Ondrej Fiser - Academia.edu (original) (raw)
Papers by Ondrej Fiser
Optical Wireless Communications, 2016
This chapter deals with the FSO link attenuation measurements at very special (severe) climatic c... more This chapter deals with the FSO link attenuation measurements at very special (severe) climatic conditions of the mountain Milesovka observatory being appropriate for the research but being not typical one. Therefore, examples of measurements from Prague, Budapest, and Milano are added. Fog attenuation (in combination with cloud) is discussed and Kim formula predicting the fog attenuation from visibility was more or less acknowledged. More accurate results are provided for rain attenuation estimation using the Carbonneau formula. Examples discussing concurrent occurrence of rain, fog, and clouds are analyzed. In the last part, we analyze the attenuation due to atmospheric turbulences concluding that the Rytov formula overestimates the attenuation on one hand, but is in good correlation with the measured attenuation on the second hand.
Various methods for analyses of scattering are mentioned and new approximate relationships are de... more Various methods for analyses of scattering are mentioned and new approximate relationships are derived. Experimental results for thin wire and several numerical simulations of forward scattering using approximate esti- mations, physical optics and exact solutions for two-di- mensional scattering are presented both for far and near fields. That allows not only accuracy analyses but also conclusions about scattering and total fields in the pres- ence of objects, which are important for many applications such as communications, bistatic and multistatic radars and electromagnetic compatibility.
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
Optical Engineering, 2013
Our correlation analysis has shown promising and surprisingly good dependence of optical signal a... more Our correlation analysis has shown promising and surprisingly good dependence of optical signal attenuation on sonic temperature, which is shown and discussed in this study. This discovered dependence is derived from measurements (periods with fog and rain events were excluded) and presented in the form of scatter plots. It is possible to express roughly that the attenuation decreases with the sonic temperature (negative correlation coefficient). Trying to understand our results, we added the explanation of the physical quantity sonic temperature in this contribution.
IEEE Photonics Technology Letters, 2013
Proceedings of ERAD, 2002
The influence of the DSD on rain attenuation computation is studied in the 10-150 GHz frequency r... more The influence of the DSD on rain attenuation computation is studied in the 10-150 GHz frequency region. The influence of particular rain drop sizes (diameters) is shown concluding that the prevailing contribution is caused by drops of the diameter close to 0.7-1.5 mm when the importance of small rain drops is increasing with the increasing frequency. A 2 step model is suggested not to be able to derive the attenuation only but also to model the rain drop spectra accurately. Conclusions are derived from the typical DSD (which was measured in the Czech Republic and corresponds to the 2.17 mm/h rain rate). The convenience of DSD analytical approximations (DSD models) is also discussed.
EURASIP Journal on Wireless Communications and Networking, 2011
This study is focused on the experimental research of the atmosphere impact on FSO link attenuati... more This study is focused on the experimental research of the atmosphere impact on FSO link attenuation. Experiment is performed on a mountain observatory Milesovka of severe weather conditions. The empirical relationships on 830 nm only between FSO attenuation A on one hand and atmospheric visibility V or wind turbulent energy ET on the other hand are presented and discussed. In the fog case it was found A= 401.4V-0.5738- 1.462 dB/60m (V in meters) while for the attenuation due to the wind turbulence ET it holds A = 2.112 - 2.213 exp(-0.2867ET) dB/60m (ET in m2s-2, it was derived for 830 nm wave length). A discussion concerning problems of the “clear air attenuation,” atmospheric turbulences and sun shine impact, which was observed as a maximum 2 dB attenuation for a few minutes with a period of 24 hours is added.
Waveguide Technologies in Photonics and Microwave Engineering [Working Title], 2019
This chapter investigates the radio-wave propagation above irregular ground, including the tropos... more This chapter investigates the radio-wave propagation above irregular ground, including the troposphere, using physical optics computation. We briefly describe used simplifications, which substantially reduce numerical simulations. Using the principle of stationary phase, we can approximate the propagation over a terrain (the PO approximation of the vector problem with a 3-D surface) with a 2-D surface. Moreover, we approximate the reflection coefficient for a surface with random deviations considering the surface standard deviation and the local Fresnel reflection coefficient for the smooth ground. We present the novel computations of physical optics for investigations of radar coverage diagrams. We consider both monostatic and bistatic radars, the far-field antenna measuring ranges, and studies of air refraction index. We validate the calculations by both experimental results and the other numerical simulations. The experimental results changed during seasons and according to terrain and troposphere conditions including vegetation, cultivation, snow, and air temperature and pressure.
2008 6th International Symposium on Communication Systems, Networks and Digital Signal Processing, 2008
ABSTRACT
2008 14th Conference on Microwave Techniques, 2008
ABSTRACT
2009 Loughborough Antennas & Propagation Conference, 2009
The results of an experimental research of attenuation due to hydrometeors at 850 nm and 93 GHz o... more The results of an experimental research of attenuation due to hydrometeors at 850 nm and 93 GHz on parallel terrestrial path over a 1-year period are given. Cumulative distributions of attenuation due to both all the hydrometeors together and the individual hydrometers at both wavelengths, the availability performances of an individual FSO system and MMW system and the improvement of availability performance of the simulated 850 nm/93 GHz hybrid system against individual systems are presented.
