Shadow Image Processing of X-Ray Screening System for Aviation Security

Safety is the key point for general, corporate, military and commercial aviation [1]. The safety is the condition, for which risks of aviation events are reduced and controlled to an acceptable level [2]. Maintaining and increasing the level of safety is the most important task for civil aviation [3, 4].

Aviation safety can be considered as a dynamic stochastic process [5, 6] that depends on many factors including airport organizational structure, reliability of aviation equipment, human factor, environmental conditions [2, 7]. The aviation safety depends on the influence of unintentional and deliberate actions. The unintentional actions are associated with the random occurrence of different aviation events. For example, the aircraft safety depends on: a) the serviceable operation of radio equipment of flight providing such as radar, navigation systems, communication devices [8]; b) the efficiency of data processing techniques for modern radio equipment in different environmental conditions [9, 10]; c) the psychological state of the pilot, especially in a stressful situation [6].

The deliberate actions are associated with aviation security. The aviation security is an important component for safety of aviation providing. The purpose of aviation security services is to ensure aviation safety, the efficiency of civil aviation airports by implementing measures to protect against acts of unlawful interference in accordance with current rules, recommended practices and procedures [11].

In order to evaluate the planning of civil aviation security measures, a general strategy should be developed taking into account the trends in the occurrence of threats and international requirements [12]. The main principles that regulate the aviation security service are following:

• –    security measures applied at a specific airport or aerodrome must be adequate to the level of threat to civil aviation that exists at a specific time;

• –    any civil aircraft may not fly outside the certain country without the permission of the civil aviation authority;

• –    any person may not be admitted on board of aircraft located in a restricted area of airport without a valid reason;

• –    any person or vehicle may not enter or pass through the restricted area of the airport without passing established security control procedures;

• –    items, as well as hand luggage, baggage, courier and express items, mail, on-board supplies excluding standard equipment of the aircraft, may not be placed on board without passing security control;

• –    all aviation personnel and other specialists (persons), whose work belongs to the branch of interests of civil aviation and concerns the interests of aviation security, may be allowed to perform such work only after they graduate appropriate training.

Based on a systematic approach and analysis, the International Civil Aviation Organization (ICAO) identified the main threats to aviation safety: hijacking of aircraft by terrorists and other criminal elements and acts of sabotage; illegal transportation of dangerous goods; dangers during aircraft flights caused by aggressive or mentally unbalanced passengers; use of surface-to-air missiles by terrorists; illegal transportation of nuclear and radioactive substances; cyberterrorism.

While planning aviation security, it is necessary to solve the following problems:

• 1.    Minimization of explosions impact. In paper [13], the analysis of using conventional explosives in attacks on airports is carried out and recommendations are given for the detection and disposal of improvised explosive devices placed in vehicles or baggage items.

• 2.    The protection of passengers and personnel. This is a primary problem, which means the practical development of permanent or temporary protection of air transport passengers, service personnel and visitors from attacks with the use of firearms and grenades [14]. Solution of this problem is associated with recommendations for the use of bulletproof fabrics, materials capable of resisting explosions or grenades, as well as for preventing (in the interests of the customs service) the transfer of contraband goods from one group of violators to another.

• 3.    Access control. Reducing the number of full-time employees who need access to restricted areas is an obvious, but often ignored security measure [15]. Baggage drop-off points are often located in restricted area where they should not be. In places where baggage is issued to passengers of international lines, the requirements of the local customs service can be ensured by other means, but taking out the baggage places from the restricted zone can significantly reduce the risk of passengers re-entering this zone and provide the impossibility to enter it by unauthorized persons.

• 4.    Perimeter protection. This problem is often treated as secondary, although the lack of such protection creates favorable conditions for terrorists to attack airport infrastructure or aircraft and is often the object of criticism from the mass media, usually in connection with some aviation incidents. Solution of this problem is associated with usage of technical devices of alarm system, security closed television systems, lighting and passive infrared detectors [16].

• 5.    Protection against cyberterrorism. Threats of cyberterrorism are new and, at the same time, the most dangerous threats of the 21st century [17]. Cyberterrorism can manifest itself in various forms. The simplest of them is psychological warfare aimed at spreading disinformation using mass media to disrupt the normal operation of airports and airlines [18]. This can cause the refusal of air passengers to fly, which will affect the economy of countries that depend on civil aviation. Other dangerous threats of cyberterrorism can lead to serious disturbances with fatal consequences for people, disorganization of airports and damage to aircraft in flight. The actions of cyberterrorists against airports and airplanes are significantly different from traditional terrorist and criminal attacks on civil aviation facilities. Cyberterrorists can, acting from one location, affect events in hundreds of other locations on a global scale.

2.    Analysis of Signal Processing at X-ray Screenning and the Research Problem Statement

Solution of this problem is associated with development of new methods for detecting DDoS attacks [19], cyber incidents [20], analysis of the security of sites and equipment with access to the Internet [21], analysis of the efficiency of the use of information web-resources [22] and others.

One of the main goals of aviation security service is to detect dangerous and prohibited objects during passengers and baggage screening [23]. For this purpose, aviation security personnel use various equipment: X-ray screening system, body-scans, metal detectors, moving ions detectors, explosive trace detectors. Modern airports use three to five levels of inspection for baggage. The screening of passengers is carried out line mode. The X-ray screening system provides information on internal structure of baggage objects and gives possibility to detect explosives, narcotics, firearms, cold weapon and other dangerous and prohibited objects [24].

According to the modern recommendations of air terminals building, it is assumed that all baggage undergoes automatic inspection with the help of X-ray screening systems. Unfortunately, the high reliability of detection of dangerous objects and materials (the probability of correct detection is above 0.99) is also accompanied by high levels of the false alarm probability (this probability is approximately equal to 0.15 ... 0.3) [24, 25]. The timely and correct detection of dangerous and prohibited objects has significant influence not only the aviation safety, but also aircraft departures and arrivals delays [26], increasing the throughput rates for each aviation security inspection line [27].

The main reasons of rather high level of the false alarm probability are:

• 1.    Dependence of detection performance on obtained image quality [28].

• 2.    Disadvantages in terms of probabilistic characteristics of imaging technologies and used algorithms for recognition of dangerous and prohibited objects while X-ray screening [29].

• 3.    Human factor [30].

• 4.    Equipment malfunction and failures [31, 32].

The human factor is taken into account mainly through the aviation personnel training. At the same time, special software is being developed, such as threat image projection. This software is installed on X-ray screening systems [33]. Threat image projection generates and puts fictitious images of dangerous objects on X-ray images of real baggage that is being checked. In addition, paper [34] analyses the color compositions obtained based on threat image projection merging algorithm. The authors proved that this algorithm increases the efficiency of detection and confidence level, provides shorter reaction times compared with standard technique of computer-based X-ray screening training images.

The methods of operational efficiency increasing suppose improvement of maintenance techniques [35, 36] and equipment diagnostics and repair [37], reliability analysis for deteriorating systems [38, 39], developing methods of statistical data processing [40, 41], implementation of control and support system for equipment lifecycle.