchronization algorithm is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively, so as to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite. A preset spatial synchronization algorithm is used to periodically process the satellite status information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite. This includes: after the radar timer on the primary satellite and the secondary satellite receives the current PPS pulse signal, the PPS pulse signal is delayed according to the relative clock difference to trigger the generation of a timing signal PRF, so as to achieve time synchronization between the primary satellite and the secondary satellite. During a preset second synchronization period, the phase synchronization error between the main satellite and each auxiliary satellite is obtained by controlling the main satellite to send phase synchronization signals to each other before and after the radar echo receiving window, thereby achieving phase synchronization between the main satellite and each auxiliary satellite. This includes: during the first half of the synchronization pulse interaction period, controlling the main satellite to transmit a radar signal and controlling the main satellite to send a first phase synchronization signal to a target auxiliary satellite before the radar echo receiving window, so that the target auxiliary satellite receives the first phase synchronization signal; the target auxiliary satellite is any one of the three auxiliary satellites; during the second half of the synchronization pulse interaction period, controlling the main satellite to transmit a radar signal and controlling the target auxiliary satellite to send a second phase synchronization signal to the main satellite before the radar echo receiving window, so that the main satellite receives the second phase synchronization signal; obtaining synchronization pulse data after the main satellite and each auxiliary satellite demodulate the phase synchronization signals they receive; and determining the phase synchronization error between the main satellite and each auxiliary satellite based on the synchronization pulse data. Wherein, the echo reception window is the time period during which the main satellite and the corresponding auxiliary satellites receive the radar echo after the main satellite transmits the radar signal; the first synchronization period is the time period before the radars on the main satellite and each of the auxiliary satellites perform echo acquisition; the second synchronization period is the time period during which the radars on the main satellite and each of the auxiliary satellites perform echo acquisition.

2. The method as described in claim 1, characterized in that, The radar reference frequency source on the main satellite and each of the auxiliary satellites adopts a GNSS disciplined crystal oscillator.

3. The method as described in claim 1, characterized in that, The preset time synchronization algorithm is expressed as follows: in, Let c be the signal reception time difference between GNSS receiving earth station A and earth station B, and c be the speed of light. The spherical distance between the receivers of Earth Station A and Earth Station B and the GNSS is denoted as . This represents the geometric distance from the receivers of Earth Station A and Earth Station B to the GNSS receiver. This represents the difference in atmospheric delay error between Earth Station A and Earth Station B. This refers to the residual error after hardware delay calibration of the satellite receiver. This represents the single difference in GNSS satellite orbit errors detected by Earth Station A and Earth Station B. The error is the single difference between the GNSS receiver noise and multipath effect detected by Earth Station A and Earth Station B.

4. The method as described in claim 1, characterized in that, The satellite status information includes the eccentricity, true anomaly, and latitudinal argument of the orbits corresponding to the primary satellite and the secondary satellite, the satellite's velocity, orbital inclination, and latitudinal argument; For near-circular orbit satellites, the preset space synchronization algorithm is expressed as: in, , e, f, and u represent the eccentricity, true anomaly, and latitudinal argument of the corresponding satellite orbits, respectively. For the speed of the corresponding satellite, The distance from the satellite to the Earth's center. Let ω be the Earth's rotational angular velocity, i be the orbital inclination of the corresponding satellite, and u be the latitudinal argument of the corresponding satellite. Yaw angle The pitch angle.

5. A satellite synchronization device based on a wheel-type formation satellite constellation, characterized in that, The wheel-type satellite formation comprises one main satellite and three auxiliary satellites, and the device includes: The acquisition unit is used to acquire the observation data obtained by the main satellite and each auxiliary satellite from the synchronous observation of the target GNSS navigation satellite, as well as the satellite status information of each satellite; The processing unit is used to process the observation data obtained by the main satellite and the auxiliary satellite respectively during a preset first synchronization period, using a preset time synchronization algorithm, to obtain the relative clock difference between the main satellite and the auxiliary satellite, so as to achieve time synchronization between the main satellite and the auxiliary satellite. Furthermore, a preset spatial synchronization algorithm is used to periodically process the satellite status information to obtain the attitude information of the primary satellite and the secondary satellite, so as to achieve spatial synchronization between the primary satellite and the secondary satellite. Specifically, after the radar timer on the primary satellite and the secondary satellite receives the current PPS pulse signal, it performs delay processing on the PPS pulse signal according to the relative clock difference, triggering the generation of a timing signal PRF to achieve time synchronization between the primary satellite and the secondary satellite. The acquisition unit is further configured to, during a preset second synchronization period, control the main satellite to send phase synchronization signals to each auxiliary satellite before and after the radar echo receiving window, and acquire the phase synchronization error between the main satellite and each auxiliary satellite to achieve phase synchronization between the main satellite and each auxiliary satellite. Specifically: during the first half of the synchronization pulse interaction period, control the main satellite to transmit a radar signal and control the main satellite to send a first phase synchronization signal to the target auxiliary satellite before the radar echo receiving window, so that the target auxiliary satellite receives the first phase synchronization signal; the target auxiliary satellite is any one of the three auxiliary satellites; during the second half of the synchronization pulse interaction period, control the main satellite to transmit a radar signal and control the target auxiliary satellite to send a second phase synchronization signal to the main satellite before the radar echo receiving window, so that the main satellite receives the second phase synchronization signal; acquire synchronization pulse data after the main satellite and each auxiliary satellite demodulate the phase synchronization signals they receive; and determine the phase synchronization error between the main satellite and each auxiliary satellite based on the synchronization pulse data between the main satellite and each auxiliary satellite. Wherein, the echo reception window is the time period during which the main satellite and the corresponding auxiliary satellites receive the radar echo after the main satellite transmits the radar signal; the first synchronization period is the time period before the radars on the main satellite and each of the auxiliary satellites perform echo acquisition; the second synchronization period is the time period during which the radars on the main satellite and each of the auxiliary satellites perform echo acquisition.

6. An electronic device, characterized in that, The electronic device includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method of any one of claims 1-4.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method described in any one of claims 1-4.

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