Abstract
Nonuniformly-rotating ship refocusing is very significant in the marine surveillance of satellite synthetic aperture radar (SAR). The majority of ship imaging algorithms is based on the inverse SAR (ISAR) technique. On the basis of the ISAR technique, several parameter estimation algorithms were proposed for nonuniformly rotating ships. But these algorithms still have problems on cross-terms and noise suppression. In this paper, a refocusing algorithm for nonuniformly rotating ships based on the bilinear extended fractional Fourier transform (BEFRFT) is proposed. The ship signal in a range bin can be modeled as a multicomponent cubic phase signal (CPS) after motion compensation. BEFRFT is a bilinear extension of fractional Fourier transform (FRFT), which can estimate the chirp rates and quadratic chirp rates of CPSs. Furthermore, BEFRFT has excellent performances on cross-terms and noise suppression. The results of simulated data and Gaofen-3 data verify the effectiveness of BEFRFT.
Highlights
In the marine surveillance of satellite synthetic aperture radar (SAR), nonuniformly-rotating ship refocusing is very significant for the detection and identification of ships
The results of ship target simulation are given to illustrate the refocusing performance of proposed bilinear extended fractional Fourier transform (BEFRFT), and the Gaofen-3 data are utilized to verify the effectiveness of BEFRFT
It can be seen that three point targets are all well-focused after applying BEFRFT
Summary
In the marine surveillance of satellite synthetic aperture radar (SAR), nonuniformly-rotating ship refocusing is very significant for the detection and identification of ships. The range-Doppler (RD) algorithm based on the ISAR technique can be utilized to coarsely focus rotating ship images. Doppler (RID) algorithm utilizes time-frequency transformations [7] instead of Fourier transformations This class of algorithms has problems of loss of resolution and cross-terms, which appear as false points in ship images. Fractional Fourier transform (FRFT) [13] is applied to estimate parameters of LFM signals in SAR imaging [5,6]. A refocusing algorithm for nonuniformly rotating ships based on the bilinear extended fractional Fourier transform (BEFRFT) is proposed. Different from FRFT, which is a LFM estimator, BEFRFT is a bilinear extension of FRFT and is proposed to estimate the parameters of CPSs. BEFRFT can effectively reduce the disturbance of cross-terms and noise, which is adaptive to low SNR conditions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
