Laser Beam Atmospheric Propagation Modelling for Aerospace LIDAR Applications

Abstract

Atmospheric effects have a significant impact on the performance of airborne and space laser systems. Traditional methods used to predict propagation effects rely heavily on simplified assumptions of the atmospheric properties and of the interactions with the laser systems. These models need to be continually improved to develop high-resolution predictors of laser performance for applications including LIDAR (light detection and ranging), free-space optical communications, remote sensing, etc. The underlying causes of laser beam attenuation in the atmosphere are examined with particular focus on dominant linear effects: absorption, scattering, turbulence, and non-linear thermal effects such as blooming, kinetic cooling, and bleaching. These phenomena are quantitatively analyzed, highlighting the key assumptions made in the empirical modelling. Absorption and scattering, as the dominant causes of attenuation, are generally well applied in models, but the impact of non-linear phenomena is less well captured and applied as it tends to be application specific. Atmospheric radiative transfer codes, such as MODTRAN, ARTS, etc., and the associated spectral databases, such as HITRAN, are the effective implementation of the total propagative effects on the laser systems. These codes are powerful, widely used tools to analyze performance. However, atmospheric radiative transfer codes make several assumptions that reduce accuracy in favor of faster processing. The key atmospheric radiative transfer models are reviewed highlighting the associated methodologies, assumptions, and application. Empirical models are found to offer a robust analysis of atmospheric propagation, which is particularly well-suited for design, development, test and evaluation (DDT&E) purposes. As such, empirical, semi-empirical, and ensemble methodologies are suggested to compliment and augment the existing atmospheric radiative transfer codes. There is scope to evolve the numerical codes and empirical approaches to better suit aerospace applications, where fast analysis is required over a range of slant paths, incidence angles, altitudes, and atmospheric properties, which are not exhaustively captured in current quantitative performance assessment methods.

Robust structured light in atmospheric turbulence

“…This corresponds to a path length of 508 m and an angle of 80 deg below the horizontal. To calculate the turbulence strength at each altitude, the Tartarski model 95 was used to calculate the values for the refractive index structure constant,…”

“…This corresponds to a path length of 508 m and an angle of 80 deg below the horizontal. To calculate the turbulence strength at each altitude, the Tartarski model 95 was used to calculate the values for the refractive index structure constant, Cn2(h)=Cn02h−b,where Cn02=4.16×10−13 m2/3 and b=4/3 are constants selected to most closely fit experimental data and h is the altitude. The slant path length through the atmospheric layer is given by Δli2=Δhi2+Δzi2, where Δhi2 is the height of the atmospheric layer and Δzi2 is the horizontal component of the beam’s path through the layer; the channel was broken up into 14 unit cells.…”

Error Analysis of Free Space Communication System Using Machine Learning

“…Simulation results for the Kim and Kruse models are evaluated and compared using different wavelengths. The attenuation for 850nm is more than for the 1550nm assuming the Kruse and Kim models [16], [17] as shown in Figure 1 and 2. This work aims to investigate FSO link performance under different frequency ranges.…”

“…The major components affecting the FSO links include fog, snow, smoke, haze, and dust, and the effect of rain is considered negligible. Various visibility models have been developed, including the Mie theory and the Kruse and Kim [15], [16], [17] models. In many applications, 1550 nm window is selected and is investigated under cumulative effects of weather instabilities and scattering.…”

Bit Error Rate Analysis in Atmospheric Turbulence Channel of Synthetic Double Vortex Beam

“…Atmospheric turbulence is a random movement of air, in which irregular changes in temperature, humidity, and pressure lead to uneven refractive index distribution of the atmosphere in general, and many constantly moving air vortices in the flowing atmosphere pose challenges to laser transmission in the atmosphere [1][2][3][4][5][6]. The vortex beam carrying orbital angular momentum has infinite quantum eigenstates of orbital angular momentum by each photon in the beam due to its infinite possibility of topological charge value, which can greatly improve the channel capacity and information transfer efficiency of the current free-space optical communication system [7][8][9][10][11][12].…”