The increasing demand for fast and economical transportation systems and raid. Ways as one of the most important transportation modes. In addition due to technological advances new trains are increasingly fast. This fact requires an improvement to the construction as well as to maintenance operations of railway systems. Knowledge of applying geophysical sensor techniques on pavements was transferred to railways by taking advantage of the ability of ground penetrating radar to map substructure conditions on a conditions on a continuous non-destructive basis.The study examines pilot sections, which are integrated in the National Railway System of Greece and are representive of the Greek Raiways regarding structural and operational elements. For the present study a Ground Penetrating Radar (GPR) system as well as the Videocar of the National Techinical University of Athens have been used. The GPR system consist of an air-coupled 1 GHz frequency antenna and a gound coupled 400 MHz antenna. Data was acquired between concrete and wood ties as well from the ballast shoulders beyond the ends of the ties, using the two antennas with multiple antenna orientations and polarizations. Automatic processing of the data was developed to quickly generate hard copy sections of radar images. Substructure conditions were observed such as thickness of the ballast and sub ballast layers, variations in layer thickness along the track, pockets of water trapped in the ballast, and soft subgrades from high water content. In addition, locations and depths of subsurface drainage popers, trenches, and utilities were quickly and continuously mapped. In addition to in-situ measurements a Globali Positions System (GPS_ was used in order to record exact coordinates of the sections under study.