Abstract
Geosynchronous Synthetic Aperture Radar (GEO SAR) has a very long Coherent Processing Interval (in the order of hundreds of seconds) compared with other SAR platforms. Thus, the current methods of rotation effect matching and ship imaging that operate within a relatively short Coherent Processing Interval (in the order of seconds) are obviously not applicable. To address this problem, a novel ship imaging method with multiple sinusoidal functions matching for rotation effects is proposed for GEO SAR. Firstly, the influence of the rotational motion of a ship on the slant range is analyzed. It can be matched with the sum of multiple sinusoidal functions, and the signal model of a ship with rotational motion is given. Then, multiple sinusoidal functions for the matching-based ship imaging method are proposed, and their procedures are presented as follows: (1) The Generalized Keystone Transform and Generalized Dechirp Process (GKTGDP) is modified to compensate for the range migration and phase caused by the motion of GEO SAR. Then, the signal is focused at the frequencies of sinusoidal functions, and the frequencies can be matched. (2) From the matched frequencies, the other parameters of sinusoidal functions can be matched by parameter searching. (3) Based on the matched results, the Back Projection Algorithm (BPA) is used to take an image of the ship with rotational motion. Finally, the effectiveness of the proposed method is verified by numerical experiments.
Highlights
Synthetic Aperture Radar (SAR) can work all day and in all weather conditions to obtain high-resolution remote sensing images [1]
It can be seen that when the radar illuminates the ship, three rotational motions that trend to sinusoidal have been projected into the slant range
The Generalized Dechirp Process (GDP) is used to compensate for the phase caused by the platform’s motion, and the frequencies of sinusoidal function can be matched in the RD domain
Summary
Synthetic Aperture Radar (SAR) can work all day and in all weather conditions to obtain high-resolution remote sensing images [1]. GEO SAR has a very long Coherent Processing Interval (CPI) of hundreds of seconds, which causes a curved synthetic aperture trajectory; a very high orbital height of GEO SAR causes non-negligible signal round-trip delay [13,25] These characteristics will cause the ship imaging to have unprecedented problems. Because the CPI in GEO SAR is in the order of hundreds of seconds, the influence of rotational motion tends to have sinusoidal character [36] and cannot be matched with the high-order Taylor series. The rotational motion introduces the sinusoidal function phase, which causes nonstationary phase modulation of the echo signals of SAR [37] This translates the focused image into several “ghost” targets [38].
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