Abstract

Stable and efficient ground moving target tracking and refocusing is a hard task in synthetic aperture radar (SAR) data processing. Since shadows in video-SAR indicate the actual positions of moving targets at different moments without any displacement, shadow-based methods provide a new approach for ground moving target processing. This paper constructs a novel framework to refocus ground moving targets by using shadows in video-SAR. To this end, an automatic-registered SAR video is first obtained using the video-SAR back-projection (v-BP) algorithm. The shadows of multiple moving targets are then tracked using a learning-based tracker, and the moving targets are ultimately refocused via a proposed moving target back-projection (m-BP) algorithm. With this framework, we can perform detecting, tracking, imaging for multiple moving targets integratedly, which significantly improves the ability of moving-target surveillance for SAR systems. Furthermore, a detailed explanation of the shadow of a moving target is presented herein. We find that the shadow of ground moving targets is affected by a target’s size, radar pitch angle, carrier frequency, synthetic aperture time, etc. With an elaborate system design, we can obtain a clear shadow of moving targets even in X or C band. By numerical experiments, we find that a deep network, such as SiamFc, can easily track shadows and precisely estimate the trajectories that meet the accuracy requirement of the trajectories for m-BP.

Highlights

  • Synthetic Aperture Radars (SAR) that are mounted on aircrafts, satellites or other platforms are usually used to obtain images of regions of interest for all-weather all-time high-resolution reconnaissance [1,2,3]

  • To analyze the signal characteristics of moving target, we model the geometry of an synthetic aperture radar (SAR) system for observing a ground moving target as shown in Figure 1, in which x denotes azimuth direction, i.e., the direction that the platform moves, y and z denote range and height directions, respectively

  • For SiamFc, the tracking time of each frame is less than 0.01 s for a single target. moving target back-projection (m-BP) has the same efficiency as the standard BP

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Summary

Introduction

Synthetic Aperture Radars (SAR) that are mounted on aircrafts, satellites or other platforms are usually used to obtain images of regions of interest for all-weather all-time high-resolution reconnaissance [1,2,3]. Ground moving target imaging is still a challenging task due to the unknown target’s trajectory. In early moving target imaging problems, a Moving Target Indicator (MTI) radar is utilized to detect moving targets and estimate the motion parameters under a relatively high signal-to-clutter ratio condition. The keystone transform [18] is popular for its capability of eliminating an arbitrary linear range migration, which might blur the moving target in the SAR image [19]

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