Mobile video recording systems.
Law and Order.- 1995 .- May,- P. 93-100.
Mobile video recording systems
Over the past few years, there has been a significant increase in the use of mobile video recording systems by the police. Currently, two types of video recording systems are used:
- based on camcorders (video cameras with a built-in portable video recorder);
- based on desktop cassette video recorders and miniature video cameras with charge-coupled devices (CCD).
The first type of systems uses specially modified compact camcorders recording on 8 mm film or standard film for home VCRs. Camcorder systems are widely used due to their versatility and lower maintenance costs compared to VCR systems. Their main advantage is that they can be taken out of the car to record events at the scene of a crime or incident, everyday situations, to collect testimony and evidence, etc. The recording time is from 20 minutes to 2 hours, which is enough to record events during road accidents and traffic violations.
Camcoders available on the market from different companies differ in their technical characteristics and video recording quality. The recording quality of camcorder video systems is usually the same as that of more expensive desktop VCR systems.
For police operations, the light sensitivity of video cameras, the image clarity (number of lines per frame) and color or black and white recording are important. The light sensitivity of a video camera is the level of illumination, expressed in lux, at which a satisfactory image can be obtained. The lower this level, the less light is required to obtain an acceptable image. This is very important, since most mobile police video systems are used at night. at low light levels.
There are currently no industry or federal standards for the sensitivity of video cameras, so one should be careful when choosing cameras for specific applications. Due to the lack of standards, a camera from one company with a sensitivity of 3 lux may not be more sensitive than a camera from another company with a sensitivity of 5 lux. With this in mind, it can be assumed that the sensitivity of camcorder moving video systems should be below 2 lux. The maximum sensitivity value can be considered to be 1 lux, since at higher sensitivity, flare from the brightest points of the observed scene may appear in the frame. The lens of the video camera is also important, which must ensure the formation of a clear and bright image in limited lighting. To obtain good image frames when shooting with a wide-angle lens or focusing on infinity, the focal length change ratio of the lens must be at least 10:1 or 12:1. The speed of the camcorder's autofocus in low light conditions is also important. Finally, the number of lines in the frame directly affects the image quality. As a rule of thumb, the more lines in a frame, the better.
The camcorder video system can be mounted directly on the wing of the vehicle, suspended from the ceiling in its body, or fixed in front of the windshield. When mounted directly on the wing of the vehicle, the camcorder is exposed to direct sunlight, which can damage the equipment and its internal electronic and mechanical components. Placing the camcorder inside the vehicle and using simple heat shielding can extend the useful life of the camcorder and eliminate the harmful effects of sunlight. However, this will worsen the ventilation conditions of the system and cause some inconvenience to the police officers in the vehicle.
The ease of use and availability of camcorders make them attractive to criminals. But the relatively low cost of a camcorder (around $2,000) does not pose a significant threat. Protecting a camcorder on a police car with a casing or a simple lock creates more inconvenience for the police officers using the camcorder than for the criminal intending to steal it. In fact, there has not been a single reported case of theft of a police camcorder, although the police currently use more than 10,000 camcorders mounted on the fenders of their cars.
With the right design of a camcorder video recording system, the police will be provided with a reliable and satisfactory service for several years. Video tape for home video recorders (VHS) allows recording images with a definition of 300-400 lines. If higher definition is required, then it is necessary to use S-VHS (super) or Hi-8 video tapes, which is associated with additional costs. In this case, the police would have to purchase special, more expensive high-definition monitors for monitoring the recording and VCRs for playback of images. However, the courts do not yet have such specialized equipment, so the costs of video systems with increased definition will be unjustified.
Various companies — manufacturers of camcorders and video recording systems — advertise their individual advantages as enabling the presentation of video tape recordings in court as evidence. When purchasing a video recording system, it is necessary to determine exactly which of its features can actually be used as evidence in court, taking into account that each additional feature affects the cost of the video system.
Evidence in court requires that the video tape record the date and time of day when the events recorded on it occurred, to prevent falsification. Although systems with recording on 8-mm tape record events in the surveillance zone, these tapes may not be accepted in court as evidence, since the frame format of the recording on them does not allow recording the date and time of occurrence of certain events.
