| Summary: | The attenuation of blue hght for ocean waters in the Northwest Atlantic has been modelled by adding the measured attenuation of light by particles to that of pure water. Comparison of the model predictions with measured total attenuation of downwelling light at 440 nm showed that the model slightly overestimated the in situ attenuation in the clearest Case I waters and underestimated attenuation in Case II waters by ∼30%, presumably due to the presence of dissolved organic substances. In spite of this, estimates of near-surface chlorophyll concentration denved from satellite colorimetric measurements at 440 nm are highly correlated with in situ concentrations It is reasoned that errors in satellite derived chlorophyll concentrations due to dissolved organic substances found in Case II waters can be greatly reduced by using measurements in the wavelength region 520–550 nm, not wavelengths >440 nm.
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