The change of the visible light ellipsometric parameters and mechanical harmonic frequencies of a hydrophobic gold surface attached to a quartz crystal are measured in aqueous solution during deposition of synperonic polymer thin film. The ellipsometry data reveal the amount of polymer mass attached to the surface, while the mechanical resonance shifts are caused by the total mass attached to the surface. Analysis of the combined ellipsometry and quartz crystal microbalance data reveal that the polymer thin film has a high water content, and we determine in-situ, for the first time, the porosity, or the water content, of a polymer thin film in aqueous solution.