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The moments of a plane wave scattered at low grazing angles from a one-dimensional perfectly reflecting rough surface are considered. The mean intensity and autocorrelation of the scattered field and the corresponding angular spectrum are obtained to second order in surface height. The derivations are based on an operator expansion of the extended (two-way) parabolic integral equation solution. The resulting operator series describes successively higher-order surface interactions between forward and backward going components. The expressions derived may be regarded as backscatter corrections to those obtained via the standard (one-way) parabolic integral equation method. [ABSTRACT FROM PUBLISHER]

We consider an oscillating electric dipole, embedded in a uniform medium with relative permittivityand relative permeability. The dipole is located near an interface with a layer with uniform material parametersand, and the second interface borders a uniform medium with parametersand. We have obtained the solutions for the electric and magnetic fields in the various regions, without any restrictions on the parameters and for any state of oscillation of the dipole (elliptical, in general). The solution involves a set of auxiliary functions, which are given as integral representations containing the Fresnel coefficients for plane waves. With this solution, the field lines of energy flow can be obtained, and we have considered the flow pattern for the simple case of a dipole oscillating perpendicular to the interface. When the material of the layer is optically thicker than the embedding medium of the dipole, energy flows more or less along straight lines. At an interface, the field lines refract, similar to optical rays. When the layer material is optically thinner, the energy flow lines curve. A portion of the energy that propagates toward the interface bends away from it before reaching the interface. Other field lines of energy flow cross the interface, but then return to the area of the dipole by crossing the interface again. This leads to an oscillation of energy back and forth through the interface. In the neighborhood of this oscillation, a concentric set of vortex tori appears. [ABSTRACT FROM AUTHOR]

With an upbeat in petroleum exploration efforts in the Middle and Upper Benue Trough, emphasis is increasingly laid on the structural setting of the basin. This work reports the results of the analysis of aeromagnetic data over the Middle Benue Trough, Nigeria. It is well known that the expression of the spectrum (radial and angular) for the total-field magnetic anomaly field has been extensively used in a variety of geologic applications ranging from depth estimates to magnetic body tops and bottoms and estimates of polarization directions and other linear features. In the same vein, matched filters are capable of separating magnetic anomalies of individual magnetic layers from the total magnetic field anomaly. Consequently, the spectra of the different layers can be separated through the matching of the observed spectra to the spectra of equivalent sources at different depths. This technique can also yield dipole equivalent layers, which might be magnetic ensemble discontinuities. The angular spectrum of the magnetic anomaly, on the other hand, is capable of yielding information on the directions of polarization vectors, as this spectrum is usually maximum in these directions. These processing tools have been briefly examined and applied to the aeromagnetic anomaly data of the Middle Benue Trough, Nigeria. The performances of the radial spectrum and matched filtered output of the field are compared. Results from the plot of log radial spectrum against the frequency numbers indicate five discernable linear segments giving depths corresponding to magnetic layers ranging from 20.62 km (highest) to 0.26 km (lowest). Results from the spectral matching yielded three dipole equivalent source layers at 0.89, 4.33, and 18.22 km, giving two corridor bands. With the sensed magnetic discontinuities at depths of 18.10 to 20.50 km (from ground level), the temperature gradient probably over the area lies between 28.80 and 25.40°C/km for the Curie temperature of 520°C. Finally, we have computed the angular spectrum of the field over this area. It is found that the angular spectrum in the mid and high frequency bands shows two peaks at 62° and 145°. Also there are peaks corresponding to the direction of polarization and the rectangular tapered window used in the analysis. [ABSTRACT FROM PUBLISHER]

We present a hybrid acoustic imaging system to directly visualize acoustic waves propagating within a single anisotropic crystalline plate. An acoustic lens (point focus, continuous wave, frequency; 180 MHz) was used to form a point source (diameter of point: approximately 5 μm) within the silicon plate. A laser interferometric system was used to visualize the acoustic wave propagation. Distinct amplitude patterns at each focal plane were experimentally visualized. The patterns are also theoretically calculated with an Angular Spectrum of Plane Waves method. [ABSTRACT FROM AUTHOR]

We used digital interference holography (DIH) for in vitro imaging of human optic nerve head and retina. Samples of peripheral retina, macula, and optic nerve head from two formaldehyde-preserved human eyes were dissected and mounted onto slides. Holograms were captured by a monochrome CCD camera (Sony XC-ST50, with 780 × 640 pixels and pixel size of ∼9 µm). Light source was a solid-state pumped dye laser with tunable wavelength range of 560-605 nm. Using about 50 wavelengths in this band, holograms were obtained and numerically reconstructed using custom software based on NI LabView. Tomographic images were produced by superposition of holograms. Holograms of all tissue samples were obtained with a signal-to-noise ratio of approximately 50 dB. Optic nerve head characteristics (shape, diameter, cup depth, and cup width) were quantified with a few micron resolution (4.06-4.8 µm). Multiple layers were distinguishable in cross-sectional images of the macula. To our knowledge, this is the first report of DIH use to image human macular and optic nerve tissue. DIH has the potential to become a useful tool for researchers and clinicians in the diagnosis and treatment of many ocular diseases, including glaucoma and a variety of macular diseases. [ABSTRACT FROM AUTHOR]