Geophysical MASINT Geophysical MASINT is a branch of Measurement and Signature Intelligence ( MASINT ) that involves phenomena transmitted through the earth ( ground , water , atmosphere ) and manmade structures including emitted or reflected sounds , pressure waves , vibrations , and magnetic field or ionosphere disturbances . According to the United States Department of Defense , MASINT is technically derived intelligence ( excluding traditional imagery IMINT and signals intelligence SIGINT ) that – when collected , processed , and analyzed by dedicated MASINT systems – results in intelligence that detects , tracks , identifies , or describes the signatures ( distinctive characteristics ) of fixed or dynamic target sources . MASINT was recognized as a formal intelligence discipline in 1986 . Another way to describe MASINT is a " non - literal " discipline . It feeds on a target ' s unintended emissive by - products , the " trails " - the spectral , chemical or RF that an object leaves behind . These trails form distinct signatures , which can be exploited as reliable discriminators to characterize specific events or disclose hidden targets . " As with many branches of MASINT , specific techniques may overlap with the six major conceptual disciplines of MASINT defined by the Center for MASINT Studies and Research , which divides MASINT into Electro - optical , Nuclear , Geophysical , Radar , Materials , and Radiofrequency disciplines . Military Requirements . Geophysical sensors have a long history in conventional military and commercial applications , from weather prediction for sailing , to fish finding for commercial fisheries , to nuclear test ban verification . New challenges , however , keep emerging . For first - world military forces opposing other conventional militaries , there is an assumption that if a target can be located , it can be destroyed . As a result , concealment and deception have taken on new criticality . " Stealth " low - observability aircraft have gotten much attention , and new surface ship designs feature observability reduction . Operating in the confusing littoral environment produces a great deal of concealing interference . Of course , submariners feel they invented low observability , and others are simply learning from them . They know that going deep or at least ultraquiet , and hiding among natural features , makes them very hard to detect . Two families of military applications , among many , represent new challenges against which geophysical MASINT can be tried . Also , see Unattended Ground Sensors . Deeply Buried Structures . One of the easiest ways for nations to protect weapons of mass destruction , command posts , and other critical structures is to bury them deeply , perhaps enlarging natural caves or disused mines . Deep burial is not only a means of protection against physical attack , as even without the use of nuclear weapons , there are deeply penetrating precision guided bombs that can attack them . Deep burial , with appropriate concealment during construction , is a way to avoid the opponent ' s knowing the buried facility ' s position well enough to direct precision guided weapons against it . Finding deeply buried structures , therefore , is a critical military requirement . The usual first step in finding a deep structure is IMINT , especially using hyperspectral IMINT sensors to help eliminate concealment . " Hyperspectral images can help reveal information not obtainable through other forms of imagery intelligence such as the moisture content of soil . This data can also help distinguish camouflage netting from natural foliage . " Still , a facility dug under a busy city would be extremely hard to find during construction . When the opponent knows that it is suspected that a deeply buried facility exists , there can be a variety of decoys and lures , such as buried heat sources to confuse infrared sensors , or simply digging holes and covering them , with nothing inside . MASINT using acoustic , seismic , and magnetic sensors would appear to have promise , but these sensors must be fairly close to the target . Magnetic Anomaly Detection ( MAD ) is used in antisubmarine water , for final localization before attack . The existence of the submarine is usually established through passive listening and refined with directional passive sensors and active sonar . Once these sensors ( as well as HUMINT and other sources ) have failed , there is promise for surveying large areas and deeply concealed facilities using gravitimetric sensors . Gravity sensors are a new field , but military requirements are making it important while the technology to do it is becoming possible . Naval Operations in Shallow Water . Especially in today ' s " green water " and " brown water " naval applications , navies are looking at MASINT solutions to meet new challenges of operating in littoral areas of operations . This symposium found it useful to look at five technology areas , which are interesting to contrast to the generally accepted categories of MASINT : acoustics and geology and geodesy / sediments / transport , nonacoustical detection ( biology / optics / chemistry ) , physical oceanography , coastal meteorology , and electromagnetic detection . Although it is unlikely there will ever be another World War II - style opposed landing on a fortified beach , another aspect of the littoral is being able to react to opportunities for amphibious warfare . Detecting shallow - water and beach mines remains a challenge , since mine warfare is a deadly " poor man ' s weapon . " While initial landings from an offshore force would be from helicopters or tiltrotor aircraft , with air cushion vehicles bringing ashore larger equipment , traditional landing craft , portable causeways , or other equipment will eventually be needed to bring heavy equipment across a beach . Shallow depth and natural underwater obstacles can block beach access to these craft and equipment , as can shallow - water mines . Synthetic Aperture Radar ( SAR ) , airborne laser detection and ranging ( LIDAR ) ) and use of bioluminescence to detect wake trails around underwater obstacles all may help solve this challenge . Moving onto and across the beach has its own challenges . Remotely operated vehicles may be able to map landing routes , and they , as well as LIDAR and multispectral imaging , may be able to detect shallow water . Once on the beach , the soil has to support heavy equipment . Techniques here include estimating soil type from multispectral imaging , or from an airdropped penetrometer that actually measures the loadbearing capacity of the surface . Weather and Sea Intelligence MASINT . The science and art of weather prediction used the ideas of measurement and signatures to predict