Estimating Parameters of Ground Moving Targets by Exploiting Shadow Features in Terahertz Video SAR

Abstract

For effective imaging, detection, and tracking with terahertz video synthetic aperture radar (THz-ViSAR), the precise parameter estimation of ground moving targets (GMTs) serves as an essential prerequisite. To obtain precise motion parameters, this article proposes a shadow-based estimation method for estimating GMT parameters applicable to THz-ViSAR. Once the initial image data of the moving target is acquired, precise imaging is achieved through envelope alignment, initial phase correction, two second-order keystone transformations, minimum entropy map drift algorithm, and phase gradient autofocus algorithm. Due to the Doppler effect, the light spots are generated at a location that deviates from the true position of the moving target. The obstructions caused by electromagnetic radiation leave shadows at the true position of the moving target. The range velocity is estimated by measuring the distance from the light spot to the shadow; the azimuthal velocity is estimated by measuring the azimuthal broadening of the light spot and shadow; the range acceleration is estimated from the Doppler frequency rate. Simulations involving cooperative moving targets and practical experiments with noncooperative targets demonstrate that accurate estimation of motion parameters is achieved by the proposed method.