Abstract
In high-resolution spaceborne synthetic aperture radar (SAR), imaging of moving ship targets is strongly influenced by ships’ complex three-axis motions, so that imaging results are fuzzy and unfocused. Yet scattered and moving information on ship targets is wholly contained in the complex image data. This paper proposes a novel SAR and inverse SAR (SAR–ISAR) hybrid imaging method to improve imaging effects, using this complex SAR image data on ship targets, and based on frequency-domain-extraction-based adaptive joint time frequency (FDE–AJTF) decomposition. First, complex SAR image data is transformed to the Doppler domain in the azimuth dimension, and the optimum azimuth data are selected. Next, the signal in each range cell is decomposed to its polynomial phase signal (PPS) components by FDE–AJTF. Finally, a two-dimensional image of the ship target at a given azimuth time is constructed directly. The feasibility and effectiveness of this proposed imaging method is verified through comparisons with conventional methods in simulation and experimental tests.
Highlights
Ships are an essential ocean target that play important roles both in the civil and military fields.Spaceborne synthetic aperture radar (SAR) has obvious advantages in ship target surveillance on the vast ocean, due to its all-time and all-weather active imaging abilities
Ship rotation leads to different movement characteristics of its scattering points, and as a result the envelope migrations are different in different range cells
The high-resolution SAR echo of a moving ship can be expressed as a high-order multicomponent polynomial phase signal [10], which may contain severe envelope migration and Doppler wrapping
Summary
Ships are an essential ocean target that play important roles both in the civil and military fields. The high-resolution SAR echo of a moving ship can be expressed as a high-order multicomponent polynomial phase signal (mc-PPS) [10], which may contain severe envelope migration and Doppler wrapping Under these circumstances, the classical time frequency analysis method cannot satisfy the processing requirements of mc-PPS. Based on FDE–AJTF decomposition, we propose a novel SAR–ISAR hybrid imaging method to solve the high-resolution imaging problems presented by a moving ship In this method, the moving ship area on the complex SAR image data is initially tailored and translated to the range-Doppler domain by Fourier transformation; the optimum azimuth data with well-aligned envelopes is selected and decomposed to PPS components by the FDE–AJTF method; and a two-dimensional. RID image is constructed from these PPS components of all range cells
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