Dependence of atmospheric refractive index structure parameter (Cn2) on the residence time and vertical distribution of aerosols

Abstract

Effects of absorbing atmospheric aerosols in modulating the tropospheric refractive index structure parameter (Cn2) are estimated using high resolution radiosonde and multi-satellite data along with a radiative transfer model. We report the influence of variations in residence time and vertical distribution of aerosols in modulating Cn2 and why the aerosol induced atmospheric heating needs to be considered while estimating a free space optical communication link budget. The results show that performance of the link is seriously affected if large concentrations of absorbing aerosols reside for a long time in the atmospheric path.

Performance of free-space optical communication systems: effect of aerosol-induced lower atmospheric warming

“…Table 1 shows the estimated vertically averaged values of C n 2 , C n 2* and d 2 T/dtdz, where C n 2 is the refractive index structure parameter calculated using the unperturbed atmospheric data, C n 2* is the same when radiative effects of perturbed aerosol fields are also incorporated and d 2 T/dtdz is the vertical gradient of aerosol-induced atmospheric heating rate. d 2 T/dtdz (a signature of vertical distribution of aerosols) influences the perturbations in C n 2 significantly compared to AOD (a signature of total aerosol columnar loading) as reported in [7]. Higher the value of d 2 T/dtdz, higher the vertical temperature gradient, thereby resulting in higher C n 2 values.…”

“…With a view to examining the radiative effects of atmospheric aerosols on the performance of FSO communication systems, aerosol parameters were perturbed following the method described in [7,8]. Long-term (2006 to 2012) averaged level 3 seasonal AOD values of 0.27, 0.34, 0.29 and 0.33 for DJF, MAM, JJAS and ON seasons and an aerosol residence time of one day were taken in the present study.…”

“…Several models are in use to estimate clear air optical turbulence [6]. Recent studies on the modulation of C n 2 due to variations in the atmospheric residence time and vertical distribution of aerosols [7,8] have clearly quantified the aerosol-induced optical scintillations through absorption, scattering and radiative effects, when they are present close to the surface or in the elevated layers [9] of the Earth's lower atmosphere (troposphere). Extinction effects of aerosols on optical turbulence [10][11][12] and FSO communication links [5,13,14] were reported earlier.…”

The Impact of Atmospheric Turbulence on Terahertz Communication

“…According to definition, the atmospheric turbulence refers to the fluctuations of refractive index caused by all fluctuations in the air such as humid, temperature, wind velocity, and atmospheric pressure [32], leading to impact on wave propagation. In practice, the atmospheric refractive index structure constant, denoted as C 2 n [33], which is used to describe the intensity of atmospheric turbulence [34], is actually a function of space and time rather than a constant. Also it is influenced by fluctuation of refractive index.…”