Broadband seismic over/under sources and their designature-deghosting

The source depth influences the frequency band of seismic data. Due to the source ghost effect, it is advantageous to deploy sources deep to enhance the low-frequency content of seismic data. But, for a given source volume, the bubble period decreases with the source depth, thereby degrading the low-frequency content. At the same time, deep sources reduce the seismic bandwidth. Deploying sources at shallower depths has the opposite effects. A shallow source provides improved high-frequency content at the cost of degraded low-frequency content due to the ghosting effect, whereas the bubble period increases with a lesser source depth, thereby slightly improving the low-frequency content. A solution to the challenge of extending the bandwidth on the low- and high-frequency side is to deploy over/under sources, in which sources are towed at two depths. We have developed a mathematical ghost model for over/under point sources fired in sequential and simultaneous modes, and we have found an inverse model, which on common receiver gathers can jointly perform designature and deghosting of the over/under source measurements. We relate the model for simultaneous mode shooting to recent work on general multidepth level array sources, with previous known solutions. Two numerical examples related to over/under sequential shooting develop the main principles and the viability of the method.

High-frequency side-scan sonar fish reconnaissance by autonomous underwater vehicles

A dichotomy between depth penetration and resolution as a function of sonar frequency, draw resolution, and beam spread challenges fish target classification from sonar. Moving high-frequency sources to depth using autonomous underwater vehicles (AUVs) mitigates this and also co-locates transducers with other AUV-mounted short-range sensors to allow a holistic approach to ecological surveys. This widely available tool with a pedigree for bottom mapping is not commonly applied to fish reconnaissance and requires the development of an interpretation of pelagic reflective features, revisitation of count methods, image-processing rather than wave-form recognition for automation, and an understanding of bias. In a series of AUV mission test cases, side-scan sonar (600 and 900 kHz) returns often resolved individual school members, spacing, size, behavior, and (infrequently) species from anatomical features and could be intuitively classified by ecologists — but also produced artifacts. Fish often followed the AUV and thus were videographed, but in doing so removed themselves from the sonar aperture. AUV-supported high-frequency side-scan holds particular promise for survey of scarce, large species or for synergistic investigation of predators and their prey because the spatial scale of observations may be similar to those of predators.

FTIR and DSC Study of Se92Te8-xSnx (x=0, 3 and 5) Chalcogenide Glasses

In the present work, DSC and FTIR study of the of Se92Te8-xSnx ( x=0, 2 and 4) glassy samples has been studied. FTIR spectra was taken in wavelength region 50-600 cm-1. The parameters like theoretical wave number and activation energy of glass transition and crystallization has been calculated by Kissinger’method and Augis and Bennett’approximation. With the addition of Sn, Far-IR spectra shift toward high frequency side and new bands starts appearing in the spectra. The Sn atom appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Activation energy of glass transition increases with Sn addition while for crystallization, it also increases except at x=1.

Dielectric Properties of 4-Cyanobiphenyl in 1,4-Dioxane Solution

The static and dynamic dielectric properties o f the title system are reported for a concentration series from about 8 mmol/1 up to 2.3 mol/I at 20 °C. The apparent moment (4.2 D , extrapolated to infinite dilution) decreases with increasing concentration, the relaxation time increases proportional to viscosity, that is, somewhat steeper than usually observed. Com parison with other molecules suggests that these features are mainly due to the high dipole moment rather than being specifically related to the prolate shape o f the molecule. The broadening o f the spectrum toward the high frequency side, on the other hand, may be due to the molecular shape.

The Effects of Overlying Layers On The Ftir Spectra of Thin Thermal Oxides On Silicon

The most intense feature in the infrared spectrum of SiO2 is the “νas band” near 1070 cm-1. Assigned to the asymmetric stretching mode, this peak exhibits a shoulder on the high frequency side of the band. In this study, Fourier transform infrared (FTIR) spectrophotometry is used to examine the effects of overlying, unpatterned layers of undoped polysilicon (poly) and of tungsten silicide (WSi) upon 0.08 μm of themal oxide grown on silicon. For the poly studies, the oxide is grown on both sides of double-side-polished wafers. 0.11 μm of poly is then deposited on each side of half of the set; 0.25 μm, on the remainder. For the WSi studies, 0.21 μm of undoped poly is deposited onto oxide grown on single-side-polished, low-oxygen wafers. WSi is then deposited on one side.For the poly set, the peak position (PP) of the “νas band” shifts from 1074 to 1071 to 1066 cm-1 when comparing the uncoated oxide, 0.11 μm poly/oxide, and 0.21 μm poly/oxide samples, respectively. As a result of the observed shifts, the high frequency shoulder becomes resolved as a broad, weak band centered near 1168 cm-1. Thus, the “νas band” appears to be a doublet, consisting of a weak high-frequency component that is insensitive to, and an intense low-frequency component that is sensitive to. overlying films. For the WSi set, the PP of the “νas band” shifts from 1068 to 1076 to 1083 cm-1 for the poly/oxide, WSi/poly/oxide, and annealed-WSi/poly/oxide samples, respectively. Possible causes for the doublet character of the “νas band” and mechanisms for the film-film interactions, such as hydrostatic pressure, are discussed.