Revised Near-Infrared Geometric and Surface Albedos of Titan

B. Han, T. Owen (Institute for Astronomy), C. McKay, E. Young (NASA Ames Research Center)

The opacity of Titan's atmosphere in the near-infrared is dominated by methane absorption, with the exception of a few narrow wavelengths where the absorption is small enough that we can probe the surface and lower atmosphere of Titan. The values in the literature for geometric and surface albedos of Titan in these methane absorption windows vary greatly (nearly an order of magnitude at 2 microns), which makes comparison and integration of the various datasets difficult at best. We present new geometric and surface albedos in the near-infrared methane absorption windows at 1.1, 1.3, 1.6, and 2.0 microns based upon datasets obtained using the KSPEC medium resolution spectrograph at the University of Hawaii 2.2 meter telescope at Mauna Kea. The geometric albedos were calculated using a self-calibration technique utilizing the simulanteous spectroscopic and K-band imaging capabilities of KSPEC and did not rely upon matching albedos in the methane absorption bands with existing published spectra (such as Fink and Larson's Titan spectra). This calibration method reduces the uncertainties due to slit misalignment and tracking errors common to spectroscopic observations. Surface albedo values derived using atmospheric models of C. McKay are discussed and their possible implications for Titan's surface composition. This work has been supported by NASA grant JPL-959217.