• Wednesday, September 18, 2019

So you want to detect a submarine?

Discussion in 'Naval Warfare' started by SvenSvensonov, Mar 4, 2015.

  1. SvenSvensonov

    SvenSvensonov PROFESSIONAL

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    Introduction


    Antisubmarine warfare, with the exception of fixed systems such as arrays of underwater hydrophones, is waged by various mobile antisubmarine craft: surface, airborne, and undersea. It is imperative that the officers and men of each type of antisubmarine force understand the characteristics, capabilities, and limitations of the other types. Only by such knowledge can they fully understand the basic concept of modern antisubmarine warfare - the integration and coordination of all forces available. Each type has certain advantages and disadvantages, and maximum effectiveness can be achieved only by coordinating all types. The basic characteristics of each force that should be evaluated are its inherent capabilities and limitations, detection methods, fire control systems, and weaponry.

    Magnetic Anomaly Detection (MAD)

    Another method of detecting a submerged submarine is through the use of MAD equipment, which uses the principle that metallic objects disturb the magnetic lines of force of the earth.

    Light, radar, or sound energy cannot pass from air into water and return to the air in any degree that is usable for airborne detection. The lines of force in a magnetic field are able to make this transition almost undisturbed, however, because magnetic lines of force pass through both water and air in similar manners. Consequently, a submarine beneath the ocean's surface, which causes a distortion or anomaly in the earth's magnetic field, can be detected from a position in the air above the submarine. The detection of this anomaly is the essential function of MAD equipment.

    ASQ-81 - often seen on Naval helos, like this SH-3H.
    Deployed_ASQ-81_magnetic_anomaly_detector_1983.JPEG

    758px-SH-3H_HS-8_with_MAD_deployed_1980.JPEG

    When a ship or submarine hull is being fabricated, it is subjected to heat (welding) and to impact (riveting). Ferrous metal contains groups of iron molecules called "domains." Each domain is a tiny magnet, and has its own magnetic field with a north and south pole. When the domains are not aligned along any axis, but point in different directions at random, there is a negligible magnetic pattern. However, if the metal is put into a constant magnetic field and its particles are agitated, as they would be by hammering or by heating, the domains tend to orient themselves so that their north poles point toward the south pole of the field, and their south poles point toward the north pole of the field. All the fields of the domains then have an additive effect, and a piece of ferrous metal so treated has a magnetic field of its own. Although the earth's magnetic field is not strong, a ship's hull contains so much steel that it acquires a significant and permanent magnetic field during construction. A ship's magnetic field has three main components: vertical, longitudinal, and athwartship, the sum total of which comprises the complete magnetic field, as shown in figure 9-3.

    The steel in a ship also has the effect of causing earth's lines of force (flux) to move out of their normal positions and be concentrated at the ship. This is called the "induced field," and varies with the heading of the ship.

    A ship's total magnetic field or "magnetic signature" at any point on the earth's surface is a combination of its permanent and induced magnetic fields. A ship's magnetic field may be reduced substantially by using degaussing coils, often in conjunction with the process of "deperming" (neutralizing the permanent magnetism of a ship); but for practical purposes it is not possible to eliminate such fields entirely.

    The lines comprising the earth's natural magnetic field do not always run straight north and south. If traced along a typical 200-kilometer path, the field twists at places to east or west and assumes different angles with the horizontal. Changes in the east-west direction are known as angles of variation, while the angle between the lines of force and the horizontal is known as the angle of dip. Short-trace variation and dip in the area of a large mass of ferrous material, although extremely minute, are measurable with a sensitive magnetometer.

    The function, then, of airborne MAD equipment is to detect the submarine-caused anomaly in the earth's magnetic field. Slant detection ranges are on the order of 500 meters from the sensor. The depth at which a submarine can be detected is a function both of the size of the submarine and how close the sensor is flown to the surface of the water.

    P-3C
    P-3C_MAD.jpg

    Improving MAD detection ranges have proved extremely difficult. Increasing the sensitivity of the MAD gear is technically feasible, but operationally, due to the nature of the magnetic anomaly, is not productive. The magnetic field of a source, such as a sub, falls off as the third power of the distance; hence an eight-fold sensitivity increase would serve merely to double the range. Additionally, magnetometers are non-directional; the physics of magnetic fields do not permit the building of instruments that would respond preferentially to a field coming from a particular direction. Hence, a valid submarine caused disturbance frequently is masked by spurious "noise". Also, the ocean floor in many areas contains magnetic ore bodies and similar formations of rock, which can confuse the signal. Further confusion comes through magnetic storms, which produce small but significant variations in the earth's field.

    MAD equipment is primarily used as a localization/targeting sensor by aircraft with optimum employment being by helicopters considering their smaller turn radius. Additionally, fixed-wing ASW aircraft MAD configurations are fixed in the tail boom, and helicopters tow the sensor on a 25 - 55 meter cable below and behind the aircraft, which reduces "noise" caused by the helicopter. Because of the relatively short detection ranges possible, MAD is not generally utilized as an initial detection sensor.

    Visual Sighting

    God save the queen, because USS Dallas sure wont!!!

    USS-Dallas.jpg


    Visual sighting is the oldest, yet the most positive, method of submarine detection. Even in this age of modern submarines, which have little recourse to the surface, the OOD and lookouts of any ship should always be alert for possible visual detection of a submarine. Aircraft, even those not normally assigned an antisubmarine mission, can use visual detection methods to particular advantage as a result of their height above the surface.

    Of particular note is the potential for periscope and periscope wake sighting, which in many tactical situations is a necessary precursor to an opposing submarine's targeting solution.

    Colombia_Submarine209_Mast.jpg

    Additionally, ASW forces need to be aware of the potential for night detection of bioluminescence; the light emitted from certain species of dinoflagellate plankton when disturbed by a moving submarine hull and its turbulent wake. This blue-green light, predominately in a 0.42 - 0.59 band, occurs in various water conditions and is most prevalent between 50 and 150 meters and where the water has steep temperature gradients. Visual detection in most cases requires a moon-less night and a relatively shallow target.

    Communications

    For many reasons it may be necessary for ships/aircraft and submerged submarines to communicate with each other. Of paramount importance is the safety of the submarine and its crew. During exercises the ship can advise the submarine when it is safe to surface. Should an emergency arise aboard the submarine, the ship can be so informed. Exercises can be started and stopped, or one in progress can be modified. Attack accuracy can be signaled by the submarine to the attacking ship. A number of devices exist which facilitate these communications. All incorporate either one or two way voice or tone/sound signal generation, utilizing sonar or sonobuoy type equipment.

    The range and quality of transmission varies with water conditions, local noise level, and reverberation effects. Under optimum sonar conditions, however, communication between ships should be possible at ranges out to 12,000 meters. Under the same conditions, submarines achieve a greater range. If the submarines are operating in a sound channel, the communication range may be many kilometers greater than that achieved by ships. Local noise, caused by ship's movement through the water, machinery, screws, etc., can reduce the range to less than half the normal range. Severe reverberation effects may also cause a significant reduction.

