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A model of diffuse attenuation of downwelling irradiance for ecosystem models
Nechad, B.; Ruddick, K. (2010). A model of diffuse attenuation of downwelling irradiance for ecosystem models, in: Frouin, R.J. et al. (Ed.) Remote Sensing of the Coastal Ocean, Land, and Atmosphere Environment. Incheon, South Korea, October 13-14, 2010. Proceedings of SPIE, the International Society for Optical Engineering, 7858. dx.doi.org/10.1117/12.872979
In: Frouin, R.J. et al. (Ed.) (2010). Remote Sensing of the Coastal Ocean, Land, and Atmosphere Environment. Incheon, South Korea, October 13-14, 2010. Proceedings of SPIE, the International Society for Optical Engineering, 7858. SPIE: Bellingham. ISBN 978-0-8194-8388-1. 308 pp., more
In: Proceedings of SPIE, the International Society for Optical Engineering. SPIE: Bellingham, WA. ISSN 0277-786X, more
Peer reviewed article  

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    VLIZ: Open Repository 231481 [ OMA ]

Author keywords
    diffuse attenuation coefficient of downwelling irradiance; average

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  • BELCOLOUR-2 : Optical remote sensing of marine, coastal and inland waters, more

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Abstract
    Estimation of the underwater attenuation of light is important to ecosystem modellers, who require information on Photosynthetically Available Radiation (PAR), and on the euphotic depth for calculation of primary production. Characterisation of these processes can be achieved by determining the diffuse attenuation coefficient of PAR, KPAR. A review of bio-optical models of the spectral diffuse attenuation coefficient for downwelling irradiance, Kd, is presented and stresses the necessity for a better knowledge and parameterization of these coefficients.
    In the second part of this work, radiative transfer simulations were carried out to model KdZ1% the spectral diffuse attenuation of downwelling irradiance averaged over the euphotic depth Z1% (depth where the downwelling irradiance is 1% of its surface value). This model takes into account the effects of varying sun zenith angle and cloud cover and needs absorption and backscattering coefficients (the inherent optical properties, IOPs) as input. It provides average and maximum relative errors of 1% and 5% respectively, for sun zenith angles [0°-50°] and of 1.7% and 12% respectively at higher sun zenith angles. A relationship was established between KdZ1% at a single wavelength (590nm) and KPAR at ZPAR1% (where PAR is 1% of its value at the surface) which allows for a direct expression of KPARZPAR1% in terms of inherent optical properties, sun angle and cloudiness. This model provides estimates of KPAR within 25% (respectively 40%) relative errors respectively with a mean relative error less than 7% (respectively 9%) for sun zenith angles ranging from 0° to 50° (respectively higher than 50°). A similar method is applied to derive a model for the diffuse attenuation of photosynthetically usable radiation, KPURZPUR1%, with similar performance.

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