A New Enceladus Global Control Network, Image Mosaic, and Updated Pointing Kernels From Cassini's 13‐Year Mission

Abstract

NASA's Cassini spacecraft spent 13 years exploring the Saturn system, including 23 targeted flybys of the small, geologically active moon Enceladus. These flybys provided a wealth of image data from Cassini's Imaging Science Subsystem. To improve the usability of the Enceladus data set, we created a new, global photogrammetric control network for Enceladus that enabled compilation of a versatile cartographic package to support geologic mapping and other investigations. The network used 586 images in four image filters with a pixel scale generally between 50 and 500 m per pixel and a phase angle less than 120° and consisted of 10,362 tie points and 173,704 individual image measures, averaging nearly 17 measures per tie point. Least squares bundle adjustment resulted in a root‐mean‐square residual of 0.45 pixel, corresponding to root‐mean‐square ground point uncertainties of 66, 51, and 46 m in latitude, longitude, and radius, respectively. Using our geodetic control network, we created new global image mosaics, coregistered flyby mosaics to support geologic mapping, and updated pointing kernels for every image used in the solution. These products, including the updated pointing kernels, are available to the community through NASA's Planetary Data System Imaging Annex. The bundle adjustment solution also yielded independently determined shape information, resulting in radii within the stated uncertainty of International Astronomical Union values. The challenges of the data set, and the technical methodology described here are applicable to bodies imaged during multiple flybys with variable viewing and illumination geometry, including other midsized satellites of Saturn, and the Europa Clipper mission.

Photometrically-corrected global infrared mosaics of Enceladus: New implications for its spectral diversity and geological activity

“…The pixel location is calculated as the intersection between Enceladus mean radius (252.1 km) and the VIMS pixel boresight (Nicholson et al, 2019). Our projected VIMS cubes are geometrically consistent with the latest ISS global map (Bland et al, 2018) as it can been on a few examples on Fig. 11.…”

Tectonics of Enceladus’ South Pole: Block Rotation of the Tiger Stripes

“…A total of 354 long rectilinear‐to‐curvilinear structures which were related to high tonal variations were identified on the Enceladus Cassini global grayscale mosaic assembled from the Cassini Imaging Science Subsystem (ISS) images by the USGS astrogeology program (Bland et al., 2018). The spatial scale of this base mosaic ranges between 500 and 50 m/pixel.…”

Improving the Usability of Galileo and Voyager Images of Jupiter's Moon Europa

“…In particular, the use of automated, rather than manual methods for locating and measuring tie points, has allowed for a greatly increased number of points per image, and points measured on multiple overlapping images, compared to what was previously being measured manually. As described in Bland, Becker et al (2018), including multiple images ("image measures") in a single tie point enables robust point localization, the determination of point location uncertainty, and the detection of outliers. Additionally, improvements in computational efficiency permit the use of nearly the entire Voyager and Galileo data set (see Section 2) and a relatively dense tie-point network.…”

“…The location of a point in three-dimensional space (e.g., latitude, longitude, radius) can be determined from just two measures, but in that case, the precision is unconstrained. With three or more measures, precision information can be obtained, and the statistical robustness of the location determination improves as the number of measures increases (see Bland, Becker et al [2018] for details).…”