11. Alarm Assessment - sandia.gov11. Alarm Assessment The Twenty-Sixth International Training Course 11-3 be investigated or assessed at a given location. To be useful, detection needs

The Twenty-Sixth International Training Course 11-1

11. Alarm Assessment

Abstract. Alarm assessment completes the detection function when a human determines whether the alarm event was activated by a real threat or a nuisance alarm. Two methods of alarm assessment are by the response force (guards) in elevated towers or by roving patrols and video coverage of each sensor sector displayed at a local alarm station. This session will primarily describe the design issues and performance criteria of a video alarm assessment system. The assessment system is composed of several cameras at remote sensor areas; a display monitor at the local end; and various transmission, switching, and recording systems. The major components include (1) the camera and lens to convert the image of the physical scene into an electrical signal, (2) the lighting system to illuminate the alarm location evenly with enough intensity for the camera and lens, (3) the transmission system to connect the remote cameras to the local video monitors so that no undesirable effects are introduced to the video signal, (4) video switching equipment to connect multiple video signals from cameras with monitors and video recorders, (5) the video recording system to produce a record of an event, (6) video monitors to convert a signal to a visual scene on the face of the output display, and (7) the video controller to interface between the alarm sensor system and the alarm assessment system. The video alarm assessment system is just one component of the total intrusion detection system. Interactions and integration issues between the video system, intrusion sensors, and the alarm control and display system must be considered.

11.1 Introduction

Purpose The purposes of assessment are to determine the cause of each sensor alarm event. This includes

determining whether the source of the alarm is a real threat or nuisance alarm.

to provide supplemental information about an intrusion, such as who, what, where, and how many.

Methods Two methods of assessment are possible: one through closed-circuit television (CCTV) coverage of each sensor sector, and the other by visual checks from posted guard towers or roving patrols. Authorized personnel can rapidly assess sensor alarms at remote locations using a video alarm assessment system. Guards within elevated towers or dispatched roving patrols can be used to make a delayed assessment that is dependent on the amount of time it takes the guards to respond to the alarmed area for the assessment determination. Time is a factor in determining the cause of the alarm. Without recorded video, the probability of making a correct assessment is reduced the longer it takes to obtain the information about the alarm. Therefore, a response from a roving patrol that could take tens of seconds may not have a high probability of a correct assessment compared to an electronic assessment system with proper recording of the alarmed event. Understanding the whole system in the analysis phase is key to designing the use of manpower or technology for alarm assessment. Assessment technology cannot stop the adversaries from accomplishing their goal. Assessment by roving patrols can also add an element of delay and instant

Define Physical Protection System Requirements

11-2 The Twenty-Sixth International Training Course

response to the assessment; however, depending on the threat, the roving patrol may have a low probability of surviving against high-level threats.

Alarm Assessment Defined

Surveillance

Defined Difference Between

Assessment and Surveillance

Alarm assessment is defined as the process of viewing the source of an intrusion detection alarm to determine the cause of the alarm. Surveillance is defined as the viewing of an area for the purpose of monitoring the area to detect an intrusion or to provide additional observation of special activities. The primary difference between alarm assessment and surveillance is that assessment is event-driven in that a human’s attention is directed to the scene of the event by the alarm; surveillance is the use of a human as the detector of the event.

Assessment and Surveillance Issues

Assessment of an exception alarm by a human operator is an efficient way of determining the cause of the alarm event. Humans have better response and concentration levels to exception events because the activity is called to the operator’s attention and the operator must then execute a specific set of procedures. This better response is validated in testing only when the exception events do not occur frequently enough (high nuisance alarms) that the exception events look like a normal occurrence. Using sensors to create an event that the human has to address using video technology avoids a single point of failure—if the video fails, the roving patrol can still be sent to make an assessment of the sensor alarm. Testing using humans1 to identify significant abnormal activities on multiple video monitors indicate that humans do not make good detectors. In fact, increasing the number of activities that the human has to perform—such as answering the phone, logging in visitors, or conducting radio communications—lowers the probability of detection. In surveillance mode of operation, the person is the detector and the assessment component; loss of video or the ability of the observer to see the protected area creates a single point of failure for detection and assessment. Many surveillance applications use the constant recording of activities not for event detection at the time of the event, but for post-event analysis of the events to determine the cause. One example of this is a casino’s use of surveillance cameras to record all activities to catch customers or employees attempting to steal from the casino. The detection is made when the casino’s surveillance staff realizes that a particular table or machine is losing more money than the odds indicate it should. The recordings are then examined to determine the cause of the loss. Although this is not a timely method, surveillance camera recording is a good application for the threat, the target, and the risk that casino is willing to take.

INFCIRC/225 Reference

INFCIRC/225/Rev.5 states, in a narrow sense, that detection is a physical phenomenon, i.e., a sensor or person determines that something needs to

1 Monitoring up to 16 Synthetic Television Pictures Showing a Great Deal of Movement, A.H. Tickner and E.C. Poulton, Ergonomics, 1973, Vol. 16 No. 4 P381-401



be investigated or assessed at a given location. To be useful, detection needs to be coupled with an assessment of what has been detected. Did a sensor detect an animal or a person? Was the sensor triggered by weather conditions resulting in a nuisance alarm? The IAEA has recognized that detection without timely assessment is not useful. Constant surveillance of inner areas is recommended as a use of the two-man rule. The IAEA recognizes that assessment and surveillance have two different functions and purposes.

