  Space telescopes for solar hard X-ray imaging provide observations made of
sampled Fourier components of the incoming photon flux. The aim of this study
is to design an image reconstruction method relying on enhanced visibility
interpolation in the Fourier domain. % methods heading (mandatory) The
interpolation-based method is applied on synthetic visibilities generated by
means of the simulation software implemented within the framework of the
Spectrometer/Telescope for Imaging X-rays (STIX) mission on board Solar
Orbiter. An application to experimental visibilities observed by the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also considered. In
order to interpolate these visibility data we have utilized an approach based
on Variably Scaled Kernels (VSKs), which are able to realize feature
augmentation by exploiting prior information on the flaring source and which
are used here, for the first time, for image reconstruction purposes.} %
results heading (mandatory) When compared to an interpolation-based
reconstruction algorithm previously introduced for RHESSI, VSKs offer
significantly better performances, particularly in the case of STIX imaging,
which is characterized by a notably sparse sampling of the Fourier domain. In
the case of RHESSI data, this novel approach is particularly reliable when
either the flaring sources are characterized by narrow, ribbon-like shapes or
high-resolution detectors are utilized for observations. % conclusions heading
(optional), leave it empty if necessary The use of VSKs for interpolating hard
X-ray visibilities allows a notable image reconstruction accuracy when the
information on the flaring source is encoded by a small set of scattered
Fourier data and when the visibility surface is affected by significant
oscillations in the frequency domain.
