Impact of Atmospheric Attenuation and Turbulence on Optical Signal Propagation in Urban Free-Space Optical Links

It is known that the effects of atmospheric turbulence and aerosol scattering degrade the propagated optical signals and thus affect the accuracy of parameters retrieval for active and passive remote sensing, namely lidar and terrestrial laser scanning or hyperspectral imaging. In this research, we describe the developed model of optical radiation transmission in an urban environment. The model allows us to control parameters such as molecular absorption, aerosol scattering, and turbulence-related effects (scintillation, beam wander, and beam broadening).

In order to estimate attenuation coefficients, we used the Kim model, named after Isaac I. Kim. Turbulence strength is quantified using the refractive index structure parameter Cn2 and the Rytov variance, and irradiance fluctuations are represented with a gamma–gamma distribution. We performed simulations using Python and evaluated the model for a ground-based sensing link over 1.2 km, where the transmit power was 5 dBm and the receiver sensitivity was −30 dBm. The model demonstrated that the attenuation due to the fog was 19.56 dB/km, with a total path loss of 26.47 dB and a received power of −21.47 dBm, for the following urban conditions: a visibility equal to 0.2 km and Cn2 equal to 10^−14 m^−2/3. We obtained a bit error rate of 2.14 × 10^−10, which is lower than the standard threshold of 10^−9. Overall, despite the substantial attenuation, the signal level was above the noise level.

The model demonstrated that atmospheric distortions can be corrected and that aerosol-driven signal degradation can be compensated for. It can be useful for tasks such as retrieving surface geophysical properties.