11.2 Video Alarm Assessment System

Analog Components

The analog components of a video alarm assessment system are shown in Figure 11–1. The assessment system is composed of cameras at the remote sensor areas; display monitors at the local end; and various transmission, switching, and recording systems. Major components include:

camera and lens lighting system transmission system video switching equipment video recorder video monitor video controller

LIGHTINGLIGHTING

CAMERACAMERA

TRANSMISSION SYSTEMTRANSMISSION SYSTEM

VIDEO CONDITIONINGSYSTEM

VIDEO CONDITIONINGSYSTEM

VIDEOSWITCHER

VIDEOSWITCHER

CONTROLLERCONTROLLER

MONITORMONITOR

VIDEORECORDER

VIDEORECORDER ALARM

INTERFACEALARM

INTERFACE

VIDEO VIDEO

VIDEO

DATA

CAMERACAMERA

MONITORMONITOR

DATA

VIDEO

VIDEO

DATA

VIDEO

VIDEO

Figure 11–1. Analog Components of Video Alarm Assessment System



Digital Components The digital components of a video alarm assessment system are shown in

Figure 11–2. The assessment system is composed of cameras at the remote sensor areas; display monitors at the local end; and various network transmission, switching, and recording systems. Major components include: camera and lens lighting system network transmission system (switches, routers, cabling) network video recorder(s) network display workstation (operator’s workstation) network video software/database server (control and application server) archive server (network recorder for archiving alarm events)

Note that there are three types of camera outputs/inputs in Figure 11-2:

IP addressable cameras – direct IP output and interface IP video encoder – converts analog video signal to IP format Digital video recorder – inputs analog video, converts signal from

analog to digital for storage, and provides digital stored video to the IP network

Any of the three types (or a combination) can be used in a digital system. The advantages, disadvantages and limitations of each must be considered.

Figure 11–2. Digital Components of Video Alarm Assessment System

LIGHTING

Archive Server

Video Display

Work Station

Network Video Recorder/Server

Alarm Information

Interface

Analog Camera

IP Addressable Camera

IP Addressable Camera

Network Switch

IP Video Encoder

Router

Control and Application

Server

Digital Video Recorder

Network Switch

Analog Camera

Analog Camera

Network Data



Analog Versus Digital

Although there is a shift toward using digital (IP) cameras, network recorders, and network workstations for processing video information, the above Figures 11-1 and 11-2 show a close functional relationship between the analog and digital world for processing video images. Discussions on the advantages and disadvantages of the use of one technology over the other involves more than a near-term cost justification. The use of either of the technologies must be balanced with the threat, target, and overall system analysis of which technology would be the better choice. Once the design requirements are stated, either a digital or analog video solution can be designed by remaining within the limitations of either technology. In general, the currently available IP cameras are as sensitive and some may have higher resolution than the analog cameras. However, video compression techniques, frame rate, network bandwidth are items to consider with digital IP systems, as they all will affect video resolution and quality. In the following discussion, much of the material is generic to both analog cameras and digital (IP) cameras. Whenever necessary, features specific to one technology or the other will be clearly indicated.

11.2.1 Camera

Convert Optical Image to Video

Signal

The basic function of the camera is to convert an optical image of the physical scene into an electrical (video) signal, suitable for transmission to a remote display area. The camera and its features are selected according to design rules defined by testing. This is done to optimize the performance of the camera to provide an image that will enable a human operator to determine the source that caused the alarm. Most modern cameras are solid-state imagers and have a variety of features to optimize the image produced by the camera. These features—including automatic gain controls, electronic shutter, adjustable gamma, and bright light source limiters—all assist in producing the best image under constantly changing environmental and lighting conditions. The camera format and the resolution of the camera are specifications provided by the manufacturer, which determine how the camera can be used in the design of an assessment system.

Image Device Format

The image device format is related to the size of the photosensitive surface and is a measure of the diagonal of the scanned rectangular (4 to 3 aspect ratio) area (see Figure 11-3). The most common formats for solid-state cameras are 8mm and 6mm, with 4mm and 2mm models used in special applications. Some of the higher resolution cameras (mega pixel) come in the 1-mm diagonal format. Frequently, the camera format is given in English units that are somewhat difficult to interpret. Although one would think that a half-inch format would convert to 12.7mm, it actually corresponds to the 8mm format. The reason for this apparent disparity is the early development of video, where the imaging device was a vacuum tube. The outer diameter of the tube was the format, but a considerably smaller area of the light-sensitive front was scanned to produce the image; therefore, the old one-inch vacuum tube had a scanned area that was 16mm in diagonal. The English-to-metric conversion is given in the following:



1. 2/3 inch = 11mm diagonal 2. 1/2 inch = 8mm diagonal 3. 1/3 inch = 6mm diagonal 4. 1/4 inch = 4mm diagonal 5. 1/8 inch = 2mm diagonal

