For land transport environment and railways in particular, the main limits of GNSS signal exploitations for an accurate and safe positioning comes from the local environment surrounding the vehicle. Obstacles induce multipath and non-line of sight signal reception that need to be detected for railway line characterization or feared event mitigation. In this paper, we show that the use of two techniques based on CN0 and camera respectively, can help to detect and label faulty events along a trajectory. The methods have been applied on a test run performed during the ERSAT GGC project in Spain. This paper presents first the techniques, then an analysis of the detections for evaluation.