Dielectric properties of amorphous and hexagonal ice in the optical limit. Upper panels: best-fit Drude representations of the dielectric properties of (a) amorphous and (b) hexagonal ice at optical frequencies, based on D. Emfietzoglou et al. (2007), compared with experimental results (J. Daniels 1971; K. Kobayashi 1983). Bottom panels: residuals between the best-fit Drude model and optical experimental data.