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The boomSAR is a mobile
ultra-wideband Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) 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 applicat ...
synthetic aperture radar Synthetic-aperture radar (SAR) is a form of radar that is used to create two-dimensional images or 3D reconstruction, three-dimensional reconstructions of objects, such as landscapes. SAR uses the motion of the radar antenna over a target regi ...
(UWB SAR) system designed by the U.S. Army Research Laboratory (ARL) in the mid-1990s to detect buried
landmines A land mine, or landmine, is an explosive weapon often concealed under or camouflaged on the ground, and designed to destroy or disable enemy targets as they pass over or near it. Land mines are divided into two types: anti-tank mines, whic ...
and IEDs. Mounted atop a 45-meter telescoping boom on a stable moving vehicle, the boomSAR transmits low frequency (50 to 1100 MHz) 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.


Characteristics

The boomSAR is a fully polarimetric system that transmits and receives low-frequency
waveform In electronics, acoustics, and related fields, the waveform of a signal is the shape of its Graph of a function, graph as a function of time, independent of its time and Magnitude (mathematics), magnitude Scale (ratio), scales and of any dis ...
s with over 1 gigahertz of usable
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
, covering a spectrum from approximately 40 MHz to 1 GHz. Its testbed radar subsystems consist of the antennae, the transmitter, the analog-to-digital (A/D) converter, the processor/data storage system, the timing and control assembly, the MOCOMP subsystem, and the operator interface computer. Much of these components are modular in nature for easy modification and upgrades and were constructed with commercial-off-the-shelf (COTS) technology to reduce costs.


Boom platform

The boom lift platform for the boomSAR is a 150-ft-high telescoping lift device with a basket which can be moved axially and radially and is able to handle a load capacity of 500 to 1000 lbs depending on the position of the telescoping arms. Built by JLG Inc, it possesses the unique capability of base movement while the boom is extended, allowing the boomSAR to conduct data collection using simulated airborne geometry. The down-look angles to the target typically varies from 45 degrees to 10 degrees depending on the range to the target and the height of the boom.


Antennas

The boomSAR utilizes two transmitting and two receiving antennas to provide the full polarization matrix (HH, HV, VH, VV) in a quasi-monostatic sense. All four antennas are 200 W, open-sided, and resistively terminated TEM horn antennas that are about two meters long with a 0.3-meter aperture. Since the subsystems were designed specifically for low-frequency UWB SAR application, the TEM horn antennas have a wide beamwidth in excess of 90 degrees and are fitted with a high-power, wide-bandwidth balun that can handle the 2-MW peak pulse of the impulse transmitter. According to later data, this antenna/balun combination is capable of transmitting a short-pulse UWB signal with a bandwidth from 40 MHz to over 2000 MHz with a pulse repetition frequency up to 1 kHz through the four TEM horn antennas.


Motion Compensation (MOCOMP) system

The boomSAR MOCOMP system consists of a computer and a geodimeter, which accounts for the motion compensation and positioning of the radar in three-dimensional space. The geodimeter consists of a robotic
laser-ranging A laser rangefinder, also known as a laser telemeter or laser distance meter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by ...
theodolite A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and ...
set up on one end of the aperture, a retro-reflector mounted on the boom lift platform near the antennas, and a control unit mounted on the base of the boom lift. As the retro-reflector moves with the boom lift platform, the theodolite tracks the horizontal and vertical angular positions of the retro-reflector and measures its range. The position of the retro-reflector is then transmitted to the geodimeter control unit using an FM radio link updated at a rate of 2.5 Hz. The control unit then proceeds to transmit the position information to the MOCOMP computer.


Processing System

The processing system relies on a VME card-cage with a Sun SPARC 5 host and eight Intel i860-based CSPI Supercard array processors to obtain the computational power needed to presume, filter, and back-project the range profiles to form the SAR image. Image processing for the boomSAR occurs in the field immediately after data collection. In order to accommodate the boomSAR's very wide bandwidth for data transfer and parallel processing opportunities, scientists at the U.S. Army Research Laboratory have investigated the use of Mercury parallel processors.


Analog-to-Digital converter

The A/D subsystem consists of a pair of Tektronix/Analytek VX2005C, 2 Gsamples/sec A/D converters, and a stable reference clock. It acts as a wide-band receiver for the radar and is uniquely capable of providing the time difference between the sample clock and the trigger event with 10 ps resolution.


