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

4.1 Through-Wall TOA Estimation 50
Table 4.3: Error in TOA estimation for through-wall scenario.
Method
Straight line between Simple wall Proposed
antenna and target compensation method
T OA[ns] 11.188 14.238 14.994
ErrT OA[%] 25.383 5.042 0.000
and frequency, as it is shown in equation (4.2.2). However, these parameters cause
neglectable modification of the propagation velocity in praxis.
4.1.5 Irregular Movement Compensation
The antenna system, or the whole radar system has to move in scanning direction
during SAR scanning. A very precise and linear scanning system can be used in a
laboratory environment. However, it is impractical in real measurement scenarios.
In scanning direction (X - axis):
For rescue or security applications a moving trolley or vehicle is used. In this case
it is almost impossible to move it with a constant velocity. Most of the migrations
require input dataset (B-scan) with linear distances between two subsequent scans.
Otherwise the output image will be deformed.
We used hand moving trolley with positioner system for measurements pictured
in Fig. 4.1.5. The information about actual position in scanning direction is
continuously saved with every received impulse response from the radar device. In
order to align all scans to the regular grid, where every two subsequent scans have
the same distances, a vector of antenna positions s in scanning direction shown in
Fig. 4.1.6 b) is created. The antenna positions in vector s are linearly dependent
on the number of scans. The calibrated and preprocessed B-scan BP n (X, k) is
interpolated through Spline interpolation Spline as:
BP C (X, k) = Spline (BP (X, k) , s) (4.1.14)
where BP C (X, k) is a B-scan with compensated irregular trolley movement in the
scanning direction. For the next processing, the BP C (X, k) in combination with
antennas positions s is used.
In looking direction (Z - axis):
The irregular movement of scanning trolley leads to a varying distance between
antenna system and scanning objects. In order to compensate this behavior during
migration, the precise distance between antenna and the wall Wdi has to be known.