so·nar
noun/ˈsəʊnɑː(r)/
/ˈsəʊnɑːr/
[uncountable]- equipment or a system for finding objects underwater using sound waves
声呐（利用声波探测水下物体的装置或系统） Oxford Collocations DictionarySonar is used before these nouns:- signal
Word Origin1940s: from so(und) na(vigation and) r(anging), on the pattern of radar.