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

Abstract

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.

In situ measurements and model calculations of primary production in turbid waters

“…On the basis of these results, we derived the spectral values of the diffuse attenuation coefficient (Arst et al 2002, Arst 2003.…”

“…After, we converted these results into Einst m -2 h -1 (Dera 1992, Arst 2003, we could compute the necessary values of q(Δλ,z = 0). For determination of the spectral diffuse attenuation coefficients K d (Δλ) for intervals Δλ, we used the spectra of c(Δλ), measured from corresponding water samples in the laboratory, and the model described in Arst et al (1997Arst et al ( , 2002 and Arst (2003).…”

Reconstruction of long-term changes of the underwater light field in large shallow lakes Peipsi and Võrtsjärv, North-East Europe

“…In these conditions, we considered d,PAR K calculated from the measured beam attenuation spectra more reliable. For the years 2002-2007, for which measured beam attenuation spectra were available, we calculated d,PAR K from d ( ) K λ using a model developed by Arst et al (2002) and Arst (2003 were found applying the iteration method (Arst et al, 2002;Arst, 2003). Then the spectra of ( ) b λ in the range of 400-700 nm were found using the power law (Herlevi et al, 1999;Arst, 2003).…”

Quantification of a Primary Production Model Using Two Versions of the Spectral Distribution of the Phytoplankton Absorption Coefficient

“…Spectra of the beam attenuation coefficient in the 400-700-nm wavelength range for water samples were obtained with a Hitachi U-3010 laboratory spectrophotometer. These results allowed to derive not only the spectral values of the diffuse attenuation coefficient but also K d,PAR [9,14].…”