Figure 11–3. Format

11.2.2 Lenses

Lens Selection Parameters

Lens selection parameters are interdependent variables and vary with the designer’s assessment objectives, including the manner in which the video alarm assessment system will interface with the intrusion sensing system and the response force. In general, the main purpose of lens selection is to cover as much of the desired area as possible with a minimum number of cameras while retaining an acceptable degree of overall far-field target resolution. The parameters that must be considered in proper lens selection include:

format focal length f-number C or CS mount special application features (aspherical, coatings, neutral density

spot filters, broad band transmission, color correction)

Lens Format The lens format size defines the maximum usable image created by the lens. Standard lens formats are matched to the format of the camera selected. While a larger format lens on a smaller format camera is perfectly fine, a smaller format lens should not be used on a larger format camera because the edges of the image will be darkened and appear as a circle. This effect



is called vignette or tunnel vision.

Focal Length and Field of View

Focal length is the single most important factor in proper lens selection. It determines the relative magnification of the object. The magnification determines the horizontal and vertical field of view. Since the format of a lens is known, the angular fields of view (horizontal and vertical angles covered by the lens) can be calculated, thus defining the width and height of the field of view for the camera for any object distance.

F-Number Another important lens parameter is its aperture setting called an F-stop, which is the lens’ measure of its ability to gather light. The smaller the f-stop, the more light is collected by the lens; therefore, a small f-stop (1.2 to 1.8) is desirable for exterior assessment applications. The number is the ratio of the lens focal length to the aperture opening in mm. For example, a 25mm lens with an aperture opening of 20.7mm would have an F-stop of 1.2.

Lens Mounts There are two common mounts for most lenses—C (Cine)-Mount and CS (Cine-short)-Mount. The threads for the two mounts are identical: 1" diameter 32 threads per inch. C-Mount uses 17.52mm flange back distance, while the CS-Mount uses a 12.5mm flange back distance. CS-Mount cameras can be converted to C-Mount by using a 5-mm spacer element; however, CS-Mount lenses cannot be used with C-Mount cameras (the camera cannot be brought into focus).

Special Features Lenses may have other features that can enhance the performance of the lens. Some are aspherical to allow better focusing of the image to the sensor image (flatter field). Some have automatic iris aperture controls that work with the camera circuitry to allow for automatic adjustment of the light levels, including neutral density filters in the center of the lens. This allows for a greater magnitude reduction of bright light when the iris aperture is smaller than the neutral density spot. Some lenses have special coatings to enhance or filter certain wavelengths of light energy to optimize the lens performance. Some lenses have broader bandwidth transmissions to enhance the transmission of near IR (from 800nm to 1100nm), which is usable to solid state cameras not equipped with IR cut filters. Another important aspect is color correction. While this aspect is important on color cameras, it is also important for black and white cameras to avoid soft focus due to different wavelengths of light focusing at different points.

Levels of Resolution

Selection of a camera and lens combination for a video alarm assessment system starts with the determination of the degree of resolution to be required. Three levels of resolution may be considered: detection—the ability to detect the presence of an object in the area of

interest

classification—increased resolution provides sufficient information to determine what is present by class (animal, blowing debris, man)

identification—improved resolution sufficient to uniquely identify an



object on the basis of details of appearance

The selection of one of the three levels of resolution depends on the threat and any other requirements for the video system to perform the assessment or surveillance task. Empirical testing has determined that detection can occur on a full frame of video with only 2 to 3 pixels, classification can occur with 8 to 12 pixels (horizontal), and identification can occur with 13 to 21 pixels (horizontal) across the width of the object (Figure 11-4). Further testing indicates that a human presenting the smallest profile to a perimeter camera has a 30cm square cross-section. This testing indicates that 8 pixels or 6 horizontal television lines (HTVL) divided on that cross-sectional target is sufficient with average contrast and motion to distinguish (classify) a nuisance alarm source from a human intruder.

Camera Resolution Specification

Camera resolution is stated in the manufacturer’s literature. It can take the form of one of two numbers and sometimes is stated with both numbers. The first specification term would be “pixels,” these are the individual photosensitive elements found in all (analog or digital) solid state cameras that actually convert the image scene into an electrical signal. Because this imager device or chip contains the individual pixel elements, some manufacturers state the horizontal and vertical count of these pixels or cells as the resolution of the camera. The Institute of Radio Engineers and the National Association of Broadcasters were responsible for defining video camera resolution units during the early years of television. The cameras in that time all had a 3:4 aspect ratio (rectangular area). In order for the horizontal units and vertical units to be the same dimensionally, the resolution was measured over a square area of the image (the full height and ¾ of the width).

