Otakar Jicha

Estimation of the Radio Refractivity Gradient From Diffraction Loss Measurements

The aim of this paper is to show that the gradient of the vertical radio refractivity profile of air near the ground can be estimated from measurements of electromagnetic wave strength. Diffraction can be used as the basic physical principle for non-line-of-sight radio links, where an obstacle covers some parts of the Fresnel zones, and therefore, the strength of electromagnetic wave is proportional to the ratio of coverage. The method, which is simple and easy to implement, is verified by measured data, and comparisons with meteorological measurements are presented.

Vertical Dependence of Refractive Index Structure Constant in Lowest Troposphere

Vertical profiles of atmospheric refractivity are indirectly measured at heights of up to 150 m above the ground using meteorological sensors located at 19 heights. The structure constant of the refractive index Cn is calculated from data measured over a one-year period using its definition relation. Linear regression in heights is applied to a structure constant vertical dependence to obtain single and joint annual statistics of the near ground value of Cn and of its vertical gradient in the lowest troposphere. Approximate probability models are given with Cn being log-normal and the vertical gradient normally distributed.

On the Uncertainty of Refractivity Height Profile Measurements

The standard uncertainty of indirect refractivity measurements gained from measurements of pressure, temperature, and humidity is discussed herein. The resulting uncertainty is derived theoretically, based on propagating uncertainties of meteorological sensors through a refractivity calculation, with an example of its impact on actual measurements of a vertical refractivity profile and its gradient also submitted.

Atmospheric refractivity profiles and microwave propagation on a terrestrial path - Experiment and simulation

The results of experimental measurement of atmospheric refractivity profiles and microwave propagation characteristics at 11 GHz carried out recently at the Podebrady site in the Czech Republic are presented. Long term statistics of atmospheric refractivity were obtained from the tower measurement of temperature, pressure and relative humidity of air. Microwave propagation during clear air conditions was observed concurrently on the 50 km long terrestrial path Prague-Podebrady with several receivers located in different heights above the ground. Propagation of electromagnetic waves was modeled using the parabolic equation method and compared with measured data.

Effective earth radius variation and diffraction fading on terrestrial path

Effective earth radius factor (k factor) is an important parameter for the assessment of clear-air propagation on terrestrial paths. Its variation obtained from the measurement of vertical distribution of atmospheric refractivity is studied in the paper. Two year statistics of the k factor are given for the whole year and different months. The related clear-air propagation impairment on the 10 GHz terrestrial path is shown in the example. A typical diffraction fading event is analyzed by a comparison of measured time evolution of received signal level and of a simulated one using measured refractivity. A direct correspondence between the time evolution of the effective earth radius factor and of attenuation due to reduced path clearance is so demonstrated.

On the short-term time evolution of elevated ducting layers

Vertical profiles of atmospheric refractivity are obtained from the tower measurement of temperature and humidity profiles with a vertical resolution less than eight meters and a time resolution one minute. Profiles are described using a modified Webster model with model parameters fitted by nonlinear regression. The time series of fitted parameters show the short-term time evolution of elevated ducting layers. Several typical examples of evolving ducting layers are provided and discussed.

Single and joint statistics of ducting layer parameters determined from vertical profiles of atmospheric refractivity

Vertical profiles of atmospheric refractivity measured on 150 m mast are fitted with a modified Webster duct model. Time series of duct model parameters are obtained with one minute resolution. Empirical single and joint statistics of duct model parameters are determined from 7 month data. Interrelations between the duct parameters are discussed.

Long-term measurements of refractive index structure constant in atmospheric boundary layer

Results of long-term measurements of the refractive index structure constant in the boundary layer are introduced. The measurements were made on a 150-meter-high lattice mast equipped by nineteen meteorological sensors and one pressure sensor at the bottom of the mast. The Kolmogorov statistical theory of turbulence was used to calculate the refractive index structure constant C2n, allowing us to present annual cumulative distribution functions (CDFs) and seasonal quantiles. The quantiles of measured height dependence of the refractive index structure constant are also shown and compared with existing models (Hufnagel/Andrews/Phillips, SLC Day and Gurvich). Parameters of a linear model were calculated to fit the measured median height profile of the refractive index structure constant with the uncertainty of measurements also being addressed.