Radar MASINT

See Counter-battery radar

Three US radar systems exist for detecting hostile artillery fire and backtracking to its source, serving the dual requirements of warning of incoming fires and counterattacking the firer. While they are intended to be used in three tiers against artillery of different ranges, there can be a problem of having a threat of an unexpected type fired into an area covered by the wrong tier. Proper site selection and preparation is necessary for all types.[6]

Proper planning includes avoiding clutter sources such as land surfaces, vegetation, buildings, complex terrain, aircraft (particularly rotary wing) and particulate matter kicked up by wind or aircraft. The enemy may attempt to avoid the directional radar systems or even use electronic countermeasures, so active patrolling, and activating the radar at random times and in random directions will act as a counter-countermeasure. Complementary acoustic and electro-optical systems can compensate for the lack of omnidirectional coverage by the AN/TPQ-36 and AN/TPQ-37.

To complement the counterartillery radars, additional MASINT sensors include acoustic and electro-optical systems.

A variety of ground-to-ground radars serve in counterbattery and surveillance roles, and also have some capability to detect helicopters. The LCMR, AN/TPQ-36, and AN/TPQ-37 radars are ideally used in a layered detection system, for short, medium, and long range detection. LCMR is omnidirectional, but the other two are directional and need cueing from omnidirectional sensors such as the combined electro-optical and acoustic Rocket Launch Spotter or a pure acoustic system such as HALO or UTAMS

These 1980-vintage systems are not man-portable, and are directional, but they do have longer range than the LCMR.

Physically heavier than the LCMR, the AN/TPQ-36 Firefinder radar can detect cannon, rockets, and mortars within its range:

• Artillery: 14,500 meters
• Mortars: 18,000 meters
• Rockets: 24,000 meters

AN/TPQ-36 medium-range Firefinder being positioned

It has a moving rather than omnidirectional antenna. Current improvements are intended to replace its old control computer with a laptop, enhance performance in high clutter environments, and increase the probability of detecting certain rockets.

First intended to provide a third tier against long-range threats, the AN/TPQ-37 Firefinder radar basic software filters out all other radar tracks with signatures of lesser-ranged threats. New software, required by the mortar threat in the Balkans, allows it to duplicate the Q-36 mortar detection range of 18 kilometers, while still detecting longer-range threats. Proper crew training should compensate for the reduced clutter rejection caused by accepting mortar signatures.

Long-range AN/TPQ-37

Standard TPQ-36/37 radars are semi-manual in their plotting. An Israeli enhancement makes the plotting fully digital .[7]

Portable, and intended for tactical use, is the man-portable surveillance and target acquisition radar (MSTAR), originally developed for British use in artillery spotting, as the primary users of MSTAR, like its predecessor, were and are artillery observation parties, although it may be used for ground reconnaissance and surveillance. The MSTAR entered UK service in early 1991, slightly accelerated for use in the Gulf War. Its official UK designation is Radar, GS, No 22. MSTAR was developed and produced in UK in the mid 1980s by Thorn EMI Electronics (now part of Thales).

It is a Doppler radar operating in the J Band, and is capable of detecting, recognising and tracking helicopters, slow moving fixed-wing aircraft, tracked and wheeled vehicles and troops, as well as observing and adjusting the fall of shot. The US uses it used as AN/PPS-5B and −5C Ground Surveillance Radar (GSR) Sets, and Australia calls its version AMSTAR.

The GSR is a ground-to-ground surveillance radar set for use by units such as infantry and tank battalions. and BCT RSTA units. It can detect and locate moving personnel at ranges of 6 km and vehicles at ranges of 10 km, day or night under virtually all weather conditions. The radar has a maximum display range of 10,000 meters and the radar can alert the operator both aurally and visually.[8] The APS/PPS-15 is a lighter, shorter ranged version intended for airborne, light infantry, and special operations force use. These radars are more MASINT then general purpose radar, as the simpler ones have very little imaging power, but perhaps a light or sound indicating the direction and range of the threat.

Recognizing the threat of ground surveillance radar,[9] the Australian military is exploring personal radar warning receivers (RWR), approximately the size of a credit card, and intended principally for special operations forces who have to evade ground surveillance radar.

