Stephan Dill

3D Tower-Turntable ISAR Imaging

This paper studies the effects of peculiarities of an experimental stepped-frequency measurement system in a tower-turntable setup on three-dimensional inverse synthetic aperture radar imaging by simulation of ideal point scatterers. Particular a phase drift, an offset of the elevation rotation center and near range distortion have to be compensated. Furthermore, first imaging results of measured 3D data will be presented.

Study of passive MMW personnel imaging with respect to suspicious and common concealed objects for security applications

Microwaves in the range of 1-300 GHz are used in many respects for remote sensing applications. Besides radar sensors particularly passive measurement methods are used for two-dimensional imaging. The imaging of persons and critical infrastructures for security purposes is of increasing interest particularly for transportation services or public events. Personnel inspection with respect to weapons and explosives becomes an important mean concerning terrorist attacks. Microwaves can penetrate clothing and a multitude of other materials and allow the detection of hidden objects by monitoring dielectric anomalies. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions without artificial exposure of persons or areas. Some millimeter-wave radiometric imaging devices with respect to low cost are investigated. Measurement results of some typical personnel screening scenarios are discussed. Requirements for future operational systems are outlined.

Application of microwave radiometry for buried landmine detection

In this paper we illustrate the phenomenological background, the design, and some experimental results of a multi-spectral low frequency microwave radiometer as a part of a multi-sensor mine detection system. The overall system is intended to work in a hand-held operation allowing the use in areas of difficult access without excluding missions in more friendly environments. Thus the radiometer antenna is operated in an extreme near-field mode to achieve a corresponding ground resolution in the order of the active antenna aperture size. In particular, the radiometer receiver is swept in low-bandwidth steps through a broad microwave (MW) frequency range to vary the penetration depth and the reflectivity properties of the actually observed ground part. This can provide significantly increased information about the location and shape of buried objects for discrimination purposes. The relevant theoretical aspects of this interference based effects are illustrated and attempts to interpret the spectrum for specific layered arrangements as in the case of buried objects are presented.

High-resolution passive millimeter-wave imaging technologies for reconnaissance and surveillance

This paper addresses the use of high resolution aperture synthesis radiometry for the purpose of reconnaissance and surveillance on an Unmanned Aerial Vehicle (UAV) platform. A short introduction to the military background for the applicability of this technique is given. The phenomenology of microwave radiometry is shortly introduced and range considerations are outlined. The principles of aperture synthesis are presented and a first design idea based on previous investigations for a low-expense system is given. Based on that the imaging performance of the system is investigated using a typical brightness temperature scene from earlier linescanner measurements at 90GHz. The array thinning, the finite sensitivity, and the impact of non-ideal flight maneuvers are discussed. It is shown, that the low-expense system is able to produce satisfying results for target detection.

Passive microwave remote sensing for security applications

The security of persons or sensitive infrastructures is of increasing importance. Passive microwave remote sensing allows a daytime-independent non-destructive observation and examination of the objects of interest without artificial exposure under nearly all weather conditions. The penetration capability of microwaves enables the detection of hidden objects. Examples for various imaging experiments are shown. The experimental systems are used to investigate basic key parameters for the specific applications like suitable frequency band, required spatial resolution, sensitivity, and field of view. Systems close to real-time are under investigation and development.

The monitoring of critical infrastructures using microwave radiometers

Microwaves in the range of 1-300 GHz are used in many respects for remote sensing applications. Besides radar sensors particularly passive measurement methods are used for two-dimensional imaging. The imaging of persons and critical infrastructures for security purposes is of increasing interest particularly for transportation services or public events. Personnel inspection with respect to weapons and explosives becomes an important mean concerning terrorist attacks. Microwaves can penetrate clothing and a multitude of other materials and allow the detection of hidden objects by monitoring dielectric anomalies. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions without artificial exposure of persons or areas. The performance of millimeter-wave radiometric imaging with respect to wide-area surveillance is investigated. Measurement results of some typical critical infrastructure scenarios are discussed. Requirements for future operational systems are outlined exploring a radiometric range equation.

