Spectral backscattering coefficient in coastal waters

Based on 186 field observations in the Oslo Fjord of irradiance and radiance and 105 laboratory measurements of beam attenuation, this analysis demonstrates that the ratio between the backscattering coefficient b(pb) and the scattering coefficient bp of the particles is wavelength dependent and not a constant value. The mean values of b(pb)/b(p) at the different wavelengths are close to Petzold's 0.017-0.019 from the San Diego Harbor at 515 nm. For all wavelengths and stations (630 observations) the mean value of b(pb)/b(p) is 0.020, the standard deviation of the dataset is 0.015, half of the ratios are greater than 0.020, more than 10% are greater 0.030 and about 5% greater than 0.040. The numerical magnitude of these ratios indicates that small particles are the cause of the latter deviations from the 'Petzold case'. An example from the northern border of the Skagerrak shows a spectral shape of b(pb) that can be approximated by lambda(-1.54), lambda being the wavelength, while b(p) is roughly proportional to lambda(-0.41). The spectral shape of b(pb)/b(p) becomes similar tolambda(-1.12). During a dinoflagellate bloom in the inner part of the Oslo Fjord direct measurements of b(pb) have revealed a slope of b(pb)similar tolambda(-1.59). The spectral shape of the mean values of b(p)(lambda) in the Oslo Fjord, based on the 105 observations, can be approximated by the function similar tolambda(-0.67), while the spectral shapes of b(pb)(lambda) and b(pb)(lambda)/b(p)(lambda) display a greater variety of forms.