More sophisticated desktop video recorder systems, sometimes called super video systems, provide police departments and agencies with video and audio recordings for a full (8-hour) work shift. Unlike camcorder systems, they require additional measures during installation and maintenance. Video recorders are mounted permanently (usually in a vehicle) and covered with a special protective casing that ensures the safety of the video tapes. This casing protects the video recorder from unauthorized access, fire, and theft. Police personnel must undergo special training in the use of video recorder systems, which, if used correctly, can record more information than is necessary to complete the task.
The configuration of the video recorder system allows for the inclusion of various interfaces that expand its functionality: an interface with a radar measuring the speed of vehicles; protection against recording based on previously made video recordings; switching on emergency lighting; switching on a covertly worn microphone; indication on the display of the date and time of day, as well as two lines of characters of the generated information. Some of these functions can also be performed by camcorder video systems.
Miniature CCD video cameras, black-and-white and color, are used for filming in video recording systems. Several such cameras can be used in one video recording system, which expands the surveillance capabilities. The main parameters of video cameras are sensitivity (minimum illumination in lux) and the size of the chip with a matrix of charge-coupled devices. The sensitivity of a black-and-white video camera should be below 2 lux, and a color one — about 5 lux. With such sensitivity, to obtain an acceptable color image, it is necessary to turn on all the vehicle's lighting devices for external illumination. The size of the chip with a matrix of light-sensitive elements (1/2″ or 1/3″) does not significantly affect the image quality. The cost of a color video camera is twice as high as a black-and-white camera. Only black-and-white video cameras are sensitive to infrared radiation and can be used when conducting operations at night.The camera of the mobile video recorder system is its only element that can be easily replaced in case of failure. If the video recorder is faulty, the car in which it is installed must be taken out of service for repair of the system, and if the car is faulty, the system cannot be used,
An important part of a mobile video system is the sound recording equipment. Police officers often have to operate outside the camera's field of view. But a good audio system with sufficient range can clearly record their messages, which can be used later as evidence. For sound recording, the audio system should have a miniature microphone with a cardioid polar pattern, good sensitivity and a dynamic range of 120 dB. To transmit audio information, two transmitters are used, operating at close frequencies in the 170-215 MHz range to implement diversity reception at distances of at least 300 m in urban areas.
The use of a mobile video system is greatly facilitated by the presence of a video monitor. It allows the operator to ensure that the system is functioning properly upon initial switch-on, as well as to match the «frames» of the camera and the VCR. The monitor also shows whether the illumination of the observed scene corresponds to the quality of the video recording. The monitor is of great help in training police officers. CRT monitors and liquid crystal displays are popular. The first type of monitors have a larger screen, but also a greater weight (from 0.5 to 1 kg) compared to liquid crystal displays. The second type of monitors reproduce high-quality color images, but their operation is affected by extreme temperatures. Black and white CRT monitors are cheaper than color or black and white liquid crystal displays.A serious problem when using mobile video systems is protection from radio interference. Its influence can cause erasure of the image on the monitor, damage to the electronic components of the system and deterioration of the video recording quality. Strong magnetic fields can completely disrupt the operation of video cameras. A high level of radio interference is observed in urban areas, especially near powerful radio stations. Therefore, mobile video systems must have some built-in elements of protection against radio interference. A certain effect is provided by the use of interference suppression filters, shielding of all protruding wires and cables, proper grounding of some elements of the system. These measures can reduce the influence of radio interference to some acceptable level.
Most applications of mobile video recording systems require ensuring their physical security. The measures necessary for this are determined by the level of actual or potential threats. Manufacturers of systems take different approaches to solving this problem. Some of them do not apply any security measures, others suggest placing the system in lockable steel cases with access to the video tape by a digital lock code or secretly installing video recorders in the driver's cabin of a car. However, these measures do not always justify themselves and can only lead to an increase in the cost of the system. The most reliable means of ensuring the security of the system is a well-trained operator. The portability of camcorders plays an important role in ensuring security. In fact, to date, there has not been a single officially registered case of theft or loss of tapes of police video systems.