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El-Darymli K.,Northern Radar Inc. | Gill E.W.,Memorial University of Newfoundland | McGuire P.,Memorial University of Newfoundland | Power D.,C CORE | Moloney C.,Memorial University of Newfoundland
IEEE Access | Year: 2015

In analyzing single-channel synthetic aperture radar (SAR) imagery, three interrelated questions often arise. First, should one use the detected or the complex-valued image? Second, what is the 'best' statistical model? Finally, what constitutes the 'best' signal processing methods? This paper addresses these questions from the overarching perspective of the generalized central limit theorem, which underpins nonlinear signal processing. A novel procedure for characterizing the nonlinear dynamics in SAR imagery is proposed. To apply the procedure, three complementary 1-D abstractions for a 2-D SAR chip are introduced. Our analysis is demonstrated on real-world datasets from multiple SAR sensors. The nonlinear dynamics are found to be resolution dependent. As the SAR chip is detected, nonlinear effects are found to be obliterated (i.e., for magnitude-detection) or altered (i.e., for power-detection). In the presence of extended targets (i.e., nonlinear scatterers), it is recommended to use the complex-valued chip rather than the detected one. Furthermore, to exploit the intrinsic nonlinear statistics, it is advised to utilize relevant nonlinear signal analysis techniques. © 2013 IEEE.


Walsh J.,Northern Radar Inc. | Walsh J.,Memorial University of Newfoundland | Huang W.,Memorial University of Newfoundland | Gill E.,Memorial University of Newfoundland
IEEE Transactions on Antennas and Propagation | Year: 2012

The second-order high frequency (HF) radar cross section (RCS) of the ocean surface, normalized to the area of the scattering patch, is derived for the case in which the radar transmitting and receiving antennas are mounted on a swaying platform or barge. The second-order result includes both electromagnetic and hydrodynamic contributions. The derivation for the hydrodynamic patch scatter component, for time pulsed radars, is based on the first-order RCS found in the counterpart of this paper by replacing the first-order ocean wave spectrum with the second-order ocean wave spectrum. The electromagnetic patch scatter development begins with a general expression for the bistatically received second-order electric field in which platform sway is introduced. Based on an assumption that the ocean surface can be described as a Fourier series whose coefficients are random variables, the second-order monostatic RCS is developed. The resulting second-order cross section is found to consist of Bessel functions and no singularity exists in the newly derived electromagnetic coupling coefficient. Simulation results for the new RCS are also provided to indicate the effects of barge motion under a variety of sea states. © 1963-2012 IEEE.


Walsh J.,Northern Radar Inc. | Walsh J.,Memorial University of Newfoundland | Huang W.,Memorial University of Newfoundland | Gill E.,Memorial University of Newfoundland
IEEE Transactions on Antennas and Propagation | Year: 2010

The first-order high frequency surface wave radar (HFSWR) cross section of the ocean surface is derived for the case of the transmitting and receiving antenna being mounted on a floating, but otherwise fixed, ocean platform. It is assumed that the sway component of the platform or barge motion is responsible for observed differences in the cross section compared to that for the fixed antenna case. Based on earlier work, a general expression for the bistatically received first-order electric field, which consists of a two-dimensional spatial convolution, is presented and reduced to integral form. Then, it is assumed that the surface can be described by a Fourier series whose coefficients are zero-mean Gaussian random variables, and from there the analysis proceeds for the backscatter case. The integrals are taken to the time domain, with the source field being that of a barge-mounted omnidirectional vertically polarized pulsed dipole antenna. Subsequently, the first-order monostatic radar cross section is developed and found to consist of Bessel functions. Simulation results for the new cross section are also provided to show the effects of barge motion under different sea states and operating frequencies. It is seen that the results have important implications in the application of HFSWR technology to ocean remote sensing. © 2006 IEEE.


Walsh J.,Northern Radar Inc. | Walsh J.,Memorial University of Newfoundland | Gill E.W.,Memorial University of Newfoundland | Huang W.,Memorial University of Newfoundland | Chen S.,Memorial University of Newfoundland
IEEE Transactions on Antennas and Propagation | Year: 2015

An analytic high-frequency (HF) radar cross section model for ionosphere-ocean propagation is presented. Based on earlier work, an expression for the first-order received electric field after a single scatter from each of the ionosphere and sea surface is derived and reduced to integral form. The field integrals are taken to the time domain, with the source field being that of a vertically polarized pulsed dipole antenna. Subsequently, the first-order radar cross section for the mixed path mode of ionospheric clutter is developed. The ionosphere reflection coefficient used in the analysis is assumed to be a stochastic process with an associated spectral density function to account for phase variations along the surface associated with nonuniformity of the signal path. Simulation results for the new cross section are also provided. It is shown numerically that the expected magnitude of the ionosphere clutter, under reasonable assumptions, exceeds the dominant first-order ocean clutter for the same apparent range by 50-60 dB. Further, it is spread in Doppler, depending on the ionosphere horizontal velocity and reflecting path nonuniformity. Also, this component can be presented from a certain minimum range, depending on ionosphere virtual height, to the maximum radar range. © 1963-2012 IEEE.


Walsh J.,Memorial University of Newfoundland | Walsh J.,Northern Radar Inc. | Huang W.,Memorial University of Newfoundland | Gill E.,Memorial University of Newfoundland
IEEE National Radar Conference - Proceedings | Year: 2012

When the transmitting and/or receiving antennas of a high high-frequency (HF) radar are mounted on a floating platform, which is subject to sway, it is known that motion introduces additional features in the Doppler spectra of the signal scattered from the ocean surface. Following techniques in earlier work which examined these features up to second order for scatter from a patch of ocean remote from the antennas, we consider second-order effects arising from a single scatter near the antennas followed or preceded by a scatter on the remote patch. The derivation begins with a general expression for the bistatically received second-order electric field in which platform sway is introduced. This is then reduced to the monostatic case. Having developed the monostatic equations, and assuming the ocean surface to be representable as zero-mean Gaussian process, the corresponding second-order monostatic radar cross section (RCS) is developed. As in the earlier analyses for patch scatter, the new contributions to the RCS appear as Bessel functions, which give rise to extra spectral content not appearing in the fixed-antenna results. However, simulations of the new RCS, including antenna sway under a variety of sea states, suggest that while the new second-order effects are visible in the spectrum, they are generally smaller than first-order effects, except at specific Doppler frequencies. © 2012 IEEE.

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