Sonar

noun (uncountable in generic use; countable for specific systems: 'a hull-mounted sonar')

/ˈsəʊnɑː/

An acronym for Sound Navigation and Ranging — a technique that uses the propagation and reflection of sound waves (acoustic signals) through water to detect, locate, classify, and track submerged objects such as submarines, underwater mines, and sea-floor features. Active sonar emits pulses and listens for echoes; passive sonar only listens for sounds emitted by targets. In UPSC/defence context, sonar is central to anti-submarine warfare (ASW) — a key capability gap India is addressing through P-8I Poseidon maritime patrol aircraft (12 ordered), the DRDO NACS (Nagin Hull-Mounted Active-cum-Passive Sonar for the Nilgiri-class frigates), and the Project 75I submarine programme's indigenous sonar systems.

✍️ Usage in a UPSC answer

The Indian Navy's Project 75I submarine programme mandates the integration of an indigenous advanced hull-mounted sonar system, developed by DRDO, reflecting India's strategic imperative to reduce acoustic-warfare dependence on foreign Original Equipment Manufacturers in a region where Chinese submarine deployments in the Indian Ocean have intensified.

Synonyms

acoustic detectionunderwater rangingecho ranginghydroacousticsactive acoustic system

Antonyms

radar (electromagneticnot acoustic)optical detectionvisual surveillance

🌱 Word Family

sonar (n), sonar array (n phrase), active sonar (n phrase), passive sonar (n phrase), hydrophone (n, component), acoustic (adj, related), SOSUS (Sound Surveillance System, acronym)

🔡 Root

Acronym: Sound Navigation And Ranging; sound from Latin sonus = sound; analogy with RADAR (Radio Detection And Ranging, coined 1940)

📜 Etymology

The acronym SONAR was coined in 1944 by the US Navy physicist Frederick Vinton Hunt, on the model of the earlier RADAR. Underwater acoustic detection itself (hydrophones) was developed during World War I (1914–18) by Allied navies to counter German U-boat submarine campaigns, with Paul Langevin's piezoelectric transducer (1917) as a foundational invention.

🧠 Memory Hook

SONAR = Sound Navigation And Ranging — the underwater cousin of RADAR (Radio Detection And Ranging). Both are acronyms; both detect by bouncing a wave off a target; but SONAR uses SOUND (which travels well in water) while RADAR uses RADIO waves (which don't penetrate water). Bats use biological sonar (echolocation) — the same physics at animal scale.

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