Posts

DRI

The Use of Johnson’s Criteria for Thermal Camera and Systems Performance

When customers are considering which thermal security camera or system to buy, one of the first questions asked of thermal imager manufacturers is usually: “At what distance can the IR camera detect a target?”. In other words, what is the camera’s ability to capture very small details at great distances? When thinking about effective surveillance, it is indeed a good criterion to differentiate one sensor from another.

No matter which manufacturer you are buying from, the answer given to this question will almost always include the “DRI ranges” expression. DRI refers to the distance at which a target can be Detected, Recognized, or Identified, based on certain universally accepted parameters. In order to select the right sensor for your defense, security, or surveillance needs, these DRI ranges have to be, first, perfectly defined, but also assessed with regards to globally adopted industrial standards. Enter Johnson’s criteria.

The Origin of Johnson’s Criteria

In 1958, at the first ever “Night Vision Image Intensifier Symposium”, John Johnson, a night vision scientist at the U.S. Army’s “Night Vision and Electronic Sensors Directorate” (NVESD), presented a paper named the “Analysis of Image Forming Systems”. Johnson’s paper defined a clear system with criteria and methodology for predicting an observer’s ability to find and assess targets using image intensifying equipment (such as thermal cameras), under various conditions. It worked well, and it was the first of its kind.

Johnson’s Criteria Definitions

Johnson’s model provided definitive criteria for calculating the maximum range at which “Detection, Recognition, and Identification (D, R, I)” could take place, with a 50% probability of success. (Orientation was also discussed, but this parameter is not used or recognized today).  Although newer methodologies for D,R,I exist today, such as NVESD’s “Night Vision Image Performance Model” (NV-IPM), the “Johnson’s Criteria” system was groundbreaking for its time, was the accepted standard in the defense industry for many years, and is still widely used in the security industry today.

Detection

Johnson defined “Detection” as the ability to subtend 1 TV line pair (+/- 0.25 line pairs) across the critical dimension of the subject (this translates to 2 pixels when using an LCD monitor). At the range that this occurs, regardless of target type, the observer could detect that a subject was in the field of view, 50% of the time. Today, many security camera companies loosely follow Johnson’s Criteria and define their camera’s “Detection” performance range as the ability to subtend either 1.5 or 2 pixels on the target, using various target sizes.

Recognition

Johnson defined “Recognition” as the ability to subtend 4 TV line pairs (+/- 0.8 line pairs) across the critical dimension of the subject (this translates to 8 +/- 1 pixels when using an LCD monitor). At the range that this occurs, regardless of target type, the observer determines the type of subject, a human or a car for example, 50% of the time. Today many security camera companies typically define their cameras “Recognition” performance range as the ability to subtend 6 pixels on the target, using various target sizes.

Identification

Johnson defined “Identification” as the ability to subtend 6.4 TV line pairs (+/- 1.5 line pairs) across the critical dimension of the subject (this translates to 12 +/- 3 pixels when using an LCD monitor). At the range that this occurs, regardless of target type, the observer could detect the subject. Today many security camera companies loosely follow Johnson’s Criteria and define their cameras “Identification” performance range as the ability to subtend 12 pixels on the target, using various target sizes.

dri4

Johnson’s Criteria in the Security Industry

DRI ranges, expressed in kilometers (or miles), can usually be found in the specification table of infrared camera brochures, or in a description of the cameras features. While a very helpful jumping off point for narrowing down the options and homing in on the best systems, customers would be doing themselves a disservice to only look at DRI. This is because today the application of Johnson’s criteria varies somewhat across the security industry. In most instances, documentation uses simplified or modified versions of the criteria, but they do all generally follow similar rules.

Typically, most companies use twelve pixels on the target for identification, six for recognition, and two for detection (sometimes 1.5). However, the target size can vary greatly. Normally the defense industry “NATO” target size (2.3×2.3 meters) is used for calculating the performance range for detecting vehicles, but for a human target, various target sizes can be found. It is important when selecting your thermal camera to keep in mind that in any given document, the target size for a human can range from 1.7-1.83 meters tall and from 0.3- 0.75 meters wide, and factor this into your decision-making process.