phenomena , long before there were any electronic sensors . Masters of sailing ships might have no more sophisticated instrument than a wetted finger raised to the wind , and the flapping of sails . Weather information , in the normal course of military operations , has a major effect on tactics . High winds and low pressures can change artillery trajectories . High and low temperatures cause both people and equipment to require special protection . Aspects of weather , however , also can be measured and compared with signatures , to confirm or reject the findings of other sensors . The state of the art is to fuse meteorological , oceanographic , and acoustic data in a variety of display modes . Temperature , salinity and sound speed can be displayed horizontally , vertically , or in three - dimensional perspective . Predicting Weather based on Measurements and Signatures . While early sailors had no sensors beyond their five senses , the modern meteorologist has a wide range of geophysical and electro - optical measuring devices , operating on platforms from the bottom of the sea to deep space . Prediction based on these measurements are based on signatures of past weather events , a deep understanding of theory , and computational models . Weather predictions can give significant negative intelligence , when the signature of some combat system is such that it can operate only under certain weather conditions . Weather has long been an extremely critical part of modern military operations , as when the decision to land at Normandy on June 6 , rather than June 5 , 1944 depended on Dwight D . Eisenhower ' s trust in his staff weather advisor , Group Captain James Martin Stagg . It is rarely understood that something as fast as a ballistic missile reentry vehicle , or as " smart " as a precision guided munition , can still be affected by winds in the target area . As part of Unattended Ground Sensors . The Remote Miniature Weather Station ( RMWS ) , from System Innovations , is an air - droppable version with a lightweight , expendable and modular system with two components : a meteorological ( MET ) sensor and a ceilometer ( cloud ceiling height ) with limited MET . The basic MET system is surface - based and measures wind speed and direction , horizontal visibility , surface atmospheric pressure , air temperature and relative humidity . The ceilometer sensor determines cloud height and discrete cloud layers . The system provides near - real - time data capable of 24 - hour operation for 60 days . The RMWS can also go in with US Air Force Special Operations combat weathermen The man - portable version , brought in by combat weathermen , has an additional function , as remote miniature ceilometer . Designed to measure multiple layer cloud ceiling heights and then send that data via satellite communications link to an operator display , the system uses a Neodinum YAG ( NdYAG ) , 4 megawatt non - eye safe laser . According to one weatherman , " We have to watch that one , ” he said . “ Leaving it out there basically we ’ re worried about civilian populace going out there and playing with it — firing the laser and there goes somebody ’ s eye . There are two different units [ to RMWS ] . One has the laser and one doesn ’ t . The basic difference is the one with the laser is going to give you cloud height . " Hydrographic Sensors . Hydrographic MASINT is subtly different from weather , in that it considers factors such as water temperature and salinity , biologic activities , and other factors that have a major effect on sensors and weapons used in shallow water . ASW equipment , especially acoustic performance depends on the season the specific coastal site . Water column conditions , such as temperature , salinity , and turbidity are more variable in shallow than deep water . Water depth will influence bottom bounce conditions , as will the material of the bottom . Seasonal water column conditions ( particularly summer versus winter ) are inherently more variable in shallow water than in deep water . While much attention is given to shallow waters of the littoral , other areas have unique hydrographic characteristics . A submarine tactical development activity observed , " Fresh water eddies exist in many areas of the world . As we have experienced recently in the Gulf of Mexico using the Tactical Oceanographic Monitoring System ( TOMS ) , there exist very distinct surface ducts that causes the Submarine Fleet Mission Program Library ( SFMPL ) sonar prediction to be unreliable . Accurate bathythermic information is paramount and a precursor for accurate sonar predictions . ” Temperature and Salinity . Critical to the prediction of sound , needed by active and passive MASINT systems operating in water is knowing the temperature and salinity at specific depths . Antisubmarine aircraft , ships , and submarines can release independent sensors that measure the water temperature at various depths . The water temperature is critically important in acoustic detections , as changes in water temperature at thermocline s can act as a " barrier " or " layer " to acoustic propagation . To hunt a submarine , which is aware of water temperature , the hunter must drop acoustic sensors below the thermocline . Water conductivity is used as a surrogate marker for salinity . The current and most recently developed software , however , does not give information on suspended material in the water or bottom characteristics , both considered critical in shallow - water operations . The US Navy does this by dropping expendable probes , which transmit to a recorder , of 1978 - 1980 vintage , the AN / BQH - 7 for submarines and the AN / BQH - 71 for surface ships . While the redesign of the late seventies did introduce digital logic , the devices kept hard - to - maintain analog recorders , and maintainability became critical by 1995 . A project was begun to extend with COTS components , to result in the AN / BQH - 7 / 7A EC - 3 . In 1994 - 5 , the maintainability of the in - service units became critical . Variables in selecting the appropriate probe include : Biomass . Large schools of fish contain enough entrapped air to conceal the sea floor , or manmade underwater vehicles and structures . Fishfinder s , developed for commercial and recreational fishing , are specialized sonars that can identify acoustic reflections between the surface and the bottom . Variations on commercial equipment are apt to be needed , especially in littoral areas rich in marine life . Sea Bottom Measurement . A variety of sensors can be used to characterise the sea bottom into , for example , mud , sand , and gravel . Active acoustic sensors are the most obvious , but there is potential information from gravitimetric sensors , electro - optical and