Abstract

The synthetic aperture radar (SAR) is an important means of ship surveillance, but the motion of the ship leads to azimuth position offset, false targets, and azimuth defocusing for the spaceborne high-resolution and wide-swath (HRWS) SAR system, causing the degradation of imaging quality. The automatic identification system (AIS) can provide real-time information of the ships, which is an important auxiliary method for ship surveillance. Up to now, the traditional fusion of SAR and AIS mainly has focused on location matching and auxiliary recognition, and the next generation of GaoFen-3 (GF-3NG) satellite is equipped with both a SAR sensor and an AIS sensor to obtain the SAR images and simultaneous AIS information of ships. Consequently, this paper proposes a novel scheme to improve the imaging quality of moving ships for GF-3NG using AIS information. In this paper, through introducing the virtual stationary target, the slant range derivation (SRD) algorithm is proposed to estimate the radial velocity (RV) and the radial acceleration (RA) between the ship and the SAR platform relative to the stationary scene. According to the calculated RV, the azimuth position offset can be estimated and the ship can be repositioned on the image. After that, the traditional method is conducted to suppress the false targets. Finally, the method of using the RA to refocus ship slices is proposed. Additionally, the experiment results based on real data illustrate the effectiveness of the proposed methods.

Highlights

  • With the continuous improvement of the resolution and surveying width of the spaceborne synthetic aperture radar (SAR), the spaceborne SAR has gradually become an important means of ship surveillance [1,2,3,4]

  • The automatic identification system (AIS) data for the experiment are provided by the commercial company [25]

  • In the radial velocity (RV) estimation, the difference between the results of the slant range derivation (SRD) algorithm and the other three methods was within 0.61 m/s, and from the relocation results of Figure 8, the SRD algorithm and velocity projection (VP) algorithm were more accurate than the maximum likelihood (ML)-based and time-domain correlation (TDC) algorithm with lower computational complexity

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Summary

Introduction

With the continuous improvement of the resolution and surveying width of the spaceborne synthetic aperture radar (SAR), the spaceborne SAR has gradually become an important means of ship surveillance [1,2,3,4]. The Doppler effect between the SAR and target is the key to achieve high azimuth resolution, but the motion of the ship on the sea surface introduces an extra Doppler frequency shift, which results in the azimuth position offset and azimuth defocus of the ship after imaging [5,6,7]. There are false targets along the azimuth in multichannel mode. All of these damage the quality of the SAR image, which is not conducive to ship surveillance. Scholars have proposed a large number of algorithms to estimate the motion of the ship in order to improve

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