Speckle imaging of Titan at 2 microns: surface albedo, haze optical depth, and tropospheric clouds 1996–1998

We present results from 14 nights of observations of Titan in 1996–1998 using near-infrared (centered at 2.1 microns) speckle imaging at the 10-meter W.M. Keck Telescope. The observations have a spatial resolution of 0.06 arcseconds. We detect bright clouds on three days in October 1998, with a brightness about 0.5% of the brightness of Titan. Using a 16-stream radiative transfer model (DISORT) to model the central equatorial longitude of each image, we construct a suite of surface albedo models parameterized by the optical depth of Titanʹs hydrocarbon haze layer. From this we conclude that Titanʹs equatorial surface albedo has plausible values in the range of 0–0.20. Titanʹs minimum haze optical depth cannot be constrained from this modeling, but an upper limit of 0.3 at this wavelength range is found. More accurate determination of Titanʹs surface albedo and haze optical depth, especially at higher latitudes, will require a model that fully considers the 3-dimensional nature of Titanʹs atmosphere.