Wave optics simulations of plane-wave propagation in non-Kolmogorov turbulence

Abstract

We explore the practical limits for wave optics simulations of plane-wave propagation in non-Kolmogorov turbulence using the split-step method and thin phase screens. These limits inform two simulation campaigns where the relationship between volume turbulence strength and normalized intensity variance for various non-Kolmogorov power laws is explored. We find that simulation of power-law exponents near 3 are limited to turbulence strengths with Rytov numbers of 7 when the simulation side-length sampling rate is limited to 8192. Under these same conditions, it is possible to simulate volume turbulence strength out to Rytov numbers of 12 for Kolmogorov turbulence out to a power-law exponent of 4. We also demonstrate that the peak scintillation and Rytov number where peak scintillation occurs increases approximately linearly with the power-law exponent. Also, if turbulence strength is fixed, the relationship between the scintillation index and power law depends on the operating regime. In weak turbulence, the relationship is negative, and it is positive in strong turbulence. This work also emphasizes the importance of properly scaling turbulence strength when comparing results between different mediums with different power laws and the influence and importance of defining inner and outer scales in these simulations.

Propagation geometry and its effect on peak scintillation of intensity

“…In Figure 4 I show the result of repeating the WOS campaign from 16 but evaluating scintillation at each propagation step. In this way, the WOS should, in principle, be comparable to ERT.…”

“…Each plot is referenced by the maximum Rytov number possible for that turbulence strength over the 5 km path length used in. 16 Also included in the figure are predictions from ERT (solid gray) using the same values of C 2 n and path length from the WOS. Clearly, even when ERT and WOS are evaluated equivalently significant disagreement remains between the two approaches.…”

“…However, recent works have shown significant disagreement in both field experiments 13 and extensive WOS campaigns. [14][15][16][17][18] It seems likely that ERT can be applied less broadly than originally conceived or at least more work is required to resolve these discrepancies.…”

“…In this work, I compare results of ERT and an extensive WOS campaign from 16 and explore discrepancies in the focusing region near peak scintillation. I will also show how ERT has been commonly misinterpreted.…”

“…Later, in Ref. 16 we repeated our WOS but this time with an explicit inner scale, l 0 of 5 mm and an outer scale , L 0 , of 1 m. Note that these are the same values used in Figure 9.6 of Ref. 11.…”