Means for searching for explosive objects by indirect signs.

Means of searching for explosive objects by indirect signs.

Petrenko Evgeny Sergeevich

MEANS OF SEARCHING FOR EXPLOSIVE OBJECTS BY INDIRECT SIGNS

At present, both in Russia and abroad, a number of means of searching for explosive charges (HE) and explosive objects (EO) have been developed and produced, both by direct and indirect signs.

A direct sign of VOP is the presence of EV or its individual components.

The issues of searching for explosive ordnance by direct signs are considered in sufficient detail in the article [1]

Indirect signs of explosive ordnance include: the presence of characteristic metal and plastic parts, semiconductor devices (diodes, transistors, integrated microcircuits), explosive devices, wire lines, antennas, a certain shape of the body (cylinder, parallelepiped), etc.

The history of the development of explosive and explosive ordnance detection equipment has developed in such a way that at present, both in Russia and abroad, the most developed equipment is the one whose operation is based on the detection of these indirect signs.

The widest range of metal detectors (metal detectors, induction mine detectors), the first examples of which were created in the 1930s, are represented by metal detectors. They are designed to detect explosive ordnance by the presence of metal housings or fairly massive (more than 3 — 5 g) fuse parts.

The operation of metal detectors is based either on the harmonic method, which allows detecting metal objects by measuring the parameters of the signal induced in them (phase and amplitude), excited by a harmonic current, or on the method of transient processes, which allows detecting a metal body by the secondary current fading in it, excited by single pulses.

Metal detectors designed for personal inspection are divided into stationary (for example, the domestic series “Poisk-3” – photo 1) and portable non-selective and selective (for example, domestic models 7202-A – photo 2 and 7215) with a maximum linear size from 0.15 to 0.4 m and a weight of 0.25 … 1.2 kg.

Portable induction mine detectors usually consist of a sensor and a signal processing unit with an indication system, structurally placed on a rod (photo 3). The devices are powered by batteries with a voltage of 6 — 12 V. The weight of mine detectors is within 2 — 5 kg.

Modern induction mine detectors can detect anti-tank mines with metal bodies (such as TM-62M) in the ground at depths of up to 0.5 — 1.2 m, and small objects (such as machine gun cartridges) at depths of up to 0.1 — 0.4 m.

The width of the detection zone for these objects is 0.2 — 1.2 m.

Photo 1. Stationary metal detector
of the “Poisk” series

Photo 2. Portable metal detector 7202 A

The average search rate of most modern mine detectors is within 120 — 400 m2/h and is determined mainly by the presence of foreign metal objects (interference), which are especially numerous in residential areas and human economic activity, as well as in places of military operations.

Photo 3. Induction mine detector
IMP-2

Some examples of modern induction mine detectors equipped with signal processing systems based on the use of microprocessors allow for selective search of objects (for example, objects made of non-ferrous metals against the background of ferrous metal objects or vice versa). Representative examples of such mine detectors are Grand Master Hunter CXIII, White Eagle-2 made in the USA and “Medusa” (Russia) (photo 4).

With built-in microprocessors and high-quality sensors, further improvement of such devices is possible due to improvement of signal processing algorithms without significant design changes to sensors and body parts, which was implemented in the domestic selective induction mine detector “Medusa”.

This mine detector differs from its foreign counterparts both in its improved selective search capabilities (primarily in urban and industrial areas) and in its greater sensitivity when searching for mines installed in the ground, which has been confirmed by the results of comparative tests.

In particular, this model allows detecting the TS-50 anti-personnel mine (Italy), infamous in Afghanistan, at the standard installation depth, which is still an unattainable result in other similar devices.

This mine detector is effective in searching for explosive ordnance, firearms and bladed weapons, cartridges, bullets, and shells in urban and industrial environments with a significant amount of metal structures, household metal waste, significant soil mineralization, and intense electromagnetic interference.

One of the operating modes is searching for objects of a given type only, ignoring all other objects. A conditional visual two-dimensional image of the object is displayed on the liquid crystal display.

