Biying Lu

Detection of Human Beings in Motion Behind the Wall Using SAR Interferogram

This letter presents a novel change detection technique based on stepped-frequency continuous-wave synthetic aperture radar interferometry to detect human beings in motion inside a building. The proposed approach to moving-target indication consists of radar image formation, noncoherent energy change detection, and interferometric phase detection. Experimental results demonstrated that the proposed approach can dramatically reduce false alarms compared with a conventional noncoherent change detection approach.

Moving Target Imaging and Ghost Mitigation in Through-the-Wall Sensing Application

Human is one kind of the most interesting targets in through-the-wall imaging. In high-resolution imaging applications, human is no longer a point target. Therefore, the previous signal models constructed by point target assumption cannot accurately describe real characteristics of EM propagation. We construct the signal models based on extended target theory in this paper. Compared with previous works, the main contributions are as follows. Firstly, human is considered as an extended target. The expressions of target scattering and wall reflections are derived. Secondly, target scattering is no longer isotropic in new model. A new kind of ghost problem which is caused by target obscuring in EM propagation is discovered and exploited. Thirdly, to improve image quality in moving target imaging, an efficient approach which adopts CFAR, clustering method, and spatial geometry relationship is proposed to remove the ghosts. The derived models are shown to agree with synthetic and experimental results. And the efficiency of proposed method is also validated, which illuminates that the ghosts are efficiently mitigated and the image quality is significantly improved.

Building interior layout reconstruction from through-the-wall radar image using MST-based method

In order to reconstruct the building interior layout from the through-the-wall radar image, this paper proposes a method based on minimum spanning tree (MST) which comes from the graph theory. The building layout graph (BLG) model is firstly established using the wall-wall-floor trihedrals inside the building. The vertex set and the edge set including the weight between any two nodes of the graph are defined afterwards. Then, the MST-based method is used to reconstruct the building interior layout. We have also improved the traditional method by applying the MST model with restricted conditions to solve the reconstruction problem when there exist interference targets in a building. The anechoic chamber measurements are carried out to demonstrate the suitability and efficacy of the MST-based method.

Phase coherence factor for mitigation of sidelobe artifacts in through-the-wall radar imaging

Abstract The phase coherence factor (PCF) is revised according to stepped frequency signal imaging radar, adding additional phase diversity in frequency domain. Then, it is applied to through-the-wall moving target indication processing for side and grating lobe artifacts mitigation. Experimental results show that PCF weighting approach can suppress both side and grating lobe artifacts effectively for through-the-wall images.

Shadow Effect Mitigation in Indication of Moving Human Behind Wall via MIMO TWIR

In through-wall indication of a moving human target in enclosed structures, a shadow effect because of the human target blocking parts from illumination on the back wall will emerge, referred to as a “ghost” in indication results. The shadow ghost moves as the human target does, which makes causal change detection (CD) invalid to separate them. To mitigate the shadow ghost, we analyze its differences from the moving human target. Based on the difference that the illumination is only blocked in partial channels of the multiple-input-multiple-output (MIMO) array while target echoes exist in most channels and the fact that shadow ghosts overlap more between successive indication results than the imaged targets as a result of their larger size, we proposed a mitigation method including a coherence factor and noncausal CD processing. Through-wall experiments via a MIMO through-wall imaging radar validate the proposed method.

Spatial Spectrum-Based Imaging for UWB Through-the-Wall MIMO Arrays

To keep the system complexity at a reasonable level and conform to the propagation demands, MIMO arrays are usually sparse in through-the-wall applications, which results in corrupted and gapped data. The corresponding imaging results are seriously affected by the high-level sidelobes. To solve this problem, a new imaging model for ultra-wideband (UWB) MIMO arrays is constructed via spatial spectrum theory in this paper. Based on the model, the characteristics of the spatial spectrum for the MIMO array and its effects on imaging are discussed. To improve the imaging quality, a through-the-wall imaging enhancement method is proposed via spatial spectrum estimation. Synthetic and experimental results show that, unlike the conventional amplitude weighting methods and nonlinear techniques, the proposed method can efficiently suppress sidelobes in the imagery, especially for the sparse MIMO array, and consequently improve the target image quality without degrading the mainlobe resolution. The proposed method has been successfully used in our real through-the-wall radar system.

Design and Analysis of Ultra-Wideband Split Transmit Virtual Aperture Array for Through-the-Wall Imaging

The concept of virtual aperture and the point spread function for designing and characterizing ultra-wideband near-field multiple-input multiple-output active imaging array are investigated. Combining the approach of virtual aperture desynthesis with the monostatic-to-bistatic equivalence theorem, a kind of linear UWB MIMO array, the split transmit virtual aperture (STVA) array, was designed for through-the-wall imaging. Given the virtual aperture, the STVA array is the shortest in physical aperture length. The imaging performance of the designed STVA array in the near field is fully analyzed through both numerical and measured data. The designed STVA array has been successfully applied to imaging moving targets inside buildings.

Stationary human micro-motion trajectory extraction based on edge detection in through-the-wall radar

Stationary human micro-motion trajectory in slow time range domain provides more original motion information, including periodical respiration and heart beating, as well as random body movement and sudden body shaking, whose range often outstrips the periodical movement. Phase contour, amplitude contour and peak locus are all the represent of stationary human micro-motion trajectory. Due to the phase sudden change from π to -π, the phase contour is more robust and stable than the other two loci. In this paper, a stationary human micro-motion trajectory extraction approach based on edge detection is presented. Firstly, the stationary human micro-motion model is established and the effect brought by the wall is analyzed. Then the phase contour in slow-time range domain is introduced as a representation of micro-motion trajectory. Finally, the phase contour extraction based on edge detection is presented. Experimental results demonstrate that the proposed approach can extract stationary human trajectory correctly and accurately, after band pass filtering, the vital sign of human breathing can be extracted effectively.

Three-dimensional imaging for UWB though-the-wall radar

In through-the-wall imaging, the three-dimensional (3D)imaging results are much more efficient in detecting and identifying targets than two-dimensional imaging results. To getting the high-quality imaging results, the 3-D BP imaging method is adapted and the crucial problem about the signal propagation delay is rigorously derived. Based on the derivation results, a compensation method is proposed for refocusing the targets in 3D imaging application. By using this method, the effects of the wall can be compensated and more accurate information of the targets can be obtained. Experimental data processing results validate the conclusion of this paper.

Wall clutter mitigation in through-the-wall MIMO radar application

In through-the-wall imaging, wall reflections are so strong that targets behind walls are usually obscured and invisible in the image, which severely affects the detection and further processing. Aimed at the wall clutter mitigation problems in through-the-wall MIMO radar application, the information of the signal characteristics and antennas’ geometric relationship is deeply analyzed and optimally used. Based on this information, two variables “dealing signal” and “reference signal” are defined. Then a wall clutter method is proposed and its algorithm flow is given. The method can be efficient to mitigate the wall clutter and easy to realize. Full numerical electromagnetic simulations validate the efficiency of the method.