Browsing by Author "Li, Yuanhao"

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    Improving 2D resolution in geosynchronous SAR via spatial spectrum synthesis: method and verification
    (IEEE, 2024-02-01) Chen, Xinyan; Chen, Zhiyang; Li, Yuanhao; Hu, Cheng; Dong, Xichao; Hobbs, Stephen
    Geosynchronous synthetic aperture radar (GEO SAR) has the advantages of a short revisit time and a large beam footprint. Enhancing spatial resolution has become a hotspot in spaceborne SAR research areas. The existing designs of GEO SAR suffer from the problem of poor resolution (greater than 10 m) and cause low-precision observation in urban areas. First time, this article points out that GEO SAR has the ability to improve the two-dimensional (2-D) resolution of SAR images by spatial spectrum synthesis based on 2-D baselines, and proposes models and a signal processing method involved in GEO SAR spectrum synthesis. The 2-D spatial baselines of GEO SAR are analyzed and evaluated first based on satellite software and real ephemeris from Beidou Inclined Geosynchronous Orbit (IGSO) navigation satellites to demonstrate the potential of 2-D resolution improvement. Then the analytical models of the spectral shape and relative spectral shift between GEO SAR images are derived. Furthermore, a 2-D spectrum synthesis algorithm suitable for GEO SAR is also proposed, where we use deramping operation instead of the traditional spectrum shifting process. Nonideal factors are considered in the processing of synthesized. In addition, performances of the proposed algorithm, including the resolution improvement factor, the amplitude fluctuation, and the critical baseline, are constructed. Finally, computer simulations and equivalent experiments based on Beidou IGSO navigation satellites verify the proposed algorithm.
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    Research progress on geosynchronous synthetic aperture radar
    (Elsevier, 2021-05-04) Hu, Cheng; Chen, Zhiyang; Li, Yuanhao; Dong, Xichao; Hobbs, Stephen
    Based on its ability to obtain two-dimensional (2D) high-resolution images in all-time and all-weather conditions, spaceborne synthetic aperture radar (SAR) has become an important remote sensing technique and the study of such systems has entered a period of vigorous development. Advanced imaging modes such as radar interferometry, tomography, and multi-static imaging, have been demonstrated. However, current in-orbit spaceborne SARs, which all operate in low Earth orbits, have relatively long revisit times ranging from several days to dozens of days, restricting their temporal sampling rate. Geosynchronous SAR (GEO SAR) is an active research area because it provides significant new capability, especially its much-improved temporal sampling. This paper reviews the research progress of GEO SAR technologies in detail. Two typical orbit schemes are presented, followed by the corresponding key issues, including system design, echo focusing, main disturbance factors, repeat-track interferometry, etc, inherent to these schemes. Both analysis and solution research of the above key issues are described. GEO SAR concepts involving multiple platforms are described, including the GEO SAR constellation, GEO-LEO/airborne/unmanned aerial vehicle bistatic SAR, and formation flying GEO SAR (FF-GEO SAR). Due to the high potential of FF-GEO SAR for three-dimensional (3D) deformation retrieval and coherence-based SAR tomography (TomoSAR), we have recently carried out some research related to FF-GEO SAR. This research, which is also discussed in this paper, includes developing a formation design method and an improved TomoSAR processing algorithm. It is found that GEO SAR will continue to be an active topic in the aspect of data processing and multi-platform concept in the near future.