Contribution of Raman scattering to water-leaving radiance: a reexamination

We have reexamined the contribution of Raman scattering to the water-leaving radiance in case 1 waters by carrying out radiative transfer simulations that combine the latest reported measurements of the absorption coefficient of pure water with direct measurements of the spectral variation of the Raman-scattering coefficient. The resulting contribution of Raman scattering is then compared with experimental measurements of the water-leaving radiance, and the fractional contribution of radiance produced by Raman scattering to the total radiance measured at a given wavelength is determined. The results show that (1) the contribution of Raman scattering to the water-leaving radiance in an ocean of pure seawater is as much as 50-100% larger than earlier predictions, and (2) the Raman contribution does not decay as rapidly with increasing concentrations of chlorophyllouslike pigments C as predicted earlier. In fact, the Raman fraction for C 8% at wavelengths of interest in ocean color remote sensing and therefore cannot be ignored in ocean color modeling.     

Normalized water-leaving radiance: revisiting the influence of surface roughness

Many spaceborne sensors have been deployed to image the ocean in the visible portion of the spectrum. Information regarding the concentration of water constituents is contained in the water-leaving radiance-the radiance that is backscattered out of the water and subsequently propagates to the top of the atmosphere. Recognizing that it depends on the viewing and Sun geometry, ways have been sought to normalize this radiance to a single Sun-viewing geometry--forming the normalized water-leaving radiance. This requires understanding both the bidirectional nature of the upwelling radiance just beneath the surface and the interaction of this radiance with the air-water interface. I believe that the latter has been incorrectly computed in the past when a water surface roughened by the wind is considered. The presented computation suggests that, for wind speeds as high as 20 m/s, the influence of surface roughness is small for a wide range of Sun-viewing geometries, i.e., the transmittance of the (whitecap-free) air-water interface is nearly identical (within 0.01) to that for a flat interface.     

Remote sensing of ocean color: assessment of water-leaving radiance bidirectional effects on atmospheric diffuse transmittance

Two factors influence the diffuse transmittance (t) of water-leaving radiance (L(w)) to the top of the atmosphere: the angular distribution of upwelling radiance beneath the sea surface (L(u)) and the concentration and optical properties of aerosols in the atmosphere. We examine these factors and (1) show that the error in L(w) that is induced by assuming L(u) is uniform (i.e., in treating the subsurface reflectance by the water body as Lambertian) is significant in comparison with the other errors expected in L(w) only at low phytoplankton concentration and then only in the blue region of the spectrum; (2) show that when radiance ratios are used in biophysical algorithms the effect of the uniform- L (u) approximation is even smaller; and (3) provide an avenue for introducing accurate computation of the uniform L(u) diffuse transmittance into atmospheric correction algorithms. In an Appendix the reciprocity principle is derived for a medium in which the refractive index is a continuous function of position.     

Assessment of a bidirectional reflectance distribution correction of above-water and satellite water-leaving radiance in coastal waters

Water-leaving radiances, retrieved from in situ or satellite measurements, need to be corrected for the bidirectional properties of the measured light in order to standardize the data and make them comparable with each other. The current operational algorithm for the correction of bidirectional effects from the satellite ocean color data is optimized for typical oceanic waters. However, versions of bidirectional reflectance correction algorithms specifically tuned for typical coastal waters and other case 2 conditions are particularly needed to improve the overall quality of those data. In order to analyze the bidirectional reflectance distribution function (BRDF) of case 2 waters, a dataset of typical remote sensing reflectances was generated through radiative transfer simulations for a large range of viewing and illumination geometries. Based on this simulated dataset, a case 2 water focused remote sensing reflectance model is proposed to correct above-water and satellite water-leaving radiance data for bidirectional effects. The proposed model is first validated with a one year time series of in situ above-water measurements acquired by collocated multispectral and hyperspectral radiometers, which have different viewing geometries installed at the Long Island Sound Coastal Observatory (LISCO). Match-ups and intercomparisons performed on these concurrent measurements show that the proposed algorithm outperforms the algorithm currently in use at all wavelengths, with average improvement of 2.4% over the spectral range. LISCO's time series data have also been used to evaluate improvements in match-up comparisons of Moderate Resolution Imaging Spectroradiometer satellite data when the proposed BRDF correction is used in lieu of the current algorithm. It is shown that the discrepancies between coincident in-situ sea-based and satellite data decreased by 3.15% with the use of the proposed algorithm. This confirms the advantages of the proposed model over the current one, demonstrating the need for a specific case 2 water BRDF correction algorithm as well as the feasibility of enhancing performance of current and future satellite ocean color remote sensing missions for monitoring of typical coastal waters.     

