Abstract
Time-domain algorithms have significant performance advantages for missile-borne synthetic aperture radar (SAR) focusing with diving movement. However, due to the diving curve trajectory of the missile platform, the range and angular histories of the target become very sensitive to unknown tomography, which provides difficulties for SAR algorithm development. To address this problem, we have proposed a new fast factorized back-projection (FFBP) algorithm with reduced topography sensibility for missile-borne SAR focusing. The new algorithm was designed based on an orthogonal cylindrical coordinate (OCC) system, in which the cross section of a cylinder in the coordinate system is approximately orthogonal to the diving curve trajectory. Owing to the acquisition symmetry of the OCC system, the range and the angular histories of the grid in the OCC geometry become less dependent of the topography in every recursion of FFBP implementation, which can dramatically reduce the adverse effects of unknown topography and achieve high focusing performance. In the simulation, echo signal based on a set of typical parameters from a missile-borne SAR system is generated with unknown tomography. Promising results with 1 m resolution are finally achieved, which demonstrates the performance of the proposed algorithm. The limitation of the algorithm is also discussed in the final part, which will facilitate the development of raw data processes in practical application.
Highlights
Due to the ability to work in all weather and all day and night, the synthetic aperture radar (SAR) has become a significant tool for microwave remote sensing [1,2,3,4]
The new algorithm was designed based on an orthogonal cylindrical coordinate (OCC) system, in which the cross section of a cylinder in the OCC system is approximately orthogonal to the diving curve trajectory
In OCC-based fast factorized back-projection (FFBP) algorithm, we introduce angular error of ∆β which denotes the difference between β0 and β1, which is dependent on the curvature of the trajectory as well as the tomography of the observing target
Summary
Due to the ability to work in all weather and all day and night, the synthetic aperture radar (SAR) has become a significant tool for microwave remote sensing [1,2,3,4]. FDAs are based on the foundation of the classic azimuth-invariant assumption that may not be valid in missile-borne SAR focusing with a diving curve trajectory as well as varying velocity, as this introduces difficulties to the algorithm development [11] This motivates us to study TDAs to obtain better focusing performance. In conventional monostatic airborne SAR, the radar platform generally moves along a linear trajectory In this case, the acquisition geometry is fit to a circular cylindrical symmetry [11], which makes precise calculations of the range and angular histories in FFBP recursion independent from the tomography information of target. In the application of missile-borne SAR, the currently used acquisition no longer satisfies circular cylindrical symmetry due to the diving curve trajectory, cause range, and angular histories in FFBP recursion being highly dependent on the tomography.
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