Friday, March 14, 2008

Cassini - Eerie Saturn Radio Emissions

The baudline scientific visualizer was used to investigate some eerie Saturn radio emissions captured by the Cassini spacecraft. NASA believes that the source of these radio waves are related to the auroras near the poles of Saturn. The 27 minute radio emission signal was collected by Cassini's radio and plasma wave instrument and has been compressed down to a 73.5 second audio file for playback.

This signal looks and sounds a lot like Earth VLF chorus with fading blobs of spectrum moving up and down in frequency. The large blocks visible throughout the spectrogram are interesting looking artifacts that could be synthesis or compression related. Another interesting artifact are the horizontal scan lines that can be seen in the zoomed in spectrogram image below:

The NTSC-like horizontal scan line artifacts could be synthesis based or they could be related to how the Cassini sensors operate. Baudline's periodicity bars measured the scan lines to have a repetitive spacing of 0.1487 seconds which when multiplied by the 5000 sample becomes 743.5 samples. Adjusting for a 73.5 second to 27 minute file expansion, a reciprocal factor of 22.04, the number of samples becomes 16386.7 samples which is very close to 16384 a power of 2 and a popular buffer size.