radar sensors for making inferences from the water surface , etc . Relatively simple sonars such as echo sounders can be promoted to seafloor classification systems via add - on modules , converting echo parameters into sediment type . Different algorithms exist , but they are all based on changes in the energy or shape of the reflected sounder pings . Side - scan sonar s can be used to derive maps of the topography of an area by moving the sonar across it just above the bottom . Multibeam hull - mounted sonars are not as precise as a sensor near the bottom , but both can give reasonable three - dimensional visualization . Another approach comes from greater signal processing of existing military sensors . The US Naval Research Laboratory demonstrated both seafloor characterization , as well as subsurface characteristics of the seafloor . Sensors used , in different demonstrations , included normal incidence beams from the AM / UQN - 4 surface ship depthfinder , and AN / BQN - 17 submarine fathometer ; backscatter from the Kongsberg EM - 121 commercial multibeam sonar ; AN / UQN - 4 fathometers on mine countermeasures ( MCM ) ships , and the AN / AQS - 20 mine - hunting system . These produced the " Bottom and Subsurface Characterization " graphic . Weather effects on chemical , biological , and radiological weapon propagation . One of the improvements in the Fuchs 2 reconnaissance vehicle is adding onboard weather instrumentations , including data such as wind direction and speed ; , air and ground temperature ; barometric pressure and humidity . Acoustic MASINT . This includes the collection of passive or active emitted or reflected sounds , pressure waves or vibrations in the atmosphere ( ACOUSTINT ) or in the water ( ACINT ) or conducted through the ground Going well back into the Middle Ages , military engineers would listen to the ground for sounds of telltale digging under fortifications . In modern times , acoustic sensors were first used in the air , as with artillery ranging in World War I . Passive hydrophones were used by the World War I Allies against German submarines ; the UC - 3 , was sunk with the aid of hydrophone on 23 April 1916 . Since submerged submarines cannot use radar , passive and active acoustic systems are their primary sensors . Especially for the passive sensors , the submarine acoustic sensor operators must have extensive libraries of acoustic signatures , to identify sources of sound . In shallow water , there are sufficient challenges to conventional acoustic sensors that additional MASINT sensors may be required . Two major confounding factors are : Counterbattery and Countersniper Location and Ranging . While now primarily of historical interest , one of the first applications of acoustic and optical MASINT was locating enemy artillery by the sound of their firing and flashes respectively during World War I . Effective sound ranging was pioneered by the British Army under the leadership of the Nobel Lauriate William Bragg . Flash spotting developed in parallel in the British , French and German armies . The combination of sound ranging ( i . e . , acoustic MASINT ) and flash ranging ( i . e . , before modern optoelectronics ) gave information unprecedented for the time , in both accuracy and timeliness . Enemy gun positions were located within 25 to 100 yards , with the information coming in three minutes or less . Initial WWI Counterbattery Acoustic Systems . In the " Sound Ranging " graphic , the manned Listening ( or Advanced ) Post , is sited a few ' sound seconds ( or about 2000 yards ) forward of the line of the unattended microphones , it sends an electrical signal to the recording station to switch on the recording apparatus . The positions of the microphones are precisely known . The differences in sound time of arrival , taken from the recordings , were then used to plot the source of the sound by one of several techniques . See http : / / nigelef . tripod . com / p _ artyint - cb . htm # SoundRanging Where sound ranging is a time - of - arrival technique not dissimilar to that of modern multistatic sensors , flash spotting used optical instruments to take bearings on the flash from accurately surveyed observation posts . The location of the gun was determined by plotting the bearings reported to the same gun flashes . See http : / / nigelef . tripod . com / p _ artyint - cb . htm # FieldSurveyCoy Flash ranging , today , would be called electro - optical MASINT . Artillery sound and flash ranging remained in use through World War II and in its latest forms until the present day , although flash spotting generally ceased in the 1950s due to the widespread adoption of flashless propellants and the increasing range of artillery . Mobile counterbattery radars able to detect guns , itself a MASINT radar sensor , became available in the late 1970s , although countermortar radars appeared in World War II . These techniques paralleled radio direction finding in SIGINT that started in World War I , using graphical bearing plotting and now , with the precision time synchronization from GPS , is often time - of - arrival . Modern Acoustic Artillery Locators . Artillery positions now are located primarily with Unmanned Air Systems and IMINT or counterartillery radar , such as the widely used Swedish ArtHuR . SIGINT also may give clues to positions , both with COMINT for firing orders , and ELINT for such things as weather radar . Still , there is renewed interest in both acoustic and electro - optical systems to complement counterartillery radar . Acoustic sensors have come a long way since World War I . Typically , the acoustic sensor is part of a combined system , in which it cues radar or electro - optical sensors of greater precision , but narrower field of view . HALO . The UK ' s hostile artillery locating system ( HALO ) has been in service with the British Army since the 1990s . HALO is not as precise as radar , but especially complements the directional radars . It passively detects artillery cannon , mortars and tank guns , with 360 degree coverage and can monitor over 2 , 000 square kilometers . HALO has worked in urban areas , the mountains of the Balkans , and the deserts of Iraq . The system consists of three or more unmanned sensor positions , each with four microphones and local processing , these deduce the bearing to a gun , mortar , etc . These bearings are automatically communicated to a central processor that combines them to triangulate the source of the sound . It can compute location data on up to 8 rounds per second , and display the data to the system operator . HALO may be used in conjunction with COBRA and ArtHur counter battery radars , which are not omnidirectional , to focus on the correct sector . UTAMS . Another acoustic system