A Distributed Satellite Formation Method for SAR Three-Dimensional Tomography Applications

MA Lixiang; MA Yuechen; YIN Ke; HAN Xiaolei; CHEN Longyong; ZHANG Bingchen

doi:10.11999/JEIT260709

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MA Lixiang, MA Yuechen, YIN Ke, HAN Xiaolei, CHEN Longyong, ZHANG Bingchen. A Distributed Satellite Formation Method for SAR Three-Dimensional Tomography Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260709

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MA Lixiang, MA Yuechen, YIN Ke, HAN Xiaolei, CHEN Longyong, ZHANG Bingchen. A Distributed Satellite Formation Method for SAR Three-Dimensional Tomography Applications[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260709

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A Distributed Satellite Formation Method for SAR Three-Dimensional Tomography Applications

doi: 10.11999/JEIT260709 cstr: 32379.14.JEIT260709

1.
Insittute of Remote Sensing Satellite, Chinese Academy of Space Technology, Beijing 100094, China
2.
Insttute of Spacecraft System Engineering, Beijing 100094, China
3.
Aerospace Information Research Institute, Chinese Academy of Sciences , Beijing 100080, China

Funds: National Key Research and Development Program of China (2022YFB3901602)

Received Date: 2026-05-29
Accepted Date: 2026-10-16
Rev Recd Date: 2026-10-13

Available Online: 2026-10-25

Abstract

Abstract

Objective SAR three-dimensional tomography technology can not only overcome the issues of overlapping, perspective foreshortening, and shadowing encountered in two-dimensional SAR imaging, but also resolve the problem of height-upward scattering-point resolution, achieving true three-dimensional high-precision imaging of targets. In SAR three-dimensional tomography applications, high-resolution and high-precision imaging requires multiple observations and data accumulation over the same location. Satellite systems must conduct repeated overpass observations to accomplish this task, necessitating frequent orbit control to maintain the required satellite altitude for observation, which incurs significant system costs. Even so, the impact of temporal decorrelation cannot be eliminated. Distributed formation satellites can achieve simultaneous multi-station observation of the same region through coordinated flight of multiple satellites. However, the current typical distributed formation systems are not optimal for SAR three-dimensional tomography. This paper proposes an array formation design method tailored for tomography applications, enabling the creation of a distributed satellite airborne observation array through rational formation design. This approach achieves high-precision, high-resolution three-dimensional SAR imaging in a single pass, while also proposing formation maintenance strategies based on the stability of actual in-orbit formations, demonstrating practical application value. Methods To meet the elevation-direction array imaging requirements for SAR 3D tomography, a distributed SAR satellite three-dimensional baseline mathematical model is established by modeling the relative motion of formation satellites, which is then converted into RTN coordinates to construct the elevation-direction synthetic aperture, normal baseline, and along-track baseline required for SAR tomography. This establishes a direct correspondence between the three-dimensional baseline and the six orbital elements of formation satellites, enabling the desired baseline distribution to be achieved by directly designing the orbital parameters of formation satellites. Based on the linear array observation requirements, two types of multi-satellite formations are designed: a nested wheel abreast formation with vertically aligned satellites and a lateral abreast formation with satellites aligned along the track. Each satellite in the formation orbits the configuration center in circular and harmonic relative motion, forming an array formation at any given moment. The spatial baselines formed by the multi-satellite formations designed using this method all satisfy the array observation requirements for SAR 3D tomography applications. The article also includes simulation analysis of formation configuration divergence and proposes corresponding formation maintenance strategies, demonstrating strong engineering feasibility. Results and Discussions A nested wheel side-by-side multi-satellite formation is designed to construct a vertical aperture baseline, with the normal baseline set to zero and the latitude angles u_a=u_c. The eccentricity, semi-major axis, and perigee angle of the main satellite and follower satellites are configured according to the required vertical aperture baseline length. The latitude angle design is determined based on the required observation latitude, ensuring the maximum radial baseline occurs at the desired observation position, resulting in a radial baseline maximum amplitude of $ a{e}_{a} $, yielding a vertically aligned linear distributed SAR formation model (Figure 3 Configuration diagram of nested wheel side-by-side multi-satellite formation, Figure 4 Baseline distribution diagram of nested wheel side-by-side multi-satellite formation). To construct a normal baseline, a transverse side-by-side multi-satellite formation is designed with the radial baseline set to zero. The follower satellite's eccentricity ea is set to 0, and the right ascension difference of the ascending node ΔΩ between the main satellite and follower satellites is configured to achieve the normal baseline, with a maximum amplitude of $ |{a}_{c}({\Omega }_{a}-{\Omega }_{c})\sin {i}_{c}| $. This results in a transversely aligned linear four-satellite formation (Figure 5 Configuration diagram of transverse side-by-side multi-satellite formation, Figure 6 Baseline distribution diagram of transverse side-by-side multi-satellite formation). Both configurations provide stable array observation baselines to meet SAR 3D tomographic imaging requirements. Taking the nested wheel side-by-side four-satellite formation as an example, this study analyzes configuration divergence under atmospheric drag effects. Based on semi-major axis attenuation-induced along-track drift, a configuration maintenance strategy is proposed where the maximum elliptical center drift difference of the relative motion between two satellite groups should not exceed L_max. When$ \left| {\Delta }_{1}-{\Delta }_{2}\right| \leq {L}_{\max } $, the formation can perform SAR imaging tasks normally; when$ \left| {\Delta }_{1}-{\Delta }_{2}\right| \geq {L}_{\max } $, configuration maintenance operations are required. Comparative simulation analysis of SAR 3D tomographic imaging between the nested wheel side-by-side four-satellite formation and the cartwheel formation with a central master satellite and orbiting auxiliary satellites. Within the incidence angle range, the coherence coefficient of the proposed configuration is consistently higher than that of the cartwheel configuration. This reduces coherence loss caused by along-track separation of formation satellites, thereby facilitating higher 3D imaging accuracy (Figure 12 Comparison of doppler spectrum decorrelation with ground incidence angle). Conclusions In summary, the distributed satellite formation with nested wheel side-by-side four-satellite formation designed according to the method in this article can provide stable vertical synthetic aperture length for 3D tomographic imaging. The formation configuration maintenance strategy is simple and easy to implement, and has good engineering feasibility.The distributed satellite formation system has the advantage of obtaining multiple observations in a single flight, overcoming the disadvantage of time decorrelation in traditional multi flight observations, and has unique advantages in achieving high-precision and high-resolution 3D tomographic SAR imaging. The nested wheel formation configuration and the lateral parallel formation configuration designed in this article can form a stable vertical aperture baseline in the vertical direction for systematic linear observation. Simulation results show that the divergence drift of the nested wheel side-by-side multi-satellite formation configuration in coplanar flight in space is mainly caused by the attenuation of the semi major axis. The stability of the formation configuration can be maintained by controlling the attenuation speed of the semi major axis to meet the execution of the formation task. The calculation results align with actual formation simulation outcomes.Imaging simulation results indicate that the proposed distributed satellite formation, featuring a nested cartwheel configuration with four side-by-side satellites, can provide stable tomographic baselines for SAR 3D tomographic imaging, reduce coherence loss caused by along-track separation of the formation satellites, and enhance 3D imaging performance.The research results of this article can provide technical references for the design of next-generation 3D tomographic SAR imaging systems.

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References(15)

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