  We use multi-spacecraft observations of invididual type III radio bursts in
order to calculate the directivity of the radio emission, to be compared to the
results of ray-tracing simulations of the radio-wave propagation and probe the
plasma properties of the inner heliosphere. Ray-tracing simulations of
radio-wave propagation with anisotropic scattering on density inhomogeneities
are used to study the directivity of radio emissions. Simultaneous observations
of type III radio bursts by four widely-separated spacecraft are used to
calculate the directivity and position of the radio sources. The shape of the
directivity pattern deduced for individual events is compared to the
directivity pattern resulting from the ray-tracing simulations. We show that
simultaneous observations of type radio III bursts by 4 different probes
provide the opportunity to estimate the radio source positions and the
directivity of the radio emission. The shape of the directivity varies from one
event to another, and is consistent with anisotropic scattering of the
radio-waves.
