Imaging algorithm for circular trace scanning synthetic aperture radar using modified hyperbolic range equation

Abstract

For a circular trace scanning synthetic aperture radar (CTSSAR) system, the conventional quadratic range approximation method becomes inefficient when the squint angle exists and the integrated aperture is long. To improve the accuracy in the approximation of the range history for CTSSAR, a modified hyperbolic range equation is introduced to derive the corresponding two-dimensional spectrum and further develop the imaging algorithm for CTSSAR. Promising results prove the effectiveness of the proposed method.Introduction: Circular trace scanning synthetic aperture radar (CTSSAR) has attracted growing attention recently [1] owing to its increasing scanning speed in azimuth, which makes it suitable for widearea fast imaging. Owing to the circular shape of the trajectory, it is not efficient to use the conventional stripmap SAR processor which is based on the assumption of a rectilinear acquisition configuration. An intuitive plausible solution for this configuration is to build a matched filter to focus every pixel of the input data [2]. Although processors of this kind can deal with the nonlinear trajectories perfectly, the computational time consumed is too large to apply it to practical use. In [3], a highspeed focusing algorithm based on chirp scaling is proposed for the CTSSAR ground-based system. The wave-front construction method was used in [4] to perform CTSSAR imaging. Both the two methods are based on the quadratic range approximation. For ideal side-looking CTSSAR imaging, the quadratic approximation may be enough. When it comes to the situation where the squint mode is adopted and the integration time is long, the two-order range approximation becomes inadequate. In this Letter, a novel imaging algorithm is proposed based on the modified hyperbolic range equation. The high-order terms introduced from the circular trajectory are taken into consideration by introducing a modifying component to the hyperbolic range equation. Simulation results are provided to prove the effectiveness of the proposed method.

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