Digital Maps of Atmospheric Refractivity and Atmospheric Ducts Based on a Meteorological Observation Datasets.

The propagation of electromagnetic waves in the troposphere is significantly influenced by atmospheric refractivity and atmospheric ducts. Thus, abundant statistics on atmospheric refractivity and ducts are essential for reliable propagation prediction. In this study, we develop novel digital maps of atmospheric refractivity and atmospheric ducts based on the processing of radiosonde observation (RAOB) data and surface observation (SUOB) data collected from 2005 to 2014, including wet term of surface refractivity, refractivity gradients, and atmospheric ducts. The new digital maps, referred to as RADIO maps are defined as RADIOS and RADIOS2 maps. The RADIOS maps, which are world maps of refractivity gradients and atmospheric ducts, are obtained from data collected at radiosonde stations at 892 sites. The RADIOS2 map, which is a world map of the wet term of surface refractivity, is obtained from data collected at radiosonde and surface stations at 3218 sites. To test the consistency between RADIO maps and ITU-R ERAI (International Telecommunication Union Recommendations employing ERA-Interim (European Centre for Medium-Range Weather Forecasts Re-Analysis-interim) reanalysis data for 36 years from 1979 to 2014) maps; a comparison is performed with the cumulative distributions of refractivity gradients at two radiosonde stations. The accuracy of RADIO maps is checked through comparisons with the maximum, mean, and standard deviation of the relative errors, which are obtained from observed values and predicted values, between RADIO maps and ITU-R ERAI maps. Our results show that: 1) RADIOS2 map is consistent with the current ITU-R ERAI map with respect to the wet term of surface refractivity; 2) $\Delta N_{65\,\mathrm {m}}$ (50) and $\beta $ obtained from RADIOS maps are larger than those obtained from ITU-R ERAI maps in low-latitude coastal and marine areas; and 3) comparisons between RADIOS and ITU-R radios_duct maps (i.e., the world digital maps obtained from a 20-year (1977–1996) dataset of 661 radiosonde stations released by ITU-R P.453-14) show that ITU-R radios_duct maps predict lower occurrences of surface and elevated ducts at low latitudes. Overall, this study demonstrated that the new maps based on observations over the past ten years provide more accurate and reliable information than other traditional maps in terms of atmospheric refractivity, refractivity gradients, and atmospheric ducts. [ABSTRACT FROM AUTHOR]