Stereoscopic space observations
The SWAVES experiment onboard Solar TErrestrial RElations Observatory (STEREO), although mainly dedicated to measuring solar radio emission, also provides unique stereoscopic observations of the Jovian radio emission in a frequency range from few kHz up to ~16 MHz. A large number of non-Io and Io-controlled Jovian decametric radio emission (DAM) events has been recorded. The stereoscopic measurements facilitate unambiguous recognition of the DAM in the observed spectra as well as identification of its components by means of time delay between sequential detection of the radio bursts from the same source by two spatially separated spacecraft.
Using stereoscopic observations of the Jovian radio emission from Wind and Cassini Kaiser et al. [2000] determined the beam width (or wall thickness of the hollow cone) of the emission to be 1.5°. Due to the limited number of stereoscopic observations (only a few events) performed with angular separation <2° as seen from Jupiter (for more details see Kaiser et al. [2000]) it was difficult to draw general conclusions regarding the beam width of Jovian radiation.
The angular separation between the two STEREO spacecraft, orbiting the Sun approximately twice per year, is less than a few degrees. Therefore, the method described in Kaiser et al. [2000] is applied to determine the beaming width of the Io and non-Io DAM observed during years the 2007 – 2009 with high statistical confidence. In particular we have confirmed the previous findings that the averaged width of the DAM emission cone mantle is smaller than 1 degree. Fig. 1 shows a schematic illustration of stereoscopic observation of the Jovian „arc-like“ emission by the STEREO-A and -B spacecraft.
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