Brian R. Phelan

Design of spectrally versatile forward-looking ground-penetrating radar for detection of concealed targets

The design of high-resolution radars which can operate in theater involves a careful consideration of the radar’s radiated spectrum. While a wide bandwidth yields better target detectability and classification, it can also interfere with other devices and/or violate federal and international communication laws. Under the Army Research Laboratory (ARL) Partnerships in Research Transition (PIRT) program, we are developing a Stepped-Frequency Radar (SFR) which allows for manipulation of the radiated spectrum, while still maintaining an effective ultra-wide bandwidth for achieving good range resolution. The SFR is a forward-looking, ultra-wideband (UWB) imaging radar capable of detecting concealed targets. This paper presents the research and analysis undertaken during the design of the SFR which will eventually complement an existing ARL system, the Synchronous Impulse REconstruction (SIRE) radar. The SFR is capable of excising prohibited frequency bands, while maintaining the down-range resolution capability of the original SIRE radar. The SFR has two transmit antennas and a 16-element receive antenna array, and this configuration achieves suitable cross-range resolution for target detection. The SFR, like the SIRE radar, is a vehicle mounted, forward-looking, ground penetrating radar (GPR) capable of using synthetic aperture radar (SAR) technology for the detection of subsurface targets via 3D imaging. Many contradicting design considerations are analyzed in this paper. The selection of system bandwidth, antenna types, number of antennas, frequency synthesizers, digitizers, receive amplifiers, wideband splitters, and many other components are critical to the design of the SFR. Leveraging commercial components and SIRE sub-systems were design factors offering an expedited time to the initial implementation of the radar while reducing overall costs. This SFR design will result in an ARL asset to support obscured target detection such as improvised explosive devices (IEDs) and landmines.

Source localization using unique characterizations of multipath propagation in an urban environment

This paper proposes a method for determining the location of GSM mobile transmitters. The process discussed here estimates the location of a source without the use of multilateration or LOS techniques. A Multipath Characteristic Database (MCD) containing the multipath signatures for each possible transmitter location in an area of interest is populated via ray-tracing software simulations. The multipath characteristics of interest are Angle of Arrival (AOA), and Time Difference of Arrival (TDOA). An analysis of an eigenstructure Joint Angle and Delay Estimations (JADE) is presented, and the properties of the MCD are discussed. Since the proposed method utilizes a simulated multipath signature database the need for a priori soundings from the area of interest is eliminated, thus making this location estimation system ideal for use in hostile territories.

Design of Ultrawideband Stepped-Frequency Radar for Imaging of Obscured Targets

A stepped-frequency radar that allows for adaptability in the radiated spectrum while maintaining high-resolution radar imagery has been developed. The spectrally agile frequency-incrementing reconfigurable (SAFIRE) radar system is a vehicle-mounted, ground-penetrating radar that is capable of producing high-resolution radar imagery for the detection of obscured targets (either buried or concealed surface targets). It can be easily transitioned between forward- and side-looking orientations. The SAFIRE system is capable of precisely excising subbands within its operating bandwidth, thus making the system “spectrally agile.” It is also highly reconfigurable thereby allowing for on-the-fly adjustment of many of the system parameters. The spectrally agile and reconfigurable aspects of the SAFIRE radar together with its enhanced IF processing scheme represent a novel contribution to the state of the art. This paper discusses the system design, implementation, and performance characteristics, and also presents preliminary high-resolution imagery.

Performance analysis of spectrally versatile forward-looking ground-penetrating radar for detection of concealed targets

Stepped-Frequency Radars (SFRs) have become increasingly popular with the advent of new technologies and increasingly congested RF spectrum. SFRs have inherently high dynamic range due to their small IF bandwidths, allowing for the detection of weak target returns in the presence of clutter. The Army Research Laboratory’s (ARL) Partnership in Research Transition program has developed a preliminary SFR for imaging buried landmines and improvised explosive devices. The preliminary system utilizes two transmit antennas and four receive antennas and is meant to act as a transitional system to verify the system’s design and imaging capabilities. The SFR operates between 300 MHz and 2000 MHz, and is capable of 1-MHz step-sizes. The SFR system will eventually utilize 16-receive channels and will be mounted on ARL’s existing Forward-Looking Ground Penetrating Radar platform, as a replacement for the existing Synchronous Impulse REconstruction (SIRE) radar. An analysis of the preliminary SFRs radio frequency interference mitigation, spectral purity dynamic range, and maximum detectable range is presented here.

Performance analysis of forward-looking GPR ultra-wideband antennas for buried object detection

We are currently developing a Stepped-Frequency Radar (SFR) which utilizes a custom-made uniform linear array of 16 Vivaldi notch receive antennas and two Transverse Electromagnetic (TEM) horn transmit antennas. The SFR has an operating band of 300–2000 MHz, and a minimum frequency step-size of 1 MHz. The custom-made TEM horn antennas are used for the transmission of the SFR’s ultra-wideband (UWB) spectrum. This paper discusses a comparison analysis between a commercially available UWB antenna and the currently used TEM horns. Gain, Voltage Standing Wave Ratio (VSWR), and antenna pattern measurements for each antenna are presented. The antennas were also tested for their ability to detect buried targets in a simple stepped-frequency radar system using a network analyser as a transmitter and receiver. An analysis of the gain, VSWR, beamwidth, and measured data from radar test of each antenna was performed, providing insights into each antenna’s performance on the SFR’s ability to detect buried targets. The information provided in this paper will be useful to the radar community in exploring developmental standoff detection solutions for military applications such as obscured target detection of obstacles and explosive hazards.