Line of Resolution A line of resolution is defined as the thinnest line that can be clearly imaged by the camera and is measured by counting the number of alternating black and white lines that can be clearly imaged across the full height and ¾ of the width. Thus, if a camera can image 600 lines across ¾ of the width then the camera’s horizontal resolution is said to be 600 HTVL. Since a 600-HTVL camera can actually image 800 lines across the full width, we have to use this number in calculations for far field resolution which, is expressed as lines per unit length. The vertical resolution is determined in analog cameras by the scanning rate, which is based on the local power line frequency. In the United States, the line frequency is 60 Hz, which results in 450 vertical television lines (VTVL). Much of the rest of the world uses 50-Hz line frequency, which results in a higher vertical resolution of 540 VTVL. Digital cameras are not limited by the scanning frequency, since their signal is stored in digital memory and displayed on a computer screen rather than a video monitor. Very high resolution (mega pixel) cameras may have as many as 2048 x 1536 imaging arrays with the resolution increasing every year. A 2048 x 1536 camera would approximately represent a 1536 HTVL x 1536 VTVL resolution camera analog camera.



Pixel Elements

Figure 11-4. Image Chip Details

Resolution Limit The width of the field of view, dictated by the minimum resolution required, calculated by knowing the camera format and resolution with the chosen lens selection determines the distance from the camera to the far field of view. As seen in Figure 11-5, the resolution limit is reached sooner with shorter focal length lens than with longer focal lens; therefore, the overall sector length will be smaller.

Figure 11–5. Practical Field of View vs. Focal Length of Lens

Calculate Angular Fields of View

The following equation may be used to calculate the horizontal and vertical angular fields of view. Horizontal angular field of view = 2 • Tan1 (SI/2F) Vertical angular field of view = 0.75 • horizontal angular field of view where: SI = width of imager active scan area (mm) F = lens focal length (mm)

Draw Angular Fields of View

Angular fields of view can be drawn on site drawings using a conventional protractor and sheets of transparent (tracing) paper. These cutouts can be located arbitrarily at various points surrounding the clear zone to obtain optimal focal length/format selection and coverage of the clear zone while using a minimal number of cameras.

Alternate Technique An alternate technique is to determine the geometry of the area to be assessed and calculate a lens size. This technique may result in calculated lens requirements that do not correspond to a commercially available lens with an f-stop appropriate to planned lighting. Design iterations in which lens parameters, lighting requirements, camera type, camera placement, and



sector geometry are varied will produce a suitable system design. Many commercial lens and camera manufacturers produce or make available a lens calculator in either a manual or software version that will make these calculations.

Distance/Width Formula

D = W (f/w) w= 6.4 for 8mm format w= 4.8 for 6mm format w= 3.2 for 4mm format w= 1.6 for 2mm format

Where: D is distance from camera (m) W is width of field of view (m) f is focal length of lens (mm) w is width of imagers sensitive area (mm)

Hold three variables constant and solve for the last.

Calculation Example

A 20-meter-wide area, assessed with a 8mm format camera using a 25mm focal length, 8mm format lens, would have its camera placed 78 meters away in order to see the entire 20-meter width. D = (20 m(25mm/6.4mm)); D = 20 m(3.9); D = 78 m.

Determine the Resolution-limited

Field of View Width

The resolution-limited field-of-view width for assessment is based on test data to classify a nuisance alarm from a human intruder (estimated as a 30cm target needing 8 pixels across the target). If a black and white camera resolution indicated in the literature is 800 pixels, then the width at which 8 pixels fall on a 30 cm target would be 30 meters. Using the equation above, the distance to the resolution-limited field-of-view width can be determined to be 117 meters. D = (30 m(25mm/6.4mm)); D = 30 m(3.9); D = 117 meters.

Maximum Usable Zone Length

The maximum usable zone length is calculated based on zone width near-field distance and resolution-limited field-of-view distance at the end of the zone (Figure 11-6). It is the difference between these two numbers. For the previous example, the maximum usable zone length is 39 meters, since the resolution-limited field-of-view distance is 117 meters and the zone width near-field distance is 78; therefore, 117 m–78 m equals 39 meters. Using this technique, it is easy to determine which focal length lens is the best suited for a specific zone size. For example, if the requirement were to assess a 20-m-wide, 50-m-long zone, then a 25mm lens would not work. A longer focal length lens would be required. It is always wise to select a lens that provides adequate zone coverage with the longest maximum usable zone length.

D W w

f



Figure 11–6. Perimeter Assessment Zone Geometry

11.2.3 Camera Mounting/Support Structures

Use Stable Towers and Mounts

A recommended perimeter camera mounting height is 6 to 9 m above the assessment area surface. Recommendations for camera mounting and support structures include the following:

Mount cameras on stable towers (lattice support) and mounting structures to avoid motion or movement caused by the wind loading (i.e., solid towers).

Use towers that are not affected by varying weather conditions and change the aiming of the cameras mounted to them (i.e., wooden poles).

If wooden poles (affected by weather) are used, re-aim cameras occasionally to compensate for the long-term environmental effects to maintain the proper view of the assessment area.

Mount the cameras at heights that permit them to view the entire assessment area and sensor enclosures. Optimize the target view by using the width and length of the target (higher view), rather than only the width (lower view) of the target.

Tilt the cameras down to eliminate the horizon from the field of view and to reduce the glare effects during sunrise and sunset. This will also reduce the amount of snow and ice adhering to the camera enclosure faceplate.

Locate the tower so that it does not interfere with sensors located in the perimeter. Do not locate the tower with metal poles near a sensor that is sensitive to metal or a solid pole mounted in line to a line-of-sight sensor.



