Astrometric Reduction of Saturnian Satellites with Cassini-ISS Images Degraded by Trailed Stars

TL;DR

This paper introduces a novel automatic method for detecting and measuring trailed stars in Cassini ISS images, enabling high-precision astrometry of Saturnian satellites despite image degradation.

Contribution

A new automated technique for star center detection in degraded images is developed, improving the usability of Cassini ISS data for astrometry.

Findings

Generated 658 satellite positions with high accuracy

Residuals of 0.11 km in right ascension and 0.26 km in declination

Method effectively handles images with trailed stars

Abstract

Imaging Science Subsystem (ISS) mounted on the Cassini spacecraft has taken a lot of images, which provides an important source of high-precision astrometry of some planets and satellites. However, some of these images are degraded by trailed stars. Previously, these degraded images cannot be used for astrometry. In this paper, a new method is proposed to detect and compute the centers of these trailed stars automatically. The method is then performed on the astrometry of ISS images with trailed stars. Finally, we provided 658 astrometric positions between 2004 and 2017 of several satellites that include Enceladus, Dione, Tethys, Mimas and Rhea. Compared with the JPL ephemeris SAT427, the mean residuals of these measurements are 0.11 km and 0.26 km in right ascension and declination, respectively. Their standard deviations are 1.08 km and 1.37 km, respectively. The results show that the proposed method performs astrometric measurements of Cassini ISS images with trailed stars effectively.