    There are ways to track electronic signals emanating from submarines. This is a cable tracker, a larger system would be used to find emissions-reduced subs.
    nr252mainphoto.gif

    Because of the characteristics of underwater sound transmission, the amount of data/information that can be communicated through sonic means is severely limited. The primary and most reliable means of communications between submarines and other forces/command structure is with various radio systems that range in frequency from ELF (extremely low frequency) to UHF satellite. The major disadvantage, however, is the requirement to be at or near periscope depth to facilitate use of various antennas during communication periods. Because of this it becomes apparent that during tactical operations, the only viable form of emergent communications to a submarine is through sonic signals/voice.

    Newer forms of communications will be even more resistant to eavesdropping, such as LED communications:

    140124093708-large.jpg

    Some literature on the subject:

    http://www.jacobsschool.ucsd.edu/news/news_drupal.sfe?dept=ECE&id=1471

    Sub-surface communication in the electro-optic spectrum has generated much research and development effort. Future systems may utilize laser communications allowing short duration, submerged exchanges.

    TACTICAL CONSIDERATIONS

    Systems Performance

    ASW is an extremely varied and multi-faceted warfare area. Every scenario has its own unique set of conditions, with many different types of sensors being utilized encompassing many varied equipment, personnel and expertise. An attempt to examine all the factors that influence success in ASW is beyond the scope of this text. However, the following discussion will focus on the performance factors centered around shipboard sonar systems.

    Sonar Performance Factors

    Table 9-1 is a summary of factors affecting sonar performance and an indication of who or what controls each factor. If the controlling items from the right side are grouped, tactical sonar performance might be considered to be represented by

    Tactical Sonar Performance = Sonar design + ship design +

    ship operation + sonar operation + target design + target

    operation + sonar condition + sonar operator training +

    tactical geometry + environment

    These controlling items may be further grouped as follows:

    1. Items not under the control of the ASW commander:

    own sonar design

    own-ship design

    target design

    target operations

    tactical geometry

    environment

    2. Items under the control of the ASW commander (ship and force respectively):

    own sonar conditions

    own sonar operator training

    own-ship operation

    own sonar operation

    3. Items the ASW commander can measure:

    environment

    sonar figure of merit

    Several of these factors have been discussed earlier, and some additional ones will now be covered.

    Environmental Problems

    As has been previously stated, the environment is variable, which contributes to the degree of difficulty of the ASW detection problem. As counter to its variability, the speed profile of the environment is measurable, but it is measurable to both the hunter and the hunted. The understanding and exploitation of that which is measured will probably determine the victor, or at the minimum, determine who holds the edge in detectability vs. counterdectability in the encounter. It is generally accepted that the advantage belongs to the one who gains the initial detection in the ASW encounter.

    Table 9-1. Factors Affecting Passive Sonar Tactical Performance

    Factor Controlled by

    Target Signature Target Design Characteristics

    Target Speed

    Target Machinery Quieting

    Noise Level

    Self-Noise Own-Ship Speed (Flow Noise)

    Own-Ship Machinery Noise Field

    Ambient Noise Environment (Sea State, Wind, Shipping

    Noise, Sea Life)

    Directivity Own Sonar Array Design

    Own Sonar Operating Condition

    Own Operator Training & Condition

    Detection Threshold Own Sonar Design

    Own Sonar Operating Condition

    Own Operator Training & Condition

    Transmission Loss Environment (Sound Paths Available,

    Bottom Loss, Layer Depth, Ocean Area)

    Attenuation Own Sonar Design (Frequency)

    Additional Factors Affecting Active Sonar Tactical Performance

    Source Level Own Sonar Design (Power Available)

    Target Strength Target Aspect

    Target Reflectivity

    Reverberation Environment (Sea Structure)

    Own Sonar (Source Level)

    Some of the measurable environmental factors that will affect own-ship detectability by the enemy and own-ship capability to detect him are listed below:

    sound paths available

    shallow water vs. deep water

    layer depth

    seasonal variation in area (wind, temperature, etc.)

    local transient phenomena (rain, afternoon effect, etc.)

    currents in area of operations

    Understanding of the sound paths available is paramount in assessing the counterdetectability situation. This is based on past marine geophysical survey data, correlated with current bathymetry (BT) or sound velocity profile (SVP) measurements. The direct sound path is readily determined from current BT or SVP measurements. The viability of the bottom-bounce sound path is determinable by survey data on bottom reflectivity and bottom ab-sorption loss. The existence of convergence zones is normally based on ocean depth and knowledge of prior surveys. In the ab-sence of prior surveys, ocean depth is an acceptable basis for pre-dicting the absence or presence of a convergence zone. However, even if sound paths prediction is in error, assuming the enemy has the capability to use the sound paths most advantageous to him is a sound tactical decision.

    With respect to detection in shallow water, it has already been indicated that sonar performance may be enhanced because the ocean bottom and surface boundaries act as a duct for the chan-neling of sound. Since no precise quantitative measure of the expected improvement is available, the ASW tactical commander could view the shallow water problem as one in which ambiguities may be created by him to mask the real composition and precise presence of his forces. One can even conceive of his active sonars being used in a bistatic mode, i.e., using one ship's sonar as an ensonifying source, and any other ship's sonar or sonobuoys being used as re-ceiving or detecting sensors. Bistatic geometry creates problems in establishing precise target location. On the other hand, an in-dication of target presence may tip the tactical balance, or at least provide the tactical commander with alternative courses of action, no matter how the target presence was established.

    The depth of the bottom of the surface layer of water is a great determinant of sonar performance from a hull-mounted surface-ship sonar because the target submarine may choose to proceed below the layer. As was dicussed earlier, cross-layer detection is u-sually limited in range because of the refraction or bending of the sound rays. Shallow layers favor the submarine because by going deep below the layer, he is frequently able to detect the surface ship's radiated noise when its active sonar transmission is trapped in the surface layer and/or refracted sharply downward. The tac-tical answer to this situation from the escort point of view is to vary the vertical angle of transmission of his sonar projector so as to penetrate the layer, or to deploy a variable-depth sensor be-low the layer.

    Predictions of seasonal variation in the area of operations, based on previous surveys and observations of wind action and temperature profile, are basic data for the operational planner. When the ASW force is in situ, the tactical commander should val-idate or verify the predictions by regular periodic measurements of the ocean temperature or sound-speed structure. The length of the period between measurements should be based on observations of cur-rent weather phenomena affecting sound propagation conditions, i.e., wind, time of day, etc. It is particularly important to be aware of the surface-heating effect of the sun and of the fact that in areas of little mixing of the sea by wind-driven waves, a pos-itive temperature gradient may be developed between mid-morning and mid-afternoon that could seriously degrade surface-ship sonar per-formance. Under these conditions, hourly measurements of the environment are in order. Similarly, when conducting operations in the vicinity of currents like the Gulf Stream or the Labrador Cur-rent, where "fingers" of water with marked differences in temper-ature to that of adjacent waters is common, the tactical commander should consider hourly measurements.