11.2.4 Lighting System

Assessment Zone Illumination

For a given scene to be “visible” to a camera, the scene must be illuminated by natural or artificial light, since the reflected light from the target is what produces an image from the camera. The function of the lighting system is to illuminate the assessment zone evenly with enough intensity for the chosen camera and lens system.

Minimum Requirements

The two most important parameters of a lighting system for CCTV are its average intensity and the balance of the lightest to darkest areas in 70 percent of the field of view of the camera. The average intensity must be great enough to ensure adequate performance of the chosen camera system. A minimum of 15 lux is required for a color and 10 lux for a black and white solid-state camera system using an F1.8 or faster lens, assuming a ground surface reflectivity of 25 percent. The readings for this measurement should be determined using a calibrated light meter and be performed at a 30-cm height from the ground. The balance of illumination is characterized by the light-to-dark ratio (maximum intensity/minimum intensity) in 70 percent of the field of view of the camera. An excessive light-to-dark ratio will produce unacceptable pictures in which the bright areas appear washed out, and the darker areas appear black due to lack of light. A ratio of 6:1 should be considered maximum, with a design goal ratio of 4:1 preferable.

Lamps or Fixtures In general, vapor lamps, such as mercury or sodium, are a good choice for exterior illumination of black and white cameras because of their lighting efficiency. Some lamps have better ratios of illumination to the energy used, but these types of lamps usually have a disadvantage of a slower time to come to full luminance.

Light Fixture Height Light fixtures should be mounted well above camera height. This will prevent the camera from having to adjust for these bright light sources in the camera’s field of view.

No Lighting System Designs

Very Low Light Cameras

Thermal Cameras

Sometimes it may be desirable to design an alarm assessment system that does not employ a lighting system. These systems can be based on very-low-light cameras or thermal cameras. Very low-light cameras use image intensifier devices to amplify any ambient light to allow the camera to operate. Image intensifiers are based on electron avalanche amplification and can create a usable image with ambient light in the starlight range. However, these cameras do require some small amount of light. Moonless cloud-covered nights do not provide enough light for these cameras. For imaging in total darkness, only thermal cameras can provide a useful image. These cameras operate on the thermal energy emitted by the objects in its field of view. This infrared energy is in the 5-to-14 micron wavelength range.



The use of either of these types of cameras need to be considered carefully because these cameras can be very expensive and generally have lower resolution images, requiring more cameras over shorter alarm zones for adequate resolution. The thermal cameras also require expensive germanium optics.

11.2.5 Video Transmission System

Function and Bandwidth

The function of a video transmission system is to connect the remote cameras to the local video displays with no undesirable effects introduced to the video signal. This transmission system should have a bandwidth at least that of the cameras being used in the assessment system.

Methods of Video Transmission

Video transmission for alarm assessment purposes using multiple cameras may be accomplished in several ways using analog or digital signals. Transmission types include the following:

Coaxial cable transmission (analog) Fiber optics (digital and analog) Microwave links, optical (infrared), or other wireless systems

(digital or analog) Network connection (digital)

11.2.5.1 Bandwidth

Related to Resolution of Cameras and

Monitors

The transmission system bandwidth is related to the resolution of the cameras and monitors. Using the approximation that 80 lines of horizontal resolution are equivalent to 1 MHz of bandwidth and considering, for example, a camera with a specification of 600 lines of horizontal resolution, an analog 7.5-MHz bandwidth will be required. For maximum cost effectiveness and optimum system performance, the bandwidth capabilities of all applicable system components should match. Digital transmission can occur at various transmission rates at full resolution but at slower frame rates. Digital compression of images allows for reduction of the bandwidth required to transmit the image, but the many different compression techniques can also involve reduction of image resolution or quality.

11.2.5.2 Line Loss

Signal Conditioning for Analog Signals

All video copper/coaxial transmission cables will have resistive and reactive losses associated with them. The loss is primarily a function of the distributed conductor capacitance and core resistance. This loss is normally expressed in decibels (dB) per unit length (at various operating frequencies) or capacitance per unit length. Attenuation increases with both frequency and section length and varies widely with the particular cable type in use. For a given distance and frequency, the cable attenuation in decibels may be determined. If cable loss is greater than about 3 dB at the uppermost system operating frequency, some form of signal conditioning will be required to obtain satisfactory performance (return the analog signal to near its original condition).



11.2.5.3 Signal Conditioning for Analog Video Signals

Reason for Use The selection of equipment for signal conditioning is based primarily on the amount of attenuation experienced by the video signal during cable transmission and the amount of noise picked up during the transmission. The conditioning equipment used could be video equalizers, isolation transformers, and/or clampers.

Video Equalizers Equalizers are used to compensate for cable attenuation at higher frequencies. An equalizer at the receiving end of the cable is commonly used in installations, since many cable losses encountered are usually correctable with one equalizer at the receiving end. In addition, this location makes the necessary equalizer alignment much simpler, as the equalizer output can be adjusted while the video test signal is being monitored.

