High Spectral and Temporal Resolution Observations of Saturn Kilometric Radiation

The Cassini Radio and Plasma Wave Science (RPWS) instrument is the most capable planetary radio astronomy instrument to have been flown to the outer planets. Among other attributes, it includes a wideband receiver with 10- and 75-kHz baseband modes as well as a high-frequency down-conversion mode tunable between 125 kHz and 16 MHz that provides very high resolution spectral and temporal observations of Saturn's radio emissions. This paper presents an initial survey of dynamic spectra of Saturn kilometric radiation acquired upon approach and the first orbits of Saturn. Based on these early observations of Saturn's kilometric observations, perhaps the most succinct description of the appearance of the emissions in dynamic spectra is highly variable. The emissions display upward and downward drifting features with bandwidths down to the few hundred Hz resolution of the instrument and drift rates up to a few kHz per second. At other times, the emissions are much more diffuse or continuous, showing little spectral structure on scales of 10 or 20 kHz. Some features show very sharp upper frequency cutoffs and indistinct lower frequency cutoffs, somewhat suggestive of a caustic effect. The dynamic spectral features provide insight into the sometimes highly nonlinear nature of the cyclotron maser instability believed to generate the emissions and various processes such as diffraction within and near the radio emission source which shape the radio spectrum.