Harmonic radar is used in solving the problem of detecting and localizing electronic devices within a given measurement scene. The underlying measurement principle utilizes the frequency conversion, mixing and harmonics generation of the harmonic radars transmit signal in systems with nonlinear transfer functions. The nonlinearities in the signal transfer behavior of the targets of interest are due to electronic circuit elements and predominantly semiconductor components. Comparable to classic radar imaging techniques, it is possible to generate maps that give knowledge about the presence and the location of electronic devices within the observed scene. This work presents the current research done at the German Aerospace Center (DLR) in the field of harmonic radar. The development of a dual-mode (classic and harmonic radar) measurement system is shown. In addition, we present a signal processing algorithm for harmonic radar imaging based on wideband, pre-steered, frequency-smoothed robust capon direction-of-arrival estimation. The developed algorithm is analyzed and compared to classic imaging techniques using synthetic data. Concluding measurement results show the capabilities of the experimental measurement setup and validate the performance of the devised imaging algorithm and system demonstrator.
The task of detecting and locating landmines, unexploded ordnances (UXO) and improvised explosive devices (IEDs) is still a major challenge up to the present day. Problems such as the distance between the hazardous area and the measurement system as well as the differentiation between the target of interest and the surrounding soil are of importance in the development of the sensor system. Various types of radar based systems have been developed over the last decades to solve these problems. Compared to other methods ground penetrating synthetic aperture radar (SAR) has the ability to scan large areas from a safe standoff distance in a relatively short time. In this paper, two different imaging radar systems are compared. The first one is a ground-based SAR (GB-SAR) developed at German Aerospace Center (DLR). The other system is an unmanned aerial vehicle-based SAR (UAV-SAR) from the University of Ulm. The presented data originates from a joint campaign using the same measurement scenarios.
The detection of improvised explosive devices (IED) is still a challenging task. Important components of these IEDs are often thin pressure plate structures which connect the activator with the explosive device by wires. The detection of wires could therefore be useful to detect the IEDs, since the detection of the explosives itself by identifying specific characteristics is impossible for many sensor types, and quite expensive and time consuming for few being able to perform this task. In this paper investigations on the detection of thin wires using Multiple Input Multiple Output (MIMO) synthetic aperture radar (SAR) are discussed.
KEYWORDS: Superposition, Sensors, Soil science, 3D image processing, General packet radio service, Polarization, Land mines, Antennas, Radar, Synthetic aperture radar
A main problem of effective landmine and UXO decontamination is efficient and reliable detection and localization of
suspicious objects in reasonable time. This requirement demands for fast sensors investigating large areas with sufficient
spatial resolution and sensitivity. Ground penetrating radar (GPR) is a suitable tool and is considered as a complementing
sensor since nearly two decades. However, most GPRs operate in very close distance to ground in a rather punctual
method of operation. In contrast, synthetic aperture radar (SAR) is a technique allowing fast and laminar stand-off
investigation of an area. TIRAMI-SAR is imaging radar at lower microwaves for fast close-in detection of buried and
unburied objects on a larger area. This allows efficient confirmation of a threat by investigating such regions of detection
by other sensors. For proper object detection sufficient spatial resolution is required. Hence the SAR principle is applied.
SAR for landmine/UXO detection can be applied by side-looking radar moved on safe ground along the area of interest,
being typically the un-safe ground. Additionally, reliable detection of buried and unburied objects requires sufficient
suppression of background clutter. For that purpose TIRAMI-SAR is using several antennas in multi-static configuration
and wave polarization together with advanced SAR processing. The advantages and necessity of a multi-static antenna
configuration for this kind of GPR approach is illustrated in the paper.
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