is the US Army Unattended Transient Acoustic MASINT Sensor ( UTAMS ) , developed by the U . S . Army Research Laboratory , which detects detect mortar and rocket launches and impacts . UTAMS has three to five acoustic arrays , each with four microphones , a processor , radio link , power source , and a laptop control computer . UTAMS , which was first operational in Iraq , first tested in November 2004 at a Special Forces Operating Base ( SFOB ) in Iraq . UTAMS was used in conjunction with AN / TPQ - 36 and AN / TPQ - 37 counter - artillery radar . While UTAMS was intended principally for detecting indirect artillery fire , Special Forces and their fire support officer learned it could pinpoint improvised explosive device ( IED ) explosions and small arms / rocket - propelled grenade ( RPG ) fires . It detected Points of Origin ( POO ) up to 10 kilometers from the sensor . Analyzing the UTAMS and radar logs revealed several patterns . The opposing force was firing 60 mm mortars during observed dining hours , presumably since that gave the largest groupings of personnel and the best chance of producing heavy casualties . That would have been obvious from the impact history alone , but these MASINT sensors established a pattern of the enemy firing locations . This allowed the US forces to move mortars into range of the firing positions , give coordinates to cannon when the mortars were otherwise committed , and to use attack helicopters as a backup to both . The opponents changed to night fires , which , again , were countered with mortar , artillery , and helicopter fires . They then moved into an urban area where US artillery was not allowed to fire , but a combination of PSYOPS leaflet drops and deliberate near misses convinced the locals not to give sanctuary to the mortar crews . Originally for a Marine requirement in Afghanistan , UTAMS was combined with electro - optical MASINT to produce the Rocket Launch Spotter ( RLS ) system useful against both rockets and mortars . In the Rocket Launch Spotter ( RLS ) application , each array consists of four microphones and processing equipment . Analyzing the time delays between an acoustic wavefront ’ s interaction with each microphone in the array UTAMS provides an azimuth of origin . The azimuth from each tower is reported to the UTAMS processor at the control station , and a POO is triangulated and displayed . The UTAMS subsystem can also detect and locate the point of impact ( POI ) , but , due to the difference between the speeds of sound and light , it may take UTAMS as long as 30 seconds to determine the POO for a rocket launch 13 km away . In this application , the electro - optical component of RLS will detect the rocket POO earlier , while UTAMS may do better with the mortar prediction . Passive sea - based acoustic sensors ( hydrophones ) . Modern hydrophones convert sound to electrical energy , which then can undergo additional signal processing , or that can be transmitted immediately to a receiving station . They may be directional or omnidirectional . Navies use a variety of acoustic systems , especially passive , in antisubmarine warfare , both tactical and strategic . For tactical use , passive hydrophones , both on ships and airdropped sonobuoys , are used extensively in antisubmarine warfare . They can detect targets far further away than with active sonar , but generally will not have the precision location of active sonar , approximating it with a technique called Target Motion Analysis ( TMA ) . Passive sonar has the advantage of not revealing the position of the sensor . The Integrated Undersea Surveillance System ( IUSS ) consists of multiple subsystems in SOSUS , Fixed Distributed System ( FDS ) , and the Advanced Deployable System ( ADS or SURTASS ) . Reducing the emphasis on Cold War blue - water operations put SOSUS , with more flexible " tuna boat " sensing vessels called SURTASS being the primary blue - water long - range sensors SURTASS used longer , more sensitive towed passive acoustic arrays than could be deployed from maneuvering vessels , such as submarines and destroyers . SURTASS is now being complemented by Low Frequency Active ( LFA ) sonar ; see the sonar section . Air - dropped passive acoustic sensors . Passive sonobuoys , such as the AN / SSQ - 53F , can be directional or omnidirectional and can be set to sink to a specific depth . These would be dropped from helicopters and maritime patrol aircraft such as the P - 3 . Fixed underwater passive acoustic sensors . The US installed massive Fixed Surveillance System ( FSS , also known as SOSUS ) hydrophone arrays on the ocean floor , to track Soviet and other submarines . Surface ship passive acoustic sensors . Purely from the standpoint of detection , towed hydrophone arrays offer a long baseline and exceptional measurement capability . Towed arrays , however , are not always feasible , because when deployed , their performance can suffer , or they can suffer outright damage , from fast speeds or radical turns . A state - of - the - art British towed array , with both passive and active capabilities , is Sonar 2087 made by Thales Underwater Systems . Steerable sonar arrays on the hull or bow usually have a passive as well as active mode , as do variable - depth sonars Surface ships may have warning receivers to detect hostile sonar . Submarine passive acoustic sensors . Modern submarines have multiple passive hydrophone systems , such as a steerable array in a bow dome , fixed sensors along the sides of the submarines , and towed arrays . They also have specialized acoustic receivers , analogous to radar warning receivers , to alert the crew to the use of active sonar against their submarine . US submarines made extensive clandestine patrols to measure the signatures of Soviet submarines and surface vessels . This acoustic MASINT mission included both routine patrols of attack submarines , and submarines sent to capture the signature of a specific vessel . US antisubmarine technicians on air , surface , and subsurface platforms had extensive libraries of vessel acoustic signatures . Passive acoustic sensors can detect aircraft flying low over the sea . Land - based Passive Acoustic Sensors ( geophones ) . Vietnam - era acoustic MASINT sensors included " Acoubuoy ( 36 inches long , 26 pounds ) floated down by camouflaged parachute and caught in the trees , where it hung to listen . The Spikebuoy ( 66 inches long , 40 pounds ) planted itself in the ground like a lawn dart . Only the antenna , which looked like the stalks of weeds , was left showing above ground . " This was part of Operation Igloo White . Part of the AN / GSQ - 187 Improved Remote Battlefield Sensor System ( I - REMBASS ) is a passive acoustic sensor , which , with other MASINT sensors , detects