Bandpass-resampling effects on the retrieval of radiance and surface reflectance

Radiative transfer models are often employed to derive the surface reflectance for Earth-looking multispectral scanners or imaging spectrometers. For this purpose the calculated radiances have to be resampled with the spectral channel response functions of the instrument. Three methods of bandpass resampling the product terms of the radiative transfer equation are compared: the exact method and two commonly used approximations. Error budgets for the two approximate methods are given for typical multispectral and hyperspectral sensors. The error depends on the wavelength, bandwidth, atmospheric parameters, and atmospheric path length.     

Estimation of aerosol columnar size distribution and optical thickness from the angular distribution of radiance exiting the atmosphere: simulations

We report the results of simulations in which an algorithm developed for estimation of aerosol optical properties from the angular distribution of radiance exiting the top of the atmosphere over the oceans [Appl. Opt. 33, 4042 (1994)] is combined with a technique for carrying out radiative transfer computations by synthesis of the radiance produced by individual components of the aerosol-size distribution [Appl. Opt. 33, 7088 (1994)], to estimate the aerosol-size distribution by retrieval of the total aerosol optical thickness and the mixing ratios for a set of candidate component aerosol-size distributions. The simulations suggest that in situations in which the true size-refractive-index distribution can actually be synthesized from a combination of the candidate components, excellent retrievals of the aerosol optical thickness and the component mixing ratios are possible. An exception is the presence of strongly absorbing aerosols. The angular distribution of radiance in a single spectral band does not appear to contain sufficient information to separate weakly from strongly absorbing aerosols. However, when two spectral bands are used in the algorithm, retrievals in the case of strongly absorbing aerosols are improved. When pseudodata were simulated with an aerosol-size distribution that differed in functional form from the candidate components, excellent retrievals were still obtained as long as the refractive indices of the actual aerosol model and the candidate components were similar. This underscores the importance of component candidates having realistic indices of refraction in the various size ranges for application of the method. The examples presented all focus on the multiangle imaging spectroradiometer; however, the results should be as valid for data obtained by the use of high-altitude airborne sensors.     

An OUR-based approach to determine the toxic effects of 2,4-dichlorophenoxyacetic acid in activated sludge

This study uses the oxygen uptake rate (OUR) measurement to measure toxicity effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on activated sludges fed with the wastewater from a small domestic wastewater treatment plant and peptone-based synthetic wastewater. Two 2l lab-scale batch reactors were run in parallel with the same F/M ratios (0.4 mg COD per mg VSS per day) to assess the inhibition effects of 2,4-D concentrations between 25 and 75 mg l(-1) considering at least a 100% dilution rate, as compared with a pesticide industry effluent containing 20,000-40,000 mg l(-1) COD, reaches a central treatment plant. It was noted that the OUR was decreased to 15 and 30%, respectively, when adding 75 mg l(-1) of 2,4-D to the domestic and synthetic reactors. Meanwhile, the addition of 25 plus 50 mg l(-1) of 2,4-D in sequence to the domestic wastewater reactor did not significantly affect the OUR profile. The OUR-based inhibition definition has been used in this research since the OUR methods have been frequently used and cited in the literature to study toxicity effects. However, the origin of the sludge used in the testing is also important. Synthetic wastewater may simulate the toxicity studies but with a higher response than actual systems, since the microorganisms are considerably becoming substrate-selective.     

