RailSAR

Last updated

The railSAR, also known as the ultra-wideband Foliage Penetration Synthetic Aperture Radar (UWB FOPEN SAR), is a rail-guided, low-frequency impulse radar system that can detect and discern target objects hidden behind foliage. [1] [2] It was designed and developed by the U.S. Army Research Laboratory (ARL) in the early 1990s in order to demonstrate the capabilities of an airborne SAR for foliage and ground penetration. [3] However, since conducting accurate, repeatable measurements on an airborne platform was both challenging and expensive, the railSAR was built on the rooftop of a four-story building within the Army Research Laboratory compound along a 104-meter laser-leveled track. [1] [4]

Contents

At the time, the railSAR fell into the highest category of UWB radar systems, operating across a 950 MHz-wide band from 40 MHz to 1 GHz on a pulse strength of 2.5 megawatts. [1] [3] [4] It provided fully polarimetric, high resolution radar data and possessed 185% bandwidth compared to other radar systems that had less than 25% bandwidth. [1] [5]

Applications of the railSAR technology range from military uses such as detecting landmines and stationary targets in hiding for reconnaissance purposes to commercial uses, including cable and pipe detection, oil and water table measurements, and environmental remediation. [6]

Development

The development of the railSAR began in 1988 as part of an exploratory research program that aimed to create technology that could detect targets camouflaged or hidden by trees and foliage cover. [6] [7] While early efforts faced considerable challenges, advancements in analog-to-digital (A/D) converter technology, source technology, and signal-processing power allowed ARL researchers to produce a realizable system and grasp a better understanding of foliage and ground penetrating radar. Attention was focused particularly on analyzing the basic phenomenology of impulse radar, especially the propagation effects of targets, clutter, and targets embedded in clutter. [6]

The railSAR had four 1,35 m (4,5 ft) long, linear 200-ohm TEM horn antennas, two for transmitting and two for receiving, mounted on a rotating, non-conducting frame that was anchored on a hinged plate constructed out of aluminum honeycomb and covered in anechoic foam. The two transmit antennas were linearly polarized at ±45 degrees, and the two receive antennas had a low noise preamp and a PIN diode receiver protector. The design of the antenna was originally produced by the National Institute of Standards and Technology (NIST). An additional 0.5 meters of resistively loaded parallel plate section on the radiating end of the antennas improved the return loss at the high frequencies by absorbing some of the energy at the open aperture. An impulse transmitter behind the antenna assembly served to charge the antenna as well as discharge the antenna by using a hydrogen-pressured reed capsule to form the transmitted pulse. [1] [8]

An ARL-designed programmable gate-array-based system known as the timing and control (T&C) circuit provided drive signals to the transmitters and the receiver protectors. It also served to effectively reduce interference from other transmitters while also making sure to minimize interference to nearby receivers. Two computers passed GPIB (General Purpose Interface Bus) commands to the two Tektronix DSA602A digital oscilloscopes to measure the time between the trigger and the A/D clock edges and store the data on magneto-optical rewritable disks. The master computer controlled the movement of the cart on which the antennas were mounted. [1] [8]

In 1995, the design of the railSAR was incorporated into the development of the boomSAR in an effort to produce a mobile, high signal-to-noise radar. [2] [9] By 2016, the railSAR had been moved from the rooftop of the building to an indoor facility and had been subjected to several weight reductions and redesigns. [10]

Operation

In general, radar systems perform foliage and ground penetration more effectively with lower frequencies, because longer wavelengths can penetrate opaque structures deeper than shorter wavelengths. [11] [12] But in exchange for greater penetration capabilities, the lower frequencies provide a lower image resolution. [11]

Ultra-wideband radar is able to overcome this limitation in resolution by transmitting extremely narrow pulses, hence “impulse,” to obtain a sufficiently wide bandwidth. [13] [14] [15] However, pulse shortness comes at the cost of peak power, so much so that the peak power per frequency drops below the threshold of frequency selective receivers. [16] While the low power makes it difficult for eavesdroppers to detect the signal, the disadvantage of this trade-off manifests as significant increases in processing cost. [15] [17] In order to reliably receive a UWB signal given such low power per frequency, the UWB radar system must either open itself to noise with the use of a high sampling rate receiver, incorporate signal average which lowers the data rate, or increase to high signal transmit power which presents interference to other receivers. [16] In addition, a wider bandwidth may increase the likelihood of false alarms. [15]