SUMIRAD: a low-cost fast millimeter-wave radiometric imaging system

For many military or peace-keeping operations it is necessary to provide better situational awareness to the commander of a vehicle with respect to possible threats in his local environment (predominantly ahead), at a distance of a few ten to a few hundred meters. Such a challenging task can only be addressed adequately by a suitable multi-sensor system. As a beneficial part of that, an imaging radiometer system with a sufficiently high frame rate and field of view is considered. The radiometer, working 24 hours in all weather and sight conditions, generates quasi-optical images simplifying the microwave image interpretation. Furthermore it offers the advantage to detect and localise objects and persons under nearly all atmospheric obstacles and also extends the surveillance capabilities behind non-metallic materials like clothing or thin walls and thin vegetation. Based on constraints of low costs and the observation of a large field of view, the constructed radiometer still offers a moderate resolution at a moderate scan speed. This paper describes the challenges for the design of a vehicle-based imaging radiometer system at W band, providing high-quality images of sufficient resolution for a large field of view at a moderate frame rate. The construction is briefly outlined and imaging results for several situations are presented and discussed. Those comprise measurements on target detection and a visual comparison of different SUM (Surveillance in an Urban environment using Mobile sensors) data products.

Fully-polarimetric passive MMW imaging systems for security applications

Increasing terroristic attacks raise the danger to the public and create a new and more complex dimension of threat. This evolution must and can only be combat by the application of new counter-measures like advanced imaging technologies for wide-area surveillance and the detection of concealed dangerous objects. Passive microwave remote sensing allows a daytime independent non-destructive observation and examination of the objects of interest under nearly all weather conditions. The acquisition of polarimetric object characteristics can increase the detection capability by gathering complementary object information. Over years the DLR Microwaves and Radar Institute developed several problem-orientated radiometer imaging systems covering nearly the whole frequency spectrum between 1 GHz and 100 GHz for a multitude of applications. Actually a fully-polarimetric radiometer receiver at W band is developed in order to explore the polarimetric information content of interesting objects simultaneously. Some important theoretical characteristics of polarimetric radiometry at millimeterwaves are introduced and discussed. The actual design and construction of the receiver system is outlined and first experimental imaging results are presented.

Radiometric measurements of dielectric material properties at MMW frequencies for security applications

Microwaves can be used to detect hidden objects behind optically opaque materials. Hence, the penetration capability through such materials is of fundamental importance. In order to characterise a material of interest in the microwave region, its permittivity should be known besides its physical structure. In many cases the permittivity is unknown, inaccurately known, or known for only specific frequencies. Also very often the range of values given in the literature can have a large variability for a specific situation. In this paper we describe a procedure to determine the permittivity from radiometric free-space measurements of nearly arbitrary materials. The advantage of this method is that large material samples like brick or wooden plates, and materials like textiles, which are hard to mount in a defined way in a waveguide, can be investigated. Some representative results for MMW measurements are shown, and an estimation of the presently achieved precision is given. The first attempts showed a satisfying performance, although not for all materials and frequencies a unique solution could be found.

SUMIRAD – a near real-time MMW radiometer imaging system for threat detection in an urban environment

The armed forces are nowadays confronted with a wide variety of types of operations. During peace keeping missions in an urban environment, where small units patrol the streets with armored vehicles, the team leader is confronted with a very complex threat situation. The asymmetric imminence arises in most cases from so called IEDs (Improvised explosive devices) which are found in a multitude of versions. In order to avoid risky situations the early detection of possible threats due to advanced reconnaissance and surveillance sensors will provide an important advantage. A European consortium consisting of GMV S.A. (Spain, “Grupo Tecnològico e Industrial”), RMA (Belgium, “Royal Military Academy”), TUM (“Technische Universität München”) and DLR (Germany, “Deutsches Zentrum für Luft- und Raumfahrt”) developed in the SUM project (Surveillance in an urban environment using mobile sensors) a low-cost multi-sensor vehicle based surveillance system in order to enhance situational awareness for moving security and military patrols as well as for static checkpoints. The project was funded by the European Defense Agency (EDA) in the Joint Investment Program on Force Protection (JIP-FP). The SUMIRAD (SUM imaging radiometer) system, developed by DLR, is a fast radiometric imager and part of the SUM sensor suite. This paper will present the principle of the SUMIRAD system and its key components. Furthermore the image processing will be described. Imaging results from several measurement campaigns will be presented. The overall SUM system and the individual subsystems are presented in more detail in separate papers during this conference.