11.2.5.4 Fiber Optic Transmission

Description of Function

Fiber optics use an optical path rather than an electrical path for transmission. The conductor is a glass or plastic fiber rather than copper. A transmitter to convert the electrical signal to an optical signal is required at the camera end. At the display area, a receiver is required to convert the optical signal back to an electrical signal.

Advantages Ground loops, induced noise, and surges from lightning that can damage equipment do not occur with fiber optics. Fiber optic transmission does not require signal conditioning with equalizers, isolation transformers, or clampers, but may need repeaters to provide enough signal strength on very long cable distances.

Fiber optic transmission cables are also the most suitable means of transmitting digital video signals over long distances.



11.2.6 Analog Video Switching Equipment

Video Switchers Most perimeter alarm assessment systems use more cameras than display monitors. For this reason, a video switcher is used to connect the multiple video signals (cameras) with one or more monitoring devices (monitors and video recorders). The associated alarm sensor system generally interfaces with the switching system in such a way that an alarm in any sector causes the associated camera output to be automatically displayed on a local monitor.

Types of Switchers Single output switches are the simplest type of switcher. They connect one of a number of inputs to a single output. Only one input can be connected at a time. Multiple output switchers can switch one or more inputs to any combination of outputs. In a fully connected switcher (matrix switcher), any input can appear on any output, one input can go to all outputs, or different inputs can go to each output.

Active switchers include input and output amplifiers that provide signal isolation, impedance matching, and amplitude control. Electronic proc-essing of the video signal can be included to control the timing of switching between video signals.

Passive switchers have video signal switching paths through relay contacts or mechanical switches.

Types of Switching Systems

Some widely used switching systems include: manual switching - Switching is performed by push-button contacts

and the video signal is routed through the switcher with no electronic conditioning or timing.

sequential switching - All camera outputs are sequentially scanned; the scan rate or amount of time each image is displayed is usually adjustable.

alarm-activated switching - Alarm sector camera information is automatically presented to the output regardless of the selected input before alarm activation.

remote switching - This type of switching involves multiple switching with some of the switching executed remotely and done prior to entering the signals into the security command center.

11.2.7 Video Recording

Purpose The purpose of the video recording system is to produce a record of an event. It provides:



historical (audit trail) information for subsequent study, instant replay/stop action, an aid to real-time assessment.

Video Recorders Video recording systems include: videotape (helical scan system)—videotape has been the most prevalent

system in use for CCTV recording. This system has a relatively simple design and is inexpensive, reliable, and easy to operate if maintained properly.

digital recorders, network recorders, and networked cameras—these type of recorders are becoming the new solution to replace tape recorders and integrate digital video cameras and playback of images on a network. The industry is moving to provide integration to entry control and intrusion alarm display systems.

These systems have the same basic function of storing video data, but the characteristics of their usage and price can have a wide price range, depending on the features selected on the units.

Videotape Recorders

Videotape recorders: provide storage of large quantities of video data for long term, can store up to several hours of real-time video data, and are readily removable for later use or observation on other machines.

The mechanical components and tape interface of videotape recorders do not support continuous instantaneous recording capabilities. Components, like recording or playback heads, require frequent maintenance to preserve recording capabilities if the machine is set in a continuous ready-to-record mode. Major repairs may be needed every several months. These units are rapidly being replaced by digital versions.

Digital and Network Recorders

Digital and network recorders perform the same function of recording video images on a PC-based computer. The main differences are

Digital recorders record the video images from analog or digital cameras directly to the recorder.

Network recorders save and play the video images from network cameras or other sources of a digital video stream that reside on a computer network, eliminating the need for switchers, video monitors, character generators, or separate video transmission systems.

Network cameras can record the images at the camera and then send the images to any computer that connects to the camera through a compatible browser. Other types of network cameras will automatically send events to a massive storage device and other software allows the retrieval of the image recordings from the storage device, usually a server or network database.



Digital recorders are set up to record single or multiple analog camera signals on internal disk drives. They perform this recording task by using one or multiple interface cards that digitize the incoming camera signal and transfer that image either temporarily to memory or to a more permanent hard drive.

Compression Schemes

The number of cameras that can be recorded depends on the compression scheme used by the vendor to store the video images. Some compression schemes are performed by the hardware on the interface cards, while others use software. The main difference of the schemes is how much CPU time is used in the main PC.

Limitations of Compression

Schemes

The amount of CPU time available can limit the ability of the PC to record a large number of cameras. The amount of disk space available inside the computer may limit saving large quantities of video recordings. If too much video is being recorded and played to workstations, the network may be slowed down or the video stream may be limited from the original setup parameters.

Features of Digital and Network

Recorders

The recorders all have similar features that allow selected recording rates (frames per second) for storing information under normal, motion-active states, or by time of day. The recorders compress the images to different qualities, which reduce the amount of storage necessary for preserving the image. The higher the compression, the more recording time can be saved on the hard disk. The resolution of the played images must match the quality of the original images to be effective in the whole assessment system. The reliability of computer systems is very high, but because the recording system has moving parts, failure will occur at some time. Designers must be prepared for this problem using redundant systems, Redundant Arrays of Inexpensive Disks (RAID), or other devices to protect from losing any recorded images. Another powerful technique made possible by digital recording is pre-alarm recording. Often the source of an alarm event is difficult to assess even with recording, especially when the system may take a second or two to report the alarm. By the time the recording is started, a fast moving target can be out of the view. In this technique, all camera signals are constantly recorded until the medium is full; recording then continues with the oldest information being written over first. Whenever an alarm occurs, the system plays back the last few seconds before and a few seconds after the alarm was received, making assessment much more certain.