Wavefront propagation in turbulence: an unified approach to the derivation of angular correlation functions

A general expression of the spatial correlation functions of quantities related to the phase fluctuations of a wave that have propagated through the atmospheric turbulence are derived. A generalization of the method to integrand containing the product of an arbitrary number of hypergeometric functions is presented. The formalism is able to give the coefficients of phase-expansion functions orthogonal over an arbitrary circularly symmetric weighting function for an isotropic turbulence spectrum, as well as to describe the effect of the finite outer and inner scales of the turbulence and to describe the spherical propagation or to derive the effects of the analytical operators acting on the phase such as the derivatives of any order. The derivation of the generalized integrals with multiparameters is based on the Mellin transforms integration method.     

Optical approach to angular displacement measurement based on attenuated total reflection

An optical approach for angular displacement measurement (ADM) based on the attenuated total reflection technique is presented. As a laser beam is incident upon a planar optical waveguide, an m line is obtained by scanning the incident angle. Theoretical analysis shows that the m line sharply shifts with a tiny variation of the thickness of the waveguided layer. And the specific schemes for ADM, which are based on the angular interrogation and the intensity measurement, are analyzed. The calculated result of sensitivity demonstrates that the intensity measurement is more efficient than the angular interrogation. Furthermore, small incident angles indicate higher sensitivity to the angular displacement than relatively large incident angles for the intensity measurement.     

An analysis of the angular momentum of a light field in terms of angular harmonics

Abstract

This paper proposes an optical interpretation for the Lie algebra's symmetry operators of the paraxial wave equation. In particular, the angular momentum operator is used to derive a relation for the expression of the angular momentum of an arbitrary light field in terms of angular harmonics. Furthermore, experimental results are presented demonstrating a filter that extracts angular harmonics from different Gauss-Laguerre modes.     

An interphase approach of size effects in ductile porous materials

International Journal of Fracture - The aim of this paper is to develop a size-dependent Gurson type model. The approach is based on a micromechanical implementation of a local isotropic hardening...     

Island perturbation to the sky radiance over the ocean: simulations

Sky-radiance measurements at the sea surface can be used to estimate radiative properties of aerosols over water. We demonstrate, through Monte Carlo simulations, that significant perturbations to sky radiance over the ocean can occur when measurements are carried out with radiometers located on islands. In particular, we present examples of the influence of the physical and optical thicknesses of an aerosol layer, the azimuth of observation relative to the Sun, the size of the island, the location of the radiometer on the island, and the albedo of the island on the magnitude of the perturbation for a circular island of uniform albedo. Relative errors in sky radiance of as high as 39% were found in the blue. Simulated (perturbed) sky radiances were combined with an algorithm for retrieving the aerosol phase function P(θ), where θ is the scattering angle, and with the single-scattering albedo ω(0), to demonstrate how the perturbation can influence the retrieved values. It was found that the fractional error in the retrieved values of the product ω(0)P(θ) can be significantly greater than the fractional error in the sky radiance, because of the effects of multiple scattering. This underscores the importance of removing the island perturbation before an inversion algorithm is used. A first-order procedure for removing the island perturbation based on the values of ω(0)P(θ) retrieved from the perturbed sky radiance is proposed and is found to be effective if the island perturbation is not too large. A simplified Monte Carlo procedure that is applicable to an island of arbitrary shape and albedo distribution is presented. The procedure could be used to assess the suitability of a given island as a measurement site, and to provide a first-order correction to actual experimental measurements.     

Use of Rayleigh imaging and ray tracing to correct for beam-steering effects in turbulent flames

Laser Rayleigh imaging has been applied in a number of flow and flame studies to measure concentration or temperature distributions. Rayleigh cross sections are dependent on the index of refraction of the scattering medium. The same index of refraction changes that provide contrast in Rayleigh images can also deflect the illuminating laser sheet. By applying a ray-tracing algorithm to the detected image, it is possible to correct for some of these beam-steering effects and thereby improve the accuracy of the measured field. Additionally, the quantification of the degree of beam steering through the flow provides information on the degradation of spatial resolution in the measurement. Application of the technique in a well-studied laboratory flame is presented, along with analysis of the effects of image noise and spatial resolution on the effectiveness of the algorithm.     

