WEATHER-DEPENDENT MODEL OF COASTAL FOG ATTENUATION

Experimental particle size distributions of coastal fogs provided by other authors at three different visibilities have been fitted to a linear combination of three log-normal functions. With the parameters (modal radius, log-deviation, and amplitude) of the resulting functions, and using the visibility as the independent variable, interpolation polynomials have been derived to provide distribution functions at any visibility in between. To extrapolate the model to higher visibilities, an additional log-normal mode and an additional variable (the relative humidity) are introduced, so that the distribution function smoothly matches a maritime haze model for increasing visibilities. By means of Mie scattering calculations, the optical attenuation at any wavelength is calculated by the model under any visibility induced by a coastal fog. The attenuation in the visible region is compared with the input visibility and the polydispersion modified accordingly to provide self-consistency to the model.