The objective of this study is to explore the feasibility and accuracy of image subtraction for estimating optical turbulence. The proposed approach involves creating a differential image by subtracting consecutive recorded frames. Post processing techniques are applied to the differential image, allowing temporal changes caused directly by turbulence to be identified. Image subtraction was implemented in python and evaluated against traditional turbulence instruments such as a Scintec BLS2000 and a MZA DELTA.
This research paper discusses the application of several image-based techniques for measuring optical turbulence. University of Central Florida researchers have previously prototyped and fielded a differential disturbance tracker at the TISTEF 1 kilometer range. This effort has evolved into the development of a software suite that implements image processing techniques such as blob detection, centroid tracking, and optical flow for estimating the refractive index structure parameter. To validate each method, imagery was collected over the 1 kilometer path. The processed results were compared against measurements from an MZA DELTA system.
The TISTEF Camera and Anemometer Turbulence System (T-CATS) is a single ended instrument for estimating the refractive index structure parameter (C2n ) along a given path. This instrument was developed by the Wave Propagation Research Group and utilizes a wide-angle camera, a thermal camera, a raspberry pi zero w, and an Applied Technologies SATI-3A sonic anemometer. Kolmogorov’s equations for spatial temperature difference are used to estimate C2 n within the field of view of the thermal camera. T-CATS was deployed and evaluated at the TISTEF laser range. These data were compared to a SATI-3A sonic anemometer.
Propagation of laser beams through a turbulent atmosphere over extended ranges can cause significant beam scintillation and wander which can degrade the effectiveness of a Free Space Optical (FSO) link. The use of a spectrally broadband laser light source, with a high spatial coherence and short temporal coherence, could lead to improved performance in one or both of these areas. This experiment investigates the effect of temporal coherence on the far-field turbulence induced effects on the beam. Narrow linewidth coherent sources were compared against a broadband source over a 13.5 km slant-path. The path was instrumented with a path averaged turbulence monitoring device during data collection along with a range of other meteorological parameters to predict atmospheric parameters. Target board beam profile data was collected to measure the spatial statistics due to atmospheric turbulence along with silicon detectors to measure the temporal statistics of the atmospheric turbulence effects. This data is analyzed and compared to full diffraction wave propagation simulation results. Our analysis shows the benefit that the broadband source does not suffer as many scintillation effects as the narrow-linewidth sources.
Experiments were conducted at the TISTEF laser range to evaluate the atmospheric turbulence data of several instruments. A Scintec BLS900, BLS2000, SLS20, MZA DELTA, and an Applied Technologies SATI-3A sonic anemometer were deployed on the 1 kilometer range and recorded measurements over a multi-day period. The data was then processed to compare the calculated refractive index structure parameter (C2n ) between the instruments. The BLS2000 and DELTA were also deployed to record turbulence measurements along a 13.5 kilometer slant path from the TISTEF site to the Vehicle Assembly Building roof on Kennedy Space Center property for additional evaluation.
Atmospheric propagation experiments have been conducted over the 1km TISTEF laser range to examine the effects of turbulence, absorption and scattering on a supercontinuum laser beam. This supercontinuum laser beam has been band limited to transmit only visible wavelengths (400-850 nm). In this work, the effects of atmospheric turbulence on the supercontinuum laser will be examined.
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