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How Far Can a Person See with a Thermal Imaging Camera?

This is probably the first question raised by the owner of a Thermal Imaging Camera. This is a very good question to ask. You can see the moon at the distance of ±250 000 kilometers from earth, however it is not possible to see at such a distance with Thermal Imaging Camera.
The vision range of a Thermal Imaging Camera is only 30 – 40m meters, but the answer to “How far can a person see with a Thermal Imaging Camera?” is not as simple because it is dependent on a variety of factors such as Resolution, Range, Field of View, NETD, Camera type, and of course your budget.

Johnson’s criteria is very useful when viewing through the Thermal Imaging Camera. Johnson was a scientist specialized in electronic sensors and night vision. The criteria developed by him is related to the effective range for infrared cameras. The main target of this development was army but it is also being used in the private sector for characterizing thermal imaging systems. Three types of distinctions can be found among degrees of viewing a specific target, these are recognition, identification, and detection.

  1. Detection
    To know about the existence of an object, 1,5 or more pixels are required to cover its critical dimension. The number of resolutions used by Johnson in a staring array is 0,75 cycles.
  2. Recognition
    Recognition indicates the type of object. This draws a line between a person, truck, car, and among other objects. An object can be recognized if it subtended by 6 pixels across its critical dimension.
  3. Identification
    This term distinguishes among friend and foe. The critical dimension has to be subtended by 12 pixels at the minimum.

The factors that characterize the vision range of a Thermal Imaging Camera

Below are some of the most common factors that characterize the vision range of a Thermal Imaging Camera. We hope that this will allow you to deepen your knowledge and will help you choose the thermal camera that will best meet your needs.

1. The resolution of a thermal imaging camera

The resolution of the sensor of a thermal camera is the most important factor to take into account when talking about the vision range because it will depend on the quality of the images. Do not be misled by some manufacturers who indicate an image resolution of 640 × 480 while the thermal sensor offers only a resolution of 80 × 60. With this type of device, you will unfortunately not be able to view and capture high-quality images.

Thermal Camera resolution Example

It should be clear that the higher the resolution, the more precise the measurements on targets with the reduced surface will be, and you will see the better image quality. Devices with high thermal resolution will be able to provide you with better details that would be barely visible or invisible on cameras using low-resolution sensors.

Don’t forget that the display of a camera may have a higher resolution (in pixels) than the thermal sensor itself. This will not offer you better images because the actual level of detail is always limited by the resolution offered by the latter. In the case of a thermal sensor whose resolution is lower than that of the display, the image will be scaled in the same way that a DVD player would do it on a 4K TV.

2. Temperature Ranges

For personal use: whatever it is and DIY in general, a temperature range of -10 ° to 150 ° C is generally ideal to cover almost all uses, this will allow you to view clearly the thermal bridges around window frames, potential water leaks as well as electrical and heat problems related to heating and air conditioning.

For personal use: whatever it is and DIY in general, a temperature range of -10 ° to 150 ° C is generally ideal to cover almost all uses, this will allow you to view clearly the thermal bridges around window frames, potential water leaks as well as electrical and heat problems related to heating and air conditioning.

3. Field of View

The field of view (FOV) describes the area visible to the camera and depends on the sensor and lens installed; some thermal cameras offer the possibility of replacing the optic by installing wide-angle or telephoto lenses. For fixed-focus cameras, a larger field of view allows for a wider framing for the same distance.

Instantaneous field of view (IFOV) is the thermal camera’s ability to give resolution to details; therefore it defines the smallest object that can be reproduced on the thermal image, based on the measurement distance. In general, to obtain an accurate measurement, the object under consideration should be 2 to 3 times larger than the smallest object that can be framed and identified.

4. Noise Equivalent Temperature Difference (NETD)

The expression NETD stands for “Noise Equivalent Temperature Difference“. It, therefore, corresponds to the ability to distinguish very small differences in image thermal radiation. When the noise becomes equal to the smallest measurable temperature difference, the detector has reached its limit since it is no longer able to identify a useful thermal signal with respect to the noise. The smaller the NETD value, the better the visual accuracy. It is comparable to the measurement resolution on a digital instrument.

NETD Comparison

5. The Budget

Like many things, the budget to spend on buying a thermal camera will depend on how far you want to see with it. If you own a small house or apartment and simply want to have a thermal imaging camera to check for potential heat leaks / thermal bridges and want to make sure that there are no water leaks, hot spots on your electrical board, etc, you will be able to find an affordable and efficient device for a reasonable budget ranging from 100 € to 700 €.

If you own a large home, whether you plan to do many repairs yourself, check an old heating or cooling system, or if you are a professional who needs a thermal imaging camera for a regular use, it may be wise to opt for a semi-professional camera which turns out to be much more precise and will allow you to zoom in on the photos and thus locate more quickly and easily the potentially problematic points.

If you are a professional and your activity requires the daily use of a thermal camera (heat balance professionals, electrician, HVAC mechanic, professional building or real estate, etc…) the choice of a pro device is mandatory. The budget for a device in this range can go from 10,000 € to more according to the desired precision as well as the responsibility associated with a misreading or misdiagnosis which is a point to take into account when making the choice you make.

Many people fall into the trap of opting for a cheaper camera. This is really problematic because if the camera does not have all the features you would have liked, it will simply not be possible to use it in situations for which you have planned to do it. As a result, you will not be able to see at a longer distance. Be aware that a low-cost camera will not be able to provide the same performance as a mid-range thermal camera. This type of camera often has a low-end sensor of very low resolution coupled with a slow processor, making the processing of images long and of less quality. Therefore, you are recommended to buy a good quality camera at a reasonable price.

Now, you might be thinking that how does the thermal imaging camera work?

To understand the operation of such a camera, it should be taken into account that all objects emit infrared radiation, which is higher than the body temperature. Our eyes cannot see these emissions because their range in the electromagnetic spectrum is between visible light and microwave radiation.

To be able to build thermal images based on the infrared radiation, an infrared camera has sensors that detect heat and performs a thermogram or temperature pattern, which is sent to a processor. This is how the Thermal Imaging Camera works.

Related Questions

Below are some questions that a technician must ask himself to evaluate and choose the right thermal imaging camera for an effective thermographic survey:

  1.  Which resolution do I need?
    The thermal sensor receives infrared rays and converts them into an electrical signal. The sensor detection detail is classified in pixels; the greater the number of pixels that makes up the thermal field of view, the greater the thermal detail that can be obtained. The ideal resolution for your use should be chosen considering the distance from the object under test. In principle, the reference distance is 1 meter.
  2.  Which focus is right for me?
    Just like a normal digital camera, focusing properly is the main and most delicate action the operator must take. The sharpness cannot be changed after shooting, therefore it is necessary to place oneself as close as possible to the object under examination, according to the minimum focusing distance of the thermal camera used.
  3. Which temperature range is best?
    There is no absolute best range, but rather each application has its optimal range of measurement. Although it may seem trivial, it is always good to make sure that the thermal imaging camera has a temperature range capable of measuring all the temperatures that will be framed by the lens, even those peripheral to the external object under examination.

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