## 4 Experiments  
With the aim of detecting and classifying BEs and IEDs by the designed data collection system, the area used for the measurements was first filled with humid soil. A test sample was buried 2-3 cm under the top of the soil surface, and its position was kept constant. The sensor array was placed along the positive x-axis direction, and then data collection process was carried out by moving this sensor array along the y-axis in 25 steps. Each buried test sample was scanned along the positive z-axis at distances of 5 cm, 10 cm, 15 cm, and 20 cm from the top of the buried sample. And then the 32 \(\times\) 25 dimensions data matrices were obtained from each scan (32: Number of sensors placed along the x axis, 25: Number of scan steps of y axis). In the study, 33 different samples having different ferromagnetic properties were scanned. Ten out of thirty-three samples were explosives in standard production, and they have frequently been used for IEDs and warfare. The appearances and general physical properties of these samples are shown in Figure 7. In addition, ten out of thirty-three samples were kinds of cases having different sizes and geometries and are still being used in the IED productions. The appearances and general physical properties of these samples are given in Figure 8. The remaining 13 samples were non-explosive materials having IED geometries and yielding close results to the magnetic field images of IEDs and explosives. The appearances and general physical properties of these samples are given in Figure 9.  
Figure 8: Appearances and physical properties of the samples used as cases in improvised explosive devices (IEDs).  
Figure 7: Appearances and physical properties of the explosive samples with standard production.  
A two-dimensional gray scale image of each sample was obtained by using GUIU with the help of data matrices of 32 \(\times\) 25 dimensions recovered from the scan results. Two-dimensional gray scale images scanned at 5 cm distance for all 33 samples are given in Figure 10. As can be seen in the Figure 10, light regions indicate positive magnetic field density, whereas dark regions indicate negative magnetic field density.  
In gray scale images, the color information is stored in numerical values between 32,768 (100% white) and \(-\)32,768 (100% black) obtained from the ADC channels. The zero (gray) value indicates the combination of 50% black and 50% white and this corresponds to no magnetic field. As can be seen in Figure 11, the numbers of gray points in the images increase with the increase of scanning height in the z-axis for all samples. When the images obtained from different heights are evaluated as a whole, it can be seen that rate of the gray scale in the images does not change too much. In total, 132 different datasets were recorded as a result of the magnetic measurements carried out at 5 cm, 10 cm, 15 cm, and 20 cm distances for 33 different test samples. Each dataset actually contains a 32 \(\times\) 25-dimensional data matrix. In the classification study, 80 datasets were categorized as explosives/IEDs, and the other 52 datasets as non-explosive materials. Max, Min, \(\sigma\), KC, and AM features were calculated and used to characterize these datasets. It is important to know which features will be used in the classification. The usage of single feature is more likely to cause coincidence results in the classification. Eleven different groups were created to examine the effects of the all features for the classification. The feature groups and elements are given in Table 1.  
Figure 9: Appearances and physical properties of the non-explosive samples.  
Figure 11: Grey scale images obtained from 81 mm Mortar Ammunition, Sample 6, and Sample 21, at the heights of 5 cm, 10 cm, 15 cm, and 20 cm.  
Figure 10: Grey scale graphics obtained as a result of magnetic field scans performed at a distance of 5 cm.