[¦riv·ər ən ¦här·bər ′ād tə ‚nav·ə′gā·shən ‚sis·təm] (navigation) An all-weather system for precision navigation in harbors and harbor entrances, which provides sufficient accuracy for vessels to proceed as if visual aids did not exist, with a 50-foot (15-meter) position radius accuracy requirement at a 95% confidence level. Abbreviated RIHANS.