Information on aerosol size distribution contained in solar reflected spectral radiances

Information on the aerosol size distribution contained in the reflected solar spectral radiances detected over the oceans can be reduced into two quantities. These quantities have been determined in an unbiased way with the use of the principal components. Consequently, only one to two parameters of the size distribution can be retrieved. For a single‐mode distribution these parameters are the effective radius of the particles and the width of the size distribution. The accuracy of the retrieval depends on the view and illumination directions. Accurate knowledge of the refractive index, real and imaginary parts, is not critically important for the retrieval as long as the retrieved particles are smaller than 1.0 μm. An error budget shows that very clean conditions are not suitable for getting any information on the aerosol size distribution. A surprising result of this investigation is that the spectral reflectance of a bimodal‐lognormal distribution can be simulated very well with spectral reflectance of a single lognormal with an appropriate radius and width of distribution, σ, that do not necessarily correspond to an average of the bimodal values. The present results change drastically our philosophy regarding the retrieval scheme. Additional studies are needed to confirm the present results for nonspherical particles.