  Metric and decametric radio-emissions from the Sun are the only direct source
of information about the dynamics of non-thermal electrons in the upper corona.
In addition, the combination of spectral and imaging (sizes, shapes, and
positions) observations of low-frequency radio sources can be used as a unique
diagnostic tool to probe plasma turbulence in the solar corona and inner
heliosphere. The geometry of the low-frequency sources and its variation with
frequency are still not understood, primarily due to the relatively low spatial
resolution available for solar observations. Here we report the first detailed
multi-frequency analysis of the sizes of solar radio sources observed by the
Low-Frequency Array (LOFAR). Furthermore, we investigate the source shapes by
approximating the derived intensity distributions using 2D Gaussian profiles
with elliptical half-maximum contours. These measurements have been made
possible by a novel empirical method for evaluating the instrumental and
ionospheric effects on radio maps based on known source observations. The
obtained deconvolved sizes of the sources are found to be smaller than previous
estimations, and often show higher ellipticity. The sizes and ellipticities of
the sources inferred using 2D Gaussian approximation, and their variation with
frequency are consistent with models of anisotropic radio-wave scattering in
the solar corona.
