Description of the Saturn Small Moon Shape Models bundle V1.1
=============================================================

Bundle Generation Date: 2021-07-06
Peer Review: 2018a Asteroid Review
Discipline node: Small Bodies Node


Content description for the Saturn Small Moon Shape Models bundle
=================================================================

The shape models of Saturn's satellites have been generated from images obtained by the Imaging Science Subsystem on the Cassini Spacecraft during its orbital mission from 2004 to 2017. This system consists of a narrow angle camera with CCD image format of 1024 by 1024 pixels and an instantaneous field of view (IFOV; per pixel) of 10-6 radians. The wide angle camera has the same image format, but an IFOV of 10-5 radians per pixel.

The Cassini orbital tour included periods of different inclinations and different eccentricities. These orbital properties, as well as the need to prioritize observations during periods the spacecraft was close to Saturn and thus to the inner small satellites, meant that coverage on satellite surfaces varied in resolution and lighting greatly over latitude and longitude.  As a result, the resolution of the models can vary significantly over the surface; average uncertainties for each of the satellites modeled here are given in their respective documents attached to this PDS package.

The shape models were constructed using control point coordinates found by stereogrammetry of manually selected points on the surface, mostly ellipses fit to crater rims, and by limb and terminator constraints on the shapes. The control point solutions include camera pointing and relative positions of points on the surfaces.  These points were used to adjust an approximate model in a manner based on technique given in Thomas et al. 2002. Camera characteristics are summarized in Owen 2003; Porco et al. (2004).   The resulting shape was further modified by matching limb coordinates in images where the camera pointing was controlled by the stereogrammetry.  The discrete nature of the limb restrictions sometimes introduces artifacts visible in some model displays; these remain below the amplitudes of listed uncertainties.  Description of the techniques can be found in Simonelli et al.,1993; Thomas et al., 2002, Thomas et al., 2013. Thomas et al., 2013 gives a general survey of Saturnian small satellite results using an earlier generation of these models that have differences from current ones of well under 1 km.


Caveats to the data user
========================

Images used and their viewing geometry are listed in accompanying object_document.pdf files. Uncertainties in the shape model have been based on pixel scale and visibility in the images. These uncertainties are only rough guides, as actual errors (differences from true form) vary regionally depending on factors that include stereo convergence angles, surface contrasts, solar incidence angles, and viewing emission angles.