In a complex world with unpredictable and constantly changing threats, having better information is the key to staying ahead and mitigating the threats. Security concerns across the global landscape reinforce the need for continuous awareness of one’s environment. A capability that can provide intelligence imagery anytime, in any type of weather, is critical to enhancing situational awareness and gaining a tactical edge. That capability is provided by Synthetic Aperture Radar, or SAR.
In traditional Earth observation satellites, optical instruments sense energy in the visible, infrared, thermal, and microwave portions of the spectrum in order to produce photographs. These optical instruments are known as passive sensors because they measure energy emitted from another source; i.e. the natural energy from the sun being reflected off the surface of the Earth.
Synthetic aperture radar, or SAR, is a completely different way to generate a picture by actively illuminating the ground rather than utilizing the light from the sun as with optical images. The basic principle of any imaging radar is to emit an electromagnetic signal (which travels at the speed of light) toward a surface and record the amount of signal that bounces/echoes back, or “backscatters,” and its time delay. The resulting radar imagery is built up from the strength and time delay of the returned signal, which depends primarily on the roughness and electrical conducting properties of the observed surface and its distance from the orbiting radar. The radio waves used in SAR typically range from approximately 3 cm up to a few meters in wavelength, which is much longer than the wavelength of visible light, used in making optical images. These wavelengths fall within the microwave part of the spectrum
Synthetic aperture radar (SAR) refers to a technique for producing fine-resolution images from a resolution-limited radar system. The resolution of a radar antenna is dependent on the antenna aperture—the larger the antenna, the better the resolution. A SAR takes advantage of the motion of the antenna to achieve an apparent antenna length, or aperture, greater than its actual length. It requires that the radar be moving in a straight line, either on an airplane or, on a Satellite orbiting in space. As the antenna moves along a flight path, successive echoes are received from the same target and may be processed to give spatial resolution equivalent to an antenna as long as the distance the antenna moved when receiving the target echoes.
SAR is the only imaging system that can generate high-resolution imagery, anytime – even in inclement weather or darkness. Its microwave operating frequencies are chosen so that the radar imaging is unaffected by weather. Since SAR instruments don’t depend on the Sun’s energy to collect surface data, SAR satellites can operate just as well during the day or night.
Synthetic aperture radar (SAR) while seeing through the darkness, clouds, and rain, can detect changes in habitat, levels of water and moisture, effects of natural or human disturbance, and changes in the Earth’s surface after events such as earthquakes or sinkholes openings. Additionally, SAR signals can penetrate through clouds to “see” the covered surface underneath, allowing satellites to have a full view of the Earth’s surface regardless of atmospheric or lighting conditions. SAR can also “see” through other types of cover such as smoke, vegetation, snow, or sand, depending on the satellite’s designated operating band (which indicates the sensor’s associated frequency and wavelength).
SAR bands are helpful in categorizing the penetration strength and thus the potential applications of a satellite, such as Germany’s TanDEM-X (low-penetration X-band), Canada’s RCM (moderate-penetration C-band), and Japan’s ALOS-2 (high-penetration L-band).
Synthetic Aperture Radar (SAR) principle
A SAR system consists of a transmitter, a receiver, an antenna (including a pointing or steering mechanism), image processor and display unit.
Side-imaging radar is different from a forward-looking radar, such as weather radar. Forward-looking radar cannot create images. A side-imaging radar antenna, which amplifies the transmitted and received signal, is carried in an airplane or an orbiting satellite, can be used to make an image of the ground below.
Such a radar image is formed by transmitting pulses of radio frequency (RF) energy towards the ground and to the side of the aircraft, and measuring the strength of the return (sometimes called an “echo”) and the length of time it takes to make the round trip back to the antenna. In this manner, the ground is “scanned” in two dimensions. One dimension is the “range” dimension. Objects are placed along in this dimension according to their distance from the radar. The second dimension is the “along-track” (or “cross-range” or “azimuth”) dimension. In this dimension, the ground is scanned by the beam moving across the ground at a rate equal to the speed of the platform (aircraft or satellite), and objects are placed in this dimension according to the position of the aircraft along the track. An image is built up from the reflected signals in both dimensions.
In “real aperture radar,” the range resolution is defined by the width of the pulses transmitted from the antenna. The azimuth resolution is determined by the width of the beam’s footprint on the ground, and the width of the beam is inversely proportional to the antenna length. A short antenna length corresponds to a wide beamwidth (beam footprint on the ground).