Statistical approach to roughness-induced shielding effects

A new theoretical concept is introduced to describe the roughness‐induced shielding effects in metallic materials. This approach is based on the statistics of the local ratio between the characteristic microstuctural distance and the plastic zone size. A general equation involving both the crack branching and the crack closure phenomena is derived in the frame of linear elastic fracture mechanics under the assumption of remote mode I loading. It enables the determination of the intrinsic values of both the fracture toughness and the fatigue crack growth threshold. Moreover, the roughness‐induced component can be separated from other closure components, such as the plasticity or oxide‐induced closure. In order to estimate the total roughness‐induced shielding effect only standard materials data such as the yield stress, the mean grain size, the surface roughness and the fracture mode are necessary. Examples of applications concerning static fracture and fatigue are presented for selected metallic materials.     

Reciprocity principle applicable to reflected radiance measurements and the searchlight problem

In a recent paper by Di Girolamo et al. [J. Geophys. Res. D 103, 8795 (1998)] a heuristic argument was used to derive a reciprocity principle applicable to reflected solar radiation measurements. Here a formal derivation of this reciprocity principle is presented. It is also demonstrated that a purely spatial reciprocal relationship exists between one-dimensional radiative transfer theory and the three-dimensional searchlight problem for horizontally homogeneous media.     

An approach to the measurement of single-machine flexibility

Flexibility of manufacturing systems has been recognized as one of the vital competitive priorities in manufacturing strategy. However, the meaning and implementation of flexibility remain blurred. The main reason could be that the attributes of manufacturing system flexibility are many and complicated. This research suggests that there are at least two factors that should be considerednamely, efficiency and versatility-in the measurement of manufacturing flexibility. The entropy approach, which was extended from information theory and has been applied comprehensively in the research of market diversity in the economics field, has its limitations in the measurement of manufacturing flexibility. It depicts only the factor of versatility, and not that of efficiency. This research proposes a combination of the entropy approach and the efficiency frontier approach, Data Envelopment Analysis (DEA), for the measurement of manufacturing flexibility. This approach has been applied to the measurement of single machine flexibility and a straightforward example is exhibited in this research.     

Using the local approach to evaluate scaling effects in ductile fracture

This paper uses a local model to predict ductile fracture in geometrically similar structures of different sizes containing either sharp cracks or blunt stress concentrators. Simple theoretical considerations suggest that when fracture occurs by quasi-isotropic void growth, fracture initiation at blunt notches follows replica scaling, whereas fracture initiation at sharp cracks does not. Simulations with a local fracture model of fracture events in (1) fatigue precracked compact specimens and (2) three-point-bend bars containing blunt notches confirm these conclusions. However, a comparison of simulations with actual experimental results with HY-130 steel specimens leads to mixed conclusions. Predicted and observed behaviors for fracture at sharp cracks agree well, but the discrepancy is considerable for fracture initiating at blunt notches loaded in bending. Significant scaling effects are observed in the experiments for the conditions of fracture initiation at blunt notches. Fractographic analysis reveals that the reason for this discrepancy is a difference in the micromechanisms controlling fracture at sharp cracks as opposed to blunt notches. At sharp cracks, quasi-isotropic void growth dominates, whereas fracture initiates at blunt notches by a shear localization process and the nucleation, growth, and coalescence of voids in a mixed shear and tensile deformation field. The transition from one mode to the other may be governed by the hardening rate and, if so, is material dependent. Therefore, when using local fracture models for predicting fracture under generalized geometric and loading conditions, care must be taken, that the micromechanisms of ductile fracture invoked in the actual material match those assumed by the local fracture model. If this correspondence is verified, local fracture models can be used to predict fracture conditions and associated scaling effects for situations not amenable to treatment by classical elasto-plastic fracture mechanics. However, new or expanded models that can treat ductile fracture in localized shear zones should be developed to realize the full potential of these local fracture methodologies. This revised version was published online in August 2006 with corrections to the Cover Date.