Compressed sensing and finite isotropic wavelets for the STIX reconstruction problem

STIX is a X-ray imaging spectroscopy device to be mounted as part of the Solar Orbiter cluster. Its goal is to provide images and spectra of solar flaring regions. The device provides 30 measurements of the incoming photon flux which can be interpreted as spatial Fourier samples. In this paper we present a method for reconstructing the intensity image from the few provided measurements. The proposed algorithm is based on compressed sensing theory. In order to provide the needed sparsity, we build an isotropic wavelet transform which is very appropriate for the STIX measurements. The evaluation on two simulated solar flares shows the potential of the algorithm in reconstructing hard X-ray maps from STIX measurements.