Analysis of the covariance function and aperture averaged fluctuations of irradiance to calculate Cn2

Galen D. Cauble; David T. Wayne

doi:10.1117/12.2276694

18 September 2017 Analysis of the covariance function and aperture averaged fluctuations of irradiance to calculate Cn₂

Galen D. Cauble, David T. Wayne

Proceedings Volume 10408, Laser Communication and Propagation through the Atmosphere and Oceans VI; 104080D (2017) https://doi.org/10.1117/12.2276694
Event: SPIE Optical Engineering + Applications, 2017, San Diego, California, United States

Abstract

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 Cn²from 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 instrumentation.

Conference Presentation

Citation Download Citation

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 (18 September 2017); https://doi.org/10.1117/12.2276694

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