Selecting and using a thermal imaging camera for wildfire – Part 1

For wildfire, the use of a thermal imaging camera (TIC) can have significant benefits. However, like any other item of firefighting equipment it also has limitations and standard practices and procedures must still be followed. Incorrectly interpreting displayed images could mean failure to identify objects, and may compromise safety, effectiveness and efficiency.

Form and function of hand-held cameras

While hand-held, helmet- and mask-mounted cameras are available for structural firefighting, hand-held cameras are arguably the best option for wildfire use. They come in a range of sizes, features and designs and can vary from 180g to 1.6kg.

Sensor array format – Microbolometers with either VOx or a-Si sensors are used today in fire service cameras. The sensor or Focal Plan Array (FPA) consists of an array of pixels that are set in horizontal and vertical lines. Fire service array formats are generally set up with a ratio of 4:3 in landscape format. There have been some recent cameras that have the sensor and display in ‘portrait’ 3:4 format, resulting in a reduction in the width of the camera, making them more compact.

Sensor refresh rate is measured in hertz (Hz) and equates to the refresh rate (or frame update rate) and is the number of times per second that a new image is ‘created’ by the sensor. Fire service TICs can usually range in performance between 9Hz and 60Hz. Cameras with lower refresh rates may produce a ‘choppy’ image if panning with the camera or the object being viewed is moving.

Sensor resolution – The introduction of Microbolometer sensors initially saw 160×120 and 320×240 pixel arrays, with 384×288 sensors entering service around 2011. 80×60 sensors have also been offered on some cameras and more recently 192×144, 206×156 and 240×180 sensors. A higher pixel count results in a higher-resolution image.

Sensitivity or Noise Equivalent Temperature Difference (NETD) – Measured in millikelvins (mK), the lower the number the greater the sensitivity to detect slight differences in temperature.

Field of view (FOV) – The camera’s FOV will determine the size of the area that can be viewed at any time. A narrow FOV will display a smaller area than a camera with a wider FOV. The FOV is important in determining the image quality in relation to the sensor resolution; a high-resolution sensor may have a wider FOV.

Screen display – Typical screen displays are 61, 69, 76, 90, 101 or 109mm diagonally. Screen size can be a compromise between the physical size and weight of the camera and an image that is easy to view.

Battery type and run time – Most cameras have removable rechargeable batteries and come with a spare battery. Some small-format cameras may have an inbuilt rechargeable battery. Run time can vary from 2 to 8 hours depending on the make and model. This may be an important consideration if working remotely away from a vehicle or other power supply.

Camera features and software – Manufactures offer a range of standard and additional features including laser pointers, flashlights, image and video recording/transmission, visual sensors, rangefinders, compass, tracking equipment, to name a few. Software has allowed for colourisation, optional camera operating modes, digital zoom and the ability to blend the infrared and visual images as well as IR image enhancement.

Camera selection for wildfire use

Some manufacturers classify thermal equipment for the structural environment as either:

• Situational awareness (personal camera) – generally single button or simplified operation, designed for navigation in a structure and basic tasks.
• Tactical (decision making or crew camera) – offering a higher resolution and wider field of view, further features and operating modes, designed for more complex tasks and interpretation of incident conditions.

In more general terms we could arguably put cameras into three categories:

• Basic/small format – single or simplified operating modes, weighing under 700g, they may have a smaller viewing screen, a low refresh rate under 20Hz and may have a narrow FOV.
• Mid-range – single or simplified operating modes, 160×120 to 320×240 sensor, 69mm (diagonal) or larger viewing screen, a FOV of 40° or greater and a refresh rate of 25Hz or more.
• Advanced – Additional operating modes and features, 320×240 or 384×288 sensor, 90mm (diagonal) or larger viewing screen, a FOV greater than 47° and a refresh rate of 50Hz or more.

Camera features and modes

Cameras can range from single button operation with one operating mode (standard mode or TI Basic), while others may have a choice of screen palettes, optional modes and features. While some of these features may be useful for structural firefighting or Hazmat applications, for example, they may have little use for wildfire. However, features designed specifically for structure fire overhaul are generally an advantage for wildfire hotspot detection and mopping up. Some of these that are available from different manufacturers include:

Visual/Thermal blended image: The blending of the digital and visual image together can provide key aspects of the visual scene on top of a full thermal image.

Operating modes: Some cameras provide a size-up or overhaul mode that provides onscreen colourisation at a lower temperature, while others may have manual adjustment for the onscreen colour threshold. This will provide a visual colour indication at the adjusted temperature setting.

