TY CONF TI CALCULATION OF THE SPATIAL COHERENCE FUNCTION OF A SPHERICAL WAVE PROPAGATING IN A TURBULENT ATMOSPHERE BASED ON THE HELMHOLTZ EQUATION KW spherical wave KW coherence KW turbulent atmosphere KW wave equation JO International Symposium Atmospheric and Ocean Optics. Atmospheric Physics AU Banakh, V.A. AU Falits, A.V. AU Zaloznaya, I.V. PY 2026 PB V.E. Zuev Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences