McEwen, A., Turtle, E., Perry, J., Dawson, D., Fussner, S., Collins, G., Porco, C., Johnson, T., Soderblom, L. (2005). "Mapping and Monitoring the Surface of Titan." American Astronomical Society, DPS meeting #37, #53.04.


Abstract
Cassini Imaging can best see down to the surface of Titan in a narrow bandpass filter at 938 nm, but the haze optical depth (2) makes mapping at high resolution a challenge. We acquire multiple (3-5) images of each footprint with long exposure times to achieve a high signal-to-noise ratio, use techniques to enhance the surface contrast, and mosaic sets of images. Only albedo variations can be seen, not topographic shading, and the smallest features resolved have dimensions of 1 km. We expect to acquire near-global coverage and to search for changes in repeat coverage. The flyby geometries to date have enabled coverage of 3 regions at scales of 2 km or better: the south-polar region, the anti-Saturn equatorial region, and the sub-Saturn equatorial region. No obvious surface changes have been detected. We have mapped 6 circular patterns that could mark impact structures, two of these have been imaged by Cassini RADAR, confirming that they are craters, and showing that crater diameter estimates based on albedo may be off by 50%. Titan's uppermost crust must be geologically young, less than 500 Myr. The south-polar region is of special interest due to relatively abundant convective clouds and possible methane rain, we speculate that linear markings could be fluvial channels or valleys and that an especially dark region with smooth boundaries (230 x 70 km) could be a hydrocarbon lake or lakebed. Most of the south-polar clouds move with the zonal flow, but a few remain stationary, suggesting methane sources such as pools of liquid or subsurface venting.