Optical properties of solid and liquid sulfur at visible and infrared wavelengths

Mapping SO2 Frost on Io by the Modeling of NIMS Hyperspectral Images

“…The optical properties of both SO 2 and S 8 are needed in the UV, VIS, and NIR. At 350 nm, α S 8 ≈ 10 4 cm −1 ; it then decreases to ≈400 cm −1 at 410 nm (Hapke and Nelson 1975) and to ≈0.1 cm −1 at 633 nm to stay approximately constant beyond (Sasson et al 1985). Between these reference points we interpolate log(α S 8 ) linearly.…”

Volcanogenic Sulfur on Earth and Io: Composition and Spectroscopy

“…Io's visible reflectance spectra, notably an absorption edge near 0.4 µm, resemble those of elemental sulfur and certain sulfur compounds (Wamsteker et al 1974, Nash and Fanale 1977, Nelson and Hapke 1978, Fanale et al 1979, Smythe et al 1979, Veverka et al 1979, Pieri et al 1984, Sasson et al 1985, Nash 1987, Nash and Moses 1988. Consistent with the composition of Io's atmosphere, neutral cloud, and plasma torus, no conclusive evidence of silicates on Io has been obtained by reflectance spectroscopy, although Galileo SSI data indicate a 0.9-µm feature possibly due to Fe-Mg silicates (Geissler et al 1999).…”

“…1. The spectrum of pure orthorhombic sulfur (Bass 1953, Srb and Vaöko 1962, Meyer et al 1971, Meyer 1976, Gradie and Veverka 1984, Hammel et al 1985, Sasson et al 1985 is merely suggestive of Io's surface, but in detail it is a poor match (Young 1984, Hammel et al 1985. Irradiation, impurities, and other factors modify the reflectance of sulfur and make mapping of sulfur difficult.…”

Experimental system for the study of planetary surface materials' BRDF

“…As for the sulfur and SO 2 deposits on Io, the sample seems to display a backscattering behavior . This is a surprising result since the absorption coefficient of sulfur at A = 900nm is very small («2.5 10~2cm~1 (Sasson et al, 1985)) and other transparent materials, like H2O ice, generally exhibit a forward scattering behavior. The physical origin of this behavior is not yet understood but the high value of the real part of the refractive index of sulfur (n-1.95), leading to a reflection coefficient at the interfaces larger than 10%, may contribute to favor backscattering by the grains.…”