Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

4.3 Highlighting of a Building Contours 67
4.3 Highlighting of a Building Contours
Any actual information about a building interior could be very useful before entering
dangerous area. It could be used to plan strategies in a lot of rescue and
security applications. In this section, we introduce an imaging of the inner and
outer building contours from the outside using through-wall UWB radar. For that
purpose the preprocessing, calibration, and imaging is performed. The image processing
method for highlighting of the building walls using Hough Transform (HT)
with assumed knowledge about the direction of walls is presented. The algorithm
was tested on real measured data acquired from a M-sequence UWB radar system.
4.3.1 Preprocessing and Imaging
Several preprocessing and calibration steps as well as imaging have to be applied
before the highlighting of a building contours would be performed. After the
building was scanned by SAR scanning (Section 2.3), the dataset was interpolated
in time domain (Section 2.4.1), the time zero was estimated (Section 2.4.2),
the crosstalk was removed (Section 2.4.3), and the dataset was deconvolved with
impulse response of whole radar system (Section 2.4.4). The irregular trolley movement
(Section 4.1.5) and antenna beam was compensated (Section 4.1.6). SAR
imaging based on geometrical approach described in Section 2.5.2 was used as the
migration.
In order to reconstruct the wave propagation through the wall more precisely,
the TOA that takes into the account wall parameters was computed during SAR
image formation, as it is described in Section 4.1. In addition, the attenuation of
the wave propagation and looses were compensated in two ways:
Attenuation inside the wall: The wave penetrating through the wall is attenuated
much more considerably in the wall than it is attenuated in the air. The
attenuation inside the wall mostly depends on the wall conductivity σw, that can
be easily measured by time domain reflectometry (Section 4.2). The magnitude of
the wave behind the wall is given by (4.2.3) and (4.2.4):
aw = a0e
0 v
u "r
u
−Dw@2πf
t εwµw 1+( 2
σw
2πfεw )2 #
−1
1
A
(4.3.1)
where a0 is a magnitude of the incident wave before the wall and aw is a magnitude
of the wave behind the wall.
Spread losses in the air: The magnitude of the wave is reduced with distance
even in the air. Such attenuation is called spread losses [67]. The spread losses
for long distances such as few meters should not be neglected. A very simple and