Because the radar signal loses energy as it travels – at a rate equivalent to the beam width (wavelength / antenna size) – by the time it hits the surface, the beam has spread dramatically. For example, with a signal wavelength of 10 centimeters and an antenna of 10 meters in diameter, the beam width is 1/100 radians (0.6 degrees). From an altitude of 1,000 kilometers, the resulting beam width on the ground becomes a very large 10 km, producing an image resolution which is insufficient for most applications. Because flying an antenna large enough to generate a reasonable azimuth resolution, in space, is prohibitive, this limits the spatial resolution in the azimuth direction. SAR is the solution to this dilemma as it can vastly improve the resolution.
The development of advanced processing algorithms solved this problem, leading to a new generation of imaging radars called Synthetic Aperture Radar. A Synthetic Aperture Radar (SAR), or SAR, is a coherent mostly airborne or spaceborne sidelooking radar system which utilizes the flight path of the platform to simulate an extremely large antenna or aperture electronically, and that generates high-resolution remote sensing imagery.
As a target (like a ship) first enters the radar beam, the backscattered echoes from each transmitted pulse begin to be recorded. As the platform continues to move forward, all echoes from the target for each pulse are recorded during the entire time that the target is within the beam. The point at which the target leaves the view of the radar beam some time later, determines the length of the simulated or synthesized antenna. The synthesized expanding beamwidth, combined with the increased time a target is within the beam as ground range increases, balance each other, such that the resolution remains constant across the entire swath.
Over time, individual transmit/receive cycles (PRT’s) are completed with the data from each cycle being stored electronically. The signal processing uses magnitude and phase of the received signals over successive pulses from elements of a synthetic aperture. After a given number of cycles, the stored data is recombined (taking into account the Doppler effects inherent in the different transmitter to target geometry in each succeeding cycle) to create a high resolution image of the terrain being over flown. The SAR works similar of a phased array, but contrary of a large number of the parallel antenna elements of a phased array, SAR uses one antenna in time-multiplex. The different geometric positions of the antenna elements are result of the moving platform now.
For SAR, Spatial resolution, the ability to resolve objects on the ground, differs in the range direction (perpendicular to the flight direction) compared to the azimuth direction (parallel to the flight direction). The nominal slant range resolution is ∆r = Cτ/2 where τ is the pulse length, C is the speed of light and θ is the look angle. The factor of 2 accounts for the 2-way travel time of the pulse. The ground range resolution is geometrically related to the slant range resolution Rr = Cτ / (2 sin θ).
Note the ground range resolution is infinite for vertical look angle and improves as look angle is increased. Also note that the range resolution is independent of the height of the spacecraft H. The range resolution can be improved by increasing the bandwidth of the radar. Usually, the radar bandwidth is a small fraction of the carrier frequency so shorter wavelength radar does not necessarily enable higher range resolution.
The achievable azimuth resolution of a SAR is approximately equal to one-half the length of the actual (real) antenna and does not depend on platform altitude (distance). The requirements are: Stable, full-coherent transmitter; An efficient and powerful SAR-processor, and Exactly knowledge of the flight path and the velocity of the platform. Using such a technique, radar designers are able to achieve resolutions which would require real aperture antennas so large as to be impractical with arrays ranging in size up to 10 m.
The resolution of SAR systems, which indicates the minimal distance of two small targets in the scene which can be separated in the SAR image, has been improved over the last decades up to the order of a decimetre.
Interpreting SAR Images
For most purposes, the transmitted signal can be thought of as a single frequency sinusoid wave (S-shaped) with a well-defined amplitude (height) and phase. SAR processing provides a complex image: a pixel with associated amplitude and phase. Once calibrated, the pixel’s amplitude is proportional to the reflectance of the surface. The phase is proportional to the distance the wave traveled between the radar and the ground, any delays due to traveling through the atmosphere, and any phase contribution imparted by the reflectance from the surface.
The interpretation of synthetic aperture radar (SAR) images is not straightforward. The reasons include the non-intuitive, side-looking geometry. Here are some general rules of thumb:
- Regions of calm water and other smooth surfaces appear black, because the radar pulse reflects away from the spacecraft.
- Rough surfaces appear brighter, as they reflect the radar in all directions, and more of the energy is scattered back to the antenna. Rough surface backscatter even more brightly when it is wet.
