A method for three-dimensional tomographic detection of interplanetary shock waves in satellite formations

Abstract

This invention discloses a method for three-dimensional tomographic imaging detection of interplanetary shock waves in satellite formations. The method includes the following steps: 1) Designing a satellite formation configuration with uniformly distributed interferometric baselines using an optimization algorithm based on observation requirements and satellite engineering constraints; 2) Measuring the baseline between any two satellites in the formation; 3) Combining all inter-satellite baselines to obtain three-dimensional spatial frequency sampling points for each frequency, forming a spatial transfer function; 4) Setting M observation frequencies for the interferometric imaging spectrometer, and obtaining tomographic surfaces corresponding to different heliocentric distances for each frequency point through inter-satellite interference; 5) Based on the principle of interferometric imaging, using a transformation algorithm from the spatial frequency domain to the spatial domain, sequentially performing two-dimensional imaging inversion on tomographic surfaces at different heliocentric distances, and then synthesizing a three-dimensional tomographic image; 6) Repeating steps 2) to 5) to achieve continuous observation and imaging, forming a three-dimensional tomographic image that evolves over time.

Description

Technical Field

[0001] This invention belongs to the field of satellite formation technology, and in particular relates to a method for three-dimensional tomographic imaging detection of interplanetary shock waves in satellite formations. Background Technology

[0002] The source of catastrophic space weather on Earth is the Sun's violent eruptive activity. High-speed plasma clouds released by solar eruptions propagate outwards through interplanetary space, and if they reach Earth, they can cause catastrophic space weather events. Imaging and monitoring solar eruptive activity and the propagation of coronal mass ejections (CMEs) through interplanetary space can provide high-precision Earth space weather forecasts. However, current observational capabilities primarily focus on observing the Sun and corona, using various models to predict whether interplanetary shocks will reach Earth and to estimate their arrival time. The forecast accuracy, arrival time precision, and timeliness are not yet adequate to meet the needs of operational space weather forecasting and comprehensive solar-terrestrial space physics research.

[0003] In terms of detection methods, observations of the solar corona and coronal mass ejections (CMEs) both domestically and internationally primarily utilize white light. However, when the shock wave is far from the Sun, white light scattering is weak, making accurate observation difficult. Furthermore, due to the "central obstruction" effect, the white light radiation of CMEs moving along the Sun-Earth line cannot be observed, thus preventing the observation of CME events directly affecting Earth's motion. In the radio band, the radio radiation driven by CME shock waves is brighter than the Sun itself, and radio detection does not require obstructing the Sun, allowing direct detection of shock-driven radio radiation along the Sun-Earth line. However, due to the influence of the Earth's ionosphere, ground-based radio detection frequencies are all above 10 MHz, only allowing observation of radio radiation within a few solar radii, and preventing the detection of CME interplanetary propagation. Currently, estimating the arrival time of CMEs at Earth mainly relies on spectral measurements of space-based low-frequency radio waves below 10 MHz. However, low-frequency radio spectrum detection detects an all-sky integrated signal, only determining the distance of the shock wave to the Sun, not the direction of shock wave propagation or the distance between the shock wave and Earth. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a three-dimensional tomographic imaging method for detecting interplanetary shock waves in satellite formations.

[0005] To achieve the above objectives, this invention proposes a three-dimensional tomographic detection method for interplanetary shock waves in satellite formations, based on an interferometric imaging spectrometer carried by a satellite. The method includes:

[0006] Step 1) Based on observation requirements and satellite engineering constraints, design a satellite formation configuration with uniform interferometric baseline distribution using an optimization algorithm;

[0007] Step 2) Measure the baseline between any two satellites in the satellite formation;

[0008] Step 3) Combine all inter-satellite baselines to obtain three-dimensional spatial frequency sampling points for each frequency, forming a spatial transfer function;

[0009] Step 4) Set M observation frequency points for the interferometric imaging spectrometer, and obtain the tomographic surface corresponding to different heliocentric distances for each frequency point through inter-satellite interference;

[0010] Step 5) Based on the principle of interferometric imaging, using the transformation algorithm from the spatial frequency domain to the spatial domain, two-dimensional imaging inversion is performed on the tomographic surfaces at different heliocentric distances in sequence, and then a three-dimensional tomographic image is synthesized.

[0011] Step 6) Repeat steps 2) to 5) to achieve continuous observation and imaging, forming a three-dimensional tomographic image that evolves over time.

[0012] As an improvement to the above method, the uniform distribution of the interference baseline in step 1) specifically includes: the distance distribution and direction distribution of the projected baseline are uniform on the plane perpendicular to the Sun-Earth line, and the angle of the interference baseline rotates with the orbital period, requiring only a small amount of propellant for orbital maintenance and formation keeping.