However, the combination of low frequency and high resolution present in UWB radars proved to be extremely desirable for foliage and ground penetration, in which the increased bandwidth presented a distinct advantage over its costs. [15] In an effort to attain the necessary frequencies for adequate penetration while balancing the processing costs associated with ultra-wideband, the railSAR was designed to identify mine clusters over very large areas rather than detect each individual mine hidden in the soil and foliage. [9]

The railSAR was initially constructed to look north over the north parking lot of the ARL compound as its target area, which was mainly populated by deciduous trees. [1] The radar system required about 80 hours to collect one complete aperture of high-resolution, fully polarimetric data. Its peak power was at 500 kW with a pulse repetition frequency of 40 Hz, and the average transmitted power was about 20 mW. Creating the radar image required the railSAR to limit the Fourier processing to very small patches within the image area. [4]

Despite its use of low-frequency signals, the railSAR was capable of achieving high resolution by moving along the rail and transmitting and receiving returns in the direction perpendicular to the line of motion along the rail. [6] During performance analysis tests, the railSAR achieved a recognition probability of 90 percent with a relatively low false-alarm rate. Closer inspection revealed that the individual false alarms were generally triggered by objects in the images rather than random noise. [4]

See also

Related Research Articles

<span class="mw-page-title-main">Radar</span> Object detection system using radio waves

Radar is a radiolocation system that uses radio waves to determine the distance (ranging), angle (azimuth), and radial velocity of objects relative to the site. It is used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.

<span class="mw-page-title-main">Doppler radar</span> Type of radar equipment

A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. The term applies to radar systems in many domains like aviation, police radar detectors, navigation, meteorology, etc.

Ultra-wideband is a radio technology that can use a very low energy level for short-range, high-bandwidth communications over a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging. Most recent applications target sensor data collection, precise locating, and tracking. UWB support started to appear in high-end smartphones in 2019.

<span class="mw-page-title-main">Synthetic-aperture radar</span> Form of radar used to create images of landscapes

Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional stationary beam-scanning radars. SAR is typically mounted on a moving platform, such as an aircraft or spacecraft, and has its origins in an advanced form of side looking airborne radar (SLAR). The distance the SAR device travels over a target during the period when the target scene is illuminated creates the large synthetic antenna aperture. Typically, the larger the aperture, the higher the image resolution will be, regardless of whether the aperture is physical or synthetic – this allows SAR to create high-resolution images with comparatively small physical antennas. For a fixed antenna size and orientation, objects which are further away remain illuminated longer – therefore SAR has the property of creating larger synthetic apertures for more distant objects, which results in a consistent spatial resolution over a range of viewing distances.

<span class="mw-page-title-main">Electromagnetic interference</span> Disturbance in an electrical circuit due to external sources of radio waves

Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction. The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data. Both human-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras. EMI frequently affects AM radios. It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.

<span class="mw-page-title-main">Imaging radar</span> Application of radar which is used to create two-dimensional images

Imaging radar is an application of radar which is used to create two-dimensional images, typically of landscapes. Imaging radar provides its light to illuminate an area on the ground and take a picture at radio wavelengths. It uses an antenna and digital computer storage to record its images. In a radar image, one can see only the energy that was reflected back towards the radar antenna. The radar moves along a flight path and the area illuminated by the radar, or footprint, is moved along the surface in a swath, building the image as it does so.

Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with omnidirectional reception/transmission is known as the directivity of the array.

<span class="mw-page-title-main">Pulse-Doppler radar</span> Type of radar system

A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.

A low-probability-of-intercept radar (LPIR) is a radar employing measures to avoid detection by passive radar detection equipment while it is searching for a target or engaged in target tracking. This characteristic is desirable in a radar because it allows finding and tracking an opponent without alerting them to the radar's presence. This also protects the radar installation from anti-radiation missiles (ARMs).

Inverse synthetic-aperture radar (ISAR) is a radar technique using radar imaging to generate a two-dimensional high resolution image of a target. It is analogous to conventional SAR, except that ISAR technology uses the movement of the target rather than the emitter to create the synthetic aperture. ISAR radars have a significant role aboard maritime patrol aircraft to provide them with radar image of sufficient quality to allow it to be used for target recognition purposes. In situations where other radars display only a single unidentifiable bright moving pixel, the ISAR image is often adequate to discriminate between various missiles, military aircraft, and civilian aircraft.

