Chapter 3: Vehicle-Mounted GPR System for Landmine Detection

3.4 Quick Detection Algorithm 39
1 z′+
w 2
e( r′ ) = dze( )
w
∫ r (3.11)
z′−w
2
The appropriate window width may depend on the wavelength of the system, and
the most effective width is a semi-period of a trace. The data are normalized by the
maximum value in each depth slice, and summed values with respect to depth are
projected to a map.
pxy ( , ) = ∫ dz
e () r
max ( )
xy ,
[ e r ]
(3.12)
In the actual demining test for a sensor, detected targets are rated with the
confidence. The confidence rating is defined as shown in Table 3.2. To calculate the
confidence ratings, the map p( xy , ) is normalized again and is thresholded.
xy ,
( , ) − min [ pxy ( , )]
xy ,
[ p xy] − [ pxy]
pxy
pxy ˆ( , ) =
max ( , ) min ( , )
xy ,
⎧ 0 0 ≤ p( xy , ) ≤th1
⎪
25 th1 < p( x, y)
≤th2
⎪
prate( xy , ) = ⎨ 50 th2 < pxy ( , ) ≤th3
⎪ 70 th3 < p( x, y)
≤ th4
⎪
⎪ ⎩100 th4
< p( x, y) ≤1
(3.13)
(3.14)
The four thresholds should be defined by analyzing the stochastic distribution of
p( xy. , )
This algorithm is not a trace-by-trace process, because the algorithm uses the
migrated data and the normalization in Eq. (3.12) is taken in a two-dimensional
space. Thus, the rating in Eq. (3.14) is not an absolute evaluation. It compares the
energy of the trace with neighboring ones meaning a relative evaluation. If the
ground surface is relatively flat and no large terrain changes, this algorithm might
work well. If not, it however could output errors.