Abstract

As an emerging orbital system with flexibility and brand application prospects, the highly elliptical orbit synthetic aperture radar (HEO SAR) can achieve both a low orbit detailed survey and continuous earth surface observation in high orbit, which could be applied to marine reconnaissance and surveillance. However, due to its large eccentricity, two challenges have been faced in the signal processing of HEO SAR at present. The first challenge is that the traditional equivalent squint range model (ESRM) fails to accurately describe the entire range for the whole orbit period including the perigee, the apogee, and the squint subduction section. The second one is to exploit an efficient HEO SAR imaging algorithm in the squinted case which solves the problem that traditional imaging algorithm fails to achieve the focused imaging processing of HEO SAR during the entire orbit period. In this paper, a novel imaging algorithm for HEO SAR is presented. Firstly, the signal model based on the geometric configuration of the large elliptical orbit is established and the Doppler parameter characteristics of SAR are analyzed. Secondly, due to the particularity of Doppler parameters variation in the whole period of HEO, the equivalent velocity and equivalent squint angle used in MESRM can no longer be applied, a refined fourth-order equivalent squint range model(R4-ESRM) that is suitable for HEO SAR is developed by introducing fourth-order Doppler parameter into Modified ESRM (MESRM), which accurately reconstructs the range history of HEO SAR. Finally, a novel imaging algorithm combining azimuth resampling and time-frequency domain hybrid correlation based on R4-ESRM is derived. Simulation is performed to demonstrate the feasibility and validity of the presented algorithm and range model, showing that it achieves the precise phase compensation and well focusing.

Highlights

  • The highly elliptical orbit is mainly used in space exploration, communication and remote sensing engineering practice that enables a good observation of coverage characteristics

  • The imaging simulation experiments are performed at apogee and the squint subduction section of HEO to compare the focusing results based on R4-equivalent squint range model (ESRM) and other range model for different case by using the proposed imaging algorithm, respectively

  • A refined fourth-order equivalent squint range model and imaging method for slide spotlight synthetic aperture radar (SAR) are proposed for highly elliptical orbit

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Summary

Introduction

The highly elliptical orbit is mainly used in space exploration, communication and remote sensing engineering practice that enables a good observation of coverage characteristics. The eccentricity of the highly elliptical orbit is generally greater than 0.6, its perigee height is usually 500 km, and the apogee height is up to 50,000 km. The HEO satellite moves near the apogee for about two-thirds of the orbit period, and it can realize that more than 90% of the arcs in cycle are located over the northern and southern hemispheres.

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