Acoustic systems have driven detection, innovation and new generations of quieting technologies in the undersea warfare realm for decades
By Kris Osborn, President, Warrior
Acoustic systems have driven detection, innovation and new generations of quieting technologies in the undersea warfare realm for decades, as they have become more precise, better networked and longer range. In recent years, the US Navy has made great progress in developing certain kinds of emerging technologies capable of capturing higher resolution images and connecting manned submarines to drones and unmanned underwater vehicles.
Innovations in this area are a key part of why the US Navy has continued to operate with what many regard as undersea superiority, a tactical and strategic advantage too large and significant to calculate. Unlike surface ships or aircraft more easily detected by satellite surveillance, enemy radar and line-of-sight detection technologies, submarines can quietly and secretly lurk in high-threat areas to hold enemies at risk without being easily detected.
New Detection Threats
Sonar systems and acoustic detection will likely be here for decades into the future, yet there are a series of non-acoustic detection technologies which may be changing this equation.
A significant essay from the Navy Submarine League called “Non-Acoustic Means of Submarine Detection” analyzes a number of key non-acoustic detection measures which are improving rapidly and likely to be implemented by potential adversaries. One major area of exploration relates to detecting disturbances in the earth’s magnetic field, something devices can measure.
“As a large piece of ferrous metal, the steel-hulled submarine causes a local disturbance in the earth’s magnetic field,” the essay explains.
Significantly, the essay explains that if a submarine is built with “non-magnetic” materials its signature is decreased but not eliminated completely.
“Submarines contain a large amount of metal that becomes magnetized in the course of normal operations. The permanent magnetic field associated with the submarine remains until active measures are used to demagnetize it,” the Naval Submarine League essay essay explains.
The U.S. currently deploys two types of MAD equipment on its ASW aircraft. These systems can detect the submarine magnetic field at no more than a few thousand feet, the essay says.
Boundary layer water flow
There are “bioluminescent” organisms beneath the sea which generate a natural “light,” something which submarines can detect. This detection possibility is caused by “boundary layer” phenomenology, referring to the water flow surrounding a moving submarine. This water movement generated as the submarine transits the undersea realm, can generate movement of undersea organisms as well, including ones that generate detectable light.
“These organisms can generate light when they are physically stimulated in the boundary layer of a submarine or in its wake. This phenomenon has been studied as a method for detecting submarines from the air or space,” the essay explains.
Waves
Another method of non-acoustic detection pertains to somewhat self-evident or easily observable variables such as “submarine-generated waves on the surface of the Ocean.” When submarines are moving at shallow depths or traveling at high speeds, they of course generate detectable surface waves. However, these waves can be obscured or hidden by larger wind-generated surface waves.
There are also internal waves of great significance which generate surface signatures that are not visible to the human eye. Radar systems, however, can detect some of the changes in moving surface water generated by undersea oscillations and water movements caused by submarines. However, much like surface wind, there are many reasons why water can move beneath the surface, so there are also some limitations to this kind of detection method.
Also, not surprisingly, thermal sensors can detect small changes in the water temperature caused by submarine movements. In a manner somewhat similar to how an infrared sensor would detect a heat-signature emitting from an enemy fighter or engine vehicle, temperature-detecting technology can quickly discern differences likely to indicate the presence of a submarine.
“A moving submarine may also change the temperature of the sea surface by mixing lower cooler water with upper water, thereby leaving a trail of cool surface water that could be detected with infrared (heat) sensors,” the essay says.
Laser Detection
The Navy Submarine League essay further explains that “laser detection” may emerge as the most promising area of non-acoustic submarine detection. Overall, electromagnetic signals have little ability to travel underwater except in some “ultra-low-frequency” waveforms, yet the sea is “transparent” to blue-green light which electromagnetic light “pings” from a laser can detect.
“The sea is relatively transparent to blue-green light. A burst of blue-green laser light could penetrate the sea, reflect off an object, and return to the sensor. The round-trip travel time of the laser burst indicates the depth of the object, but cannot discriminate, for example, between a large whale and a submarine,” the essay says.
Since the speed of light is a known or fixed quantity, and the length of travel time can be determined, algorithms can then discern the exact distance of an object. Quite similar to a laser rangefinder on land, the time of travel can be determined. Once exact speed and time of travel are known, an algorithm can quickly calculate the distance. In these cases, a blue-green laser light might be able to “see” or “find” a submarine at certain depths.
Kris Osborn is the Military Technology Editor of 19FortyFive and President of Warrior Maven – Center for Military Modernization. Osborn previously served at the Pentagon as a highly qualified expert in the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Masters Degree in Comparative Literature from Columbia University.