A radar system uses a radio-frequency electromagnetic signal reflected from a target to determine information about that target. In any radar system, the signal transmitted and received will exhibit many of the characteristics described below.

Radar engineering details are technical details pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment. This includes field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. Radar sensors are classified by application, architecture, radar mode, platform, and propagation window.

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).

<span class="mw-page-title-main">Radio</span> Technology of using radio waves to carry information

Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver. Radio is widely used in modern technology, in radio communication, radar, radio navigation, remote control, remote sensing, and other applications.

Moving target indication (MTI) is a mode of operation of a radar to discriminate a target against the clutter. It describes a variety of techniques used for finding moving objects, like an aircraft, and filter out unmoving ones, like hills or trees. It contrasts with the modern stationary target indication (STI) technique, which uses details of the signal to directly determine the mechanical properties of the reflecting objects and thereby find targets whether they are moving or not.

<span class="mw-page-title-main">Counter-IED equipment</span>

Counter-IED equipment are created primarily for military and law enforcement. They are used for standoff detection of explosives and explosive precursor components and defeating the Improvised Explosive Devices (IEDs) devices themselves as part of a broader counter-terrorism, counter-insurgency, or law enforcement effort.

<span class="mw-page-title-main">High Resolution Wide Swath SAR imaging</span>

High Resolution Wide Swath (HRWS) imaging is an important branch in synthetic aperture radar (SAR) imaging, a remote sensing technique capable of providing high resolution images independent of weather conditions and sunlight illumination. This makes SAR very attractive for the systematic observation of dynamic processes on the Earth's surface, which is useful for environmental monitoring, earth resource mapping and military systems.

The Synchronous Impulse Reconstruction (SIRE) radar is a multiple-input, multiple-output (MIMO) radar system designed to detect landmines and improvised explosive devices (IEDs). It consists of a low frequency, impulse-based ultra-wideband (UWB) radar that uses 16 receivers with 2 transmitters at the ends of the 2 meter-wide receive array that send alternating, orthogonal waveforms into the ground and return signals reflected from targets in a given area. The SIRE radar system comes mounted on top of a vehicle and receives signals that form images that uncover up to 33 meters in the direction that the transmitters are facing. It is able to collect and process data as part of an affordable and lightweight package due to slow (40 MHz) yet inexpensive analog-to-digital (A/D) converters that sample the wide bandwidth of radar signals. It uses a GPS and Augmented Reality (AR) technology in conjunction with camera to create a live video stream with a more comprehensive visual display of the targets.

The boomSAR is a mobile ultra-wideband synthetic aperture radar system designed by the U.S. Army Research Laboratory (ARL) in the mid-1990s to detect buried landmines and IEDs. Mounted atop a 45-meter telescoping boom on a stable moving vehicle, the boomSAR transmits low frequency short-pulse UWB signals over the side of the vehicle to scope out a 300-meter range area starting 50 meters from the base of the boom. It travels at an approximate rate of 1 km/hour and requires a relatively flat road that is wide enough to accommodate its 18 ft-wide base.

The Spectrally Agile Frequency-Incrementing Reconfigurable (SAFIRE) radar is a vehicle-mounted, forward-looking ground-penetrating radar (FLGPR) system designed to detect buried or hidden explosive hazards. It was developed by the U.S. Army Research Laboratory (ARL) in 2016 as part of a long generation of ultra-wideband (UWB) and synthetic aperture radar (SAR) systems created to combat buried landmines and IEDs. Past iterations include the railSAR, the boomSAR, and the SIRE radar.

