## 1 Introduction  
Systems being used to detect buried explosives (BE) should classify material as to whether it is an explosive or not, and give an alert to the operator. Conversely, in order to increase the speed of the system, ignorance of some data to be evaluated as an explosive can reduce reliability, and this may cause some problems which will not be compensated for. The low false alarm rate (FAR) and fast detection feature are two important parameters in BE and improvised explosive device (IED) detection systems. High computational efficiency is required in the algorithm operated for optimum FAR and fast detection features [1]. For reliable operation, the buried explosive detection (BED) system should be able to interpret as much data as possible and assist the operator in the decision-making process [2]. IEDs randomly placed underground by illegal organizations have different properties from the explosives used by armed forces for defense purposes. Traditional BED systems broadcast signals underground while scanning the IEDs. If IEDs are buried with a circuit detecting the BED system's broadcast frequency, the presence of the BED system will cause the IED to explode. In order to prevent such situations and IEDs from detonating, the detection method has to be passive; i.e., the BED system should not broadcast a signal during its operation. Underground object detection hardware is used in military applications, civil engineering, geological sciences, location sciences, archaeological researches, health applications, biological researches, etc. The specific properties of the object to be detected are important in the selection of the BED technique. If the object to be detected is an IED, many features must be analyzed in the selection of the BED method. There are two basic BED techniques; namely, mass analysis and trace analysis [3; 4]. In the trace analysis technique, the remains of the explosive molecules in the air or soil are analyzed. In the mass analysis technique, the explosive is detected visually. The mass analysis technique is preferred more often for military purposes because it is faster. Ground penetrating radar [5; 6; 7; 8; 9; 10; 11; 12; 13], electromagnetic induction [1; 14; 15], nuclear quadrupole resonance [4; 16; 17; 18], acoustic seismic [1; 19; 20; 21; 22], and neutron-based measurement [23; 24; 25; 26; 27; 28] are the most important methods using mass analysis technique. In all of these methods, an underground signal is broadcast and the reflected signal from the buried object is evaluated by the BED system. The measurement made in this way is an active measurement, and the broadcast signal may cause the BE or IED to explode, as previously mentioned. It is possible to detect the underground explosives with a passive measurement system without emitting a signal to the BE. BED by the magnetic anomaly (MA) method can be applied in the following two ways:  
1. The BE is exposed to a high level, constant magnetic field, and measurements are made with magnetic field measurement sensors over it. MA is detected, and the BE is interpreted by means of the data obtained [29; 30; 31; 32]. Since an external fixed magnetic field is applied to the BE, the measurement made in this way is named an active measurement. 2. The natural magnetic field of the earth is used to detect BE. Magnetic field lines of the earth can be considered linear for short distances. When an object is placed underground, deviations occur in linear magnetic field lines. In other words, different anomalies occur in the region where the object is buried compared to the region where the object is not buried. This measurement is a passive technique, and BEs and IEDs can be detected by evaluating these anomalies [33; 34; 35; 36; 37]. In this study, the MA method was used to detect BE and IED having ferromagnetic contents with passive measurements, and a scanning system was developed to image these objects. Magnetic field scans of 33 different samples were made at different distances.