Channels on Titan and the Earth: Lessons from Planform Images in Low-Resolution SAR

Abstract:

The Cassini-Huygens mission produced unprecedented images of Titan’s surface, revealing channel networks strikingly similar to those found on Earth. We present a map of all observable channels on Titan—excluding those in the highly incised labyrinth terrains—which are visible in the Cassini Synthetic Aperture Radar (SAR) dataset. The Cassini dataset, however, has relatively low spatial resolution and image quality compared to data typically used to map terrestrial channels. As a result, traditional methods for characterizing river networks would not necessarily yield accurate results on Titan. To determine which metrics would hold when mapping from lower-quality images, we present an analysis using Earth analogs. Using three terrestrial river networks with similar scales to those observed on Titan, we mapped channels in high-resolution visible images, medium-resolution SAR images, and low-resolution SAR images with and without added speckle noise. We then observed the differences in channels mapped from each image and compared the results of the channel metrics in each case. We found that metrics such as branching angle and drainage density varied significantly with image resolution. Similarly, network geometry was found to change unpredictably with resolution and would therefore not be an ideal metric for interpreting Titan’s channel networks. Channel width, basin length and width, and minimum drainage area were all relatively constant as resolution varied, leading us to conclude that these metrics would produce reasonable results on Titan. On Titan, we observe a dichotomy in the number of observed channels between the northern and southern midlatitudes and poles. These observations are consistent with greater fluvial activity at polar locations than at the equator.