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

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. The new correction method does not assume zero absorption in the near infrared (NIR), does not assume a wavelength independent scattering phase function, but does require simultaneous measurements of spectrally matched particulate backscattering. The new method is based on an iterative approach that assumes that the scattering phase function can be adequately modeled from estimates of particulate backscattering ratio and Fournier-Forand phase functions. It is applied to sets of in situ data representative of clear ocean water, moderately turbid coastal water and highly turbid coastal water. Initial results suggest significantly higher levels of attenuation and absorption than those obtained using previously published scattering error correction procedures. Scattering signals from each correction procedure have similar magnitudes but significant differences in spectral distribution are observed

Evaluation and improvement of an iterative scattering correction scheme for in situ absorption and attenuation measurements

The performance of several scattering correction schemes for reflecting-tube absorption and beam attenuation measurements is evaluated with data collected in European shelf seas. Standard scattering correction procedures for absorption measurements perform poorly because of nonzero absorption in the near infrared and wavelength-dependent scattering phase functions. A previously described iterative correction procedure based on Monte Carlo simulations of the Western Environmental Technologies Laboratories (WET Labs) ac-9 and independent estimates of particle backscattering initially performs poorly, but is greatly improved when realistic losses at flow-tube walls are incorporated into the model. The updated Monte Carlo scattering correction provides excellent agreement with independent absorption and attenuation measurements made with a point-source integrating-cavity absorption meter (PSICAM) and a Laser In Situ Scattering and Transmissometer (LISST, Sequoia Scientific), respectively. Implications for historic datasets and requirements for application to future datasets are discussed

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

The links between marine plastic litter and the air-sea flux of greenhouse gases

Climate change and plastic pollution are two of the most pressing environmental challenges caused by human activity, and they are directly and indirectly linked. We focus on the relationship between marine plastic litter and the air-sea flux of greenhouse gases (GHGs). Marine plastic litter has the potential to both enhance and reduce oceanic GHG fluxes, but this depends on many factors that are not well understood. Different kinds of plastic behave quite differently in the sea, affecting air-sea gas exchange in different, largely unknown, ways. The mechanisms of air-sea exchange of GHGs have been extensively studied and if air-sea gas transfer coefficients and concentrations of the gas in water and air are known, calculating the resulting GHG fluxes is reasonably straightforward. However, relatively little is known about the consequences of marine plastic litter for gas transfer coefficients, concentrations, and fluxes. Here we evaluate the most important aspects controlling the exchange of GHGs between the sea and the atmosphere and how marine plastic litter could change these. The aim is to move towards improving air-sea GHG flux calculations in the presence of plastic litter and we have largely limited ourselves to identifying processes, rather than estimating relative importance

Zator tętnicy środkowej siatkówki jako pierwsza manifestacja kliniczna w postaci powikłania zatorowo-zakrzepowego jednopłatkowej zastawki aortalnej — opis przypadku

Unicuspid aortic valve (UAV) is a rare congenital anomaly of the aortic valve. An overview of publications on the subject matter suggests that the estimated frequency of its occurrence is 0.02%. The article presents the case of a 40-year-old patient with an UAV with severe aortic stenosis. Unicuspid aortic valve is most frequently congenital, but the case analysed in this study is considered to have originated from one of two possible causes: it can be a congenital defect, in the form of a slit-shaped unicomissural or an acquired defect, in the form of degenerative aortic valve stenosis. A thromboembolic complication, presenting as a central retinal artery occlusion, was the first manifestation of the disease in the examined case, the symptoms invol-ving sudden loss of vision. The patient was referred for cardiologic diagnostic tests, which revealed severe aortic stenosis. The patient underwent successful surgery, in which the aortic valve was replaced by a mechanical prosthesis. The authors emphasise the need to pay particular attention to patients with signs and symptoms of thromboembolism who should be referred for cardiologic diagnostic tests aimed at finding the underlying causes of such complications.Jednopłatkowa zastawka aortalna (UAV) jest rzadką wrodzoną wadą zastawki aortalnej. Przegląd literatury sugeruje, że szacowana częstość jej występowania wynosi 0,02%. W artykule przedstawiono przypadek 40-letniego pacjenta z UAV z ciężką stenozą. Etiologia jednopłatkowej zastawki aortalnej jest najczęściej wrodzona, jednak w opisanym przypadku rozpatruje się ją na dwóch możliwych podłożach — jako wadę wrodzoną o podtypie slit-shaped unicomissural lub jako wadę nabytą o degeneracyjnej postaci zwężenia zastawki. Pierwszą manifestacją choroby u pacjenta było powikłanie zakrzepowo-zatorowe w postaci zatoru tętnicy środkowej siatkówki objawiające się nagłym zaniewidzeniem. Chorego skierowano na diagnostykę kardiologiczną, w ramach której wykazano ciężką stenozę aortalną. Pacjent przebył skuteczny zabieg wymiany zastawki aortalnej na protezę mechaniczną. Autorzy podkreślają potrzebę zwracania uwagi na pacjentów z wszelkimi objawami zakrzepowo-zatorowymi i kierowania ich na diagnostykę kardiologiczną w celu poszukiwania przyczyn takich powikłań

Transfer across the air-sea interface

The efficiency of transfer of gases and particles across the air-sea interface is controlled by several physical, biological and chemical processes in the atmosphere and water which are described here (including waves, large- and small-scale turbulence, bubbles, sea spray, rain and surface films). For a deeper understanding of relevant transport mechanisms, several models have been developed, ranging from conceptual models to numerical models. Most frequently the transfer is described by various functional dependencies of the wind speed, but more detailed descriptions need additional information. The study of gas transfer mechanisms uses a variety of experimental methods ranging from laboratory studies to carbon budgets, mass balance methods, micrometeorological techniques and thermographic techniques. Different methods resolve the transfer at different scales of time and space; this is important to take into account when comparing different results. Air-sea transfer is relevant in a wide range of applications, for example, local and regional fluxes, global models, remote sensing and computations of global inventories. The sensitivity of global models to the description of transfer velocity is limited; it is however likely that the formulations are more important when the resolution increases and other processes in models are improved. For global flux estimates using inventories or remote sensing products the accuracy of the transfer formulation as well as the accuracy of the wind field is crucial

Effect of ship shadow on in-water irradiance measurements

Calculations of the effect of the ship's shadow on in-water irradiance measurement errors were performed with a Monte Carlo radiance transfer algorithm. The algorithm contained the Cox-Munk wave-slope probability function. A simple 3-D model of the rectangular underwater part of a ship was used. The effect was calculated as a function of sea-water absorption, surface roughness (depending on an assumed wind velocity of up to 15 m s-1) with various wind velocities and directions, length and depth of the ship, distance of instrument from the ship, and bow-to-sun angle