Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Article Citation - WoS: 3Citation - Scopus: 5Depth Dependence of Oceanic Turbulence Optical Power Spectrum Under Any Temperature and Salinity Concentration(Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, YahyaThe Oceanic Turbulence Optical Power Spectrum (OTOPS) with depth variations is acquired under any temperature and salinity concentration. It is supposed that specific medium is the Atlantic Ocean at high latitude and the Pacific Ocean at high, mid and low latitudes. For the OTOPS model, a depth-varying functions that include low-latitude, high- and mid-latitude-summer and mid-latitude-winter salinity and temperature changes are found. With the help of the equations for the temperature and salinity changes, figures are obtained for the eddy diffusivity ratio depth of seawater and OTOPS model against the depth and kappa at these media. In the ocean, downlink (uplink) is defined as the optical wireless communication link where the receiver (transmitter) is located at a deeper point than the transmitter (receiver), i.e., in the downlink, optical signal proceeds from a point close to ocean surface to deeper ocean and in the uplink, optical signal proceeds from deeper ocean to a point close to ocean surface. In this paper, the OTOPS model is investigated on how its properties change in the underwater environment in downlink and uplink. Different behavior of the OTOPS model is exhibited.Article Citation - WoS: 5Citation - Scopus: 6Underwater Turbulence Effect on Optical Imaging(Iop Publishing Ltd, 2022) Gokce, Muhsin Caner; Baykal, Yahya; Ata, YalcinModulation transfer function (MTF) of oceanic turbulence plays an essential role in the design and quality of underwater image sensing systems capturing optical signals. MTF gives clues about the characteristics of turbulence which can help image reconstruction where the image resolution can be increased in this way. In the paper, under the conditions of weak turbulence and Gaussian beam propagation, we derive the modulation transfer function for short-exposure and long-exposure images based on the recently developed turbulence spectrum model: Oceanic turbulence optical power spectrum (OTOPS). With the aid of the OTOPS model, the effect of measurable turbulence parameters, namely average temperature, average salinity concentration, and temperature-salinity gradient ratios, as well as imaging system parameters, namely receiver aperture radius and wavelength of the laser source on the MTF are reported. Obtained results indicate that MTF rapidly decreases with increasing relative spatial frequency and turbulence strength. Turbulence becomes stronger with the increase in the average temperature, average salinity concentration, energy dissipation rate, temperature-salinity gradient ratio and with the decrease in the temperature dissipation rate, wavelength.Article Citation - WoS: 15Citation - Scopus: 19Adaptive Optics Effect on Performance of Bpsk-Sim Oceanic Optical Wireless Communication Systems With Aperture Averaging in Weak Turbulence(Pergamon-elsevier Science Ltd, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerTurbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Intensity Correlations of Flat-Topped Beams in Oceanic Turbulence(Taylor & Francis Ltd, 2020) Baykal, YahyaIntensity correlations of flat-topped beams are formulated and evaluated in oceanic turbulence. Variations of the intensity correlations are examined against the diagonal distance from different starting points at the receiver plane, for the various number of beams composing the flat-topped beam, for various starting points at the receiver and for various source sizes. Also, the variations of the intensity correlations are investigated against the ratio of temperature to salinity contributions to the refractive index spectrum for the various number of beams composing the flat-topped beam, against the rate of dissipation of mean-squared temperature for various starting points at the receiver plane and against the rate of dissipation of kinetic energy per unit mass of fluid for various source sizes.Article Citation - WoS: 11Citation - Scopus: 12Anisotropy Effect on Performance of Ppm Optical Wireless Oceanic Communication Links(Pergamon-elsevier Science Ltd, 2019) Baykal, YahyaThe performance, quantified by the bit-error-rate (BER), of M-ary pulse position modulated (PPM) optical wireless oceanic communication (OWOC) link is investigated when such a link operates in anisotropic weak oceanic turbulence. For this purpose, formulations of the average received power and the scintillation index of collimated Gaussian optical beam detected by a point detector are developed for anisotropic weak oceanic turbulence, which in turn are employed in the BER expression of the PPM OWOC links. BER is evaluated under various turbulence parameters of anisotropic oceanic turbulence, M of M-ary PPM, data bit rate, average current gain of avalanche photodiode (APD). For any investigated parameter, it is found that the BER performance of M-ary PPM OWOC links is improved as the ocean becomes more anisotropic. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 21Citation - Scopus: 21Signal-To Ratio Reduction Due To Oceanic Turbulence in Oceanic Wireless Optical Communication Links(Elsevier Science Bv, 2018) Baykal, YahyaThe effect of oceanic turbulence on the signal-to-noise ratio (SNR) at the receiver of an oceanic wireless optical communication (OWOC) link is studied. To quantify such effect, the metric employed is the reduction in the SNR when oceanic turbulence is present. SNR reduction due to oceanic turbulence is formulated by subtracting the 10 log (SNR) evaluated at the receiver in the presence of turbulence from the 10 log (SNR) evaluated at the receiver in the absence of turbulence. Classical SNR formula which is function of the received optical power, noise and optical detector parameters is utilized. As the average received power, our earlier result that uses a Gaussian optical source field and a finite Gaussian receiver aperture in atmospheric turbulence is adapted for oceanic turbulence and such found average received power is inserted in the SNR expression. OWOC links that use collimated Gaussian optical sources at the transmitter and PIN photodiode, avalanche photodiode (APD) at the receiver, are analyzed. Results that present the variations of the SNR reduction due to oceanic turbulence against the changes in the source, oceanic turbulence and the optical receiver parameters are reported.Article Citation - WoS: 23Citation - Scopus: 23Ber of Asymmetrical Optical Beams in Oceanic and Marine Atmospheric Media(Elsevier Science Bv, 2017) Baykal, YahyaThe average bit-error-rate (BER) performances of asymmetrical optical Gaussian beams propagating in oceanic and marine atmospheric turbulence are examined. Both type of media are assumed to exhibit weak turbulence. The effect of asymmetry factor on the BER performance are investigated in conjunction with the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and the rate of dissipation of kinetic energy per unit mass of fluid, and with the marine atmospheric link parameters of the link length and the structure constant. Also, the variations of the BER against the source size of various asymmetrical beams are scrutinized in both oceanic and marine atmospheric media.Article Citation - WoS: 28Citation - Scopus: 30Effect of Anisotropy on Intensity Fluctuations in Oceanic Turbulence(Taylor & Francis Ltd, 2018) Baykal, YahyaFor an optical spherical wave propagating in an oceanic turbulent medium, the effect of anisotropy on the received intensity fluctuations is investigated. For different anisotropy factors, the variations of the scintillation index vs. the ratio that determines the relative strength of temperature and salinity in the index fluctuations, the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, viscosity, link length and the wavelength are plotted. It is found that, for all the oceanic turbulence and the link parameters of interest, as the medium becomes more anisotropic, the intensity of the optical spherical wave fluctuates less. It is concluded that the performance of an optical wireless communication systems (OWCS) operating in anisotropic oceanic turbulence is better than the performance of OWCS operating in isotropic oceanic turbulence.