An Atmospheric Optical Turbulence Structure Parameter Measurements System Based on Direct RI Sensing Using High-Resolution Fiber-Optic Sensors

Authors

• Matej Njegovec, University of Maribor
• Simon Pevec, University of Maribor
• Vedran Budinski, University of Maribor
• Boris Macuh, University of Maribor
• Melissa K. Beason, Air Force Institute of TechnologyFollow
• Denis Onlagic, University of Maribor

Document Type

Article

Publication Date

8-10-2026

Abstract

The paper presents a method to characterize the refractive index structure parameter (C_n²) associated with optical turbulence directly. The characterization system is based on miniature, high‑resolution, all‑fiber refractive index (RI) sensors. The refractive index sensors employ open‑path, low‑finesse Fabry–Perot interferometers that are approximately 8 mm long and 200 μm in diameter. The active part of the interferometers is made of ultra‑low‑expansion glass, which eliminates the influence of thermal expansion on the refractive index measurements. The proposed refractive index sensor, operating in a differential configuration, achieved a resolution of 2×10^-9 RIU using a custom‑designed spectral interrogation system running at a sampling rate of 20 Hz. An experimentally produced C_n² sensor was tested in a controlled environment using a turbulence generator, where it demonstrated a resolution of approximately 2×10^-17 m^-2/3 for 30 cm separation. Across a wide range of turbulence regimes, the results were consistent with those obtained from high‑resolution all‑fiber temperature sensors. The C_n² sensor was tested in both laboratory and field environments. In these settings, the C_n² values obtained from the refractive index sensors matched those derived from temperature‑based sensors closely, with only minor deviations. These differences require further investigation, but may be attributed, at least partially, to additional atmospheric fluctuations—such as pressure and humidity—that cannot be detected by temperature sensors.

Comments

© 2026 The Authors.

This article is published by IEEE, licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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DOI

10.1109/TGRS.2026.3722273

Source Publication

IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892 | eISSN 1558-0644)

Recommended Citation

M. Njegovec, S. Pevec, V. Budinski, B. Macuh, M. Beason and D. Đonlagic, "An Atmospheric Optical Turbulence Structure Parameter Measurements System Based on Direct RI Sensing Using High-Resolution Fiber-Optic Sensors," in IEEE Transactions on Geoscience and Remote Sensing, vol. 64, pp. 4111212-4111212, 2026, Art no. 4111212, doi: 10.1109/TGRS.2026.3722273.