Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE
Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE
Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE
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2.5 <strong>Radar</strong> <strong>Imaging</strong> Methods Overview 19<br />
2.5.4 Differential SAR<br />
The wall is mostly represented in a long area of the migrated image. Sometimes<br />
the objects behind the wall are overlapped by the wall reflection. Differential SAR<br />
(DSAR) is a method for elimination of direct reflection from the walls proposed<br />
by Mojtaba Dehmollaian et al. [45] in 2009. The idea is similar to applying background<br />
subtraction for detection of moving objects behind the wall. Although<br />
during SAR scanning all the scanned objects seems to move, the reflection from<br />
the first wall is almost the same for two successive antenna positions. However,<br />
the reflection from the object behind the wall is not the same, as it can be seen in<br />
Fig. 2.5.2. Before the SAR imaging is applied, the matrix of difference signal is<br />
Z<br />
Antenna at two<br />
successive positions<br />
<strong>Wall</strong><br />
reflections<br />
TOA W<br />
TOA W<br />
TOA T<br />
Target<br />
reflections<br />
TOA T+�<br />
Target<br />
<strong>Wall</strong><br />
Fig. 2.5.2: Differential SAR model for monostatic approach.<br />
obtained by substracting two successive impulse responses:<br />
B∆ = VR(n + 1) − VR(n). (2.5.10)<br />
Computing the SAR image with B∆ leads to elimination of direct reflection from<br />
the first wall. This can increase a signal-to-clutter ratio of small objects behind<br />
the wall. The wall has to be homogenous and scan has to be performed in parallel<br />
to the wall in order to obtain the same wall reflection in two successive antenna<br />
positions.<br />
X