SONAR and modern naval warfare

Gatineau in the snow

Arguably, submarines are the greatest threat to a modern carrier battle group. Aircraft can be detected at long range using over the horizon RADAR and picket ships. Subs generally need to be located using SONAR, though magnetic anomaly detection can sometimes locate them as well.

Warm surface waters are separated from the chilly bulk of the ocean by a layer called the themocline. The fact that this layer reflects sound makes SONAR based detection across it highly challenging: especially when the contact is something as quiet as a modern hunter-killer submarine. It is possible to use active sonar (the pinging thing from movies), but the sound produced by such systems reveals your position to others for a distance ten times greater than the effective detection range of the device. It also horribly damages the ears of whales, especially when used at crazy amplitudes like 250 decibels.

One way to deal with the thermocline problem while still using undetectable passive SONAR is to use a towed variable depth sonar array. For a ship, that would be pulled along beneath the thermocline. For a sub, it would probably be deployed above the layer. Another approach is to exploit convergence zones. Because of the nature of water under pressure, sound gets reflected off the ocean floor and back to the surface at intervals of 61 km. Sounds originating in one place can thus be best detected at points forming concentric circles.

Problems with SONAR are much worse in shallow waters, where high levels of noise from animals, waves, and tide noise make passive SONAR pretty useless. As such, modern navies avoid such waters as much as possible and behave as though they have already been detected by enemy forces whenever forced to operate within them.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

9 thoughts on “SONAR and modern naval warfare”

  1. You have certainly been shooting for diversity these last few days. What led to you investigating this?

  2. Litty,

    This comic basically explains it perfectly.

    It was something along the lines of: Coral Sea -> Cruiser -> Depth charge -> Submarine -> Naval warfare tactics -> Carrier Battle Group -> Carrier Battle Group Tactics.

  3. Ballistic Missile Submarines: The Only Way to Go

    April 24, 2007

    Russia and China are both in the process of fielding a new class of ballistic missile submarines. These submarines, longtime prudent investments for states with nuclear weapons, are becoming an essential — and ultimately, the only — option for a survivable nuclear deterrent.

  4. Missile technology
    Peril on the sea
    Naval warfare: As anti-ship missile and torpedo technologies improve, a new seaborne arms race could be on the horizon

    Jun 10th 2010

    THE West has some formidable missiles designed to sink warships. Three of the most deadly are America’s Harpoon, France’s Exocet and the Swedish RBS-15. These all fly close to the speed of sound for up to about 200km (124 miles) using precision-guidance systems to skim over land or water. This makes them difficult to detect. And even if they are spotted, the missiles can fly in unpredictable patterns, which makes it harder to shoot them down. They then punch a warhead, weighing as much as 200kg (440lbs), into a moving ship with devastating consequences.

    Despite all this, missile defences can be effective. Shooting at missiles with rapid-firing guns, or anti-missile missiles, can bring them down. The incoming missile’s electronics can also be scrambled with blasts of electromagnetic radiation, such as microwaves. And decoys can be fired to trick the missile’s homing sensors and lure it away from the vessel under attack. But missile attacks on ships are rare, so it is difficult to know just how safe a ship really is—especially if an attacker launches a dozen or so missiles at once.

    One particular anti-ship missile has become especially worrying for Western defence chiefs. This is because it is even more fearsome than anything NATO countries and their allies now use. The Russian-made missile is called the Club and it can carry bigger warheads farther than any anti-ship missile the West can launch.

  5. In oceanography, a sofar bomb (SOund Fixing And Ranging bomb), occasionally also referred to as a sofar disc, is a long-range position-fixing system that uses explosive sounds in the deep sound channel of the ocean to pinpoint the location of ships or crashed planes. This depth of water is ideal for the device, as the minimal speed of sound helps with the positioning calculations and improves the signal’s traveling ability. A position is determined from the differences in arrival times at receiving stations of known geographic locations. The useful range from the signal sources to the receiver can exceed 3,000 miles (4,800 km).

  6. What would happen if U.S. nuclear attack submarines—some of the most sophisticated and expensive American weapons of war—suddenly became obsolete? Imagine a scenario where these important systems became the hunted instead of the hunter, or just as technologically backward as the massive battleships of years past. Think that sounds completely insane? If advances in big data and new detection methods fuse with the anti-access/area denial (A2/AD) ambitions of nations like China and Russia, naval planners around the world might have to go back to the drawing board.

  7. ” Since the Cold War submarines, particularly quiet American ones, have been considered largely immune to adversary A2/AD capabilities. But the ability of submarines to hide through quieting alone will decrease as each successive decibel of noise reduction becomes more expensive and as new detection methods mature that rely on phenomena other than sounds emanating from a submarine. These techniques include lower frequency active sonar and non-acoustic methods that detect submarine wakes or (at short ranges) bounce laser or light-emitting diode (LED) light off a submarine hull. The physics behind most of these alternative techniques has been known for decades, but was not exploited because computer processors were too slow to run the detailed models needed to see small changes in the environment caused by a quiet submarine. Today, “big data” processing enables advanced navies to run sophisticated oceanographic models in real time to exploit these detection techniques. As they become more prevalent, they could make some coastal areas too hazardous for manned submarines.”

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