The COBRA DANE ground station radar is an "AN/FPS-108, a phased array L-Band antenna containing 15,360 radiating elements occupying 95% of the roughly 100 by 100-foot (30 m) area of one face of the building housing the system. The antenna is oriented toward the west, monitoring the northern Pacific missile test areas.[10]"

Night view of the AN/FPS-108 Cobra Dane RADAR

Methods continue to evolve. COBRA JUDY was intended to gather information on long-range missiles, in a strategic role. One developmental system, COBRA GEMINI,[11] is intended to complement COBRA JUDY. It can be used for observing long-range missiles, but is also appropriate for theater-level weapons, which may be addressed in regional arms limitation agreements, such as the Missile Technology Control Regime (MCTR). Where COBRA JUDY is built into a ship, this dual frequency (S- and X-band) radar is transportable, capable of operating on ships or on land, and optimized for monitoring medium range ballistic missiles and antimissile systems. It is air-transportable to deal with sudden monitoring contingencies.

Aft view of the USNS Observation Island showing the location of the AN/SPQ-11 Cobra Judy array.

The AN/SPQ-11 Cobra Judy radar, on USNS Observation Island (T-AGM-23), could also be guided by the COBRA BALL electro-optical sensors on an RC-135. Cobra Judy was supplemented by Cobra Gemini on USNS Invincible (T-AGM-24) starting around 2000 and was replaced by Cobra King in 2014 on USNS Howard O. Lorenzen (T-AGM-25).[12][13]

The Soviet Union used a number of radar-equipped ocean reconnaissance satellites (RORSAT), which used strong radar systems, powered by an onboard nuclear reactor, to visualize vessels. These operated in the "pushbroom" manner, scanning a swath straight down.

US radar satellites, however, have emphasized SAR and ISAR.

This technique, first demonstrated in the 1970s from an army airborne system, has evolved considerably. At first, it estimated the angle-of-arrival of backscatter power from a pixel on the ground by comparing the phase difference of the backscattered wave as measured at two different locations. This information along with the traditional range and azimuth (Doppler) information allowed one to locate the imaged pixel in three-dimensions, and hence estimate the elevation of that pixel. Elevation-mapping interferometric SAR systems have since become an important remote sensing technology, with a very specific height-mapping mission. Interferometric SAR systems can now be obtained as commercial off-the-shelf (COTS) products.

Detection of mines, both on the active battlefield and in reconstituting nations with unexploded ordnance (UXO) remains a critical problem. As part of the Strategic Environmental Research and Development Program (SERDP), the U.S. Army Research Laboratory (ARL), starting in 1997, began an effort to collect, under extremely controlled condition, a library of UXO signatures.

As part of a larger research initiative to create technology that could detect targets buried or hidden by foliage, the U.S. Army Research Laboratory (ARL) developed multiple UWB SAR radar systems with promising object-penetration capabilities. These radar systems were fully polarimetric and were generally designed to be mounted on an all-terrain vehicle for mobile applications on the battlefield.  Examples of ARL-designed UWB SAR systems include the railSAR, the boomSAR, the SIRE radar, and the SAFIRE radar.[17][18]

The railSAR was among the earliest of the UWB SAR technology at ARL and was constructed as a stationary, rail-guided impulse radar system.[19] It was then incorporated into the development of the boomSAR in 1995, which emulated the functions of an airborne radar system.[20] Afterwards, the UWB SAR technology was eventually transferred onto a vehicle-based platform like with the SIRE radar and the SAFIRE radar for greater access and mobility.[17]

Once the basic terrain signature is known, signatures are being collected from terrain that has been disturbed in a controlled manner. One such environment is at the Yuma Proving Grounds, a desert area where an existing Unexploded Ordnance (UXO) test site, the Steel Crater Test Area, has been used for a variety of sensor calibrations. It contains buried land mines, wires, pipes, vehicles, 55-gallon drums, storage containers and arms caches. For the Army studies to define the signatures of UXO detection, over 600 additional pieces of inert UXO were added to the Steel Crater Test Area, including bombs (250, 500, 750, 1000, and 2000 lb), mortars (60 and 81 mm), artillery shells (105 and 155 mm), 2.75-in. rockets, cluster submunitions (M42, BLU-63, M68, BLU-97, and M118), and mines (Gator, VS1.6, M12, PMN, and POM-Z).