    Acoustic Emission Control Policy (EMCON)

    Acoustic counter detection of active sonars can be accomplished at ranges much greater than that of the active sonar. Therefore, it is safe to assume that an adversary cannot be surprised when active systems are used unless transmission, for purposes of final pre-cision target location, occurs immediately prior to weapon firing. At the same time, it is very important to limit other acoustic e-missions to limit an adversary's ability to detect, identify, and target friendly units by sophisticated passive methods. Acoustic emission control (acoustic EMCON) is a method of limiting emitted noises and of using them to create an ambiguous acoustic environ-ment, thus forcing an adversary to come to very close range to re-solve his fire control and identification problems prior to firing a weapon. Ships and submarines are designed with noise reduction as a primary consideration. Operating procedures can be modified to control acoustic emissions, including practices such as turn count masking (where a multi-engine ship would operate her main engines at different RPM to confuse an adversary as to its actual speed). Other methods might include the use of sprint and drift tactics to vary the composite radiated noise signal level generated within a group of ships. Acoustic Countermeasures are covered in more detail in.

    Sonar decoy
    antisonar-facing.png

    SUBMARINES AND ANTISUBMARINE WARFARE IN THE FUTURE

    No one can say just what warfare will be like in the future, but it can be conjectured clearly enough to show that submarines will have much to do with determining who has overall command of the sea.

    Due to the fact that the principals of sound propagation through the water remain physical constants, in some respects ASW of the future will resemble that of World War II. There will be great differences, however, primarily attributed to the vast improvements in submarine and shipboard quieting technologies. Figure ( ) provides a historical perspective on the relative improvements in source levels of U.S. and Russian submarines. It is clear passive sensing of modern submarines is becoming difficult at best. With no control over target source levels and very little control over ambient noise, it becomes incumbent on systems designers and operators to maximize passive detection thresholds and directivity indices, along with continual implementation of self noise level improvements.

    Continued emphasis will be placed on development of new sensor types and radical new concepts applied to current technologies. Some examples of innovation on the research and development forefront include:

    - Fiber optic towed array: allowing higher data rates, and longer, lighter cables

    - Satellite and aircraft based laser detection: Use of the electro-optic spectrum for ASW detection is receiving much attention. Implementation remains in the distant future, however.

    - Low frequency active towed arrays: With variable length and depth cables and longer range active sonar sources, the tactical disadvantage of active ASW revealing ownship position is reduced.

    SUMMARY

    Antisubmarine warfare is waged by surface, airborne, undersea, and shore-based forces, each with its own unique capabilities. Me-thods of detecting submarines include sonar, radar, electronic sup-port measures, and magnetic anomaly detection. Of these, sonar is the most widely used and is capable of the three basic functions of echo-ranging (active), listening (passive), and communications. The device in a sonar for acoustic to electrical (and vice versa) energy conversion is the transducer. Simple versions of transduc-ers, designed for listening only, are called hydrophones. Active sonar transducers fall into two basic types, searchlight and scan-ning, with the latter being the most useful for tactical detection. Other types of sonars include variable-depth sonar, high-resolution sonar, towed array sonar systems, sonobuoys, echo sounders, and communications systems. The phenomenon of doppler shift due to a moving target is useful for target classification. Tactical con-siderations in the employment of sonar are grouped into those that the ASW commander can control, those that he cannot, and those that he can measure. The concept of EMCON is as applicable to acoustic emissions as it is to radio and radar. The submarine is a formid-able adversary, and sonar remains the best method of detecting it.

    @Nihonjin1051 @Gabriel92 @AUSTERLITZ @jhungary @Slav Defence
     
    Last edited: Mar 5, 2015
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  2. WAJsal

    WAJsal MODERATOR

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    Great thread,thank's for the information,even though i did not understand some of the things.
     
  3. Gufi

    Gufi PDF THINK TANK: ANALYST

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    how will led communication be read? I is lost:ashamed:
     
  4. Indos

    Indos PDF THINK TANK: ANALYST

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    Did you the one who wrote this article @SvenSvensonov ..........?

    I will give you positive rating if you can confirm that ......... 8-)

    I will read this one later thoroughly, but my point that I want to give here is that detecting submarine is always a difficult effort, particularly if the contested area is a quite large area. Defending my country will become a very huge task. Thanks for this by the way.
     
  5. Manticore

    Manticore ADVISORS

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    stuck
     
  6. SvenSvensonov

    SvenSvensonov PROFESSIONAL

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    Cool!!! And thanks! I'll be updating the info from time-to-time.

    That's a new system, I can't give technical details on it, but I will say that it will work similar to Fiber-Optic cables, just at longer distances, and with computers decyphering the signals into readable text.

    SPAWAR, the organization I was assigned to, is responsible for tracking subs.

    However, here's a patent filing that describes two-way sub communications using LED.

    BACKGROUND OF THE INVENTION
    1. Field of the Invention

    The present invention relates to submarine laser communication (SLC) systems, and more particularly to secure two-way communication systems and techniques for providing high quality duplex communication in real time between an aircraft and a submerged submarine at operational depths and speeds.

    2. Description of the Prior Art

    From the time that the first submarine slipped beneath the ocean surface, there has been a need for two-way (duplex) communications with them. Since that first submarine, communication technologies have substantially improved basic submarine communications; however, for various reasons no one system has been completely satisfactory. Current methods of communication generally require the submarine either to surface or to send a probe to the surface, neither of which is very desirable. Such action potentially exposes the submarine to its adversary, it limits the submarine's overall maneuverability when in use, and it detracts from the submarine's mission. Because a submarine is most vulnerable when it attempts to communicate, the present solution when far from home is basically no communication at all.

    Of the present systems, one (known as an ELF system) uses an extremely-low frequency modulated carrier, and a second uses very-low frequency (VLF) carrier signals. The ELF system with transmitters in Wisconsin and Michigan uses the skin effect of the earth to send very high power signals to distant submarines at relatively shallow depths; however, the system is characterized by extremely low data rates (on the order of minutes per character), is unidirectional, is non-selective, and at present requires the submerged vessel to trail a long antenna wire to receive the signals. Its main advantage is that it is a completely covert system, (i.e; secure), and a submerged submarine can receive ELF signals to depths of several hundred feet whether in open water or under an ice pack. The VLF system, unlike the ELF system, has usable data rates for message traffic delivery, but a communicating submarine must be close to the surface (within 10 meters) to receive a transmission. If the high-power shore-based antenna is inoperable, a transmitting airplane must trail a long antenna wire (the TACAMO system) to communicate over a significant ocean area. A submarine's vulnerability is increased during the period of communication. Like the ELF system, the VLF system provides only one-way communications. This combined with their low message delivery rate makes them undesirable for tactical operations.

    Communication satellites have also been used (e.g. SSIXS) to provide a form of two-way communications with submarines. Such satellite systems overcome numerous shortcomings of the VLF and ELF systems, but suffer from the submarine's need to surface an antenna to communicate, which dictates that a submarine must be at least at periscope depth to communicate or float a buoy on the ocean surface. To minimize this period of vulnerability, a form of burst communication is utilized. Even with burst communication the potential for detection of the uplink remains high, and therefore, this technique does not offer truly covert operation. Other submarine communication systems use slot buoys having built-in UHF transmitters. The submarine releases the buoys underwater to float to the surface where a prerecorded message is then transmitted generally after a delay of many minutes. When the transmission is complete, the surface buoy self-destructs and sinks to the ocean bottom. As with the VLF and ELF systems, this method of communication is one-way and is often quite delayed to limit the exposure of the submarine. Both the releasable buoys and the satellite transmission suffer from the disadvantage of potentially revealing the approximate position of the submarine.