- Any slopes lead to geometric distortions. Steeper angles lead to more extreme layover, in which the signals from the tops of mountains or other tall objects “lay over” on top of other signals, effectively creating foreshortening. Mountaintops always appear to tip towards the sensor.
- Layover is highlighted by bright pixel values. The various combinations of the polarization for the transmitted and received signals have a large impact on the backscattering of the signal. The right choice of polarization can help emphasize particular topographic features.
- In urban areas, it is at times challenging to determine the orbit direction. All buildings that are perfectly perpendicularly aligned to the flight direction show very bright returns.
- Surface variations near the size of the radar’s wavelength cause strong backscattering. If the wavelength is a few centimeters long, dirt clods and leaves might backscatter brightly.
- A longer wavelength would be more likely to scatter off boulders than dirt clods, or tree trunks rather than leaves.
- Wind-roughened water can backscatter brightly when the resulting waves are close in size to the incident radar’s wavelength.
- Hills and other large-scale surface variations tend to appear bright on one side and dim on the other. (The side that appears bright was facing the SAR.)
- Due to the reflectivity and angular structure of buildings, bridges and other human-made objects, these targets tend to behave as corner reflectors which are used for calibrating SAR instruments and show up as bright spots in a SAR image.
SAR images are so amazingly clear and crisp that SAR has been for a diverse range of military and science applications. This includes earth resources monitoring, agricultural and land use, ocean spill monitoring, polar ice assessment, intelligence acquisition, battlefield reconnaissance and weapon delivery. For remote sensing a couple of earth-observing satellites are currently in operation, having imaging sensors working in different spectral areas.
SAR for Security
Given the increased threats of environmental phenomena to national and global security, SAR can provide additional information to assess and respond to climate change, ecosystem loss, natural disasters, and more.
Agriculture. Differences in surface roughness are indicative of field ploughing, soil tillage, and crop harvesting.
Floods. Differences in surface reflection can help distinguish heavy flooding, light flooding, urban areas, and permanent bodies of water.
Land subsidence. Differences in measurements over time can reveal displacements of land, such as sinking ground caused by the extraction of underground natural resources.
Snow cover. Differences in surface reflection can help forecast snowmelt by distinguishing wet snow, dry snow, and snow-free areas.
Wildfires. Penetration through thick smoke can provide more accurate and timely information about the extent of a forest fire and can help quantify vegetation loss.
Wetlands. Penetration through wetland areas can reveal flooded vegetation where land is covered by shallow water.
SAR technology trends
Beyond the overall availability of SAR images there are further pros for the utilization of radar. The coherent nature of SAR enables the user to process images of subsequent overflights for interferometrical analyses. Synthetic Aperture Radar, which is typically used to create radar images, works by sending out radar pulses over an area as the platform moves around the area. The reflected radar pulses are then recorded and compiled into a high-resolution image. Inverse Synthetic Aperture Radar works similarly—instead of utilizing the movement of platform, ISAR is dependent on target movement.
Depending on the radar wavelength the radar signal will be reflected by vegetation or the ground structure. With the choice of a concrete centre frequency of the SAR sensor, the developer decides about the appearance of the resulting radar images. Different combinations of the transmit and receive polarization can also be used for instance to classify the kind of vegetation. Advanced classification algorithms are able to identify military objects in the scene which is of great interest.
Operation of a bi- or multi-static configuration offers some more advantages. The receiver system, including expensive acquisition electronics, need not to transmit any energy and thus can be designed hardly detectable. Stealth targets feature a minimized mono-static radar cross section (RCS). Target echoes might be considerably higher in a bi-static configuration so the probability of detection will be increased.
Demands for increased resolution and smaller components have led to quantum leaps in the development of new SAR technologies, including foliage penetration, dual band (UHF/VHF) sensors, and ground moving target indication capabilities. In the future, SAR will be used not only for remote sensing, or as an important contribution to surveillance and reconnaissance in conflict areas, but for many more applications such as a true imaging component in automotive sensors, or in highly interesting indoor applications.
SAR meets the military’s need for an all-weather, day/night sensor that could produce high quality reconnaissance imagery in adverse weather and restricted visibility conditions. These features and the ability to image large areas with fine resolution in a relatively short period of time make this sensor useful for many military applications.
Imaging radars provide several capabilities for the military, including reconnaissance, surveillance and targeting applications. Because of their ability to operate under inclement weather conditions and differing times of day, they are sometimes used for treaty verification and navigation.