Initial processing and analysis of forward- and side-looking data from the Spectrally Agile Frequency-Incrementing Reconfigurable (SAFIRE) radar

A new, versatile, UHF/L band, ultrawideband (UWB), vehicle-mounted radar system developed at the U.S. Army Research Laboratory (ARL) has recently been exercised at an arid U.S. test site. The unique switching scheme implemented to record data from all receive channels is described, along with the current calibration procedure. Radar and global positioning system (GPS) data collected in both forwardand side-looking configurations are processed, and synthetic aperture radar (SAR) images are formed. Results are presented for various target emplacement scenarios.

Indoor experimental facility for airborne synthetic aperture radar (SAR) configurations – rail-SAR

The Army Research Laboratory (ARL) is developing an indoor experimental facility to evaluate and assess airborne synthetic-aperture-radar-(SAR)-based detection capabilities. The rail-SAR is located in a multi-use facility that also provides a base for research and development in the area of autonomous robotic navigation. Radar explosive hazard detection is one key sensordevelopment area to be investigated at this indoor facility. In particular, the mostly wooden, multi-story building houses a two (2) story housing structure and an open area built over a large sandbox. The housing structure includes reconfigurable indoor walls which enable the realization of multiple See-Through-The-Wall (STTW) scenarios. The open sandbox, on the other hand, allows for surface and buried explosive hazard scenarios. The indoor facility is not rated for true explosive hazard materials so all targets will need to be inert and contain surrogate explosive fills. In this paper we discuss the current system status and describe data collection exercises conducted using canonical targets and frequencies that may be of interest to designers of ultra-wideband (UWB) airborne, ground penetrating SAR systems. A bi-static antenna configuration will be used to investigate the effects of varying airborne SAR parameters such as depression angle, bandwidth, and integration angle, for various target types and deployment scenarios. Canonical targets data were used to evaluate overall facility capabilities and limitations. These data is analyzed and summarized for future evaluations. Finally, processing techniques for dealing with RF multi-path and RFI due to operating inside the indoor facility are described in detail. Discussion of this facility and its capabilities and limitations will provide the explosive hazard community with a great airborne platform asset for sensor to target assessment.

Examination of radar imagery from recent data collections using the spectrally agile frequency-incrementing reconfigurable (SAFIRE) radar system

The US Army Research Laboratory (ARL) has recently developed the Spectrally Agile Frequency-Incrementing Reconfigurable (SAFIRE) radar system during its ongoing research to provide ground vehicular standoff detection and classification of obscured and/or buried explosive hazards. The system is a stepped-frequency radar (SFR) that can be reconfigured to omit operation within specific sub-bands of its 1700 MHz operating band (300 MHz to 2000 MHz). It employs two transmit antennas and an array of 16 receive antennas; the antenna types are quad-ridged horn and Vivaldi, respectively. The system is vehicle-mounted and can be interchanged between forward- or side-looking configurations. In order to assess and evaluate the performance of the SAFIRE radar system in a realistic deployment scenario, ARL has collected SAFIRE data using militarily-relevant threats at an arid US Army test site. This paper presents an examination of radar imagery from these data collection campaigns. A discussion on the image formation techniques is presented and recently processed radar imagery is provided. A summary of the radars performance is presented and recommendations for further improvements are discussed.

Optimized radar design parameters for synthetic aperture radar with limited swath

In areas of conflict around the globe, buried or obscured explosive hazards pose a frequent danger to both civilians and military personnel. Research in radar technology to preemptively detect these hazards has been ongoing for more than two decades. The U.S. Army Research Laboratory (ARL) is currently developing a low noise, ultra-wideband, spectrally-agile radar system to be implemented on an aerial platform. An airborne ground- penetrating radar (GPR) simulation was developed to aid future hardware design efforts. Measured antenna beam patterns are input into the simulation and used to calculate the antenna’s footprint on the ground. With the antenna footprint specified, resolution cells are created within the footprint based on synthetic aperture radar (SAR) phenomenology. A 2D-Gaussian function is used to represent the main lobe of the antenna (which is derived from the 3-dB beam-width of the antenna in the E- and H-planes). The radar cross section (RCS) of each resolution cell is then found using a model for normalized clutter RCS, which incorporates the system geometry. Point-like and distributed targets can be inserted into the simulation by adjusting the RCS of specific resolution cells. Finally, these parameters are implemented in a signal model, and different waveforms can be simulated, and their peak side lobe level (PSLL) and integrated side lobe ratio (ISLR) can be compared.

CATS: A Color and Thermal Stereo Benchmark

Stereo matching is a well researched area using visibleband color cameras. Thermal images are typically lower resolution, have less texture, and are noisier compared to their visible-band counterparts and are more challenging for stereo matching algorithms. Previous benchmarks for stereo matching either focus entirely on visible-band cameras or contain only a single thermal camera. We present the Color And Thermal Stereo (CATS) benchmark, a dataset consisting of stereo thermal, stereo color, and cross-modality image pairs with high accuracy ground truth (