In this study, variations of soil radon concentration and parameters which most probably control these variations are measured in situ, in a temporal high-resolution fashion and for a necessarily long time period in order to determine correlations between the soil radon concentrations and possible controlling parameters. For this purpose, in total six monitoring stations from three sites (four stations in Gebze, one in Armutlu and one in Sarıköy) in Western Turkey were established. At these sites during the time period of 18 months from April 2008 to November 2010, eight different parameters (soil radon, soil temperature, soil moisture, air temperature, air pressure, precipitation, wind speed, wind direction) were recorded. Hereby, soil radon was measured every 15 min, and soil temperature, soil moisture, air temperature, air pressure, precipitation, wind speed and wind direction were recorded every 60 min. The time series of each measured parameter were then processed by Empirical Mode Decomposition (EMD) in order to obtain different frequency signals. Finally, correlation coefficients between these parameters were determined. This study shows that when multiple parameters are measured in situ, continuously and for a period longer than one year, results may provide better understanding of the behavior of soil radon. In particular, moisture and temperature of soil have to be measured and interpreted synchronously with soil radon gas concentrations. Thus, soil radon time series can more reliably used in earthquake forecast studies as well as indoor radon risk mitigation studies. [ABSTRACT FROM AUTHOR]