    None of the aforementioned communication techniques has any IFF (identify, friend or foe) capability when the submarine is at operational depths and speed, and all of the transmissions can be intercepted and/or Jammed by an adversary. The consequence of these limitations is that the submarine has limited utility for coordinated activities, and moreover, it must constantly be wary of being mistaken as an adversary by a member of its own naval group In effect, present submarine communication systems inhibit the submarine from simultaneously performing its mission and communicating with its own naval group, which results in limiting the tactical missions of submarines.

    Over the last 10 to 15 years various suggestions, studies and field experiments have been done to show the feasability of using lasers of suitable wavelengths to communicate between submarines and aircraft and/or satellites. Blue or blue-green lasers have been chosen because light transmission through water is best at or near 490 nm. Transmission falls off rapidly below 400 nm and above 550 nm. Although satellite-to-submarine communications has been suggested (e.g; see U.S. Pat. No. 4,764,982). such systems are currently impractical using existing technology.

    A tactical and covert two-way communications channel between an aircraft and a submarine operating at operational depths and speeds would provide: (1) very useful and timely information, for example, over-the horizon target information; (2) coordination of ASH maneuvers between an aircraft and a submarine; and (3) coordination of a surface fleet and submarines in a direct or associated direct support role. A covert communications system would preferably include an IFF capability so that a submarine could identify itself to a supporting aircraft without revealing its location to an enemy, and the aircraft could positively identify the fleet submarine and eliminate the confusion between a friendly asset and an adversary.

    This invention is directed to a practical laser communication system which overcomes these problems.

    A general object of the invention is to provide a secure laser communication system capability between submerged platforms, such as submarines and aircraft.

    Another object is the provision of a submarine communication system having a low probability of intercept and that does not inadvertently expose the location of the submarine.

    Another object is the provision of a submarine communication system that does not require the submarine to surface any antenna or otherwise reveal its location to surface ships or aircraft.

    Another object is the provision of a submarine communication system that is operational in all weather conditions.

    An additional object is the provision of such a communication system that is operational in full sunlight or at night.

    A further object of this invention is the provision of a communication system that will allow two-way communication with a submarine at operational depths and speeds.

    SUMMARY OF THE INVENTION
    In accordance with the teachings of the present invention, these and other objectives are achieved through a secure laser communication system providing two-way (duplex) communication between a submerged platform and an airborne platform travelling above the region of the submerged platform. Two transceivers, one in the submerged platform and one in the airborne platform, provide the transmit and receive functions. Each transceiver has a pulse-modulated (blue-green) laser transmitter and a corresponding optical receiver for receiving and demodulating the pulse position modulated (PPM) blue-green beam. The communication system has two modes of operation: an acquisition mode, during which the airborne platform searches for the location of the submerged submarine, and a communicating mode, during which duplex communication takes place between the airborne transceiver and the submerged transceiver. In the acquisition mode, the airborne transceiver transmits a downlink beam containing an IFF code and encoded supervisory data so that when the submarine transceiver receives the downlink beam it can verify the identity of the sender. The encoded supervisory data contains among other things path information for setting the output beam power from the submarine. The airborne transmitter has an optical scanner with variable beam divergence control to produce either a pushbroom beam or a spot beam. The pushbroom beam has an elongated elliptically-shaped cross-sectional pattern, whereas the spot beam is a narrower and circularly-symmetric beam which is deflected from side-to-side transverse to the direction of travel of the aircraft.

    In one embodiment of this invention, both receivers employ an atomic resonance filter (ARF) to separate the blue-green beam from any background light. When the downlink beam traverses an area within range of the submerged platform, its receiver detects the beam and converts the light pulses to equivalent electrical pulses. A signal processor in the receiver decodes the PPM pulses and verifies the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source. When verified the submerged laser transmits an uplink beam response at the same blue-green wavelength, but timed so that the light pulses are time interleaved with the downlink pulses. The uplink transmit power is carefully controlled to the minimum power level required by the airborne receiver to recover the uplink beam. The downlink supervisory data enable the underwater transmit controller to determine and adjust the desired minimum output beam power required. As soon as the airborne receiver verifies the IFF code in the uplink beam, the acquisition handshake is complete and the system switches to the communication mode. Messages are conveyed for the duration of time that the airborne platform receiver is within range of the uplink beam.

    From Patent US5038406 - Secure two-way submarine communication system - Google Patents





    Since this thread is on sub detection, i'll also offer ways to avoid detection. One of those is improved communications.


    RUN WIRED, RUN DEEP: SUBS MAY FINALLY GET ONLINE

    A NUCLEAR SUBMARINE in deep dive may be the last place on Earth where it’s impossible to get a phone call, a text message or the day’s dose of spam. But all that may soon be over, if a Lockheed-led program works out as planned.

    The subs glide quietly along the depths of the ocean for weeks at a time, isolated from communication with surface dwellers save arcane one-way messages delivered at very low bit rates by Extremely Low Frequency (3-3000 Hz) or Very Low Frequency transmissions (3000-30,000 Hz). In order for subs to respond, or if communication beyond slow alphanumerics is required, they must come up for air or stick an antenna above the water.

    “Most people think our submarines … can make phone calls whenever they want at a moment’s notice … but our subs do not have that luxury,” says Rod Reints, the man in charge of a Lockheed Martin-led program to bring submarine communications into the 21st century.

    At the center of Communications at Speed and Depth program is new technology that could enable stealth submarines to be as connected to the Defense Department’s Global Information Grid as any Navy ship. Within a few years, all U.S. Navy subs will be equipped with expendable high-tech communications buoys that will allow two-way real-time chat, data transfer and e-mail.

    It seems so much simpler than other attempts at connection with underwater vessels.

    Until a few years ago, mind-bogglingly large (as in 52 miles long) ELF and VLF antennas were the state-of-the-art in stealth submarine communication. At such low frequencies, the earth itself must be recruited to generate the signals, which is why subs can only receive, and not send them. The resulting antennas are tens of miles long and generate complaints from neighbors paranoid about possible electromagnetic health effects. There are only a handful of ELF transmitters in the entire world, two in the United States: one in Michigan and one in Wisconsin.

    Then, there’s the High Frequency Active Auroral Research Program, which tested out ways to use the upper atmosphere as an antenna replacement. The Alaskan array can excite the earth’s ionosphere with high-frequency radio waves, inducing it to emit the extremely low-frequency bands needed to covertly penetrate saltwater.

    Recent underwater-comm research has transitioned to higher frequency bands in more compact packages (compared to tens of miles, that’s not difficult). Qinetiq’s Seadeep will enable two-way communication with U.S. subs using airborne blue-green lasers. Raytheon’s Deep Siren is a program of expendable pager buoys that can relay messages from satellites to submarines acoustically, but it can only transmit one way.

    Comms at Speed and Depth will be the first two-way underwater communication system for submarines. The exact depth at which subs will be able to deploy the buoys is classified, but Reints asserts that the length of the buoy cables is “measured in miles, and it’s long enough to allow the submarine to launch at significant depth and continue at normal operational speeds during a mission.”