vehicles and personnel on a battlefield . Passive acoustic sensors provide additional measurements that can be compared with signatures , and used to complement other sensors . I - REMBASS control will integrate , in approximately 2008 , with the . For example , a ground search radar may not be able to differentiate between a tank and a truck moving at the same speed . Adding acoustic information , however , may quickly distinguish between them . Active Acoustic Sensors and Supporting Measurements . Combatant vessels , of course , made extensive use of active sonar , which is yet another acoustic MASINT sensor . Besides the obvious application in antisubmarine warfare , specialized active acoustic systems have roles in : Various synthetic aperture sonars have been built in the laboratory and some have entered use in mine - hunting and search systems . An explanation of their operation is given in synthetic aperture sonar . Water Surface , Fish Interference and Bottom Characterization . The water surface and bottom are reflecting and scattering boundaries . Large schools of fish , with air in their swim bladder balance apparatus , can also have a significant effect on acoustic propagation . For many purposes , but not all naval tactical applications , the sea - air surface can be thought of as a perfect reflector . " The effects of the seafloor and the sea surface on acoustic systems in shallow water are highly complex , making range predictions difficult . Multi - path degradation affects overall figure of merit and active classification . As a result , false target identifications are frequent . " The acoustic impedance mismatch between water and the bottom is generally much less than at the surface and is more complex . It depends on the bottom material types and depth of the layers . Theories have been developed for predicting the sound propagation in the bottom in this case , for example by Biot and by Buckingham . Water Surface . For high frequency sonars ( above about 1 kHz ) or when the sea is rough , some of the incident sound is scattered , and this is taken into account by assigning a reflection coefficient whose magnitude is less than one . Rather than measuring surface effects directly from a ship , radar MASINT , in aircraft or satellites , may give better measurements . These measurements would then be transmitted to the vessel ' s acoustic signal processor . Under Ice . A surface covered with ice , of course , is tremendously difference than even storm - driven water . Purely from a collision avoidance and acoustic propagation , a submarine needs to know how close it is to the bottom of ice . Less obvious is the need to know the three - dimensional structure of the ice , because submarines may need to break through it to launch missiles , to raise4 electronic masts , or to surface the boat . Three - dimensional ice information also can tell the submarine captain whether antisubmarine warfare aircraft can detect or attack the boat . The state of the art is providing the submarine with a three - dimensional visualization of the ice above : the lowest part ( ice keel ) and the ice canopy . While sound will propagate differently in ice than liquid water , the ice still needs to be considered as a volume , to understand the nature of reverberations within it . Bottom . A typical basic depth measuring device is the US AN / UQN - 4A . Both the water surface and bottom are reflecting and scattering boundaries . For many purposes , but not all naval tactical applications , the sea - air surface can be thought of as a perfect reflector . In reality , there are complex interactions of water surface activity , seafloor characteristics , water temperature and salinity , and other factors that make " . . . range predictions difficult . Multi - path degradation affects overall figure of merit and active classification . As a result , false target identifications are frequent . " This device , however , does not give information on the characteristics of the bottom . In many respects , commercial fishing and marine scientists have equipment that is perceived as needed for shallow water operation . Biologic Effects on Sonar Reflection . A further complication is the presence of wind generated bubbles or fish close to the sea surface . . The bubbles can also form plume s that absorb some of the incident and scattered sound , and scatter some of the sound themselves . This problem is distinct from biologic interference caused by acoustic energy generated by marine life , such as the squeaks of porpoises and other cetacean s , and measured by acoustic receivers . The signatures of biologic sound generators need to be differentiated from more deadly denizens of the depths . Classifying biologics is a very good example of an acoustic MASINT process . Surface Combatants . Modern surface combatants with an ASW mission will have a variety of active systems , with a hull - or bow - mounted array , protected from water by a rubber dome ; a " variable - depth " dipping sonar on a cable , and , especially on smaller vessels , a fixed acoustic generator and receiver . Some , but not all , vessels carry passive towed arrays , or combined active - passive arrays . These depend on target noise , which , in the combined littoral environment of ultraquiet submarines in the presence of much ambient noise . Vessels that have deployed towed arrays cannot make radical course maneuvers . Especially when active capabilities are included , the array can be treated as a bistatic or multistatic sensor , and act as a synthetic aperture sonar ( SAS ) For ships that cooperate with aircraft , they will need a data link to sonobuoys and a sonobuoy signal processor , unless the aircraft has extensive processing capability and can send information that can be accepted directly by tactical computers and displays . Signal processors not only analyze the signals , but constantly track propagation conditions . The former is usually considered part of a particular sonar , but the US Navy has a separate propagation predictor called the AN / UYQ - 25B ( V ) Sonar " in situ " Mode Assessment System ( SIMAS ) Echo Tracker Classifiers ( ETC ) are adjuncts , with a clear MASINT flavor , to existing surface ship sonars ETC is an application of synthetic aperture sonar ( SAS ) . SAS is already used for minehunting , but could help existing surface combatants , as well as future vessels and unmanned surface vehicles ( USV ) , detect threats , such as very silent air - independent propulsion non - nuclear submarines , outside torpedo range . Torpedo range , especially in shallow water , is considered anything greater than 10 nmi . Conventional active sonar may be more effective than towed arrays , but the small size of modern littoral submarines