See-around-corners with radar - Annual report 2008
Publish date: 2009-01-08
Report number: FOI-R--2687--SE
Pages: 33
Written in: Swedish
Keywords:
- see-around-corner
- radar
- doppler radar
- diffraction
- reflection
- urban
- environment
Abstract
This annual report summarizes the second-year activities and describes the most interesting results of the three-year strategic research project "Radar for detection of human activity around corners". The aim of the project is a technical evaluation, by measurements and calculations, of the idea to use the bending (diffraction) of radar waves around corners and/or their reflection in opposite house walls and faces to detect moving objects off the line of sight. Both methods present the advantage of keeping one's own sensor system and soldier off the line of sight to the enemy and hence diminish the risk of detection and elimination. The basic idea of using the radar in this manner has been drawn up by the FOI and could be regarded as being of a pioneering nature, since the conducted literature search produced no specific work with a see-around-corners application. Most references dealt with communication applications in the urban scenario. The conclusions from this year's measurements with light concrete walls, where the target objects have consisted of radar reflectors, largely coincide with the conclusions from last year's measurements with metallic walls. The experiments show that moving metal reflectors behind concrete corners can be detected from their radar return. Both target returns from diffraction (bending) around the corner and from multiple reflections between opposite walls have been detected. The diffracted radiation is considerably weaker than that from the multiple reflections. The difference with respect to metal walls is that the concrete absorbs part of the incident radiation, and has a greater component of diffuse scattering than the smoother metal wall, but the measurements show that the targets are still easy to detect with the actual geometry. Preliminary sample tests of measurements of a moving human behind a corner, also being conducted this year, show that the Doppler signal from the person is unambiguously detectable. An analysis of these measurements will be made in 2009. Measurements have been made of five building-face-like surfaces with the aim to investigate how different types of roughness affect the reflection properties. In order to reduce the influence of the material properties on the reflection, the surfaces were coated with silver paint. In the measurements the reflection was measured as a function of frequency (2-20 GHz), polarization and incidence angle. The results show that the reflection is concentrated to the specular direction when the roughness is small compared to the wavelength. The measurements show further that the polarization choice may be significant if the surface structure contains clear preference directions. Furthermore, calculations with the so-called bump-mapping method have been made to compare the resulting field images when a radar illuminates a plane wall face and a rough one, respectively. With the used parameter choice for the surface roughness, an unexpectedly small difference results between the field images.