Marine radar interrogator-transponder target detection, identification,

Abstract

A marine radar interrogator-transponder navigation and collision avoidance system provides facilities for early detection of, identification of, and communication with cooperating marine vessels. For these purposes, a general coded call may be transmitted by own ship to all other ships in radio range, the reply then being returned from each answering ship with the coded identification of that ship. In this manner, the other ships may be identified. Own ship may call a specific second ship or a shore based transponder, the called transponder returning only the coded message it received. Own ship may call a specific second ship causing an alarm to call the ship's operator to a radio telephone, the identical coded message being reradiated. The invention provides means for application in cooperative systems using a finite number of such discrete interrogator-transponder addresses for receiving proper replies from responding transponders lying on a radial line with respect to own ship so that the replies are not destroyed by overlap. Other problems are solved related to the use of a finite number of addresses which may be less than the expected population of addressed ships, rendering it possible that two or more transponders will reply with the same address codes.