TY - JOUR
T1 - Titan's surface and troposphere, investigated with ground-based, near-infrared observations
AU - Griffith, Caitlin A.
AU - Owen, Tobias
AU - Wagener, Richard
N1 - Funding Information:
We thank B. N. Khare, L. R. Brown, L. P. Giver, and A. R. W. McKellar for helpful information about laboratory spectroscopic data and for the use of unpublished data. R. D. Cess and D. Katz helped us develop our atmospheric models. A. T. Tokunaga and T. Y. Brooke provided valuable training in the use of the Cooled-Grating Array Spectrometer. R. F. Knacke and two referees (A. Coustenis and one anonymous) provided editorial comments on the manuscript. We also thank M. G. Tomasko, L. Doose, C. P. McKay, and O. B. Toon for illuminating discussions on the properties of Titan's haze. This research was supported in part by NASA Grant NGR 33-015-141.
PY - 1991/10
Y1 - 1991/10
N2 - New observations of Titan's near-infrared spectrum (4000-5000 cm-1) combined with points taken from Fink and Larson's (1979) spectrum (4000-12500 cm-1) provide information on Titan's haze, possible clouds, surface albedo, and atmospheric abundance of H2. In the near-infrared, the main features in Titan's spectrum result from absorption of solar radiation by CH4. The strength of this absorption varies considerably with wavelength, allowing us to probe various atmospheric levels down to the surface itself by choosing specific wavelengths for analysis. At 4715 cm-1, the pressure-induced S(1) fundamental band of H2 lies in the wings of CH4 bands. Based on current values for the CH4 line parameters, Titan's spectrum can be best interpreted with a volume mixing ratio of H2 between 0.5 and 1.0%. Our observations suggest the existence of an optically thin CH4 cloud layer. The optical depths that we derive for Titan's haze and clouds are small enough to allow us to sense the surface of Titan at 4900, 6250, and 7700 cm-1. The most plausible interpretation of the albedos determined at these wavenumbers suggests a surface dominated by "dirty" water ice. A global ethane ocean is not compatible with these albedos.
AB - New observations of Titan's near-infrared spectrum (4000-5000 cm-1) combined with points taken from Fink and Larson's (1979) spectrum (4000-12500 cm-1) provide information on Titan's haze, possible clouds, surface albedo, and atmospheric abundance of H2. In the near-infrared, the main features in Titan's spectrum result from absorption of solar radiation by CH4. The strength of this absorption varies considerably with wavelength, allowing us to probe various atmospheric levels down to the surface itself by choosing specific wavelengths for analysis. At 4715 cm-1, the pressure-induced S(1) fundamental band of H2 lies in the wings of CH4 bands. Based on current values for the CH4 line parameters, Titan's spectrum can be best interpreted with a volume mixing ratio of H2 between 0.5 and 1.0%. Our observations suggest the existence of an optically thin CH4 cloud layer. The optical depths that we derive for Titan's haze and clouds are small enough to allow us to sense the surface of Titan at 4900, 6250, and 7700 cm-1. The most plausible interpretation of the albedos determined at these wavenumbers suggests a surface dominated by "dirty" water ice. A global ethane ocean is not compatible with these albedos.
UR - http://www.scopus.com/inward/record.url?scp=0026411479&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0026411479&partnerID=8YFLogxK
U2 - 10.1016/0019-1035(91)90219-J
DO - 10.1016/0019-1035(91)90219-J
M3 - Article
C2 - 11538707
AN - SCOPUS:0026411479
SN - 0019-1035
VL - 93
SP - 362
EP - 378
JO - Icarus
JF - Icarus
IS - 2
ER -