Noise reduction in helioseismic power spectra by non-orthogonal wavelets S. K. Solanki, C. Régulo, M. Fligge and A. G. Kosovichev A&A, 379 3 (2001) 1039-1044 Published online: 15 December 2001 DOI: 10.1051/0004-6361:20011254