Optical Wireless Communications, 2016
This chapter deals with the FSO link attenuation measurements at very special (severe) climatic c... more This chapter deals with the FSO link attenuation measurements at very special (severe) climatic conditions of the mountain Milesovka observatory being appropriate for the research but being not typical one. Therefore, examples of measurements from Prague, Budapest, and Milano are added. Fog attenuation (in combination with cloud) is discussed and Kim formula predicting the fog attenuation from visibility was more or less acknowledged. More accurate results are provided for rain attenuation estimation using the Carbonneau formula. Examples discussing concurrent occurrence of rain, fog, and clouds are analyzed. In the last part, we analyze the attenuation due to atmospheric turbulences concluding that the Rytov formula overestimates the attenuation on one hand, but is in good correlation with the measured attenuation on the second hand.
Various methods for analyses of scattering are mentioned and new approximate relationships are de... more Various methods for analyses of scattering are mentioned and new approximate relationships are derived. Experimental results for thin wire and several numerical simulations of forward scattering using approximate esti- mations, physical optics and exact solutions for two-di- mensional scattering are presented both for far and near fields. That allows not only accuracy analyses but also conclusions about scattering and total fields in the pres- ence of objects, which are important for many applications such as communications, bistatic and multistatic radars and electromagnetic compatibility.
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
Optical Engineering, 2013
Our correlation analysis has shown promising and surprisingly good dependence of optical signal a... more Our correlation analysis has shown promising and surprisingly good dependence of optical signal attenuation on sonic temperature, which is shown and discussed in this study. This discovered dependence is derived from measurements (periods with fog and rain events were excluded) and presented in the form of scatter plots. It is possible to express roughly that the attenuation decreases with the sonic temperature (negative correlation coefficient). Trying to understand our results, we added the explanation of the physical quantity sonic temperature in this contribution.
IEEE Photonics Technology Letters, 2013
Proceedings of ERAD, 2002
The influence of the DSD on rain attenuation computation is studied in the 10-150 GHz frequency r... more The influence of the DSD on rain attenuation computation is studied in the 10-150 GHz frequency region. The influence of particular rain drop sizes (diameters) is shown concluding that the prevailing contribution is caused by drops of the diameter close to 0.7-1.5 mm when the importance of small rain drops is increasing with the increasing frequency. A 2 step model is suggested not to be able to derive the attenuation only but also to model the rain drop spectra accurately. Conclusions are derived from the typical DSD (which was measured in the Czech Republic and corresponds to the 2.17 mm/h rain rate). The convenience of DSD analytical approximations (DSD models) is also discussed.
EURASIP Journal on Wireless Communications and Networking, 2011
This study is focused on the experimental research of the atmosphere impact on FSO link attenuati... more This study is focused on the experimental research of the atmosphere impact on FSO link attenuation. Experiment is performed on a mountain observatory Milesovka of severe weather conditions. The empirical relationships on 830 nm only between FSO attenuation A on one hand and atmospheric visibility V or wind turbulent energy ET on the other hand are presented and discussed. In the fog case it was found A= 401.4V-0.5738- 1.462 dB/60m (V in meters) while for the attenuation due to the wind turbulence ET it holds A = 2.112 - 2.213 exp(-0.2867ET) dB/60m (ET in m2s-2, it was derived for 830 nm wave length). A discussion concerning problems of the “clear air attenuation,” atmospheric turbulences and sun shine impact, which was observed as a maximum 2 dB attenuation for a few minutes with a period of 24 hours is added.
Waveguide Technologies in Photonics and Microwave Engineering [Working Title], 2019
This chapter investigates the radio-wave propagation above irregular ground, including the tropos... more This chapter investigates the radio-wave propagation above irregular ground, including the troposphere, using physical optics computation. We briefly describe used simplifications, which substantially reduce numerical simulations. Using the principle of stationary phase, we can approximate the propagation over a terrain (the PO approximation of the vector problem with a 3-D surface) with a 2-D surface. Moreover, we approximate the reflection coefficient for a surface with random deviations considering the surface standard deviation and the local Fresnel reflection coefficient for the smooth ground. We present the novel computations of physical optics for investigations of radar coverage diagrams. We consider both monostatic and bistatic radars, the far-field antenna measuring ranges, and studies of air refraction index. We validate the calculations by both experimental results and the other numerical simulations. The experimental results changed during seasons and according to terrain and troposphere conditions including vegetation, cultivation, snow, and air temperature and pressure.
2008 6th International Symposium on Communication Systems, Networks and Digital Signal Processing, 2008
ABSTRACT
2008 14th Conference on Microwave Techniques, 2008
ABSTRACT
2009 Loughborough Antennas & Propagation Conference, 2009
The results of an experimental research of attenuation due to hydrometeors at 850 nm and 93 GHz o... more The results of an experimental research of attenuation due to hydrometeors at 850 nm and 93 GHz on parallel terrestrial path over a 1-year period are given. Cumulative distributions of attenuation due to both all the hydrometeors together and the individual hydrometers at both wavelengths, the availability performances of an individual FSO system and MMW system and the improvement of availability performance of the simulated 850 nm/93 GHz hybrid system against individual systems are presented.