Scientists continually seek to improve atmospheric turbulence models. Employing Fourier telescopy techniques, we have assessed the effect of humidity, temperature, atmospheric pressure, and airflow velocity on horizontal-path, ground-level turbulence. The measurements were made at different times of day. Turbulence parameters investigated include Cn2, the scintillation index σ2I, and the inner scale l0 . The results showed temporal movement patterns of the turbulence to be consistent with Taylor’s frozen turbulence theory. We plan to compare the results of these outdoor measurements with measurements conducted indoors with an optical turbulence generator. Fourier telescopy measurements rely on the distant interference of two mutually-coherent and frequency-offset laser beams, the resulting moving interference fringe pattern “beating” against a fixed grating, such as a Ronchi ruling, and yielding a photo-detected signal that can be analyzed statistically to infer turbulence parameters. Preliminary study suggests that the Fourier telescopy-based measurements can provide more information on turbulence parameters than can measurements made with single laser beams. The basic experimental setup will be described, along with results of the experiments.
Different theories including Kolmogorov have been valid to explain and model physic phenomenal like vertical atmospheric turbulence. In horizontal path, we still have many questions, due to weather problems and consequences that it generates. To emulate some conditions of environment, we built an Optical Turbulence Generator (OTG) having spatial, humidity and temperature, measurements that were captured in the same time from optical synchronization. This development was made using digital modules as ADC (Analog to Digital Converters) and communications protocol as SPI. We all made from microcontrollers. On the other hand, to measure optical signal, we used a photomultiplier tube (PMT) where captured the intensity of fringes that shifted with a known frequency.
Outcomes show temporal shift and phase drive from dependent samples (in time domain) that correspond with frozen turbulence given by Taylor theory. Parameters studied were C2n, scintillation and inner scale in temporal patterns and analysis of their relationship with the physical associated variables. These patterns were taken from Young Interferometer in laboratory room scale. In the future, we hope with these studies, we will can implement an experiment to characterize atmospheric turbulence in a long distance, placed in the equatorial weather zone.
The Kolmogorov’s theory has been used to explain physical phenomena like the vertical turbulence in atmosphere, others recent works have made new advances and have improved K41 theory. In addition, this theory has been applied to studying different issues associated to measure atmospheric effects, and have special interest to find answers in optics to questions as e.g. at ground level, Could it find edges of two or more close objects, from a distant observer? (Classic resolution problem). Although this subject is still open, we did a model using the statistics of the centroid and the diameter of the laser beam propagated under horizontal turbulence at ground level until the object plane. The goal is to measure efficiently the turbulence effects in the long horizontal path propagation of electromagnetic wave. Natural movement of laser beam within the cavity needs be subtracted from the total transversal displacement in order to obtain a best approach. This simple proposed method is used to find the actual statistics of the centroid and beam diameter on the object plane where the turbulence introduces an additional transversal shift. And it has been tested for different values of horizontal distances under non-controlled environment in a synchronized acquisition scheme. Finally, we show test results in open very strong turbulence with high controlled temperature. This paper presents the implemented tests mainly into laboratory and discuss issues to resolve.
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