In this paper a comparative study of three ground traffic surveillance systems for airports based on different sensing technologies is presented. The first two solutions are based on video-based surveillance, while the third one is based on signal-based surveillance. More specifically, the first solution employs a network of smart cameras, whereas the second utilizes multiple autonomous tracking units to capture and process images from one or more pre-calibrated cameras. The third solution is based on a novel magnetic sensing technology, which detects ferromagnetic objects such as vehicle motors, aircraft engines and landing gears through their deformation of the Earthpsilas magnetic field. Evaluation and analysis of the performance of these systems, based on real test results in different European airports are presented. The proposed systems are flexible, scalable and suitable for a broad field of monitoring and surveillance applications.