    Three buoys are in development by Lockheed Martin and two subcontractors, Ultra Electronics Ocean Systems and Erapsco. Two of them are tethered to the sub and communicate with it using fiber optic cable. One is equipped for communication with the Iridium satellite constellation, the other for UHF. The third is a freewheeling acoustic-to-RF buoy. It can be dropped out of an aircraft or even launched out of a sub’s trash shoot.

    The buoy batteries for the tethered systems last for up to 30 minutes. Once it loses power, the buoy scuttles itself. The untethered buoys are designed to be deployed for three days.

    Phone calls are technically possible with the new system. Reints says that although his team made an Iridium test call last April, “voice is not the intended purpose right now.”

    The first buoys are supposed to be delivered to the Navy for operational testing by January 2011.

    All of this underwater communicativeness might just take the thrill out of boomer movies. What kind of drama will stoke the next Crimson Tide if the captain and XO get crystal clear instructions from D.C. that they can verify real-time?

    From Run Wired, Run Deep: Subs May Finally Get Online | WIRED
     
    Last edited: Mar 4, 2015
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  7. SvenSvensonov

    SvenSvensonov PROFESSIONAL

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    LASER Detection

    Shooting laser beams at a submarine won't destroy it, but new technology being tested by the U.S. Navy could help find enemy subs.

    "Instead of dumping hardware (into the ocean) you could shoot a light pulse into the water and generate acoustic signals," said Ted Jones of the Naval Research Laboratory, who presented his results at a recent meeting of the Acoustical Society of America.

    "With this, you could do communications, acoustic navigation beacons or sonar."

    The Navy scientists induce sound waves with lasers using two distinct, but similar techniques. Both techniques employ machines to create pulsed green lasers.

    Both techniques penetrate the water anywhere from a few millimeters to about 66 feet deep. Once the laser reaches the desired depth, both techniques flash boil a tiny area of water, which expands to the size of a BB.

    The manner in which this reaction is created is what separates the two techniques. The first technique spreads energy over time. The second spreads energy over space.

    The first method blasts several different wavelengths of light. Each wavelength travels at a slightly different speed through air and water. When all of the wavelengths catch up with one another, the concentrated energy boils the water.

    The second methods shoots the same wavelength of light, but over a wide area. The water acts like a lens, focusing the laser beams onto one specific area, which then boils.

    The shock wave created by either method can travel several miles and can be used for several purposes. One would be for one-way communication with underwater vessels. Triggering pressure waves in a specific order could allow a plane to communicate with underwater vessels via basic Morse code, or, more likely, says Jones, with a complex, encoded pattern of pulses.

    Another use for laser-induced sound waves would be for mapping the ocean floor. When they hit a submerged object, the pressure waves bounce back. A nearby submarine or buoy could detect the pattern of those waves and create a map of the ocean floor, or the location of other submarines in the area.

    All of this could be possible with laser-triggered sonar, if it is ever used in the field. For now though, Jones' experiments are limited to the laboratory.

    Although Vogel thinks there are still several issues that would need to be resolved before the technique could be used in the field, "this may be a unique approach that could achieve something that you cannot achieve by other means."




    Remote Sensing Techniques: From an Australian Perspective @jhungary

    Australia is a unique nation facing a massive submarine presence without adequate countermeasures. Those from India, the US, China, Japan, even Russia often frequent the Australian waters and region. What is there recourse? Let's explore some remote sensing techniques.

    *Note, these are applicable to any nation, but the focus is on Australia due to it;s unique "friendship" with global submarines.

    Introduction:

    Conventional mission proven technologies for the detection of submerged vessels involve both acoustic and non-acoustic techniques. These techniques are highly effective in sector location of submerged vessels. However, their ability to conduct wide area surveillance (WAS) and provide regular reporting is limited. Submerged vessels may also be detectable using oceanographic remote sensing technologies. Elevated sensors on a Low Earth Orbit (LEO) satellite, or aboard an Uninhabited Aerial Vehicle (UAV), may provide improved capabilities to satisfy the spatial and temporal requirements of WAS. This article considers the potential application of oceanographic remote sensing techniques to the detection of submerged vessels.

    Acoustic techniques comprise active and passive sonar which requires the insertion of sensors into the water either to detect sound waves produced by the vessel’s propulsion systems (passive) or detect reflected sound waves emitted by the sensor system itself (active). Detected information is transmitted back to an air or seaborne platform where processing is carried out. Besides visual detection, the primary non-acoustic method is Magnetic Anomaly Detection (MAD). This technology is mature and is used by the RAN and the RAAF’s long-range maritime patrol aircraft.

    There are several emerging techniques in oceanographic remote sensing for detecting submerged vessels. These methods range from the direct detection of the vessel structure, to indirect detection through analysis of the effect the vessel has on the surrounding marine environment. Advances in technology, such as detector sensitivity, are now making the operational use of these techniques more feasible.

    Wide Area Surveillance:

    Conventional acoustic and non-acoustic detection techniques have limited application to wide area surveillance (WAS). A predominant reason is the limited range of the detection technique due to the nature of the physical phenomena being sensed. For example, MAD detects the local disturbance in the earth’s magnetic field caused by a concentrated ferromagnetic body (e.g. a vessel’s hull). However, given that magnetic field strength reduces with the cube of the distance, the range of such sensors is limited; current sensors are only effective out to a few thousand feet. Acoustic detection over a wide area requires the extensive deployment of sonar buoys or towed arrays and the data fusion of their responses to provide a surveillance picture.

    Another limitation of conventional techniques to WAS concerns revisit time, that is, the period between successive surveillance of the same area. The entire Royal Australian Navy (RAN) fleet would, at maximum effort, have difficulty maintaining adequate coverage over Northern Australia alone, with each vessel being required to cover about 300 km of coast each day. The minimum revisit time required to provide adequate warning of a vessel’s advance across our closest maritime approach is about five hours (around half a vessel’s transit time). Moreover, it takes around 25 days for a maritime patrol aircraft to provide repeated radar coverage of Australia’s area of direct military interest (ADMI). This estimate suggests that revisit times for acoustic coverage of the ADMI would be significant.

    Elevated sensors in LEO, or on high-altitude UAVs, may provide an opportunity to satisfy the spatial and temporal requirements of WAS. While platform issues are of interest, this article will focus on the merits of the sensing techniques. Contributing factors include advances in minimising submarine signatures making passive acoustic detection increasingly difficult.

    Environmental Characteristics:

    There are two methods by which a submerged vessel could be located: direct and indirect detection. Direct detection involves locating the vessel structure itself; the indirect method involves the detection of environmental anomalies caused by the presence of a submerged vessel.

    Direct Detection
    Submerged vessels may be directly detectable by observing how a hull absorbs or reflects blue-green laser light (450-550 nm). This response could be used to create an image with the vessel appearing as either a bright spot in the normal background scattering of the ocean, or as a hole.

    Indirect Detection
    All other methods of detection are by indirect means. These are classified into: physical surface effects, optical effects and thermal effects.

