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The time-reversal effects on super-resolution in random scattering media are analysed using numerical finite-difference time-domain (FDTD) simulations. The analytical solutions and results have been presented previously in the literature, which provide confirmation of spot-size reduction and also explanations of the shower curtain effects and backscattering enhancement. However, the analytical solutions are based on several approximations. Thus, validation of the analytical results against realistic scattering events is necessary. Two-dimensional FDTD Monte Carlo simulations have been employed for this investigation to simulate wave propagation and scattering in a random medium. The scattering environments are created by randomly locating cylindrical rods in the background medium. The simulation process involves a point source emitting a Gaussian pulse wave that propagates through the scattering medium, gets time-reversed, and then back-propagated into the same scattering medium. The focusing behaviours i...

A new technique is proposed for subsurface detection of buried objects using the angular correlation function (ACF) measurement of scattered waves. Compared with the traditional detection technique which relies on radar cross section (intensity) measurement, this new ACF-based technique results in better signal-to-clutter ratio and thus higher target visibility. Laboratory experiments were conducted at millimetre-wave (80–105 GHz) and X-band (7–13 GHz) frequencies to illustrate the potential effectiveness of this new correlation approach over the traditional cross section approach.

An experimental study was conducted to investigate the angular memory effect of millimeter-wave scattering from two-dimensional conducting random rough surfaces. The surfaces under investigation were machine-fabricated with known Gaussian roughness statistics, and the copolarized and cross-polarized angular correlation functions (ACFs) of scattering amplitudes were measured. It was found that for the case of reference antenna positions located bistatically in a backward direction, the measured ACF exhibits broad response when single scattering dominates but two peaks when multiple scatteringdominates. These observations are in good agreement with the second-order Kirchhoff approximation (KA2). Specifically, the observed broad and peak responses are analytically identified to be due to the first-order and second-order (ladder and cyclical) scattering components, respectively, in KA2.

In this paper the angular memory effect of discrete random media in the azimuthal plane was investigated using numerical and experimental techniques. Good agreement was achieved between the experimental and numerical results. Both results showed rapid angular decorrelation in the backscattering direction, which is in direct agreement with previous studies on the angular memory effect in the two-dimensional case.

A new angular correlation phenomenon called the "angular memory effect" (AME) is applied to interferometric SAR (InSAR). Two transmitters illuminate the surface and the scattered waves are observed at two receivers. The mutual coherence function (MCF) for the scattered waves shows that the phase is linearly related to the average topographic height. This is extended to the two-frequency MCF which shows the relationship between the pulse arrival times and the height profile. The theoretical results are confirmed by experiments and numerical simulations.

A novel technique for detecting a target buried under a homogeneous medium is presented. This technique is based on a phenomenon known as the angular memory effect, and involves measurement of the angular correlation function (ACF) for scattered waves observed at antenna positions where the masking effect of the medium on the desirable target ACF return is minimized. Millimeter-wave experiments were conducted to demonstrate the effectiveness of this technique.

The traditional linear synthetic aperture radar (LSAR) flying along a linear flight path is modified to circular synthetic aperture radar (CSAR) flying along a circular flight path. When operating in down-looking spotlight mode for imaging purposes, CSAR, in comparison with LSAR, can provide higher pixel resolutions on any confocally focused plane within the volume illuminated by the antenna beams. By combining this 3D imaging technique with the circular angular memory effect, it is possible to reconstruct volume radar images in localized subsurface imaging applications where poor signal-to-noise ratio (SNR) is a critical issue. Laboratory experiments at X-band (7-13 GHz) and W-band (75-100 GHz) frequencies were conducted to illustrate the capability of CSAR to perform 3D imaging, and the analytical basis of circular angular memory effect due to random surface scattering based on the first-order Kirchhoff approximation.

Presents analytical expressions, based on the first- and second-order Kirchhoff approximations with shadowing corrections; and millimeter-wave experimental data for the angular correlation functions of electromagnetic waves scattered from two-dimensional, very rough, high-slope, metallic and dielectric surfaces. The angular correlation functions represent the correlation of the waves at different scattering angles for different incident angles at a given frequency. The angular correlations clearly show the "memory effects" and are used in the inverse problems of remote sensing of rough surface characteristics.

This paper outlines a brief study on imaging by circular SAR using two different correlation techniques in a clutter environment. The first technique calls for correlation between images over frequency using frequency correlation function (FCF) measurement; whereas, the second involves correlation images over aperture using angular correlation (ACF) measurement. Microwave SAR imaging experiments are conducted at a frequency range of 7-13 GHz to study the relative effectiveness of these SAR processing algorithms in a clutter environment. It was found that for imaging of point scatterers heavily embedded in clutter, the former (ACF technique) surpasses not only the latter (FCF technique), but also the conventional SAR processing approach, resulting in clearer images and hence enhanced target-to-clutter ratio.

A novel correlation imaging technique called frequency angular correlation function imaging (FACF) was investigated to determine its role in clutter suppression imaging. A strong response from clutter in small angle and frequency separation between correlated scattered fields has been observed. By providing larger angular and frequency separation between scattered fields in the imaging process, FACF becomes an inherent clutter suppression algorithm. Experimental microwave studies for FACF were conducted and compared to confocal SAR imaging to determine the range of clutter suppression over other techniques.