makes them difficult threats . Highly variable bottom paths , biologics , and other factors complicate sonar detection . If the target is slow - moving or waiting on the bottom , they have little or no Doppler effect , which current sonars use to recognize threats . Continual active tracking measurement of all acoustically detected objects , with recognition of signatures as deviations from ambient noise , still gives a high false alarm rate ( FAR ) with conventional sonar . SAS processing , however , improves the resolution , especially of azimuth measurements , by assembling the data from multiple pings into a synthetic beam that gives the effect of a far larger receiver . MASINT - oriented SAS measures shape characteristics and eliminates acoustically detected objects that do not conform to the signature of threats . Shape recognition is only one of the parts of the signature , which include course and Doppler when available . Air - Dropped Active Sonobuoys . Active sonobuoys , containing a sonar transmitter and receiver , can be dropped from fixed - wing maritime patrol aircraft ( e . g . , P - 3 , Nimrod , Chinese Y - 8 , Russian and Indian Bear ASW variants ) , antisubmarine helicopters , and carrier - based antisubmarine aircraft ( e . g . , S - 3 ) . While there have been some efforts to use other aircraft simply as carriers of sonobuoys , the general assumption is that the sonobuoy - carrying aircraft can issue commands to the sonobuoys and receive , and to some extent process , their signals . The Directional Hydrophone Command Activated Sonobuoy system ( DICASS ) both generate sound and listen for it . A typical modern active sonobuoy , such as the AN / SSQ 963D , generates multiple acoustic frequencies . Other active sonobuoys , such as the AN / SSQ 110B , generate small explosions as acoustic energy sources . Airborne Dipping Sonar . Antisubmarine helicopters can carry a " dipping " sonar head at the end of a cable , which the helicopter can raise from or lower into the water . The helicopter would typically dip the sonar when trying to localize a target submarine , usually in cooperation with other ASW platforms or with sonobuoys . Typically , the helicopter would raise the head after dropping an ASW weapon , to avoid damaging the sensitive receiver . Not all variants of the same basic helicopter , even assigned to ASW , carry dipping sonar ; some may trade the weight of the sonar for more sonobuoy or weapon capacity . The EH101 helicopter , used by a number of nations , has a variety of dipping sonars . The ( British ) Royal Navy version has Ferranti / Thomson - CSF sonar , while the Italian version uses the HELRAS . Russian Ka - 25 helicopters carry dipping sonar , as does the US LAMPS SH - 60 helicopter , which carries a " dipping " AQS - 13 F sonar , plus AN / SQQ - 28 ( V ) 10 sonar signal processing for active sonobuoys it drops . Surveillance Vessel Low - Frequency Active . Newer Low - Frequency Active ( LFA ) systems are controversial , as their very high sound pressures may be hazardous to whales and other marine life A decision has been made to employ LFA on SURTASS vessels , after an environmental impact statement that indicated , if LFA is used with decreased power levels in certain high - risk areas for marine life , it would be safe when employed from a moving ship . The ship motion , and the variability of the LFA signal , would limit the exposure to individual sea animals . LFA operates in the low - frequency ( LF ) acoustic band of 100 – 500 Hz . It has an active component , the LFA proper , and the passive SURTASS hydrophone array . " The active component of the system , LFA , is a set of 18 LF acoustic transmitting source elements ( called projectors ) suspended by cable from underneath an oceanographic surveillance vessel , such as the Research Vessel ( R / V ) Cory Chouest , USNS Impeccable ( T - AGOS 23 ) , and the Victorious class ( TAGOS 19 class ) . " The source level of an individual projector is 215 dB . These projectors produce the active sonar signal or “ ping . ” A " ping , " or transmission , can last between 6 and 100 seconds . The time between transmissions is typically 6 to 15 minutes with an average transmission of 60 seconds . Average duty cycle ( ratio of sound “ on ” time to total time ) is less than 20 percent . The typical duty cycle , based on historical LFA operational parameters ( 2003 to 2007 ) , is normally 7 . 5 to 10 percent . " This signal " . . . is not a continuous tone , but rather a transmission of waveforms that vary in frequency and duration . The duration of each continuous frequency sound transmission is normally 10 seconds or less . The signals are loud at the source , but levels diminish rapidly over the first kilometer . " Submarine Active Acoustic Sensors . The primary tactical active sonar of a submarine is usually in the bow , covered with a protective dome . Submarines for blue - water operations used active systems such as the AN / SQS - 26 and AN / SQS - 53 have been developed but were generally designed for convergence zone and single bottom bounce environments . Submarines that operate in the Arctic also have specialized sonar for under - ice operation ; think of an upside - down fathometer . Submarines also may have minehunting sonar . Using measurements to differentiate between biologic signatures and signatures of objects that will permanently sink the submarine is as critical a MASINT application as could be imagined . Active Acoustic Sensors for Minehunting . Sonars optimized to detect objects of the size and shapes of mines can be carried by submarines , remotely operated vehicles , surface vessels ( often on a boom or cable ) and specialized helicopters . The classic emphasis on minesweeping , and detonating the mine released from its tether using gunfire , has been replaced with the AN / SLQ - 48 ( V ) 2 mine neutralization system ( MNS ) AN / SLQ - 48 - ( remotely operated ) Mine Neutralization Vehicle . This works well for rendering save mines in deep water , by placing explosive charges on the mine and / or its tether . The AN / SLQ - 48 is not well suited to the neutralization of shallow - water mines . The vehicle tends to be underpowered and may leave on the bottom a mine that looks like a mine to any subsequent sonar search and an explosive charge subject to later detonation under proper impact conditions . There is mine - hunting sonar , as well as ( electro - optical ) television on the ROV , and AN / SQQ - 32 minehunting sonar on the ship . Acoustic sensing of large explosions . An assortment of time - synchronized sensors can characterize conventional or nuclear explosions . One pilot study , the Active Radio Interferometer for Explosion Surveillance ( ARIES ) . This technique implements an