Description of the Tethys SPC Shape Models and Assessment Products bundle V1.0 ============================================================================== Bundle Generation Date: 2025-08-22 Peer Review: 2025_Asteroid_Review Discipline node: Small Bodies Node ================================================================================ We provide three categories of data for the Saturnian satellite Tethys, all generated with the Stereophotoclinometry (SPC) software suite. These include a shape model, higher-resolution regional models, and photometric data for the regional models. A Tethys shape model, also known as a global Digital Terrain Model (DTM), was previously generated by R. Gaskell (Gaskell, 2020) using the Stereophotoclinometry (SPC) software suite and submitted to the PDS Small Bodies Node (urn:nasa:pds:gaskell.tethys.shape-model::1.0). Four regional models are provided to give higher-resolution topography on the leading hemisphere, trailing hemisphere, as well as along the equator and higher latitudes. Both the shape model and the regional models have assessment data to help understand the quality of topography. For selected Cassini images found within the regional models, four cubes were generated; I/F (reflectance), Local Phase Angle, Local Emission Angle, and Local Incidence Angle. Each photometric cube pixel represents the value at each vertex of the regional DTM, thus each pixel location in each cube represents the same location on the surface. The shape model is provided in a variety of formats. To aid the data user, filenames end with a letter to designate the format. These letters are “i”, “c”, “g”, “p”, and “o”, respectively. "i" - ICQ - Implicitly Connected Quadrilateral format, one of the smallest data size formats. It is defined in icqmodel.asc of Gaskell (2020). "c" - ISIS - The native cube format for the United States Geological Survey (USGS) Integrated Software for Imagers and Spectrometers. "g" - GeoTiff format, an expanded version of TIFF images that maintains physical geometric information, which is especially useful by GIS programs like ArcGIS. “p" - Plate vector format, an older format used by the Planetary Science community. "o" - OBJ, a plate vector format, and an Object Vector format, created by Alias Wavefront but is currently one of the most common formats for 3D models. This format is the native format for the Small Body Mapping Tool (SBMT). The regional models are provided in cube and geoTiff format (“c” and “g”) and the photometric data and assessment data is provided in cube format (“c”). The quality assessment data for the shape and regional models includes the best image resolution, number of images, best maplet resolution, and the sigma value. The quality data for the shape model is presented in 1 degree bins and for the regional model at the scale of the model, both using the USGS ISIS cube format. The assessment data show that the radius of the global DTM is everywhere good. Higher resolution regional models could be generated at many locations, even at the poles. Details about the products are given in document/productdescription.pdf, while the assessment and thumbnails of the assessment data are given in document/tethysshapeassessment.pdf and document/tethysregionaldtmassessment.pdf. These two assessment PDFs are particularly important. The SPC shape model is compared against an example Cassini image in document/tethysvisualcmp.pdf to show compatibility with the limb profile. The models were constructed using the CASSINI Imaging Science Subsystem (ISS) Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) images. Images were used irrespective of the filter. Uncalibrated images are used, and a correction for geometric distortion is used for all images. The image lists for the global model and regional models, as well as the kernel list, are included as text documents. The shape model is provided in two resolution versions for the ICQ, PLT, and OBJ. One version has a higher resolution of 1.50 km Ground Sample Distance (GSD), and the other has a lower resolution with a 5.96 km GSD since many software programs cannot read the higher resolution version. The cubes and geoTiffs of the global model have a single version, that of a GSD of 1.50 km. Since the maplets that make up the shape model usually have a higher resolution than the global model, a good rule of thumb for the global uncertainty is to base it off the shape model GSD. The uncertainty is then one to two times the shape GSD. This gives 1.50 to 3.00 km uncertainty. See document/productdescription.pdf and document/tethysregionaldtmassessment.pdf for the naming convention and for more important details of the regional DTMs. DTM leqs06283 (see productdescription.pdf) has a Ground Sample Distance (GSD) of 335 m and a size of 170 by 170 km, and is centered at -6 Lat, 283 E Lon. DTM lhln19244 has a GSD of 335 m and a size of 270 by 270 km, and is centered at 19 Lat, 244 E Lon. DTM teqs04076 has a GSD of 400 m and a size of 200 by 200 km, and is centered at -4 Lat, 76 E Lon. DTM thln21112 has a GSD of 235 m and a size of 160 by 160 km, and is centered at 21 Lat, 112 E Lon. In general the uncertainties for these models follows the 1 to 2 times the GSD rule, but in some areas with poorer image resolution it is 1 to 2 times the image resolution. Caveats to the data user ======================== The photometric cubes have values for all pixels, but only pixels that correspond to non-zero values in the reflectance cube (i.e. I/F or “ioverf") are valid. Sample/line values that are zero in the reflectance cube are also invalid for the phase, emission, and incidence angles.