Watch Your Perimeter

Video surveillance for perimeter security should pay close attention to light sensitivity and other IP camera features

• By Allen Chan
• Aug 01, 2016

When it comes to securing perimeters, no two are exactly the same. Perimeters can be vast and remote like a national border, or they can be small and urban like the area surrounding a city bus terminal. Intrusion concerns can be via land, air, water or all three. Nearly any combination of factors is possible.

The one thing nearly all perimeters have in common is that they are secured by some form of video surveillance. This is generally done in combination with other security measures, such as fences, guard towers, sensors, radar, sonar or live patrols. Unlike “open campus” environments like universities and shopping malls, the goal of perimeter security is to ensure that no one crosses a defined border without being noticed.

This can be extremely challenging as security breaches can be caused for any number of reasons, even those that are completely innocent. For example, many major airports are located adjacent to bodies of water and the concern may be boats that unintentionally – or intentionally – cross into airport areas. Because it may not be feasible to install a fence, an innocent boater may come ashore and into restricted areas.

In perimeter security, the purpose of a video system is to see such occurrences and assess what response is appropriate for the situation. When it comes to video surveillance, there are a handful of technologies that can help perimeter security meet its full potential.

LIGHT SENSITIVITY: A NO. 1 PRIORITY FOR PERIMETER SECURITY

Light sensitivity is probably the single most important specification an IP camera can have. Many perimeters may not have the best lighting to cover the areas of interest, which could pose a challenge when choosing cameras. For example, a facility may be too close to a populated area where light pollution at night is a concern. Or, it simply may be impractical to install lights due to the terrain or other factors. Therefore, a camera must be able to produce good quality video in whatever ambient lighting conditions exist.

At this point, many security professionals may be wondering why light sensitivity is so important. After all, the security industry has for many years offered technologies that help cameras “see” better in the dark, such as thermal imagers and infrared (IR) light sources.

While thermal and IR imaging have their place, both present challenges when it comes to video quality. Over longer distances, objects may not be easy to recognize due to resolution. They also essentially give a “ghostlike” appearance to objects of interest, causing figures to appear washed out and almost as if they are glowing.

Using IR lighting requires that the object of interest first be within the reach of the IR illuminator. Long-range IR illuminators are available, but security cameras are typically required to capture images of objects that are both near and far. As objects get closer to the camera and the IR illuminator, they become overexposed because they are too close to the light source. This makes it difficult to use IR illumination to cover large areas with a single camera. In addition, IR illumination causes white or light objects to show up as black, and dark or black objects to show up as white, making color identification difficult.

Thermal imaging does not have the distance restrictions of IR, however, the color limitations still exist. Warm objects appear white and cool objects appear black, or vice versa. This makes it nearly impossible to describe an object or person that may be breaching a perimeter. In addition, even higher-end thermal imaging uses VGA resolution, or standard definition, imagers. This means the image is only 640x480, which is extremely small. From long distances, it becomes difficult to determine what an object is because it is not possible to magnify the image. For instance, it would be impossible to distinguish a deer from a person once the distance surpasses the capabilities of VGA resolution.

Thermal imaging works by detecting temperature, and the scene is basically a gray scale of varying temperatures. The heat signatures of objects with similar temperatures appear the same, and if person or object is in front of a structure or larger object of similar temperature, the object in front might not be visible. For example, if a person walks in front of a car with a hot engine, the heat from the engine will mask the person’s body heat and make it impossible for the thermal imager to detect the person’s presence. This tends to happen more in the summer months. A person may be walking along a perimeter, but the heat rising from the ground causes the surrounding area to have a temperature similar to body heat. In this case, the person can frequently “appear” and “disappear” as the surrounding temperature changes.

We see things in color, describe things in color, and so color plays a big factor in surveillance. Is the car white, red, tan or blue? Is the person wearing a green or black jacket? This kind of color information is critical when a security breach is in progress. Color information is also crucial forensic evidence for postincident analysis or legal prosecution. In contrast to IR and thermal imagers, IP cameras that have excellent light sensitivity can continue to create clear images with accurate color reproduction as scenes darken and turn nearly pitch black. This produces better quality video without the cost of extra equipment.

LIGHT SENSITIVITY AND VIDEO RESOLUTION

In many perimeter security installations, having the highest possible resolution video is just as important as being able to generate good images in the dark. However, as camera resolution goes up, light sensitivity goes down. This is simply because when using similar sized imagers, the sensor area to gather light becomes smaller as resolution increases.

