Vector irradiance modelling in a seawater column for assessing the detection capabilities of an oil-in-water emulsion.

The possibility of tracking oil pollution in the sea has been an issue that has been analysed for a long time, and the use of light interactions with the sea polluted with various forms of oil has been the subject of numerous studies. This paper presents the results of the Monte Carlo simulations of the fate of a large number of virtual photons to demonstrate changes in the downwelling vector irradiance and upwelling vector irradiance in oil-free seawater and analogously seawater column polluted with an oil-in-water emulsion. The analyses were carried out for eight wavelengths ranging from 412 to 676 nm, upon the assumption of an oil concentration of 10 ppm, taking into account the data of absorption and scattering properties of the southern Baltic Sea.

Modelling the upwelling radiance detected in a seawater column for oil-in-water emulsion tracking.

This study concerns changes in the solar light transfer in seawater as a result of the appearance of oil substances in the form of oil-in-water emulsions. The expected effect of the studies is to gather knowledge that would be useful in designing an optical sensor for monitoring oil substances penetrating the seawater column. The paper presents the process of the Monte Carlo modelling of the upwelling radiance detected by a virtual underwater sensor.

Light Penetrating the Seawater Column as the Indicator of Oil Suspension-Monte Carlo Modelling for the Case of the Southern Baltic Sea.

The strong need to control investments related to oil extraction and the growing demand for offshore deep-water exploration are the reasons for looking for tools to make up a global underwater monitoring system. Therefore, the current study analyses the possibility of revealing the existence of oil-in-water emulsions in the water column, based on the modelling of the downwelling radiance detected by a virtual underwater sensor. Based on the Monte Carlo simulation for the large numbers of solar photons in the water, the analyses were carried out for eight wavelengths ranging from 412 to 676 nm using dispersed oil with a concentration of 10 ppm.

Transmission across the water-air interface: resolving the impact of multiple interactions at the sea surface.

A series of Monte Carlo and HydroLight radiative transfer simulations are used to demonstrate that the traditional form of the Fresnel transmission across the water-air interface is accurate. This contradicts assertions to the contrary in a recent paper [Opt. Express25, 27086 (2017)10.

Modelling a Spectral Index to Detect Dispersed Oil in a Seawater Column Depending on the Viewing Angle: Gulf of Gdańsk Case Study.

This paper analyzes the digital modelling of radiance reflectance of the sea surface when the water column is polluted by oil-in-water emulsion. A method tracking the fate of two billion virtual solar photons was applied to obtain the angular distribution of bottom-up radiance for a plane of sunlight striking the sea surface. For the calculations, the inherent optical properties of seawater characteristic for the Gulf of Gdańsk (southern Baltic Sea) were used.

Modelling Remote Sensing Reflectance to Detect Dispersed Oil at Sea.

This paper presents a model of upwelling radiation above the seawater surface in the event of a threat of dispersed oil. The Monte Carlo method was used to simulate a large number of solar photons in the water, eventually obtaining values of remote sensing reflectance (R). Analyses were performed for the optical properties of seawater characteristic for the Gulf of Gdańsk (southern Baltic Sea).

Effective scattering phase functions for the multiple scattering regime.

The propagation of light through turbid media is of fundamental interest in a number of areas of optical science including atmospheric and oceanographic science, astrophysics and medicine amongst many others. The angular distribution of photons after a single scattering event is determined by the scattering phase function of the material the light is passing through. However, in many instances photons experience multiple scattering events and there is currently no equivalent function to describe the resulting angular distribution of photons.

Laboratory measurements of light beam depolarization on turbulent convective flow.

Laboratory measurements of light beam depolarization by a turbulent flow, corresponding to oceanic turbulence within the oceanic mixed layer, show that the depolarization rate (1x10(-5)?m(-1) to 3x10(-3)?m(-1)) correlates with turbulence strength and is consistent with polarized lidar observations [Opt. Express, 16, 1196 (2008)OPEXFF1094-408710.1364/OE.

Small-scale effects of underwater bubble clouds on ocean reflectance: 3-D modeling results.

