Raman scattering by pure water and seawater

Abstract. Over clear ocean waters, photons scattered within the water body contribute significantly to the upwelling flux. In addition to elastic scattering, inelastic Vibrational Raman Scattering (VRS) by liquid water is also playing a role and can have a strong impact on the spectral distribution of the outgoing radiance. Under clear-sky conditions, VRS has an influence on trace gas retrievals from space-borne measurements of the backscattered radiance such as from e.g. GOME (Global Ozone Monitoring Experiment). The effect is particularly important for geo-locations with small solar zenith angles and over waters with low chlorophyll concentration.In this study, a simple ocean reflectance model (Sathyendranath and Platt, 1998) accounting for VRS has been incorporated into a radiative transfer model. The model has been validated by comparison with measurements from a swimming-pool experiment dedicated to detect the effect of scattering within water on the outgoing radiation and also with selected data sets from GOME. The comparisons show good agreement between experimental and model data and highlight the important role of VRS.To evaluate the impact of VRS on trace gas retrieval, a sensitivity study was performed on synthetic data. If VRS is neglected in the data analysis, errors of more than 30% are introduced for the slant column (SC) of BrO over clear ocean scenarios. Exemplarily DOAS retrievals of BrO from real GOME measurements including and excluding a VRS compensation led to comparable results as in the sensitivity study, but with somewhat smaller differences between the two analyses.The results of this work suggest, that DOAS retrievals of atmospheric trace species from measurements of nadir viewing space-borne instruments have to take VRS scattering into account over waters with low chlorophyll concentrations, and that a simple correction term is enough to reduce the errors to an acceptable level.

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“…Bartlett et al (1998) showed that the exponent P is near to 5.3 (instead of 5 as shown in older studies).…”

Section: Backscattering Coefficients For Vrsmentioning

confidence: 75%

Inelastic scattering in ocean water and its impact on trace gas retrievals from satellite data

et al. 2003

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“…Based on the law of conservation of energy, the attenuation coefficient of the transferred beam includes the absorption and scattering coefficients. If the absorption coefficient of pure water involving visible light wavebands is 0.1 [15], the scattering coefficient of the water body in the towing tank used for this experiment can be estimated at 0.117. We designed and simulated underwater LED array lighting modules using Matlab software.…”

Section: Design and Analysis Of Underwater Led Fish-attracting Lampmentioning

confidence: 99%

Design and Analysis of an Underwater White LED Fish-Attracting Lamp and its Light Propagation

Shen

Kuo

Fang

2013

International Journal of Advanced Robotic Systems

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Light emitting diodes (LED) are a new source for replacing traditional light sources including under water illumination. As traditional underwater light sources operate under a radiative transfer model, the luminous intensity is dispersed evenly at each emission angle, with the scattering factors included in the attenuation coefficient. By contrast, LED light sources are characterized by being highly directional, causing underwater luminous energy to vary with different emission angles. Thus, the traditional theory of underwater optical transfer becomes inapplicable when an underwater LED lighting module is designed. Therefore, to construct an underwater transfer model for LED light sources, this study employed the average cosine of the underwater light field, the method for light scattering probability, the LED luminous intensity distribution curve (LIDC) and axial luminous intensity. Afterwards, an underwater LED fish-attracting lamp was designed. Experimental results showed that, compared with the simulation values, the luminous intensity of the underwater LED lighting module at all emission angles had a percentage error of less than 10%.

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“…However, as the presence of inelastic processes can make a significant contribution to the in-water light field (Stavn and Weidman, 1988;Gordon 1999), we extended that study to include the influence of Raman scattering in the inversion algorithm, i.e., to retrieve the IOP's from the AOP's when they are contaminated by Raman scattering (✗ ✗). We chose to look at Raman scattering as opposed to other inelastic processes (e.g., fluorescence of dissolved organic matter) because the Raman scattering cross sections are known (Bartlett, et al, 1998).…”

Section: Report Documentation Pagementioning

confidence: 99%

Inverse Problems in Hydrologic Radiative Transfer

Gordon¹

1999

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The long-term scientific goal of my research is to better understand the distribution of phytoplankton in the world's oceans through remote sensing their influence on the optical properties of the water. OBJECTIVESOptically, phytoplankton reveal their presence through their influence on the inherent optical properties (IOP's) of the water. The main effect of phytoplankton is to increase the absorption of light by virtue of the strong absorption by their photosynthetic (chlorophyll a) and accessory pigments. A secondary effect is to increase the backscattering coefficient of the medium in a manner that depends on the concentration of pigments. Although techniques for measuring the absorption coefficient directly (e.g., in-situ AC9 measurements or in-vitro filterpad absorption) are becoming accepted by the scientific community, laboratory techniques for measuring backscattering are tedious and subject to error, and in-situ techniques for backscattering are in their infancy. In addition, in most in-situ measurements the volume of medium that is sampled is small and may not be representative of the whole water body, even in a homogeneous medium. Thus, in the past, there has been considerable effort devoted toward indirectly inferring these IOP's by virtue of their affect on the apparent optical properties (AOP's), e.g., the diffuse reflectance of the water (the color of the water) or the downwelling irradiance attenuation coefficient. These AOP's are perhaps the most frequently measured quantities in hydrologic optics. Clearly, interpretation of such observations requires a detailed understanding of the influence of phytoplankton on the IOP's, and their link to the AOP's.The IOP ↔ AOP link forms the focus of the present research. In particular, our research is centered on deriving the IOP's from measurements of the AOP's. This is an example of the inverse problem of radiative transfer. It is important in that IOP's determined from AOP's are, by definition, sampled at a scale appropriate for radiative transfer, and for remote sensing. Also, the retrieved IOP's possess the attribute that when combined with the radiative transfer equation, they reproduce the measured AOP's. The table below summarizes in matrix form inverse problems relevant to hydrologic optics. Our goal is to fill in the uncompleted elements of the matrix.

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Raman scattering by pure water and seawater

Cited by 101 publications

References 26 publications

Inelastic scattering in ocean water and its impact on trace gas retrievals from satellite data

Inelastic scattering in ocean water and its impact on trace gas retrievals from satellite data

Design and Analysis of an Underwater White LED Fish-Attracting Lamp and its Light Propagation

Inverse Problems in Hydrologic Radiative Transfer

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