Unified Reciprocal Space Processing for Short-Range Active and Passive Imaging Systems

Aaron V Diebold,Thomas Fromenteze,Ettien Kpre,David R Smith,Mohammadreza F Imani,Cyril Decroze

doi:10.1109/ojap.2021.3136903

Abstract

Large scale sensing systems increasingly operate in short-range geometries, providing three-dimensional imaging capabilities that leverage the large number of degrees of freedom of distributed arrays. The two most powerful modes of operation include active, multiple-input multiple-output arrays, in which an image is processed from signals measured using different pairs of transmitting and receiving antennas; and passive, synthetic aperture interferometric radiometer arrays, which can image using ambient, non-cooperative radiation by processing signals measured at different receiving antenna pairs. In this paper, we explore the analogy between these two imaging modes, and outline a generalized framework for analyzing these systems in the array near field. Focusing on the similarities between the formalisms describing the operation of generic active and passive systems, it is proposed, to our knowledge for the first time in the scientific literature, to adapt a Fourier-based imaging technique optimized for short-range active MIMO systems to passive technologies, interrogating the emissivity of a spatially distributed target. The systematic method presented in this paper provides a framework for characterizing and optimizing short range coherent or incoherent systems used in threat detection and non-destructive testing applications.

Highlights

Achieving fast and accurate imaging performance at wavelength-scale resolution is a widespread concern in a growing number of applications, giving rise to a diversity of architectures within the scientific community
Active systems that utilize coherent illumination can recover an image from scattered field measurements, with optimal performance usually realized by multiple-input multiple-output (MIMO) systems that process a complete collection of transmit-receive signal pairs
We find that a MIMO radar system retrieves a set of signals related to the target susceptibility by a pair of Green’s function terms

Summary

Introduction

Achieving fast and accurate imaging performance at wavelength-scale resolution is a widespread concern in a growing number of applications, giving rise to a diversity of architectures within the scientific community. Active systems that utilize coherent illumination can recover an image from scattered field measurements, with optimal performance usually realized by multiple-input multiple-output (MIMO) systems that process a complete collection of transmit-receive signal pairs Such architectures, though largely proposed and demonstrated in large-scale radar applications, are increasingly utilized for buried threat detection [1], [2], [3], [4] and structural monitoring [5], [6] in short-range configurations [7]. Such systems are referred to as synthetic aperture interferometric radiometers (SAIR) The radiation in these scenarios can be of a thermal nature according to the gray body radiation principle, or can be generated by non-cooperative sources such as radio transmitters and noise sources [8]. As in the case of active systems, techniques pioneered in large-scale radio frequency systems have since been distilled into deployable systems for passive imaging of noise sources [9], [10], [11], [12] and imaging with ambient wifi signals [13], [14]

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Conclusion