The Need to look at the Bigger Picture

Because end-users often place a high value on the written specifications of the camera, marketing departments are under pressure to use performance calculations that make their cameras look better than the competitors. However, since these calculations typically do not take environmental factors into account, customers should ask their thermal camera providers to explain the other elements and benefits of each camera they are offering, and how they will perform in a variety of conditions. A modified approach that considers parameters such as these can better help in choosing the right thermal camera or system for your needs.

Modern Drone Threats and Detection Solutions

The drone market is booming

According to a 2016 report, revenues from drone sales are expected to top $12 billion by 2021. Shipments of consumer drones are expected to more than quadruple over the next five years, while the military sector will continue to lead all other sectors in drone spending. Drones or UAV’s (unmanned aerial vehicles) have become a part of everything, and are now in the news on a daily basis, from terrorist activities, to issues over restricted airspace. The list of applications is virtually endless, and includes hunting poachers, perimeter security, aiding firefighters, building diagnostics, surveillance, counter-terrorism, and more.

New technology means new threats

The models on the market now are small and getting smaller, and they can go anywhere. They are also more available, and more affordable than ever before. While the continual development of new technologies provides more versatile capabilities for defense and civilian applications, it also creates new possibilities for terrorist organizations. Some terrorist groups are taking advantage of these capabilities, using drones to achieve their objectives. As the technology advances, so too will the range of commercially available drones, facilitating greater standoff distances and decreasing the likelihood of detection of the drone operator.

With great distribution comes great risk

Drones with the ability to deliver a payload can now be purchased by anyone for a few hundred US dollars. ISIS, for example, is using plastic commercial drones to drop grenades on military and civilian targets, and to monitor enemy troop movements, while their propaganda videos encourage drone attacks worldwide. Event organizers and security teams need to be prepared for a variety of different scenarios, with new threats evolving all the time. The greatest fear is what would happen if a terrorist organization used drone technology to attack a major public event or other place where people gather. These risks are unacceptable and require a comprehensive solution. We need to be able to protect our military bases, nuclear facilities, prisons, transportation hubs, and public events from weaponized drones.

How do we protect valuable assets against these threats?

Because they have become so small and so cheap, UAV’s are now a fact of life, and must be taken into consideration when building your event or perimeter security plan. The list of “anti-drone” solutions is almost as long as the list of uses for drones, and includes net firing “drone-catcher” drones, guns, lasers, missiles, jamming viruses to drop them out of the air, software to take control, operator location… and many more. If there is one problem that most of these solutions share, it is that they all rely on accurate threat detection in order to have a chance at success. But how do you detect something as small as a plastic consumer drone? Small and fast, some are even virtually undetectable in daylight. Without detection, all these other solutions will be ineffective. From this we see that detection solutions are at the core of any drone threat response system. Without detection, the effectiveness of any solution will be limited.

A range of detection solutions

Current detection options for drones include radar, acoustic detection, and thermal imaging. These solutions range in effectiveness based on a number of conditions. When we consider the fact that drones are not limited by daylight and can also operate at night, we begin to understand that any solution to successfully protect against drone attacks will require the ability to detect drones at night, even in complete darkness. Counter measures need to include a comprehensive security plan that includes technology capable of answering this threat. Nighttime vision solutions are limited, and include traditional night vision, infrared (IR or “thermal imaging”) cameras, and near infrared cameras.

Thermal imaging is not night vision

Like near IR cameras, night vision goggles and scopes see visible light, like your eyes, and make images from enhancing or adding visible light to the region of interest. Thermal cameras on the other hand, “see” heat, not light. The more heat an object gives off, the more thermal contrast it generates, and the easier it is to see. Because of this, thermal imaging even functions in zero-light conditions. It also has extreme long-range capabilities, making it ideal for drone detection. Thermal security and surveillance cameras and systems are therefore an excellent solution for drone detection, and can even be paired with other sensors to increase effectiveness.