Secchi disk science: Visual optics of natural waters1

Preisendorfer, Rudolph W.

doi:10.4319/lo.1986.31.5.0909

Cited by 457 publications

(327 citation statements)

References 10 publications

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“…It has been suggested on theoretical grounds that attenuation coefficients for diffuse underwater light should not be computed from transparency measurements (Kirk 1983(Kirk , 1985Preisendorfer 1986). However, it is clear that reciprocal kransparency is proportional to the attenuation coefficient for the most-penetrating waveband of underwater light and that seawater transparency also is closely related to the attenuation coefficient for this waveband.…”

Section: Discussionmentioning

confidence: 99%

Effects of algae on the Secchi transparency of the southeastern Mediterranean Sea

Megard

Berman

1989

Limnology & Oceanography

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The mean transparency (37.5 m) measured by Secchi disk at "blue-water" pelagic sampling stations in the southeastern Mediterranean Sea during 3 yr was greater than in most other seawater. Our measurements in the Mediterranean and those by others in the English Channel, Atlantic Ocean, and Pacific Ocean obey the Lambert-Bouguer law if it is specified that transparency depends on the vertical attenuation coefficient for downward irradiance in the waveband of underwater sunlight that has lowest attenuance. Mean downward irradiance (+95% C.L.) at the depth where a Secchi disk disappears, calculated from 187 paired estimates of transparency and attenuation coefficients from these oceanic regions, is 22-t 1% of surface irradiance in this waveband. This value is significantly larger than the value (18%) that has been used widely since an early study by Poole and Atkins, who calculated attenuation coefficients incorrectly.As predicted by the Lambert-Bouguer law, reciprocal transparency was proportional to the attenuation coefficient for the most-penetrating waveband. Attenuance of this waveband and reciprocal transparency both increase linearly with increasing concentration of phytoplankton chlorophyll in pelagic water. Chlorophyll concentrations in pelagic Mediterranean water were very low (0.02-O. 14 mg m-3), but attenuance by units of phytoplankton chlorophyll was about 10 times larger than in more productive seawater, probably because blue light was predominant and many of the phytoplankton were very small coccolithophorids (cell diameters < 10 pm) with optically dispersive cell surfaces.Measurements of transparency by Secchi disk are as accurate and precise as estimates of attenuation coefficients calculated from irradiances measured at sea with photoelectric sensors. The Poole-Atkins equation for transparency in terms of the waveband with lowest attenuance describes the variation of transparency as well as the Duntley-Preiscndorfer equation does. Much of the information needed for interpreting satellite ocean-color imagery could be obtained very efficiently with closely spaced measurements of transparency from surface vessels during synoptic cruises.Planktonic algae can cause large variations in the transparency of seawater, especially in the open ocean. It is becoming increasingly important to understand how algae can cause such variability, because there is a global pattern of marine transparency. The transparency map compiled recently by Lewis et al. ( 1988) shows a pattern that is very similar to those of phytoplankton chlorophyll concentrations in- AcknowledgmentsContribution 308 from the University of Minnesota Limnological Research Center and also a contribution from Israel Oceanographic and Limnological Research, Ltd. Financial support provided by the U.S. Aid Program and the University of Minnesota Graduate School.We thank Y. Azov and A. Schneller for their assistance and J. T. 0. Kirk and A. Morel for critical comments and valuable suggestions on the manuscript.

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Section: Discussionmentioning

confidence: 99%

Effects of algae on the Secchi transparency of the southeastern Mediterranean Sea

Megard

Berman

1989

Limnology & Oceanography

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“…Light scattering by particles, a fundamental process regulating radiative transfer in water (Kirk 2011), is important in determining apparent optical properties (AOPs, depend on geometry of the light field) of interest, including clarity (Preisendorfer 1986) and the remote sensing signal (Woźniak and Stramski 2004). The total scattering coefficient (b; m 21 ), corresponding to the integration of the volume-scattering function over all directions (Kirk 2011), quantifies a central feature of the light-scattering regime.…”

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confidence: 99%

Long‐term study of minerogenic particle optics in Cayuga Lake, New York

Effler

Peng

2014

Limnology & Oceanography

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The dynamics of light scattering by minerogenic particles in the upper waters of Cayuga Lake, New York, were characterized for the spring-autumn interval of 8 yr (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) at pelagic and nearshore sites with a scanning electron microscope interfaced with automated image and x-ray analyses (SAX). SAX results were used to estimate the minerogenic scattering coefficient ( Light scattering by particles, a fundamental process regulating radiative transfer in water (Kirk 2011), is important in determining apparent optical properties (AOPs, depend on geometry of the light field) of interest, including clarity (Preisendorfer 1986) and the remote sensing signal (Woźniak and Stramski 2004). The total scattering coefficient (b; m 21 ), corresponding to the integration of the volume-scattering function over all directions (Kirk 2011), quantifies a central feature of the light-scattering regime. b is an inherent optical property, independent of the geometry of the light field. The magnitude and spectral features of the particulate component of scattering, b p (which greatly exceeds that due to water), depend on multiple attributes of a particle population, including the number concentration (N), the particle size distribution (PSD), the composition of the individual particles and their shapes (Babin et al. 2003).The particle populations of aquatic ecosystems are heterogeneous, varying in time and space and differing greatly among systems in response to an array of drivers (Stramski et al. , 2007Peng and Effler 2011). Protocols for resolving the various components of light scattering are needed to understand these differences and dynamics, and to identify their origins and drivers, objectives that are consistent with the reductionist approach advocated by Stramski and co-workers (Stramski et al. 2001(Stramski et al. , 2007 where V is the sample volume, N m is the number of minerogenic particles in a sampled volume of water, and PA m,i is the projected area (m 2 ) of minerogenic particle i. Q bm,i depends on the complex refractive index (m i , function of composition) and size (d i ) of the particle, and the wavelength of light (l). This SAX-Mie approach supports further partitioning of b m into contributions according to size and particularly composition (e.g., clay minerals, quartz, and calcite) of particles Effler 2010, 2011). Early research with the SAX-Mie approach had appropriately focused first on testing the credibility of the forward estimates of b m for a range of particle assemblage conditions (see

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Section: Secchi Disk Depthsmentioning

confidence: 99%

“…The depth of disappearance is a visual measure of the clarity of the water (Wetzel, 1983;Preisendorfer, 1986). The depth of disappearance is inversely proportional to the average amount of organic and inorganic matter along the path of light in the water (Preisendorfer, 1986). Secchi disk depth was measured in this study to determine the water quality characteristics of the three dams and also to examine the effect of water transfers on the water quality of the recipient Von Bach Dam.…”

Section: Secchi Disk Depthsmentioning

confidence: 99%