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

4.4 Measurements of the Practical Scenarios 81
differ depending on the chosen interpretation method. Subfigure a) e.g. Fig.
A.0.1 a) shows the photo of object behind the wall. Subfigure b) e.g. Fig. A.0.1
b) shows 1D cross-range plot mostly at position X = 1 m what corresponds to the
object position and X = 0.3 m what corresponds to the position where object is
absent. Subfigure c) e.g. Fig. A.0.1 c) shows 2D image of the scanned environment
including the target, the front and the rear wall. After migration the image consists
from positive and negative values. Dividing values into the both positive and
negative do not have any physical interpretation in image. Therefore, an absolute
value from Hilbert transform is imaged here in order to be closer to the ”energy”
representation. Subfigure d) e.g. Fig. A.0.1 d) shows the same 2D image as in c).
However, only a zoomed region where the object occurs is imaged. The colormap
is also changed in order to enhance the target visibility. Subfigure e) e.g. Fig.
A.0.1 e) shows 3D image of scanned environment including the target, the front
and the rear wall. The third dimension represents the ”magnitude” of the image.
Both, the positive and the negative values are imaged. Colormap differs from the
one used in subfigures c). Subfigure f) e.g. Fig. A.0.1 f) shows the same 3D image
as in c). However, only a zoomed region where the object occurs is imaged. Such
representation helps to concentrate on the object especially when the front wall
dominates in the migrated image.
From the Figures in Appendix A it can be seen that the most visible objects
behind the brick wall are the metallic ones with the flat surface placed in parallel
with the scanning direction. The metallic fire extinguisher with rounded surface
is also clearly visible. However, a small sphere covered with aluminum foil with
diameter only 20 cm is almost invisible behind a such wall. Subfigures A.0.7
b), d), and f) can help to find the position of the sphere. Even if the wooden
cupboard is the biggest object that was scanned, the wood and glass are not
a good reflectors for electromagnetic waves at such frequencies. Therefore, the
magnitudes of cupboard in both directions are similar with much smaller objects
but the metallic ones, sometimes even smaller. A clear watter is not the best
conductor for direct current, however even the small aquarium filled with clear
watter is a good reflector for electromagnetic waves at the used frequencies. The
dimensions of the objects in scanning - X direction can be estimated with relatively
good precision. However, dimensions of the objects in looking - Z direction can be
estimated very difficultly from the migrated images. It is because of a most of the
energy reflected from the front surface of the object and only hardly penetrate into
the object, reflect from the rear surface and penetrate back to the receive antenna
through the object and the wall. Such handicap can be eliminated by scanning of
the objects from at least two sides.
Based on the previous analysis, the most of the objects in the room could
be imaged with the UWB radar device through the brick wall. The methods for
image representation should be chosen according to the scanned objects and also