Is Instantaneous Recording Required?

The decision to use a particular recorder depends on whether the capabilities for instantaneous recording, pre-alarm, or playback are required. Digital recorders may be used if: the assessment area is large and contains no barriers or other delay elements,



allowing an intruder to pass through quickly (in less than 5 seconds).

multiple simultaneous alarms can be expected, requiring successive observation and assessment.

the system operator is required to perform other functions that may prevent him from assessing alarms within a very short time after he has received the report of their occurrence.

The assessment must happen quickly and accurately so that the response force can be notified if necessary.

11.2.8 Video Display

Monitor Description Video monitors and computer displays provide a visual scene on the face of the output display. For maximum picture detail, the analog monitors should have a bandwidth of at least that of the cameras being used in the assessment system. For digital systems, the display should be capable of displaying the digital image in full resolution.

Technical Information for

Analog Monitors

Analog monitors are similar to home television receivers in function but generally have wider bandwidths and do not have radio frequency tuning. Low-impedance (75 ohm) or high-impedance (looping) inputs are normally provided. High-impedance looping allows a single video signal to drive multiple inputs (loads).

Technical Information for

Digital Displays

Digital displays are basically high-resolution computer monitors. They can be older-type cathode ray tubes (CRT), but are most often liquid crystal display (LCD) or plasma displays. This new generation of flat screen displays provide higher resolution and higher contrast than older CRT monitors.

Analog System Performance Issues

The level of performance (resolution) for all components must be the same as the other system components. This is a major design consideration because the video picture monitor is the final output in most assessment systems. The lowest resolution component will limit the monitor’s capability of producing a high-quality image. Monitor resolution is frequently expressed at a certain level of screen brightness or luminance. Different resolutions can be specified for the center (where resolution is normally highest) and corners of the screen. Monitors having 700 to 800 television lines of horizontal resolution are often used in 525-line-scan-rate systems operating at up to 10 MHz of horizontal system bandwidth.

11.2.9 Video Controller

Description The video controller is the main interface between the alarm sensor system and the alarm assessment system. This controller will automatically control the inputs and outputs of the switcher, keep track of the recorder, and display the scenes on the monitor. It may be part of the network recorders program, but often must be controlled by a separate computer or computer



program.

Components The video controller:

may consist of a stand-alone computer commanding matrix switchers, recorders, and other video alarm assessment equipment (analog).

may consist of parts of the network recording system and therefore does not necessarily need the switchers, video monitors, and other video equipment used to display an analog video signal.

can, in some cases, use matrix switchers that have complex functions as the video controller.

The video controller may be part of the alarm, communication, and display program and hardware, which is now integrated with certain digital and network recorder systems. With this type of system control, all alarm data, switching/recording commands, and status information can be transferred between the video system and the “host” system through one communication line. This type of system allows the host system to be free to process other data while the video controller is handling the video alarm assessment data. With large complex assessment systems, the video controller might be required to interface with time/date generators, character inserters, video presence detectors, environmental housing controls, and any other part of the assessment system reporting or requesting current information.

11.3 Additional Design Considerations

Interactions of Video System with

Display Systems

The video alarm assessment system should be designed as a component of the total intrusion detection system. Consideration of the interactions between the video system with the intrusion sensors and display system during the conceptual design phase will allow for the performance of the integrated system to be optimized. Considerations include: Site/sector layout—the layout of sensors so that assessment is possible at

a reasonable cost

Video/sensor interference—the design of the assessment system so as not to contribute to the cause of sensor nuisance alarms

Monitor location—the location of video monitors in the display system to be optimized to human factor considerations of function and frequency of use

Construction—common construction and installation requirements to form integrated control and display functions, not a scattered and haphazard assembly of equipment forced to fit within a space that is inadequate



Lighting Requirements—adequate interior and exterior lighting is necessary at all times to allow rapid assessment of alarms, which may require different types of lights for different tasks that may take place at the display console

11.3.1 Site/Sector Layout

Criteria for Perimeter

Assessment System

One requirement of a perimeter assessment system is to display all of the clear/isolation zone including as much as possible of the inner and outer fences. Camera/lens selection and camera tower positioning must ensure classification of any visible cause of fence and sensor alarms for the clear/isolation zone at any time. For these reasons, it is important that the following criteria be observed:

Make the spacing between the inner and outer fence uniform. Consider the minimum width restrictions for the clear/isolation

zone. Perform grading or removal of vegetation of the clear/isolation

zone. Provide adequate area illumination. Be sure that the expected cause of nuisance alarm sources can be

clearly observed in the field of view of the camera.