Floating, high temperature curser: This feature places a moving crosshair on the single hottest object within the FOV, indicating the warmest object. That may or may not be a ‘hotspot’ but can provide an indicator for further investigation if required.

Other useful accessories can include:

• Laser pointer: Under the right light conditions and at short distance it provides clear and time-saving communication when indicating the location of a target to another person.
• Flashlight: Some cameras have a built-in flashlight, which is a useful feature at night and in a similar way to a laser pointer can also indicate the centre of the FOV.
• Digital zoom: Available on some cameras as a 2x or 2–4x digital zoom. This feature can be used when it is difficult to access a hotspot, for example when examining an elevated hotspot or one that is in a hazardous area. In that situation it can also reduce the FOV and sometimes improve the thermal contrast of the image.
• Image/video capture: May be convenient as information to pass on to fire investigators and as a record for ongoing work or significant areas of concern.

TIC use at wildfires

Cameras have become more affordable and we are at a point where TICs are broadly available. Basic and intermediate cameras may be suitable for locating larger hotspots or checking known areas of concern to help ensure complete extinguishment.

Advanced cameras with additional specialist features may increase the ability to locate smaller hotspots at greater distances with a wider FOV taking in a larger area and being able to scan more efficiently because of the quicker refresh rate.

The actual use and deployment of TIC equipment and their operators can be tailored to suit the needs and requirements of the incident.

Cameras can be used to assist during size-up and fire attack; however, for wildfire their use may be more beneficial during mopping up, patrolling or rechecking previous work. That can also include follow-up on the ground of aerial infrared detection.

Getting the most out of a TIC at wildfires

Without a TIC we may rely on sensory clues such as what we can see, smell or feel. With a TIC, these observations are still important as any anomaly that we can identify we can then verify quickly with the TIC in conjunction with other conventional means such as digging or cutting away material to investigate further.

TICs identify thermal energy that is invisible to the human eye. We need to consider how TICs work, how they detect energy and the factors that will affect image interpretation in the wildfire environment. Infrared energy can be emitted, absorbed, reflected and transmitted and that energy can be transferred by means of convection, conduction and radiation.

A TIC will only detect the temperature of surfaces, so in a wildfire environment radiant energy that is line of sight may be relatively easy to identify. For objects that are smouldering inside logs, stumps, trees or underground, we need to consider the mechanism of heat transfer. That could be a combination of conduction through the material or convection energy. Soil and timber are efficient insulators of energy compared to other materials so energy transfer may not always be evident. In some cases, radiant energy that isn’t within line of sight may have been absorbed by another object close by that can be identified. In all cases we need to be able to recognise an anomaly and then investigate it further.

The term ‘thermal contrast’ describes how well objects stand out from one another. High thermal contrast means there is clear definition of objects within the FOV due to variations in surface temperature. This is particularly important for hotspot detection. Outdoors, the emitted energy from the sun can be absorbed by rocks, soils and vegetation, warming them to create a situation of low thermal contrast with hotspots at near equal temperatures. Early in the day hotspots may stand out clearly, but later in the day the absorbed energy from the sun can significantly reduce the thermal contrast. Background energy from the sun can cast not only a visual shadow but also a thermal shadow, making objects that are in the shade easy to identify and those that aren’t difficult.

The use of water or foam can cool surface temperatures and particularly foam can mask them from view for significant amounts of time.

Regardless of the temperature and amount of energy, a small object or an object a long distance away or not in line of sight may be difficult or unable to be identified.

Firefighter safety when using a TIC at wildfires

Follow standard wildfire safety procedures, always wear appropriate and approved Personal Protective Clothing (PPC) and never work alone. Ensure that everyone is always visually looking for hazards so that risks are avoided. Be adequately briefed including a safety brief and have a radio if working out of voice communications with other crew members. A risk and hazard tree assessment should be considered with hazard treatment or removal done as required. The TIC can be used to scan from a safe distance if required.

Conclusion

Purchase price may be a factor, but camera selection may be a compromise between a light-weight compact camera that is convenient to carry for locating larger hotspots and checking extinguishment or a larger fully featured camera that may be able detect smaller objects with a higher-resolution sensor, larger FOV and screen size.

To get the most out of your TIC, training and an understanding of how the camera works and its features is important. A TIC like any other item of firefighting equipment has limitations and understanding these are vital. Standard practices and procedures must still be followed to ensure that safety and the task outcomes are not compromised.

For more information, email G.Parker@cfa.vic.gov.au