The Automatic Identification System (AIS) is a short-range coastal tracking system currently used on ships. It was developed to provide identification and positioning information to both vessels and shore stations. AIS transponders automatically broadcast information at regular intervals. Navigational status data is transmitted every 2 to 180 seconds, depending on a vessel's activity. In addition, voyage related data is broadcast every 6 minutes. These signals are received by AIS transponders installed on other ships or by land-based systems.