This paper presents two different test methods for camouflage layers (CL) like nets or foam based structures. The
effectiveness of CL in preventing radar detection and recognition of targets depends on the interaction of CL properties
as absorption and diffuse scattering with target specific scattering properties. This fact is taken into account by
representing target backscattering as interference of different types of GTD contributions and evaluating the impact of
CL onto these individual contributions separately. The first method investigates how a CL under test alters these
individual scattering contributions and which "new" contributions are produced by "self-scattering" at the CL. This
information is gained by applying ISAR imaging technique to a test structure with different types of scattering
contributions. The second test method aims for separating the effects of absorption and "diffuse scattering" in case of a
planar metallic plate covered by CL. For this, the equivalent source distribution in the plane of the CL is reconstructed
from bistatic scattering data. Both test methods were verified by experimental results obtained from X-band
measurements at different CL and proved to be well suited for an application specific evaluation of camouflage
structures from different manufacturers.
Inverse synthetic aperture radar (ISAR) imaging techniques based on indoor near field backscattering measurements
turns out to be a powerful tool for diagnostic purposes in radar cross-section (RCS) reduction and for deriving RCS
target models, viable for radar systems operating at larger distances, e.g. under far field conditions. This paper presents
an advanced 3-D imaging approach, where in addition to the turntable rotation the antenna is moved along a linear path
chosen in accordance with the geometry of the target and the aspect angle of interest. For reconstructing the reflectivity
distribution a configuration-specific grid of spatial sampling points is employed which reduces the complexity of
determining correct values for the scattering amplitudes. The reflectivity distribution reproduces the backscattering seen
from an antenna moved along a finite surface (synthetic 2-D-aperture) in the scattering near field of the target, but is to
be used to model backscattering for antennas at larger distances, e.g. in the far field. Therefore, the feasibility of this
approach is discussed with respect to different applications, i.e. for the diagnostic of RCS reduction and for
deterministic or statistical RCS models. Results obtained for a car as X-band radar target are presented in order to verify
the features of the imaging system.
In conjunction with measures for target detection and classification as well as for the corresponding counteractive
measures spatially resolved radar signatures are of high importance. To allow the implementation of different
techniques for radar backscattering characterization an indoor measurement range was realized. It uses a hall of size 35
x 20 x 8 m3 which is equipped with a 7-m-diameter target turntable with 70-tons capacity. A crane allows the antennas
to be moved along horizontal paths with very high accuracy (0.1mm). In this range different measurement systems,
related to different methods for target characterization were realized. This contribution reviews the most important
features of the employed concepts and provides a critical comparison as well as a discussion about the limitations of
these approaches. All concepts aim for a decomposition of the radar backscattering into contributions assigned to
substructures being considerably smaller than the overall size of the target. For microwave frequencies (e. g. X-band) a
3-D-ISAR approach provides resolution cells with linear dimensions of about 1-2 wavelengths and a corresponding
deterministic target model. For the millimeter-wave regime (W-band) an alternative approach based on directive
antennas and time-gating was implemented and provides the parameters of a spatially resolved stochastic target model.
Automatic target detection (ATR) depends on the surrounding clutter as well as on the target signatures.
Swiss DoD has established a measurement-platform in the W-Band frequency frame to generate the necessary data's .
The wavelength of the W-Band is extreme smaller than the target dimension and the footprint of the antenna does not illuminate the entire target. This have the result, that the actual echo-signal correlates strongly to the view angle.
The signature of a target is so complex for any evaluation, that it is necessary to create a statistic model with virtual scatters. As an example this model can be integrated in simulations of smart ammunition effectiveness.
With data of a statistical model it is possible to:
1. to evaluate the object according its RCS.
2. to create the necessary camouflage-precaution against radar-seekers and check there efficiency.
3. Detection probabilities of a target in different clutter conditions.
4. to identify strong reflectors and thereby reduce the RCS value of the target.
Robustness of automatic target recognition (ATR) to varying observation conditions and countermeasures is substantially increased by use of multispectral sensors. Assessment of such ATR systems is performed by captive flight tests and simulations (HWIL or complete modeling). Although the clutter components of a scene can be generated with specified statistics, clutter maps directly obtained from measurement are required for validation of a simulation. In addition, urban scenes have non-stationary characteristics and are difficult to simulate. The present paper describes a scanner, data acquisition and processing system used for the generation of realistic clutter maps incorporating infrared, passive and active millimeter wave channels. The sensors are mounted on a helicopter with coincident line-of-sight, enabling us to measure consistent clutter signatures under varying observation conditions. Position and attitude data from GPS and an inertial measurement unit, respectively, are used to geometrically correct the raw scanner data. After sensor calibration the original voltage signals are converted to physical units, i.e. temperatures and reflectivities, describing the clutter independently of the scanning sensor, thus allowing us the use of the clutter maps in tests of a priori unknown multispectral sensors. The data correction procedures are described and results are presented.