# Tropospheric Refraction

__Refractivity Profile Estimation__

As the atmospheric conditions, expressed in terms of radio refractivity, can considerably influence the performance of radio communication links and radar systems, there is a need for reliable prediction of refractivity structure in the lower atmosphere. The usual methods of direct refractive index measurement by means of radiosounding and refractometers can usually only give a rough idea of the refractivity distribution. The basic disadvantage of the radiosonde, resulting from its occasional, although regular, launching, is that it is not able to provide a detailed idea of refractivity structure time development. In recent years, matched field processing methods representing indirect methods of refractivity structure sounding have turned out to be suitable alternative to direct means of measurement.

These methods have been used in the electromagnetic domain to estimate the refractivity structure in the troposphere. In tropospheric propagation, measurement values at a vertical receiver array are usually compared with values obtained by simulation with various refractivity profiles as an environmental parameter. The refractivity estimation is determined by the parameter that gives the best fit between the measurement and the simulation. Similar estimation techniques exist relying on fitting simulation results and measurement data from radar.

__Propagation in a Laterally Inhomogeneous Atmosphere__

Although the assumption of a horizontally homogeneous atmosphere is justifiable in most cases, situations can occur where the horizontal variability of the atmosphere is of some importance.

__New Implementation Techniques ror Ray-Tracing and Parabolic Equation__

- Analytic ray-tracing
- Domain decomposition for the split-step parabolic equation

__Supported by__

- Basic Research of Radiometeorology Properties of Tropospheric Ducting Layers by Using Artificial Intelligence Methods, Czech Science Foundation, grant no. P102/10/1901, 2010-2012
- Research on Electromagnetic Wave Refraction and Refractivity Height Profiles in Troposphere, Czech Science Foundation, grant no. GA102/07/0955, 2007-2009

__Selected papers__

__Jicha, O. - Pechac, P. - Kvicera, V. - Grabner, M.: Estimation of the Radio Refractivity Gradient from Diffraction Loss Measurements, IEEE Transactions on Geoscience and Remote Sensing. 2013, vol. 51, no. 1, p. 12-18. DOI: 10.1109/TGRS.2012.2199995, ISSN 0196-289.__- Jicha, O. - Pechac, P. - Kvicera, V. - Grabner, M.: On the Uncertainty of Refractivity Height Profile Measurements, IEEE Antennas and Wireless Propagation Letters. 2011, vol. 10, p. 983-986. ISSN 1536-1225.
- Valtr, P. - Pechac, P. - Kvicera, V. - Grabner, M.: Estimation of the Refractivity Structure of the Lower Troposphere from Measurements on a Terrestrial Multiple-Receiver Radio Link, IEEE Transactions on Antennas and Propagation. 2011, vol. 59, no. 5, p. 1707-1715. ISSN 0018-926X.
- Valtr, P. - Pechac, P. - Kvicera, V. - Grabner, M.: A Terrestrial Multiple-Receiver Radio Link Experiment at 10.7 GHz - Comparisons of Results with Parabolic Equation Calculations. Radioengineering. 2010, vol. 19, no. 1, Part II, p. 117-121. ISSN 1210-2512.
- Valtr, P. - Pechac, P.: Domain Decomposition Algorithm for Complex Boundary Modeling using the Fourier Split-Step Parabolic Equation. IEEE Antennas and Wireless Propagation Letters. 2007, vol. 6, no. 1, p. 152-155. ISSN 1536-1225.
- Valtr, P. - Pechac, P.: The Influence of Horizontally Variable Refractive Index Height Profile on Radio Horizon Range. IEEE Antennas and Wireless Propagation Letters. 2005, vol. 4, no. 1, p. 489-491. ISSN 1536-1225.
- Valtr, P. - Pechac, P.: Tropospheric Refraction Modeling Using Ray-Tracing and Parabolic Equation. Radioengineering. 2005, vol. 14, no. 4, p. 98-104. ISSN 1210-2512.
- Valtr, P. - Pechac, P. - Kvicera, V. - Grabner, M.: A Radiowave Propagation Study In Urban Environment Using The Fourier Split-Step Parabolic Equation. In Proceeding of the 2nd European Conference on Antennas and Propagation, Edinburgh. The Institution of Engineering and Technology (IET), 2007, ISBN 978-0-86341-842-6.
- Valtr, P. - Pechac, P. - Kvicera, V. - Grabner, M.: Implementation Issues of the Matched Field Processing Method of Refractivity Structure Sounding. In Proceeding of the 2nd European Conference on Antennas and Propagation, Edinburgh. The Institution of Engineering and Technology (IET), 2007, ISBN 978-0-86341-842-6.
- Valtr, P. - Pechac, P.: Analytic Tropospheric Ray-tracing Model for Constant Refractivity Gradient Profiles. In Proceedings of The European Conference on Antennas and Propagation: EuCAP 2006. 2006, ISBN 92-9092-937-5.