A Global Mosaic of Titan's Surface Albedo using Cassini Images
Abstract
We present a global mosaic of Titan's surface albedo made from 9873 Cassini ISS (Imaging Science Subsystem) images at 938 nm wavelength. It covers Titan without image seams, gives calibrated normal albedos, and shows small features with relatively high signal-to-noise ratios due to averaging many images. The scale is 16 pixels per degree or 2.8 km in latitude. Our mosaic helps in the interpretation of the global distributions of key terrains such as dark dunes, lakes, large river channels, and tectonic structures in connection with existing data by RADAR, VIMS, and DISR. The absolute albedo calibration makes our mosaic useful for deriving compositional constraints. In some areas, the new mosaic has higher spatial resolution than Cassini data at other wavelengths. The mosaic has some deficiencies that we are working to address within the next year. It contains cloud features at some locations that we will identify and remove. It also contains minor camera artifacts that are 50 times enhanced since only 2 % of the detected light probes Titan's surface. Light scattered from aerosols in the atmosphere is most of the remaining 98 %. The absolute geometric calibration onto Titan's coordinate system of currently 5-10 km accuracy will also be improved. The mosaic captures averages from many images taken over 13 years of Cassini operations at Saturn. We found some systematic variations between different observations of the same surface area. Based on the correlation with observational parameters, we divide them into atmospheric contributions from clouds and seasonal haze variations and surface contributions from variations in the phase coefficient and temporal changes. We hope to detect surface changes due to methane rainfall, subsequent dryout, evaporite deposits, shrinking and expanding lakes, and perhaps unexpected processes. Titan's thick haze at 938 nm hides its surface well, but the large data set of 20,000 ISS images has the power to reveal tiny variations with high statistical significance. We will even examine ISS data at a shorter wavelength, 750 nm, where the haze is even thicker. This work was supported by the Cassini project.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5021602K