A Ship Imaging Method with Rotational Motion Based on Empirical Modal Decomposition

Airborne synthetic aperture radar (SAR) provides high-resolution images of ships. Long synthetic aperture time ensures high resolution. The motion of the ship causes complex and small oscillatory changes in the range, which blurs the results of conventional imaging. To address this problem, this paper studies a ship imaging method with rotational motion based on Empirical Mode Decomposition (EMD). Firstly, the influence of ship's rotational motion on the range is analyzed. It can be approximated as the sum of multiple sinusoidal functions, and the signal model of the ship is given. And then the signal model is extended using the Bessel function and Euler formula. The imaginary part of its azimuth can be expressed as the sum of multiple sinusoidal functions. As a result, a ship imaging method based on EMD is proposed. (1) After migration correction, the signal is passed through the EMD to obtain some Intrinsic Mode Functions (IMFs). The frequencies of the sinusoidal functions are shown on the IMFs. (2) We match its other parameters by parameter search. After the influence of the sine is matched, the range-Doppler (R-D) map has a single focused image. Finally, the effectiveness of the proposed method is verified by experimental simulation.