operational system for monitoring ionospheric pressure waves resulting from surface or atmospheric nuclear or chemical explosives . Explosions produce pressure waves that can be detected by measuring phase variations between signals generated by ground stations along two different paths to a satellite . This is a very modernized version , on a larger scale , of World War I sound ranging . As can many sensors , ARIES can be used for additional purposes . Collaborations are being pursued with the Space Forecast Center to use ARIES data for total electron content measures on a global scale , and with the meteorology / global environment community to monitor global climate change ( via tropospheric water vapor content measurements ) , and by the general ionospheric physics community to study travelling ionospheric disturbances . Sensors relatively close to a nuclear event , or a high - explosive test simulating a nuclear event , can detect , using acoustic methods , the pressure produced by the blast . These include infrasound microbarograph s ( acoustic pressure sensors ) that detect very low - frequency sound waves in the atmosphere produced by natural and man - made events . Closely related to the microbarographs , but detecting pressure waves in water , are hydro - acoustic sensors , both underwater microphones and specialized seismic sensors that detect the motion of islands . Seismic MASINT . US Army Field Manual 2 - 0 defines seismic intelligence as " The passive collection and measurement of seismic waves or vibrations in the earth surface . " One strategic application of seismic intelligence makes use of the science of seismology to locate and characterize nuclear testing , especially underground testing . Seismic sensors also can characterize large conventional explosions that are used in testing the high - explosive components of nuclear weapons . Seismic intelligence also can help locate such things as large underground construction projects . Since many areas of the world have a great deal of natural seismic activity , seismic MASINT is one of the emphatic arguments that there must be a long - term commitment to measuring , even during peacetime , so that the signatures of natural behavior is known before it is necessary to search for variations from signatures . Strategic Seismic MASINT . For nuclear test detection , seismic intelligence is limited by the " threshold principle " coined in 1960 by George Kistiakowsky , which recognized that while detection technology would continue to improve , there would be a threshold below which small explosions could not be detected . Tactical Seismic MASINT . The most common sensor in the Vietnam - era " McNamara Line " of remote sensors was the ADSID ( Air - Delivered Seismic Intrusion Detector ) sensed earth motion to detect people and vehicles . It resembled the Spikebuoy , except it was smaller and lighter ( 31 inches long , 25 pounds ) . The challenge for the seismic sensors ( and for the analysts ) was not so much in detecting the people and the trucks as it was in separating out the false alarms generated by wind , thunder , rain , earth tremors , and animals — especially frogs . " Vibration MASINT . This subdiscipline is also called piezoelectric MASINT after the sensor most often used to sense vibration , but vibration detectors need not be piezoelectric . Note that some discussions treat seismic and vibration sensors as a subset of acoustic MASINT . Other possible detectors could be moving coil or surface acoustic wave . . Vibration , as a form of geophysical energy to be sensed , has similarities to acoustic and seismic MASINT , but also has distinct differences that make it useful , especially in unattended ground sensors ( UGS ) . In the UGS application , one advantage of a piezoelectric sensor is that it generates electricity when triggered , rather than consuming electricity , an important consideration for remote sensors whose lifetime may be determined by their battery capacity . While acoustic signals at sea travel through water , on land , they can be assumed to come through the air . Vibration , however , is conducted through a solid medium on land . It has a higher frequency than is typical of seismic conducted signals . A typical detector , the Thales MA2772 vibration is a piezoelectric cable , shallowly buried below the ground surface , and extended for 750 meters . Two variants are available , a high - sensitivity version for personnel detection , and lower - sensitivity version to detect vehicles . Using two or more sensors will determine the direction of travel , from the sequence in which the sensors trigger . In addition to being buried , piezoelectric vibration detectors , in a cable form factor , also are used as part of high - security fencing . They can be embedded in walls or other structures that need protection . Magnetic MASINT . A magnetometer is a scientific instrument used to measure the strength and / or direction of the magnetic field in the vicinity of the instrument . The measurements they make can be compared to signatures of vehicles on land , submarines underwater , and atmospheric radio propagation conditions . They come in two basic types : Earth ' s magnetism varies from place to place and differences in the Earth ' s magnetic field ( the magnetosphere ) can be caused by two things : Metal detectors use electromagnetic induction to detect metal . They can also determine the changes in existing magnetic fields caused by metallic objects . Indicating Loops for detecting Submarines . One of the first means for detecting submerged submarines , first installed by the Royal Navy in 1914 , was the effect of their passage over an anti - submarine indicator loop on the bottom of a body of water . A metal object passing over it , such as a submarine , will , even if degaussed , have enough magnetic properties to induce a current in the loop ' s cable . . In this case , the motion of the metal submarine across the indicating coil acts as an oscillator , producing electrical current . MAD . A magnetic anomaly detector ( MAD ) is an instrument used to detect minute variations in the Earth ' s magnetic field . The term refers specifically to magnetometer s used either by military forces to detect submarine s ( a mass of ferromagnetic material creates a detectable disturbance in the magnetic field ) Magnetic anomaly detectors were first employed to detect submarines during World War II . MAD gear was used by both Japanese and U . S . anti - submarine forces , either towed by ship or mounted in aircraft to detect shallow submerged enemy submarines . After the war , the U . S . Navy continued to develop MAD gear as a parallel development with sonar detection technologies . To reduce interference from electrical equipment or metal in the fuselage of the aircraft , the MAD sensor is placed at the end of a boom or a towed aerodynamic device . Even so , the submarine must be very near the aircraft ' s position and close to the sea surface for detection of the change or anomaly . The detection range is normally related to the distance between the sensor and the submarine . The size of the submarine and its hull composition determine the detection range . MAD devices are usually mounted on aircraft 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 - Russia n Alfa class submarine , was constructed out of titanium . This light , strong material , as well as a unique nuclear power system , allowed the submarine to break speed and depth records for operational boats . It was thought that nonferrous titanium would defeat magnetic ASW sensors , but this was not the case . to give dramatic submerged performance and protection from detection by MAD sensors , is still detectable . 