Passive Synthetic Aperture Imaging Research Articles

S-LRLA: A New Kind of Low Redundant Linear Array

As a notable sparse array, low redundant linear array (LRLA) plays an important role in lots of areas, especially in the areas of passive synthetic aperture imaging and direction-of-arrival (DOA) estimation. The existing LRLAs have a problem that they generally contain some dense segments of unit-spaced elements, which restricts the element aperture and hence the radiometric sensitivity and simultaneously causes serious mutual coupling effect that deteriorates the array performance. To solve this problem, a new kind of sparse array named super LRLA (S-LRLA) is proposed in this article. The key characteristic of S-LRLA is that it has no unit-spaced sensor pairs but has the largest continuous difference coarray spanning from 2 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N - 2$ </tex-math></inline-formula> with a redundancy of less than 2. Lots of S-LRLAs are obtained by using a differential evolution (DE) method. On this basis, two types of S-LRLAs, including seven closed-formed patterns and two semiclosed-formed patterns, are discovered. The property and designing factors of S-LRLA are analyzed. Furthermore, the adapted S-LRLA (AS-LRLA) with full difference coarray is also discussed. Comparisons with other prominent arrays are finally presented to demonstrate the superiority of AS-LRLA.

Resolution Analysis of Passive Synthetic Aperture Imaging of Fast Moving Objects

In this paper we introduce and analyze a passive synthetic aperture radar system motivated by space surveillance radar networks for detecting, tracking, imaging, and identifying small debris (aka target) in low-earth orbit. We propose a system with a powerful transmitter on the ground and one or several flying receiver platforms. Each platform can separate the direct signals from the source, coming from below, and the reflected signals, coming from above. In the case of a single receiver platform, the image is formed by cross correlating the Doppler-compensated direct and reflected signals. We show that its resolution is described by the ideal Rayleigh resolution formulas. That is, range resolution is proportional to the transmitter pulse width, and the cross-range resolutions are determined by the synthetic angular cones determined by the target and receiver trajectories. However, the one-receiver imaging modality is not capable of determining both the target location and velocity. In the case of multipl...

Passive synthetic aperture imaging with limited noise sources

We consider a passive synthetic aperture imaging problem. A single moving receiver antenna records random signals generated by one or several distant noise sources and backscattered by one or several reflectors. The sources emit noise signals modeled by stationary random processes. The reflectors can be imaged by summing the autocorrelation functions of the received signals computed over successive time windows, corrected for Doppler factors and migrated by appropriate travel times. In particular, the Doppler effect plays an important role and it can be used for resolution enhancement. When the noise source positions are not known, the reflector can be localized with an accuracy proportional to the reciprocal of the noise bandwidth, even when only a very small number of sources are available. When the noise source positions are known, the reflector can be localized with a cross range resolution proportional to the carrier wavelength and inversely proportional to the length of the receiver trajectory (i.e. the synthetic aperture), and with a range resolution proportional to the reciprocal of the bandwidth, even with only one noise source.

Passive Synthetic Aperture Imaging

We consider passive synthetic aperture imaging where a single moving receiver antenna records signals that are generated by distant unknown noise sources and backscattered by one or several reflectors. The reflectors can be imaged by migrating the autocorrelation functions of the received signals. We compare this passive synthetic aperture imaging with the usual, active synthetic aperture imaging. In the usual synthetic aperture imaging the moving receiver antenna is also a transmitter, and imaging is done by application of a matched filter to the recorded signals. We show that image resolution is the same in both active and passive synthetic aperture imaging, provided that the illumination in the passive case is rich enough.

Passive Synthetic Aperture Hitchhiker Imaging of Ground Moving Targets - Part 2: Performance Analysis.

In Part 1 of this work, we present a passive synthetic aperture imaging and velocity estimation method for ground moving targets using a network of passive receivers. The method involves inversion of a Radon transform type forward model via a novel filtered backprojection approach combined with entropy optimization. The method is applicable to noncooperative transmitters of opportunity where the transmitter locations and transmitted waveforms are unknown. Furthermore, it can image multiple targets moving at different velocities in arbitrary imaging geometries. In this paper, we present a detailed analysis of the performance of our method. First the resolution analysis in position and velocity spaces is presented. The analysis identifies several factors that contribute positively or negativity towards position and velocity resolution. Next, we present a novel theory to analyze and predict smearing artifacts in position images due to error in velocity estimation of moving targets. Specifically, we show that small errors in the velocity estimation result in small positioning errors. We present extensive numerical simulations to demonstrate the theoretical results. While our primary interest lies in radar, the theory, methods and algorithms introduced in our work are also applicable to passive acoustic, seismic, and microwave imaging.

An improved scheme for passive synthetic aperture photonic imaging

An improved scheme for passive synthetic aperture imaging is proposed. With this new technique, the radiation signal from field of view (FOV) is received and its frequency is down-converted to intermediate frequency (IF). The IF signals are modulated to light-wave by electro-optical phase modulators and transmitted in fiber. At the end of the fiber, a downscaled fiber array is formed according to the receiver array. The image of FOV is obtained with the fiber array. The principles of passive synthetic aperture photonic imaging technique are analyzed deeply and its properties are compared with traditional imaging method of synthetic aperture. By simulation, the spread function of spot source and the image signal-noise-ratio are investigated using the new imaging approach with FOV radiation from different incidence angles. The introduced scheme can reconstruct the target image and perfect the present synthetic aperture imaging systems.

电光调制在被动综合孔径成像探测中的应用

电光调制在被动综合孔径成像探测中的应用

Passive synthetic aperture imaging using an achromatic grating interferometer

Synthetic aperture imaging with active systems is relatively well developed. The implementation of passive systems, on the other hand, is being hindered by a low SNR and the difficulty in achieving 2-D aperture fill. The achromaticity of the grating interferometer permits the use of a wider instantaneous spectral bandwidth to produce better SNR, and it provides a simple means to synthesize a 2-D aperture. A passive synthetic aperture imaging approach implemented with an achromatic grating interferometer is described, and laboratory experimental results are presented to demonstrate the proposed concept.