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Insights Current Events: 03 November 2014

Indian-built Scorpene to carry critical DRDO system

India’s defence establishment will be fully responsible for a DRDO-developed critical propulsion system that will go into the last two of the six Scorpene submarines being built under technology transfer at Mazagon Dock, Mumbai, say the original makers of the submarine.

The system, called air-independent propulsion (AIP), enhances the underwater endurance of conventional (diesel-electric) submarines. Without it, they are forced to surface to periscope depth to recharge their batteries — a position where they are most susceptible to detection — at more frequent intervals.

Scorpene-class submarine:

The Scorpène class submarines are a class of diesel-electric attack submarine jointly developed by the French DCN and the Spanish company Navantia and now by DCNS. It features diesel propulsion and an additional air-independent propulsion (AIP) system.

Air-independent propulsion:

Air-independent propulsion (AIP) is any technology which allows a non-nuclear submarine to operate without the need to access atmospheric oxygen (by surfacing or using a snorkel). AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels. The DCNS system, known as MESMA (Module d’Energie Sous-Marine Autonome), is based on the combustion of stored oxygen and ethanol to augment battery-powered propulsion.

Notably, a submarine is about stealth. It is a weapons platform not visible to the naked eye. AIP significantly improves stealth because it enables a submarine to generate electricity for services and battery charging and propulsion while completely submerged.

AIP systems are auxiliary, like a smaller hull inserted in the main body. They generate electricity, powering a submarine’s to operate and also generate oxygen, lighting and amenities for crew. Accordingly, they enable conventional diesel-electric submarines to remain submerged for two to three weeks at a time. Without AIP, diesel-electric submarines have to come up to snorkeling depths just below the surface or surface at shorter intervals so that the diesel engines can recharge their batteries. This significantly increases the risk of detection.

A submarine’s diesel engines can only be started once the snorkel has cleared the surface to take in oxygen in the fresh air. Snorkeling depth is about the same as periscope depth. AIP significantly improves stealth because it enables a submarine to generate electricity for services and battery charging and propulsion while completely submerged.

A benefit of this approach is that it can be retrofitted into existing submarine hulls by inserting an additional hull section. AIP does not normally provide the endurance or power to replace the atmospheric dependent propulsion, but allows it to remain submerged longer than a more conventionally propelled submarine. A typical conventional power plant will provide 3 megawatts maximum, and an AIP source around 10% of that. A nuclear submarine’s propulsion plant is usually much greater than 20 megawatts. Another advantage is that the Non-nuclear submarines running on battery power or AIP can be virtually silent.

Sources: The Hindu, Wiki.


Navies of friendly countries keen on Indian sonars

India is looking to export indigenously developed hull-mounted sonars and negotiations are at an advanced stage with the navies of three to four friendly nations.

SONAR (an acronym for Sound Navigation and Ranging) is used to detect underwater targets. Like radar, used to detect long-range aerial and other targets, sonars have applications in underwater surveillance, communication and marine navigation.

It is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves. There are two types of sonar—active and passive.

Active Sonar: Active sonar transducers emit an acoustic signal or pulse of sound into the water. If an object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer. If the transducer is equipped with the ability to receive signals, it measures the strength of the signal. By determining the time between the emission of the sound pulse and its reception, the transducer can determine the range and orientation of the object.

Passive Sonar: Passive sonar systems are used primarily to detect noise from marine objects (such as submarines or ships) and marine animals like whales. Unlike active sonar, passive sonar does not emit its own signal, which is an advantage for military vessels that do not want to be found or for scientific missions that concentrate on quietly “listening” to the ocean. Rather, it only detects sound waves coming towards it. Passive sonar cannot measure the range of an object unless it is used in conjunction with other passive listening devices. Multiple passive sonar devices may allow for triangulation of a sound source.

Modern naval warfare makes extensive use of both passive and active sonar from water-borne vessels, aircraft and fixed installations. Although active sonar was used by surface craft in World War II, submarines avoided the use of active sonar due to the potential for revealing their presence and position to enemy forces. However, the advent of modern signal-processing enabled the use of passive sonar as a primary means for search and detection operations.

Active sonar is used by submarines when if the tactical situation dictates it is more important to determine the position of a hostile submarine than conceal their own position. With surface ships it might be assumed that the threat is already tracking the ship with satellite data. Any vessel around the emitting sonar will detect the emission. Having heard the signal, it is easy to identify the sonar equipment used (usually with its frequency) and its position (with the sound wave’s energy). Active sonar is similar to radar in that, while it allows detection of targets at a certain range, it also enables the emitter to be detected at a far greater range, which is undesirable.

Passive sonar has several advantages. Most importantly, it is silent. If the target radiated noise level is high enough, it can have a greater range than active sonar, and allows the target to be identified. Since any motorized object makes some noise, it may in principle be detected, depending on the level of noise emitted and the ambient noise level in the area, as well as the technology used.

Passive sonar is stealthy and very useful. However, it requires high-tech electronic components and is costly. It is generally deployed on expensive ships in the form of arrays to enhance detection. Surface ships use it to good effect; it is even better used by submarines, and it is also used by airplanes and helicopters.

SONARs are also used in Anti-submarine warfare, Torpedoes, Mines, Aircraft, Underwater communications, Ocean surveillance and Underwater security. Civil applications of SONAR include Fisheries, Echo sounding, Net location, Vehicle location etc.

Scientific applications of SONAR include Biomass estimation, Wave measurement, Water velocity measurement, Bottom type assessment etc.

Effect on Marine Animals:

Research has shown that use of active sonar can lead to mass strandings marine mammals. Beaked whales, the most common casualty of the strandings, have been shown to be highly sensitive to mid-frequency active sonar. Other marine mammals such as the blue whale also flee away from the source of the sonar.

Some marine animals, such as whales and dolphins, use echolocation systems, sometimes called biosonar to locate predators and prey. It is conjectured that active sonar transmitters could confuse these animals and interfere with basic biological functions such as feeding and mating.

High intensity sonar sounds can create a small temporary shift in the hearing threshold of some fish.

Sources: The Hindu, Wiki.