This is particularly noticeable as users move from full HD IP cameras to megapixel or even 4K cameras. While most HD cameras are perfectly capable of generating decent color video under only moonlit conditions, most megapixel and 4K cameras have poorer minimum illumination ratings than their full HD counterparts. This means they require more light to produce usable images and will switch from color mode to black-and-white mode before an HD camera.

Better light sensitivity ratings for megapixel and 4K cameras can be achieved by using a full-frame 35mm sensor, using a back-illuminated sensor structure, using noise-reduction techniques, or slowing down the camera’s shutter speed to allow in more light.

When resolution is a key concern, any of these can vastly improve the camera’s overall light sensitivity characteristics while still maintaining megapixel and 4K resolution. In the darkest conditions, 35mm sensors or back-illuminated sensors will work much better than cameras that try to increase gain by using noise-reduction techniques or slower shutter speeds. Unless the scene is static, slower shutter speeds will increase the blurriness of moving objects.

There are no standard specifications for camera sensitivity in the security industry, so even cameras that claim to have the same ratings can perform very differently. Therefore, it’s critical for security professionals to do their homework by asking the right questions regarding how the minimum illumination sensitivity figures are specified. Better yet, onsite testing is the best way to identify the megapixel and 4K cameras with the best light sensitivity performance, color reproduction, and noise reduction.

LIGHT SENSITIVITY’S IMPACT ON ANALYTICS

Having cameras with better light sensitivity is also beneficial for any perimeter security application that is running analytics. When a camera’s images become too dark, blurry or grainy, then the accuracy of analytics software is negatively impacted resulting in an increase of false positives, or false alarms.

For example, high image quality is needed in order for the analytics software to determine if an object crawling over a fence is a person or an animal, or if a face matches one from the watch list. If the object in question is shadowed, or appears ghost-like from thermal or IR imaging, then the analytics software cannot work to its full potential.

DYNAMIC RANGE AND LIGHT RESPONSE

Wide dynamic range (WDR) relates to light sensitivity, but it’s not just for low-light conditions. The dynamic range of a camera is rated in decibels (dB) and determines the capability of the camera to see the darkest and brightest areas of a scene at the same time. The higher the rating, the better the camera should operate in any difficult lighting condition, light or dark. This can include excessively bright light from the sun shining directly into the camera or high-contrast scenes like a parking lot where some cars are in the sun and some are shaded by trees. Dynamic range technology allows clear images to be seen in light and dark areas simultaneously, rather than overexposing or underexposing various areas.

As with light sensitivity, there are no standards for how a camera’s dynamic range is derived. Some products can say 90dB, and some will say 100dB, but when tested side by side, the 90dB performs better than the one with 100dB. So, any products being considered should be tested side by side to determine which performs the best.

Another aspect to consider is how fast a camera responds to sudden or extreme light changes. The response characteristics of each product can be vastly different, and unfortunately, there is no specification at all for light response. Some cameras can take 10 to 15 seconds to adjust to a sudden and drastic lighting change, like from bright headlights flashing into the lens on a dark night. In perimeter security applications, even a few seconds could make the difference between detecting an intruder and missing the security breach entirely.

A NOTE ABOUT VIEWING ANGLES AND ZOOM

Viewing angles are another important consideration in perimeter security. Depending on the situation, views may need to be wide and shallow, or narrow and deep, so lenses should be chosen accordingly.

Similar to camera selection, choosing the right lens comes with its own set of considerations regarding light sensitivity. The longer (or deeper) the view needs to be, the more light the lens needs in order to generate the same quality image as a wider angle lens. Increasing the f-stop even one increment will increase the lens’ depth of field, but it also doubles its light requirements. Therefore, security professionals need to figure out how to either generate additional light, or compensate with a more light-sensitive camera.

With the growing prevalence of 4K cameras in security installations, it’s also important to keep in mind a few things about 4K cameras, their viewing angles, and their ability to zoom in on distant objects. Given the same viewing distance and parameters, a 4K camera produces video that is four times better than full HD, and 27 times better than VGA. It can also allow users to expand their wide area surveillance yet still capture, magnify and examine the smallest parts of a scene. But like other fixed IP cameras, a 4K camera can be configured to see either wide angles or far into the distance. It cannot do both at the same time. This is where using a PTZ camera in conjunction with a 4K camera can be beneficial.

PERIMETER SECURITY FOR TODAY AND TOMORROW

Without a doubt, securing perimeters is one of the toughest jobs in the security industry. Each one is different and presents a unique set of challenges. When purchasing and deploying surveillance cameras, it is often best to find the ones that can do the job, rather than purely looking at costs. Just as with our daily life, using the right tool for the job will make things easier and faster, and it will be more cost effective in the long run.

This article originally appeared in the August 2016 issue of Security Today.