From Event: SPIE Optical Engineering + Applications, 2017
The growth of optical communication has created a need to correctly characterize the atmospheric channel. Atmospheric
turbulence along a given channel can drastically affect optical communication signal quality. One means of
characterizing atmospheric turbulence is through measurement of the refractive index structure parameter, Cn2. When
calculating Cn2 from the scintillation index, σΙ2,the point aperture scintillation index is required. Direct measurement of
the point aperture scintillation index is difficult at long ranges due to the light collecting abilities of small apertures.
When aperture size is increased past the atmospheric correlation width, aperture averaging decreases the scintillation
index below that of the point aperture scintillation index. While the aperture averaging factor can be calculated from
theory, it does not often agree with experimental results. Direct measurement of the aperture averaging factor via the
pupil plane irradiance covariance function allows conversion from the aperture averaged scintillation index to the point
aperture scintillation index. Using a finite aperture, camera, and detector, the aperture averaged scintillation index and
aperture averaging factor are measured in parallel and the point aperture scintillation index is calculated. A new
instrument built by SSC Pacific was used to collect scintillation data at the Townes Institute Science and Technology
Experimentation Facility (TISTEF). This new instrument’s data was then compared to BLS900 data. The results show
that direct measurement of the aperture averaging factor is achievable using a camera and matches well with groundtruth
Galen D. Cauble and David T. Wayne, "Analysis of the covariance function and aperture averaged fluctuations of irradiance to calculate Cn2," Proc. SPIE 10408, Laser Communication and Propagation through the Atmosphere and Oceans VI, 104080D (Presented at SPIE Optical Engineering + Applications: August 08, 2017; Published: 18 September 2017); https://doi.org/10.1117/12.2276694.
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