Jupiter's low‐frequency radio spectrum from Cassini/Radio and Plasma Wave Science (RPWS) absolute flux density measurements

Abstract

We apply the calibration method developed by Dulk et al. [2001] to the data from the Cassini/Radio and Plasma Wave Science (RPWS) High‐Frequency Receiver in order to derive flux density measurements of six components of the Jovian low‐frequency radio spectrum over the full frequency range of the instrument (3.5 kHz to 16.1 MHz). The estimated accuracy is better than 50%, i.e., much less than the intrinsic variations of the flux densities of these radiosources. It is mainly limited by the accuracy of the model used for the radio galactic background. Instrumental parameters such as the antennas' effective lengths and base capacitance are constrained in the calibration process. From 6 months of calibrated data centered on the Cassini‐Jupiter flyby, we derive the average and peak Jovian radio spectrum between 3.5 and 16.1 MHz and its range of fluctuations, from which we deduce constraints on the beaming of the various radio components and estimate the power emitted by each component. Our calibration procedure also allows us to compare Cassini measurements of the Jovian radio spectrum with ground‐based measurements performed, e.g., in Nançay above the ionospheric cutoff (10−15 MHz). It will be used to derive absolute flux measurements during the Saturn tour.