Classification of fine structures of Saturn kilometric radiation

Saturn kilometric radiation (SKR) is thought to be created by the cyclotron maser instability along auroral magnetic field lines, where radio emissions are generated near the electron cyclotron frequency at the source. Using the Wideband Receiver (WBR) of the Cassini Radio and Plasma Wave Science (RPWS) instrument it was possible to create dynamic spectra of high temporal and spectral resolution. They display the radio wave intensity as a function of time and frequency with a temporal resolution of a fraction of a second and a spectral resolution of ~0.1 kHz. 

In these dynamic spectra one can find a plethora of various fine structures which we classify in the following way: We first simply distinguish between 0-dimensional structures (dots), 1-dimensional structures (lines), and 2-dimensional structures (areas). For areas we require a minimum extension of 5 seconds in time and 5 kHz in frequency. Our main focus is on the lines, where we again distinguish between the four classes of horizontal lines, vertical lines, and lines with a positive or a negative slope (going to higher or lower frequencies). For the latter two it is thought that they are related to downward or upward moving radiation sources, i.e. bunches of energetic electrons moving down or up along the magnetic field lines. Using these simple 6 classes (DOTS, HORZ, VERT, POSS, NEGS, AREA) it is already possible to classify about 80% of all spectra showing SKR. Unclassified spectra contain no clear linear elements and mostly consist of patchy structures with holes that do not fulfill the minimum size requirement (5 s, 5 kHz) to be classified as areas. Linear elements appear in about one third of the spectra in the frequency range from 100 kHz to 1 MHz. Some spectra can of course be mixed and show dots, lines and areas, but in our classification we prioritize lines over areas and dots.