In military applications, a synthetic aperture radar is used to detect surface features, like building complexes and missile sites, and topographical features of the surrounding terrain. Thus, it is used in battlefield reconnaissance, weapon guidance, and mission planning for future operations.
The high-resolution images created by radar imaging allows the military to distinguish between terrain and manmade targets and is capable of detecting and analyzing the location, speed, size and radar cross section of on-the-move targets. Because they rely on radar rather than infrared or optical wavelengths, imaging radars can also detect targets hidden by foliage as well as some underground targets.
Military researchers are looking to develop a next-generation imaging radar that doesn’t rely on movement, while producing 3D images regardless of bad weather, tree cover or other obstructions. In 2014, DARPA launched its Advanced Scanning Technology for Imaging Radars (ASTIR) program. The program is looking to develop technologies to demonstrate new imaging radar architecture.
Earlier generation of SARs for military use had been large, complex, and expensive. Additionally, they have been mounted on special purpose, single mission aircraft which are costly to operate. Nowadays the situation has changed. A small, modular SAR, called Miniature Synthetic Aperture Radar (MSAR) are available which can be mounted with relative ease on Unmanned Aerial Vehicles (UAV), helicopters, or on multi-mission aircraft such as the F-16, F/A-18, or on the F-14.
The latest generation SAR like PrecISR™, HENSOLDT’s new family of airborne multi-mission surveillance radars offer high performance and compact design, comprises of the newest generation gallium nitride AESA antenna technology with two dimensional e-scan capability, combined with large bandwidth multi-channel radar core electronics and integrated radar signal processing.
Maritime domain awareness
Maritime Domain Awareness is the understanding of all aspects relating to the maritime domain that may have an effect on the security, economy or environment of a country bordering the sea. The monitoring of ships can be done by taking advantage of Synthetic Aperture Radar imagery which allows for the monitoring of large portions of the Earth.
With SAR satellite data, one can obtain knowledge about marine activities taking place in the country’s waters. Obtaining information of every operation, either legal or unlawful, happening in your EEZ will enable you to plan and execute interdiction efforts, stop illegal transits, protect sea-lanes, and accomplish other goals related to security and safety of the nation.
With SAR satellite data you can detect vessels in the area of your interest at the predefined frequency. Combining this information with AIS data will allow you to get detailed information on collaborative vessels that have AIS broadcast, and on dark ships that have their AIS transponders purposely turned off. Automatic Identification System transmit geographical ship coordinates which allow operators to track ships. Frequent detection of dark vessels, including semi-submersible ships, will enable you to take timely actions and prevent negative economic, environmental and security-related impacts of these suspicious operations.
HRL develops Advanced Scanning Technology for Imaging Radars (ASTIR)
Recently, the Harvard Robotics Laboratory (HRL), participating in the ASTIR project, has developed a high-resolution, low-power coded aperture subreflector array (CASA) that can potentially see weapons or explosives concealed on a person, at tactically safe distances.
The HRL approach leverages Coded aperture radar, a technology invented, developed, and demonstrated at HRL, to develop a Coded Aperture Subreflector Array (CASA) for affordable, high-resolution radar imaging without the need for a moving platform. This technology provides a scalable approach with unsurpassed pattern control, flexibility in operating frequency and digital beamforming at the sub-array level. CASA achieves low latency 3D imaging by modulating both transmitted and received radar signals with binary phase codes, inverting the known codes to determine the individual element signals, then applying weights to digitally construct independent (multiplicative) transmit and receive beams.
HRL will be applying their expertise in millimeter wave sensors, including antenna arrays, silicon micromachining, wafer bonding and ASIC design and implementation, to evaluate and demonstrate CASA performance and manufacturability.
Capella Space’s first SAR imagery satellite will provide imagery as well as in-house analytics for interpreting that data to US Navy
The first satellite in Capella Space’s planned constellation was successfully deployed to orbit Aug. 31,2020 bringing the company one step closer to its vision of offering global on-demand synthetic aperture radar imagery — a capability in which the U.S. government has expressed increasing interest. Dubbed “Sequoia” by Capella Space, this first publicly available satellite in what is expected to be a 36-satellite constellation will be able to deliver synthetic aperture radar, or SAR, imagery of the Middle East, the Korean Peninsula, Japan, Europe, Southeast Asia, Africa and the United States. Customers for this imagery include the U.S. government.
