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.
KEYWORDS: Atmospheric modeling, Radiometry, Sensors, X band, Radar, Temperature metrology, Imaging systems, Data modeling, Atmospheric sensing, Extremely high frequency
For MW and MMW radar and radiometer measurements the influence of atmosphere like attenuation and path delay is more pronounced at higher frequencies. The sensors group of DLR Microwaves and Radar Institute operates the experimental radar System IoSiS (Imaging of satellites in space) at X band at the DLR ground station Weilheim in southern Germany. The radar images of the satellites in LEO (low earth orbit) are acquired in the ISAR mode (Inverse synthetic aperture radar) over a wide elevation angle of the steered Tx/Rx antenna. For the image processing and object focusing it is important to know the atmospheric attenuation and path delay variation over the wide synthetic aperture angle. The use of atmospheric models in order to retrieve the necessary parameters leads to some uncertainties since the models are mainly on a global scale and do not consider regional and seasonal conditions. Therefore the authors intend to refine an existing atmospheric model based on radiometric profiling measurements of the atmosphere for different weather conditions. The paper shows the measurement setup, mention briefly the Ulaby and ITU atmosphere models and show first experimental radiometer measurements of the atmospheric brightness temperature at four frequencies, namely at X, Ka, W and D band.
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: Synthetic aperture radar, Radar, Antennas, Land mines, Polarization, General packet radio service, 3D image processing, Soil science, Sensors, Superposition
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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