[0013] As an improvement to the above method, the optimization algorithm in step 1) includes genetic algorithm, particle algorithm and ant colony algorithm.

[0014] As an improvement to the above method, step 3) specifically includes:

[0015] Construct an observation coordinate system S(X'Y'Z'), where the Z' axis is the direction of distance from the sun's center, and the X'Y' plane is the plane perpendicular to the direction of distance from the sun's center. Select the projection direction of the north axis onto the X'Y' plane as the X' axis. Combine all inter-satellite baseline vectors and transform them to the observation coordinate system through coordinate transformation to form a spatial transfer function, thereby obtaining the baseline coordinate data for image inversion.

[0016] As an improvement to the above method, step 4) specifically includes:

[0017] M observation frequencies are set for the interferometric imaging spectrometer. Interferometric visibility data for each observation frequency is obtained through inter-satellite interference. Based on the different distances from the shock wave to the sun corresponding to the interferometric visibility data of different frequencies, M layers of curved surfaces with different heliocentric distances are formed.

[0018] As an improvement to the above method, step 5) specifically includes:

[0019] For M observation frequency points f k k = 1, 2, ..., M, and the two-dimensional projected baselines are respectively The obtained visibility function is In the observation coordinate system, the direction cosines of each point on the tomographic surface are (ξ, η). Based on the principle of interferometric imaging, M two-dimensional images are calculated, i.e. Among them, frequency point f k Corresponding two-dimensional image Satisfy the following formula:

[0020]

[0021] In the formula, j represents the imaginary part;

[0022] A three-dimensional tomographic image is synthesized from M two-dimensional images.

[0023] As an improvement to the above method, the time-evolving three-dimensional tomographic image in step 6) is:

[0024] As an improvement to the above method, step 3) is further preceded by: based on the baseline measurement accuracy requirements, based on the absolute orbital elements of each satellite in the satellite formation configuration, combined with the orbital dynamics characteristics and the inter-satellite baseline measured in real time in step 2), further improving the baseline determination accuracy through post-processing.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1. In terms of detection methods, observations of the solar corona and coronal mass ejections (CMEs) both domestically and internationally mainly use white light. However, when the shock wave is far from the sun, the white light scattering is weak, making it difficult to truly observe. Furthermore, due to the "central blocking" effect, the white light radiation of CMEs moving in the direction of the Sun-Earth line cannot be observed, and CME events that directly affect the Earth's motion cannot be observed. In contrast, this invention, in the radio band, shows that the radio radiation driven by the CME shock wave is brighter than the sun itself. Radio detection does not require blocking the sun and can directly detect shock-driven radio radiation in the direction of the Sun-Earth line.

[0027] 2. Ground-based radio detection frequencies are all above 10MHz, which can only observe radio radiation within a few solar radii and cannot detect the interplanetary propagation of CMEs. Currently, estimating the arrival time of CMEs to Earth mainly relies on spectral measurements of space-based low-frequency radio waves below 10MHz. However, low-frequency radio spectrum detection detects the entire-sky integrated signal, which can only determine the distance of the shock wave to the Sun, but cannot determine the propagation direction of the shock wave or the distance between the shock wave and Earth. This invention proposes a three-dimensional tomographic imaging detection method for interplanetary shock waves using satellite formations. Utilizing the frequency drift characteristics of solar type II radio bursts, the method performs layering along the distance direction in Sun-Earth space, synthesizing multi-frequency two-dimensional images into a three-dimensional tomographic image, which intuitively provides the propagation direction of the shock wave and its distance from Earth. Attached Figure Description

[0028] Figure 1 This is a flowchart of the three-dimensional tomographic imaging detection method for interplanetary shock waves in satellite formations according to the present invention;

[0029] Figure 2 This is a schematic diagram of the Earth J2000 coordinate system and the observation coordinate system S(X'Y'Z');

[0030] Figure 3 This is a schematic diagram illustrating the principle of three-dimensional tomography spatial resolution.

[0031] Figure 4 It is a simulation of the solar wind propagation process;

[0032] Figure 5 This is a schematic diagram of a 1000km sun-synchronous orbit;

[0033] Figure 6 It is a schematic diagram of the orbital trajectory of the 8 satellites in formation;

[0034] Figure 7 This is a schematic diagram of the projected baseline in the observation coordinate system;

[0035] Figure 8 It is a three-dimensional tomographic image at time T0;

[0036] Figure 9 It is a three-dimensional tomographic image at time T1. Detailed Implementation

[0037] This invention proposes a three-dimensional tomographic imaging method for detecting interplanetary shocks using satellite formations. Radio imaging is achieved above the ionosphere through multi-satellite interferometry, and three-dimensional tomography is realized through multi-frequency imaging. Multiple satellites carry low-frequency interferometric imaging spectrometers, each independently detecting the low-frequency radio spectrum. Simultaneously, inter-satellite interferometry is used to acquire low-frequency radio images at multiple frequencies, thus achieving three-dimensional tomographic detection of interplanetary shocks.