We examined the effect of individual bubble clouds on remote-sensing reflectance of the ocean with a 3-D Monte Carlo model of radiative transfer. The concentrations and size distribution of bubbles were defined based on acoustical measurements of bubbles in the surface ocean. The light scattering properties of bubbles for various void fractions were calculated using Mie scattering theory.

Scattering error corrections for in situ absorption and attenuation measurements.

Monte Carlo simulations are used to establish a weighting function that describes the collection of angular scattering for the WETLabs AC-9 reflecting tube absorption meter. The equivalent weighting function for the AC-9 attenuation sensor is found to be well approximated by a binary step function with photons scattered between zero and the collection half-width angle contributing to the scattering error and photons scattered at larger angles making zero contribution. A new scattering error correction procedure is developed that accounts for scattering collection artifacts in both absorption and attenuation measurements.

Ocean color remote sensing: choosing the correct depth weighting function.

Values of reflectance and remote sensing reflectance are proportional to the ratio of sea water backscattering to absorption. However, in vertically non-homogeneous waters, this fraction needs to be depth weighted. The usual practice uses normalized vertical transmittance profiles as the weighting function.

Improved method of Fournier-Forand marine phase function parameterization.

Volume scattering functions (VSFs) and other optical seawater parameters were measured during a cruise in the Southern Baltic. Phase functions (PFs) calculated from VSFs were compared with Fournier-Forand phase functions parameterized with backscattering ratios. Due to significant divergences between experimental and modeled data a new method of Fournier-Forand phase function parameterization is proposed.

Influence of forward and multiple light scatter on the measurement of beam attenuation in highly scattering marine environments.

Using three-dimensional Monte Carlo radiative transfer simulations, we examine the effect of beam transmissometer geometry on the relative error in the measurement of the beam-attenuation coefficient in an aquatic environment characterized by intense light scattering, especially within submerged bubble clouds entrained by surface-wave breaking. We discuss the forward-scattering error associated with the detection of photons scattered at small angles (< 1 degrees) and the multiple-scattering error associated with the detection of photons scattered more than once along the path length of the instrument. Several scattering phase functions describing bubble clouds at different bubble void fractions in the water are considered.

Effect of 3-D instrument casing shape on the self-shading of in-water upwelling irradiance.

The self-shading measurement error of the upwelling irradiance caused by the presence of a typical cylindrical housing of an optical instrument was calculated with the 3-D Monte-Carlo code as a function of the housing dimensions and of the optical parameters of seawater. The resulting values were compared to the self-shading error for a flat disk of the same diameter, originally used to establish self-shading error estimations universally used in marine optics. The results show that the self-shading of upwelling irradiance is underestimated by up to 25% producing a significant underestimation of the measured upwelling irradiance, and therefore reflectance, especially in turbid waters.

Modelling the bidirectional reflectance distribution function (BRDF) of seawater polluted by an oil film.

The Bi-directional Reflectance Distribution Function (BRDF) of both clean seawaters and those polluted with oil film was determined using the Monte Carlo radiative transfer technique in which the spectrum of complex refractive index of Romashkino crude oil and the optical properties of case II water for chosen wavelengths was considered. The BRDF values were recorded for 1836 solid angular sectors of throughout the upper hemisphere. The visibility of areas polluted with oil observed from various directions and for various wavelengths is discussed.

Estimation of scattering error in spectrophotometric measurements of light absorption by aquatic particles from three-dimensional radiative transfer simulations.

We present an approach based on three-dimensional Monte Carlo radiative transfer simulations for estimating scattering error in measurements of light absorption by aquatic particles with a typical laboratory double-beam spectrophotometer. The scattering error is calculated by combining the weighting function describing the angular distribution of photon losses that are due to scattering on suspended particles with the volume scattering function of particles. We applied this method to absorption measurements made on marine phytoplankton, a diatom Thalassiosira pseudonana and a cyanobacterium Synechococcus.

Modeling the remotely sensed optical contrast caused by oil suspended in the sea water column.

The reflectance of sea areas polluted by an oil-in-water emulsion was modeled using the radiance transfer Monte Carlo code. Example results of the contrast function parameterized by the observation angle for various angles of incident sunlight, various sea surface roughness states and two optically different types of seawaters are presented.