Resolving Full-Wave Through-Wall Transmission Effects in Multi-Static Synthetic Aperture Radar

Abstract

Through-wall synthetic aperture radar (SAR) imaging is of significant interest for security purposes, in particular when using multi-static SAR systems consisting of multiple distributed radar transmitters and receivers to improve resolution and the ability to recognise objects. Yet there is a significant challenge in forming focused, useful images due to multiple scattering effects through walls, whereas standard SAR imaging has an inherent single scattering assumption. This may be exacerbated with multi-static collections, since different scattering events will be observed from each angle and the data may not coherently combine well in a naive manner. To overcome this, we propose an image formation method which resolves full-wave effects through an approximately known wall or other arbitrary obstacle, which itself has some unknown "nuisance" parameters that are determined as part of the reconstruction to provide well focused images. The method is more flexible and realistic than existing methods which treat a single wall as a flat layered medium, whilst being significantly computationally cheaper than full-wave methods, strongly motivated by practical considerations for through-wall SAR.

Figures (9)

• Figure 1: Experimental multi-static collection geometry used for simulations relative to the wall location and image extent. The flight paths of the transmit and first receiver are shown in red (solid), of the second receiver in green, and of the third receiver in blue. The angles between the lines bisecting the flightpath to the scene centre (dotted lines) are given in table \ref{['tab: radar params']}, referred to as the "bi-static angles". Also highlighted by black-dotted lines are the lines of sight from the widest extent of antenna positions to the scene centre.
• Figure 2: Reconstruction results of through-wall data for three point scatterers, using (a) the standard SAR model and (b) the exact through-wall model. The true location of scatterers are overlaid as grey dots, and the corner of the wall is at $(-2,-2)^T$.
• Figure 3: Convergence of the reconstructions using FISTA, for the standard SAR model $\epsilon_r=1$ shown in blue, and the exact through-wall model $\epsilon_r=3$ in orange.
• Figure 4: Overlaid magnitude of back-projection images for a single point target at the origin behind a corner wall. A separate image is formed from data of each bi-static pair in the multi-static collection. These are colourised and overlaid such that pixels taking the same value in each image which appear grey-scale, or otherwise tinted towards red, green or blue if the image is brighter in the corresponding image. Red, green and blue image colour channels also correspond to the antenna flight paths shown in \ref{['fig: geometry']}.
• Figure 5: Sidelobe pattern of backprojection images scaled to peak amplitude of the main lobe, shown in log scale. Blue shows the standard SAR model, and orange the through-wall SAR model.