The effect of particle characteristics on the beam attenuation coefficient and output from an optical backscatter sensor

1994 ◽  
Vol 28 (3-4) ◽  
pp. 245-248 ◽  
Author(s):  
E. J. Benns ◽  
D. A. Pilgrim
Keyword(s):  
Attenuation Coefficient ◽  
Beam Attenuation ◽  
Particle Characteristics ◽  
Optical Backscatter Sensor ◽  
Beam Attenuation Coefficient

The vertical structure of the water column according to optical data

2021 ◽  
pp. 245-252
Author(s):  
V.I. Burenkov ◽  
◽  
V.A. Artemiev ◽  
Keyword(s):  
Attenuation Coefficient ◽  
Barents Sea ◽  
Optical Data ◽  
Time Variability ◽  
Beam Attenuation ◽  
The Barents Sea ◽  
Close Relationship ◽  
Suspended Matter Concentration ◽  
High Space ◽  
Beam Attenuation Coefficient

Vertical profiles of the beam attenuation coefficient in different regions of the Barents Sea are analyzed. Data obtained show high space-time variability of seawater optical properties. In particular, the area affected by the river inflow (Pechora Sea) is distinguished. Very high values of the beam attenuation coefficient are observed in areas of coccolithophore blooms. There are a number of features associated with the flow of Atlantic waters into the Barents Sea. A close relationship between the seawater beam attenuation coefficient and total suspended matter concentration is shown. The corresponding regression equation is obtained.

Calculating Irradiance Penetration into Water Bodies from the Measured Beam Attenuation Coefficient, II: Application of the Improved Model to Different Types of Lakes

2002 ◽  
Vol 33 (2-3) ◽  
pp. 227-240 ◽  
Author(s):  
Helgi Arst ◽  
Ants Erm ◽  
Anu Reinart ◽  
Liis Sipelgas ◽  
Antti Herlevi
Keyword(s):  
Attenuation Coefficient ◽  
Water Samples ◽  
Water Bodies ◽  
Diffuse Attenuation Coefficient ◽  
Beam Attenuation ◽  
Underwater Light Climate ◽  
Different Types ◽  
Underwater Irradiance ◽  
Beam Attenuation Coefficient

The method suggested earlier for estimating the spectra of diffuse attenuation coefficient of light in the water bodies relying on the beam attenuation coefficient measured from water samples, was improved and applied to different types of lakes. Measurement data obtained in 1994-95 and 1997-98 for 18 Estonian and Finnish lakes were used. The spectra of two characteristics were available for our investigations: 1) beam attenuation coefficient estimated from water samples in the laboratory with a spectrophotometer Hitachi U1000; 2) vertical irradiance (diffuse) attenuation coefficient measured in situ with an underwater spectroradiometer LI 1800UW. A total of 70 spectra were considered. Relying on these data the parameters of our earlier model were changed. The criterion of the efficiency of the new version of our model is the coincidence of the spectra of diffuse attenuation coefficient derived from Hitachi U1000 data (Kdc) with those obtained by underwater irradiance measurements (Kdm). Correlation analysis of the model's results gave the relationship Kdm=1.0023Kdc with correlation coefficient 0.961. The respective values of mean relative difference and standard deviation were 5.4% and 0.55 m−1. This method may be useful in conditions where in situ measuring of underwater irradiance spectra cannot be performed because of weather conditions. As the measurement of the underwater radiation field is often a complicated and expensive procedure, our numerical method may be useful for estimating the underwater light climate.

Turbidity in the northern Great Barrier Reef lagoon in the wet season, March 1989

1994 ◽  
Vol 45 (4) ◽  
pp. 585 ◽  
Author(s):  
LJ Hamilton
Keyword(s):  
Great Barrier Reef ◽  
Attenuation Coefficient ◽  
Quantitative Relation ◽  
Barrier Reef ◽  
Wet Season ◽  
Secchi Disc ◽  
Reef Lagoon ◽  
Secchi Disc Depth ◽  
Beam Attenuation ◽  
Beam Attenuation Coefficient

In 1989, a typical wet season was experienced in northern Queensland, with low winds and long calm periods. Turbidity in upper waters of the Great Barrier Reef lagoon broadly had a simple distribution that could be modelled from bottom depth contour values alone, without introducing wind speed or bottom type. In the absence of major storm and cyclone events, this result appears to be general, based on the similarity between March 1989 survey data and Secchi disc climatology. The simple distribution arises because the main turbidity sources are riverine discharges, with little entrainment of bottom sediment into the upper column, except in shallower waters. Fresh, highly turbid riverine influxes are generally confined close inshore, with salinity and Secchi contours parallel to shore, forming cross-shelf gradients. A semi-quantitative relation was found between sea surface colour and Secchi disc depth. Examination of nephelometric turbidity stratification showed that satellite and Secchi data should be more useful for subsurface turbidity inference between Cooktown and Innisfail than in Princess Charlotte Bay, with horizontal and vertical stratifications, respectively, observed in those areas. Highest nephelometric turbidity was seen from Cooktown to Innisfail. Beam attenuation coefficient in oceanic waters outside the reef appeared to be dominated by absorption, with lagoon waters influenced by scattering. A method is suggested to enable approximate transfer of beam attenuation coefficient measured by a transmissometer operating at a single wavelength to beam attenuation coefficient at other wavelengths, using coincident measurements of Secchi disc depths made with filters.

Load-based approaches for modelling visual clarity in streams at regional scale

2013 ◽  
Vol 67 (5) ◽  
pp. 1092-1096 ◽  
Author(s):  
A. H. Elliott ◽  
R. J. Davies-Colley ◽  
A. Parshotam ◽  
D. Ballantine
Keyword(s):  
Water Quality ◽  
Attenuation Coefficient ◽  
Cross Section ◽  
Water Discharge ◽  
Regional Scale ◽  
Rock Types ◽  
Beam Attenuation ◽  
Optical Cross Section ◽  
Water Volumes ◽  
Beam Attenuation Coefficient

Reduction of visual clarity in streams by diffuse sources of fine sediment is a cause of water quality impairment in New Zealand and internationally. In this paper we introduce the concept of a load of optical cross section (LOCS), which can be used for load-based management of light-attenuating substances and for water quality models that are based on mass accounting. In this approach, the beam attenuation coefficient (units of m–1) is estimated from the inverse of the visual clarity (units of m) measured with a black disc. This beam attenuation coefficient can also be considered as an optical cross section (OCS) per volume of water, analogous to a concentration. The instantaneous ‘flux’ of cross section is obtained from the attenuation coefficient multiplied by the water discharge, and this can be accumulated over time to give an accumulated ‘load’ of cross section (LOCS). Moreover, OCS is a conservative quantity, in the sense that the OCS of two combined water volumes is the sum of the OCS of the individual water volumes (barring effects such as coagulation, settling, or sorption). The LOCS can be calculated for a water quality station using rating curve methods applied to measured time series of visual clarity and flow. This approach was applied to the sites in New Zealand's National Rivers Water Quality Network (NRWQN). Although the attenuation coefficient follows roughly a power relation with flow at some sites, more flexible loess rating curves are required at other sites. The hybrid mechanistic–statistical catchment model SPARROW (SPAtially Referenced Regressions On Watershed attributes), which is based on a mass balance for mean annual load, was then applied to the NRWQN dataset. Preliminary results from this model are presented, highlighting the importance of factors related to erosion, such as rainfall, slope, hardness of catchment rock types, and the influence of pastoral development on the load of optical cross section.

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