Kochi, India, — The Naval Physical and Oceanographic Laboratory (NPOL), a laboratory of the Defence Research and Development Organisation (DRDO), has issued a tender for 10 sets of VLH-1000 hydrophones, supporting India's efforts to develop indigenous underwater acoustic sensors for submarine detection and surveillance.
The tender, referenced as NPOL/27SOT108/LP, was issued on October 23, 2026. It seeks five sets of Type-I hydrophones with a diameter of 124 mm and five sets of Type-II sensors measuring 94.5 mm. Bids must be submitted by November 10, 2026, with technical bids scheduled to open on November 11. The contract value has not been disclosed.
Technical Details of VLH-1000 Hydrophones
Hydrophones function as underwater microphones, converting sound pressure into electrical signals to detect acoustic activity from ships, submarines, and other underwater sources.
The VLH-1000 sensors will incorporate NPOL-developed lead zirconate titanate (PZT) ceramics. The two sensor sizes are intended to cover a wider range of acoustic frequencies, supporting underwater sound detection.
The hydrophones will feature Grade-2 titanium housings, along with fibre-reinforced plastic (FRP) washers and mild steel moulds. These materials are intended to provide structural durability under high-pressure deep-sea conditions.
However, the exact operating depth, sensitivity levels, and pressure ratings of the sensors have not been disclosed in the available programme details.
Role in Indian Navy’s Anti-Submarine Warfare
The VLH-1000 hydrophones are passive Very Low Frequency (VLF) acoustic sensors designed to support underwater surveillance and the Indian Navy's Anti-Submarine Warfare (ASW) capabilities.
Unlike active sonar systems that transmit acoustic signals, passive hydrophones listen for sounds generated by underwater vessels. This allows them to monitor underwater activity without emitting signals that could reveal the sensor's location.
Acoustic detection can provide an indication of submarine activity, while additional processing and information from other sensors are required for accurate identification and tracking.
The procurement supports India's efforts to strengthen its domestic underwater surveillance capabilities and reduce reliance on imported components for critical naval sensor systems.
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