Asymptotic theory of the finite beam scintillations (Charnotskii, WRM, 1994, JOSA A, 2010) provides an exhaustive
description of the dependence of the beam scintillation index on the propagation conditions, beam size and focusing.
However the complexity of the asymptotic configuration makes it difficult to apply these results for the practical
calculations of the scintillation index (SI). We propose an estimation technique and demonstrate some examples of the
calculations of the scintillation index dependence on the propagation path length, initial beam size, wavelength and
turbulence strength for the beam geometries and propagation scenarios that are typical for applications. We suggest
simple analytic bridging approximations that connect the specific asymptotes with the accuracy sufficient for the
engineering estimates. Proposed technique covers propagation of the wide, narrow, collimated and focused beams under
the weak and strong scintillation conditions.
Direct numeric simulation of the beam waves propagation through turbulence expediently complements the
asymptotic theory being most efficient when the governing scales difference is not very large. We performed numerical
simulations of the beam wave propagation through turbulence for conditions that partially overlap with the major
parameter space domains of the asymptotic theory. The results of the numeric simulation are used to confirm the
asymptotic theory and estimate the accuracy of the bridging approximations.