Abstract
AbstractRiver valleys have been observed on Titan at all latitudes by the Cassini‐Huygens mission. Just like water on Earth, liquid methane carves into the substrate to form a complex network of rivers, particularly stunning in the images acquired near the equator by the Huygens probe. To better understand the processes at work that form these landscapes, one needs an accurate digital terrain model (DTM) of this region. The first and to date the only existing DTM of the Huygens landing site was produced by the U.S. Geological Survey (USGS) from high‐resolution images acquired by the DISR (Descent Imager/Spectral Radiometer) cameras on board the Huygens probe and using the SOCET SET photogrammetric software. However, this DTM displays inconsistencies, primarily due to nonoptimal viewing geometries and to the poor quality of the original data, unsuitable for photogrammetric reconstruction. We investigate a new approach, benefiting from a recent reprocessing of the DISR images correcting both the radiometric and geometric distortions. For the DTM reconstruction, we use MicMac, a photogrammetry software based on automatic open‐source shape‐from‐motion algorithms. To overcome challenges such as data quality and image complexity (unusual geometric configuration), we developed a specific pipeline that we detailed and documented in this article. In particular, we take advantage of geomorphic considerations to assess ambiguity on the internal calibration and the global orientation of the stereo model. Besides the novelty in this approach, the resulting DTM obtained offers the best spatial sampling of Titan's surface available and a significant improvement over the previous results.
Highlights
After 13 years of observations by the Cassini-Huygens mission (Cassini orbiter and Huygens lander), Titan, Saturn’s largest moon, turned out to be a unique body in theSolar System
The USGS-digital terrain model (DTM) is the best topographic model of the Huygens landing area produced to date, it is limited by the qual101 ity of the data and the mapping technology
The DISR images are decompressed and post-processed after transmission to Earth: (1) their photometric stretch is square root expanded to restore the 12-bit depth; (2) they are flat-field corrected to eliminate the photometric distortions of the cameras; (3) the dark current is removed using the camera model at the exposure temperature; (4) the electronic shutter effect caused by data clocking is compensated for; (5) the images are further flat fielded to remove artifacts seen at the highest altitudes; (6) the stretch is enhanced to increase the dynamics; and (7) the bad pixels are replaced by their neighbors
Summary
We create a new digital terrain model (DTM) of the Huygens landing site that offers the best available resolution of river valleys on Titan. The complexity of the data set requires a tailor-made reconstruction procedure that is detailed. The workflow uses re-processed Huygens/DISR images and an automated shapefrom-motion algorithm to improve an earlier DTM. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, paginati–o1n– and proofreading process which may lead to differences between this version and the Version of Record.
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