The mine detector has a function for changing the operating frequency to ensure the possibility of parallel operation of several devices in close proximity to each other.

Photo 4. Selective induction
mine detector “Medusa”

It should be noted that all metal detectors without exception, and especially pulse ones, have the disadvantage of being able to trigger certain types of fuses for engineer mines with magnetic target sensors and homemade electronic and electromechanical fuses.

A special class of metal detectors is represented by bomb detectors (ferrolocators) — means for searching for buried (in the ground or water to a depth of 1 — 6 m) large metal objects made of ferromagnetic materials weighing from several tens to several hundred kilograms.

Such devices allow detecting ammunition (large-caliber shells, aerial bombs), weapons depots located in the ground, and underground utilities.

The bomb detectors operate based on the above-mentioned harmonic method (Gemini, Gemini-3), the transient process method (IMB), and the magnetometric method (OGF-L and FT-600A – photo 5).

Photo 5. Ferrolocator (bomb detector) FT-600A

The operation of magnetometric devices is based on measuring the distortions of the Earth's magnetic field caused by the presence of massive metal objects.

It should be noted that this method allows detecting only ferromagnetic objects (made of steel and cast iron).

At the same time, these devices allow in some cases, in addition to detecting an object, to determine its depth with an accuracy of 15 — 20%, as well as its shape, size and orientation in the ground.

Modern induction mine detectors and bomb detectors are structurally made in land or underwater versions, and the operating depth of the latter version of the devices is up to 10 — 30 m.

The characteristics of modern domestic mine detectors are given in Table 1.

Table 1. Main tactical and technical characteristics of mine detectors

Note:
PTM – anti-tank mine;
PPM – anti-personnel mine.

To detect wire lines for controlling explosive devices, so-called cable detectors and line-finding equipment can be used.

The operation of such devices is based on the detection of secondary electromagnetic fields induced in wire lines by signals from radio broadcasting stations (so-called passive devices) or excited using special devices included in the cable detector and line-finding equipment kit (so-called active devices).

The main purpose of such devices is usually to search for power and telephone cables or metal pipelines located at depths of up to several meters and having sufficient length (at least 20 … 30 meters).

In this regard, detection of wire lines for controlling explosive devices depends significantly on the length of the line and the depth of its occurrence. The domestic passive cable locator R-299 ensures detection of wires such as field telephone wires with a minimum line length of 25 — 30 m at a depth of up to 0.15 m.

The Abris line locator complex is distinguished by its higher efficiency and functionality when solving similar problems (the maximum detection depth of some objects can be up to 8 .. 10 m).

The advantages of cable detectors include the relatively small weight of the devices (2-3 kg), as well as the ability to detect the location and depth of wires with an accuracy of up to 20-25%.

Radio wave detectors (radio wave mine detectors or locators) can be used to detect explosive ordnance and many other objects hidden in homogeneous environments (soil, walls, etc.).

The operation of the devices is based on the emission of an electromagnetic ultra-high-frequency signal (2.0 GHz and more) and the subsequent analysis of the reflected signal from objects that have a contrast in permittivity with respect to the environment in which they are located.

Because of this, it is possible to detect almost any objects — not only metal objects, but also other inhomogeneities, such as voids, plastic and wooden objects (including against the background of other objects or behind them).

A domestic example of a radio wave mine detector is the MMP mine detector (photo 6), one of the operating modes of which is radio wave.

Unfortunately, such mine detectors in radio wave mode have such significant drawbacks as low noise immunity and search speed, especially in urban and industrial conditions.

Photo 6. Mine detector MMP

Basically, such devices are used to search for anti-tank mines in casings made of any material in relatively homogeneous soils at a depth of up to 0.15 — 0.2 m.

Devices for searching for inhomogeneities (camouflaged objects) «Raskan-2» and «Cyclops-5» have higher capabilities for detecting explosive remnants and other objects in various environments at a depth of up to 0.22 m. They provide the formation of a two-dimensional image of a fragment of the surface being studied on the PC monitor screen with the possibility of subsequent study of the resulting image.