References

  1. 1 2 3 4 5 6 7 McCorkle, John (November 15, 1993). Del Grande, Nancy K.; Cindrich, Ivan; Johnson, Peter B. (eds.). "Early results from the Army Research Laboratory ultrawide-bandwidth foliage penetration SAR". Underground and Obscured Object Imaging and Detection. 1942: 88–95. Bibcode:1993SPIE.1942...88M. doi:10.1117/12.160352. S2CID   123322305.
  2. 1 2 Ressler, Marc (May 31, 1996). "The Army Research Laboratory ultra wideband BoomSAR". IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium. Vol. 3. pp. 1886–1888. doi:10.1109/IGARSS.1996.516828. ISBN   0-7803-3068-4. S2CID   62582116.
  3. 1 2 Peterson, John; Arredondo, Ruby; Chao, Tien-Hsin; Friedman, Gary; LaBaw, Clayton; Lam, Barbara; Moynihan, Philip; Tupman, Jack (March 1, 1995). "Sensor technology Assessment for Ordnance and Explosive Waste Detection and Location" (PDF). Defense Technical Information Center. Archived from the original on November 1, 2019. Retrieved November 1, 2019.
  4. 1 2 3 4 Sabio, Vincent (August 1994). "Target Recognition in Ultra-Wideband SAR Imagery" (PDF). Final Report. Bibcode:1994arl..reptR....S. ARL-TR-378. Archived from the original on November 1, 2019. Retrieved November 1, 2019.
  5. ↑ Miller, Timothy; Potter, Lee; McCorckle, John (October 1997). "RFI suppression for ultra wideband radar". IEEE Transactions on Aerospace and Electronic Systems. 33 (4): 1142–1156. Bibcode:1997ITAES..33.1142M. doi:10.1109/7.625096. ISSN   1557-9603. S2CID   35421145.
  6. 1 2 3 4 Ressler, Marc; Happ, Lynn; Nguyen, Lam; Ton, Tuan; Bennett, Matthew (May 8, 1995). "The Army Research Laboratory ultra-wide band testbed radars". Proceedings International Radar Conference. pp. 686–691. doi:10.1109/RADAR.1995.522632. ISBN   0-7803-2121-9. S2CID   110186067.
  7. ↑ Kovel, Steven; Brand, John (January 1995). "Research Support for the Depth and Simultaneous Attack Battle Lab" (PDF). Defense Technical Information Center. Archived (PDF) from the original on November 1, 2019. Retrieved November 1, 2019.
  8. 1 2 Ressler, Marc; McCorkle, John (1995). "Evolution of the Army Research Laboratory Ultra-Wideband Test Bed". In Carin, Lawrence; Felson, Leopold (eds.). Ultra-Wideband, Short-Pulse Electromagnetics 2. Berlin, Germany: Springer Science & Business Media. pp. 109–123. ISBN   978-1489913968.
  9. 1 2 Carin, L.; Geng, N.; McClure, M.; Sichina, J.; Lam Nguyen (1999). "Ultra-wide-band synthetic-aperture radar for mine-field detection". IEEE Antennas and Propagation Magazine. 41 (1): 18–33. Bibcode:1999IAPM...41...18C. doi:10.1109/74.755021.
  10. ↑ Ranney, Kenneth; Phelan, Brian; Sherbondy, Kelly (May 12, 2016). Ranney, Kenneth I; Doerry, Armin (eds.). "Fully polarimetric data from the ARL RailSAR". Radar Sensor Technology XX. 9829: 98291R. Bibcode:2016SPIE.9829E..1RR. doi:10.1117/12.2228851. S2CID   124419915.
  11. 1 2 Wolff, Christian. "Ground penetrating radar". radartutorial.eu. Retrieved November 1, 2019.
  12. ↑ Podest, Erika (November 29, 2017). "Basics of Synthetic Aperture Radar (SAR)" (PDF). ARSET. Retrieved November 1, 2019.
  13. ↑ Paulose, Abraham (June 1994). "High Radar Range Resolution with the Step Frequency Waveform" (PDF). Defense Technical Information Center: 7. Bibcode:1994MsT..........7P. ADA284611. Archived from the original on November 1, 2019. Retrieved November 1, 2019.
  14. ↑ Frenzel, Louis (November 11, 2002). "Ultrawideband Wireless: Not-So-New Technology Comes Into Its Own". Electronic Design. Retrieved November 1, 2019.
  15. 1 2 3 4 Fowler, Charles; Entzminger, John; Corum, James (November 1990). "Report: Assessment of Ultra-Wideband (UWB) Technology" (PDF). Virginia Tech VLSI for Telecommunications. Retrieved November 1, 2019.
  16. 1 2 Barrett, Terence (July 2000). "History of UltraWideBand (UWB) Radar & Communications: Pioneers and Innovators". Progress in Electromagnetics Symposium. S2CID   15576832.
  17. ↑ McCorkle, John (March 1, 2002). "Why Such Uproar Over Ultrawideband?". Electrical Engineering Times. Retrieved November 1, 2019.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.