    Physical Surface Effects
    The major physical surface characteristic is the wake developed by a vessel when it is mobile. The characteristics of the wake will be a function of the speed, depth and size of the vessel. Three separate hydrodynamic phenomena are either directly or indirectly caused by the wake: the Benoulli hump, Kelvin waves, and the surface effect of internal waves.

    The Benoulli Hump. If a submarine travels at high speed near the surface of the ocean it produces a characteristic hump of water which is sometimes referred to as the Benoulli hump. The size of the Benoulli hump decreases rapidly with submarine speed and depth. For example, the height of the hump reduces from about six centimetres to one millimetre when a given submarine reduces it’s speed and increases it’s depth from 20 knots and 50 metres to five knots and 100 metres, respectively.

    Kelvin Waves. Kelvin waves are produced by both ships and submarines and are responsible for the characteristic “V” shaped wake that can be seen to linger behind a moving vessel. They have an angle of approximately 39º which is independent of the size of the vessel or the speed at which it is travelling. Kelvin waves, like the Benoulli hump, reduce rapidly in size with submarine speed and depth. Using the above example, the wave size reduces from about two centimetres to immeasurably small.

    Internal Waves. Internal waves are periodic variations in the temperature and density of water at depths near a thermocline, an ocean layer in which the temperature drops and the density rises sharply with increasing depth. The period of internal waves, known as the Brunt-Vaisala period, varies with time and location but is typically between 10 and 100 minutes. The displacement of water associated with internal waves is influenced by many factors, including atmospheric pressure variations, ocean currents, and the presence of a submarine. In addition, internal waves are often formed in areas where the ocean bottom is irregular and the tidal range is large. Internal waves are rendered visible on the surface because the internal currents generated modulate the small scale surface waves overlying the internal waves, which leads to periodic variations in surface roughness.

    In the case of Benoulli humps and Kelvin waves it is clear that reasonable precautions could be taken to avoid detection by limiting speed and remaining at sufficient depth. However, this is not the case with internal waves which seems to be the most promising physical effect to exploit for the detection of submerged vehicles over a wide area.

    Optical Effects

    The oceans are populated with organisms that either emit light when they are disturbed (known as bioluminescence), or scatter light under all conditions. Such effects may be detectable above the ocean surface and may be used to reveal the location of subsurface vessels.

    Bioluminescence. The turbulent wake of a moving submarine will naturally cause a local disturbance of the surrounding bioluminescent organism population inducing them to emit light. The blue-green component of this light will propagate the greatest distance and may well be detectable beyond the ocean’s surface. The intensity of blue-green light is attenuated by a maximum factor of approximately two for every seven meters it travels through water. At this rate, light passing upward through 50m of water will be attenuated by about 21dB; through 200m of water the attenuation would be around 86dB. It may be possible that a turbulent wake could rise to the surface bringing the bioluminescence with it, however it is more likely that the wake would collapse behind the submarine due to suppression by distinct ocean layers. Another possibility is that the emission of light by excited organisms at one depth may induce other organisms closer to the surface to emit light. While it has been reported that relays of such empathic responses have been observed, what is

    not known is whether such a mechanism could reveal the location of a submarine. Furthermore, there appears to be very little knowledge at this time regarding the geographic, seasonal and depth distributions of such organisms. One major limitation for the detection of bioluminescence is the overpowering background noise contributed by the sun and the moon which would render a detection system useless during the day-time and possibly also under certain night-time conditions.

    Light Scatterers. There are layers of organisms in the ocean which scatter light. The motion of these layers caused by vessel generated internal waves may be detectable. However, again the geographic, seasonal and depth distributions of such organisms is not well known.

    Thermal Effects

    All active submerged vessels generate heat which is dissipated through the seawater (conventional and nuclear submarines), as well as through the atmosphere (conventional submarines).

    Thermal Transfer to Surrounding Seawater. Conventional and nuclear submarines draw in substantial quantities of seawater specifically for the purpose of cooling. In the case of a nuclear submarine producing about 190 MW of useful power, about 188 MW of heat energy is released into the ocean. While this appears to be massive, heat transfer calculations reveal that at a speed of about five knots, the temperature immediately behind the submarine only rises by about 0.2 degrees Celsius. This temperature differential will diminish rapidly as the submarine moves further away. In addition, this slightly warmer water, as it rises to the surface could, depending on the depth it was generated, eventually encounter water of the same density at which point it will rise no further and therefore not be detectable on the surface.

    Thermal Transfer to the Atmosphere. Unlike nuclear submarines, diesel powered conventional submarines need to surface periodically in order to recharge their batteries. This process, known as snorting, requires two pipes to be raised near or above the surface. The first pipe, raised above the surface, is used to draw in fresh air to run the diesels. The second pipe is usually kept just below the surface and allows exhaust gases (and, therefore, heat) to escape. The heat emitted through the exhaust gases of a conventional submarine may be detectable above the normal sea temperature. The major limitation with this method of detection is that a conventional submarine in normal operation only needs to snort for about two hours in every 24.

    Detection Techniques:

    Direct Detection

    The ability of Laser radar, or LIDAR (LIght Detection And Ranging), to penetrate the water’s surface, reflect from an object and then be detected remotely, makes this sensor a potential candidate for the detection of submarines. However, this technique is limited by the inability of LIDAR to penetrate clouds and other high attenuation effects caused by fog, haze and atmospheric pollutants15. Despite these limitations, it is reported that the Swedish have used this technique to detect submarines in national waters from an airborne platform16, although the effectiveness of this system is not known. In addition, the US Defense Advanced Research Projects Agency (DARPA) has developed and tested an airborne LIDAR system for the purpose of detecting mines at sea17. The system, known as the Airborne Laser Radar Mine Sensor (ALARMS), uses a pulsed blue-green laser operating at 510 nm. Trials of the system showed that the laser shadow cast by the object under inspection produced the best results at depths of up to 200m. An Australian application of LIDAR, the Laser Airborne Depth Sounder (LADS), uses the time difference between surface (blue) and the sub-surface (green) reflections of a 532 nm (yellow-green) laser, for sub-surface laser ranging.

    To improve the accuracy of depth soundings using lasers, an understanding of effects such as turbidity (absorption and scattering) of the water is required. A number of techniques using low frequency electromagnetic pulses (Electromagnetic Bathymetry), used for airborne prospecting for mineral deposits, has the potential to measure subsurface targets with no restriction due to turbidity. However, with all such measurements, some false targets are likely to be observed due to returns from other submerged objects such as whales.

    Indirect Detection

    Physical Surface Effects

    The physical surface effects caused by a submerged vessel may be detectable either by accurate measurement of the ocean surface height or by imaging the ocean’s surface. LIDAR is well suited for precision measurement18 and may be suitable for the detection of the Benoulli hump or Kelvin waves. However, the effectiveness of this technique will be severely limited by the depth and speed of a submarine. Synthetic Aperture Radar (SAR) is well known for its ability to monitor wave patterns and determine sea surface roughness19, and has been shown to successfully detect internal waves.