Development

The boomSAR originated as an extension of the railSAR, a rail-guided UWB SAR system built on the rooftop of an ARL building. Once the railSAR displayed promising results from early foliage and ground penetration field trials, plans were made to transition the railSAR technology onto a mobile platform. The initial goal behind the development of the boomSAR was to emulate the functions of an airborne radar system in order to better understand its full potential. Unlike an airborne system, the boomSAR provided a cost-effective method of determining the upper bound of performance for this approach to radar through precisely controlled and repeatable experiments. In 1999, ARL collaborated with researchers in academia and industry to develop modeling and processing algorithms for the boomSAR. These include models for method of moments (MoM) and fast multipole method (FMM), which contributed to the development of
automatic target recognition Automatic target recognition (ATR) is the ability for an algorithm or device to recognize targets or other objects based on data obtained from sensors. Target recognition was initially done by using an audible representation of the received signal ...
algorithms for penetration systems. The boomSAR technology was later repurposed by the U.S. Army Research Laboratory to develop the UWB Synchronous Impulse Reconstruction (SIRE) radar, which mounted the SAR system on an
all-terrain vehicle An all-terrain vehicle (ATV), also known as a light utility vehicle (LUV), a quad bike or quad (if it has four wheels), as defined by the American National Standards Institute (ANSI), is a vehicle that travels on low-pressure tires, has a seat ...
without the boom lift.


Testing


Aberdeen Proving Ground Test

In 1995, an initial data collection trial for the boomSAR was conducted at Aberdeen Proving Ground (APG) in Maryland to test its foliage and ground penetration capabilities. The testing site was characterized by a
deciduous forest In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, after flo ...
of varying density as well as straight and curved roads through the foliage that could accommodate the width of the boom lift. During the test, canonical targets and tactical targets were hidden in the forest or buried in the soil for the boomSAR to detect. The canonical targets included dipoles, trihedrals, and dihedrals arranged to test both radar calibration and performance, while tactical targets consisted of commercial utility cargo vehicles and HMMWVs placed around the site. The data collected from the APG test was later used to study methods for distinguishing vehicles from background clutter. Analysts determined that trees and vehicles have different frequency characteristics and that the difference in characteristics could aid automatic target discrimination processing.


Yuma Proving Ground Test

In the late 1990s, two separate data collection efforts were conducted at Yuma Proving Ground in Arizona and
Eglin Air Force Base Eglin Air Force Base is a United States Air Force (USAF) base in the western Florida panhandle, located about southwest of Valparaiso, Florida, Valparaiso in Okaloosa County, Florida, Okaloosa County. The host unit at Eglin is the 96th Test ...
in Florida as part of a research initiative sponsored by the Strategic Environmental Research and Development Program (SERDP) to enhance the detection of unexploded landmines. At Yuma Proving Ground, the trials were held at the Steel Crater Test Site, which partly overlapped with the neighboring Phillips Drop Zone and divided the area into two sections. The section overlapping the Phillips Drop Zone featured an almost homogeneous soil layer and was virtually free of vegetation due to the soil having been turned over to a depth of about 2 feet. In contrast to the plowed section, the natural section was relatively untouched. During the test, the plowed section had more than 600 inert targets buried in the ground such as artillery shells, rockets, mortar shells, submunitions, bombs, and mines (M-20 anti-tank mines and Valmara 69 mines) as well as false targets like magnetic rocks, animal burrows, and soda cans. These inert targets were buried at different depths (surface to 2 meters deep) and entry angles (0 to 90 degrees) in order to provide a comprehensive performance evaluation for the boomSAR. On the other hand, the natural section predominantly featured tactical targets like vehicles, although it also had some mines, wires, and pipes hidden as well. The boomSAR was tasked with detecting the targets while driving down the nearby Corral Road. According to the results of the trial, the M-20 mines were visible in both frequency bands when they were placed close to the surface, those that were deeply buried could not be detected in the high frequency band. On the other hand, the Valmara 69 mines could not be detected in the low frequency band but were somewhat visible in the high band. For this data, the researchers concluded that the boomSAR was better suited for using lower frequencies to find the deeply buried M-20 mines and higher frequencies for detecting the much smaller Valmara mines.


See also

*
Ultra-wideband Ultra-wideband (UWB, ultra wideband, ultra-wide band and ultraband) 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 applicat ...
* RailSAR * SIRE radar * SAFIRE radar


References

{{reflist Military technology Mine warfare countermeasures Radar Synthetic aperture radar