A New Enceladus Global Control Network, Image Mosaic, and Updated Pointing Kernels From Cassini's 13‐Year Mission
2018
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.
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