    Recent developments in Laser Doppler Velocimetry, a mature technology, may now permit the remote measurement of fluid parcel velocities in the ocean using the Doppler shift of a laser beam. However, a number of artefacts such as the effects of waves, and turbulence in the ocean, will also cause a

    Doppler shift of the laser beam. Preliminary studies suggest that these artefacts can be eliminated, but further studies of the phenomenology and signal processing are needed to confirm the feasibility of the technique. The military application of this technology includes the detection of the propeller wakes, and possibly internal waves.

    The Seasat satellite launched in 1978 effectively imaged ocean surface features such as internal waves and ship wakes using SAR20.

    Subsequent reports of a coastal region. Claim that Russian scientists have demonstrated a way of detecting submerged submarines using microwaves reflected from internal wave generated surface effects21. These claims were further investigated in July 1992 by an unclassified joint US/Russian experiment which clearly detected waves beneath the surface, although no submarines were used in the experiment22. The experiment made use of, among other things, SAR imagery from the ERS-1 satellite which was complimented by in situ and other remotely sensed data.

    Optical Effects
    The successful detection of bioluminescence will require visible spectrum radiometers with sufficient spatial and radiometric resolution to enable the low level of emitted light penetrating the surface to be detected. One major limitation of this technique, however, is that it is limited, at the best, to use at night. Further investigation is needed to determine resolution requirements. The scattering of sunlight (or moonlight) from the movement of marine organisms or surface effects caused by internal waves has been observed using ship-borne optical sensors23 and may be possible using elevated sensors.

    Thermal Effects
    Passive. Methods for remotely detecting localised increases in water temperature include the measurement of thermal infra-red and microwave radiation. The localised intensity of this radiation is highly dependent on submarine depth and speed. As previously discussed, the temperature increase due to the presence of even a large nuclear submarine is very small and would only provide a weak surface signature. However, the snorting of conventional submarines may be detectable as a localised point source on the ocean surface. Landsat 5 carries IR sensors with an instantaneous field of view of 120m x 120m24 and some sensors have a 0.1ºC thermal precision capability25. Even at such resolutions it is unlikely that the average temperature rise over a 120m x 120m area would be detectable.

    Active. Water, when irradiated with a laser beam, exhibits strong Raman scattering; the ratio of energies in the two strongest scattered lines is temperature dependent. Even though passive detection may be minimal, preliminary estimates indicate that a system based on LADS should have the capability to measure temperatures to an accuracy of at least 0.1ºC to a depth of 50m in moderately clear water, with a depth resolution of about 1m.

    Conclusion

    Conventional detection of submerged vessels has involved both acoustic and non-acoustic techniques. Several contemporary oceanographic remote sensing techniques, ranging from direct detection of the vessel structure using laser light, to indirect detection using analysis of the effect the vessel has on the surrounding marine environment, have potential for application in this area.

    The direct detection of submerged vessels using blue-green laser light appears to have merit based on airborne applications by the Swedish. US defence researchers have also successfully used this technique to detect underwater mines. Such successes indicate there is merit in investigating the feasibility of a space-based submarine detection systems based on LIDAR.

    Submerged vessels also generate a diverse range of indirect effects on the surrounding marine environment; these are categorised as physical, optical and thermal effects. While such effects are highly variable, being dependent on submarine type and operational parameters, they do provide potential means of detecting submerged vessels using both airborne and elevated sensors.

    Physical effects range from the production of a wake which may be detectable on the surface, to the generation of internal waves which manifest themselves through subtle surface effects. Of the physical effects, detection of internal waves is probably the most realistic approach; detection of Kelvin waves and the Benoulli hump is severely limited by submarine depth and speed. Indeed the detection of internal waves using SAR is an area where the majority of research seems to have focussed.

    Optical effects range from the stimulation of marine micro-organisms to emit light (bioluminescence), to the scattering of light by the movement of organisms in an internal wave. The scattering of light from the surface effects of internal waves is perhaps the most promising detection phenomena of the optical effects. While this technique has been experimentally verified, it is probably only feasible during the day or in the presence of sufficient moonlight. The potential for detection of a submerged vessel via its bioluminescent wake requires more research to determine if this is even feasible. This technique will require highly sensitive electro-optical sensors to detect the relatively low levels of light produced. Furthermore, its restriction to night-time use makes its use impractical as a singular surveillance sensing technique.

    The most significant thermal effects are caused through the heat sinking of nuclear submarines and the snorting of conventional submarines. A nuclear submarine’s cooling water thermal discharge appears unlikely to be detectable unless the submarine is stationary and also at, or near, the surface; the most likely scenario is when the vessel is in port. The detection of a conventional submarine snorting may be more feasible, although the opportunities to observe this procedure are infrequent (two hours in 24) and not practical for some approaches to the Australian coast. Preliminary estimates indicate that an active system based on LADS should have the capability to measure thermal changes.

    The detection of submerged vessels continues to be an area of active research interest, for both military and civilian applications. While current mission proven methods use acoustic and non-acoustic techniques, advances in a range of technologies are continuing to make optoelectronic techniques more feasible. Several airborne platforms have demonstrated the viability of a number of these sensors. Their development into elevated sensors may provide an opportunity to satisfy demanding WAS and revisit time requirements.

    Sources:

    ACRES Data Sheet on Mapper Products and Processing Options, August 1989.

    Babbage, R., A Coast Too Long: Defending Australia Beyond the 1990s, Allen and Unwin, Sydney 1990.

    Beardsley, T., Making Waves, Scientific American, February 1993.

    Gale, Squadron Leader W., The Potential of Satellites for Wide Area Surveillance of Australia, Air Power Studies Centre, RAAF Fairbairn, 1991.

    Gasparovic, R.F., Etkin, V.S., An overview of the Joint US/Russia Internal Wave Remote Sensing Experiment, IGARSS ‘94.

    Hill, J.R., Anti-Submarine Warfare, Ian Allan Ltd, 1984.

    Marriott, J., Submarine: the Capital Ship of Today, Ian Allan Ltd, 1986.

    Naval Mine Warfare, Sonars: Still a Bright Future, International Defense Review Supplement, November 1989.

    Report of the SCOR Working Group, Opportunities and Problems in Satellite Measurements of the Sea, Unesco Technical Papers in Marine Science - 46 1986.

    Scully-Power, P. and Stevenson, R.E., Swallowing the Transparency Pill, Proceedings/December 1987.

    Skolnik, M.I., Introduction to Radar Systems, McGraw-Hill, 2nd Edition 1980.

    Stefanik, T., The Nonacoustic Detection of Submarines, Scientific American, March 1988.

    Titov, V.I., Investigation of variations of Long Surface Wave Parameters by Optical Techniques During JUSREX 1992, IGARSS ‘94.
     
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  8. AUSTERLITZ

    AUSTERLITZ SENIOR MEMBER

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    Truly brilliant,its alot to take in,but brilliant for the layman as a basic idea.
     
  9. The SC

    The SC ELITE MEMBER

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    The US had "seemingly" some thousands of ocean floar sensors all over the world to detect the former USSR subs...
    But lately one Akula sub went missing and undetected near the US shores!?
     
  10. wiseone2

    wiseone2 BANNED

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    Does Magnetic Anomaly Detection pick up submarines made with titanium hulls ?
     
