Investigating the spatiotemporal distribution of refractivity structure index in low-speed flow field by moiré deflectometry

Abstract Atmospheric optical turbulence is a significant restraint on free-space optical communication and atmospheric laser transmission, whose intensity is generally quantified by the refractivity structure index. In this paper, moiré deflectometry is applied to study the combined effects of thermal disturbance and flow speed on the spatiotemporal distribution of the refractivity structure index. Firstly, three sets of comparative experiments are conducted, and 3600 frames of moiré fringes are captured within an hour in each set. Then, the spatiotemporal distribution is obtained based on the theoretical relationship between the refractivity structure index and the phase information recorded by moiré fringes. Finally, its regularities under different experimental conditions are comparatively analyzed. The findings reveal that both thermal disturbance and flow speed will change the intensity of optical turbulence. And, although the latter has a much weaker impact than the former, their combined effects will increase the intensity by three orders of magnitude. In this process, the contribution of thermal disturbance accounts for more than 75%. In short, the related results could provide some insights for research on atmospheric optical detection and communication.