Fast and accurate model of underwater scalar irradiance

Abstract

A spectral model of scalar irradiance with depth is applied to calculations of photosynthetically available radiation for a vertically homogeneous water column. The model runs more than 14,000 times faster than the full Hydrolight code, while it limits the percentage error to 2.20% and the maximum error to less than 4.78%. The distribution of incident sky radiance and the effects of a wind-roughened surface are integrated into this model. It can be applied to case 1 waters as well as to case 2 waters that happen to be gelbstoff rich, and the volume-scattering phase function can be generated dynamically based on the backscatter fraction. This new model is both fast and accurate and is, therefore, suitable for use interactively in models of the oceanic system, such as biogeochemical models or the heat budget part of global circulation models. It can also be applied by use of remote-sensing data to improve light-field calculations as a function of depth, which is needed for the estimation of global ocean carbon production and the ocean heat budget.

Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods

“…[25] Finally, although the diffuse attenuation coefficient is an apparent optical property (AOP) that varies with Sun angle [Gordon, 1989;Liu et al, 2002], the expressions of equation (3) or equation (5) do not account for that source of variability in some well-defined systematic fashion. Because the ratio of R rs (490)/R rs (555) or other spectral ratios of R rs (l) are not sensitive to Sun angle variation Morel and Gentili, 1993], the difference between K d (490) derived from the R rs (l) ratio and the measured K d (490) includes the variation introduced by changes in Sun angle.…”

“…[3] K d (l) is an apparent optical property [Preisendorfer, 1976], so it varies to some extent with solar zenith angle, sky and surface conditions, as well as with depth even within the well mixed water column [Gordon, 1989;Liu et al, 2002]. In ocean color remote sensing, the commonly used quantity is the vertically averaged value of K d (l) in the surface mixed layer, denoted in this article as K d (l) or K d for brevity.…”

Euphotic zone depth: Its derivation and implication to ocean‐color remote sensing

“…[4] To incorporate the dependence of subsurface light field on other water constituents (such as CDOM), Liu et al [2002] developed a numerical model (via look-up-table) that uses information about chlorophyll concentration, CDOM absorption and particle scattering coefficient as inputs to describe the vertical distribution of downwelling irradiance. This approach, similar as those based on Case-1 assumption [Morel and Antoine, 1994;Ohlmann and Siegel, 2000;Sathyendranath et al, 1989a], however, still requires accurate information about chlorophyll concentration when applied to ocean-color remote sensing.…”

Comparison of marine insolation estimating methods in the adriatic sea

“…Consequently, much of our understanding of ocean dynamics hinges on the quantification of solar radiation reaching surface waters. Accurate estimates of photosynthetically-active radiation (PAR), for example, are central to calculating phytoplankton photosynthesis rates (Liu et al 2002).…”

“…Use of RTMs is particularly important for calculating phytoplankton photosynthesis in marine ecosystem models (Liu et al 2002). However, most of the weather forecasting models used to generate the meteorological inputs for RTMs do not spectrally-resolve solar-irradiance, nor do they produce the conversion factors for PAR needed to calculate phytoplankton production.…”