Radar MASINT is a subdiscipline of measurement and signature intelligence (MASINT) and refers to intelligence gathering activities that bring together disparate elements that do not fit within the definitions of signals intelligence (SIGINT), imagery intelligence (IMINT), or human intelligence (HUMINT).
According to the United States Department of Defense, MASINT is technically derived intelligence (excluding traditional imagery IMINT and signals intelligence) that – when collected, processed, and analyzed by dedicated MASINT systems – results in intelligence that detects, tracks, identifies, or describes the distinctive characteristics target sources. in the US MASINT was recognized as a formal intelligence discipline in 1986.
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.
Radar MASINT is complementary to SIGINT. While the ELINT subdiscipline of SIGINT analyzes the structure of radar directed on a target, radar MASINT is concerned with using specialized radar techniques that measure characteristics of targets.
Another MASINT subdiscipline, radiofrequency MASINT, considers the unintentional radiation emitted from a radar transmitter (e.g., sidelobes)
MASINT radar sensors may be on space, sea, air, and fixed or mobile platforms. Specialized MASINT radar techniques include line-of-sight (LOS), over-the-horizon, synthetic aperture radar (SAR), inverse synthetic aperture radar (ISAR) and multistatic. It involves the active or passive collection of energy reflected from a target or object by LOS, bistatic, or over-the-horizon radar systems. RADINT collection provides information on radar cross-sections, tracking, precise spatial measurements of components, motion and radar reflectance, and absorption characteristics for dynamic targets and objectives.
Radar MASINT can be active, with the MASINT platform both transmitting and receiving. In multistatic applications, there is physical separation among two or more receivers and transmitters. MASINT can also passively receive signals reflected from an enemy beam.
As with many intelligence disciplines, it can be a challenge to integrate the technologies into the active services, so they can be used by warfighters. Still, radar has characteristics especially appropriate for MASINT. While there are radars (ISAR) that can produce images, radar pictures are generally not as sharp as those taken by optical sensors, but radar is largely independent of day or night, cloud or sun. Radar can penetrate many materials, such as wooden buildings. Improving the resolution of an imaging radar requires that the antenna size is many times that of the radar wavelength. Wavelength is inversely proportional to frequency, so increasing the radar frequency can improve resolution. It can be difficult to generate high power at the higher frequencies, or problems such as attenuation by water in the atmosphere limit performance. In general, for a fixed sensor, electro-optical sensors, in UV, visual, or infrared spectra, will outperform imaging radar.
SAR and ISAR are means of combining multiple radar samples, taken over time, to create the effect of a much larger antenna, far larger than would physically be possible, for a given radar frequency. As SAR and ISAR develop better resolution, there can be an argument if they still are MASINT sensors, or if they create images sufficiently sharp that they properly are IMINT sensors. Radar can also merge with other sensors to give even more information, such as moving target indicator. Radar generally must acquire its images from an angle, which often means that it can look into the sides of buildings, producing a movie-like record over time, and being able to form three-dimensional views over time.
Line-of-sight radar MASINT
Counterartillery radar
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.
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
AN/TPQ-36 and −37 counterartillery radars
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
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.
Standard TPQ-36/37 radars are semi-manual in their plotting. An Israeli enhancement makes the plotting fully digital .
Ground surveillance radar
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. 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, 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.
Fixed or semimobile ground installations
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 area of one face of the building housing the system. The antenna is oriented toward the west, monitoring the northern Pacific missile test areas."
Methods continue to evolve. COBRA JUDY was intended to gather information on long-range missiles, in a strategic role. One developmental system, COBRA GEMINI, 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.
Ship-based
The AN/SPQ-11 Cobra Judy radar, on , could also be guided by the COBRA BALL electro-optical sensors on an RC-135. Cobra Judy was supplemented by Cobra Gemini on starting around 2000 and was replaced by Cobra King in 2014 on .
Active line-of-sight satellite radar
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.
Synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) MASINT
A synthetic aperture radar (SAR) system, exploits the fast movement of an aircraft or satellite, simulating a large antenna by combining samples over time. This simulation is called the synthetic aperture.
Coupled with other MASINT and IMINT sensors, SAR can provide a high-resolution day and night collection capability. Recorded over time, it can be excellent for tracking changes. When operated at appropriate frequencies, it has ground- and water-penetrating capability, and is good for picking objects out of deliberate or natural clutter.
SAR is not, however, a trivial computational task. As the real antenna moves past the target, the range between target and antenna changes, which must be considered in synthesizing the aperture. In discussing SAR principles, Sandia National Laboratories also notes that, "for fine resolution systems, the range and azimuth processing is coupled (dependent on each other) which also greatly increases the computational processing".
In spite of the difficulties, SAR has evolved to a size that can fit aboard a UAV. Flying on the MQ-1 Predator, the Northrop Grumman AN/ZPQ-1 Tactical Endurance Synthetic Aperture Radar (Tesar) started operations, in March 1996, over Bosnia. The AN/ZPQ-1 uses a radar signal in the 10 – 20 GHz J-band, and can work in strip map, spot map, and MTI modes. These modes are applicable to a wide range of MASINT sensors.