For various applications involving the propagation of light through the atmosphere, anisotropy of optical turbulence must be accounted for. At this point, however, there is no consensus about how to realistically model anisotropic turbulence. It is well established that at length scales small compared to a certain outer length scale, L0, fully developed, optical turbulence is locally homogeneous and isotropic and is well described by the Obukhov- Corrsin similarity theory. At scales large compared to L0, however, the turbulence is usually anisotropic, and the Obukhov-Corrsin similarity theory is no longer valid.
In this paper, we discuss two questions: first, how to define and predict L0; and second, how to model the 3D refractive-index spectrum, Φn(κx, κy, κz), for wavenumbers comparable to and smaller than 1/L0. We will address both questions on the basis of classical theoretical concepts and by means of field observations. The classical concepts include Tatarskii’s original definition of L0, the Richardson criterion, and the Monin- Obukhov similarity theory. Field observations include in-situ measurements by means of ultrasonic anemometer-thermometers and fine-wire turbulence sensors.
Tatarskii’s first book on wave propagation through the turbulent atmosphere was published in English in 1961 and describes what we refer to as the classical theory of optical turbulence. It relies on a number of simplifying assumptions, such as the assumption of locally homogeneous and isotropic, fully developed turbulence; the Corrsin-Obukhov similarity theory; Taylor’s frozen-turbulence hypothesis; and the assumption of weak scattering. In this invited presentation, we review and discuss non-classical models of optical turbulence, which account for non-classical effects and phenomena, including anisotropy, intermittency, outer-scale effects, and non-Gaussianity of refractive-index increments.
It is known that certain geometrical-optics predictions often agree well with optical turbulence field observations even though theoretical constraints for ignoring diffraction may be violated. Geometrical optics assumptions can simplify analyses, and ray optics can significantly reduce simulation computation time. Here, an investigation into angle-of-arrival fluctuations is presented involving wave optics and geometrical (ray) optics computer simulations of a plane wave of visible light propagating through a turbulent refractive-index field. The simulation and Rytov-based theory results for the variances of aperture-filtered angle-of-arrival fluctuations generally agree well for weak scattering (Rytov variance, σR2≲0.2), but for increasing Rytov variance, the simulation results demonstrate a positive slope that can be significantly shallower than that predicted by the theory. For weak-to-moderate scattering regimes (σR2≲2.67), a comparison of the ray and wave results show they match for aperture diameters greater than about two Fresnel lengths. This result is consistent with a previous theoretical analysis by Cheon and Muschinski. For the strongest scattering case studied (σR2=26.7), the wave and ray simulations match for aperture diameters greater than about 10 Fresnel lengths. For smaller apertures, we attribute the disparity between the wave and ray simulation results to a Fresnel filtering effect.
The analysis of optical propagation through both deterministic and stochastic refractive-index fields may be substantially
simplified if diffraction effects can be neglected. With regard to simplification, it is known that certain geometricaloptics
predictions often agree well with field observations but it is not always clear why this is so. Here, a new
investigation of this issue is presented involving wave optics and geometrical (ray) optics computer simulations of a
beam of visible light propagating through fully turbulent, homogeneous and isotropic refractive-index fields. We
compare the computationally simulated, aperture-averaged angle-of-arrival variances (for aperture diameters ranging
from 0.5 to 13 Fresnel lengths) with theoretical predictions based on the Rytov theory.
Airborne synthetic aperture radar (SAR) imaging systems have reached a degree of accuracy and sophistication that requires the validity of the free-space approximation for radio-wave propagation to be questioned. Based on the thin-lens approximation, a closed-form model for the focal length of a gravity wave-modulated refractive-index interface in the lower troposphere is developed. The model corroborates the suggestion that mesoscale, quasi-deterministic variations of the clear-air radio refractive-index field can cause diffraction patterns on the ground that are consistent with reflectivity artifacts occasionally seen in SAR images, particularly in those collected at long ranges, short wavelengths, and small grazing angles.
Conference Committee Involvement (5)
Laser Communication and Propagation through the Atmosphere and Oceans XIV
3 August 2025 | San Diego, California, United States
Environmental Effects on Light Propagation and Adaptive Systems VII
18 September 2024 | Edinburgh, United Kingdom
Laser Communication and Propagation through the Atmosphere and Oceans XIII
20 August 2024 | San Diego, California, United States
Environmental Effects on Light Propagation and Adaptive Systems VI
5 September 2023 | Amsterdam, Netherlands
Laser Communication and Propagation through the Atmosphere and Oceans XII
22 August 2023 | San Diego, California, United States
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.