[0038] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0039] Example 1

[0040] like Figure 1 As shown, embodiments of the present invention propose a three-dimensional tomographic imaging method for detecting interplanetary shock waves in satellite formations, as described in detail below:

[0041] Step 1) Select an appropriate orbit based on observation requirements and satellite engineering constraints. For example, the target orbit should be a sun-synchronous orbit to meet the need for continuous solar observation. The optimal formation should ensure uniform baseline length and direction distribution; for example, the solar projection should be roughly circular with radius R. Design a formation configuration of N satellites to ensure uniform distribution of inter-satellite interferometric baselines in both distance and direction.

[0042] Let the orbital elements of the central satellite (or virtual central satellite) be (a0, e0, i0, ω0, Ω0, M0), and the orbital elements surrounding the satellite be: (a k ,e k i k ,ω k ,Ω k M k (k = 1, 2, ..., N-1). Various optimization algorithms are used to ensure that the resulting baseline length and direction are uniformly distributed. Optimization algorithms include: genetic algorithms, particle algorithms, ant colony algorithms, etc. Baseline uniformity metrics include: the Cornwell index, a distribution uniformity measurement function, etc.

[0043] Step 2) Measure the baseline vector (satellite spacing and baseline direction) between any two satellites autonomously or using the Global Navigation Satellite System.

[0044] Let Δr be the three-dimensional detection baseline formed by every two satellites. i,j (u,v,w), normalized to wavelength units, where i,j=1,...,N.

[0045] Step 3) Based on the baseline measurement accuracy requirements, the baseline determination accuracy can be further improved by post-processing based on the absolute orbital elements of each satellite obtained in Step 1), combined with the orbital dynamics characteristics and the inter-satellite baseline measured in real time in Step 2).

[0046] Step 4) Combine all inter-satellite baselines to obtain three-dimensional spatial frequency sampling points for each frequency, form a spatial transfer function, and provide baseline coordinate data for image inversion.

[0047] Construct an observation coordinate system S(X'Y'Z'), where the Z' axis is the direction of heliocentric distance, and the X'Y' plane is a plane perpendicular to the direction of heliocentric distance. The X' axis is selected within the X'Y' plane (e.g., the projection direction of the north axis onto the X'Y' plane). Based on the three-dimensional detection baseline obtained in steps 2) and 3), transform it to the observation coordinate system through coordinate transformation to form a spatial transfer function, obtaining the baseline coordinate data for image inversion. Figure 2 The diagram shows the Earth J2000 coordinate system and the observation coordinate system S (X'Y'Z'). Step 5): The interferometric imaging spectrometer carried by the satellite is set with M observation frequencies. Through inter-satellite interference, the interferometric visibility data of each frequency is obtained. The detection data of different frequencies correspond to different distances of the shock wave from the sun, forming M layers of images with different heliocentric distances.

[0048] Figure 3This is a schematic diagram illustrating the principle of spatial resolution in M-layer images. The interaction of charged particle streams emanating from the Sun generates shock waves. During interplanetary propagation, the farther away from the Sun, the larger the area of ​​the shock wave dispersed in space, as shown by the blue regions at different distances in the figure below. Utilizing the frequency drift characteristics of solar type II radio bursts, the frequency decreases with distance from the Sun, i.e., f1>f2>…>f M For space satellite arrays with the same physical aperture, the detection frequency varies depending on the distance. The farther away from the sun, the lower the spatial resolution, as shown by the grid density in the blue area in the figure below.

[0049] Step 6) Using the three-dimensional baselines of M frequency points obtained in Step 4) and the interference data of M frequency points obtained in Step 5), based on the principle of interferometric imaging, and using the transformation algorithm from the spatial frequency domain to the spatial domain, two-dimensional imaging inversion is performed on the tomographic surfaces at different heliocentric distances in sequence, and the M two-dimensional images are synthesized into a three-dimensional tomographic image.

[0050] Taking M=10 as an example, there are M tomographic surfaces, corresponding to the observation frequency f. k k = 1, 2, ..., 10. The two-dimensional projection baselines are respectively The obtained visibility function is Let the direction cosines of each point on the tomographic surface in the observation coordinate system be (ξ, η). Based on the principle of interferometric imaging, M two-dimensional images are calculated, i.e.

[0051] Step 7) Repeat steps 2 to 6) to achieve continuous observation and imaging, forming a three-dimensional tomographic image that evolves over time, i.e.