Unlike X-ray equipment, which requires the object being examined to be placed between the X-ray source and the receiving device, in this device, as in other radars, the transmitting and receiving devices are located on the same side of the probed surface.

To search for various objects in sheltered environments at depths from 0.3 m to 20 … 30 m using the radio wave method, the OKO series of ground penetrating radars (photos 7, 8) can be used, the main characteristics of which are given in Table 2.

X-ray inspection systems are designed for express inspection of baggage, containers, parcels and structural elements of buildings, structures and vehicles for the presence of explosive hazards, weapons and other unauthorized items and hiding places.

A characteristic feature of all X-ray complexes without exception is the presence of a emitting device (X-ray apparatus) and a receiving device — a screen (X-ray television converter), between which the object under study must be located.

Unfortunately, for this reason, in practice it is not always possible to directly use such a complex without first moving the object under study, in particular, in the case of placing baggage suspected of containing a hazardous substance in the corner of a room or in a niche.

In addition, there is a risk of some types of electronic and electromechanical (primarily homemade) fuses being triggered when exposed to X-rays.

AB500	AB700 and AB1200
Photo 7. Georadar series “OKO-M” with antenna units

Photo 8. Georadar series “OKO-M1” with
antenna units AB250 and AB400

Table 2. Main characteristics of the OKO series ground penetrating radars

Nevertheless, X-ray inspection systems have become widespread throughout the world, primarily in the stationary version, often called introvisors. Representative examples of portable X-ray systems are “Shmel-90/K” (photo 9), “Shmel-240TV (television), “Norka” and fluoroscopes of the FP series (Russia).

In the Shmel series of complexes, in order to increase the safety of personnel searching for and identifying explosive devices, the ability to remotely turn on the X-ray machine is provided, and in the Shmel-240TV complex, the ability to remotely receive and computerize images is also provided. Such complexes can be delivered to the object under study by dragging or using remotely controlled devices.

Photo 9. Portable X-ray
complex “Shmel-90/K”

All devices have biological protection of the operator from reverse and lateral radiation, allowing work without the use of special means of protection from X-ray radiation.

For the non-contact detection of activated clock (mechanical, electromechanical and electronic) and electronic fuses of other types, the device “Pifon-3M” (photo 10) has been developed

The device is made in the form of a police baton and, being passive, does not emit any signals.

Detection range of fuses, cm:

• mechanical clocks 20 — 100
• electromechanical clocks 15 — 40
• electronic clocks 1 — 5
• other electronic types 1 — 10

Photo 10. Detector of sentries and
electronic fuses “Pifon-3M”

Non-linear radars are designed to detect electronic devices containing semiconductor devices (diodes, transistors, integrated circuits, etc.) with non-linear volt-ampere characteristics.

Such devices include electronic and electromechanical fuses (including command and actuator units of radio fuses), radio bookmarks and other electronic devices.

The operation of nonlinear radars is based on irradiation of the surveyed area, premises, etc. with a probing signal of the ultra-high frequency range (pulse or harmonic) and reception of the re-radiated signal containing (in the case of the presence of semiconductor devices or a metal-oxide-metal transition) higher harmonics of the probing signal.

As a rule, the receiving device of a nonlinear radar is tuned to the second (or second and third) harmonic of the probing signal.

Representative examples of nonlinear radars produced by the domestic industry are Ob-A (Ob-AL), NR-900 EM, NR-m (photo 11), Cyclone M, Rodnik 23. In terms of their technical parameters, domestic devices are not only not inferior to Western analogues, but in some cases surpass them.

It should be noted that when using nonlinear radars, there is a possibility of triggering some types of electronic fuses (especially homemade ones) due to:

• induction in the wires of the electric detonator of an electric potential (EMF) sufficient to trigger the electric detonator, regardless of the presence or absence of electrical contact with the power source of the fuse;
• breakdown of the p-n junction in the transistor (thyristor) of the electronic key of the fuse and closing the electrical contact of the electric detonator to the power source.

