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Thermal Imaging: AXIS Q1941

by Benchmark

Thermal imaging is often touted as an alternative to video surveillance, but for many smart applications it offers other benefits. For long range detection in large and open areas, it’s hard to beat the technology. However, it is vital that those implementing it understand exactly what they’re going to get!

The debate over the value of thermal imaging has been going on for many years. While a few customers have realised the value of the technology, it has also not been on the agenda for a large number of sites for one reason: in the past thermal imaging was price-prohibitive.

In recent years, that has changed significantly. Today some thermal imagers are available for the same cost as a good quality video camera, and we’re even seeing the first devices that are the same cost as budget video cameras.

With affordable thermal imaging available today, is it worth investigating the value of thermal imaging as a detection tool?

The assessment was carried out in a site with a long and open perimeter. It was carried out in late Spring and the weather was typically British, with day temperature highs of 12 degrees C and night time temperature lows of 6 degrees C. It was predominantly cloudy with periods of rain and drizzle.

Defining identification

When we talk about identification we are usually looking at the ability to positively identify an individual. To achieve this there is a requirement for highly detailed images that can prove the identity of an individual, or person-specific data with a full audit trail that can establish their presence in a given place at a given time, without doubt.

In thermal imaging, the definition of ‘identification’ is based upon the Johnson Criteria, a performance index created nearly 70 years ago to judge the accuracy of night vision goggles. These consider identification as there being something of interest there, which is acceptable in a theatre of combat.

Modern implementations of the Johnson Criteria claim that 12 pixels of information are required for identification. Despite this being wholly at odds with the definition understood by the law enforcement market, manufacturers still use it as a specification for their products.

Because of the image detail included in a thermal image, it is not possible to achieve identification of an individual. However, in order to have some certainty that a target is a human, we felt that as a rule of thumb usable ranges could be as little as 20 per cent of the claimed figures.

Lens considerations

Thermal imagers and video cameras both require lenses, but that’s where the similarities stop. For those familiar with video lenses, the optics for thermal imagers present a different proposition. However, the good news is that you are unlikely to have to do move than specify a focal length.

While video lenses are made from ground glass, thermal imaging lenses are not, as thermography is obstructed by glass. Instead the units use lenses from of a variety of materials, the most common being Germanium. Lenses are fixed focal length and are usually factory configured, so they don’t require focusing.

Thermal imager lenses have a variety of focal lengths, and the performance is similar to video lenses. Short focal lengths offer wide angles of view with less magnification, and longer focal lengths have a narrower field of view with more magnification.

Thermal positives

Thermal imagers really come into their own in challenging conditions. In periods of twilight or darkness, fog or inclement weather, thermography can deliver consistent images which identify the presence of intruders. When motion is present, it does become much easier to determine whether a target is human or an animal.

Thermal imagers also work well with intelligent video analytics. Because these tools work on the visual information in a stream, they are more successful with the almost default white hot palettes.

Small differences in resolution do make a difference, but with realistic expectations most thermal devices can be used to add value to a solution. The real question is whether the devices are worth the investment.

Value for money?

In the past it was hard to justify the use of thermal imaging on many sites. Today things have changed, and whilst the new breed of low cost imagers are very price competitive, the available performance must be understood.

The performance often comes down to resolution and lens. Skimp on either and the range of the unit is reduced. There are imagers that cost the same as budget cameras, but their usefulness – and subsequently their value for money – is limited. They will be fine in a few applications, but not for all.

If you’re looking for thermal imagers that will deliver detail and detection over ranges of 100 to 200 metres, then the cost will likely be around the same for a very high end security camera.

Given the abilities of such devices, the cost can be justified and the thermal imagers do represent good value for money for mainstream applications.

For most, this middle ground is where thermal imaging makes sense. High end imagers are the domain of high risk sites with deep pockets and the low end units lack the quality needed for credible security.

Axis Communications AXIS Q1941-E

The AXIS Q1941-E is an external thermal imager. It is available with a range of lenses; our unit was a 19mm model. It utilises a 17µm uncooled vanadium oxide microbolometer. The thermal imager is equipped with motion detection, but also supports third party analytics via the Axis ACAP programme.

The thermal imager incorporates Zipstream technology to manage bit-rate requirements, and includes a full range of options for further stream management.

The AXIS Q1941-E is supplied with a utilities CD which includes a software program for addressing the units. Axis Communications has one of the most consistently dependable utilities, and once more it worked as expected. Once configured the next task is to set a password for the root user. Initial set-up screens are shown using M-JPEG compression; if you want to use H.264 an additional plug-in will be loaded. The process is automatic

The menus are well designed, and through the use of tabs it is simple to navigate quickly to the required elements. Set-up is very simple, and any installers or integrators who are familiar with the Axis interface will feel immediately at home.

The streams from the AXIS Q1941 have a high degree of detail. It does have a slightly higher resolution than some of the low cost imagers, but the differentiation in the images makes detection a lot simpler.

With motion it is very obvious what you’re looking at, even out to distances of close to 200 metres.
Visual detection is very good, and the use of motion detection is good. If you’re looking for more advanced video analysis, then an add-on application from an ACAP partner is recommended.

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