[0052] Simulation Examples

[0053] Using 8 satellites in a 1000km sun-synchronous orbit and 10 tomographic surfaces as an example, a simulation is conducted. A suitable corona-interplanetary background solar wind density model is employed to simulate the interplanetary propagation process of the solar wind in Sun-Earth space. For each moment, M two-dimensional images are synthesized into a three-dimensional tomographic image. Continuous observation and imaging allow for the dynamic acquisition of the continuous propagation process of the shock wave in Sun-Earth space, such as... Figure 4 As shown.

[0054] The image centers on the Sun, and the colors represent particle density during the propagation of the solar wind. The cross-sectional view visually illustrates the propagation of shock waves from the Sun to Earth in the Sun-Earth space.

[0055] The target orbit is a 1000km sun-synchronous orbit, with 8 satellites flying in formation: 1 central satellite and 7 orbiting satellites. The formation's projection towards the sun is roughly circular, with a radius of 50km. An example of the target orbit is shown below. Figure 5 As shown:

[0056] A schematic diagram of the orbital trajectory of the 8 satellites in formation is shown below. Figure 6 As shown.

[0057] Taking 1 hour as an example, the baseline formed by 8 satellites is as follows: Figure 7 As shown.

[0058] Figure 8 , Figure 9 Simulation results of daily three-dimensional tomographic imaging at 10 frequency points at times T0 and T1 are presented respectively.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for three-dimensional tomography of interplanetary shock waves of a satellite formation, realized based on an interferometric imager carried by a satellite, the method comprising: Step 1) designing a satellite formation configuration with uniform baseline distribution by using an optimization algorithm according to observation requirements and satellite engineering constraints; Step 2) measuring the baseline between any two satellites in the satellite formation; Step 3) combining all inter-satellite baselines to obtain three-dimensional spatial frequency sampling points at each frequency and form a spatial transfer function; Step 4) setting M observation frequencies for the interferometric imager, obtaining a tomographic surface corresponding to different heliocentric distances at each frequency point through inter-satellite interference; Step 5) based on the principle of interferometric imaging, using a spatial frequency domain to spatial domain transformation algorithm, sequentially performing two-dimensional imaging inversion on the tomographic surface at different heliocentric distances, and then synthesizing a three-dimensional tomographic image; Step 6) repeating steps 2) to 5) to realize continuous observation and imaging, and forming a three-dimensional tomographic image evolving over time.

2. The method according to claim 1, wherein, The uniform baseline distribution of step 1) specifically includes that the distance distribution and direction distribution of the baseline are uniform in the plane perpendicular to the line connecting the sun and the earth, the baseline angle rotates with the orbit period, and only a set of propellants are needed for orbit maintenance and formation maintenance.

3. The method of claim 1, wherein, The optimization algorithm of step 1) includes genetic algorithm, particle algorithm and ant colony algorithm.

4. The method of tomographic probing of interplanetary shock waves of a satellite formation according to claim 1, characterized in that, Step 3) specifically includes: An observation coordinate system S(X'Y'Z') is constructed, the Z' axis is the heliocentric distance direction, the X'Y' plane is the plane perpendicular to the heliocentric distance direction, the projection direction of the north celestial pole in the X'Y' plane is selected as the X' axis, all inter-satellite baseline vectors are combined and converted to the observation coordinate system through coordinate transformation to form a spatial transfer function and obtain baseline coordinate data for image inversion.

5. The method of claim 1, wherein, Step 4) specifically includes: M observation frequencies are set for the interferometric imager, the interference visibility data of each observation frequency is obtained through inter-satellite interference, and M layers of surfaces at different heliocentric distances are formed according to the different distances of the shock wave to the sun corresponding to the interference visibility data at different frequencies.

6. The method of tomographic imaging of interplanetary shocks of a satellite formation according to claim 1, wherein, Step 5) specifically includes: For M observation frequencies f k , k = 1, 2, …, M, the two-dimensional projection base lines are respectively The obtained visibility function is In the observation coordinate system, the direction cosine of each point on the tomographic surface is (ξ, η), and according to the interference imaging principle, M two-dimensional images are calculated, that is Wherein, the frequency f k corresponding two-dimensional image satisfies the following formula: In the formula, j represents the imaginary part; M two-dimensional images are synthesized to form a three-dimensional tomographic image.

7. The method of tomographic imaging of interplanetary shocks of a satellite formation according to claim 6, characterized in that, The time-evolving three-dimensional tomographic images of step 6) are 8. The method of tomographic probing of interplanetary shock waves of a satellite formation according to claim 1, characterized in that, Before step 3), it further includes: according to the baseline measurement accuracy requirement, according to the absolute orbit elements of each satellite in the satellite formation configuration, combining the orbit dynamics characteristics and the real-time measured inter-satellite baseline of step 2), the baseline determination accuracy is further improved through post-processing.

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