The four year FSO link attenuation measurement concurrently with most important meteorological parameters was performed at our mountain observatory Milesovka. In this contribution we summarize and classify different atmospheric phenomena after the FSO link attenuation quantity. For all particular phenomena the CD curves, typical events and simple dependences on relevant atmospheric parameter(s) are presented. We consider the following phenomena (approximate specific attenuation in dB/km in brackets): 1. Fog and cloud (hundreds dB/km) 2. Rain and snow (tens dB/km) 3. Atmospheric turbulence (unit dB) 4. Clear air attenuation due to water vapour (unit dB or less)
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.
Attenuation of electromagnetic waves at 860 nm and 58 GHz due to scattering in rain is measured on the terrestrial paths simultaneously with rain intensity. The relationship between rain intensity and rain attenuation of light is analyzed using the Marshal-Palmer drop size distribution model and the Mie scattering theory. The pertinent power law model is derived from drop size distribution parameters. An empirical composite power law model is proposed and fitted to the dataset extracted from rain attenuation events recorded during a seven-year experiment in Prague. Observed average rain attenuation of light at intensities larger than about 5 mm/h is lower than attenuation predicted by standard models. Rain attenuation measured at 58 GHz is larger than attenuation at 860 nm for rain intensities in the range from 0.1 to 100 mm/h.
Institute of Atmospheric Physics of Czech Academy measures atmospheric attenuation on 60 m experimental FSO link
on 830 and 1550 nm for more than three years. Visibility sensors and two 3D sonic anemometers on both transmitting
and receiving site, rain gauge and many sensors enabling the refractivity index computation are spaced along the optical
link. Meteorological visibility, wind turbulent energy, sonic temperature, structure index and rain rate are correlated with
measured attenuation. FSO link attenuation dependence on the above mentioned parameters is analyzed. The paper
shows also basic statistical behavior of the long-term FSO signal level and also the simulation of hybrid link techniques.
The paper deals with the results of a propagation study on a fixed hybrid Free Space Optical (FSO) and Radio
Frequency (RF) system operating in 850 nm / 58 GHz bands. Propagation models for the availability assessment of both
FSO and RF links were examined against a comprehensive database of meteorological attenuation events. The
influences of individual hydrometeors were analyzed and the availability performances of the simulated FSO/MMW
hybrid link were evaluated. The study pointed out that visibility and rainfall measurements can be only used for the raw
assessment of availability performance due to the concurrent occurrence of different attenuation effect.
The specific results of a propagation study carried out on a free space optical link working at 850 nm on an 853 m long
terrestrial path over a 4-year period from August 2004 to July 2008 are presented. The records of both the observed fade
events and the concurrent meteorological conditions were processed. Individual recorded attenuation events were
classified according to the types of individual hydrometeors (rain, rain with hail, snow and fog) that occurred. Fog
attenuation events were analyzed in detail and were subdivided into the attenuation events due to fog only, and to
combinations of fog with rain, fog with snow, and fog with rain and snow, respectively. The cumulative distributions of
attenuation due to fog events for four individual year periods, the entire 4-year period, the individual worst months and
the average worst month from the four-year period are presented. It is shown that not only attenuation due to fog only but
also attenuation due to fog combined with other hydrometeors may have a significant impact on the attenuation of the
optical beam. The assessments of availability performance and error performance parameters are given. The use of
measured visibility data for the calculation of attenuation is discussed.
Institute of Atmospheric Physics measures atmospheric attenuation on experimental FSO link on 850 and 1550 nm for
more than one year. Experimental site is located at meteorological observatory on the isolated mountain with frequent
fog, low clouds and strong wind occurrence. Measured attenuation is correlated with the wind turbulence intensity,
visibility and LWC. Simple empirical models estimating attenuation on FSO link from meteorological parameters are
formulated and verified through the experiment described. The paper shows also basic statistical behavior of the longterm
FSO signal level in extreme conditions.
A dual optical wireless test link works with two different optical wavelengths in spectral windows of 850 nm and
1550 nm. The transceivers of the link are placed on the highest peak of the Czech Central Mountains (Milesovka
Mountain) so that the transmission path is oriented almost in a vertical direction. The installation site is situated in a
locality with the harshest climate in the Czech Republic with extreme attenuation conditions. The almost vertically
oriented path of the link allows analyzing the impact of the different atmospheric layers on the signal transmission. The
monitoring of the received power and the archiving of the appropriate data are constantly provided. The relationship
between the link attenuation and the atmospheric visibility has been investigated. The results of this experiment are
The complex model of terrestrial FSO link is based on two models: the power-budget model of a given link (steady
model) and the installation site model (statistical model). The steady model is represented by the power balance
equation and the power level diagram. The statistical model consists in the knowledge of cumulative exceedance
probability of the random atmospheric attenuation coefficient. The parameters of the statistical model depend only on
the atmospheric phenomena on installation site. Data from more than 200 sites in Italy, France and Germany are