Scattering of interplanetary radio waves at kilometric wavelengths

[1] We report on measurements of the angular size of Jovian radio sources measured by the URAP instrument on the Ulysses spacecraft. The angular size is found to be substantially larger than that expected from the geometric size of the source, which is essentially a point source when viewed from Ulysses. This increase in size is due to scattering of the radio waves caused by fluctuations in the electron density along the path of the radiation. The angular size varies with wavelength as expected for such scattering, and the magnitude of the scattering is in rough agreement with, though less than, results of previous investigations in the slow solar wind. The magnitude of the scattering is found to vary substantially for different radio events, most likely due to changes in the density and/or fluctuation level along the path of the radiation. These measurements are especially suited to determining scattering parameters as the source is point-like and precisely located. Our results confirm that interplanetary scattering imposes important constraints on low-frequency radio observations by new spacecraft missions.