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 . Vehicle Detectors . The Remotely Emplaced Battlefield Surveillance System ( REMBASS ) is a US Army program for detecting the presence , speed , and direction of a ferrous object , such as a tank . Coupled with acoustic sensors that recognize the sound signature of a tank , it could offer high accuracy . It also collects weather information . The Army ' s AN / GSQ - 187 Improved Remote Battlefield Sensor System ( I - REMBASS ) includes both magnetic - only and combined passive infrared / magnetic intrusion detectors . The DT - 561 / GSQ hand emplaced MAG " sensor detects vehicles ( tracked or wheeled ) and personnel carrying ferrous metal . It also provides information on which to base a count of objects passing through its detection zone and reports their direction of travel relative to its location . The monitor uses two different ( MAG and IR ) sensors and their identification codes to determine direction of travel . Magnetic detonators and countermeasures . Magnetic sensors , much more sophisticated than the early inductive loops , can trigger the explosion of mines or torpedoes . Early in World War II , the US tried to put magnetic torpedo exploder far beyond the limits of the technology of the time , and had to disable it , and then work on also - unreliable contact fuzing , to make torpedoes more than blunt objects than banged into hulls . Since water is incompressible , an explosion under the keel of a vessel is far more destructive than one at the air - water interface . Torpedo and mine designers want to place the explosions in that vulnerable spot , and countermeasures designers want to hide the magnetic signature of a vessel . Signature is especially relevant here , as mines may be made selective for warships , merchant vessel unlikely to be hardened against underwater explosions , or submarines . A basic countermeasure , started in World War II , was degaussing , but it is impossible to remove all magnetic properties . Detecting landmines . Landmines often contain enough ferrous metal to be detectable with appropriate magnetic sensors . Sophisticated mines , however , may also sense a metal - detection oscillator , and , under preprogrammed conditions , detonate to deter demining personnel . Not all landmines have enough metal to activate a magnetic detector . While , unfortunately , the greatest number of unmapped minefields are in parts of the world that cannot afford high technology , a variety of MASINT sensors could help demining . These would include ground - mapping radar , thermal and multispectral imaging , and perhaps synthetic aperture radar to detect disturbed soil . Gravitimetric MASINT . While high school physics students are told that the value of gravity is 9 . 8 meters per second squared , they also learn Newton ' s equation that predicts that gravity is a function of mass . Given sufficiently sensitive instrumentation , it is possible to detect variations in gravity from the different densities of natural materials : the value of gravity will be greater on top of a granite monolith than over a sand beach . Again with sufficiently sensitive instrumentation , it should be possible to detect gravitational differences between solid rock , and rock excavated for a hidden facility . Streland 2003 points out that the instrumentation indeed must be sensitive : variations of the force of gravity on the earth ’ s surface are on the order of 10 of the average value . A practical gravitimetric detector of buried facilities would need to be able to measure " less than one one millionth of the force that caused the apple to fall on Sir Isaac Newton ’ s head . " To be practical , it would be necessary for the sensor to be able to be used while in motion , measuring the change in gravity between locations . This change over distance is called the " gravity gradient " , which can be measured with a gravity gradiometer . Developing an operationally useful gravity gradiometer is a major technical challenge . One type , the SQUID Superconducting Quantum Interference Device gradiometer , may have adequate sensitivity , but it needs extreme cryogenic cooling , even if in space , a logistic nightmare . Another technique , far more operationally practical but lacking the necessary sensitivity , is the Gravity Recovery and Climate Experiment ( GRACE ) technique , currently using radar to measure the distance between pairs of satellites , whose orbits will change based on gravity . Substituting lasers for radar will make GRACE more sensitive , but probably not sensitive enough . A more promising technique , although still in the laboratory , is quantum gradiometry , which is an extension of atomic clock techniques , much like those in GPS . Off - the - shelf atomic clocks measure changes in atomic waves over time rather than the spatial changes measured in a quantum gravity gradiometer . One advantage of using GRACE in satellites is that measurements can be made from a number of points over time , with a resulting improvement as seen in synthetic aperture radar and sonar . Still , finding deeply buried structures of human scale is a tougher problem than the initial goals of finding mineral deposits and ocean currents . To make this operationally feasible , there would have to be a launcher to put fairly heavy satellites into polar orbits , and as many earth stations as possible to reduce the need for large on - board storage of the large amounts of data the sensors will produce . Finally , there needs to be a way to convert the measurements into a form that can be compared against available signatures in geodetic data bases . Those data bases would need significant improvement , from measured data , to become sufficiently precise that a buried facility signature would stand out .