Unlike traditional electro-optical satellite imagery, which can be degraded or denied by adverse lighting conditions or weather, SAR creates images with radar, meaning it can produce images regardless of the weather or lighting conditions. Additionally, SAR sensors can provide data on material properties, moisture content, precise movements, and elevation, meaning that SAR can be used to build 3D recreations of a given geographical area. Capella says its planned SAR satellite constellation will be able to collect sub-0.5 meter imagery, capable of identifying various types of aircraft or vehicles at ground level.
The Navy signed a contract with the company through the Defense Innovation Unit’s Commercial Solutions Opening. Under the new contract, Capella will provide imagery as well as in-house analytics for interpreting that data. The Navy deal is just the latest military and intelligence contract for the company.
Synthetic Aperture Radar for Helicopter Landing in Degraded Visual Environments
The development of sensors to assist helicopter landing in degraded visual environments (DVEs) is currently an important US Army requirement addressing the Survivability of Future Vertical Lift Platforms program, one of the Army’s modernization priorities.
Over the past three decades, dozens of rotary-wing aircraft crashes have been responsible for a large number of casualties to US and coalition forces in different parts of the world. Out of these crashes, at least 75% have occurred in brownout conditions, where dirt or dust is stirred up and recirculated by the rotor blades, creating low- or zero-visibility environments for the pilots. Research and development efforts to mitigate this issue starting in the early 2000s recommended several possible solutions based on optical, IR, and radar sensors. Unfortunately, most of these solutions have proven to be either ineffective or they involved unacceptable size, weight, power, and/or cost (SWAP-C), leaving the Army with a capability gap to be filled.
The US Army Research Laboratory (ARL) is currently working on a sensor solution to this problem based on millimeter-wave (MMW) imaging radar technology. The main idea behind this sensor is to combine a linear antenna array with the radar platform motion to obtain a high-resolution 3-D terrain map of the landing zone. This information would be passed to the pilot via a helmet-mounted display to assist in deciding whether the landing zone is safe. Several previous efforts in developing similar sensors, based on passive or active MMW technology, have focused heavily on 2-D antenna arrays working in scanning mode to obtain a terrain map. These efforts generally produced devices that proved either too expensive, unreliable, and/or inaccurate for the required task.
The ARL-proposed solution leverages advanced radar imaging methodology, together with the current boom in commercial MMW RF technology (driven by developments in autonomous car navigation and 5-G wireless communications), to produce a reliable, low-SWAP-C sensor prototype addressing this requirement.
The proposed radar system will use a linear antenna array and the forward-looking synthetic aperture radar (FLSAR) concept to achieve the stated goals. A linear antenna array mounted on the rotorcraft’s front end will provide the required cross-range resolution, while the transmitted signal bandwidth (up to 1 GHz) will provide downrange resolution. To achieve resolution in the vertical dimension, the radar will exploit small elevation angle deviations in the helicopter flight path, which naturally occur when the pilot prepares for landing. Overall, this new radar sensor concept represents a significant shift in implementation from a hardware-heavy solution to an emphasis on signal processing and computational power, with large potential cost savings and performance improvements.
As part of this research, a detailed analysis of the 3-D imaging performance of the proposed radar system was performed by investigating the point spread function (PSF). The emphasis was on synthetic aperture radar (SAR) and antenna array processing, which are key to this sensor’s implementation.
US Air Force assesses bomb damage using synthetic aperture radar in test reported in Dec 2020
The 422nd Test and Evaluation squadron conducted at Synthetic Aperture Radar Map Bomb Hit Assessment on December 15, 2020. During this test, two F-15Es dropped live Joint Direct Attack Munitions, while other weapons systems including F-15Es, F-35s, F-16s, FA-18s, RQ-4, MQ-9, U-2 and joint partners used SAR Mapping technology to assess if the bombs hit and destroyed the intended targets.
“The objective of the test is to determine our ability and timeline to conduct real time strike assessment using synthetic aperture radar maps,” said Maj Derek Anderson, director of operations, 706th Fighter Squadron. “Synthetic aperture radar maps allow manned and unmanned platforms to image target areas from long ranges and through weather.” This test was ultimately designed to find a new way to effectively close the kill chain – confirming destruction of the target. SAR Mapping technology isn’t new technology, but this test puts it to use in a way that can solve an issue for the warfighter in dynamic fights.
“Operating in Europe or the Pacific we can expect weather and the need to remain beyond the operating range of current electro-optical and infrared sensors due to threats,” said Anderson. “This test helped us develop platform and package level tactics, techniques and procedures that will inform operational and strategic level decisions.”
