Analysis of Hypersonic Platform-Borne SAR Imaging: A Physical Perspective

Gezhao Niu,Lihao Song,Liang Zhao,Bowen Bai,Yanming Liu,Xiaoping Li,Hui Zhou

doi:10.3390/rs13234943

Abstract

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.

Highlights

Hypersonic platform-borne synthetic aperture radar (SAR) imaging has a promising application prospect [1,2,3,4,5]
The attenuation caused by plasma sheath will seriously affect the range compressed result and further affect SAR imaging quality
As the value of electron density of plasma sheath has a large varying range, for a specific carrier frequency, the conditions including that carrier frequency is larger than the plasma frequency, the carrier frequency is close to the plasma frequency, and the carrier frequency is smaller than the plasma frequency will probably happen

Summary

Introduction

Hypersonic platform-borne synthetic aperture radar (SAR) imaging has a promising application prospect [1,2,3,4,5]. The SAR signal model under plasma sheath should be established and verified, and the effect of plasma sheath on hypersonic platform-borne SAR imaging should be clarified. The study of SAR signal model under plasma sheath is a new problem and is fundamental for hypersonic platform-borne SAR imaging. The SAR signal propagates through plasma twice and the transmission effect caused by plasma sheath is coupled into the SAR signal. In this study, hypersonic platform-borne SAR signal model under plasma sheath is established theoretically and verified experimentally. From the theoretical and experimental results, it can be found that the plasma sheath will bring significant amplitude attenuation of SAR signal, which will cause the decrease of peak value of range compressed signal This phenomenon is important and will significantly affect SAR imaging quality.

Introduction of of Hypersonic

Experimental Verification of the SAR Signal Model under Plasma Sheath

Schematic

13. Signal

Results and Discussion

Point Target Response under Plasma Sheath

The Factors Determining SAR Imaging Quality

Conclusions