Asymptotic light field in the presence of a bubble-layer

We report that the submerged microbubbles are an efficient source of diffuse radiance and may contribute to a rapid transition to the diffuse asymptotic regime. In this asymptotic regime an average cosine is easily predictable and measurable.Comment: 4 pages, 3 Postscript figures, opex2.sty (enclosed), also available from the Optical Society of America htpp://epubs.osa.org/oearchive/pdf/11948.pd

Longitudinal shear of bi-material with interfacial crack considering friction

Побудовано точний розв’язок антиплоскої задачі для біматеріалу з міжфазною тріщиною, навантаженого неоднорідним нормальним стиском та циклічним навантаженням у поздовжньому напрямку. Методом функцій стрибка задача зведена до системи сингулярних інтегральних рівнянь для стрибків зміщень і напружень у зонах проковзування з тертям. Проаналізовано вплив параметрів навантажування і тертя на розміри цих зон та дисипацію енергії.The present paper investigates the anti-plane problem for a semi-homogeneous bi-material with the closed interface crack considering sliding friction. Solid is exposed to the combined cyclic loading in the longitudinal direction and arbitrary normal load required to prevent loss of contact between the sliding surfaces of the cracks. It is assumed that the load on each step of loading increases from zero to its maximum monotonically and slowly enough not to consider the effect of inertia. Using jump function method the problem is reduced to the solution of singular integral equations with a Cauchy-type kernel for the jumps of displacements and stresses in areas with sliding friction. This solution allows us to obtain explicit expressions for displacements, stress intensity factors and energy dissipation. Analyzing of the elasticity problem involving friction under the variable (cyclic) loading requires consideration of the history of loading. No incremental formulation is necessary for solving of this problem on each local step because of quasi-statically way of the step loading. To take account of cyclical loading multistep method of solution is proposed. The basis of this technique is the idea of consideration at every step of loading previous step stresses and displacements as the residual. Correctness of the obtained solution is justified. Evolution of the slip zone in matrix is considered at different stages of loading. Critical load values for determining the onset of slip are investigated. Available size of slip zone with an increase in loading is determined from the condition of equality to zero the stress intensity factor. Upon reaching the second critical value of the load, when the slip zone size matches the size of the crack, there are singular stresses in the crack threshold and non-zero values of stress intensity factors. We numerically analyze the effect of friction and loading parameters on the size of slip zone and stress intensity factors. It is discovered that the slip zone appears and grows fastest when it pressing normal stresses are minimal. Growth rate of slip zone also promotes increasing the distance of application points of concentrated power factors from her. The growth coefficient of friction significantly reduces the intensity of the stresses in the vicinity of the ends of the crack. Energy dissipation for all examined cases of loading was calculated

Signal of single scattering albedo in water leaving polarization

The purpose of this article is to examine whether the change in single scattering albedo in the surface layer of the sea will cause significantchanges in the polarization of light emerging from the sea. The results of a polarization resolving Monte Carlo radiative transfer calculationsare presented. Bubble clouds of different bubble concentrations are used to achieve a wide range of single scattering albedo variability. Thevariability of the polarization signal is largest in the direction looking towards the sun which is unfortunate due to sun reflection. Howeverthe variability is also significant at direction perpendicular to solar azimuth angle which should it make possible to use this signal in remotesensing. The polarization degree of water leaving radiation, together with reflectance can be used to determine the backscattering ratio ofthe observed sea water

Polarization imaging over sea surface - a method for measurements of Stokes components angular distribution

This article describes a method for determining the angular distribution of light polarization over a roughened surface of the sea. Our method relies on measurements of the Stokes vector elements using a polarization imaging camera that operates using the Division of Focal Plane (DoFP) method. It uses special monochrome CCD array in which the neighbouring cells, instead of recording different colours (red green and blue), are equipped with micropolarizers of four directions (0, 45, 90 and 135 degrees).We combined the camera with a fish-eye lens of Field of View (FoV) > 180 deg. Such a large FoV allowed us to crop out the fragment of the frame along the circular horizon, showing a view covering all directions of the hemisphere. Because of complicated optical design of the fish-eye lens (light refraction on surfaces of parts of the lens) connected to the sensor we checked the accuracy of the measurement system. A method to determine the accuracy of measured polarization is based on comparison of the experimentally obtained rotation matrix with its theoretical form. Such a comparison showed that the maximum error of Stokes vector elements depended on zenith angle and reached as much as 24% for light coming from just above the horizon, but decreased rapidly with decreasing zenith angle to the value of 12% for the angles 10° off the edge of FoV.Moreover we present the preliminary results prepared over rough sea surface. These results include total intensity of light, Degree of Linear Polarization (DoLP) and their standard deviations. The results have been averaged over one thousand frames of a movie. These results indicate that the maximum polarization is observed near the reflection of the sun, and the signal coming from below the surface may be observed at zenith angles far from the vertical direction

Monte Carlo Study of the Scattering Error of a Quartz Reflective Absorption Tube

A Monte Carlo model was used to study the scattering error of an absorption meter with a divergent light beam and a limited acceptance angle of the receiver. Reflections at both ends of the tube were taken into account. Calculations of the effect of varying optical properties of water as well as the receiver geometry were performed. A weighting function showing the scattering error quantitatively as a function of angle was introduced. Some cases of practical interest are discussed

Asymptotic light field in the presence of a bubble-layer

We report that the submerged microbubbles are an efficient source of diffuse radiance and may contribute to a rapid transition to the diffuse asymptotic regime. In this asymptotic regime an average cosine is easily predictable and measurable.This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/home.cfm. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.Keywords: Ocean optics, Multiple Scatterin

Key Uncertainties in the Recent Air‐Sea Flux of CO 2

The contemporary air-sea flux of CO2 is investigated by the use of an air-sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air-sea gas transfer velocity are used to evaluate the combined standard uncertainty resulting from several sources of error. Depending on expert opinion, a standard uncertainty in transfer velocity of either ~5% or ~10% can be argued and that will contribute a proportional error in air-sea flux. The limited sampling of upper ocean fCO2 is readily apparent in the Surface Ocean CO2 Atlas (SOCAT) databases. The effect of sparse sampling on the calculated fluxes was investigated by a bootstrap method; i.e. treating each ship cruise to an oceanic region as a random episode and creating 10 synthetic datasets by randomly selecting episodes with replacement. Convincing values of global net air-sea flux can only be achieved using upper ocean data collected over several decades, but referenced to a standard year. The global annual referenced values are robust to sparse sampling, but seasonal and regional values exhibit more sampling uncertainty. Additional uncertainties are related to thermal and haline effects and to aspects of air-sea gas exchange not captured by standard models. An estimate of global net CO2 exchange referenced to 2010 of -3.0 ± 0.6 Pg C yr-1 is proposed, where the uncertainty derives primarily from uncertainty in the transfer velocit