Photo 11. Nonlinear radars NR-900EM and NR-m

In addition, there is a certain probability of failure of various types of electronic equipment that fall within the radiation pattern of non-linear radars.

The advantages of non-linear radars are ease of operation, low requirements for operator qualifications and high detection accuracy, especially in the version equipped with a laser target designator (Ob-AL), coaxial with the axis of the emitter antenna.

The search process using such devices consists of a sequential inspection (irradiation) of a room (area of ​​terrain, etc.).

The operation of radars is practically unaffected by obstacles in the form of brick or wooden walls, furniture, etc.

At the same time, this circumstance serves as a source of false signals (for example, from electronic equipment located behind the wall in the adjacent room). To eliminate this drawback, the receiver sensitivity is adjusted.

The depth of detection of search objects in the ground by non-linear radars depends on its humidity and, as a rule, does not exceed 0.15 m.

In some cases, for remote detection at a distance of up to several tens of meters of explosive ordnance placed on the ground surface, and especially anti-personnel fragmentation mines with a tension, seismic or optical target sensor, the portable computer thermograph “IRTIS-220” (photo 12) can be effectively used. It provides visualization of thermal fields and remote determination of the temperature of various objects.

Photo 12. Portable computer
thermograph “IRTIS-220”

When searching for explosive hazards on the ground surface, including in cases with protective and deforming near infrared spectrum coloring, there are often moments during the day when the gradient (difference) in temperatures of the sought objects and the background is significant.

For example, such moments occur during sunrise or sunset, after rain or dew.

The portable computer thermograph “IRTIS-220”, having a sensitivity to temperature differences of about 0.05 ° C, ensures the detection of explosive hazards in these conditions, including those partially hidden by vegetation.

In addition, there are options for active thermal impact on the underlying surface in order to further increase the temperature gradient of the sought objects and the background, when conditions for detecting objects buried in the ground can be ensured.

Naturally, this device is effective, first of all, when used in open areas with a minimum of natural (rocks) and artificial (household and construction waste) inhomogeneities on the soil surface.

For visual inspection of hard-to-reach areas and cavities in buildings, structures and vehicles, rigid and flexible endoscopes (photo 13) based on fiber-optic technology, as well as mirrors on rods (including those with IR illumination and the ability to transmit images to a video monitor) can be used.

Photo 13. Flexible endoscope

Search for anti-personnel high-explosive and anti-tank (anti-bottom and anti-track) mines in the ground can be carried out by contact using a probe on a rod.

The method can be effectively used, first of all, to search for engineer mines on “soft” soils with a limited number of mechanical inhomogeneities.

Since the trigger force of most pressure fuses of anti-personnel mines is 0.2…5 kg, there is a possibility of triggering such mines when using this method, especially with low operator qualifications.

In addition, there are known cases in world practice of using explosive devices with anti-probe switches that are triggered when trying to detect them with a metal probe. To increase the safety of searching for anti-personnel mines in the ground, it is advisable to use a sapper's protective suit with special anti-mine shoes.

It is advisable to note another aspect (inattention to which has already resulted in casualties) of inspecting various objects for explosive hazards, weapons, explosives and narcotics.

If a suspicious object with an unknown substance is detected in one way or another, before identifying it, consider the substance to be explosive, taking all appropriate precautions for the personnel conducting this work and the surrounding area.

Only after there is complete confidence that there is no danger of an explosion can one begin to detect, identify and seize narcotic and other potent substances, for example, using the NarcoCvet or Litmus-3 express test kit for these substances. The reverse order of actions is unacceptable.

As the above shows, there is no universal means that ensures a reliable search for explosives, explosive devices and other explosive devices in any conditions.

It is advisable to solve the problems of detecting explosive devices by using various search tools and other equipment, as well as special tactical techniques. Moreover, the set of tools is determined by the specific conditions of the task, the level of personnel qualifications and financial capabilities.

Literature:
1. Petrov S.I. On the assessment of the possibility of detecting explosives and devices containing them.//Special equipment, No. 4, 2001.