Recent SAR launches
In recent years, several companies have raised money to build and launch constellations of small SAR satellites. Two have succeeded so far. Finland’s Iceye operates five X-band SAR satellites. San Francisco-based Capella Space began releasing imagery in October from its first operational satellite, Sequoia, which also operates in X-band.
Spacety plans to build, launch and operate a constellation of 56 small SAR satellites. Chinese startup Spacety released the first images from Hisea-1, a C-band Synthetic Aperture Radar (SAR) satellite, launched Dec. 22 on China’s new Long March 8 medium-lift rocket.
Sep 2020 – IMSAR and Primoco UAV successfully performed the integration and preliminary flight testing of the NSP-7 Synthetic Aperture Radar on the Primoco One 150 UAV. The live flight tests in the Czech Republic verified the aircraft performance and confirmed flight endurance of up to 10 hours. With the SAR radar installed on the portside of the fuselage, the payload bay remains unobstructed and it also allows simultaneous installation and operation of the EO/IR surveillance system.
Sep 2020 – Finnish start-up ICEYE, which has been building and operating a constellation of Synthetic-Aperture Radar (SAR) small satellites, raised another USD 87 million Series C round of financing. The round was led by the existing investor True Ventures and includes participation by OTB Ventures. This brings the total funding for the company to USD 152 million since its founding in 2014. The company has already launched a total of five SAR satellites and is planning to launch an additional four later this year, with a plan to add eight more by 2021.
Also, ISRO and NASA are working together on the NASA-ISRO Synthetic Aperture Radar (NISAR) mission, to launch a dual frequency synthetic aperture radar satellite by 2021. The satellite is expected to cost around USD 1.5 billion that aims to study global environmental change and natural disasters.
The synthetic aperture radar market was valued at USD 3.32 billion in 2020, and it is expected to reach USD 6.47 billion by 2026, at a CAGR of 11.6%, during the forecast period (2021 – 2026). Synthetic aperture radar (SAR) is a technique which uses signal processing, to improve the resolution beyond the limitation of physical antenna aperture. With the growing demand for satellite imagery and situational awareness in emergency situations, the need for robust change detection methods is continuously increasing. Various infrastructure damage detection methods have been advanced in recent years, which is expected to increase the adoption in the synthetic aperture radar market.
Synthetic aperture radars (SAR) have numerous applications, including terrain structural information for mineral exploration, oil spill boundaries on the water to environmentalists, and investigating and gathering information for military operations, among various others. The last two decades have witnessed unprecedented growth in the satellite-based earth observation segment.
There are multiple potential applications of SAR, such as biomass estimation, crops monitoring, vegetation cover mapping, mineral exploration, ice dynamics modelling, forest fire, oil spill, and biological water monitoring. Some of these are yet to be adequately explored, since lower cost electronics are just beginning to make SAR technology economical, for smaller scale use. SAR images of the ocean surface are utilized to detect a variety of ocean features, such as refracting oceanic internal waves, surface gravity waves, wind fields, oceanic fronts, coastal eddies, and intense low pressure systems (for instance, hurricanes and polar lows), since they all affect the short wind waves, responsible for radar backscatter.
Moreover, factors, such as increasing demand for enhanced imaging technologies for remote sensing and security concerns, specifically to counter terrorism in the Middle East and Asia-Pacific, and the need for continuous awareness of the environment, are expected to drive the synthetic aperture radar market.
The increase in the military and defense spending is enabling the defense sector to develop missiles with improved precision targeting. Compared to an airborne SAR, missile-borne SAR has various important characteristics, such as high flight speed with straight movement and a large squint angle, which are crucial elements in measuring the precision in real-time.
With applications, such as weapons fire-control (missiles or guns) and accuracy control, intelligence, surveillance, and reconnaissance missions, air, and spaceborne SAR systems are expected to witness a high adoption over ground-based systems. Moreover, in the defense sector, wide-area surveillance has diverse applications, such as monitoring remote areas for human movement, coast guard vessels, offshore missile platforms, and the establishment of perimeter security. Technological developments have led to the increasing adoption of unmanned airborne surveillance (UAS) systems or drones.
Major players in SAR market are Airbus SE, ASELSAN AS, BAE Systems Plc, Israel Aerospace Industries Ltd., Leonardo Spa, Lockheed Martin Corp., Northrop Grumman Corp., Raytheon Technologies Corp., Saab AB and Thales Group
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