  11. SvenSvensonov

    SvenSvensonov PROFESSIONAL

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    Yes:

    There is some misunderstanding of the mechanism of detection of submarines in water using the MAD boom system. Magnetic moment displacement is ostensibly the main disturbance, yet submarines are detectable even when oriented parallel to the Earth's magnetic field, despite construction with non-ferromagnetic hulls. For example, the Soviet-Russian Alfa class submarine, whose hull is constructed out of titanium to give dramatic submerged performance and protection from detection by MAD sensors, is still detectable.

    This is due in part to the fact that even submarines with titanium hull will still have a substantial content of ferromagnetic materials as the nuclear reactor, steam turbines, auxiliary diesel engines and numerous other systems manufactured from steel and nickel alloys.

    Since titanium structures are detectable, MAD sensors do not directly detect deviations in the earth's magnetic field. Instead, they may be described as long-range electric and electromagnetic field detector arrays of great sensitivity.

    An electric field is set up in conductors experiencing a variation in physical environmental conditions, providing that they are contiguous and possess sufficient mass. Particularly in submarine hulls, there is a measurable temperature difference between the bottom and top of the hull producing a related salinity difference, as salinity is affected by temperature of water. The difference in salinity creates an electric potential across the hull. An electric current then flows through the hull, between the laminae of sea-water separated by depth and temperature. The resulting dynamic electric field produces an electromagnetic field of its own, and thus even a titanium hull will be detectable on a MAD scope, as will a surface ship for the same reason.
     
    Last edited: May 6, 2015
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  12. Donatello

    Donatello PDF THINK TANK: ANALYST

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    I am sure there must be some sort of counter measure Magnetic based device that Submarine can use to confuse the MAD....like flares for IR, Sound for torpedoes and Chaffs for radar guided missiles.
     
  13. SvenSvensonov

    SvenSvensonov PROFESSIONAL

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    You can put a lot of countermeasures on a submarine. From rubber

    [​IMG]

    or sonar-decoys

    [​IMG]

    to fool sound detection, to ECM protocols and emissions reduction methods to prevent electronic eavesdropping, to the use of low-frequency sounds to communication and evade listening systems and the black coloration of a submarine's outer surface to limit visual detection... some submarines even carry anti-aircraft missiles to defeat helicopters.

    [​IMG]

    Perhaps MAD detection evasion exists too in the form of an expendable countermeasure:partay:? An expendable countermeasure that creates a higher EM signature to mask a submarine's. Who can say?

    However, real-world repeatable methods already do exist. False positives are a daily occurrence for sub-detection crews due to organic and non-organic, non-manmade sources of interference. Ore deposits, animals, underwater volcanoes (anything significantly large and capable of producing an EM field, one that can disrupt/distort Earth's EM field), plenty of things that can fool MAD detection and produce false positives that MAD crews must account for and investigate. A skilled submariner will come to know where natural emissions occur and can use these to prevent MAD detection.

    Unfortunately for the sub crew, remote sensing from non-MAD methods is advanced enough to track subs without measuring their magnetic signature.
     
    Last edited: May 7, 2015
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  14. Fenrir

    Fenrir FULL MEMBER

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    BAE Systems to develop MAD ASW drone to help Navy P-8A find submarines from high altitudes

    BAE Systems to develop MAD ASW drone to help Navy P-8A find submarines from high altitudes
    [​IMG]

    ARLINGTON, Va., 14 Jan. 2015. Anti-submarine warfare (ASW) experts at BAE Systems are developing an unmanned aerial vehicle (UAV) sensor payload able to look for submerged enemy submarines by detecting small variations in the Earth's magnetic field.

    Officials of the U.S. Office of Naval Research (ONR) in Arlington, Va., announced an $8.9 million contract this week to the BAE Systems Electronic Systems segment in Merrimack, N.H., for the High Altitude ASW (HAASW) Unmanned Targeting Air System (UTAS) program for the Navy Boeing P-8A Poseidon maritime patrol jet.

    HAASW UTAS seeks to integrate a magnetic anomaly detector (MAD) and algorithms for use on an air-launched drone that the P-8A will use to detect and pinpoint enemy submarines.

    A MAD instrument detects minute variations in the Earth's magnetic field. A submerged submarine represents a mass of ferromagnetic material that creates a detectable disturbance in the Earth's magnetic field.

    The Navy's predecessor to the P-8A -- the Lockheed Martin P-3 Orion four-engine turboprop aircraft -- has a MAD sensor attached to the back that looks like a large stinger that protrudes backward from the plane's tail.

    The P-8A -- a maritime patrol version of the Boeing 737-800 single-aisle passenger jet -- was designed without the built-in MAD instrument largely because the P-8 is designed to operate primarily at high altitudes. The MAD sensor works best at low altitudes.

    To compensate for the lack of a built-in MAD instrument, the P-8 will use an unmanned drone equipped with the HAASW UTAS MAD sensor and algorithms.

    Although the P-8A is capable of low-altitude operations, it is designed primarily for use at relatively high altitudes to enable the aircraft to keep watch over large ocean areas and fly as fuel-efficiently as possible.

    The plane is being designed not only with the HAASW UTAS to enable the aircraft to use a MAD instrument from high altitudes, but also with sonobuoys designed to launch from high altitudes and cover large areas of the ocean.

    The P-8A also is being equipped with a flying torpedo called the High Altitude Anti-Submarine Warfare Weapon Capability (HAAWC) Air Launch Accessory (ALA) that can be released from altitudes as high as 30,000 feet.

    [​IMG]

    These high-altitude torpedoes are Navy Mark 54 lightweight torpedoes with add-n kits that enable the weapons to glide through the air to attack enemy submarines from long ranges and high altitudes.

    Fixed-wing aircraft like the P-3 normally release conventional torpedoes from very low altitudes or with small parachutes to ease the torpedoes into the water gently.

    The HAAWC ALA turns the Raytheon Mark 54 torpedo into a glide weapon. As the flying torpedo reaches the water, it jettisons wings and other air-control surfaces and takes on its original role as a smart torpedo that can detect, track, and attack enemy submarines autonomously.

    [​IMG]

    The P-8A also is being designed to work together with the Northrop Grumman RQ-4N Triton Broad Area Maritime Surveillance (BAMS) large UAV -- a maritime-patrol version of the Global Hawk long-range surveillance UAV.

    One or more Triton UAVs can detect and track hostile submarines from high or low altitudes, and the P-8A can look for submerged submarines and launch torpedo attacks from high altitudes. The MAD instrument-equipped HAAWC ALA drone will add to the new P-8A's ASW capabilities.
     
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  15. Fenrir

    Fenrir FULL MEMBER

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    HAAWC

    *This relates to the above post

    [​IMG]

    Features HAAWC
    • Starting from a great height and distance from a non-hazardous
    • Highest accuracy afforded by GPS and inertial navigation system
    • Increases the survival of the aircraft and crew
    • Low cost
    • High-precision delivery

    Properties
    • dimensions allow placement in the inner compartment of aircraft P-8A and P-3C
    • Dimensions: length 2900 mm, width 558 mm, height 533 mm
    • Minimizes temperature effects on the Mk54 and Mk46 torpedoes
    • Uses everyday suspension on the P-3
    • Uses ordinary torpedo Mk54 and Mk46
     
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