In the 1990s, a new SAR application of coherent SAR showed the ability the detection and measurement of very small changes in the earth's surface. The simplest form of this technology, known as coherent change detection (CCD), had obvious military and intelligence applications, and is now a valuable tool for analysts. CCD complements other sensors: knowing that the surface changed may mean that analysts can direct ground-penetrating radar on it, measure thermal signatures to see if something is generating heat under the ground, etc.

Compare radar CCD and optical equivalents of the same subject. The CCD would not have been affected by night or weather.

Moving target indications (MTI), at first, might seem just an adjunct to imaging radar, allowing the operator to focus on the moving target. That which makes them peculiarly MASINT, however is, especially in combination with other sensors and reference material, allows the measurement of a movement signature. For example, a tank and a truck both might be measured at 40 km/h when on a road. If both turn onto unpaved ground, however, the signature of the truck is that it might slow significantly, or demonstrate much lateral instability. The tracked vehicle, however, might exhibit a signature of not slowing when going off-pavement.

There are several electronic approaches to MTI. One is a refinement of CCD.[21] Differential interferometric SAR is even more precise than CCD. Its use in measuring the ground motion of earthquakes can complement seismic sensors for detecting concealed underground explosions, or the characteristics of those above ground.

Current research and development involves multiple coherent SAR collections to make even more sensitive measurements, with the capability to detect motion as small as 1 mm per year. The new techniques address many of the limiting factors associated with SAR interferometry, such as atmospheric induced distortions.[22]

UHF and VHF SAR have begun limited operations on Army RC-12 aircraft and may be implemented on the Global Hawk.[23] DARPA's WATCH-IT program developed robust low false alarm density change detection software to detect vehicles and smaller targets under foliage, under camouflage and in urban clutter, and developed tomographic (3D) imaging to detect and identify targets that have not relocated. VHF/UHF SAR for building penetration, urban mapping and performing change detection of objects inside buildings.

Terrain characterization technologies were also developed, including the abilities to rapidly generate bald-earth terrain height estimates and to classify terrain features from multipass VHF/UHF SAR imagery. In September 2004, DARPA demonstrated real-time onboard change detection (vehicles and IEDs) and rapid ground-station tomographic processing, as well as rapid generation of bald earth digital elevation models (DEMs) using stereo processing. In parallel, the Air Force Targets Under Trees (TUT) program enhanced the VHF SAR by adding a 10 km swath width VHF-only mode, developing a real-time VHF change detection capability/

Human activities generate a great deal of radio energy, as in communications, navigation, and entertainment applications. Some of these sources provide enough energy such that their reflection or transillumination can enable passive covert radar (PSR) MASINT, which is also called passive coherent location (PCL).

A foreign transmitter, preferably a purpose-built radar transmitter such as used in air traffic control, but really any powerful transmitted such as TV or FM, potentially can produce reflected signals that do not return to the designated receiver of the foreign radar operator. A signal may reflect such that it can be intercepted and fed into a friendly radar receiver, giving at least information on the presence of a radar target illuminated by the foreign transmitter. This is the simple case with the unintended reflection going to a single radar support receiver.

Interferometry is also possible with such systems.[30] This is especially attractive for naval vessels, which, since they often travel in groups, will have different times difference of arrival (TDOA) of the reflections from the foreign receiver. To restate an important difference, basic PCR works with a single radar receiver and conventional display format, from a single reflection. TDOA works with a set of reflections, from the same target, arriving at multiple points.[31] "Passive sensors are shown to make a valuable contribution to the air defence mission."

Another group evaluated the PCR technology in an environment like that of a naval task group[32] Ships have more space, and thus the equipment and power are less limited than for airborne or man-portable systems. This British study tested illumination with a Watchman air traffic control pulse doppler radar, and a Bridgemaster marine radar, against experimental receiver types. The researchers also developed simulations of the system.

Against the marine transmitter, the receiver combined a square-law: Power-level detector with cross-collation of a local copy of the pulse against the received signal. This method improved sensitivity for poorer time resolution, because correlated peaks are twice the width of uncorrelated peaks.

Using the air traffic control illuminator, the receiver used pulse compression filtering of a chirp signal, which provided processing gain along with the ability to separate closely spaced targets. This also implemented a moving target indicator that suppressed clutter, but it was recognized that an MTI signal would not be available in a noncooperative environment. They concluded their work demonstrated feasible convergence of PCR and TDOA, using a shipborne R-ESM system with communications among the receivers, such that the processed signal is an interferometric process.