Changes from these criteria will generally reduce system efficiency and increase overall system cost by increasing the camera and equipment requirements to achieve an acceptable level of system effectiveness.

Multiple Cameras The effect of using more than one camera to assess a single alarm should be considered. In some systems, with a small number of cameras or with particular video coverage requirements, multiple cameras per alarm may provide excellent assessment without an undue duplication of display and recording equipment. Large systems will tend to be simpler if each alarm is assessed by only one camera since decisions regarding the camera to be switched will be simpler.

Video System Could Affect Sensor

System

Typical exterior systems require installation of camera towers near the area where sensors are installed. Tower height and location must be chosen so that pole vibration caused by wind does not create a source of seismic energy sufficient to cause buried sensor cables to alarm. The construction material of the camera tower, whether the tower is solid or can be seen through, must be considered with the sensors nearby so as not to interfere with the sensitivity of the sensor. Power, video, and control lines must be placed where electronic noise cannot be induced between video cables and sensor cables.

Choose Monitor Location to Mini-mize Interference

Video monitors should be installed in the system control console in a location that allows effective, rapid assessment without interference from other system controls and outputs, using human factors engineering considerations of function and frequency of use.



Combine

Construction Efforts

Installing cables, installing power distribution, and modifying buildings for equipment installation will be common for many parts of an intrusion detec-tion system. Decreased construction costs and more effective system design will result from combining requirements.

Use of Pan Tilt mounts and Zoom

Lenses

Some video alarm assessment system designs seek to reduce the number of cameras used by employing pan tilt mounts and zoom lenses (the combination of these mounts and lenses are often referred as pan tilt zoom [PTZ] cameras). These cameras can be redirected to view the area where an alarm occurred often within a second or less. Older systems had to be manually controlled while newer PTZ systems can be programmed with presets that cause the camera to automatically slew to the alarm scene as soon as the alarm is received. With this approach, as many as four or five alarm zones can be covered by a single camera. However there some disadvantages associated with the use of this approach.

Downsides of the Use of PTZ

Cameras

One of the main disadvantages of the use of PTZ cameras is in the case of multiple simultaneous alarms within the zones covered by the single camera. The system will not allow recording of all of these scenes and, without prioritization, there will be some question as to which alarm the camera will slew to. The use of PTZ cameras preclude the use of pre-alarm recording, since the camera will unlikely be aimed at the source of an alarm prior to the alarm occurring. Also, the mechanical PT mount may require more frequent repairs.

Use of PTZ

Cameras Must be Carefully

Considered

So the question is: should PTZ cameras be used? To answer this question, the designer must carefully consider some design requirements. Does the security level of the system require immediate assessment of simultaneous alarms? Is pre-alarm recording required? Will the budget allow dedicated cameras for each alarm zone? The answers to these questions will help determine whether PTZ cameras are the correct solution for the system design.

11.4 Alarm Assessment by Response Force

Alternate Alarm Assessment

Video alarm assessment can be complemented by visual checks from towers or roving patrols. There are situations in which alarm assessment will have to be done by the response force. If the video alarm assessment system is not operable (maintenance, weather) or if the video alarm assessment is not adequate for a particular situation, the response force must be able to assess the alarm.

Timely Assessment Response force members in towers or those sent to the alarm location can assess alarms. In either case, the alarm must be assessed soon after it is reported. It is important that the response force be well protected and that they have some way of signaling if they are under duress. The probability of a correct assessment decreases as the time to arrive at the assessment location increases.



Effective Guards Towers

Guards in towers can provide effective assessment if the number, design, and placement of the towers are adequate to provide complete visual coverage of the perimeter.

11.5 Summary

Purpose Detection is not complete without assessment. Timely assessment optimizes the probability of a correct assessment, therefore allowing the initiation of the response force.

Assessment Methods

Assessment of alarms can be performed with video equipment, the response force, or a combination of both. If the video alarm assessment system is not operable, the response force must be able to assess alarms from towers or roving patrols. The number, design, and placement of towers must be adequate to provide complete visual coverage of the entire perimeter. A patrol must be able to respond quickly, have duress alarm capability, and have some method of protection if the adversaries attempt to neutralize the responding patrol before the assessment of the alarm can be communicated.

Major Components Video Alarm Assessment

System

The following major components were discussed:

Camera and lens to convert an optical image of the physical scene into an electrical signal

Lighting system to illuminate the alarm location evenly with enough intensity for the camera and lens

Transmission system to connect the remote cameras to the local video monitors

Video switching equipment to connect video signals from multiple cam-eras to monitors and video recorders

Video recording system to produce a record of an event

Video monitors to convert an electrical signal to a visual scene

Video controller to interface between the alarm sensor system and the alarm assessment system

Design Considerations

The alarm assessment system must be designed as a component of the intrusion detection system. Interactions between the video system, intrusion sensors, and display system must be considered. The design of the assessment system should optimize the operations of all components in the assessment system to maximize the use of the equipment for its design purpose during non-idea conditions generated by the environment or by the adversary.

Documents

11. Alarm Assessment - sandia.gov11. Alarm Assessment The Twenty-Sixth International Training Course 11-3 be investigated or assessed at a given location. To be useful, detection needs