The usage of a hypersonic platform for remote sensing application has promising prospects, especially for hypersonic platform-borne synthetic aperture radar (SAR) imaging. However, the high-speed of hypersonic platform will lead to extreme friction between the platform and air, which will cause the ionization of air. The ionized gas forms the plasma sheath wrapped around the hypersonic platform. The plasma sheath will severely affect the propagation of SAR signal and further affect the SAR imaging. Therefore, hypersonic platform-borne SAR imaging should be studied from a physical perspective. In this paper, hypersonic platform-borne SAR imaging under plasma sheath is analyzed. The SAR signal propagation in plasma sheath is computed using scatter matrix method. The proposed SAR signal model is verified by using a ground experiment system. Moreover, the effect of attenuation caused by plasma sheath on SAR imaging is studied under different SAR parameters and plasma sheath. The result shows that attenuation caused by plasma sheath will degrade the SAR imaging quality and even cause the point and area targets to be submerged into the noise. The real SAR images under plasma sheath also illustrate this phenomenon. Furthermore, by studying imaging results under different SAR and plasma parameters, it can be concluded that the severe degradation of SAR imaging quality appears at condition of high plasma sheath electron density and low SAR carrier frequency. The work in this paper will be beneficial for the study of hypersonic platform-borne SAR imaging and design of hypersonic SAR imaging systems in the future.

中文翻译：

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高超声速平台载 SAR 成像分析：物理视角

高超声速平台在遥感应用中的应用前景广阔，特别是在高超声速平台载合成孔径雷达（SAR）成像方面。然而，高超声速平台的高速会导致平台与空气之间产生极大的摩擦，从而导致空气电离。电离气体形成包裹在高超音速平台周围的等离子体鞘。等离子体鞘层会严重影响SAR信号的传播，进而影响SAR成像。因此，应从物理角度研究高超声速平台载SAR成像。本文对等离子体鞘下高超声速平台载SAR成像进行了分析。使用散射矩阵方法计算等离子体鞘中的 SAR 信号传播。通过使用地面实验系统验证了所提出的SAR信号模型。而且，研究了不同SAR参数和等离子体鞘层下等离子体鞘层衰减对SAR成像的影响。结果表明，等离子体鞘层引起的衰减会降低SAR成像质量，甚至会导致点目标和面目标淹没在噪声中。等离子鞘下的真实SAR图像也说明了这一现象。此外，通过研究不同SAR和等离子体参数下的成像结果，可以得出结论，在高等离子体鞘电子密度和低SAR载频条件下，SAR成像质量出现严重下降。本文的工作将有利于今后高超声速平台载SAR成像的研究和高超声速SAR成像系统的设计。