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全文摘要次数: 190 全文下载次数: 258
引用本文:

DOI:

10.11834/jrs.20210378

收稿日期:

2020-08-31

修改日期:

2021-03-31

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基于GPS-R的双基地SAR移动目标成像方法研究
何振宇, 杨扬, 陈武, 翁多杰
香港理工大学 土地测量及地理资讯学系
摘要:

全球导航卫星系统反射 (global navigation satellite system reflectometry,GNSS-R)做双基地合成孔径雷达(简称GNSS-SAR)是近年来的新兴研究方向。当前GNSS-SAR成像的主要对象是地表静态目标,关于动目标成像的研究非常少。为了扩大GNSS-SAR的应用范围,本文以全球定位系统(global positioning system, GPS)卫星作为照射源,提出一种基于频域的动目标成像方法应用于海面移动船只成像。本文首先构建了双基地几何模型,然后推导了一种近似的双基地距离历程用于描述目标回波的方位向相位变化。采用Keystone变换校正由目标运动导致的未知距离单元徙动,采用基于短时傅里叶(short time Fourier transform,STFT)+随机抽样一致性(random sample consensus,RANSAC)的方法估计目标的移动速度。最后,推导了方位向匹配压缩以实现动目标成像。采集的现场实验数据用于验证本文的方法。实验结果分别从速度估计、垂直距离估计、船长度估计和判断目标移动方向四个方面验证了本文方法的有效性。

Bistatic SAR moving target imaging algorithm study based on GPS-R signal
Abstract:

Global navigation satellite system reflectometry (GNSS-R) is a typical fusion application of both remote sensing and navigation technology and has become a potential research direction. In recent years, using GNSS-R to construct a passive bistatic synthetic aperture radar (called as GNSS-SAR) has drawn much attention from the research community. Current investigations of GNSS-SAR concentrate on the static objects on land. However, few contributions to the moving target imaging can be found in this novel field. Imaging moving target is a long-standing subject for modern SAR systems. But traditional GNSS-SAR image formation algorithms cannot be directly applied for the moving target due to the unknown motion. As a result, the moving target will be smeared and shifted in the static SAR image. To extend the application of GNSS-SAR, this paper selects global positioning system (GPS) satellite as the illuminator of opportunity and proposes a frequency domain-based moving target image formation algorithm that has a higher processing efficiency than the traditional time domain-based GNSS-SAR algorithm. To image the moving target, the frequency domain-based algorithm should solve three main problems: (1) The unknown range cell migration induced by the moving target should be corrected. (2) The velocity of the moving target should be estimated. (3) The azimuth compression derivation should be performed due to the bistatic acquisition geometry. To deal with the main problems, this paper selects maritime moving ships as the targets of interest and constructs a bistatic acquisition geometry where the receiver and the satellite are stationary during the observation time while the trajectory of the moving target perpendicular to the line of sight of the receiver antenna is used as a synthetic aperture. Based on the bistatic acquisition geometry, an approximate bistatic range history is first deduced to describe the azimuthal phase variation of the target signal. Then, a Keystone transform is employed to address the unknown range cell migration, and a method based on short-time Fourier transform (STFT) and random sample consensus (RANSAC) is proposed to estimate the velocity. Finally, a derivation of azimuth compression is conducted to accomplish the moving target imaging. Field experiments were carried out to validate the proposed moving target image formation algorithm. The experimental results show that: (1) The proposed velocity estimation method can obtain the velocity in a low signal-to-noise ratio scene where the least square method cannot work. Due to the long observation time, the fluctuations of the target complex reflectivity will affect the velocity estimation results, leading to errors. But the errors between the estimated velocities from two groups of experimental data and the ground truth do not exceed 0.6 m/s. (2) Two targets shown in the SAR image have good accordance with the ground truth in terms of the target-to-receiver vertical distances along the Range axis and the ships" length along the Cross-range axis. (3) The designed azimuth matched filter can help judge the target’s moving direction. But this capability will disappear with the quasi-monostatic configuration. Therefore, the feasibility of the proposed moving image formation algorithm has been confirmed. The proposed algorithm can be used for monitoring the moving ship target and obtain the target’s velocity, length, vertical distance and moving direction in the future.

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